A NEW STARTING-MOTOR MECHANISM.
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Ingenious Device Brought Out by C. A. Vandervell and Co., Ltd., as an Alternative• to the Bendix Pinion.
ALTHOUGEE starting motors are not yet used to any considerable extent on the heavier type of commercial vehicle, they are now quite extensively employed for the delivery-van type of chassis. In most cases the, starting motor is mounted near to the tail end of the crankcase and conveys power to a gear ring on the flywheel through the meditun of a sliding Bentlix •pinion. This device, while eminently practical and capable of giving satisfactory results in service, ties the designer to a definite location for the starting motor and limits the gear reduction which can be obtained, there being a minimum diameter below which the size of the pinion cannot be taken and, of course, a limit to the size of the ring gear also..
To overcome these difficulties a new device has been' brought out by C. A. Vandervell and Co., Ltd., which enables the designer to put the starting motor where he will, gives any gear reduction required and works with a commendable degree of silence. Erietly,_ the principle involved is to employ .a worm and wheel drive in conjunction with an automatic cone clutch for engagement purposes.
Worm Drive and Cone Clutch.
The worm is mounted on splines at the end of the starting motor shaft and meshes with a worm wheel which rides upon a shaft that can be coupled to any convenient rotating part of the engine. On one face of the worm wheel there is a ring of saw-teeth, with inclined faces, adjacent to which is a floating member of the cone clutch on which similar teeth are formed. Next to this again is the mating member of the clutch, which is securely fixed to the shaft on which it is monnted.
When' the starter button is depressed the worm and wheel commerce to revolve, but the floating clutch member tends to lag behind owing to its inertia. The tapered nature of the
engaging teeth therefore causes this member to travel along the shaft and engage with the other cone member, so conveying the drive. As soon as the engine commences to revolve under its own power the load on the clutch is reversed, the keyed member tending to overrun the floating member, so that the latter becomes automatically withdrawn.
So long as the hititor drivel; the engine the heavy torque, acting through the inclined tee-th, produces an end thrust C38
which is adequate for the purpose of keeping the clutch members together and preventing slip. On the other hand, the angle of the cones is chosen at such a figure that there is no tendency for them to join together, the surfaces freeing themselves directly the engine starts up.
If a backfire should occur, so that the engine revolves, momentarily, in the reyerse direction, the gear is unharmed . because the helix angle of the worm is sufficiently steep to
permit of reversibility ; in other words, when the crankshaft rotates in the wrong direction the drive is transmitted back through the worm gear and causes the starting motor to rotate also. •
An ingenious feature is the way in which the gear is safeguarded from the shock occurring when the dutch engages. As previously mentioned, the worm is mounted on splines and, as a matter of fact, it is free to float endwise on these splines within certain limits. This section is resisted by a stiff coil sPrieg, and, consequently, when the starter commences to .work and the clutch engages, the sudden increase of torque causes the worm to ride up the splines against the action of the spring. The mechanism is thereby iesulated from shock.
We have seen the device in operation and can vouch for the fact that the drive is picked up very smoothly and that no slipping occurs after the clutch has engaged. Silence of operation is another commendable feature.
A Compact Unit.
The aluminium ‘cage which carries the worm wheel and clutch forms a compact unit and is fitted with a flange of Standardized dimensions suitable for the, attachment of any starting motor. This unit can be arranged to drive through the timing e or can be coupled to a crankshaft or gearshaft. On the demonstration car the starting motor was mounted vertically, but, of course, this point is immaterial.
A useful feature is the way in which a shaft can he taken right through the gear so that it can be employed to convey the drive from the engine to any other component. For example, on the demonstration car this through shaft was coupled to the timing gear at one end and to the dynamo at the ()thee. It would also be possible to mount the device in front of the crankcase with one end of the shaft secured to the crankshaft and the other secured to the starting-handle dogs.
This gear is not suitable for sale to the ordinary motor vehicle user, but is one which, without doubt, many chassis manufacturers will take up in due course. The makers and patentees are C. A. Vandervell and Co., Ltd.. Warple Way, .Acton, London, W.3.