A Practical
Page 48
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SPRAG
SPRAGGING device called the Saifgo has been tested quite extensively during the past 12 months, and was submitted to us the other day fitted to a Morris-Oxford car ; we understand that it is being tried by a number of commercial-vehicle users and has already attracted favourable comment from the engineers of insurance companies. Needless to say, a thoroughly satisfactory device of this kind would greatly add to the safety of all types of vehicle, particularly in hilly districts, and would make things easier for the driver when restarting on a steep gradient.
The Saifgo sprag consists essentially of a wheel with ratchet teeth, driven off the gearbox niainshaft, surrounding which is a casing containing four pawls and a control ring. A partial rotation of the ring has the effect of raising the pawls to inoperative positions, and this movement is automatically effected when the gear lever is in top, second speed or reverse speed positions. When the lever is in neutral or in first speed the pawls drop into ' engagement in readiness to provide a spragging action.
A very ingenious and yet simple earn-plate mechanism is used to interconnect the gear lever with the control lever which moves the ring, this plate being provided with Lshaped and V-shaped slots, as shown in the diagrammatic drawing reproduced—a drawing which is really self-explanatory.
As the result of this arrangement, if the vehicle to which this sprag is fitted is being driven uphill and is brought to rest, the driver has only to push the gear lever into neutral in order to make the sprag operative and so to prevent any run-back from occurring. There is thus no need to employ the brakes, and the sprag continues to hold the vehicle when first speed is engaged for getting away again.
When testing the car to which the
Saifgoevice had been fitted we noticed particularly (on a steep gradient of about 1 in 7) that the amount of running back after coming to rest was practically negligible. This is due to the fact that the pairs of pawls are offset to the extent Of half a tooth, so that the maximum backlash which can occur is only equivalent to half the pitch of the ratchet teeth.
A practical feature of the device, which should make it easy to fit, is that its length, measured along theaxis of the shaft, is very small, amounting to less than an inch in the case of a private car. The parent concern is the Motor Safety and Free Gear Co., Ltd. 20, Saville Row, Newcastle-on-Tyne. We are told that in the Newcastle district a number of motor coaches has been fitted with the Saifgo sprag with highly successful results.