Hydraulic brake system

A hydraulic brake system having a hydraulic cylinder including a piston used for brake pressure modulation disposed between a master brake cylinder and at least one wheel brake cylinder in which the piston of the hydraulic cylinder is actuated mechanically by an electric-motor-driven centrifugal positioner. In an anti-skid system, the hydraulic cylinder can be used in combination with the centrifugal positioner for rapid reduction of brake pressure. It is also possible to embody the hydraulic cylinder and centrifugal positioner such that a brake boosting or anti-slip regulation takes place upon actuation of the centrifugal positioner. By the use of a centrifugal positioner, the piston can be displaced quickly and very precisely for either increasing or reducing brake pressure.

BACKGROUND OF THE INVENTION 
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. 
OBJECT AND SUMMARY OF THE INVENTION 
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.

DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENT 
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.