Independent wheel dynamometers
A limitation of the conventional rolling road dynamometer is that it is unable to simulate cornering, during which the wheels rotate at differing speeds, wheel spin and skidding. With the increased adoption of electronically controlled traction and braking (ABS), there is a growing requirement for test beds that can simulate these conditions. There are two types of solution:
• Four roll-set rolling roads. These machines range from end-of-line rigs consisting of four sets of independent double-roller units, to complex development test rigs, some having steered articulation of each roll unit. The production rigs permit the checking of onboard vehicle control systems, transducers and system wiring by simulation of differential resistance and speeds of rotation. The development of
hybrid vehicles may give impetus to the development of independent four-wheel chassis dynamometers since some designs are based on individual wheel drive motors. Electronically controlled transmission systems on 4×4 vehicles also require this type of dynamometer to simulate the road conditions for which they are designed to compensate.
• Wheel substitution dynamometers. A major problem faced by engineers carrying out NVH testing on a chassis dynamometer is that tyre noise can dominate sound measurements. One answer is to absorb the power of each drive wheel with an individual dynamometer. If the wheel hub is modified the vehicle can still sit on its tyres, giving approximately the correct damping effect, while the tyre contact and windage noise is eliminated. Alternatively, the wheels may be removed and the individual wheel dynamometers used to support the vehicle. The dynamometers should be four-quadrant machines, to simulate both driving and coasting/braking conditions. Hydrostatic, a.c. and d.c. machines have been used for this application.
Independent wheel dynamometers
A limitation of the conventional rolling road dynamometer is that it is unable to simulate cornering, during which the wheels rotate at differing speeds, wheel spin and skidding. With the increased adoption of electronically controlled traction and braking (ABS), there is a growing requirement for test beds that can simulate these conditions. There are two types of solution:
• Four roll-set rolling roads. These machines range from end-of-line rigs consisting of four sets of independent double-roller units, to complex development test rigs, some having steered articulation of each roll unit. The production rigs permit the checking of onboard vehicle control systems, transducers and system wiring by simulation of differential resistance and speeds of rotation. The development of
hybrid vehicles may give impetus to the development of independent four-wheel chassis dynamometers since some designs are based on individual wheel drive motors. Electronically controlled transmission systems on 4×4 vehicles also require this type of dynamometer to simulate the road conditions for which they are designed to compensate.
• Wheel substitution dynamometers. A major problem faced by engineers carrying out NVH testing on a chassis dynamometer is that tyre noise can dominate sound measurements. One answer is to absorb the power of each drive wheel with an individual dynamometer. If the wheel hub is modified the vehicle can still sit on its tyres, giving approximately the correct damping effect, while the tyre contact and windage noise is eliminated. Alternatively, the wheels may be removed and the individual wheel dynamometers used to support the vehicle. The dynamometers should be four-quadrant machines, to simulate both driving and coasting/braking conditions. Hydrostatic, a.c. and d.c. machines have been used for this application.
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