The essential
A wheel force transducer, a wheel torque transducer or a wheel pulse transducer has a stator that must not turn with the wheel. A rod holds it to the vehicle body. That link causes two errors: a rod that moves in its holder is read as wheel rotation, and a steered wheel changes the angle reference used to resolve the loads into vehicle axes. The Precision Vehicle Stator Restraint (PVSR) removes the first, the Stator Angle Correction (SAC) device the second.
Why hold the stator?
The encoder measures the angle between the rotor, which turns with the wheel, and the stator. Any stator movement is read as wheel rotation. The restraint attaches to the vehicle body and holds a restraining rod fixed to the stator.
What goes wrong at low speed?
With the original Magnetic Vehicle Stator Restraint (MVSR), nothing holds the rod in place inside its holder. Any rod movement appears in the angle, speed and distance data.
- Stop and go test: a slight oscillation on stopping and a backward pulse when the brake was released, both caused by the rod.
- Hard stop test: the recorded oscillation was significantly larger than with the PVSR.
- Rod moved by hand: large noise. The same noise can occur on uneven terrain.
What does the precision restraint change?
The PVSR adds a disk brush insert in the holder that keeps the rod centered. Its flexible magnetic sheet holds on a flat or curved vehicle body.
- Use it when wheel rotation is measured at near-zero speed.
- Use it when the rotation may change between forward and reverse.
- Rod moved by hand: no displacement and no noise.
What error does steering add?
When the wheel is steered, a stator held from the body no longer gives the correct angle reference. The wheel force transducer uses the rotational angle in the coordinate transformation to vehicle axes, so the loads are resolved with the wrong angle.
- An over-the-wheel bracket steers with the wheel and avoids the error, but it attaches to the steering knuckle and to the front of the tire, and is difficult to install.
- Without a bracket or the SAC device, the error has to be compensated in post-processing.
What does the angle correction device do?
The SAC device corrects the rotational angle signal in real time. The corrected angle goes into the coordinate transformation, so steering adds no angle error during dynamic tests.
- Replaces the over-the-wheel bracket on steered wheels.
- Internal encoder accuracy of ≤ 0.25°.
- Used with the standard amplifier, slip ring assembly, cable and CT2 interface box.
- Fits vehicles from small cars to trucks.
- Compatible with all Michigan Scientific digital-at-the-wheel wheel force transducers, including those already in service.
- Rated IP67.
Documents to download
To remember
- Near-zero speed, stop and go, reversing: use the PVSR.
- Steered wheels with a wheel force transducer: use the SAC device.
- Both remove the error at the source, so no post-processing correction is needed.