Understanding advanced electric power steering technologies

Oct. 1, 2017
With advanced electric power steering technologies, it has become critical to understand that power steering is not simply driver operated.

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.

At the heart of the system is a windshield-mounted camera with a complex latch and cover. The camera and its positioning within the windshield-mounted bracket require special attention during service after the replacement of related parts or in the case of a collision. Within Toyota service information, Toyota specifies the following considerations when working with the camera:

  • When replacing the forward recognition camera, replace it with a new one.
  • Do not touch the camera lens. If the camera lens has been touched, do not use the forward recognition camera.
  • If the forward recognition camera has been struck or dropped, replace it with a new one.
  • If the forward recognition camera is not properly installed, forward recognition camera optical axis learning cannot be performed properly. Make sure the forward recognition camera is installed securely.
  • Replace the forward recognition camera if there is any foreign matter on the camera lens.
  • When replacing the windshield glass of a vehicle equipped with a forward recognition camera, make sure to use a Toyota genuine part. If a non-Toyota genuine part is used, the forward recognition camera may not be able to be installed due to a missing bracket. Also, the dynamic radar cruise control system, lane departure alert system, pre-collision system, forward recognition camera system or automatic high beam system may not operate properly due to a difference in the transmissivity or black ceramic border.
  • If the forward recognition camera bracket is deformed or damaged, replace it together with the windshield glass.
  • If there is any foreign matter on the area of the windshield glass in front of the forward recognition camera, clean the windshield glass before installing the forward recognition camera.  

Once component replacement is carried out, a calibration of the system will need to be performed. This will require the use of a factory service tool (Techstream for Toyota Lexus products). While aftermarket scan tool platforms are scrambling to make these services functional within their tools, the factory tool may still be required until that becomes a reality. In addition to the scan tool, a set of special service tools will be required to aim and adjust the camera. These tools provide a stand and in some cases a series of reflectors designed to be positioned at specific distances during the calibration process. To this point, there has been no standardization between manufacturers to aid the independent repair industry in providing this service to its customers. This means that a proprietary target and special service tool set may be required for each brand of vehicle you plan to service. The other complication is the lack of a standardized source for the distribution of these tools, requiring the independent shop to contact the respective manufacturers and purchase through different vendors. Add to this the extensive cost of these tools and you have a new service area that will cost quite a bit to get involved in.

Toyota utilizes a special service tool stand and a target that can be printed from the service information to perform a calibration of the forward-facing camera. A plumb bob is used to determine the center line of the vehicle.

If you plan on offering these calibration services to your customer base you will need to address the space you have available in the shop to do it. Shops with limited square footage may be excluded as a large amount of flat, level, perfectly lit space will be necessary to carry out this procedure. Toyota requires an unobstructed, level area of 10’ x 10’ in front of the vehicle. This sole requirement prohibits many shops from performing this function. There are numerous considerations in regard to lighting location and potential shadows as well as images in the detection area of the camera that can all affect the ability to carry out a calibration. It is a good idea to have a very specific dedicated area in your shop to perform this function. Consider visiting your local body shop and ask them if you can have some large pieces of scrap cardboard to place as a backdrop behind the target. A hood box (or a few of them) work well for this.

Once you have decided to take the plunge into these types of services, consider that the first time you perform one of these services there will be a considerable learning curve, so plan on spending a rather large amount of time setting up — a few hours at least the first time out.

Peter Pernice, an instructor at Suffolk County Community College, measures to determine target placement. Specific locations need to be determined in order to perform the calibration of the forward camera.

To prepare, the tire pressure needs to be set to spec and the windshield will need to be cleaned. A target must be printed from the service information and will need to be measured and compared to the size specifications outlined. The target will then have to be positioned at precise locations determined by laying out a series of lines and performing several precise measurements. This begins with finding the center line of the vehicle with a plumb bob and following precise instructions from the service information. For this very reason, this is a job for a competent, process-oriented technician. Once the measurements have been made and target locations determined, the scan tool will be used to complete the process. All said and done, this took a group of seasoned techs and instructors an average of around two hours to complete the first time.

While not an impossible task, the idea of performing these calibrations may leave you feeling like this is just another tool to buy and another task to perform. While you may be correct in your thinking, you might consider this is the tip of the iceberg of where EPS and its related systems are headed.

(Photo courtesy of Dave Macholz, Toyota Information System) New generations of EPS have a wealth of diagnostic trouble codes available to aid in system diagnosis.
(Photo courtesy of Toyota Media) The 2016 Prius introduced the use of a forward recognition camera that is used to keep the vehicle in its lane via the EPS system.

Overall diagnostics on EPS systems have become a bit more manageable with the availability of diagnostic trouble codes and live data. In some cases, a broader set of diagnostic information may be available. Toyota’s vehicle control history data provides such insight by allowing the technician to view events as they happened with corresponding key cycles. Think of this as freeze frame data that is enhanced. The vehicle control history information began with the 2016 Prius, but is making its way across product lines, allowing a technician a new data set for diagnostics.

The EPS system will continue to evolve and with the anticipated push towards driverless vehicles the systems that utilize EPS will continue to grow. As with any technology, read service information to understand the system you are working on, build a coherent plan and begin your diagnosis. Don’t forget that a scientific approach to diagnosis includes taking data, performing tests to confirm and rule out hypotheses and using the entire process to come to a solid diagnosis.

About the Author

Dave Macholz | Contributing Editor

Dave Macholz is an instructor for the Toyota T-TEN, Honda PACT and general automotive programs at Suffolk County Community College in Selden, NY. He is an ASE CMAT and L1 technician and holds a NY State teaching certification in vehicle repair. 

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