NSK started mass producing ball screw units for electric hydraulic brake systems at Saitama Plant in March 2018 and at Akagi Plant (NSK Steering Systems) in January 2020. This three-part series will feature the perspectives of the people who created this product. For this article, we talk to one of the key engineers who worked on the product to share his thoughts about the design process.

Meeting the Growing Need for Electric Brakes

Ball screw units are found in automotive brake boosters for electric hydraulic brake systems. The booster is used to reduce the amount of force that the driver needs to apply to the brake pedal in order to stop the vehicle. Vacuum boosters have been the main design for this component, traditionally, and they use the suction of negative pressure created by the engine to enhance brake pedal pressure. However, by using a ball screw and an electric motor, the brakes can be applied even before the driver steps on the pedal.

The move to make brake boosters electric began with the growing demand for electric and hybrid vehicles (EVs and HEVs). Since these vehicles feature smaller gas engines or no engines at all, there is insufficient or no suction pressure that can be used for braking. This led to growing demand for electric boosters. In recent years, the heightened need for greater vehicle safety has also increased demand for electric boosters. Starting in November 2021, all new vehicles in Japan will be required to have autonomous emergency braking systems. Accordingly, we expect the demand for ball-screw-type electric hydraulic brake systems to increase as automakers strive to meet the higher safety standards.

◆Autonomous Emergency Braking Systems Becoming Mandatory in Near Future

HidenoriThere is a global trend toward requiring installation of autonomous emergency braking systems to prevent collisions and save lives. In fact, these systems will be mandatory for new vehicles sold in Japan in from November 2021 onward. There is always a need for improved vehicle safety, and we expect that ball-screw-type braking systems will be the dominant product in the market by 2023 or 2024. This is based on current pace of orders and the importance our customers are placing on the outstanding responsiveness achieved by ball-screw-type systems. This allows the time between obstacle detection and brake application to be as short as possible.

◆Making the Most of All of Our Knowledge

There are several kinds of electric brake boosters, including the slide screw type, but the ball screw type is the most promising. One reason is the outstanding responsiveness it provides. Since there are tiny balls between the screw and the nut, the ball screw delivers very smooth motion. This allows the electric brake motor to activate instantly, resulting in exceptional responsiveness. Going forward, the market for electric brakes will have even higher requirements of electric brakes, and they will have to work effectively even in larger vehicles like pickups. The ball-screw-type system is considered optimal for larger vehicles as well, thanks to its superior responsiveness, which enables rapid, powerful braking.

In developing our ball screw unit, we put particular emphasis on reducing size and weight. NSK has been working on developing these ball screws for 10 years, leveraging feedback from various customers. During this process, the focus has always been on how to reduce the number of components while maintaining the same quality. Parts that are smaller and lighter are easier for customers to incorporate into their products. Thanks to the knowledge we amassed in this process, NSK's latest ball screw unit features an integrated ball screw support structural components, as well as an integrated support bearing. This makes the unit smaller and lighter than ever.

Focusing on Customer Satisfaction

Since this kind of project was a first for NSK, we explained its necessity to each department involved. This enabled us to move toward mass production with a shared understanding. While holding a total of around 100 weekly meetings with customers, we employed a process of trial and error to ensure that customer needs were met for size and cost.

Product designers like me have to consider where and how the product will be used. Although it would have been easy to get carried away and just focus on the product itself, we first had to consider the structure of the braking system and the vehicles it would go into. It was critical to take the customer's perspective, and also to anticipate the opinions people in the other NSK departments would have on our design drawings. I want to continue making design proposals that focus on customer satisfaction, by maintaining a perspective that is as broad as possible. By continuing to gain experience, I hope to help create a world where serious traffic accidents are a thing of the past.