Mandatory load sensing recommended to MoT
Page 42
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CLAYTON DEWANDRE SUBMITS REPORT
ON BRAKING PROBLEMS BY Paul Brockington
OThe value of load-sensing valves in terms of handling stability and stopping distance is highlighted in a report issued by the Clayton Dewandre Co. Ltd., Lincoln. A copy of the report has been sent to the Minister of Transport with the recommendation that the use of sensing valves should be mandatory on all heavy vehicles.
It is pointed out in the report that antiskid systems will be applied to heavy vehicles in due course and that their use will eliminate the need for compromise that now exists in attempting to combine vehicle stability and the ability to stop in the minimum distance. It is also noted that a braking force that is distributed between the axles in fixed proportions cannot ensure that the best possible stopping distance is obtainable under varying conditions of road surface and axle loading.
The author of the report, Mr. B. R. Shilton, emphasizes that front wheel locking does not impair the stability of a rigid or artic vehicle and that locking the driving axle of an articulated vehicle can cause jackknifing. He states that load-sensing valves should be applied to the rear axle of a rigid vehicle and to the driving and rear axle of an artic. Mr. Shilton also draws attention to the braking problem created by the wide variation in the brake pedal effort required to obtain a given acceleration because of load changes. He says that this problem is overcome by using suitable sensing valves which raise the pedal effort required for check braking of the vehicle when unladen to within a few pounds of the effort needed when the vehicle is laden. Involuntary overbraking of an unladen vehicle is difficult to avoid, he observes, if the pedal effort required is too small.
Data are given in the report showing the extra braking distances from 40 mph of a rigid and an artic not equipped with a loadsensing valve system on a slippery road, a wet road and a dry road. In the case of the rigid the extra required is 55ft, 50f1 and 30ft respectively, while the artic needs an extra 35ft. 45ft and 25ft respectively.
"Adhesion utilization" is the term used in the report_ to define the deceleration that can be obtained on a particular road surface without wheel locking divided by the deceleration that could he obtained if optimum braking-force distribution were provided. As the diagrams relating to an artic show, a much more
favourable adhesion utilization is obtained at virtually all coefficients of road adhesion when the vehicle is unladen if it is equipped with a load-sensing system. The system gives a comparable advantage if it is fitted to a rigid vehicle.
• The 1968 "Fork Truck Driver of the Year" competition will be held on September 25 and 26 at the Drill Hall, Stretford Road, Manchester. The competition is sponsored by the British Industrial Truck Association and supported by the Institute of Materials Handling and many safety organizations.