The wheel speed sensor is the essential component the ABS ECU uses to calculate vehicle speed and to determine whether wheel lock occurs. For example, rear wheel speed signal is used as a referecnce value, for vehicle speed, in front wheel drive vehicles, and if a difference between front and rear wheel speed occurs, then ABS control is performed. Wheel speed sensor is active hall-sensor type and good at temperature and noise chariteristic. Digital wave is produced as tone wheel rotate according as hall sensor principle. Frequency of duty wave is changed in proportion to rotation of tone wheel and HECU calculate vehicle speed by this frequency.
The ABS ECU monitors the wheel speed sensor signal continuously. This code is set if no wheel speed signals within 10msec to 20msec when the vehicle speed is more than 43km/h or an abnormal speed change ratio is detected. Or this code is set if interference on one or more wheels for 20sec with the brake pedal applied or for 5sec when the brake pedal is not applied. Warning lamp is turned OFF if the detected fault is not more than when the IG KEY is turned to ON again, and wheel speeds are more than 12 Km/h
Item | Detecting Condition | Possible cause | |
Case1 | DTC Strategy | ● Static Start-up monitoring | ● Improper installation of wheel speed sensor ● Abnormal Rotor and wheel bearing ● Faulty Wheel speed sensor(RL) ● Faulty HECU |
Monitoring Period | ● When starting after IG ON ● When restarting after vehicle speed become less then approx. 3km/h ● After monitoring approx. 12 Km/h of wheel speed when HECU detect speed less then 1.8Km/h, wheel speed is monitored every 18Km/h after corresponding speed of timing(1.8Km/h). | ||
Enable conditions | ● Any wheel velocity ＜ approx. 1.8Km/h | ||
Fail Safe | ● Sensor failure outside the ABS control cycle ABS is switched off immediately. ● Sensor failure inside the ABS control cycle 1. If only one wheel is in ABS control and a sensor fault is detected at this wheel, then : ABS is switched off immediately. 2. If several wheels are in ABS control, then : ABS is switched off at the end of ABS control. ● If a sensor fault occurs on a front wheel, pressure is increased ; on a rear wheel, pressure is controled in suitable pressure. (until switch off). ● ABS and EBD control of the corresponding wheel is no longer possible. | ||
Case2 | DTC Strategy | ● Dynamic monitoring | |
Monitoring Period | ● Continuous if Speed of Wheel > approx. 43 km/h, if Vehicle speed > approx. 43 km/h | ||
Enable conditions | ● No wheel speed signals within 70ms to 80ms at a vehicle speed > approx. 43 km/h. Dynamic monitoring is disabled in the event of aquaplaning or interference. | ||
Fail Safe | ● Sensor failure outside the ABS control cycle ABS is switched off immediately. ● Sensor failure inside the ABS control cycle 1. If only one wheel is in ABS control and a sensor fault is detected at this wheel, then : ABS is switched off immediately. 2. If several wheels are in ABS control, then : ABS is switched off at the end of ABS control. ● If a sensor fault occurs on a front wheel, pressure is increased ; on a rear wheel, pressure is decreased(until switch off). ABS control of the corresponding wheel is no longer possible. ● The ABS warning lamp is activated and the EBD warning lamp is not activated. | ||
Case3 | DTC Strategy | ● Wheel Speed difference monitoring | |
Monitoring Period | ● Continuously | ||
Enable conditions | ● Max. wheel speed difference is chosen as bellow 1. (FL wheel speed - RL wheel speed) 2. (FR wheel speed - RR wheel speed) 3. (FL wheel speed - FR wheel speed) - 1.1m/s (Approx.4km/h) 4. (RL wheel speed - RR wheel speed) -1.1m/s (Approx. 4km/h) ● Vehicle < 100Km/h If wheel speed difference is contrinued as bellow, fault is detected. 1. 1.7m/s (Approx.6km/h) ≤ Max.wheel speed diff.< 3.3m/s (Approx. 12km/h) for 18sec 2. 3.3m/s (Approx.12km/h) ≤ Max. wheel speed diff. for 9sec ● Vehicle > 100Km/h If wheel speed difference is contrinued as bellow, fault is detected 1. (6% * vehicle speed) ≤ Max.wheel speed diff.< (12% * vehicle speed) for 18sec 2. (12%*vehicle speed) ≤ Max. wheel speed diff. for 9 sec ● Spinning wheel, decelerating wheel 1. If any wheel is doing a shows strong deceleration (e.g. caused by hand brake) the fault detection filter time is set to 18s. 2. If any spinning wheel is detected the fault detection filter time is set to 72s. | ||
Fail Safe | ● ABS is switched off immediately. ABS control of a faulty wheel is not longer possible. ● If a sensor fault occurs on a front wheel, pressure is increased ; on a rear wheel, pressure is decreased (until switch off). ● The ABS warning lamp is activated and the EBD warning lamp is not activated. | ||
Case4 | DTC Strategy | ● Long-term interference monitoring | |
Monitoring Period | ● Continuously | ||
Enable conditions | ● Interference on one or more wheels for 20s with the brake pedal applied or for 5s when the brake pedal is not applied. | ||
Fail Safe | ● Sensor failure outside the ABS control cycle ABS is switched off immediately ● Sensor failure inside the ABS control cycle 1. If only one wheel is in ABS control and a sensor fault is detected at this wheel, then : ABS is switched off immediately. 2. If several wheels are in ABS control, then : ABS is switched off at the end of ABS control. ● ABS and EBD control of the corresponding wheel is no longer possible. |
