Published by Hyundai Motor company, september 2005 Centennial ESP (Electronic Stability Program, TEVES MK25)

2 HYDRAULIC BRAKE ASSIST SYSTEM Construction + [Tandem booster + Mater cylinder with the pressure sensors] [ESP hydraulic unit]

3 General Purpose The purpose of the HBAS is to assist the driver in emergency barking situations with active pressure build-up in the brake system. The ABS control should be reached as quickly and safely as possible. Design The hydraulic brake assist system is based on the components of the ESP MK25. The following components are used by HBAS: - inlet valve - outlet valve - Electric shuttle valve - TCS valve - 2 pressure sensors in the master cylinder - brake-light switch - vehicle speed The function of the HABS is integrated in the software of the ESP control unit. HYDRAULIC BRAKE ASSIST SYSTEM

4 HECU Pressure Sensor Emergency condition occurs. Detect emergency. (M/C pressure sensor) Detect emergency. (M/C pressure sensor) Execute an emergency decision logic. (ECU) Execute an emergency decision logic. (ECU) Increase brake pressure until the wheel slip occurs. Increase brake pressure until the wheel slip occurs. Execute an ABS control logic. [Control logic flow] Operating condition - over 20 bar - over 1100 bar/sec - over 7 km/h HYDRAULIC BRAKE ASSIST SYSTEM

5 Hydraulic operation HYDRAULIC BRAKE ASSIST SYSTEM

6 Description of function When the HBAS control logic recognizes that there is an emergency braking situation, the block valve is opened and the TCS valve is closed. The ESP pump starts up and increases the braking pressure in a split second to the locking pressure level above the level set by the driver. The ABS then keeps the individual wheels from being overbraked. Only 2 wheels are depicted in the illustration, but the HBAS works on all 4 wheels. Triggering criteria are: - violation of the minimum speed - violation of the minimum pressure - violation of the minimum pressure build-up time - actuation of the brake light switch Hydraulic operation HYDRAULIC BRAKE ASSIST SYSTEM

7 ABS in add on design (Integrated type) With these systems, a hydraulic ABS control unit is inserted into the hydraulic braking system between tandem master cylinder and the wheel brakes. By adding wheel sensors with gear wheels and an electronic ABS control unit, the system is converted into an electronic anti-lock braking system. The system consists of the following conventional components: - Brake booster - Tandem master cylinder - Wheel brakes (disc or drum) - Hydraulic ABS control unit - Electronic ABS control unit - Wheel sensors with tone wheels ESP GENERAL

8 Traction Control System (BTCS/FTCS ) This system is an extension of the well-known ABS function to incorporate BTCS (Brake Intervention Traction Control System) and FTCS (Full Traction Control System) which controls engine torque. ESP GENERAL

9 ESP (Electronic Stability Program) Combines the ABS and TCS components with additional sensors monitoring yaw, lateral acceleration and the drivers intention (steer angle sensor). * ESPAYC AYC * ESP: ABS + TCS + AYC (Active Yaw Control) ESP GENERAL

10 ESP is based on the MK25 ABS Hydraulic System of Continental Teves. ESP recognizes critical driving conditions, such as panic reactions in dangerous situations, and stabilizes the vehicle by wheel-individual braking and engine control intervention with no need for actuating the brake or the gas pedal. ESP adds a further function known as Active Yaw Control (AYC) to the ABS, TCS, EBD and EDC functions. Whereas the ABS/TCS function controls wheel slip during braking and acceleration and, thus, mainly intervenes in the longitudinal dynamics of the vehicle, active yaw control stabilizes the vehicle about its vertical axis. This is achieved by wheel-individual brake intervention and adaptation of the momentary engine torque with no need for any action to be taken by the driver. ESP essentially consists of three assemblies: the sensors, the electronic control unit and actuators. Sensors measure the position of the steering wheel, the pressure in the master brake cylinder, the yaw velocity (yaw rate) and the acceleration transverse to the vehicle (lateral acceleration). This makes it possible to compare the drivers intention with the momentary vehicle behavior so that in the event of interfering deviations with adverse affect on driving safety the electronic control unit can initiate appropriate corrective action. ESP GENERAL

11 The electronic control unit incorporates the technological experience accumulated in connection with the MK20 system, but has been substantially expanded in terms of capacity and monitoring concept in order to permit the additional sensor signals and arithmetic operations to be processed and converted into corresponding valve, pump and engine control commands. Tow 16-bit processors and one 8-bit processor, which monitor each other, cooperate to handle these requirements. Of course, the stability control feature works under all driving and operating conditions. Under certain driving conditions, the ABS/TCS function can be activated simultaneously with the ESP function in response to a command by the driver. In the event of a failure of the stability control function, the basic safety function, ABS, is still maintained. [ESP unit installation] ESP GENERAL

12 Electronic ESP Control Unit The electronic control unit performs the following functions: controlling the ESP, ABS, TCS, EBD functions continuous monitoring of all electrical components diagnostic help during servicing in the workshop In the integrated control unit, the coils of the solenoid valves are integrated into the control unit housing. The necessary relays (master relay and electric motor relay) are mounted on the circuit board of the electronic control unit as solid state relays. Applications of the ESP control unit The signal produced by the sensors are evaluated in the electronic control unit. From the information received, the control unit must first compute the following variables: *yaw rate, *longitudinal acceleration, *lateral acceleration, *pressure in hydraulic system, *wheel speed, *reference speed, *deference speed, *slip ESP UNIT

13 Electronic ESP Control Unit Reference speed The reference speed is the mean, I.e. average speed of all wheel speeds determined by simple approximation. Simplified ABS control If, during braking, one wheel speed deviates from the reference speed, the ABS control unit attempts to correct that wheel sped by modulating the brake pressure until it again matches the reference speed. When all four wheels tend to lock, all four wheels speeds suddenly deviate from the previously determined reference speed. In that case, the control cycle is initiated again in order to again correct the wheel speed by modulating the brake pressure. ESP UNIT

14 What triggers an ESP intervention? A criterion for ESP intervention exists when the yaw rate sensor senses an oversteering or understeering tendency of at least 4°/s (threshold depends on speed). If the plausibility analysis shows the same situation, action is taken to stabilize the driving condition. In the event of oversteering Braking intervention takes place at the wheels on the outside of the bend. Most of the braking force is introduced via the front wheel, which is caused to slip up to 50% so that the centrifugal force contributes to stabilizing the vehicle. In this case, the ABS logic is blotted out by ESP for the wheels with ESP intervention. In the event of understeering Braking intervention takes place at the wheels on the inside of the bend. In this case, the greater force is introduced via the rear wheel so that the lateral force is selectively reduced in exact does to stabilize the vehicle. The ABS logic is again blotted out by ESP for the wheels with ESP intervention. - Increase of brake pressure on the inside brakes - Decrease of brake pressure on the outside brakes if suitable - Control powertrain if necessary BASIC FUNCTIONS OF ESP

15 In the event of understeering & oversteering If the car is understeered with the front wheels pushing outward, a compensating yawing moment which returns the car body to the desired curse is built up by braking the rear wheel on the inside of the bend. If a swerving tail end shows that the car is in danger of oversteering, the front wheel on the outside of the bend is braked. The compensating yawing moment, which now acts in the clockwise direction, turns the car back into the desired direction. Compensating yawing moment Brake force BASIC FUNCTIONS OF ESP

16 In the event of understeering Without control Control RR wheel braking Generated Moment Normal direction BASIC FUNCTIONS OF ESP

17 In the event of oversteering FL wheel braking Non-control Control Normal direction Generated Moment BASIC FUNCTIONS OF ESP

18 TCS overriding ESP At the driven axle only. Here, ESP intervention is overridden by the TCS logic, which means that the lesser of two requested brake pressure is adjusted at the wheel. However, unlike pure TCS intervention this type of intervention uses the ESP pressure modulator. The reason for this is that the hydraulic system is detuned by the precharging pump, which is always active during an ESP intervention. ESP overriding ABS If an ABS intervention appears to be necessary while an EPS control cycle is in progress, the ABS logic is overridden by ESP. As the ESP system causes a wheel to slip up to 50% in order to stabilize the vehicle, the resulting wheel sensor signals would confuse the ABS logic (outside the ABS working range). Engine torque under the influence of both ESP and TCS If both ESP and TCS attempt reduce the engine torque, the higher reduction takes precedence. BASIC FUNCTIONS OF ESP

19 In the hydraulic control unit of the MK25 system, pump valve block Are grouped together in one housing, forming one compact unit with the electric motor. The pump and valve concepts are largely identical with the proven MK20 ABS production system. The pump itself is a silenced two-circuit pump driven by an electric motor. The solenoid valves which modulates the pressuring during ESP control are also integrated. For a diagonal brake circuit split (K), four pairs of valves (4 inlet valves, 4 outlet valves) are provided for modulating the pressure at the wheels plus two isolating valves and two electrically operated shuttle valves. The common housing furthermore accommodates a low-pressure accumulator and a silencing chamber for each brake circuit. HYDRAULIC CONTROL UNIT

20 Hydraulic circuit In idling position In this position, the inlet valve and the TCS valve are open, the electrically operated shuttle valve and the outlet valve are closed. HYDRAULIC CONTROL UNIT Shuttle valve TCS valve Outlet valve Inlet valve Motor

21 Hydraulic flow In braking position In this position, the inlet valve and the TCS valve are open, the outlet valve and the electrically operated shuttle valve remain closed. HYDRAULIC CONTROL UNIT Shuttle valve TCS valve Outlet valve Inlet valve Motor In braking position In this position, the inlet valve and the TCS valve are open, the outlet valve and the electrically operated shuttle valve remain closed. Shuttle valve TCS valve Outlet valve Inlet valve Motor In braking position In this position, the inlet valve and the TCS valve are open, the outlet valve and the electrically operated shuttle valve remain closed.

22 Hydraulic flow In ESP control position (pressure increase) The on/off booster builds up a pressure of approximately 10 bar in order to enable the ESP pump to suck brake fluid at low temperatures. In this position, the inlet valve is driven in a pulsed cycle. The TCS valve is closed. The outlet valve remains closed. The electrically operated shuttle valve is opened. The hydraulic pressure is led to the wheel brakes which are to be applied for a brief period of time. HYDRAULIC CONTROL UNIT Shuttle valve TCS valve Outlet valve Inlet valve Motor

23 Hydraulic flow In ESP control position (pressure dump) In this position, the TCS valve remains closed and the electrically operated shuttle valve is also being opened. The inlet valve is getting closed and the outlet valve comes to open releasing the brake pressure in the wheel cylinder. HYDRAULIC CONTROL UNIT Shuttle valve TCS valve Outlet valve Inlet valve Motor

24 MK25 ESP MK25 TCS Hydraulic circuit comparison between ESP and TCS HYDRAULIC CONTROL UNIT

25 Hydraulic shuttle valve and electric shuttle valve MK25 ESPMK20 TCS Electric shuttle valve Hydraulic shuttle valve HYDRAULIC CONTROL UNIT

26 Differences between the hydraulic shuttle vale used for ABS/TCS and the electric shuttle valve used for ESP General Like the hydraulic shuttle valve of a TCS system, the electric shuttle valve is located between the suction side of the pump and the master cylinder. With the braking system depressurized, the hydraulic shuttle valve is open and closes as soon as a pressure between 1.5 and 2.5 bar is reached in the braking system. The hydraulic shuttle valve opens automatically when the pressure drops below 1.5 bar. The electric shuttle valve is closed at all times, regardless of the pressure applied. It can only be opened by the electronic control unit. Hydraulic shuttle valve and electric shuttle valve HYDRAULIC CONTROL UNIT

27 Why the change from the hydraulic shuttle valve to the electric shuttle valve? When an ESP intervention is required, the ESP pump delivers brake fluid under pressure to that brake caliper which is to contribute to stabilizing the driving condition. To reduce the reaction time, brake fluid which has been precharged to approximately 10 bar (active brake booster) is made available on the suction side of the pump. This precharging pressure, though comparatively low, would close a hydraulic shuttle valve so that the pump would not be able to deliver brake fluid and build up pressure. An electric shuttle valve opened by the electronic control unit is able to overcome this pressure. Hydraulic shuttle valve and electric shuttle valve HYDRAULIC CONTROL UNIT

28 Suction (right side of pump) The pump piston moves to the left and the suction valve opens and brake fluid is sucked in. Pressure increase (left side of pump) The left piston moves to the left and the pressure valve opens and pressure is built up. Motor pump Suction Dump HYDRAULIC CONTROL UNIT

29 Filling and bleeding at the high-vacuum filling station To fill the braking system of a vehicle equipped with ESP, the electric shuttle valves must be activated by the electronic control unit via the diagnostics in addition to the four outlet valves. Otherwise, the space between the pump suction side and the electric shuttle valve would not be filled. The valves may not be activated for more than 90 seconds. If the valves must remain open for more than 90 seconds, they must be driven in a pulsed cycle with a frequency of 0.5Hz. Filling and bleeding in the rework location If a braking system requires afterbleeding in the course of vehicle production, the electric shuttle valves must be activated together with the isolating valves when bleeding the secondary circuit. With the electric shuttle valves closed, the ABS pump is unable to suck brake fluid from the fluid reservoir. Filling and bleeding in the workshop location When a hydraulic unit is replaced in the workshop, no special action is required because replacement parts are always delivered prefilled so that the pump circuit need not be bled. Filling and bleeding HYDRAULIC CONTROL UNIT

30 LOCATION OF ESP COMPONENTS

31 INPUTS AND OUTPUTS Sensor cluster Pressure sensor 2EA Brake switch ESP / TCS OFF S/W Motor pump Solenoid valves ABS,EBD W/L TCS/ESP F/L CAN communication with ETCM ESPCMESPCM WSS (FL) WSS (FR) WSS (RL) WSS (RR) Steering angle sensor TCS/ESP W/L InputsOutputs

32 CAN communication ESP INPUTS

33 CAN communication data from ETCM ESP INPUTS

34 Active wheel speed sensor [Front wheel sensor][Rear wheel sensor] Installation location: - Front wheel sensor: on the Front hub - Rear wheel sensor: on the Rear hub ESP INPUTS

35 Active wheel speed sensor Specification Type: MR(Magnetic Resistance) type Supplying power: DC 12V Output current: I L = 7mA, I H = 14mA Air gap: cannot be measured and adjusted - Front: ~ mm - Rear: ~ mm Teeth of tone wheel: 49 Supporting magnet Sensor element ESP INPUTS

36 Active wheel speed sensor Function of the active sensor system When moving, the sensor gear touches two of the resistors, disrupting the measuring bridge, and we generate a sinusoidal signal. The evaluation electronics converts the sinusoidal signal into a square wave signal. The signal can be processed directly by the ABS control unit. Checking routing for the active wheel sensor The wheel sensors are constantly checked electrically by the control unit. In addition, the sensor signal is checked while the vehicle is running. If there is a malfunction or a non-plausible physically possible signal, the ABS is switched off and the ABS warning lamp is switched on. ESP INPUTS

37 Active wheel speed sensor 11.3V13.6V 13.3V [Ignition key ON][Driving at low speed] ESP INPUTS

38 ItemPassive sensorActive sensor Sensor SizeLarger Smaller (possibly smaller by 40~50%) One ChipImpossibleGood Mass production MediumGood Zero Speed Cannot be detected at low speed ( 3km/h or less) Nearly 0 KPH (Intelligent Type) Temp. -40 ~ ~ +150 Air-gap Sensitivity Sensitive (V out 1/(gap) 2 ) Max.: 1.3mm Dull (frequency change) Max.: 3.0mm Anti-noisePoorGood Passive vs. Active wheel speed sensor ESP INPUTS

39 Sensor cluster (Yaw rate sensor + Lateral acceleration sensor) The lateral acceleration sensor and the yaw rate sensor are important components of the ESP. The cluster links these sensors to an on-board computer unit and to a CAN interface, incased in a sturdy housing, that is mounted on the chassis. Its modular concept allows the integration of further sensor functions. ESP INPUTS

40 Sensor cluster (Yaw rate sensor + Lateral acceleration sensor) [Location: under the center console box] ESP INPUTS

41 Sensor cluster (Hi-scan data on a level surface) [Current data][CAN communication signal] CAN-Hi CAN-Lo ESP INPUTS

42 Sensor cluster (Hi-scan data while turning left) [While turning fast][While turning less fast] ESP INPUTS

43 [While turning fast][While turning less fast] Sensor cluster (Hi-scan data while turning right) ESP INPUTS

44 Sensor cluster (Hi-scan data while leaning left) [at 90°][at 45°] ESP INPUTS

45 Sensor cluster (Hi-scan data while leaning right) [at 90°][at 45°] ESP INPUTS

46 Sensor cluster (Hi-scan data when the sensor connector is open) ESP INPUTS

47 Yaw rate sensor Application Detect the yawing motion of the vehicle, triggering an ESP control intervention if the yaw velocity reaches round about 4°/s (= full circle in 90s) Installation position Tuning forks vertical Required accuracy of position: max. ±3° tolerance to maintain full comfort failure to maintain the specified installation position will result in asymmetrical control ESP INPUTS

48 Yaw rate sensor Design and function The yaw rate sensor relies on the action of microscopic tuning forks. The plane in which these forks vibrate shifts when the car turns about its vertical axis. This shift is evaluated electronically. Failsafe A faulty yaw rate sensor produces an output signal of 0V. Specification - Supply voltage : 4.75 ~ 5.25V - Zero position : 2.5V - Operation : 27mV (°/s) 11.3 MHz 11 MHz ESP INPUTS

49 Lateral acceleration sensor Application Sense the lateral acceleration of the vehicle Design In the interior of the sensor, a small mass element is attached to a movable lever arm which is deflected by lateral acceleration. Other The signal of the lateral acceleration sensor alone cannot trigger an ESP intervention. The sensor is mainly used for estimating the coefficient of friction. The installation location of the lateral acceleration sensor is more critical than that of the yaw rate sensor(lever arm). The installation location may not be changed after repairs. ESP INPUTS

50 Lateral acceleration sensor Function Between two electrically charged stationary plates having the same polarity, an electrically charged silicon element having the opposite polarity is attached to the end of a cantilever arm. Between these three plates, two electric fields are generated by the capacitances C1 and C2. The capacitances C1 and C2 change in response to lateral acceleration. This change can be used to calculate the direction and amount of lateral acceleration acting on the vehicle. The same sensor can also be used as longitudinal acceleration sensor if it is installed in the direction of travel. For 0g lateral acceleration, the sensor produces an output signal with a voltage of 2.5V. ESP INPUTS

51 ST 1 ST N ST 2 Slit plate Hole ST 1 ST 2 ST N L H L H L H Steering angle sensor Application - Location: Inside steering wheel - Calculate the steering amount and direction - 3 Input Signals (ST 1, ST 2, ST N) - ST N detects the neutral position of steering wheel ESP INPUTS

52 Specification - Sensor type : Photo interrupt type - Sensor output type : Open Collector Type - Output pulse quantity :45pulse (Pulse cycle 8°) - Duty ratio : 50±10% - Phase difference of outputs : 2.0 ±0.6° - Supply voltage :IGN1(8~16V) - Output voltage :1.3V OL2.0V, 3.3V OH4.0V - Maximum rotational velocity : 1,500°/s Steering angle sensor STN ESP INPUTS

53 Steering angle sensor output (while turning right) [ST1, ST2][ST1, STN] ST1 ST2 ST1 STN ESP INPUTS

54 Steering angle sensor output (while turning left) [ST1, ST2][ST1, STN] ST1 ST2 ST1 STN ESP INPUTS

55 Steering angle sensor (When the sensor connector is open) [Diagnostic trouble code][Current data] ESP INPUTS

56 Pressure sensor Application Sense the drivers braking intentions (braking while an ESP intervention is in progress) Control the precharging pressure Design The sensor consists of two ceramic disks, one of which is stationary and the other movable. The distance between these disks changes when pressure is applied. Failsafe Guaranteed by redundant installation Installation The sensors are mounted on the TMC (primary and secondary circuits) ESP INPUTS

57 Pressure sensor Function The pressure sensors operate on the principle of changing capacitance. The distance (s) between the disks and, thus, the capacitance changes when pressure is applied to the movable disk by a braking intervention. The characteristic of the sensor is linearized. The fluid displacement of the sensor is negligible. Max. measurable pressure: 170 bar Specification - Supply voltage : 4.75 ~ 5.25V - Zero position : 0.5V - Operation : 23mV/bar s s1s1 ESP INPUTS

58 Pressure sensor t Output](V)Upper fault area lower fault area zero point [Sensor characteristics][Output signal] ESP INPUTS

59 ESP switch The ESP switch deactivates the ESP and TCS functions. The ESP switch is located in the center console of the vehicle. The system is generally active after each new start and is only deactivated by actuating the ESP switch. This facilitates - rocking to free the vehicle in deep snow or loose surface material - driving with snow chains - operation of the vehicle on a brake test bench The ABS function is fully maintained. The system is reactivated by actuating the ESP a second time. With the ESP switch, the ESP system can only be deactivated when the vehicle is stationary or traveling at low speed. The system cannot be deactivated while an ESP intervention is in progress. ESP INPUTS

60 FAILSAFE Electronic controller for ABS, TCS and ESP Block diagram

61 Safety concept of the ESP control unit In an emergency, it is vital that all ESP components function with absolute reliability. For this reason, various safety options must be available which guarantee the function of the system. The most important of these safety options are: self-test of the electronic control unit peripheral test of the connected assemblies Safety and monitoring system Turning on the ignition activates a self-test of the electronic control unit. After staring, all electric connections are monitored continuously. During the trip, the solenoid valves are checked at regular intervals by means of passive test pulses. In addition, all sensor signals are monitored continuously. The separation of brake circuits enables the ABS function to be maintained if one brake circuit should fail. This means that the driving stability of the vehicle is maintained during critical braking maneuvers. For workshop diagnosis, all faults detected are stored in a nonvolatile memory in the ESP control unit for retrieval in the workshop location. FAILSAFE

62 System monitoring The following items are controlled by the ECU: 12 valves Booster (solenoid valve) ABS pump ABS/ESP warning lamps The following items are monitored by the ECU: electronic control unit (include pump and valves) wheel speed sensors yaw rate sensor lateral acceleration sensor longitudinal acceleration sensor (all-wheel drive vehicle only) pressure sensor onboard voltage CAN bus communication The steering wheel angle sensor monitors itself and signals its state to the electronic control unit via the CAN bus. The warning lamps, the brake light switch and the ESP on/off switch are not monitored. FAILSAFE

63 Warning lamp control 1)EBD warning lamp control 2)ABS warning lamp control 3)TCS/ESP warning lamp control 4)TCS/ESP function lamp control FAILSAFE

64 1) EBD warning lamp control The EBD warning lamp is on : - During the initialization phase (3seconds) - In the event of inhibition of EBD functions - Depending on the warning lamp module, when the controller is switched off as long as voltage is applied at the ignition terminal (IG1) 2) ABS warning lamp control The ABS warning lamp is on : - During the initialization phase (3seconds) - In the event of inhibition of ABS functions (include ECE-ABS mode) - Depending on the warning lamp module, when the controller is switched off as long as voltage is applied at the ignition terminal (IG1) - During diagnostics FAILSAFE

65 3) TCS/ESP OFF warning lamp control The TCS/ESP warning lamp is on : - During the initialization phase (3seconds) - In the event of inhibition of TCS/ESP functions - During diagnostics. 4) TCS/ESP function lamp control The TCS/ESP function lamp is on : - During the initialization phase (3seconds) The TCS/ESP function lamp is blinking : - During TCS/ESP control - At the ESP off mode depending on ESP off switch, ESP control is available and ESP function lamp is blinking only when brake is turned on by driver. FAILSAFE

66 TCS/ESP OFF warning lamp & TCS/ESP function lamp The ESP warning lamp lights up briefly when the ignition is turned on and is extinguished as soon as the peripherals have been checked. During an ESP/TCS control cycle, the ESP function lamp flashes to show the driver that the system is active and that the vehicle is at the limit of its physical capabilities. Detection of the fault in the ESP system causes the ESP warning lamp to light up and remain on. The ESP system is then inactive, the ABS function is fully maintained. FAILSAFE

67 DTC list DIAGNOSIS

68 DTC list DIAGNOSIS

69 Pressure sensor 1 Pressure sensor 2 Sensor cluster FR FL RR RL ABS1 ABS2 POWER SIG OUT GND POWER SIG OUT GND POWER GND CAN2-LO CAN2-HI ESP WIRING DIAGRAM