Heavy Duty: Vehicle Stability Systems

Stability and rollover systems: Can your fleet afford NOT to have these?


The electronic stability control system effectively builds off both ABS and roll stability control, but as a full stability control system also addresses roll and directional instabilities, using additional sensors.

“When you’re going around a slippery curve and the vehicle starts to under-steer, the system will automatically intervene and apply individual foundation brakes to try to generate a counteractive force to kick the vehicle around so it’s going in a direction that the driver is pointing it,” Korn says.

As the vehicle is being driven, the turn angle sensor lets the system know where the driver is pointing the vehicle, the yaw-rate sensor and lateral accelerometer tell the system where the vehicle is going, and when there is a mismatch, the system will automatically intervene. During an under-steer, it will automatically activate one of the tractor drive axle brakes to create that counteractive force. During an over-steer, it will activate one of the steer active brakes, to try to correct the vehicle directionally.

The trailer-based Roll Stability Support system also helps minimize rollover tendencies, says Korn.

“It works very similar to the tractor system except when it senses a high level of lateral acceleration, it will only apply the trailer axle brakes,” Korn says. “The goal of that intervention is to slow the combination vehicle down to reduce lateral acceleration, which will reduce the rollover tendency.”

In December, Meritor introduced RSSplus, an updated system for trailers. It can be easily retrofitted, and according to the company, new diagnostics have made troubleshooting easier, and mechanics are likely to be more “hands on” with this system because they can install it themselves. The system will be available later in the first quarter.

BENDIX

Elyria, OH-based Bendix Commercial Vehicle Systems offers both roll and full stability systems. Electrics marketing manager Fred Andersky says while the rollover system can help prevent trucks from going around a turn too fast, the full system (ESP) adds a steer angle and yaw rate sensor to sense the spin on the axis of the vehicle, which helps out with loss of control-type situations.

Rollovers are really the secondary event when an accident occurs, he says, and the full stability system is better equipped to keep the truck headed in the right direction.

“Something happens that the driver has to make a maneuver that starts as a loss of control and then results in a rollover,” Andersky says. “The ESP system helps mitigate loss of control in those situations and goes a step further, and in slide-skid jackknife situations, this helps as well. A roll-only system doesn’t have that yaw rate sensor and steer angle sensor to figure out what’s going on, so it can’t help. With a full stability system, we’re braking the vehicle on all the axles, because the best way to get a vehicle under control is to slow it down as quick as possible, and the best way to slow it down is to cut the throttle and hit the brakes.”

The full system is also able to use specific brakes, rather than hitting them all at the same time.

“In a rollover type of scenario, you want to slow it down quick, so you hit all the brakes, and so the more brakes you’re hitting the better,” Andersky says. “But in a loss of control scenario, you may only want to hit the right front steer axle brake and the trailer brakes to help get the vehicle back in line and help the driver keep that control.”

Andersky said he has seen building interest in the full system from fleets in the last two years, especially when officials get to experience it first-hand.

“When you get them in the seat of the vehicle and they go through the maneuvers, that’s when they really see the value of it,” Andersky says.

Still, no system is fail-safe, he points out.

“It doesn’t replace a good driver or good driving practices,” he says, “And there is the basic physics—if a driver goes into a 25-mile per hour turn at 60 miles per hour, the system is going to intervene, but the laws of physics don’t get violated, and he’s going over.”

HALDEX

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