Hydrostatic Drives for Municipal Works Vehicles

Hydrostatic Drives for Municipal Works Vehicles

1.0 Introduction
The vast majority of municipal works vehicles in
the western world today are equipped with
hydrostatic travel and service drives.
This is true of every power range, from less than
10 kW to over 180 kW, and is attributable to the
high demands imposed on the drive system,
particularly as regards the following aspects:
– High operational safety
– Easy handling
– Integrated safety functions

Ecological aspects are also becoming more

important:
– Low-noise operation
– Use of biodegradable fluids to prevent pollution
– Low fuel consumption

Thanks to their particular advantages, hydrostatic

transmissions can meet these requirements for the
travel drive and for the service drive:
– Load limiting control of the diesel engine Fig. 1: Municipal works vehicles
– Pressure cut-out by the variable displacement
pump, ensuring loss-free protection for the
drive as a whole
– Pressure cut-out in the variable-speed motor
– Power control over the full conversion range
– Control of the transmission at constant diesel DA
speed
– Rpm-dependent control of the transmission via
the diesel engine
– Inching function
– Demand-based control of the working
hydraulics

Engine
A4VG /
A10VG A6VM

Leo Oberwalleney / VMT2/E

Fig. 2: Hydrostatic drive for municipal works vehicles
Brueninghaus Hydromatik GmbH
Elchingen plant
Phone +49 (0) 7308 / 82 24 24
Fax +49 (0) 7308 / 53 38
E-Mail: leo.oberwalleney@bru-hyd.com

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2.0 Cost-efficient Drives for

low Power Ranges

Operating pressure (rpm)

450
The pressure of costs is particularly high for small
municipal vehicles. Design engineers are compelled
to look around for low-cost solutions without 350
giving up the advantages of a hydrostatic drive. For
this reason, Brueninghaus Hydromatik has
considerably enlarged the block of components
250
making up the MHD group (medium high
pressure).
A10VG / A10VO
Advantages of MHD components:
– Low-cost versions A10VM / A10VE
– Availability of matching sizes A10FM
– Compact design, higher power density
– Large range of open and closed-loop control
devices MD 250 bar MHD 350 bar HD 450 bar
– Cost savings for installation / piping Medium pressure Medium high pressure High pressure

To meet the specific requirements of the various

Fig. 3: Medium high-pressure range MHD
vehicles, the correct choice of open and closed-loop
control elements must be taken into account in the
planning phase. The solutions are always tailored b) Hydraulic direct control DG
to the practical case in question. Complex control The “direct control” DG is a very simple and low-
mechanisms are not always required. cost type of hydraulic pump control. The control pSt
pressure pst is applied directly to the pump control
a) Mechanical pivot control MD cylinder via control pressure generators from
Basic control with direct mechanical action on the Rexroth with optimized characteristics (pressure
swashplate, e.g. via a foot pedal for controlling reducing valve).
speed and direction.
Features:
Features: – No mechanical parts
– Low cost – No zero-position problems
– Integrated internal gear pump and MHD low- – Soft, jerk-free travel, progressive pedal
pressure valves adjustment Fig. 5: Variable displacement pump A10VG,
– Swivel cradle mounted in rolling bearings for – Load limiting control through pump reset forces with hydraulic direct control
low control and retaining forces (dependent on – Feed rate dependent on load
pressure, speed and swivel angle)
– Mechanical spring centering for zero positioning
– 100% through drive, e.g. for tandem pump
Acceleration pedal
2TH6 R - 2TH7 R

Constant
pSt
acceleration
x1 x2 G
0
A10VM
B
ESP FR

Motor

A10VG S
FR:Reset forces
Fig. 4: Variable displacement pump A10VG
18MD, mechanical pivot control Fig. 6: Hydraulic direct control DG

226 RE 00 207/10.00
 Hydrostatic Drives for Municipal Works Vehicles

c) Flange-mounted flushing and boost

pressure valve
If a flushing valve on the motor side is impossible
for technical reasons, this valve can also be flanged
directly onto the service ports of the A10VG pump
on the primary side.

Features:
– Simple piping resulting in cost savings
– Variable flushing rate from 4 to 22 L/min,
depending on deflector plate setting
– Pressure sustaining valve (16 bar) to maintain
the minimum boost pressure

Flushing volume by
orifice selection

Fig. 7: Variable displacement pump A10VG with flange-mounted flushing and boost pressure
valve

3.0 Hydrostatic Transmission

with Wheel Motors and
Switchable claw
Switchable Differential Lock Mechanical cross connection, coupling
Due to their resolved design, transmissions with 100% limited-slip action
wheel motors offer considerable advantages to the Cross differential lock,
design engineer, although the majority of can be switched on and off
machines will require a solution preventing the MCR
drive wheels from slipping.
The multi-pump solution is basically not new.
Rexroth has taken a new approach with its MCR
motors by creating a mechanical system for each
axle via a switchable claw coupling. Since the
deviation in speed is slight, it can be switched on
and off electrohydraulically even while driving.
2-pump system
Longitudinal differential
lock, permanent

Radial piston motor MCR

Fig. 8: Hydrostatic transmission with MCR wheel motors and switchable differential lock

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4.0 Hydrostatic Transmission

Load limiting control as
with combined Control Inching a function of ground Direction of travel
System function speed / engine speed
EP
DA HW
HD
In other words:
– Automotive travel with variable diesel speed
– Proportional travel with constant diesel speed

EPD/DA
In “multi-functional vehicles” and working HDD/DA HA
vehicles, automotive driving can be of advantage Hand-operated HWD/DA DA I II
for travelling on the road, when the ground speed accelerator lever
is controlled exclusively via the accelerator pedal
Motor PTO
as in a passenger car. During the actual work
process, on the other hand, it is better to operate
with constant throttle (constant speed of the PTO Variable
Accelerator Variable
shaft, fan, sweeper, etc.) with infinitely variable pedal displacement
Through drive displacement
ground speed, usually in the lower speed range. pump
motor
for PTO shaft

These two states can be optimized with the aid of Fig. 9: Hydrostatic transmission with combined control system
a “combination control”, i.e.
– automotive travel and
– working with constant throttle.

Control unit
While the direction of travel and the maximum Pressure cut-off
speed are preset via any chosen control unit (HW-
HD-EP), the coordinating DA control valve
controls the diesel in accordance with the load
limits and ensures a speed-dependent build-up of
control pressure for automotive driving when
travelling on the road.
This robust and cost-efficient control element has
already become an established part in many
transmission systems for municipal works vehicles. DA control
The variable-speed motor A6VM with HA1U valve A6VM
control (HA = dependent on high pressure) on the
secondary side has become established for high- Bild 10: Variable Displacement pump A4VG Bild 11: Variable Displacement motor A6VM
speed vehicles.

Features:
– Automatic control, i.e. traction is increased
without external signals
– Full power transmission with constant working
pressure
– Integrated electrical or hydraulic override for the
operation in progress

Fig. 12: Multi-functional vehicle Fig. 13: Multi-functional vehicle

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5.0 Hydrostatic Transmission

with Microprocessor
Control Selection: Micro-
controller
Ground Direction work / road Service
Electronic systems are becoming more and more BB-3 speed of travel travel brake +
widespread. Such complex functions as: FGR

RS 232
– motor pump control, Programming, software
diagnostics
– gearbox management,
via PC, BB3
– diesel engine management,
– traction control for single-wheel drives and
– implement hydraulics, etc.
CAN-Bus

cannot be implemented without the help of

microcontrollers.

Almost all municipal works vehicles are equipped

for different driving modes, such as: Implement hydraulics 1 2
– working, Steering
– road travel or
– repositioning.
The advantages of electronic systems are
particularly useful here, as they permit adjustment A4VG...EPD A10VO
A6VM
of the operating modes and characteristic curves. Travel drive Implement hydraulics Travel drive
Electronic injection pump
Example: Driving program with load
limiting control (FGR)
Fig. 14: Hydrostatic transmission with microprocessor control
– Controlled driving and braking through
downstream pump – motor control.
– Programmed control of the engine strain
– The drive is controlled independently of
temperature and viscosity
– Data are exchanged with the diesel engine via
a CAN bus interface
– Limitation of the maximum diesel speed (over-
speed safety)
– Can be optimized with the control box BB3 or
BODEM software during commissioning
– Easy access for diagnostic purposes and
troubleshooting

“Limp home” concepts are available for

emergency operation so that the vehicle can be
towed home or drive at low speed via redundant
sensors, for example.

The use of electronics essentially presupposes that:

a) the service personnel have been duly instructed
and trained and
b) appropriate equipment / diagnostic tools are
available.
Fig. 15: Road sweeper

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6.0 Hydrostatic Transmission

with Mechanical Bridging

Traction effort
MC
+

A “hydromechanical drive” may prove the best BB-3

Software

answer for vehicles with extensive road travel. 1

Such a drive combines the familiar advantages of
a hydrostatic drive with the high efficiency of a
mechanical drive.
The vehicle is driven entirely by the hydrostatic
system in the working range, while this is bridged
mechanically for road travel. The changeover is
effected automatically via an electrically actuated
clutch while driving. The switching point can be
defined by the gear ratio as desired, for instance 2
Hydrostatic
at 30 km/h. The complete drive is controlled by a
drive with losses
microcontroller.
low-loss
Advantages of the system:
– Lower fuel consumption
– Lower driving noise b
– Smaller hydraulic components and oil cooler
a
Switching
Combined mechanical and hydrostatic travel drive
3
point
is widely used throughout the world particularly Mechanical drive
in large road sweepers, in which a conventional
truck chassis is modified to include a special
0 10 20 30 40 50 60
gearbox in the drive train.
Speed v
This gearbox accommodates the hydraulic
components for both the hydrostatic travel drive
Fig. 16: Hydrostatic transmission with mechanical bridging and automatic changeover
and the working hydraulics. Two operating modes
can be selected, usually when the vehicle is
stationary: Hydraulic
power flow
a) Mechanical travel drive
for road travel via the truck gearbox, hydraulic
components are at a standstill.

b) Hydrostatic travel drive

for working, e.g.
vf = 0 – 12 km/h for sweeping
= 0 – 25 km/h for repositioning

The advantages of the hydrostatic drive make

themselves fully felt here:
– Infinite adjustment of the feed rate without Mechanical
engaging the clutch and changing gear power flow
– Easy change of direction, more convenient
operation
– Eminently suitable for braking
– Low fuel consumption and low noise emissions
due to driving at lower drive speeds

Fig. 17: Mechanical truck drive with coordinating hydrostatic system (example: large road sweeper)

230 RE 00 207/10.00
 Hydrostatic Drives for Municipal Works Vehicles

7.0 Suction Blower Drive for

Sweepers
The intake turbine is variously positioned in the
compact sweepers. Our 40° axial piston motor
A2FM/A2FE in bent-axis design has proved
particularly suitable for mounting the fanwheel
directly.
Due to the O arrangement of the taper roller
bearings, the drive shaft is rigidly clamped and the
generously dimensioned taper roller bearings can
effectively absorb the axial and above all radial
loads (Fq). Our plug-in motor A2FE has proved
particularly suitable here on account of the
recessed flange.

Advantages:
– Ideally suited for direct mounting of the turbine
– Very high efficiency, large speed reserves, low-
noise operation
– Compact, suitable for low overall heights
– Integrated speed sensor
– Integrated bypass valve for delayed fan switch-
off

Fig. 18: Suction Blower Drive for Sweeper

Fig. 19: Large Road Sweeper

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232 RE 00 207/10.00