Cruise Control Decel Functionality

wwestFebruary 3, 2007

Since late in the last century manufacturers have been doing almost everything possible, conceivable, to improve the safety factor of vehicles with automatic transmissions when operating on low traction surfaces, most especially FWD or front torque biased AWD vehicles wherein engine compression braking will be the most detrimental.

It has now become common knowledge throughout the industry that engine braking on the front wheels will oftentimes interfere with the operation of ABS to the detriment, obviously, of the owners/passengers.

For those with long term stick shifting experience think about how often you wish for a clutch as you drive along in wintertime with your automatic shift transmission, especially a FWD one.

Most new owners manuals state quite explicitly that engine braking cannot be attained absent a manual downshift and in some cases not even then unless you disable, completely turn off, cruise control.

This whole widspread episode of throttle delay, 1-2 second downshifting delay/hesitation has arisen as the result of widespread industry adoption of a new automatic transmission shift pattern/sequence adopted late in the last century.

The technique involves quickly upshifting these electronically controlled transmissions/transaxles upon any FULL lift-thottle event wherein should the current gear ratio be retained would result in a significant level of engine braking. The idea is to improve the safety factor by virtually eliminating engine braking that cannot be overcome by the operator absent a quick shift into neutral, an action currently recommended by the AAA, but of itself fraught with peril.

So, rather than retarding the timing, as was previously done, to reduce the road speed of cruise control, I wouldn't be at all surprised to see the use of rear braking only via the traction control system to initially slow the vehicle.

But it is now pretty clear that applying the brakes, in total, to do this will be potentially safer, overall, than the use of engine braking which cannot be alleviated by the anti-locking braking system should it subsequently be needed.

Even slight engine braking on an extremely slippery surface, an icy bridge deck comes to mind, can easily result in loss of control even on a RWD vehicle, but the potential for loss of control of a FWD in these insatnces rises dramatically in comparison.

Be careful out there....

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**For those with long term stick shifting experience think about how often you wish for a clutch as you drive along in wintertime with your automatic shift transmission, especially a FWD one.**

I have thought about it, and the answer is never. The front wheel drive POS Ford Tempo with an automatic and studed tires all around, no abs, is the easiest thing I've ever driven in the snow and freezing rain bar none. That includes rear wheel drive cars and pickups, 4x4 pickups and sport-utes. One negative with a clutch on ice, or mud for that matter is if you get stuck, it's hard if not impossible to rock the vehicle forward and back to get a tire back where it can get traction. Simple with an automatic.

    Bookmark   February 3, 2007 at 10:55PM
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