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60 per cent Efficiency for New vehicle Brakes—Draft Code

1st January 1965, Page 22
1st January 1965
Page 22
Page 22, 1st January 1965 — 60 per cent Efficiency for New vehicle Brakes—Draft Code
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THE draft code of practice on commercial vehicle braking requirements was issued on Tuesday by the Minister of Transport. Intended as a guide to manufacturers, copies of the draft have been circulated to members of the organizations represented on the working party which drew it up. These include the Road Haulage Association, Traders Road Transport Association, Society of Motor Manufacturers and Traders, Transport and General Workers Union, Road Research Laboratory, A.A. and R.A.C.

The working party was set up last October to recommend to the Minister amendments needed in the Construction and Use Regulations governing brakes, so as to take advantage of the higher weights allowed last August, subject to vehicle plating and attainment of minimum brake efficiencies.

The draft code recommends that new vehicles should have a maximum brake performance of not less than 0.6g and, when on the road, not less than 0-5g.

DRAFT CODE OF PRACTICE FOR PLATED VEHICLE BRAKES Notes One of the conditions attached to the higher vehicle weights set out in Statutory Instrument 1964 No, 1169 was that braking efficiencies of 50% and 257 had to be obtainable by two independent means. The S.M.M.T. painted out to the Ministry of Transport that the present regulations on the layout of braking systems might hamper the attainment of such braking efficiencies. The Ministry replied that consideration would be given to the authorization by Special Order of braking systems which did not comply in all respects with the current regulations, prqvided that they were otherwise acceptable. This Code of Practice was conceived as a means of setting out the principles of brake design likely to be readily acceptable to the Minister in this context.

The Code is closely allied to the braking proposals developed by the Economic Commission for Europe which the Ministry has accepted as the pattern for future British braking regulations for all vehicles. The E.C.E. braking standards are set out in terms of stopping distances from certain speeds and it is anticipated that the.revised British regulations will be in this same form. Nevertheless, the standards in this Code are in terms of maximum brake performances, since these can be directly related to the brake efficiencies in the current regulations, for the purposes of which the Code came into being.

In this Code the expression '' emergency brake" includes the braking applied through the third or auxiliary line of a three-line system.

THE CODE 1. The braking system or braking systems of a motor vehicle, or as the case may be, a combination of vehicles (being a combination including a motor vehicle and a trailer or trailers) shall have not less than two separate controls available to the driver when in his seat, which between them control the service brake, the emergency brake and the parking brake. •• The service brake control shall be separate from the parking brake control.

2. The service brake of a motor vehicle, or as -the case may be, a combination of vehicles, shall have a maximum brake performance of . not less than 0.68 when the vehicle is new and 0.5g when it is in use on the road.

3. In the event of failure of any. part of the service brake, other than a fixed member, or the control, a vehicle • or as the case may be, a combination of vehicles, shall have art emergency brake (which may be combined with either the service brake or the' parking brake), which shall have a maximum. brake performance of not less than 0.3g when the vehicle is new and 0.25g when it is in use on the road.

4. There shall be a parking brake capable of being held on by mechanical action to hold the vehicle or combination of vehicles' on a 19% gradient when the vehicle is new and on a 16% gradient when it is in use on the road, without the assistance a any stored energy. The action of setting the parking brake shall release any stored energy which assists the application of the parking brake. Provided that in the case of a system incorporating a spring device which applies themarking brake by direct mechanical action and is capable of being applied and released by the driver at wilt, the mechanical energy or the spring shall not be regarded as stored energy.

5. With respect to teats of brake performance the following test conditions shall apply. For a new vehicle tests shall be carried out when ills Maded to its maximum perrnissible weight and also when empty and if considered desirable at loads between these two limits. For a vehicle in mate on the -road, tests shall be carried out with the vehicle as loaded at the time of test. The forces applied to the service brake pedal and the emergency brake control during brake testing shall not exceed 154 lb. and 132 lb. respectively. Tests shall be carried out from a speed of 25 m.p.h. when the temperature of the brake drum is not in excess of /00°C. During this test there shall be no abnormal wheel locking during braking, no deviation of the vehicle from its course and no abnormal judder. 6. In the case of a braking system assisted or. ' operated by air pressure the design of the system shall be based on an air pressure of 85 p.s.i. to give a service brake performance of 0.6g in the case of a motor vehicle alone. In the case of a motor vehicle authorized to draw a trailer, the requirement of paragraph 12 shall be satisfied in respect of the trailer and the overall service brake performance for the vehicle combination shall be 0-6g. 7. Any failure in the supply of energy stored for the service brake or emergency brake of a -vehicle, or combination of vehicles shall give warning to the driver by means of a buzzer or similar audible device to indicate which system or section of a split system .•• has failed.

8. The performance of both sections of a split system shall be capable of being checked separately for the purposes of type approval or annual inspection. 9. The parking brake may be in the form of:—

Ii) a multi-pull brake but shall not also Serge as the emergency brake unless the emergency brake becomes effective at the first pull; (ii) a parking lock or similar device provided there is no means of disconnection between the lock and the wheels and there is a separate service brake and emergency brake each with its own control.

10. The service brake of a motor vehicle or vehicle combination shall act directly on all the wheels. This requirement will be met by a brake which acts between the wheels and any differential in a driving axle.

11. In the case of an articulated vehicle combination when both fully loaded and light the distribution of braking between axles shall be such as to minimize lots of directional control and pariicutarty jackknifing on wet or icy roads. To this end the emergency brake shall be capable of applying some braking on the trailer wheels and shall avoid over braking and Locking the rear wheels of the tractor.

The above requirements shall be Met in a manner which does not prevent the brakes of the tractor from satisfying the standards of brake performance required when it is operating alone.

12. In the case of a tractor-trailer combination, the individual units of which are both plated the braking systems of each unit shall be designed so that any such •tractor and trailer or as the case may be, any such tractor and semi-trailer can be coupled together whilst preserving the design characteristics of the braking systems.

To achieve this, the combination shall be equipped with a three line air pressure braking system designed to meet the recommendations contained in para. (6) of this Code and the semi-trailer portion alone shall be designed to contribute a total braking force at the periphery of the braked wheels of 0-5W, W being the maximum weight transmitted to the road by the. wheels of the semi-trailer, In the case of a separate trailer the total braking force shall be 0-6W.

13. Every brake pressure reservoir shall have a low pressure audible warning device set to come into operation when the pressure in the reservoir falls to • a value equivalent to 70% of its normal pressure. The capacity of any such reservoir shall be such that it is possible to make an adequate number of full brake applications before the warning device comes into operation,

14. Disconnection between a tractor and trailer shall cause the trailer brakes to be applied automatically and remain applied for at least 30 minutes.

Disconnection of a trailer or failure of its brakes • shall leave the tractor brakes capable of satisfying the standards of brake performance required when it is operating alone.

15. Every trailer shall have a parking brake capable of being held on by mechanical action to hold the trailer or semi-trailer when it is detached from the drawing vehicle, on a 19% gradient when the vehicle is new and, on a 16% gradient when it is in use on the road.

16. The time lag between operation of the service brake control and the achievement of the required braking performance shall not exceed 06 secs.

17. There shall be no excessive brake fade.


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