JPH11348587A - Hydraulic four-wheel drive vehicle - Google Patents

Abstract

(57) [Problem] To reduce the size of an input clutch and simplify control. Further, energy loss is reduced by eliminating the need for an auxiliary hydraulic pump or an electromagnetic switching valve for the output clutch. SOLUTION: An input clutch 22 is frictionally engaged by an electromagnetic force of an electromagnet 22m to rotationally drive a four-wheel drive hydraulic pump 24 to switch from two-wheel drive to four-wheel drive. The engagement state is self-maintained by the discharge hydraulic pressure of the hydraulic pump 24, and when the difference between the rotational speeds of the front and rear wheels becomes small in the four-wheel drive state and the discharge hydraulic pressure becomes low, it is automatically released and switched to two-wheel drive. Output clutch 3
0 indicates that when the four-wheel drive hydraulic pump 24 is rotationally driven during four-wheel drive, frictional engagement is automatically performed by the discharge hydraulic pressure, and the four-wheel drive hydraulic pump is switched when four-wheel drive is switched to two-wheel drive. When the discharge hydraulic pressure of the pump 24 is lowered, it is automatically released, so that a special hydraulic circuit and control for the output clutch 30 are not required.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of a hydraulic four-wheel drive vehicle.

[0002]

2. Description of the Related Art (a) A traveling drive source for rotating one of the front and rear wheels, (b) a four-wheel drive hydraulic pump connected to the traveling drive source and driven for rotation, and (c) (D) a hydraulic motor driven to rotate by the discharge hydraulic pressure of the four-wheel drive hydraulic pump to rotate the other of the front and rear wheels, and (d) a power transmission path between the four-wheel drive hydraulic pump and the travel drive source. There has been proposed a hydraulic four-wheel drive vehicle having an input clutch arranged. The device described in Japanese Patent Application Laid-Open No. 4-92727 is an example of such a device, in which an electromagnetic clutch is used as an input clutch. Japanese Utility Model Laid-Open No. 7-8042 discloses a hydraulic motor that is driven by a hydraulic motor in order to prevent energy loss from being caused to rotate when two wheels are driven by rotation of the wheel (the other of the front and rear wheels). A hydraulic four-wheel drive vehicle is provided that has a hydraulic output clutch in the power transmission path between the two wheels and supplies hydraulic pressure from an auxiliary hydraulic pump to connect the hydraulic motor and wheels only during four-wheel drive. Are listed.

[0003]

However, in the former case (the device described in Japanese Patent Application Laid-Open No. 4-92727), it is necessary to generate a necessary transmission torque by electromagnetic force, so that the input clutch becomes large. was there.
Further, in the case where a predetermined rotation difference occurs between the front and rear wheels, that is, in a standby type four-wheel drive vehicle that automatically switches to four-wheel drive when one of the wheels directly driven by the driving source for slippage slips. It is necessary to detect the slip state and perform ON / OFF control of the electromagnetic clutch at an appropriate timing.

On the other hand, in the latter case (the device described in Japanese Utility Model Laid-Open No. 7-8042), an auxiliary hydraulic pump is provided separately from the four-wheel drive hydraulic pump to engage the hydraulic clutch, and the hydraulic switching valve controls the hydraulic pressure. Supply and stop are switched, which requires a complicated hydraulic circuit and switching control. In addition, since the auxiliary hydraulic pump is constantly driven, a sufficient energy loss reduction effect cannot always be obtained. Was.

The present invention has been made in view of the above circumstances, and a first object of the present invention is to reduce the size of an input clutch and to simplify the control thereof. An object is to reduce energy loss by eliminating the need for an auxiliary hydraulic pump or an electromagnetic switching valve for an output clutch.

[0006]

In order to achieve the above object, the first invention comprises: (a) a driving source for driving one of the front and rear wheels to rotate; and (b) a driving source connected to the driving source. (C) a hydraulic motor that is rotationally driven by the discharge hydraulic pressure of the four-wheel drive hydraulic pump to rotate the other of the front and rear wheels, and (d) the four-wheel drive. A hydraulic four-wheel drive vehicle having an input clutch disposed on a power transmission path between the hydraulic pump for driving and the driving source for traveling, (e) the input clutch comprises: A hydraulic clutch for transmitting power by being frictionally engaged by the discharge hydraulic pressure of the pump. (F) When switching from two-wheel drive to four-wheel drive, the four-wheel drive hydraulic pump is rotated to drive the input clutch. By the discharge hydraulic pressure of the four-wheel drive hydraulic pump. And having a trigger means for engaged.

According to a second invention, in the hydraulic four-wheel drive vehicle according to the first invention, (a) the input clutch is a hydraulic clutch with an electromagnet which can be frictionally engaged by electromagnetic force in addition to hydraulic pressure;
(b) The trigger means rotates the four-wheel drive hydraulic pump by exciting the electromagnet and frictionally engaging the input clutch.

The third invention comprises (a) a traveling drive source for rotating one of the front and rear wheels, (b) a four-wheel drive hydraulic pump connected to the traveling drive source and driven to rotate, c) Part 4
(D) a hydraulic motor, which is rotationally driven by the discharge hydraulic pressure of the wheel drive hydraulic pump and rotationally drives the other of the front and rear wheels, and (d) is disposed in a power transmission path between the four-wheel drive hydraulic pump and the traveling drive source. (E) disposed in a power transmission path between the hydraulic motor and the other of the front and rear wheels to discharge the four-wheel drive hydraulic pump. It has a hydraulic output clutch that transmits power by being frictionally engaged by hydraulic pressure.

[0009]

In the hydraulic four-wheel drive vehicle according to the first aspect of the present invention, since a hydraulic clutch is used as an input clutch, a large pressing force can be easily obtained as compared with an electromagnetic clutch, and a small size can be obtained. In addition, an inexpensive clutch can be employed. The hydraulic clutch is frictionally engaged by the discharge hydraulic pressure of the four-wheel drive hydraulic pump. When switching from two-wheel drive to four-wheel drive, the four-wheel drive hydraulic pump is rotated by the trigger means. As a result, frictional engagement is performed by the discharge hydraulic pressure and the engaged state is self-maintained, so that a dedicated hydraulic pump is not required. Further, when the peripheral speed difference between the front and rear wheels is reduced in the four-wheel drive state, in other words, when the slip state is substantially eliminated or when the vehicle shifts from turning to straight running, the load on the four-wheel drive hydraulic pump is reduced. However, the input clutch (hydraulic clutch) can be automatically released in accordance with the decrease in the discharge hydraulic pressure. It is not necessary to control the switching from the drive to the two-wheel drive.

In the second invention, a hydraulic clutch with an electromagnet is used as the input clutch, and the four-wheel drive hydraulic pump is rotated by being frictionally engaged by the electromagnet. Is automatically held, the switching from the two-wheel drive to the four-wheel drive can be automatically performed by monitoring the slip state of the front and rear wheels. Since the electromagnet is used as trigger means, its electromagnetic force may be small, and a small and inexpensive electromagnet can be employed.

In the third invention, a hydraulic output clutch is provided in a power transmission path between the hydraulic motor and the other of the front and rear wheels, and the output clutch is a discharge hydraulic pressure of the four-wheel drive hydraulic pump. 4
At the time of two-wheel drive in which the wheel drive hydraulic pump is not driven to rotate, the output clutch is released, and energy loss due to the rotation (rotating) of the hydraulic motor is avoided. Also, 4
When the four-wheel drive hydraulic pump is rotationally driven during wheel drive,
The output clutch is automatically frictionally engaged by the discharge hydraulic pressure, and the output clutch is automatically released as the discharge hydraulic pressure of the four-wheel drive hydraulic pump decreases when switching from four-wheel drive to two-wheel drive. Therefore, a special hydraulic circuit and control for the output clutch are not required, and energy loss is reduced because a dedicated auxiliary hydraulic pump that is constantly driven to rotate is not required.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The hydraulic four-wheel drive vehicle according to the present invention can be used, for example, in a two-wheel drive mode in which only one of the wheels driven directly by a drive source for driving travels, and the front and rear wheels slip or turn. When there is a difference in peripheral speed, the other wheel is automatically driven to rotate to four-wheel drive, while the difference in peripheral speed between the front and rear wheels is reduced and the slip condition is almost eliminated, or when the vehicle is traveling substantially straight. It is preferably applied to a standby type hydraulic four-wheel drive vehicle that performs two-wheel drive when it enters the state, but other types such as those that can be switched between two-wheel drive and four-wheel drive by a driver's switch operation It can also be applied to a hydraulic four-wheel drive vehicle. Note that the peripheral speed difference between the front and rear wheels is equivalent to the rotational speed difference if the outer diameters of the front and rear wheels are the same, and is substantially zero during non-slip or straight running.

In a standby type hydraulic four-wheel drive vehicle, for example, a four-wheel drive hydraulic pump is driven to rotate at a rotational speed corresponding to the rotational speed of one of the front and rear wheels, and the front and rear wheels are driven in the event of a slip or the like. The input clutch and the output clutch are engaged in response to the difference in peripheral speed between the input clutch and the output clutch. Desirably, the clutch is automatically released. Even when the peripheral speed difference between the front and rear wheels is substantially zero, the engagement state of the input clutch and the output clutch is maintained by the discharge hydraulic pressure of the four-wheel drive hydraulic pump, and the other wheel is driven by a predetermined torque. It is also possible to rotate four wheels as needed, in order to ensure running stability even when the peripheral speed difference between the front and rear wheels is small, such as during non-slip or straight running. It can be switched to driving.

In order to secure the starting performance on a predetermined low μ road uphill road and the running stability during turning, the other driving force of the front and rear wheels may be relatively small, so that an excessive torque is required. By adopting an input clutch that has a torque capacity that causes a slip when transmitted, not only the input clutch but also the four-wheel drive hydraulic pump, hydraulic motor, and output clutch can be small, light and inexpensive. Can be adopted.

In the first invention and the second invention, the output clutch of the third invention is not necessarily required, but the first invention and the second invention
It is desirable to provide a hydraulic output clutch by applying the third invention to the invention. It is also possible to provide a one-way clutch or an electromagnetic clutch instead of the output clutch of the third invention.

The input clutch is disposed, for example, between one of the wheels driven directly by the driving source for traveling and the four-wheel drive hydraulic pump, and has a rotational speed corresponding to the rotational speed of one of the wheels. It is desirable that the wheel drive hydraulic pump be configured to rotate. Specifically, it is desirable to dispose it between an input member of a differential device (such as a ring gear of a bevel gear type differential device) that distributes driving force to one of the left and right wheels and a four-wheel drive hydraulic pump. The driving source for traveling is gasoline engine, diesel engine, electric motor, etc.
Various drive sources can be employed.

As the hydraulic clutch used as the input clutch of the first invention, a dry single-plate or multi-plate clutch is preferably used, but a wet clutch can also be used. The same applies to the hydraulic output clutch of the third invention.

The trigger means includes an electromagnet of a hydraulic clutch with an electromagnet used as an input clutch as in the second invention, and also enables, for example, a four-wheel drive hydraulic pump to be rotationally driven by an electric motor. And 2
When switching from the wheel drive to the four-wheel drive, the four-wheel drive hydraulic pump may be rotationally driven by the electric motor, and the input clutch may be frictionally engaged by the discharge hydraulic pressure. In addition, such a trigger means may be provided at least until a predetermined period of time at which the engagement state of the input clutch is self-held by the discharge hydraulic pressure of the four-wheel drive hydraulic pump, or when the discharge hydraulic pressure reaches a predetermined value. The four-wheel drive hydraulic pump is configured to be rotationally driven until the trigger release condition is satisfied. However, during the four-wheel drive, the operating state may be continued such as maintaining the electromagnet in the excited state. good.
Note that the driver mechanically frictionally engages the input clutch by manual operation, stepping operation, or the like, or operates the electromagnet or the electric motor by a switch operation to achieve 4
Trigger means for rotating and driving the wheel drive hydraulic pump may be employed.

The hydraulic four-wheel drive vehicle according to the first and second aspects of the present invention monitors the peripheral speed difference between the front and rear wheels and, when the peripheral speed difference exceeds a predetermined value, triggers the four-wheel drive hydraulic pump. It is desirable to have a switching control means for automatically switching from two-wheel drive to four-wheel drive by rotationally driving the motor. The switching control means is configured to forcibly release the input clutch by switching a hydraulic circuit, for example, when the slip state of one wheel is substantially eliminated, and to switch from four-wheel drive to two-wheel drive. Can also.

In the third invention, the hydraulic clutch and the trigger means of the first invention and the second invention are not necessarily required.
The first invention and the second invention can be applied to the invention. Various clutches such as a meshing clutch and an electromagnetic clutch can be adopted as the input clutch. Two-wheel drive and four-wheel drive by engaging and disengaging the input clutch by a driver's switching operation or switch operation. And can be switched.

For example, when there is no differential device for the left and right wheels, a pair of output clutches is provided between the hydraulic pump and the left and right wheels. During two-wheel drive with the output clutch released, the left and right wheels can rotate freely, thereby avoiding the tight corner braking phenomenon.
When a differential device that distributes power to the left and right wheels is provided and the left and right wheels are driven to rotate from the hydraulic pump via the differential device, a single output clutch is provided between the differential device and the hydraulic pump. It may be provided, or a pair of output clutches may be provided between the differential and the left and right wheels. When a pair of hydraulic pumps are provided so as to rotate the left and right wheels, respectively, an output clutch may be provided between the pair of hydraulic pumps and the wheels. The output clutch is frictionally engaged prior to the rotation of the hydraulic motor or as the rotation of the hydraulic motor rises due to the rotational resistance of the hydraulic motor and the flow resistance of the hydraulic oil, and the torque of the hydraulic motor is applied to the wheels. To communicate.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a drive system of a hydraulic four-wheel drive vehicle 10 according to one embodiment of the present invention. The drive system includes an engine 12 as a driving source, an automatic transmission 14 and a bevel gear type differential 16. The driving force is transmitted to the left and right front wheels 18 via the vehicle, and the front wheels 18 are always driven as drive wheels. Further, a distribution gear 20 is meshed with a ring gear 16a which is an input member of the differential device 16, and a four-wheel drive hydraulic pump 24 is rotationally driven via an input clutch 22. The right and left rear wheels 32 are rotationally driven via a pair of output clutches 30 by rotating a hydraulic motor 28 connected via an oil passage 26 shown by the discharge hydraulic pressure of the four-wheel drive hydraulic pump 24. You. The front wheel 18 corresponds to one of the front and rear wheels, and the rear wheel 32 corresponds to the other of the front and rear wheels. Further, the outer diameters of the front wheel 18 and the rear wheel 32 are equal, and the peripheral speed difference corresponds to the rotational speed difference.

The input clutch 22 is a dry single-plate or multi-plate hydraulic clutch that is frictionally engaged by the discharge hydraulic pressure of the four-wheel drive hydraulic pump 24. The input clutch 22 has an electromagnet 22m as trigger means. Even the electromagnetic force of 22 m can be frictionally engaged. Therefore, when switching from two-wheel drive to four-wheel drive, the electromagnet 2
When 2 m is temporarily excited and the input clutch 22 is frictionally engaged, the four-wheel drive hydraulic pump 24 is rotationally driven, and the input clutch 22 is frictionally engaged by the discharge hydraulic pressure. Even if the excitation of the electromagnet 22m is released, the engaged state of the input clutch 22 is maintained by itself.
When the load on the four-wheel drive hydraulic pump 24 decreases and the discharge hydraulic pressure decreases, the input clutch 22 is automatically released, the rotation of the four-wheel drive hydraulic pump 24 stops, and the four-wheel drive Switch to two-wheel drive.

Similarly to the input clutch 22, the output clutch 30 is a dry single-plate or multi-plate hydraulic clutch which is frictionally engaged by the discharge hydraulic pressure of the four-wheel drive hydraulic pump 24. Prior to the rotation of the hydraulic motor 28 due to the flow resistance of the hydraulic oil and the like,
Alternatively, the clutch is frictionally engaged with the rotation of the hydraulic motor 28 and transmits the torque of the hydraulic motor 28 to the rear wheel 32.
The required flow rate per rotation of the hydraulic motor 28 is substantially the same as the discharge flow rate of the four-wheel drive hydraulic pump 24 per one rotation of the front wheel 18, so that the four-wheel drive hydraulic pump 24 discharges during four-wheel drive. The hydraulic pressure increases as the difference between the rotational speeds of the front and rear wheels (= front wheel rotational speed−rear wheel rotational speed) ΔN increases, and decreases as the rotational speed difference ΔN decreases. When ΔN ≒ 0, the flow resistance of the oil passage 26 increases. The hydraulic pressure becomes relatively small due to such factors.

As shown in FIG. 2, a relay 3 is connected to an electromagnet 22m of the input clutch 22 from a vehicle-mounted battery 34.
An excitation current is supplied via the reference numeral 6. The relay 36 supplies an exciting current to the electromagnet 22m for a predetermined period of time when a trigger signal is supplied from an ABS (antilock brake system) ECU 38. The ABS ECU 38 includes a CPU, RA
M, a microcomputer having a ROM, etc.
By performing signal processing according to a program stored in advance in M, the rotational speed difference ΔN between the front and rear wheels is detected based on the wheel speeds supplied from the wheel speed sensors 40 to 46, and the rotational speed difference ΔN is determined in advance. Predetermined value, for example, 5 km /
When the value exceeds h, a trigger signal is output to the relay 36. That is, the hydraulic four-wheel drive vehicle 10 of this embodiment
In the two-wheel drive state in which only the front wheels 18 are driven, the rear wheels 32 are automatically driven to rotate when the rotational speed difference ΔN between the front and rear wheels exceeds a predetermined value, for example, when a slip occurs on a low μ road uphill or when turning. This is a standby four-wheel drive vehicle that switches to four-wheel drive. When the rotational speed difference ΔN (peripheral speed difference) between the front and rear wheels exceeds a predetermined value, the ABS ECU 38 automatically drives the four-wheel drive hydraulic pump 24 to rotate from the two-wheel drive to the four-wheel drive by trigger means. It functions as switching control means for switching. Note that the rotational speed difference ΔN is determined, for example, by subtracting the average rotational speed of the left and right rear wheels from the average rotational speed of the left and right front wheels.

Next, an operation at the time of starting on a low μ road uphill road will be described with reference to FIGS. In step S1 of FIG. 3, the ABS EC determines whether the front wheel 18 is slipping.
It is determined by U38 whether or not the rotational speed difference ΔN between the front and rear wheels has exceeded a predetermined value.
Perform 2 or less. In step S2, the ECU for ABS
A trigger signal is output from 38 to a relay 36, and an exciting current is supplied from the battery 34 to the electromagnet 22m for a predetermined time. The input clutch 22 is driven by the electromagnetic force of the electromagnet 22m.
Are frictionally engaged, and the four-wheel drive hydraulic pump 24 is rotationally driven as shown in step S3. Time t _{1 in} FIG.
Is the time at which the determination in step S1 was YES and the trigger signal was output.

When the four-wheel drive hydraulic pump 24 is driven to rotate, the discharge hydraulic pressure increases as shown in step S4, and when the engagement hydraulic pressure Pc of the input clutch 22 is exceeded, the electromagnet 22
Even if the excitation of m is released, the engaged state is maintained by itself. The energizing time of the exciting current of the relay 36 (t _{2 in} FIG. 4)
At −t ₁ ), a predetermined time is set in advance so that the excitation of the electromagnet 22m is released after the discharge oil pressure exceeds the engagement oil pressure Pc. The output clutch 30 is also frictionally engaged with the discharge hydraulic pressure similarly to the input clutch 22.

In step S5, the hydraulic motor 28 is driven to rotate by the discharge hydraulic pressure of the four-wheel drive hydraulic pump 24, and the driving force is transmitted to the left and right rear wheels 32 via the output clutch 30. The driving torque of the front wheels 18 decreases. Then, with the decrease in the front wheel driving torque, the traction (driving force) of the front wheel 18 is restored as shown in step S6, and the front wheel 18 and the rear wheel 32 enter a four-wheel drive state. When the rotational speed of the rear wheel 32 increases as shown in step S7 and the rotational speed difference ΔN between the front and rear wheels decreases as shown in step S8, the load on the hydraulic motor 28 and further on the four-wheel drive hydraulic pump 24 decreases. I do. When the load is reduced, discharge pressure of the hydraulic pump 24 is reduced for 4-wheel drive as shown in step S10, the engagement pressure when the Pc is lower than the (time t ₃ in FIG. 4) the input clutch 22 is a return spring such as It is released according to the biasing force of. As a result, the rotation of the four-wheel drive hydraulic pump 24 is stopped, the power transmission to the rear wheel 32 is cut off, and the front wheel 18 is brought into a two-wheel drive state. The output clutch 30 is also released according to the urging force of the return spring or the like as the discharge hydraulic pressure decreases.

Here, the description has been given of the case where the vehicle is started on an uphill road having a low μ road. However, even when the vehicle is turning at a high speed, if the rotational speed difference ΔN between the front and rear wheels exceeds a predetermined value, the vehicle is driven in a four-wheel drive state, and excellent running is achieved. Stability is obtained. Hydraulic four-wheel drive vehicle 10 of the present embodiment
Is a standby type four-wheel drive vehicle mainly intended to ensure starting performance on a low μ road uphill road and running stability performance when turning, and the driving force of the rear wheel 32 during four-wheel drive is relatively small. An input clutch 22 having a torque capacity that will cause a slip when excessive torque is transmitted is employed.

Here, the hydraulic four-wheel drive vehicle 10 of this embodiment
Since a hydraulic clutch is used as the input clutch 22, a large pressing force can be easily obtained as compared with the electromagnetic clutch, and a small and inexpensive clutch can be adopted. The input clutch 22 is connected to the electromagnet 22.
When the trigger signal is output from the ABS ECU 38 and the excitation current is supplied from the relay 36, the electromagnetic force of the electromagnet 22m causes frictional engagement, and the four-wheel drive hydraulic pump 24 is rotationally driven. As a result, the two-wheel drive is automatically switched to the four-wheel drive, and the engagement state is self-maintained by the discharge hydraulic pressure of the four-wheel drive hydraulic pump 24, so that a dedicated hydraulic pump is not required. When the rotational speed difference ΔN between the front and rear wheels is reduced in the wheel drive state and the load on the four-wheel drive hydraulic pump 24 is reduced to lower the discharge hydraulic pressure, the input clutch 22 is automatically released to switch to two-wheel drive. Therefore, the switching control from the four-wheel drive to the two-wheel drive at the time of opening, that is, the two-wheel drive is unnecessary. The above electromagnet 22m
Is used as a trigger means, its electromagnetic force may be small, and a small and inexpensive electromagnet 22m can be employed.

A hydraulic output clutch 30 is disposed in a power transmission path between the hydraulic motor 28 and the rear wheel 32, and the output clutch 30 is connected to the discharge pump of the four-wheel drive hydraulic pump 24. Since the clutch is frictionally engaged by the hydraulic pressure, the output clutch 30 is released at the time of two-wheel drive in which the four-wheel drive hydraulic pump 24 is not rotationally driven, and energy loss due to rotation (rotating) of the hydraulic motor 28 is avoided. . Furthermore, a four-wheel drive hydraulic pump 2
When the 4 is driven to rotate, the output clutch 30 is automatically frictionally engaged by the discharge hydraulic pressure, and when the discharge hydraulic pressure of the four-wheel drive hydraulic pump 24 decreases at the time of switching from four-wheel drive to two-wheel drive, Since the output clutch 30 is automatically released, a special hydraulic circuit and control for the output clutch 30 are not required, and a dedicated auxiliary hydraulic pump that is constantly driven to rotate is not required, so that energy loss is prevented. Is reduced.

The hydraulic four-wheel drive vehicle 10 of this embodiment
Is a standby type four-wheel drive vehicle intended to ensure starting performance on a low μ road uphill road and stable running performance when turning, and the driving force of the rear wheel 32 during four-wheel drive is relatively small. Since the input clutch 22 having a torque capacity that causes slippage when excessive torque is transmitted is adopted, the four-wheel drive hydraulic pump 24, the hydraulic motor 28, and the output clutch 30 are small. A lightweight and inexpensive device can be adopted, and the apparatus is configured at a low cost as a whole.

In this embodiment, since the driving force is directly transmitted from the hydraulic motor 28 to the rear wheel 32 via the output clutch 30, the left and right rear wheels 32 are rigidly connected during the four-wheel drive. Running stability is obtained, and at the time of two-wheel drive in which the output clutch 30 is released, the left and right rear wheels 32 can freely rotate, thereby avoiding the tight corner braking phenomenon.

In the above embodiment, the rear wheel 32 is not provided with a differential. However, as shown in FIG. 5, a bevel gear type, a planetary gear type, etc. are provided between the hydraulic motor 28 and the pair of output clutches 30. 6 may be provided, and FIG.
A single output clutch 30 may be provided between the hydraulic motor 28 and the differential device 40 as described above, thereby preventing the tight corner braking phenomenon during four-wheel drive. It is also possible to provide the hydraulic motor 28 and the output clutch 30 on the pair of rear wheels 32, respectively.

The embodiments of the present invention have been described in detail with reference to the drawings. However, these are merely examples, and the present invention is based on the knowledge of those skilled in the art. Can be implemented.

[0036]

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a drive system of a standby type hydraulic four-wheel drive vehicle according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a control system of an input clutch with an electromagnet of the hydraulic four-wheel drive vehicle of FIG. 1;

FIG. 3 is a flowchart illustrating a switching operation between two-wheel drive and four-wheel drive of the hydraulic four-wheel drive vehicle in FIG. 1;

FIG. 4 is a time chart showing changes of respective parts at the time of the switching operation of FIG. 3;

FIG. 5 is a configuration diagram illustrating another embodiment having a rear wheel differential device.

FIG. 6 is a configuration diagram for explaining still another embodiment having a rear wheel differential device.

[Explanation of symbols]

 10: hydraulic four-wheel drive vehicle 12: engine (drive source for driving) 18: front wheel (one of front and rear wheels) 22: input clutch 22m: electromagnet (trigger means) 24: four-wheel drive hydraulic pump 28: hydraulic motor 30: output clutch 32: rear wheel (the other of the front and rear wheels)

Claims (3)

[Claims] A drive source for driving one of the front and rear wheels to rotate, a hydraulic pump for four-wheel drive connected to the drive source for rotation, and a discharge hydraulic pressure of the hydraulic pump for four-wheel drive A hydraulic motor having a hydraulic motor rotationally driven to rotate the other of the front and rear wheels, and an input clutch disposed in a power transmission path between the four-wheel drive hydraulic pump and the traveling drive source In the four-wheel drive vehicle, the input clutch is a hydraulic clutch that transmits power by being frictionally engaged by the discharge hydraulic pressure of the four-wheel drive hydraulic pump, and is used when switching from two-wheel drive to four-wheel drive. A hydraulic four-wheel drive vehicle comprising: trigger means for rotating a four-wheel drive hydraulic pump to frictionally engage the input clutch with a discharge oil pressure of the four-wheel drive hydraulic pump. 2. The input clutch is a hydraulic clutch with an electromagnet that can be frictionally engaged not only by hydraulic pressure but also by electromagnetic force, and the trigger means excites the electromagnet and frictionally engages the input clutch. The hydraulic four-wheel drive vehicle according to claim 1, wherein the four-wheel drive hydraulic pump is driven to rotate. 3. A drive source for driving one of the front and rear wheels to rotate, a hydraulic pump for four-wheel drive connected to the drive source for rotation, and a discharge hydraulic pressure of the hydraulic pump for four-wheel drive A hydraulic motor having a hydraulic motor rotationally driven to rotate the other of the front and rear wheels, and an input clutch disposed in a power transmission path between the four-wheel drive hydraulic pump and the traveling drive source In a four-wheel drive vehicle, a hydraulic system that is disposed in a power transmission path between the hydraulic motor and the other of the front and rear wheels and that transmits power by being frictionally engaged by discharge hydraulic pressure of the four-wheel drive hydraulic pump. Hydraulic type 4 having an output clutch
Wheel drive vehicles.