An Automatic Infinitely Variable Gear
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Important Development of the Austrian Beier Friction-type Multi-speed Gearbox A. FULLY automatic version of the Beier gearbox, a unit which provides an infinitely variable ystem of ratios by employing friction uses, has been developed to operate in :onjunction with a bus engine developng 140 b.h.p. at 2,000 r.p.rn. The vhole gear is accommodated in a flyvheel housing having a diatineter of 'bout 22 in., the axial length of the issembly being 9 in. The gear also provides for automatic clutch operation
old a reverse, .
In Germany, the Beier gearbox has peen fitted to a number of Volkswagen :ars which have covered large mileages, ;co that the reliability and efficiency of he friction discs have therefore been !stablished. Present development 'work s being related to methods of control o provide acceptable operational tharacteristics rather than to evolution Pf improved disc assemblies.
The principle of the gear is that thanges of ratio are obtained by varyng the centre distances between sets of uses, the number of which are multiplied to reduce the coefficient of friction :o 0.01. Neglecting the effect of other rotating parts, the efficiency increases from 85 per cent, on the lower ratios of about 5 to 1 to over 95 per cent. on higher ratios.
A Road-vehicle Version The automatic gear for automotive ase is comprised essentially of an epicyclic assembly with multiple sets of tapered discs taking the place of planet gears, and a set of flanged discs forming the sun gear. The planet discs are mounted on swinging-arms fitted with counterweights which tend to reduce the centre distances with an increase in speed.
Torque is transmitted to the output shaft through face cams which impose an axial thrust on the sun discs in proportion to the torque and tend to "squeeze out" the tapered planet discs. Thus, control is a function of both road speed and torque, the combined effect of which depends upon the weight of the counterweights and the shape of the cams. When the speed of the output shaft approaches 15 per cent. to 20 per cent. of engine speed, a braking device automatically locks the assembly to the carrier to provide direct drive and eliminate internal friction,
A freewheel is an essential part of the mechanism and it operates in all ratios of less than unity, but the freewheel can be locked to enable the engine to be employed as a brake when required. Gears on splined shafts of the planet discs are meshed with gears on the swinging-arm pivot pins, which are carried by the flywheel housing. Gears integral with the pivot pin gears are in mesh with a ring gear on the inside of a carrier, and a wire-coil freewheel is located between the carrier and the housing. Locking the freewheel not only gives an overrun drive of the power unit when the vehicle is travelling forward, but can be used to provide reverse gear when the vehicle has been brought to rest with the engine running.
The freewheel also acts as an automatic clutch because at low engine speeds it allows the ring gear to run forward freely. With an increase in speed, movement of the planet discs inwards reduces the speed of the gear carrier and eventually reverses the direction in which the torque is applied. Counter rotation is prevented by the freewheel and the vehicle then moves forward.
If the freewheel control be linked to the brake mechanism so that it is actuated by initial movement of the pedal, the engine is used for braking on the overrun before the friction brakes are applied and a separate lever is unnecessary.
In the latest design of automotive transmission, an auxiliary planet system is incorporated in the unit, with which a positive type of reverse action is obtained and which provides two gear ranges with different speed-torque characteristics.
In automatic • form, the rated efficiency of the gear is 88 per cent, at a ratio of 2 to 1 and over 90 per cent. at a ratio of about 1.25 to 1 when
the locking device for direct drive is about to come into operation. At a ratio of 3 to 1 the efficiency is 75 per cent, and at 5 to 1, 65 per cent.
It is pointed out by a technician of the company that the efficiency of the transmission compares very favourably with that of a typical torque converter, which may have an efficiency of 85 per cent, at a ratio of 2 to 1, but possibly not more than 65 per cent, at a ratio 1.3 to 1 or lower. If a unit were built without automatic control, it would follow the design of the industrial nonplanetary type in which power is transmitted by the discs direct from the driving to the driven member. This would have a higher efficiency at the lower ratios.
For most vehicle applications, the normal type of splash lubrication, using engine oil, is suitable, but for transmissions operating continuously at low ratios, a pump is incorporated to circulate the oil for cooling purposes. It is emphasized that a high oil pressure is not required for satisfactory operation.
A Multiplicity of Discs The way in which the planet and sun discs can be multiplied to increase the load capacity is of particular importance. In a unit for the transmission of 125 b.h.p. at 4,000 r.p.m., eight sets of planet discs with a total of 80 discs mesh with 12 sun discs with 96 points of contact. The diameter of the housing is 151 in. and the axial length, including the space occupied by an auxiliary planet train, is 10i in. Each set of planet discs is separated into two groups, only one of which would be used for an engine developing half the output at the same speed.
One obvious advantage of the transmission is that maximum power is available at any road speed, and therefore a power unit With a lower output could be employed for a given load.
Dr. Joseph Beier, of Austria, designed the gear, and the Beier Infinitely Variable Gear Co., Ltd., 19 Ebury Street, London, S.W.1, are the representatives in this country.