A New Preselective Synchromesh Gearbox
Page 53
If you've noticed an error in this article please click here to report it so we can fix it.
Five-speed Transmissionwith Automatic Change Introduced by the David Brown Concern
ANentirely new five-speed transmission-unit with many novel features is exhibited at the show by David Brown and Sons (Huddersfield), Ltd., Lockwood, Huddersfield, the Wellknown concern of geak.sp.ecialists. The second, third and fifth-e (overspeed) ratios are obtained through. helical gearing in constant. mesh, . these and the fourth (direct) ratio .
being engaged throngh dogs with I synchrornes.h
cones. Sliding spur gears provide first and reverse speeds., • ..!..
The six selector rods are arranged in align-. •. meatand the direction : in which they :move to engage "their : respective'
dog clutches isthe same in each case. At the
end of each 1--4-fel there is a finger; and the set of six is so arranged that the fingers radiate from a common centre. Consequently, any one of them can be picked up by rotating a fork, This selecting fork is operated by a gear lever (working in a quadrant) hrmigh the medium of small spur gears and a quick-thread device; one of the gears is pierced with holes which interlock with a fixed peg.
Sufficient " lost motion " is allowed in the gear-lever control system to permit the lever to be moved to the extent of one gear, up or down. Such movement exerts spring pressure on the
selecting fork in the appropriate direction, but movement is prevented by the interlocking peg.
When ready, the driver has only to depress the clutch pedal; this. action first disengages the clutch and then (it the pedal be fully depressed) frees the gear previously engaged and allows the fork to pick up the next gear. Upon releasing the pedal the preselected gear is brought into action, followed by clutch engagement.
As a further step, a power shift has been incorporated by using a cylinder connected to the inlet pipe of the engine. Valves are so arranged that if the driver declutches fully with the throttle wide the b changes down by one gear.
Conversely, if the clutch pedal be depressed with the accelerator released the box changes up—again to the extent of one gear. In every case the gear lever moves simultaneously and so shows clearly which ratio is in use. Furthermore, the driver can, at any time, preselect and engage a different ratio if he so desires.
This ingenious gearbox embodies a. new form of synchromesh mechanism in which the shoulders on a number of pins delay dog engagement until the cones have synchronized the speeds. The whole mechanism has been designed by Dr. H. E. Merritt, assistant chief engineer to the com pany concerned. '