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BOSCH HELPS DRIVE STEERING SENSING.

Article Excerpt
To capitalize on the increasing opportunities(particularly in higher-end, smaller European and Japanese, as well as North American vehicles)for steering sensors that are used in electric power steering (EPS), electronic stability program (ESP), and that can have application in other chassis systems, Robert Bosch Corporation(Stuttgart, Germany/Farmington Hills, MI, 248-553-9000)(www.bosch.com) has been significantly expanding its products offerings, development activities, and product road map in the steering sensors area.

Bosch's steering angle sensors (which use magnetoresistive magnetic field sensor elements), and their combined torque and angle sensor (TAS)(based on optical sensing,) are designed to help advance and streamline steering sensor technology and to propel the adoption electric power steering systems, which can allow for more accurate vehicle control and enhanced energy savings and fuel economy, compared to conventional power steering systems.

Electrically powered steering uses an electric motor to drive either the power steering hydraulic pump (electro-hydraulic steering) or the steering linkage directly (direct electric steering). The power steering function is independent of engine speed, thereby conserving energy. Electric power steering systems can be very compact (packaged with the steering gear)and simpler than conventional hydraulic power steering systems to design, install, and maintain. The EPS is suitable for small-engine vehicles, since it is not parasitic and only draws power on demand. The 1990 Acura NSX was reportedly the first production vehicle to use a fully electronic steering rack.

The EPS system benefits from having input about the torque the driver applies to the steering column when he/she turns the car and input about steering angle/angular position (or rotation speed and direction). Production EPS systems have tended to use angle sensors or angular position sensors as steering sensors. Such sensors may provide inferred information about driver-generated steering torque.

Class III steering angle sensors have multi-turn measurement capability, a true power-on function, and provide an output of steering angle, as well as continuous self-test capability.

Class II steering sensors provide an absolute measurement of steering wheel angle over 180 to 360 degrees, a true power-on function, and an output of steering angle velocity.

Class I steering sensors provide two phase-shifted digital signals for steering velocity or relative angle measurement, and do not have plausibility checking capability.

Steering sensors in EPS allow for such benefits as varying steering support according to driving speed (which makes it easier to steer and maneuver the vehicle), more precise directional stability at high speeds, and can facilitate other functions, such as lane-keeping and intervention to influence driving dynamics.

Currently, the types of sensing technologies used in steering angle/position sensors include, for example, potentiometric, magnetic (e.g., anisotropic magnetoresistive, inductive) and optical. At present, steering systems are primarily used in EPS systems, primarily on European and Japanese vehicles.

In ESP systems-which help the driver regain control the car under adverse conditions (i.e., skidding),and can override the driver's inputs to the brake or accelerator to correct for under-steering or over-steering-the steering wheel angle sensor (in conjunction with signals from wheel speed sensors) provides input for computing the vehicle's intended...

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