Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2001-01-08
2001-11-27
Schwartz, Christopher P. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C188S358000, C060S547100
Reexamination Certificate
active
06322162
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an actuating device for an electrohydraulic vehicle brake system, with an emergency brake cylinder which comprises a piston, the latter being displaceable in a housing, and which can be actuated by means of a brake pedal, and a simulation device for simulating a force/displacement action of the brake pedal, wherein the simulation device is connected in series and disposed after the emergency brake cylinder in the direction of force from the brake pedal to the emergency brake cylinder. The invention also relates to an electrohydraulic vehicle brake system with an actuating device of this kind.
A braking requirement of a driver is detected at the brake pedal, for example, in an electrohydraulic vehicle brake system and, according to this braking requirement and optionally further influencing variables, brake pressure is applied to brakes of the vehicle brake system via an electrohydraulic system (not illustrated in detail here) provided with a motor-driven pressure source. Should the electrohydraulic system fail (for example if the supply voltage in the vehicle drops), this becomes inactive, which may lead to critical running conditions, as no—or only a low—brake pressure can be applied to the brakes by the electrohydraulic system. In order that the vehicle may also be braked in such a case at least with a minimum delay according to legal requirements, a conventional hydraulic emergency actuating system is usually provided in addition to the electrohydraulic system.
DE 196 38 102 C1 describes an actuating device of the type mentioned in which a master brake cylinder can be actuated via a brake pedal. When the electrohydraulic system is inactive the master brake cylinder is connected by valve arrangements to the vehicle brakes in order that the latter may be actuated in an emergency. When the electrohydraulic system is active the master brake cylinder is connected by the valve arrangements to a simulation device which simulates the force/displacement action of the brake pedal which can be experienced by the driver according to a conventional, purely hydraulic vehicle brake system. There is a constant hydraulic connection between pressure chambers of the master brake cylinder and the simulation device when an electrohydraulic system is active. The simulation device is therefore connected in series and disposed after the master brake cylinder in the direction of force from the brake pedal to the master brake cylinder. The simulation device is in this case subject to the high pressure level in the master brake cylinder. This places a substantial load on sealing elements of the simulation device, which reduces their service life and thus the safety of the vehicle brake system.
It is also necessary when actuating the simulation device to overcome the restoring forces of spring elements disposed in the master brake cylinder, which causes difficulty in matching the force/displacement action of the brake pedal which can be experienced, in particular for the initial displacement range, with little force.
A further problem arises if the electrohydraulic system is deactivated or fails while the brake pedal is actuated. In this case the quantity of brake fluid which can be supplied to the vehicle brake is reduced by the quantity which had previously been supplied to the simulation device when the electrohydraulic system was still active. The braking power in an emergency actuation system of this kind is thus restricted and the braking distance of the vehicle undesirably long.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to improve an actuating device of the type initially mentioned such that it overcomes the above-mentioned disadvantages.
This object is achieved according to the invention by an actuating device as described above for an electrohydraulic vehicle brake system in which the emergency brake cylinder is supported at the simulation device and its piston can be locked relative to the housing such that the simulation device can be mechanically actuated by the emergency brake cylinder.
The simulation device is hydraulically uncoupled from the emergency brake cylinder by the actuating device according to the invention, so that there is no possibility of an y influence by the high pressure in the emergency brake cylinder, which would have adverse consequences. The simulation device can be operated at a considerably lower pressure level than the emergency brake cylinder, which means that sealing elements of the simulation device are not loaded to such a high degree.
A pneumatically sprung simulation device, for example, is also rendered possible by the hydraulic uncoupling. A further advantage lies in the fact that it is not absolutely necessary for the simulation device to be hydraulically damped, but this may instead be in the form of a simulation device with a purely mechanical spring arrangement.
According to an advantageous development of the actuating device according to the invention, the emergency brake cylinder is supported with its housing at the simulation device and its piston can be actuated by the brake pedal. The coupling between the brake pedal and the emergency brake cylinder may therefore be formed in the conventional manner. The housing of the emergency brake cylinder may alternatively also be moved by the brake pedal and the piston supported at the simulation device.
The actuating device is developed to advantage by providing the simulation device with a stop which can be moved against the action of at least one spring arrangement. A simulation device which is operated solely mechanically is possible as a result of such a development.
As an alternative to or combined with the development just described, the simulation device may comprise a wall which can be moved against the action of hydraulic damping. A simulation device of this kind enables the force/displacement action of a brake pedal to be simulated in a particularly precise manner.
According to a development of the invention, the stop or the wall of the simulation device is firmly connected to the housing of the emergency brake cylinder and the latter is guided with mobility in a housing of the simulation device. This provides the advantage of a very compact structure of the actuating device, as the emergency brake cylinder and the simulation device are of a telescopic configuration, so that relatively little installation space is required.
According to an advantageous configuration, the wall of the housing of the simulation device is divided into two 30 working chambers which can be connected in throttled fashion or unthrottled fashion or shut off from one another by means of at least one valve arrangement. A valve arrangement of this kind enables the force set against an actuation of the brake pedal by the simulation device to be adapted for different displacement ranges of the brake pedal.
Because the effective working faces in each case associated with the wall in the working chambers are of equal size in an advantageous configuration, the wall may be displaced in the housing of the simulation device while the volume of both working chambers together remains the same, so that there is no need to supply hydraulic fluid from outside of the simulation device.
The actuating device is also developed to advantage by connecting one of the working chambers to a reservoir for hydraulic fluid. It is thus possible to deliver the hydraulic fluid expelled from the working chamber into the reservoir and optionally dispense with a second working chamber.
According to a further advantageous configuration, a valve is disposed in a line between the working chamber connected to the reservoir and the reservoir such that, when the electrohydraulic system is active, the connection is blocked when the brake pedal is actuated and is opened when the actuation of the brake pedal is eased off. This valve, which may be formed as a non-return valve, for example, prevents hydraulic fluid from flowing out into the reservoir, so that this fluid can only flow into the s
Lucas Industries Public Limited Company
MacMillan Sobanski & Todd LLC
Schwartz Christopher P.
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