SsangYong Actyon Sports II. Manual — part 150

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4892-01

3) Basic ABS Control

Operation of ABS control unit

▶

Applications of the ABS control unit The signals

produced by the wheel sensors are evaluated

in the electronic control unit. From the

information received, the control unit must first

compute the following variables:

Wheel speed

Reference speed

Deceleration

Slip

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Reference speed

▶

The reference speed is the mean, I.e. average speed of all wheel speeds determined by simple

approximation.

Simplified ABS control

▶

If, during braking, one wheel speed deviates from the reference speed, the ABS control unit attempts to

correct that wheel speed by modulating the brake pressure until it again matches the reference speed.

When all four wheels tend to lock, all four wheels speeds suddenly deviate from the previously

determined reference speed. In that case, the control cycle is initiated again in order to again correct the

wheel speed by modulating the brake pressure.

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4) ABS Control Pattern

The ABS control is performed by comparing the reference speed with each wheel speed. Firstly, it is

determined whether the vehicle is in the deceleration or acceleration state using the wheel speed

change ratio. Then, a signal is transmitted to the valve.

Finally, the brake pressure is adjusted via the signal.

△V: Vehicle speed

Vref: Vehicle speed reference

Vw: Wheel speed

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5) EBD (Electronic Brake Force Distribution) System

System description

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As an add-on logic to the ABS base algorithm, EBD works in a range in which the intervention

thresholds for ABS control are not reached yet.

EBD ensures that the rear wheels are sensitively monitored for slip with respect to the front axle. If slip is

detected, the inlet valves for the rear wheels are switched to pressure hold to prevent a further increase

in pressure at the rear-wheel breaks, thus electronically reproducing

a pressure-reduction function at the rear-wheel brakes.

ABS features an enhanced algorithm which includes control of the brake force distribution between the

front and rear axles. This is called Electronic Brake Distribution. In an unloading car condition the brake

efficiency is comparable to the conventional system but for a fully loaded vehicle the efficiency of the

EBD system is higher due to the better use of rear axle braking capability.

Advantages

▶

Elimination of conventional proportioning valve

EBD utilizes the existing rear axle wheel speed

sensor to monitor rear wheel slip.

Based on many variables in algorithm a

pressure hold, increase and/or decrease

pulsetrain may be triggered at the rear wheels

insuring vehicle stability.

Vehicle approaches the ideal brake force

distribution (front to rear).

Constant brake force distribution during vehicle

lifetime.

EBD function is monitored via ABS safety logic

(conventional proportioning valves are not

monitorable).

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Ideal distribution

EBD start point

Cut-in point

Fixed distribution

1.

2.

3.

4.

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6. HYDRAULIC CIRCUIT OF ABS

1) Normal Brake Operation (ABS is not working) Mode

If the driver depress the brake pedal so that the ABS does not operate, the hydraulic pressure in the

master cylinder increases through the vacuum booster and it is delivered to the wheel via the normal

open inlet valve. At this moment, the normally-closed outlet valve is closed The speed of the wheel that

hydraulic pressure is delivered reduces gradually.

Solenoid valve

Valve Open/Close

Pump motor

Inlet valve - Normal open (NO) valve

Open

OFF

Outlet valve - Normal close (NC) valve

Close