Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1998-06-15
1999-11-23
Graham, Matthew C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
3031131, B60T 1116
Patent
active
059887680
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention is based on a hydraulic brake system for road vehicles.
DE 43 43 386 A1, U.S. Pat. No. 5,544,948, has already disclosed a hydraulic brake system of this kind, with a master cylinder which has a movable piston that acts on a path simulator spring when the service brake is actuated. The spring is comprised of an elastomer with closed-pored, gas-filled cells. It produces a progressive characteristic curve of the pedal, i.e. as the brake pedal path increases, a progressively increasing opposing force comes into effect. The movement of the piston when the pedal is actuated is only possible when pressure fluid can be displaced into the reservoir from the second pressure chamber of the master cylinder. To this end, a line connection is established, which leads from the master cylinder, contains an electromagnetically switchable shutoff valve, and leads into the pressure fluid reservoir. Furthermore, an electronic control unit is provided for controlling this shutoff valve, the booster pressure source, and other solenoid valves that are used for brake pressure modulation in wheel brake cylinders. Apart from the fact that the spring can cause problems in long-term behavior, it requires a special embodiment of the control unit in order to control the shutoff valve, which makes the brake system more costly.
ADVANTAGES OF THE INVENTION
The hydraulic brake system according to the invention has the advantage over the prior art that the electromagnetically switchable shutoff valve is replaced by one that is mechanically controlled, which permits a simplification of the control unit. When the service brake is active, the first valve is closed so that the third valve keeps the communication open between the second pressure chamber of the master cylinder and the pressure fluid reservoir, and the path simulator spring is actuated. However, if the service brake fails and the first pressure chamber of the master cylinder communicates with the brake circuit, then after a partial stroke of the first piston, the third valve shuts off the exchange of pressure fluid from the second pressure chamber to the pressure fluid reservoir. The path simulator spring is therefore not active.
The embodiment of the invention achieves a space-saving disposition of the third valve. In addition, no connecting lines disposed outside the master cylinder are required between the third valve and the pressure fluid reservoir.
Because of the mechanical coupling of the tappet to the first piston, the modification of the brake system according to the invention distinguishes itself by means of a high functional reliability of the third valve.
When the service brake is active and the second piston can therefore be moved, the embodiment of the second piston achieves in a simple manner an always constant communication between the second pressure chamber and the pressure fluid reservoir.
The embodiment of the invention discloses a path simulator spring which is resistant to pressure fluid and maintains constant properties over the service life of the vehicle.
An embodiment that is favorable for technical manufacturing reasons, particularly in two-circuit master cylinders, is found with a modification of the invention, because it avoids the necessity of finely machining a very deep bore.
BRIEF DESCRIPTION OF THE DRAWINGS
An exemplary embodiment of the invention is shown in simplified form in the drawings and will be explained in more detail in the description below.
FIG. 1 shows a circuit diagram of a hydraulic brake system for passenger vehicles,
FIG. 2 is a longitudinal section through a master cylinder used in the brake system, as a first exemplary embodiment, and
FIG. 3 is a longitudinal section through a master cylinder that has been modified in relation to FIG. 2, as a second exemplary embodiment.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
A hydraulic brake system 10 for passenger vehicles, which is represented in FIG. 1, has a brake circuit I associated with the wheel brakes 11, 12 of the front axle, VA, of the vehicle and
REFERENCES:
patent: 4730877 (1988-03-01), Seibert et al.
patent: 4777643 (1988-10-01), Leiber
patent: 5332302 (1994-07-01), Maas
patent: 5449225 (1995-09-01), Burgdorf et al.
Kaessmann Andreas
Schaefer Ernst-Dieter
Schunck Eberhardt
Graham Matthew C.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
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