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ABS Chassis and Braking System: Types, Advantages, and Evaluation

Learn about the history, types, advantages, and evaluation of ABS (Antilock Braking System) for vehicles. Understand how ABS helps retain directional stability, stops faster, and maintains maximum control of the vehicle. Explore the different types of ABS systems and their effectiveness in various road conditions.

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ABS Chassis and Braking System: Types, Advantages, and Evaluation

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  1. University Kuala Lumpur Malaysia France Institute CHASSIS AND BRAKING SYSTEM 2 ABS GENERAL prepared by : Nor Hisham Bin Mohamed Mahayudin

  2. HISTORY OF ABS 1952 ABS for aircraft by Dunlop 1969 Rear-wheel-only ABS by Ford & Kelsey Hayes 1971 Four-wheel ABS by Chrysler & Bendix 1978 Mass production of Bosch ABS Systems with Mercedes Benz 1984 Integrated ABS system by ITT-Teves Since the early 1990s ABS began to be offered on the mid-size and compact cars due to a significant cost reduction and increased efficiency of the system prepared by : Nor Hisham Bin Mohamed Mahayudin

  3. ADVANTAGES OF ABS • retains directional stability (Vehicle Stability) • stops faster (Shortened Stopping distance, except gravel, fresh snow..) • retains maximum control of vehicle (Steerability) • ① If the front wheels lock • - it is no longer possible to steer the car • ② If the rear wheels lock • - the car can become unstable and can start to skid sideways prepared by : Nor Hisham Bin Mohamed Mahayudin

  4. ADVANTAGES OF ABS Braking at cornering [Without ABS] [With ABS] prepared by : Nor Hisham Bin Mohamed Mahayudin

  5. [Braking without ABS] [Braking with ABS] Low μ road High μ road surface Low μ road High μ road surface ADVANTAGES OF ABS If a car on the different conditions of surface brakes, the wheels on the slippery surface easily lock up and the vehicle begins to spin. But ABS provides vehicle stability until it stops. prepared by : Nor Hisham Bin Mohamed Mahayudin

  6. ABS TYPES There are 4 type of ABS System • 4-Sensor 4- Channel type • 4-Sensor 3-Channel type • 3-Sensor 3-Channel type • 1-Sensor 1- Channel type prepared by : Nor Hisham Bin Mohamed Mahayudin

  7. ABS TYPES 4-Sensor 4-Channel type This type is generally used for FF(Front engine Front driving) car which has X-brake lines. Front wheels are independently controlled and rear wheel control usually follows a select-low logic for vehicle stability while ABS operation. 4-Sensor 3-Channel type This type is generally used for FR(Front engine Rear driving) car which has H-brake lines. Front wheels are independently controlled and rear wheels are controlled together by on brake pipe on the basis of select-low logic. 3-Sensor 3-Channel type Front wheels are controlled independently but rear wheels are controlled together by one wheel speed sensor(ex. On the differential ring gear). 1-Sensor 1-Channel type Only control the rear wheel pressure by one sensor. prepared by : Nor Hisham Bin Mohamed Mahayudin

  8. System Evaluation All wheels independent control Good Fair Good X line or H line 4 sensors 4-channel Frt: Independent control Rr: Select Low Good Good Fair Frt : Independent control 4 sensors 3-channel H line Good Good Fair Rr: Selesct Low Frt : Independent control 3 sensors 3-channel H line Good Good Fair Rr : Selesct Low 1 sensor 1-channel H line No Rr : Selesct Low Fair No prepared by : Nor Hisham Bin Mohamed Mahayudin

  9. ABS TYPES 1) 4-Sensor 4-Channel type (Independent control type) This type has 4 wheel sensors and 4 hydraulic control channels and controls each wheel independently. Steering safety and stopping distance maintains optimum condition on the homogeneous road surface. However, on the split-μ road surface, uneven braking force between left wheels and right wheels generates a Yawing Moment of the vehicle body resulting in vehicle instability. Therefore, most of vehicles with a 4 channel ABS incorporates a select low logic on rear wheels to maintain the vehicle stability at any road conditions. [FF car, X-line brake system] prepared by : Nor Hisham Bin Mohamed Mahayudin

  10. ABS TYPES 2) 4-Sensor 4-Channel type (Front wheels: independent control, ear wheels: Select low control ) In case of FF(Front engine Front driving) car, most vehicle weight concentrated on front wheels and the center of the mass of vehicle also moves forward while braking allowing almost 70% of braking force to be controlled by front wheels. This means that most braking power is generated by front wheels and to get a maximum braking efficiency while ABS operation, independent control of front wheels is necessarily required. However, rear wheels which performs relatively less braking force are very important to guarantees vehicle safety while braking. That is, while ABS operation of rear wheels on the split road surface, independent control of rear wheel generates uneven braking force resulting in vehicle yawing moment. To prevent this yawing and to maintain vehicle safety with ABS operation on any kinds of road surface, rear wheel braking pressure is managed according to the wheel which shows more lock-up tendency. This control concept is called ‘Select-low control’. prepared by : Nor Hisham Bin Mohamed Mahayudin

  11. ABS TYPES 3) 4-Sensor 3-Channel type (Front wheels: independent control, Rear wheels: Select low control ) Vehicle with H-bake line system has this ABS control system. 2 channels are for front wheels and the other one is for rear wheel control. Rear wheels are controlled together by a select low control logic. In case of X-brake line system, 2 channels (2 brake ports in the ABS unit) are required to control rear wheel pressure because each rear wheel belongs to different brake line. [FR car, H-line brake system] prepared by : Nor Hisham Bin Mohamed Mahayudin

  12. ABS TYPES 4) 1-Sensor 1-Channel type (Rear wheels: Select low control ) Vehicle with H-bake line system. Only controls rear wheel pressure. One wheel speed sensor is installed on a rear differential detecting rear wheel speed. Front wheels are locked up while heavy braking, vehicle loses its steering stability and stopping distance on a low-μ road surface also increases. This system helps vehicle have a straight stop. [FR car, H-line brake system] prepared by : Nor Hisham Bin Mohamed Mahayudin

  13. ABS COMPONENTS • ABS consists of: • wheel speed sensors which detects a wheel lock-up tendency, on the basis of wheel speed sensor signal • a ABSCM(Control Module) which outputs control signal • HCU(Hydraulic Control Unit) which supplies brake pressure to each wheel according to the ABSCM output signals. prepared by : Nor Hisham Bin Mohamed Mahayudin

  14. ABS GENERAL CONSTRUCTION prepared by : Nor Hisham Bin Mohamed Mahayudin

  15. (SECTION 1) 1 2 3 4 5 6 ABS COMPONENTS ( Wheel Speed Sensor ) 1 Electronic Cable 2 Permanent Magnet 3 Housing 4 Winding 5 Pole Pin 6 Tone Wheel prepared by : Nor Hisham Bin Mohamed Mahayudin

  16. ABS COMPONENTS ( Wheel Speed Sensor ) (SECTION 2) 1 Electronic Cable 2 Permanent Magnet 3 Housing 4 Housing Block 5 Pole Pin 6 Winding 7 Air gap 8 Tone wheel prepared by : Nor Hisham Bin Mohamed Mahayudin

  17. ABS COMPONENTS ( Wheel Speed Sensor ) 1 Magnet 2 Winding 3 Tone Wheel 4 Rotates 5 High Speed 6 Low Speed 7 Air Gap When the Tone Wheel rotates, the magnetic field changes and induces a voltage in the winding. - Permanent magnetic ▶ produce a voltage - Higher speeds ▶ produce a higher frequency - Lower speeds ▶ produce a lower frequency prepared by : Nor Hisham Bin Mohamed Mahayudin

  18. ABS COMPONENTS ( Wheel Speed Sensor ) WAVE FORM 1 (Minimum P-P voltage) 150mV or more at over 7 KPH prepared by : Nor Hisham Bin Mohamed Mahayudin

  19. ABS COMPONENTS ( Wheel Speed Sensor ) WAVE FORM 2 (At low speed) prepared by : Nor Hisham Bin Mohamed Mahayudin

  20. ABS COMPONENTS ( Wheel Speed Sensor ) WAVE FORM 3 (At high speed) prepared by : Nor Hisham Bin Mohamed Mahayudin

  21. ABS COMPONENTS ( ABSCM ) ABSCM(Control Module) From the wheel speed sensor signals, ABSCM calculates an estimated acceleration, deceleration and slip ratio. This controls solenoid valves and return pumps to prevent a wheel lock-up. Moreover, ABSCM manages a system monitoring circuit and turn off itself to protect the system if a system faulty is detected. Driver can recognize a system malfunction when ABS warning lamp comes on. prepared by : Nor Hisham Bin Mohamed Mahayudin

  22. ABS COMPONENTS ( ABSCM ) • 1) Basic Composition of ABSCM • If ABS fails, ABSCM should inhibit the system operation to guarantee the system safety. Because abnormal solenoid valve operation can affect the brake pressure on wheels. With this reason, ABSCM can analyze and prepare all kinds of possible faulty causes. • To install the ABSCM directly on the HCU(Hydraulic Control Unit), semiconductors inside ABSCM ( on general ) should resist at the temperature range of –40 ~ +125 ° C. Owing to the enhanced technology on semiconductor and size reduction, Integrated type (ABSCM+HCU) is popularly used worldwide. For example, Bosch ABS version 5.0 or higher, version MK-20i or higher of TEVES and EBC 325 of Kelsey Hayes are representative integrated ABS. prepared by : Nor Hisham Bin Mohamed Mahayudin

  23. ABS COMPONENTS ( ABSCM ) • All inputs are double-monitored and double-calculated. Inputs are also double-monitored. Moreover, to prevent a improper operation of ECU, two microprocessors compare and monitors their results And ECU is additionally monitored by SAS(Safety Assurance System) or intelligent Watch-Dog to prevent a ECU’s wrong operation. • One IC controls solenoids at each channel and a Power MOSFET with a very reliable protect circuit is substituted for relays which handled solenoid operation and big current while motor operation. • Furthermore, motor speed control is being employed to reduce excessive pumping and Kick-Back. 16 bit of microprocessor is used for the better ABS performance and wheel speed calculation which requests around 5msec of one cycle operating time. prepared by : Nor Hisham Bin Mohamed Mahayudin

  24. ABS COMPONENTS ( ABSCM ) • ABSCM consists of several basic circuits below. • a) Wheel Speed Sensor Input Amplification circuit • From each wheel speed sensors installed each wheel, alternating current waveforms in proportion to the vehicle speed come in the circuit. • The waveforms are amplified and converted into the square waveforms, and are sent to the Microcontroller. • According to ABS types, the number of wheel speed sensors changes and the number of amplification circuit also changes. prepared by : Nor Hisham Bin Mohamed Mahayudin

  25. ABS COMPONENTS ( ABSCM ) • b) Microcontroller • From each wheel speed information, this calculates a Reference Speed, Slip Ratio, Acceleration/Deceleration rates and performs solenoid valve & motor operation. • This circuit detects the wheel speed sensor waveforms generated by the teeth of sensor rotor at every moment. • Microcontroller calculates a reference speed by integrating a momentary wheel speed and then compares the reference speed and a momentary wheel speed to estimate a slip ratio and an acceleration/deceleration rates. • Solenoid valve activation circuit outputs pressure dump, hold, increasing signals to the lock-up wheels’ solenoids according to the estimated control signals like a slip ratio, acceleration/deceleration rates. prepared by : Nor Hisham Bin Mohamed Mahayudin

  26. ABS COMPONENTS ( ABSCM ) • c) Solenoid Valve activation circuit • This circuit controls the solenoid valve current and turns it on or off on the basis of the pressure dump, hold, increasing signal from the Microcontroller. • d) Voltage Regulator, Motor Relay & Failsafe Relay Driver circuit, Lamp Driver circuit, Communication circuit • Monitors the supply voltage(5V, 12V) being used for ABSCM is stable within the threshold voltage range. This detects a system failure and activates valve relay, motor relay. System faulty is detected, ABS system is down because a valve/motor relay comes off and ABS warning lamp turns on to inform the driver of system failure. While ABS failure, normal braking is available. prepared by : Nor Hisham Bin Mohamed Mahayudin

  27. ABS COMPONENTS ( ABSCM ) prepared by : Nor Hisham Bin Mohamed Mahayudin

  28. ABS COMPONENTS ( ABSCM ) • 2) Safety Circuit • Ignition switch turns on, ABSCM performs a self-test until the vehicle speed reaches certain speed and also monitors system while driving. • When a system failure is detected, firstly stops the ABS function and illuminates ABS warning lamp to inform the driver of system breakdown. • Even in case of an ABS breakdown, conventional brake is still available. After turn the IG off and turn it on, if a system faulty is not detected, warning lamp turns off and system comes normal. prepared by : Nor Hisham Bin Mohamed Mahayudin

  29. ABS COMPONENTS ( ABSCM ) • a) Initial Self-Testing after the IG on,(vehicle stops) • When the IG switch turns on and the voltage comes in ABSCM, followed procedures performs. a.1) Microprocessor function check - Makes an Watchdog Error and check if the error is detected - Checks the ROM data - Checks the RAM data whether data reading, writing is normal - Checks the A/D(Analog /Digital) Converter operation - Checks the communication between two microprocessor prepared by : Nor Hisham Bin Mohamed Mahayudin

  30. ABS COMPONENTS a.2) Valve Relay function check - Activates a valve relay and check the operation a.3) Fail Memory function check - Checks the fail memory of a microprocessor b) Initial Self-Testing while a vehicle begins to move A vehicle begins to move, ABSCM performs actuators’ function test. b.1) Solenoid Valve function test - Checks the solenoid valve function and monitors its operation prepared by : Nor Hisham Bin Mohamed Mahayudin

  31. ABS COMPONENTS ( ABSCM ) b.2) Motor function test - Operates a motor and check its condition. According to the ABS makers, the self-testing time of motor can be considerably different. But mostly, self-testing is performs at the beginning of vehicle driving or at the end of ABS operation. b.3) Wheel Speed Sensor signal check - Checks whether all wheel speed sensor signals c) System test while driving After completing the initial self-test, ABS system is check by two microprocessor and other circuits surrounding. If a faulty is detected, microprocessor finally confirms it and the corresponding error code is memorized in ABSCM. prepared by : Nor Hisham Bin Mohamed Mahayudin

  32. ABS COMPONENTS ( ABSCM ) c.1) Voltage test (12V, 5V) - Checks the supplied 12 voltage and 5 voltage inside ABSCM is normal. But the momentary voltage drop caused by ABS operation or motor operation is considered while monitoring 12 voltage. c.2) Valve Relay operation test - While ABS operation, valve relay is activated. ABSCM watchdogs a valve relay operation. c.3) Calculation Result comparison between two microprocessor Usually, there are two microprocessors inside ABSCM and they perform the same operation at the same time. They compare their results each other and identify their sameness. This comparison concept guarantees the system trust and can detect the system failure at an early stage. prepared by : Nor Hisham Bin Mohamed Mahayudin

  33. ABS COMPONENTS ( ABSCM ) c.4) Microprocessor operation test - Monitors microprocessor’s normality. c.5) ROM Data check - Performs a Check Sum of ROM data and confirms the program’s normality. d) Display Self Diagnosis When a system faulty is detected by a safety circuit, ABS function stops illuminating the ABS warning lamp. ABSCM displays trouble codes via a scan tool. With the scan tool, activates solenoid valves and motor. prepared by : Nor Hisham Bin Mohamed Mahayudin

  34. ABS COMPONENTS ( HCU ). HCU prepared by : Nor Hisham Bin Mohamed Mahayudin

  35. ABS COMPONENTS ( HCU )- HCU Circuit. Master cylinder Check valve HPA(High Pressure Accumulator) Plunger pump LPA (Low Pressure Accumulator) FR Wheel Cylinder FL Wheel Cylinder RR Wheel Cylinder RL Wheel Cylinder prepared by : Nor Hisham Bin Mohamed Mahayudin

  36. ABS COMPONENTS ( HCU )- Check Valve It allows the flow of brake fluid in a single direction. When the brake pedal is depressed, brake fluid flows through solenoid valves to the wheel cylinders. This time the check valve is closed. When the brake pedal is released, wheel cylinder brake fluid opens the check valve, which cause the wheel cylinder brake fluid to return to the master cylinder through the check valve and solenoid valves. Check valve operation allows wheel cylinder brake fluid to bypass the narrow passage of the solenoid valves and return to the master cylinder more quickly. prepared by : Nor Hisham Bin Mohamed Mahayudin

  37. Flow valve Flow valve From master cylinder From master cylinder A C Spool Orifice hall B B To wheel cylinder To motor From wheel cylinder ABS COMPONENTS ( HCU ) SOLENOID VALVE & FLOW VALVE Solenoid valve (OFF) Solenoid valve (ON) prepared by : Nor Hisham Bin Mohamed Mahayudin

  38. ABS COMPONENTS ( HCU ) FLOW VLAVE - Orifice controls hydraulic pressure to the brake caliper. - Flow Valve operates by Solenoid Valve. - Four Flow Valves, onefor each wheel prepared by : Nor Hisham Bin Mohamed Mahayudin

  39. ABS COMPONENTS ( HCU ) SOLENOID VALVE - Located at the bottom of the Flow Valve - Operated by the ABS CM - Controls the position of Flow Valve - Four Solenoid Valves in the modulator prepared by : Nor Hisham Bin Mohamed Mahayudin

  40. ABS COMPONENTS ( HCU ) EXPANDER CHAMBER - High pressure storage tank during ABS operation -Two Expander Chambers, One for each brake circuit Expander Chamber prepared by : Nor Hisham Bin Mohamed Mahayudin

  41. ABS COMPONENTS ( HCU ) MOTOR PUMP - Returns brake fluid from the accumulator to the master cylinder - Supplies additional hydraulic pressure during ABS operation - Two Pumps driven by one Motor (One Pump for each brake circuit) prepared by : Nor Hisham Bin Mohamed Mahayudin

  42. ABS COMPONENTS ( HCU ) DAMPER CHAMBER - Minimizes pressure pulses to the master cylinder - Prevents excessive brake pedal pulsation during ABS operation - Two Damper Chamber in the modulator, one for each brake circuit prepared by : Nor Hisham Bin Mohamed Mahayudin

  43. ABS OPERATION CONTROL LOGIC 1. Wheel speed of each wheel is always monitored . 2. Vehicle speed is calculated from the wheel speed inputs and inserted acceleration and deceleration parameters. 3. Wheel acceleration and deceleration are computed from the wheel speed input. 4. A reference speed is calculated from the vehicle speed and acceleration parameters. 5. Dump mode is implemented when the wheel speed is less than the reference speed or the wheel deceleration is greater than the deceleration limit. 6. Increase mode begins when the wheel speed or acceleration exceeds the reference speed or acceleration limit. prepared by : Nor Hisham Bin Mohamed Mahayudin

  44. ABS OPERATION Normal Braking As well known from the conventional brake system, the pedal force applied by the driver is assisted by a vacuum booster. Actuation of pedal is built up in the brake circuits. Out of ABS range, no current flows from the ABSCM to the inlet and outlet solenoid valves. The braking pressure from the master cylinder is delivered to each wheel cylinder via the inlet solenoid valve. prepared by : Nor Hisham Bin Mohamed Mahayudin

  45. ABS OPERATION Pressure Hold When a wheel lock-up begins, the ABSCM sends electrical current to the inlet solenoid valve. This allows the valve to overcome the spring force closing the inlet port and cutting off the passage between the master cylinder and the wheel cylinder. This time outlet valve is not activated remaining it closed. Therefore Brake fluid pressure acting on the wheel cylinder is hold at its current level. prepared by : Nor Hisham Bin Mohamed Mahayudin

  46. ABS OPERATION Pressure Dump Wheel speed decreases further while brake pressure is held at its current level, the ABSCM sends electrical current to the outlet solenoid valve as well as the inlet solenoid valve. Outlet port remains open and the passage between the wheel cylinder and the low pressure accumulator. Brake fluid inside the wheel cylinder flows out to the low pressure accumulator, reducing brake pressure in the wheel cylinder. The fluid in the low pressure accumulator dumps out to the master cylinder by the plunger pump. prepared by : Nor Hisham Bin Mohamed Mahayudin

  47. ABS OPERATION Pressure Increase Wheel speed start to increase during the brake fluid pressure hold or after the pressure decrease, the ABSCM assumes that there is no possibility of wheel lock-up, and so it turns off current to the inlet solenoid and outlet solenoid. This cause both vales to be returned to their home position by their springs, opening the inlet port and closing the outlet port. Since the inlet port is open and the outlet port is closed, the brake fluid pressure of the master cylinder reaches the wheel cylinder just as with normal braking, so wheel cylinder brake fluid pressure increases. prepared by : Nor Hisham Bin Mohamed Mahayudin

  48. Q & A prepared by : Nor Hisham Bin Mohamed Mahayudin

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