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 source including a motor of a hybrid vehicle (HEV vehicle) to drive wheels.

Background Art

[0002] In this type of power transmission device, a first gear and a second gear composed of helical gears are coaxially arranged and housed in a case, and these first gear and second gear are meshed with gears connected to torque generation sources such as an engine, a motor, or drive wheels during regeneration, respectively. When the first gear and the second gear transmit torque from the torque generation source, the angles (directions) of the helical teeth of the first gear and the second gear are set so that thrust forces in the direction (axial direction) opposite to each other are generated between these first gear and second gear (see, for example, Patent Document 1). Among the torques from the torque generation source, the accelerating torque, which is the torque in the forward direction with respect to the traveling direction, is transmitted from the engine or the motor, and the decelerating torque, which is the torque in the reverse direction with respect to the traveling direction, is transmitted from the drive wheels.

[0003] By the way, in the above power transmission device, due to the fluctuation of the rotation of the helical gear, the gear member vibrates in the thrust direction, and the generation of rattling noise caused by the collision of this gear member with the case becomes a problem.

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

[0005] Further, Patent Document 3 proposes a power transmission device including a speed reducer having a plurality of helical gears rotatably supported by bearings, in which the limit value of the torque generated in the drive motor during reverse driving of the vehicle is set lower than the limit value of the torque generated in the drive motor during forward driving. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6083333 [Patent Document 2] Patent No. 5812182 [Patent Document 3] Patent No. 6459370 [Overview of the project] [Problems that the invention aims to solve]

[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 has been made in view of the above problems, and its objective is to provide a power transmission device that can suppress localized strength reduction and wear caused by gears meshing at specific points. Furthermore, the objective of the present invention is to simplify the overall system configuration and extend its lifespan by incorporating the power transmission device, and to improve the energy efficiency of hybrid vehicles and the like by enabling improved power transmission efficiency without separately providing devices that require special power. [Means for solving the problem]

[0009] To achieve the above objective, the present invention provides a first gear (G1) and a second gear (G2), both composed of helical gears, arranged to be movable coaxially in at least opposing 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 source, respectively, and when torque from the torque source is transmitted by the first gear (G1) and the second gear (G2), thrust forces (Fi, Fo) are generated in directions opposite to the first gear (G1) and the second gear (G2), respectively. In a 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 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 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 opposing directions.

[0010] According to the power transmission device of the present invention, a first gear (G1) and a second gear (G2) are fitted coaxially 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 their opposing directions exceeds the absolute value of their maximum static friction force (Fpmax), the first gear (G1) and the second gear (G2) are configured to move in their opposing directions. As a result, the meshing regions of the first gear (G1) and the gear that meshes with it, and the meshing regions of the second gear (G2) and the gear that meshes with it, fluctuate in the axial direction according to the absolute value of the sum of the thrust forces (Fi, Fo) of the first gear (G1) and the second gear (G2) in their opposing directions. As a result, in power transmission via the first gear (G1) and the second gear (G2) by the power transmission device, the first gear (G1) and the gear that meshes with it, and the second gear (G2) and the gear that meshes with it, do not always mesh at the same point, and the meshing point moves in the axial direction. Therefore, despite the relatively simple configuration, it is possible to suppress localized strength reduction and wear caused by the first gear (G1) and the gear that meshes with it, and the second gear (G2) and the gear that meshes with it, 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) is defined as the 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) is defined as the second thrust force. In this configuration, 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) 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) move inward.

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

[0013] Furthermore, the first thrust force may be configured to be generated when a negative torque is transmitted and the second thrust force may be generated when a positive torque is transmitted, or the first thrust force may be configured to be generated when a positive torque is transmitted and the second thrust force may be generated when a negative torque is transmitted. Here, the acceleration torque acting on the first and second gears when the vehicle moves forward, or the deceleration torque acting on the first and second gears when the vehicle moves backward, is referred to as positive torque, and the deceleration torque acting on the first and second gears when the vehicle moves forward, or the acceleration torque acting on the first and second gears 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, the system may be configured such that when the magnitude of the positive or negative torque reaches 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 reaches a predetermined second torque, the second thrust force exceeds the absolute value of the maximum static friction force (Fpmax), causing the first gear (G1) and the second gear (G2) to move in opposing 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] Further, the absolute value of the maximum static friction force (Fpmax) is a value larger than the third thrust force of the preload, and when the force obtained by adding 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 be configured to move inward in the same axis respectively.

[0020] According to this configuration, by setting the maximum static friction force to a value larger than the third thrust force of the preload, it is possible to set a region where the first gear or the second gear does not move when there is no second thrust force. As a result, the time (period) during which the first gear or the second gear moves can be made longer, so that local wear of the first gear or the second gear can be more effectively suppressed.

[0021] Further, in this power transmission device, 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) are provided, and the first shaft (10) and the second shaft (3) are fitted together by a press-fitting portion (13a) formed by press-fitting the inner peripheral surface of the first shaft (10) and the outer peripheral surface of the second shaft (3) to 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 in the press-fitting 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 peripheral surface and the outer peripheral surface of the press-fitting portion.

[0023] Further, this 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 (G1) meshes with a drive gear (G4) connected to the power source, the second gear (G2) meshes with a driven gear (G6) connected to the drive wheel, the deceleration torque is a torque generated when the vehicle decelerates, and the acceleration torque may be a torque generated when the vehicle accelerates.

[0024] According to this configuration, the first gear or the second gear is set to move by thrust forces with different directions during deceleration and acceleration of the vehicle, respectively. Thereby, it becomes possible to move the meshing point of the first gear or the second gear during deceleration and acceleration of the vehicle, respectively.

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

[0026] Generally, the acceleration of a vehicle has a relatively larger torque than deceleration and occurs more frequently. According to this configuration, it becomes possible to reliably return the first gear or the second gear that has moved during deceleration to its initial position during acceleration.

[0027] Further, the vehicle is a hybrid vehicle including a motor as the power source, and the deceleration torque may be the 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 including a motor as the power source, it is possible to perform a large amount of regeneration by the motor for improving fuel efficiency while suppressing wear of the tooth surfaces of the gears included in the power transmission device including the first gear or the second gear.

Effects of the Invention

[0029] According to the power transmission device according to the present invention, it is possible to suppress local strength reduction and wear caused by meshing of gears at specific parts.

Brief Description of the Drawings

[0030] [Figure 1] It is a cross-sectional view of a main part of the power transmission device according to the present invention. [Figure 2] It is a partial side view of an end portion of a countershaft showing a spiral groove formed on the outer periphery of the countershaft. <00001 [Figure 3] This is a schematic cross-sectional view showing the forces acting on the first gear and the second gear when a reduction torque is transmitted to the first gear and the second gear of the power transmission device according to the present invention. [Figure 4] This figure shows 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] This is a schematic diagram of the tooth surfaces of the first and fourth gears, showing the change in the meshing position between them. [Modes for carrying out the invention]

[0031] Embodiments of the present invention will be described below with reference to the accompanying drawings.

[0032] [Configuration of the power transmission system] 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 Figure 1 is installed in a hybrid electric vehicle (HEV) that runs using an engine (not shown) and an electric motor as drive sources (torque sources). It transmits the power output from the engine and electric motor to a pair of left and right drive wheels (not shown), and its main components are as follows.

[0034] In other words, a first gear G1 and a second gear G2, both composed of helical gears, are coaxially arranged and housed within the case 2 of the power transmission device 1. Here, the first gear G1 and the second gear G2 are positioned on a hollow counter shaft 3, which is the second shaft. A hollow boss portion (first shaft) 10 is formed on the first gear G1, and one axial end of the counter shaft 3 (the left end in Figure 1) is press-fitted into this hollow boss portion 10. The second gear G2 is integrally formed on the outer circumference of the counter shaft 3. The press-fit portion of the boss portion 10 onto the counter shaft 3 is indicated by reference numeral 13a.

[0035] Furthermore, a multi-plate clutch CL is positioned between the first gear G1 and the second gear G2 in the axial direction (left-right direction in Figure 1) of the counter shaft 3, and the third gear G3 is fitted to the other axial end of the counter shaft 3 (right end in Figure 1). Here, the counter shaft 3 is rotatably supported at one axial end (left end in Figure 1) 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 at the other axial end (right end in Figure 1) 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 the axial thrust force generated in the first gear G1 and the second gear G2. It should be noted that, although not shown in the illustration, other configurations are also possible, such as one in which the outer ring and one in the inner ring of a ball bearing are movably fitted to allow movement in the thrust direction. Furthermore, in the power transmission device 1 of this embodiment, the provision of tapered roller bearings 4 and 5 allows for a predetermined amount of movement of the first gear G1, second gear G2, and third gear G3 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 a drive wheel (not shown) during braking to the second gear G2. 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 a torque source, as shown in Figure 5, inward 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 is moving forward, and the operation when the first gear G1 and the second gear G2 transmit acceleration torque from the torque source. Here, we will explain using torque transmission when the vehicle is moving forward as an example, but similar operation and effects can be achieved when the vehicle is moving backward (although the direction of the thrust force, which will be described later, will be reversed). Figure 3 is a schematic cross-sectional view showing the forces acting on the first gear G1 and the second gear G2 when they transmit deceleration torque from the drive wheels; Figure 4 is a graph showing the relationship between the thrust force acting on the first gear G1 and the second gear G2 and the amount of displacement 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 Figure 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 Figure 3). In Figures 3 and 5, the spring-like objects between case 2 and washer 11, and between case 2 and shim 12, schematically represent the elastic force of case 2, which is an elastic body. In the graph in Figure 4, acceleration torque is shown in the positive direction (force) on the horizontal axis of the graph, and deceleration torque is shown in the negative direction (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 we let Fpmax be 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, then there is a relationship between the static friction force Fp and the maximum static friction force Fpmax: Fp ≤ Fpmax. Therefore, as long as 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] Then, the following relationship exists between the first thrust force (Fi+Fo) acting on the first gear G1, the first preload Fm and 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 is met, the first gear G1 and the second gear G2 move outward from each other (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 This indicates.

[0050] Then, from the state where the first gear G1 has moved to point c shown in Figure 4, as the deceleration torque transmitted to the first gear G1 decreases, the first gear G1 moves inward (towards the second gear G2) from point c to point d along the straight line B in Figure 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 of the preloads acting on the first gear G1 and the second gear G2 (Ff+Fm). In other words, as long as 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) is greater than the kinetic friction force Fpmov acting on the press-fit portion 13a, i.e., 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 this relationship is met, the inward movement of the first gear G1 stops. This stopped state of the first gear G1 continues until the first thrust force (Fi+Fo) generated between the first gear G1 and the second gear G2 decreases to zero, that is, along the straight line C shown in Figure 4 from point d to point e.

[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 source, inward thrust forces Fi and Fo are generated in the first gear G1 and the second gear G2, respectively, as shown in Figure 5. 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 is sometimes referred to as the second thrust force. In addition, the first gear G1 and the second gear G2 receive inward preloads Fm and Ff from case 2, respectively.

[0053] Therefore, if we consider the direction of force acting to the right in Figure 5 as "+" and the direction of force acting to the left as "-", when acceleration torque is transmitted from a torque generating source such as an engine or motor to the first gear G1 and the second gear G2, and the axially movable first gear G1 remains stationary, the following relationship holds 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| …(6)

[0054] On the other hand, the relative order of the following equations: |Fi+Fo-(Ff+Fm)|>|Fpmax| …(7) When this condition is met, the first gear G1 moves inward (towards the second gear G2 (counter shaft 3)).

[0055] In other words, the first gear G1 moves inward along the line D from point e in Figure 4 and returns to its initial position (point a shown in Figure 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 fitted together by press-fitting at the press-fitting section 13a on the same axis to generate a predetermined friction force (static friction force Fp, maximum static friction force Fpmax, dynamic friction force Fpmov). When outward thrust forces Fi and Fo act on the first gear G1 and the second gear G2, respectively, the first gear G1 moves outward, causing the meshing region of the first gear G1 with the fourth gear G4 to fluctuate in the axial direction. Therefore, the first gear G1 and the fourth gear G4 do not always mesh at the same point, and the meshing point moves in the axial direction. In this embodiment, the case in which only the first gear G1 moves outward (away from the second gear G2) was described as an example, but a configuration in which both the first gear G1 and the second gear G2 can move in opposing directions may also be adopted.

[0057] Therefore, according to this embodiment, the effect is obtained that localized strength deficiency and wear caused by the meshing of the first gear G1 and the fourth gear G4 at specific points can be suppressed. Here, Figure 6 is a schematic diagram of the tooth surfaces of both gears showing the change in the meshing position of the first gear G1 and the fourth gear G4. When the first thrust force (outward thrust force) Fi, Fo acts 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 position of the solid line to the position of the dashed line, and the meshing region of the first gear G1 and the fourth gear G4 moves outward (to the left in Figure 6) by ε1. As a result, the meshing region of the first gear G1 and the fourth gear G4 fluctuates alternately in the axial direction, and the first gear G1 and the fourth gear G4 do not always mesh at the same point, and 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 gears are small, the first gear G1 and the second gear G2 do not move, thus preventing a decrease in responsiveness due to misalignment of the meshing during power transmission. In particular, the change in the meshing position at the start of power 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 amount of movement of these gears increases, and they receive high torque in a position where they are normally not meshed, thus suppressing localized strength reduction and wear of the tooth surfaces.

[0059] Furthermore, in this embodiment, the first gear G1 and the fourth gear G4 have the same hardness, and the number of teeth in the fourth gear G4 is less than that of the first gear G1. This reduces the replacement cost of the fourth gear G4, which wears out first due to its fewer teeth. Also, because the width of the fourth gear is set wider than that of the first gear G1, even if the first gear G1 moves axially, the meshing width between the first gear G1 and the fourth gear G4 can be secured, ensuring reliable power transmission between the first gear G1 and the fourth gear G4.

[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 axis 10 Boss section of the first gear (first shaft) 11 Washers 12 Sims 13. Fitting part 13a Press-fit section 13b Spline section 20 Retaining member 21. Clutch guide (other components) CL Clutch Ff Second pre-pressure Fi thrust force generated in the first gear (first and second thrust forces) Fm First pre-pressure 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, both composed of helical gears, are arranged coaxially and movable in at least opposite directions, and housed within a case. The first gear and the second gear are meshed with gears connected to a torque generating source, In a power transmission device in which the angles of the helical teeth of the first gear and the second gear are set such that when the torque from the torque source is transmitted between the first gear and the second gear, thrust forces are generated in directions relative to the first gear and the second gear, The first gear and the second gear are fitted together by press-fitting so that they are movable on the same axis by the thrust force and generate a predetermined maximum static friction force. When torque is transmitted from the torque source, if the absolute value of the sum of the thrust forces generated in the first gear and the second gear exceeds the absolute value of the maximum static friction force, the first gear and the second gear move in opposing directions, and the meshing region between the first gear or the second gear and the gear that meshes with it fluctuates in the axial direction. A power transmission device characterized by the following features.

2. The absolute value of the sum of the outward thrust forces generated in the first gear and the second gear is defined as the first thrust force. If the absolute value of the sum of the inward thrust forces generated in the first gear and the second gear is defined as the 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 move outward, The first gear and the second gear are configured to move inward when the second thrust force exceeds the absolute value of the maximum static friction force. The power transmission device according to feature 1.

3. The first thrust force is generated when deceleration torque is transmitted, and the second thrust force is generated when acceleration torque is transmitted. The power transmission device according to claim 2.

4. The first thrust force is generated when acceleration torque is transmitted, and the second thrust force is generated when deceleration torque is transmitted. The power transmission device according to claim 2.

5. When the magnitude of the deceleration torque or acceleration torque becomes 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 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. The first gear and the second gear are configured to move in opposite directions. The power transmission device according to claim 3 or 4, characterized by the feature described above.

6. If the absolute value of the sum of the inward preloads applied to the first gear and the second gear respectively through the press-fitting is defined as the third thrust force, The first gear and the second gear are configured to move outward when the first thrust force exceeds the sum of the absolute value of the maximum static friction force and the third thrust force. 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, The first gear and the second gear are configured to move inward on the same axis when the sum of the second thrust force and the third thrust force exceeds the absolute value of the maximum static friction force. The power transmission device according to claim 6.

8. A first shaft, at least partially hollow, is formed on the 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 by a press-fit portion formed by press-fitting the inner circumferential surface of the first shaft and the outer circumferential surface of the second shaft into each other. The aforementioned maximum static friction force is the maximum static friction force between the inner surface and the outer surface of the press-fit portion. The power transmission device according to feature 1.

9. The aforementioned power transmission device is a power transmission device mounted on a vehicle, The torque source is the power source or 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. The deceleration torque is the torque generated when the vehicle is decelerating, and the acceleration torque is the torque generated when the vehicle is accelerating. The power transmission device according to claim 3 or 4, characterized by the feature described above.

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

11. The aforementioned vehicle is a hybrid vehicle that includes a motor as its power source, The aforementioned deceleration torque is the torque generated during regeneration by the motor. The power transmission device according to feature 9.

12. The hardness of the first gear and the drive gear are the same, and the number of teeth of the first gear is greater than the number of teeth of the drive gear. The power transmission device according to feature 9.

13. The power transmission device according to claim 9, characterized in that the tooth width of the drive gear is wider than the tooth width of the first gear.

14. A helical groove is formed in the press-fit portion, and the direction of the helical groove's oscillation is set so that oil is discharged through the helical groove when the first gear moves. The power transmission device according to feature 8.

15. A retaining member is provided that contacts another member to suppress the tilting of the first gear when the first gear tilts. The power transmission device according to feature 1.

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