Solenoid-operated Exhaust Brake for Oil Engines
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AN exhaust obturator brake, operated electrically through the initial pressure on the brake pedal, was demonstrated in London on Monday by the makers, Thomas Ash and Co., Ltd., 19 Rea Street, South, Birmingham. z: A light pressure switch, incorporated in the brake-pedal pad, is connected to the vehicle battery and to asolenoid controlling the butterfly valve in the obturator, thus closing the exhaust when the brake pedal is depressed and causing pressure build-up in the engine.
The obturator is an iron casting and is supplied in kit form with flanges to mate With the exhaust .manifold and .silencer pipe of any oil-engined vehicle, It is interposed between the manifold and silencer pipe and. has provision for mounting the solenoid. A bore dimension of 3f-'„ in. is standard for vehicles having exhaust pipes up to 3 in. diameter, and the butterfly valve is slightly offset by the bosses in the main casting.. The butterfly valve is relieved .at the sides so that the. engine will not stall when the brake pedal is applied and the vehicle is stationary. .
The butterfly valve spindle is sealed against exhaust leakage -and extended for attaching a spring-loaded lever which is held in the open position until the solenoid takes 'control. As the valve, is operated every time the pedal is used; there is no tendency for the formation of carbon, .which • might cause partial seizure. The 4-amp. solenoid and obturator, .complete with ,flanges, weighs 25 lb., and the unit with pedal switch costs £29 10s. The -pedal supplied
with the kit is rubber covered and has a contact switch which is spring loaded for a 31 lb. effort. •
The Ashanco electrically operated exhaust brake, as it is termed, was demonstrated on an -A.E.C.-Beadle coach operated by Maidstone and District Motor Services, Ltd. The vehicle was fitted with the A.E.C. 7.7-litre oil engine, having a centrifugal-weight fuel-injection-pump governor. The coach had a registered weight-of 6 tons 12i cwh and carried 34 passengers on test from the centre of London to Kent.
On the first trial down Titsey Hill, a 440-yd. gradient of 1 in 12 average and 1 in 6 maximum, the solenoid was disconnected and the normal drum brakes were required continuously to prevent overrunning with second gear engaged. The drums were hot at tM bottom of the'hill. A subsequent test was made with the solenoid in circuit, and the coach descended the hill with the engine brake applied, again with second gear engaged and at about the same speed as the initial run. The normal braking system Was not used in the second test, and the efficiency of the obturator was again shown when the coach was held at a constant speed on a 1-in-9 section of the hill.
At present the exhaust brake device is made only for centrifugally governed injection pumps, but another unit, for use with pneumatically governed injection equipment, is also being. developed. it. is understood that the exhaust brake will also be made for petrol-entined vehicles.,