The EHB is a brake-by-wire system that replaces parts of the mechanical components with electronic components, the brake pedal is no longer directly connected to the brake cylinder, and the driver operation is captured by the sensor as a control intention. The hydraulic actuator completes the braking operation, making up for the deficiencies caused by the traditional braking system design and principle, giving maximum freedom in braking control, thereby making full use of the road surface adhesion and improving the braking efficiency.
The development of the EHB system is a relatively new type of braking system. The development time of the EHB is short, but the development prospects are broad. Major auto manufacturers and research institutions are actively developing this system.
In 1994, Analogy used Saber simulation to develop a control system for EHB. In 1996, Bosch conducted a real-vehicle test on the EHB system developed by the company and obtained satisfactory results. The system has also achieved great success in practical applications. The effect is obvious in shortening the braking distance and ensuring vehicle stability. . Companies such as Tianhe, Delphi, and Continental Weiss have also developed similar EHB systems in succession and obtained a series of patents around 2000-2002.
In September 2001, the new Mercedes-Benz SL sports car equipped with the Sensotronic Brake Control system was exhibited for the first time at the Frankfurt International Motor Show. In 2002, the system was equipped on the new Mercedes E-Class, 2003. Equipped with the Estate model, Bosch first introduced the four-wheel drive SBC installed on the Mercedes-Benz E-Class 4matic. This is the first time that the EHB system has been used in series production. South Korea's Mando Corporation, the mainland's Twis, and TRW have made progress in the development of the EHB system, and began to be General Motors, Ford, and Daimler. Chrysler and other car manufacturers supply.
The advantages of the EHB system The traditional braking system is shown in Fig. 1. The brake master cylinder and the brake wheel cylinder are connected through a brake pipe. The brake pressure is directly input by the manpower through the brake pedal, and the vacuum booster is used as the auxiliary power source. It is also limited by the degree of engine vacuum. This structural feature limits the establishment of brake pressure, the distribution of braking forces for each wheel, and the integrated control with other systems, and has limited potential for further improvement of the braking effect.
Fig. 2 is a schematic diagram of the EHB system. Since the EHB system changes the pressure establishment mode, the pedal force no longer affects the braking force, it compensates for the deficiencies caused by the traditional braking system design and principle, and has many advantages that are unmatched by conventional braking systems. :
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1. In the traditional braking system, the characteristics of the system components may change after an emergency braking or long-term braking, thereby affecting the braking performance. With the EHB control system, the change in the mechanical characteristics of the components can be compensated by the control algorithm to make the brakes. The pressure level and pedal travel are always the same.
2. Due to the high pressure level of the accumulator, the high-pressure brake fluid enters the brake wheel cylinder through the control of the high-speed on-off valve, and the braking process is smooth and soft. In the case of emergency braking, the brake pressure rise gradient is large and the attainable brake pressure is also higher. The brake pressure of the brake shoe (clamp) to the brake drum (disc) is precisely adjusted by feedback from the wheel cylinder pressure sensor, eliminating brake noise.
3. The brake characteristics of the traditional brake system cannot be changed at will, but the EHB system analyzes the driver’s intention, judges different braking behaviors, and provides the most reasonable pressure change characteristics.
4. The traditional braking system can only achieve the distribution of front and rear brake pressures to a certain extent. However, the EHB system has a great deal of freedom in the four-wheel pressure distribution, which is significant when braking on roads with different adhesion coefficients.
5. The power of a conventional brake system using a vacuum booster is affected by engine speed and load, while the braking capability of the EHB system is not affected by the engine vacuum.
6. Since the brake sensor detects the speed of the pedal and the pedal stroke, the electronic control unit adjusts the brake pressure accordingly, and the manufacturer can change the control algorithm and the pedal according to different models and statistics of the driving habits of the driver. The sensory simulator provides the driver with different pedal feels, making the EHB highly portable.
7. When the traditional brake system performs ABS work, the pressure in the brake pipe fluctuates, causing the brake pedal to oscillate. Inexperienced drivers tend to reduce the pedal force and thus consciously reduce the braking effect. EHB solves this problem completely because the pedal and the brake pipe are not directly connected, not only can ensure that each wheel will not be locked, but also release the brake quickly, the braking process is safe and efficient, and has minimal impact on power loss.
In addition to the basic functions such as basic braking and ABS that can be achieved with conventional braking systems, the EHB can achieve other, more excellent auxiliary functions.
8. When the vehicle is running on a rainy or wet road, according to the action of the windshield wiper, the EHB system can emit weak brake pulses at regular intervals to clear the water film on the brake lining to eliminate the brake. The phenomenon of water decay ensures reliable braking.
9. Most drivers are hesitant to apply braking force in the event of an emergency and have insufficient pedal force to cause a dangerous situation. The EHB adjusts the braking force (distinguished by the pedal stroke and pedal acceleration) by correctly recognizing the driver's intention to avoid the lack of braking force.
10. When it is necessary to maintain the parking state, the system can apply a certain braking force to the wheels, even if the driver releases the brake pedal, it can still generate a certain brake pressure on the wheels, reduce the burden on the driver, improve driving comfort, and achieve Electronic Parking Brake (EPB).
11. In the event of traffic congestion, the system and the accelerator pedal unit sensor cooperate with each other, and the judgment is made through the analysis and calculation of the electronic control unit. The driver only needs to control the accelerator pedal. Once the foot is removed from the accelerator pedal, the EHB system will automatically Apply a certain amount of braking force to slow down the parking. In this way, the driver does not need to switch frequently between the accelerator pedal and the brake pedal.
The composition and working principle of the EHB system are shown in Fig. 2. The EHB system is mainly composed of a brake pedal unit, an electronic control unit (ECU), a hydraulic control unit (HCU) and a series of sensors.
1. The brake pedal unit includes a pedal feel simulator, a pedal force sensor or/and a pedal travel sensor, and a brake pedal. The pedal sensation simulator is an important part of the EHB system, providing the driver with a similar pedal feel (pedal reaction and pedal travel) to that of a conventional brake system, enabling him to perform braking operations according to his own habits and experience. Pedal sensors are used to monitor the driver's intention to operate. Pedal travel sensors are generally used. Few pedal force sensors are used, and both are used simultaneously to provide redundant sensors and can be used for fault diagnosis. Fig. 3 shows the production of the electronic brake pedal unit by Continental Twis.
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2. Hydraulic Control Unit (HCU)
The brake pressure regulating device is used to increase the pressure of the wheel. Figure 4 shows the hydraulic control unit (HCU) of the EWI with ECU.
The HCU generally includes the following parts:
Hydraulic control system independent of the brake pedal. The system has an energy supply system consisting of a motor, a pump and a high-pressure accumulator. It is connected to the brake wheel cylinder via brake lines and directional control valves to control the flow of brake fluid. / Flow out of the brake wheel cylinder to achieve brake pressure control.
Human-driven emergency braking system When the servo system has a serious failure, the brake fluid is driven by the human-driven master cylinder into the brake wheel cylinder to ensure that the most basic braking force decelerates the vehicle and stops it.
The balancing valve is provided with a balancing valve between two brake wheel cylinders on the same axis. In addition to the conditions for independent braking control of the wheels, the balancing valves are all in a power-off state to ensure the coaxial wheels on both sides. Balance of braking force.
3. Sensors include wheel speed sensors, pressure sensors, and temperature sensors for monitoring the wheel motion status, wheel cylinder pressure feedback control, and correction control for different temperature ranges.
Figure 5 shows a patent issued by Bosch on the EHB system with a pedal feel simulator, a service brake system with hydraulic servo control and a manpower-operated emergency brake system. The servo system controls the pressure of the four wheels, and the manpower emergency braking system can only control the two front wheels. The system has a total of 14 solenoid valves, which are two-position two-way valves.
In the normal service brake, when the brake light switch is triggered, the electronic control unit determines that the brake occurs, the pedal stroke sensor senses the driver's braking intention, and then the power is turned off to close the isolation valve, under the action of human power from the brake master cylinder. The output brake fluid enters the pedal feel simulator, giving the driver the same feeling as when operating a conventional brake system.
The energy needed for wheel braking is provided by the power source and sent to each wheel cylinder via the main oil supply pipeline. The wheel cylinder oil inlet valve and the outlet valve can realize the pressure control of each wheel cylinder. A balance valve is provided between the coaxial two-wheel cylinders to maintain the coordination of the braking forces of the two wheels during normal braking.
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EHB control The braking action to be implemented by the EHB is divided into basic braking and controlled braking.
The so-called basic braking means that the driver applies a large or small pedal force according to his intentions to control the deceleration of the vehicle and ensure his desired direction of travel. The value of the pedal force is not enough to make the wheels locked. . At this time, the EHB system must fully reflect the driver's intentions and give the wheel driver the desired braking force.
Controlled braking refers to braking that is performed with the necessary additional intervention. That is, when the driver wants to take an emergency full brake on the vehicle and strongly and quickly depresses the brake pedal, the EHB system should recognize this requirement, while giving the wheel a sufficient brake pressure, The brake pressure on the brake is controlled to prevent the wheels from locking up and the vehicle's braking stability from deteriorating.
The EHB system can also incorporate a variety of vehicle control systems: the system integrates anti-skid functions when the vehicle is started or accelerated on low-attachment roads and when the vehicle is moving from high-adhering to low-adherent surfaces; the EHB system adopts the wheel system when the vehicle turns. Active vehicle stability control; In addition, the aforementioned automatic water function, electronic assisted brake function, electronic parking brake function, etc. are all controlled brakes.
The EHB system has the superiority that the traditional braking system cannot match. However, the EHB system still uses the electrohydraulic control method. In the strict sense, it is not a purely linear controlled actuation system. Compared with the electromechanical braking system EMB, the EHB system is currently Technology is more mature and therefore has excellent development prospects in the short term.
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The development of the EHB system is a relatively new type of braking system. The development time of the EHB is short, but the development prospects are broad. Major auto manufacturers and research institutions are actively developing this system.
In 1994, Analogy used Saber simulation to develop a control system for EHB. In 1996, Bosch conducted a real-vehicle test on the EHB system developed by the company and obtained satisfactory results. The system has also achieved great success in practical applications. The effect is obvious in shortening the braking distance and ensuring vehicle stability. . Companies such as Tianhe, Delphi, and Continental Weiss have also developed similar EHB systems in succession and obtained a series of patents around 2000-2002.
In September 2001, the new Mercedes-Benz SL sports car equipped with the Sensotronic Brake Control system was exhibited for the first time at the Frankfurt International Motor Show. In 2002, the system was equipped on the new Mercedes E-Class, 2003. Equipped with the Estate model, Bosch first introduced the four-wheel drive SBC installed on the Mercedes-Benz E-Class 4matic. This is the first time that the EHB system has been used in series production. South Korea's Mando Corporation, the mainland's Twis, and TRW have made progress in the development of the EHB system, and began to be General Motors, Ford, and Daimler. Chrysler and other car manufacturers supply.
The advantages of the EHB system The traditional braking system is shown in Fig. 1. The brake master cylinder and the brake wheel cylinder are connected through a brake pipe. The brake pressure is directly input by the manpower through the brake pedal, and the vacuum booster is used as the auxiliary power source. It is also limited by the degree of engine vacuum. This structural feature limits the establishment of brake pressure, the distribution of braking forces for each wheel, and the integrated control with other systems, and has limited potential for further improvement of the braking effect.
Fig. 2 is a schematic diagram of the EHB system. Since the EHB system changes the pressure establishment mode, the pedal force no longer affects the braking force, it compensates for the deficiencies caused by the traditional braking system design and principle, and has many advantages that are unmatched by conventional braking systems. :
1. In the traditional braking system, the characteristics of the system components may change after an emergency braking or long-term braking, thereby affecting the braking performance. With the EHB control system, the change in the mechanical characteristics of the components can be compensated by the control algorithm to make the brakes. The pressure level and pedal travel are always the same.
2. Due to the high pressure level of the accumulator, the high-pressure brake fluid enters the brake wheel cylinder through the control of the high-speed on-off valve, and the braking process is smooth and soft. In the case of emergency braking, the brake pressure rise gradient is large and the attainable brake pressure is also higher. The brake pressure of the brake shoe (clamp) to the brake drum (disc) is precisely adjusted by feedback from the wheel cylinder pressure sensor, eliminating brake noise.
3. The brake characteristics of the traditional brake system cannot be changed at will, but the EHB system analyzes the driver’s intention, judges different braking behaviors, and provides the most reasonable pressure change characteristics.
4. The traditional braking system can only achieve the distribution of front and rear brake pressures to a certain extent. However, the EHB system has a great deal of freedom in the four-wheel pressure distribution, which is significant when braking on roads with different adhesion coefficients.
5. The power of a conventional brake system using a vacuum booster is affected by engine speed and load, while the braking capability of the EHB system is not affected by the engine vacuum.
6. Since the brake sensor detects the speed of the pedal and the pedal stroke, the electronic control unit adjusts the brake pressure accordingly, and the manufacturer can change the control algorithm and the pedal according to different models and statistics of the driving habits of the driver. The sensory simulator provides the driver with different pedal feels, making the EHB highly portable.
7. When the traditional brake system performs ABS work, the pressure in the brake pipe fluctuates, causing the brake pedal to oscillate. Inexperienced drivers tend to reduce the pedal force and thus consciously reduce the braking effect. EHB solves this problem completely because the pedal and the brake pipe are not directly connected, not only can ensure that each wheel will not be locked, but also release the brake quickly, the braking process is safe and efficient, and has minimal impact on power loss.
In addition to the basic functions such as basic braking and ABS that can be achieved with conventional braking systems, the EHB can achieve other, more excellent auxiliary functions.
8. When the vehicle is running on a rainy or wet road, according to the action of the windshield wiper, the EHB system can emit weak brake pulses at regular intervals to clear the water film on the brake lining to eliminate the brake. The phenomenon of water decay ensures reliable braking.
9. Most drivers are hesitant to apply braking force in the event of an emergency and have insufficient pedal force to cause a dangerous situation. The EHB adjusts the braking force (distinguished by the pedal stroke and pedal acceleration) by correctly recognizing the driver's intention to avoid the lack of braking force.
10. When it is necessary to maintain the parking state, the system can apply a certain braking force to the wheels, even if the driver releases the brake pedal, it can still generate a certain brake pressure on the wheels, reduce the burden on the driver, improve driving comfort, and achieve Electronic Parking Brake (EPB).
11. In the event of traffic congestion, the system and the accelerator pedal unit sensor cooperate with each other, and the judgment is made through the analysis and calculation of the electronic control unit. The driver only needs to control the accelerator pedal. Once the foot is removed from the accelerator pedal, the EHB system will automatically Apply a certain amount of braking force to slow down the parking. In this way, the driver does not need to switch frequently between the accelerator pedal and the brake pedal.
The composition and working principle of the EHB system are shown in Fig. 2. The EHB system is mainly composed of a brake pedal unit, an electronic control unit (ECU), a hydraulic control unit (HCU) and a series of sensors.
1. The brake pedal unit includes a pedal feel simulator, a pedal force sensor or/and a pedal travel sensor, and a brake pedal. The pedal sensation simulator is an important part of the EHB system, providing the driver with a similar pedal feel (pedal reaction and pedal travel) to that of a conventional brake system, enabling him to perform braking operations according to his own habits and experience. Pedal sensors are used to monitor the driver's intention to operate. Pedal travel sensors are generally used. Few pedal force sensors are used, and both are used simultaneously to provide redundant sensors and can be used for fault diagnosis. Fig. 3 shows the production of the electronic brake pedal unit by Continental Twis.
2. Hydraulic Control Unit (HCU)
The brake pressure regulating device is used to increase the pressure of the wheel. Figure 4 shows the hydraulic control unit (HCU) of the EWI with ECU.
The HCU generally includes the following parts:
Hydraulic control system independent of the brake pedal. The system has an energy supply system consisting of a motor, a pump and a high-pressure accumulator. It is connected to the brake wheel cylinder via brake lines and directional control valves to control the flow of brake fluid. / Flow out of the brake wheel cylinder to achieve brake pressure control.
Human-driven emergency braking system When the servo system has a serious failure, the brake fluid is driven by the human-driven master cylinder into the brake wheel cylinder to ensure that the most basic braking force decelerates the vehicle and stops it.
The balancing valve is provided with a balancing valve between two brake wheel cylinders on the same axis. In addition to the conditions for independent braking control of the wheels, the balancing valves are all in a power-off state to ensure the coaxial wheels on both sides. Balance of braking force.
3. Sensors include wheel speed sensors, pressure sensors, and temperature sensors for monitoring the wheel motion status, wheel cylinder pressure feedback control, and correction control for different temperature ranges.
Figure 5 shows a patent issued by Bosch on the EHB system with a pedal feel simulator, a service brake system with hydraulic servo control and a manpower-operated emergency brake system. The servo system controls the pressure of the four wheels, and the manpower emergency braking system can only control the two front wheels. The system has a total of 14 solenoid valves, which are two-position two-way valves.
In the normal service brake, when the brake light switch is triggered, the electronic control unit determines that the brake occurs, the pedal stroke sensor senses the driver's braking intention, and then the power is turned off to close the isolation valve, under the action of human power from the brake master cylinder. The output brake fluid enters the pedal feel simulator, giving the driver the same feeling as when operating a conventional brake system.
The energy needed for wheel braking is provided by the power source and sent to each wheel cylinder via the main oil supply pipeline. The wheel cylinder oil inlet valve and the outlet valve can realize the pressure control of each wheel cylinder. A balance valve is provided between the coaxial two-wheel cylinders to maintain the coordination of the braking forces of the two wheels during normal braking.
EHB control The braking action to be implemented by the EHB is divided into basic braking and controlled braking.
The so-called basic braking means that the driver applies a large or small pedal force according to his intentions to control the deceleration of the vehicle and ensure his desired direction of travel. The value of the pedal force is not enough to make the wheels locked. . At this time, the EHB system must fully reflect the driver's intentions and give the wheel driver the desired braking force.
Controlled braking refers to braking that is performed with the necessary additional intervention. That is, when the driver wants to take an emergency full brake on the vehicle and strongly and quickly depresses the brake pedal, the EHB system should recognize this requirement, while giving the wheel a sufficient brake pressure, The brake pressure on the brake is controlled to prevent the wheels from locking up and the vehicle's braking stability from deteriorating.
The EHB system can also incorporate a variety of vehicle control systems: the system integrates anti-skid functions when the vehicle is started or accelerated on low-attachment roads and when the vehicle is moving from high-adhering to low-adherent surfaces; the EHB system adopts the wheel system when the vehicle turns. Active vehicle stability control; In addition, the aforementioned automatic water function, electronic assisted brake function, electronic parking brake function, etc. are all controlled brakes.
The EHB system has the superiority that the traditional braking system cannot match. However, the EHB system still uses the electrohydraulic control method. In the strict sense, it is not a purely linear controlled actuation system. Compared with the electromechanical braking system EMB, the EHB system is currently Technology is more mature and therefore has excellent development prospects in the short term.
Automotive Electronic Network is a comprehensive portal to provide you with the latest Beidou satellite navigation, GPS navigation, car audio, DVD navigation, driving recorder, parking sensor information and automotive electronics industry resources!
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