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Author Topic: Why not a power control?  (Read 2864 times)

Offline Geezer

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Why not a power control?
« on: 08/09/2010 07:10:05 »
My Dodgy Ram (aka "The Sheepie Truck") has a cruise control - which is quite useful in these parts. It's also helpful for staying within the speed limits and thereby avoiding any unpleasantness with the local constabulary.

However, there are some rather steep inclines around here. When I get on one, the cruise control will faithfully try to maintain the "set" speed, even if it means cranking the engine up to excessive RPMs. It's not much of a problem when the truck is lightly loaded, but if I'm pulling a trailer, it's a bit alarming when the transmission drops into low gear and the engine starts howling.

I'd like to be able to tell the cruise control to put a limit the engine power output somehow. I wonder if any vehicles have that capability?


 

Offline tommya300

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Why not a power control?
« Reply #1 on: 08/09/2010 11:50:09 »
"I'd like to be able to tell the cruise control to put a limit the engine power output somehow. I wonder if any vehicles have that capability? "

I wonder is a standard transmission, manual shift, stick shift hurst a man's doggy power wagon little less shee-pie vehicle, (a truck with a clutch), would respond differently?
« Last Edit: 08/09/2010 11:55:27 by tommya300 »
 

Offline peppercorn

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Why not a power control?
« Reply #2 on: 08/09/2010 12:43:56 »
I can't say I know of any vehicles that have such an adjustment, but in these days of engine maps setting all parameters, it would seem simple enough to have an additional cruise control map that is not so aggressive in trying to keep at the speed set.
Whether any manufacturer would bother allowing the driver to 'dial-in' the maximum revs, hp or mpg would seem unlikely. A progressively Eco-to-Sport setting that governs the vehicles general responsiveness seems to be increasingly common now.

If you don't mind buggering around with your own vehicle, you could probably modify the engine's aggressiveness in CC mode (as well as elsewhere) by adding a switched-in resistor to the O2 sensor (?).
 

Offline graham.d

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Why not a power control?
« Reply #3 on: 08/09/2010 13:05:50 »
"I'd like to be able to tell the cruise control to put a limit the engine power output somehow"

It's what the driver's for. Are you asleep in the back? :-)

Many modern cars have rev limiters which should cause an internal argument which the rev limiter will win, but it may still be howling a bit. It has to be a driver choice at what degree of howl vs what speed for going up an incline.

Years ago I had an early Ford Anglia (with the 100E side-valve engine) and took it over the Hardknot and Wrynose passes in the lake district (1 in 3 but much steeper on the bends!). Also it had only 3 gears with no synchromesh on first - by the time you double declutched you were going backwards. A frightening experience, and you are worrying about manually slowing down to avoid a gear change; pah!

I noticed my new car (I have had others between the Anglia and this one) actually applies the brakes, if I had accelerated above the cruise control setting, to quickly restore the speed. I didn't know this feature was there so it surprised me rather. 
 

Offline Geezer

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Why not a power control?
« Reply #4 on: 08/09/2010 17:14:41 »
"I'd like to be able to tell the cruise control to put a limit the engine power output somehow"

It's what the driver's for. Are you asleep in the back? :-)


No, not asleep, just watching TV. (Kidding!)

I forgot to mention - it tends to do the same thing even when my foot is controlling the accelerator. It's particularly bad on the Northern section of Interstate 15 in Montana. That route crosses the Continental Divide three times, so the engine is a bit short on oxygen and really having to work hard.

My cruise does not apply the brakes, but it will shift into a lower gear and use engine braking on a descent.

My first car was a 1955 VW. I think the engine produced (allegedly) 35 hp, but considering the miles that were on it, it might have been more like 25 hp. You don't get too much for 35 quid!
 

Offline SeanB

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Why not a power control?
« Reply #5 on: 08/09/2010 20:34:56 »
Ideally an auto box should be coupled with the engine management and the cruise control,. and should disengage when the load is so high that the box has to change to a lower gear. This is common on most manual cars, as they disconnect the cruise control if either the brake or clutch is depressed, or if you press the disengage switch on the cruise control unit.

The only time this would be a problem with an auto box is if it is an aftermarket unit, and is only connected to the brake switch ( and you get very funny behaviour from it when both brake lights fail) and has no other input other than vehicle speed, and only controls the throttle position via a vacuum actuator. A built in ( from the vehicle manufacturer) unit would be integrated to respond to gear changes correctly, and most modern vehicles with electronic management have this built in by default, even though the cruise control may be an option only on the top end vehicles. It is cheaper to have the software there and not used whilst adding it via the switch assembly and loom to a few models is much cheaper as the software testing cost is amortised over a larger number of units.

Ideally though you need to be actually in control of the vehicle at all times, the use of a cruise control is best on a flat plain, or a gentle rise or fall. Using it in a mountain pass is a certain path ( pun intended) to a vehicle shaped hole in the ARMCO railing, and a funeral pyre somewhere down the mountain ( I have seen many of these, all caused by driver error in the selection of a correct speed for the conditions) for the vehicle and cargo, human and others.

One pass near me has 5m high concrete skirts on the steepest hairpins, it has reduced the number of flying taxis a lot, although a few have managed to make it over despite this and the steel railing inside them. Fun going down there with a boat, I always stopped at the top and selected 1st gear, and still had to brake all the way down, dodging the kamikaze drivers passing me with the praying passengers.
« Last Edit: 08/09/2010 20:46:24 by SeanB »
 

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Why not a power control?
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