--Collect the "Automotive Driving Automation Classification" (GB/T 40429-2021)--
The in-line chassis of automatic driving is our usual hand and foot, which is used to do control execution and is the core hardware of automatic driving control technology.
This article is a knowledge concept map, for reference only
About the chassis
When it comes to car chassis, we are no strangers. It is generally composed of sub-systems such as suspension system, intake and exhaust system, transmission system, fuel system, gear pedal system, suspension system, steering system, wheel tire system, brake system and so on.
About inline control
Remote control by wire = Drive-by-wire or X-by-wire, i.e. the use of wire (electrical signal) to replace mechanical, hydraulic or pneumatic forms of connection, so that there is no need to rely on the driver's force or torque input.
The wire control system mainly has five subsystems: steer-by-wire, throttle-by-wire, actuation by-wire, suspension-by-wire, and shift-by-wire.
Among them, for the automatic driving system, the three subsystems of wire control throttle, steer-by-wire, and line-controlled movement are particularly important.
Controlled-by-wire throttle (TBW)
The wire-controlled throttle = TBW, i.e. Throo-by-wire, or Accelerator-by-wire.
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Mechatronics (wire control)
In the early days of traditional cars, the throttle control worked by connecting the throttle foot pedal and the throttle connecting version by a cable or tie rod, so that the method of controlling the throttle through mechanical devices, although the reaction delay was small, but also had great limitations, there was no way to cope with various working conditions under complex roads, nor could I control fuel consumption and emissions well.
Mechanical throttle
A wire-controlled throttle (i.e., an electronic throttle) is then created, which is controlled by using wires instead of cables or levers, and electrical signals generated by the position of the accelerator pedal to the ECU for engine control. The mechanical connection between the pedal and the throttle is eliminated, and the displacement of the throttle foot pedal is detected (this displacement represents the driver's driving intention), the displacement signal is transmitted to the ECU, the calculation is processed to obtain the best throttle opening, and then the throttle control motor is driven. The throttle-by-wire system consists mainly of a throttle pedal and displacement sensor, an ECU (electronic control unit) and a data bus (responsible for communication with other ECUs), a motor and a throttle.
Wire-controlled throttle
principle
How does the master computer control the throttle? The most common method is to connect a dedicated controller between the accelerator foot pedal and the ECU, when in automatic driving mode, the controller will accept the signal of the main control computer to transmit to the ECU; and the automatic driving mode is not started, the controller only acts as a relay to transmit the electrical signal of the accelerator pedal to the ECU.
The throttle is controlled by wire for autonomous driving
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Cruise control is the basic application of the line control throttle, and all vehicles with cruise control function are equipped with wired controlled throttle. From the perspective of development stage, the current penetration rate of wire control throttle is close to 100%, which is relatively mature. Even for traditional fuel vehicles, the wire-controlled throttle is basically the standard configuration, while hybrid and electric vehicles are completely wired throttle. Therefore, in the application of automatic driving, the modification and implementation of the throttle by wire is relatively easy.
In addition to foreign suppliers (Bosch, Continental, Denso, Magneti-Marelli, Hitachi, Delphi Technologies, SKF, etc.), domestic suppliers (HELLA, UMC, Ningbo Gaofa, Aolian Electronics, Kaizhong, etc.) also participated. However, EFI actuators, ECUs and other technologies are in the hands of international parts giants, the industrial pattern is relatively stable, so the participation of domestic enterprises is still in a low state, localization is the future direction of efforts in the field of wire control throttle.
Steer-by-wire (SBW)
Steer-by-wire = SBW, or Steeling By Wire, steer-by-wire controls the precise control of the path and direction of autonomous driving.
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The steering system completes a series of evolutions of mechanical hydraulic assist electric control hydraulic power assist electric assist.
Mechanical Steering System (MS)
Mechanical steering system = Manual Steering, is the earliest car steering system. The so-called mechanical type is based on the driver's force and the use of all-mechanical mechanisms such as steering wheel, steering gear and steering transmission mechanism to achieve steering. By turning the steering wheel, the reducer in the steering gear is increased in torque, and then the steering knuckle is controlled by the tie rod to complete the vehicle steering.
Advantages: The MS system is reliable and simple in structure. Disadvantages: Due to the reaction force of the ground facing the tire directly to the steering wheel, the steering wheel burden is too heavy when parking and driving at low speeds.
Mechanical steering system
Hydraulic Power Steering (HPS)
Hydraulic power steering system = Hydraulic Power Steering is mainly composed of oil pump, tubing, oil tank, pressure fluid control valve, transmission belt and so on. The power source of the HPS system is the engine, the driver only needs a slight force to turn the steering wheel, the use of the engine power to drive the oil pump, steering control valve to control the direction of oil flow and oil pressure, to provide steering power to the mechanical steering.
Advantages: HpS system has better power and handling stability at low to medium speeds. Disadvantages: When driving at high speed, because the steering wheel gives the driver force feedback is too small, the driver's sense of road is poor, and the fixed power effect will make the steering wheel too sensitive. Secondly, in order to maintain pressure, whether or not the steering power is needed, the engine always drives the oil pump to rotate, resulting in a waste of engine energy.
Hydraulic power steering
Electronically Controlled Hydraulic Power Steering (EHPS)
Electro Hydraulic Power Steering = Electro Hydraulic Power Steering, compared to HPS systems, EHPS adds electronic control units, including power steering ECUs, solenoid valves and vehicle speed sensors. Through the real-time monitoring of the speed of the vehicle speed sensor, the electronic control unit obtains the data and changes the oil pressure by controlling the opening degree of the steering control valve, so as to realize the adjustment of the steering power.
Advantages: The EHPS system can change the size of the steering power provided according to the speed of the vehicle, so that when driving at high speeds, the body is more stable and the feel is better. Disadvantages: Its structure is complex, the cost is high, and it has the common disease caused by the hydraulic system, which is a transition stage between hydraulic assistance and electric assistance.
Electronically controlled hydraulic power steering system
Electric Power Steering (EPS)
Electric power steering system = Electric Power Steering is mainly composed of ECU, steering torque sensor, power motor and deceleration mechanism. The principle is that when the driver rotates the steering wheel, the torque sensor detects the steering of the steering wheel and the size of the torque, transmits the voltage signal to the ECU, and the ECU calculates and issues instructions to the motor controller according to the information detected by the torque sensor, so that the motor outputs the steering power torque of the corresponding size and direction, thereby generating power. EpS system according to the installation position of the booster motor, can be divided into steering shaft booster type, gear assist type, rack assist type three forms.
Advantages: compact structure, small space, simple parts structure, easy installation, low maintenance costs; with the motor as the power, the motor is only started when needed, the power consumption is less, which improves the fuel economy of the car; it can provide different boosts for the car steering at different speeds in real time, ensuring that the car is light and flexible at low speed, stable and reliable when driving at high speed; the power size can be adjusted by software, which can take into account the steering lightness at low speed and the control stability at high speed, and the positive performance is good.
Electric power steering
Steer-by-Wire (SBW)
Steering By Wire is developed on EPS, which has redundant features relative to EPS and can achieve faster response times than EPS. For L3 and above self-driving cars, some will be separated from the driver's control, so the automatic driving control system for the steering system and other requirements of accurate control, high reliability, only the steer-by-wire steering can meet the requirements, so it has become the future development trend of the steering system.
principle
Steer-by-wire means that between the steering wheel and the steering rack is a steering system connected and controlled by wire control (electronic signal), that is, there is no direct physical connection such as hydraulic or mechanical between them. The steering system by wire is mainly divided into three parts: the steering wheel system, including the steering wheel, torque sensor, steering angle sensor, torque feedback motor and mechanical transmission device; electronic control system, including vehicle speed sensor, can also increase the swing angle speed sensor, acceleration sensor and electronic control unit to improve the vehicle's handling stability; steering system, including angular displacement sensor, steering motor, gear rack steering mechanism and other mechanical steering devices.
First, the steering wheel converts the driver's steering intent into a digital signal through sensors, which is then transmitted to the steering rack actuator. At the same time, simulated steering wheel torque feedback is provided according to different speeds and driving conditions, so as to realize functions such as steering wheel realenching and driving feel. The steering rack actuator receives a signal from the steering wheel actuator and converts the steering wheel angle signal into a tire swing based on the driver's steering intent. Electrical signal instructions are sent to the booster motor to control the steering system.
What is the difference between EPS (Electric Power Steering) and SBW (Steer-by-Wire)?
SBW cancels the mechanical connection between the steering wheel and the wheel, uses sensors to obtain the steering wheel angle data, and then processes the calculation and output of the driving force data by the ECU, and uses the motor to push the steering machine to turn the wheels. Eps, on the other hand, increase steering forces based on the driver's corner.
merit:
The mechanical connection between the steering system function modules is omitted, reducing noise and vibration;
Saves space for high-level placement of sensors, computing units or other entertainment systems;
Eliminates the safety hazard of injuring the driver caused by the backward movement of the steering column in the crash accident;
Steering wheel angle and steering torque can be designed independently to adapt to different types of "feel".
shortcoming:
In terms of information security, there is a risk of being hacked.
Steer-by-wire system
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From the current perspective of the entire market, the steer-by-wire is still in the early stages of development, the current penetration rate is extremely low, and only a small number of models are equipped, such as the Infiniti Q50 and Q60 equipped with steer-by-wire. The steer-by-wire system has higher requirements for technology, capital, safety, etc., and it is expected that in the short term, the steer-by-wire products will also be controlled by giants such as Bosch and ZF. With the gradual penetration of intelligent driving in L3 and above, line control is expected to explode. According to the forecast of relevant institutions, the average annual compound growth rate of the market space of line control in 2020-2025 can reach 166%.
Line Control Actuation (BBW)
Brake By Wire, the most difficult, but also the most critical technology in the online control chassis technology. The line control dynamic system controls the chassis safety and stability control of automatic driving, and only with good braking performance (including fast response speed, good smoothness, etc.), can we provide a good guarantee for our safety.
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Similar to the development process of throttle and steering technology, braking technology has undergone a development process from mechanical braking to pressure braking to electronic braking.
Mechanical braking system
The braking energy of the mechanical braking system is completely provided by the driver, who manipulates a simple set of mechanical devices to apply force to the brakes to achieve the braking effect.
Disadvantages: Insufficient braking force. Because the cars at this stage are still in their infancy, they have a simple structure, small mass, and low speed, so the braking force requirements are not high. Now the mechanical braking system can no longer be found in ordinary cars, and the mechanical braking system is still used in some low-speed agricultural vehicles and tractors.
Pressure braking system
Later, as the mass of the car became larger and faster, pressure assist devices began to appear. The first thing that is generated is the pneumatic press, i.e. the vacuum assist device. Using compressed air as a power source, the pressure of the compressed air generated by the engine driving the air compressor is converted into mechanical thrust to make the wheels rotate.
Disadvantages: Pneumatic compression reaction is slow, and the braking force is large but difficult to control. Because the pneumatic braking system relies on compressed air to help, there must be air compressors, gas storage cylinders, brake valves and other devices with large volumes, which can only be used by vehicles with space permitting, and are mostly used in medium and heavy vehicles.
With the development of hydraulic technology, hydraulic braking systems have been realized. Hydraulic braking, is the driver to apply pressure to the brake pedal force through the pusher to the main cylinder piston to compress the brake fluid, the brake fluid through the tubing to increase the pressure of the brake wheel cylinder, the wheel cylinder piston under the pressure of the brake shoe pressure to the brake drum, under the action of the friction pad to reduce the speed or stop rotating, thereby generating braking force.
Disadvantages: brake operation is laborious, and the braking force is not as large as pneumatic compression; after excessive heating, part of the brake fluid vaporizes, forming bubbles in the pipeline, seriously affecting hydraulic transmission, reducing the efficiency of the brake system, or even completely invalid. Advantages: short lag time; small wheel cylinder size, can be installed inside the brake, directly as the opening mechanism of the brake shoe or the compression mechanism of the brake block, without the need for brake arms and other transmission parts, so that the structure is simple, the quality is small; the mechanical efficiency is high, and the hydraulic system has a self-lubricating effect.
Hydraulic linear control (non-pure wire control)
Due to the gradual emergence of anti-lock braking system (ABS) and body stability control system (ESP), the wire control dynamic system has slowly developed on the traditional braking system. Hydraulic linear control dynamic EHB = Electro-Hydraulic Brake, based on the traditional hydraulic brake system, with electronic devices to replace the function of a part of the mechanical components, the use of brake fluid as a power transmission medium, the control unit and actuator layout is more concentrated, there is a hydraulic backup system, can also be called centralized, wet braking system.
During normal operation, the hydraulic connection between the brake pedal and the brake is disconnected and the backup valve is closed. The electronic pedal is equipped with a pedal feeling simulator and electronic sensors, and the ECU can judge the driver's braking intention through the sensor signal and brake by clicking to drive the hydraulic pump. When the electronic system fails, the backup valve opens and the EHB system becomes a conventional hydraulic system.
Disadvantages: the structure of the hydraulic system is complex, it is easy to leak liquids, there are safety hazards, and the cost and maintenance costs are high.
Advantages: Due to the backup braking system, the safety is high, and it is the preferred solution at this stage.
principle
Hydraulic braking has been widely used is now a very mature technology, with the improvement of people's braking performance requirements, anti-lock braking system, drive anti-skid control system, electronic stability control program, active collision avoidance technology and other functions gradually integrated into the braking system, and with the development of electric vehicles, the control device of the brake system will gradually be electronic, electronic can be more accurate, more efficient to achieve braking. The mechanical connection is gradually reduced, the power transmission between the brake pedal and the brake is separated, and replaced by a wire connection, the wire transmits energy, and the data line transmits the signal, so this kind of braking is called line control movement.
Line control dynamic EMB
EMB=Electro-Mechanical Brake, that is, mechanical line control action. The EMB is also known as a distributed, dry braking system. The biggest difference from the EHB is that it no longer requires brake fluid and hydraulic components, and the braking torque is completely generated by an actuator driven by an electric motor mounted on 4 tires. The ECU of the EMB system drives and controls the actuator motor to generate the required braking force based on the brake pedal sensor signal and the vehicle status signal such as vehicle speed.
merit:
The response speed is greatly improved;
Simplifies the structure of the braking system, facilitates assembly and maintenance;
With the removal of brake fluid, environmental pollution is reduced.
shortcoming:
High reliability requirements, the need to backup system to ensure reliability;
Motor power limitation power is insufficient;
The working environment is harsh, and the semiconductor parts near the brake pads cannot withstand the high temperatures.
These problems have hindered the mass production of EMB systems in the short term. At present, EMB is still in the research stage, but EMB is the future direction of development.
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At this stage, hybrid vehicles basically use EHB with high-voltage accumulators as the core, and electric vehicles basically use EHB. From the current perspective of the entire market, the line control is still in the early stages of development, the current penetration rate is low, only a small number of models are equipped, and the configuration rate of new energy vehicles is relatively high. With the gradual penetration of new energy vehicles and L3 and above automatic driving, line control is expected to break out. According to the forecast of relevant institutions, the average annual compound growth rate of the market space in the line control movement from 2020 to 2025 can reach 23%.
The main suppliers include Bosch, ZF, Continental and other international parts giants, the current domestic development is relatively good Bethel, Top Group, Wanan Technology, etc., but the industry is still in the early stages of development, and is expected to gain a place in the future market competition.
The key to wire technology: safety and redundancy
From the more mature wire-controlled throttle, to the still low market penetration of the wire steering, and then to the line control movement that is still in the research stage, we have a general understanding. Overall, chassis-by-wire technology is constantly evolving. Among them, safety is the most basic and core element for cars, especially automatic driving above L3. Although the original pure mechanical control is inefficient, it is highly reliable; although the wire control technology is suitable for automatic driving, it also faces the hidden dangers caused by the failure of electronic software. Only by implementing double or even multiple redundancy in function can we ensure that its basic function can still be realized in the event of a certain failure.
Reproduced from the daily automatic driving, the views in the text are only for sharing and exchange, do not represent the position of this public account, such as copyright and other issues, please inform, we will deal with it in a timely manner.
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