Two-speed transmission, method of learning μ-v characteristics of said two-speed transmission, and method of controlling gearshift by said two-speed transmission

Abstract

[Problem] To prevent the occurrence of gearshift shock in a two-speed transmission which is able to shift a reduction ratio between two stages, high and low. [Solution] A two-speed transmission 1 is provided with a learning function in which, on condition that predetermined learning start conditions are met, mode changeover between a first mode and a second mode is carried out, and in the inertia phase during the mode changeover, the coefficient of friction between first friction plates 30 and second friction plates 31 is computed on the basis of the output torque of a drive motor 2 and the angular acceleration of the output shaft 11 of the drive motor 2, to obtain a μ–V property, which is the relationship between the coefficient of friction μ, and differential rotation V, which is the difference in the rotational speeds of any two elements among the elements constituting a planetary transmission mechanism 9.

Description

Two-speed transmission, method for learning μ-V characteristics of said two-speed transmission, and method for controlling speed change of said two-speed transmission

[0001] The present disclosure relates to a two-speed transmission for switching the reduction ratio between an input member and an output member between two levels, high and low, a method for learning the μ-V characteristics of the two-speed transmission, and a method for controlling the speed change of the two-speed transmission.

[0002] In response to the recent trend toward reducing fossil fuel consumption, research into electric vehicles and hybrid vehicles has progressed, and some vehicles are now being implemented. Unlike internal combustion engines (engines) that are powered by directly burning fossil fuels, electric motors, which are the power source for electric vehicles and hybrid vehicles, have output shaft torque and rotational speed characteristics that are favorable for automotive use. In other words, because they generally generate maximum torque at start-up, they do not necessarily need to be equipped with a transmission like ordinary vehicles that use internal combustion engines as their power source.

[0003] However, even when an electric motor is used as the drive source, the provision of a transmission can improve acceleration and high-speed performance. Specifically, the provision of a transmission can make the relationship between the vehicle's running speed and acceleration smoother, similar to that of a vehicle equipped with a gasoline engine and a transmission in its power transmission system. This point will be explained with reference to FIG. 41.

[0004] For example, if a power transmission device with a large reduction ratio is placed between the output shaft of the electric motor and the input part of the differential gear connected to the drive wheels, the relationship between the acceleration (G) and running speed (km / h) of the electric vehicle will be as shown by the solid line a in Figure 41. In other words, the electric vehicle will have excellent acceleration performance at low speeds, but will not be able to run at high speeds. In contrast, if a power transmission device with a small reduction ratio is placed between the output shaft and the input part, the relationship will be as shown by the dotted line b in Figure 41. In other words, the electric vehicle will be able to run at high speeds, but its acceleration performance at low speeds will be impaired.

[0005] On the other hand, if a transmission is provided between the output shaft and the input section and the reduction ratio of this transmission is changed according to the vehicle speed, a characteristic can be obtained in which the portion of the solid line a to the left of point P is continuous with the portion of the chain line b to the right of point P. This characteristic is roughly equivalent to that of a gasoline engine vehicle with a similar output, shown by the dashed line c in Figure 41, and it can be seen that in terms of acceleration performance and high-speed performance, performance equivalent to that of a gasoline engine vehicle with a transmission provided in the power transmission system can be obtained.

[0006] Japanese Patent Laid-Open Publication No. 05-116549 discloses the structure of an electric vehicle drive unit in which the torque of the output shaft of an electric motor is increased by a two-stage transmission consisting of a pair of planetary gear mechanisms and a pair of brakes, and then transmitted to a differential gear. In this electric vehicle drive unit, the reduction ratio between the output shaft of the electric motor and the differential gear can be switched between high and low by switching the pair of brakes between an engaged state and a disengaged state, thereby switching the components of the pair of planetary gear mechanisms between a rotatable state and a non-rotatable state.

[0007] Japanese Patent Application Publication No. 05-116549

[0008] In automobiles, including electric vehicles, preventing shocks (gear-shift shocks) that occur when switching the reduction ratio is important in terms of ensuring ride comfort, etc. In the electric vehicle drive device described in JP 05-116549 A, by appropriately controlling the timing for switching between the connected and disconnected states of a pair of brakes and the output torque and rotation speed of the motor that serves as the drive source, and adjusting the torque transmitted to each brake, it is possible to switch the reduction ratio while maintaining a constant rotational torque of the output shaft, thereby preventing the occurrence of gear-shift shocks.

[0009] The torque transmitted to the brake can be calculated based on the relative rotational speed (relative rotational speed) between the frictional engagement elements, i.e., the dependency of the friction coefficient on the slip speed (μ-V characteristic), and the force pressing the frictional engagement elements together. The friction coefficient between the frictional engagement elements of the brake changes with changes in the operating environment and aging, and this causes the μ-V characteristic to change, as shown by the change from the solid line to the dashed line in Figure 42. Therefore, if the μ-V characteristic changes with aging or changes in the external environment, it may become impossible to accurately estimate the torque transmitted to the brake when switching the reduction ratio, which could result in gear shift shock.

[0010] In view of the circumstances described above, the present disclosure aims to realize a structure in a two-speed transmission that can switch the reduction ratio between two levels, high and low, that can learn the μ-V characteristics that change with use, thereby making it possible to prevent the occurrence of gear shift shock regardless of changes in the usage environment or deterioration over time.

[0011] One aspect of the present disclosure relates to a two-speed transmission. The two-speed transmission according to one aspect of the present disclosure includes a planetary transmission mechanism, an input member, an output member, a drive motor, a rotation transmission state switching device, and a friction engagement device.

[0012] The planetary transmission mechanism includes an input element connected to the input member, an output element connected to the output member and rotatable relative to the input element, and a rotating element rotatable relative to the input element and the output element.

[0013] The planetary transmission mechanism includes a sun element, a ring element supported around the sun element so as to be rotatable relative to the sun element, a carrier element supported so as to be rotatable relative to the sun element and the ring element, and a plurality of planetary elements engaged with the sun element and the ring element so as to be able to transmit torque and rotatably supported on the carrier element.

[0014] The input element is composed of one of the sun element, the ring element, and the carrier element.

[0015] The output element is composed of one of the sun element, the ring element, and the carrier element, which is separate from the input element.

[0016] The rotating elements are composed of the sun element, the ring element, and the carrier element, excluding the input element and the output element.

[0017] The drive motor rotates the input member directly or via a reducer.

[0018] The rotation transmission state switching device is disposed between the rotating element and a fixed portion that does not rotate even during use, and switches between a free mode in which the rotating element is rotatable relative to the fixed portion and a locked mode in which the rotating element is not rotatable.

[0019] The friction engagement device has at least one first friction plate and at least one second friction plate supported to allow relative axial displacement, and is arranged between any two of the sun element, the ring element, and the carrier element. By pressing the first friction plate and the second friction plate against each other, the device switches to a connection mode in which the two elements rotate together, and by releasing the force pressing the first friction plate and the second friction plate against each other, the device switches to a disconnection mode in which the two elements rotate relative to each other.

[0020] The two-speed transmission has a first mode in which the rotation transmission state switching device is in the free mode and the friction engagement device is in the connected mode, and a second mode in which the rotation transmission state switching device is in the locked mode and the friction engagement device is in the disconnected mode.

[0021] The two-speed transmission switches between the first mode and the second mode, provided that predetermined learning start conditions are met, and during the inertia phase of the mode switching, calculates the friction coefficient between the first friction plate and the second friction plate based on the output torque of the drive motor and the angular acceleration of the output shaft of the drive motor, thereby having a learning function to obtain the μ-V characteristic, which is the relationship between the friction coefficient and the differential rotation, which is the difference in rotation speed between any two of the elements.

[0022] In a two-speed transmission according to one aspect of the present disclosure, when the learning function is executed, the rotation speed of the output shaft of the drive motor is kept constant, and after mode switching between the first mode and the second mode is initiated, it can be determined that the inertia phase has started on the condition that the amount of change per unit time in the differential rotation exceeds a predetermined threshold value.

[0023] A two-speed transmission according to one aspect of the present disclosure can be equipped with a control function that, when switching between the first mode and the second mode, controls the output torque of the drive motor and the magnitude of the force pressing the first friction plate and the second friction plate against each other based on the μ-V characteristics obtained by the learning function.

[0024] In the two-speed transmission according to one aspect of the present disclosure, the friction engagement device can include an elastic biasing member, a cam device, and an electric actuator.

[0025] The elastic biasing member elastically biases the first friction plate and the second friction plate in a direction in which they are pressed against each other.

[0026] The cam device has a drive cam and a driven cam supported to be rotatable relative to the drive cam and displaceable relative to the drive cam in the axial direction. As the drive cam rotates, the cam device displaces the driven cam relative to the drive cam in a direction increasing the axial distance between the drive cam and the driven cam, thereby pressing the elastic biasing member in a direction to release the force pressing the first friction plate and the second friction plate against each other.

[0027] The electric actuator has a shift motor and a shift reducer, and the drive cam is rotationally driven by the shift motor via the shift reducer.

[0028] In the two-speed transmission according to one aspect of the present disclosure, the friction engagement device may include a return spring that elastically biases the first friction plate and the second friction plate in a direction separating them from each other.

[0029] In a two-speed transmission according to one aspect of the present disclosure, the rotation transmission state switching device can have a one-way clutch mode in which rotation of the rotating element relative to the fixed part is only permitted in a predetermined direction, and rotation of the rotating element relative to the fixed part in a direction opposite to the predetermined direction is prevented.

[0030] In this case, the rotation transmission state switching device may be provided with a function to set the rotation transmission state switching device to the one-way clutch mode while the friction engagement device is being switched from the disconnection mode to the connection mode and / or while the friction engagement device is being switched from the connection mode to the disconnection mode.

[0031] One aspect of the present disclosure relates to a method for learning a μ-V characteristic, which is the relationship between a friction coefficient between the first friction plate and the second friction plate and a differential rotation, which is the difference in rotation speed between any two of the elements, in a two-speed transmission. The method for learning the μ-V characteristic of the two-speed transmission includes: switching between the first mode and the second mode on the condition that a predetermined learning start condition is satisfied; and, during the inertia phase of the mode switching, calculating the friction coefficient based on the output torque of the drive motor and the angular acceleration of the output shaft of the drive motor, thereby obtaining the μ-V characteristic.

[0032] One aspect of the present disclosure relates to a shift control method for the two-speed transmission, the shift control method including: a learning step of obtaining the μ-V characteristic by the μ-V characteristic learning method; and a step of controlling, when switching between the first mode and the second mode, the output torque of the drive motor and the magnitude of the force pressing the first friction plate and the second friction plate against each other, based on the μ-V characteristic obtained in the learning step.

[0033] The present disclosure can be implemented by appropriately combining the above-described aspects as long as no contradiction occurs.

[0034] According to one aspect of the present disclosure, a two-speed transmission, a method for learning the μ-V characteristics of the two-speed transmission, and a method for controlling gear shifting of the two-speed transmission make it possible to learn the μ-V characteristics that change with use, thereby providing a two-speed transmission that can prevent gear shift shock from occurring regardless of changes in the usage environment or deterioration over time.

[0035] FIG. 1 is a cross-sectional view schematically illustrating a drive system incorporating a two-speed transmission according to a first embodiment of the present disclosure. FIG. 2(a) is a diagram illustrating a torque transmission path in a low reduction ratio mode of the two-speed transmission according to the first embodiment, and FIG. 2(b) is a diagram illustrating a torque transmission path in a high reduction ratio mode of the two-speed transmission according to the first embodiment. FIG. 3 is a perspective view of the two-speed transmission according to the first embodiment. FIG. 4 is a cross-sectional view of the two-speed transmission according to the first embodiment. FIG. 5 is a perspective view of the two-speed transmission according to the first embodiment with a planetary transmission mechanism removed. FIG. 6 is a cross-sectional view of the two-speed transmission according to the first embodiment with the planetary transmission mechanism removed. FIG. 7 is an exploded perspective view of the two-speed transmission according to the first embodiment. FIG. 8 is an exploded perspective view of a worm and two support bearings removed from a friction engagement device constituting the two-speed transmission according to the first embodiment. FIG. 9 is an exploded perspective view of a first friction plate and a second friction plate removed from the friction engagement device. FIG. 10 is an enlarged view of portion X in FIG. 4. FIG. 11 is a perspective view showing a drive cam removed from the friction engagement device. FIG. 12 is an exploded perspective view showing a driven cam and rolling elements removed from the friction engagement device. FIG. 13(a) is a perspective view showing a flange portion of a rotating member and a pressing member removed from the two-speed transmission of the first example, and FIG. 13(b) is an exploded perspective view showing the flange portion of the rotating member and the pressing member removed. FIGS. 14(A) to 14(D) are schematic views of the cam device of the friction engagement device as seen from the radially outer side. FIG. 15 is a perspective view of the rotation transmission state switching device constituting the two-speed transmission of the first example, as seen from the other axial side. FIG. 16 is an exploded perspective view of the rotation transmission state switching device. FIG. 17 is an end view of the rotation transmission state switching device as seen from the other axial side with the selector plate removed. FIG. 18 is an enlarged view of portion Y in FIG. 17. Fig. 19(A) is a schematic diagram showing the engagement relationship between the first engagement pawl and the second engagement pawl and the engagement recess and the protrusion in the free mode of the rotation transmission state switching device, Fig. 19(B) is a schematic diagram showing the engagement relationship in the lock mode, and Fig. 19(C) is a schematic diagram showing the engagement relationship in the one-way clutch mode. Fig. 20 is a diagram showing the modes of the friction engagement device and the modes of the rotation transmission state switching device in the two-speed transmission of the first example.21(a) and 21(b) are diagrams showing the relationship between the rotation angle of the drive cam and the output torque and current value of the shift motor when the friction engagement device is switched from the connection mode to the disconnection mode. FIG. 21(a) is a diagram showing the case where the first friction plate and the second friction plate are brand new and not worn, and FIG. 21(b) is a diagram showing the case where the first friction plate and the second friction plate have significantly progressed to wear. FIG. 22 is a cross-sectional view showing the state where the friction engagement device has been switched to the connection mode. FIG. 23 is a cross-sectional view showing the state where the pressing member and the piston are in contact with each other while the friction engagement device is being switched from the connection mode to the disconnection mode. FIG. 24 is a cross-sectional view showing the state where the friction engagement device has been switched to the disconnection mode. FIG. 25 is a flowchart showing the operation when the two-speed transmission of the first example is switched from the high reduction ratio mode to the low reduction ratio mode. FIG. 26 is a diagram showing the time changes of each parameter when the two-speed transmission of the first example is switched from the high reduction ratio mode to the low reduction ratio mode. FIG. 27 is a cross-sectional view showing a portion of a two-speed transmission of a comparative example. FIG. 28 is a diagram schematically showing an engaged state and a disengaged state of a first friction engagement device and a second friction engagement device in a two-speed transmission of a comparative example. FIG. 29 is a diagram corresponding to FIG. 20 showing a two-speed transmission of a modified example of the first example. FIG. 30 is a schematic diagram showing a two-speed transmission of a second example embodiment of the present invention. FIG. 31 is a schematic diagram showing a two-speed transmission of a third example embodiment of the present invention. FIG. 32 is a schematic diagram showing a two-speed transmission of a fourth example embodiment of the present invention. FIG. 33 is a schematic diagram showing a two-speed transmission of a fifth example embodiment of the present invention. FIG. 34 is a schematic diagram showing a two-speed transmission of a sixth example embodiment of the present invention. FIG. 35 is a schematic diagram showing a two-speed transmission of a seventh example embodiment of the present invention. FIG. 36 is a schematic diagram showing a two-speed transmission of an eighth example embodiment of the present invention. Fig. 37 is a schematic diagram showing a two-speed transmission according to a ninth embodiment of the present invention. Fig. 38 is a schematic diagram showing a two-speed transmission according to a tenth embodiment of the present invention. Fig. 39 is a schematic diagram showing a two-speed transmission according to an eleventh embodiment of the present invention. Fig. 40 is a schematic diagram showing a two-speed transmission according to a twelfth embodiment of the present invention. Fig. 41 is a diagram for explaining the effect of incorporating a transmission into a drive device using an electric motor as a drive source.FIG. 42 is a diagram showing the μ-V characteristics.

[0036] 1 to 26. A two-speed transmission 1 of this example increases the output torque of a drive motor 2, which is a drive source, i.e., reduces the rotation, or transmits the torque to a differential device 3 without increasing it.

[0037] 1 to 2(b), in order to facilitate understanding of the invention, the elements constituting the two-speed transmission 1 and the differential device 3 are shown in a schematic manner.

[0038] The two-speed transmission 1 of this example includes a drive motor 2 , an input member 4 , an output member 5 , a friction engagement device 7 , a rotation transmission state switching device 8 , and a planetary transmission mechanism 9 .

[0039] The input member 4 is formed of a housing that accommodates the two-speed transmission 1, and is rotatably supported by a fixed part 10 that does not rotate even during use, by a rolling bearing (not shown). In this example, the input member 4 is cylindrical (hollow). The input member 4 also has an input gear 13 at one end in the axial direction (the right side in FIG. 1 ) that meshes with a drive gear 12 provided on the output shaft 11 of the drive motor 2.

[0040] The output member 5 is supported coaxially with the input member 4 and rotatably relative to the input member 4. In this example, the output member 5 is supported radially inside the cylindrical input member 4 via a rolling bearing (not shown) or the like to be rotatable relative to the input member 4. The output member 5 also has an output gear 14 at one axial end. The output gear 14 meshes with a gear provided in the input portion of the differential device 3. The output member 5 drives the input portion of the differential device 3 to rotate.

[0041] The drive motor 2 rotates the input member 4 via a gear-type reducer consisting of a drive gear 12 and an input gear 13 .

[0042] The planetary transmission mechanism 9 includes an input element connected to the input member 4, an output element connected to the output member 5 and rotatable relative to the input element, and a rotating element rotatable relative to the input element and the output element.

[0043] The planetary transmission mechanism 9 has a sun element, a ring element supported around the sun element so as to be rotatable relative to the sun element, a carrier element supported so as to be rotatable relative to the sun element and the ring element, and a plurality of planetary elements engaged with the sun element and the ring element so as to be able to transmit torque and rotatably supported on the carrier element.

[0044] The input element is composed of one of the sun element, the ring element, and the carrier element.

[0045] The output element is composed of one of the sun element, the ring element, and the carrier element, which is separate from the input element.

[0046] The rotating elements are composed of the sun element, the ring element, and the carrier element, excluding the input element and the output element.

[0047] In this example, the planetary transmission mechanism 9 is configured by a planetary gear mechanism in which gears mesh with each other. That is, the sun element is configured by a sun gear 101, the ring element is configured by a ring gear 102, the carrier element is configured by a carrier 103, and the multiple planetary elements are configured by multiple planetary gears 104. Therefore, the planetary transmission mechanism 9 is configured by a single-pinion planetary gear mechanism in which each of the multiple planetary gears 104 meshes with both the sun gear 101 and the ring gear 102.

[0048] When implementing the present disclosure, the planetary reduction mechanism may be a double-pinion planetary gear mechanism. Alternatively, the planetary speed change mechanism may be configured with a planetary roller mechanism. In this case, the sun element is configured with a sun roller, the ring element is configured with a ring roller, and the plurality of planetary elements are configured with a plurality of planetary rollers.

[0049] In this example, the sun gear 101 is provided at one axial end of the rotating member 6 .

[0050] The rotating member 6 is supported coaxially with the input member 4 and the output member 5 and is capable of relative rotation with respect to the input member 4 and the output member 5. More specifically, the rotating member 6 is rotatably supported with respect to the fixed part 10 via the rotation transmission state switching device 8, a cam device 28 that constitutes the friction engagement device 7, and a radial bearing 38 that supports a drive cam 34 that constitutes the cam device 28 so that the drive cam 34 is rotatable with respect to the rotating member 6.

[0051] The rotating member 6 has a small-diameter flange portion 15 that protrudes radially outward in an axially intermediate portion, and also has a flange portion 16 that protrudes radially outward in a portion located on the other axial side (the left side in Figure 1) of the small-diameter flange portion 15.

[0052] The flange portion 16 has a hollow circular plate-shaped first circular ring portion 18, a first cylindrical portion 19 bent from the radially outer end of the first circular ring portion 18 toward the other axial side, a hollow circular plate-shaped second circular ring portion 20 bent from the axially outer end of the first cylindrical portion 19 toward the other axial side, and a second cylindrical portion 21 bent from the radially outer end of the second circular ring portion 20 toward the other axial side. The first circular ring portion 18 has partial arc-shaped through holes 17 at multiple locations in its radially intermediate portion for inserting partial cylindrical portions 63 of the pressing members 58 that constitute the friction engagement device 7.

[0053] In this example, the rotating member 6 is constructed by externally fitting and fixing a stepped cylindrical member 23, as shown on the left side of Figure 13(b), onto a shaft member 22 having a small-diameter flange portion 15. That is, the stepped cylindrical member 23 has a flange portion 16 and a small-diameter cylindrical portion 24 that is bent axially from the radially inner end of the first annular portion 18 of the flange portion 16 toward the other side. The female spline portion 25 provided on the inner peripheral surface of the small-diameter cylindrical portion 24 is spline-engaged with a male spline portion provided on the outer peripheral surface of the shaft member 22, thereby supporting and fixing the stepped cylindrical member 23 to the shaft member 22. However, the rotating member can also be constructed by connecting and fixing the stepped cylindrical member and the shaft member by press-fitting, welding, or the like.

[0054] In this example, the rotating element is constituted by a sun gear 101 .

[0055] The ring gear 102 is disposed around the sun gear 101 and coaxially therewith, and is connected to the input member 4 so as to be able to transmit torque. In this example, the ring gear 102 is provided at an intermediate portion of the input member 4 in the axial direction.

[0056] In this example, the input element is constituted by a ring gear 102 .

[0057] The carrier 103 is disposed coaxially with the sun gear 101 and the ring gear 102 and between the sun gear 101 and the ring gear 102 in the radial direction, and is connected to the output member 5 so as to be able to transmit torque.

[0058] In this example, the output element is constituted by a carrier 103 .

[0059] The plurality of planetary gears 104 mesh with the sun gear 101 and the ring gear 102. Each of the plurality of planetary gears 104 is supported by the carrier 103 so as to be able to rotate (spin) around its own central axis.

[0060] The rotation transmission state switching device 8 is disposed between the rotating element (in this example, the sun gear 101) and a fixed part 10 that does not rotate even during use, and switches between a free mode in which the rotating element, the sun gear 101, can rotate relative to the fixed part 10, and a locked mode in which it cannot rotate.

[0061] In this example, the rotation transmission state switching device 8 includes a first member 71 and a second member 72 arranged coaxially with each other, and a mode select member 73 that rotates in accordance with the rotation of the drive cam 34, as shown in Figures 15 to 18.

[0062] The first member 71 is connected to the sun gear 101 so as to be able to transmit torque, and the second member 72 is supported and fixed to the fixed part 10. The rotation transmission state switching device 8 of this example has a free mode in which rotation of the first member 71 relative to the fixed part 10 is permitted regardless of the rotation direction of the first member 71, a locked mode in which rotation of the first member 71 relative to the fixed part 10 is prevented regardless of the rotation direction of the first member 71, and a one-way clutch mode in which rotation of the first member 71 only in a predetermined direction is permitted. Specifically, the rotation transmission state switching device 8 of this example switches among the free mode, the locked mode, and the one-way clutch mode based on the rotation of the mode selector member 73.

[0063] The first member 71 has a gear-shaped concave-convex portion 76 on its outer peripheral surface, where engaging recesses 74 and protrusions 75 are alternately arranged in the circumferential direction. The first member 71 has an outer diameter side concave-convex engaging portion 77 on its inner peripheral surface, where concaves and protrusions are alternately arranged in the circumferential direction. The outer diameter side concave-convex engaging portion 77 engages with an inner diameter side concave-convex engaging portion 78 provided on the outer peripheral surface of the second cylindrical portion 21 of the rotating member 6, whereby the first member 71 is supported so as to be unable to rotate relative to the rotating member 6, and rotates integrally with the rotating member 6 and the sun gear 101.

[0064] The second member 72 is supported around the first member 71 coaxially with the first member 71 and capable of relative rotation with respect to the first member 71. The inner circumferential surface of the second member 72 faces the tip surfaces of the convex portions 75 of the first member 71 via a gap. The second member 72 has an inner diameter side concave-convex engaging portion 79 on its outer circumferential surface, which is made up of concave and convex portions alternately arranged in the circumferential direction. The second member 72 is supported so as to be unable to rotate relative to the fixed part 10 by engaging the inner diameter side concave-convex engaging portion 79 with an outer diameter side concave-convex engaging portion provided on the inner circumferential surface of the fixed part 10.

[0065] The second member 72 comprises a base 80 having a rectangular cross-sectional shape, and a cylindrical portion 81 that protrudes from the radially outer end of one axial side of the base 80 over the entire circumference toward one axial side.

[0066] The base portion 80 has a plurality of first holding recesses 82 and a plurality of second holding recesses 83 (six of each in the illustrated example) that are alternately arranged in the circumferential direction.

[0067] Each first retaining recess 82 opens to the inner circumferential surface and the other axial side surface of the base 80. Each first retaining recess 82 includes a spring retaining portion 84a and a pedestal portion 85a. When viewed from the other axial side, the spring retaining portion 84a has a generally rectangular opening shape with its major axis extending radially outward as it approaches one circumferential side (the front clockwise side in FIGS. 17 to 19 ). The pedestal portion 85a has a generally circular opening shape when viewed from the other axial side, and is disposed adjacent to the other circumferential side of the spring retaining portion 84a (the rear clockwise side in FIGS. 17 to 19 ).

[0068] Each second retaining recess 83 is open to the inner peripheral surface and the other axial side surface of the base 80, and includes a spring retaining portion 84b and a pedestal portion 85b. When viewed from the other axial side, the second retaining recess 83 has a shape symmetrical to the first retaining recess 82 with respect to an imaginary plane including the central axis of the second member 72.

[0069] In order to realize the free mode, the locked mode, and the one-way clutch mode, the rotation transmission state switching device 8 has a first pawl member 86, a second pawl member 87, a first pawl biasing member 88, and a second pawl biasing member 89 between the first member 71 and the second member 72. In this example, the first pawl members 86, the second pawl members 87, the first pawl biasing members 88, and the second pawl biasing members 89 are plural and the same in number.

[0070] Each of the first claw members 86 includes a first base portion 90 and a first engagement claw 91 .

[0071] The first base 90 is configured in an approximately cylindrical shape and is supported (pivoted) on the pedestal portion 85 a of the first holding recess 82 so as to be able to swing about a pivot axis parallel to the central axis of the second member 72 .

[0072] The first engagement claw 91 is configured in a generally flat plate shape and extends circumferentially to one side from the first base 90. The other axial side portion of the first engagement claw 91 faces (engages with) the outer circumferential surface of the annular protrusion 92 of the mode select member 73, and the other axial side portion faces (engages with) the uneven portion 76 of the first member 71 (engages with the engagement recess 74 so as to be able to be engaged with and disengaged from the engagement recess 74).

[0073] Each second claw member 87 includes a second base portion 93 swingably supported on the pedestal portion 85b of the second retaining recess 83, and a second engagement claw 94 extending toward the other circumferential side from the second base portion 93. When viewed from the other axial side, the second claw member 87 has a shape symmetrical to the first engagement claw 91 with respect to an imaginary plane including the center axis of the second member 72, and is disposed symmetrical to the first engagement claw 91.

[0074] The first claw biasing member 88 elastically biases the first engaging claw 91 of the first claw member 86 in a direction to engage with the engaging recess 74 of the first member 71. That is, the first claw biasing member 88 applies a biasing force to the first claw member 86 in a direction to cause the first claw member 86 to swing clockwise in FIG. 18 around the central axis (pivot) of the first base 90. Specifically, the first claw biasing member 88 is formed of an elastic member such as a coil spring, and is held in an elastically compressed state between the bottom surface (surface facing radially inward) of the spring holding portion 84a of the first holding recess 82 and the radially outer surface of the first engaging claw 91.

[0075] , and is configured from an elastic member similar to the first claw biasing member 88, and when viewed from the other axial side, is disposed symmetrically to the first claw biasing member 88 with respect to an imaginary plane including the central axis of the second member 72. That is, the second claw biasing member 89 is held in an elastically compressed state between the bottom surface of the spring holding portion 84b of the second holding recess 83 and the radially outer surface of the second engaging claw 94, and elastically biases the second engaging claw 94 of the second claw member 87 in a direction to engage with the engaging recess 74 of the first member 71.

[0076] As shown in Figure 16, the mode select member 73 has a substantially circular plate-shaped base 95 and an annular protrusion 92 that protrudes from the radial middle of the other axial side of the base 95 around the entire circumference toward the other axial side.

[0077] The base portion 95 has plate-side engagement holes 96 at a plurality of locations (three locations in the illustrated example) at equally spaced intervals in the circumferential direction in a radially intermediate portion of the other axial side surface. One axial end of the pin portion 50 fits (engages) into each plate-side engagement hole 96 without rattle. In other words, the mode select member 73 rotates integrally with the drive cam 34 (in the same direction and at the same speed).

[0078] The annular convex portion 92 has protrusions 97 that protrude radially outward at multiple locations on the outer circumferential surface. That is, the annular convex portion 92 has a gear-shaped uneven portion 98 on the outer circumferential surface, in which protrusions 97 and recesses are alternately arranged in the circumferential direction.

[0079] The first member 71, the second member 72, and the mode select member 73 are combined by a cover body 99 and a retaining ring 100 so as to be capable of relative rotation but not capable of relative axial displacement (so as to prevent inadvertent separation in the axial direction), thereby forming the rotation transmission state switching device 8.

[0080] With the first member 71 disposed radially inside one axial side portion of the base 80 of the second member 72, a circular ring-shaped lid body 99 is supported and fixed by screws to one axial side surface of the second member 72, with the other axial side surface of the radially inner portion of the lid body 99 facing one axial side surface of the first member 71. This prevents the first member 71 from displacing axially to one side relative to the second member 72.

[0081] The annular protrusion 92 of the mode select member 73 is disposed radially inside the other axial side portion of the base 80 of the second member 72, with the tip surface (one axial side surface) of the annular protrusion 92 in sliding contact with or closely facing the other axial side surface of the first member 71, and with one axial side surface of the radially outer portion of the base 95 in sliding contact with or closely facing the other axial side surface of the base 80 of the second member 72. A retaining ring 100 is engaged with the end on the other axial side of the inner circumferential surface of the cylindrical portion 81 of the second member 72. This prevents the first member 71 and the mode select member 73 from displacing axially toward the other side relative to the second member 72.

[0082] The rotation transmission state switching device 8 is configured to be able to switch between free mode, locked mode, and one-way clutch mode by switching the engagement state between the first engagement claw 91 of the first claw member 86 and the engagement recess 74 of the first member 71, and the engagement state between the second engagement claw 94 of the second claw member 87 and the engagement recess 74, based on the rotation of the mode select member 73.

[0083] <Free mode> In the free mode, the circumferential phase of the mode select member 73 relative to the second member 72 is adjusted, and as shown in FIG. 19(A), the protrusion 97 pushes the first engagement claw 91 radially outward against the elastic force of the first claw biasing member 88, and also pushes the second engagement claw 94 radially outward against the elastic force of the second claw biasing member 89.

[0084] This disengages the engagement recess 74 of the first member 71 from the first engagement claw 91 and the second engagement claw 94. In this state, rotation of the first member 71 relative to the second member 72 is permitted regardless of the relative rotation direction between the first member 71 and the second member 72. In other words, rotation of the first member 71 relative to the fixed part 10 is permitted regardless of the rotation direction of the first member 71.

[0085] <Lock Mode> In the lock mode, the circumferential phase of the mode select member 73 relative to the second member 72 is adjusted, and as shown in Figure 19 (B) , the protrusion 97 is positioned in a portion circumferentially offset from the first engagement claw 91 of the first claw member 86 and the second engagement claw 94 of the second claw member 87. In other words, the phases of the recesses in the uneven portion 98 and the first engagement claw 91 and second engagement claw 94 are matched in the circumferential direction.

[0086] As a result, the engagement recess 74 of the first member 71 engages with the first engagement claw 91 and the second engagement claw 94. In this state, rotation of the first member 71 relative to the second member 72 is prevented, regardless of the relative rotation direction between the first member 71 and the second member 72. In other words, rotation of the first member 71 relative to the fixed part 10 is prevented, regardless of the rotation direction of the first member 71.

[0087] <One-way clutch mode> In the one-way clutch mode, the circumferential phase of the mode select member 73 relative to the second member 72 is adjusted, and as shown in Figure 19 (C), the protrusion 97 pushes only the second engagement claw 94 radially outward against the elastic force of the second claw biasing member 89.

[0088] As a result, the engagement recess 74 of the first member 71 engages with the first engagement claw 91, and the engagement recess 74 disengages from the second engagement claw 94. In this state, only rotation of the first member 71 relative to the second member 72 in the predetermined direction (clockwise in FIG. 19C) is permitted, and rotation in the direction opposite to the predetermined direction (counterclockwise in FIG. 19C) is prevented.

[0089] That is, when the first member 71 attempts to rotate in the predetermined direction relative to the second member 72, the convex portion 75 of the concave-convex portion 76 pushes the first engagement pawl 91 radially outward against the elastic force of the first pawl biasing member 88. As a result, rotation of the first member 71 in the predetermined direction is permitted. On the other hand, when the first member 71 attempts to rotate in the direction opposite to the predetermined direction relative to the second member 72, engagement between the engagement recess 74 and the first engagement pawl 91 prevents rotation of the first member 71 in the direction opposite to the predetermined direction. In short, the rotation transmission state switching device 8 operates as a ratchet-type one-way clutch.

[0090] The predetermined direction coincides with the normal rotation direction of the input member 4. The normal rotation direction of the input member 4 refers to the rotation direction of the input member 4 when moving the automobile forward.

[0091] The friction engagement device 7 has at least one first friction plate 30 and at least one second friction plate 31 supported to allow relative axial displacement, and is arranged between any two of the sun element (sun gear 101), the ring element (ring gear 102), and the carrier element (carrier 103). By pressing the first friction plate 30 and the second friction plate 31 against each other, the device switches to a connection mode in which the two elements rotate together, and by releasing the force pressing the first friction plate 30 and the second friction plate 31 against each other, the device switches to a disconnection mode in which the two elements rotate relative to each other.

[0092] In this example, the friction engagement device 7 is provided between the sun gear 101 and the ring gear 102, and in the connected mode, the sun gear 101 and the ring gear 102 rotate together, and in the disconnected mode, the sun gear 101 and the ring gear 102 rotate relative to each other. As a result, torque is transmitted between the input member 4 and the rotating member 6 in the connected mode, and torque is not transmitted between the input member 4 and the rotating member 6 in the disconnected mode.

[0093] In this example, the friction engagement device 7 includes a friction engagement portion 26 , an elastic biasing member 27 , a cam device 28 , and an electric actuator 29 .

[0094] In this example, the friction engagement portion 26 is composed of a multi-plate clutch in which a plurality of first friction plates 30 supported by the rotating member 6 and a plurality of second friction plates 31 supported by the input member 4 are alternately stacked.

[0095] The plurality of first friction plates 30 are supported on the outer peripheral surface of the first cylindrical portion 19 so as to be capable of axial displacement but not capable of relative rotation with respect to the first cylindrical portion 19 .

[0096] The plurality of second friction plates 31 are supported on the inner peripheral surface of the other axial end of the input member 4 so as to be capable of axial displacement but not capable of relative rotation with respect to the input member 4 .

[0097] The elastic biasing member 27 is provided between the rotating member 6 and the friction engagement portion 26, and elastically biases the first friction plate 30 and the second friction plate 31 in a direction pressing them against each other. In this example, the elastic biasing member 27 has a piston 32 and an elastic member 33.

[0098] The piston 32 is supported so as to be displaceable in the axial direction relative to the rotating member 6. In this example, the piston 32 is configured in the shape of a hollow circular plate, and is supported around a portion of the rotating member 6 between the small diameter flange portion 15 and the flange portion 16 in the axial direction so as to be displaceable in the axial direction relative to the rotating member 6. The other axial end face of the radially outer portion of the piston 32 faces one axial side face of the first friction plate 30 or the second friction plate 31 that is located furthest axially from one of the first friction plate 30 and the second friction plate 31.

[0099] The elastic member 33 is provided between the rotating member 6 and the piston 32. In this example, the elastic member 33 is sandwiched in an elastically compressed state between the other axial side surface of the small-diameter flange portion 15 of the rotating member 6 and one axial side surface of the piston 32. In other words, the elastic biasing member 27 elastically biases the first friction plate 30 or the second friction plate 31 closest to one axial side toward the other axial side via the piston 32 by the force of the elastic member 33 attempting to elastically restore its original shape, thereby elastically biasing the first friction plate 30 and the second friction plate 31 in a direction in which they are pressed against each other.

[0100] In this example, the elastic member 33 is composed of at least one disc spring (two disc springs in this example). However, when implementing the present disclosure, the specific configuration of the elastic member is not particularly limited. For example, the elastic member may be composed of at least one coil spring.

[0101] The cam device 28 has a drive cam 34 and a driven cam 35 that is supported so as to be capable of relative rotation and axial displacement relative to the drive cam 34. As the drive cam 34 rotates, the cam device 28 relatively displaces the driven cam 35 in a direction that increases the axial distance between the drive cam 34, thereby pressing the elastic biasing member 27 in a direction that releases the force pressing the first friction plate 30 and the second friction plate 31 against each other.

[0102] In this example, the drive cam 34 is supported relative to the rotating member 6 so as to be rotatable relative to the rotating member 6 and the input member 4, but so as not to be displaceable in the axial direction relative to the rotating member 6. Specifically, as shown in Figure 4 and other figures, the drive cam 34 is supported by a cylindrical member 37, a radial bearing 38, and an angular ball bearing 39 so as to be rotatable relative to the rotating member 6.

[0103] The tubular member 37 has a cylindrical portion 40 and an outward flange portion 41 that is bent radially outward from the other axial end of the cylindrical portion 40. The outward flange portion 41 of the tubular member 37 is supported and fixed to the fixing part 10 by screwing or the like.

[0104] The radial bearing 38 has an inner ring 42 fitted and fixed to the outside of the other axial end of the rotating member 6, an outer ring 43 fitted and fixed to the inside of the cylindrical portion 40 of the tubular member 37, and a plurality of rolling elements 44 arranged to roll freely between the inner ring 42 and the outer ring 43. In the example shown, the radial bearing 38 is configured as a double-row deep groove ball bearing that uses balls as the rolling elements 44. However, the radial bearing is not particularly limited as long as it can support radial and axial loads, and can also be configured as a deep groove ball bearing, a radial angular contact ball bearing, a radial tapered roller bearing, or the like, for example.

[0105] The angular ball bearing 39 has an inner ring 45 fitted and fixed to the outside of the cylindrical portion 40 of the tubular member 37, an outer ring 46 fitted and fixed to the inside of the drive cam 34, and a plurality of balls 47 arranged freely rotatably between the inner ring 45 and the outer ring 46.

[0106] In this example, the drive cam 34 has wheel teeth 49, which are helical gears, on its outer surface, and also has pin portions 50 that protrude toward one side in the axial direction at multiple locations (three locations in the illustrated example) circumferentially in the radially middle part of one side in the axial direction.

[0107] The driven cam 35 is disposed around the rotating member 6 so as to be displaceable only in the axial direction. In this example, the driven cam 35 has a hollow circular plate shape, and is supported so as to be displaceable in the axial direction relative to the fixed part 10. In this example, a female spline portion 51 provided on the inner peripheral surface of the driven cam 35 is spline-engaged with a male spline portion 52 provided on the outer peripheral surface of one axial side portion of the cylindrical portion 40 of the tubular member 37, thereby supporting the driven cam 35 so as to be displaceable in the axial direction relative to the fixed part 10.

[0108] However, the method of supporting the driven cam relative to the fixed part is not particularly limited as long as it can support the driven cam relative to the fixed part so that it can be displaced only in the axial direction. For example, the driven cam can be supported so that it can be displaced in the axial direction relative to the fixed part by keying a convex portion on one of the driven cam or the fixed part with a concave groove on the other.

[0109] 12, driven cam 35 has rectangular holes 53 penetrating in the axial direction at a plurality of circumferential locations (three locations in the illustrated example) in a radially intermediate portion, and has support plate portions 54a, 54b each having a substantially semicircular plate shape that protrudes toward the other axial direction from both radially opposite portions of rectangular hole 53. Of support plate portions 54a, 54b, the radially outer support plate portion 54a has a support hole 55 which is a circular hole penetrating in the radial direction, and radially inner support plate portion 54b has a support recess 56 with a circular opening on its radially outer surface.

[0110] The driven cam 35 faces the piston 32 of the elastic biasing member 27 via a thrust bearing 57 and a pressing member 58 .

[0111] The thrust bearing 57 is provided between the pressing member 58 and the driven cam 35. The thrust bearing 57 has a pair of raceways 59 a, 59 b and a plurality of rolling elements 60 that are arranged to roll freely between the pair of raceways 59 a, 59 b. Of the pair of raceways 59 a, 59 b, the raceway 59 b on the other axial side is supported and fixed to the driven cam 35.

[0112] The pressing member 58 has a cylindrical base 62 and partial cylindrical portions 63 that protrude toward one axial direction from multiple circumferential locations (three locations in the illustrated example) on one axial end of the base 62. One axially-located raceway ring 59a of a pair of raceways 59a, 59b of the thrust bearing 57 is supported and fixed to the other axial end of the base 62. The partial cylindrical portion 63 is inserted into the through-hole 17 of the rotating member 6, and the tip end (one axial end) of the partial cylindrical portion 63 faces a radially intermediate portion of the other axial side surface of the piston 32.

[0113] In this example, a preload applying means 61 for applying a preload to the thrust bearing 57 is provided between the pressing member 58 and the rotating member 6. The preload applying means 61 is sandwiched in an elastically compressed state between the pressing member 58 and the other axial side surface of the first circular ring portion 18 of the flange portion 16 that constitutes the rotating member 6. As a result, even when the piston 32 is pressed axially toward one side against the elastic restoring force of the elastic member 33, as shown in FIG. 2( b ), a preload is applied to the thrust bearing 57 and the thrust bearing 57 is prevented from falling out from between the elastic biasing member 27 and the cam device 28.

[0114] The elastic force of the preload applying means 61 is smaller than the elastic restoring force of the elastic member 33. The preload applying means 61 can be formed, for example, by at least one disc spring or at least one coil spring. In this example, the preload applying means 61 is formed by one coil spring.

[0115] In this example, the cam device 28 has a plurality of rolling elements 36 (three in this example) and a driving cam surface 48 provided on the driving cam 34 as means for relatively displacing the driving cam 34 and the driven cam 35.

[0116] 11, the drive cam surface 48 is formed by arranging an equal number of recesses and protrusions alternately in the circumferential direction on the radially inner portion of one axial side surface of the drive cam 34. As shown in Figures 14(A) to 14(D), the drive cam surface 48 is formed by arranging a first bottom portion 48a, a first inclined surface portion 48b, a first flat surface portion 48c, a second inclined surface portion 48d, a second bottom portion 48e, a third inclined surface portion 48f, a second flat surface portion 48g, and a fourth inclined surface portion 48h in this order, the number of times being repeated being equal to the number of rolling elements 36 (three times in this example).

[0117] Of the drive cam surface 48, the first flat surface portion 48c and the second flat surface portion 48g are located on one side in the axial direction, i.e., at the tip of the convex portion, and the first bottom portion 48a and the second bottom portion 48e are located on the other side in the axial direction. The inclination angles of the third inclined surface portion 48f and the fourth inclined surface portion 48h with respect to an imaginary plane P perpendicular to the central axis of the drive cam 34 are larger than that of the first inclined surface portion 48b with respect to the imaginary plane P.

[0118] The inclination angle of the first inclined surface portion 48b and the inclination angles of the third inclined surface portion 48f and the fourth inclined surface portion 48h are all set to a magnitude that allows the rolling element 36 to move in a rolling-down manner or a climbing-up manner. The third inclined surface portion 48f and the fourth inclined surface portion 48h are inclined in opposite directions and have the same inclination angle.

[0119] However, the inclination angles of the third inclined surface portion 48 f and the fourth inclined surface portion 48 h may be different from each other. Also, the inclination angle of the first inclined surface portion 48 b may be the same as the inclination angles of the third inclined surface portion 48 f and the fourth inclined surface portion 48 h.

[0120] The inclination angle of the second inclined surface portion 48d with respect to the imaginary plane P can be set to any value as long as the rolling elements 36 can ride up on it.

[0121] Each of the rolling elements 36 has a cylindrical shape and is supported for rotation on the support plate portions 54a, 54b via a columnar support shaft 64 and a plurality of rollers 65. That is, the outer end of the support shaft 64 in the radial direction centered on the central axis of the driven cam 35 is fitted and fixed in the support hole 55 of the radially outer support plate portion 54a, and the inner end of the support shaft 64 in the radial direction centered on the central axis of the driven cam 35 is fitted and fixed in the support recess 56 of the radially inner support plate portion 54b.

[0122] The rollers 65 are held so as to be freely rollable between the inner peripheral surface of the rolling element 36 and the outer peripheral surface of the axially middle portion of the support shaft 64. As a result, the rolling element 36 is supported by the driven cam 35 so as to be freely rotatable (spinning) about a rotation axis C that faces in a radial direction and is centered on the central axis of the driven cam 35.

[0123] With the rolling elements 36 supported by the driven cam 35, one axial side portion of the rolling elements 36 is disposed inside the rectangular hole 53. The outer peripheral surface of each of the rolling elements 36 is in rolling contact with the driving cam surface 48 provided on the other axial side surface of the driving cam 34.

[0124] In the two-speed transmission 1 of this example, the driving cam 34 is driven to rotate, and the amount of the rolling body 36 that rides up from the first bottom 48a or the second bottom 48e of the driving cam surface 48 is increased or decreased, thereby moving the driven cam 35 in the axial direction and switching the friction engagement portion 26 between the connected state and the disconnected state.

[0125] When the friction engagement portion 26 is in a disconnected state, as shown in Figures 14(B) and 14(D), the rolling body 36 is positioned on the first flat surface portion 48c or the second flat surface portion 48g of the drive cam surface 48, or the amount of riding on the first inclined surface portion 48b, the second inclined surface portion 48d, the third inclined surface portion 48f, or the fourth inclined surface portion 48h is increased.

[0126] By moving the driven cam 35 to one axial side, which is the direction in which the axial distance between it and the driving cam 34 increases, the piston 32 of the elastic biasing member 27 is pressed toward one axial side via the thrust bearing 57 and the pressing member 58, and the elastic member 33 is elastically compressed. This reduces and ultimately eliminates the force pressing the first friction plate 30 and the second friction plate 31 against each other. In this way, the friction engagement portion 26 is disconnected, and the friction engagement device 7 switches to the disconnection mode.

[0127] In contrast, when the friction engagement portion 26 is in the connected state, as shown in Figures 14(A) and 14(C), the rolling body 36 is positioned on the first bottom portion 48a or the second bottom portion 48e of the drive cam surface 48, or the amount of riding up onto the first inclined surface portion 48b, the second inclined surface portion 48d, the third inclined surface portion 48f, or the fourth inclined surface portion 48h is reduced.

[0128] This causes the driven cam 35 to move in the other axial direction, which is the direction in which the axial distance between the driving cam 34 and the driven cam 35 decreases, thereby reducing the force of the elastic biasing member 27 pressing the piston 32 toward one axial side. When the force pressing the piston 32 toward one axial side decreases, the piston 32, thrust bearing 57, and pressing member 58 are pressed toward the other axial side mainly by the elastic restoring force of the first friction plate 30 and the elastic member 33, and the first friction plate 30 or the second friction plate 31 closest to one axial side is pressed toward the other axial side by the piston 32. Therefore, the first friction plate 30 and the second friction plate 31 press against each other, the friction engagement portion 26 is engaged, and the friction engagement device 7 switches to the engaged mode.

[0129] In the two-speed transmission 1 of this example, the driven cam 35 can be reliably displaced in the axial direction based on the rotation of the drive cam 34, and the mode switching of the two-speed transmission 1 can be performed with high precision.

[0130] When balls are used as rolling elements, slippage may occur at the rolling contact area between the rolling element surface and the driving cam surface when the driving cam is rotated. If slippage occurs at the rolling contact area between the rolling element surface and the driving cam surface, the driven cam may not be able to displace in the axial direction, or the amount of axial displacement of the driven cam relative to the amount of rotation of the driving cam may not be sufficient.

[0131] In the two-speed transmission 1 of this example, rollers are used as the rolling elements 36, and the rolling elements 36 are supported to rotate (spin) freely relative to the driven cam 35 about a rotation axis C that faces in a radial direction from the central axis of the driven cam 35. This prevents slippage at the rolling contact area between the outer circumferential surface of the rolling elements 36 and the driving cam surface 48, and ensures that the driven cam 35 can be displaced in the axial direction based on the rotation of the driving cam 34. As a result, the mode switching of the two-speed transmission 1 can be performed with high precision. However, balls can also be used as the rolling elements that make up the cam device.

[0132] In this example, the cam device 28 is configured by sandwiching the rolling element 36 between the driving cam 34 and the driven cam 35, but when implementing the present disclosure, the cam device is not particularly limited as long as it can press the elastic biasing member in a direction that releases the force pressing the first friction plate and the second friction plate against each other, and any other known means can also be applied.

[0133] For example, the cam device may have a structure in which a rolling element is arranged between the driving cam surface of the driving cam and the driven cam surface of the driven cam, a structure in which the driving cam surface of the driving cam and the driven cam surface of the driven cam are directly engaged (sliding), or a structure in which a driven cam has a guide groove on its outer circumferential surface that extends circumferentially and changes in the axial direction, and a driving cam has an engaging protrusion that engages with the guide groove to enable displacement along the guide groove.

[0134] The electric actuator 29 has a shift motor 66 and a reducer 67 , and the shift motor 66 drives the drive cam 34 to rotate via the reducer 67 .

[0135] In this example, the reducer 67 is a worm reducer. That is, the reducer 67 is configured by meshing worm teeth provided on the outer peripheral surface of a worm 68 connected to the output shaft of the shift motor 66 with wheel teeth 49 provided on the outer peripheral surface of the drive cam 34. The worm 68 is rotatably supported with respect to the fixed part 10 by a pair of support bearings 69 a, 69 b.

[0136] However, the reducer 67 can also be constructed by meshing a spur gear or bevel gear provided on the output shaft of the electric motor with a spur gear or bevel gear provided on the drive cam, or by stretching a belt or chain between the output shaft of the electric motor and the drive cam.

[0137] In this example, a return spring 70 is further provided between the first friction plate 30 and the second friction plate 31, which elastically biases the first friction plate 30 and the second friction plate 31 in a direction that widens the gap between them. The elastic force of the return spring 70 is smaller than the elastic restoring force of the elastic member 33 of the elastic biasing member 27. When the frictional engagement portion 26 is to be put into a disconnected state, the action of the return spring 70 widens the gap between the first friction plate 30 and the second friction plate 31, making it possible to reliably disconnect the frictional engagement portion 26.

[0138] The two-speed transmission 1 of this example has a first mode in which the rotation transmission state switching device 8 is in free mode and the friction engagement device 7 is in connected mode, and a second mode in which the rotation transmission state switching device 8 is in locked mode and the friction engagement device 7 is in disconnected mode.

[0139] Specifically, when the two-speed transmission 1 is switched to the first mode by setting the rotation transmission state switching device 8 to the free mode and the friction engagement device 7 to the connected mode, the planetary transmission mechanism 9 is placed in a glued state in which the entire planetary transmission mechanism 9 rotates as a single unit. In this state, the torque input to the input member 4 is transmitted to the output member 5 as is without being increased.

[0140] In contrast, when the two-speed transmission 1 is switched to the second mode by setting the rotation transmission state switching device 8 to the lock mode and the friction engagement device 7 to the disengagement mode, the torque input to the input member 4 is increased by the planetary transmission mechanism 9 and then transmitted to the output member 5. That is, in the two-speed transmission 1 of this example, the first mode corresponds to a low reduction ratio mode in which the reduction ratio between the input member 4 and the output member 5 is small, and the second mode corresponds to a high reduction ratio mode in which the reduction ratio is larger than that in the low reduction ratio mode.

[0141] The two-speed transmission 1 of this example passes through a reduction ratio switching mode during switching from the high reduction ratio mode (second mode) to the low reduction ratio mode (first mode). Furthermore, the two-speed transmission 1 of this example can also be switched to a neutral mode in which torque is not transmitted between the input member 4 and the output member 5, and a parking mode in which rotation of the output member 5 is locked.

[0142] <Low Reduction Ratio Mode (First Mode)> To switch the two-speed transmission 1 to the low reduction ratio mode, the friction engagement device 7 is switched to the connection mode, and the rotation transmission state switching device 8 is switched to the free mode.

[0143] In this example, the driving cam 34 is rotated by the electric actuator 29, causing the rolling element 36 to be positioned at the first bottom portion 48a of the driving cam surface 48, and displacing the driven cam 35 in a direction (toward the other axial side) that reduces the axial distance between the driving cam 34 and the driven cam 35. This causes the force of the elastic biasing member 27 that presses the piston 32 toward one axial side to be lost.

[0144] The piston 32, thrust bearing 57, and pressing member 58 are pressed toward the other axial side mainly by the elastic restoring force of the first friction plate 30 and the elastic member 33, and the piston 32 presses the first friction plate 30 or the second friction plate 31 closest to one axial side toward the other axial side.

[0145] As a result, the first friction plate 30 and the second friction plate 31 are pressed against each other, the friction engagement portion 26 is connected, and the friction engagement device 7 is switched to the connection mode. As a result, the input member 4 and the rotating member 6 rotate integrally, and the sun gear 101 and the ring gear 102 rotate integrally.

[0146] When the friction engagement device 7 is switched to the connection mode, the circumferential phase of the mode select member 73 relative to the second member 72 is adjusted, and as shown in Figure 19 (A), the protrusion 97 pushes the first engagement claw 91 radially outward and also pushes the second engagement claw 94 radially outward.

[0147] As a result, the engagement recess 74 of the first member 71 disengages from the first engagement claw 91 and the second engagement claw 94, and the rotation transmission state switching device 8 switches to a free mode in which the rotation of the first member 71 relative to the second member 72 is permitted regardless of the relative rotation direction between the first member 71 and the second member 72. As a result, the rotation of the rotating member 6 relative to the fixed part 10 is permitted, and the rotation of the sun gear 101 is permitted.

[0148] In the low reduction ratio mode, the sun gear 101, ring gear 102, and carrier 103 rotate in the same direction and at the same speed, and the entire planetary transmission mechanism 9 rotates as a unit, creating a glued state. Therefore, the rotational torque of the input member 4 is transmitted in this order to the input member 4, carrier 103, and output member 5, as shown by the thick line in Figure 2(a), and is extracted from the output member 5.

[0149] <High Reduction Ratio Mode (Second Mode)> To switch the two-speed transmission 1 to the high reduction ratio mode, the friction engagement device 7 is switched to the disengagement mode, and the rotation transmission state switching device 8 is switched to the lock mode.

[0150] In this example, by rotating the drive cam 34 using the electric actuator 29, the rolling element 36 is positioned on the first flat surface portion 48c of the drive cam surface 48, and the driven cam 35 is displaced in a direction (to one axial side) that increases the axial distance between the drive cam 34 and the driven cam 35. This presses the piston 32 of the elastic biasing member 27 toward one axial side via the thrust bearing 57 and the pressing member 58, elastically compressing the elastic member 33 and eliminating the force pressing the first friction plate 30 and the second friction plate 31 against each other.

[0151] The action of the return spring 70 widens the gap between the first friction plate 30 and the second friction plate 31, and the friction engagement portion 26 is disconnected, switching the friction engagement device 7 to the disconnection mode. As a result, the input member 4 and the rotating member 6 begin to rotate relative to each other, and the sun gear 101 and the ring gear 102 become rotatable relative to each other.

[0152] By switching the friction engagement device 7 to the cutting mode and simultaneously adjusting the circumferential phase of the mode select member 73 relative to the second member 72, the protrusion 97 is positioned at a position circumferentially offset from the first engagement claw 91 and the second engagement claw 94, as shown in Figure 19 (B).

[0153] As a result, the engagement recess 74 of the first member 71 engages with the first engagement claw 91 and the second engagement claw 94, and the rotation transmission state switching device 8 switches to a lock mode in which rotation of the first member 71 relative to the second member 72 is prevented, regardless of the relative rotation direction between the first member 71 and the second member 72. As a result, rotation of the rotating member 6 relative to the fixed part 10 is prevented, and rotation of the sun gear 101 is prevented.

[0154] 2B, the rotational torque of the input member 4 is transmitted in the following order: input member 4, ring gear 102, rotational motion of planetary gear 104, orbital motion of planetary gear 104 based on meshing with sun gear 101, carrier 103, and output member 5, and is then extracted from the output member 5. In the high reduction ratio mode, the reduction ratio between the input member 4 and the output member 5 is determined by the gear ratio of ring gear 102 and sun gear 101 (number of teeth of ring gear 102 / number of teeth of sun gear 101).

[0155] In the two-speed transmission 1 of this example, the reduction ratio between the input member 4 and the output member 5 can be switched between two levels, high and low, by switching the mode of the friction engagement device 7 and the mode of the rotation transmission state switching device 8 based on the rotational driving of one drive cam 34 by one electric actuator 29.

[0156] Specifically, for example, when the power input to the input member 4 is in a low-speed, high-torque region, the two-speed transmission 1 is switched to a high reduction ratio mode, and when the power is input to the input member 4 is in a high-speed, low-torque region, the two-speed transmission 1 is switched to a low reduction ratio mode. As a result, the acceleration performance and high-speed performance of an electric vehicle or hybrid vehicle running solely using an electric motor as a drive source can be made to have characteristics that are continuous between the portion of the solid line a to the left of point P in Figure 41 and the portion of the chain line b to the right of point P, and are similar to those of a gasoline engine vehicle shown by the dashed line c in Figure 41.

[0157] In the two-speed transmission 1 of this example, the mode of the friction engagement device 7 and the mode of the rotation transmission state switching device 8 are switched based on the rotational driving of one drive cam 34 by the electric actuator 29. In other words, the two-speed transmission 1 of this example does not require a hydraulic system to control friction engagement devices such as clutches and brakes. This allows for simplification of the system in electric vehicles and hybrid vehicles, reducing costs and improving fuel economy.

[0158] When implementing the two-speed transmission of the present disclosure, the mode switching of the friction engagement device and the mode switching of the rotation transmission state switching device can be performed by separate actuators.

[0159] In this example, in order to prevent the occurrence of shift shock that accompanies switching from the high reduction ratio mode to the low reduction ratio mode, the output torque and rotation speed Rs of the drive motor 2 and the rotation speed of the shift motor 66 are controlled, and the two-speed transmission 1 is switched to the reduction ratio switching mode. This prevents discontinuous changes in the rotation torque of the output member 5, and allows switching from the high reduction ratio mode to the low reduction ratio mode.

[0160] <Reduction ratio switching mode> When the two-speed transmission 1 starts to switch from the high reduction ratio mode to the low reduction ratio mode, first, based on adjusting the circumferential phase of the mode select member 73 relative to the second member 72, the protrusion 97 pushes only the second engagement claw 94 radially outward against the elastic force of the second claw biasing member 89, as shown in Figure 19 (C).

[0161] As a result, only the first engagement claw 91 engages with the engagement recess 74 of the first member 71, and the rotation transmission state switching device 8 switches to a one-way clutch mode that allows only rotation of the first member 71 relative to the second member 72 in the specified direction (the specified direction in Figure 19 (C)) and prevents rotation in the direction opposite to the specified direction.

[0162] At the same time as or after the rotation transmission state switching device 8 switches to the one-way clutch mode, the friction engagement device 7 starts to switch from the disconnection mode to the connection mode. During the switching of the friction engagement device 7 from the disconnection mode to the connection mode, the rolling element 36 moves down the first inclined surface portion 48b of the drive cam surface 48 based on the rotation of the drive cam 34 from the state shown in Figure 14(B) to the state shown in Figure 14(A).

[0163] As the amount of the rolling element 36 riding up from the first bottom portion 48a of the drive cam surface 48 gradually decreases, the force pressing the first friction plate 30 and the second friction plate 31 against each other gradually increases (the fastening force F of the friction engagement portion 26 gradually increases). At this time, the input member 4 rotates while sliding (while making sliding contact) both axial side surfaces of the second friction plate 31 against both axial side surfaces of the first friction plate 30.

[0164] As the fastening force F of the friction engagement portion 26 gradually increases during rotation of the input member 4 in the forward direction, the torque applied to the second member 72 of the rotation transmission state switching device 8 in the direction opposite to the predetermined direction gradually decreases. At this time, because the rotation transmission state switching device 8 is switched to the one-way clutch mode, the second member 72 does not rotate even if torque is applied to the second member 72 in the direction opposite to the predetermined direction. After the torque applied to the second member 72 in the direction opposite to the predetermined direction gradually decreases to zero, the direction of the torque applied to the second member 72 reverses (torque in the predetermined direction is applied to the second member 72), and at that moment, the second member 72 is permitted to rotate in the predetermined direction.

[0165] <Neutral Mode> To switch the two-speed transmission 1 to the neutral mode, the friction engagement device 7 is switched to the disengagement mode, and the rotation transmission state switching device 8 is switched to the free mode.

[0166] As the driving cam 34 is rotated by the electric actuator 29, the rolling element 36 is positioned on the second flat surface portion 48g of the driving cam surface 48, and the driven cam 35 is displaced in a direction (to one axial side) that increases the axial distance between the driving cam 34 and the driven cam 35. This presses the piston 32 of the elastic biasing member 27 toward one axial side via the thrust bearing 57 and the pressing member 58, elastically compressing the elastic member 33 and eliminating the force pressing the first friction plate 30 and the second friction plate 31 against each other.

[0167] The action of the return spring 70 widens the gap between the first friction plate 30 and the second friction plate 31, and the friction engagement portion 26 is disconnected, switching the friction engagement device 7 to the disconnection mode. As a result, the input member 4 and the rotating member 6 begin to rotate relative to each other, and the sun gear 101 and the ring gear 102 become rotatable relative to each other.

[0168] When the friction engagement device 7 is switched to the connection mode, the circumferential phase of the mode select member 73 relative to the second member 72 is adjusted, and as shown in Figure 19 (A), the protrusion 97 pushes the first engagement claw 91 radially outward and also pushes the second engagement claw 94 radially outward.

[0169] As a result, the engagement recess 74 of the first member 71 disengages from the first engagement claw 91 and the second engagement claw 94, and the rotation transmission state switching device 8 switches to a free mode in which the rotation of the first member 71 relative to the second member 72 is permitted regardless of the relative rotation direction between the first member 71 and the second member 72. As a result, the rotation of the rotating member 6 relative to the fixed part 10 is permitted, and the rotation of the sun gear 101 is permitted.

[0170] In the neutral mode, the input member 4 and the output member 5 rotate freely relative to each other, and no torque is transmitted between the input member 4 and the output member 5 .

[0171] <Parking Lock Mode> To switch the two-speed transmission 1 to the parking lock mode, the friction engagement device 7 is switched to the connection mode, and the rotation transmission state switching device 8 is switched to the lock mode.

[0172] When the driving cam 34 is rotated by the electric actuator 29, the rolling element 36 is positioned at the second bottom portion 48e of the driving cam surface 48, and the driven cam 35 is displaced in a direction that reduces the axial distance between the driving cam 34 and the driven cam 35 (toward the other axial side). This causes the force of the elastic biasing member 27 pressing the piston 32 toward one axial side to be lost. Then, the piston 32, the thrust bearing 57, and the pressing member 58 are pressed toward the other axial side mainly by the elastic restoring forces of the first friction plate 30 and the elastic member 33, and the first friction plate 30 or the second friction plate 31 closest to one axial side is pressed toward the other axial side by the piston 32.

[0173] As a result, the first friction plate 30 and the second friction plate 31 are pressed against each other, the friction engagement portion 26 is engaged, and the friction engagement device 7 is switched to the engaged mode. As a result, rotation of the input member 4 relative to the rotating member 6 is prevented, and rotation of the ring gear 102 relative to the sun gear 101 is prevented.

[0174] At the same time as switching the friction engagement device 7 to the connection mode, the circumferential phase of the mode select member 73 relative to the second member 72 is adjusted, and the protrusion 97 is positioned in a portion circumferentially offset from the first engagement claw 91 and the second engagement claw 94, as shown in Figure 19 (B).

[0175] As a result, the engagement recess 74 of the first member 71 engages with the first engagement claw 91 and the second engagement claw 94, and the rotation transmission state switching device 8 switches to a lock mode in which rotation of the first member 71 relative to the second member 72 is prevented, regardless of the relative rotation direction between the first member 71 and the second member 72. As a result, rotation of the rotating member 6 relative to the fixed part 10 is prevented, and rotation of the sun gear 101 is prevented.

[0176] In the parking lock mode, the input member 4 and the output member 5 are locked from rotation.

[0177] 25 and 26, a description will be given of the control of the drive motor 2 and the shift motor 66 for preventing discontinuous (sudden) changes in the rotational torque of the output member 5 and preventing the occurrence of gear shift shock when switching from the high reduction ratio mode to the low reduction ratio mode. Below, an example will be described in which the rotational torque of the output member 5 is maintained approximately constant before and after switching from the high reduction ratio mode to the low reduction ratio mode.

[0178] When switching from the high reduction ratio mode to the low reduction ratio mode is initiated based on conditions such as the vehicle running speed and accelerator opening, the electric actuator 29 first rotates the drive cam 34, thereby switching the rotation transmission state switching device 8 to the one-way clutch mode, and then adjusting the phase of the drive cam 34 in the rotation direction to the clutch touch point θ ｆ (S1).

[0179] Clutch touch point θ ｆ is the point at which the elastic biasing member 27 starts to generate a force that presses the first friction plate 30 and the second friction plate 31 against each other. In other words, the clutch touch point θ ｆ is the point at which the other axial end of the piston 32 begins to come into contact with the first friction plate 30 or the second friction plate 31 located at the most axial side, i.e., the clutch clearance C ｆ (see FIG. 24) is the point where the clutch touch point θ ｆ is calculated in advance using a function to be described later.

[0180] The phase of the drive cam 34 in the rotation direction is defined as the clutch touch point θ ｆ When the drive cam 34 is moved to the position indicated by arrow S1, the system transitions to the torque phase (S2). In the torque phase, the electric actuator 29 rotates the drive cam 34 at a predetermined number of rotations (rotational speed), thereby gradually increasing the pressing force between the first friction plate 30 and the second friction plate 31, i.e., the fastening force F of the friction engagement portion 26, by reducing the amount of the rolling elements 36 that climb up from the first bottom portion 48a. At the same time, the output torque of the drive motor 2 is gradually increased.

[0181] That is, if the output torque of the drive motor 2 is maintained constant, in the torque phase, as the fastening force F of the friction engagement portion 26 increases, the torque transmitted to the friction engagement portion 26 increases, resulting in a decrease in the rotational torque of the output member 5. In the two-speed transmission 1 of this example, the output torque of the drive motor 2 is gradually increased in accordance with the increase in the fastening force F of the friction engagement portion 26, i.e., the amount of rotation of the drive cam 34, so that the rotational torque of the output member 5 can be maintained approximately constant regardless of the increase in the fastening force F of the friction engagement portion 26.

[0182] The relationship between the amount of rotation of the drive cam 34 and the increase in output torque of the drive motor 2 is determined in advance by experiment or calculation. In this example, the rotation speed of the drive cam 34 in S2 is set to be smaller than the rotation speed of the drive cam 34 in S1. However, the rotation speed of the drive cam 34 in S2 can also be set to be the same as the rotation speed of the drive cam 34 in S1, or can be set to be larger than the rotation speed of the drive cam 34 in S1.

[0183] More specifically, in S2, the drive cam 34 is rotated by a predetermined angle, and at the same time, the output torque of the drive motor 2 is increased by an amount corresponding to the amount of rotation of the drive cam 34. In the next S3, it is determined whether the torque phase has ended.

[0184] In the torque phase, as the fastening force F of the frictional engagement portion 26 increases, the clutch torque, which is the torque transmitted to (passing through) the frictional engagement portion 26, increases, and the torque applied to the second member 72 of the rotation transmission state switching device 8 in the direction opposite to the predetermined direction gradually decreases. After the torque applied to the second member 72 in the direction opposite to the predetermined direction gradually decreases to zero, the direction of the torque applied to the second member 72 reverses (torque in the predetermined direction is applied to the second member 72). At that moment, the second member 72 is permitted to rotate in the predetermined direction, and the sun gear 101 is permitted to rotate. When the sun gear 101 rotates, the rotation speed Rs of the output shaft 11 of the drive motor 2 begins to decrease.

[0185] In the two-speed transmission 1 of this example, it is determined that the torque phase has ended when it is determined that the rotation speed Rs of the output shaft 11 has decreased by a predetermined value or more, based on the output signal of the rotation sensor attached to the output shaft 11 of the drive motor 2. This determination is made based on the rotation sensor attached to the output shaft 11 of the drive motor 2.

[0186] If it is determined that the rotation speed Rs of the output shaft 11 is substantially constant, that is, the amount of decrease in the rotation speed Rs of the output shaft 11 is smaller than the predetermined value and the torque phase has not ended, the process returns to S2.

[0187] In S3, if it is determined that the amount of decrease in the rotational speed Rs of the output shaft 11 is equal to or greater than a predetermined value and the torque phase has ended, the process moves to the inertia phase (S4-1 to S4-3).

[0188] In the inertia phase, first, the output torque of the drive motor 2 is quickly reduced to promote a further decrease in the rotation speed Rs of the output shaft 11 (S4-1). The amount of reduction in the output torque of the drive motor 2 is not particularly limited as long as it promotes a further decrease in the rotation speed Rs of the output shaft 11. Specifically, for example, the output torque of the drive motor 2 can be reduced to 0 or a negative value.

[0189] When the rotation speed Rs of the output shaft 11 begins to decrease, the output torque of the drive motor 2 is increased so that the rotational torque of the input member 4 becomes the target torque, which is the rotational torque that should be output by the output member 5 when the two-speed transmission 1 has completed switching to the low reduction ratio mode (S4-2). In this example, because the rotational torque of the output member 5 is kept substantially constant before and after switching from the high reduction ratio mode to the low reduction ratio mode, the output torque of the drive motor 2 is increased until the rotational torque of the input member 4 becomes equal to the rotational torque of the output member 5 at the start of switching from the high reduction ratio mode to the low reduction ratio mode.

[0190] The rate at which the output torque of the drive motor 2 is increased is controlled so that the rotational torque of the input member 4 can be increased to the target torque by the time the inertia phase is completed. In this example, the output torque of the drive motor 2 is controlled based on the friction coefficient μ between the first friction plates 30 and the second friction plates 31 and the difference (differential rotation) V between the input rotational speed Rin and the output rotational speed Rout of the frictional engagement unit 26. The input rotational speed Rin of the frictional engagement unit 26 is the rotational speed of the first friction plates 30, and in this example, is the same as the rotational speed of the ring gear 102 and the rotational speed of the input member 4. Furthermore, the output rotational speed Rout of the frictional engagement unit 26 is the rotational speed of the second friction plates 31, and in this example, is the same as the rotational speed of the sun gear 101.

[0191] In the two-speed transmission 1 of this example, as the rotation speed Rs of the output shaft 11 decreases, the rotation speed of the input member 4 decreases, and as the differential rotation V becomes smaller, the output torque of the drive motor 2 is increased, and when the differential rotation V becomes 0, the rotation torque of the input member 4 is controlled to become the target torque. The μ-V characteristic, which is the relationship between the friction coefficient μ and the differential rotation V, is obtained in advance using a function described below.

[0192] Next, in S4-3, it is determined whether the differential rotation speed V is 0. In the two-speed transmission 1 of this example, when the differential rotation speed V becomes 0 and the input rotation speed Rin and output rotation speed Rout of the friction engagement unit 26 become equal, the planetary transmission mechanism 9 enters a glued state, and the rotation speed of the input member 4 and the rotation speed of the output member 5 become equal.

[0193] In this example, it is determined whether the rotation speed difference V is 0 by determining whether the rotation speed of the input member 4 is equal to the rotation speed of the output member 5. Specifically, it is determined whether the difference ΔR between the rotation speed of the input member 4 and the rotation speed of the output member 5 falls within a predetermined range. This determination is made based on the output signals of rotation sensors attached to the output shaft 11 or the input member 4 and the output member 5, respectively.

[0194] If it is determined that the difference ΔR is not within the predetermined range, that is, the differential rotation V is not 0, S4-3 is executed again after a predetermined time has elapsed.

[0195] If it is determined that the difference ΔR is within a predetermined range, that is, the differential rotation V is 0, it is determined that the inertia phase has ended, and the process proceeds to the next step S5.

[0196] In S5, the electric actuator 29 rotates the driving cam 34 to a predetermined circumferential phase, positioning the rolling element 36 at the first bottom portion 48a of the driving cam surface 48, and displacing the driven cam 35 toward the other axial side in a direction that reduces the axial distance between the driving cam 34 and the driven cam 35. As a result, the piston clearance C between the end of one axial side of the pressing member 58 and the other axial side of the piston 32 is reduced. ｐ In other words, the piston clearance C ｐ is set to 0 or more, preferably greater than 0.

[0197] After the rolling element 36 has been moved to the first bottom portion 48a, the process proceeds to "End." As a result of the above, the two-speed transmission 1 is switched from the high reduction ratio mode to the low reduction ratio mode. Thereafter, the phase of the drive cam 34 in the circumferential direction is maintained, thereby maintaining the two-speed transmission 1 in the low reduction ratio mode.

[0198] In the two-speed transmission 1 of this example, by controlling the drive motor 2 and the shift motor 66, it is possible to prevent a (sudden) change in the rotational torque of the output member 5 and prevent the occurrence of gear shift shock, even when switching between the high reduction ratio mode and the low reduction ratio mode. However, in order to prevent the occurrence of gear shift shock, the timing for controlling the output torque and rotation speed Rs of the drive motor 2 and the rotation of the shift motor 66 becomes important.

[0199] For example, if the phase of the drive cam 34 in the rotation direction is ｆ If the process proceeds to S2 and the output torque of the drive motor 2 is increased even though the torque has not yet reached this value, there is a possibility that the rotational torque of the output member 5 will increase inadvertently, as shown by the dashed line in Figure 26 (F).

[0200] As the two-speed transmission 1 is used, the amount of wear on the first friction plate 30 and the second friction plate 31 increases, and the amount of pressure required by the elastic biasing member 27 to press the first friction plate 30 or the second friction plate 31 on the axially most side toward the other axial side in order to switch the friction engagement device 7 to the connection mode increases.

[0201] In other words, the amount of pressure required by the cam device 28 to press the piston 32 to one side in the axial direction when switching the friction engagement device 7 to the disengagement mode decreases. As a result, the relationship between the rotation angle θ of the drive cam 34 and the current value A of the shift motor 66 changes from the state shown in Figure 21(a) to the state shown in Figure 21(b). In other words, as the amount of wear of the first friction plate 30 and the second friction plate 31 increases, the clutch touch point θ ｆ becomes smaller.

[0202] 21(a) and 21(b) are diagrams showing the relationship between the rotation angle θ of the drive cam 34 and the output torque T and current value A of the shift motor 66 when the friction engagement device 7 is switched from the connection mode to the disconnection mode. Fig. 21(a) shows the case where the first friction plates 30 and the second friction plates 31 are new and not worn, while Fig. 21(b) shows the case where the first friction plates 30 and the second friction plates 31 have worn significantly.

[0203] When the wear amount of the first friction plate 30 and the second friction plate 31 increases, the piston touch point θ ｐ The piston touch point θ ｐ is the point at which the elastic biasing member 27 starts to be pressed in a direction to release the force pressing the first friction plate 30 and the second friction plate 31 against each other when the drive cam 34 is rotated in a direction to switch the friction engagement portion 26 from the connected state to the disconnected state. ｐ When the drive cam 34 is rotated in a direction to switch the friction engagement portion 26 from the disconnected state to the connected state, the piston clearance C between the end of one axial side of the pressing member 58 and the other axial side of the piston 32 is ｐ (See FIG. 22) begins to occur.

[0204] The two-speed transmission 1 of this example has a function for preventing shift shock regardless of wear of the first friction plate 30 and the second friction plate 31. Specifically, the two-speed transmission 1 of this example has a piston touch point θ ｐ The first function is to detect the clutch touch point θ ｆ and a second function of detecting the rotation amount of the drive cam 34 when switching between the high reduction ratio mode and the low reduction ratio mode. ｐ and / or clutch touch point θ ｆ and a third function of adjusting based on the

[0205] 21(a) and 21(b), when the mode of the friction engagement device 7 is switched, the output torque T of the shift motor 66 and the current value A of the shift motor 66 change in the same manner. ｐ and clutch touch point θ ｆ is detected based on the current value A of the shift motor 66 when the friction engagement device 7 is switched from the connection mode to the disconnection mode.

[0206] When the friction engagement device 7 is switched to the connection mode, the rolling element 36 of the cam device 28 is located at the first bottom portion 48a of the drive cam surface 48. In this state, as shown in FIG. 22 , a piston clearance C is formed between one axial end of the pressing member 58 and the other axial side surface of the piston 32. ｐ This piston clearance C ｐ Based on the presence of the elastic member 33, displacement of the piston 32 toward the other axial side is permitted. Therefore, the piston 32 is elastically pressed toward the other axial side by the force of the elastic member 33 attempting to elastically restore its original shape, and the piston 32 presses the first friction plate 30 or the second friction plate 31 closest to one axial side toward the other axial side, causing the first friction plate 30 and the second friction plate 31 to press against each other.

[0207] To switch the friction engagement device 7 from the connection mode to the disconnection mode, the drive cam 34 is rotated in the predetermined direction by energizing the shift motor 66, thereby increasing the amount of the rolling element 36 that climbs above the first bottom portion 48a. At this time, the current value A of the shift motor 66 remains substantially constant (range α in FIGS. 21(a) and 21(b)), except for a temporary starting current.

[0208] When the pressing member 58 is moved toward one axial side by increasing the amount of the rolling element 36 riding up from the first bottom portion 48a, the end of the pressing member 58 on one axial side comes into contact with the other axial side surface of the piston 32, as shown in FIG. ｐ becomes 0.

[0209] 23, when drive cam 34 is further rotated in the predetermined direction by shift motor 66, driven cam 35 presses piston 32 toward one axial direction via pressing member 58 against the elastic restoring force of elastic member 33. In this state, part of the elastic restoring force of elastic member 33 is borne by cam device 28 via pressing member 58 and thrust bearing 57, and the remainder is borne by fixed part 10 via friction engagement portion 26 and rotation transmission state switching device 8.

[0210] As the piston 32 is pressed toward one side in the axial direction, the force pressing the first friction plate 30 and the second friction plate 31 against each other gradually decreases, mainly based on the elastic restoring force of the second friction plate 31 and the elastic member 33. In other words, the fastening force F of the friction engagement portion 26 gradually decreases.

[0211] While the fastening force F of the frictional engagement portion 26 is gradually reduced, the current value A of the shift motor 66 increases at a substantially constant rate (slope) (range β in FIGS. 21A and 21B). That is, the rate of increase of the current value A in range β is greater than the rate of increase of the current value A in range α.

[0212] In the two-speed transmission 1 of this example, after the first function starts energizing the shift motor 66 to switch the friction engagement device 7 from the engagement mode to the disengagement mode, the phase (rotation angle from a reference position (for example, an initial position where the rolling element 36 is located at the bottom of the recess)) θ in the rotation direction of the drive cam 34 when the current value A of the shift motor 66 starts to increase at an increasing rate equal to or greater than a predetermined first threshold value is calculated by multiplying the phase θ by the piston clearance C ｐ Piston touch point θ where ｐ The first threshold value can be determined in advance by experiment, simulation, or the like.

[0213] The rate of increase in the current value A is the increase ΔA in the current value A per unit rotation angle Δθ of the drive cam 34. When the drive cam 34 is rotated in the predetermined direction at a constant rotation speed, the increase ΔA in the current value A per unit time can also be used for the determination.

[0214] The fastening force F of the friction engagement portion 26 gradually decreases, and from that moment on, as shown in FIG. 24, a clutch clearance C is generated between the other axial end of the piston 32 and the first friction plate 30 or the second friction plate 31 located furthest to one axial side. ｆ Clutch clearance C ｆ When this force begins to occur, almost all of the elastic restoring force of the elastic member 33 is borne by the cam device 28 via the pressing member 58 and the thrust bearing 57 .

[0215] In this way, the clutch clearance C ｆ After this begins to occur, current value A of shift motor 66 increases slowly and logarithmically (range γ in FIGS. 21(a) and 21(b)). That is, the rate of increase of current value A in range γ is smaller than the rate of increase of current value A in range β.

[0216] In the two-speed transmission 1 of this example, when the friction engagement device 7 is switched from the engagement mode to the disengagement mode, the phase of the drive cam 34 in the rotation direction is changed to the piston touch point θ ｐThe phase θ in the rotation direction of the drive cam 34 when the rate of increase of the current value A of the shift motor 66 becomes equal to or less than the second threshold value after exceeding the second threshold value is defined as the clutch clearance C. ｆ Clutch touch point θ becomes 0 ｆ The second threshold value is smaller than the first threshold value. The second threshold value can be determined in advance by experiment, simulation, or the like.

[0217] Piston touch point θ ｐ and clutch touch point θ ｆ The detection of (a) can be performed at any timing as long as it does not impede the running of the automobile equipped with the two-speed transmission 1. Specifically, it can be performed, for example, immediately after the ignition key is turned on, or when the two-speed transmission 1 is switched from the low reduction ratio mode to the high reduction ratio mode, such as during kickdown acceleration or engine braking.

[0218] However, if the above operation is performed while the vehicle is running, there is a problem that the drive cam 34 cannot be driven at an arbitrary rotation speed. ｐ and clutch touch point θ ｆ It is preferable to detect the piston touch point θ while the vehicle is stopped, such as immediately after the ignition key is turned on. ｐ and clutch touch point θ ｆ The detection can be performed every time when the detection can be performed, or can be performed when a predetermined time has passed since the previous detection.

[0219] In the two-speed transmission 1 of this example, when switching between the high reduction ratio mode and the low reduction ratio mode, the rotation amount of the drive cam 34, which is rotationally driven by the shift motor 66 via the reducer 67, is calculated based on the piston touch point θ ｐ and / or the clutch touch point θ detected by the second function. ｆSpecifically, for example, when the rotational torque of the output member 5 is maintained substantially constant before and after switching from the high reduction ratio mode to the low reduction ratio mode, in S1, the clutch touch point θ detected by the second function is used as the target value of the phase in the rotational direction of the drive cam 34. ｆ Use.

[0220] In the two-speed transmission 1 of this example, the piston touch point θ ｐ and clutch touch point θ ｆ Even if the initial position is changed, the corrected piston touch point θ ｐ and clutch touch point θ ｆ Therefore, according to the two-speed transmission 1 of this embodiment, it is possible to prevent the occurrence of gear shift shock regardless of the wear of the first friction plates 30 and the second friction plates 31.

[0221] The two-speed transmission 1 in this example switches modes between a first mode (in this example, a low reduction ratio mode) and a second mode (in this example, a high reduction ratio mode) on the condition that predetermined learning start conditions are satisfied, and during the inertia phase during the mode switching, calculates the friction coefficient between the first friction plate 30 and the second friction plate 31 based on the output torque of the drive motor 2 and the angular acceleration of the output shaft 11 of the drive motor 2, thereby obtaining the μ-V characteristic, which is the relationship between the friction coefficient and the differential rotation, which is the difference in rotation speed between any two of the elements (in this example, the sun gear 101 and the ring gear 102), (executing a μ-V characteristic learning method).

[0222] The two-speed transmission 1 in this example has the function of controlling the output torque of the drive motor 2 and the magnitude of the force pressing the first friction plate 30 and the second friction plate 31 against each other (executing the speed change control method of the two-speed transmission 1) based on the μ-V characteristic obtained by the learning function when switching between the first mode (in this example, low reduction ratio mode) and the second mode (in this example, high reduction ratio mode).

[0223] The μ-V characteristic of the friction engagement unit 26 changes with changes in the operating environment, such as the oil temperature of the lubricating oil and the surface temperature of the contact area (sliding area) between the first friction plate 30 and the second friction plate 31, as well as with deterioration over time. The two-speed transmission 1 of this example executes a learning function that obtains the μ-V characteristic of the friction engagement unit 26 on the condition that predetermined learning start conditions are satisfied, and also executes a speed change control function that, when switching between the high reduction ratio mode and the low reduction ratio mode, controls the output torque of the drive motor 2 in the torque phase and the magnitude of the force pressing the first friction plate 30 and the second friction plate 31 against each other in the inertia phase, i.e., the fastening force F of the friction engagement unit 26, based on the μ-V characteristic obtained by the learning function.

[0224] In the learning function of the two-speed transmission 1 in this example, the difference V between the input rotation speed and the output rotation speed to the friction engagement portion 26 (the difference between the rotation speed of the first friction plate 30 and the rotation speed of the second friction plate 31, the differential rotation) is used as the difference in rotation speed between any two of the elements (in this example, the sun gear 101 and the ring gear 102).

[0225] The learning start condition can be any condition as long as it does not interfere with the running of the automobile equipped with the two-speed transmission 1 and allows the two-speed transmission 1 to switch between the high reduction ratio mode and the low reduction ratio mode. For example, the learning start condition can be implemented when the automobile is running and the two-speed transmission 1 is switched from the high reduction ratio mode to the low reduction ratio mode, or from the low reduction ratio mode to the high reduction ratio mode.

[0226] The μ-V characteristic learning function can be executed every time the learning function can be executed. Alternatively, the learning start conditions can include the passage of a predetermined time since the previous execution and / or the occurrence of a change in the operating environment, such as a change in the lubricating oil temperature, the surface temperature of the sliding contact portion between the first friction plate 30 and the second friction plate 31, or the outside air temperature by a predetermined temperature or more.

[0227] The timing for executing the learning function can be set to be immediately before the mode switch between the high reduction ratio mode and the low reduction ratio mode, i.e., after the execution of the learning function has begun, provided that predetermined learning conditions are satisfied, or the learning function can be set to be executed immediately after the mode switch, i.e., immediately after the mode switch has begun.

[0228] Specifically, mode switching between the high reduction ratio mode and the low reduction ratio mode is performed so that the rotational torque and rotational speed Rout of the output member 5 can be maintained approximately constant before and after the mode switching. The μ-V characteristic is learned during the inertia phase during switching from the high reduction ratio mode to the low reduction ratio mode and / or from the low reduction ratio mode to the high reduction ratio mode. Below, a case where the μ-V characteristic is learned during the inertia phase during switching from the high reduction ratio mode to the low reduction ratio mode will be described.

[0229] The changeover from the high reduction ratio mode to the low reduction ratio mode is started, and the phase θ in the rotation direction of the drive cam 34 reaches the clutch touch point θ ｆ Thereafter, as the phase θ in the rotational direction of the drive cam 34 increases, the two-speed transmission 1 passes through the torque phase and the inertia phase in that order, and is then switched to the low reduction ratio mode.

[0230] As shown in FIG. 26, in the torque phase, the differential rotation V does not change and is maintained constant, whereas the clutch torque Tcl transmitted to (passing through) the friction engagement portion 26 increases.

[0231] During the inertia phase, the clutch torque Tcl does not change and is maintained constant, whereas the rotation speed Rs of the output shaft 11 of the drive motor 2 begins to decrease. When the rotation speed Rs of the output shaft 11 decreases, the rotation speed Rin of the input member 4 also decreases, and therefore the differential rotation V, which is the difference between the input rotation speed Rin and the output rotation speed Rout of the friction engagement unit 26, decreases.

[0232] It can be determined that the inertia phase has started when the differential rotation V has started to decrease, i.e., when the amount of change dV / dt of the differential rotation V per unit time exceeds a predetermined threshold. Specifically, in this example, it is determined that the inertia phase has started when it is determined that the rotation speed Rs of the output shaft 11 of the drive motor 2 has decreased by more than a predetermined value based on the output signal of the rotation sensor attached to the output shaft 11 of the drive motor 2.

[0233] In the inertia phase, the rotational torque Tin of the input member 4 and the angular acceleration dω of the input member 4 ｉｎ Further, the friction coefficient μ between the first friction plate 30 and the second friction plate 31 is calculated based on the clutch torque Tcl and the clutch load Fcl, and the μ-V characteristic, which is the relationship between the friction coefficient μ and the differential rotation V, is obtained.

[0234] In the two-speed transmission 1 of this example, the clutch torque Tcl [N·m] in the inertia phase can be calculated by the following equation (1).

[0235] In equation (1), α represents the reduction ratio of the planetary transmission mechanism 9 (= number of teeth of the sun gear 101 / number of teeth of the ring gear 102). ｉｎ represents the inertia (moment of inertia) of the part connected to the input member 4. The part connected to the input member 4 is a part that rotates integrally with the input member 4 regardless of the mode of the friction engagement device 7 and the mode of the rotation transmission state switching device 8. That is, I ｉｎ is the inertia of the combined body consisting of the input member 4, the ring gear 102, and the plurality of first friction plates 30.

[0236] I ｓｕｎ represents the inertia of the portion connected to the sun gear 101. The portion connected to the sun gear 101 rotates integrally with the sun gear 101 when the sun gear 101 rotates, regardless of the mode of the friction engagement device 7 and the mode of the rotation transmission state switching device 8, and does not rotate when the sun gear 101 does not rotate. That is, I ｓｕｎis the inertia of the combined body consisting of the rotating member 6, the sun gear 101, the plurality of second friction plates 31, and the first member 71.

[0237] The clutch torque Tcl in the inertia phase can also be calculated by the following equation (2).

[0238] In equation (2), Fcl represents the force that presses the first friction plate 30 and the second friction plate 31 against each other, i.e., the clutch load. The clutch load Fcl can be determined in advance by experiment or calculation at the time of shipment from a factory, or at the time of shipment and / or inspection of a vehicle equipped with the two-speed transmission 1, in relation to the phase θ in the rotational direction of the drive cam 34.

[0239] Rcl represents the effective radius of the friction engagement portion 26. The effective radius Rcl may be set to ¼ of the sum of the outer diameter and the inner diameter of the sliding contact portion between the first friction plate 30 and the second friction plate 31, or may be set to a radius such that the area of ​​the radially outer portion of the sliding contact portion between the first friction plate 30 and the second friction plate 31 is equal to the area of ​​the radially inner portion.

[0240] By modifying equation (2), the following equation (3) is obtained.

[0241] Furthermore, by substituting equation (1) into equation (3), the friction coefficient μ can be expressed by the following equation (4).

[0242] In equation (4), the rotational torque Tin of the input member 4 can be calculated based on the command value (control value) Tmot of the torque generated by the drive motor 2. That is, the rotational torque Tin of the input member 4 can be calculated by the following equation (5).

[0243] In equation (5), β represents the reduction ratio between the drive gear 12 and the input gear 13 (=number of teeth of the input gear 13 / number of teeth of the drive gear 12).

[0244] In equation (4), the angular acceleration dω of the input member 4 ｉｎ / dt can be obtained based on the output signal of a rotational speed sensor attached to the input member 4 or the output shaft 11 of the drive motor 2. The clutch load Fcl can be estimated from a relationship obtained in advance by experiment or calculation, based on the phase θ in the rotational direction of the drive cam 34.

[0245] As described above, in the inertia phase, the rotational torque Tin of the input member 4 and the angular acceleration dω of the input member 4 ｉｎ / dt, and further, the friction coefficient μ between the first friction plate 30 and the second friction plate 31 can be calculated based on the clutch torque Tcl and the clutch load Fcl.

[0246] The differential rotation V can be determined based on the output signals of rotation speed sensors attached to the input member 4 and the output member 5, respectively.

[0247] In the two-speed transmission 1 of this example, by determining the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase when switching from the high reduction ratio mode to the low reduction ratio mode, it is possible to determine the μ-V characteristic as shown in Figure 42. The μ-V characteristic is stored as a map or equation in the memory of a controller (not shown).

[0248] In reality, the clutch load Fcl also changes over time due to factors such as wear of the first friction plates 30 and the second friction plates 31 and deterioration of the elastic member 33 and the return spring 70. However, in the two-speed transmission 1 of this example, as shown in equations (4) and (5), the friction coefficient μ is calculated based on the clutch load Fcl that is determined in advance by experiment or calculation at the time of factory shipment, or at the time of shipment and / or inspection of a vehicle equipped with the two-speed transmission 1. This makes it possible to obtain a μ-V characteristic that includes the influence of changes in the clutch load Fcl over time.

[0249] In the above explanation, the μ-V characteristic is learned during the inertia phase during the switch from the high reduction ratio mode to the low reduction ratio mode. However, the μ-V characteristic can also be learned during the inertia phase during the switch from the low reduction ratio mode to the high reduction ratio mode.

[0250] The speed change control function of the two-speed transmission 1 of this example controls the output torque of the drive motor 2 in the torque phase and the fastening force F of the friction engagement unit 26 in the inertia phase based on the μ-V characteristics determined by the learning function when switching between the high reduction ratio mode and the low reduction ratio mode, thereby controlling the rotational torque of the output member 5. To control the fastening force F of the friction engagement unit 26, specifically, the shift motor 66 is controlled to control the rotation of the drive cam 34.

[0251] Even if the friction coefficient μ of the friction engagement portion 26 changes due to factors such as changes in the operating environment or deterioration over time, the two-speed transmission 1 of this example can perform gear shift control based on the μ-V characteristic that has been corrected for the amount of variation due to these factors. Therefore, with the two-speed transmission 1 of this example, it is possible to prevent gear shift shock from occurring regardless of the effects on the friction coefficient μ of factors such as changes in the operating environment or deterioration over time.

[0252] In the two-speed transmission 1 of this example, the reduction ratio change mode is passed through on the way to change from the high reduction ratio mode to the low reduction ratio mode, so that it is possible to suppress torque loss while suppressing the shift shock that accompanies the mode change. The reason for this will be explained with reference to Figures 27 and 28.

[0253] 27 shows a portion of a two-speed transmission of a comparative example. The two-speed transmission of the comparative example includes a first friction engagement device 105 that switches whether or not relative rotation is permitted between the input member 4 and the rotating member 6, in other words, whether or not relative rotation is permitted between the ring gear 102 and the sun gear 101, and a second friction engagement device 106 that switches whether or not rotation of the rotating member 6 is permitted relative to the fixed part 10, in other words, whether or not rotation of the sun gear 101 is permitted. That is, the two-speed transmission of the comparative example employs a second friction engagement device 106 that switches modes by pressing or separating the first friction plate 30 and the second friction plate 31 together, instead of the rotation transmission state switching device 8 of the two-speed transmission of the present example.

[0254] In the comparative example, the driving cam 34z of the cam device 28z is rotationally driven by an electric actuator, and the mode of the first friction engagement device 105 and the mode of the second friction engagement device 106 are switched based on the axial displacement of the first driven cam 107 and the second driven cam 108. The first driven cam 107 and the second driven cam 108 are displaced in different phases from each other as the driving cam 34z rotates (they are displaced (advanced and retreated) in opposite directions in the axial direction).

[0255] In the two-speed transmission of the comparative example, during switching from a high reduction ratio mode with a large reduction ratio to a low reduction ratio mode with a small reduction ratio, the fastening force of the first friction engagement device 105 gradually increases and the fastening force of the second friction engagement device 106 gradually decreases, as shown in Figure 28. For this reason, during switching from the high reduction ratio mode to the low reduction ratio mode, if the fastening force of the second friction engagement device 106 gradually decreases and becomes insufficient, the sun gear 101 is dragged by the revolution of the planetary gear 104, and a loss of torque occurs between the rotating member 6 and the fixed part 10.

[0256] In the two-speed transmission of the comparative example, as the fastening force of the first friction engagement device 105 gradually increases, the torque applied to the sun gear 101 in the direction opposite to the predetermined direction gradually decreases to zero, and then the direction of the torque applied to the sun gear 101 reverses. However, in the two-speed transmission of the comparative example, the fastening force of the second friction engagement device 106 cannot be made sufficiently large at the moment when the direction of the torque applied to the sun gear 101 reverses and the revolution direction of the planetary gear 104 and the rotation direction of the sun gear 101 coincide with each other. As a result, the sun gear 101 is dragged relative to the fixed part 10, and a loss of torque occurs between the sun gear 101 and the fixed part 10.

[0257] In the two-speed transmission 1 of this example, in order to switch from the high reduction ratio mode to the low reduction ratio mode based on the rotation of the drive cam 34, the rotation transmission state switching device 8 is set to the one-way clutch mode before the friction engagement device 7 starts to switch from the disengagement mode to the engagement mode. Therefore, in order to switch the friction engagement device 7 from the disengagement mode to the engagement mode, the fastening force F of the friction engagement portion 26 is gradually increased so that the sun gear 101 is allowed to rotate in the predetermined direction at the moment the direction of the torque applied to the sun gear 101 reverses. Therefore, it is possible to suppress torque loss in the two-speed transmission 1 while suppressing the shift shock associated with the mode switch.

[0258] In the reduction ratio switching mode, the reduction ratio between the input member 4 and the output member 5 is the same as the reduction ratio in the high reduction ratio mode when the fastening force F of the friction engagement portions 26 is small enough to prevent torque loss at the contact portions between both axial side surfaces of the first friction plates 30 and both axial side surfaces of the second friction plates 31. On the other hand, in a state where the fastening force F of the friction engagement portions 26 has increased to a magnitude large enough to transmit torque without causing slippage at the contact portions between both axial side surfaces of the first friction plates 30 and both axial side surfaces of the second friction plates 31, the reduction ratio is the same as the reduction ratio in the low reduction ratio mode, i.e., 1.

[0259] When the fastening force F of the friction engagement portion 26 is such that slippage occurs at the contact points between both axial side surfaces of the first friction plate 30 and both axial side surfaces of the second friction plate 31, the reduction ratio between the input member 4 and the output member 5 becomes a value that corresponds to the magnitude of the input torque, the rotational speed, etc.

[0260] When the input member 4 is rotating in the forward direction and the mode is being switched from the high reduction ratio mode to the reduction ratio switching mode, torque is applied to the second member 72 of the rotation transmission state switching device 8 in the direction opposite to the predetermined direction. Here, the rotation transmission state switching device 8 prevents the second member 72 from rotating in the direction opposite to the predetermined direction even during the switch from the lock mode to the one-way clutch mode. In other words, the reduction ratio between the input member 4 and the output member 5 during the switch from the high reduction ratio mode to the reduction ratio switching mode is the same as the reduction ratio in the high reduction ratio mode.

[0261] When the input member 4 is rotating in the forward direction and during switching from the reduction ratio switching mode to the low reduction ratio mode, torque is applied in the predetermined direction to the second member 72 of the rotation transmission state switching device 8. Here, in the rotation transmission state switching device 8, rotation of the second member 72 in the predetermined direction is permitted even during switching from the one-way clutch mode to the free mode.

[0262] When the input member 4 rotates in the reverse direction, that is, when an automobile equipped with the two-speed transmission 1 of this example is reversing, the vehicle rarely travels at high speed. For this reason, when the input member 4 is rotating in the reverse direction, by switching from the high reduction ratio mode to the low reduction ratio mode, as is the case when the input member 4 is rotating in the forward direction, there is little need to switch to the reduction ratio switching mode that allows rotation of the sun gear 101 at the moment the direction of the torque applied to the sun gear 101 is reversed by switching the friction engagement device 7 to the one-way clutch mode.

[0263] Even when the input member 4 rotates in the forward direction, the vehicle is mainly in a deceleration state when switching from the low reduction ratio mode to the high reduction ratio mode. In this case, power is not transmitted from the input member 4 to the output member 5, so there is little need to switch the two-speed transmission 1 to the reduction ratio switching mode.

[0264] According to the two-speed transmission 1 of this embodiment, it is possible to ensure good torque transmission efficiency, the reason for which will be explained next.

[0265] When cam device 28 generates a pressing force, that is, when driven cam 35 presses piston 32 toward one axial side via thrust bearing 57 and pressing member 58 (the state shown in FIG. 2B ), a force toward one axial side is applied to thrust bearing 57. Furthermore, a reaction force caused by driven cam 35 pressing piston 32 toward one axial side is applied to radial bearing 38 toward the other axial side via rolling elements 36 and driving cam 34.

[0266] A bearing ring 59a on one axial side of thrust bearing 57 is supported by rotating member 6 via pressing member 58 and piston 32, and a bearing ring 59b on the other axial side is supported by fixed part 10 via cam device 28, angular contact ball bearing 39, and cylindrical member 37. An inner ring 42 of radial bearing 38 is fitted and fixed to the outside of rotating member 6, and an outer ring 43 is supported by drive cam 34 of cam device 28 via cylindrical member 37 and angular contact ball bearing 39.

[0267] In the two-speed transmission 1 of this example, when the cam device 28 generates a pressing force, i.e., when the piston 32 is pressed toward one side in the axial direction, the axial dimension of the elastic member 33 elastically contracts, and the force pressing the first friction plate 30 and the second friction plate 31 against each other is released, and the friction engagement device 7 is disconnected, the rotation transmission state switching device 8 is in the lock mode. In the high reduction ratio mode in which the friction engagement device 7 is disconnected and the rotation transmission state switching device 8 has switched to the lock mode, relative rotation of the rotating member 6 with respect to the fixed part 10 is prevented.

[0268] In this state, the raceway ring 59a on one axial side and the raceway ring 59b on the other axial side that constitute the thrust bearing 57 do not rotate relative to each other, and the inner ring 42 and the outer ring 43 that constitute the radial bearing 38 do not rotate relative to each other. In other words, when an axial force (left and right direction in FIG. 2B ) is applied to the thrust bearing 57 and the radial bearing 38 and rolling resistance increases, the raceway ring 59a on one axial side and the raceway ring 59b on the other axial side that constitute the thrust bearing 57 do not rotate relative to each other, and the inner ring 42 and the outer ring 43 that constitute the radial bearing 38 do not rotate relative to each other. This makes it possible to prevent torque loss in the thrust bearing 57 and the radial bearing 38.

[0269] The pressing force generated by cam device 28 is applied from driven cam 35 to one side in the axial direction on rotating member 6 via pressing member 58, thrust bearing 57, piston 32, and elastic member 33. In contrast, the reaction force caused by the pressing force generated by cam device 28 is applied from drive cam 34 to the other side in the axial direction on rotating member 6 via radial bearing 38. In this way, the axial forces caused by the pressing forces generated by cam device 28 cancel each other out (are offset) within rotating member 6.

[0270] In a state where the rotation transmission state switching device 8 is switched to the free mode and the relative rotation of the rotating member 6 with respect to the fixed part 10 is permitted (the state shown in FIG. 2A), the friction engagement device 7 is connected and the cam device 28 does not generate a pressing force. In this state, no axial force (the left-right direction in FIG. 2A) associated with the pressing force generated by the cam device 28 is applied to the thrust bearing 57 and the radial bearing 38, so the rolling resistance of the thrust bearing 57 and the radial bearing 38 does not increase unnecessarily and torque loss does not become excessively large.

[0271] In the two-speed transmission 1 of this example, except for a short period during mode switching, the thrust bearing 57 and radial bearing 38 do not rotate when the axial force caused by the pressing force generated by the cam device 28 is applied and the rolling resistance is large. Therefore, it is possible to prevent excessive torque loss from occurring in the thrust bearing 57 and radial bearing 38, and it is possible to ensure good torque transmission efficiency of the two-speed transmission 1.

[0272] However, the two-speed transmission of the present disclosure can also be applied to a structure that does not have a one-way clutch mode, that is, that includes a rotation transmission state switching device that has only a free mode and a locked mode. In such a modified example, when switching from the high reduction ratio mode to the low reduction ratio mode, as shown in Figure 29, the rotation transmission state switching device is switched from the locked mode to the free mode, and then the friction engagement device is switched from the disengaged mode to the engaged mode.

[0273] 30 shows a second example of the embodiment of the present disclosure. The two-speed transmission 1a of this example is different from the two-speed transmission 1 of the first example only in the arrangement of the friction engagement device 7a. Specifically, in this example, the friction engagement device 7a is arranged between the sun gear 101 and the carrier 103.

[0274] In the two-speed transmission 1a of this example, when the rotation transmission state switching device 8 is set to the free mode and the friction engagement device 7a is set to the connected mode, the two-speed transmission 1a is switched to the first mode, and the planetary transmission mechanism 9 is placed in a glued state in which the entirety rotates as a single unit. In other words, the torque input to the input member 4 is transmitted to the output member 5 as is without being amplified.

[0275] In contrast, when the two-speed transmission 1a is switched to the second mode by setting the rotation transmission state switching device 8 to the lock mode and the friction engagement device 7a to the disengagement mode, the torque input to the input member 4 is increased by the planetary speed change mechanism 9 and then transmitted to the output member 5. Specifically, the rotational torque of the input member 4 is transmitted in the following order: the input member 4, the ring gear 102, the rotational motion of the planetary gear 104, the revolutional motion of the planetary gear 104 based on the meshing with the sun gear 101, the carrier 103, and the output member 5, and is then extracted from the output member 5.

[0276] In this example, the first mode corresponds to a low reduction ratio mode in which the reduction ratio between the input member 4 and the output member 5 is small, and the second mode corresponds to a high reduction ratio mode in which the reduction ratio is larger than that in the low reduction ratio mode.

[0277] In the two-speed transmission 1a of this example, too, the μ-V characteristic can be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the high reduction ratio mode and the low reduction ratio mode. In the two-speed transmission 1a of this example, the friction coefficient μ can be obtained by the following equation (6).

[0278] In the two-speed transmission 1a of this example, when switching between the high reduction ratio mode and the low reduction ratio mode, the output torque of the drive motor 2 in the torque phase and the fastening force F of the friction engagement portion 26 in the inertia phase can be controlled based on the μ-V characteristic determined by the learning function, and the occurrence of gear shift shock can be prevented regardless of the effects on the friction coefficient μ due to changes in the usage environment, deterioration over time, etc. The configuration and effects of the other parts of the second example are the same as those of the first example.

[0279] 31 shows a third example of the embodiment of the present disclosure. The two-speed transmission 1b of this example is also different from the two-speed transmission 1 of the first example and the two-speed transmission 1a of the second example only in the arrangement of the friction engagement device 7b. Specifically, in this example, the friction engagement device 7b is arranged between the ring gear 102 and the carrier 103.

[0280] When the two-speed transmission 1b of this example is switched to the first mode, the planetary transmission mechanism 9 is in a glued state, and the torque input to the input member 4 is not increased and is transmitted as is to the output member 5. In contrast, when the two-speed transmission 1b is switched to the second mode, the torque input to the input member 4 is increased by the planetary transmission mechanism 9 and then transmitted to the output member 5b.

[0281] In the two-speed transmission 1b of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the high reduction ratio mode, which is the second mode, and the low reduction ratio mode, which is the first mode. In the two-speed transmission 1b of this example, the friction coefficient μ can be obtained by the following equation (7).

[0282] The configuration and effects of the other parts of the third example are similar to those of the first and second examples.

[0283] 32 shows a fourth example of an embodiment of the present disclosure. In a two-speed transmission 1c of this example, an input member 4a is connected to a sun gear 101 of a planetary transmission mechanism 9 so as to be able to transmit torque, and an output member 5a is connected to a carrier 103 so as to be able to transmit torque. A friction engagement device 7c is disposed between the sun gear 101 and the carrier 103, and a rotation transmission state switching device 8a is disposed between a fixed portion 10 and a ring gear 102.

[0284] When the two-speed transmission 1c of this example is switched to the first mode by setting the rotation transmission state switching device 8 to the free mode and the friction engagement device 7c to the engaged mode, the planetary speed change mechanism 9 is in the glued state. In other words, the torque input to the input member 4a is transmitted as is to the output member 5a.

[0285] When the two-speed transmission 1c is switched to the second mode by setting the rotation transmission state switching device 8a to the lock mode and the friction engagement device 7c to the disengagement mode, the torque input to the input member 4a is amplified by the planetary transmission mechanism 9 and then transmitted to the output member 5a. Specifically, the rotational torque of the input member 4a is transmitted in the order of the input member 4a, the sun gear 101, the rotational motion of the planetary gear 104, the revolutional motion of the planetary gear 104 based on the meshing with the ring gear 102, the carrier 103, and the output member 5a, and is then taken out from the output member 5a.

[0286] In the two-speed transmission 1c of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during the switch from the high reduction ratio mode, which is the second mode, to the low reduction ratio mode, which is the first mode. In the two-speed transmission 1c of this example, the friction coefficient μ can be obtained by the following equation (8).

[0287] (8) I in the formula ｒｉｎｇrepresents the inertia of the portion connected to the ring gear 102. The portion connected to the ring gear 102 rotates integrally with the ring gear 102 when the ring gear 102 rotates, regardless of the mode of the friction engagement device 7c and the mode of the rotation transmission state switching device 8a, and does not rotate when the ring gear 102 does not rotate. The configuration and effects of the other portions of the fourth example are the same as those of the first example.

[0288] 33 shows a fifth example of the embodiment of the present disclosure. The two-speed transmission 1d of this example is different from the two-speed transmission 1c of the fourth example only in the arrangement of the friction engagement device 7d. Specifically, in this example, the friction engagement device 7d is arranged between the ring gear 102 and the carrier 103.

[0289] In the two-speed transmission 1d of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the second mode, which is the high reduction ratio mode, and the first mode, which is the low reduction ratio mode. In the two-speed transmission 1d of this example, the friction coefficient μ can be obtained by the following equation (9).

[0290] The remaining configuration and effects of the fifth example are similar to those of the first and fourth examples.

[0291] 34 shows a sixth example of the embodiment of the present disclosure. In a two-speed transmission 1e of this example, only the arrangement of the friction engagement device 7e is changed from the two-speed transmission 1c of the fourth example and the two-speed transmission 1d of the fifth example. Specifically, in this example, the friction engagement device 7e is arranged between the sun gear 101 and the ring gear 102.

[0292] In the two-speed transmission 1e of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the high reduction ratio mode, which is the second mode, and the low reduction ratio mode, which is the first mode. In the two-speed transmission 1e of this example, the friction coefficient μ can be obtained by the following equation (10).

[0293] The other configurations and effects of the sixth example are similar to those of the first and fourth examples.

[0294] 35 shows a seventh example of an embodiment of the present disclosure. In a two-speed transmission if of this example, the planetary transmission mechanism 9a is configured as a double-pinion planetary gear mechanism. That is, the planetary transmission mechanism 9a includes a plurality of inner diameter side planetary gears 104a meshed with a sun gear 101a and a plurality of outer diameter side planetary gears 104b meshed with a ring gear 102a. The inner diameter side planetary gears 104a and the outer diameter side planetary gears 104b are meshed with each other and rotatably supported by a carrier 103a.

[0295] In this example, the input member 4b is connected to the carrier 103a so as to be able to transmit torque, and the output member 5b is connected to the ring gear 102a so as to be able to transmit torque. The friction engagement device 7f is disposed between the sun gear 101a and the carrier 103a, and the rotation transmission state switching device 8b is disposed between the fixed part 10 and the sun gear 101a.

[0296] When the two-speed transmission 1f of this example is switched to the first mode by setting the rotation transmission state switching device 8b to the free mode and the friction engagement device 7f to the engaged mode, the planetary speed change mechanism 9a is in the glued state, i.e., the torque input to the input member 4b is transmitted as is to the output member 5b.

[0297] When the two-speed transmission 1f is switched to the second mode by setting the rotation transmission state switching device 8b to the lock mode and the friction engagement device 7f to the disengagement mode, the torque input to the input member 4b is amplified by the planetary transmission mechanism 9a and then transmitted to the output member 5b. Specifically, the rotational torque of the input member 4b is transmitted in the following order: the input member 4b, the carrier 103a, the revolution of the planetary gears 104a and 104b, the rotation of the inner diameter side planetary gear 104a based on meshing with the sun gear 101a, the rotation of the outer diameter side planetary gear 104b, the ring gear 102a, and the output member 5b, and is then extracted from the output member 5b.

[0298] In the two-speed transmission 1f of this example, too, the μ-V characteristic can be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the second mode, which is the high reduction ratio mode, and the first mode, which is the low reduction ratio mode. In the two-speed transmission 1f of this example, the friction coefficient μ can be obtained by the following equation (11).

[0299] The configuration and effects of the other parts of the seventh example are the same as those of the first example.

[0300] 36 shows an eighth example of the embodiment of the present disclosure. A two-speed transmission 1g of this example is different from the two-speed transmission 1f of the seventh example only in the arrangement of the friction engagement device 7g. Specifically, in this example, the friction engagement device 7g is arranged between the ring gear 102a and the carrier 103a.

[0301] In the two-speed transmission 1g of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the second mode, which is the high reduction ratio mode, and the first mode, which is the low reduction ratio mode. In the two-speed transmission 1g of this example, the friction coefficient μ can be obtained by the following equation (12).

[0302] The remaining configuration and effects of the eighth example are the same as those of the first and seventh examples.

[0303] 37 shows a ninth example of the embodiment of the present disclosure. A two-speed transmission 1h of this example is different from the two-speed transmission 1f of the seventh example and the two-speed transmission 1g of the eighth example only in the arrangement of the friction engagement device 7h. Specifically, in this example, the friction engagement device 7h is arranged between the sun gear 101a and the ring gear 102a.

[0304] In the two-speed transmission 1h of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the high reduction ratio mode, which is the second mode, and the low reduction ratio mode, which is the first mode. In the two-speed transmission 1h of this example, the friction coefficient μ can be obtained by the following equation (13).

[0305] The configuration and effects of other parts of the ninth example are similar to those of the first and seventh examples.

[0306] 38 shows a tenth example of an embodiment of the present disclosure. In a two-speed transmission 1i of this example, an input member 4c is connected to a sun gear 101a of a planetary transmission mechanism 9a so as to be able to transmit torque, and an output member 5c is connected to a ring gear 102a so as to be able to transmit torque. A friction engagement device 7i is disposed between the sun gear 101a and a carrier 103a, and a rotation transmission state switching device 8c is disposed between a fixed portion 10 and the carrier 103a.

[0307] When the two-speed transmission 1i of this example is switched to the first mode by setting the rotation transmission state switching device 8c to the free mode and the friction engagement device 7i to the engaged mode, the planetary speed change mechanism 9a is in the glued state, i.e., the torque input to the input member 4c is transmitted as is to the output member 5c.

[0308] In contrast, when the two-speed transmission 1i is switched to the second mode by setting the rotation transmission state switching device 8c to the lock mode and the friction engagement device 7i to the disengagement mode, the torque input to the input member 4c is amplified by the planetary transmission mechanism 9a and then transmitted to the output member 5c. Specifically, the rotational torque of the input member 4c is transmitted in the following order: the input member 4c, the sun gear 101a, the rotation of the inner diameter side planetary gear 104a, the rotation of the outer diameter side planetary gear 104b, the ring gear 102a, and the output member 5c, and is then extracted from the output member 5c.

[0309] In the two-speed transmission 1i of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the high reduction ratio mode, which is the second mode, and the low reduction ratio mode, which is the first mode. In the two-speed transmission 1i of this example, the friction coefficient μ can be obtained by the following equation (14).

[0310] (14) I in the formula ｃａｒｒｉｅｒ represents the inertia of the portion connected to the carrier 103a. The portion connected to the carrier 103a rotates integrally with the carrier 103a when the carrier 103a rotates, regardless of the mode of the friction engagement device 7i and the mode of the rotation transmission state switching device 8c, and does not rotate when the carrier 103a does not rotate. The configurations and effects of the other portions of the tenth example are the same as those of the first and seventh examples.

[0311] 39 shows an eleventh example of the embodiment of the present disclosure. The two-speed transmission 1j of this example is different from the two-speed transmission 1i of the tenth example only in the arrangement of the friction engagement device 7j. Specifically, in this example, the friction engagement device 7j is arranged between the ring gear 102a and the carrier 103a.

[0312] In the two-speed transmission 1j of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the high reduction ratio mode, which is the second mode, and the low reduction ratio mode, which is the first mode. In the two-speed transmission 1j of this example, the friction coefficient μ can be obtained by the following equation (15).

[0313] The remaining configuration and effects of the eleventh example are the same as those of the first and tenth examples.

[0314] 40 shows a twelfth example of the embodiment of the present disclosure. The two-speed transmission 1k of this example is different from the two-speed transmission 1i of the tenth example and the two-speed transmission 1j of the eleventh example only in the arrangement of the friction engagement device 7k. Specifically, in this example, the friction engagement device 7k is arranged between the sun gear 101a and the ring gear 102a.

[0315] In the two-speed transmission 1k of this example, the μ-V characteristic can also be obtained by calculating the friction coefficient μ and the differential rotation V at predetermined time intervals during the inertia phase during mode switching between the second mode, which is the high reduction ratio mode, and the first mode, which is the low reduction ratio mode. In the two-speed transmission 1k of this example, the friction coefficient μ can be obtained by the following equation (16).

[0316] The remaining configurations and effects of the twelfth example are the same as those of the first and tenth examples.

[0317] DESCRIPTION OF SYMBOLS 1, 1a to 1k Two-speed transmission 2 Drive motor 3 Differential device 4, 4a to 4c Input member 5, 5a to 5c Output member 6 Rotating member 7, 7a to 7k Friction engagement device 8, 8a to 8c Rotation transmission state switching device 9, 9a Planetary transmission mechanism 10 Fixed portion 11 Output shaft 12 Drive gear 13 Input gear 14 Output gear 15 Small diameter flange portion 16 Flange portion 17 Through hole 18 First circular ring portion 19 First cylindrical portion 20 Second circular ring portion 21 Second cylindrical portion 22 Shaft member 23 Stepped cylindrical member 24 Small diameter cylindrical portion 25 Female spline portion 26 Friction engagement portion 27 Elastic biasing member 28, 28z Cam device 29 Electric actuator 30 First friction plate 31 Second friction plate 32 Piston 33 Elastic member 34, 34z Drive cam 35 Driven cam 36 Rolling element 37 Cylindrical member 38 Radial bearing 39 Angular contact ball bearing 40 Cylindrical portion 41 Outward flange portion 42 Inner ring 43 Outer ring 44 Rolling element 45 Inner ring 46 Outer ring 47 Ball 48 Drive cam surface 48a First bottom portion 48b First inclined surface portion 48c First flat surface portion 48d Second inclined surface portion 48e Second bottom portion 48f Third inclined surface portion 48g Second flat surface portion 48h Fourth inclined surface portion 49 Wheel tooth 50 Pin portion 51 Female spline portion 52 Male spline portion 53 Rectangular hole 54a, 54b Support plate portion 55 Support hole 56 Support recess 57 Thrust bearing 58 Pressing member 59a, 59b Raceway ring 60 Rolling element 61 Preload applying means 62 Base portion 63 Partial cylindrical portion 64 Support shaft 65 Roller 66 Shift motor 67 Reducer 68 Worm 69a, 69b Support bearing 70 Return spring 71 First member 72 Second member 73 Mode select member 74 Engaging recess 75 Convex portion 76 Concave-convex portion 77 Outer diameter side concave-convex engaging portion 78 Inner diameter side concave-convex engaging portion 79 Inner diameter side concave-convex engaging portion 80 Base portion 81 Cylindrical portion 82 First retaining recess 83 Second retaining recess 84a, 84b Spring retaining portion 85a, 85b Pedestal portion 86 First pawl member87 Second claw member 88 First claw biasing member 89 Second claw biasing member 90 First base 91 First engagement claw 92 Annular convex portion 93 Second base 94 Second engagement claw 95 Base 96 Plate-side engagement hole 97 Projection 98 Concave-convex portion 99 Cover 100 Retaining ring 101, 101a Sun gear 102, 102a Ring gear 103, 103a Carrier 104, 104a, 104b Planetary gear 105 First friction engagement device 106 Second friction engagement device 107 First driven cam 108 Second driven cam

Claims

1. The transmission includes a planetary transmission mechanism, an input member, an output member, a drive motor, a rotation transmission state switching device, and a friction engagement device, the planetary transmission mechanism includes an input element connected to the input member, an output element connected to the output member and rotatable relative to the input element, and a rotating element rotatable relative to the input element and the output element, The planetary transmission mechanism includes a sun element, a ring element supported around the sun element to be rotatable relative to the sun element, a carrier element supported to be rotatable relative to the sun element and the ring element, and a plurality of planetary elements engaged with the sun element and the ring element to transmit torque and rotatably supported by the carrier element, the input element is one of the sun element, the ring element, and the carrier element; the output element is one of the sun element, the ring element, and the carrier element, and is configured by an element other than the input element; the rotating element is composed of the sun element, the ring element, and the carrier element, excluding the input element and the output element; The drive motor rotates the input member directly or via a reducer, the rotation transmission state switching device is disposed between the rotating element and a fixed portion that does not rotate even during use, and switches between a free mode in which the rotating element is rotatable relative to the fixed portion and a locked mode in which the rotating element is not rotatable relative to the fixed portion; the friction engagement device has at least one first friction plate and at least one second friction plate supported to allow relative displacement in the axial direction, and is disposed between any two of the sun element, the ring element, and the carrier element, and switches to a connection mode in which any two elements rotate integrally by pressing the first friction plate and the second friction plate against each other, and switches to a disconnection mode in which any two elements rotate relative to each other by releasing the force pressing the first friction plate and the second friction plate against each other; a first mode in which the rotation transmission state switching device is in the free mode and the friction engagement device is in the connected mode, and a second mode in which the rotation transmission state switching device is in the lock mode and the friction engagement device is in the disconnected mode; and a learning function for performing mode switching between the first mode and the second mode on the condition that a predetermined learning start condition is satisfied, and calculating a friction coefficient between the first friction plate and the second friction plate based on an output torque of the drive motor and an angular acceleration of an output shaft of the drive motor during an inertia phase during the mode switching, thereby obtaining a μ-V characteristic which is a relationship between the friction coefficient and a differential rotation which is a difference in rotation speed between any two of the elements; Two-speed transmission.

2. 2. The two-speed transmission according to claim 1, wherein, when executing the learning function, after starting mode switching between the first mode and the second mode with the rotation speed of the output shaft of the drive motor kept constant, it is determined that the inertia phase has started on the condition that an amount of change in the differential rotation per unit time exceeds a predetermined threshold value.

3. 2. The two-speed transmission according to claim 1, further comprising a control function for controlling the output torque of the drive motor and the magnitude of the force pressing the first friction plate and the second friction plate against each other based on the μ-V characteristic obtained by the learning function when switching between the first mode and the second mode.

4. The friction engagement device is an elastic biasing member that elastically biases the first friction plate and the second friction plate in a direction in which they are pressed against each other; a cam device having a drive cam and a driven cam supported to be capable of relative rotation with respect to the drive cam and relative displacement in the axial direction, the cam device pressing the elastic biasing member in a direction to release the force pressing the first friction plate and the second friction plate against each other by relatively displacing the driven cam in a direction to increase the axial distance between the drive cam and the drive cam as the drive cam rotates; an electric actuator having a shift motor and a shift reduction gear, the electric actuator rotatingly driving the drive cam by the shift motor via the shift reduction gear; The two-speed transmission of claim 1 .

5. 5. The two-speed transmission according to claim 4, wherein the friction engagement device includes a return spring that elastically urges the first friction plate and the second friction plate in a direction separating them from each other.

6. 2. The two-speed transmission according to claim 1, wherein the rotation transmission state switching device has a one-way clutch mode in which only rotation of the rotating element relative to the fixed part in a predetermined direction is permitted and rotation of the rotating element relative to the fixed part in a direction opposite to the predetermined direction is prevented.

7. 7. The two-speed transmission according to claim 6, further comprising a function of setting the rotation transmission state switching device to the one-way clutch mode while the friction engagement device is being switched from the disengagement mode to the connection mode and / or while the friction engagement device is being switched from the connection mode to the disengagement mode.

8. The transmission includes a planetary transmission mechanism, an input member, an output member, a drive motor, a rotation transmission state switching device, and a friction engagement device, the planetary transmission mechanism includes an input element connected to the input member, an output element connected to the output member and rotatable relative to the input element, and a rotating element rotatable relative to the input element and the output element, The planetary transmission mechanism includes a sun element, a ring element supported around the sun element to be rotatable relative to the sun element, a carrier element supported to be rotatable relative to the sun element and the ring element, and a plurality of planetary elements engaged with the sun element and the ring element to transmit torque and rotatably supported by the carrier element, the input element is one of the sun element, the ring element, and the carrier element; the output element is one of the sun element, the ring element, and the carrier element, and is configured by an element other than the input element; the rotating element is composed of the sun element, the ring element, and the carrier element, excluding the input element and the output element; The drive motor rotates the input member directly or via a reducer, the rotation transmission state switching device is disposed between the rotating element and a fixed portion that does not rotate even during use, and switches between a free mode in which the rotating element is rotatable relative to the fixed portion and a locked mode in which the rotating element is not rotatable relative to the fixed portion; the friction engagement device has at least one first friction plate and at least one second friction plate supported to allow relative displacement in the axial direction, and is disposed between any two of the sun element, the ring element, and the carrier element, and switches to a connection mode in which any two elements rotate integrally by pressing the first friction plate and the second friction plate against each other, and switches to a disconnection mode in which any two elements rotate relative to each other by releasing the force pressing the first friction plate and the second friction plate against each other; a first mode in which the rotation transmission state switching device is in the free mode and the friction engagement device is in the connected mode, and a second mode in which the rotation transmission state switching device is in the lock mode and the friction engagement device is in the disconnected mode. In a two-speed transmission, On the condition that a predetermined learning start condition is satisfied, mode switching is performed between the first mode and the second mode, and during an inertia phase during the mode switching, a friction coefficient between the first friction plate and the second friction plate is calculated based on an output torque of the drive motor and an angular acceleration of an output shaft of the drive motor, thereby obtaining a μ-V characteristic which is a relationship between the friction coefficient and a differential rotation which is a difference in rotation speed between any two of the elements. A method for learning the μ-V characteristics of a two-speed transmission.

9. The transmission includes an input member, an output member, a planetary transmission mechanism, a drive motor, a rotation transmission state switching device, and a friction engagement device, the planetary transmission mechanism includes an input element connected to the input member, an output element connected to the output member and rotatable relative to the input element, and a rotating element rotatable relative to the input element and the output element, The planetary transmission mechanism includes a sun element, a ring element supported around the sun element to be rotatable relative to the sun element, a carrier element supported to be rotatable relative to the sun element and the ring element, and a plurality of planetary elements engaged with the sun element and the ring element to transmit torque and rotatably supported by the carrier element, the input element is one of the sun element, the ring element, and the carrier element; the output element is one of the sun element, the ring element, and the carrier element, and is configured by an element other than the input element; the rotating element is composed of the sun element, the ring element, and the carrier element, excluding the input element and the output element; The drive motor rotates the input member directly or via a reducer, the rotation transmission state switching device is disposed between the rotating element and a fixed portion that does not rotate even during use, and switches between a free mode in which the rotating element is rotatable relative to the fixed portion and a locked mode in which the rotating element is not rotatable relative to the fixed portion; the friction engagement device has at least one first friction plate and at least one second friction plate supported to allow relative displacement in the axial direction, and is disposed between any two of the sun element, the ring element, and the carrier element, and switches to a connection mode in which any two elements rotate integrally by pressing the first friction plate and the second friction plate against each other, and switches to a disconnection mode in which any two elements rotate relative to each other by releasing the force pressing the first friction plate and the second friction plate against each other; a first mode in which the rotation transmission state switching device is in the free mode and the friction engagement device is in the connected mode, and a second mode in which the rotation transmission state switching device is in the lock mode and the friction engagement device is in the disconnected mode. A method for controlling a two-speed transmission, comprising the steps of: A learning step of obtaining the μ-V characteristic by the μ-V characteristic learning method according to claim 8; a step of controlling an output torque of the drive motor and a magnitude of a force pressing the first friction plate and the second friction plate against each other based on the μ-V characteristic obtained in the learning step when switching between the first mode and the second mode; Equipped with A method for controlling a two-speed transmission.