Fluid-pressure and analogous brake systems – Multiple fluid-receiving devices – Multiple motors
Patent
1992-07-27
1994-02-15
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Multiple fluid-receiving devices
Multiple motors
303 20, 303 221, 188112R, B60T 720, B60T 1366
Patent
active
052860949
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the control of the braking forces in tractor-trailer combinations of road vehicles, either separate tractors and trailers joined by a drawbar, or vehicles with semi-trailers.
When the brakes are applied it is desirable that the braking forces should be such that trailer neither tries to overrun the tractor (indicating that it is not being braked enough) nor produces an additional drag load on the tractor (indicating that it is being braked too hard). The first situation can lead to jack-knifing and the second may lead to trailer swing. In both cases the minimum distance in which the combination can be brought to a halt is greater than it would be in the ideal condition, in which both are braked equally.
This ideal situation is difficult to achieve, bearing in mind that the weight of both vehicles, but especially of the trailer in the case of load-carrying vehicles, can vary widely between the unladen and fully laden conditions; a braking force appropriate to the fully laden condition would certainly cause the brakes to lock in the unladen vehicle.
Attempts have been made to solve this problem. It has been proposed, for example to adjust the braking force applied to the trailer, as a proportion of that applied to the tractor, manually in accordance with the known load being carried on the trailer at the time. Clearly this is impractical in normal commercial use and will soon fail to be implemented.
A better solution is that disclosed in British Patent Specification No. 497 179 of Daimler-Benz, in which, in an electric braking system, an electric signal dependent on the amount by which the trailer overruns the tractor is obtained from a linear potentiometer connected between relatively movable parts of the drawbar, and is used to control the application of the electric brakes on the trailer.
A somewhat similar solution, again applied primarily to electric brakes, is that disclosed in a U.S. Pat. No. 3,955,652 of A. B. Linde International, in which a pressure-sensitive transmitter in the coupling between the tractor and the trailer senses the pressure and pull on the coupling and controls an amplifier which is responsive to the magnitude and direction of the pressure and pull to control the supply of power to the brakes. The transmitter is stated to be actuated by very small movements, allowing the coupling unit to be substantially rigid. The system is operative to influence the brakes on the trailer every time the brake light circuit is closed by depression of the brake pedal.
A more recent proposal is that disclosed in U.S. Pat. No. 4,763,958 of VBG Produkter AB. However here the load on the trailer is sensed primarily not by the coupling but by a mechanical feeler arrangement driven by an electric motor through a lead screw and detecting the relative clearance between the chassis of the trailer and an axle, i.e., the static deflection of the road springs. Only secondary to this is an on-off sensing arrangement in the tractor-trailer coupling, employing two limit switches which detect when the push or pull in the coupling exceeds a predetermined amount and, when that happens, they complete an electric circuit to a motor which drives in one direction or the other an adjustable pressure-reducing valve in the compressed air supply to the brakes on the trailer.
Finally, in International (PCT) Patent Application No. W087/05571 of Saramo there is disclosed an arrangement in which the measurement of the force in the coupling is substantially linear in both directions, i.e. both in push and in pull, and the control equipment, indeed the whole apparatus is particularly suitable for mounting on the tractor vehicle, especially as a subsequent modification to an existing brake installation. The sensing is by means of an electrical resistance strain-gauge type of load cell, mounted in the coupling with substantial pre-loading to enable it to sense both positive and negative forces.
A major source of weakness in the known systems is the sensor. In our co-pending British patent application No. 90
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Bloxwich Engineering Limited
Oberleitner Robert J.
Poon Peter M.
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