Sauer Danfoss 51 Series User manual

Series 51
Bent Axis
Variable Motors
Service Manual

Bent Axis Variable Displacement Motors Series 51
2
●The Series 51 - Advanced Technology Today
●The Most Technically Advanced Hydraulic Units in the Industry
●SAE Flange and Cartridge Motors
●Cartridge Motors designed for Direct Installation in Compact
Planetary Drives
●Large Displacement Ratio (5:1)
●Complete Family of Control Systems
●Proven Reliability and Performance
●Optimum Product Configurations
●Compact, Lightweight
Motorsequippedwithcontrolsnormallystartatmaxi-
mumdisplacement. Thisprovidesmaximumstarting
torque (high acceleration).
The controls may utilize externally or internally sup-
plied servo pressure. They may be overridden by a
pressure compensator which functions when the
motor is operating in motor and pump modes. A
defeat option is available to disable the pressure
compensator override when the motor is running in
pump mode.
The pressure compensator option features a low
pressure rise (short ramp) to provide optimal power
utilization throughout the entire displacement range
of the motor. The pressure compensator is also
available as a stand-alone regulator.
Series 51 Variable Displacement Motors are bent
axis design units, incorporating spherical pistons.
Thesemotorsaredesignedprimarilytobecombined
withotherproductsinclosedcircuitsystemstotrans-
fer and control hydraulic power.
Series 51 Motors have a large maximum / minimum
displacement ratio (5 to 1) and high output speed
capabilities.SAEflangeandcartridgemotorconfigu-
rations are available.
A complete family of controls and regulators is avai-
lable to fulfill the requirements of a wide range of
applications.
Front page: Option - hydraulic two-position control
Copyright 1992-1997, Sauer-Sundstrand Company.
All rights reserved. Contents subject to change. Printed in U.S.A. 0992H
General Description

Bent Axis Variable Displacement Motors Series 51
3
Contents
Introduction ......................................................................................................................................................4
Basic Hydraulic Circuits ...................................................................................................................................4
General Description of the Series 51 Variable Displacement Motors ..............................................................5
Functional Description......................................................................................................................................6
Technical Specifications and Data - Variable Displacement Motors ..............................................................20
Safety Precautions .........................................................................................................................................21
Gauge Installation ..........................................................................................................................................23
Start-Up Procedure and Maintenance............................................................................................................25
Component Inspection and Adjustment .........................................................................................................27
Troubleshooting .............................................................................................................................................37
Exploded View of the Series 51 Variable Motor .............................................................................................41
Minor Repair and Replacement - Variable Motor...........................................................................................51
General .....................................................................................................................................................51
Shaft Seal (SAE Flange Configuration) ....................................................................................................52
Shaft Seal (Cartridge Configuration).........................................................................................................53
Loop Flushing Shuttle Valve (Option)........................................................................................................54
Charge Pressure Relief Valve...................................................................................................................55
MinimumAngle Servo Cover ....................................................................................................................55
Hydraulic 2-Position Control (Type N2).....................................................................................................56
Electrohydraulic 2-Position Controls (Types E1•E2 and F1•F2) ...............................................................57
Electric 2-Position Controls (Type S1) ......................................................................................................58
Hydraulic Proportional Control (Type HZ) .................................................................................................59
Hydraulic Proportional Control (Type HS).................................................................................................60
Hydraulic Proportional Control with MaximumAngle Over-ride (Types H1•H2 or K1•K2) ........................61
Two Connection Hydraulic Proportional Control (Type HP) ......................................................................62
Two Connection Hydraulic Proportional Control for “Dual Path” Vehicles (Type HC) ...............................64
Electrohydraulic Proportional Control (Types EP and EQ)........................................................................68
Pressure Control Pilot (PCP) Valve for Electrohydraulic Proportional Control (Types EP and EQ)..........70
Multi-function Block...................................................................................................................................71
Pressure Compensator Regulator (Type PC) ...........................................................................................76
Control Orifices .........................................................................................................................................77
Plug / Fitting Torques ................................................................................................................................77
0 - 1

Bent Axis Variable Displacement Motors Series 51
4
Introduction
Dirt or contamination is the greatest enemy of any
type of hydraulic equipment. The greatest possible
cleanliness is necessary when starting up the sys-
tem,changingfilters,or performinganyotherservice
procedure.
For Technical Information on Series 51 motors, refer
to publication BLN-10042 or 368753.
For Fluid Quality Requirements, refer to publication
BLN-9987 or 697581.
Sauer-Sundstrand provides a complete repair serv-
ice for its products. Contact any Sauer-Sundstrand
Authorized Service Center for details. Sauer-Sund-
strandAuthorizedServiceCenterlocationsarelisted
in publication BLN-2-40527 or 698266.
The purpose of this manual is to provide information
necessary for the normal servicing of the Series 51
family of variable displacement hydrostatic motors.
This manual includes unit and component descrip-
tion, troubleshooting, adjustments, and minor repair
procedures. By following the procedures in this
manual, inspections and minor repairs may be per-
formed without affecting the unit warranty.
A Series 51 motor does occasionally require servic-
ing,andtheseunitsaredesignedtomeetthisrequire-
ment.
Many repairs or adjustments can be completed with-
out removing the unit from the vehicle or machine,
providedtheunitisaccessibleandcanbethoroughly
cleaned before beginning any procedures.
INPUT PV MV
CASE
DRAIN
LINE
OUTPUT
FLOW (BI-DIRECTIONAL)
RESERVOIR
51000001
Fig. 0-1 - Basic Closed Circuit
Closed Circuit
Themainportsofthepumpareconnectedbyhydrau-
lic lines to the main ports of the motor. Fluid flows in
eitherdirectionfromthe pumptothemotorthen back
tothepumpinthisclosedcircuit.Eitherofthehydrau-
lic lines can be under high pressure. The direction
and speed of fluid flow (and the motor output shaft
rotation)dependsonthepositionofthepumpswash-
plate. The system pressure is determined by the
machine load.
Open Circuit
Theoutletportofthepumpisconnectedbyahydrau-
liclinetoadirectionalcontrolvalve.Theworkingports
of this valve are connected to the main ports of the
motor. When the valve is actuated, fluid flows first
fromthepumptothevalve.Thevalvethendirectsthe
fluid to the motor in either direction. The direction of
fluid flow (and motor output shaft rotation) depends
onthedirectionthecontrolvalveisshifted.Thespeed
of fluid flow (and motor output shaft speed) depends
on pump output volume and the distance the control
valve is shifted. The system pressure is determined
by the machine load.
Fluid returning from the motor is routed through the
controlvalve tothereservoir. Additionalcomponents
maybe necessarytoprovide dynamicbrakingandto
deal with over-running loads.
Basic Hydraulic Circuits
51000002
Fig. 0-2 - Basic Open Circuit
INPUT PUMP MV
CASE
DRAIN
LINE
OUTPUT
FLOW
(BI-DIRECTIONAL)
RESERVOIR
FLOW
(UNI-DIRECTIONAL)
CONTROL VALVE
0 - 2

Bent Axis Variable Displacement Motors Series 51
5
General Description of the Series 51 Variable Displacement Motors
The Series 51 variable displacement hydraulic mo-
torsusesphericalpistonsandpistonrings. Theangle
between the cylinder block and the output shaft can
be set between 32°and 6°, providing a 5 to 1
maximum to minimum displacement ratio.
At maximum displacement, the motor will provide a
certain maximum output shaft torque and minimum
speed corresponding to the pressure and flow sup-
plied to the motor. Under the same input conditions
butatminimumdisplacement,theshaftspeed willbe
approximatelyfive(5)timesfasterwhiletheavailable
outputtorquewilldecreasetoapproximatelyone-fifth
(1/5) the full displacement value. The displacement
is changed by a servo piston which is connected to
the valve segment.
Various hydraulic and electrohydraulic controls may
bemountedonthemotorendcaptocontroltheservo
piston and the motor displacement. Servo pressure
oilmayeitherbesuppliedinternallyfromthemotor,or
externally.
ForallcontrolsexcepttheN2andPC,servopressure
oilissuppliedtoafour(4)wayspoolvalveinthemotor
end cap. When a combination of pilot pressure (or
force)fromanexternal controlassemblyandinternal
springforceshiftsthisvalve,servopressureisrouted
to move the servo piston and change the motor’s
displacement.
Asynchronizingshaft,withsphericalrollers,synchro-
nizes the rotation of the output shaft and the cylinder
block. The ball end of each piston runs in a socket
bushing, pressed into the output shaft. There are no
other parts used to connect the pistons to the shaft.
Twotaperedroller bearings support the output shaft.
Fig. 10-1 - Sectional view of Series 51 variable displacement motor (SAE Flange
Configuration) with Hydraulic Proportional Control
P001 196
Pressure Compensator
Override
Servo Piston
Cylinder
Charge Pressure
Relief Valve
Piston Synchronizing
Shaft
Tapered Roller Bearings
Bearing Plate
Valve Segment
Hydraulic
Proportional
Control
Minimum
Displacement Limiter
Control
Pressure
Port
10 - 1

Bent Axis Variable Displacement Motors Series 51
6
Functional Description
Fig. 10-2 - Loop
Flushing
Components
Loop Flushing
Series 51 motors used in closed circuit applications
incorporate an integral loop flushing valve as stan-
dard equipment. Installations that require additional
fluid to be removed from the main hydraulic circuit
because of fluid cooling requirements, or circuits
requiring the removal of excessive contamination
from the high pressure circuit, can benefit from loop
flushing. Series 51 motors used in open circuit appli-
cations may have the optional loop flushing defeat
components installed.
Series 51 motors equipped with an integral loop
flushing valve also include a charge pressure relief
valve. The setting of the motor charge relief valve
affects the function of the flushing circuit. Higher
motor charge relief settings reduce the loop flushing
flow and increase the flow over the pump charge
pressure relief valve when the circuit is operating.
Lower motor charge relief settings increase the loop
flushing flow and may increase the motor case pres-
sure when the circuit is operating.
Anappropriatecombinationofpumpandmotorcharge
pressure settings should be maintained to insure the
proper function of the loop flushing circuit. Correct
chargepressuremustbe maintainedunderallcondi-
tions of operation to maintain pump control perfor-
mance in closed loop systems.
NOTE: An optional orifice may be installed between
themotorcharge relief and the motor caseto
limit the maximum flushing oil flow.
51000003 Fig. 10-3 - Loop
Flushing Defeat
Components
51000004
10 - 2

Bent Axis Variable Displacement Motors Series 51
7
Functional Description (Continued)
Fig. 10-4 - Minimum Displacement Limiter
with Tamper Resistant Cap (Cartridge
Motor Configuration Shown)
Fig. 10-6 - Internal Servo Pressure Supply
Screen with Multi-function Block and/or
Control Removed (Plug for External
Supply)
5100007
Fig. 10-7 - External Servo Pressure Supply
Fitting (Plug for Internal Supply)
51000008
Fig. 10-5 - Maximum Displacement Limiter
Screw
51000006
51000005
Displacement Limiters
All Series 51 motors incorporate mechanical dis-
placement limiters. The minimum displacement of
themotorcanbe limitedwithinthestandardrange by
a set screw in the motor housing. The maximum
displacementcanbelimitedwithspacersinstalledon
the servo piston.
Controls - General
A wide range of control options is available for the
Series 51 motors. These include pilot operated
Electrohydraulic 2-Position Controls, Hydraulic Pro-
portional Controls (single or two [2] connection), and
ElectrohydraulicProportionalControls.Adirectlyop-
erated Hydraulic 2-Position Control and a Pressure
Compensator regulator are also available.
The Series 51 variable motor servo piston (except
when equipped with N2 control or the PC regulator)
maybeoperatedeitherbyservopressureoilsupplied
internallyfromthemainportsofthemotor,orbyservo
pressure oil supplied from an external source. (The
N2control usesservopressure suppliedbyanexter-
nal control valve. The PC regulator obtains servo
pressure from the main ports of the motor.)
Orifice plugs are installed in the control spool sleeve
intheendcaptoregulatetheflowofoilfromtheservo
piston to the motor housing. Orifice plugs may be
installed in the end cap to regulate the flow of servo
pressure supply oil to the control valve, and to regu-
late the flow of oil from the control valve to the servo
piston.
10 - 3

Bent Axis Variable Displacement Motors Series 51
8
Fig. 10-8 - Series 51 Motor with N2 Control
Hydraulic 2-Position Control (Type N2)
This is a two (2) position (maximum - minimum
displacement) control, consisting of a cover plate
mounted on the end cap. An external control valve
supplies servo pressure from an external source
directly to the servo piston. PCOR is not available
with the N2 control.
When servo pressure is supplied to port “Y1,” the
settingpistonmovestothemaximummotordisplace-
ment position. When servo pressure is supplied to
port “Y2,” the setting piston moves to the minimum
motor displacement position.
Orificesmaybeinstalled in the external control valve
or its connections to regulate the speed of servo
piston movement.
Functional Description (Continued)
51000011
Fig. 10-10 - N2 Control Schematic
U4 (opt.)
max.
disp.
M2
M1
(M4) Y1 Y2 (M3)
M6
L2
B
A
L1

Fig. 10-9 - N2 Control Components 51000010
51000009
10 - 4

Bent Axis Variable Displacement Motors Series 51
9
Functional Description (Continued)
51000013
Fig. 10-11 - Series 51 Motor with E1•E2 or
F1•F2 Control
51000012
Fig. 10-12 - E1•E2 and F1•F2 Control
Components
X3 (M5)
Servo press,
external
M9
U5
(plug for
ext. servo
press.) T1
T7,
T8
T2
T3
max.
disp.
B1
A1
M2
M1
M4 M3M6
L2
B
A
Servo
Pressure
internal L1
E1•E2
M7
M8
U4 (opt.)
F1•F2
51000014
Fig. 10-13 - E1•E2 and F1•F2 Control
Schematic
Electrohydraulic 2-Position Control (Types
E1•E2 and F1•F2)
A12or24VDCsolenoidvalve,mountedonthemulti-
function block, connects the end of the control valve
spool in the end cap with pilot pressure (provided by
the shuttle spool in the multi-function block) or with
the motor case. The control valve in the end cap is
biased by a threshold spring, and controls oil flow to
theendsofthe servo piston. Servo pressure may be
supplied from an external source or internally by the
shuttle spool in the multi-function block. PCOR is
available with these controls.
With the E1 and E2 controls, energizing the solenoid
will cause the motor to shift to minimum displace-
ment. Whenthe solenoid isnotenergized,the motor
is held at maximum displacement.
With the F1 and F2 controls, energizing the solenoid
causes the motor to shift to maximum displacement.
Whenthesolenoidisnotenergized,themotorisheld
at minimum displacement.
10 - 5

Bent Axis Variable Displacement Motors Series 51
10
Functional Description (Continued)
Electric 2-Position Control (Type S1)
A 12 VDC solenoid valve, mounted on the multi-
function block, directly operates the control valve
spoolintheend cap.Thecontrolvalvein theendcap
is biased by a threshold spring, and controls oil flow
to the ends of the servo piston. Servo pressure may
be supplied from an external source or internally by
theshuttlespoolinthemulti-functionblock. PCORis
available with this control.
With the S1 control, energizing the solenoid causes
the motor to shift to maximum displacement. When
the solenoid is not energized, the motor is held at
minimum displacement.
51000163
Fig. 10-14 - Series 51 Motor with S1 Control
51000162
Fig. 10-15 - S1 Control Components
X3 (M5)
Servo press,
external
M9
U5
(plug for
ext. servo
press.) T1
T7,
T8
T2
T3
max.
disp.
B1
A1
M2
M1
M4 M3M6
L2
B
A
Servo
Pressure
internal L1
S1
U4 (opt.)
51000085
Fig. 10-16 - S1 Control Schematic
10 - 6

Bent Axis Variable Displacement Motors Series 51
11
Functional Description (Continued)
Fig. 10-17 - Series 51 Motor with HZ
Control
Hydraulic Proportional Control (Type HZ)
The HZ control consists of a cover plate mounted
directly on the end cap. A ball type shuttle valve
providesinternalservopressuresupplytothecontrol
valve in the end cap. PCOR is not available with the
HZ control.
Feedback springs (single spring for 060, 080 and
110) and a threshold spring are installed in the end
cap. The feedback springs and threshold spring
provide a force on the end of the control spool. The
force of the threshold spring is externally adjustable
with an adjusting screw. The feedback spring is
positionedbetweenthecontrol spoolandafeedback
lug attached to the servo piston. The force of the
feedback spring increases as the motor’s displace-
ment decreases.
Pilotoilpressurefromanexternalsourceisappliedto
the end of the control spool opposite the feedback
and threshold springs. An increase in pilot pressure
(above the threshold pressure and within the modu-
lating pressure range) will result in a decrease in
motor displacement, while a decrease in pilot pres-
sure will result in an increase in motor displacement.
51000017
Fig. 10-19 - HZ Control Schematic
U4 (opt.)
X3 (M5)
Servo press,
external
M9
U5 (plug for
ext. servo press.) T1
T7,
T8
T2
T3
Servo
Pressure
internal
max.
disp.
M2
B
M1
A
L2 M4 M3M6
L1
M7
X1
51000015
51000016
Fig. 10-18 - HZ Control Components
10 - 7

Bent Axis Variable Displacement Motors Series 51
12
Fig. 10-20 - Series 51 Motor with HS
Control
Hydraulic Proportional Control (Type HS)
The HS control consists of a cover plate (with a
hydraulic port) mounted on the multi-function block.
Servo pressure may be supplied from an external
source or internally by the shuttle spool in the multi-
function block. PCOR is available with this control.
The function of the HS control is identical to the
function of the HZ control.
Functional Description (Continued)
51000018
Servo
Pressure
internal
max.
disp.
M2
B
M1
A
L2 M4 M3M6
B1
A1
L1
M7 X1
U4 (opt.)
X3 (M5)
Servo press,
external
M9
U5 (plug for
ext. servo press.) T1
T7,
T8
T2
T3
X1
M7
X1
M7
HS
H1•H2
K1•K2
Fig. 10-22 - HS, H1•H2, and K1•K2 Control
Schematic
51000022
Fig. 10-21 - HS Control Components 51000019
10 - 8

Bent Axis Variable Displacement Motors Series 51
13
Functional Description (Continued)
51000020
Fig. 10-23 - Series 51 Motor with H1•H2
Control
Hydraulic Proportional Control with
Electric Override (Types H1•H2 and K1•K2)
The function of the H1•H2 and K1•K2 controls is
similar to the function of the HS control. A 12 or 24
VDCsolenoidvalve is installed between the external
pilot pressure source and the control spool.
With the H1•H2 controls, energizing the solenoid
allowsthecontroltofunctionasanHScontrol. When
thesolenoidisnotenergized,pilotpressureisblocked
andtheendofthecontrolspoolisdrainedtothemotor
case,causingthemotortoshifttomaximumdisplace-
ment.
With the K1•K2 controls, energizing the solenoid
blockspilotpressureanddrainstheendofthecontrol
spool to the motor case, causing the motor to shift to
maximum displacement. When the solenoid is not
energized, the control functions as an HS control.
51000021
Fig. 10-25 - H1•H2 and K1•K2 Control
Components
51000167
Fig. 10-24 - Series 51 Motor with K1•K2
Control
10 - 9

Bent Axis Variable Displacement Motors Series 51
14
Functional Description (Continued)
Fig. 10-26 - Series 51 Motor with HP
Control
U4 (opt.)
Servo
Press,
internal
max.
disp.
M2
M1
L2 M4 M3M6
X2 X1
B1
A1
B
A
X3 (M5)
Servo press,
external
L1
M9
U5 (plug for
ext. servo press.) T1
T7,
T8
T2
T3
Fig. 10-28 - HP Control Schematic 51000025
Fig. 10-27 - HP Control Components 51000024
51000023
Two Line Hydraulic Proportional Control
(Type HP)
This control consists of a valve block with two (2)
hydraulic ports mounted on the multi-function block.
The valve block incorporates a shuttle spool and a
pilot piston with centering springs. A pin transmits
force from the pilot piston to the control spool in the
end cap. Feedback springs (single spring for 060,
080, and 110) and a threshold spring are installed in
theendcap. ThesespringsfunctionsimilartotheHS
control. Servo pressure may be supplied from an
externalsourceorinternallybytheshuttlespoolinthe
multi-function block. PCOR is available with this
control.
Two pilot pressures are provided to the control. The
shuttle spool directs the higher pilot pressure to the
end of the pilot piston opposite the feedback spring,
andthelowerpressuretotheoppositesideofthepilot
piston. The rod transmits a force, proportional to the
difference of the pilot pressures, to the control spool.
An increase in the difference between the pilot pres-
sureswillresultinadecreasein motordisplacement,
whileadecreasewillresultinanincreaseindisplace-
ment.
10 - 10

Bent Axis Variable Displacement Motors Series 51
15
Functional Description (Continued)
Fig. 10-29 - Series 51 Motor with HC
Control
51000158
Two Line Hydraulic Proportional Control
for “Dual-Path” Vehicles (Type HC)
TheHCcontroloperatesinasimilarmannertotheHP
control, however the HC control is optimized for use
in “dual-path” drive vehicles. This control consists of
avalveblockwith two(2)hydraulicportsmounted on
the end cap. The valve block incorporates a shuttle
spool and a pilot piston with centering springs. A pin
transmits force from the pilot piston to the control
spool in the end cap.
A bleed valve is provided to eliminate any air which
mightbecometrappedinthepilotpistonoilpassages.
Feedbacksprings are installed in theend cap. Servo
pressure is supplied internally by a ball type shuttle
valve in the control housing. PCOR is not available
with this control.
Two pilot pressures are provided to the control. The
shuttle spool directs the higher pilot pressure to the
endofthepilot piston opposite the feedback springs,
andthelowerpressuretotheoppositesideofthepilot
piston. The pin transmits a force, proportional to the
difference of the pilot pressures, to the control spool.
An increase in the difference between the pilot pres-
sureswillresultinadecreasein motordisplacement,
whileadecreasewillresultinanincreaseindisplace-
ment. The feedback springs in the end cap have
differing spring rates and operate in parallel (060,
080,and110)orseries(160or250)toprovidealinear
relationship between motor displacement and pilot
pressure differential.
51000111
Fig. 10-30 - HC Control Components
U4 (opt.)
max.
disp.
M2
M1
L2 M4 M3M6
X2 X1
B
A
M5
L1
M9
T1
T7,
T8
T2
T3
Fig. 10-31 - HC Control Schematic 51000160
10 - 11

Bent Axis Variable Displacement Motors Series 51
16
Functional Description (Continued)
Electrohydraulic Proportional Control
(Types EP and EQ)
Thiscontrolconsistsof avalveblockandPCP (Pres-
sure Control Pilot) valve mounted on the multi-func-
tionblock. Thevalveblockincorporatesapilotpiston
withcenteringsprings. Apintransmitsforcefromthe
pilot piston to the control spool in the end cap.
Feedback springs (single spring for 060, 080, and
110) and a threshold spring are installed in the end
cap.These springsfunctionsimilar totheHScontrol.
Servo pressure may be supplied from an external
source or internally by the shuttle spool in the multi-
function block. PCOR is available with this control.
Anexternal pilot pressure source isconnected to the
inlet of the PCP valve, which produces differential
pilot pressures proportional to the current through it.
These pressures are applied to the pilot piston. The
operation of this control is similar to that of the HP
Control, with the motor displacement being propor-
tional to the current through the PCP valve.
An increase in current (above the threshold current)
willresult in a decrease inmotor displacement, while
adecreasewillresult in an increase in displacement.
Fig. 10-32 - Series 51 Motor with EP Control
(EQ Similar)
51000026
U4 (opt.)
X3 (M5)
Servo press,
external
M9
U5 (plug for
ext. servo press.) T1
T7,
T8
T2
T3
Servo
Pressure
internal
max.
disp.
M2
M1
L2 M4 M3M6
M7 X1 M8
B1
A1
B
A
L1
Fig. 10-34 - EP and EQ Control Schematic
51000028
Fig. 10-33- EQ Control Components (EP
Similar)
51000027
10 - 12

Bent Axis Variable Displacement Motors Series 51
17
Functional Description (Continued)
Fig. 10-36 - Multi-function Block with Servo
Pressure Supply Shuttle Spool
Fig. 10-35 - Multi-function Block (Without
Control)
51000029
51000030
Multi-function Block Components
The Multi-function Valve Block includes a shuttle
valve which provides internally supplied servo pres-
sure, and an optional Pressure Compensator Over-
Ride (PCOR) function with optional brake pressure
defeat.
Servo Pressure Supply
For internal supply, the multi-function block incorpo-
ratesashuttlespoolwithinternalcheckballvalvethat
routesoilfromthemaincircuitportsofthemotortothe
control valve in the end cap. “High side” pressure is
provided to the servo control valve in the end cap.
For external supply, the connection between the
shuttlespoolandtheservocontrolvalveisblockedin
the end cap. The external pressure supply to the
servo control valve connects to a port (“M5”) on the
end cap.
Pressure Compensator Over-Ride (PCOR)
The Pressure Compensator Over-Ride (PCOR) sys-
temincludesaspoolvalvelocatedinthePCORblock
which is attached to the multi-function block. This
system increases the motor displacement at system
pressuresabovethe PCOR valve setting. (Pressure
Compensator Over-Ride is not available with the N2
and HZ controls, or the PC regulator.)
For bi-directional PCOR operation, the shuttle valve
in the multi-function block routes system high pres-
sure to the PCOR spool valve. For single direction
PCORoperation,thePCORspoolvalveisconnected
toone(1)sideoftheclosedloopthroughpassagesin
the multi-function block
When system pressure exceeds the PCOR setting,
the spool valve moves to connect the displacement
reducing end of the servo piston to the motor case,
and the displacement increasing end of the servo
piston to system pressure. This increases the motor
displacement,whichreducesthemotoroutputspeed.
When the PCOR valve closes, control of the servo
piston returns to the control spool in the motor end
cap.
Fig. 10-37 - Multi-function Block with PCOR
Block and Spool Valve (K1•K2 Control
Shown)
51000031
10 - 13

Bent Axis Variable Displacement Motors Series 51
18
Functional Description (Continued)
Fig. 10-38 - Multi-function Block with PCOR
Defeat Spool Components
51000032
Standard with Defeat
Pressure Compensator Override
XA XB
Shuttle Valve
PCOR
Valve
Defeat
Spool
A1
B1
A1
B1
Shuttle Valve
PCOR
Valve
U7
T5
U6
U7
U6 T6
T4
Fig. 10-39 - PCOR and PCOR with Defeat
Schematic
51000033
An optional “brake pressure defeat” spool may be
installed in the multi-function block. When used with
the PCOR, this spool assures that the PCOR does
notcausethe motor displacement to increase during
deceleration (which could cause pump overspeed).
Pressure from a source such as the pump servos or
an external valve, shifts the defeat spool to block the
high pressure supply to the PCOR valve from the
“deceleration” side of the closed loop. Either bi-
directionalorsingledirectionPCORoperationcanbe
specified when PCOR defeat is installed.
PCOR Brake Pressure Defeat Operation
Rotation High pressure Control pressure
port on port
CW A XB
CCW B XA
10 - 14

Bent Axis Variable Displacement Motors Series 51
19
Functional Description (Continued)
Pressure Compensator Regulator (Type
PC)
In this regulator, the Pressure Compensator system
in the multi-function block assembly controls the
motor displacement. At system pressures below the
compensator setting, the servo piston is maintained
in the minimum motor displacement position. When
systempressure exceedsthePOR setting,hydraulic
pressure acts on the servo piston to increase the
motor displacement.
With the Pressure Compensator regulator, an in-
crease in system pressure (above the setting pres-
sure) will result in an increase in motor displacement
and output torque, and a decrease in motor shaft
speed.
Fig. 10-40 - Series 51 Motor with PC
Regulator
51000034
U4 (opt.)
M9
T1
T7
max.
disp.
M2
M1
L2 M4 M3M6
B
A
L1
M5
T5 U7
U6
51000036
Fig. 10-42 - PC Regulator Schematic
Fig. 10-41 - PC Regulator Components51000035
10 - 15

Bent Axis Variable Displacement Motors Series 51
20
Frame Size
Dimension 060 080 110 160 250
Displacement maximum cm360.0 80.7 109.9 160.9 250.0
in33.66 4.92 6.71 9.82 15.26
minimum cm312.0 16.1 22.0 32.2 50.0
in30.73 0.98 1.34 1.96 3.05
Continuous speed at max disp min-1 (rpm) 3600 3100 2800 2500 2200
at min disp min-1 (rpm) 5600 5000 4500 4000 3400
Max. speed at max disp min-1 (rpm) 4400 4000 3600 3200 2700
at min disp min-1 (rpm) 7000 6250 5600 5000 4250
Theoretical at max disp Nm / bar 0.95 1.28 1.75 2.56 3.98
torque lbf•in / 1000 psi 583 784 1067 1563 2428
at min disp Nm / bar 0.19 0.26 0.35 0.51 0.80
lbf•in / 1000 psi 117 156 214 313 486
Max. continuous Q max L / min 216 250 308 402 550
flow gal / min 57 66 81 106 145
Max. corner power Pcorner max kW 336 403 492 644 850
hp 450 540 660 864 1140
Mass moment J kg • m20.0046 0.0071 0.0128 0.0234 0.0480
of inertia lbf • ft20.1092 0.1685 0.3037 0.5553 1.1580
Weight m kg 28 32 44 56 86
(with control N2) lb 62 71 97 123 190
Technical Specifications and Data - Variable Displacement Motors
Design
Piston motor with variable displacement, bent axis
construction.
Type of Mounting
SAE four (4) bolt flange – SAE Flange Configuration.
Two (2) bolt flange – Cartridge Motor Configuration.
Pipe Connections
Main pressure ports: SAE flange
Remaining ports: SAE O-ring thread
Direction of Rotation
Clockwise and counter-clockwise.
Installation Position
Installation position discretionary. The housing must
always be filled with hydraulic fluid.
System Pressure Range, Input
Max: 480 bar (6960 psi)
Min: 10 bar (145 psi)
Case Pressure
Max. Continuous: 3 bar (44 psi)
Intermittent (Cold start): 5 bar (73 psi)
Hydraulic Fluid
Refer to Sauer-Sundstrand publication BLN-9887 or
697581.
Temperature 1)
ϑmin = -40°C (-40°F), intermittent, cold start
ϑ nominal = 104°C (220°F), continuous
ϑmax = 115°C (240°F), intermittent
1) at the hottest point, normally the case drain line.
Hydraulic fluid viscosity must be as shown below.
Fluid Viscosity Limits
νmin = 5 mm2/s (42 SUS) intermittent
νmin = 6.4 mm2/s (47 SUS) min. continuous
νmin = 13 mm2/s (70 SUS) optimum
νmax = 110 mm2/s (510 SUS) max. continuous
νmax = 1600 mm2/s (7400 SUS) intermittent, cold start
Filtration
Acceptable contamination level: ISO Code 18/13 or
better. Refer to Sauer-Sundstrand publication BLN-9887
or 697581.
10 - 16