RV Fuel Efficiency, Cruise Control Vrs. The Operator

A Thought from Lug_Nut. First introduced by Chrysler in 1958, Autocruise, or cruise control, was a primitive device to automatically maintain a given travel speed.  It basically was a vacuum controlled linkage that was connected to the throttle valve on the carburetor.  If the vehicle speed dropped below that of the set speed, the linkage would simply pull the throttle valve until the desired speed was accomplished.

Over the years, and with the coming of the electronic controlled engines, the cruise control advanced rapidly in newer technology.  Now the cruise control is a highly developed micro processor controlled device commanded by the onboard ECM (Electronic Control Module).  It is now capable of being programmed to manage the fuel delivery in a manner most efficient for fuel consumption while still maintaining a given desired vehicle speed.

Earlier cruise controls tended to operate in an “all or nothing” fashion when the vehicle was confronted with a rolling series of slight grades and descents at highway speeds.  But, unlike these older designs, the newer controllers have a preprogrammed buffer that prevents the knee jerk reaction experienced prior.  This buffer is in the form of a preset speed tolerance called “The Droop Settings”.  The droop settings are calibrated to allow the vehicle to fall or gain a given amount from the set speed with very little or no reaction.  Therefore short rises may require very little or no throttle.  Additionally, they also have the ability to apply proportionate power when needed.

The fact that cruise control modules are now micro processor controlled gives them the ability to share communication with other devices.  Radar, for example, such as Eaton’s Vorad, TRW or Delphi can communicate with the cruise device and offer what is termed as “Active Cruise Control”.  With this setup, radar sensors located in the front bumper, guard for traffic travelling ahead.  If a vehicle appears within a set range, the Vorad communicates to the cruise control module and the controller automatically reduces speed to match that of the car ahead.  This feature can be found on many higher priced cars and has been available on some motor coaches.

Cruise control modules generally come with the parameters preprogrammed by the vehicle maker.  These defaults fit most applications.  In the case of motor coaches, and in particular, diesel pushers, other features may be enabled.  The following are examples of additional features that may already be programmed or possibly can be.

• Increased warm up neutral idle control (Depressing the “Resume” or “Set” button selects and adjusts a higher idle while in neutral)
• Last speed memory (Remembers the last set speed even after being shutdown and restarted
• Automatic compression brake activation management (Shifts down at 6 MPH over speed and applies Jake at about 8 MPH over speed if the compression brake is on)
• Automatically disengage the Jake brake and select up shift (Both the engagement and disengagement of the compression braking system is done with extreme smoothness
• Fuel flow stopped (During the employment of the Jake brake fuel, to the injectors is turned off)
• One push per one mile per hour (Once cruise is engaged, one push equals one mile per hour, set reduces, resume increases)

If some of these features are not currently available on your cruise control, they can usually be programmed by your engine service provider or you may be able to get the cables and software to do it yourself with a laptop.

So, now to the question, can a modern cruise control manage the throttle more fuel efficiently than the operator?

Providing the cruise control module is programmed optimally for the specific vehicle, I believe there is no question.  This, of course, may be subject to a few exceptions including the possibility of a highly skilled operator under certain circumstances.

So, what’s your take?  Do you use your cruise control to help reduce fuel consumption?

Keeping You Cruising      –     Lug_Nut     –      Peter Mercer