A Servo-brake Assembly
Page 62
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DATENT No. 640,542 comes from I Servo-Frein .Dewandre S.A., Liege, Belgium, and deals with the control of power-assisted brakes as applied to heavy, vehicles. The essence of the patent is the means for controlling the action so that the driver is aware of the degree of braking being applied.
. Referring to the drawing, I is an inlet for:oil 'under pressure, and 2 an. escape port.; Li: operation, the driver's pedalrod (3) is moved :to the left, and after taking. up the clearance (4) moves the pistonsvalve (5) to the left. The first effect is to close the central exit port when the piston-valve meets a sealing disc (6), after which further movement opens. the pressure-inlet valve: (7). The incoming oil then forces the power.piston (8) tothe rightand, so applies the
brakes. • .
The degree. of oil pressure developed in the braking action is transmitted to
t h e piston-Valve, a,15 d.. through it back to the pedal rod, thus giving the required indication to the driver. The scheme allows for direct 'manual operation Xhould the power fail: in these circurnStanceS .as soon as the clearance round pivot 9 has been taken up, the pedal would work the power-piston rod.
A STEERING BOX FOR TRACTORS
ASTEERING box intended .mainly for tractors, is shown in patent No. 640,315, by R, Bishop and R. Johnston, Flowton Priory, Harpenden, Herts. The advantage of the design is that it enables .a high reduction to be obtained simply and in a small space.
The drawing shows a section in which
is the rockshaft and 2 the steering column. The latter is threaded and works in a nut (3), which slides up or down on a pair of guide columns (4). A slot in the nut engages a roller-and-pin (5) on the rockshaft crank, so that rising or falling of the the nut turns the shaft. A similar slot (6) on the other side of the nut works a second rock
shaft, which is .not shown in the drawing, in the opposite direction.
A SAFETY SWITCH FOR STARTERS
IF an engine should backfire I when being started, and the starter be re-engaged during the backward rotation,considerable damage can be, done to the pinion and the flywheel ring. A scheme to render this impossible forms the subject of patent No. 640,940, which comes from Bendix Aviation Corporation. South Bend. Indiana, U.S.A.
The patent refers to
• starting switches which are operated by a solenoid wired into a small control circuit. In this auxiliary . circuit is inserted the device shown in the drawing. When the circuit is closed, a solenoid (1) causes a small rocking lever ,(2) to descend and rub on some revolving, part of the engine such as the flywheel ; (3). The, control ,circuit includes a contact (4) and.a quadrant strip (5).
If the engine be stationary, contact is satisfactorily made between these two points. If it be running forwards (anti-clockwise) contact is still made, because, although the lever lacks, the contact point is
still on the strip. But if the engine be running backwards, the rocking lever is moved the other way into a position in which the contact point is resting on an insulating surface.
LIGHT-ALLOY BRAKE DRUMS
DRAKE drums, made in light alloy Li but faced on their inner surface with hard metal, are used, but it is found that the joint between the two parts forms a serious barrier to the conduction of heat. An improved .method of construction in which this defect is absent, forms the subject of patent No. 640,963, which comes from the British Aluminium Casting (1903), Co., Ltd., Dartmouth Road, Birmingham, 40.
In the proposed scheme, a drum cast in aluminium alloy is used, and the interior facing is formed by the electrodeposition of a hard metal, so that there is no break in the continuity. Suitable materials are, for the drum, Y alloy or Lo-Ex, and for the lining a primary coat of nickel 0.008 in. deep, followed by a layer of hard chromium 0.003 in. thick.
The alloy drum is first machined to size and, after nickelling, is ground. A final, fine grinding or honing is given after the chromium has been applied.
One important adsrantage of the scheme is that there is no substantial increase in weight, such as is the case when east-iron liners are secured or cast in place in a light-metal drum. COMPOSITE BEARING METALS
THE latest ideas for the build-up of multi-layer hearing strip is tontamed in patent No, 641,130, which comes from General MotorsCorporation, Detroit, Michigan, U.S.A. The proposed strip is made mainly of aluminium or an alloy thereof, faced with
a lead-rich bearing surface. •
A typical example of hearing metal is lead 95 -per cent., and tin .5 per cent., although other metals such as indium may be .present! The thickness is of the -order of 0.001 in. or less. The patent gives full details of the composition of the plating baths .used, and the current densities employed.,
A 'SELF-ENERGIZING BRAKE
D RAKE mechanism providing a selfUP -servo action, is shown irt patent No. ,640,539, by M. Bonnebeau, Pavilionssous-bois, France. The arrangement is said to be particularly suitable for heavy vehicles.
Referring to the drawing, a single expander is used, in this case a hydraulic cylinder (1) containing apposed pistons. Each-shoe is made in two pieces, a leading part (2) and a main portion (3). The leading portion pivots about a floating pin (4) on the main one, and is provided with a tail (5) which abuts against a fixed pin. At the bottom, the main shoes are slidably held inside cheeks of a rocking arm (6).
In operation, assuming clockwise rotation, the pistons press evenly outwards on both leading shoes, but the right-hand one forces its tail against the fixed pin and so .applies an increased force to its lower shoe. The latter slides in the bottom cam, which then tilts and brings its curved portion into contact with the drum. Additional force is thus 'created and transmitted through the left-hand set, making itself felt as reaction on the pedal and thereby giving the driver a sense of feel.