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19th January 1926
Page 19
Page 20
Page 19, 19th January 1926 — FOUR-WHEEL-BRAKE CONTROL.
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-Details of a New Method of Interlocking the Rubury-Alford and Alder Front Brakes with the Rear Brakes so that Freeing of Both Off-side Wheels Occurs When Cornering.

ASYSTEM of brake control which presents undoubted features of merit and should assist greatly in the promotion of safety, is now being embodied in the operating gear of the Rubury-Alford and Alder brakes.

Quite recently, in an article on the subject of front-wheel braking contributed by Capt. J. M. Rubury, R.A.S.C., the dangers arising from loss of adhesion between the wheels of a vehicle and the road were pointed out, and it was shown that if both front wheels are locked, partieularly when cornering, this danger may be emphasized, and, in fact. result in a complete loss of control of the vehicle, as the power of steering will be absent.

To avoid such a contingency It has been the practice amongst many makers employing four-wheel brakes so to allocate the braking power that the bulk of it takes effect on the rear wheels. This is an unsatisfactory method, for, as a matter of fact, when the brakes are applied rapidly much of the effective weight of the vehicle is thrown forward upon the front wheels, and in those vehicles running at fairly high speed's a greater all-round braking efficiency could actually be obtained by permitting more of the braking power to be obtained from the front wheels. In the Rubery-Alford and Alder system safety when cornering ig definitely assured by releasing the outer front wheel just short of the skidding point, and advantage of this feature is taken in the new form of control which has been adopted. This consists in

linking together the front and rear brakes on each side of the vehicle through the medium of a compensator. To its simplest form this compensator takes the shape of a rocking bar carry ing two pulleys, around which the cable running to the front and rear brakes is passed; this permits the cable to adjust itself to give equal tension at each side of the rocking cross-bar by which the brakes are applied.

. It is easy to follow what happens when braking is carried out. We will suppose that the .effort is so divided that the front and rear wheels give equal braking power. When running along the straight, applying the brakes vigorously might cause some of the wheeli to lock, when the vehicle would probably begin to swerve to one side or the other, unless perfectly adjusted. Immediately such a skid begins the driver would automatically turn the steering wheel slightly to correct it, upon which the brake on the outer front wheel will begin to release, according to the amount of lock, and this releasing action will be transmitted via the compensating device to the outer Tear wheel. . In this way an anti-skid tendency will be definitely afforded by one wheel on each axle, and not only by one at the front, and the car will immediately obtain a grip on the road.

Furthermore, the simplicity of the control is such that a considerable reduction in the nuraber of working parts and joints, as compared with the ordin ary four-wheel-brake operating gear, is obtained, and this allows greater power being applied direct to the brakes, for the reason that, with so little loss of travel in the pedal, greater leverage can be provided.

We were recently afforded an opportunity for testing a light vehicle equipped with this new method of brake interlocking. To begin with, the brakes at one side were partly released so that their action was very unequal, and it was then found possible on a wet road to skid the wheels at one side without those at the other.

Applying the pedal suddenly at about 40 m.p.h. on a moist and slippery portion of the Great West Road, the locking of the wheels at one side caused the vehicle to swerve, but immediately the steering was turned to correct the skid the braking effort on the two locked wheels was partially released, the vehicle answered the wheel and immediately resumed its correct path, although the pressure on the brake pedal was not decreased. The feeling of security thus engendered was so surprising that we repeated the test on several occasions, with the same result.

We also tried the effect of turning corners at a fair speed and applying the brakes on the corners, without any drastic results. With the brakes in this condition tests showed that the stepping distance from 35 m.p.h. was 14 yards on a dry road. Later propei adjustment was carried out, and, incidentally, this was very easily affected by rotating one thumbscrew at each side, and with the brakes in good condition, the stopping distance from 35 m.p.h. proved to be "Di yards on a dry surface and 13 yards on an extremely greasy portion of the road.

We understand that the system can well be applied to vehicles up to a loading capacity of two tons, but beyond this size some form of power assistance, or, in other words, a servo device, should be incorporated.


People: J. M. Rubury

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