What is PS? Please note that it is not ESP (Electronic Body Stability System), don't confuse it.

Its full name is electric power steering system, whether it is HPS or EHPS, the essence is still a hydraulic system. From the appearance, there are steering oil pots.

The advantages of EPS

At the end of the last century, automotive engineers tried to use electric motors to drive steering gears, so electric power steering systems came out. It is also called electronic power steering system, namely Electric Power Steering, or EPS for short.

EPS is a purely electric steering system in the true sense. The computer directly controls the power-assisted motor, which easily overcomes the various century-old problems of the steering system. Its main advantages are as follows.

1) Through the program, it is easy to realize the variable speed assist, which is no longer restricted by the mechanical system;

2) It can easily modify the weight of the feel to adapt to the preferences of car owners in different countries and regions. SAIC Volkswagen’s Touran is the first local model of Volkswagen’s PQ35 platform. The first batch of Touran that year used the OBD side to customize the EPS assistance level. I remember that there are 14 options for the steering wheel from light to heavy. Unfortunately, out of conservative considerations, the factory quickly blocked this permission;

3) It only consumes electricity when turning, and the fuel consumption of the whole vehicle is reduced by 3%-5%. To tap the potential of the engine, a 4% reduction in fuel consumption does not lose power, and the cost is huge. This is also one of the important reasons why many car companies that take pride in handling have to compromise with EPS;

4) The power assist is no longer restricted by the engine, the engine stall does not affect the steering, the engine has one less load (power booster), the idle torque management is also convenient, there is more power for acceleration, the acceleration performance of 100 kilometers is inexplicably improved by one Cut off

5) Integrated steering system, the assembly efficiency of the whole vehicle is extremely high, shortening the cycle of vehicle manufacturing;

6) Good consistency of product characteristics, not affected by ambient temperature, and lifetime maintenance-free;

7) The raw materials are environmentally friendly and can be easily recycled and reused;

8) The computer system is very convenient for calibration and fault diagnosis;

9) The computer can actively intervene in the steering, and automatic parking becomes possible;

10) There is no need for the friendly reminder that "the steering wheel will be suffocated" is no longer needed.

It is precisely because of these advantages that EPS has caused dozens of domestic and large enterprises to invest and develop in the early 10 years of this century, but in fact, EPS has high technical barriers. It is too late for all living beings to realize its true meaning. Until today, few survivors have survived. Not much.

EPS is not a perfect system

Of course, EPS also has its inherent drawbacks. This is only really clear to developers, so I'm just a little long-winded here.

1) EPS almost completely eliminates road feedback, and the rebound of the steering wheel is all "helped" by the computer, so it makes the driver feel "wearing a cover". For models that are not properly tuned, this set is still "dry". Because of this problem, BMW started to apply EPS very late. In 2005, when I was still developing the ZF steering system in Germany, BMW's EPS tuning work was nearing the end. As a result, it didn't start a large number of applications until 2010. Due to the strong voice of car owners, BMW's M department was once the only department in the company that rejected EPS. Today, Porsche sports cars also have to use EPS in exchange for higher fuel economy and reduced hardware complexity.

EPS used by Porsche 911 (made by ZF)

2) The booster power is limited, which is not suitable for heavy-duty cars. In other words, if you want to use them on heavy-duty cars, you need to spend more money and effort to squeeze more installation space. If you only rely on increasing the size to deal with heavier models, you will soon encounter system bottlenecks. Later, people focused on finding a more efficient motor. With limited power consumption, the potential of the system was further improved, so that EPS could aspire to a car with a weight of 1.8 tons.

3) The load requirements of the automobile power system are comprehensively improved, which poses new challenges to the generator power and battery life;

4) The cost is higher than that of ordinary HPS, and huge output is needed to share the development investment;

5) Insensitive to deviation caused by inconsistent front wheel air pressure. If the two front tire pressures are inconsistent, the driver is not easy to perceive it and may condone excessive tire wear;

6) Due to the motor's natural torque fluctuation and neutral "dead zone", designers need to spend a lot of cost to make the EPS boosting feel close to the slick HPS;

7) An extremely complete consideration must be given to safety failures. This is a system in which electrical signals "have the final say", which means that it is entirely possible that it will automatically turn cramping and cause car crashes. Therefore, compared with the safety logic design and the hazards of product failures, the realization of power assistance and correcting feel as performance is only the first step in the long march. This is also one of the important reasons why many domestic EPS development units had to rush to close. The richer the company, the better the product, the more professional the company can receive orders, the higher the positioning, the more profitable the company. , The company with more output is able to control the product failure rate, and the company with the stronger brand will have more people chasing after its products. Therefore, the EPS market is one of the few markets that dare not fight for the price.

EPS of Volkswagen PQ35 platform (made by ZF)

With its annual output of several million sets of EPS and huge R&D investment, ZF has become the industry’s recognized provider of EPS products with the highest technology and best performance. Of course, the price can be imagined. No matter what new model is to be equipped with EPS, car manufacturers will harass ZF. I even heard from many domestic car companies that as long as ZF really wants to provide a package, price and bidding are not a problem.

However, at the beginning of 2015, under the influence of the anti-monopoly department, ZF’s steering gear business was fully acquired by the Bosch (BOSCH) Group, but that was already after I left and started my business. I simply talk more here.

Of course, there are some well-known EPS manufacturers in the United States and Japan. For example, column-type EPS is one of the areas that Japan’s NSK company focuses on (the motor is installed on the steering column in the cab).

In recent years, more and more models are equipped with EPS. Most of the new sedans launched by Volkswagen, Audi, BMW and Mercedes-Benz are equipped with EPS as standard for all series, and many domestic companies are not to be outdone. Considering that EPS is more expensive than HPS, on the other hand, car prices continue to fall, and car manufacturing costs continue to compress, car manufacturers must rack their brains to make room for high-tech products.