سیستم کنترل کشش خودرو
ساعت ٩:۱٠ ‎ق.ظ روز ۱۳۸۸/۱٠/٢٥  کلمات کلیدی: tcs ، کشش خودرو ، خودرو ، سیستم کنترل

 TCS (Traction control system ) 1

Critical driving situations are not restricted to braking; they can also occur during standing start and moving acceleration (specially on slippery gradients) and during cornering. These conditions can present drivers with more than they can handle. The result: Dangerous driving errors.

TCS traction control is designed to solve these problems. The primary purpose of TCS, an expanded version of ABS, is to reduce the demands placed on the driver by maintaining vehicle stability and steering response under acceleration (provided that the physical limits are not exceeded).


TCS does this by adapting the engine torque to levels corresponding to the traction available at the road surface before the situation becomes critical (Figure 1).

 

                                          Figure1

By combining TCS and ABS it is possible to obtain higher levels of safety through dual-purpose application of system components.

Base system

 

The TCS traction control system must be capable of inhibiting wheel-spin during initial or moving acceleration under the following conditions:

                                              When the lane is slippery on one or both sides    

 As the vehicle emerges from iced over parking lots and highway shoulders,- During acceleration when cornering, and

When starting off on a gradient (closed loop control of applied tractive force based on regulation of brake pressure at the potentially spinning wheel

The traction-control system must also intervene in the following situations:

 When a wheel spins

 The same as when it locks

 The lateral forces that it can transmit are limited; the vehicle becomes instable and the rear fishtails.

TCS maintain vehicle stability for enhanced safety.

 Spin-slip also leads to increased tread wear and drive train stress (e.g., differential). TCS avoids the drive train loads that occur when a spinning wheel suddenly finds traction on a high adhesion surface.

 TCS must be ready to intervene automatically at all times. TCS employs the difference in slip rates at the drive wheels to distinguish between cornering and acceleration slippage. The tires do not "drag" in tight radius corners, as can occur with a differential lock. Limited slip and locking differentials cannot always inhibit wheel spin resulting from excess throttle applications. In contrast, TCS also regulates the engine output to ensure that the wheels retain traction.

 The system responds to conditions in the physical threshold range by triggering a warning lamp to alert the driver.

 MSR engine drag torque control

TCS can be expanded and complemented with the addition of a supplementary MSR engine drag torque control device. When shifting down, or when the throttle closes suddenly on low traction road surfaces, the engine's brakingeffect can lead to excessive braking slip at the drive wheels.

MSR responds by initiating a small increase in the engine's torque to reduce the braking effect at wheels to a level commensurate with vehicle stability.

TCS must be able to intervene irrespective of the driver's throttle input. It is therefore necessary to replace the mechanical linkage between accelerator pedal and throttle valve (on gasoline engines), or between the pedal and control lever on the injection pump (on diesel engines), with ETC "electronic throttle control" (alternatively know as "drive-by-wire" etc.). ETC assigns TCS control commands priority over driver inputs.

A pedal travel sensor converts the position of the accelerator pedal into an electrical signal. The ETC control unit consults programmed factors and signals from other sensors (e.g., temperature, engine speed) in converting this pedal signal into a control voltage for the electric servomotor. The servomotor actuates the throttle valve (or pump control lever on diesels) and relays the position back to the ECU (Figure 2)1

Operation

When the driver depresses the accelerator, engine torque and the resulting drive torque both increase. If the road surface is capable of providing adequate "support" for this increased torque, then the vehicle can accelerate without restriction.

However, at least one of the drive wheels will start to spin as soon as the drive torque exceeds the physical maximum that can be applied through the road. The result is a reduction in effective tractive force, while the attendant loss of lateral adhesion leads to vehicle instability.

Within fractions of a second, TCS responds by regulating drive wheel slip page down to the optimum level.

As figure 1 illustrated, variations in torque balance MB can be employed to influence the monitored wheel speeds v1 and v1 - and with them the drive slip λ - at each of the drive wheels.

The torque balance MB consists of the drive torque MA, braking torque MB and the road - surface factor MS (representing the torque that can be transferred to the road surface).

On vehicles with spark ignition engine, the drive torque MA is regulated using the following systems:

 Throttle valve (throttle-valve adjustment

 Ignition system (advance angle adjustment, suppression of individual ignition pulses- Injection system (suppression of individual injection pulses

Figure3                  

On diesel equipped vehicles the drive torque MA is regulated by adjusting the control lever on the injection pump (reduction of injected fuel quantity).

The brake system can be used to control the braking torque MB at the individual wheels. For this, the ABS hydraulic system must be expanded accordingly.

Figure 3 compares the response delays associated with various types of TCS intervention in the engine management.

As the illustration shows, in the case of 2-wheel-drive vehicles, the relatively extended response delays mean that it is not possible to obtain satisfactory results with control based exclusively on throttle valve adjustments