I propose this as a fair test for all new
cars equipped with an automatic transmission.
Start the engine and warm to normal
Place car on a level surface 50 feet in
front of a steel pole
Shift the transmission lever into Drive
Take all feet from the pedals
Steer car, if it moves, directly into pole
If car is still operational and/or salable
60 seconds later, it passes test
Well, I don't know about your car, but my car
would fail miserably. Let it be known to all that many accidents have been
caused by the innate tendency of cars with automatics to "creep", or
go ahead on their own, with no input from the driver. It should be the
characteristic of all cars, on a level surface, not to move when all pedals
You can easily demonstrate just how much
torque is transferred to the driving wheels with the engine at idle and in
gear. Jack up the vehicle so the two driving wheels are in the air. For
vehicles not equipped with "Positraction®" or equivalent, block one
wheel so the differential gear will only drive the opposite wheel. The other
wheel will turn with considerable torque. This torque is the cause of the
undesirable creep. Caution: Do not try to stop the turning with your
hands; it is impossible and could be dangerous if tried. It is even dangerous
to stop it by sliding a block under the wheel because the torque may be enough
to drive the car off the jack. You have been warned!!
People have been injured and even killed by
creep. Usually, it is a case of contributory negligence where a driver leaves
his car in neutral, brake off, and gets out of the car to do something like
shut the garage door. A child shifts the transmission into gear and the car
moves. It ends when the car crashes into a fixed object, hopefully before the
child panics and jumps out, risking getting run over. Sometimes people have
been crushed or run over by their own cars. In traffic, sometimes a car will
creep into the back end of another, if the driver is inattentive or relaxes
brake pressure. It is brake pressure that controls creep in ordinary driving.
The earliest transmissions, notably the
Hydramatic® of 1938 and a number of years following surprisingly had little or
no creep. The reason was their use of
single or dual fluid couplings. A fluid coupling is illustrated at right. Fluid couplings
are quite inefficient at engine idle and did not transfer significant torque.
In later years, beginning in the early '50s, torque converters replaced fluid
couplings in many makes. The torque converter made for a cheaper and more
efficient transmission because it eliminated the need for one planetary gear
system. However, it had the undesirable trait of transmitting torque even at
idle, causing notorious creep. Packard realized the undesirability and
possible dangers of creep and developed a rather crude method of controlling
it. Studebaker-Packard automatics utilized an internal brake mechanism to absorb the
torque before it could reach the output shaft. Other makes ignored creep as
did the public. We now seem to think it is normal and natural for all our cars
to want to go on their own whether or not we want them to, when the gear
selector is in a drive position or reverse.
How can today's transmissions overcome creep?
I think the most elegant solution lies in the design of a variable pitch
stator. The stator is the third element which fluid couplings do not have. The
stator redirects fluid flow between the drive member (pump) and the driven
member (turbine). A present day torque converter is shown schematically here. The fixed stator as used in all present designs is always in
the helping direction; that is, in torque multiplication. Thus, torque is
always transmitted to the converter at all engine speeds. What is needed is a
variable pitch stator whose blade angles can be changed by a hydraulic servo
to a torque neutral position at idle, with feet off the pedals. It the car
begins to roll backwards, a sensor can detect wheel rotation and the blade
angles can be increased to provide just enough torque to prevent backwards
vehicle movement. When the driver pressed on the throttle pedal, the blades
would be adjusted to normal torque multiplication and the car would accelerate
normally. The transition could be made seamless, with no engine runaway
tendencies. An added benefit would be improved engine-assisted braking from
road speed. Drivers of conventional transmission equipped cars often downshift through
the gears to use engine compression to assist braking. Often service brakes
don't have to be used at speeds above 30 mph. Such is never the case with
automatics; they are notorious for being very poor performers in this regard.
A variable stator could be self adjusting to maximize torque transfer from
turbine to pump during deceleration providing better engine braking and saving
the brakes from wear and possible overheating.
The manufacturers have prior knowledge of the
extreme hazard of creep and have been put on notice to expedite the solution.
Buyers of expensive makes should test drive before purchase and insist that
this inherent defect be remedied as a condition of continued patronage.