JPH02221B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved actuator for an anti-skid device that prevents wheels from locking.

The anti-skid device consists of a wheel speed detector that constantly detects the rotational speed of the wheels, a control unit that calculates and logically processes the deceleration, slip rate, etc. of the wheels based on the signals from the wheel speed detector, and and an actuator that controls the brake pressure in the brake cylinder based on the signal.

Among these, some actuators for anti-skid devices have the following configuration. (For example, see Utility Model Application Publication No. 53-124993.) In other words, a cut valve that blocks the passage connecting the master cylinder and the brake cylinder, a pressure chamber provided between the cut valve and the brake cylinder, and a pressure chamber that moves inside the housing. a servo piston that is freely arranged and partitions a variable pressure chamber and a low pressure chamber that is constantly in communication with a low pressure source; a hydraulic plunger that opens and closes the cut valve and increases or decreases the volume of the pressure chamber by movement of the servo piston; A switching valve that connects a chamber to the low pressure source and a high pressure source, and a spring that is provided in the low pressure chamber and biases the hydraulic plunger through the servo piston in a direction in which the cut valve opens. There is something I did.

In this type of actuator, when the wheels tend to lock up due to applying excessive brake pressure while the vehicle is running on a low-friction road surface such as an icy road, a brake pressure release signal is used to switch the switching valve to increase the pressure in the transformation chamber. The hydraulic plunger is moved in the direction in which the cut valve closes and the volume of the pressure chamber increases (movement in this direction is referred to as 〓backward〓
) to reduce the brake pressure to near zero. This is because the friction coefficient of the road surface is small, so the resistance that the tires receive from the road surface is small, and in order to recover the wheel rotation due to this small resistance, the braking force due to the brake pressure must be smaller than the recovery rotational force due to this resistance. This is because it has to be done. Note that the required retraction amount of the hydraulic plunger is approximately proportional to the magnitude of the brake pressure in the brake cylinder immediately before the actuator is actuated.

However, on a low-friction road surface, even if the brake pressure is reduced to near zero, the recovery of wheel rotation is slow, and the brake pressure release signal from the control unit continues to be generated for a relatively long time, causing the switching valve to reduce the pressure in the transformation chamber to high pressure. The state of communicating with the source often continues.

Therefore, in the case where the hydraulic plunger and the servo piston can come into contact with each other and separate from each other, even after the brake pressure in the brake cylinder becomes zero and the hydraulic plunger stops moving backward, the servo piston continues to move backward, causing the servo piston to move back. A so-called servo piston overstroke, in which the piston moves away from the hydraulic plunger, often occurs.

In addition, in the case where the hydraulic plunger and the servo piston are integrated, the hydraulic plunger continues to move backward even after the brake pressure in the brake cylinder becomes zero, increasing the volume of the pressure chamber and increasing the pressure on the brake cylinder side. This will cause negative pressure to occur.

Therefore, when the above occurs, even if the brake pressure release signal disappears and the brake pressure build-up signal is generated, the servo piston moves forward, canceling the overstroke and restarting the servo. The brake pressure remains below zero until the piston contacts the hydraulic plunger or until the hydraulic plunger moves forward together with the servo piston to reduce the volume of the pressure chamber and eliminate the negative pressure generated in the brake cylinder. There is a problem in that the braking distance is not increased, but the brake pressure release period becomes longer, and the brake pressure becomes too relaxed and the braking distance increases.

In an attempt to solve these problems,
An example of providing a valve that shuts off the passage connecting the switching valve and the variable pressure chamber by the movement of the hydraulic plunger away from the servo piston (see Japanese Patent Application Laid-open No. 47-43673), when negative pressure is generated on the brake cylinder side of the cut valve. An example of installing a valve that communicates the brake cylinder side with the master cylinder side (Japanese Patent Laid-Open No. 53
-Refer to Publication No. 57369), but in the former case, even if the switching valve switches to communicate the variable pressure chamber with the low pressure source, the valve overcomes the spring force that biases it in the valve closing direction. Since the hydraulic plunger does not open until a pressure difference is created, the hydraulic plunger does not move forward immediately in response to switching of the switching valve, and as a result, the above-mentioned problem cannot be reliably solved. Also, in the latter case,
Since the hydraulic fluid on the master cylinder side is supplied until there is no negative pressure on the brake cylinder side, there is a drawback that the amount of operation of the master cylinder suddenly increases, making the driver feel uneasy.

The present invention has been made in view of the above-mentioned problems, and is an anti-skid device that prevents an increase in the braking distance by setting the servo piston in a state that can prevent excessive movement of the servo piston in advance when the brake is applied on a low-friction road surface. In order to achieve this purpose, in response to a low friction road surface signal being output from a road surface discriminator that determines the coefficient of friction of the road surface at the start of braking, the servo piston's maximum It is equipped with an adjuster that adjusts the amount of movement to a small value.

By doing this, when the brakes are applied while driving on a low-friction road surface, the regulator operates to reduce the maximum travel distance of the servo piston, so that the brake pressure release signal that occurs after the start of brake application is In response, the servo piston retracts the hydraulic plunger until the brake pressure is reduced to zero, and even if the brake pressure release signal continues to be generated, the servo piston is prevented from retracting by the regulator. Therefore, after the brake pressure is reduced to zero, the servo piston does not move away from the hydraulic plunger or retract the hydraulic pressure so as to cause the plunger to create a negative pressure on the brake cylinder side. In response, the brake pressure can be increased immediately.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIG. 1 is an overall view of a brake device including an actuator for an anti-skid device according to an embodiment of the present invention.

1 is an actuator for an anti-skid device, and the actuator 1 is composed of a hydraulic section A, a servo section B, a switching valve section C, and a regulator D.

A cylinder 3 containing a cut valve 2 is arranged in the hydraulic section A. The cut valve 2 is composed of a sphere 4 and a valve seat 5. The valve seat 5 is formed on the side surface of a protrusion 7 provided on the inner wall of the cylinder hole 6 of the cylinder 3, and the sphere 4 is movable into the cylinder hole 6. The valve seat 5 is inserted into the valve seat 5 and is constantly pressed toward the valve seat 5 by a pressing spring 8. The inlet port 9 of the cylinder 3 communicates with a separate tandem master cylinder 11 via a conduit 10, and the outlet port 12 communicates with a separate tandem master cylinder 11 via a conduit 10.
It communicates with brake cylinders 16, 17 of separately provided rear wheels 14, 15 via. This cut valve 2 moves the ball 4 in response to the retreat of the hydraulic plunger 24.
By seating on the valve seat 5, communication between the master cylinder 11 and the brake cylinders 16 and 17 is cut off. The master cylinder 11 is connected to the front wheel 1 through a conduit 18 separate from the system on the conduit 10 side.
It also communicates with brake cylinders 21 and 22 of 9 and 20. Reference numeral 50 denotes a brake switch attached to the vehicle body opposite to the brake cylinder 51, and the switch 50 becomes conductive when the brake pedal 51 is depressed.

Further, on the right side of the cylinder hole 6 with respect to the cut valve 2, there is provided a pressure chamber 23 with a variable volume that constantly communicates with the brake cylinders 16 and 17. The hydraulic plunger 24 has a left end that can move into and out of contact with the sphere 4 in order to open and close the cut valve 2, and a right end that can move into and out of contact with the servo piston 37, and has a right end that moves into and out of the cylinder hole 6 to increase or decrease the volume of the pressure chamber 23. is movable. 25 is a spacer placed on the stepped portion 26 of the cylinder 3, and 27 is the pressure chamber 23 and a variable pressure chamber 35, which will be described later.
28 is a ring that protects the seal cup 27, 29 is a spacer, 3
0 is a fixing member for fixing the spacer 29, and 31 is a dust seal fitted onto the protrusion of the fixing member 30.

A housing 32 is installed in the servo section B, and an opening 34 is closed in the housing 32 by a lid 33 bolted to the cylinder 3.
Further, the housing 32 has a servo piston 3 that divides the inside thereof into two chambers, a variable pressure chamber 35 and a low pressure chamber 36.
7 is inserted. The piston 37 is in the variable pressure chamber 3
It is movable along the outer circumferential surface 38 of the cylinder 3 according to the pressure difference between the cylinder 5 and the low pressure chamber 36. Further, a seat 39 that comes into contact with the hydraulic plunger 24 is attached to the servo piston 37 . 40 is a diaphragm, and the diaphragm 40
and the low pressure chamber 36,
Servo piston 37, housing 32 and lid 33
Both the inner and outer circumferential edges are fixed by the servo piston 37, forming an assembly with the servo piston 37. 41 is the cylinder 3 and the lid 33
The seal ring 41 maintains airtightness between the variable pressure chamber 35 and the atmosphere surrounding the actuator 1, which is a high pressure source. Further, a spring 44 is tensioned in the low pressure chamber 36 with an elastic member 43 interposed between the bottom surface 42 of the housing 32 and the servo piston 37. A conduit 45 is welded to the housing 32 with one end opened to a low pressure chamber 36, and the conduit 45 is connected to the intake manifold 4 of the engine, which is a low pressure source, through a conduit 53 and a check valve 47.
8, so that the low pressure chamber 36 and the low pressure source are always in communication.

The switching valve section C consists of a two-position valve 52, and the valve 52
communicates with the intake manifold 48 and the variable pressure chamber 35 via a conduit 53 and a check valve 47, respectively,
A first position e that blocks communication between the variable pressure chamber 35 and the atmosphere, which is a high pressure source; and a second position f that blocks communication between the variable pressure chamber 35 and the intake manifold 48 and communicates the variable pressure chamber 35 with the atmosphere. and has. The solenoid 56 of the valve 52 is connected to a separate control unit 55.
make an electrical connection. The control unit 55 is
Equipped with a known circuit configuration, wheels 14 (not shown),
It is electrically connected to a wheel speed detector that constantly detects the rotation speed of 15. The control unit 55 receives the signal from the wheel speed detector, calculates the wheel speed, deceleration, acceleration, slip rate, etc., and supplies a brake pressure release signal to the solenoid 56 based on the results of these calculations.

The solenoid 56 of the valve 52 is demagnetized when the control unit 55 is not generating a brake pressure release signal, that is, when applying brake pressure, the valve 52 is in the first position e, and the brake pressure release signal is not generated. When this occurs, it is energized and the valve 52 is switched to the second position f.

The regulator D includes an adjustment circuit 57, an adjustment valve 58, and an adjustment action section 59, and adjusts the maximum movement amount of the servo piston 37.

As shown in FIG. 2, the adjustment circuit 57 uses an output terminal 60 of the brake switch 50, an output terminal 61 of a pressure switch 85 (described later), and an output terminal 62 of the control unit 55 as input terminals. Terminal 61 is connected to the negative input terminal of AND circuit 63. The other input terminal of the AND circuit 63 is the terminal 6
Connect with 2. Further, the output terminal of the AND circuit 63 is connected to an off delay timer 64. The off-delay timer 64 outputs 1 when the input becomes 1, and thereafter holds 1 for a predetermined time even if the input becomes 0. The output terminal of the timer 64 is an AND circuit 65
Connect to one input end of the The other input end of the AND circuit 65 is connected to the terminal 61. AND circuit 6
The output terminal of 5 is connected to an off delay timer 67. This off-delay timer 67 is the previous off-delay timer 64.
It has the same effect as . The output terminal of the off-delay timer 67 is connected to the negative input terminal of an AND circuit 68. Further, the other two input terminals of the AND circuit 68 are connected to the terminal 60 and the terminal 61, respectively. The output end of the AND circuit 68 is connected to a solenoid 69 of the regulating valve 58.

The regulating valve 58 consists of a two-position valve, and the valve 58 includes:
A first position g that connects the conduit 70 and the conduit 71 connected to the conduit 53 and blocks the communication between the conduit 71 and the atmosphere;
It has a second position h that communicates the conduit 71 with the atmosphere. The solenoid 69 is demagnetized when the output of the regulating circuit 57 is 0, the valve 58 is in the first position g,
When the output of the adjustment circuit 57 becomes 1, it is excited and the valve 58
switches to the second position h.

A frame body 73 having an opening 72 is fixed to the adjustment action portion 59 so as to protrude from the housing bottom surface 42 . 74 is a cylinder;
is fitted between the frame 73 and a protrusion 75 protruding from the housing bottom surface 42 into the housing 32 . 76 is an adjustment piston, and the piston 76 forms a notch passage portion 77 at the right end,
It is fitted so as to be movable along the cylinder 74. Then, the frame 73, the cylinder 74, the protrusion 7
5 and the adjusting piston 76 form a chamber 78 and a chamber 79. Room 78 is notch passage section 7
It is in constant communication with a conduit 71 via 7. The adjustment piston 76 is always urged rightward by a spring 80, and normally comes into contact with the frame 73, that is, is located at the right end of the movement range, and when the adjustment valve 58 is switched to the second position h, When the atmosphere is introduced into the adjusting piston 78, the adjusting piston 76 moves to the left against the urging force of the spring 80 and comes into contact with the protrusion 75, that is, it is located at the left end of the movement range. The servo piston 37 is attached to the protrusion 75.
An opening 81 larger than the diameter of the servo piston tip 37' is formed so that the tip 37' can come into contact with the adjustment piston 76, and an opening 81 is formed that is larger than the diameter of the servo piston tip 37'.
It communicates with 6.

The adjustment piston 76 functions to limit movement of the servo piston 37 to the right. This adjustment piston 76 can hold the servo piston 37 at a position where it contacts the protrusion 75, and the conditions for this holding are as follows.

That is, although the diameters of the left and right surfaces of the adjustment piston 76 shown in FIG. The force is the product of the biasing force of the servo piston 37 that contacts the adjustment piston 76 and biases it in the right direction, the biasing force of the spring 80, the effective pressure receiving area of the left surface of the adjustment piston 76, and the pressure in the low pressure chamber 36. It is sufficient that the force is greater than the force acting on the left surface of the adjustment piston 76 due to the sum of the forces.

82 and 83 are seal rings that maintain airtightness between the chamber 78 and the chamber 79; the seal ring 82 fits around the outer periphery of the piston 76, and the seal ring 83
fits into the groove of the cylinder 74. 84 is room 79
This is a seal ring that maintains airtightness between the air and the atmosphere.

The pressure switch 85 is a road surface discriminator that discriminates the coefficient of friction of the road surface. This pressure switch 85 has
A casing 88 is provided which is formed by a member 86 and a member 87, both of non-conductive material. 89 is a pressure piston made of an electrically conductive material, and the piston 89 divides the inside of the casing 88 into a chamber 90 and a chamber 91.
is fitted into the casing 88 so as to be movable along the sliding surface 93 of the member 86, and the central portion 101 is movable along the groove surface 94 formed by both the members 86 and 87. Further, the room 90 is connected to the conduit 13 via the conduit 96.
It communicates with Furthermore, a seal ring 95 is fitted around the outer periphery of a tip end 92 of the piston 89 to provide a liquid-tight seal between a chamber 90 and a chamber 91 . Also,
The pressure piston 89 is constantly biased to the left by a spring 97 provided in the chamber 91. in this case,
The biasing force of the spring 97 is such that the pressure inside the chamber 90 is 40 kg/
cm ² , the size is such that the forces acting on the piston 89 in the left and right directions are balanced. This value of 40 kg/cm ² is set when driving on a low-friction road surface, and when the driver applies the brakes, the wheels tend to lock and actuator 1 is activated before the brake pressure rises to 40 kg/cm ² . However, this is due to the fact that the brake pressure is designed not to exceed 40 kg/cm ² .
Reference numerals 98 and 99 indicate hanging rods made of a conductive material, and the hanging rods 98 and 99 are fixed to the member 87 so as to protrude inwardly and outwardly thereof. Hanging rod 98 is electrically connected to battery power source 100, while hanging rod 99 is electrically connected to regulating circuit 57. And spring 97
If the urging force applied to the right side of the piston 89 by the pressure fluid is larger than the urging force applied to the left side of the piston 89 by the pressure fluid, the piston 89 and the suspension rod 9
8 and 99 are in contact with each other, and the pressure switch 85 is in the conductive state.In the opposite case, the piston 89 and the suspension rods 98 and 99 are separated, and the pressure switch is in the cutoff state.

Further, when the adjustment piston 76 is in contact with the protrusion 75, that is, located at the left end of the movement range, and the servo piston 37 is in contact with the lid 33, the distance between the adjustment piston 76 and the servo piston 37 is the distance between the brake cylinder Brake pressure in 16 and 17 is 40Kg/
cm ² , the brake cylinders 16 and 17 are
This is the distance necessary to reduce the internal pressure to zero.

Further, the adjustment piston 76 comes into contact with the frame 73,
That is, it is located at the right end of the movement range, and the servo piston 37
when the adjusting piston 7 is in contact with the lid 33
6 and the servo piston 37, the brake pressure in the brake cylinders 16 and 17 is 100Kg/cm ²
This distance is required to bring the pressure in the brake cylinders 16, 17 to zero by retracting the servo piston 37 and the hydraulic plunger 24 at this time.

The operation of the actuator 1 for an anti-skid device having such a configuration will be described below.

The figure shows the actuator 1 in a non-operating state when the driver is not depressing the brake cylinder 51. That is, the two-position valve 52 is in the first position e.
The variable pressure chamber 35 and the low pressure chamber 36 are both at a low pressure equal to the pressure inside the intake manifold 48, and the servo piston 37 comes into contact with the back surface of the lid 33 due to the biasing force of the spring 44, and the hydraulic plunger 24
opens the cut valve 2 and opens the master cylinder 11.
and the brake cylinders 16, 17. Also, since the brake switch 50 is in the cutoff state and the pressure inside the conduit 96 is zero, the pressure switch 8
5 is in a conductive state, but the brake cylinder terminal 6
0 is in the cutoff state, so the solenoid 69 is demagnetized and the two-way valve 58 is in the first position. Therefore, the chamber 78 of the adjustment action section 59 is in a low pressure state, and the adjustment piston 76 is in contact with the frame 73 due to the biasing force of the spring 80.

Suppose that in such a state, the driver depresses the brake pedal 51 while the vehicle is running so as to generate brake pressures of the following magnitudes.

[When the brake pressure is 40 kg/cm ² or less] In this case, the output of the terminal 60 of the brake switch 50 is 1, and the pressure switch 85 is
Since the pressure piston 89 is in contact with the suspension rods 98 and 99 and is in a conductive state, that is, in a state where a low friction road surface signal is output, the output of the terminal 61 in FIG. Regardless of the output state, the outputs of the AND circuit 63, timer 64, AND circuit 65, and timer 67 are 0, and the output of the AND circuit 68 is 1.
Therefore, the solenoid 69 is energized and excited. Therefore, the two-position valve 58 is switched to the second position h, the atmosphere is introduced into the chamber 78 of the adjustment action section 59, and the adjustment piston 76 moves to the left against the tension of the spring 80 and protrudes. It is held in contact with the portion 75. That is, it is located at the left end of the movement range.

Therefore, if the driving road surface is a low friction road surface,
When the wheels show a tendency to lock due to the driver's braking action, the solenoid 56 is energized by a brake pressure release signal from the control unit 55, the two-position valve 52 is switched to the second position f, and the atmospheric pressure is changed. It is introduced into the chamber 35. Therefore, the assembly of the servo piston 37 and the diaphragm 40 moves back to the right against the biasing force of the spring 44. As this assembly retreats, the hydraulic plunger 24 receiving hydraulic pressure from the master cylinder 11 also retreats,
Cut valve 2 closes. After that, when the atmosphere is further introduced into the variable pressure chamber 35, the servo piston 37 moves back further, and the hydraulic plunger 24
is also moved backward by the pressure already supplied to the brake cylinders 16 and 17, and the volume of the pressure chamber 23 increases. As a result, the pressure supplied to the brake cylinders 16, 17 is reduced, the rotation of the rear wheels 14, 15 is restored, and locking is prevented.

At this time, as described above, the adjustment piston 76
Since the servo piston 37 is held close to the servo piston 37 side, the amount of movement of the servo piston 37 until it comes into contact with the adjustment piston 76 is small.

The servo piston 37 then adjusts the adjustment piston 7.
6, there is no further retraction of the servo piston 37 even though the brake pressure release signal is still occurring. That is, there is no overstroke of the servo piston 37. Thereafter, when the rotation of the wheel is restored, the brake pressure release signal from the control unit 55 disappears, and the degaussing signal is transmitted to the solenoid 56, the valve 52 is switched to the first position e, and the pressure inside the transformation chamber 35 is The pressure decreases and the servo piston 37 and diaphragm 40 assembly advances to the left. At this time, the hydraulic plunger 24
Since it remains in contact with the servo piston 37,
It moves forward in response to the forward movement of the servo piston 37.
Therefore, the volume inside the pressure chamber 23 immediately decreases,
The brake pressure in the brake cylinders 16, 17 increases quickly.

Then, if the brake pressure increases too much, valve 5
2 switches again to e position, and brake cylinder 1
The brake pressure in 6, 17 drops again.

In addition, if the driving road surface is a high friction road surface,
The wheels show no tendency to lock, the valve 52 does not switch, and the servo piston 37 does not retract. Therefore, the cut valve 2 is kept open, and the brake pressure generated in the master cylinder 11 is directly transmitted to the brake cylinders 16 and 17.

[When the brake pressure is greater than 40Kg/ ^cm2 ] In this case, apply to a road surface with high friction. That is, the hydraulic pressure in the chamber 90 that biases the pressure piston 89 to the right becomes greater than the biasing force of the spring 97 that acts on the pressure piston 89 to the left, and the pressure piston 89 moves to the right, causing the suspension rod to move. 98,9
9, the pressure switch 85 is shut off.

In this case, in FIG. 2, the output of the terminal 60 of the brake switch 50 is 1, the output of the terminal 61 of the pressure switch 85 is 0, and the output of the AND circuit 68 is 0, so the solenoid of the regulating valve 58 is 69 is demagnetized. Therefore, the regulating valve 58 is switched to the first position g again, the pressure in the chamber 78 of the regulating action section 59 becomes low again, and the regulating piston 76 moves to the right inside the cylinder 74 by the biasing force of the spring 80. and is held at the right end of the movement area. Therefore, the amount of movement of the servo piston 37 until it comes into contact with the adjustment piston 76 becomes large.

When this brake pressure is greater than 40 kg/cm ² and the wheels show a tendency to lock, the control unit 55 generates a brake pressure release signal, the valve 52 is switched to the second position f, and the pressure changer chamber is filled with air. is introduced, the assembly of the servo piston 37 and the diaphragm 40 moves to the right against the biasing force of the spring 44, and the hydraulic plunger 24 also moves accordingly.

Therefore, the volume inside the pressure chamber 23 increases, and the brake pressure inside the brake cylinders 16 and 17 increases by 40°C.
It may drop below Kg/ ^cm2 . However, before the brake pressure drops to 40 kg/cm ² or less, the output of the pressure switch terminal 61 is 0, and the output of the control unit terminal 62 is 1, so the output of the AND circuit 63 is 1. Yes, timer 6
4 is activated and outputs 1. Therefore, when the brake pressure decreases below 40 kg/cm ² and the output of the terminal 61 becomes 1, the output of the AND circuit 63 becomes 0, but the timer 64 maintains the output at 1 for a predetermined period of time, and the AND circuit The output of 65 becomes 1. Therefore, the output of the timer 67 becomes 1 and the AND circuit 6
8 is set to 0, and the solenoid 69 of the regulating valve 58
is demagnetized and the adjustment piston 76 is held at the right end of the movement range. If the output of the timer 64 becomes 0 while the brake pressure remains below 400 kg/cm ² , the output of the AND circuit 65 becomes 0, but the output of the timer 67 remains at 1 for a predetermined period of time. Therefore, the adjustment piston 76 is held at the right end of the movement range as described above.

Thereafter, the rotation of the wheel is restored, the valve 56 is switched to the first position e, and the brake pressure is increased to 40 kg/cm ² again.
If it becomes larger, the output of terminal 61 becomes 0.
Therefore, the output of the AND circuit 68 is still 0,
The adjustment piston 76 is held at the right end of the movement range.

In this way, even if the locking tendency occurs when the brake pressure is 40 kg/cm ² or more, the adjustment piston 76 that determines the maximum amount of movement of the servo piston 37 remains held at the right end of the movement range, and the servo piston 37
The amount of movement of brake cylinder 7 is large, and brake cylinder 16,
The amount of rightward movement of the hydraulic plunger 24 necessary to bring the pressure inside the hydraulic plunger 17 to zero is ensured. In reality, because the frictional force between the high-friction road surface and the tires is large,
Before the pressure in the brake cylinders 16, 17 drops to near zero, the rotation of the wheels is restored, the output of the control unit 55 becomes zero, and the valve 52 switches to the first position e. Then, hydraulic plunger 2
4 maintains a state of contact with the servo piston 37, so it immediately moves forward to the left together with the servo piston 37, and the brake pressure in the brake cylinders 16, 17 increases.

Then, if that brake pressure increases too much,
Switch valve 52 to position e to reduce brake pressure again.

Further, when the road surface is rapidly changed from a high-friction road surface to a low-friction road surface when the brake is applied, the following is the case.

The brake pressure applied when driving on a high friction road is 40
When it is greater than Kg/cm ² , the valve 58 is in the first position g and the adjusting piston 76 is at the right end of its travel range, as described above. At this time, suppose, for example, that the wheels do not show a tendency to lock. If the vehicle suddenly encounters a low-friction road surface in this state, the wheels tend to lock up. In this case, the brake pressure is reduced to 40 kg/cm ^{2 or} less by a command from the control unit 55, but the solenoid 69 maintains a demagnetized state, and the maximum movement amount of the servo piston 37 is large. Therefore, the amount of movement of the hydraulic plunger 24 necessary to reduce the brake pressure before the wheel shows a locking tendency to zero after the wheel shows a locking tendency is secured, and the brake pressure in the brake cylinders 16, 17 is secured. There is no such thing as low pressure or lack of pressure.

Then, when the rotation of the wheel is restored and the valve 52 is switched to the first position e, the hydraulic plunger 24 immediately moves to the left together with the servo piston 37,
Brake pressure increases quickly.

Even if the brake pressure is 40 Kg/cm ² or higher and the wheels tend to lock, even if the vehicle enters a low-friction road surface, the adjusting piston 76 is held at the right end of its travel range in the same way as described above.

If the brake pressure applied by the driver is less than 40Kg/ ^cm2 , even if it is greater than 40Kg/ ^cm2 , when the brake pressure control is finished and the vehicle reaches the desired speed,
or when the driver stops, the driver presses the brake pedal 51
Release the pressure. With this release, the brake pressure in the master cylinder 11 decreases and the cut valve 2 opens, so the brake cylinder 16,
Brake fluid from 17 to conduit 13, outlet port 1
2, the pressure chamber 23, the inlet port 9, and the conduit, and the brake fluid from the brake cylinders 21, 22 passes through the conduit 18 to the master cylinder 11.
Reflux to.

In this way, in this embodiment, the coefficient of friction of the road surface is determined by the pressure switch 85, which detects whether the magnitude of the brake pressure in the brake cylinders 16, 17 is below a predetermined value (40 kg/cm ² ). and an adjustment piston 7 that adjusts the amount of movement of the servo piston 37 to a small value according to the output of the switch 85.
6 is activated, the wheels tend to lock due to the braking action when driving on low-friction roads.
When the control unit 55 operates and the servo piston moves back to the right, the servo piston 37
The amount of movement is reduced by the adjustment piston 76 that has moved to the left end of the movement range, and overstroke of the servo piston 37 is prevented. Therefore, immediately after the brake pressure release signal disappears, the hydraulic plunger 2
4 is pressed by the servo piston 37 and moves forward to the left, and the brake pressure in the brake cylinders 16 and 17 immediately increases, so that sufficient brake pressure can be applied to the wheels without increasing the control distance.

In addition, when driving on high-friction roads, the specified value (40Kg/cm ² )
When applying the brakes with higher pressure, the road surface suddenly shifts to a lower friction surface and the wheels tend to lock up.
When the brake pressure is controlled below the predetermined value,
Since the adjustment piston 76 is held at the right end of its movement range, the maximum movement amount of the servo piston 37 is large, and the pressure inside the brake cylinders 16 and 17 can be reliably reduced to near zero, thereby preventing insufficient brake reduction. do not have.

It should be noted that the present invention is not limited to the illustrated embodiment, and modifications can be made based on the technical idea of the present invention.

For example, the biasing force of the spring 97 of the pressure switch 85 that determines the friction coefficient of the road surface is large enough to balance the forces acting in both the left and right directions of the pressure piston 89 when the pressure in the brake cylinders 16 and 17 is 40 kg/cm ² . However, the size of 40Kg/cm ² is not absolute and can be changed.

In addition, the adjustment piston 76 located at the right end of the movement range
The distance between the servo piston 37 and the servo piston 37 in contact with the lid 33 is the distance between the servo piston 37 and the servo piston 37 when the brake pressure in the brake cylinders 16 and 17 is 100 kg/ ^cm2.
Although the distance is required to reduce the pressure to zero by retreating, the distance does not have to be equivalent to 100 kg/cm ² .

Further, the holding position of the adjustment piston 76 has only two positions, the right end of the movement range and the left end of the movement range, depending on whether the pressure in the brake cylinders 16, 17 is below a predetermined value (40 kg/cm ² ). However, when the pressure in the brake cylinders 16 and 17 is at a plurality of predetermined values with different magnitudes, the servo piston 37
may be stopped in stages in the middle of its movement range, or may be analog displacement in which movement is stopped continuously.

Furthermore, a deceleration response switch attached to the vehicle body may be used instead of the pressure switch 85 as a road surface discriminator for discriminating the coefficient of friction of the road surface.

In addition, it is introduced into the chamber 78 of the adjustment action section 59,
The high pressure source acting on the right side of the adjusting piston 76 may be compressed air instead of the atmosphere.

Although the two-position valve 52 is used as the switching valve, the three-position valve 52 has an intermediate position to maintain brake pressure.
It may also be a position valve.

In addition, the servo piston 37 and the adjustment piston 76
A buffer member may be attached to at least one of the contact surfaces.

Further, the actuator 1 may be provided separately for the rear wheels 16 and 17, and the wheel speed detector and the actuator 1 may be separately provided for the front wheels 19 and 20 as well.

Further, the present invention can also be applied to an actuator in which a hydraulic plunger is integrated with a servo piston.

As is clear from the above, according to the present invention, the maximum travel distance of the servo piston is adjusted to a smaller value in response to a low friction road surface signal being output from the road surface discriminator that determines the coefficient of friction of the road surface at the start of brake operation. The provision of a regulator prevents the movement of the servo piston, which would be ineffective when applying brake pressure, and allows the pressure to rise quickly after the pressure drops, thereby reducing the braking distance. It has the effect of preventing

[Brief explanation of drawings]

FIG. 1 is an overall view of a brake system including an actuator for an anti-skid device showing one embodiment of the present invention, and FIG. 2 is a detailed view of the adjustment circuit shown in FIG. 1. 37... Servo piston, 57... Adjustment circuit, 58
...Adjustment valve, 59...Adjustment action section, 85...Pressure switch.

Claims (1)

[Claims] 1. A cut valve that blocks the passage connecting the master cylinder and the brake cylinder, a pressure chamber provided between the cut valve and the brake cylinder, and a low pressure chamber that is movably arranged inside the housing and constantly communicates with the variable pressure chamber and a low pressure source. A servo piston that partitions the chamber, a hydraulic plunger that opens and closes the cut valve and increases or decreases the volume of the pressure chamber by movement of the servo piston, and communicates with the variable pressure chamber so that it can be freely switched between the low pressure source and the high pressure source. and a spring provided in the low pressure chamber and urging the hydraulic plunger via the servo piston in the direction in which the cut valve opens. An actuator for an anti-skid device, characterized in that an adjuster is provided for adjusting the maximum travel amount of the servo piston to a smaller value in response to a low friction road surface signal outputted from a discriminator at the start of brake operation.