Do Speed Govenors on Diesels really Save Fuel?

[M.D. Holloway]

I would think so - it restricts RPM right? So if thats the case wouldn't it only allow you to get to speed to the optimal speed on a highway to be most fuel efficiant?

[island911]

aero drag on a sqr plate goes up with the sqr root of velocity.

[BeeMaster]

Yes but if you pick the correct size engine first (don't go over sized or under)it help more.
And a good driver. Further more a good manual with a good driver, heck even with a bad driver a real manual transmission will get far better mpg than a automatic.
6.5-8 manual, 5-6 with a automatic.

[VINMAN]

I find with my diesel, if I set the cruise control at 65, I get the optimum mileage.

[Joe Bob]

Poorman's cruise control when you firewall it.....also, I agree most diesel powered rides are hardly aerodynamic.

[M.D. Holloway]

Any reason to think that fuel economy would actually suffer cuz of an after market fit of a govenor?

[VINMAN]

Are you talking about governing speed or engine RPMs? I can see restricting RPMs, hurting performance and causing lower MPGs.

[M.D. Holloway]

I have to dig around and find out what type of govenor was used...

[VINMAN]

Most of our newer firetrucks are speed governed.

[M.D. Holloway]

OK, seems like there are several types of governor technology available...

- hydraulic speed droop type governor is designed for use on small diesel, gas, or gasoline engines where isochronous control is not required. The design of the speed droop governor is such that the governor operates at a slower speed as engine load increases. It is through this characteristic that stability of the system is achieved and division of load between paralleled units is made possible.

- Pressure Compensated governor is a speed-droop or isochronous governor for controlling the speed of small diesel, gas, and gasoline engines, or small steam or industrial gas turbines. The governor is used to control engines or turbines driving alternators, dc generators, pumps, or compressors.

- dial and lever governors feature lever or dial speed adjustment, a spring-driven, oil-damped ballhead which filters frequency torsional vibrations, an optional speed adjusting motor, electric, oil, water, or pneumatic shutdown, optional droop, and have a wide speed range available.

- Pressure compensated, isochronous control type governor widely used for controlling speed for all types of diesel or gas engines and steam turbines, driving pumps and compressors.

- EGB Governor/Actuator is used with analog or digital electronic controls that provide a proportional 20-160 mA signal to control dual fuel, diesel, and gasoline engines, and gas and steam turbines driving electrical or mechanical loads. During normal operation, the electronic control and actuator section of the EGB regulates fuel to the prime mover. Upon loss of electronic control signal, the standard EGB is adjusted to cause prime mover shutdown. An electronic, pneumatic, or manual starting device is then used to allow prime mover starting and operation under ballhead control. The ballhead section also regulates fuel if the control fails in such a manner as to call for maximum fuel. The EGB governor/ actuator can also be factory set to give maximum fuel (reverse action) on electronic control signal loss. The self-contained hydraulic oil supply makes the governor easy to maintain in almost any installation environment.

[M.D. Holloway]

Vinny, you guys prolly do short runs but have you noticed an improvement or decline in fuel economy?

[BeeMaster]

Just to clarify my first comment was about 12liter, quad axle dump trucks,
And mph speed governing.

[VINMAN]

Honestly we really don't keep track of it. Its rare when we can get our rigs up to full speed, except when we get calls where we can take the highway. They are limited to 65mph. Most of our calls are less then a mile or so from any of our stations.

[M.D. Holloway]

and

The governors, used on heavy-duty truck applications and construction equipment, fall into one of two basic categories:
• Limiting-speed governors, sometimes referred to as minimum/maximum models since they are intended to control the idle and maximum speed settings of the engine. Normally there is no governor control in the intermediate range, being regulated by the position of the throttle linkage.
• Variable-speed or all range governors that are designed to control the speed of the engine regardless of the throttle setting.
Other types of governors used on diesel engines are as follows:
1. Constant-speed, intended to maintain the engine at a single speed from no load to full load.
2. Load limiting, to limit the load applied to the engine at any given speed. Prevents overloading the engine at whatever speed it may be running.
3. Load-control, used for adjusting to the amount of load applied at the engine to suit the speed at which it is set to run.
4. Pressure regulating, used on an engine driving a pump to maintain a constant inlet or outlet pressure on the pump.
At this time on heavy-duty truck and construction equipment applications, straight mechanically designed units dominate the governor used on nonelectronic fuel injection systems.

[wdfifteen]

I think governors on road going diesels restrict ground speed, not engine speed, but things are changing fast. There could be some that restrict manifold pressure for all I know. There used to be mechanical/pneumatic governors that did just that.
The description of variable speed governors is not what we use for gasoline engines. A variable speed governor will maintain engine RPM relative to the setting of the throttle. WOT it will maintain maximum rated RPM. At half throttle it will maintain half maximum rated RPM, etc.

[island911]

Originally Posted by M.D. Holloway

Vinny, you guys prolly do short runs but have you noticed an improvement or decline in fuel economy?

What are you thinking, Mike? ...that maybe the volumetric (in)efficiencies (and mixing) of a slower running engine will out-pace the rapidly increasing load of speed?

You'll have a tough time coming up with a scenario where that happens.

hmmm.. If a rig can NOT get to it's tallest gear, that could be a problem for fuel economy.

[M.D. Holloway]

Thats what I was thinking - I had a friend call me stating that he saw a reduction in fuel economy after govenors were installed and wanted to understand if it was a cause/effect, correlation or co-inky-dink...

[BeeMaster]

Originally Posted by M.D. Holloway

Thats what I was thinking - I had a friend call me stating that he saw a reduction in fuel economy after govenors were installed and wanted to understand if it was a cause/effect, correlation or co-inky-dink...

What type of truck does he have? What engine/transmission, in his top gear at what rpm does He hit the speed governed?

[M.D. Holloway]

Over the road fleet - I think they run mostly International Navistar but I will look into it.

[Tervuren]

Originally Posted by BeeMaster

Yes but if you pick the correct size engine first (don't go over sized)it help more.
And a good driver. Further more a good manual with a good driver, heck even with a bad driver a real manual transmission will get far better mpg than a automatic.
6.5-8 manual, 5-6 with a automatic.

A over-stroke engine at lower RPM is going to be more efficient than a smaller engine size that would require a higher RPM for the same power.

What I've heard from some one I know that ran a trucking company, if that an RPM governor makes the driver actually use his gear box, rather than revving up to redline, and skipping gears. HUGE fuel savings in this case.

A speed governor helps in that the drag at higher speeds increases quite stiffly. From a safety stand point, I'm not sure I'd go this route.