American Exhaust Brake Introduced To This Country
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1-1 A NEW vehicle engine brake which,
unlike conventional exhaust brakes, does not rely on pressurized exhaust manifolds, has been developed by Jacobs Manufacturing Co., Hartford. Connecticut, USA, and has now been introduced into this country.
The first unit to go into service here has been fitted to an ERF powered by an NH series Cummins engine, and ia recent test is claimed to have held a vehicle combination of 30 tons for about mile to a speed of 10 m.p.h. down a gradient of I in 6. It has been installed by B. and W. Motors Ltd., of Wolverhampton, for Joseph Foulkes (Wednesfield) ltd.
Consisting of electrically controlled hydraulic units fitted in the form of sandwiches between the. rocker-gear carrier and the rocker-cover, operation is by depressing the exhaust valve rockers just as the pistons reach the end of the compression strokes.. This action dissipates the charge of compressed air in the cylinder to the atmosphere before it has the effect of forcing the piston downward on the next power stroke, so changing the characteristics of the power-producing diesel engine to that of a power-absorbing air compressor.
T a k i lig its hydraulic oil from the engine lubricating oil system when fitted to a Cummins NH .engine, the unit works as follows.
When the solenoid is brought into action by the driver-controlled switch— which operates automatically as soon as the throttle pedal is released—oil is permitted to flow through a control valve to a master piston which is forced into contact with the top of the injectorrocker arm. At the same time oil is supplied to a slave piston located above the exhaust rocker, with just enough pressure to charge the system between it and the master piston.
As the injector rocker begins its upward travel, the loaded master piston is forced upwards. causing a ball check valve in the corn rot valve to close. The high oil pressure generated by the dis placement in the master cylinder. being unable to escape tramthe circuit, forces the slave piston down on the exhaust valve rocker which opens the combustion chamber to the atmosphere. • It is claimed that the Jacobs engine brake will do up to 80 per cent of all the service braking required on a vehicle in normal conditions, and that when operating under severe conditions—such as descending a long, steep hill—it will almost eliminate any severe application of the wheel brakes, thus leaving them cold and at peak efficiency for any emergency that might arise. Experience in the USA and Canada has shown that it is possible to obtain up to five times the normal life from brake linings.
Tailor-made for each type of engine, the Jacobs engine brake is at present available for C.:timmins NH series, General Motors 71 series, and for Mack END 711 engines. Manufacture in the UK is to start in due course and brakes for other types and makes of engine are under consideration.