JP2963174B2 - Power transmission device for four-wheel drive vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] <Industrial Application Field> The present invention relates to a power transmission device for a four-wheel drive vehicle configured to be able to drive a front wheel and a rear wheel with a common engine. About.

<Prior Art> As one type of four-wheel drive vehicle, one of the front and rear axles is directly connected to the engine, and the other axle (main drive shaft) is used.
From Japanese Patent Application Laid-Open No. H11-163, there is known a device in which a driving torque is transmitted to the other axle (slave drive shaft) via a relative circuit speed-responsive viscous fluid break. Such a viscous fluid stamp has a characteristic that a transmission torque changes according to a rotation speed difference between the main and slave drive shafts, and when the rotation speed difference between the main and slave drive shafts exceeds a certain limit. The main and slave drive shafts are substantially directly connected.
Therefore, in view of this point, it is necessary to set the withstand torque strength of both the main and slave drive shafts equally. On the other hand,
When the rotational speed difference between the slave drive shafts is extremely small, the torque transmitted to the slave drive shaft is substantially equal to zero, and the burden on the slave drive shaft in this state is extremely small. In view of such circumstances, a technique is proposed in which the upper limit of the transmission torque to the slave drive shaft is specified, whereby the substantial load on the slave drive shaft side member is reduced, and the weight of the entire drive system is reduced. Has been proposed in JP-A-63-49526.

<Problems to be Solved by the Invention> By the way, continuous running in a state where the effective effective diameters of the front and rear wheels are different from each other by mounting a spare tire or mounting a non-slip when traveling on a snowy road. May be forced to In such a state, a rotational speed difference always occurs between the front and rear wheels, and even in a traveling state where it is not necessary to transmit torque between the main and slave drive shafts, the slave drive shaft is also used. Unnecessarily large torque will be transmitted. In other words, in normal running, torque transmission between the main and slave drive shafts only needs to consider the transient state, whereas when the tire diameter is different as described above, Thus, torque is transmitted.

In general, it is known that as a mechanical property of a metal material, even if the stress is equal to or lower than the breaking stress, if this acts repeatedly, so-called metal fatigue occurs, and the stress lower than the breaking stress leads to destruction. Particularly, in a high-speed running state, the number of repetitions of the stress applied per unit time increases, so that fatigue is more likely to progress, and it is considered that the critical stress is substantially reduced. Therefore, in order to be able to withstand continuous running in a state where the effective diameters of the main and slave drive wheels are different from each other, the safety factor must be set higher by that amount. As described above, there is an inconvenience that reduction in weight cannot be achieved in practice by merely specifying the upper limit of the transmission torque to the slave drive shaft.

The present invention has been devised to eliminate such inconveniences, and its main purpose is to induce metal fatigue in consideration of running in a state where the diameters of the main and slave drive wheels are different from each other. It is an object of the present invention to provide a power transmission device for a four-wheel drive vehicle improved so that a continuous load torque as described above does not act on the driven member.

[Constitution of the Invention] <Means for Solving the Problems> According to the present invention, such a purpose is achieved by a first member that rotates interlockingly with a front wheel, a second member that rotates interlockingly with a rear wheel, and the first member. A power transmission device for a four-wheel drive vehicle, comprising: a torque transmission device interposed between a member and the second member, the torque transmission device changing a transmission torque according to a rotation speed difference between the front wheel and the rear wheel. Power transmission for a four-wheel drive vehicle, comprising: transmission torque limiting means for defining an upper limit of the transmission torque of the torque transmission device; and means for reducing the transmission torque of the torque transmission device as the vehicle speed increases. This is achieved by providing a device.

<Operation> According to such a configuration, the upper limit of the transmission torque between the main and slave drive shafts is set to an appropriate predetermined value, and the transmission torque capacity decreases as the traveling speed increases. Therefore, particularly at the time of starting acceleration (at low speed) where the main drive wheel is likely to slip, the torque is sufficiently transmitted from the main drive wheel to the slave drive wheel, and at the time of high-speed running where the possibility of the main drive wheel slipping is low. Substantial transmission torque is reduced. Accordingly, the transmission of the driving torque to the sub-drive shaft side member in the continuous traveling in a state where the diameters of the front wheel and the rear wheel are different from each other (particularly, the diameter of the main drive wheel is smaller) can be reduced. The setting of the strength margin of the side member can be reduced.

<Embodiment> Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a skeleton diagram showing a power transmission system of a four-wheel drive vehicle to which a power transmission device according to the present invention is applied.
The output of the engine 1 is input to the front-wheel-side differential 3 via the transmission 2. The output of the differential 3 is transmitted to the left and right front wheels 5 via the drive shaft 4.

The output of the engine 1 input to the differential device 3 is input to a power transmission device 7 described later via a bevel gear device 6, and the output of the power transmission device 7 is output to a rear wheel side via a bevel gear device 8. It is transmitted to the differential device 9. The output of the differential device 9 is transmitted to each of the left and right rear wheels 11 via the drive shaft 10.

The power transmission device 7 includes a first hydraulic pump 21 that is driven in conjunction with an output shaft of the front wheel bevel gear device 6 and a second hydraulic pump that is driven in conjunction with an input shaft of the rear wheel bevel gear device 8. twenty two
The output shaft of the front wheel bevel gear device 6 and the rear wheel bevel gear device 8
And a first hydraulic pump 21 and a second hydraulic pump 21.
A fluid pressure control circuit (to be described in detail later) for controlling the flow of oil related to the clutch 22 and the clutch 23 is provided.

Here, the gear ratios of the front and rear bevel gear devices 6 and 8 are set to different values, and the relationship between the rotational speed of the hydraulic pump and the rotational speed of the wheels is as follows.

This means that the increase rate of the pump rotation speed with respect to the wheel rotation speed is larger in the second hydraulic pump 22 than in the front and rear wheels 5, as shown in FIG.
If the rotation speeds of 11 are the same, the rotation speed of the second hydraulic pump 22 is higher, and the difference between the rotation speeds of the two hydraulic pumps 21 and 22 is directly proportional to the wheel rotation speed. Means to increase.

The first fluid pressure pump 21 includes a gear pump or a vane pump. The first port 24 serves as a discharge port when the vehicle moves forward and serves as a suction port when the vehicle moves backward. The second port serves as a suction port when moving forward and serves as a discharge port when moving backward.
25 and has. The second hydraulic pump 22 is also constituted by a gear pump or a vane pump, and has a third port 26 serving as a suction port when the vehicle moves forward and serving as a discharge port when moving backward, and a fourth port 27 serving as a discharge port when moving forward and serving as a suction port when moving backward. And The first port 24 and the third port 26 are connected to each other through a first connection oil passage 28, and the second port 25 and the fourth port 27 are connected to the second connection oil passage 29. Are connected through a connection.

Here, the first and second hydraulic pumps 21 and 22 have different chamber capacities from each other, and the discharge amount per rotation of the first hydraulic pump 21 is equal to the discharge amount per rotation of the second hydraulic pump 22. Is set to be smaller than the discharge amount.
This is because if the speed ratio between the front and rear axles 4 and 10 and the pump shaft is the same, and the effective diameter of the front and rear wheels 5 and 11 is the same, the rate of change of the discharge amount according to the wheel rotation speed is , Second hydraulic pump
22 is larger, which means that the difference between the discharge rates of the two hydraulic pumps 21 and 22 increases in direct proportion to the wheel rotation speed (FIG. 3).

The first connection oil passage 28 and the second connection oil passage 29 are connected to the operation hydraulic chamber 30 of the fluid pressure operation clutch 23 via a switching valve 31. The switching valve 31 is mainly composed of a spool valve that switches depending on whether the transmission 2 is in the forward gear or the reverse gear, and is divided into two valve chambers 32 and 33, and a first valve. When the differential pressure between the first valve chamber 32 and the second chamber 33 reaches a predetermined value, the one-way valve 34 that regulates the flow from the chamber 32 toward the second valve chamber 33 becomes a predetermined value. It has a relief valve 35 that communicates with the second valve chamber 33 and allows a flow from the first valve chamber 32 to the second valve chamber 33. By the operation of the switching valve 31,
At the time of forward movement, as shown in FIG.
29 and the oil tank 36 communicate with each other via the second valve chamber 33, and between the first connecting oil passage 28 and the clutch operating hydraulic chamber 30 is a bypass oil passage 37a and a first valve chamber 32. Hydraulic supply oil passage 37
When the pressure acting on the hydraulic pressure chamber 30 of the clutch exceeds a predetermined value, the pressure is released to the oil tank 36 via the relief valve 35. At the time of retreat, as shown in FIG. 2, the communication between the first connection oil passage 28 and the oil tank 36 is communicated via the second valve chamber 33, and the operation of the second connection oil passage 29 and the clutch is performed. The hydraulic chamber 30 communicates with the hydraulic chamber 30 via a first valve chamber 32, and when the pressure acting on the hydraulic chamber 30 for operating the clutch exceeds a predetermined value, the pressure is released to the tank 36 via the relief valve 35. Has become.

Further, an oil supply passage 37b for supplying hydraulic oil for connecting between the first valve chamber 32 and the hydraulic operating chamber 30 of the clutch communicates with the oil level of the tank 36 via a branch passage having an orifice 38.

Next, the operation of the above embodiment will be described in order according to each state.

During forward start acceleration, the front wheels 5
Only one may rotate in a slip condition. At this time, only the first fluid pressure pump 21 rotates together with the front wheel 5, so that the oil tank 36 is connected to the second valve chamber 33 and the second connecting oil passage 29.
The oil sucked into the second port 25 through the first port 24 is supplied to the bypass oil passage 37a discharged from the first port 24 to the first connection oil passage 28.
Into the first valve chamber 32 and the operating hydraulic supply oil passage 37b.
The hydraulic pressure is applied to the operating hydraulic chamber 30 of the clutch via the control unit.
Thereby, the clutch 23 is engaged, and the front wheel 5 and the rear wheel 11 are connected.

Here, the transmission torque of the clutch is directly proportional to the oil pressure on the upstream side of the orifice determined by the flow rate of the orifice 38, and this oil pressure changes in proportion to the square of the difference between the discharge amounts (suction amounts) of the two hydraulic pumps 21 and 22. I do. Further, the upper limit value of the transmission torque of the clutch 23 can be appropriately set by setting the opening pressure of the relief valve 35 (FIG. 4).

When the clutch 23 is engaged and the driving torque is distributed to the rear wheels, the oil discharged from the first hydraulic pump 21 is sucked into the second hydraulic pump 22 according to the increase in the rotation speed of the rear wheels 11. Become like The engagement force of the clutch 23 according to the difference between the discharge amount of the first hydraulic pump 21 and the suction amount of the second hydraulic pump 22,
That is, the transmission torque to the rear wheel automatically changes,
When the discharge amounts (suction amounts) of the second fluid pressure pumps 21 and 22 are balanced with each other, the discharge pressure to the working hydraulic supply oil passage 37b is not generated, and the engagement of the clutch 23 is released.

Here, a first fluid pressure pump 21 that is driven by the front wheel 5 that is directly driven by the engine 1 and a second fluid that is driven by the rear wheel 11 that is driven by the power transmission device 7 is transmitted. The balance point of the discharge amount (suction amount) with the pressure pump 22 is determined because the operating characteristics of the two fluid pressure pumps 21 and 22 are set in the relationship shown in FIG. Appears at a time higher than the rear wheel 11. The difference between the rotational speeds of the front and rear wheels 5 and 11 at this balance point increases as the vehicle speed increases. These characteristics are the front and rear wheels 5
11 indicates that the magnitude of the clutch transmission torque for the same rotational speed difference decreases as the vehicle speed increases. This means that the transmission torque capacity of the clutch 23, that is, the operation limiting force, decreases as the vehicle speed increases (FIG. 4).

At the time of forward slow acceleration, slow deceleration and constant speed traveling,
If the front wheel 5 and the rear wheel 11 have the same diameter, both wheels rotate at substantially the same rotational element speed. If the front and rear wheels 5 and 11 have the same rotational speed, the discharge amount of the first hydraulic pump 21 is always lower than the suction amount of the second hydraulic pump 22, and the discharge amount of the second hydraulic pump 22 is lower. This will always exceed the suction amount of the first fluid pressure pump 21. Then, the oil discharged from the first port 24 is exclusively sucked into the third port 26, and a part of the oil discharged from the fourth port 27 is partially discharged from the second connecting oil passage 29, the second valve chamber 33, the one-way valve 34,
The fluid returns to the third port 26 via the first valve chamber 32, the bypass oil passage 37a, and the first connection oil passage 28. As a result, the pipe internal pressure does not reach the operating pressure of the clutch 23 in the first connecting oil passage 28, and no driving force is transmitted to the rear wheel 11.

When only the front wheels 5 step on a road surface having a low coefficient of friction during traveling at a constant speed, or when the vehicle is suddenly accelerated, the front wheels 5 may transiently slip. In such a state, the discharge amount from the first port 24
If the rotation speed of the front wheels 5 exceeds that of the rear wheels 11 so as to exceed the suction amount into the second hydraulic pump 22, the second hydraulic pump 22 will not be able to fully suck the oil discharged from the first hydraulic pump 21. The hydraulic pressure corresponding to the difference between the discharge amount (suction amount) of 21 and 22 is the first
It occurs in the connection oil passage 28. This oil pressure is supplied to the bypass oil passage 37a.
The first valve chamber 32 is guided to the working hydraulic chamber 30 of the clutch via the working hydraulic supply oil passage 37b. As a result, the clutch 23 is engaged, and the drive torque is distributed to the rear wheels 11. When the driving torque is distributed to the rear wheels by engaging the clutch 23, the engaging force of the clutch 23 according to the rotational speed difference between the front and rear wheels, that is, the torque transmitted to the rear wheels, as described above. Automatically changes, but in this case, the magnitude of the transmission torque with respect to the rotational speed difference decreases as the vehicle speed increases.

When a braking force is applied to the wheels, the distribution of the braking force between the front and rear wheels is generally set higher on the front wheel side, so that the front wheel 5 locks earlier than the rear wheel 11 during sudden braking or the like. Also,
Since the engine brake from the constant speed operation only acts on the front wheels 5, the rotational speed of the front wheels 5 also transiently changes in this case.
Lower than 11. When the rotation speed of the front wheel 5 becomes lower than that of the rear wheel 11, the discharge amount of the first hydraulic pump 21 becomes the second speed.
Since the amount of suction is less than the suction amount of the fluid pressure pump 22, no discharge pressure is generated to the hydraulic pressure supply oil passage 37b, and the clutch 23 is not engaged. Therefore, the connection between the front and rear wheels is disconnected. At this time, part of the oil discharged from the fourth port 27 is supplied to the second connecting oil passage 29, the second valve chamber 33, the one-way valve 34, the first valve chamber 32, and the bypass oil passage 37a.
-Reflux to the third port 26 via the first connecting oil passage 28.

When the front wheel 5 is completely locked, the first hydraulic pump 21 stops and only the second hydraulic pump 22 rotates. Then, the oil discharged from the fourth port 27 to the second connecting oil passage 29 is supplied to the second valve chamber.
33, one-way valve 34, first valve chamber 32, bypass oil passage 37a, first
The whole amount recirculates to the third port 26 via the connecting oil passage 28. Therefore, also in this case, the clutch 23 is not engaged, and the connection between the front and rear wheels is disconnected.

At the time of retreat, the rotation directions of the first and second fluid pressure pumps 21 and 22 are both reversed, and the relationship between the discharge port and the suction port is opposite to that described above. It is done in the same way as when.

During the backward start acceleration, only the first hydraulic pump 21 temporarily rotates. Then, as shown in FIG. 2, the oil tank 36 transfers the second valve chamber 33, the bypass oil passage 37a, and the first connection oil passage 2 to each other.
The oil sucked into the first port 24 via 8 is discharged from the second port 25 to the second connecting oil passage 29, and is transferred to the clutch operating hydraulic chamber 30 via the first valve chamber 32 and the operating hydraulic supply oil passage 37b. Apply hydraulic pressure. As a result, the clutch 23 is connected and the rear wheel
The drive torque is distributed to 11.

As in the case of the forward movement, a part of the oil discharged from the first hydraulic pump 21 is absorbed by the second hydraulic pump 22 in accordance with the increase in the rotation speed on the rear wheel side. The hydraulic pressure acting on the working hydraulic chamber 30 of the clutch changes according to the difference in the discharge amount (suction amount) of the pressure pumps 21 and 22, and the torque distribution ratio to the rear wheels changes, and the discharge of the two hydraulic pressure pumps 21 and 22 Amount (inhalation amount)
Are in a mutually balanced state, the hydraulic pressure does not act on the working hydraulic chamber 30 of the clutch, and the connection between the front and rear wheels is disconnected.

At the time of reverse slow acceleration, slow deceleration and constant speed traveling,
Similarly to the forward movement, the discharge amount of the first hydraulic pump 21 is always lower than the suction amount of the second hydraulic pump 22, and the discharge amount of the second hydraulic pump 22 is lower than the suction amount of the first hydraulic pump 21. Will always exceed. Then, the oil discharged from the second port 25 is sucked into the fourth port 27, and a part of the oil discharged from the third port 26 is supplied to the first connecting oil passage 28, the bypass oil passage 37a, and the second valve chamber 3.
3. Reflux to the fourth port 27 via the one-way valve 34, the first valve chamber 32, and the second connecting oil passage 29. As a result, the internal pressure of the second connecting oil passage 29 does not reach the operating pressure of the clutch 23, and no driving force is transmitted to the rear wheel 11.

The front wheel 5 enters a slip state due to a sudden acceleration or the like from the backward constant speed traveling, and the rotational speed of the front wheel 5 increases as the discharge amount of the first hydraulic pump 21 exceeds the suction amount of the second hydraulic pump 22. Above that, the oil discharged from the first hydraulic pump 21 cannot be completely sucked by the second hydraulic pump 22, so that the hydraulic pressure corresponding to the difference between the discharge amounts (suction amounts) of the two pumps 21 and 22 becomes the second oil.
It occurs in the connecting oil passage 29. This hydraulic pressure is guided to the working hydraulic chamber 30 of the clutch via the first valve chamber 32 and the working hydraulic supply oil passage 37b. As a result, the clutch 23 is engaged, and the drive torque is distributed to the rear wheels 11.

At the time of reverse braking, since the rotation speed of the first hydraulic pump 21 is lower than that of the second hydraulic pump 22, no discharge pressure to the working hydraulic supply oil passage 37b is generated, and the clutch 23 is not engaged. Therefore, the connection between the front and rear wheels is disconnected. At this time, part of the discharge oil of the second hydraulic pump 22 from the third port 26 is supplied to the first connection oil passage 28, the bypass oil passage 37a, the second valve chamber 33,
The fluid returns to the fourth port 27 via the one-way valve 34, the first valve chamber 32, and the second connecting oil passage 29. When the front wheel 5 is completely locked, the oil discharged from the third port 26 is supplied to the first connecting oil passage 28, the bypass oil passage 37a, the second valve chamber 33, the one-way valve 34, the first valve chamber 32.
-The whole amount is recirculated to the fourth port 27 via the second connecting oil passage 29. Therefore, also in this case, the clutch 23 is not engaged, and the connection between the front and rear wheels is disconnected.

Next, the operation when the effective diameters of the front and rear wheels are different from each other will be described.

Assuming that the effective diameter of the front wheels 5 driven directly by the engine 1 is smaller than the effective diameter of the rear wheels 11 driven via the power transmission device 7, in this case, both the front and rear wheels 5
-Even if 11 reaches a constant speed running state in which neither slip nor lock occurs, the front wheel rotation speed will always exceed the rear wheel rotation speed. Here, since the effective diameter difference between the front and rear wheels 5 and 11 is a constant, the rotation speed difference between the two wheels 5 and 11 increases in direct proportion to the traveling speed. Then, the first and second fluid pressure pumps 21 and 22
The engagement force of the clutch 23 increases in accordance with the difference in the discharge amount (suction amount) of the clutch, but the difference in the discharge amount (suction amount) increases, and the hydraulic pressure acting on the operating hydraulic chamber 30 of the clutch decreases to a predetermined value. If it exceeds, the relief valve 35 opens, and excessive torque transmission to the rear wheel 11 is suppressed.

By the way, as described above, the front and rear bevel gear devices 6
8 are set to different values, the discharge capacity of the first hydraulic pump 21 is set smaller than that of the second hydraulic pump 22, and the discharge capacity decreases as the differential limiting force increases. Therefore, even if the rotational speed difference due to the effective diameter difference between the two wheels 5 and 11 increases, unnecessary increase in transmission torque does not occur.

From these facts, the rotational speed difference caused by the difference between the effective diameters of the front and rear wheels is within a range in which the discharge amount of the first hydraulic pump 21 during traveling at a constant speed does not exceed that of the second hydraulic pump 22. It can be said that unnecessary torque transmission to the rear wheels can be avoided.

Further, when the effective diameter of the rear wheel 11, which is the driven wheel, is smaller, the rotation speed of the rear wheel 11 becomes higher, which is regarded as substantially equivalent to the state where the front wheel 5 is braked. Since the connection between the front and rear wheels 5 and 11 is disconnected and torque transmission is not performed, there is no possibility that actual harm may occur due to a difference in effective diameter between the front and rear wheels.

As described above, in the configuration of the present invention, the first
The actual discharge capacity of the second hydraulic pumps 21 and 22 is smaller in the first hydraulic pump 21 driven in conjunction with the front wheel 5. Therefore, if the front and rear wheels 5 and 11 have the same diameter, the hydraulic pressure (transmitted torque) acting on the differential hydraulic chamber 30 of the clutch disappears before the rotational speeds of the front and rear wheels 5 and 11 become equal. . This corresponds to the setting of the differential limiting force between the front and rear wheels being somewhat lower, but in practice, as shown in FIG. The difference in rotational speed between the rear wheels decreases as the vehicle speed decreases.Therefore, at low vehicle speeds where there is often a need to transmit drive torque to the rear wheels, such as when starting, the difference in rotational speed between the front and rear wheels And sufficient drive torque is transmitted to the rear wheels.

As means for reducing the transmission torque of the clutch 23 in accordance with an increase in the vehicle speed, the first and second fluid pressure pumps 21 and 22 may have different chamber volumes from each other.
Alternatively, whether the speed ratio between the fluid pressure pump and the wheel is different between the front and the rear may be implemented independently, or both may be combined as in the present embodiment.

FIGS. 5 and 6 show a modified embodiment of the present invention. The same reference numerals are given to parts common to the embodiment shown in FIGS. 1 and 2, and only different parts are shown. This will be described below.

In the above embodiment, the working hydraulic chamber 30 and the oil tank
In this embodiment, the hydraulic fluid supply passage 37b is communicated with a passage branched from the clutch hydraulic pressure supply passage 37b. However, in this embodiment, an additional orifice 38 having an orifice 38 between the hydraulic hydraulic chamber 30 and the oil tank 36 is provided. Communication path 47 is provided. According to this, when the pressure oil is supplied from the clutch hydraulic pressure supply passage 37b to the hydraulic pressure chamber 30, the air in the hydraulic pressure chamber 30 can be quickly discharged, so that the operational responsiveness of the clutch 23 is further improved. be able to.

Also in the case of the present embodiment, the characteristics of the clutch operating oil pressure are determined by the relief flow rate through the orifice 38, and the operating procedure of the clutch 23 is the same as in the first embodiment.

[Effects of the Invention] As described above, according to the present invention, even when the vehicle travels in a state where the effective diameters of the front and rear wheels are different from each other, unnecessary torque transmission to the driven wheels is not required. It is possible to substantially reduce the fatigue resistance of each member constituting the path for transmitting the driving torque to the wheels. Therefore, a great effect can be achieved in promoting weight reduction of the driven wheel side member.
In addition, at low speeds where there is a lot of opportunity to transmit the driving torque, such as during start-up acceleration, a sufficient driving torque is transmitted according to the rotational speed difference between the front and rear wheels, so that the practical performance as a four-wheel drive vehicle is not impaired.

[Brief description of the drawings]

FIG. 1 is a skeleton diagram showing an overall configuration of a power transmission system of a four-wheel drive vehicle according to the present invention, and FIG. 2 is a hydraulic circuit diagram in a retreated state. FIG. 3 and FIG. 4 are graphs showing characteristics of the device of the present invention. FIG. 5 is a skeleton diagram similar to FIG. 1 showing a modified embodiment of the present invention, and FIG. 6 is a hydraulic circuit diagram showing the modified embodiment corresponding to the state of FIG. 1 ... engine, 2 ... transmission, 3 ... differential device, 4 ...
... drive shaft, 5 ... front wheel, 6 ... bevel gear device,
7 ... power transmission device, 8 ... bevel gear device, 9 ... differential device, 10 ... drive shaft, 11 ... rear wheel, 21 ... first
Fluid pressure pump, 22 second fluid pressure pump, 23 fluid pressure operated clutch (torque transmitting device), 24 first port,
25 second port, 26 third port, 27 fourth port, 28 first connecting oil passage, 29 second connecting oil passage, 30
Operating hydraulic chamber, 31 switching valve, 32 first valve chamber, 33 second valve chamber, 34 one-way valve, 35 relief valve (transmission torque limiting means), 36 oil tank , 37a …… Bypass oil passage, 37b …… Hydraulic oil supply oil passage, 38 …… Orifice, 4
7 …… Communication passage

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B60K 17/34-17/348

Claims (1)

(57) [Claims] A first member that rotates in conjunction with a front wheel, a second member that rotates in conjunction with a rear wheel, and the front wheel and the rear wheel interposed between the first member and the second member. A torque transmission device that changes a transmission torque according to a rotation speed difference between the torque transmission device and a transmission torque limiting unit that defines an upper limit of a transmission torque of the torque transmission device; Means for reducing the transmission torque of the transmission device as the vehicle speed increases. 4. A power transmission device for a four-wheel drive vehicle.