DAF CF65, CF75, CF85 Series . Manual — part 931

©

200423

1-1

General

BRAKING PERFORMANCE AND BRAKE EQUALISATION

ΧΦ65/75/85 series

6

6

1. GENERAL

1.1 INTRODUCTION

How is a good braking performance of a vehicle
combination (truck and trailer vehicle) achieved,
both for new vehicle combinations and following
brake reconditioning, while still guaranteeing
interchangeability?
The vehicles should meet the legal requirements
and all settings should be in accordance with the
directives. However, adhering to the directives
does not necessarily mean that there will be no
brake problems.

Note:
Trucks and trailer vehicles may be fitted with an
EBS brake system or a non-EBS brake system
(conventional brake system).

The adjustability of an EBS brake system is
limited, since brake equalisation is managed
as a control function by the EBS control system.

BRAKING PERFORMANCE AND BRAKE EQUALISATION

1-2

©

200423

General

6

ΧΦ65/75/85 series

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1.2 WHAT IS A VEHICLE COMBINATION WITH A GOOD BRAKING

PERFORMANCE?

A vehicle combination of which, in laden condition
and with a 1 to 3 bar pressure at the service
coupling head, the braking deceleration of the
tractive unit is the same or virtually the same
as that of the drawn vehicle.

Fn

Gd

F

Fn

Gd

F

Z

m.a

Fn

Gd

F

Fn

Gd

F

Fn

Gd

F

Z

G

G

m.a

R600023

G

weight

m

= mass

α

= deceleration (m x a is the force

chang ing the axle load)

Dynamic axle load: during braking, changes
the load on each axle.

F

= braking force (Fmax = Gd x m)

Gd

= dynamic axle load

m

= the friction coefficient between tyre and

road

Fn

= braking force of the wheel brake

©

200423

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General

BRAKING PERFORMANCE AND BRAKE EQUALISATION

ΧΦ65/75/85 series

6

6

When problems occur which are related to the
brake system, such as excessive brake-lining
wear, brake vibrations or the vehicle pulling
to one side during braking, the cause should
primarily be sought in an unbalanced distribution
of braking forces.

-

for vehicle combinations:

-

between prime mover and trailer vehicle.

-

for rigid vehicles:

-

between the different axles.

-

if the vehicle has disc brakes and drum brakes

Conditions for a practical distribution of
braking forces
-

Both the prime mover and the trailer vehicle
should have a sufficiently effective brake
system without mechanical defects
or failures in the air system.

With vehicle combinations the braking
performance level of the trailer vehicle without
EBS may be noticeably lower than that of the
truck. This means that the prime mover has
to provide a disproportionately large part of the
deceleration required for the total vehicle
combination. As the brakes of the trailer vehicle
will consequently be subjected to low loads only,
their condition will deteriorate (risk of glazing),
which will lead to even higher overloading of the
prime mover brakes. Therefore, it is important
that the adjustment is correct, as dangerous
situations can arise where the trailer is jostling the
prime mover.

a

R600024

a

a

a

R600025

BRAKING PERFORMANCE AND BRAKE EQUALISATION

1-4

©

200423

General

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ΧΦ65/75/85 series

6

Possible causes of poor braking performance
of a trailer vehicle
-

Unduly large brake-chamber stroke.

-

Incorrect position of the brake levers
(drum brakes).

-

Damaged diaphragms in the brake chambers.

-

Greasy, glazed or fully worn linings.

-

The mechanical part of the wheel brake does
not operate smoothly.

-

A leak in the brake system.

-

A blockage in the brake pipe system.

-

Not all the valves are in good working order.

-

Incorrect setting of the load sensing valve
(conventional brake system).

The starting point is that the braking forces
between the axles of the vehicle combination
should be distributed in proportion to the axle
loads. This will also distribute the temperature
correctly over the axles.
Whether this will give the correct distribution
between prime mover and trailer vehicle depends
not only on the quality of the two brake systems,
but also on a correct balancing of the braking
pressures. With non-EBS tractors and trucks,
the latter can be achieved by adjusting the brake
pressure advance between tractor and trailer in
such a way that at the most frequently used brake
pressures, i.e. 2 - 3 bar on the service line,
the braking performance of the tractive unit is the
same as that of the trailer vehicle.
This can entail a change in the brake pressure
advance set by the factory.

R600026

m1

m3

m4

F1

F :

1

F2

F3

F4

F2 F3

4

m 2

m1

m3 m4

m 2

:

F

:

=

:

:

: