JP3125555B2 - Hydraulic pressure booster abnormality detection 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 hydraulic pressure booster provided with a hydraulic pressure control valve for reducing the hydraulic pressure of a hydraulic pressure source to a power pressure corresponding to the operating force of an operating member and a power piston operated by the power pressure. The present invention relates to a device for detecting an abnormality of the device.

[0002]

2. Description of the Related Art Japanese Unexamined Utility Model Publication No. 2-103865 discloses an abnormality detecting device for a hydraulic booster of this type.
A differential pressure switch which outputs a signal when the power pressure of a hydraulic booster is smaller than a hydraulic pressure of a master cylinder driven by the output of the hydraulic booster by a set value or more is described. If a signal is output by the differential pressure switch, it is determined that the power pressure corresponding to the operating force of the operating member is not generated by the hydraulic pressure control valve in the hydraulic pressure booster, that is, the hydraulic pressure booster is in an abnormal state. Is done.
On the other hand, Japanese Utility Model Laid-Open Publication No. 2-33772 discloses a pressure detecting means for detecting the hydraulic pressure of the accumulator. Based on the output signal from the pressure detecting means, a hydraulic pump or the like is controlled so that the hydraulic pressure of the accumulator is maintained within a set range.

[0003]

However, since the above differential pressure switch is expensive, there is a problem that the cost of the hydraulic pressure booster abnormality detecting device is high. On the other hand, if the above-mentioned pressure detecting means is used, it is possible to detect that the hydraulic pressure booster cannot generate the power pressure at low cost. If the output value of the pressure detecting means decreases, the hydraulic pressure of the accumulator decreases due to liquid leakage, failure of the hydraulic pump, and the like, and it can be understood that power pressure cannot be generated in the hydraulic booster. However, the abnormality of the hydraulic pressure booster itself cannot be detected. In view of the above circumstances, an object of the present invention is to provide a hydraulic booster abnormality detection device that can detect an abnormality of a hydraulic booster itself at low cost.

[0004]

SUMMARY OF THE INVENTION The gist of the present invention is to provide a hydraulic booster abnormality detecting device which detects an amount of pressure decrease of an accumulator when an operating member changes from a non-operating state to an operating state. An object of the present invention is to include an amount detection unit and a hydraulic booster abnormality determination unit that determines that the hydraulic booster is abnormal when the pressure reduction amount detected by the pressure reduction amount detection unit is smaller than a set value.

Here, even if the hydraulic booster abnormality determining means determines the abnormality of the hydraulic pressure booster based on a single pressure decrease amount detected by the pressure decrease amount detecting means, the hydraulic booster abnormality determination means calculates the average value of a plurality of times. The determination may be made based on this.

[0006]

In the hydraulic booster abnormality detecting device according to the present invention, when the pressure drop amount of the accumulator when the operating member changes from the non-operating state to the operating state is smaller than the set value, the hydraulic booster itself is abnormal. It is determined that there is. The set value is, for example, a minimum pressure drop amount that is considered to occur when the driver operates the operation member normally, and occurs when the operation of the operation member is stopped halfway or the operation member is accidentally touched. It is set to a magnitude between the pressure drop amount.

In the hydraulic booster, the hydraulic pressure of the accumulator is reduced by a hydraulic pressure control valve to a power pressure corresponding to the operating force of the operating member, and the power piston is operated by the power pressure. Therefore, each time the operating member is changed from the non-operating state to the operating state, a substantially constant amount of hydraulic fluid is consumed in the hydraulic pressure booster, and the hydraulic pressure of the accumulator is reduced by that much. On the other hand, if an abnormality occurs in the hydraulic pressure control valve and the hydraulic fluid does not flow into the hydraulic booster from the accumulator, the hydraulic pressure of the accumulator hardly decreases even when the operating member changes from the non-operating state to the operating state.
The pressure drop becomes smaller than the set value.

[0008]

Therefore, according to the hydraulic brake device of the present invention, an expensive differential pressure switch is not required, so that the cost of the hydraulic booster abnormality detecting device can be reduced. Further, if the existing pressure detecting means is used as the pressure drop detecting means of the present invention, the cost can be further reduced.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be enumerated below and explanations related thereto will be given. (1) The hydraulic pressure booster abnormality determining means determines the abnormality of the hydraulic pressure booster based on a plurality of average values of the pressure drop amount detected by the pressure drop amount detecting means. The hydraulic pressure booster abnormality detection device according to 1. If the determination as to whether or not the hydraulic pressure booster is abnormal is made based on the average value of the pressure drop amount for a plurality of times, it is possible to accurately determine whether or not the hydraulic pressure booster is abnormal. For example,
When the operation force of the operation member is extremely small or when the operation is stopped halfway, the accumulator pressure drop amount becomes smaller than the set value, and it is determined that the hydraulic pressure booster is abnormal even though it is normal This is because there is a danger of being caught.

(2) The hydraulic pressure booster abnormality determination means continues the determination even after the hydraulic pressure booster has once determined that the hydraulic pressure booster is abnormal and outputs abnormality occurrence information, and cancels the abnormality occurrence information when it returns to normal. 2. The hydraulic booster abnormality detecting device according to claim 1, further comprising a canceling means. If the abnormality of the hydraulic pressure booster is to be detected as early as possible or sensitively, there is an increased danger that an abnormality is erroneously determined even though the abnormality has not actually occurred. Therefore, providing the canceling means is effective in detecting an abnormality at an early stage while reducing the adverse effect of the erroneous determination.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydraulic brake device for a vehicle having a hydraulic booster abnormality detecting device according to one embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, reference numeral 10 denotes a master cylinder, and reference numeral 12 denotes a hydraulic booster. A cylinder bore 16 is formed in the housing 14 of the master cylinder 10, and a first pressure piston 18 and a second pressure piston 20 are fitted in a liquid-tight and slidable manner.
A first pressurizing chamber 22 and a second pressurizing chamber 24 are formed on the front side (left side in the drawing) of the first and second pressurizing pistons 18 and 20, respectively. The hydraulic pressure generated in the first pressurizing chamber 22 is supplied to the wheel cylinders 34, 36 of the brakes of the left and right front wheels 30, 32 through the liquid passage 28, and the second pressurizing chamber 2
The hydraulic pressure generated in the right and left rear wheels 4
2, 44 brake wheel cylinders 46, 48.

Left and right front wheels 30, 32 and left and right rear wheels 42, 44
Are anti-skid actuators 50 and 52, respectively.
The anti-skid control is performed by this.
Although these actuators 50 and 52 are not shown,
Combination of two solenoid on-off valves, three-position solenoid directional control valve,
Alternatively, each of the wheels 30, 32, 42, and 44 is provided with an electromagnetic hydraulic pressure control device including a proportional-type electromagnetic hydraulic pressure control valve.
By controlling the hydraulic pressures of the wheel cylinders 34, 36, 46, and 48, the slip ratio of each wheel is maintained in an appropriate range. This actuator 50,5
The control of No. 2 is performed by the control device 56, but since it is a well-known control, detailed description will be omitted.

An annular groove 60 is formed on the outer peripheral surface of the first pressurizing piston 18, and this annular groove 60
It is connected to a reservoir 64 as a low pressure source via a check valve. The reservoir 64 is provided with a level warning switch 66 that detects a decrease in the liquid amount and generates a signal, and the detection signal is supplied to the control device 56. An ignition switch 68 and an alarm device 69 are connected to the control device 56. The alarm device 69 includes one or more alarm devices such as a lamp, a display, a buzzer, a speaker, and a vibrator, and notifies the driver of an abnormality of the hydraulic pressure booster 12 by light, characters, sound, vibration, and the like.

The housing 70 of the hydraulic booster 12 is formed integrally with the housing 14 of the master cylinder 10. A power piston 72 is fitted to the housing 70 concentrically with the second pressurizing piston 20 in a liquid-tight and slidable manner, so that the inside of the housing 70 is connected to a low-pressure chamber communicating with the reservoir 64 at the front side of the power piston 70. It is divided into a chamber 76 and a power pressure chamber 78. A small-diameter portion 80 extends from a central portion of the rear surface of the power piston 72, and penetrates an end wall of the housing 70 in a liquid-tight and slidable manner to be exposed to the atmosphere. This small diameter portion 80
Inside, a bottomed hole 82 is formed from the rear end face, and a reaction piston 84 is fitted in this hole in a liquid-tight and slidable manner. The reaction piston 84 has a stepped shape, and a space 88 between the small diameter portion 86 and the bottom surface of the bottomed hole 82 is communicated with the power pressure chamber 78 by a communication passage 90. The hydraulic pressure in the power pressure chamber 78 acts on the reaction piston 84, and a reaction force having a magnitude proportional to the hydraulic pressure is applied to the input rod 92.

An input rod 92 has a reaction piston 84 caulked at its tip, a rear end connected to a brake pedal 94 as an operation member, and urged in a retreating direction by a return spring 96. The reaction piston 84 has a movement limit relative to the power piston 72.
Also functions as a return spring. The retracted end position of the power piston 72 is located at the housing 7 of the stopper projection 98.
The actuation force is transmitted by the relay piston 100 to the second pressurizing piston 20.
A brake switch 102 is attached to the brake pedal 94, and it is detected that the brake pedal 94 is depressed.

The hydraulic booster 12 has a hydraulic control valve 110. The hydraulic pressure control valve 110 includes a valve housing 112 fitted in a bottomed hole formed in the housing 70 and fixed by screwing, and a valve spool 114 fitted in a liquid-tight and slidable manner. Have. A communication hole 116 is formed in the valve spool 114, and the valve spool 114 connects the low-pressure port 118 to the power pressure chamber 78 through the communication hole 116 and blocks the high-pressure port 120 at the normal position shown in the drawing. The valve spool 114 moves forward from this position by a certain distance (moves to the left in the figure) to shut off both the low-pressure port 118 and the high-pressure port 120, and further advances to shut off the low-pressure port 118 and increase the pressure. The port 120 is brought into communication with the power pressure chamber 78.

The movement of the valve spool 114 is caused by the advance of the reaction piston 84 relative to the power piston 72. Valve spool 11
4 is connected to a driving member 122 via a spring 124. The driving member 122 is connected to a link mechanism 126.
Power piston 72 and reaction piston 84
It is engaged with. The link mechanism 126 includes a first link 130 and a second link 132 that are rotatably connected to each other by a pin 128, and one end of the first link 130 is turned around a pin 134 fixed to the housing 70. It is movably supported, and the other end is engaged with a reaction piston 84.

On the other hand, one end of the second link 132 is rotatably engaged with the drive member 122, and the other end is engaged with the small diameter portion 80 of the power piston 72. Therefore, when the reaction piston 84 advances relatively to the power piston 72, the movement is
6 is converted into forward movement of the valve spool 114,
The hydraulic control valve 110 will be switched as described above. A spring 136 is provided to bias the driving member 122 and the valve spool 114 in the backward direction.

The hydraulic pressure control valve 110 is connected to the low pressure port 11
8, connected to the reservoir 64 by the liquid passage 150, and connected to the accumulator 154 by the high-pressure port 120 and the liquid passage 152. The working fluid of the reservoir 64 is pressurized and stored in the accumulator 154 by the pump 156 and supplied to the hydraulic booster 12. A pressure sensor 160 is provided between the accumulator 154 of the liquid passage 152 and the high-pressure port 120, and a detection signal thereof is supplied to the control device 56. The pressure sensor 160 detects the hydraulic pressure of the accumulator 154. Based on the output value, the pressure sensor 160 controls the motor 162 that drives the pump 156 so that the accumulator hydraulic pressure is maintained within a predetermined setting range. Controlled. That is, the motor 162 driving the pump 156, the accumulator fluid pressure, as shown in FIG. 2, is driven if it becomes lower than the lower limit value P _d, is the fluid pressure is stopped and becomes the upper limit value P _u . Further, as described later, it is determined whether or not the hydraulic booster 12 is abnormal based on the detection value of the pressure sensor 160.

On the other hand, the annular groove 60 of the first pressurizing piston 18 of the master cylinder 12 is connected to the power pressure chamber 78 of the hydraulic booster 12 via the liquid passage 180.
Therefore, the hydraulic pressure in the power pressure chamber 78 is supplied to the wheel cylinders 34 and 38 via the liquid passage 180, the annular groove 60, the communication passage 182, the first pressurizing chamber 22, and the liquid passage 28. In the middle of the liquid passage 180, an electromagnetic on-off valve 184
Is provided. The solenoid on-off valve 184 is switched to the open position by the excitation of the solenoid, and the wheel cylinders 34 and 36 are connected to the power pressure chamber 78 via the first pressurizing chamber 22.

In the middle of the liquid passages 28 and 40, electromagnetic directional control valves 188 and 190 are provided, respectively. The electromagnetic directional valve 188 is always in the illustrated first position,
Although the wheel cylinders 34 and 36 are communicated with the first pressurizing chamber 22, during anti-skid control, the wheel cylinders 34 and 36 are switched to the second position to communicate the wheel cylinders 34 and 36 with the power pressure chamber 78. Similarly, the electromagnetic directional control valve 190 is
The first position where the wheel cylinders 46 and 48 communicate with the second pressure chamber 24 and the second position where the wheel cylinders 46 and 48 communicate with the power pressure chamber 78 are switched.

The operation of the hydraulic brake device will be described below. When the ignition switch 68 is turned on, the electromagnetic on-off valve 184 is switched to the open state, and the first pressurizing chamber 2
A power pressure chamber 78 is communicated with 2. The solenoid directional valves 188, 190 are kept in the first position. The wheel cylinders 34 and 36 are provided in the first pressure chamber 22
Reference numerals 6 and 48 communicate with the second pressurizing chamber 24, respectively.

When the brake pedal 94 is depressed (changed from the non-operating state to the operating state), the brake switch 102 is turned on, the input rod 92 is advanced, and the valve spool 114 is advanced. The power pressure chamber 78 is shut off from the low-pressure port 118, and communicates with the high-pressure port 120 so that the brake fluid (operating fluid) of the accumulator 154 flows. A part thereof is supplied to the wheel cylinders 34 and 36 via the liquid passage 180 and the first pressurizing chamber 22. On the other hand, when the fluid pressure in the power pressure chamber 78 rises, the power piston 72 is moved forward,
The relative displacement between the reaction piston 84 and the power piston 72 decreases. The valve spool 114 is retracted, and the high pressure port 120 and the low pressure port 118 are shut off. As described above, since the hydraulic pressure control valve 110 is operated based on the relative displacement between the reaction piston 84 and the power piston 72, the brake pedal 84
In any position, the hydraulic pressure in the power pressure chamber 78 is controlled to a magnitude corresponding to the operating force of the brake pedal 94. Further, the second pressurizing piston 20 is advanced with the advance of the power piston 72, and the brake fluid in the second pressurizing chamber 24 is supplied to the wheel cylinders 46 and 48.

The power pressure in the power pressure chamber 78 is controlled by the hydraulic pressure control valve 1.
The pressure reduction is controlled by 10 to a size corresponding to the operation force of the brake pedal 94. The accumulator 154 supplies brake fluid necessary for operating the hydraulic booster 12 and brake fluid necessary for operating the wheel cylinders 34 and 36, and the amount of these brake fluids is exactly proportional to the operation stroke of the brake pedal 94. No, but it increases as the operation stroke increases. Therefore, the accumulator 15
As shown by the solid line in FIG. 2, the hydraulic pressure of No. 4 decreases as the operation proceeds.

FIG. 2 shows a change in hydraulic pressure when the operation of depressing the brake pedal 94 and immediately releasing it is repeated.
Since the accumulator 154 is filled with nitrogen gas, the nitrogen gas adiabatically expands with the supply of the brake fluid from the accumulator 154 to the hydraulic pressure control valve 110,
The pressure drops. Then, when the supply of the brake fluid from the accumulator 154 is stopped and the volume expansion of the nitrogen gas stops, the nitrogen gas absorbs heat from the surroundings and the temperature rises. Accordingly, the pressure of the nitrogen gas increases, and the hydraulic pressure of the accumulator 154 recovers accordingly.

In the hydraulic pressure control valve 110, the first link 130 and the second link 132 rotate due to the failure of the valve spool 114 to move normally due to foreign matter or the like or the failure of the link mechanism 126. When the relative movement of the reaction piston 84 with respect to the power piston 72 is not transmitted to the valve spool 114 due to the disappearance, and when the hydraulic booster 12 itself is abnormal, the pressure drop amount of the accumulator 154 is indicated by a broken line in FIG. Very small or zero as illustrated. When the valve spool 114 cannot move normally, the high pressure port 120 does not communicate with the power pressure chamber 78 with a sufficient flow area or remains shut off, so that the brake fluid of the accumulator 154 is supplied to the power pressure chamber 78. This is because it is difficult to supply or it is not supplied at all.

In this embodiment, whether or not the hydraulic booster 12 is abnormal is determined by executing an abnormality determining program for the hydraulic booster 12 stored in a ROM (not shown) of the control device 56. The output value (maximum value) of the pressure sensor 160 at the time when the brake switch 102 is switched from OFF to ON and the output value (maximum value) of the pressure sensor 160 while the brake switch 102 is outputting the ON signal and when the anti-skid control is not performed A difference ΔP _i (a pressure drop amount) from the minimum value is calculated, a plurality of the differences ΔP _i are stored, and an average value of these differences <ΔP _n > is calculated based on the following equation. <ΔP _n > = (ΔP ₁ + ΔP ₂ +... + ΔP _n ) / n It is determined whether or not this average value <ΔP _n > is within a predetermined setting range. Here, the abnormality determination program of the hydraulic pressure booster 12 indicates that the motor 162 is being driven.
That is, it is not executed while the hydraulic pressure of the accumulator 154 is being controlled.

The lower limit of the setting range is set to a value slightly smaller than the lowest pressure drop of the accumulator 154 which is considered to occur when the driver operates the brake pedal 94 normally. This lower limit value is the liquid of the accumulator 154 generated when the brake switch 102 is turned on by putting a foot on the brake pedal 94 in preparation for operation, or when the operation is started but immediately stopped. This is a value larger than the pressure reduction amount. If the average value <ΔP _n > is smaller than the lower limit, it is determined that the hydraulic booster 12 is abnormal.

In this embodiment, whether the hydraulic booster 12 is abnormal or not is determined by the accumulator 1 when the brake pedal 94 is operated once from the non-operation state to the operation state.
The determination is made based on the average value of the pressure drop amounts in a plurality of operations, not the pressure drop amount of 54. If it is determined based on the amount of one pressure decrease, the brake pedal 94
The brake switch 102 is turned on even if the pedaling force of the accumulator 154 is very small and the pedaling force is very small.
In this case, it is considered that the operating state has been set, and even if the hydraulic pressure booster 12 is normal, there is a possibility that the hydraulic pressure booster 12 may be erroneously determined to be abnormal. Further, the control device 56 continues the abnormality determination even after the abnormality occurrence information has been output once, and cancels the abnormality occurrence information when the abnormality is resolved. The abnormality determination program is created in such a manner, and the part of the control device 56 that executes this part of the abnormality determination program constitutes a canceling unit.

In this embodiment, an upper limit is set. The upper limit is the hydraulic pressure booster 12, the liquid passage 18
0, solenoid on-off valve 184, master cylinder 10, liquid passage 2
8, electromagnetic directional control valve 188, wheel cylinder 34, 3
The pressure is set to a value slightly smaller than the pressure drop amount of the accumulator 154 which is considered to be caused by a liquid leakage or the like such as 6. If liquid leakage occurs in any of the above components,
Since the amount of pressure drop due to the operation of the brake pedal 94 increases, if the average value <ΔP _n > is larger than the upper limit value, it is determined that liquid leakage has occurred.

When the average value <ΔP _n > is within the set range and it is determined that the hydraulic pressure booster 12, the accumulator 154, and the like are normal, the slip ratio of the wheel with respect to the road surface μ during braking is determined. When it becomes excessive, anti-skid control is started. The electromagnetic directional control valves 188 and 190 are switched to the second position, and the anti-skid actuator 5
0 and 52 are communicated with the power pressure chamber 78. Anti-skid control is performed using the accumulator 154 as a hydraulic pressure source.

On the other hand, if it is determined that the average value <ΔP _n > is not within the set range and the hydraulic pressure booster 12 and the like are abnormal, abnormality occurrence information is output, and the electromagnetic on-off valve 1
84 is switched to the closed position, and the first pressurizing chamber 22 is disconnected from the power pressure chamber 78. Further, even if the slip ratio becomes excessive, the anti-skid control is not started, and the electromagnetic directional control valves 188 and 190 are kept at the first position. Further, the alarm device 69 is operated according to the abnormality occurrence information, and the occurrence of the abnormality is notified to the driver.

As described above, in the hydraulic brake device of the present embodiment, the abnormality of the hydraulic booster 12 is detected by the pressure sensor 1.
It is detected based on the 60 output values. For this reason, the differential pressure switch, which is conventionally required, is not required, and the cost of the hydraulic booster abnormality detecting device can be reduced. In addition, the abnormality of the hydraulic pressure booster 12 indicates that the accumulator 154
Since the pressure is detected based on the output value of the pressure sensor 160 which has been conventionally provided to control the hydraulic pressure, the cost can be further reduced.

Further, based on the detection value of the pressure sensor 160, there is an advantage that not only abnormality of the hydraulic pressure booster 12 but also abnormality of liquid leakage can be detected. Also, the first pressurizing chamber 2
2, a hydraulic pressure having a height corresponding to the depression of the brake pedal 94 is generated.
Since the brake fluid is mainly supplied from the power pressure chamber 78, the first pressurizing piston 18 hardly moves forward, and the depression stroke of the brake pedal 94 is correspondingly small.

In the above embodiment, the average value <Δ
P_nIs determined between the upper limit and the lower limit.
It is determined whether it is smaller than the lower limit
It may just be done. The hydraulic booster 12 is abnormal
Whether or not there is an average value <ΔP _n> Is less than the lower limit
This is because the determination can be made only based on whether or not the determination is made. In addition, hydraulic
The average value of the pressure drop amount for a plurality of times <Δ
P_n>, But the average
Instead of a value, it is detected based on the amount of one pressure drop
It may be. In that case, despite being normal
Is incorrectly determined to be abnormal, and the anti-skid control
Execution may be prohibited or an alarm may be issued.
Gain, but then anti-skid control
If the execution prohibition etc. of the is canceled, it does not matter. In addition, liquid
The determination of abnormality of the pressure booster 12 is based on the operation of the brake pedal 94.
It may be performed only when the work force is above the set value.
No. In this way, detection is performed based on the amount of pressure decrease at one time.
Even if it is issued, erroneous determination can be reduced.

Further, in the above embodiment, when the abnormality of the hydraulic booster 12 is detected, the execution of the anti-skid control is prohibited. However, the abnormality of the hydraulic booster 12 is notified. It may just be done. Further, the present invention can be applied to a hydraulic brake device not provided with an anti-skid control device. Further, the present invention can be applied not only to a vehicle hydraulic brake device but also to a machine tool or the like having a hydraulic device.

In the above embodiment, the hydraulic pressure of the accumulator 154 is supplied to the wheel cylinders 34 and 36. However, the hydraulic pressure of the accumulator 154 may not be supplied. Further, the hydraulic pressure control 110
Is connected to at least the accumulator 154 and the reservoir 64, and controls the communication state between the power pressure chamber 78 and the accumulator 154 or the reservoir 64 in accordance with the operation force of the brake pedal 94, Any mode may be used as long as the hydraulic pressure of the accumulator 154 is reduced according to the operating force of the brake pedal 94 and the hydraulic pressure can be transmitted to the power pressure chamber 78. Although not specifically exemplified, the present invention can be implemented in various modified and improved forms based on the knowledge of those skilled in the art without departing from the scope of the claims.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an entire hydraulic brake device including a hydraulic booster abnormality detecting device according to an embodiment of the present invention.

FIG. 2 is a graph showing a state in which the accumulator pressure is reduced when a brake pedal is depressed in the hydraulic brake device.

[Explanation of symbols]

 Reference Signs List 12 hydraulic booster 56 control device 72 power piston 78 power pressure chamber 94 brake pedal 102 brake switch 110 control valve 154 accumulator 160 pressure sensor

Claims (1)

(57) [Claims] 1. An apparatus for detecting an abnormality of a hydraulic booster having a hydraulic pressure control valve for controlling a hydraulic pressure of an accumulator to a power pressure corresponding to an operating force of an operating member and a power piston operated by the power pressure. A pressure drop amount detecting means for detecting a pressure drop amount of the accumulator when the operating member is changed from a non-operating state to an operating state; and a pressure drop amount detected by the pressure drop amount detecting means is larger than a set value. A hydraulic booster abnormality detecting device for determining that the hydraulic booster is abnormal when the value is smaller.