Following a review of four-wheel-brake development, the author quotes from a scientific note relative to four-wheel-braking action on a car that is rounding a curve, published by the French Academy of Science, and the conclusion therefrom that front-wheel brakes have a direct retarding effect on the motion of translation and, in addition, a direct retarding effect upon the instantaneous motion of rotation of the car about its own center of gravity. Further, from another article, he quotes authority for the theoretical advantage of four-wheel brakes on heavy down-grades.
Subsequently to an amplified statement that satisfactory operation of a four-wheel-brake system, from the driver's viewpoint and with reference to pedal-travel and pedal-pressure, constitutes the real problem, comparisons are made between internal-expanding and external-contracting types and the servo-brake is discussed with special reference to the Perrot system. The advantages of the author's four-wheel-brake system are set forth specifically, brake-system design is discussed in general and comments are made upon brake-lining, front springs and various precautionary measures that must be incorporated. He explains his non-use of equalizers and cites seven specific important items that should govern all four-wheel-brake design, as well as stating his ideas regarding the future development of the motor-car chassis, as affected by the present trend of brake-system practice.
This paper begins with a review of four-wheel-brake development, starting with the experiments of the late P. L. Renouf, in England, in 1904. I believe Mr. Renouf's patent is almost basic; but it is a front-wheel and not a four-wheel-brake patent. The brakes were applied to the two front steering-wheels of a three-wheel vehicle, as shown in Fig. 1, and were operated by a cable that ran down into the king-pin over a pulley at the top. In 1906, Allen-Liversidge patented, in England, a front-wheel-brake system that was experimented with extensively in England between 1906 and 1909. This system was defective in several ways and passed out of use. In 1909, both the Perrot and the Isotta systems were evolved, both English patents covering the fundamentals that are used by these two systems today, except that the Isotta system made use of a vertical king-pin. The first application of front-wheel brakes was exhibited to the English public at the Olympia Show in 1910, where some half-dozen different makes of car having brakes on the front wheels were on view. The most notable examples were the Argyll cars with the Perrot system, the Crossley, Arrol-Johnston, Thames and others, with various modifications of the Allen-Liversidge patents. The construction of the Allen-Liversidge design was peculiar. The main brake-control passed through the king-pin, and the layout was such that torsion was set-up at certain times in a way that locked the steering. Obviously, this was wrong.
On all these cars the front-wheel brakes were applied by the pedal alone, the rear-wheel brakes being applied by the hand lever. With this layout it was very easy to lock the front wheels by the use of the pedal, and the rear wheels by using the hand lever, especially under greasy road conditions. Some accidents occurred, and manufacturers and drivers feared to use these brakes. As a result, except for the Argyll cars, the front-wheel brakes disappeared entirely from British cars. In 1912, the pedal and the hand lever were arranged so that they would both operate on all four brakes. Incorporated with this true four-wheel-brake system was the diagonal braking system that is well known to all automotive engineers from the discussion that has been in progress in this Country for the last 2 or 3 years. This system, which is outlined in Fig. 2, employed one equalizer that equalized the braking pressure between the left-hand front and the right-hand rear, and between the right-hand
front and the left-hand rear wheels respectively, there being no equalization between the diagonal wheels that were connected together. The primary reason for this diagonal braking was to comply with the English law that required two independent brakes. The layout was such that, if any one operating member broke, two brakes on diagonally opposite wheels of the car were still operative.
front and the left-hand rear wheels respectively, there being no equalization between the diagonal wheels that were connected together. The primary reason for this diagonal braking was to comply with the English law that required two independent brakes. The layout was such that, if any one operating member broke, two brakes on diagonally opposite wheels of the car were still operative.