BENDIX MC-12 MODULATOR CONTROLLER ASSY Guide de dépannage télécharger pdf (Page 39)

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Driver

Right Steer

Axle

Left Steer

Axle

Right Additional

Axle

Left Additional

Axle

Right Drive

Axle

Left Drive

Axle

only one pressure modulator valve). In the case of a

6S/5M arrangement, the PMV controls both wheels on

the additional axle. The additional axle wheels would

receive equal brake pressure, based on the wheel

that is currently experiencing the most wheel slip.

Normal Braking

During normal braking, air brake pressure is delivered

through the ABS PMV and into the brake chamber. If

the ECU does not detect excessive wheel slip, it will

not activate ABS control, and the vehicle stops with

normal braking.

Retarder Brake System Control

On surfaces with low traction, application of the

retarder can lead to high levels of wheel slip at the

drive axle wheels, which can adversely affect vehicle

stability. To avoid this, some Bendix ECU controllers

are designed to switch off the retarder as soon as a

lock-up is detected at one (or more) of the drive axle

wheels. In these cases, when the ECU is placed in

the ABS off-road mode, it will switch off the retarder

only when ABS is active on a steer axle wheel and a

drive axle wheel.

Optional ABS Off-Road Mode

When used on some off-road surfaces, (for example,

loose gravel), ABS provides superior vehicle steerability

and stability, however there is the potential for stopping

distances to be longer than without ABS. This is

because locked-up wheels on gravel, etc. tend to plow

up the road surface in front of the tires.

Bendix Premium ECUs have an optional ABS off-road

control mode that more effectively accommodates

these soft road conditions and shortens stopping

distances while maintaining optimal vehicle steerability

and stability. Care must be taken, however, not to

use the ABS off-road mode on normal, paved road

surfaces (since vehicle stability and steerability may be

reduced), so the ABS Indicator Lamp ﬂ ashes to show

the driver that the ABS off-road mode is being used.

All-Wheel Drive (AWD) Vehicles

AWD vehicles with an engaged interaxle differential

(steer axle to rear axle)/AWD transfer case may have

negative effects on ABS performance. Optimum

ABS performance is achieved when the lockable

differentials are disengaged, allowing individual wheel

control.

Premium ECUs can be programmed speciﬁ cally for

this conﬁ guration to control the differential lock/unlock

solenoid in the AWD transfer case. When programmed

to do so, the ECU will disengage the locked interaxle/

AWD transfer case during an ABS event and reengage

it once the ABS event has ended.

ATC Operation

ATC Functional Overview

Just as ABS improves vehicle stability during braking,

ABS systems with ATC improve vehicle stability

and traction during vehicle acceleration. The ATC

function uses the same wheel speed information and

modulator control as the ABS function. The ECU

detects excessive drive wheel speed, compares the

speed of the front, non-driven wheels, and reacts to

help bring the wheel spin under control. The ECU

can be conﬁ gured to use engine torque limiting and/or

differential braking to control wheel spin. For optimal

ATC performance, both methods are recommended.

Differential Braking

Differential braking is automatically activated when

drive wheel(s) on one side of the vehicle are spinning,

which typically occur on asphalt road surfaces with

patches of ice. The traction system will then lightly

apply the brake to the drive wheel(s) that are spinning.

The vehicle differential will then drive the wheels on

the other side of the vehicle. Differential braking is

available at vehicle speeds up to 25 MPH.

Truck and Tractor ABS Operation; ATC

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BENDIX MC-12 MODULATOR CONTROLLER ASSY Guide de dépannage Page 39

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