General ABS Function Under rapid braking or sloppy road condition by rain or snow, braking a vehicle in running is apt to generate skid condition The skid may decrease braking force to increase braking distance, generate spin by traverse slipping, and/or disable steering control, resulting to an accident Therefore the ABS system is designed to prevent from wheel locking and slip upon braking for ensuring : Stability, 2.Steer ability, and Optimum braking power and stopping distance Skid : A vehicle may slip to move without wheel rotation upon braking Slip rate (λ) Upon braking a vehicle which is running, slip rate changes from to 100% until the wheels are locked and the vehicle stops completely The slip rate l may be indicated as the below : λ = Vehicle speed － Wheel speed / Vehicle speed × 100(%) The slip rate (λ) and the surface friction coefficient (μB) may be correlated as the illustration The slip rate (λ) at the max.mB differs by the road condition but the max range is approx, 8~30% The cornering force (transversely slip preventing force) decreases with increasing slip rate Once wheels are locked, surface friction coefficient μB decreases and slip friction coefficient μS becomes to '0', and then wheels are easy to slip In fact locked rear wheels generate spinning and locked front wheels disables steer ability The ABS system controls braking force to maintain the slip rate in the range of 8~30%, in order to generate max surface friction coefficient, control slip friction coefficient at higher range, and provide stability and steer ability ABS Effect The ABS system provides stable braking under extreme condition Even braking rapidly on frozen or snowy road, wheels are not locked and maintain max friction with the road surface to provide optimum braking distance Restricting the pressure in the chamber locked at the wheel side on the road surface, the system ensures straight forward motion The driver may acquire correct alignment of the vehicle by adjusting the steering wheel only a little ABS configuration Full air brake Air over hydraulic brake Principle Parts functions Wheel speed sensor The 4-channel ABS uses four wheel speed sensors The sensor consists of a permanent magnet connected to metal rod, around which a coil has been wound A pulse wheel mounted to the hub induces an alternating voltage in the sensor coil The frequency of the alternating voltage is managed signal in the control unit 2.ABS/ASR control unit The ABS/ASR control unit is designed in digital type and possess dual microprocessors, with the following four features: (1)Input stage The unit checks the wheel speed signal (2)Computer The computer calculates the brake slip/traction and wheel deceleration/wheel acceleration control signal, and energize the output stage when wheels are about to be locked or spin (3)Output stage The unit energizes interface and axle weight distribution unit for controlling the pressure control valve, the solenoid valve, and the engine (4)Power supply The unit supplies stable voltage for the control unit operation The built-in protective device prevents electrical interference from applying to the vehicle electrical circuit Pressure control valve (1 channel) Each wheel is not controlled by a channel control valve The pressure control valve includes two diaphragm type valves (for pressure modulation, and for outlet) that are guided and controlled by the solenoid valves Upon normal braking, compressed air freely pass through the pressure control valve to the brake cylinder If one of wheels is about to be locked, the ABS/ASR control unit energizes both solenoid valves to lower the pressure in the brake cylinder The pressure modulation valve operates to modulate the pressure When the pressure is rising no current flows in the two solenoid valves 4.Solenoid valve The solenoid valves are connected with two 3/2 solenoid valves that are pilot-controlled When wheel's are about to spin, the valve energizes the axle brake cylinder driven by compressed air Two control plungers are controlled by the solenoid valves When current is interrupted, power supply is close and the cylinder connections are open outwards ABS control When the drive press the brake pedal, the pressure is supplied to the brake cylinder (or air chamber), and result to wheel deceleration When the brake slip is lower than the ABS system reaction limit value, the braking power is not controlled The ABS/ASR valve rises In order to provide the most proper pressure in the brake cylinder, the pressure decreases, is maintained, or increases in accordance with friction coefficient between tires, road surface, and vehicle steering The illustration indicates the ABS control feature on wheels upon braking At time t1, the pressure in the brake cylinder increases and the wheel speed decreases At time t2, the wheel deceleration and the slip rate increase above the limit, and the wheel is about to be locked With closing the pressure modulation valve and opening the exhaust valve, the pressure in the brake cylinder increases until the wheel speed increases again at time t3 Closing the exhaust valve, the pressure is maintained at a certain level to time t4 Then the slip value l =0 approximately, and the wheel acceleration reached the value that may raise the pressure again Then instantly opening and closing the pressure modulation valve, the pressure becomes pulse-up until time t5 The wheel deceleration and slip is higher than the limit again, and the pressure rise again The control cycle repeats until the vehicle stops actually Yaw moment on the front axle When the friction coefficients are significantly different between right and left wheels (for example when the road is frozen at outer side), corrective control feature is applied to the front axle accommodating between short braking distance and steering corrective value Constraining pressure rising and braking force on wheels, the yaw moment is restricted within the range that vehicle control is possible under rapid braking condition Friction force between tire and surface Friction force between tires and road surface when other conditions are same, friction forces between tires and road surfaces are virtually same for starting and braking conditions Friction force measurement (friction coefficient) differs by road condition, weather condition, tread type, and especially braking and wheel slip (Refer to illustration 7) In usual, braking motive force is within the stable area of slip curve In general rapid braking increases brake slip and decrease friction force With higher brake slip, wheels have lower traverse force for stability and steer ability of the vehicle The ABS system is designed primarily for stability and steer ability of the vehicle Friction force on running as well as on braking relies particularly on slip between tires and road surfaces With higher wheel slip, traction and running stability decreases With lowest wheel friction, differential function provides driving power performance when there are faults present Speed sensor System configuration : Air over hydraulic brake ABS control Failure WL Front left Front right Front left speed sensor NO¹ IC IC IC ON Front right speed sensor IC NO¹ IC IC ON Rear left speed sensor SL SL NO IC ON Rear right speed sensor SL SL IC NO ON Mixed up speed sensors NO NO NO NO ON Tire size, alignment error NO NO NO NO ON Two speed sensor errors or one speed sensor error and one PMV error NO NO NO NO ON IC : individual control Rear left Rear right SL : Select low WL : Warning lamp 1) Brake pressure is modulated according to behavior of not affected wheel System configuration : Full air brake ABS control Failure WL Front left Front right Front left speed sensor NO¹ IC¹ IC IC ON Front right speed sensor IC¹ NO¹ IC IC ON Rear left speed sensor MIC MIC NO IC ON Rear right speed sensor MIC MIC IC NO ON Mixed up speed sensors NO NO NO NO ON Tire size, alignment error NO NO NO NO ON Two speed sensor errors or one speed sensor error and one PMV error NO NO NO NO ON Rear left Rear right IC : individual control SL : Select low MIC : Modified individual control 1) MIC if affected wheel is on high m side PMV errors System configuration : Full air brake ABS control Failure WL Front left Front right Valve solenoid front left shorted low or broken wire or valve ground front left broken wire NO IC IC IC ON Valve solenoid front right shorted IC NO IC IC ON Rear left Rear right low or broken wire or valve ground front right broken wire Valve solenoid rear left shorted low or broken wire or valve ground rear left broken wire MIC MIC NO IC ON Valve solenoid rear right shorted low or broken wire or valve ground rear right broken wire MIC MIC IC NO ON Any valve solenoid or valve ground shorted high NO NO NO NO ON Valve ground shorted low MIC MIC IC IC ON Two valve error or one valve error and one speed sensor error NO NO NO NO ON System configuration : Air over hydraulic brake ABS control Failure WL Front left Front right Valve solenoid front left shorted low or broken wire or valve ground front left broken wire NO NO IC IC ON Valve solenoid front right shorted low or broken wire or valve ground front right broken wire SL SL NO IC ON Valve solenoid rear right shorted low or broken wire or valve ground rear right broken wire SL SL IC NO ON Any valve solenoid or valve ground shorted high NO NO NO NO ON Valve ground shorted low SL SL IC IC ON Two valve error or one valve error and one speed sensor error NO NO NO NO ON Rear left Rear right Power supply errors ABS control Failure Front left Front Rear left Rear right WL right GND shorted high or broken wire NO NO NO NO ON U_PMV or U_ECU over voltage or low voltage¹ NO NO NO NO ON U_PMV or U_ECU broken wire NO NO NO NO ON : Errors are reversible (can reast) provided they not occur during ABS cycles Miscellaneous errors ABS control Failure WL Front left Front right NO NO NO NO ON Internal relay always ON YES¹ YES¹ YES¹ YES¹ ON RET shorted high or shorted low or broken wire YES¹ YES¹ YES¹ YES¹ ON CAN interface bus off YES¹ YES¹ YES¹ YES¹ ON CAN interface error on message ERC1 YES¹ YES¹ YES¹ YES¹ ON Internal ECU failure or internal relay switch failure Safety monitoring Rear left Rear right Safety monitoring The ABS system satisfies highest safety and reliability requirements Prior to starting the vehicle, microcomputers perform self-diagnosis and check other computers, and then monitor wheel spin sensor, pressure modulation valve, wiring harness, and the whole ABS system Finding a failure the ABS system becomes wholly or partly inoperable and the warning lamp comes on The service brake system is still operable 2.Self-diagnostic feature In addition to the safety monitoring system, the self-diagnostic feature built in the ABS control unit enables to remove the failure immediately and safely Upon failure detection by the ABS control unit, the failure code is stored in the computer that may be read later at a service shop Then temporary failures including poor contraction at plug connection may be found and eliminated soonest How to read the failure code Failure codes may be read using a Hi-scan and self-diagnosis by blink signals of the lamp Self-diagnosis on a vehicle ABS lamp When a problem occurs in using the ABS system, the red ABS lamp comes on for warning in order to facilitate finding the trouble area by self-diagnosis In normal condition, the ABS lamp comes on upon switching the battery power on and extinguished upon starting the vehicle and during running If a trouble occurs in the ABS system during running, the ABS lamp comes on even or running 2.Diagnostic method The blink code device reads out error codes of 16 systems that are stored in the ECU system configuration and error memory The device checks the brake signal, as well The blink codes may be read using the ASR lamp, and troubles read with the self-diagnostic button may be identified using the blink code table Blink code configuration In order to operate the blink code, keep the self-diagnostic button pressed for two seconds and then release it Pressing the button once it will indicate the system configuration and an error code Press the self-diagnostic button once again to read error codes The ASR lamp indicates an error code each time pressing the button After reading out all error codes stored in the memory using the blink codes, the last stored code may be read continually Quitting self-diagnosis for 5minutes or more, or switching the starting key off and on again, the selfdiagnostic feature reads all information again from the beginning, the system configuration Each error code including the brake signal failure, includes three blocks The first block may be read at 100's digit, the second block at 10's digit, and the third block at 1's digit 4.Failure memory erasion Then ABS ECU will erase all error codes when the diagnostic push button is pressed during power on 5.Safety measure Upon ABS failure Failed circuit Operate as a non-ABS brake Other circuits ABS operation At least the ABS system may operate just same as a non-ABS brake Hi-scan check Turn the starting key off 2.Connect a Hi-scan with the data link connector located under the low crash pad panel Turn the starting key on 4.Using the Hi-scan, check DTCs 5.Upon repairing or correcting the problem, turn the starting switch and clear stored error codes using the clear key Disconnect the Hi-scan ... including the brake signal failure, includes three blocks The first block may be read at 100''s digit, the second block at 10''s digit, and the third block at 1''s digit 4.Failure memory erasion Then... wheels are locked, surface friction coefficient μB decreases and slip friction coefficient μS becomes to ''0'', and then wheels are easy to slip In fact locked rear wheels generate spinning and locked... or snowy road, wheels are not locked and maintain max friction with the road surface to provide optimum braking distance Restricting the pressure in the chamber locked at the wheel side on the