Hydraulic Brake System

The invention relates to a hydraulic brake system as defined hereinafter.

Hydraulic brake systems, as they are used in motor vehicles, have a master brake cylinder that is mechanically actuated by a brake pedal, causing the buildup of a corresponding brake pressure in the brake lines leading to the wheel brake cylinders. To prevent locking of the wheels, or skidding, so-called anti-lock or anti-skid brake systems (ABS) are known, in which the brake pressure is reduced as soon as skidding is detected or is at least imminent. To this end, a hydraulic cylinder disposed between the master brake cylinder and the wheel brake cylinder can be provided, the piston of which, by mechanical actuation, effects a lowering or modulation of brake pressure. The additional hydraulic cylinder may also be disposed such that an increasing of brake pressure is attained when it is mechanically actuated. In that case, the hydraulic cylinder functions as a brake booster. A buildup of brake pressure at the driven wheels that is independent of the driver offers the opportunity for anti-slip regulation (ASR).

U.S. Pat. No. 4,083,609 discloses a hydraulic cylinder the piston of which is displaceable via its piston rod by a positioning mechanism embodied as an electromagnet. However, the use of an electromagnet as the positioning mechanism has the disadvantage that the system is relatively sluggish and is unsuited to relatively large piston deflections and cannot bring to bear the great forces appropriate for the pressures involved.

The new hydraulic brake system disclosed herein has the advantage over the prior art that an electric-motor-driven centrifugal positioner can be accelerated quickly and makes great tractive or pressure forces possible. The tractive or pressure forces can also be apportioned very sensitively by means of appropriate speed governing.

The piston disposed in the hydraulic cylinder can be supported in floating fashion, with the piston communicating on one end wiht the master brake cylinder and on the other end with one or more wheel brake cylinders. If the master brake cylinder is now actuated, then the piston inside the cylinder shifts out of its position of repose, causing the pressure in the brake lines leading to the wheel brake cylinders to be increased. If there is a tendency to skidding or wheel locking, this can be detected by a well known electronic anti-skid system, and the electric motor associated with the centrifugal positioner can be put into operation via electrical control switches. With the tractive or pressure forces derived from the centrifugal positioner, the floatingly supported piston is thereby moved at least slightly toward its outset position, causing a corresponding pressure drop in the brake lines leading to the wheel brake cylinders and preventing locking of the wheels.

The centrifugal positioner may be embodied in a manner known per se, such that it converts centrifugal force into tractive or pressure forces. Via articulated levers, the forces of rotation are converted into translational forces. Spring elements may also engage the centrifugal positioner, causing it to assume a defined final position when at a standstill.

The hydraulic cylinder may also be connected to a branch brake line, in order to effect a brake pressure increase, or optionally a brake pressure reduction, when the hydraulic cylinder is actuated by means of the centrifugal positioner.

The use of a centrifugal positioner has the advantage of high adjustment speed or dynamics, as compared with conventional systems, because the centrifugal positioner always works in one rotational direction. if the engine fails, the brake system according to the invention has the advantage that normal braking action is unimpaired. In this system, it is also unnecessary to monitor the outset position, because as a result of the spring-actuated restoration, the outset position is always automatically reached. With this system, a desired nonlinear transition between normal operation and anti-slip regulation is also possible.

The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings.

FIG. 1 shows a hydraulic brake system having an additional hydraulic cylinder, the piston of which is disposed in a floating manner and is mechanically displaceable via a centrifugal positioner that generates tractive forces;

FIG. 2 shows an arrangement corresponding to FIG. 1, but in which a centrifugal positioner that generates pressure forces is used;

FIG. 3 shows a brake system in which the additional hydraulic cylinder is connected to a branch of the brake line;

FIGS. 3a and 3b show versions of specialized valves for the brake system shown in FIG. 3;

FIGS. 4 and 5 show two exemplary embodiments of centrifugal positioners; and

FIGS. 6a, 6b and 7 show further exemplary embodiments in each of which a centrifugal positioner is associated with the master brake cylinder.

In the brake system shown in FIG. 1, one of a plurality of wheel brake cylinders RBZ and the master brake cylinder HBZ, which is actuatable from a foot pedal 1, are shown. An additional hydraulic cylinder 3 is incorporated into the brake line 2 leading from the master brake cylinder HBZ to the wheel brake cylinder RBZ and has a floatingly supported piston 4. In its position of repose, the piston 4 is pressed against a stop 6 by a compression spring 5. Via a piston rod 7, the piston 4 is connected to a positioning device 8, which has a centrifugal positioner 9 that is actuated by an electric motor M. The positioning device 9 also prevents rotation of the piston 7 relative to the tie rod 10. The tie rod 10 is provided between the piston rod 7 and the centrifugal positioner 9 for transmitting the tractive forces generated by rotations of the centrifugal positioner 9.

The electric motor M is controlled by an anti-skid system ABS, which in a manner known per se monitors locking or a tendency to locking at the wheels 11 and detects locking, if it occurs. If by actuation of the foot pedal 1, the brake pressure in the chamber 12 of the hydraulic cylinder 3 oriented toward the master brake cylinder HBZ is increased, this causes the displacement of the piston 4 in the direction of the arrow b, causing the generation of a corresponding brake pressure in the chamber 13. If the brake pressure in the chamber 13 reaches a value that causes locking of one of the wheels 11, then the electric motor M is put into operation by a signal from the anti-skid system ABS represented in block form. By this means, via the motor shaft 14, the centrifugal adjuster 9 is made to rotate, so that its flyweights 15 are moved outward. Via rotary articulations 16, 17 and via the tie rod 10, the piston 4 is thus retracted counter to the direction of the arrow b, resulting in a lowering of the brake pressure in the chamber 13 at the wheel brake cylinders RBZ. Once the braking event is over, the spring 5 returns the piston 4 to the position shown.

The bypass 18 that is operative between the chambers 12 and 13 has a very severe taper 19, which allows only a long-term pressure equalization or volumetric equalization between the chambers 12 and 13. For the duration of a braking event, this bypass 18 has only a negligible effect on the operability of the system.

In the embodiment of a brake system shown in FIG. 2, instead of a centrifugal positioner that generates tractive force, a centrifugal positioner 20 is used that upon rotation exerts pressure via a pressure rod 21 upon the piston rod 7. Otherwise, the function of this brake system is identical to that of the brake system shown in FIG. 1.

In FIG. 3, another exemplary embodiment is shown, in which the master brake cylinder HBZ communicates with the wheel brake cylinders RBZ via a first electromagnetic stop valve 22. An additional hydraulic cylinder 25, the piston of which is actuatable by means of a centrifugal positioner 26, is connected via a second electromagnetic stop valve 34 to a branch 23. The centrifugal positioner 26 is driven by an electric motor M, which once again is controlled by an anti-skid system ABS. The second stop valve 24 is bridged by means of a check valve 27.

If the master brake cylinder is actuated via the foot pedal 1, the pressure in the brake line 2 rises until such time as a tendency to locking, or locking itself, at the wheel 11 is detected by the anti-skid system ABS. The valve 22 is thereupon closed, and the valve 24 is opened to reduce the brake pressure. The piston 28 located in the hydraulic cylinder 25 is now moved by the brake pressure in the direction of the arrow c, counter to the force of the springs 29, resulting in a reduction of brake force. If the motor shaft 30 is now set into rotation by the electric motor M, the flyweights of the centrifugal positioner move outward in response to the rotation and return the piston 28. This return can also take place with the valve closed, since when the master brake cylinder HBZ is not actuated the brake fluid can be returned via the check valve 27.

In FIG. 3a and FIG. 3b, two versions of 2/2-way valves 22' and 24' are shown, which can be used instead of the valves 22, 24 used in FIG. 3. By using these valves, the check valve 27 (FIG. 3) can be dispensed with.

In FIG. 4, a further variant of a centrifugal positioner is shown, in which the flyweights move outward counter to spring forces, and the piston located in the cylinder is moved in the direction d. In contrast to the embodiments shown in FIGS. 1-3, this variant is used not to effect a primary pressure reduction, but rather a pressure buildup, thereby acting as the pressure producing means of a drive slip regulation system or brake booster.

FIG. 5 shows a version of a centrifugal positioner in which pressure can be exerted upon the piston via articulated rotary cranks 31. For this embodiment, the effect is again as described for FIG. 4.

In the hydraulic brake system shown in FIG. 6a, a centrifugal positioner 32 is used which upon rotation displacesthe associated piston 34 in the hydraulic cylinder 35 in the direction of the arrow e. Instead of the centrifugal positioner 32, the centrifugal positioner 33 shown in FIG. 6b can be used, which upon rotation moves the piston 36 connected to it in the direction of the arrow f. In both cases, upon rotation of the centrifugal positioner, a buildup of pressure in the hydraulic cylinders 35, 37 is attained. Via hydraulic lines 38, the hydraulic cylinders 35, 37 communicate with the master brake cylinder 39, which contains two rigidly coupled pistons 40, 41, which can be actuated by means of a pedal 1 counter to a spring 42. The annular chamber C associated with the piston 41, like the annular chamber D, communicates with a hydraulic supply container VB.

In a manner known per se, a differential pressure switch DDS can recognize a circuit failure if a predetermined pressure difference between the annular chambers C and D is exceeded and can trigger a warning signal; optionally, it can also effect a limitation of the boosting action, to counter the danger of overbraking or of a pressure overload on the intact circuit.

With the centrifugal positioners 32, 33, highly dynamic brake pressure modulation is attainable.

A further exemplary embodiment shown in FIG. 7 has a master brake cylinder 43 the pistons 44 and 45 of which are not coupled rigidly together. That is, a conventional masterbrake cylinder can be used, which can communicate via a hydraulic line 38 with centrifugal positioners 32, 33 such as those shown in FIG. 6a. The hydraulic lines 46, 47 lead to the brake circuits I, II.

The foregoing invention relates to preferred exemplary embodiments of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.