PERMANENT RECORD BRAKE TESTING
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By John F. Moon, A.M.I.R.T.E. APARTICULAR feature of the annual reports of the Licensing Authorities for 1961-62, which were issued at the beginning of August, was the strong criticism )f the low standards of maintenance evident on many ;oods vehicles. The reports gave the impression, furthernore, that the L.A.s wished they could devote more :nforcement staff to this matter. Mr. W. P. S. Ormond, :he Eastern LA., had a lot to say about maintenance, and .eported that special brake-efficiency checks which had
)een held on trunk roads had revealed a low standard, 10 per cent of the vehicles checked having received prohi )itiou notices. He put this down to overloading and lack if maintenance, and remarked that the standard of naintenance had deteriorated slightly during the year.
Many operators are no doubt aware that their vehicles, when overladen and driven at high speeds, do not have ip-top brakes, but the time for maintenance of the braking ;ystern is not always available, let alone the time and 'acilities for regularly checking the braking efficiency or he vehicles. Of course, there are various brake-testing
neteN available on the British market, but a number of hese require a certain amount of experience to be interpreted intelligently, and it is unlikely that the transport engineer, garage foreman or any other responsible official in the average organization would be able to spare the time to conduct individual brake tests on each of the vehicles in his charge.
This would not necessarily apply in very large transport companies, but it is a decided drawback in the case of smaller organizations and one which partly contributes to the poor standard of brake maintenance prevalent in this country. A further difficulty—and one which is not always appreciated by responsible people who should know better—is that it is virtually impossible to assess a vehicle's performance when it is unladen; therefore, brake tests must be carried out while the vehicle is loaded to at least the manufacturers' recommended figure, and preferably the overload figure at which the vehicle is almost certain to be operated.
The question of testing a vehicle's brakes when in the laden condition can be resolved only by making that vehicle available for a (comparatively) short length of time between the collection and delivery points so that the workshop personnel can get their hands on it. However, I do not propose to offer any indication as to how this desirable aim might be achieved!
Having got the laden vehicle, the next problem is that of sparing somebody for a long enough period to give the brakes a test on a suitable level, fairly traffic-free stretch of road—somebody who can be relied upon to submit a clear report to the person in charge of maintenance as to the state of the brakes. Obviously, such a person is not going to be free at any time, on any day, so what is really needed is a sort of robot that will record the braking performance while the vehicle is in the charge of its normal driver, who, whilst probably very competent at driving, is not necessarily sufficiently qualified to report on braking performance.
"Robot" Brake Tester Such a robot does, fortunately, exist, and has done for a number of years, for there are several thousands of this particular recording brake-testing instrument in daily use.
The equipment referred to is the Churchill 999 brakeefficiency recorder, made by V. L. Churchill and Co. Ltd., Great South West' Road, Bedfont, Feltham, Middx, and retailing at 04 10s. Not only does the Churchill 999 make a permanent record of a vehicle's maximum braking efficiency, but it has the additional advantage of recording the presence of any braking unbalance which is sufficient to cause the vehicle to deviate from a straight line when decelerating.
The Churchill instrument, which has been fully approved by the Ministry of Transport in connection with its vehicletesting programme, weighs approximately 27 lb. Although not as small as non-recording meters, it is still compact enough to be used in confined spaces and, in fact, in virtually any vehicle that has a level floor area at least 10 in. long and 7 in. wide.
The maximum deceleration in a horizontal plane expressed in terms of a percentage of " g " (the numerical value of the acceleration due to gravity) is recorded by means of a damped pendulum on a thin paper card, the lower end of the' pendulum being fitted with a lightly sprung ball-point pen. Damping is given by permanent magnets which act on a vane attached to the pendulum spindle, a very slight amount of additional damping being given by the friction of the pen ball on the card.
• There are three spring-loaded levelling screws to permit accurate setting of the instrument on the vehicle floor, and a spirit-level bubble at the top of the pendulum arm ensures correct initial setting. The test card, which must be obtained from Churchill as the specification of the paper and its size are governed by very fine limits, is approximately 9.25 in. long and 2.125 in, wide, and it is held in the instrument by one simple locking clip.
• The instrument is extremely straightforward to use once it has been correctly levelled, and it gives accurate readings from any speed above 8 m.p.h. A new card has to be inserted before each individual test stop, but otherwise there is nothing for the tester to do, whilst the permankt record enables the person responsible for the condition of the• vehicle's brakes to see at a glance whether there has been any deterioration in braking performance since the last te5 It would thus be possible for this person to keep a fi of the braking performance of each of the vehicles in h fleet assuming that tests were carried out, say, once month, and such a record might hold an operator in goc stead in the event of one of his vehicles being involved an accident and resulting action being taken against th operator on the grounds of braking inefficiency. At lea the presence of the cards would indicate that the operat, had been carrying out regular braking-efficiency tests.
Of course, as with every type of deceleration meter, on maximum braking efficiency is measured, and no allowan is made for braking-system delay, as occurs with powe assisted or full-air-pressure brakes. This type of met does, however, indicate whether there has been a falling-c in braking performance, even if it gives no indication overall stopping distance from any particular speed. 1 the case of the Churchill meter, there is the added adva] tage that a record is taken also of any side pull, this heir possible because the pendulum is mounted in gimbals, so' thus free to move sideways if the vehicle swerves durir the stop.