The era of autonomous driving cannot do without the help of wire-controlled steering systems

"Turn left and the car will go right; turn right and the car will go left." This magical operation is achieved by changing parameter settings. This is the wire-controlled steering system developed by Bosch .

Those who don't often delve into technology may be a little confused. What is a steer-by-wire system? How is it different from a traditional steering system? Based on the above questions, this time the Chief Mobility Officer will talk to you about the "History of the Development of Steering Systems" based on the steer-by-wire system developed by Bosch.

The past and present of the steering system

The development history of automobile steering can be roughly divided into four stages: mechanical steering system, mechanical hydraulic power steering system, electronic hydraulic power steering system and electronic power steering system.

Mechanical steering system (Manual Steering , MS for short): As the name suggests, this system uses the driver's physical strength as the steering energy, and all force transmission parts are mechanical.

The disadvantage of this method is obvious: the reaction force between the tires and the ground is directly transmitted to the steering wheel, which makes it very difficult to turn the steering wheel (especially when turning on the spot). That is why the older generation always says that driving is a physical job.

In summary, mechanical steering has reliable performance and simple structure, but it is laborious to operate and not very sensitive. Worse still, it may cause arm fractures if the steering wheel is not held firmly, especially when driving a truck with a heavy load and deadweight.

Mechanical steering system (Manual Steering, MS for short): As the name suggests, this system uses the driver's physical strength as the steering energy, and all force transmission parts are mechanical.

The disadvantage of this method is obvious: the reaction force between the tires and the ground is directly transmitted to the steering wheel, which makes it very difficult to turn the steering wheel (especially when turning on the spot). That is why the older generation always says that driving is a physical job.

In summary, mechanical steering has reliable performance and simple structure, but it is laborious to operate and not very sensitive. Worse still, it may cause arm fractures if the steering wheel is not held firmly, especially when driving a truck with a heavy load and deadweight.

Mechanical hydraulic power steering system (Hydraulic Power Steering, referred to as HPS): After a period of use, everyone found that mechanical steering operation is really laborious and easy to hurt the driver. So, the mechanical hydraulic power steering system came into being.

The principle of this technology is to use the power of the engine to drive the oil pump to provide hydraulic assistance to the mechanical steering. In use, the driver only needs to use a slight force to turn the steering wheel, which is easier to operate than before. However, since the steering wheel gives the driver too little force feedback, it is easy to cause the latter to lose road feel (especially when driving at high speeds, the steering wheel is too light, which will cause unstable body control). In addition, in order to maintain pressure, the system must always be in working state regardless of whether steering assistance is needed, which will also cause high energy consumption.

Electro Hydraulic Power Steering (EHPS): In order to improve the driver's control feeling and solve the problem of high energy consumption, the electronic hydraulic power steering system was born. Its principle is basically the same as that of mechanical hydraulic power steering, except that the oil pump is driven by an electric motor and the power steering force is variable. The vehicle speed is monitored by the speed sensor , and the electronic control unit obtains data and changes the oil pressure by controlling the opening degree of the steering control valve, thereby adjusting the magnitude of the steering power steering force.

For experienced drivers who love driving, it is a great blessing that the power assist can be matched according to the vehicle speed. From now on, the vehicle will have less power assist at high speeds, making it feel more stable; and more power assist at low speeds, making driving easier.

Electronic Power Steering (EPS): This system can be divided into three modes: steering shaft power-assisted, gear power-assisted, and rack power-assisted, depending on the installation position of the power-assisted motor. The principle is to use the drive motor to directly drive the steering shaft or steering gear, and finally let the steering rack directly realize power steering under the electronic control unit. The biggest advantage of this solution is that it eliminates the power steering oil pump, hose, hydraulic oil, conveyor belt and pulley installed on the engine required by the hydraulic power-assisted system.

相比传统液压动力转向系统，电动助力转向系统具有以下优点：只有在转向时电机才会提供动力，可以显著降低能耗；助力大小可以通过软件调整，能够兼顾低速时的转向轻便性和高速时的操纵稳定性，回正性能好；结构紧凑，提升了车内空间效率；可通过程序的设置，使电动助力转向系统易于匹配不同车型，缩短生产和开发周期。

What is steer-by-wire?

Facing the upcoming era of autonomous driving , traditional steering systems can no longer meet the control requirements of autonomous driving functions. Therefore, Bosch recently launched a wire-controlled steering system. The technical principle of this system is fundamentally different from that of traditional steering systems.

Different eras have different demands for vehicles.

"Autonomous driving" is a hot topic nowadays. Both traditional OEMs and new car manufacturers are developing autonomous driving technology.

In response to current market demand, Bosch has launched a wire-controlled steering system.

The technical principle of Bosch's wire-controlled steering system is to eliminate the existing physical connection between the upper and lower parts of the steering system. It realizes the non-mechanical connection between the upper steering and the lower steering, and its structure is divided into two parts: the steering wheel actuator and the steering rack actuator:

First, the steering wheel actuator converts the driver's steering intention into a digital signal through the sensor, which is then transmitted to the steering rack actuator. At the same time, it provides simulated steering wheel torque feedback according to different vehicle speeds and driving conditions, thereby achieving functions such as steering wheel return and driving feel.

The steering rack actuator receives a signal from the steering wheel actuator and converts the steering wheel angle signal into tire swing according to the driver's steering intention.

Bosch officials said: Eliminating the intermediate shaft will have many benefits. First, it will reduce the number of product types of vehicle manufacturers and reduce costs. For example, the steering systems for left-hand drive and right-hand drive are currently two products. But after eliminating the intermediate shaft, the steering systems for left-hand drive and right-hand drive can become one system. Second, the variable steering ratio function can be transferred to more models with lower prices.

At present, some vehicles need to make different gear profiles mechanically to achieve variable transmission ratios, which is costly and complex. If a steer-by-wire system is used, the transmission ratio can be set through software and parameters, which is flexible while reducing costs and shortening development cycles.

Advantages and disadvantages of steer-by-wire

Advantage:

There is no hard connection between the steering wheel and the steering gear. Unlike the Infiniti Q50's steer-by-wire system (which still has a mechanical intermediate shaft as a redundant design), the system developed by Bosch completely eliminates the intermediate shaft design, eliminating the transmission of mechanical connection shocks and reducing noise and vibration.

The steering ratio can be adjusted at will. The system can achieve a variety of different driving modes through the adjustment of software parameters, such as comfort mode and sports mode (sports mode will provide more road feedback).

The small space it occupies provides more space for the layout of other components in the cabin, for example, more legroom for the driver.

Disadvantages:

For performance cars and sports cars that emphasize driving pleasure, the road feel is insufficient and the driving pleasure is poor. Personally, I think the lack of hard connection leads to false road feel feedback.

Once a quality problem occurs, the consequences are disastrous. Take the Infiniti Q50 recall as an example. Due to the deviation of the control unit program of the wire-controlled active steering system, when the engine is started with the battery at low voltage, the control unit may misjudge the steering wheel angle, resulting in a difference in the steering wheel and wheel rotation angles. In this case, even if the steering wheel is turned to the neutral position, the wheels may not return to the straight position, resulting in the vehicle being unable to start straight or turn as the driver intended, which is very dangerous.

In terms of information security, there is a risk of being hacked. Because pure electronic signals are used to perform data transmission, the system has the potential for being hacked to a certain extent. On the other hand, the wire control steering cancels the traditional physical connection, which means that after the vehicle is controlled by hackers, the driver in the car completely loses the ability to control the vehicle. Of course, Bosch claims that the company will build a sufficiently secure firewall. However, once the system becomes part of the Internet of Vehicles, no one can guarantee 100% security.

Of course, in the face of the reliability and safety issues of wire-controlled steering, Bosch officials also gave an answer. They emphasized: "Our system architecture, such as the vehicle power supply, communication, signal, steering system motor, and processor, all adopt a fully redundant system solution. It is equivalent to having two systems working in parallel in real time. When one system fails, the other system can continue to ensure that the steering command is executed."