DAF CF65, CF75, CF85 Series . Manual — part 969

©

200423

1-1

General

STEERING PUMP

ΧΦ65/75/85 series

7

4

1. GENERAL

1.1 OVERVIEW DRAWING, STEERING PUMP LUK VT72A, VT77 AND LF77

11

12 13 14 15 16

17

14

1

3

5

6

8

7

6 7

4

2

9 10

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1.

Prop shaft

2.

Housing

3.

Ball bearing

4.

Double oil seal

5.

O-ring

6.

Stator

7.

Partitions

8.

O-ring

9.

Cover

10.

Flow control valve

11.

Circlip

12.

Bearing bush

13.

Thrust plate

14.

Rotor

15.

Thrust plate

16.

Sealing ring

17.

Spring

STEERING PUMP

1-2

©

200423

General

4

ΧΦ65/75/85 series

7

1.2 OVERVIEW DRAWING, EMERGENCY STEERING PUMP

1

2

3 4 5

6 7

8 9 12 14 15

17

19

18

16

13

11

10

9

8

7

6

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1.

Gear wheel

11.

Bearing bush

2.

Double oil seal

12.

Bore

3.

Housing

13.

Plunger/delivery valve channel

4.

Bearing bush

14.

Bearing bush

5.

Shaft

15.

Supply line

6.

Plug

16.

Delivery valve

7.

Plunger

17.

Suction valve

8.

Spring guide

18.

Cushioning chamber

9.

Spring

19.

Delivery line

10.

Eccentric

©

200423

1-3

General

STEERING PUMP

ΧΦ65/75/85 series

7

4

1.3 OPERATION OF THE STEERING PUMP

The below description refers to the LUK VT72A,

VT77 and LF77 pumps. Although the ZF 7685

pump differs from the LUK pumps, operation of

the ZF 7685 is identical to that of the LUK pumps.

The pump can be divided into a pump and a

control part.

The pump part consists of the shaft (1), the

rotor (14), the partitions (7) fitted, the stator (6)

and the thrust plates (13) and (15).

The control part is located in the pump cover and

consists of a calibrated opening in the internal

delivery pipe and the flow control valve (10) with

spring (17).

The shaft (1) is borne by the ball bearing (3) and

the bearing bush (12).

The ball bearing (3) is lubricated with engine oil.

The bearing bush (12) is lubricated with steering

oil.

The shaft is sealed using a double-sealing oil

seal (4).

The stator (6) is locked between the thrust

plates (13) and (15).

The O-ring (8) and the seal (16) press the thrust

plate (15) against the stator (6) and the rotor (14),

thus sealing off these components.

11

12 13 14 15 16

17

14

1

3

5

6

8

7

6 7

4

2

9 10

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STEERING PUMP

1-4

©

200423

General

4

ΧΦ65/75/85 series

7

If the pump starts building up pressure, the oil

pressure also reaches the back of the thrust

plate (15). As a result the thrust plate is pressed

even tighter against the stator and the rotor and

even better sealing is achieved.

The centrifugal force moves the partitions (7)

partially out of the rotor (14) to the outside,

pressing them against the stator's (6) running

surface.

Two subsequent partitions each form a separate

space, sealed off at the sides by the thrust

plates (13) and (15). These spaces form the

pumping chambers.

The elliptical shape of the stator's (6) interior

results twice per revolution in a volume increase

in each pumping chamber, the suction stroke

(angular displacement A) and twice per revolution

in a volume decrease, the delivery stroke

(angular displacement B).

The two spaces in which the volume is increased

are connected to the supply pipe (a). The two

spaces in which the volume is decreased are

connected to the delivery pipe (b).

To achieve adequate sealing between the

partitions and the stator, the undersides of the

partitions are connected to the pump's internal

delivery pipe. This construction presses the

partitions against the stator, resulting in optimal

sealing.

When starting up the pump this sealing is not yet

optimal, and the pump is non-regenerative. That

is why the steering oil reservoir must always be

positioned higher than the steering pump.

When the pump is pressurised, it does become

regenerative, thus causing a negative pressure in

the supply pipe.

A

a

b

A

a

B

b

B

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