Patent Description:
A transmission having at least two sets each made of a drive gear and a driven gear which come into engagement with each other is known. In the technique disclosed in Patent Literature <NUM>, in each of a first shaft to which drive force of a drive source (for example, an engine) is transmitted and a second shaft parallel to the first shaft, at least two sets each made of a drive gear and a driven gear which come into engagement with each other are disposed. A hub arranged adjacent to the drive gear or the driven gear is coupled to the first shaft or the second shaft, and a clutch ring is disposed in the outer periphery of the hub. The drive gear or the driven gear is provided with first dog tooth in an end face in the axial direction. In the clutch ring, second dog tooth which engage with the first dog tooth are provided in the end face in the axial direction.

In a state where the second dog tooth in the clutch ring engage with the first dog tooth in a low-speed gear and torque is transmitted, when the second dog tooth in another clutch ring engage with the first dog tooth in a high-speed gear, thrust in the axial direction is generated in the clutch ring whose second dog tooth engage with the first dog tooth in the low-speed gear whose rotational speed is lower as compared with the high-speed gear. When the clutch ring is pushed toward the axial direction by the thrust, the first dog tooth in the low-speed gear and the second dog tooth in the clutch ring are disengaged, and a high-speed gear is achieved. In such a manner, running-out of torque at the time of shift can be solved.

Patent Literature <NUM>: <CIT>. Also Document <CIT> discloses the state of the art.

The above-described technique, however, has a problem. Since the rotational speed of the first dog tooth and that of the second dog tooth just before engagement of the first dog tooth and the second dog tooth are different, an impact (engagement sound and shock) occurs when the second dog tooth come into engagement with the first dog tooth.

The present invention has been made to solve the problem, and an object of the invention is to provide a power transmission device in which an impact can be reduced while solving running-out of torque at the time of shift.

To achieve the object, a power transmission device of the present invention includes: a friction clutch transmitting/interrupting power between a drive shaft coupled to a drive source and a first shaft; and a transmission to which power is applied by the first shaft. The transmission has: a second shaft disposed in parallel to the first shaft; a fixed gear disposed to one of the first shaft or the second shaft in a relatively unrotatable manner; an idle gear disposed to the other one of the first shaft or the second shaft in a relatively rotatable manner; at least two annular-shaped hubs coupled to the first shaft or the second shaft and arranged adjacent to the idle gear; and a clutch ring disposed to the outer periphery of each of the hubs so as to be able to move in the axial direction and so as not to be able to rotate with respect to the hub. An end face in the axial direction of the fixed gear or the idle gear is provided with a first dog tooth, and an end face in the axial direction of the clutch ring is provided with a second dog tooth which engages with the first dog tooth. At least one of the hub, the clutch ring, the fixed gear, and the idle gear has a thrust generation part which applies thrust in the axial direction to the clutch ring, when the second dog tooth comes into engagement with the first dog tooth, the thrust making another first dog tooth and another second dog tooth separate from each other. When the maximum torque (Nm) of the drive source is set as x and inertia moment (kgm<NUM>) of the friction clutch is set as y, y ≤ <NUM> × <NUM>-<NUM>x is satisfied.

According to a first mode, by the thrust generation part of the transmission, when the second dog tooth of the clutch ring engages with the first dog tooth, thrust in the axial direction which makes another first dog tooth and the second dog tooth of another clutch ring separate from each other is applied to the clutch ring, and a high-speed gear is accomplished. Therefore, running-out of torque at the time of the shift can be solved.

An impact when the second dog tooth engages with the first dog tooth increases as the difference between kinetic energy of a member which engages with the first dog tooth and kinetic energy of a member coupled to the second dog tooth immediately before engagement of the second dog tooth with the first dog tooth is larger. The kinetic energy of a rotating member is proportional to the inertia moment of the member. To the inertia moment of members including the friction clutch coupled to the second dog tooth, the contribution of the inertia moment of the friction clutch is large. The size and the torque capacity of the friction clutch are influenced by the maximum torque of the drive source, and exert an influence on the inertia moment of the friction clutch.

Consequently, by satisfying y ≤ <NUM> × <NUM>-<NUM>x (where x (kgm<NUM>) is the maximum torque of the drive source and y is the inertia moment (Nm) of the friction clutch), the difference between kinetic energy of a member including the friction clutch coupled to the second dog tooth and kinetic energy of a member coupled to the first dog tooth immediately before engagement of the second dog tooth with the first dog tooth is reduced, and kinetic energy released when the first dog tooth engages with the second dog tooth, that is, an impact can be reduced.

According to a second mode, the friction clutch in the first mode is a wet multiplate clutch. Consequently, by making the outside diameter of the clutch plate smaller while assuring the torque capacity, the inertia moment of the friction clutch can be reduced. Therefore, it is advantageous to reduce an impact.

According to a third mode, in the second mode, a first case houses the transmission, and a second case houses the friction clutch. The second case is separated from the first case. Therefore, oil appropriate to lubrication can be filled in the first and second cases.

According to a fourth mode, in the second mode, both of the friction clutch and the transmission are housed in a case. Therefore, the friction clutch and the gear can be lubricated with oil of one kind.

Hereinafter, preferred embodiments of the present invention will be described with reference to the appended drawings. First, a schematic configuration of a power transmission device <NUM> in an embodiment of the present invention will be described with reference to <FIG> is a skeleton diagram of the power transmission device <NUM>. The power transmission device <NUM> has a transmission <NUM> and a friction clutch <NUM>. The transmission <NUM> has a first shaft <NUM> to which power is input from a drive shaft <NUM>, and a second shaft <NUM> disposed in parallel to the first shaft <NUM>. The friction clutch <NUM> is disposed between the drive shaft <NUM> and the first shaft <NUM> to transmit/interrupt power between the drive shaft <NUM> and the first shaft <NUM>. In the embodiment, the power transmission device <NUM> is mounted in a vehicle (not illustrated).

The drive shaft <NUM> is coupled to a drive source S such as an engine. The first shaft <NUM> and the second shaft <NUM> support a first-speed gear <NUM>, a second-speed gear <NUM>, a third-speed gear <NUM>, a fourth-speed gear <NUM>, a fifth-speed gear <NUM>, and a sixth-speed gear <NUM> as a transmission gear of multiple speeds.

The first-speed gear <NUM> has a drive gear <NUM> fixed to the first shaft <NUM> in a relatively unrotatable manner and a driven gear <NUM> fixed to the second shaft <NUM> in a relatively rotatable manner while being engaged with the drive gear <NUM>. The second-speed gear <NUM> has a drive gear <NUM> fixed to the first shaft <NUM> in a relatively rotatable manner and a driven gear <NUM> fixed to the second shaft <NUM> in a relatively unrotatable manner while being engaged with the drive gear <NUM>. The third-speed gear <NUM> has a drive gear <NUM> fixed to the first shaft <NUM> in a relatively unrotatable manner and a driven gear <NUM> fixed to the second shaft <NUM> in a relatively rotatable manner while being engaged with the drive gear <NUM>. The fourth-speed gear <NUM> has a drive gear <NUM> fixed to the first shaft <NUM> in a relatively rotatable manner and a driven gear <NUM> fixed to the second shaft <NUM> in a relatively unrotatable manner while being engaged with the drive gear <NUM>. The fifth-speed gear <NUM> has a drive gear <NUM> fixed to the first shaft <NUM> in a relatively rotatable manner and a driven gear <NUM> fixed to the second shaft <NUM> in a relatively unrotatable manner while being engaged with the drive gear <NUM>. The sixth-speed gear <NUM> has a drive gear <NUM> fixed to the first shaft <NUM> in a relatively rotatable manner and a driven gear <NUM> fixed to the second shaft <NUM> in a relatively unrotatable manner while being engaged with the drive gear <NUM>.

The drive gears <NUM> and <NUM> and the driven gears <NUM>, <NUM>, <NUM>, and <NUM> are fixed gears which are fixed in the axial direction and disposed so as not to be rotatable relative to the axis. The drive gears <NUM>, <NUM>, <NUM>, and <NUM> and the driven gears <NUM> and <NUM> are idle gears which are fixed in the axial direction and disposed so as to be rotatable relative to the axis.

A dog clutch <NUM> selectively coupling the gears to the first shaft <NUM> and the second shaft <NUM> has a hub <NUM> which is coupled to the first shaft <NUM> and the second shaft <NUM>, a clutch ring <NUM> disposed to the hub <NUM>, and a shift device <NUM> setting the position in the axial direction of the clutch ring <NUM>.

The hub <NUM> is an annular-shaped member which is fixed in a relatively unrotatable manner to each of the second shaft <NUM> between the driven gears <NUM> and <NUM>, the first shaft <NUM> between the drive gears <NUM> and <NUM>, and the first shaft <NUM> between the drive gears <NUM> and <NUM>. In the end faces in the axial direction of the driven gears <NUM> and <NUM> and the drive gears <NUM>, <NUM>, <NUM>, and <NUM>, first dog tooth <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> projecting in the axial direction toward the hubs <NUM> are provided, respectively.

The clutch ring <NUM> is an annular-shaped member which is attached to the hub <NUM>. The clutch ring <NUM> is disposed unrotatably with respect to the hub <NUM> and movably in the axial direction. The clutch ring <NUM> is provided with second dog tooth <NUM> (refer to <FIG>) projecting in the axial direction. When the clutch ring <NUM> moves in the axial direction and the first dog tooth <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> and the second dog tooth <NUM> selectively engage, any of the first-speed gear <NUM>, the second-speed gear <NUM>, the third-speed gear <NUM>, the fourth-speed gear <NUM>, the fifth-speed gear <NUM>, and the sixth-speed gear <NUM> selectively couples to the first shaft <NUM> via the hub <NUM> and the clutch ring <NUM> to perform gear shift.

The shift device <NUM> has shift forks <NUM>, <NUM>, and <NUM> each of which is engaged with the clutch ring <NUM>, shift arms <NUM>, <NUM>, and <NUM> coupled to the shift forks <NUM>, <NUM>, and <NUM>, respectively, and a column-shaped shift drum <NUM>. The shift drum <NUM> is fixed to a first case <NUM> and rotates axially by a motor (not illustrated). End parts of the shift arms <NUM>, <NUM>, and <NUM> engage in cam grooves <NUM>, <NUM>, and <NUM>, respectively, which are formed in the periphery of the shift drum <NUM>.

The shift drum <NUM> rotates on the basis of an operation signal of a shift lever (not illustrated) or an accelerator position and a vehicle speed signal or the like according to the operation of an accelerator pedal (not illustrated). When the shift drum <NUM> rotates, the shift forks <NUM>, <NUM>, and <NUM> move in the axial direction via the shift arms <NUM>, <NUM>, and <NUM> guided by the cam grooves <NUM>, <NUM>, and <NUM>. By the shift forks <NUM>, <NUM>, and <NUM>, the clutch rings <NUM> move in the axial direction.

Referring to <FIG>, the clutch ring <NUM> will be described. <FIG> is a perspective view of the clutch ring <NUM>. As illustrated in <FIG>, the clutch ring <NUM> has a ring <NUM> extending in an annular shape around the center axis O as a center and the plurality of second dog tooth <NUM> projecting from an end face <NUM> in the axial direction of the ring <NUM> toward both sides in the axial direction. The center axes O of the clutch rings <NUM> disposed for the first shaft <NUM> and the second shaft <NUM> coincide with the center axes of the first shaft <NUM> and the second shaft <NUM>. Each of the second dog tooth <NUM> has a third tooth <NUM> and a fourth tooth <NUM> whose length in the axial direction is shorter than that of the third tooth <NUM>. Each of the second dog tooth <NUM> has a third plane <NUM> facing one side in the circumferential direction and a fourth plane <NUM>, as a plane on the side opposite to the third plane <NUM>, facing the other side in the circumferential direction.

In the second dog tooth <NUM>, the third tooth <NUM> and the fourth tooth <NUM> are disposed alternately in the circumferential direction. The third plane <NUM> is an inclined plane which is inclined with respect to a virtual plane <NUM> (refer to <FIG>) parallel to the center axis O. The fourth plane <NUM> is a plane parallel to the center axis O. In the inner peripheral face of the clutch ring <NUM>, the tooth <NUM> parallel to the center axis O are formed. In the embodiment, the tooth <NUM> are formed only on the inside of the third tooth <NUM>, and the tooth <NUM> extend along the entire length of each of the third tooth <NUM>.

In parts in which the third tooth <NUM> continue in the inner face of the ring <NUM> facing the side of the center axis O, the tooth <NUM> parallel to the center axis O are formed. The tooth <NUM> continue seamlessly in the ring <NUM> and the third tooth <NUM> projected from the end face <NUM> of the ring <NUM>. It prevents the tooth <NUM> from being easily broken.

In the embodiment, the tooth <NUM> are formed only in the second dog tooth <NUM>. The expression "the tooth <NUM> are formed only in the second dog tooth <NUM>" includes formation of the tooth continued to the tooth <NUM> in the second dog tooth <NUM> in the inner face of the ring <NUM>. However, it does not include formation of tooth which are not continued to the tooth <NUM> of the second dog tooth <NUM>, in the inner face of the ring <NUM>.

<FIG> is a perspective view of the hub <NUM> for which the clutch ring <NUM> is disposed. In the inner circumferential face of the hub <NUM>, a spline <NUM> which is coupled to the first shaft <NUM> or the second shaft <NUM> (refer to <FIG>) is formed. In parts in which the tooth <NUM> of the clutch ring <NUM> are disposed in the outer circumferential face of the hub <NUM>, grooves <NUM> parallel to the center axis O are formed. The grooves <NUM> are formed in the entire length in the axial direction of the hub <NUM>. Since the tooth <NUM> formed in the clutch ring <NUM> engage in the grooves <NUM> of the hub <NUM>, the clutch ring <NUM> can move in the axial direction with respect to the hub <NUM>, but the clutch ring <NUM> cannot rotate about the hub <NUM>.

When the tooth <NUM> engage in the grooves <NUM> in the hub <NUM>, the clutch ring <NUM> moves in the axial direction while transmitting torque. As a result, since force is applied to the tooth <NUM> parallel to the center axis O, even there is a gap in the radial direction between the tooth <NUM> and the grooves <NUM>, a part extending in the axial direction of the groove <NUM> comes into contact with a part extending in the axial direction of the tooth <NUM> and the moment of the clutch ring <NUM> is suppressed, so that inclination of the clutch ring <NUM> with respect to the center axis O of the hub <NUM> can be suppressed.

The shapes of the grooves <NUM> and the tooth <NUM> are not particularly limited. In a side view, for example, the grooves <NUM> and the tooth <NUM> are properly set to a shape surrounded by curves such as involute curves or rectangular shapes. Obviously, a ball or a rolling member which is rolling in the groove <NUM> can be provided for the tooth <NUM>, or the tooth <NUM> can be provided with a ball or a rolling member in the groove <NUM>. It can further reduce the friction between the tooth <NUM> and the grooves <NUM>.

The third plane <NUM> of the second dog tooth <NUM> is inclined so as to become closer to the fourth plane <NUM> with distance from the ring <NUM> in the axial direction. The inclination angle of the third plane <NUM> with respect to the virtual plane <NUM> parallel to the center axis O is set as θ. A radius Rd of a circle passing the center of gravity of the third plane <NUM> (the distance between the center axis O and the center of gravity of the third plane <NUM>) is larger than a radius Rh of a reference circle of the groove <NUM> (the distance between the center axis O and the reference circle of the groove <NUM>) only by the amount of the thickness in the radial direction of the second dog tooth <NUM>.

Referring to <FIG>, the friction clutch <NUM> will be described. <FIG> is a partial cross section of the friction clutch <NUM>. In the embodiment, the friction clutch <NUM> is a wet multiplate clutch. The friction clutch <NUM> is housed in a second case <NUM> filled with lubricating oil and adjusts the torque transmitted from the drive shaft <NUM> to the first shaft <NUM>. Since the second case <NUM> in which the friction clutch <NUM> is housed is separated from the first case <NUM> (refer to <FIG>) in which the transmission <NUM> is housed, oil appropriate for lubrication can be put in each of the first case <NUM> and the second case <NUM>. For example, gear oil is injected in the first case <NUM>, and the second case <NUM> is filled with clutch fluid.

The friction clutch <NUM> has a clutch drum <NUM> coupled to the drive shaft <NUM>, a clutch hub <NUM> coupled to the first shaft <NUM>, and a clutch plate <NUM> disposed between the clutch drum <NUM> and the clutch hub <NUM>. The clutch plate <NUM> is supported by the clutch drum <NUM> and the clutch hub <NUM> so as to be movable in the axial direction. A pressing member <NUM> adjusts force of fastening between the clutch drum <NUM> and the clutch hub <NUM> by the clutch plate <NUM>. The pressing member <NUM> is energized to the direction of interrupting the transmission of the torque by a spring <NUM> disposed between the clutch drum <NUM> and the clutch hub <NUM>. By the driving of an actuator <NUM>, the pressing member <NUM> moves in the axial direction of increasing the torque transmitted by the clutch plate <NUM>.

The actuator <NUM> has a motor <NUM> and a decelerator <NUM> decelerating the output of the motor <NUM>. The decelerator <NUM> is fixed to the second case <NUM>, and the motor <NUM> is fixed to the second case <NUM> via a bracket (not illustrated). The torque of the motor <NUM> is converted to force in the axial direction by a converting mechanism <NUM>.

The converting mechanism <NUM> is a ball cam capable of steplessly adjusting the fastening power of the clutch plate <NUM> with precision. The converting mechanism <NUM> has a first plate <NUM> on the drive side and a second plate <NUM> and a ball <NUM> on the reaction force side. The first plate <NUM> and the second plate <NUM> are supported rotatably by the outer periphery of the first shaft <NUM>. The movement in the axial direction with respect to the first shaft <NUM> of the second plate <NUM> is regulated, and the first plate <NUM> is disposed to the pressing member <NUM> via a thrust bearing. The tip of the first plate <NUM> engages with a gear <NUM> connected to the output shaft of the decelerator <NUM>. In cam faces where the first plate <NUM> and the second plate <NUM> face each other, a plurality of grooves having predetermined phase differences are formed on the same circle whose center is the rotation center of the cam faces, and the ball <NUM> is rotatably sandwiched by the cam faces. The ball <NUM> may be replaced by a roller.

In the case of fastening the friction clutch <NUM>, when the first plate <NUM> rotates with respect to the second plate <NUM> via the gear <NUM> of the decelerator <NUM>, the first plate <NUM> moves toward the pressing member <NUM> while being pressed by the ball <NUM>. When the pressing member <NUM> is pressed to the axial direction by the first plate <NUM>, the pressing member <NUM> presses the clutch plate <NUM>. On the other hand, in the case of cancelling the fastening of the friction clutch <NUM>, the gear <NUM> of the decelerator <NUM> rotates in the reverse direction, so that the first plate <NUM> moves to the direction away from the pressing member <NUM>, and the pressing member <NUM> weakens the power of pressing the clutch plate <NUM>.

The friction clutch <NUM> adjusts the engagement state of the clutch plate <NUM> at the time of gear shifting of the transmission <NUM> to adjust the rotation transmitted to the first shaft <NUM> by the drive shaft <NUM>. When the maximum torque (N·m) of the drive source S is x, and inertia moment (kg·m<NUM>) of the friction clutch <NUM> is y, the friction clutch <NUM> is set so as to satisfy y ≤ <NUM> × <NUM>-<NUM>x. The inertia moment of the friction clutch <NUM> is a total value of the inertia moments of the clutch drum <NUM>, the clutch hub <NUM>, the clutch plate <NUM>, the pressing member <NUM>, and the spring <NUM>.

With reference to <FIG>, the operation of the transmission <NUM> at the time of gear shifting (shifting up) to a higher-speed gear will be described. In the embodiment, as an example, gear shifting from the fourth-speed gear <NUM> to the fifth-speed gear <NUM> will be described. Since operations of gearshifting to the other gears are similar, an operation of shifting up to another gear and an operation of shifting down to another gear will not be described.

First, referring to <FIG> and <FIG>, the operation of the transmission <NUM> at the time of a low-speed gear (fourth-speed gear <NUM>) will be described. <FIG> is a schematic diagram of the transmission <NUM> at the time of coast travel in a low-speed gear (fourth-speed gear <NUM>), and <FIG> is a schematic diagram of the transmission <NUM> at the time of drive travel in a low-speed gear (fourth-speed gear <NUM>). In <FIG>, the rotation direction of the drive gears <NUM> and <NUM>, the hub <NUM>, and the clutch ring <NUM> is downward along the plane of paper (the direction of the arrow R).

As illustrated in <FIG>, in the drive gear <NUM>, the first dog tooth <NUM> which engage with the second dog tooth <NUM> of the clutch ring <NUM> are formed in the end face in the axial direction of the drive gear <NUM>. The first dog tooth <NUM> has a first tooth <NUM> and a second tooth <NUM> whose length in the axial direction is shorter than the length of the first tooth <NUM>. The first dog tooth <NUM> has a first plane <NUM> facing one side of the circumferential direction and a second plane <NUM> facing the other side of the circumferential direction as a plane on the side opposite to the first plane <NUM>. The first plane <NUM> is opposed to the third plane <NUM> of the clutch ring <NUM>. The second plane <NUM> is opposed to the fourth plane <NUM> of the clutch ring <NUM>.

Each of the first plane <NUM> and the third plane <NUM> is an inclined plane which generates thrust by which the drive gear <NUM> and the clutch ring <NUM> separate from each other in the axial direction in accordance with the torque in the direction of making the first plane <NUM> and the third plane <NUM> come into contact. The first plane <NUM> is inclined so as to come closer to the second plane <NUM> with distance from the drive gear <NUM>. The inclination angle θ of the first plane <NUM> with respect to the virtual plane <NUM> (refer to <FIG>) parallel to the center axis O is the same as the inclination angle θ of the third plane <NUM>.

The second plane <NUM> and the fourth plane <NUM> are planes in which the drive gear <NUM> and the clutch ring <NUM> do not separate in the axial direction at the time of transmitting the torque by making the second plane <NUM> and the fourth plane <NUM> come into contact with each other. In the embodiment, the second plane <NUM> is a plane parallel to the center axis O.

In the drive gear <NUM>, the first dog tooth <NUM> which engage with the second dog tooth <NUM> in the clutch ring <NUM> are formed in the end face in the axial direction of the drive gear <NUM>. The first dog tooth <NUM> has a first tooth <NUM> and a second tooth <NUM> whose length in the axial direction is shorter than the length of the first tooth <NUM>. The first dog tooth <NUM> has a first plane <NUM> facing one side of the circumferential direction and a second plane <NUM> facing the other side of the circumferential direction as a plane on the side opposite to the first plane <NUM>. The first plane <NUM> is opposed to the third plane <NUM> of the clutch ring <NUM>. The second plane <NUM> is opposed to the fourth plane <NUM> of the clutch ring <NUM>.

Each of the first plane <NUM> and the third plane <NUM> is an inclined plane (thrust generation part) which generates thrust by which the drive gear <NUM> and the clutch ring <NUM> separate from each other in the axial direction in accordance with the torque in the direction of making the first plane <NUM> and the third plane <NUM> come into contact. The first plane <NUM> is inclined so as to come closer to the second plane <NUM> with distance from the drive gear <NUM>. The inclination angle θ of the first plane <NUM> with respect to the virtual plane <NUM> (refer to <FIG>) parallel to the center axis O is the same as the inclination angle θ of the third plane <NUM>.

As illustrated in <FIG>, at the time of fourth-speed travel, the shift fork <NUM> becomes closer to the drive gear <NUM> of the fourth-speed gear <NUM> by the cam groove <NUM> in the shift drum <NUM> and the shift arm <NUM>, and the second dog tooth <NUM> in the clutch ring <NUM> engage with the first dog tooth <NUM> in the drive gear <NUM>. At this time, the tooth <NUM> in the clutch ring <NUM> engage with the grooves <NUM> in the hub <NUM>, and the clutch ring <NUM> moves in the axial direction. Since the tooth <NUM> are formed on the inside of the second dog tooth <NUM> (third tooth <NUM>), as compared with the case where the tooth <NUM> are formed only on the inside of the ring <NUM>, the length in the axial direction of the tooth <NUM> can be assured. As a result, when the clutch ring <NUM> moves in the axial direction, the clutch ring <NUM> can be prevented from easily inclined with respect to the hub <NUM>. On the other hand, in the fifth-speed gear <NUM>, the second dog tooth <NUM> in the clutch ring <NUM> and the first dog tooth <NUM> in the drive gear <NUM> are separated in the axial direction by the shift drum <NUM>.

At the time of coast travel in which the power is transmitted from the driven gear <NUM> of the fourth-speed gear <NUM> (refer to <FIG>) to the drive gear <NUM>, the drive gear <NUM> rotates faster than the clutch ring <NUM>, so that the first plane <NUM> of the drive gear <NUM> comes into contact with the third plane <NUM> of the clutch ring <NUM>. At this time, a gap in the circumferential direction is generated between the second plane <NUM> and the fourth plane <NUM>.

The first plane <NUM> and the third plane <NUM> generate thrust by which the drive gear <NUM> and the clutch ring <NUM> separate from each other in the axial direction in accordance with the torque at the time of coasting. However, a top part 99a (regulation part) of the cam groove <NUM> of the shift drum <NUM> regulates movement in the axial direction of the shift arm <NUM> and the shift fork <NUM>, so that engagement between the second dog tooth <NUM> of the clutch ring <NUM> and the first do tooth <NUM> of the drive gear <NUM> is maintained, and the state where the third plane <NUM> of the clutch ring <NUM> is in contact with the first plane <NUM> of the drive gear <NUM> is maintained.

As illustrated in <FIG>, at the time of drive travel in which the power is transmitted from the drive gear <NUM> is transmitted to the driven gear <NUM> (refer to <FIG>), the clutch ring <NUM> rotates faster than the drive gear <NUM>, so that the fourth plane <NUM> of the clutch ring <NUM> comes into contact with the second plane <NUM> of the drive gear <NUM>. At this time, a gap in the circumferential direction is generated between the first plane <NUM> and the third plane <NUM>.

At the time of transmitting the torque by making the second plane <NUM> and the fourth plane <NUM> come into contact with each other, the drive gear <NUM> and the clutch ring <NUM> do not separate in the axial direction, so that jump-out of the gear is prevented by regulation of the movement in the axial direction of the shift arm <NUM> and the shift fork <NUM> by the top part 99a of the cam groove <NUM> of the shift drum <NUM>, friction between the second plane <NUM> and the fourth plane <NUM>, and the like, and the drive torque is transmitted.

<FIG> is a schematic diagram of the transmission <NUM> during shift from a low-speed gear (fourth-speed gear <NUM>) to a high-speed gear (fifth-speed gear <NUM>), and <FIG> is a schematic diagram of the transmission <NUM> at the time of drive travel in a high-speed gear (fifth-speed gear <NUM>). The arrow S illustrated in <FIG> and <FIG> denotes the rotation direction at the time of shift-up of the shift drum <NUM>.

As illustrated in <FIG>, at the time of drive travel when the power is transmitted from the drive gear <NUM> to the driven gear <NUM> (refer to <FIG>), when the shift drum <NUM> is rotated while the engagement of the friction clutch <NUM> is kept and shift-up operation to a higher-speed gear (fifth-speed gear <NUM>) is performed, the shift fork <NUM> comes closer to the drive gear <NUM> of the fifth-speed gear <NUM> by the cam groove <NUM> of the shift drum <NUM> and the shift arm <NUM>, and the tip of the third tooth <NUM> in the clutch ring <NUM> comes into contact with the tip of the first tooth <NUM> in the drive gear <NUM>. Since the third tooth <NUM> in the clutch ring <NUM> is longer than the fourth tooth <NUM> in the axial direction, engagement between the third tooth <NUM> of the second dog tooth <NUM> and the first dog tooth (first tooth <NUM>) in the drive gear <NUM> can be made easier.

On the other hand, in the fourth-speed gear <NUM>, the top part 99a of the cam groove <NUM> releases the shift arm <NUM>. Consequently, a gap G by which the clutch ring <NUM> can be separated in the axial direction from the drive gear <NUM> is created between the shift arm <NUM> and the cam groove <NUM>. However, in the case where the power is transmitted from the drive gear <NUM> to the driven gear <NUM> (refer to <FIG>) by making the second plane <NUM> and the fourth plane <NUM> come into contact with each other in the fourth-speed gear <NUM>, the thrust which separates the drive gear <NUM> and the clutch ring <NUM> in the axial direction does not generated, so that the state where the second dog tooth <NUM> in the clutch ring <NUM> and the first dog tooth <NUM> in the drive gear <NUM> engage with each other is maintained.

When the first dog tooth <NUM> (first tooth <NUM>) of the drive gear <NUM> of the fifth-speed gear <NUM> engage with the second dog tooth <NUM> (third tooth <NUM>) of the clutch ring <NUM> in a state where the drive gear <NUM> of the fourth-speed gear <NUM> and the second dog tooth <NUM> of the clutch ring <NUM> engage with each other, since the fifth-speed gear <NUM> rotates faster than the fourth-speed gear <NUM>, the fourth-speed side becomes the coast state, and the fifth-speed side becomes the drive state by internal circulating torque.

The fifth-speed gear <NUM> is in the drive state where the second plane <NUM> and the fourth plane <NUM> are in contact, and the thrust which makes the drive gear <NUM> and the clutch ring <NUM> separate in the axial direction is not generated. Consequently, the shift fork <NUM> comes closer to the drive gear <NUM> by the cam groove <NUM> of the shift drum <NUM> and the shift arm <NUM>, and the engagement between the second dog tooth <NUM> of the clutch ring <NUM> and the first dog tooth <NUM> of the drive gear <NUM> becomes tighter.

Since the tooth <NUM> are formed only on the inside of the third tooth <NUM> in the clutch ring <NUM>, when the third tooth <NUM> come to engage with the first dog tooth <NUM>, torque is transmitted between the clutch ring <NUM> and the hub <NUM> via the first dog tooth <NUM>, the third tooth <NUM>, and the tooth <NUM>. Consequently, as compared with the case where the tooth <NUM> are not formed on the inside of the third tooth <NUM> and the tooth <NUM> are formed on the inside of the fourth tooth <NUM> and the ring <NUM>, breakage of the ring <NUM> starting from the corner formed by the third tooth <NUM> and the ring <NUM> due to application of the force in the rotation direction when the third tooth <NUM> and the first dog tooth <NUM> (first tooth <NUM>) come into engagement with each other can be suppressed.

In addition, as compared with the case where the tooth <NUM> are formed not only on the inside of the third tooth <NUM> but also on the inside of the fourth tooth <NUM> and the ring <NUM>, decrease in the sectional area of the clutch ring <NUM> due to the tooth <NUM> can be suppressed. Therefore, durability of the clutch ring <NUM> can be improved. Further, as compared with the case where the tooth <NUM> are formed not only on the inside of the third tooth <NUM> but also on the inside of the fourth tooth <NUM> and the ring <NUM>, the area of the tooth <NUM> which rub against the grooves <NUM> can be reduced, so that friction between the groove <NUM> and the tooth <NUM> can be prevented from increasing.

On the other hand, the fourth-speed gear <NUM> is in the coast state where the first plane <NUM> and the third plane <NUM> are in contact with each other. By the inclination angle θ of the first plane <NUM> and the third plane <NUM>, thrust by which the drive gear <NUM> and the clutch ring <NUM> separate in the axial direction is generated according to torque. The tooth <NUM> formed in the inner peripheral face of the clutch ring <NUM> engage in the grooves <NUM> formed in the outer peripheral face of the hub <NUM> and, by the thrust, the clutch ring <NUM> moves in the axial direction while transmitting torque only by the amount of the gap G of the cam grooves <NUM>.

As a result, the part extending in the axial direction of the groove <NUM> comes into contact with the part extending in the axial direction of the tooth <NUM>, so that the clutch ring <NUM> does not easily tilt with respect to the hub <NUM>, and the moment of the power of the clutch ring <NUM> can be suppressed. It can suppress friction of the tooth <NUM> which moves in the axial direction while rubbing against the groove <NUM>. As a result, sound and vibration generated when the drive gear <NUM> and the clutch ring <NUM> separate from each other in the axial direction can be suppressed.

It is now set that the inclination angle of the first plane <NUM> and the third plane <NUM> is θ, the radius of the circle passing the center of gravity of the third plane <NUM> is Rd, the radius of the reference circle of the groove <NUM> is Rh, coefficient of friction between the first plane <NUM> and the third plane <NUM> is µd, and coefficient of friction between the groove <NUM> and the tooth <NUM> is µh. The hub <NUM> and the clutch ring <NUM> are set so as to satisfy tan(θ-µd)/Rd-µh/Rh > <NUM>. By the setting, the drive gear <NUM> and the clutch ring <NUM> can be smoothly separated from each other in the axial direction by the internal circulating torque by the thrust in the axial direction according to the inclination angle θ of the first plane <NUM> and the third plane <NUM>. Therefore, a shock occurring at the time of gear shift can be suppressed.

As illustrated in <FIG>, when the gear shift to the fifth-speed gear <NUM> is completed by the shift drum <NUM>, in the fourth-speed gear <NUM>, the top part 99b of the cam groove <NUM> in the shift drum <NUM> regulates movement in the axial direction of the shift arm <NUM> and the shift fork <NUM>. By the regulation, the state where the clutch ring <NUM> and the drive gear <NUM> are separated is maintained. In the fifth-speed gear <NUM>, a top part 100a of the cam groove <NUM> in the shift drum <NUM> regulates the movement in the axial direction of the shift arm <NUM> and the shift fork <NUM>, so that engagement between the second dog tooth <NUM> of the clutch ring <NUM> and the first dog tooth <NUM> of the drive gear <NUM> is maintained.

At the time of drive travel when the power is transmitted from the drive gear <NUM> to the driven gear <NUM> (refer to <FIG>), the clutch ring <NUM> rotates faster than the drive gear <NUM>, so that the fourth plane <NUM> of the clutch ring <NUM> is in contact with the second plane <NUM> of the drive gear <NUM>. At this time, a gap in the circumferential direction is created between the first plane <NUM> and the third plane <NUM>.

Since the drive gear <NUM> and the clutch ring <NUM> are not apart from each other in the axial direction when torque is transmitted by making the second plane <NUM> and the fourth plane <NUM> come into contact with each other, gear jump-out is prevented by regulation of movement in the axial direction of the shift arm <NUM> and the shift fork <NUM> by the top part 100a of the cam groove <NUM> in the shift drum <NUM>, friction between the second plane <NUM> and the fourth plane <NUM>, and the like, and the drive torque is transmitted.

At the time of coast drive in which power is transmitted from the driven gear <NUM> (refer to <FIG>) to the drive gear <NUM>, the drive gear <NUM> rotates faster than the clutch ring <NUM>, so that the first plane <NUM> of the drive gear <NUM> comes into contact with the third plane <NUM> of the clutch ring <NUM>. At this time, a gap in the circumferential direction is created between the second plane <NUM> and the fourth plane <NUM>.

The first plane <NUM> and the third plane <NUM> generate thrust to separate the drive gear <NUM> and the clutch ring <NUM> from each other in the axial direction in accordance with the torque at the time of coasting. However, the top part 100a (regulation part) of the cam groove <NUM> in the shift drum <NUM> regulates the movement in the axial direction of the shift arm <NUM> and the shift fork <NUM>, so that engagement between the second dog tooth <NUM> in the clutch ring <NUM> and the first dog tooth <NUM> in the drive gear <NUM> is maintained, and the state where the third plane <NUM> of the clutch ring <NUM> is in contact with the first plane <NUM> of the drive gear <NUM> is maintained.

As described above, in the transmission <NUM>, when the second dog tooth <NUM> of the clutch ring <NUM> engage with the first dog tooth <NUM> and <NUM> in the two transmission gears (the fourth-speed gear <NUM> and the fifth-speed gear <NUM>) of different transmission gear ratios at the time of gear shift from a low-speed gear to a high-speed gear, by internal circulating torque, the clutch ring <NUM> coupled to the low-speed transmission gear (fourth-speed gear <NUM>) having the lower rotational speed as compared with the high-speed transmission gear (fifth-speed gear <NUM>) is pushed in the axial direction by the thrust generated between the first plane <NUM> and the third plane <NUM>. When the high-speed transmission gear (fifth-speed gear <NUM>) and the clutch ring <NUM> are coupled, the low-speed transmission gear (fourth-speed gear <NUM>) and the clutch ring <NUM> are separated and the high-speed gear is accomplished, so that running-out of torque at the time of gear shift can be prevented.

The present invention will be described more specifically by an example. However, the present invention is not limited to the example.

An examiner made five prototypes in which inertia moments of the friction clutch <NUM> are different by making the size of the friction clutchs110 different, of the power transmission device <NUM> in the embodiment. The conditions of the prototypes are the same except for the inertia moments of the friction clutch <NUM>. To the drive shafts <NUM> of the prototypes, crank shafts of five kinds of engines (drive sources S) of different maximum torques are coupled.

The examiner made a test of starting each of the engines in a state where the friction clutches <NUM> are disengaged, engaging the friction clutches <NUM>, setting the transmission <NUM> to the third speed, after that, setting each of the engines to the rotational speed at which the maximum torque is generated, and shifting up to the fourth speed while the friction clutches <NUM> are kept engaged. The examiner made sensory evaluation on an impact (engagement sound and shock) when the second dog tooth <NUM> of the clutch ring <NUM> come into engagement with the first dog tooth <NUM> of the drive gear <NUM>.

<FIG> is a diagram illustrating the relation between the maximum torque of the drive source S, the inertia moment of the friction clutch <NUM>, and an impact. Each of open squares in <FIG> indicates a combination by which an impact giving an uncomfortable feeling to the examiner is generated (a combination between the maximum torque of the drive source S and the inertia moment of the friction clutch <NUM>). Each of closed circles in <FIG> indicates a combination by which an impact not giving an uncomfortable feeling to the examiner is generated.

The equation of the straight line illustrated in <FIG> is y = <NUM> × <NUM>-<NUM>x where x is the maximum torque (Nm) of the drive source S (engine) and y is the inertia moment (kgm<NUM>) of the friction clutch <NUM>. It was made clear by the examination that when y ≤ <NUM> × <NUM>-<NUM>x is satisfied, the impact at the time of gear shift can be reduced.

The friction clutch <NUM> when y ≤ <NUM> × <NUM>-<NUM>x is satisfied is a wet multiplate clutch. Since a wet multiplate clutch can assure torque capacity even when the outside diameter of the clutch plate <NUM> is small, the inertia moment can be reduced while assuring the torque capacity. Therefore, it is advantageous to reduce an impact at the time of gear shift.

Although the present invention has been described above on the basis of the embodiment, it can be easily assumed that the invention is not limited to the embodiment and various improvements and modifications are possible without departing from the gist of the present invention. For example, the number and disposition of gears of the transmission <NUM>, the shapes of the cam grooves <NUM> and <NUM> formed in the shift drum <NUM>, the number and shape of the grooves <NUM> formed in the hub <NUM>, the number and the shape of the tooth <NUM> formed in the clutch ring <NUM>, and the like can be properly set.

In the embodiment, the case where the second plane <NUM> of the first dog tooth <NUM> provided for the drive gear <NUM>, the second plane <NUM> of the first dog tooth <NUM> provided for the drive gear <NUM>, and the fourth plane <NUM> of the second dog tooth <NUM> provided for the clutch ring <NUM> are planes parallel to the center axis O has been described. However, the present invention is not limited to the case. When the second planes <NUM> and <NUM> and the fourth plane <NUM> are in contact to transmit torque, it is sufficient that the resultant force of the component in the axial direction of the force by the torque and the component in the axial direction in the friction force between the second planes <NUM> and <NUM> and the fourth plane <NUM> does not act in the direction of separating the clutch ring <NUM> from the drive gears <NUM> and <NUM>. As long as the relation is satisfied, the second planes <NUM> and <NUM> and the fourth plane <NUM> may be inclined with respect to the virtual plane (not illustrated) parallel to the center axis O.

In the embodiment, the case of the thrust generating part of generating thrust which separates the drive gear <NUM> and the clutch ring <NUM> in the axial direction in accordance with the torque, by the first plane <NUM> of the first dog tooth <NUM> provided for the drive gear <NUM> and the third plane <NUM> of the second dog tooth <NUM> provided for the clutch ring <NUM> has been described. However, the present invention is not limited to the case. For example, like the transmission described in <CIT>, obviously, it is possible to set the inclination angle of each of the first plane <NUM> and the third plane <NUM> to almost zero, provide a column-shaped projection for the clutch ring <NUM> in place of the tooth <NUM> provided for the clutch ring <NUM>, form a cam groove in a V shape which is inclined with respect to the plane including the center axis O in the peripheral face of the hub <NUM> in place of the parallel groove <NUM> provided for the hub <NUM>, and dispose the projection of the clutch ring <NUM> in the cam groove. Also in the case of using the cam groove in the hub <NUM> and the projection of the clutch ring <NUM> as the thrust generating part, function effects similar to those of the embodiment can be realized.

Although the case of mounting the power transmission device <NUM> in a car has been described in the embodiment, the present invention is not limited to the case. Obviously, the power transmission device <NUM> can be mounted in a construction machine, an industrial vehicle, an agricultural machine, and the like. In this case as well, an impact (sound) at the time of gear shift can be reduced while preventing running-out of torque at the time of gear shift by the power transmission device <NUM>. Therefore, idling of the first shaft <NUM> is prevented and the fuel consumption can be also improved.

Claim 1:
A power transmission device (<NUM>) comprising:
a friction clutch (<NUM>) transmitting/interrupting power between a drive shaft (<NUM>) coupled to a drive source (S) and a first shaft (<NUM>); and
a transmission (<NUM>) to which power is applied by the first shaft (<NUM>),
wherein the transmission (<NUM>) has:
a second shaft (<NUM>) disposed in parallel to the first shaft (<NUM>);
a fixed gear (<NUM>) disposed to one of the first shaft (<NUM>) or the second shaft (<NUM>) in a relatively unrotatable manner;
an idle gear (<NUM>) disposed to the other one of the first shaft (<NUM>) or the second shaft (<NUM>) in a relatively rotatable manner;
at least two annular-shaped hubs (<NUM>) coupled to the first shaft (<NUM>) or the second shaft (<NUM>) and arranged adjacent to the idle gear (<NUM>); and
a clutch ring (<NUM>) disposed to the outer periphery of each of the hubs (<NUM>) so as to be able to move in the axial direction and so as not to be able to rotate with respect to the hub (<NUM>),
an end face in the axial direction of the fixed gear (<NUM>) or the idle gear (<NUM>) is provided with a first dog tooth (<NUM>),
an end face in the axial direction of the clutch ring (<NUM>) is provided with the second dog tooth (<NUM>) which engages with the first dog tooth (<NUM>),
at least one of the hub (<NUM>), the clutch ring (<NUM>), the fixed gear (<NUM>), and the idle gear (<NUM>) has a thrust generation part which applies thrust in the axial direction to the clutch ring (<NUM>), when the second dog tooth (<NUM>) comes into engagement with the first dog tooth (<NUM>), the thrust making another first dog tooth (<NUM>) and another second dog tooth (<NUM>) separate from each other, and
when the maximum torque (Nm) of the drive source (S) is set as x and inertia moment (kgm<NUM>) of the friction clutch (<NUM>) is set as y, y ≤ <NUM> × <NUM>-<NUM>x is satisfied.