New Hobbs Automatic Drive Suits All Engines A N automatic transmission
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system that represents a striking development, inasmuch as it is claimed to be suitable for small engines as well as large and is more compact and less expensive than other systems of American origin, has been produced by Hobbs Transmission, Ltd., 78 Russell Terrace, Leamington Spa. It will be exhibited at the Commercial Motor Show.
Known as the Mecha-matic, it is wholly mechanical in operation. It is the result of more than 10 years' research to evolve .a system which would cause no loss of power and afford the driver a good measure of overriding control when desirable. The company say that there is every prospect that some large British• vehicle manufacturers will shortly fit Mecha-matic drive.
Fuel Savings The transmission has been tested and found satisfactory for a wide range of commercial vehicles, and has been shown to effect marked savings in fuel consumption compared with the use of normal gearboxes. The system comprises five units. A clutch unit is bolted to the engine flywheel and contains two hydraulically actuated friction clutches. The spinner plate of the front clutch is mounted on a shaft, and the spinner plate of the rear clutch on a sleeve surrounding the shaft.
Brakes of similar construction to the clutches hold elements of the gearing Stationary. A hydraulic unit embodies a pump driven from the clutch to deliver oil under pressure when, the engine is running. An automatic governor valve and a manually operated selector valve direct oil under pressure to the clutches and brakes, and a kick-down valve varies the speeds at which the ratios are automatically changed.
A rear pump driven from the output shaft delivers oil for operating the governor valve and actuating the clutches and brakes when it is required to start the engine by towing or running downhill. Elements in the gear train connect the output shaft with the spinner plates of the clutches and brakes. Different ratios are obtained by engagement of the various plates.
As road and engine speeds vary, so does oil pressure. As speed rises, increasing pressure moves the governor valve up against its spring until a second jet is uncovered. In this state, oil is directed at the next brake diaphragm and the next upward ratio is selected. Upward changes. take place at higher speeds than downward to avoid " hunting between the gears.
When coming to rest, the clutches are disengaged and bottom gear is selected by means of . a valve attached to the clutches. When the engine is idling, oil pressure is so low that the push-off springs on the clutches effect disengagement. As engine speed rises, centrifugal force on the valve causes it to mcive outwards, closing the exhaust port and bringing hydraulic pressure to bear to effect the engagement of bottom gear.
If the driver decides to leave gear changing to the mechanism, he selects " Automatic " on a steering column quadrant. Special attention has been paid to obtaining a smooth start from rest and to eliminating " creep " while idling.
If the driver requires high speeds in the gears, he may use the kick-down valve, and to meet any unusual condition, each of the gear ratios may be manually selected by means of the control lever.
The manufacturers say that the system opens up a new field of applications as its claimed advantages are applicable to medium and heavy goods vehicles, as well as public service vehicles. A Mecha-matic gearbox suitable for a 14-litre engine is to be exhibited at the Show.
Mr. H. F. Hobbs began experiments in this field in 1921. Prototypes were tested before and during the last war in various cars and armoured vehicles, since when units have been installed for testing in a variety of petroland oil-enginerl vehicles.