Electric Drives
and Controls

Hydraulics

Linear Motion andAssembly Technologies

Pneumatics

Hydraulics in Mobile Equipment

Hydraulics in Mobile Equipment

Bosch Rexroth AG
Drive & Control Academy
Bahnhofplatz 297070 Würzburg, Germany
Telephone: +49 9352 181920
E-mail: media@boschrexroth.dewww.boschrexroth.com/trainingmedia

R961000791
ISBN 978-3-9816398-0-3

Service		3

Table of contents
1
1.1
1.2
1.3
1.4
1.5
1.6
1.7

Introduction
Definition
Market situation
Applications
Systems
Special features
Development trends
Structure of a hydraulic system

9
9
9
10
12
13
13
14

2
2.1
2.1.1
2.1.2
2.2
2.2.1
2.2.2
2.2.3
2.2.4
2.2.5
2.2.6
2.3
2.3.1
2.3.2
2.3.3
2.4

Pumps and hydraulic motors in general
Function
Pumps
Hydromotoren
Performance ratings
Displacement V
Operating pressure
Vacuum in the suction line
Cavitation
Pressure in pump/motor housing
Efficiency
Calculation formulae for pumps and hydraulic motors
Volumetric flow qv, number of revolutions n, displacement volume V
Pressure p, torque M, displacement volume VPower P, pressure p, volumetric flow qv
Pump construction types

15
15
15
15
15
15
16
16
16
16
17
19
19
19
20
21

3
3.1
3.2
3.3
3.4
3.5

23
23
24
24
25

3.6
3.7
3.8
3.9
3.10
3.11
3.11.1
3.11.2
3.11.33.11.43.12
3.12.1
3.12.2
3.13
3.14
3.14.1
3.14.2
3.14.3

Gear pumps and motors
Construction
Operating principles (Pump)
Axial gap sealing
Radial sealing
Tooth face sealing
Discharge of trapped oil
Outrigger bearings
Sizes
Multiple gear pumps
Flanges and shaftsGear pumps with incorporated valves
Specifications and operating limits
Pressure
Rotational speed
Temperature
Noise
Pumps with optimized noise reduction
DUO gear pumps
Silence pumpNotes on commissioning
Gear motors
Motors for one direction of rotation
Reversible motors
Size chart

25
26
26
26
27
27
28
28
28
28
28
29
29
30
30
31
31
31
32

4
4.1
4.2
4.2.1
4.2.2
4.2.3
4.2.4
4.3

Electro-hydraulic pumps
Function
Eigenschaften
Type of motor winding
Motor characteristics
Duty types
Performance curves
Commissioning instructions

33
33
33
33
34
34
35
36

4

5
5.1
5.2
5.3
5.4
5.4.1
5.4.2
5.4.3
5.5
5.6

Compact power units
Function
Construction
Sizes
FeaturesDuty types
Characteristic curves - DC motor
Characteristic curves - 3-phase AC motors and AC motors
Valve block
Compact power units EP9 with proportional technology

37
37
37
39
39
39
40
41
41
42

6
6.1
6.1.1
6.1.2
6.1.3
6.2
6.3
6.3.1
6.3.2

Check valves
Check valves
Types of construction and graphic symbols
Construction
Application of check valves
Shuttle valve
Pilot-operated check valves
Function and graphic symbol
Double check valve, pilot-operated (shutoff block)

43
43
43
43
44
44
45
45
46

7
7.1
7.1.1
7.1.2
7.1.3
7.1.4
7.1.5
7.2

Pressure-control valves
Pressure-relief valves
Function
Graphic symbols
Types of construction
Features
Variants
Check valves and pressure relief valves

47
47
47
48
48
49
50
51

8
8.1
8.1.1
8.1.2
8.1.3
8.2
8.3
8.3.1
8.4
8.4.1
8.4.2
8.5
8.5.1
8.6
8.6.1
8.7

Flow control valves
General information
Flow formula
Calculation diagram for orifices
Flow diversion
Orifices and throttle valves
Throttle check valves
Throttle check valves for incorporation
The 2-way flow control valve
Principle of operation
Graphical symbols
The 3-way-flow control valve
Constructive design
Pilot-operated flow-control valves
Constructive design
Flow dividing valve, double-acting

53
53
53
54
54
55
55
56
56
57
58
58
59
60
60
61

9
9.1
9.2
9.2.1
9.2.2
9.2.3
9.2.4
9.3
9.3.1
9.3.2
9.4
9.5
9.6
9.7
9.8
9.9
9.9.1

Directional Control Valves – General Information
PurposeDesignation and graphical symbols (DIN/ISO 1219)
Variants of flow designs
Actuation
Designation of valve positions
Basic position/Start position
Construction types
Seated valves
Spool valves
Inner sealing in spool valves
Spool types and their symbols
Flow resistanceDisturbing forces acting at the valve spool
Operating limits
Switching transitions
High-precision control

63
63
63
64
64
65
65
66
66
66
66
67
68
68
69
69
69

		5

9.9.2
9.9.3
9.9.4
9.9.5

Overlapping during operation
Control diagram
Opening behavior
Switching time

70
70
71
71

10
10.1
10.2
10.2.110.2.210.2.310.2.410.2.510.2.610.2.710.2.810.2.910.3
10.3.1
10.3.210.3.310.3.410.3.510.3.610.4
10.4.1
10.4.210.4.310.4.410.4.510.4.610.4.710.4.810.5
10.5.1
10.5.210.5.310.5.410.5.510.5.610.6
10.6.1
10.6.2
10.7

Basic circuits in mobile hydraulics
Introduction
Constant flow system (open center system)
Basic circuit
Extended circuit
ressure loss in neutral circulation P  RPower losses in the high-precision control range (transitional position)
Limit range behavior
Overlapping
Control characteristics
Actuation force at the valve spool
Advantages and dis-advantages of the system
Constant pressure system (closed center system
Basic circuit
Extended circuit
Pressure loss in the neutral position
Power breakdown
Limit range behavior
Advantages and dis-advantages of the system
Load-compensated system with constant displace-ment pump (open center load sensing system)
Basic circuit
Extended circuit
Pressure loss in the neutral circulation P  RPower breakdown
Limit range behavior
Control characteristics
Actuation force at the valve spool
Advantages and dis-advantages of the system
Load-compensated system with variable displacement pump (closed center load sensing system)
Basic circuit
Extended circuit
Pressure loss in neutral circulation P  RPower breakdown
Limit range behavior
Advantages and dis-advantages of the system
Individual pressure compensators
Primary pressure compensator
Secondary pressure compensators
Electro-hydraulic load sensing system

73
73
73
73
74
75
76
76
77
78
78
78
79
79
80
81
81
81
81
82
82
83
84
84
85
85
86
86
86
86
87
88
88
88
88
89
89
90
91

11
11.1
11.2
11.3
11.3.1
11.3.2
11.4
11.4.1
11.4.211.4.311.4.411.4.511.4.6
11.5
11.5.1
11.5.2
11.6
11.6.1
11.6.2

Directional control valve blocks in mobile hydraulics
Construction of a direc-tional control valve block
Overview
SB 1 – OC series
Modular system
Construction of a directional control valve
SB 23 OC series
Modular system
Subplate
Directional control valve
Extra equipment in the ports of the consuming devices
Additional functions in the inlet port
Additional functions in the operation axis
SBE series
Modular system
Construction of a directional control valve
SB 12 LS series
Modular system
Subplate, basic version ∆p = 3 bar [A1]

93
93
94
95
96
97
99
99
101
101
102
102
103
104
105
106
107
107
109

6

11.6.311.6.411.6.511.6.611.6.711.6.811.6.911.7
11.7.1
11.7.211.8
11.8.1
11.8.211.8.311.8.4

Subplate with ∆p 2.5 bar / 7 bar [A2] switchover capability
Directional control valve
Additional equipment in the ports of the consuming devices
Additional equipment in the inlet
Additional equipment in the actuation axis of the switching elements
Remote controls
Electro-hydraulic control [EHS]
SB 23 LS Series
Modular system
Directional control valve
Interconnection of directional control valve blocks
Relay link for OC blocks
Relay link LS block to OC block
Relay link with two LS blocks
Parallel connection of two LS blocks

110
111
112
114
116
117
119
126
126
128
129
129
129
130
130

12
12.1
12.1.1
12.2
12.2.112.2.212.2.312.2.412.2.512.2.612.3
12.3.112.3.212.3.312.4
12.4.112.4.2

Applications
Jacks
Jacks with electro-hydraulic pumps
TrucksDrives for platform lifts of trucks
Truck loading craneElevating work platforms
Winter equipment for clearing roads
Truck axle lifter and Robson drive
Vehicle fan drive
Fork-lift trucks
Electric stackers with a simple OC system
Electric stacker with speed-controlled pump drive
Stackers with combustion engines and an OC LS system
Wheel loaders
Working hydraulics
Hydro-pneumatic vibration damping

131
131
131
132
132
133
134
135
136
136
137
137
138
139
140
140
141

13
13.1
13.2
13.3
13.3.113.3.1.1
13.3.1.2
13.3.1.3
13.3.1.4
13.3.213.3.2.1
13.3.2.2
13.3.2.3
13.3.2.4
13.3.2.5
13.3.313.3.3.1
13.3.3.2
13.3.3.3
13.3.3.4
13.3.3.5
13.3.3.6
13.3.3.7
13.3.413.4
13.4.113.4.213.4.313.4.413.4.5

Electro-hydraulic hitch control (EHR) for tractors
General information
Construction
System components
Servo solenoid valves
EHR4 servo solenoid valve
EHR 5 servo solenoid valve
EHR 23 OC servo solenoid valve
EHR 23 LS servo solenoid valve
Digital electronic control unit
Block diagram
EHR-D wiring
EHR-D wiring harness
Safety devices
System diagnosis
Sensors
Draft sensor
Inductive position sensor
Inductive angle sensor
Pressure sensor
Characteristic curves
Radar sensor
Inductive speed sensor
Control panel
Operating modes
Position control
Draft control
Mixed control
Slip control in draft
Pressure control

143
143
143
144
144
145
147
148
149
150
150
151
151
152
152
153
153
154
155
156
157
158
158
159
160
160
160
160
161
162

		7

13.4.613.4.713.4.813.4.913.5
13.5.1
13.5.213.5.3
13.6

Vibration damping
External control
Front control
Weighing function
Circuit examples
Tractor with OC system and EHR
Tractors with OC LS system and EHR
Tractors with CC-LS-system and EHR
CAN bus in a tractor

163
164
165
165
166
166
167
171
173

14
14.1
14.2
14.2.114.2.214.3
14.3.114.3.214.3.314.3.414.3.514.3.6

Hydrostatic fan drives in motor vehicles
Function
LayoutSingle-channel system
Multi-channel system
Components
Gear motor with integrated pilot-operated proportional pressure-relief valve
Proportional pressure-relief valve
Single-channel electronic unit
Multi-channel electronic unit
PTC fluid temperature sensor
PTC temperature sensor for air

175
175
176
176
176
177
177
177
178
179
179
180

15
15.1
15.2
15.2.115.2.215.2.315.2.3.1
15.2.3.2
15.2.415.2.515.2.5.1
15.2.5.2
15.2.5.3
15.2.615.3
15.3.1
15.3.215.3.315.3.415.4
15.4.1
15.4.215.4.3
15.5

CAN bus technology in mobile hydraulics
Applications of CAN bus technology
Functioning of the CAN network
CAN layer model
OSI layer 1: Physical medium
OSI layer 2
OSI layer 2a (MAC): method of access
OSI layer 2b (LLC): bit-oriented message exchange
Error detection and signaling
CAN controller
CAN controllers with buffer memory (BasicCAN)
CAN controllers with object memory (FullCAN)
CAN controller for I/O tasks
OSI layer 7: Applications
CANopen - Overview 	
Message Identifier Assignment System
Objects
Data exchange with PDOs
Device modeling and device profiles
Applications
Agricultural machinery
Forklifts/Stackers
Building machinery
Advantages in the mobile sector

181
181
182
183
183
184
184
185
187
190
190
190
190
191
191
192
192
192
193
194
194
195
195
195

16
16.1
16.2
16.2.116.2.216.2.3

Fluids in mobile hydraulics
Functions of the hydraulic fluid
Classification of hydraulic fluids
Hydraulic fluids on a mineral oil baseHardly inflammable fluids
Environmentally friendly hydraulic fluids

197
197
197
197
198
198

Electro-hydraulic hitch control (EHR)

13.3.3 Sensors
13.3.3.1 Draft sensor

mounting

F

R

pressure

draft

coils

F

The draft sensor takes the form of abearing pin with which the lower guiderods of the implement are connectedto the tractor. It replaces a merely
mechanical bolt which would normally
be found in this place. Shear stresses
occur at the bearing, and these are
evaluated as a magneto-elastic effect.
This effect occurs in ferromagnetic
materials and makes use of the dependence of magnetic permeability on
mechanical shear strain.
Operating principle
The magneto-elastic effect is measured by means of primary and secondary coils in a central bore of thesensor. In non-load condition, a symmetrical magnetic field is formed between the poles by means of the primary coil. If tensile or traction forces are
introduced, the magnetic propertiesof the originally isotropic materialchange. Subsequently, the magnetic
field becomes unsymmetrical. Thus, amagnetic potential difference occurs
between the secondary poles. Thisdifference causes a magnetic flux
through the secondary circuit so thata voltage is induced in the secondary
coils. This voltage is proportional tothe influencing force.
The electronics are integrated in thesensor.

L

integrated
electronics
Fig. 13.12 Operating principle of EHR draft measurement of power

Fig. 13.13 Construction of the draft sensor

1 Primary coil
2 Secondary coil
3 Primary pole area
4 Secondary pole area
5 Steel sleevea symmetrical magnetic fieldb asymmetrical magnetic field

Fig. 13.14 Operating principle of the draft sensor

153

154

Electro-hydraulic hitch control (EHR)

13.3.3.2 Inductive position sensor

coils

The position of the hitch is sensed via
a cam disk by a position sensor whose
output is transformed into an electric
signal. The position sensor operates according to the principle of theinductive voltage divider and basicallyconsists of a coil with center tapping
and a mobile ferrite core which is moved by the cam disk of the hitch. The
inductive voltage divider is supplied byalternating current which is generated
by means of integrated electronics.
The output signal is demodulated(rectified).
Features- Axially mobile scanner with spring
preload- Inductive position sensor element
based on the differential throttle
measuring principle- Integrated electronics with temperature compensation- Output signal proportional to position- Precise balance adjustment for
zero and sensitivity

integrated
electronics

ferrite coreFig. 13.15 Construction of the inductive position sensor

U S2

U S1

~U P

∆U

R
0
L
Oscillator

Synchronous
demodulator

Fig. 13.16 Operating principle of the inductive position sensor

Fig. 13.17 External version of the inductive position sensor

Filter PT2UA

Electro-hydraulic hitch control (EHR)

13.3.3.3 Inductive angle sensor

Statorintegrated
electronics

Rotor
Fig. 13.18 Construction of the inductive angle sensor

The inductive angle sensor serves toregister information on angles. It also
works according to the principle of theinductive voltage divider. The mechanical information on angles is relayed
via the shaft to the rotor made of soft,
magnetic material. The eccentricity of
the rotor causes the induction in thetwo coils to change depending on
the position of the angle. The output
signal is demodulated and is available
as a voltage signal for processing.
Features- Inductive angle sensor element
based on the differential throttle
principle- Shaft can be turned mechanically- Integrated electronics with temperature compensation- Output signal proportional to angle- Precise balance adjustment for
zero and sensitivityαStator

Rotor

UM
≈U

Fig. 13.19 Operating principle of the inductive angle sensor

155

156

Electro-hydraulic hitch control (EHR)

13.3.3.4 Pressure sensor

1

p

2

3

4

U

The pressure sensor operates according to the thin-layer strain gauge sensor principle. Its measuring
element is a stainless-steel membraneon which thin-layer measuring resistors are applied by means of vacuum
evaporation.
This is a robust solution which provides high precision, high long-term
stability and a low dead volume. The
sensor evaluation electronics areintegrated.
1 connecting part2 membrane
3 flexible circuit
4 evaluation circuit
5 connecting plug
6 housing/shell
Features- Pressure sensor element, consisting of a stainless steel membrane(spring material), with thin-layer
strain gauge sensor and full bridge
circuitry- Integrated electronics with temperature compensation- Output signal proportional to pressure- Precise balance adjustment for
zero and sensitivity- 3-pin plug connector
Installation instructions- Position the pressure sensor as
close to the consuming device aspossible- Installation position as vertical as
possible, plug facing downward,
so that the dead volume is bled
automatically- Pressure medium: hydraulic oil- other fluids and gases on request

Fig. 13.20

65Construction of the pressure sensor

UV-U Br +U Br -

UV+p

Fig. 13.21

Operating principle of the pressure sensor

Electro-hydraulic hitch control (EHR)

signal voltage

Volt
7.5

supply voltage 10 Volt

draft
100
pressure100
2.5

measuring range
Fig. 13.22

Characteristic curve for draft sensors

V
7,5

supply voltage 10 Voltsignal voltage

13.3.3.5 Characteristic curves
Due to the unipolar supply voltage in
vehicles, certain specifications must
be set for the value range of the test
signals of the single sensors. The active signal range is thus set between
2.5 … 7.5 V.
The zero point setting takes place
at 2.5 V for position and pressure
sensors, whereas the zero point
setting for draft sensors occurs at 5 V.
Anything below this voltage is considered a draft force, anything above apressure force.

2,50Fig. 13.23

measuring range

100

Characteristic curve for position and pressure sensors

157

158

Electro-hydraulic hitch control (EHR)

13.3.3.6 Radar sensorv

UTwo signals are required for slip sensing, one for the actual speed and one
for the theoretical speed. A radar sensor which operates according to the
Doppler principle is used for measuring the driving speed. It supplies an
output signal which is proportional tothe actual driving speed; this output
signal is standardized to 130 impulses
per meter of driven path.
In addition to slip control, the output
signal can also be used for display
and other control functions.

Fig. 13.24

Radar sensor

Fig. 13.25

Inductive speed sensor

Specifications
Speed range:
0.4 - 70 km/h
Accuracy:		
±1%
Output signal:
36.6 Hz/km/h 				132 pulses/mManufacturer: e. g. Dickey-John (F)13.3.3.7 Inductive speed sensor

Two signals are required for slip sensing, one for the actual and one for thetheoretical speed. An inductive speed
sensor which is integrated in the gearis used for measuring the theoretical
driving speed.
Features
The soft-iron core of the speed sensor,
which is encircled by a winding, islocated opposite a rotating tooth lockwasher. The soft-iron core is connected to a permanent magnet, the magnetic field of which spans the tooth
lock washer. On rotation, tooth goes
into gash and vice versa. In this way,
AC voltage, the frequency of which
is suitable for speed determination, is
induced in the coil.
Application
This inductive speed sensor is suited

to a variety of uses in the recordingof speed. It measures engine speed
or wheel speed fully contactless andwear-free and converts them to electric signals.

Electro-hydraulic hitch control (EHR)

13.3.4 Control panel
Control panels must be adjusted tothe cabin design. Therefore they aredesigned by the tractor manufacturer.
Normally, they contain the following
functions- Lift-control lever- Setpoint potentiometer- Selection-Draft control- Operating mode selector- Lowering velocity- LED slip display- LED error diagnosis
Dependent on the number of functions
and on customer requirements, further
operation and display elements can beprovided, e. g. for slip control, pressure control or vibration damping. The
Lifting and Lowering functions can not
only be controlled on the control panel
but also manually, from the rear of the
tractor, by means of buttons.

2aCircuit diagram[1] Lift-control lever
4 positions:aTransport, Liftingb
Stopc
Control, LoweringdNeutral, Rapid retraction		(spring return)[2] Lock (transport)[3] Lowering speed setting[4] Setpoint setting for hitch positions[5] Limit upper end position[6] Mixture; infinitely variable setting
between draft and position control[7] Lamp: Diagnosis[8] Lamp: Lifting[9] Lamp: Lowering

1

b

c

d

7

9

8

6

3

5

4

Fig. 13.26

EHR control panel

Fig. 13.27

Circuit diagram for a simple EHR control panel

159

160

13.4

Electro-hydraulic hitch control (EHR)

tronic draft sensors (6/14), which areconstructed as bearing pins, sense theoccurring draft and pressure forces inthe trailing linkages. The draft setpoint
which is necessary for achieving theworking depth is set at the control
panel (10/11). The draft setpoint only
becomes effective when draft control
is selected, not when position control is selected. The draft is adjusted
by varying the working depth of theattached implement (e. g. plough).

Operating modes

13.4.1 Position control
Position control is used to transport
attached implements to a specified
position in relation to the tractor. The
distance to the ground is pre-selectedby means of the setpoint setting at
the control panel (10/11). The position sensor (9), which is operated bya cam disk on the hitch, supplies theactual value as the feedback signal
for position control. The electronic
control unit (12) processes the setpoint and the actual value to achieve a
manipulated variable which is supplied
to the servo solenoid valve (2/3). At
the start and at the end of operation,
the lifting control lever brings the hitch
out of the controlled position or into it.
The lowering velocity is adjustable.

13.4.3 Mixed control
In this case, the control deviationsof position and draft are mixed in an
adjustable ratio at the control panel
and then processed as the control variable. Mixed control allows variations
in working depth due to fluctuations insoil resistance, which occur with puredraft control, to be reduced.

13.4.2 Draft control
Draft control is used in ploughs orlisters. In this case, the controlled
variable is the force at the trailinglinkage. If it can be kept constant, itmeans that the tractor power is being
used optimally, for instance whenploughing undulating land and inhomogeneous soil.
In the case of draft control, two elec-

3

2

10

11

12

9

11

working depth

4Fig. 13.28

5

Operating principle of position, draft and slip control

6Electro-hydraulic hitch control (EHR)

13.4.4 Slip control in draft
With optimum utilization of the draft ofa tractor in the field, a relatively large
slip of the drive wheels is physicallyunavoidable. If the slip, however,exceeds values of 25 to 30%, unacceptable disadvantages occur. For atargeted slip control, the actual driving
speed is ascertained by means of aradar sensor (4) and compared to the
speed sensor. (5). Increasing slip
has the same effect on the controller
as increasing draft, i. e. the hitch israised with increasing slip, and thus
decreases the draft of the devices byreducing the working depth. The slip
control is actuated by the operating
mode switch at the control panel(10/11).

Draft

soil
y
r
d

wet soildraft control
Bosch slip control

Slip control offers the following advantages:- savings in both time and fuel,- reduced tire wear,- the soil is treated with greatercare,- the driver is under less strain,- the vehicle does not get stuck.

Slip

Fig. 13.29

The effect of slip control

motor

fast lift
position
draft

controlpanel

rear-end
actuation

set point value+_I

actual controller
value

mix ratio

α α. S +(1- α ). F
mixture

Q
valve

S
hitch

F
ploughposition sensor draft

S
F+σStandard function draft and position control

Fig. 13.30

static coefficientof friction gears

soil

Block diagram of the position, draft and slip control

tractorF+ σ+permissable
slip

VR -VTVRslip
σslipping action
Slip control function

161

162

Electro-hydraulic hitch control (EHR)

13.4.5 Pressure control
Pressure control enables optimum
packing of the soil by means of packing rollers. To control the pressure
force of working devices, it is sensed
by a pressure sensor (1) and fed to thecontrol electronics as the actual value.
In the arrangement shown, the loadpressure (2) is varied by the weight (3)which can be hydraulically adjusted.
The control is maintained very precisely in dynamic movements as well, e. g.
in the pitching of the tractor.

3

1

Fig. 13.31

Fig. 13.32

Active vibration damping

2

Pressure control

Electric Drives
and Controls

Hydraulics

Linear Motion andAssembly Technologies

Pneumatics

Hydraulics in Mobile Equipment

Hydraulics in Mobile Equipment

Bosch Rexroth AG
Drive & Control Academy
Bahnhofplatz 297070 Würzburg, Germany
Telephone: +49 9352 181920
E-mail: media@boschrexroth.dewww.boschrexroth.com/trainingmedia

R961000791
ISBN 978-3-9816398-0-3

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