Twin-range Gearbox in Production
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SINCE the prototype of a new eightspeed gearbox with a built-in epicyclic train was displayed by the Moss Gear Co., Ltd., Tyburn, Birmingham, at the 1956 Commercial Motor Show, the company have developed a range of sixand eight-speed units of basically similar design, but incorporating a number of improvements. Limited production has been started and both types will be available within a few weeks.
The epicyclic gear is located at the forward end of the gearbox. The planet carrier of the train is directly coupled to the input shaft and the maximum load on the gears is limited accordingly to the input torque in all ratios. The ring gear is controlled by a hydraulically operated brake band, actuation of which causes the sun gear to rotate at a higher speed. A direct and an overdrive top gear are provided by the epicyclic train, which can also be employed in conjunction with the indirect gears.
In the case of the six-speed gearbox the low range of ratios comprises a bottom gear of 6.14 to 1, a third gear of 2.18 to 1 and the direct top. The auxiliary epicyclic unit provides a high range of which the second gear has a ratio of 4.3 to 1, fourth gear a ratio of 1.52 to 1 and overdrive-top a ratio of 1.43 to 1A direct top in the high range is also available as an alternative feature.
The six-speed unit has a torque rating of 240 lb,-ft. and the rating of the eightspeed gearbox is 300 lb.-ft. Units with other ratings are being developed.
Another feature of the gearbox is a hillholder, which is effective when any of the gears is engaged.
The weight of the six-speed unit is only 1 cwt, greater than that of a Moss standard five-speed gearbox, and the length is increased by 2 in.
A Dodge 5-ton test vehicle equipped with a six-speed unit has now covered over 50,000 miles. The last 45,000 miles have been completed without adjustment of the brake band or dismantling any of the components. During a run in the vehicle with a full toad a representative