The New Salerni Gearbox Tested
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An Interesting Device Employing Epicyclic Gears
1-1 A REPRESENTATIVE of The Coramenial Motor has recently carried out various tests on a private car equipped with the new Salerni gearbox. It enables a gear lever to be placed on the steering column, changes of gear being effected simply by moving the lever and then raising or reducing the engine speed by means of the accelerator, according to whether the change is to a lower or a higher ratio.
The clutch is used only for getting away from a standstill, and for changing into first speed or reyerse ; consequently an automatic clutch would be very suitable and Mr. Salerni is at present working upon a hydraulic mechanism of this nature.
The gearbox consists of epicyclic gears capable of providing four forward speeds and a reverse, and with the various parts held stationary or clutched together, as required, by means of mechanism of the Salerni type Introduced• as a coupling two years ago. This mechanism, it will be recalled, consists of a claw clutch provided with a floating guard ring which prevents the claws from engaging if the speeds are dissimilar. Applied to the gearbox it provides positive control and shockless engagement.
An accompanying diagram shows the arrangement of the gears, there being in the actual box two sun wheels and three planetary pairs; all teeth are of helical form. Top gear is direct with clutches (on the driven shaft) engaging the dogs 3 and 4, so that the whole unit
revolves en masse. To obtain third speed the dogs (4) are released, but the driven shaft continues to engage with the dogs (3). The annulus will then slow down, and when it comes to rest a data automatically engages the teeth (B). The annulus is thus held stationary so that the drive is conveyed through the rolling and rotating planets.
For second speed dogs 3 are still engaged, but the detent is freed from the teeth (B) ; a second detent then automatically picks up the teeth (A), so soon as these come to rest, so .holding the cage stationary. The planets then convey the drive, as in the back-gear of a lathe, with the annulus member idle. These forward speeds are engaged by a servo mechanism and are controlled
by the hand lever and accelerator, as already described.
First speed and reverse speed are in the nature of emergency ratios, the former being obtained through the dogs (2) when the teeth (B) are held stationary. For reverse, teeth A are held stationary and the drive obtained through the dogs (1).
It remains to be mentioned that by an ingenious system of rolling surfaces adjacent to the gear teeth the inventor bas been able to do away with the concentric bushes ordinarily required in epicyclic gearing. The box has not yet been given a prolonged test but appears to be carefully designed with the parts running at moderate speeds and light loads.