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STEADY AS SHE GOES
Page 61
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The ESP skid-prevention system is said to save more lives than airbags; Cohn Barnett tested the latest version and was very impressed.
To the general public ESP stands for Extra Sensory Perception, which is not a million miles away from the function of ESP on vans. Here it stands for Electronic Stability Programme, and its ability to detect and prevent skids seems almost supernatural.
While some van manufacturers still haven't made basic ESP available as an option, the new Mercedes-Benz Sprinter and Volkswagen Crafter come with the latest version as standard. CM visited Mercedes' Unterturkheini proving ground at Stuttgart ahead of the main Sprinter launch to test the latest system.
The previous generation ESP, standard on Mere vans since 2003,combines yaw/lateral acceleration and steering angle sensors with the existing ABS road wheel speed sensors to detect the deviation from normal that heralds the onset of a skid.
Once a potential skid is detected the system's electronic brain prevents it developing with a combination of engine torque reduction and the application of individual wheel brakes to maintain the correct line.
Adaptive ESP as described by Mercedes, or "Bosch ESP version 8.1", adds one important component to the inventory: a longitudinal acceleration sensor, As well as providing data on acceleration in a straight line, it can identify the van's weight and centre of gravity.
Critical factor
This is a critical factor for vans, as the difference in dynamic behaviour between unladen and fully loaded conditions is considerably greater than in a passenger car.The extra input allows the electronics to provide a much more accurate response to abnormal situations.
Adaptive ESP brings with it a raft of three letter acronyms so beloved of vehicle mark eteers).These include ROM (Roll Over Mitigation), RMI (Roll Movement Intervention) and USC (Under-Steering Control), providing subtly different types of intervention for varying types of impending doom.
We tested the main features on the proving ground. First was the infamous 'elk test': the VDA sudden lane change manoeuvre which simulates avoiding a stationary object by moving left, then returning to the right lane a couple of vehicle lengths later.
Starting at 50km/h proved too easy; the manoeuvre was completed with no hint of loss of control. Even at SOkm/h, the only limit was how fast and accurately the steering wheel could be spun to move the extra-long Sprinter's body through the tightly packed cones.
Flat to the floor
We then moved to the steering pad,where a couple of inches of fresh snow helped to further reduce an already low coefficient of friction.
Driving an unladen van with foot flat to the floor made the electronics take over and limit our speed to just under 50km/h,leaving the vehicle under perfect control. Even standing on the brakes at this speed simply resulted in a fully-controlled. drama-free stop.
Repeating the exercise with the van loaded to half its maximum payload had the same result, except the electronics detected the extra weight and we lapped about 3km/h siower.lhe stabilising brake pulses were noticeably firmer with a load on board.
The optional AAS (Start-off Assist System) is a development of the hill-hold device which has been standard on larger Mercedes trucks.
In the case of the Sprinter, with neutral selected and the footbrake applied, it will maintain braking for up to two seconds, allowing time to select first and move off. If you need more than two seconds a light touch on the throttle pedal will maintain brake hold indefinitely. On the proving ground's test hills it performed exactly as advertised, either forwards or in reverse. •