power transmission device

Abstract

To provide a power transmission device capable of suppressing localized strength reduction and wear caused by gears meshing with each other at specific locations. [Solution] A first gear G1 and a second gear G2, which are helical gears, are arranged so as to be movable in opposite directions on the same axis and housed in a case 2, and the first gear G1 and the second gear G2 are meshed with gears G4 and G6, respectively, which are connected to a torque generation source, so that when the first gear G1 and the second gear G2 transmit torque from the torque generation source, thrust forces Fi and Fo in opposite directions are generated in the first gear G1 and the second gear G2, respectively. In the power transmission device 1, in which the angles of the helical teeth of the first gear G1 and the second gear G2 are set respectively, the first gear G1 and the second gear G2 are fitted together on the same axis so as to generate a predetermined maximum static friction force Fpmax, and when the absolute value of the sum of the thrust forces Fi and Fo generated in the first gear G1 and the second gear G2 respectively exceeds the absolute value of the maximum static friction force Fpmax, the first gear G1 and the second gear G2 move in opposite directions.

Description

[Technical Field]

[0001] The present invention relates to a power transmission device for transmitting power (torque) from a power generation source including a motor of a hybrid vehicle (HEV) to drive wheels, for example. [Background technology]

[0002] Known power transmission devices of this type include a first gear and a second gear, each made up of helical gears, housed coaxially in a case, which are meshed with gears connected to a torque generation source such as an engine or a motor, or a drive wheel during regeneration, and in which the angles (directions) of the helical teeth of the first gear and the second gear are set so that thrust forces in opposing directions (axial directions) are generated in the first gear and the second gear when the first gear and the second gear transmit torque from the torque generation source (see, for example, Patent Document 1). Of the torque from the torque generation source, acceleration torque, which is torque in the forward direction relative to the direction of travel, is transmitted from the engine or the motor, and deceleration torque, which is torque in the reverse direction relative to the direction of travel, is transmitted from the drive wheel.

[0003] However, in the above power transmission device, fluctuations in the rotation of the helical gear cause the gear member to vibrate in the thrust direction, and this gear member collides with the case, causing a rattle noise, which becomes a problem.

[0004] Therefore, Patent Document 2 proposes a configuration in which an inner wall is formed inside the case, extending from the outer wall of the case toward the inside of the case, and an elastic member is interposed between the inner wall and the helical gear in a preloaded state to press the helical gear against the inner wall.

[0005] Furthermore, Patent Document 3 proposes a power transmission device equipped with a reducer having a plurality of helical gears rotatably supported by bearings, in which the limit value of the torque generated in the drive motor when the vehicle is driven in reverse is set lower than the limit value of the torque generated in the drive motor when the vehicle is driven in forward direction. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6083333 [Patent Document 2] Patent No. 5812182 [Patent Document 3] Patent No. 6459370 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the power transmission devices proposed in Patent Documents 1 to 3 have the problem that localized strength reduction and wear occur due to the meshing of helical gears at specific points.

[0008] The present invention was made in consideration of the above problems, and its purpose is to provide a power transmission device that can suppress localized strength reduction and wear caused by gears meshing at specific locations. Another purpose of the present invention is to simplify the overall system configuration and extend the life of the power transmission device by providing such a power transmission device, and to improve the energy efficiency of hybrid vehicles and the like by enabling improved power transmission efficiency without the need for a separate device requiring special power. [Means for solving the problem]

[0009] In order to achieve the above object, the present invention provides a gear transmission system in which a first gear (G1) and a second gear (G2) made up of helical gears are arranged coaxially so as to be movable at least in opposite directions and housed in a case (2), the first gear (G1) and the second gear (G2) are meshed with gears (G4, G6) connected to a torque generation source, respectively, and thrust forces (Fi, Fo) are generated in opposite directions to the first gear (G1) and the second gear (G2) when the first gear (G1) and the second gear (G2) transmit torque from the torque generation source, respectively. In the power transmission device (1), in which the angles of the helical teeth of the first gear (G1) and the second gear (G2) are set respectively, the first gear (G1) and the second gear (G2) are fitted together on the same axis so as to generate a predetermined maximum static friction force (Fpmax), and when the absolute value of the sum of the thrust forces (Fi, Fo) of the first gear (G1) and the second gear (G2) in the opposing directions exceeds the absolute value of the maximum static friction force (Fpmax), the first gear (G1) and the second gear (G2) are configured to move in the opposing directions.

[0010] According to the power transmission device of the present invention, the first gear (G1) and the second gear (G2) are fitted together on the same axis so as to generate a predetermined static friction force (Fp), and when the absolute value of the sum of the thrust forces (Fi, Fo) of the first gear (G1) and the second gear (G2) in the opposing directions exceeds the absolute value of the maximum static friction force (Fpmax), the first gear (G1) and the second gear (G2) move in the opposing directions, respectively.Therefore, the meshing area between the first gear (G1) and the gear meshing with it, and the meshing area between the second gear (G2) and the gear meshing with it, fluctuate in the axial direction depending on the absolute value of the sum of the thrust forces (Fi, Fo) of the first gear (G1) and the second gear (G2) in the opposing directions. As a result, in power transmission by the power transmission device via the first gear (G1) and the second gear (G2), the first gear (G1) and the gear meshing therewith, and the second gear (G2) and the gear meshing therewith, do not always mesh at the same point, but the meshing points move in the axial direction. Therefore, even with a relatively simple configuration, it is possible to suppress localized strength reduction and wear due to the first gear (G1) and the gear meshing therewith, and the second gear (G2) and the gear meshing therewith, meshing at specific points.

[0011] Here, the absolute value of the sum of the outward thrust forces (Fi, Fo) generated in each of the first gear (G1) and the second gear (G2) may be defined as a first thrust force, and the absolute value of the sum of the inward thrust forces (Fi, Fo) generated in each of the first gear (G1) and the second gear (G2) may be defined as a second thrust force. When the first thrust force exceeds the absolute value of the maximum static friction force (Fpmax), the first gear (G1) and the second gear (G2) may each move outward, and when the second thrust force exceeds the absolute value of the maximum static friction force (Fpmax), the first gear (G1) and the second gear (G2) may each move inward.

[0012] According to this configuration, when thrust forces in different directions exceed the maximum static friction force generated between the first gear and the second gear, the first gear and the second gear are set to move in the direction of the thrust forces generated, respectively. This makes it possible to move the meshing point of the first gear or the second gear by changing the direction of the thrust forces.

[0013] The first thrust force may be generated when a torque in the negative direction is transmitted, and the second thrust force may be generated when a torque in the positive direction is transmitted, or the first thrust force may be generated when a torque in the positive direction is transmitted, and the second thrust force may be generated when a torque in the negative direction is transmitted. Note that, here, the acceleration torque acting on the first gear and the second gear when the vehicle moves forward or the deceleration torque acting on the first gear and the second gear when the vehicle moves backward is referred to as positive torque, and the deceleration torque acting on the first gear and the second gear when the vehicle moves forward or the acceleration torque acting on the first gear and the second gear when the vehicle moves backward is referred to as negative torque.

[0014] In this configuration, the first gear and the second gear move due to thrust forces of different directions generated by torques in different directions. This makes it possible to move the meshing point of either the first gear or the second gear by changing the direction of the torque acting on them.

[0015] Furthermore, when the magnitude of the torque in the positive direction or the torque in the negative direction becomes a predetermined first torque, the first thrust force exceeds the absolute value of the maximum static friction force (Fpmax), and when the magnitude of the torque in the opposite direction to the first torque becomes a predetermined second torque, the second thrust force exceeds the absolute value of the maximum static friction force (Fpmax), and the first gear (G1) and the second gear (G2) may be configured to move in opposite directions.

[0016] This configuration ensures that when the magnitude of positive or negative torque exceeds a predetermined torque, the first and second gears move in opposite directions. As a result, they do not move at low torque levels below the predetermined torque, thus suppressing the decrease in responsiveness caused by torque transmission delay due to misalignment, especially at the start of power transmission. Furthermore, for example, if the first or second gear has moved in one direction due to negative torque, applying positive torque can move it in the other direction and return it to its initial position. Additionally, because the first or second gear moves when the torque increases, it receives high torque in a position where it is normally not engaged, thus suppressing localized strength reduction and wear.

[0017] Furthermore, if the third thrust force is defined as the absolute value of the sum of the inward thrust forces (Fm, Ff) applied to the first gear (G1) and the second gear (G2) respectively in case (2), then the first thrust force may be configured to move outward when it exceeds the absolute value of the sum of the maximum static friction force (Fpmax) and the third thrust force.

[0018] In this configuration, when the first thrust force exceeds the sum of the maximum static friction force and the third thrust force, the first gear and the second gear move outward. This prevents the first gear or the second gear from moving abruptly when the first thrust force exceeds the maximum static friction force, allowing for stable control of the amount of movement of the first gear or the second gear. The third thrust force is a preload applied inward from the case to the first gear and the second gear. Since the preload is applied by the case, which is made of aluminum casting or the like, the preload increases in proportion to the amount of movement of the first gear. Therefore, the preload increases in the high torque range, improving the support rigidity of the first gear and the second gear. This suppresses tilting in the range where tilting of the first gear or the second gear becomes significant, thereby suppressing wear on the first gear or the second gear, and also suppressing the deterioration of vibration and noise associated with the tilting of the first gear or the second gear.

[0019] In addition, the absolute value of the maximum static friction force (Fpmax) may be greater than the third thrust force, and when the combined force of the second thrust force and the third thrust force exceeds the absolute value of the maximum static friction force (Fpmax), the first gear (G1) and the second gear (G2) may move inward on the same axis.

[0020] According to this configuration, by setting the maximum static friction force to a value greater than the third thrust force of the preload, it is possible to set a region in which the first gear or the second gear will not move without the second thrust force, which makes it possible to extend the time (period) during which the first gear or the second gear moves, thereby more effectively suppressing local wear of the first gear or the second gear.

[0021] Furthermore, this power transmission device may include a hollow first shaft (10) formed on the central axis of the first gear (G1) and a second shaft (3) formed on the central axis of the second gear (G2), and the first shaft (10) and the second shaft (3) may be fitted together at a press-fit portion (13a) formed by pressing the inner peripheral surface of the first shaft (10) and the outer peripheral surface of the second shaft (3) into each other, and the maximum static friction force (Fpmax) may be the maximum static friction force between the inner peripheral surface and the outer peripheral surface at the press-fit portion (13a).

[0022] According to this configuration, it is possible to move the meshing point of the first gear or the second gear by a relatively simple method of appropriately adjusting the diameter dimensions of the inner circumferential surface and the outer circumferential surface of the press-fit portion.

[0023] Furthermore, this power transmission device may be a power transmission device mounted on a vehicle, the torque generating source may be a power source or a drive wheel of the vehicle, the first gear (G1) may mesh with a drive gear (G4) connected to the power source, the second gear (G2) may mesh with a driven gear (G6) connected to the drive wheel, the deceleration torque may be a torque generated when the vehicle decelerates, and the acceleration torque may be a torque generated when the vehicle accelerates.

[0024] With this configuration, the first gear or the second gear is set to move due to thrust forces of different directions when the vehicle is decelerating and accelerating, respectively, which makes it possible to move the meshing point of the first gear or the second gear when the vehicle is decelerating and accelerating, respectively.

[0025] In addition, the first thrust force (Fi, Fo) may be generated when deceleration torque is transmitted to the first gear (G1) and the second gear (G2), and the second thrust force (Fi, Fo) may be generated when acceleration torque is transmitted to the first gear (G1) and the second gear (G2).

[0026] Generally, acceleration of a vehicle requires a relatively larger torque than deceleration and occurs more frequently. With this configuration, the first gear or second gear that has moved during deceleration can be reliably returned to its initial position during acceleration.

[0027] The vehicle may be a hybrid vehicle including a motor as the power source, and the deceleration torque may be torque generated during regeneration by the motor.

[0028] According to this configuration, by using the power transmission device of the present invention in a hybrid vehicle that includes a motor as a power source, it is possible to suppress wear on the tooth surfaces of the gears included in the power transmission device, including the first gear or the second gear, while also enabling more regeneration by the motor to improve fuel efficiency. [Effects of the Invention]

[0029] According to the power transmission device of the present invention, it is possible to suppress localized strength reduction and wear caused by gears meshing with each other at specific points. [Brief explanation of the drawings]

[0030] [Figure 1] This is a cross-sectional view of the main part of a power transmission device according to the present invention. [Figure 2] This is a partial side view of the end of the counter shaft, showing the spiral groove formed on the outer circumference of the counter shaft. [Figure 3] 3 is a schematic cross-sectional view showing forces acting on a first gear and a second gear when a deceleration torque is transmitted to the first gear and the second gear of the power transmission device according to the present invention. FIG. [Figure 4] FIG. 10 is a diagram showing the relationship between the thrust force acting on the first gear and the second gear and the amount of movement of the first gear when deceleration torque or acceleration torque is transmitted to the first gear and the second gear of the power transmission device according to the present invention. [Figure 5] This is a schematic cross-sectional view showing the forces acting on the first gear and the second gear when acceleration torque is transmitted to the first gear and the second gear of the power transmission device according to the present invention. [Figure 6] 5 is a schematic view of the tooth surfaces of the first gear and the fourth gear, showing changes in the meshing position between the first gear and the fourth gear. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0031] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

[0032] [Power transmission device configuration] First, the configuration of the main part of the power transmission device according to the present invention will be explained with reference to Figure 1.

[0033] The power transmission device 1 shown in FIG. 1 is mounted on a hybrid vehicle (HEV) that runs using an engine and an electric motor (not shown) as drive sources (torque generating sources), and transmits the power output from the engine and the electric motor to a pair of left and right drive wheels (not shown). Its main configuration is as follows:

[0034] That is, a first gear G1 and a second gear G2, which are helical gears, are coaxially arranged and housed within a case 2 of the power transmission device 1. Here, the first gear G1 and the second gear G2 are arranged on a hollow countershaft 3, which is the second shaft. A hollow boss portion (first shaft) 10 is formed on the first gear G1, and one axial end (the left end in FIG. 1) of the countershaft 3 is press-fitted into the hollow boss portion 10. The second gear G2 is formed integrally with the outer periphery of the countershaft 3. The portion of the boss portion 10 that is press-fitted into the countershaft 3 is indicated by reference numeral 13a.

[0035] A multi-plate clutch CL is disposed between the first gear G1 and the second gear G2 in the axial direction of the countershaft 3 (left-right direction in FIG. 1 ), and a third gear G3 is fitted to the other axial end of the countershaft 3 (right end in FIG. 1 ). One axial end (left end in FIG. 1 ) of the countershaft 3 is rotatably supported by the case 2 by a tapered roller bearing 4 fitted in the radial gap between the first gear G1 and the case 2, and the other axial end (right end in FIG. 1 ) is rotatably supported by a tapered roller bearing 5 fitted in the radial gap between the third gear G3 and the case 2. The tapered roller bearings 4 and 5 function to receive axial thrust forces generated in the first gear G1 and the second gear G2. While not shown, the present invention is not limited to the tapered roller bearings 4 and 5. Alternatively, a configuration in which one of the outer and inner rings of a ball bearing is movably fitted to allow movement in the thrust direction may be employed. Furthermore, in the power transmission device 1 of this embodiment, the provision of tapered roller bearings 4 and 5 allows the first gear G1, the second gear G2, and the third gear G3 to move a predetermined amount in the thrust direction, and it is possible to shift the meshing range of the first gear G1 and the fourth gear G4 within the range of this predetermined amount of movement.

[0036] Incidentally, within case 2, an intermediate shaft 6 is arranged parallel and horizontally to the counter shaft 3, and both axial ends of this intermediate shaft 6 are rotatably supported by ball bearings 7 and 8 in case 2. A fourth gear G4, which is a drive gear directly connected to a drive motor (not shown), is integrally formed at one axial end of the intermediate shaft 6 (left end in Figure 1), and this fourth gear G4 meshes with the first gear G1. A parking gear G5, used to fix the vehicle when it is parked, is fixed to the other axial end of the intermediate shaft 6 (right end in Figure 1), and this parking gear G5 meshes with another gear (not shown). Furthermore, the second gear G2 is meshed with a sixth gear G6 (see Figure 3), which transmits the rotation of the drive wheel (not shown) to the second gear G2 during braking, and the regenerative torque from the drive wheel is transmitted to a drive motor (not shown) via the sixth gear G6, the second gear G2, the first gear G1, and the fourth gear G4.

[0037] The clutch CL selectively rotates the seventh gear G7, which is rotatably supported on the counter shaft 3 by a ball bearing 9. When the clutch CL is ON (connected), power from the engine, which is the drive source, is transmitted to the counter shaft 3 through the seventh gear G7. When the clutch CL is OFF (disconnected), no power from the engine is transmitted to the counter shaft 3. The first gear G1 is fitted with a retaining member 20 to suppress tilting caused by thrust force generated in the first gear G1. This retaining member 20 contacts the clutch guide 21 of the clutch CL, thereby suppressing tilting of the first gear G1. By suppressing tilting of the first gear G1 in this way, the natural frequency of the first gear G1 changes, and the generation of noise and vibration due to resonance is suppressed.

[0038] In this embodiment, the hardness of the first gear G1, the second gear G2, and the fourth gear (drive gear) G4 are the same, but the number of teeth of the fourth gear G4 is set to be less than the number of teeth of the first gear G1. By setting it in this way, the fourth gear G4, which has fewer teeth, will wear out first, and the cost required for replacing the fourth gear G4, which is integrally formed with the intermediate shaft 6, can be reduced. In addition, in this embodiment, the width of the fourth gear G4, which is a drive gear, is set to be wider than the width of the first gear G1. Therefore, even if the first gear G1 moves in the axial direction as described later, the meshing width between the first gear G1 and the fourth gear G4 can be secured, and power transmission by these first gear G1 and fourth gear G4 can be reliably performed.

[0039] Incidentally, the first gear G1 and the second gear G2, which are coaxially arranged on the counter shaft 3, are helical gears as described above. The angle (direction) of the helical teeth of each helical gear is set so that when the first gear G1 and the second gear G2 transmit torque from the torque source, thrust forces Fi and Fo are generated in directions opposite to the first gear G1 and the second gear G2 (opposite directions to each other) (see Figures 3 and 5). Specifically, when the first gear G1 and the second gear G2 transmit deceleration torque from the torque source, as shown in Figure 3, outward thrust forces (hereinafter referred to as "first thrust force") Fi and Fo are generated in the first gear G1 and the second gear G2, respectively. Conversely, when the first gear G1 and the second gear G2 transmit acceleration torque from the torque generation source, as shown in FIG. 5, inward (approaching) thrust forces (hereinafter referred to as "second thrust forces") Fi and Fo are generated in the first gear G1 and the second gear G2, respectively.

[0040] Furthermore, as described above, the inner circumferential surface of the hollow boss portion 10 of the first gear G1 is press-fitted with the outer circumferential surface of the press-fit portion 13a shown in Figure 1, and the spline portion 13b is spline-fitted to the outer circumferential surface of one axial end (left end in Figure 1) of the counter shaft 3. Therefore, the counter shaft 3 and the first gear G1 always rotate together. The press-fit portion 13a and the spline portion 13b constitute a fitting portion 13 into which the boss portion 10 of the first gear G1 and one axial end of the counter shaft 3 are fitted. In addition, as shown in Figure 2, a helical groove 3a is formed on the outer circumferential surface of the counter shaft 3 in the press-fit portion 13a into which the first gear G1 is press-fitted, with a constant pitch width. By forming the helical groove 3a on the outer circumferential surface of the press-fit portion 13a into which the boss portion 10 of the first gear G1 of the counter shaft 3 is press-fitted, the press-fit load can be reduced without reducing the width of the part that supports the load due to press-fitting. Furthermore, by orienting the helical groove 3a in the direction in which oil is discharged when the first gear G1 moves axially, contamination (foreign matter) contained in the oil of the press-fit portion 13a can be effectively discharged via the helical groove 3a. As shown in Figure 2, multiple spline grooves 3b are formed at the end of the counter shaft 3 (the position corresponding to the spline portion 13b). Also, as shown in Figure 1, the second gear G2 is integrally formed on the outer circumference of the counter shaft 3.

[0041] In this embodiment, as shown in Figure 1, a ring-shaped washer 11 is interposed in the axial gap between the case 2 and the tapered roller bearing 4, and a preload (first preload) Fm is applied to the first gear G1 from the case 2 in the direction of the second gear G2 (to the right in Figure 1) via this washer 11. Also, a ring-shaped shim 12 is interposed in the axial gap between the case 2 and the tapered roller bearing 5, and a preload (second preload) Ff is applied to the second gear G2 from the case 2 in the direction of the first gear G1 (to the left in Figure 1) via this shim 12. By providing the shim 12, the dimension between the tapered roller bearing 4 and the case 2 can be adjusted, making it possible to easily adjust so that the desired preload is applied to the first gear and the second gear by the elastic force of the case 2 when the case 2 is assembled.

[0042] [Operation of power transmission system] Next, the operation of the power transmission device 1 configured as described above will be explained below, specifically, the operation when the first gear G1 and the second gear G2 transmit deceleration torque from the drive wheels when the vehicle moves forward, and the operation when the first gear G1 and the second gear G2 transmit acceleration torque from the torque generation source. Note that, although the explanation here takes torque transmission when the vehicle moves forward as an example, the same operation and effect can be achieved when the vehicle moves backward (although the direction of the thrust force described below is reversed). Figure 3 is a schematic cross-sectional view showing the forces acting on the first gear G1 and the second gear G2 when the first gear G1 and the second gear G2 transmit deceleration torque from the drive wheels, Figure 4 is a diagram (graph) showing the relationship between the thrust force acting on the first gear G1 and the second gear G2 and the amount of movement of the first gear G1 when deceleration torque or acceleration torque is transmitted to the first gear G1 and the second gear G2, and Figure 5 is a schematic cross-sectional view showing the forces acting on the first gear G1 and the second gear G2 when acceleration torque is transmitted to the first gear G1 and the second gear G2. In this specification, the acceleration torque acting on the first gear G1 and the second gear G2 when the vehicle moves forward or the deceleration torque acting on the first gear G1 and the second gear G2 when the vehicle moves backward is referred to as positive torque (see FIG. 5), and the deceleration torque acting on the first gear G1 and the second gear G2 when the vehicle moves forward or the acceleration torque acting on the first gear G1 and the second gear G2 when the vehicle moves backward is referred to as negative torque (see FIG. 3). In FIGS. 3 and 5, the spring-like objects between the case 2 and the washer 11 and between the case 2 and the shim 12 are schematic representations of the elastic force of the case 2, which is an elastic body. In the graph of FIG. 4, the acceleration torque is represented by a positive force on the horizontal axis of the graph, and the deceleration torque is represented by a negative force on the horizontal axis of the graph.

[0043] 1) When the first gear and the second gear transmit reduction torque: When the first gear G1 and the second gear G2 transmit a deceleration torque, which is torque in the opposite direction to the direction of travel from the drive wheels, as shown in the schematic diagram in Figure 3, outward thrust forces Fi and Fo are simultaneously generated in the first gear G1 and the second gear G2, which share the same torque transmission path. In this specification, the absolute value of the sum of the outward thrust forces Fi and Fo generated in the first gear G1 and the second gear G2 is sometimes referred to as the first thrust force. In addition, the first gear G1 and the second gear G2 receive inward preloads Fm and Ff from case 2, respectively. Hereinafter, the preload Fm applied to the first gear G1 from case 2 will be referred to as the "first preload," and the preload Ff applied to the second gear G2 from case 2 via shim 12 will be referred to as the "second preload."

[0044] In this embodiment, the first gear G1 is press-fitted onto the counter shaft 3, which has the second gear G2 integrally formed with it. The first gear G1 can move outward along the counter shaft 3 by an amount equal to the elastic deformation of the case 2 (away from the second gear G2 (to the left in Figure 3)) within a predetermined range permitted by the tapered roller bearings 4 and 5. Here, the frictional force (static friction force Fp, maximum static friction force Fpmax, dynamic friction force Fpmov) generated at the press-fit portion 13a of the first gear G1 onto the counter shaft 3 when the first gear G1 moves outward acts in the opposite direction to the direction of movement of the first gear G1.

[0045] Therefore, if we consider the direction of force acting to the right in Figure 3 as "+" and the direction of force acting to the left as "-", when the first gear G1, which is movable in the axial direction, is stationary and does not move, the following relationship holds between the first thrust force (Fi+Fo) acting on the first gear G1, the first preload Fm, the static friction force Fp of the press-fit portion 13a of the first gear G1, and the second preload Ff acting on the second gear G2. Fi + Fo = Fp + Fm + Ff …(1)

[0046] Here, if the maximum static friction force when slippage (relative displacement in the thrust direction between the first gear G1 and the second gear G2) occurs in the press-fit portion 13a is defined as Fpmax, there is a relationship Fp≦Fpmax between the static friction force Fp and the maximum static friction force Fpmax, so while the first gear G1 is stationary and not moving, the relationship shown in the following equation holds. |Fi+Fo-(Ff+Fm)|≦|Fpmax| …(2)

[0047] In other words, at points a to b along the straight line E shown in Figure 4, the first thrust force (Fi+Fo) acting on the first gear G1 and the second gear G2 due to the transmission of deceleration torque to the first gear G1 and the second gear G2, and the sum of the first preload Fm, which is a positive biasing force acting on the first gear G1 from case 2, and the second preload Ff, which is a negative biasing force acting on the second gear G2 from case 2, (Ff+Fm) is less than or equal to the maximum static friction force Fpmax of the press-fit portion 13a, so the first gear G1 remains stationary and does not move.

[0048] The following magnitude relationship exists between the first thrust force (Fi+Fo) acting on the first gear G1, the first preload Fm, the maximum static friction force Fpmax of the press-fit portion 13a, and the second preload Ff acting on the second gear G2: |Fi+Fo-(Ff+Fm)|>|Fpmax| …(3) When this condition holds, the first gear G1 and the second gear G2 move outward (away from each other).

[0049] In other words, at points b to c shown in Figure 4, when the reduction torque is transmitted to the first gear G1 and the second gear G2, the difference between the first thrust force (Fi+Fo) acting on the first gear G1 and the second gear G2 and the sum of the preloads acting on the first gear G1 and the second gear G2 (Ff+Fm) becomes greater than the maximum static friction force Fpmax of the press-fit section 13a, causing the first gear G1 to move outward (away from the second gear G2, to the left in Figure 3), and the amount of this movement x increases along the straight line A shown in Figure 4. Then, at point c shown in Figure 4, where the first thrust force (Fi+Fo) acting on the first gear G1 is at its maximum, the amount of outward movement x of the first gear G1 reaches its maximum value x. max Shows.

[0050] 4, when the deceleration torque transmitted to the first gear G1 decreases, the first gear G1 moves inward (toward the second gear G2) from point c to point d along the straight line B in FIG. 4 due to the difference between the first thrust force (Fi+Fo) acting on the first gear G1 and the second gear G2 and the sum (Ff+Fm) of the preloads acting on the first gear G1 and the second gear G2. In other words, while the difference between the first thrust force (Fi+Fo) acting on the first gear G1 and the second gear G2 and the sum (Ff+Fm) of the preloads acting on the first gear G1 and the second gear G2 is greater than the kinetic friction force Fpmov acting on the press-fit portion 13a, that is, as expressed by the following equation: |Fi+Fo-(Ff+Fm)|>|Fpmov| …(4) The first gear G1 moves inward only while the relationship holds true.

[0051] And then, the following equation: |Fi+Fo-(Ff+Fm)|=|Fpmov| …(5) When the above relationship is established, the inward movement of first gear G1 stops. This stopped state of first gear G1 continues until the first thrust force (Fi + Fo) generated between first gear G1 and second gear G2 decreases to 0, that is, from point d to point e along line C shown in Figure 4.

[0052] 2) When the first gear and the second gear transmit acceleration torque: On the other hand, when the first gear G1 and the second gear G2 transmit acceleration torque, which is torque in the forward direction relative to the direction of travel from the torque generation source, inward thrust forces Fi and Fo are generated in the first gear G1 and the second gear G2, respectively, as shown in Fig. 5. Note that in this specification, the absolute value of the sum of the inward thrust forces Fi and Fo generated in the first gear G1 and the second gear G2, respectively, is sometimes referred to as the second thrust force. In addition, the first gear G1 and the second gear G2 are subjected to inward preloads Fm and Ff, respectively, from the case 2.

[0053] Therefore, if the direction of action of a force in the rightward direction in FIG. 5 is defined as "+" and the direction of action of a force in the opposite, leftward direction as "-", when acceleration torque is transmitted from a torque generating source such as an engine or a motor to the first gear G1 and the second gear G2, if the first gear G1, which is movable in the axial direction, is stationary and does not move, the relationship shown in the following equation holds among the first thrust force (Fi+Fo) and first preload Fm acting on the first gear G1, the maximum static friction force Fpmax of the press-fit portion 13a, and the second preload Ff acting on the second gear G2. |Fi+Fo-(Ff+Fm)|≦|Fpmax| …(6)

[0054] On the other hand, the magnitude relationship of the following equations: |Fi+Fo-(Ff+Fm)|>|Fpmax| …(7) When this condition holds, the first gear G1 moves inward (in a direction approaching the second gear G2) (with respect to the second gear G2 (counter shaft 3)).

[0055] That is, the first gear G1 moves inward from point e in FIG. 4 along the straight line D and returns to the initial position (point a shown in FIG. 4).

[0056] As described above, in the power transmission device 1 according to this embodiment, the first gear G1 and the second gear G2 are press-fitted into each other at the press-fit portion 13a to generate predetermined frictional forces (static frictional force Fp, maximum static frictional force Fpmax, and kinetic frictional force Fpmov) on the same axis. When outward thrust forces Fi and Fo act on the first gear G1 and the second gear G2, respectively (directions moving away from each other), the first gear G1 moves outward. This causes the meshing area of ​​the first gear G1 with the fourth gear G4 to vary in the axial direction. Therefore, the first gear G1 and the fourth gear G4 do not always mesh at the same location, and the meshing point moves in the axial direction. Note that, although the present embodiment has been described as an example in which only the first gear G1 moves outward (in the direction away from the second gear G2), a configuration in which both the first gear G1 and the second gear G2 can move in opposite directions may also be employed.

[0057] Therefore, according to this embodiment, it is possible to suppress localized insufficient strength and wear due to meshing of the first gear G1 and the fourth gear G4 at specific locations. FIG. 6 is a schematic diagram of the tooth flanks of the first gear G1 and the fourth gear G4, showing changes in the meshing position between the two gears. When first thrust forces (outward thrust forces) Fi and Fo act on the first gear G1 and the second gear G2 during deceleration torque transmission, as shown in the figure, the first gear G1 moves outward from the solid-line position to the dashed-line position, and the meshing area between the first gear G1 and the fourth gear G4 moves outward (to the left in FIG. 6) by ε1. As a result, the meshing area between the first gear G1 and the fourth gear G4 alternates in the axial direction, and the first gear G1 and the fourth gear G4 do not always mesh at the same location, but the meshing point moves in the axial direction.

[0058] Furthermore, when the torque transmitted to the first gear G1 and the second gear G2 is small and the thrust forces Fi and Fo acting on these first gear G1 and second gear G2 are small, the first gear G1 and the second gear G2 do not move, preventing a decrease in responsiveness due to meshing misalignment during drive force transmission. In particular, the change in meshing position at the start of drive force transmission prevents a decrease in responsiveness due to torque transmission delay. Conversely, when the torque transmitted to the first gear G1 and the second gear G2 is large, the movement of these first gear G1 and the second gear G2 increases, resulting in high torque being received at positions where there is normally no meshing, thereby suppressing localized strength reduction and wear on the tooth surfaces.

[0059] Additionally, in this embodiment, the first gear G1 and the fourth gear G4 have the same hardness and the number of teeth of the fourth gear G4 is smaller than that of the first gear G1, which reduces the cost of replacing the fourth gear G4, which has fewer teeth and wears out first. Also, because the width of the fourth gear is set wider than the width of the first gear G1, even if the first gear G1 moves in the axial direction, the meshing width between the first gear G1 and the fourth gear G4 can be ensured, and power transmission by the first gear G1 and the fourth gear G4 can be reliably performed.

[0060] Furthermore, in this embodiment, a helical groove 3a is formed on the outer circumference of the press-fit portion 13a into which the first gear G1 of the counter shaft 3 is press-fitted. This allows for appropriate adjustment of the press-fit load of the first gear G1 without reducing the width that supports the load. Additionally, the twisting direction of the helical groove 3a is aligned with the direction in which oil is discharged when the first gear G1 moves axially, thus effectively discharging contamination (foreign matter) contained in the oil.

[0061] Furthermore, in this embodiment, a retaining member 20 is attached to the first gear G1 to suppress the tilting of the first gear G1 due to the thrust force generated in the first gear G1, thereby preventing the first gear G1 from tilting. As a result of suppressing the tilting of the first gear G1 in this way, the natural frequency of the first gear G1 changes, and the generation of noise and vibration due to resonance is suppressed.

[0062] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the technical ideas described in the claims, specification, and drawings. For example, in the above embodiment, the case of the power transmission device housing the first gear and the second gear was described as a single case 2, but the case may be a configuration in which multiple members (multiple divided cases) are combined. In that case, preload is applied to the first gear and the second gear from each member (each divided case). [Explanation of symbols]

[0063] 1 Power transmission device 2 cases 3 Counter axis (second axis) 3a spiral groove 3b spline groove 4,5 Tapered roller bearings 6 Intermediate shaft 10 Boss part of 1st gear (1st shaft) 11 Washer 12 Sim 13 Fitting part 13a Press-fit part 13b Spline section 20 Holding member 21 Clutch guide (other parts) CL Clutch Ff Second preload Fi Thrust force generated in the first gear (first and second thrust forces) Fm First preload Fo Thrust force generated in the second gear (first and second thrust forces) Fp Static friction force Fpmax Maximum static friction force Fpmov dynamic friction force G1 1st gear G2 2nd gear G4 4th gear (drive gear) G6 6th gear (driven gear)

Claims

1. a first gear and a second gear, each of which is a helical gear, are disposed coaxially and movable at least in opposite directions and housed in a case; meshing the first gear and the second gear with gears connected to a torque generating source; In a power transmission device, the angles of the helical teeth of the first gear and the second gear are set so that thrust forces in directions opposite to each other are generated in the first gear and the second gear when the first gear and the second gear transmit torque from the torque generation source, the first gear and the second gear are engaged with each other on the same axis so as to generate a predetermined maximum static friction force; When the absolute value of the sum of the thrust forces of the first gear and the second gear in the opposing directions exceeds the absolute value of the maximum static friction force, the first gear and the second gear are configured to move in the opposing directions. A power transmission device characterized by:

2. an absolute value of a sum of the outward thrust forces generated in the first gear and the second gear is defined as a first thrust force; When the absolute value of the sum of the inward thrust forces generated in the first gear and the second gear is defined as a second thrust force, when the first thrust force exceeds the absolute value of the maximum static friction force, the first gear and the second gear each move outward; When the second thrust force exceeds the absolute value of the maximum static friction force, the first gear and the second gear are configured to move inward.

2. The power transmission device according to claim 1.

3. The first thrust force is generated when torque is transmitted in a negative direction, and the second thrust force is generated when torque is transmitted in a positive direction.

3. The power transmission device according to claim 2.

4. The first thrust force is generated when torque is transmitted in a positive direction, and the second thrust force is generated when torque is transmitted in a negative direction.

3. The power transmission device according to claim 2.

5. When the magnitude of the torque in the positive direction or the torque in the negative direction reaches a predetermined first torque, the first thrust force exceeds the absolute value of the maximum static friction force, When the magnitude of the torque in the direction opposite to the first torque becomes a predetermined second torque, the second thrust force exceeds the absolute value of the maximum static friction force, The first gear and the second gear are configured to move in opposite directions.

5. The power transmission device according to claim 3 or 4.

6. When the absolute value of the sum of the inward thrust forces applied to the first gear and the second gear by the case is defined as a third thrust force, When the first thrust force exceeds the sum of the absolute value of the maximum static friction force and the third thrust force, the first gear and the second gear are configured to move outward.

3. The power transmission device according to claim 2.

7. the absolute value of the maximum static friction force is greater than the third thrust force, When the combined force of the second thrust force and the third thrust force exceeds the absolute value of the maximum static friction force, the first gear and the second gear are configured to move inward on the same axis.

7. The power transmission device according to claim 6.

8. a first shaft having at least a hollow portion formed on a central axis of the first gear; a second shaft formed on the central axis of the second gear; Equipped with the first shaft and the second shaft are fitted together at a press-fit portion formed by press-fitting an inner peripheral surface of the first shaft and an outer peripheral surface of the second shaft, The maximum static friction force is the maximum static friction force between the inner circumferential surface and the outer circumferential surface of the press-fit portion.

2. The power transmission device according to claim 1.

9. the power transmission device is a power transmission device mounted on a vehicle, The torque generation source is a power source or a drive wheel of the vehicle, the first gear meshes with a drive gear connected to the power source, and the second gear meshes with a driven gear connected to the drive wheel; 5. The power transmission device according to claim 3, wherein the deceleration torque is a torque generated when the vehicle is decelerating, and the acceleration torque is a torque generated when the vehicle is accelerating.

10. 10. The power transmission device according to claim 9, wherein the first thrust force is generated when a deceleration torque is transmitted to the first gear and the second gear, and the second thrust force is generated when an acceleration torque is transmitted to the first gear and the second gear.

11. The vehicle is a hybrid vehicle including a motor as the power source, 10. The power transmission device according to claim 9, wherein the deceleration torque is a torque generated during regeneration by the motor.

12. 10. The power transmission device according to claim 9, wherein the first gear and the drive gear have the same hardness, and the number of teeth of the first gear is smaller than the number of teeth of the drive gear.

13. 10. The power transmission device according to claim 9, wherein a face width of the drive gear is wider than a face width of the first gear.

14. A spiral groove is formed in the press-fit portion, and the twisting direction of the spiral groove is set to a direction in which oil is discharged along the spiral groove when the first gear moves.

9. The power transmission device according to claim 8.

15. A pressing member is provided to bring the first gear into contact with another member when the first gear falls.

2. The power transmission device according to claim 1.

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