Diagnosing electric power steering systems requires an understanding of voltage, current and loads, and a technician needs to understand how the modules and sensors work together to determine the level of assist as well as what’s going on with the system. In this Tire Review Continental Tire Garage Studio video, we’ll walk you through five things you’re going to want to know about diagnosing the power steering system.
First, let’s talk about the motor. Most electric power steering systems use an electric motor, oftentimes with a brushless design and an operating voltage range of between 9 and 16 volts.
The motor uses a rotational sensor that determines its position. On some systems, if the module is replaced or the toe has been changed, the end-stops of the steering system must be learned so the motor doesn’t push the rack past the maximum steering angle. This might be an additional step the technician has to make on top of calibrating the steering angle sensor.
Second, you’ll want to be familiar with the electric power steering module. The module contains the drivers, signal generators, and MOSFET switches that power and control the electric motor. The module also contains a current monitor circuit that measures the amps the motor is using. The current monitor and other inputs determine the temperature of the motor using an algorithm that even factors in the ambient temperature.
If the system detects a condition that could cause the motor to overheat, the module will reduce the amount of current going to the motor. In this case, the system might go into a fail-safe mode and alert the driver with a warning light or message.
Third, if you don’t already think of your customers’ vehicles as rolling computers, it’s time to start. The electric power steering system has sophisticated software that can regulate not only the amount of assist, but also how the steering feels to the driver. The software also regulates the temperature of the motor. OEMs will often release updates for the power steering module, and these updates can help to resolve intermittent problems and codes that could cause the light to come on and make the system enter into a fail-safe mode.
Fourth, let’s discuss “dampening bumps.” Electric power steering can help to dampen shocks in the steering wheel due to irregularities in the road. It uses speed and steering wheel position information to determine the amount of dampening. However, this mode may also trick the driver into thinking something is wrong. If the steering happens to enter this mode while the vehicle is parked with the engine on, the driver might notice small movements in the wheel. Worry not, it’s all good.
Last but not least, it’s time to talk about the next generation of power steering. Manufacturers such as Ford, Audi, Mercedes-Benz, Honda and GM are introducing steering systems with variable ratios on some platforms. Some automakers are also calling this adaptive steering.
Variable-ratio steering changes the relationship between the driver’s actions at the steering wheel and how much the front wheels turn. With variable ratio steering, the ratio continually changes with vehicle speed, optimizing the steering response in all conditions.
At lower speeds, such as when pulling into a parking space or maneuvering in tight areas, fewer turns of the steering wheel are required. At highway speeds, the system optimizes steering response, letting the vehicle react more smoothly to each steering input.
In systems from Ford and Mercedes-Benz, you’ll find a precision-controlled actuator placed inside the steering wheel. That actuator is an electric motor and gearing system that can essentially add to or subtract from a driver’s steering inputs. The result is a better driving experience at all speeds, regardless of vehicle size or class.
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