ESP≠EPS Electric Power Steering System Development and Future

ESP? Isn't it a vehicle stability control system? You may know this. What about EPS? Are you confused immediately? What on earth is this thing that looks so similar to ESP? It turns out that the Chinese name of EPS is Electric Power Steering System.

Everyone knows that in the past, cars did not have power steering. In order to reduce the effort of operation, the steering wheel was designed to be large, so that some effort can be saved during operation. But nowadays, most cars have power steering to assist the driver in steering.

Power steering is also called power steering. It refers to a device that can reduce the force of operating the steering wheel with the help of external force. Nowadays, most cars use power steering, so even weak women can operate and drive.

The development of automobile power steering can be roughly divided into the earliest hydraulic power steering (HPS), electronic hydraulic power steering (EHPS), and electronic power steering (EPS). The overall development direction is that each generation is more labor-saving, comfortable, and easy to operate than the previous one. With the rapid development of electronic technology, EPS has gradually replaced HPS.

EPS has the best value proposition for vehicle manufacturers

At present, hydraulic systems are widely used in commercial vehicles because of their simplicity, roughness and high output. Passenger cars, on the other hand, pursue comfort and portability, so hydraulic systems are relatively rarely used in them. In addition, passenger cars have a higher premium than commercial vehicles, so some new technologies are also dared to be applied to passenger cars for verification.

Since the EPS motor directly establishes a transmission relationship with the mechanical steering gear, the safety risks caused by hydraulic system failure are directly avoided. In addition, EPS can realize active self-centering and lane deviation correction. It helps the driver to quickly center the wheels and grasp the driving trajectory in continuous curves. Because the hydraulic system is cancelled, the EPS power-assistance characteristics can truly change dynamically with the vehicle speed, which directly improves the previous disadvantage of unclear sense of direction when the vehicle is driving at high speed.

Although the cost of EPS system is higher than that of HPS system, vehicle manufacturers will still choose the more expensive EPS products. This is because most countries in the world have formulated more stringent automobile energy conservation and emission reduction regulations. Therefore, from the perspective of steering system, EPS has the best value positioning for vehicle manufacturers. And according to our statistics, the switch from HPS to EPS system in China has completed about 80% of the market space. And more cars will be equipped with EPS steering system.

From the perspective of enterprises, in the Chinese electric power steering system market, foreign-funded or joint venture enterprises have a market share of about 80%, occupying a monopoly position, while Chinese local enterprises have a market share of less than 20%. Currently, major global steering system suppliers such as Japan's JTEKT, Germany's ZF, Japan's Seiko, and the United States' TRW have all established EPS production bases in China. A number of Chinese local enterprises with a production capacity of more than 1 million sets have emerged, such as Yilida and Yubei.

The development of electric power steering system in China started later than that in foreign countries, and it also faced a series of problems such as lack of systematic research on steering system, so it faced great challenges. The first company in China to use electric power steering system was Changhe Beidouxing, which then started the transformation of domestic steering system. With the development of domestic automobile industry, domestic electric power steering system was integrated with international advanced technology and introduced, which enabled the rapid development of EPS (electric resistance steering system) system in my country.

Due to the unclear definition of domestic industry standards for EPS, the mismatch between products produced by different manufacturers is also an important problem that needs to be solved as soon as possible.

Judging from the supporting relationship between EPS manufacturers and automobile OEMs, Bosch, JTEKT, Nexteer and Zhuzhou Elite are currently the EPS manufacturers with the largest supporting volumes. The four major suppliers account for more than 80% of the supporting share in China's ESP market, and the supporting vehicle models cover almost all domestic mainstream passenger car manufacturers.

Commercial vehicles are the epitome of electric and hydraulic steering

Although EPS is popular in the passenger car market, the commercial vehicle market, especially the large and medium-sized truck market, needs a relatively cheap hydraulic power steering system with clear feedback on the road feel.

At present, the electric hydraulic power steering system (EHPS) of commercial vehicles replaces the engine-driven hydraulic pump in the traditional HPS with a motor-driven hydraulic pump to provide steering assistance. With the development of electronic control technology, the motor drive system of the EHPS of traditional commercial vehicles has gradually transitioned from the initial large-volume, large-mass, and low-efficiency asynchronous motor drive system to a small-volume, light-mass, and high-efficiency permanent magnet synchronous motor drive system. At the same time, with the maturity of speed sensorless technology and permanent magnet synchronous motor parameter online identification technology, speed sensorless permanent magnet synchronous motor control systems have also been widely used.

With the development of technology, EHPS for commercial vehicles will gradually develop towards high safety, high power density, high integration, high efficiency, high EMC/EMI level and intelligence. The control unit of the future electric hydraulic power steering system (EHPS) will be integrated into an all-in-one system or integrated into the drive motor to support high reliability requirements. At the same time, the EMC/EMI level requirements for the electric hydraulic power steering system (EHPS) are getting higher and higher.

In terms of intelligence, all working states of the drive motor will be calculated by the drive control unit according to the vehicle's driving speed, steering wheel steering angle and other signals to reach the most ideal state, thereby controlling the speed of the power-assisted motor to drive the hydraulic pump to provide the necessary pressure and flow. This not only saves energy consumption to a certain extent, but also ensures that the driver can get a good steering feel at different vehicle speeds.

Moreover, autonomous driving technology is becoming the latest trend in the global commercial vehicle industry. In addition to complex perception and decision-making capabilities, it also places higher demands on vehicle control technology. These control technologies mainly include acceleration, braking and steering functions. They add electronic control technology on the basis of traditional mechanical hydraulic technology. 

Bosch's steering business has a wide range of product lines in the commercial vehicle field. In response to the emerging autonomous driving technology, it has launched a steering system that can achieve semi-autonomous driving. This electro-hydraulic steering system called Servotwin is mainly used for heavy-duty commercial vehicles. It is the result of an innovative combination of the RB-Servocom® recirculating ball gear power steering system and an electronic control unit. The system provides speed-based steering assistance and has active return and various driving assistance functions. The electronic circuit in the system replaces the second hydraulic circuit previously required for commercial vehicles with two steering shafts.

In China, on May 7, 2019, Xiqing District of Tianjin successfully held the first domestic commercial vehicle platoon following standard verification in the acceleration, deceleration and lane change of autonomous driving platoon, which marked that the development of autonomous driving in China's truck industry had completed a dialogue with the future. During the platoon lane change process of this standard verification, the Foton Auman EST autonomous driving model adopted the ZF ReAX electro-hydraulic steering system.

It is understood that the ReAX electro-hydraulic steering device precision steering combines the market-leading automotive electric steering technology with its mature commercial vehicle hydraulic steering machine, making it more precise when steering automatically. In addition, the ZF electric power steering device may provide support for future wire-controlled steering applications. The unique advantage of the ReAX electro-hydraulic steering system is that it is an important part of the driver assistance system (ADAS) and the autonomous driving function, and these two systems are important aids to improve vehicle safety, reduce the burden of control, and improve the logistics process. It can be seen that EHPS is almost the main technology in the future commercial vehicle market, and EPS+HPS has also achieved a perfect combination of modern and traditional.

People's car review

Don't underestimate it. The steering system is perhaps the most difficult part of car design to achieve perfection, and the most difficult part to please people, because not only is it difficult to master if the reaction is too fast or too slow, but many factors will affect the steering performance, especially the suspension system. Most of its components will affect steering. Even the width of the tire and the air pressure will affect the way you feel when holding the steering wheel.

Therefore, this key technology is also in the hands of foreign auto parts giants. If the Chinese auto industry is to catch up with the world's advanced level, it must start with these specific technical aspects and proceed steadily. I believe that the day when we stand at the top of the world is not far away.