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Special Edition

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RP-EPS or rack parallel type electric power steering

Newly Developing EPS for Medium/Large Vehicles with a Vision of Future Car Society

JTEKT’s electric power steering (EPS) boasts the top share in the world, and of the three basic functions of a car (travel, turn and stop), focuses on “turn” and is helping to improve safety and comfort. Amidst predictions that even medium to large-sized vehicles, which conventionally adopt hydraulic power steering, will make the transition to EPS, JTEKT developed a new EPS for medium/large-sized vehicles in 2016 and has commenced its mass production.

With a forward vision to support advanced driver-assistance and autonomous driving

EPS can be broadly divided into two types; column assist type and rack assist type. The column assist type EPS is suitable for small vehicles as its motor and the computer that controls this motor (ECU) are located in the vehicle’s interior cabin. Meanwhile, the rack assist type EPS has its motor and ECU located close to the vehicle’s tire therefore has minimal power loss due to friction and is suited to medium/large-sized vehicles which require relatively higher steering performance. JTEKT stands out from other EPS manufacturers due to the diverse product lineup we offer for both EPS types. In particular, we currently occupy the highest share of the global market for our column assist type EPS. Moving forward, JTEKT plans to focus on popularizing and expanding our rack assist type EPS also. “It is predicted that, in order to support advanced driver assistance and autonomous driving, even large vehicles and luxury cars which conventionally adopted hydraulic power steering, will make the transition to EPS. We have developed a new rack assist product in order to answer this market need.” (Yamamoto)

Achieving one of the smallest packaging sizes in the world.
Received the Innovative Technique Award from Toyota Motor Corporation.

Incorporating world-first technology to achieve high comfort and quietness

“RP (rack parallel) -EPS” is one of the newly developed rack assist type products. This system’s reduction gear uses a bearing specially designed through cooperation between engineers from JTEKT’s steering and bearing businesses to achieve one of the smallest packaging sizes in the world and improve onboard mountability. Moreover, by incorporating JTEKT’s original innovative ideas in the mechanism known as the ball screw, the RP-EPS offers smoother and more comfortable steering, in addition to quietness.

“Our new ball screw design is the first of its kind in the world to be used for auto parts. I was in charge of design, but truly believe it would not have been possible to accomplish this without the close collaboration between the Production Engineering and Manufacturing departments.” (Asakura) “ The design is completely new so we had to make mass production equipment like none ever seen before too. The task of doing this was extremely difficult but our sense of achievement when we succeeded made it all worthwhile.” (Mizuno) “ It was extremely challenging to develop mass production equipment that could provide both high accuracy and high efficiency but thanks to the cooperation of the Machine Tools & Mechatronics Operations Headquarters and JTEKT group companies, we achieved our goal.” (Yoshida)

* RP-EPS is a registered trademark of JTEKT Corporation.

A high-level safety design conforming to international standards

In 2011, JTEKT established a development process that conformed to the international functional safety standard, ISO26262 and, in 2014, developed the world’s first column type EPS with a redundant design. “Redundant design” refers to a safe design whereby systems are duplicated so that even if one system fails during vehicle operation, it will be possible to continue providing assistance to steering wheel operation. Based on our experience in this area, a redundant design was adopted for the torque sensor and motor drive unit in the newly developed RP-EPS also.

Striving to be a body of engineers capable of providing new values

Mass production of RP-EPS began at Hanazono Plant in December 2016. It was adopted on the Lexus models, LC500h and LC500, released in March 2017. Moreover, in order to meet an increased demand for EPS in medium/large-sized vehicles, JTEKT has established a plan for global production, including mass production in Tennessee, U.S. (commenced in June 2017) and China (scheduled to commence in 2019). “We went through a trial-and-error process to find a way to improve the steering experience even further. I truly feel we overcame this challenge and succeeded at our goal due to all members of the Design, Production Engineering and Manufacturing departments uniting as one and combining their strengths.” (Yamada) “ In this project, various conflicting opinions emerged such as ‘we want new ideas’, ‘we want higher accuracy mass production equipment’, ‘we want to keep costs down’ and so on and I feel I did a good job at balancing all of these.” (Suzuki) “ I want to continue contributing to the creation of cars which consumers find even more appealing through the development of new steering systems. I want JTEKT to be a body of engineers that doesn’t just meet market needs, but also offers new values.” (Yamamoto)