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1 ABS/TCS/ESP TRAINING GUIDE HYDRAULIC FUNDAMENTALS HYDRAULIC FUNDAMENTALS PASCAL’s Law In the early seventeenth century, Pascal, a French scientist, discovered the hydraulic lever Through controlled laboratory experiments, he proved that force and motion could be transferred by means of a confined liquid Further experimentation with weights and pistons of varying size, Pascal also found that mechanical advantage or force multiplication could be obtained in a hydraulic pressure system, and that the relationships between force and distance were exactly the same as with a mechanical lever From the laboratory data that Pascal collected, he formulated Pascal’s Law, which states : “Pressure on a confined fluid is transmitted equally in all directions and acts with equal force on equal areas.” This law is a little complex to completely understand as it stands right now The following illustrations and explanations break down each concept and discuss them thoroughly enough for easy understanding and retention HYDRAULIC FUNDAMENTALS PASCAL’s Law 100 kgf 10 kgf Area : 1m2 Area : 10m2 P1=10kgf/m2 Hydraulic fluid HYDRAULIC FUNDAMENTALS Force A simplified definition of the term force is : the push or pull exerted on an object There are two major kinds of forces : friction and gravity The force of gravity is nothing more than the mass, or weight of an object In other words, if a steel block weighing 100 kg is sitting on the floor, then it is exerting a downward force of 100 kg on the floor The force of friction is present when two objects attempt to move against one another If the same 100 kg block were slid across the floor, there is a dragging feeling involved This feeling is the force of friction between the block and the floor When concerned with hydraulic valves, a third force is also involved This force is called spring force Spring force is the force a spring produces when it is compressed or stretched The common unit used to measure this or any force is the kilogram (kg), or a division of the kilogram such as the gram (g) HYDRAULIC FUNDAMENTALS Pressure Pressure is nothing more than force (kg) divided by area (m 2), or force per unit area Given the same 100kg block used above and an area of 10m2 on the floor ; the pressure exerted by the block is : 100kg/10m or 10kg per square meter Pressure On a Confined Fluid Pressure is exerted on a confined fluid by applying a force to some given area in contact with the fluid A good example of this would be if a cylinder is filled with a fluid, and a piston is closely fitted to the cylinder wall having a force applied to it, thus, pressure will be developed in the fluid Of course, no pressure will be created if the fluid is not confined It will simply “leak” past the piston There must be a resistance to flow in order to create pressure Piston sealing, therefore, is extremely important HYDRAULIC FUNDAMENTALS in hydraulic operation The force exerted is downward (gravity) ; although, the principle remains the same no matter which direction is taken The pressure created in the fluid is equal to the force applied ; divided by the piston area If the force is 100 kg, and the piston area is 10m 2, then pressure created equals 10kg/m2 = 100kg/10m2 Another interpretation of Pascal’s Law is that : “Pressure on a confined fluid is transmitted undiminished in all directions.” Regardless of container shape or size, the pressure will be maintained throughout, as long as the fluid is confined In other words, the pressure in the fluid is the same everywhere The pressure at the top near the piston is exactly same as it is at the bottom of the container, thus, the pressure at the sides of the container is exactly the same as at top and bottom HYDRAULIC FUNDAMENTALS Force Multiplication Going back to the previous figure and using the 10kg/m created in the illustration, a force of 1,000kg can be moved with another force of only 100kg The secret of force multiplication in hydraulic systems is the total fluid contact area employed The figure shows an area that is ten times larger than the original area The pressure created with the smaller 100kg input is 10kg/m2 The concept “Pressure is the same everywhere”, means that the pressure underneath the larger piston is also 10 kg/m Reverting back to the formula used before : Pressure = Force/Area or P = F/A, and by means of simple algebra, the output force may be found Example : 10kg/m2 = F(kg) / 100m2 This concept is extremely important as it is used in the actual design and operation of all shift valves and limiting valves in the valve body of the transaxle It is nothing more than using a difference of area to create a difference in pressure in order to move an object HYDRAULIC FUNDAMENTALS Piston Travel Returning to the small and large piston area discussion The relationship with a mechanical lever is the same, only with a lever it’s a weight-todistance output rather a pressure-to-area output Referring to following figure, using the same forces and areas as in the previous example ; it is shown that the smaller piston has to move ten times the distance required to move the larger piston 1m Therefore, for every meter the larger piston moves, the smaller one moves ten meters This principle is true in other instances, also A common garage floor jack is a good example To raise a car weighing 1,000kg, an effort of only 25kg may be required But for every meter the car moves upward, the jack handle moves many times that distance downward A hydraulic ram is another good example where total input distance will be greater than the total output distance The forces required in each case are reversed That is, very little effort is required to produce a greater effort HYDRAULIC FUNDAMENTALS Hydraulic System Now that some of the basic principles of hydraulics have been covered and understood, it is time to explore hydraulic systems and see how they work Every pressure type hydraulic system has certain basic components This discussion will center on what these components are and what their function is in the system Later on, the actual systems in the transaxle will be covered in detail The figure reveals a basic hydraulic system that can be used in almost any situation requiring work to be performed The basic components in this system are : Reservoir, Pump, Valving, Pressure lines, Actuating mechanism or mechanisms The Fluid Reservoir Since almost all fluids are nearly incompressible, the hydraulic system needs fluid to function correctly The reservoir or sump, as it is sometimes called, is a storehouse for the fluid until it is needed in the 10 ESP INPUTS 535 Pressure sensor Output](V) Upper fault area 5.0 4.75 0.5 zero point 0.25 0.0 t lower fault area [Sensor characteristics] [Output signal] ESP INPUTS 536 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 FAILSAFE 537 Block diagram Electronic controller for ABS, TCS and ESP FAILSAFE 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 538 FAILSAFE 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 539 FAILSAFE 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 540 FAILSAFE 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 541 FAILSAFE 542 FAILSAFE 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 543 FAILSAFE 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 544 FAILSAFE Active ABS/EBD warning output 545 FAILSAFE Passive ESP WL/FL Output 546 DIAGNOSIS 547 DTC list DTC Trouble location C1604 ECU Hardware C1700 Variant no coding C1200 Wheel speed sensor front left –electrical C1201 Wheel speed sensor front left –extrapolate C1202 Wheel speed sensor front left –other C1203 Wheel speed sensor front right –electrical C1204 Wheel speed sensor front right –extrapolate C1205 Wheel speed sensor front right –other C1206 Wheel speed sensor rear left –electrical C1207 Wheel speed sensor rear left –extrapolate C1208 Wheel speed sensor rear left –other C1209 Wheel speed sensor rear right –electrical C1210 Wheel speed sensor rear right –extrapolate C1211 Wheel speed sensor rear right –other C2112 Valve relay DIAGNOSIS 548 DTC list DTC Trouble location C1235 Pressure sensor (primary) –electrical C1236 Pressure sensor (secondary) –electrical C1237 Pressure sensor –other C1259 Steering wheel sensor –electrical C1260 Steering wheel sensor –signal/other C1282 Yawrate & lateral G sensor –electrical C1283 Yawrate & lateral G sensor –signal/other C1101 Battery Over voltage C1102 Battery Under voltage C1513 Brake lamp switch C2402 Motor C1616 CAN Bus off C1611 CAN timeout EMS C1612 CAN timeout TCU C1503 TCS/ESP Switch C2227 Excessive temperature of brake disk ESP WIRING DIAGRAM ABS1 ABS2 Pressure sensor Pressure sensor Sensor cluster FR FL RR RL POWER SIG OUT GND POWER SIG OUT GND POWER GND CAN2-LO CAN2-HI 549 ... 16 ABS GENERAL A BRIEF 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. .. become unstable and can start to skid sideways 18 ADVANTAGES OF ABS 19 Braking at cornering [Without ABS] [With ABS] ADVANTAGES OF ABS 20 If a car on the different conditions of surface brakes,... vehicle begins to spin But ABS provides vehicle stability until it stops [Braking without ABS] Low μ road [Braking with ABS] Low μ road High μ road surface High μ road surface ABS TYPES 4-Sensor 4-Channel