JP2585385Y2 - Anti-lock device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brake system mounted on a vehicle having one front axle and two rear axles, and relates to an antilock device for preventing locking of wheels.

[0002]

2. Description of the Related Art Conventionally, there is an antilock brake system for a large vehicle having three axes described in Japanese Utility Model Laid-Open Publication No. 3-83169.

FIG. 5 shows the configuration of the antilock brake system described in the above publication. The conventional example shown in FIG.
The front shaft has left and right front wheels 151 and 152, the first rear shaft has left and right drive wheels 153 and 154, and the second rear shaft has left driven wheels 155 and 156. The left and right driving wheels 1
The vehicle includes first and second speed sensors S101 and S102 for detecting the rotation speeds of the left and right front wheels 151 and 152, and third and fourth speed sensors S103 and S104 for detecting the rotation speeds of the left and right front wheels 151 and 152. The speed values detected by these speed sensors S1 to S4 are:
It is output to a control unit (not shown) as a speed signal.

The brake valve 107 and the left and right front wheels 151,
Relay valve 1 between each wheel cylinder 152
The third braking control unit 130 is interposed via 08. The third brake control unit 130 converts a pneumatic pressure from the brake valve side into a hydraulic pressure and supplies the hydraulic pressure to the wheel cylinder side, and a hydraulic pressure supplied to the third air master cylinder 131. It is constituted by a third modulator 132 to be controlled. Incidentally, so as to operate appropriately by the operation signal from the third modulator 13 2 controller.

Similarly, a first air master cylinder 111 and a first modulator 112 are provided between the brake valve 107 and each wheel cylinder of the left driving wheel 153 and the left driven wheel 155 via a relay valve 109. The first braking control unit 110 is interposed, and the left driving wheel 15
3 and the brake pressure applied to each wheel cylinder of the left driven wheel 155.

A second air master cylinder 121 and a second modulator 122 are provided between the brake valve 107 and each wheel cylinder of the right driving wheel 154 and the right driven wheel 156 via a relay valve 109. The second drive control unit 120 is interposed, and the right drive wheel 15
4 and the brake pressure applied to each wheel cylinder of the right driven wheel 156.

In this conventional example, the left driving wheel 153 and the left driven wheel 155 are controlled by the first braking control unit 110 independently of the right wheel. The right driving wheel 154 and the right driven wheel 156 are controlled by the second braking control unit 120 independently of the left wheel.

[0008]

In the prior art, the left driving wheel and the left driven wheel on the rear wheel side are controlled at the same pressure. Similarly, the right driving wheel and the right driven wheel are controlled at the same pressure. For this reason, when the friction coefficient value of the tire or brake friction material of the driven wheel is higher than the value of the drive wheel, the driven wheel may be locked. Particularly, in the case of the anti-lock control, fine control of each wheel is required, so that when the driven wheel is locked, the anti-lock performance is reduced.

As a method of solving such a problem,
In consideration of the difference in the friction coefficient between the tire of the driving wheel and the driven wheel and the friction coefficient of the brake friction material, it is conceivable that the pressure is reduced and supplied to the driven wheel during braking. However, in this case, the load on the driving wheel side increases,
The brake friction material on the drive wheel side deteriorates early.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide an antilock device capable of performing good wheel lock prevention control in a vehicle having three axes.

[0011]

According to the present invention, a front shaft F having left and right front wheels 51 and 52 on the front side and a left and right driving wheel 5 on the rear side are provided.
Rear shaft R1 having left and right driven wheels 55, 56
A first braking control unit 10 for controlling a braking force of the left driving wheel 53 and the left driven wheel 55, and a right driving wheel 54 and a right driven wheel 5
6, a second braking control unit 20 for controlling the braking force, first detecting means S1 for detecting the rotational speed of the left driving wheel, and second detecting means S2 for detecting the rotational speed of the right driving wheel.
A control unit 90 for inputting signals from the detection means S1 and S2, and a first unit which is interposed between the first braking control unit 10 and the left driven wheel brake and capable of shutting off a passing pressure. A cut valve 73, a first proportioning valve 71 provided on a path that bypasses the first cut valve 73, and reduces the pressure at a constant rate when the input pressure becomes equal to or higher than a set pressure value and outputs the reduced pressure; Control unit 20
A second cut valve 74 interposed between the second cut valve 74 and the brake for the right driven wheel and capable of shutting off a passing pressure; A second proportioning valve 72 that outputs a reduced pressure at a fixed ratio when the value becomes equal to or more than the value. When the control unit 90 determines the lock possibility of the left driving wheel 53 based on a signal from the first detection unit S1, The first proportioning valve 7 is controlled by controlling the first braking control unit 10 and closing the first cut valve 73.
When pressure is supplied to the left driven wheel brake via only 1 and the possibility of locking the right driving wheel 54 is determined based on a signal from the second detection means S2, the second braking control device 20 is controlled and The second cut valve 74 is closed to supply pressure to the right driven wheel brake only through the second proportioning valve 72, thereby providing an anti-lock device for preventing each wheel from being locked.

Further, a third braking control unit 30 for controlling the braking force of the left and right front wheels 51 and 52, third detecting means S3 for detecting the rotational speed of the left front wheel, and detecting the rotational speed of the right front wheel. The control unit 90 determines whether the left and right front wheels 51 and 52 can be locked based on signals from the third and fourth detection units S3 and S4. 30 to control the front left and right wheels 51,
It is desirable to prevent locking of 52.

[0013]

The control section 90 includes third and fourth detecting means S3 and S4.
When the lock possibility of the left and right front wheels 51 and 52 is determined based on the signal from the controller, the third brake control unit 30 is controlled to control the brake pressure supplied to the left and right front wheel brakes and the left and right driven wheel brakes.

Further, the control section 90 includes a first detecting means S1.
When the lock possibility of the left driving wheel 53 is determined based on the signal from the controller, the first brake control unit 10 is controlled to control the brake pressure supplied to the left driving wheel brake and the left driven wheel brake and to perform the first cut. Close the valve 73 and
The pressure is supplied to the left driven wheel brake only through the proportioning valve 71. Further, the control unit 90 controls the second
When the lock possibility of the right driving wheel 53 is determined based on the signal from the detection means S2, the second brake control unit 20 is controlled to control the brake pressure supplied to the right driving wheel brake and the right driven wheel brake, and The second cut valve 74 is closed to supply pressure to the right driven wheel brake only through the second proportioning valve 72. At this time, when the pressures input from the first and second brake control units 10 and 20 become equal to or higher than the set pressure values, the proportioning valves 71 and 73 respectively increase the brake pressure to the left and right driven wheel brakes at a fixed ratio. Supply under reduced pressure.

If the control unit 90 does not determine the possibility of locking the wheels during the braking operation, the first and second cut valves 7
Reference numerals 3 and 74 maintain the open state, and the left and right driven wheel brakes are continuously supplied with the same brake pressure as the pressure supplied to the left and right drive wheel brakes.

As described above, only in the case of the anti-lock control, the brake pressure supplied to the driven wheel brake is controlled to be lower than that of the drive wheel when the brake pressure is equal to or higher than the set pressure value. To reliably prevent

The left and right driving wheels and driven wheels are controlled independently.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIGS. As shown in FIG. 2, the wheel lock prevention device of this embodiment includes a front front shaft F, a rear first rear shaft R1, and a second rear shaft R1.
It has three axes, the rear axis R2.

The front shaft F is provided with a left front wheel 51 and a right front wheel 52. The first rear shaft R1 includes a left driving wheel 53 and a right driving wheel 54, and the second rear shaft R2
Is provided with a left driven wheel 55 and a right driven wheel 56. The front left wheel 51 is provided with a wheel cylinder 61, and the front right wheel 52 is provided with a wheel cylinder 62. The left drive wheel 53 is provided with a wheel cylinder 63, and the right drive wheel 54 is provided with a wheel cylinder 63. Further, the left driven wheel 55 is provided with a wheel cylinder 65, and the right driven wheel 56 is provided with a wheel cylinder 66.

Then, first to fourth speed sensors S as detecting means for detecting the rotational speeds of the driving wheels and the front wheels.
1 to S4 are provided on the left and right driving wheels 53 and 54 and the left and right front wheels 51 and 52, respectively. Each speed sensor S calculates a speed value based on the rotation amount of each wheel.

Referring to FIG. 1, the state of the piping of the brake pressure for braking the vehicle will be described. The air tank 80
It communicates with a brake valve 7 that is opened and closed by a driver's operation of a brake pedal. This brake valve 7
The first pipe A communicates with the front wheel side relay valve 8 and the second pipe B connects with the rear wheel side relay valve 9.
Has been contacted.

The relay valve 8 further communicates with a third brake control unit 30 for supplying brake fluid pressure to the wheel cylinders 61 and 62 via a third brake control unit pipe a.

The third brake control unit 30 and the wheel cylinders 61 and 62 are in communication with each other through a front wheel pipe C. The relay valve 9 is connected to the first brake control unit 10 that supplies brake fluid pressure to the wheel cylinder 63 of the left drive wheel 53 and the wheel cylinder 65 of the left driven wheel 55 via the first brake control unit pipe b1. Communicating. Further, the relay valve 9 is connected to the first brake control device pipe b.
The second brake control device unit 20 that supplies brake fluid pressure to the wheel cylinder 64 of the right drive wheel 54 and the wheel cylinder 66 of the right driven wheel 56 via a second brake control device unit pipe b2 branched from 1. ing.

The third braking control unit 30 converts a pneumatic pressure from the brake valve 7 side into a hydraulic pressure and supplies the hydraulic pressure to the wheel cylinder side. And a third modulator 32 for controlling the hydraulic pressure. The third modulator 32 is appropriately operated by an operation signal from the control unit 90.

[0025] Similarly, the first brake control device 10 Ru Tei is composed of a first air master cylinder 11 first modulator 12. Further, the second braking control unit 20
Is the second air master cylinder 21 and the second modulator 22
Ru Tei is composed of a.

The pressure converted to the hydraulic pressure by the first braking control unit 10 passes through the pipe D for the left rear wheel, and the pipe D for the left rear wheel.
Drive wheel 53 via left drive wheel pipe d1 branched from
Of the left driven wheel 55 and the wheel cylinder 65 of the left driven wheel 55 via the left driven wheel pipe d3.

The pressure converted into the hydraulic pressure by the second brake control unit 20 passes through the right rear wheel pipe E and branches off from the right rear wheel pipe E via the right drive wheel pipe e1. While being supplied to the wheel cylinder 64 of the right drive wheel 54,
The power is supplied to the wheel cylinder 66 of the right driven wheel 56 via the right driven wheel pipe e3.

The left drive wheel pipe d1 of the left rear wheel pipe D
A first cut valve 73 capable of shutting off the hydraulic pressure from the first brake control unit 10 is provided between the first brake control unit 10 and the left driven wheel pipe d3.
Is interposed. Further, the first cut valve 73
On the bypass pipe d2 that bypasses the
A first proportioning valve 71 for controlling the pressure of the fluid passing through is provided. Similarly, the right rear wheel piping E
A second cut valve 74 that can shut off the hydraulic pressure from the second braking control unit 20 is interposed between the right drive wheel pipe e1 and the right driven wheel pipe e3. Further, on a bypass pipe e2 that bypasses the second cut valve 74, a second pressure that controls a hydraulic pressure passing through the bypass pipe e2 is provided.
A proportioning valve 72 is interposed.

Each of the proportioning valves 71, 7
2 is such that a built-in valve (not shown) starts operating when the input hydraulic pressure exceeds a set pressure value, and the output hydraulic pressure is reduced at a constant rate. In other words, the brake pressure supplied to the driven wheels through the bypass pipes d2 and e2 is such that a brake pressure lower than the brake pressure supplied to the drive wheels is supplied when the set pressure value is exceeded. Become.

The brake pressure supplied to the wheel cylinder of each wheel is transmitted as follows. That is,
The pressure applied to the wheel cylinders 61 and 62 of the front wheels is such that air from the air tank 80 reaches the relay valve 8 via the brake valve 7 as a signal pressure, and the relay valve 8 applies air pressure corresponding to the signal pressure to the air tank 80. → Via the third modulator 32 → Supply to the third air master cylinder 31, convert the air pressure to hydraulic pressure by the third air master cylinder 31, → Front wheel side wheel cylinder 61,
Supply pressure to 62.

The pressure applied to the wheel cylinder 63 of the left driving wheel is such that the air from the air tank 80 reaches the relay valve 9 via the brake valve 7 as a signal pressure, and the relay valve 9 applies pneumatic pressure corresponding to the signal pressure. Is taken directly from the air tank 80 and sent to the first modulator 12. The air that has passed through the first modulator 12 is supplied to the first air master cylinder 11 and the air pressure is converted into hydraulic pressure by the first air master cylinder 11. This hydraulic pressure is applied to the left rear wheel pipe D and the drive wheels. It is supplied to the wheel cylinder 63 via the pipe d1. The hydraulic pressure from the first air master cylinder 11 is transmitted via the left rear wheel pipe D and the driven wheel pipe d3.
It is also supplied to the wheel cylinder 65 of the left driven wheel. The hydraulic pressure to the wheel cylinder 65 is controlled by the first cut valve 7
If 3 is closed, → pipe D for left rear wheel → bypass pipe d2 → passes through first proportioning valve 71 on bypass pipe d2 → via pipe d3 for driven wheel →
It is supplied to the wheel cylinder 65.

The right drive wheel cylinder 64,
The pressure to 66 is such that the air from the air tank 80 reaches the relay valve 9 via the brake valve 7 as a signal pressure, and the relay valve 9 directly takes in the air pressure corresponding to the signal pressure from the air tank 80 → 2 to the modulator 22. The air that has passed through the second modulator 22 is supplied to the second air master cylinder 21 and the air pressure is converted into hydraulic pressure by the second air master cylinder 21. This hydraulic pressure is used for the right rear wheel pipe E and the drive wheels. Via pipe e1 → wheel cylinder 6
4 is supplied. Further, the second air master cylinder 2
The hydraulic pressure from 1 is: → pipe E for right rear wheel and pipe e for driven wheel
3 to the wheel cylinder 66 of the right driven wheel. When the second cut valve 74 is closed, the hydraulic pressure to the wheel cylinder 66 passes through the left rear wheel pipe D → the bypass pipe e2 → the second proportioning valve 72 on the bypass pipe e2 → Piping for driven wheel e
3 to the wheel cylinder 66.

The first to fourth speed sensors S1 to S4
Is connected to the control unit 90 (ECU) as shown in FIG. The hold valve (not shown) and the decay valve (not shown) in each modulator of the first to third brake control units 10, 20, and 30 are appropriately opened and closed by the signal from the control unit 90, Lock is prevented.

Signals from the third and fourth speed sensors S3 and S4 are sent to a control unit 90 via a select row circuit 92.
Is output to In the select row circuit 92, the lower one of the third speed sensor S3 and the fourth speed sensor S4 is selected, and a signal is output to the controller 90. That is, the left and right front wheels 5
The speed signal of the wheel having the higher lock possibility among 1, 52 is selected.

When the control unit 90 determines that the front wheels can be locked based on a signal from the third speed sensor S3 or the fourth speed sensor S4, the control unit 90 controls the pressure in the third air master cylinder 31 by the third modulator 32. To adjust the hydraulic pressure in the wheel cylinders 61 and 62 so that the front wheels are not locked.

When the control unit 90 determines the possibility of locking the left driving wheel 53 based on the speed signal from the first speed sensor S1, the control unit 90 controls the pressure in the first air master cylinder 11 by the first modulator 12 To control the brake pressure in the wheel cylinder 63 to prevent the left driving wheel 53 from locking.

When the control unit 90 determines the possibility of locking the right driving wheel 54 based on the speed signal from the second speed sensor S2, the control unit 90 controls the pressure in the second air master cylinder 21 by the second modulator 22. Thus, the brake pressure in the wheel cylinder 64 is adjusted to prevent the right driving wheel 54 from locking.

Next, the operation of this embodiment will be described. When the driver operates the brake pedal to release the brake valve 7, air pressure corresponding to the signal pressure from the first pipe A is supplied to the third brake control device 30 via the relay valve 8. Then, the third braking control unit 30 operates to activate the front wheel 5.
The brake pressure is supplied to the wheel cylinders 61 and 62 of the first and second wheels 52.

At the same time, air pressure corresponding to the signal pressure from the second pipe B is supplied to the first brake control unit 10 and the second brake control unit 20 via the relay valve 9. Then, the first brake control unit 10 operates to supply the brake pressure to the wheel cylinder 63 and the wheel cylinder 65, and the second brake control unit 20 operates to apply the brake pressure to the wheel cylinder 64 and the wheel cylinder 66. Supply. In this way, brake braking of each wheel is performed.

During the normal brake braking as described above, the pressure supplied to the wheel cylinders 65 and 66 of the left and right driven wheels is increased by the drive wheels since the first and second cut valves 73 and 74 are open. The same pressure as the hydraulic pressure supplied to the wheel cylinders 63 and 64 on the side is supplied.

When the control unit 90 determines that at least one of the front wheels 51 and 52 can be locked based on the signals from the third and fourth speed sensors S3 and S4 during the brake braking, the control unit 90 performs the third braking. An operation signal is output to the control unit 30. The third braking control unit 30 receives a command from the control unit 90 and controls the wheel cylinder 6 through the front wheel pipe C.
The brake pressure supplied to the front wheels 1 and 62 is appropriately reduced, held, and repressurized to prevent the front wheels 51 and 52 from being locked.

When the control unit 90 determines that the left driving wheel 53 can be locked based on the signal from the first speed sensor S1, the control unit 90 outputs an operation signal to the first brake control unit 10. The first braking control unit 10 includes the control unit 9
0, the brake pressure supplied to the left rear wheel pipe D is appropriately reduced, maintained, and re-pressurized.
3 to prevent the left driving wheel 53 from being locked.

Further, based on the signal from the second speed sensor S2, when the control unit 90 calculates the lock possibility of the right driving wheel 54, the control unit 90 executes the second braking control unit 20.
Outputs the operation signal to The second braking control unit 20 adjusts the pressure in the wheel cylinder 64 by appropriately reducing, holding, and re-pressing the brake pressure supplied to the right rear wheel pipe E according to a command from the control unit 90, and 54 is prevented from being locked.

When such antilock brake braking is being performed, the first and second cut valves 73 and 74
When the antilock control start signal is input from the control unit 90, the block is immediately closed. Therefore, the pressure of the left and right driven wheels to the wheel cylinders 65 and 66 is supplied through the bypass pipes d2 and e2. At this time, if the hydraulic pressure passing through the bypass pipes d2 and e2 exceeds the set pressure value, the first and second proportioning valves 7
The pressure is reduced at a fixed ratio in the wheel cylinders 72 and 72 and supplied to the wheel cylinders 65 and 66. That is, since the driven wheels are braked in accordance with the lock possibility state of the drive wheels, when the friction coefficient of the tires and the brake friction material on the driven wheel side is larger than the drive wheel side, they are supplied to the drive wheel side and the driven wheel side. If the brake pressures are the same, the driven wheels will lock. Therefore,
As shown in FIG. 4, the first and second proportioning valves 71 and 72 enable the brake pressure to be supplied to the left and right driven wheels to be reduced and supplied as compared to the brake pressure supplied to the left and right drive wheels. It is. To Q ₁ Figure 4 shows a liquid pressure distribution and the actual driving wheel and the driven wheel side. Also, Q
₂ shows the case of supplying a brake pressure to the driven wheel side without passing through the proportioning valve, a hydraulic pressure distribution of the driving wheel side and the driven wheel side. The branch point P between Q ₁ and Q ₂
Is the set pressure value of the proportioning valve.

As described above, according to the present embodiment, during the antilock control, since the first and second cut valves are closed, the brake pressure supplied to the left and right driven wheels is equal to or higher than the set pressure. In this case, the pressure is lower than the brake pressure supplied to the left and right drive wheels. Therefore, it is possible to reliably prevent the driven wheel from being locked.

During normal brake braking, the first and second cut valves are open, so that the brake pressure supplied to the left and right driven wheels and the left and right driven wheels are the same. For this reason, it has become possible to obtain a highly accurate anti-lock device without reducing the braking force during normal brake braking. Further, the wear speeds of the brake friction material on the driving wheel side and the brake friction material on the driven wheel side are almost the same, so that a biased load is not applied to the brake friction material on the drive wheel side. Therefore, it is possible to prevent early deterioration of the brake friction material on the driving wheel side.

As described above, in the present embodiment, the anti-lock device for the two-axle vehicle is provided with an anti-lock device capable of performing good wheel lock prevention control with a simple configuration by changing the piping by adding only the cut valve and the proportioning valve. Can be provided.

In this embodiment, the front wheel speed signal is input to the control unit 90 via the select row circuit.
It is also possible to incorporate the function of the select row circuit in 0.

Although the present embodiment employs an air-over hydraulic brake system that converts air pressure into hydraulic pressure and supplies brake pressure to a wheel cylinder, the present invention can also be applied to a full air brake system.

The first and second cut valves may be closed by inputting an exhaust brake stop signal.

[0051]

According to the present invention, it is possible to provide an anti-lock device capable of performing good wheel lock prevention control in a vehicle having three axes.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an antilock device according to an embodiment of the present invention.

FIG. 2 is a layout diagram of a wheel shaft in the embodiment.

FIG. 3 is a configuration diagram of each component in the embodiment.

FIG. 4 is a diagram showing a hydraulic pressure ratio between a driving wheel and a driven wheel in the embodiment.

FIG. 5 is a configuration diagram of a conventional example.

[Explanation of symbols]

7. Brake valve 8. Relay valve 9. Relay valve 10. First brake control unit 11. First air master cylinder 12. First modulator 20. Second brake control unit 21 .. Second air master cylinder 22 Second modulator 30 Third brake control unit 31 Third air master cylinder 32 Third modulator 51 Left front wheel 52 Right front wheel 53 Left driving wheel 54 right drive wheel 55 left driven wheel 56 right driven wheel 61-66 wheel cylinder (brake for each wheel) 71 first proportioning valve 72 second proportioning valve 73 First cut valve 74 Second cut valve 80 Air tank 90 Control unit (ECU) 92 Select row circuit A First pipe a Third Piping for dynamic control unit B..2 piping b1..Piping for first braking control unit b2..Piping for second braking control unit C..Piping for front wheel D..Piping for left rear wheel d1.・ Left drive wheel piping d2 ・ ・ Bypass piping d3 ・ ・ Left driven wheel piping E ・ ・ Right rear wheel piping e1 ・ ・ Right drive wheel piping e2 ・ ・ Bypass piping e3 ・ ・ Right driven wheel piping F ・Front axis R1 First rear axis R2 Second rear axis S1 to S4 First to fourth speed sensors (first to fourth
Detection means)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B60T 8/32-8/58

Claims (2)

(57) [Scope of request for utility model registration] 1. A front shaft (F) having left and right front wheels (51, 52) on the front side, a first rear shaft (R1) having left and right driving wheels (53, 54) on the rear side, and left and right driven wheels (55, 52). 56) a second rear axle (R2), comprising: a first braking control unit (10) for controlling a braking force of the left driving wheel (53) and the left driven wheel (55); Second control for controlling the braking force of the driving wheel (54) and the right driven wheel (56)
A braking control unit (20), and first detection means (S) for detecting a rotation speed of the left driving wheel.
1), a second detecting means (S2) for detecting the rotational speed of the right driving wheel, a control section (90) for inputting signals from the detecting means S1 and S2, and the first braking control section. (10) a first interposed between the left driven wheel brake and the left driven wheel brake, which can shut off a passing pressure;
The cut valve (73) and the first cut valve (7
A first proportioning valve (71) that is provided on a path bypassing 3) and that reduces the pressure at a fixed ratio and outputs the reduced pressure when the input pressure exceeds a set pressure value; and the second braking control unit (20). A second interposed member between the right driven wheel brake and the right driven wheel brake, which can shut off a passing pressure;
The cut valve (74) and the second cut valve (7
A second proportioning valve (72) that is provided on a path bypassing 4) and that reduces the pressure at a constant rate and outputs the reduced pressure when the input pressure becomes equal to or higher than a set pressure value; When the lock possibility of the left driving wheel (53) is determined based on a signal from the first detection means (S1), the first brake control unit (10) is controlled and the first cut valve (73) is closed. A pressure is supplied to the left driven wheel brake via only the first proportioning valve (71), and the second detecting means (S2) is supplied.
When the possibility of locking of the right driving wheel (54) is determined based on the signal from the controller, the second braking control unit (20) is controlled, and the second cut valve (74) is closed to close the second proportioning valve (54). 72) An anti-lock device that supplies pressure to the right driven wheel brake via only the above and prevents locking of each wheel. 2. A third braking control unit (30) for controlling a braking force of the left and right front wheels (51, 52); third detecting means (S3) for detecting a rotation speed of the left front wheel; A fourth detection unit (S4) for detecting a rotation speed of the front wheel, wherein the control unit (90) includes the third and fourth detection units (S4).
When the possibility of locking the left and right front wheels (51, 52) is determined based on the signal from the third braking control unit (3, S4), the third braking control unit (3
2. The anti-lock device according to claim 1, wherein the anti-lock device is controlled to prevent locking of the left and right front wheels.