A FRICTION AUTOMATIC TORQUE CONVERTER.
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Details of a Simple Variable-speed Gear.
WHEN considering the various points in the design of the aver: age motor vehicle there is one part of the Mechanism which must be looked upon as being apparently crude in principle, although probably excellent in so far as the manner in which the principle has been carried out is coucerned. We refer to the gearbox, which, with its definite ratios (seldom more than three or four) and the fact that its handling still necessitates some degree of skill on the part of the driver, is not to be compared with a type•of transmission which -would provide an infinite number of gear ratios between the highest and lowest desirable and which might be, to a great extent, automatic in its action.
In this connection we were afforded last week an opportunity.for making a test run and personal driving trial of a light vehicle with an engine of 8 h.p. rating equipped with a remarkably simple and effective automatic variablespeed gear or torque converter, known as the R.A.V.S., which has been placed on the market by Robertson Automatic Variable Speed Gear Co., Ltd., 30, Duke Street, Piccadilly, London, S.W.)..
Smooth and Rapid Acceleration.
We noted, first of all, that for the size of engine the acceleration was most surprising. When limed, it was found that to accelerate from 10 m.p.h. to 30 m.p.h. on the level took 13 seconds. The control is almost startingly Most noticeable is the absence of a clutch pedal, and only one foot is used in driving, this being used either for the accelerator or the foot brake, as required. There is no change-speed lever in the strict sense of the word, but a central lever which provides hand control of the gear s provided, this being necessary only when it is desired to climb exceptional hills with the engine running at a higher speed than it would be when employed with the automatic control, or in order to obtain specially rapid acceleration.
When starting off from rest it is necessary merely to depress the accelerator and, immediately the engine begins to speed up, the gear takes up the load and the vehicle commences to move. There is no jumping or hesitation, nothing but the even, rapid acceleration until the gear is automatically brought into "top," which is direct drive—and really direct at that, for no pinions are revolving except in the back axle, there is no drag by oil ; in fact, the drive is equivalent to a plain shaft from engine to axle. To slow up in traffic, the pressure of the foot on the accelerator pedal is reduced,
and the gear automatically adjusts itself to the 'ratio required for running at the particular speed desired. Directly the accelerator is altogether released and the vehicle stops, the gear is automatically brought into neutral.
The ease of hill-climbing with this gear is a revelation. If desired, the automaticity of the gear can be relied upon, and this is perfectly satisfactory for ordinary hills, but with a particularly steep incline it is desirable to utilize the additional control giving a lower ratio and thus allowing the engine to speed up to a greater _extent than is normally permitted by the automatic action.
There can be no such thing as stalling the engine, for, below a certain engine speed, neutral is automatically obtained.
One of our tests was to stop and restart on Swain's Lane, Hampstead, which has a maximum gradient of 1 in 41. Here a start was made on the Steepest part with the utmost ease and without any sign of slip occurring, ex-. eept in the clutch provided for this specific purpose. .
The surprising part about this gear is its extreme simplicity and the small number of parts utilized in its construction. The principles involved can easily be understood, but we shall have to give a word picture as, owing to the restrictions in connection with the obtaining of foreign patents, the sponsoring company does not wish for drawings to be included at this stage of the developments.
Within the engine flywheel is a centrifugal , governor and sliding over the flywheel is a casing ending in a slightly coned face, the conical surface being convex and forming the driving portion of a friction gear. Cams are so arranged that as the engine speeds up and the governor weights fly out, the sliding member is forced outwards towards a drum carrying a ring of friction material conforming to the shape of the sliding member. At the hack of this drum is a single-plate clutch of straightforward construction with a single ring of friction material. The driven member of this clutch takes the torque to the propeller shaft. For straight-through drive, the parts are all in line, but for the lower gears the floating drum forming the friction member is moved to a position either above or to the side of the drive line, according to the particular design, so that the engaging portion of its friction ring is close to the centre of the metal, coned face of the sliding member.
Now we will see what happens when the accelerator is depressed. The governor forces the sliding member into contact with the friction member, and as this has at first no load no slip occurs between the two. The movement continuing brings the plate clutch into action, and this provides the take-up.
Obtaining Automatic Gear Control.
We still have, however, to explaie how the automatic control is obtained. It is effected by employiug the torque reaction between the engine and the propeller shaft, this being transmitted to an arm so connected to the friction member that as the torque increases this . member is brought nearer and nearer into alignment -with the flywheel Until,finally, in top gear, it is actually in line, the whole gear then constituting a positively engaged clutch. 13y adjusting the torque arm, various degrees of automaticity can be obtained ; thus, for exceptionally hilly country, gear ratios as a whole can be reduced, and this without interfering with the final-drive gearing, but if the top gear be too high for normal running, it would be advisable to lower the axle ratio.
Reverse is obtained by utilizing a small auxiliary gear.
The accessibility of this gear is smell that it can be removed from a vehicle in a few minutes. Every part is 60 simple that it can easily be understood by a novice, whilst fresh friction material can be fitted at a cost of 5s:
The central control lever is known by the company as the joystick, and can be used for many purposes, to not ell of which has reference been made. Hy it, the engine can be restarted while the vehicle is running, so that the vehicle can coast down inclines with the engine stopped, and the engine be restarted by merely pushing, the lever forward ; it also secures a free-engine position so that a car could not be started by unauthorized persons, even if they did press upon the accelerator.
Silent in Operation.
An important point is that the gear is quite silent. There is none of that rumbling which so often occurs in tho type of friction drive where the actual friction surfaces act as a clutch, thus causing fiats.
It will be realized that there is a certain amount of end pressure both on the flywheel and on the clutch plate. This is cared for by thrust races.
The gear already built is suitable for vehicles having engines of approximately 10 h.p., but a type for large commercial vehicles, such as buses, is now in hand, and one gear is actually being built for a 20-ton tank.