Drivers control centre differential system

ABSTRACT:

This paper is focused on the description of the new Driver's Control Center Differential system that appropriately controls the differential limiting force of center differential LSD depending on running conditions of a vehicle. The new DCCD system evolved provides control that follow operations of the driver.

KEYWORDS:

Driver's Control Center Differential, electromagnetic clutch, mechanical LSD.

I. INTRODUCTION:

with the driver's image is enabled, preventing occurrence of understeer and oversteer.

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Picture of the center differential

All-wheel drive performance cars are rare enough. But the car would be even more unique if the driver can choose the value of the torque split between the front and rear wheels. Whether the driver makes adjustments to torque distribution in the manual mode via the console-mounted control wheel or entrusts distribution decisions to the DCCD control module through the automatic mode, the ratio of front/rear torque distribution can vary from 35 percent front/65 percent rear to 50 percent front/50 percent rear.

The system consists of a center differential of planetary gear type provided with LSD function, a steering angle sensor, a yaw rate sensor, a lateral G sensor, a DCCD control module and other components. Hybrid LSD mechanism using conventional electromagnetic clutch LSD mechanism added with torque-sensitive mechanical LSD mechanism allows approximate coincidence between the vehicle acceleration/deceleration and LSD clutch differential limiting timings, resulting in linear LSD characteristics acquired through driver's accelerator operation. Thus, the driver can more freely control the vehicle by easily grasping behavior of the vehicle.

In addition, the steering angle sensor let the DCCD control module know the driver's intension of turning. In combination with the yaw rate and lateral G sensors, it adjusts the electromagnetic clutch LSD differential limiting force based on the running path imaged by the driver and the actual behavior of the vehicle. Thus, cornering in better accordance

Parts of the DCCD and their respective locations:

- Rear differential oil temperature switch
- Manual mode switch
- Control dial
- Driver-controllable center differential module
- Parking brake switch
- Driver-controllable center differential indicator light
- ABSCU & H/U
- Stop light switch
- Throttle position sensor
- Accelerator position sensor
- Lateral G sensor
- Transmission assembly
- Center differential

Functions of the components:

- Rear differential oil temperature switch: Sends a signal to the driver-controllable center differential control unit if the rear differential oil temperature rises abnormally.
- Manual mode switch: Switches the driver-controllable center differential control mode between auto and manual.
- Control dial: Enables to manually select the locking rate of the center differential in a range from 0% to 100%.
- Driver-controllable center differential module: Processes the signals from various sensors and switches and controls the current to the driver- controllable center differential.
- Parking brake switch: Sends information on the parking brake operational status to the driver- controllable center differential control unit.
- Driver-controllable center differential indicator light: Indicates the locking rate of the center differential in a range from 0% to 100%.
- ABSCU & H/U: Sends ABS monitor signals to the driver-controllable center differential control unit.
- Stop light switch Sends information on the brakes’ operational status to the driver-controllable center differential control unit.
- Throttle position sensor: Sends information on the throttle valve opening to the driver-controllable center differential control unit.
- Lateral G sensor: Sends information on acceleration of the vehicle in lateral directions to the driver- controllable center differential control unit.

II. CENTRE DIFFERENTIAL

In response to the signal from the driver-controllable center differential control unit, the current is varied to change the transmitting torque of the multi-plate clutch and control the differential torque.

The center differential consists of three components: a planetary gear unit differential, a torque-sensitive mechanical LSD mechanism and an electromagnetic clutch LSD mechanism.

Engine output power input from the transmission driven shaft to the center differential goes through the planetary gear unit and is transmitted to the front wheel side from the drive pinion shaft penetrating through the drive shaft and to the rear wheel side from the transfer drive gear.

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Power flow as given in the flow chart below the power is transmitted:

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Power flow diagram 1

III. MECHANICAL LSD MECHANISM

The torque-sensitive mechanical LSD mechanism consists of a torque cam, main clutch and main clutch hub mounted to the sun gear and planetary shaft. The differential limiting function is achieved by restraining free rotation of the planetary gear unit when the main clutch is engaged with the torque cam.

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Figure 2 Differential limiting function of torque-sensitive mechanical LSD mechanism

When torque input is to the center differential by acceleration or deceleration, the torque cam transmits the torque from the sun gear to the planetary shaft, generating force that moves the planetary shaft leftward in the figure given above.

This force moves the main clutch hub mounted to the planetary shaft leftward in the figure, causing the main clutch to be engaged. Because the main clutch outer periphery is connected to rear wheels through the differential case and its inner periphery to front wheels through the main clutch hub and planetary shaft, engagement of the main clutch causes to limit the differential action of the planetary gear unit.

The main clutch engagement force is determined by the leftward force generated by the torque cam; therefore, the differential limiting force generated by the mechanical LSD automatically changes in proportion to the engine driving force (accelerator pedal travel).

IV. ELECTROMAGNET CLUTCH LSD MECHANISM

The electromagnetic clutch LSD mechanism consists of a main clutch, an intermediate clutch, a pilot clutch, an armature, a coil, six balls placed between the pilot clutch hub and intermediate pressure plate and other components.

This LSD mechanism carries out differential limiting by converting braking force of the pilot clutch to main clutch engagement force by the balls and intermediate pressure plate.

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When inactive

While the coil is DE energized, the pilot clutch is freed, allowing the pilot clutch hub, balls and intermediate pressure plate (connected to the sun gear through the main clutch hub) to turn idle with approximately the same rotational speed as the sun gear. In this state, the electromagnetic clutch LSD makes no differential limiting.

When active

When the coil is energized, its magnetic force attracts the armature to engage the pilot clutch. As the result, the pilot clutch hub is locked onto the differential case. (The pilot clutch engagement force varies by current flowing through the coil.) If rotational difference between the sun and internal gears is generated due to a slip in any of tires with the pilot clutch engaged, a phase difference that depends on the pilot clutch engagement force is generated between the intermediate pressure plate connected to the sun gear and the pilot clutch hub (connected to the internal gear through the differential case).

As the result, the balls placed between the intermediate pressure plate and pilot clutch hub are given a force that presses the intermediate pressure plate leftward, causing the intermediate and main clutches to be engaged with each other. Connection between the intermediate and main clutch limits the differential action between the sun and internal gears. The force given to the balls that presses the intermediate pressure plate leftward is determined by the pilot clutch engagement force. Therefore, the differential limiting force of the electromagnetic clutch LSD can be controlled by adjusting the pilot clutch engagement force with current applied to the coil.

V. OPERATION

MANUAL MODE OPERATION

Pressing the Manual Mode switch causes the DCCD system to be placed in manual mode. In this mode, the control dial can be used to arbitrarily adjust the magnetic clutch LSD limiting force ranging from free to lock.

The DCCD control module gives certain current determined by setting on the control dial to the coil. It causes the magnetic clutch LSD differential limiting force to be fixed to a certain value.

When the control dial is set to its lowest position, the coil current is zero and the magnetic clutch LSD is free, with only the mechanical LSD functioning.

When the control dial is set to the LOCK position, the coil current is the maximum, with the highest differential limiting force generated by the magnetic clutch LSD.

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AUTO MODE OPERATION

In auto mode, the differential limiting force of the electromagnetic clutch LSD is automatically adjusted according to the driver's intention and vehicle driving conditions. Various controls including engine driving force sensitive control and ABS differential signal input control, this section discusses system operations including the vehicle running characteristics, using an example of cornering control.

- Engine driving force sensitive control

Optimum control of the electromagnetic clutch LSD engagement force, estimating the driving force from the Aut0 mode 0perati0n 1 throttle travel, engine rotational speed and prospective gear ratio, aiming to compensate the mechanical LSD characteristics.

- ABS differential signal input control

Control of electromagnetic clutch LSD engagement force so that the ABS system performance can be maximized.

- Brake switch signal input control

Control of electromagnetic clutch LSD engagement force so that the brake performance can be maximized.

- Parking brake switch signal input control

Releasing the electromagnetic clutch LSD when the parking brake is applied.

- Tight cornering control

Reducing the electromagnetic clutch LSD engagement force during turning at low speed to prevent occurrence of tight corner braking phenomena.

- Slip control

Controlling the electromagnetic clutch LSD engagement force depending on the slippage, if any, detected through four wheel speed signals.

- Cornering control

Control that satisfies both controllability and stability of a turning vehicle. Maintaining the best cornering performance by controlling the pilot clutch engagement force based on the driver's intention and vehicle turning conditions determined from a steering angle, yaw rate and lateral G sensors and vehicle speed

VI. ADVANTAGES

1) Variation of driving force in short period of time such as turbo lag can be followed without delay.

2) Engine driving force and mechanical LSD differential limiting force during turning

- When the vehicle is braked (A) while running: To enhance safety of the vehicle during braking the restriction force of the center differential is controlled toward the free state.
- When the vehicle is in between the turn-in point (B) and clipping point (C): When the vehicle is running from the turn-in point toward the clipping point, the throttle opening increases (vehicle accelerates) and a signal from the lateral G sensor is input. Accordingly the center differential restriction torque is gradually increased to improve the cornering ability.
- When the vehicle is in between the clipping point (C) and exit point (D): When the vehicle is running past the clipping point toward the exit point, the input from the lateral G sensor decreases. Accordingly the control interprets this as the vehicle is tracking out from the corner and increases the restricting force of the center differential toward the locked state to maintain traction.

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3) Controls giving priority to driver's intention: DCCD control module can know the driver's intention to turn from steering angle sensor signal. By reflecting this information to the electromagnetic clutch LSD control, excessive understeer or oversteer during turning can be avoided, allowing cornering as imaged by the driver.

VII. CONCLUSION

The DCCD concept is pure power in driver’s control.

This concept aims to reach the highest performance. Handling has been improved along with the comfort of the drivers by the use of the sensors and control module in the auto mode.

As well as in the manual mode DCCD provides the advantage of changing the torque biasing as per the driver’s intention.

VIII. REFRENCES

i. en.volkswagen.com/ en/ innovation- and. ../zentraldifferenzial.html
ii. www.lezo.hu/szerkezettan/hajtas/eroatvitel/.../DCCD_4kerek hajtas.pdf
iii. www.lezo.hu/szerkezettan/hajtas/eroatvitel/.../DCCD_4kerek hajtas.pdf
iv. By M J Nunne, Light and Heavy Vehicle Technology, four wheel drive systems.
v. Hillier's Fundamentals of Motor Vehicle Technology, Book 1