From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Article from 'The Motor' magazine detailing the suspension and braking system of the Bentley Mark V.
| Identifier | ExFiles\Box 160\5\ scan0229 | |
| Date | 29th January 1941 | |
| The Motor 566 January 29, 1941. Contd. The Bentley Mark V chassis. The system employed has been laid out to secure three main objectives—simplicity, stability and elimination of road noise. Suspension Details The last mentioned is tackled by the free use of rubber brushes and buffers to isolate the springs and links from the frame. It will be seen that coil springs are used together with triangulated wishbones. Further, that the arms of the bottom wishbone are spread wide apart so that the rear arm becomes, in effect, a brake torque member. The top wishbone embraces a piston-type hydraulic shock-absorber, this having a fixed adjustment whereas the rear shock absorbers have an over-riding control adjusted by the driver to suit various conditions. The bottom wishbones are much longer than the top and the back ones are slotted so as to permit a steering rod to pass through them. The '' geometry '' of the system is such that the roll centre is appreciably above ground level, the castor angle is held nearly constant (increasing slightly towards full travel as is desirable) and the tyre scrub caused by the absence of front-wheel parallelism is small and does not adversely affect tyre life. Naturally, the coil springs have a very low rate and hence the front suspension is very much softer than on previous, conventionally sprung, Bentleys. There is a powerful anti-roll bar connecting the wheels which confers good stability with cornering, and stability with under severe braking is assured by the wide spacing of the bottom wishbones, the proportion of the front braking effort being 57 per cent. The brakes, themselves, are outstanding in performance and highly interesting in design. Deeply ribbed 14-in. drums are used, the shoes being expanded by the well-known Girling wedge and roller expanders. They are linked by rods to a friction servo device driven at 1-30th engine speed from the rear end of the gearbox. A Simple Brake Servo Motor In principle, this servo is similar to those previously used on Bentley-Rolls-Royce products, but its design has been greatly simplified without in any way detracting from its efficiency. As will be seen from a drawing, the brake pedal is connected to a sleeve (A) having internal cams which react against the fixed cam plate (B), rollers being interposed to give free motion. The reaction between these cams presses the hitherto stationary disc (C) against the rotating fabric-lined disc (D) which is driven from the gearbox. Friction then turns stationary disc (C) so that the peg (E) on its face comes up against the hollow cam which in turn pulls the rod (F) that is connected to the four-wheel brakes. The servo is operative in reverse when the discs move, of course, in the opposite sense and the rod (G) travels the full length of the slot, the brakes then being applied through the servo mechanism as before. Enclosing the moving disc is a corrugated copper spring (H) which keeps out mud and dust and at the same time forces the driven plate away from the friction-lined driven member when pedal pressure is released. The system is fully progressive, the driver having full control and the pedal pressures needed for maximum retardation not exceeding 70 lb. The brake linkage on both front and rear axles is ingenious and contributes in no small measure to the steadiness of braking in all circumstances. At the front end the use of cables is general when mechanical brakes are coupled with independent front suspension systems. The drawings show how this expedient has been avoided by the Bentley designers who employ a system of rods in tension with links so placed that the arcs described by the brake rods are the same as those described by the suspension links. The Braking The rear brakes are actuated by simple tension transverse rods in the normal Girling manner, but the fore-and-aft linkage is specially designed to [Diagram Labels] BRAKE CROSS ROD RUBBER LOCATIONS RADIUS ROD BRAKE CROSS ROD FORE AND AFT BRAKE ROD DETAILED REFINEMENTS.—Smooth braking unaffected by rear axle movements is assured by the device shown above. The swinging radius arm carries the rear brake pivot and the fore and aft brake rod. The unit is flexibly connected to the rear axle through the rubber buffers shown in the drawing. SPRINGING AND STOPPING.—These two views of the front wheel mountings show the open coil springs and the disposition of the wishbones, the spread of the bottom links being so wide that the rear member acts as a torque rod. Neat mounting of the shock absorber will be seen, also the clever manner in which the brake rods are so linked and located that they swing through the same arcs as the wheel-mounting members. A15 | ||