DAF LF45, LF55 Series. Manual - part 476

©

 200436

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General

BRAKING PERFORMANCE AND BRAKE EQUALISATION

ΛΦ45/55 series

6

5

1. GENERAL

1.1 INTRODUCTION

How is a good braking performance of a vehicle 

combination (truck and trailer vehicle) achieved 

while still guaranteeing interchangeability both for 

new vehicle combinations and for combinations 

following brake reconditioning?

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.

BRAKING PERFORMANCE AND BRAKE EQUALISATION

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General

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ΛΦ45/55 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.

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.

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

a =

deceleration (m x a is the force 

changing 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

a

R600024

a

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General

BRAKING PERFORMANCE AND BRAKE EQUALISATION

ΛΦ45/55 series

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5

-

for rigid vehicles:

-

between the different axles.

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 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. It is therefore important that the 

adjustment is correct, as dangerous situations 

can arise where the trailer is jostling the prime 

mover.

Possible causes of poor braking performance 

of a trailer vehicle

-

unduly large brake-chamber stroke.

-

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.

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 brake 

pressures. The latter can be achieved by 

adjusting the advance between tractor and drawn 

vehicle 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 prime mover 

is the same as that of the trailer vehicle.

This can entail a change in the brake pressure 

advance set by the factory.

a

a

R600025

R600026

m1

m3

m4

F1

F :

1

F2

F3

F4

F2 F3

4

m 2

m1

m3 m4

m 2

:

F

:

=

:

:

:

BRAKING PERFORMANCE AND BRAKE EQUALISATION

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General

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1.3 BRAKE EQUALISATION MEASUREMENT BY MEANS OF BRAKE 

DYNAMOMETER

1.

Make sure the vehicle combination is in 

laden condition. A laden combination 

makes for a more reliable and accurate 

measurement. Furthermore, the maximum 

braking performance will be achieved when 

the vehicle combination is in laden condition.

2.

The braking forces must be measured on a 

system with warm brakes. (Normal operating 

temperature.)

3.

The brake linings must have been bedded in. 

Only then can a reliable verdict on the 

braking forces be obtained.

4.

Write down the braking forces of the various 

axles on the "brake equalisation form for 

brake dynamometer" at the following brake 

pressures, measured at the service coupling 

head:

p = 0.5 - 1.0 - 1.5 - 2.0 - 3.0 - 4.0 - 5.0 bar.

5.

Using the data on the "brake equalisation 

form for brake dynamometer", calculate the 

braking deceleration percentages.

6.

Plot the calculated values in the "brake 

equalisation form for brake dynamometer" in 

the appropriate EC band graph and evaluate 

the measured brake equalisation.

p

R600028