Corolla Electric Power Steering PE10-008
16 June, 2010
Outline• Steering Development
• Steering Testing and Standards
• Field Information
• Clarifying Customer Feedback
• Explanation of “Wander” or “Drift”
• Simulation & Comparative Testing
• Toyota Assessment
’09-10 Corolla Steering Development• Based on market research and competitor vehicle
benchmarking, Toyota aimed to improve:– Steering feel– Vehicle agility– Ride comfort
• In dynamic testing, development vehicles compared favorably to other models
Developmental Dynamic Safety Testing
Confidential Information Redacted
Developmental Dynamic Safety Testing
Confidential Information Redacted
Description of the EPS system System Outline
• New for the 2009MY Corolla and Matrix as standard equipment
• Utilizes an electric motor and reduction mechanism to provide assist torque to the steering shaft
• ECU calculates the appropriate amount of assist to provide to the steering shaft
• The benefits include improved overall fuel economy
Description of the EPS systemDesign Concept
Confidential Information Redacted
Steering Testing & Standards
• Toyota has 3 standards:
Steering effort when slowly operating steering wheel at standstill
Steering effort when quickly operating steering wheel at standstill
Vehicle behavior and steering characteristics before and after EPS fail-safe mode activation
• Vehicles surpass all standards above
• Also complies with ECE 79 (Europe) and GB 171675 (China) which specify steering effort for normal driving and when steering assist fails.
Steering Effort Criteria
• Corolla EPS surpasses regulatory requirements for steering effort under power assist failure
Criteria & Recommended Values of Steering Effort
Field Information
• VOQ’s - Over 80% of VOQ’s had descriptions of steering “wander” or “drift”
• Consumer Complaints - A majority of complaints received by Toyota
also appear to generally describe a steering “wander” or “drift”
• Warranty - A high percentage of claims involve adjustment (such as wheel alignment) rather than parts replacement
• Field Reports - Majority of reports are not related to “wander” or “drift”
• Crash Cases - Insufficient information is available on crashes to assess cause, but no defective parts found in those vehicles which were inspected
Clarifying Customer Feedback
• Toyota interviewed 107 customers (all submitted VOQ’s) to understand their complaint of steering “wander” or “drift”
• 90% described what can be characterized as a vehicle “wander” or “sensitive” steering
• Toyota engineers inspected and drove 87 of those vehicles
• In all vehicles, no defect was found in the steering system
• Steering feel of all vehicles was found to be consistent with design intent and within acceptable production variation with no significant deviation
Explanation of “Wander” or “Drift”
• Based on the design concept, the neutral area steering effort is slightly stiff
• Vehicle reacts when steering input exceeds the self centering force of the vehicle
• When self centering force is exceeded, the vehicle moves according to the steering angle
• Some customers may complain of a delay at this transition point and perceive slightly “stiff” steering
Explanation of “Wander” or “Drift”
Undulation
Slant
Cross Wind
“Drift”
“Wander”
Disturbance
• Based on road conditions and external inputs, some customers may perceive a “wander” or “drift” due to the slightly stiff on-center feel
“Wander”
Simulation & Comparative Testing
• Based on 87 vehicle evaluations, Toyota set up a test vehicle
• Test vehicle was configured with steering and suspension components considered 3 standard deviations from normal production to represent the most extreme case for stiff steering feel from a design point of view
• The test vehicle was evaluated dynamically to assess steering effort
and stability
• Steering angle and vehicle direction were evaluated against road undulations and compared to other vehicles
• Test vehicle compared favorably to other models evaluated
Simulation & Comparative Testing
Confidential Information Redacted
Simulation & Comparative Testing
Confidential Information Redacted
Simulation & Comparative Testing
Confidential Information Redacted
Toyota Assessment
• Corolla steering is stable and controllable
• “Wander” or “Drift” is perceived by some drivers due to slightly stiff steering “feel” in the on-center position
• Steering effort and feel is comparable to a variety of other vehicles
• Steering “feel” may be “different” from customer’s previous experience, but is no different than the feel of driving a different vehicle than usual (e.g. a rental vehicle)
Toyota Assessment
• No defect is present in the EPS system
• The design and performance of the EPS are appropriate and no unreasonable safety risk is presented
• This is a customer satisfaction issue that will be addressed by a differently calibrated EPS ECU for those owners who prefer a “lighter” steering feel
Vehicles Available to Drive
• Test vehicle (described above)
• Repurchased vehicle
• Toyota purchased the vehicle (ODI # 10308501) from a customer who complained of “touchy” steering and experienced
vehicle “wander” on the freeway
• The customer primarily operated the vehicle in the Sacramento, CA area and perceived a “wander” at speeds above 45mph
• Customer submitted VOQ after learning from a news story that “this is a real safety issue, coupled with the gas pedal issue”
• Toyota evaluated the vehicle and found no defect present in the
EPS system