MOTORING

Nelson Evening Mail, Volume LXIII, 30 March 1929, Page 4

MOTORING

BRAKING DEVICE SWISS INVENTION SUCCESSFU U BRITISH TESTS By reason of t;he ease with which it can be incorporated in existing,designs the vacuum, servo brake is becoming decidedly popular. There are several interesting points in a new vacuum servo, known as the Radertseher, which is t lie design of a Swiss engineer, and is made by Radertscher Vacuum-brake, &.Id., Northolt Road, South Harrow, [Middlesex, England. Not (he least of the advantages claimed is the fact that the operating cylinder is entirely enclosed and is thus thoroughly protected against dust and mud.

In principle tho Radertscher brake follows existing designs in that the depression in tjic induction pipe is communicated to a cylinder in which slides a piston, the other side of the piston being ppon to the atmosphere. Thus, when the control valve is actuated by the braikc pedal the pressure on the side of the piston is reduced below that of tlic atmosphere, and, as atmospheric pressure is acting upon the other side 'bf the piston, the result is that tin; piston travels along (he cylinder audi in so doing exerts a pull on the brak.v operating gear, thus materially assisting the effort exerted by the driver on the pedal. To make these: operations quite clear a concrete case may be taken; suppose that the "suction" of the engine reduces the pressure on the one side of the piston to 101 b. per sq. in., then as atmospheric, pressure is 14.71 b per sq. in. the result will be a pressure of M.7 —10, or 4.71 b. per sq. in., on the piston, and supposing that the area of the piston is 10 sq. in., the pull exerted bv it on the brake gear will be 471 b. OPERATING CYLINDER The operating cylinder of this new brake is entirely enclosed, and the piston is connected by links to a pivoted lever which forms the connection to the brake gear. One end of the cylinder is connected by a pipe to the control valve, which is really an adjustable air inlet allowing the action of the brake cylinder to be controlled to a considerable extent. For example, if this regulating valve be almost closed air can only enter the one end of the brake cylinder comparatively slowly, and the braking power developed will be small, whereas if the valve be opened so that no restriction is placed upon the air entering the cylinder the maximum braking will be achieved. As the control valve is separate from the cylinder it can be mounted in any convenient position, and may, for example, bo placed on the dashboard beneath the bonnet. It consists essentially of a small cylinder in which is a double-ended piston held in position by light coil springs bearing on each end. One end of the piston is of larger diameter than the other end, and normally the piston is held by the springs so that the larger end closes the port in communication with the pipe connected to the induction manifold, the smaller end of the piston being clear of the port which is in communication with the air, so that atmospheric pressure exists on both sides of the piston in the operating cylinder. THE CONTROLLING SYSTEM The Bowden control connected to. the brake pedal operates a small belli crank level on the control valve, ancf when the brake pedal is depressed moves the small piston valve along its' passage, closing the air port and putting the "suction" port in communica- 1 tion with the pipe leading to the brake cylinder, so that the piston moves along the cylinder and applies the brakes. The degree to which the brakes are applied depends upon the extent to which the pedal is depressed, for, owing to the difference in the size of the ends of the control valve piston, an automatic controlling action is given, and the extent to which the control piston moves is governed not only by the actual movement of the Bowden control but also by the "suction." On a two-litre Lagonda speed model fitted with this brake some interesting tests were carried out, for in the original control valve arrangements were made whereby an automatic application of the brake was caused when the accelerator pedal was entirely released. The automatic action could be cut out by setting the throttle opening so that the engine ran a little faster than its ordinary idling speed, and at first the automatic action proved a little confusing, as it was necessary for the driver to remember that lie should not release the accelerator completely, otherwise the brakes were applied with some vigour. By exercising care for a few minutes, however, one becomes quickly accustomed to the automatic action as regards brake application, but it was apt to be a little troublesome in changing gear and in preventing a I clean, noiseless change being obtained : with certainity. Accordingly, the automatic control was put out of action and the foot brake relied upon aB in normal driving, and then the brake proved to have many good points. ONE GREASE GUN NIPPLE On a wet, smooth surface the car was brought to rest from a speed of 40 m.p.h. in a distance of 84ft, and from 25 m.p.h. the distance necessary was only 24ft. A test was then made from 25 m.p.h. using the automatic control, and it was found that the distance necessary was 50ft. there being a distinct lag' after releasing the accelerator before the brakes were applied. In both cases the action of the brake was extremely smooth and progressive, and very little pressure was necessary on the brake pedal. Incidentally, the regulating valve referred to was not adjusted to give the maximum braking effort, but to provide that degree of braking which seemed best for ordinary running. The automatic control may not be standardised, but will be available if required As regards attention necessary to maintain the brake in efficient working order, there is only one grease gun nipple on the operating cylinder for lubrication of the piston, and this needs only very occasional attention. No price has yet been definitely settled, but it is expected to be in the neighbourhood of £ls (in England) for a car of medium size, such as the Austin Twelve. Fitting is a particularly easy matter since the brake cylinder has only to be rigidly attached to the chassis in a suitable place, and the control valve and regulating valve fixed to the dash, the units joined by suitable copper pipes to each other and to the induction manifold, and the Bowden control attached to the ordinary brake pedal of the car.