SsangYong Korando III (2010 year). Manual - part 237

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KAMM circle

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Before we go into the Kamm circle, you should 

know that a tire offers a maximum of 100 % 

transmissibility. It is all the same for the tire 

whether we require 100 % in the direction of 

braking or in the direction of the acting lateral 

force, e.g. when driving round curves. If we drive 

into a curve too fast and the tire requires 100 % 

transmissibility as cornering force, the tire cannot 

transmit any additional brake force. In spite of the 

ABS the car is carried out of the curve. The 

relationship between brake force B and cornering 

force S is shown very clearly in the Kamm circle. If 

we put a vehicle wheel in this circle, the 

relationship becomes even clearer. In this 

relationship: as long as the acting forces and the 

resulting force remain within the circle, the vehicle 

is stable to drive. If a force exceeds the circle, the 

vehicle leaves the road.

Brake force

When depressing the brake pedal the brake force 

increases to the maximum, then the brake force 

decreases until the wheel locks.

Cornering force

The cornering force is a maximum when the 

wheel is turning freely with zero slip. When 

braking the cornering force falls to zero if the 

wheel locks (slip 100 %).

ABS operating range

The operating range starts just before the 

maximum brake force and ends in maximum, for 

the unstable range then begins, in which no 

further modulation is possible. The ABS controls 

the regulation of the brake pressure so that the 

brake force only becomes great enough for a 

sufficient proportion of cornering force to remain. 

With ABS we remain in the Kamm circle as long 

as the car is driving sensibly. We will leave driving 

physics with these statements and turn to the 

braking systems with and without ABS.

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Brake and cornering force

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3) Basic ABS Control

Operation of ABS control unit

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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

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

approximation.

Simplified ABS control

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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.

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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

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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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