Fluid-pressure and analogous brake systems – Multiple fluid-receiving devices – Multiple motors
Reexamination Certificate
1999-11-17
2001-08-14
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Multiple fluid-receiving devices
Multiple motors
C188S00300R, C188S11200R, C303S015000, C303S022100, C303S009690, C303S020000
Reexamination Certificate
active
06273522
ABSTRACT:
The present invention is concerned with trailer brake control systems in motor vehicles, which operate without the use of additional onboard sensors.
The requirement for a full control of a towing vehicle (tractor) and a semi-trailer during braking is such as to generate the need for deceleration control of the tractor in combination with a simultaneous adjustment of trailer braking levels so as to achieve coupling force control in a manner such as to cause each of the tractor and trailer to exert a fair share of the overall braking effort. This situation is equivalent to an equal utilization of adhesion between tractor and trailer and is recognized as being efficient on lining wear and in generating the most stable condition during braking, since skidding will only result from reduced surface adhesion and not from unbalanced braking distribution. Reduced lining wear results from the equitable braking balance in energy absorption which keeps the lining temperatures at their lowest mean level.
EP0303 827 teaches a dual mode trailer control system employing proportional braking as described above for best stability at higher deceleration levels plus, at lower braking demands, a balanced braking regime under which braking is made at levels which depend upon the size and number of axle brakes. However, this approach is not suited to unknown trailer types where numbers and sizes of brakes can vary substantially as different trailers are picked up during road operations.
The requirement of proportional braking distribution between tractor and trailer is the preferred mode in the industry and a number of methods of achieving this have been suggested, in the main requiring measurements of coupling force in two planes for semi-trailers.
Our EP0370 671 discloses a means for controlling the braking distribution and overall combined vehicle deceleration but requires some form of measurement of vehicle deceleration-and of coupling forces in order to achieve these ends simultaneously.
EP0433 362 disclosed a trailer control system in which errors between demand and achieved deceleration automatically cause the trailer braking proportion to be adjusted accordingly. This makes the assumption that any errors in combined vehicle braking must have resulted from variations in trailer braking only. In practice, this is not always the case as the towing vehicle brakes are subject to the same sources of variation in performance as the trailer brakes and correction when made should be directed to that part of the combination which contains the source of braking error levels. Many cases exist where there are variations in both parts of the combination, maybe to different extents, and the present invention attempts to focus suitable corrective adjustment to both said parts of the vehicle in a co-ordinated manner so as to prevent wrongly applied corrections having to be later reversed as the other vehicle half is adjusted. An important feature of the present invention is the requirement for measurement only of deceleration of the combination, saving the significant cost of measuring the coupling forces or of deriving these forces from tenuous processing of vehicle axle load changes and interpreting these from serious levels of noise generated by road Irregularities which are a part of practical vehicle operation.
It is envisaged that trailer braking parameter variations are likely to predominate in sourcing vehicle retardation variations and thereby causing braking errors. However, considering the case of a towing vehicle with better than expected braking performance linked to a trailer with under-performing brakes leads, a simple control system might conclude from the low deceleration errors, that the combination is correctly braked when the distribution is quite clearly in error.
An object of the present application is to provide a system which, although employing only deceleration measurement, has the ability to correct braking in both parts of the vehicle and thereby control both overall deceleration and braking distribution.
The control of semi-trailer braking requires that the system be able to examine the performance of each part of vehicle but this cannot be achieved totally independently. However, it is practical to examine the tractor or trailer performance alone if done with care and then to examine the combined performance in order to assess the braking effectiveness of the other part of the vehicle, so as to be able to apply individual corrections to each part as described above.
Examination of the trailer-only performance can be undertaken preferably after combination braking is established because of the delay in response of the trailer brakes which would make it appear that the vehicle brakes were not responding. Thus all axle braking, once established, would revert to trailer-only braking by slowly removing tractor braking while at the same time increasing trailer braking to compensate for this loss in total braking effort which would otherwise exist. Trailer braking effectiveness is then assessed by relating overall deceleration achieved to the driver demand, allowing for the total combination mass and the boost in trailer braking.
However, since more parameters are known on the tractor and are more constant than trailer characteristics which could change with every new trailer picked up, it is deemed preferable to brake the tractor-only on certain stops and then to assess the trailer performance when braking the combination, The present Application will concentrate on this strategy but recognises that the trailer-only alternative is technically equally possible.
The performance of the tractor-only is most easily assessed -by examining the retardation against demand, for the tractor without a trailer coupled and this will be done whenever the opportunity presents but it is recognised that some vehicles never operate in this mode and for those that do, the braking pressures ate so low, particularly on the rear axle(s) due to the light loading that it does not represent a real test of serious braking.
In accordance with the present invention there is provided an electronic braking system (EBS) suitable for commercial vehicles which tow trailers, which has on the towing vehicle, braking control of all the axles and a means of setting the braking demand for the trailer which is so adjusted as to equalize the braking effect at the road surface between said towing vehicle and trailer, characterized by the employment of two adaptive control loops which are adjusted in turn in a manner to achieve. single direction co-ordination between the loops wherein tractor braking errors are allowed for in the braking of the trailer in order to set respectively the towing vehicle and trailer braking to levels where overall train mean decelerations approximate closely to those corresponding levels demanded by the driver and at the same time set the distribution of braking to seek to achieve equal braking effect at the road surface between the tractor and trailer, further characterized by the use of deceleration errors in said repeated adjustment of the two adaptive control loops.
In a preferred embodiment, the towing vehicle adaptive control loop is adjusted after selected vehicle stops on the basis of the measured error between the drivers braking demand and the deceleration of the tractor/trailer combination when braked by the axles of the towing vehicle alone.
Advantageously during periods of towing vehicle-only braking deceleration is maintained with the normal proportion to the demand, by an increase of towing vehicle braking so as to provide additional braking forces to compensate for the absence of trailer braking, said increase being set in relation to the ratio of mass (Mt) of the rear part of the trailer which is normally braked by the trailer brakes, to the total mass (Mf+Mr) being supported on the towing vehicle axles.
Preferably, the towing vehicle-only braking of the combination takes place only at predetermined but variable intervals and only on selected brake applications where the bra
Feetenby Paul
Hurst David Charles
McCann Dennis John
Butler Douglas C.
Carlson & Gaskey & Olds
Meritor Heavy Vehicle Systems LLC
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