- The Dennis Patent Automatic Clutch and Easy-Change
- by Tim Stubbs
In February 2002, the Owners Newsletter carried a copy of a 1932 advertisement
for an Automatic Clutch / Easy Gear-Change - available on new chassis for
an extra £40. This was a little-known Dennis product, even amongst
ardent enthusiasts, and it was only when Gerry Bixley came up with his researches,
we were able to answer the question "what was this?"
This, it turns out, was an electro-vacuum operated device which
was worked by the driver using a push button beside the pedals. The gearbox
was fitted with an additional dog-clutch at the output end, no doubt similar
to the dog clutches with shaped teeth as used in the overdrive part of the
normal 5-speed Lance/Lancet gearboxes. The operation of the special push
button activated a solenoid which in turn used a vacuum piston arrangement
(similar to a vacuum brake servo) to operate the 'Easy-Change' mechanism.
- On pressing the button, the vacuum piston rapidly disengaged the normal
clutch, the additional dog clutch and operated the existing clutch-stop,
this stopping the rotation of all the gearbox shafts. The driver was then
able to select any desired gear with the gearbox stationary and, on releasing
the button, the dog clutch and then the main clutch were gradually re-engaged.
Dennis publicity claims - "It's so simple!" and refers to the
"sub-conscious mental strain which is probably the greatest contributor
to fatigue in drivers" who have to change gear by the old-fashioned
double de-clutching method! Or was it a way forward to compete with other
manufacturers who were developing fluid flywheels and epicyclic gearboxes
to make the driver's work easier.
It was undoubtedly an ingenious piece of Dennis design but the general
lack of information about the "uncanny" gadget suggests that the
idea was short lived, possibly even unsuccessful. Can any of our more senior
members shed any further light on the system? Has anyone ever heard of one
in operation? It would be interesting to hear.
- Click on drawing to see an enlargement
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