Bosch Develops New Torque Sensor for Electric Power Steering
02 March 2010
Bosch’s new TSS (torque sensor steering) torque sensor for EPS systems. Click to enlarge. |
Bosch has developed a new TSS (torque sensor steering) torque sensor specifically for electric power steering (EPS). The new TSS allows sensitive measurement of the steering force exerted by the driver. Based on the measured values, an electronic control unit determines how much steering support the electric servo motor needs to deliver—adapted to the condition of the road surface and vehicle speed.
Electric power steering is a more energy-efficient alternative to hydraulic power steering; use of EPS can reduce fuel consumption by up to 0.5 liters per 100 kilometers driven. EPS also provides a foundation for attractive, new driver assistance functions such as lane-departure warning systems or parking assistants. Market observers expect that every second steering system will be electric by 2016; the current figure is approximately every third.
Bosch TSS steering torque sensor |
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Its ultra-fine torque resolution makes the TSS a basis for precise, energy-efficient intervention in the servo drive. The steering torque sensor’s compact construction also makes it suitable for installation in both the passenger and the engine compartment. The TSS is currently subject to endurance testing and vehicle testing. Samples are already available from Bosch Automotive Electronics. Rollout of series production is planned for mid-2010.
Installed on the torsion bar in the steering column, the TSS uses a contact-free magnetic measurement principle to ascertain torque. The TSS twists in direct proportion to the increase in steering force caused by the frictional resistance between the tires and the road.
Two concentric rings enclosing the torsion bar measure the twisting angle. One ring uses multipolar permanent magnets to generate static magnetic fields, which strike Hall sensors through “windows” in the second ring. The measured quantity is the magnetic flux reaching the two Hall sensors. This contact-free and therefore wear-free measurement process is highly precise.
Twisting angles as small as 0.002° cause quantifiable changes in the magnetic flux. Due to the redundancy of the electronic components, the sensor satisfies all the requirements for modern safety systems. In order to compensate for temperature effects, the TSS has an internal temperature sensor. When the vehicle is driving straight ahead, the TSS identifies the 0° steering angle in a separate measurement process, and relays this information to the electronic control unit as an index signal.
GM just recalled 1.3 small cars like the Cobalt that can have power steering failures and cause hard steering below 15 mph. Which brings up a safety issue in general. What happens if a hydraulic valve fails and goes full on? What happens when an electric drive shorts and the motor goes full on?
Posted by: SJC | 02 March 2010 at 10:11 AM
it was my impression that the nimh patent ended a few years ago so anyone can make it but more importantly nimh is of no concern. lithium is so much better.
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Parking Sensors
Posted by: Account Deleted | 26 February 2011 at 03:37 AM