04-03-2011, 04:43 PM
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Abstract
The automotive industry is replacing more and more hydraulic systems by electronic systems. This not only reduces the weight of vehicles, but also has the potential for a large number of new features. One of these applications is the brake-by-wire technology for the braking system. This paper deals with different brake-by-wire technologies namely Electro-Hydraulic Braking (EHB) and Electro-Mechanical Braking (EMB). EHB systems consists of electric motors and ECU (Electronic Control Unit) connected with hydraulic system to the wheels while EMB systems have dry electric components connected to the wheels through the ECU. EHB contains hydraulic backup while EMB does not have it thus its components must be designed failsafe
1. Introduction
Power braking systems are bulky and complex. They rely on mechanical linkages, airtight vacuum seals, and hydraulics. When the brake pedal is pressed, the force is amplified using a lever. From there a vacuum generated from the engine is used to assist the brake pedal motion. That motion is transferred through hydraulic fluid in all directions until it reaches the braking unit on each wheel. This complex configuration can be simplified and improved using Brake-by-Wire. Two levels of Brake-by-Wire exist. The first is called Electric Hydraulic Braking (EHB). In EHB electric pumps and valves are used to power and control the hydraulic elements. This reduces the power draw on the engine and eliminates some of the large cumbersome interfaces. The second level of Brake-by-Wire is called Electric Mechanical Braking (EMB). EMB consists of sensors on the brake pedal, a control unit, and electromechanical actuators at each wheel. This system holds the greatest potential for control and variability.
In the automotive industry there has been an increased emphasis on vehicle safety. Improvement in brake technology has greatly contributed to stable running of vehicles. Increased functionality has resulted in products like ABS[Antilock braking System], ESC, and brake assist. An example of the increased functionality of automotive brakes is improvement in control techniques for hydraulic brakes. Furthermore, in an effort to continue this improvement in functionality and reduction in environmental impact, automotive components manufacturers and car manufacturers are developing electromechanical brake (EMB) systems.
The principle of EHB is based on separating the hydraulic connection between the brake pedal and the wheel brake. Braking as we know it today, by depressing the brake pedal, will be replaced by an actuation unit consisting of a pedal feel simulator and sensors to pick up driver commands. Signals coming from this unit together with other sensors are transmitted electrically (by wire) to an electronic control unit (ECU), which in turn conveys the sensed brake pressure to the conventional wheel brakes. The functions of EHB are compatible with all known systems such as ABS, EBD, TCS, ESP and BA, and, what's more; EHB offers great potential for additional functions.
EHB's brake pedal is connected to the pedal feel simulator. Contrary to the mechanical/hydraulic combination, the pedal no longer vibrates, thus lessening the risk of an inexperienced driver erroneously reducing brake pressure and terminating the ABS control mode. The electronic control unit computes the amount of braking deceleration desired by the driver from the sensed pedal travel and actuation force. A motor-pump assembly builds up the necessary hydraulic pressure in the brake system instead of the driver inducing the braking power via a vacuum brake booster.
The electro-mechanical brake even goes one step further and eliminates the brake cylinder, brake lines and hoses, as all these components are replaced by electric wiring. The use of electrics reduces maintenance expense, and also eliminates the expense of brake fluid disposal. EMB likewise measures the force of the driver's intention to brake the vehicle via sensors monitoring the system in the brake-pedal feel simulator. The ECU processes the signals received, links them where appropriate to data from other sensors and control systems, and calculates – in a jiffy for each wheel – the force to be generated by the brake caliper when pressing the brake pads onto the brake disc.
The wheel brake modules essentially consist of an electric control unit, an electric motor and a transmission system. The electric motor and transmission system form the so-called actuator which generates the brake application forces in the brake caliper. Each of the four actuators is in a position to deliver forces of up to several tons in just a matter of milliseconds.
Power requirements for EMB are high and would overload the capabilities of conventional 12 volt systems installed in today's vehicles. Therefore the electro-mechanical brake is designed for a working voltage of 42 volts. However, that voltage is not supplied to the EMB directly from the vehicle's battery. Extra batteries are available to offset any current peaks. This splitting of the power supply within the vehicle makes it possible to satisfy the actuator's power requirements without straining the on-board power supply system itself. Also, in an emergency, the car driver benefits from the extra batteries because the higher storage capacity enables the vehicle to continue its journey even though, say, a defective generator is unable to supply any more charging current to the vehicle battery. Moreover, such an EMB design is in line with current requirements to split the hydraulic brake system into two separate circuits.
2. Electro-Hydraulic Braking Systems (EMB)
The EHB system is a system which senses the driver's will of braking through the pedal simulator and controls the braking pressures to each wheels. The system is also a hydraulic Brake by Wire system. The conventional brakes in the past was activated directly through a purely mechanical device, is now implemented through electro-mechanical means by way of signal transfer to and from an Electronic Control Unit. Optionally, the ECU may apply additional “intelligence” based upon input from other sensors outside of the driver’s influence. Electro-Hydraulic Brake is not a true “by-wire” system with the thought process that the physical wires do not extend all the way to the wheel brakes. However, in the true sense of the definition, any EHB vehicle may be braked with an electrical “joystick” completely independent of the traditional brake pedal. It just so happens that hydraulic fluid is used to transmit energy from the actuator to the wheel brakes. This configuration offers the distinct advantage that the current production wheel brakes may be maintained while an integral, manually applied, hydraulic failsafe backup system may be directly incorporated in the EHB system.
Compared to the operation of conventional braking systems, by depressing the brake pedal with the Electro-Hydraulic Braking System (EHB), the appropriate command is transmitted electronically to the electronic controller of the hydraulic unit. This determines the optimum braking pressure and actuates the brake calipers hydraulically
Abstract
The automotive industry is replacing more and more hydraulic systems by electronic systems. This not only reduces the weight of vehicles, but also has the potential for a large number of new features. One of these applications is the brake-by-wire technology for the braking system. This paper deals with different brake-by-wire technologies namely Electro-Hydraulic Braking (EHB) and Electro-Mechanical Braking (EMB). EHB systems consists of electric motors and ECU (Electronic Control Unit) connected with hydraulic system to the wheels while EMB systems have dry electric components connected to the wheels through the ECU. EHB contains hydraulic backup while EMB does not have it thus its components must be designed failsafe
1. Introduction
Power braking systems are bulky and complex. They rely on mechanical linkages, airtight vacuum seals, and hydraulics. When the brake pedal is pressed, the force is amplified using a lever. From there a vacuum generated from the engine is used to assist the brake pedal motion. That motion is transferred through hydraulic fluid in all directions until it reaches the braking unit on each wheel. This complex configuration can be simplified and improved using Brake-by-Wire. Two levels of Brake-by-Wire exist. The first is called Electric Hydraulic Braking (EHB). In EHB electric pumps and valves are used to power and control the hydraulic elements. This reduces the power draw on the engine and eliminates some of the large cumbersome interfaces. The second level of Brake-by-Wire is called Electric Mechanical Braking (EMB). EMB consists of sensors on the brake pedal, a control unit, and electromechanical actuators at each wheel. This system holds the greatest potential for control and variability.
In the automotive industry there has been an increased emphasis on vehicle safety. Improvement in brake technology has greatly contributed to stable running of vehicles. Increased functionality has resulted in products like ABS[Antilock braking System], ESC, and brake assist. An example of the increased functionality of automotive brakes is improvement in control techniques for hydraulic brakes. Furthermore, in an effort to continue this improvement in functionality and reduction in environmental impact, automotive components manufacturers and car manufacturers are developing electromechanical brake (EMB) systems.
The principle of EHB is based on separating the hydraulic connection between the brake pedal and the wheel brake. Braking as we know it today, by depressing the brake pedal, will be replaced by an actuation unit consisting of a pedal feel simulator and sensors to pick up driver commands. Signals coming from this unit together with other sensors are transmitted electrically (by wire) to an electronic control unit (ECU), which in turn conveys the sensed brake pressure to the conventional wheel brakes. The functions of EHB are compatible with all known systems such as ABS, EBD, TCS, ESP and BA, and, what's more; EHB offers great potential for additional functions.
EHB's brake pedal is connected to the pedal feel simulator. Contrary to the mechanical/hydraulic combination, the pedal no longer vibrates, thus lessening the risk of an inexperienced driver erroneously reducing brake pressure and terminating the ABS control mode. The electronic control unit computes the amount of braking deceleration desired by the driver from the sensed pedal travel and actuation force. A motor-pump assembly builds up the necessary hydraulic pressure in the brake system instead of the driver inducing the braking power via a vacuum brake booster.
The electro-mechanical brake even goes one step further and eliminates the brake cylinder, brake lines and hoses, as all these components are replaced by electric wiring. The use of electrics reduces maintenance expense, and also eliminates the expense of brake fluid disposal. EMB likewise measures the force of the driver's intention to brake the vehicle via sensors monitoring the system in the brake-pedal feel simulator. The ECU processes the signals received, links them where appropriate to data from other sensors and control systems, and calculates – in a jiffy for each wheel – the force to be generated by the brake caliper when pressing the brake pads onto the brake disc.
The wheel brake modules essentially consist of an electric control unit, an electric motor and a transmission system. The electric motor and transmission system form the so-called actuator which generates the brake application forces in the brake caliper. Each of the four actuators is in a position to deliver forces of up to several tons in just a matter of milliseconds.
Power requirements for EMB are high and would overload the capabilities of conventional 12 volt systems installed in today's vehicles. Therefore the electro-mechanical brake is designed for a working voltage of 42 volts. However, that voltage is not supplied to the EMB directly from the vehicle's battery. Extra batteries are available to offset any current peaks. This splitting of the power supply within the vehicle makes it possible to satisfy the actuator's power requirements without straining the on-board power supply system itself. Also, in an emergency, the car driver benefits from the extra batteries because the higher storage capacity enables the vehicle to continue its journey even though, say, a defective generator is unable to supply any more charging current to the vehicle battery. Moreover, such an EMB design is in line with current requirements to split the hydraulic brake system into two separate circuits.
2. Electro-Hydraulic Braking Systems (EMB)
The EHB system is a system which senses the driver's will of braking through the pedal simulator and controls the braking pressures to each wheels. The system is also a hydraulic Brake by Wire system. The conventional brakes in the past was activated directly through a purely mechanical device, is now implemented through electro-mechanical means by way of signal transfer to and from an Electronic Control Unit. Optionally, the ECU may apply additional “intelligence” based upon input from other sensors outside of the driver’s influence. Electro-Hydraulic Brake is not a true “by-wire” system with the thought process that the physical wires do not extend all the way to the wheel brakes. However, in the true sense of the definition, any EHB vehicle may be braked with an electrical “joystick” completely independent of the traditional brake pedal. It just so happens that hydraulic fluid is used to transmit energy from the actuator to the wheel brakes. This configuration offers the distinct advantage that the current production wheel brakes may be maintained while an integral, manually applied, hydraulic failsafe backup system may be directly incorporated in the EHB system.
Compared to the operation of conventional braking systems, by depressing the brake pedal with the Electro-Hydraulic Braking System (EHB), the appropriate command is transmitted electronically to the electronic controller of the hydraulic unit. This determines the optimum braking pressure and actuates the brake calipers hydraulically
