Fluid-pressure and analogous brake systems – With pump
Patent
1995-05-30
1996-08-20
Butler, Douglas C.
Fluid-pressure and analogous brake systems
With pump
188181C, 30312212, B60T 832
Patent
active
055472656
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to ABS (anti-lock) braking systems for road vehicles, for example as shown in EP 020485.
ABS systems are controlled by a dedicated electronic control unit (ECU) which is powered by the vehicle battery/alternator supply. The system includes control of valves in the hydraulic supply to the brake actuators at the individual axles or wheels, the hydraulic fluid being delivered to the solenoid valves from a hydraulic pump driven by an electric motor.
The voltage range within which typical ABS control systems are designed to operate is specified in terms of the voltage at the power supply connection of the ECU. However, the voltage at this point, and its relationship to voltages at other locations within the system, will depend upon details of the particular vehicle-type in which is it installed, for example, on the length and gauge of the cables, and on the fusing arrangements and the number of other vehicle systems (e.g. audio, ventilation etc.) which share the same power supply distribution cable.
It is normally considered to be impractical to design and approve different system hardware (e.g. pump-motors) to suit each individual installation, for example on cost considerations alone. Furthermore, the voltage available at the pump motor depends upon the current being drawn along the supply cable, which depends in turn upon how hard the driver is pressing the brake pedal. Thus, the worst case condition only occurs when the driver is pressing very hard. However, designing for the worst case installation with regard to this particular function is also generally considered to be uneconomic because it results in the vast majority of installations being over-engineered, and therefore potentially uncompetitive on price grounds.
In a worst case situation with a relatively small volt-drop from the battery to the ECU, but a relatively large volt drop from the battery to the pump-motor, a considerable increase in pump motor power rating may be needed in order to maintain the energy balance of the system all the way down to the minimum voltage threshold at which the ECU will operate. The use of a smaller motor could result in the pump being unable to scavenge all the fluid dumped from the brakes, so that the chambers of the expander fill up, brake pressure can no longer be reduced in response to solenoid energisation and the wheels lock. The sequence of wheel-lock cannot be predetermined, and so vehicle instability may result. Thus, the use in itself of smaller pump motors in the existing systems is not an acceptable option.
An object of the present invention is to establish a more acceptable solution to this problem.
In accordance with the present invention, the magnitude of the pump motor voltage is compared with a predetermined reference value and the physical demand upon the pump motor is arranged to be reduced if the measured magnitude of the voltage is below said predetermined reference value.
In one embodiment, for example, the physical demand on the pump motor is reduced by arranging for the control channel(s) controlling the brake actuator(s) at one or more of the front wheels of the vehicle to be inhibited, whereby full ABS control is only available on the other wheels (including the rear wheels). Inhibiting ABS activity at one or more of the front wheels reduces the amount of fluid dumped into the expander chamber and therefore the rate at which the fluid volume that the pump must return to the higher pressure actuation circuit. This ensures that the expander chambers do not become saturated.
The voltage measurement is preferably made within the ECU itself but can equally well be made in additional hardware provided for the purpose.
The reference value or voltage can be a predetermined value based upon examination of the electrical installation of the specific vehicle. The value for a particular typical installation might be for example, 9 volts but this will vary from vehicle model to model as well as vehicle to vehicle.
Usually, the aforegoing measurement would be made actually
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Harris Alan L.
Turner Dennis
Butler Douglas C.
Lucas Industries PLC
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