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Understanding advanced electric power steering technologies

Sunday, October 1, 2017 - 07:00
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Electric or electronic power steering (EPS) has been around now for over a decade. The technology is by no means new at this point and we have written a few times on this subject here at Motor Age over the course of the last few years. However, the emerging technologies that utilize the EPS system provide a new twist. 

We are familiar at this point with technologies including electric-driven steering racks and columns, steering control units and various inputs including torque sensors, steering angle sensors and the like. The introduction of electric power steering occurred due to two major requirements: the ability to have power assist on a vehicle without a belt-driven hydraulic steering pump, which began with the Toyota Prius and is now utilized across the EV/HEV market. The other purpose was the need to reduce parasitic engine load in the form of a belt-driven pump with the goal of improving fuel economy. Assist is only provided when driver input via the steering wheel deviates from a straight-ahead position. The steering angle sensor and torque sensor work together with the power steering ECU to determine the amount of assist needed. This “on-demand” style of steering assist minimizes electric consumption, which reduces the field current on the alternator and ultimately improves fuel economy. The overall feel of steering systems has greatly improved as a result. When driving these EPS steering vehicles, it is hard not to notice how the steering effort for the driver has been greatly reduced.

(Photo courtesy of Subaru Media) Subaru’s Eyesight system is an example of how manufacturers are connecting technology to the EPS system to improve driver safety.

From driver assist to?
In its basic implementation, the electric power steering system seems rather simple. The complexity increases due to the inputs to the steering ECU via the CAN communication network. Manufacturers utilize engine RPM via the engine control module, vehicle speed and braking data from the ABS/skid control ECU, as well as inputs from safety systems including forward recognition cameras. It is important to mention that the driver is no longer the sole input for steering and steering assist. Manufacturers have now begun to implement new strategies for utilizing the EPS system after years of researching driverless vehicle technologies. While we are not quite yet ready for driverless vehicles, we are beginning to see the foreshadowing, much of which ties into the EPS system. Safety systems such as ABS, stability control and cruise control systems are beginning to utilize the steering system to perform such tasks as performing steering correction to stabilize a skidding or rolling vehicle and other tasks like keeping a tired and dozing driver in their lane. Diagnosis of these systems will require a thorough understanding of electrical principles, multiplex communication systems as well as the use of aftermarket or factory tooling to retrieve DTCs and perform functions such as steering angle resets, diagnosis of communication issues and the calibration of advanced camera and radar systems. Access to factory service information and diagrams will be essential, which means that an ability to process complex system strategies and apply them to a well-planned diagnostic strategy will be paramount. Factory tooling is currently the only way to carry out ancillary services such as forward recognition camera adjustment/calibration, should one need to be performed in the event of a collision or when replacing related system parts such as a windshield.  

Lane Keep Assist, lane watch and lane departure warning systems are just a few of the proprietary names used for a safety system that utilizes a forward recognition camera and in some instances multiple cameras and/or sensors to maintain the vehicle’s position within the lane while utilizing cruise control or whenever the lane departure system is activated during normal driving. This is done through the ability of the forward-facing camera to detect the painted reflective lane lines on the road. If a driver begins to fall asleep, the driver may drift in the lane. When the forward recognition camera and steering sensor corroborate that the driver is not intending to change lanes and is drifting, these systems will communicate with the steering ECU and correct the position within the lane.

(Photo courtesy of Subaru Media) Subaru utilizes a forward-facing camera to help keep the driver in their lane via the EPS system.

An example

With the introduction of the 2016 Prius, Toyota introduced Toyota Safety Sense (TSS). TSS is now a standard feature across the Toyota product line and in most cases, includes lane departure warning with steering assist function. It is important to note that this type of technology is across just about every brand at this point. For our purposes, here we will look at Toyota’s version of this technology. While attending a national instructor training event, I took part in a new-model 2016 Prius course that focused on this system and the diagnosis and calibration of the camera and millimeter radar system. This system is now making its way into the entire Toyota product lineup. While this system is specific to Toyota, it paints a picture of the complexities of the systems that relate to the EPS system.

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