How To Drive A Motorcar
A Key To The Subtleties Of Motoring
År: 1915
Forlag: Temple Press Ltd.
Sted: London
Udgave: 2
Sider: 138
UDK: 629.113 How
Written and illustrated by the Staff of "The Motor"
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PRACTICE IN DOUBLE DECLUTCHING
The movements may be enumerated thuswise :—
(1) Declutch and allow the accelerator pedal to come
up to the ordinary slow running position.
(2) Gear lever to neutral.
(3) Let the clutch in and accelerate the engine by
depressing the pedal for, say, a full second.
(4) Clutch.out, and gear lever into the third speed.
(5) Let the clutch in again and accelerate in the
ordinary manner.
One must admit that, written out in full, it is in
appearance rather complicated. The whole series of
movements, however, can, when one is really au fait
with them, be accomplished well under two seconds,
which, if one is to make a scientific and silent change
at any required engine or car speed, is not an excessive
time in which the car is to lose momentum. The
neutral position has to be regarded as if it were another
gear between the top and the third, though in practice,
of course, it is nothing more than a mechanical move-
ment utilized to serve a scientific purpose.
Let us now come to our diagrams again and find out
the why and wherefore of the movement in theory.
In top gear we have the wheel (e) in engagement with
the dogs on the wheel (a), the only connection with the
layshaft (1) being through the medium of the con-
stantly meshing pinions (a and b). We remember,
however, that the wheel (a), if revolving at 1000 r.p.m.,
means a speed to the wheel (b) and the layshaft of only
500 r.p.m. Now, to come from this top gear into the
third, it is necessary to engage the two wheels (j and
e). We remember, however, that j has 30 teeth and
e 30 teeth, so that, in order for a change to be effected
silently, the speed of the layshaft (1) must be in a
proportion of 30 to 30, or, in other words, must be just
the same speed as the primary shaft, which is, of
course, 1000 r.p.m. Assume, then, that we are going
along with the wheel (a) (and therefore on top gear ou
the wheel e) doing 1000 r.p.m., and it is desired to
change into the third gear. Then, if we assume that
the loss in momentum is such as to bring the speed of
tbo wheel (e), which, of course, is connected all the
97 G