PREVOST LE MIRAGE XLII BUS SHELLS Maintenance Manual Download

Page: 473 / 1260

REVISED 5/31/05

ABS OPERATION

Bendix

ABS uses wheel speed sensors, ABS pressure

modulator valves, and an ECU to control either four or

six wheels of a vehicle. The EC-60

™

controller monitors

individual wheel turning motion during braking and adjusts

or modulates the brake pressure at the wheel end. When

excessive wheel slip, or wheel lock-up is detected, the

EC-60

™

controller will activate the pressure modulator

valves to automatically reduce the brake pressure at one

or more of the wheel ends. By these actions, the ABS

system helps to maintain the vehicle's lateral stability and

steerability during heavy brake applications and during

braking on slippery surfaces.

Steer Axle Control

Although both wheels of the steer axle have their own

wheel speed sensor and pressure modulator valve, the

EC-60

™

controller blends the applied braking force between

the two steering axle brakes. This Bendix patented brake

application control, called Modiﬁed Individual Regulation

(MIR), is designed to help reduce steering wheel pull

during an ABS event on road surfaces with poor traction

(or areas of poor traction, e.g. asphalt road surfaces with

patches of ice).

Single Drive Axle Control (4x2 Vehicle)

For vehicles with a single rear drive axle (4x2), the brakes

are operated independently by the EC-60

™

controller,

based on the individual wheel behavior.

Dual Drive Axle Control (4S/4M Conﬁguration)

For vehicles with dual drive axles (6x4) using a 4S/4M

conﬁguration, one ABS modulator controls both right-side

rear wheels and the other modulator controls both left-

side rear wheels. Both wheels on each side receive equal

brake pressure during an ABS stop. The rear wheel speed

sensors must be installed on the axle with the lightest

load.

Dual Rear Axle Control (6S/6M Conﬁguration)

For vehicles with dual rear axles (6x4, 6x2) using a 6S/6M

conﬁguration, the rear wheels are controlled independently.

Therefore, brake application pressure at each wheel is

adjusted according to the individual wheel behavior on

the road surface.

6x2 Vehicles with 6S/5M Conﬁguration

6x2 vehicles can utilize a 6S/5M conﬁguration, with the

additional axle (a non-driven rear axle) having two sensors,

but only one Pressure Modulator Valve. In this case, 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, 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 normal vehicle service braking is applied.

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 prevent this, the EC-60

™

controller switches off the

retarder as soon as a lock-up is detected at one (or more)

of the drive axle wheels.
When the ECU is placed in the ABS off-road mode (on

vehicles equipped with this optional feature), 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

On some road conditions, particularly when the driving

surface is soft, the stopping distance with conventional ABS

may be longer than without ABS. This can occur when a

locked wheel on soft ground or loose gravel plows up the road

surface in front of the tire, changing the rolling friction value.

Although vehicle stopping distance with a locked wheel (in

the absence of ABS) may be shorter than corresponding

stopping distance with conventional ABS control, vehicle

steerability and stability would be reduced.
Advanced EC-60

™

controllers have an optional dash switch

initiated modiﬁed ABS control mode (know as "offroad

ABS) that more effectively accommodates these soft road

conditions to shorten stopping distance while maintaining

optimal vehicle steerability and stability.

The EC-60

™

controller will perform a PMV chuff test on all

installed modulators in the following order:
•   Steer Axle Right PMV
•   Steer Axle Left PMV
•   Drive Axle Right PMV
•   Drive Axle Left PMV
•   Additional Axle Right PMV
•   Additional Axle Left PMV
•   Drive Axle TCV
The pattern will then repeat itself.

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