Module 2 4WD (TRUYỀN LỰC BỐN BÁNH CHỦ ĐỘNG(BẢN TIẾNG ANH )

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)

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LESSON

2.1 Overview 37

2.1.1 Introduction 37

2.1.2 4WD Types 38

2.1.3 History of 4WD 39

2.2 Components 41

2.2.1 Main Components & 4WD Layout 41

2.2.2 Transfer Case 43

2.2.3 Rear Differential 44

2.2.4 Driveline 45

2.2.5 4WD ECU 46

2.2.6 4WD Coupling 47

2.2.7 4WD Lock Switch 48

2.2.8 4WD Lock Lamp & Warning Lamp 49

2.3 Control 51

2.3.1 In / Output Elements 51

2.3.2 Coupling Control Mode 52

2.4 4WD Type Comparison 53

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

2.5.1 Towing of 4 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

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The main reason for the usage of 4 WD system is to improve the overall traction of the vehicle.

For easy understanding we define traction as the maximum amount of driving force the tire can applyagainst the ground The major benefit of a four-wheel drive is the potential to double the amount oflongitudinal force the tires can apply to the ground This helps in a variety of situations, such as lowfriction road (e.g snow covered road)

Figure 2-1 Comparison between 2WD and 4WD

In the example on the right side a road with a partly slippery surface is given In the case of a 2 WD vehiclethe required torque to move the vehicle is higher than the available traction As a result the wheels startspinning and the vehicle gets stuck A 4 WD vehicle on the same spot will transfer more torque to the rearwheels on the not slippery part, so that the torque acting at the front wheels and rear wheels is below theavailable traction: the vehicle will move forward (simplified general sample: the exact condition of torquetransfer 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 thetwo 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 (wheelslip), therefore static contact provides better traction than dynamic contact Wheel slip: it occurs when theforce applied to a tire exceeds the traction available to that tire The possible traction force is reduced inthis case, as explained before The weight transfer due to vehicle acceleration and cornering influencesthe possible traction of the tires, as the weight acting on the individual tire changes

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 asophisticated full time four wheel drive system is much more expensive then a simple one or a 2 WD Other differences in the constructions may depend for example on the base vehicle, whether it is a frontwheel drive or a rear wheel drive vehicle Also to consider is the general type of vehicle and its foreseenusage, for example a sporty passenger car or a pick up used for heavy duty operation etc Cars which aredesigned for heavy duty generally have a reduction section incorporated in the drive line to increase theavailable torque if necessary Having the cost advantage the demerit of a part time system is that it shouldnot be driven in 4 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 timefour wheel drive generally is equipped with a center differential( or in rare cases with a viscous couplinginstead), and therefore can be used also on a dry road in 4 WD mode without any problem The same

is valid for the all wheel drive or permanent four wheel drive The difference is that the 4 WD can not beswitched off In case of the All wheel drive there is no high and low section in the transfer, as the vehiclesare designed for on road use only Please note that the terms given above might be used different forexample depending on the manufacturer Recently electronically controlled system are developed, whichuse the 4WD automatically and only in the case it is required

▪ Switch OFF: AUTO modeon

▪ Switch ON: FW/RWpower distribution fixed

at 50:50 (speed 40km/h↑:power distributionautomatically changed to100:0)

1) EST (Electric Shift Transfer)

EST is standard on all models and trims for part-time 4WD, allowing drivers to “shift on the fly” betweentwo- and four-wheel-drive modes at speeds up to 80 km/h

▪ 4WD mode

• 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, HIGHmode)

• 4L mode: For getting out of rough roads and when maximum towing power is required (drivingpower 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-roadtraction, handling agility and steering precision

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3) ITM & ITCC & DEHA

ITM (Interactive Torque Management), ITCC (Intelligent Torque Controlled Coupling) and DEHA (DirectElectro Hydraulic Actuator) are essentially identical technologies, with only their names and componentsvarying 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 withimproved controllability There is no LOW mode for selection Turning the switch on fixes the front/rearwheel driving power at 50:50

▪ 4WD mode

• 4WD LOCK mode: For slippery road conditions, e.g unpaved, snow and rain (driving power of50:50, HIGH mode)

4 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 andthe vehicle is in 4WD mode (50:50), indicated by the 4WD lock lamp As there is no center differentialtight corner wind up will occur in this condition In standard mode (lock switch off) the torque distributionbetween front and rear axle is controlled based on the inputs from the throttle position sensor, wheel speedsensors and the steering angle sensor As 4WD condition is only used when required (basically : wheelslip 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

The gear train consists of two conventional gears, a ring gear and a bevel gear With active ITM couplingthe power is transferred via the gear train, the propeller shaft, the activated 4WD coupling to the reardifferential and finally to the rear wheels In the case the 4WD coupling is not activated the gears in thetransfer and the propeller shaft turn free and only the front wheels are driven.

of a try road, a high force is required before the tire starts slipping, therefore the stress on the drive line ishigh.

2) Principle

A simple, conventional 4WD system with standard (open) differentials still can loose traction relatively easilyunder certain conditions An open differential can send only the amount of torque to the tires that won'tcause the tire with the least traction to slip The transferable torque therefore might not be enough to getthe car out of stuck condition if both axles are on a slippery surface (as indicated in the picture) , becausethe tires on it will start to slip In the shown situation this would mean that both right side wheels will spinand the car will not move As this is not desirable for real off road use, there are some ways to improve asystem like this

The application of 4WD couplings largely depends on the type of system in use Further information will

be provided in the System Types section to follow In this chapter, the concept of 4WD couplings will beoutlined using the viscous coupling as an example

Figure 2-2 4WD Coupling according to Types

Let’s have a closer look to the operation of a viscous coupling this is EST system’s coupling It is commonlyused to link the back wheels to the front wheels so that when one set of wheels starts to slip, torque will

be transferred to the other set Therefore as a sample lets have a look at a viscous coupling between thefront and rear axle

Figure 2-3 Location of ITM Coupling

Figure 2-4 Structure of a Coupling (left) / Mode of Power Transmission (right)

When one set of wheels starts to spin faster, for example because it is slipping, the set of plates connected

to those wheels spins faster than the others The viscous fluid between the plates, tries to catch up withthe faster disks, dragging the slower disks along This transfers torque to the slower moving wheels: thewheels that are not slipping The higher the speed of the plates is relative to each other, the more torquethe viscous coupling transfers from one set to the other

is triggered automatically by the ECU, without the intervention of the driver, so that the driving power isappropriately transmitted to the front/rear wheels.

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1 When the 4WD system fails, 4WD Warning Lamp flashes on the cluster.

2 Selecting 4WD LOCK mode turns on the 4WD LOCK MODE Lamp on the dashboard.

3 In AUTO mode, there is no indicator.

4 The 4WD ECU and the cluster use CAN communication.

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All the described operations are controlled by the 4WD ECU It processes the input signals and controlsthe outputs The following input signals are provided to the ECU.

Braking condition from Braking Signal/ABS active signal: in 4WD mode all wheels are mechanicallyconnected therefore a locked wheel would influence all other wheels, leading to a difficult controllablebraking habit of the vehicle Therefore the 4WD is disabled when the ABS becomes active

Input torque based on throttle position sensor signal, to decide the right amount of torque distribution (byduty control of the EMC)

Cornering status from the steering wheel angle sensor to prevent wind up of the drive train during cornering.The steering angle sensor receives signals through CAN communication with MDPS; if a vehicle has noMDPS, signals are received from ESC

Vehicle speed and wheel speed difference (front & rear) from wheel speed sensors to detect slip condition

of the wheels and control the torque distribution accordingly

All this signals are used to control the duty to the EMC and thereby the torque share of the axles, which

is the main output signal Other outputs than the EMC control are the 4WD lock lamp, the 4 WD warninglamp and the diagnosis signal

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1) Operation Sequence Depending on Driving Conditions

Normal driving Cornering

During normaldriving, most of thedriving power istransferred to thefront wheels

The driving powerappropriate for thevehicle’s turningradius and speed

is transmitted tothe rear wheels

Wheel slip Locking

When one orboth front wheelsare slipping, thedriving powerappropriate forthe degree of slip

is transferred tothe rear wheels

Maximizes thetorque on roughroads (activatedonly when thevehicle speed isbelow 40 km/h)

2) Driving Power Distribution

Mode Front/rear Wheel Driving

Power Distribution Description of Operation

AUTO MODE

(normal driving)

100:0 - 50:50(variable control)

The driving power between the front and rearwheels are variably controlled by the 4WD ECUcontrol logic depending on the road surface anddriving conditions (quick acceleration, cornering,etc.)

LOCK MODE

(rough driving)

50:50 - 50:50(fixed distribution ratio)

This mode is used for handling tough conditions,such as sand, mud, snow, and puddles WithLOCK mode ON, the system minimizes front/rearwheel slipping by evenly distributing the drivingpower to the front/rear wheels in a 50:50 ratio

In order to prevent tight corner braking whilecornering, however, it regulates driving poweraccording to the cornering angle, and sets avehicle speed limit condition to avoid dangerdue to sudden changes of conditions in thevehicle running at a high speed (LOCK mode isdeactivated at the speed of 40 km/h or higher.)

2.4.1 Comparison ITM & ITCC & DEHA

Manufacturer BorgWarner (US) JTEKT (Japan) Wia Magna Powertrain

Inspect ECU / magnetic coil / ball

lamp / wet friction materia

ECU / magnetic coil / balllamp / wet friction material

ECU / motor / hydraulicpump /piston / wet friction

materialInput Sensor

Wheel speed sensorAPS SAS

Wheel speed sensor

ECU control - magneticcoil - primary clutch (1st)

- ball lamp - main clutch(secondary) - Drivingpower transferred torear wheels

ECU control motor hydraulic pump - piston

clutch Delivers rearwheel driving power

External

Appearance

Refer to the preceding portion of this section for the mechanism and components of 4WD As thecomponents and mechanism of the coupling, a main component of 4WD systems, differ by system, theITM coupling will be explained on the following page.

● Overview

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 applycam, the steel balls and the secondary clutch The two clutches are both multi disc type clutches Theprimary clutch is used to create pressure on the secondary clutch via the apply cam

• 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 SpeedSensor, Brake Signal as well as ABS signal

• EMC Coil energizes to operate the Primary Clutch

• 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 ofthe Secondary Clutch

• While braking: performs a different control logic to get efficient braking

Figure 2-5 EMC Operation

2) Main Components

The 4WD drive line comprises of less parts than other systems, resulting in reduced weight and reducedfuel consumption The system is based on a front wheel drive power train and consists of the following mainparts : 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 wheelspeed sensors, the 4 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 4 WDlock lamp Full lock mode is available up to a vehicle speed of 30 km/h