The torque sensor performs the same function as the torsion bar and spool valve in a hydraulic system. The electronic sensor uses a torsion bar in the same manner as in the spool valve. There are three different types of electronic torque sensors, and they are classified as contact and non-contact types.
Hall-type sensors monitor the twist of the torsion bar by measuring the change in magnetic flux generated by its position to the vanes located on the sensor stator rings. Contact-type torque sensors use a wiper attached to the torsion bar and voltage divider attached to the rotating bridge attached to the motor shaft to measure the twist of the torsion bar.
The rotating bridge uses contact brushes that connect to the sensor housing and connector to receive power, ground and transfer the voltage signal to the controller Fig. The electric steering system will retain the hand wheel speed sensor HWSS for both speed and position. It will retain the four voltage divider circuits and a wiper. The voltage dividers are constructed of a resistive material on a film powered by a five-volt reference to make four degree sensing elements.
The wiper has a contact that rides on the resistive film and supplies the output signal to the controller. The signal ranges from 0. For example: The sensor produces 0.
It functions like a hydraulic-assist system, only that the hydraulic pressure is created by an electric motor, rather than driving the pump off the engine. This gets rid of the wasted-energy complaint noted earlier but doesn't enable all of the features possible with electric power steering. Only a few vehicles, including some heavy-duty pickup trucks, currently use this system. If you're interested in a deep dive into the mechanics of how steering assist is created in either hydraulic or electric power steering systems, check out this Car and Driver technical explainer.
Here at Car and Driver, the three major steering characteristics we evaluate in every vehicle we test are effort, response, and feedback. Two of those—effort and feedback—took a turn for the worse in early EPS systems, which didn't replicate the highly evolved, natural feel-for-the-road imparted by hydraulic systems. This made it hard to sense when a vehicle's tires were running out grip and starting to slip. Although driving enthusiasts like us were, not surprisingly, up in arms about these negative developments , they actually affected all drivers—and still do.
There's a real-world need for vivid feeling through the steering wheel when a vehicle is approaching its limits—say, when it's about to skid on a surface that's slick from rain, snow, or ice. A vehicle with more communicative steering makes for a better-informed, safer, and more confident driver in all situations.
However, the good news is that engineers have spent much time and effort through the years evolving electric power steering and creating sophisticated algorithms that faithfully re-create the steering sensations lost after the switch from hydraulic units.
They let you know what the front tires are doing just as faithfully as the old hydraulic steering systems did—which is a very positive development for both cars and their drivers. New Cars. Buyer's Guide. One system that was created to help increase fuel efficiency is electronic power steering EPS. Electronic power steering or electronic power assisted steering EPAS is comprised of four main parts; the motor, reduction gear, torque sensor, and a module that collects and sends out information.
Despite what you may have heard, EPS systems still use the classic rack and pinion set up, which is controlled by the module. Performance cars these days also need to produce a set of modes for the driver to pick from and most of them include a steering adjustment. This is not convenient for hydraulics as the hydraulic fluid being pumped through the system will have a set viscosity how easily a fluid flows therefore some alternate form of restriction has to be used.
The motors are usually placed either at the base of the steering column or directly on the steering rack and have become a fairly simple solution to advancing power steering into the 21st Century. Electronic sensors pick up the amount of steering lock being applied and add in a proportional amount of additional force to the steering input.
Electrical charge is used to rotate the motor and through energy transfer, a lateral force is produced that aids the movement along the steering rack. The main argument against eletronics is steering feel. As hydraulics are tactile due to the presence of a viscous fluid, they are loved by purists due to the amount of feedback that can be transferred through the steering rack and back to the steering wheel.
So, when electric steering systems first came into play, many road testers complained about a lack of feedback. Due to electricity effectively being a non-tactile commodity, it is a fair assumption to make that very little reaction force will make its way back through an electric motor.
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