Gear unit with built-in parking lock unit

Abstract

A gear unit used in combination with a power source having a hollow output shaft is provided with: a differential gear set having a rotation axis common to the output shaft; a countershaft fixedly including a first gear engaged with the output shaft and a second gear engaged with the differential gear set, wherein the first gear and the second gear constitute a reduction gear set; a housing including an outer wall separating the differential gear set and the countershaft from the outside; and a parking gear disposed axially opposite the first gear outside the second gear and fixed to the countershaft.

Description

TECHNICAL FIELD

[0001] The disclosure herein relates to a gear unit usable as a double shaft reduction gear set when used in combination with an electric motor having a hollow output shaft, and in particular to a reduction gear unit having a built-in parking lock unit. BACKGROUND

[0002] In the field of vehicle technology, many technologies in which an electric motor is used instead of an internal combustion engine are under study. Torque generated by the electric motor is generally multiplied by a reduction gear set and then output to a vehicle axle via a differential. In order to constitute a drive unit of a vehicle in a compact form and facilitate its handling, the reduction gear set and the differential are sometimes packaged in a single unit and further integrated with the electric motor. In this configuration, the differential can be coaxial with the electric motor, in which case its output shaft can be formed in a hollow shape so as to pass one of the vehicle axles therethrough.

[0003] The drive unit of the above type can be provided with a built-in parking lock unit. Japanese Patent Application Publication No. 2021-95956A and International Publication WO 2020 / 067281A1 disclose related technology. SUMMARY

[0004] As will be readily appreciated, the drive unit contains a large number of elements as described above. How these elements are arranged and packaged in the housing should be considered a technical problem. For example, if elements are added next to an electric motor having a transverse shaft, the drive unit must naturally elongate in the transverse direction, while the opposite needs to shorten the vehicle axle. Such an axially shortened axle has insufficient rocking ability and thus can adversely affect the ride quality of the vehicle. Alternatively, if its size is not increased in the axial direction but in its height direction, the center of mass will be set upward and the stability of the vehicle will be impaired. The technology disclosed below is designed to solve these problems.

[0005] According to an aspect, a gear unit for use in combination with a power source having a hollow output shaft is provided with: a differential gear set having a common rotational axis with the output shaft; a countershaft fixedly including a first gear meshing with the output shaft and a second gear meshing with the differential gear set, wherein the first and second gears constitute a reduction gear set; a housing including an outer wall separating the differential gear set and the countershaft from the outside; and a parking gear disposed axially opposite the first gear outside the second gear and fixed to the countershaft. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 is a perspective view of a gear unit in combination with a power source.

[0007] Figure 2It is a plan view of the gear unit combined with the power source.

[0008] Figure 3 This is a cross-sectional view of the gear unit taken from below, using a plane passing through both the axis of the differential and the axis of the countershaft.

[0009] Figure 4 Is Figure 2 The side view of the gear unit, shown at line IV-IV, where it separates from the power source and is viewed from the side of the power source.

[0010] Figure 5 From and Figure 4 Viewed from the opposite side as shown and from the side Figure 3 The cross-sectional side view of the gear unit shown is taken by line VV. Detailed Implementation

[0011] Exemplary embodiments will now be described with reference to the accompanying drawings.

[0012] The accompanying drawings are not necessarily drawn to scale, and therefore special attention should be paid to the fact that the dimensional relationships are not limited to those shown therein. In each drawing, arrows F, A, R, L, U, and D indicate directions. In a typical embodiment, these directions correspond to forward, backward, right, left, up, and down depending on the vehicle, but the left-right or up-down orientation of the device may be reversed, or the device may rotate or tilt in any other direction.

[0013] According to this embodiment, the gear unit 1 is a reduction gear used in combination with a power source 3 (such as an electric motor) having a hollow output shaft 5, and the reduction gear is equipped with a parking lock device 7. Of course, it can be used in combination with an internal combustion engine or a so-called hybrid system instead of an electric motor.

[0014] Combination Figure 1 and Figure 2 Main reference Figure 3 The gear unit 1 is housed in a housing that can be detachably combined with the power source 3. The housing also has an outer wall 11, a partition wall 13, and a cover 15 that can be detachably combined together. Of course, the housing can accommodate any other components.

[0015] One end of the output shaft 5 extends beyond the cover 15 and protrudes into the gear unit 1. This end is toothed to have gear teeth, or is combined with a toothed gear as a separate unit. The output shaft 5 is hollow to define a cylindrical cavity 5T, the dimensions of which are set to allow the right axle to pass through it.

[0016] The gear unit 1 has a differential gear set 21 and a countershaft 31 that mesh with each other in the housing.

[0017] The differential gear set 21 has a common rotation axis X with the output shaft 5 and is rotatable about the rotation axis X. The countershaft 31 is rotatable about a countershaft axis C which is parallel to but not identical with the rotation axis X and is engaged with both the output shaft 5 and the differential gear set 21. The differential gear set 21 receives torque via the countershaft 31 and differentially distributes the torque to the two axles by the side gears 27R, 27L. The right axle passes through the cavity 5T to be coupled with the right side gear 27R, and the left axle passes through the opening of the outer wall 11 to be coupled with the left side gear 27L.

[0018] The differential gear set 21 is provided with a differential case 23 which forms an approximately cylindrical shape which is approximately symmetrical about the axis X, for example. Boss portions protrude from both ends of the differential case 23, respectively, and are rotatably supported by the housing. The differential case 23 is fixed with gear teeth 25 on its outer periphery, for example, so as to be engaged with the countershaft 31. The gear teeth 25, which are preferably in the form of helical gears, can be formed directly on the differential case 23, but can be a separate body which is combined with the differential case 23.

[0019] The differential gear set 21 can be of the bevel gear type as exemplarily shown in the drawings and is provided with a pinion shaft fixed to the differential case 23 and a pinion rotatably supported thereby to differentially distribute torque to the side gears 27R, 27L which are engaged with the pinion. Of course, any other type of gear such as face gears or planetary gears can be applied to the differential gear set 21. Furthermore, the differential gear set 21 can be provided with a limited slip mechanism or a differential lock mechanism.

[0020] The countershaft 31 is fixedly provided with a first gear 33 of large diameter and a second gear 35 of small diameter, both of which are preferably helical gears. The first gear 33 is engaged with the output shaft 5, and the second gear 35 is engaged with the gear teeth 25 of the differential gear set 21. The difference in diameter makes the combination of the gears a reduction gear set so that the combination multiplies the torque and transmits it to the differential gear set 21. The first gear 33 can be, for example, a disc about the countershaft axis C, and gear teeth are formed on its periphery. It can be formed integrally with the countershaft 31, but for the sake of ease of production, it can be produced as a separate body and coupled with the countershaft 31. For such a coupling, for example, a spline coupling or a lug coupling is applicable, or welding or press fitting can be used. The second gear 35 can be formed integrally with the countershaft 31 or produced as a separate body and combined with the shaft. From the Figure 3 It will be readily understood that, since no particular element is interposed between the first gear 33 and the second gear 35, the first gear 33 and the second gear 35 can be brought possibly close to each other. This is advantageous in reducing the size of the gear unit 1 in the direction of the axes C and X.

[0021] In combination Figure 5 With reference to Figure 3The layshaft 31 also immovably has a parking gear 37, which constitutes the parking lock device 7. Needless to say, the parking gear 37 is disposed axially outside the first gear 33 and the second gear 35, or axially opposite the first gear 33 outside the second gear 35 and closest to the end of the power source 3 farthest away. Specifically, the parking gear 37 is very close to the outer wall 11, and can be disposed between the bearing 39L described later and the second gear 35. From Figure 3 It is easy to understand from Figure 3 that this arrangement does not affect the size of the gear unit 1 in the axial direction (lateral direction in the example shown in the drawing), and thus is advantageous in reducing the size of the gear unit 1. The parking gear 37 is also disc-shaped and has teeth on the outer periphery to have locking teeth different from the gear teeth. The parking gear 37 can be integral with the layshaft 31, but in order to facilitate production, it can be produced as a separate body and fixed to the layshaft 31 by press fitting, spline coupling, or the like.

[0022] Referring mainly to Figure 5 , the parking lock device 7 also has a pawl 43 to be engaged with the parking gear 37, and an actuator 45 for driving the pawl.

[0023] The pawl 43 is pivotably supported by the outer wall 11, and engages with the parking gear 37 by swinging around the pivot to fix the layshaft 31. The pawl 43 is disposed between the second gear 35 and the outer wall 11, and also between the actuator 45 and the parking gear 37. Although not shown in the drawing, around the pivot, the pawl 43 can be provided with a spring biased in a direction that facilitates disengagement.

[0024] It is applicable to the actuator 45 that a device directly applies a rotational force to the shaft of the pawl 43 or any electric device that generates linear motion along the working axis L. As the electric device, any fluid pressure device using hydraulic or pneumatic pressure can be exemplified, while a combination of a motor and a cam mechanism can be used in a manner described later.

[0025] The actuator 45 in the illustrated example is provided with a motor 47, a spindle 49 having threads on its outer periphery, a spindle nut 51 threaded onto the spindle 49 and linearly movable along the spindle 49, and a cone 53 following the spindle nut 51 to work on the pawl 43. The motor 47 controllably generates rotational motion about the working axis X, whereby the driven spindle 49 generates linear motion. Specifically, the combination of the spindle 49 and the spindle nut 51 functions as a kind of cam mechanism. A coil spring 55 can be used to press the cone 53 against the spindle nut 51 so that the cone 53 follows the spindle nut 51. The outer side surface of the cone 53 has an appropriate profile so that the outer side surface presses the pawl 43 to generate a wobbling motion under control. Irrespective of the axial direction, the thus-configured actuator 45 is compact in the radial direction, and thus is advantageous in reducing the size of the gear unit 1. By having the working axis L perpendicular to the axes C, X as in the illustrated example, the foregoing actuator is advantageous in reducing the size of the gear unit 1 in both directions along the axes C and X.

[0026] Referring again to Figure 1 , Figure 2 and Figure 3 , the housing includes, for example, an outer wall 11, a partition wall 13, and a cover 15. These elements are separably assembled together to house and support the above-described components. The cover 15 can also serve as a cover for the power source 3.

[0027] The outer wall 11 is sized to separate the differential gear set 21 and the pinion shaft 31 from the outside. This wall can be formed as a single body by casting or the like as a whole, or can also be separated into multiple components. The outer wall 11 can generally be in the form of two adjacent tanks assembled together, which house the differential gear set 21 and the pinion shaft 31, respectively. However, of course, these tanks are in communication with each other in the internal space.

[0028] The portion corresponding to the bottom of these tanks, i.e., the side wall of the outer wall 11, is closed at the portion corresponding to the pinion shaft 31, but has an opening at the portion corresponding to the differential gear set 21. The left axle shaft passes through this opening and is coupled with the side gear 27L. In addition, a sealing member for sealing the gap between the axle shaft and the outer wall 11 liquid-tightly is generally fitted in this opening. The outer wall 11 can be provided with any through hole in addition to the above-described opening, for example, for introducing lubricating oil.

[0029] The outer wall 11 is also provided with a cylindrical portion along the tank-like portion, which protrudes in the direction of the arrow F, and the actuator 45 is housed and fixed there. As Figure 5 best shown, the pawl 43 is arranged along this portion and is pivotably supported by the outer wall 11. The portion housing the actuator 45 can be provided very close to the side wall, so that the pawl 43 is arranged in a position close to the side wall. Figure 2The side thereof is substantially aligned with the side wall in the plan view shown, and thus does not protrude from the side wall in the direction of arrow L. This is advantageous in reducing the size of the gear unit 1 in the direction of axis C, X. However, it can protrude somewhat in the direction of arrow F, and in this portion, the motor 47 and a connector 9 for electrically connecting to the motor 47 can be disposed. The connector 9 is exposed to the outside, for example, in the direction of arrow R. This arrangement is advantageous in terms of accessibility from the outside to the connector 9, and thus facilitates the work of connecting a wire harness to the connector 9. Furthermore, it is easily understood from Figure 1 and Figure 4 that the connector 9 is naturally disposed uppermost in the gear unit 1 when used in the manner as shown in the figure. This position is less likely to be affected by dirt or any foreign matter splashed from the road, and thus is advantageous in preventing malfunctions.

[0030] In conjunction with Figure 1 reference Figure 4 and Figure 5 , the parking lock device 7 protrudes forward, while the gear unit 1 as a whole is within the range of the power source 3 when viewed from the side. In particular, when the power source 3 is projected on a plane perpendicular to the rotation axis X and the secondary axis C, the differential gear set 21, the secondary shaft 31, the housing, the pawl 43, and the cam mechanism are all disposed within the range of this projection on this plane, in addition to the motor 47 and the connector 9. More specifically, it is obvious that the gear unit 1 can be designed to be compact at least in height and length in the front-rear direction.

[0031] In conjunction with Figures 1 to 3 reference Figure 4 , the housing preferably has a partition wall 13, which can support at least the differential gear set 21. In order to support the gear set, the outer wall 11 is provided with a left bearing 29L, and the partition wall 13 is provided with a right bearing 29R, and for example, roller bearings are respectively fitted therein, thereby rotatably supporting the boss portion of the differential gear set 21. In order to strengthen the support, the periphery of the partition wall 13 can extend to the peripheral wall of the housing, and can be placed entirely between the outer wall 11 and the cover 15, thereby being fixed together. The secondary shaft 31 can also be supported by the partition wall 13, or instead of the partition wall 13, by the cover 15. In any case, the secondary shaft 31 passes over the partition wall 13 to a space 59 defined by the partition wall 13 and the cover 15, and is coupled there with the first gear 33 and engages with the output shaft 5.

[0032] The partition wall 13 defines a chamber 57 in combination with the outer wall 11. The chamber 57 accommodates the differential gear set 21, the second gear 35, the parking gear 37 and the pawl 43. The first gear 33 is outside the chamber 57 and is disposed in a space 59 defined by the partition wall 13 and the cover 15. The space 59 is not separated from the chamber 57 but has an opening 41 that penetrates the partition wall 13 to allow at least mutual fluid communication. The opening 41 enables lubricating oil to circulate and, for example, oil splashed by the first gear 33 to circulate around the various elements in the gear unit 1. The opening 41 can further be sized to allow the parking gear 37 to pass through it. As will be described later, this facilitates assembly of the gear unit 1.

[0033] The cover 15 abuts the right end of the partition wall 13 and also clamps the partition wall 13 in combination with the outer wall 11, then coupling these walls together. The cover 15 has an opening through which the output shaft 5 passes, but is closed at a portion corresponding to the layshaft 31, thereby substantially isolating the interior of the gear unit 1 from the power source 3. Around the output shaft 5, any sealing member can be inserted, thereby establishing a fluid-tightness of the interior of the gear unit 1 from the power source 3. This is beneficial in terms of separation of lubricating oil in the gear unit 1 from lubricating oil in the power source 3. The portion of the cover 15 corresponding to the layshaft 31 can have a bearing 39R. Thus, the outer wall 11 can be provided with a bearing 39L, thereby causing both ends of the layshaft 31 to be supported by the bearings 39R, 39L. Needless to say, a ball bearing or the like can be interposed between the bearings 39R, 39L and the layshaft 31. Furthermore, when the hub portions of the parking gear 37 and the first gear 33 are made to abut respective inner races of these ball bearings, these inner races can serve as bases that support these gears 37 and 33 in the axial direction.

[0034] According to the above-described structure, the layshaft line C, the rotation axis X and the working axis L are set in a specific dimensional relationship. From Figure 2 And Figure 3 It will be appreciated that the parking lock device 7 can be arranged away from relatively large components such as the first gear 33 and the differential gear set 21, and close to the side wall of the housing. For example, Figure 5 It can be clearly shown that the working axis L of the actuator 45 is very close to the layshaft line C. This is advantageous in reducing the size, particularly the height, of the gear unit 1. The layshaft line C can be offset downward from the rotation axis X in order to further reduce the height dimension. Reference will be made primarily to Figure 4 And Figure 5Considering a reference plane S (horizontal if the gear unit 1 is used in the manner as shown in the attached figures) comprising the rotation axis X, the secondary axis C can have an offset Oi with respect to the reference plane S. Then, the offset O2 of the working axis L can be reduced by the offset Oi (offset Oi and offset O2 are directed in opposite directions with respect to the reference plane S). This helps to lower the actuator 45, thus reducing the height dimension of the gear unit 1. The presence of the offset Oi further results in the first gear 33 being the lowest among all the rotating elements. This facilitates the splashing and circulation of lubricating oil out from the bottom, as the outer periphery of the gear 33 sweeps the lowest point of the housing.

[0035] For example, the process for assembling the gear unit 1 is carried out in the following manner.

[0036] First, the first gear 33 and the parking gear 37 are coupled to the secondary shaft 31 comprising the first gear 35. The secondary shaft 31 thus produced is passed through the opening 41 and combined with the partition wall 13. In parallel, the differential gear set 21 is assembled and fitted with the roller bearings into the bearings 29R on the partition wall 13. By slightly moving the secondary shaft 31 laterally as a whole, the second gear 35 engages with the gear teeth 25 of the differential gear set 21.

[0037] In parallel, the respective elements of the actuator 45 are incorporated one after the other into the outer wall 11. The pawl 43 is incorporated into the outer wall 11 together with the return spring. These components are coupled as a whole with the above-mentioned assembly.

[0038] The assembly comprising these components is coupled with the cover 15 and the output shaft 5 is coupled therewith. Since the first gear 33 is a helical gear, the first gear 33 is twisted and then engaged with the output shaft 5. In this step, when the engagement of all the gears in the gear unit 1 is completed, the first gear 33 can be rotated by rotating any one of these gears. For example, by inserting a collet clamp into the left face gear 27L and rotating it slightly, for example, the first gear 33 can be rotated, thus engaging the output shaft 5 therewith.

[0039] While certain example implementations have been described above, modifications and changes thereto can occur to those skilled in the art, which modifications and changes are contemplated to be within the scope of the implementations as set forth above.

Claims

1. A gear unit for use in combination with a power source having a hollow output shaft, comprising: a differential gear set having a common axis of rotation with the output shaft; a lay shaft fixedly comprising a first gear meshing with the output shaft and a second gear meshing with the differential gear set, wherein the first and second gears constitute a reduction gear set; a housing comprising an outer wall separating the differential gear set and the lay shaft from an exterior; and a parking gear disposed axially opposite the first gear outside the second gear and fixed to the lay shaft.

2. The gear unit of claim 1, further comprising: a parking lock device comprising a pawl pivotably supported by the outer wall and engageable with the parking gear, and an actuator configured to impart a rocking motion to the pawl to disengageably engage the pawl with the parking gear.

3. The gear unit according to claim 2, wherein, the pawl is disposed between the second gear and the outer wall.

4. The gear unit according to claim 2, wherein, the pawl is disposed between the actuator and the parking gear.

5. The gear unit according to claim 2, wherein, the actuator comprises a motor configured to produce a rotational motion and a cam mechanism configured to convert the rotational motion into a linear motion for rocking the pawl, and the motor protrudes outwardly from the outer wall.

6. The gear unit of claim 1, wherein, the second gear and the parking gear are disposed in a single chamber in the housing.

7. The gear unit according to claim 6, wherein, the housing further comprises a partition wall separably combinable with the outer wall to define the chamber, and the partition wall comprises a bearing rotatably supporting the differential gear set.

8. The gear unit according to claim 7, wherein, the partition wall comprises an opening sized to allow passage of the parking gear.

9. The gear unit of claim 1, wherein, the lay shaft is offset from a reference plane comprising the axis of rotation, the gear unit further comprising: an actuator configured to produce a linear motion along a working axis, the actuator being fixed to the outer wall so as to direct the working axis perpendicularly to the axis of rotation and offset the working axis from the reference plane in a direction opposite the lay axis; and a pawl pivotably supported by the outer wall so as to be pressed by the actuator into engagement with the parking gear.

10. The gear unit according to claim 9, wherein, the actuator comprises a motor configured to produce a rotational motion and a cam mechanism configured to convert the rotational motion into a linear motion, and the motor protrudes outwardly from the outer wall.

11. The gear unit according to claim 10, wherein, the differential gear set, the lay shaft, the housing, the pawl, and the cam mechanism are disposed such that a projection of the differential gear set, the lay shaft, the housing, the pawl, and the cam mechanism on a plane perpendicular to both the axis of rotation and the lay axis is within a projection of the power source on the same plane.

12. The gear unit of claim 11, wherein, the motor is disposed to protrude from the projection of the power source.

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