Lý do chính của việc sử dụng hệ thống 4WD là để cải thiện lực kéo tổng thể của xe. Để dễ hiểu, chúng tôi định nghĩa lực kéo như là 1 lực kéo xe lớn nhất của vỏ xe để có thể thắng được lực cản của mặt đường. Lợi ích chính của 4 bánh chủ động là tăng gấp đôi lực theo chiều dọc của bánh xe lên mặt đường. Điều này giúp ích trong nhiều tình huống khác nhau như là đường ít ma sát (ví dụ: đường tuyết)
Textbook Module2 4WD (Four Wheel Drive) Module2 4WD (Four Wheel Drive) LESSON 2.1 Overview .37 O nl y 2.1.1 Introduction 37 2.1.2 4WD Types 38 2.1.3 History of 4WD 39 Components .41 Main Components & 4WD Layout 41 Transfer Case 43 Rear Differential 44 Driveline 45 4WD ECU 46 lU 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 se 2.2 2.3 na 2.2.6 4WD Coupling 47 2.2.7 4WD Lock Switch 48 2.2.8 4WD Lock Lamp & Warning Lamp 49 Control 51 2.4 tio 2.3.1 In / Output Elements 51 2.3.2 Coupling Control Mode 52 4WD Type Comparison 53 uc a 2.4.1 Comparison ITM & ITCC & DEHA 53 2.4.2 ITM (Interactive Torque Management) 54 2.4.3 ITCC (Intelligent Torque Controlled Coupling) 58 2.4.4 DEHA (Direct Torque Controlled Coupling) 61 2.5 Maintenance .65 Fo r Ed 2.5.1 Towing of WD Vehicles 65 2.5.2 Precautions (Only DEHA) 66 [Learning Objectives] ▪ Explain the function of each of the four types of 4WD ▪ Describe the system layout and list the locations, mechanisms and functions of components ▪ Explain the difference between ITM, ITCC and DEHA ▪ Take necessary actions after a part change and list the cautionary measures required for maintenance Basic Chassis Technology 35 Textbook Fo r Ed uc a tio na lU se O nl y Module2 4WD (Four Wheel Drive) 36 Basic Chassis Technology Textbook Module2 4WD (Four Wheel Drive) 2.1 Overview 2.1.1 Introduction The main reason for the usage of WD system is to improve the overall traction of the vehicle tio na lU se O nl y For easy understanding we define traction as the maximum amount of driving force the tire can apply against the ground The major benefit of a four-wheel drive is the potential to double the amount of longitudinal force the tires can apply to the ground This helps in a variety of situations, such as low friction road (e.g snow covered road) uc a Figure 2-1 Comparison between 2WD and 4WD Fo r Ed In the example on the right side a road with a partly slippery surface is given In the case of a WD vehicle the required torque to move the vehicle is higher than the available traction As a result the wheels start spinning and the vehicle gets stuck A WD vehicle on the same spot will transfer more torque to the rear wheels on the not slippery part, so that the torque acting at the front wheels and rear wheels is below the available traction: the vehicle will move forward (simplified general sample: the exact condition of torque transfer depends on the actual system layout) The following factors affect traction in general: the weight on the tire - The more weight acts on a tire, the more traction is available The coefficient of friction relates the amount of friction force between two surfaces to the force holding the two surfaces together: it is a function of the kind of tires on the vehicle and the type of surface the vehicle is driving on Important the coefficient of friction for static contact is higher than for dynamic contact (wheel slip), therefore static contact provides better traction than dynamic contact Wheel slip: it occurs when the force applied to a tire exceeds the traction available to that tire The possible traction force is reduced in this case, as explained before The weight transfer due to vehicle acceleration and cornering influences the possible traction of the tires, as the weight acting on the individual tire changes Basic Chassis Technology 37 Module2 4WD (Four Wheel Drive) 4WD Types O nl y 2.1.2 Textbook Fo r Ed uc a tio na lU se These are some possible and commonly applied layouts of 4WD systems The reason for the availability of different system is the different usage of vehicles and of course also the cost of the vehicle, as a sophisticated full time four wheel drive system is much more expensive then a simple one or a WD Other differences in the constructions may depend for example on the base vehicle, whether it is a front wheel drive or a rear wheel drive vehicle Also to consider is the general type of vehicle and its foreseen usage, for example a sporty passenger car or a pick up used for heavy duty operation etc Cars which are designed for heavy duty generally have a reduction section incorporated in the drive line to increase the available torque if necessary Having the cost advantage the demerit of a part time system is that it should not be driven in WD mode on a road with good friction co efficient As there is no center differential, the whole driveline is put under stress under this condition, which causes wear and noise A full time four wheel drive generally is equipped with a center differential( or in rare cases with a viscous coupling instead), and therefore can be used also on a dry road in WD mode without any problem The same is valid for the all wheel drive or permanent four wheel drive The difference is that the WD can not be switched off In case of the All wheel drive there is no high and low section in the transfer, as the vehicles are designed for on road use only Please note that the terms given above might be used different for example depending on the manufacturer Recently electronically controlled system are developed, which use the 4WD automatically and only in the case it is required 38 Basic Chassis Technology Textbook 2.1.3 Module2 4WD (Four Wheel Drive) History of 4WD → EST (Selective 4WD) TOD (Constant 4WD) ITM & ITCC & DEHA → ▪ Switch ON: FW/RW power distribution fixed at 50:50 (speed 40km/h↑: power distribution automatically changed to 100:0) tio 1) EST (Electric Shift Transfer) ▪ Switch OFF: AUTO mode on na lU ▪ 4H ↔ 4L: Activate switch after stopping 4H ↔ 4L: Activate switch after stopping se ▪ 2H ↔ 4H: Moving vehicle O nl y (Constant 4WD) ▪ 4WD mode uc a EST is standard on all models and trims for part-time 4WD, allowing drivers to “shift on the fly” between two- and four-wheel-drive modes at speeds up to 80 km/h • 2H mode: For normal road conditions (driving power of 0:100, HIGH mode) • 4H mode: For slippery road conditions, e.g unpaved, snow and rain (driving power of 50:50, HIGH Ed mode) • 4L mode: For getting out of rough roads and when maximum towing power is required (driving Fo r power of 50:50, LOW mode) 2) TOD (Torque On Demand) TOD electronically transfers power and torque from the rear to the front as required, enhancing off-road traction, handling agility and steering precision ▪ 4WD mode • AUTO mode: Used for normal road conditions or slippery roads, i.e snow or rain (driving power distributed automatically) • LOW mode: For getting out of rough roads and when maximum towing power is required (driving power of 50:50, LOW mode) Basic Chassis Technology 39 Module2 4WD (Four Wheel Drive) Textbook 3) ITM & ITCC & DEHA ITM (Interactive Torque Management), ITCC (Intelligent Torque Controlled Coupling) and DEHA (Direct Electro Hydraulic Actuator) are essentially identical technologies, with only their names and components varying by manufacturer The differences will be explained in detail in a section to follow These three systems, like TOD, are electronic constant 4WD modes, but of a reduced size and with improved controllability There is no LOW mode for selection Turning the switch on fixes the front/rear wheel driving power at 50:50 O nl y ▪ 4WD mode • 4WD LOCK mode: For slippery road conditions, e.g unpaved, snow and rain (driving power of Fo r Ed uc a tio na lU se 50:50, HIGH mode) 40 Basic Chassis Technology Textbook Module2 4WD (Four Wheel Drive) Components 2.2.1 Main Components & 4WD Layout uc a tio na lU se O nl y 2.2 Ed 1) Configuration Fo r 4WD system is based on a front wheel drive power train and consists of the following main parts : transfer case, propeller shaft, the coupling unit and rear differential on the mechanical side and the control module, the 4WD lock switch, the throttle position sensor, the wheel speed sensors, the steering angle sensor the WD lock lamp and the malfunction lamp When the 4WD lock is activated (possible up to a certain speed only) the coupling is fully activated and the vehicle is in 4WD mode (50:50), indicated by the 4WD lock lamp As there is no center differential tight corner wind up will occur in this condition In standard mode (lock switch off) the torque distribution between front and rear axle is controlled based on the inputs from the throttle position sensor, wheel speed sensors and the steering angle sensor As 4WD condition is only used when required (basically : wheel slip detected) the fuel consumption is reduced compared to a standard all wheel drive vehicle In the case of a problem in the system the driver is informed by the malfunction lamp Basic Chassis Technology 41 Module2 4WD (Four Wheel Drive) Textbook O nl y 2) Layout lU se The transfer case consists of the input shaft driven via the front differential by the means of splines and a gear train to supply the torque to the propeller shaft The input shaft of the transfer is hollow, so that the drive shaft of the right side front wheel can be passed trough it and connected to the front differential The gear train is used change the input shaft speed to the speed value required at the rear axle and to change the direction of the output towards the propeller shaft Fo r Ed uc a tio na The gear train consists of two conventional gears, a ring gear and a bevel gear With active ITM coupling the power is transferred via the gear train, the propeller shaft, the activated 4WD coupling to the rear differential and finally to the rear wheels In the case the 4WD coupling is not activated the gears in the transfer and the propeller shaft turn free and only the front wheels are driven 42 Basic Chassis Technology Textbook 2.2.2 Module2 4WD (Four Wheel Drive) Transfer Case Fo r Ed uc a tio na lU se O nl y A transfer is normally fitted in the transaxle of front wheel drive vehicles, and changes the direction of movement to deliver driving power to the rear wheels The oil to be used for the transfer should be gear oil (SAE 75W/90 API GL-5 grade), which should be inserted to fill up under the oil port Basic Chassis Technology 43 Module2 4WD (Four Wheel Drive) 2.2.3 Textbook Rear Differential O nl y 1) Purpose of Differential Vehicles which are not equipped with a center differential but only with the front and rear differential should only be used in WD under specific conditions, such as slippery road na lU se Driving this type of vehicle in WD on try paved road will cause high stress to the tires and the drive line This can be easily recognized during cornering, as the 1) Purpose of Differential driver will notice a wind up of the chassis and a high resistance against rolling This is caused by the fact that the rear wheels and the front wheels travel a different distance during cornering, as indicated in the picture The only way to compensate this without center differential is a (slightly) slipping tire Due to the high friction co efficient of a try road, a high force is required before the tire starts slipping, therefore the stress on the drive line is high Fo r Ed uc a tio 2) Principle A simple, conventional 4WD system with standard (open) differentials still can loose traction relatively easily under certain conditions An open differential can send only the amount of torque to the tires that won't cause the tire with the least traction to slip The transferable torque therefore might not be enough to get the car out of stuck condition if both axles are on a slippery surface (as indicated in the picture) , because the tires on it will start to slip In the shown situation this would mean that both right side wheels will spin and the car will not move As this is not desirable for real off road use, there are some ways to improve a system like this 44 Basic Chassis Technology Module2 4WD (Four Wheel Drive) 2.4.2 Textbook ITM (Interactive Torque Management) 1) Introduction Controllability of the vehicle in all driving situations is becoming an important promotional factor for All-Wheel-Drive An AWD vehicle has better road handling and is safer in all driving situations O nl y The characteristics of this system is that it is in the 2WD state at constant vehicle speed but it changes the torque distribution to rear wheels in the 4WD state according to the driving state uc a tio na lU se 2) Main Components Ed As shown in the above diagram, ITM is made up of a transfer case, propeller shaft, electronically controlled ITM coupling unit, rear differential, control module, 4WD lock switch, throttle position sensor, wheel speed sensors, steering angle sensor, WD lock lamp and malfunction lamp Fo r Refer to the preceding portion of this section for the mechanism and components of 4WD As the components and mechanism of the coupling, a main component of 4WD systems, differ by system, the ITM coupling will be explained on the following page 54 Basic Chassis Technology Textbook Module2 4WD (Four Wheel Drive) 3) ITM Coupling Items Description Operating Method EMC (Electronic Magnetic Coil) Torque 2,000Nm Weight 8kg Housing Material Aluminum Oil Mobil Fluid – LT (0.15L) Overview Fo r Ed uc a tio na lU se ● Specification O nl y ● The heart of the system is the ITM coupling (beside the electronic control unit) The main components of the coupling unit are the housing and bearings, the electro magnetic coil, the primary clutch, the apply cam, the steel balls and the secondary clutch The two clutches are both multi disc type clutches The primary clutch is used to create pressure on the secondary clutch via the apply cam Basic Chassis Technology 55 Module2 4WD (Four Wheel Drive) Components Fo r Ed uc a tio na lU se O nl y ● Textbook 56 Basic Chassis Technology Textbook ● Module2 4WD (Four Wheel Drive) Coupling Operation • Constant speed drive: almost 2WD state • Torque distribution (4WD state) changes according to the driving state (ex: sudden start, turning, at low-mu surface) by the ECU logic • Basic information: Input torque (Throttle Position Sensor), Steering Angle Sensor, Wheel Speed Sensor, Brake Signal as well as ABS signal • EMC Coil energizes to operate the Primary Clutch O nl y • The amount of electromagnetic force in the Primary Clutch decides displacement of a Base Cam • Displacement of the Base Cam increases frictional force between Inner Plates and Outer Plates of the Secondary Clutch Fo r Ed uc a tio na lU se • While braking: performs a different control logic to get efficient braking Figure 2-5 EMC Operation Basic Chassis Technology 57 Module2 4WD (Four Wheel Drive) 2.4.3 Textbook ITCC (Intelligent Torque Controlled Coupling) 1) Introduction Controllability of the vehicle in all driving situations is becoming an important promotional factor for All-Wheel-Drive An AWD vehicle has better road handling and is safer in all driving situations O nl y The characteristics of this system is that it is in the 2WD state at constant vehicle speed but it changes the torque distribution to rear wheels in the 4WD state according to the driving state The intelligent torque controlled coupling (ITCC) is a trademark of JTEKT - Toyoda Koki Automotive Systems and is applied as standard on the EN The ITCC system offers fully controllable torque transfer characteristics and extremely rapid activation and deactivation of the 4WD system automatically Ed uc a tio na lU se 2) Main Components Fo r The 4WD drive line comprises of less parts than other systems, resulting in reduced weight and reduced fuel consumption The system is based on a front wheel drive power train and consists of the following main parts : transfer case, propeller shaft, the electronically controlled ITCC coupling unit and rear differential on the mechanical side and the control module, the 4WD lock switch, the throttle position sensor, the wheel speed sensors, the WD lock lamp and the malfunction lamp on the electrical side When the 4WD lock is activated the coupling is fully activated and the vehicle is in 4WD mode (50:50), indicated by the WD lock lamp Full lock mode is available up to a vehicle speed of 30 km/h 58 Basic Chassis Technology Textbook Module2 4WD (Four Wheel Drive) 3) ITCC Coupling Items Description Operating Method EMC (Electronic Magnetic Coil) Torque 1,320Nm Weight 9Kg Housing Material Aluminum Oil ATF JWS 3309 (0.13L) – Permanent, No Exchange Overview Fo r Ed uc a tio na lU se ● Specification O nl y ● The heart of the system is the ITCC coupling (beside the electronic control unit) The unit can handle a output torque of up to 1320Nm and is filled with JWS 3309 ATF oil (same as used in Aisin F21-450 AT) which is maintenance free The main components of the coupling unit are the housing and bearings, the electro magnetic coil, the pilot clutch, the pilot cam, the main cam, the steel balls and the main clutch All clutches are multi disc type clutches The pilot clutch is used to create pressure on the main clutch via the main cam Basic Chassis Technology 59 Module2 4WD (Four Wheel Drive) ● Textbook Coupling Operation tio na lU se O nl y The input shaft of the ITCC coupling is connected to the clutch housing By energizing the electro magnetic coil, the armature is pulled towards the electro magnet The armature presses the pilot clutch discs against the clutch housing, thus connecting the pilot clutch to the input shaft The speed difference between the pilot cam and main cam created causes the steel balls between the pilot cam and main cam to move up the ball ramp Therefore the main cam is pushed towards the main clutch pack which now connects the clutch housing (input shaft) to the output shaft The applied force to the main clutch depends on the amount of pressure given by the steel balls The amount of pressure from the steel balls depends on the amount they move up on the ramp, which depends finally on the field strength of the magnetic clutch The field strength of the magnetic clutch is variable controlled by the ITCC control module via duty control Depending upon the amount of wheel slip detected on the front wheels the ITCC control module will apply the required duty to meet the target pressure created by the ball ramp mechanism In this way the control of the main clutch and the ultimate torque to the rear axle is achieved by the variable duty supply to the energizing coil and can reach any value between 100 front percent rear up to 50:50 share between front and rear Fo r Ed uc a Figure 2-6 When 2WD Figure 2-7 When 4WD 60 Basic Chassis Technology Textbook 2.4.4 Module2 4WD (Four Wheel Drive) DEHA (Direct Torque Controlled Coupling) 1) Introduction The system distributes the driving power to the front/rear wheels dynamically depending on the road surface and driving conditions to achieve optimum vehicle running performance Electronic Control Driving Power Distribution Mutual Control with Related Driving Control System O nl y Based on the signals received from various sensors, the 4WD ECU determines the road surface and driving conditions, and precisely adjusts the clamping force of the 4WD coupling (clutch) to variably regulate the portion of driving power transmitted to the rear wheels The system secures the optimum vehicle running performance through complete mutual control with the brake system, such as ABS and ESC Fo r Ed uc a tio na lU se 2) Main Components The driving torque moves from the engine/transmission to the transfer then moves to the Rear Differential Carrier via Propeller Shaft; the distribution of driving power is controlled by 4WD ECU and Coupling As shown in the above diagram, DEHA is made up of a transfer case, propeller shaft, DEAH coupling, rear differential, control module, 4WD lock switch, throttle position sensor, wheel speed sensors, steering angle sensor, 4WD lock lamp and malfunction lamp Basic Chassis Technology 61 Module2 4WD (Four Wheel Drive) Textbook 3) ITCC Coupling Items Description Operating Method Electronic Control Hydraulic Motor Torque 1,000Nm Weight 8.2Kg Housing Material Aluminum Oil Ultra low viscosity ATF (Shell TF0870) (0.485L) Overview Ed uc a tio na lU se ● Specification O nl y ● Fo r The 4WD ECU analyzes the information input, i.e., the signals from wheel speed, accelerator, steering angle, etc With this information, it controls the 4WD coupling multi-plate clutch depending on the road surface and driving conditions to distribute driving power to the front/rear wheels When the LOCK mode switch is pressed, the proportion ratio of the front/rear driving power is fixed at 50:50 At a vehicle speed of 40 km/h or higher, the mode automatically changes to AUTO, and returns to LOCK mode when the speed falls below 40 km/h again 62 Basic Chassis Technology Textbook ● Module2 4WD (Four Wheel Drive) Coupling Operation a CAN signal inputs from various sensors as the vehicle is being driven b The 4WD ECU calculates the required driving power and then provides the driving current to the actuator (electric motor + hydraulic pump) c Hydraulic pressure generated by the actuator moves the piston d Piston movement generates friction needed to clamp the clutch na lU se O nl y e The driving power is transferred to the rear wheels Fo r Ed uc a tio Figure 2-8 4WD Coupling Activated Basic Chassis Technology 63 Textbook Fo r Ed uc a tio na lU se O nl y Module2 4WD (Four Wheel Drive) 64 Basic Chassis Technology Textbook Module2 4WD (Four Wheel Drive) 2.5 Maintenance 2.5.1 Towing of WD Vehicles 1) Full-time 4WD Vehicle tio na lU se O nl y The best way to tow a full-time 4WD vehicle is to use a flatbed trailer on which you can load up a towed vehicle using a tow vehicle If you can’t get a flatbed to the job, you can use tow dollies, which lift the two front or rear wheels off the ground, while having the remaining wheels put on the jig 2) 2WD Vehicle uc a Figure 2-9 Towing of Full-time 4wd Vehicles Fo r Ed A 2WD vehicle can be towed on a flatbed by a towing trailer, or on a jig, as shown below The front wheels are lifted off the ground while keeping the rear wheels on the ground after the parking brake is released Caution! If you let a towed vehicle’s drive wheels stay on the ground, you risk severe transmission damage Figure 2-10 Towing of 2WD Vehicles Basic Chassis Technology 65 Module2 4WD (Four Wheel Drive) 2.5.2 Textbook Precautions (Only DEHA) 1) Clutch Wear Compensation Category Description Generation conditions and compensation methods The properties of clutch friction material inside the coupling change as the vehicle is driven When replacing the control module or coupling, a procedure of checking the value to compensate for such changes is required before inputting the data When replacing the coupling only: Reset the mileage saved in the ECU after replacing the coupling O nl y No compensation procedure is required ▪ Before replacing the ECU: Check the mileage saved in the ECU ▪ After the ECU is replaced: Enter the mileage that was saved in the old ECU in the new ECU after replacing it Fo r Ed uc a tio na lU Replacing the ECU only se Generation conditions and compensation methods compensation methods When replacing the ECU and coupling at the same time: 66 Basic Chassis Technology Textbook Module2 4WD (Four Wheel Drive) 2) Coupling Assembly Be sure to keep the coupling in a horizontal position • When the air bleeder in not kept in a horizontal position in the OPEN matter, the oil in the air bleeder may overflow So care should be taken when removing/installing/replacing the coupling • Before a new coupling is assembled with the rear differential, be sure to remove the plastic oil plug (no inspection capability / for plugging only) se O nl y • Regardless of the coupling being plugged or not, be sure to maintain it in a level position (Refer to the handling caution label.) lU Figure 2-11 Precautions in Handling Couplings No coupling oil inspection, replenishing or change na • When normal products are released from factory, the assembly is filled with exclusive coupling oil (ultra-low viscosity ATF Shell TF0870) • A special oil requiring neither inspection nor change • No drain plug or injection port (Unit is completely sealed.) tio Greasing the coupling spline Ed uc a When removing the coupling and assembling it with the rear differential, apply a miniscule amount of extreme-pressure molybdenum grease on the hole of the coupling spline Fo r Figure 2-12 Area of Coupling Spline Extreme-pressure molybdenum grease TECHLUBE MEGAMAX-ALPHA or equivalent NOTE Precautions when assembling the coupling and rear differential CAUTION : Extra caution should be taken not to damage the oil seal while assembling the coupling and rear differential Basic Chassis Technology 67 Textbook Fo r Ed uc a tio na lU se O nl y Module2 4WD (Four Wheel Drive) 68 Basic Chassis Technology ... the 4WD automatically and only in the case it is required 38 Basic Chassis Technology Textbook 2. 1.3 Module2 4WD (Four Wheel Drive) History of 4WD → EST (Selective 4WD) TOD (Constant 4WD) ITM... Technology Textbook 2. 2.8 Module2 4WD (Four Wheel Drive) 4WD Lock Lamp & Warning Lamp When the 4WD system fails, 4WD Warning Lamp flashes on the cluster Selecting 4WD LOCK mode turns on the 4WD LOCK MODE... higher .) Basic Chassis Technology Textbook Module2 4WD (Four Wheel Drive) 2. 4 4WD Type Comparison 2. 4.1 Comparison ITM & ITCC & DEHA BorgWarner (US) JTEKT (Japan) Wia Magna Powertrain (ROKorea) System