Fluid-pressure and analogous brake systems – Load control – Empty and load type
Patent
1994-09-26
1996-03-05
Ballato, Josie
Fluid-pressure and analogous brake systems
Load control
Empty and load type
303 9, B60T 1358, B60T 818
Patent
active
054960983
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention is concerned with increasing the efficiency of braking in vehicles fitted, in addition to wheel-mounted foundation brakes, with a transmission shaft or engine retarder and also fitted with an Electronic Braking System, sometimes known as a Brake-by-Wire System.
BACKGROUND ART
Generally, vehicles are equipped with retarders in order to have the benefit of a form of dynamic supplemental braking means which has great endurance despite being of limited capacity and having an effectiveness which falls at low speeds. The use of such retarders saves foundation (friction) brake lining wear, particularly at low braking demands. The conventional practice is for retarders to be under separate control from the foundation brakes, usually from a driver-operated hand control.
It is known from GB-A-2 080 458 to provide an electronic braking system in which control of the foundation brakes and transmission shaft or engine retarder is coordinated in response to the braking demand signal. In the system of GB-A-2 080 458, the retarder receives the full brake demand signal and is operated in an open loop, whereas the foundation friction brakes are operated in a closed loop and receive the deceleration error signal. A problem in practice with such a system, wherein the retarder receives full braking demand and a closed loop acceleration system is employed, is that, because of system delays and inherent lack of responsiveness in air brake actuation, system instability can be caused, particularly if wear, corrosion and poor maintenance cause hysteresis levels to increase. A further problem with the system of GB-A-2 080 458 arises from closing the loop using deceleration signals which are inherently noisy, being derived by a differentiation process on signals which are subject to substantial load noise disturbances. This is because the filtering required to remove much of the noise generated, results in a slow deceleration signal not adequate for dealing with fast changes in braking demand which is required of road vehicles under critical circumstances.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a control system whereby the foundation brakes and transmission shaft or engine retarder can be operated in an improved coordinated manner using an electrical braking demand signal generated by a single brake foot pedal.
In accordance with the present invention, there is provided an Electronic Braking System for a vehicle having foundation brakes and a vehicle retarder, wherein an electrical braking demand signal is generated from a single brake pedal and wherein the retarder is operated variably or in small steps as the brake pedal movement is increased from zero, or rest, up to a partial point in its movement range which is calculated to give substantially the maximum retarder power based on the total mass of the vehicle such that for a full load condition this partial point occurs at low pedal deflection and, in an unladen condition where a given retarder will produce a higher deceleration, this point occurs at a higher pedal deflection, and in both cases pushing the pedal beyond the calculated partial point causes foundation braking to be commenced to supplement the retarder torque.
Preferably, foundation braking is introduced at the front axle only and is increased with increasing pedal travel up to a point where the front axle braking effort is equal to the retarder braking effort at the rear axle, with correction being made for the axle weight ratio so that the adhesion utilization is equal between axles.
The retarder torque preferably alone provides for low level braking and is supplemented by single axle foundation braking to an increasing level as speed falls when retarder output falls, in order to maintain vehicle deceleration from a constant brake pedal input.
Advantageously, the retarder controller increases retarder drive to maintain a constant developed retarder torque until the retarder reaches maximum drive so that a further decrease in retar
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Ballato Josie
Lucas Industries Public Limited Company
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