Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-07-07
2001-04-24
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S011000, C303S113300, C303S901000
Reexamination Certificate
active
06220675
ABSTRACT:
The present invention relates to a hydraulic brake system with a master cylinder that can be actuated by means of a brake pedal, a brake line connecting the master cylinder with a brake cylinder, and a hydraulic unit with a motor-driven pump for boosting the brake force, wherein the delivery flow of the pump is supplied to the suction side of the pump via a pressure control valve within a circuit.
Hydraulic brake systems of the type described above are known from the Ate Brake Handbook, 2nd edition, 1960, pp. 60-65. In the brake systems described in the handbook, a motor-driven high-pressure pump delivers a constant flow of fluid that circulates within a circuit, flowing through a restrictor gap between a boosting valve located on the master cylinder and the piston of the master cylinder and then back to a reservoir, from which the pump draws in the pressure fluid. When the brake pedal is actuated, the boosting valve is displaced against the piston of the master cylinder, and this causes the flow in the restrictor gap to be restricted. This in turn causes pressure to be built up in the ring-shaped space between the boosting valve and the piston of the master cylinder. This pressure displaces the piston of the master cylinder in the direction of braking, and it becomes effective as pedal return force at the boosting valve. Due to the comparably higher manufacturing and operating costs as compared to vacuum brake force boosters, these known brake systems with hydraulic brake force boosting never achieved significance in practice.
Another known device for hydraulically boosting the brake force uses the energy supply already available in the motor vehicle by having the hydraulic pump for the steering servo charge a hydraulic accumulator via a pressure-controlled current regulator. The pressure fluid stored under pressure is led to a boosting piston via a control valve that is actuated by the brake pedal, and this boosting piston actuates the piston of a master cylinder. In this design, an additional pump circuit is required for a brake-slip control.
In another hydraulic brake system, known from DE 40 35 906 Al, the pressure fluid delivered by a pump is supplied, via a pressure reducing valve, to a pressure control valve that is actuated by the brake pedal. The pressure control valve regulates the pressure in the brake line depending on the force exerted on the brake pedal. The pressure reducing valve is connected to the brake line via a control line and arranged in such a way that the pressure on the inlet side of the pressure reducing valve always is 30 bar higher than the pressure in the brake line. This known brake pressure control device is not suitable for connecting several mutually independent brake circuits.
DE 44 46 525 Al describes a hydraulic motor vehicle brake system for driving stability control and anti-slip control with a brake-slip control system that works on the basis of the return principle, wherein the dual-circuit master cylinder is actuated by a vacuum brake force booster that can be regulated by means of a brake pedal. The brake system has a pump whose pressure side is connected to the brake line, and said pump operates as a recirculating pump for brake-slip control and as a brake pressure transducer for driving stability or anti-slip control. The pump is not in operation during braking procedures that do not use the control devices. When the pump operates as a brake pressure transducer, the suction side of the pump can be connected to the brake line via a valve, with a precharging pressure being generated in the brake line by means of a precharging pump in order to improve the intake action.
The object of the present invention is to create a brake system of the type mentioned above, which, firstly, is characterized by a simple design and low construction costs, secondly, can have several, mutually independent brake circuits, and, thirdly, does not need an additional energy supply for brake-slip control actions or an automatic brake actuation, e.g. driving stability control.
According to the present invention, this object is achieved in that the pump, the pressure control valve and a non-return valve that closes in the direction of the master cylinder are arranged parallel to one another in the brake line of a brake system of the type mentioned above, wherein the suction side of the pump and the outlet of the pressure control valve are connected to the master cylinder and the pressure side of the pump and the inlet of the pressure control valve are connected to the brake cylinder and wherein the pressure control valve regulates the pump pressure in dependence of the pressure in the section of the brake line connected to the master cylinder and the hydraulic surfaces of the pressure control valve are designed in such a way that the ratio between pump pressure and master cylinder pressure is greater than 1.
In the brake system according to the present invention the actuating force exerted on the brake pedal is not boosted in the master cylinder or brake pressure transducer, but in the brake line, wherein the integrated hydrodynamic pump circuit divides said brake line into a section with low pressure on the side of the master cylinder and a section with higher pressure on the side of the brake cylinders. The pump circuit also is not controlled mechanically by means of the brake pedal but through the output pressure of the master cylinder, which is applied to the control piston of the pressure control valve. The hydrodynamic pump circuit is closed with the exception of the attachments for the brake line and, consequently, it also is part of the hydrostatic brake circuit. Thus, whenever the brake force is boosted, the flow quantity of the pump always corresponds only to the pressure difference between master cylinder pressure and brake cylinder pressure. The non-return valve arranged parallel to the pump circuit ensures a direct connection between the master cylinder and the brake wheel cylinder in order to obtain a quick brake actuation independently of the pump circuit. When the pressure in the master cylinder is reduced, the pressure in the brake cylinder is reduced through the pressure control valve.
The brake system according to the present invention allows hydraulic brake force boosting with low structural costs and irrespective of other servo-systems in the vehicle. It is particularly well-suited for motor vehicles that do not have available an adequate vacuum for operating a pneumatic vacuum brake force booster. Since the brake force boosting is controlled only hydraulically in the brake system according to the present invention, it can be used with any type of master cylinder. It also is possible to integrate a hydrodynamic boosting circuit according to the present invention in an already existing brake system. Furthermore, the brake system according to the present invention offers the advantage that a brake-slip control can be obtained through few additional measures and devices, because the existing pump is used as a recirculating pump. In the same way the brake system according to the present invention can be expanded into a brake system with driving stability control through few additional measures and devices.
According to the present invention, an electric motor can be used to drive the pump, with said electric motor being switched on when a braking procedure is initiated. This does not detrimentally affect the response behavior of the brake system, since the pressure build-up while the pump is starting up is supported by the master cylinder.
According to the present invention, the pressure control valve can be designed as a pressure limiting valve, for which purpose a non-return valve closing in the direction of the pressure limiting valve is arranged between the outlet of the pressure limiting valve and the point where the control line of the pressure limiting valve runs into the brake line. Furthermore, it may be provided that the control piston of the pressure control valve be designed as a stepped piston with atmospheric pressure being appl
Continental Teves AG & Co. oHG
Graham Matthew C.
Kramer Devon
Rader & Fishman & Grauer, PLLC
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