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Vehicle Data Sources for the Accident Reconstructionist
Published in Donald E. Struble, John D. Struble, Automotive Accident Reconstruction, 2020
Donald E. Struble, John D. Struble
Understeer, Neutral Steer, and Oversteer: In crude terms, a vehicle is said to be in understeer if its turning response becomes less sensitive to the steering wheel input as the steering wheel angle increases, and in oversteer if it becomes more sensitive. A truly neutral steer vehicle would always be on the cusp between these two. In the limit, an understeering vehicle could lose all sensitivity to steer inputs and “plow out”; an oversteering vehicle could become so sensitive to steer inputs that its yaw rate cannot be controlled, and it “spins out.” More precisely, “a vehicle is in understeer … if the ratio of the steering wheel angle gradient to the overall steering ratio is greater than the Ackerman steer angle gradient.”1 Vice versa for oversteer. Since the vehicle is a nonlinear system, a vehicle could be in understeer for some inputs and oversteer for others. For more information, see SAE (Society of Automotive Engineers) Recommended Practice J670e.2
Feedback Properties of Vehicle Controls
Published in Guy H. Walker, Neville A. Stanton, Paul M. Salmon, Vehicle Feedback and Driver Situation Awareness, 2018
Guy H. Walker, Neville A. Stanton, Paul M. Salmon
In a case of understeer the driver recovers the situation by slowing down and steering harder into the bend. With oversteer the driver has to correct the slide by steering in the opposite direction of desired travel, i.e. steering into the skid. These behaviours can also be captured by transfer functions. In a case of understeer, the vehicle retains the broad characteristics of second-order control except with much increased time lag. In the case of oversteer, the vehicle assumes the characteristics of a higher-order control level (third or fourth order perhaps). This is potentially challenging for drivers.
Chassis systems
Published in Tom Denton, Advanced Automotive Fault Diagnosis, 2020
Oversteer occurs when the rear of the vehicle tends to swing outward more than the front during cornering. This is because the slip angle on the rear axle is significantly greater than the front axle. This causes the vehicle to travel in a tighter circle, hence the term oversteer. If the steering angle is not reduced, the vehicle will break away and all control will be lost. Turning the steering towards the opposite lock will reduce the front slip angle.
Handling performance optimisation for formula vehicle using multi-objectives evolutionary algorithms
Published in Vehicle System Dynamics, 2020
Additionally, the ISO 4138- steady-state circular driving behaviour: open-loop test methods [19] is a commonly used manoeuvre test to measure the steady-state response of a vehicle. It measures the understeer gradient of the vehicle when subject to lateral acceleration response. This determines the vehicle behaviour whether it is in understeer, neutral steer or oversteer condition. For safety reasons, the vehicle will not be designed to the oversteer behaviour as it is dangerous to drive where the vehicle will spin off after it has reached the vehicle critical speed [20]. Optimising those measurements are tricky, as merely minimising those responses would not necessarily produce a good handling vehicle. As those responses often fall within an acceptable range by a human driver [18,21,22].
On pre-emptive vehicle stability control
Published in Vehicle System Dynamics, 2021
Alberto Parra, Davide Tavernini, Patrick Gruber, Aldo Sorniotti, Asier Zubizarreta, Joshué Pérez
For the Base-TV, the stage cost formulation is: while the terminal cost is: where is the total force demand from the drivability controller, i.e. the respective cost function term tracks the driver input on the accelerator and (where applicable) brake pedals; is the reference yaw rate; is the rear axle sideslip angle, which is penalised to enhance stability; and , , and are the cost function weights, respectively prioritising longitudinal force tracking, reference yaw rate tracking, and rear axle slip angle reduction. In this preliminary proof-of-concept analysis of pre-emptive stability control, is purposely simple; however, it could include additional terms, e.g. to reduce energy consumption, as proposed in [27], or to prevent roll-over [11]. The consideration of , which is calculated through (18), ensures vehicle stability and avoids oversteer, which could be the result of extreme transient conditions. Only the rear axle sideslip angle is explicitly considered in the cost function, while the reduction of vehicle understeer, which tends to occur less abruptly than oversteer and is associated with the front slip angle, is implicitly addressed by the yaw rate tracking term. As a matter of fact, nearly all production vehicles tend to be understeering rather than oversteering, as understeer is usually considered more controllable by the driver and less dangerous than oversteer.