Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1999-03-19
2001-10-16
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S113300
Reexamination Certificate
active
06302497
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle brake control system capable of producing different degrees of braking force in response to the input of a brake foot pedal.
A known vehicle brake control system is operable to produce a braking force even when a brake pedal is not depressed and develop a braking force greater than a force normally obtained when the brake pedal is depressed. Such a conventional brake control system is adapted to provide traction control (TCS) and vehicle dynamic control (VDC). In the traction control mode, a controller receives information typically on wheel speed and wheel cylinder brake pressure, provided that the input of the brake pedal is absent, and brings brake pressure in wheel cylinders to the desired level so as to avoid wheel spin. In the vehicle dynamic control mode, the controller receives information typically on the actual yaw rate, lateral acceleration and steering wheel angle (or position), regardless of whether or not the input of the brake pedal is available, and brings the yaw rate to the desired rate. Conventionally, a mechanical pump is employed to increase brake pressure in the wheel cylinders. The system as a whole is thus costly.
Accordingly, it is an object of the present invention to provide a vehicle brake control system which does not require a mechanical pump to increase wheel cylinder brake pressure and is thus economical to manufacture.
SUMMARY OF THE INVENTION
According to a feature of the present invention, there is provided a brake control system comprising a brake booster including a power piston assembly by which the interior of the brake booster is divided into a constant pressure chamber and a variable pressure chamber selectively communicating with the constant pressure chamber. A first servo mechanism is designed to develop a differential pressure between the constant pressure chamber and the variable pressure chamber in response to operation (depression) of a brake pedal to produce a force corresponding to the amount of depression of the brake pedal. A second servo mechanism is also provided. A master cylinder is operatively connected to the brake booster to create hydraulic pressure in response to the output of the brake booster, and a plurality of wheel cylinders are provided for applying a braking force to respective wheels in response to the hydraulic pressure. A plurality of hydraulic lines is connected between the master cylinder and the wheel cylinders, and a plurality of corresponding pressure charging valves are provided in the hydraulic lines to allow and block communication between the master cylinder and the wheel cylinders. A plurality of pressure relief valves are provided in the hydraulic lines between the pressure charging valves and the wheel cylinders to selectively release hydraulic pressure from the hydraulic lines, and a controller is also provided and designed to control the second servo mechanism, the pressure charging valves and the pressure relief valves. The controller is operable to cause the second servo mechanism to develop a differential pressure between the constant pressure chamber and the variable pressure chamber, regardless of whether or not the brake pedal is depressed, to thereby produce a force greater than that corresponding to the amount of operation of the brake pedal.
With the pressure charging valves open, and the pressure relief valves closed, the controller is operable to control the second servo mechanism to produce an output force greater than a force normally developed in response to the output of the brake pedal. This causes the master cylinder to create hydraulic pressure greater than that corresponding to the degree of pedal depression. This results in an increase in the hydraulic pressure in the wheel cylinders. On the other hand, the hydraulic pressure in the wheel cylinders is reduced if the same control is made, but with the pressure charging valves closed, and the pressure relief valves open. This arrangement eliminates the need for a mechanical pump to increase hydraulic pressure in the wheel cylinders.
In a preferred mode, the controller is operable to control the brake booster, with any of the pressure charging valves for wheels which are not in control mode being closed, so as to cause the second servo mechanism to produce a force greater than a force normally developed in response to the output of the brake pedal, and control any of the pressure charging valves and the pressure relief valves for wheels in control mode so as to cause corresponding wheel cylinders to apply a braking force to the wheels in control mode.
In one embodiment, master cylinder hydraulic pressure sensors are connected to the controller and adapted to sense hydraulic pressure in the master cylinder. The controller controls the brake booster so that the hydraulic pressure as sensed by the master cylinder hydraulic pressure sensors is greater than hydraulic pressure required by the wheel cylinders by a predetermined amount. Advantageously, the hydraulic pressure in the wheel cylinders can be increased simply by control of the pressure charging valves and pressure relief valves. This prevents hydraulic pressure in the master cylinder from dropping and also avoids undue stress on various parts of the system such as pipe joints and seals.
In one exemplary embodiment, accumulators are provided to receive brake pressure released from the wheel cylinders through the pressure relief valves. Check valves may be connected to bypass the pressure relief valves and allow flow of brake fluid only from the accumulators to the master cylinder. In this way, the hydraulic pressure as introduced into the accumulators is returned to the master cylinder when the hydraulic pressure in the master cylinder becomes less than that in the accumulators. The pressure relief valves may be opened when the hydraulic pressure in the wheel cylinders is less than a predetermined level. This arrangement enables the brake pressure as introduced into the accumulators to be returned to the master cylinder without the need for the check valves.
Preferably, a brake fluid reservoir is connected to the master cylinder and adapted to receive hydraulic pressure released through the pressure relief valves. This arrangement eliminates the need for an accumulator to release hydraulic pressure from the wheel cylinders.
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Kramer Devon
Oberleitner Robert J.
Tokico Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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