Design and Function of ZF Vane Pumps

Design and Function
of ZF Vane Pumps
8
7
4
10
Design
The construction principle of the
ZF vane pumps is based on a
pumping element which is
usually in a light-alloy housing
(1) and consists basically of a
shaft (2), the rotor (3), ten
vanes (4), a cam ring (5) and
the pressure plate (6).
Depending on the model
range, a second pressure
plate or control plate is
used. The axial end is
formed by a cover (9) which
is also made of light alloy.
1
2
6
5
3
Functional scheme of
ZF vane pump FP 4.
4
Design and Function
The shaft is guided in the
housing by a ball bearing
or plain bearing system
– depending on the type of
drive – and connected free of
play with the rotor (3) seated
on it. The vanes (4) are located
in the ten radially arranged slots
of the rotor. The cam ring (5),
which is fixed in the housing or
cover against rotation, surrounds
the rotor together with the
lateral pressure/control plate or
cover, respectively. The two
crescent-shaped pump chambers
are situated between the
cylindrical
circumferential
surface of the rotor and the
ellipsoidal bore in the cam ring.
The volume of the chambers
results from the largest possible
9
1
2
3
4
5
Housing
Shaft
Rotor
Vane
Cam ring
6
7
8
9
10
Pressure plate
Suction chamber
Pressure chamber
Cover
Pressure relief and flow limiting valve
The performance ranges of the
vane pump model ranges as well
as the different equipment
variants in respect of mounting,
type of drive, energy saving and
attachment of an oil reservoir
can be seen from the Technical
Summary on page 19/20.
Function
Rotation of the input shaft (2)
and, with it, the rotor (3) results
in the vanes (4) located in the
rotor being forced radially by
centrifugal force on to the track
of the fixed cam ring (5). This
movement is assisted by the
pressurized oil which flows from
the pressure chamber (8) via
connections to the internal faces
of the vanes. Between the ten
vanes, ten self-contained pump
Figure at top:
ZF Vane pump FN 4.
Figure at bottom:
Basic diagram of control characteristics
with constant and falling flow rate as
well as flow rate falling in steps.
at a determined speed, e.g.
1000 rpm, and that from this
point the flow rate continuously
falls while the speed continues to
rise. The reduced flow rate
remains, however, sufficient to
allow for the maximum hydraulic
assistance to be built up at any
time. This characteristic is
influenced by a control system in
the pressure region specifically
developed by ZFLS, which results
in a reduction of hydraulic
assistance in the steering gear at
higher speeds and, thus, in a
distinct improvement of the
contact between the steering
wheel and the road surface.
Flow rate control
For special applications, it is
alternatively possible to provide
the pumps with a control characteristic falling in steps (variant C).
In this design, the flow rate is
reduced in a pronounced transition area already in the medium
speed range. This shorter phase
of transition from maximum to
minimum flow rate can be
adjusted individually by a special
valve system.
For individual matching with the
steering system, the control
characteristic of the ZF vane
pumps can optionally be set at a
flow rate which is constant,
falling or falling in steps. In the
pump design offering a constant
flow rate (see figure below;
variant A) an almost constant oil
flow is fed to the power steering
gear throughout the speed range
of the vehicle engine.
The ZF vane pump with falling
control characteristic (variant B)
is designed such that the
required flow rate is achieved
[dm3/min]
Due to the design, the oil flow
generated in the crescent-shaped
pressure chambers is directed to
the valves for pressure relief and
flow limitation (10) positioned
longitudinally or transverse to
the shaft, limited to the values
set and passed on to the
hydraulic power steering via a
hose connected to it.
cells are formed which draw oil
into the two crescent-shaped
pump chambers when the
volume is increasing and expel it
into the pressure chamber when
the volume is decreasing. Since
the shape of the cam ring means
that two suction zones and two
pressure zones always lie opposite each other, each of the ten
pump cells delivers twice its own
volume with every rotation of
the input shaft. In addition,
owing to this double-action
arrangement of the suction and
pressure zones, the hydraulic
radial forces acting upon the
rotor cancel each other out.
Flow rate
crescent segment between two
vanes and the width of the rotor
or vanes, respectively.
A
B
C
Pump speed
[rpm]
Design and Function
5
ZF Vane Pump CP 14
Design
On this pump type, the pressure
relief and flow limiting valve is
installed transverse to the input
shaft. The mounting is standardized and meets the specifications of the Association of the
German Motor Industry (VDA).
This allows easy exchange of
competitors' products.
As a rule, the ZF vane pump CP 14
on passenger cars is driven from
the vehicle engine via a pulley.
Flow rate control
For individual matching with the
steering system, the control
characteristic of this vane pump
can optionally be set at a flow
rate which is constant, falling or
falling in steps (see description
on page 5).
Energy saving
Remarkable
energy
saving
improvements can be achieved in
this model range by using the
ECO (Electronically Controlled
Orifice) valve described on pages
11/12.
ZF Vane pump CP 14 with pressed-in
suction connector.
6
ZF Vane Pump CP 14
ZF Vane Pump CP 1
Design
The CP 1 model range with its
modular design system allows
mounting in many ways, thus
ensuring optimum adaptation of
the pump to the vehicle conditions. In addition to the specific
CP 1 mounting longitudinally to
the input shaft, it is also possible
to make use of transverse bolt
connection directly to the
combustion engine. Also, it is
possible to redesign the pump
cover to allow individual variants
of mounting, e.g. as a multifunctional bracket, besides the
standard design.
Again, this pump is usually driven
by belt from the vehicle engine.
Flow rate control
For individual matching with the
steering system, the control
characteristic of the vane pump
CP 1 can optionally be set at a
flow rate which is constant,
falling or falling in steps (see
description on page 5).
Figure at bottom:
ZF Vane pump CP 1 with a multi-functional
bracket connected with the cover.
Figure at top:
ZF Vane pump CP 1 with pressed-in
suction connector.
ZF Vane Pump CP 1
7
ZF Vane Pump FP 2
Design
The pump type FP 2 was designed specifically for the pressure oil supply of hydraulic
power steering gears on small
passenger cars of the Asian market. Both the compact design –
with the pressure port moved
towards to the center – and the
reduction of hydraulic capacity
and belt pull are adapted to
match on a high degree the
requirements of these subcompact cars. An optionally fitted
pressure switch, tuned to the
electronics of the engine
management, prevents stopping
the vehicle engine at low speed.
The ZF vane pump FP 2 is provided with the standardized
mounting according to the specifications of the Association of the
German Motor Industry (VDA).
Depending on the application,
other possibilities of attachment
are feasible. The pump is belt
driven from the vehicle engine.
Flow rate control
For individual matching with the
steering system, the control
characteristic of this vane pump
can optionally be set at a flow
rate which is constant, falling or
falling in steps (see description
on page 5).
ZF Vane pump FP 2 with pressed-in
suction connector.
8
ZF Vane Pump FP 2
ZF Vane Pump FP 4
Design
As a result of the standardized
mounting which meets the
specifications of the Association of
the German Motor Industry
(VDA), this proven pump type, of
which millions have been made,
ensures easy exchange of
competitors’ products. Also, it
allows to mount the oil reservoir
directly on top of the pump. This
saves a hose line and assembly
costs. Drive is preferably by belt
driven from the vehicle engine.
Flow rate control
For individual matching with the
steering system, the control
characteristic of the vane pump
FP 4 can optionally be set at a
flow rate which is constant,
falling or falling in steps (see
description on page 5).
Energy saving
Remarkable improvements for
energy saving can be achieved in
this model range too by adapting
the ECO (Electronically Controlled Orifice) valve described
on pages 11/12.
ZF Vane pump FP 4 with pressed-in
suction connector.
ZF Vane Pump FP 4
9
ZF Vane Pump FP 6
Design
The development of the FP 6
model range achieves in particular the new target, set by the
automotive industry, of steering
pumps of higher hydraulic
capacity, for its performance
potential comprises a controlled
flow rate up to 15 dm3/min. and
a maximum pressure of 150 bar.
The function of the pumping
element and the external
dimensions of this pump are for
the most part identical to the
vane pump FP 4. Again, the
mounting is standardized and
meets the specifications of the
Association of the German Motor
Industry (VDA). This allows
easy exchange of competitors'
products. If required, a plastic oil
reservoir can be mounted in
order to save a hose line and thus
assembly costs.
Flow rate control
For individual matching with the
steering system, the control
characteristic of the vane pump
FP 6 can optionally be set at a
flow rate which is constant,
falling or falling in steps (see
description on page 5).
Energy saving
Remarkable improvements for
energy saving can be achieved in
this model range, too by using
the ECO (Electronically Controlled Orifice) valve described
on pages 11/12.
ZF Vane pump FP 6 with oil reservoir
mounted on top.
10
ZF Vane Pump FP 6
Energy Saving by
ZF Vane Pumps
6
5
Advantages:
4
8
1
12
3
2
11
10
7
• Fuel reduction by
20 to 40 % on average
• 15 to 20 °C decrease
in temperature
• approx. 35 % less power input
• reduction of neutral pressure
drop by about 4 to 6 bar
(Values depend on duty cycles
and system design)
9
800
500
400
ECE cycle
600
Driving cycle
Another important step towards
energy saving is the adaption of
an ECO valve (4) (ECO =
Electronically Controlled Orifice)
on the vane pump (1). Due to
control dependent on steering
wheel turning rate and vehicle
speed, this hydraulic control unit
generates a flow rate as needed
for the hydraulic steering system,
thus extending significantly the
functionality of the base pump.
The oil flow not needed by the
pump system is controlled chiefly
during straight ahead driving.
700
The necessary electronic control
can be integrated into the
existing vehicle electronics.
Power input [W]
Energy saving by ECO
300
200
Figure at bottom:
Pump comparison for average power
input in the driving and ECE cycles
(test method for measuring pollutant
emissions).
100
Standard vane pump
Vane pump with ECO
Figure at top:
Schematic representation of a hydraulic
steering system with a ZF vane pump
with ECO valve.
1
2
3
4
5
6
ZF vane pump
Steering gear (basic unit)
Steering valve
ECO valve
Oil cooler (if required)
Oil reservoir
7
8
9
10
11
12
Electronic control unit
Anti-vibration hose
CAN
Battery
Speed sensor
Steering wheel turning rate sensor
Energy Saving
11
6
7
8
9
3
1
5
4
2
Schematic representation of a ZF steering
pump with ECO together with a ZF Active
Steering on the basis of a ZF Servotronic 2.
Servotronic® is a registered trademark of
ZF Lenksysteme GmbH.
12
Energy Saving
1
2
3
4
5
ZF Vane pump FP 6 with ECO
ZF Servotronic 2 (basic unit)
Servotronic 2 rotary valve
Electric motor
Superposition gear system
6
7
8
9
Oil reservoir with fine filter
Electronic control unit
Hoses, anti-vibration hose
Cables to power supply, CAN,
ignition, vehicle sensors