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  #1  
Old 09-11-2004, 08:24 AM
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ABS+steering or ESP better?

What's better? It dawns on me that ABS plus the ability to steer roughly approaches what ESP intends to do. One requires driver input, the other takes over automatically. Of course ABS allows the locked up tire to rotate while ESP does the opposite and decides which tire to brake depending on a bunch of factors.
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  #2  
Old 09-11-2004, 08:19 PM
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Kuan,

ESP does something in addition to ABS and steering. It manipulates diagonal pairs of brakes, or single brakes, to keep the car headed in the direction the driver indicates he wants it headed. That kind of manuever is not available with ABS and steering alone.

Also, there are times when ESP comes into play when braking the normal way, with or without ABS, is not part of the series of commands from the driver. ESP, as implemented by MB, uses the ABS sensors, a yaw sensor and a steering angle sensor to determine what the car is doing and what the driver appears to have intended the car do. It then tries to correct, using throttle and braking, the car's course while the driver is still manipulating the steering and likely throttle or brakes.

I have yet to drive a new MB with this system and bring it into play, so I am not able to describe the system in operation from the driver's seat. But I am sure someone else can. I know what it feels like to be under or over steering severely though, with ABS, and think an extra control to dial it out would be welcome. Jim
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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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  #3  
Old 09-12-2004, 03:08 AM
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ABS+driver input only applies to braking situations. ESP on the other hand, is also triggered when the car is losing stability in a non-braking situation, e.g., going through a corner with impending under- or over-steer. Here, ESP can selectively brake wheels to maintain the car's intended direction. In addition to this, it can also modulate engine power to bring things under control.

As an aside, BMW's active steering mechanism is also part of their stability control suite, where the steering angle of the front wheels (not the steering wheel) is actually modulated to help correct oversteer (although this is logical, it somehow does not give me a good feeling that MY steering is being overridden).

Kuan, you have brought up a key concept here - driver input. We drivers are still part of the loop and should view these electronic aids as helpers in detecting adverse traction conditions or limits of adhesion, for us to be able to react appropriately. And it sure is fun 4-wheel drifting in full opposite lock on a snow-covered parking lot ...
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Old 09-12-2004, 09:01 AM
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My feeling is that almost every emergency situation starts with a foot on the brakes anyway. So once ABS kicks in, the driver then has a natural tendency to try and steer the vehicle out of trouble. I guess ESP is beneficial in the Moose avoidance maneuver but that's about the only type of maneuver in which I find that ESP would work better than plain old braking and steering.
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Old 09-12-2004, 09:44 AM
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Traction control systems are new to me I have never owned a car with anything more than ABS. But here is a fun test I tried: go to a dirt parking lot or a wet one and turn the traction control off. At least on my freinds car you can slide it sideways, and spin it around ect. (Mercedes are so much fun to slide around in ) Turn the traction control on and the car won't let you do anything! It works well, the car wouldn't spin by cranking the wheel hard over at 25-30 mph! You just feel the brakes working and the power be cut to the engine. Even on wet grass you couldn't spin the wheels, it almost makes the car to easy to drive, you just point it around a corner with your foot down and the computer does the rest.
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  #6  
Old 09-13-2004, 02:10 AM
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Quote:
Originally Posted by Kuan
My feeling is that almost every emergency situation starts with a foot on the brakes anyway. So once ABS kicks in, the driver then has a natural tendency to try and steer the vehicle out of trouble. I guess ESP is beneficial in the Moose avoidance maneuver but that's about the only type of maneuver in which I find that ESP would work better than plain old braking and steering.
Not to be argumentative, but brakes are not always the first step in an emergency. Steering is often the first. Steering and braking is also a high probability. With ESP both of these work better than ABS and the driver alone, left with turning the wheel while his brake pedal buzzes.

The reason is when you brake hard and steer the car will respond to the maximum extent the front tires can maintain a grip. Typically this results in understeer and the car turns in the direction of the driver input, but not at the same rate as he was expecting, which leads to more steering input and more understeer. ESP modulates the front and rear brakes in a sequence, based on steering input and braking pressure, as well as what the car is actually doing in response. The net result is the car ESP system eeks out additional steering performance while continuing to slow the car down at the maximum practical rate.

The system also comes into play when the car might have begun to oversteer due to poor driving surfaces, road undulations and curves, or driver input that just causes oversteer. In an oversteering situation brakes are not likely to be a good choice. ESP responds by preventing oversteer before the driver gets sideways.

All this is up to a limit of course. After the limit I suppose the car will still under or over steer out of control. The fact you are driving over your limit is identified by a warning signal on the instrument panel whenever the ESP system is activated. The gist of the message is "I just saved your butt, and you better regain control or I may not be able to help the next time."

The Moose Avoidance Test benefit attributed to ESP is a consequence of ESP preventing uncontrolled over and under steering that leads to roll overs, which then prevents roll overs. It is more a "side effect" of ESP, not the primary goal of the system. Jim
__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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  #7  
Old 09-13-2004, 08:27 AM
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It's good to be argumentative Jim and I thank you for challenging my assumptions.

I guess I'd always thought of ESP as something which kicks in only in emergency situations. I would think that under normal driving conditions one would not need ESP. Then again, all my opinions about ESP are based on my own experiences. We'll see come this winter if it works on the VW Wagon
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  #8  
Old 09-13-2004, 09:48 AM
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Kuan,

The VW system is not quite the same as the MB system, even though they use the same acronym. The VW system as it was explained to me when my daughter was looking into a Jetta TDI does not have a yaw sensor, so it pretty much does not intervene before there is a speed difference between wheels. But I believe it still manipulates each brake individually. It is less clear to me how the VW system is as functional as the MB system. Jim
__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)
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