DaimlerChrysler
Continued from the ETS section.
The M-class: an electronic traction system with new functions smoothes the way to the great off-road adventure
Even better traction and driving stability thanks to 4ETS
New technology ensures particularly quick traction control intervention
brake-pressure control for downhill driving off-road
Jan 09, 2000
The Mercedes-Benz M-class can now deal with tricky off-road situations
with even greater ease thanks to a further development of its electronically
controlled four-wheel-drive system. In its latest version the Four Wheel
Electronic Traction System (4ETS) offers additional features which provide
distinct advantages particularly when faced with steep gradients, when
driving downhill or when crawling over obstacles.
Together with the Electronic Stability Program ESP®, 4ETS is part of the standard equipment of all M-class models. When the driving situation demands it, 4ETS uses microcomputers to transfer the drive torque onto both the front and rear axle, systematically apply the brakes to spinning wheels and ensure that those wheels which have good road adhesion are given optimum traction. In this way this innovative system can replace conventional locking differentials.
Booster Preload
The latest version of the four-wheel-drive system in the M-class uses an intelligent brake force booster which builds up pressure particularly fast. This allows 4ETS to apply the brakes to spinning wheels even sooner and to make optimum use of the drive power. The system releases brake pressure in response to the driving speed, wheel acceleration and accelerator pedal position.
When the off-road reduction ratio is switched on - which in the M-class is done by pushing the "Low Range" button - any 4ETS brake pressure which may be required remains constant over a long period and even at very low speeds to ensure even better traction than has previously been the case.
Previously, when there was a continued loss of traction and the vehicle speed is less than 20 km/h (12 MPH), the pressure at which the hydraulic fluid is modulated is also influenced.
Now the active brake booster is preloaded for faster pressure buildup in the 4ETS+ cycles. Thus allows the system to brake spinning wheels faster for shorter response time and better traction.
Booster Preload Operating Parameters
speed under 6 MPH with transfer case in high range
speed under 9 MPH with transfer case in low range
Maximum of one preloading per 4ETS intervention cycle
Minimum of 500 milliseconds before the next preloading
Two Foot Mode
The modified 4ETS system offers yet another benefit when it comes to moving off on steep hills and climbing over rocks and other obstacles such as fallen tree trunks. 4ETS+ allows the driver to move off more smoothly in these cases, since in "low-range" mode the system also works if the driver pushes down the accelerator and brake pedals simultaneously to ensure that the 4ETS remains active. Two-foot mode allows traction control to function at slow speed even while the brake pedal is depressed. This allows off-road drivers the ability to feather the brake pedal with the left foot while remaining on the throttle with the right foot for more precise vehicle control at crawl speeds. Previously, brake pedal application would suspend the traction control operation to enable ABS functions. With 4ETS+, traction control and ABS can now function together at slow speed which makes it much easier to maneuver under low traction conditions.
Two Foot Mode Operating Parameters
Enabled with transfer case in low range only
Brakes must be applied. Accelerator pedal above 10%
Driving speed less than 3 MPH (5 km/h)
Two-foot mode in earlier MLs requires modification of the pedal sensor switch.
Automatic Downhill Brake Control
The modified traction system also provides even greater driving safety on slippery downhill gradients or when driving downhill in rough terrain. This is because the electronic system can automatically identify such situations and intervene the moment a wheel loses grip and the engine braking torque cannot therefore be fully exploited. 4ETS will then apply the brakes to those wheels that have a good grip on the road, thereby assuming the effect of engine braking. The brake force released by the traction system corresponds exactly to the braking torque normally made available by engine braking. This automatic build-up of brake pressure ensures that in rough terrain the M-class travels downhill at a constant speed without the driver having to take further action. The automatic brake pressure control intervenes at a speed of less than 20 km/h - 12.5 MPH provided the "low range" off-road reduction ratio is activated.
Downhill Traction Control Operating Parameters
Enabled with transfer case in low range only
Driving speed is less than 12 MPH
Throttle pedal position 5% depressed or less
The vehicle is accelerating downhill
At least one wheel has lost traction and is spinning backwards
From: rgrill@csc.com Subject: RE: [M-Class] 4ETS testing in Alabama To: m-class@moab.off-road.com Date: Tue, 29 Jan 2002 12:39:40 -0600 On the MBUSI off road course during my factory delivery, the driver demonstrated the anti-rollback feature of 4ETS+. With the transfer case in LO range, and the Touchshift in first gear, he drove nearly to the top of a steep hill, then took his foot off the accelerator. The truck actually rolled backward all the way down the hill and then the engine shut down automatically. He explained that as a safety feature. Next, he made the same maneuver in 2nd gear and the truck would use the brakes to hold any position on the hill. He said there was a special circuit in 4ETS+ for anti-rollback and hill decent that only works in 2nd gear. - RODNEY movie of the test hill, with 50% slope real player _______________________________________________ M-class mailing list M-class@lists.off-road.com http://lists.off-road.com/mailman/listinfo/m-class
The 2002+ G-Class use 4ETS like older MLs instead of 4ETS+.
4ETS+ in 2002 M-Classes can engage at speeds up to 24 MPH / 40 km/h and once engaged remain active up to 48 MPH / 80 km/h.
Four new modes, mainly for low-range
| What does it do? | 4ETS '98-'00 ML | 4ETS+ '01+ ML | |
| booster preload |
increases booster pressure under 6 MPH in high range and under 9 MPH in low range to reduce pressure build-up delay and to keep pressure constant longer |
lower pressure facilitates softer, jerkfree intervention |
reduces wheel slip, |
| two-foot mode |
disables brake pedal sensor in low range under 3 MPH - 5 km/h |
keep foot on gas |
allows feet on brake and gas, at least 10%, to feather crawling |
| automatic downhill brake control |
when losing traction also brakes the wheels with traction in low range under 20 km/h - 12.5 MPH |
use brakes |
give less than 5% gas |
anti-rollback |
in second it wont roll back, found by RODNEY |
use brakes |
use 2nd gear |
|
The only limit to the M-Class 4wd system is the friction of the road. - Gerhard Fritz |