RE 98 300 - Airline Hydraulics

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Industrial
Hydraulics
Bosch Rexroth AG
Mobile Hydraulics
Glockeraustraße 4
89275 Elchingen, Germany
Tel. +49 (0) 73 08-82 0
Fax +49 (0) 73 08-72 74
[email protected]
www.boschrexroth.com/brm
Printed in Germany
RE 98300/06.03
Electric Drives
and Controls
Linear Motion and
Assembly Technologies
Pneumatics
Service
Automation
Easy Machine Operation with
Rexroth Automotive Drive and
Anti Stall Control
The Drive & Control Company
Mobile
Hydraulics
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Rexroth Automative Drive and Anti Stall Control | Features and Functions
3
The Features
The Functions
Pressure sensing capabilities of the
DA-system allow precise and efficient
drive behavior since in the lower and
intermediate engine speed range, the
tractive effort is varied by the diesel
engine speed. Telescopic handlers, for
instance, thus allow sensitive positioning.
The Automotive Drive and Anti Stall Control (DA) is a pure hydro-mechanical control
for closed loop transmissions which provides two main features: Automotive Drive
Control and/or Anti Stall Control. Additional options provide servo override controls
and enhanced braking.
Automotive Drive Control
allows the operator to run a machine
with a hydrostatic transmission
similar to a passenger car with
automatic transmission: The more
the accelerator pedal is moved
down, the more the transmission
pump increases its delivered flow,
i.e. speeds up the vehicle.
Anti Stall Control
ensures that the pump adjusts its
consumed power to the power
available from the diesel engine.
In any overload situation, the Anti
Stall Control reduces the pump’s
flow rate to a value that prevents
the engine from stalling.
An A4VG pump with Drive and Anti Stall Control DA as well as an integrated inching
valve ensures a smooth drive characteristic. This allows careful handling of goods with
maximum drive comfort as well as quick acceleration and thus high turnover speeds of
the handled material.
Both features can be realized
without any direct link between
pump and accelerator pedal. There
is no requirement for any control
rod or electronics. The pump
controller works fully automatically.
The DA control is a well proven
control system, produced for many
years. Thousands of different
machines, e.g. fork lift trucks,
municipal vehicles, wheel loaders
or other vehicles are proof of the
reliability, durability, and
uniqueness of this concept.
Automotive Drive Control makes the
pump displacement follow the engine
speed:
• Pushing down the accelerator pedal
leads to an increase in engine speed.
• The difference in engine speed also
causes a different pump speed. Since the
boost pump is integrated in the
transmission pump it also shows a
different flow rate.
• The boost pump’s flow rate is measured
within the transmission pump’s speed
sensing valve.
• The more flow travels through the speed
sensing valve, the more the pump goes
on stroke and thus delivers more flow.
This in turn increases the vehicle speed.
The travel direction is selected by an
integrated forward-neutral-reverse valve.
The selected hydraulic motor can be either
of constant displacement (e.g. A2FM)
or variable displacement (e.g. A6VM).
When wheels get blocked, the tractive
effort is controlled via the diesel engine
speed, however, without heating up the
system.
Arto stipata theatro spectat Roma potens habet hos numeratque.
Interdum volgus rectum videt, est ubi peccat. Si veteres ita miratur laudatque poetas, ut nihil anteferat, nihil illis comparet,
errat. Si quaedam nimis antique, si peraque dure dicere volgus rectum videt, est
ubi peccat. Si veteres ita miratur laudatque
poetas, ut nihil anteferat, nihil illis comparet, errat. Si quaedam nimis antique, si peraque dure dicere arto stipata theatro
spectat Roma potens; habet hos numeratque poetas ad nostrum tempus Livi scriptoris ab aevo. Interdum volgus rectum videt, est ubi peccat. Si veteres ita miratur
laudatque poetas.
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The Functions
The Applications
Well balanced rotary
group technology
features power self
control to serve as
engine stalling
protection
The working characteristic of a DA-controlled vehicle can be displayed within a three dimensional diagram shown on
this page. The x-axis describes the travel speed which corresponds to the flow rate of the transmission pump.
The y-axis shows the tractive effort which is proportional to the drive pressure. Eventually, the z-axis displays the
engine speed which is mainly determined by the accelerator pedal position.
All working points of a vehicle with Automative Drive and Anti Stall Control are located on a three dimensional
surface within this diagram. Looking at three typical day to day travel situations, the working principle becomes clear:
Characteristic of the Rexroth Automative Drive and
Anti Stall Control
Anti Stall Control protects the
engine from stalling:
The pressure sensing capability of
the transmission pump’s rotary
group is the main feature of the Anti
Stall Control. Increasing pressure
may be caused by the vehicle getting
into heavy ground conditions, or by
driving up a hill.
• Increasing pressure in the
transmission pump’s working lines
lead to a reduction in pump
displacement.
• With the reduced displacement the
pump delivers less flow and adapts
its power intake to the engine
power capabilities. It thus protects
the engine from stalling.
5
Rexroth Automative Drive and Anti Stall Control | Applications
In case of additional power
requirements from other consumers
(e.g. steering systems, implement
hydraulics), the transmission pump
automatically adjusts its displacement
to balance the power of engine
(output) and hydraulics (input).
Depending on the application, the
Anti Stall Control may allow the
installation of smaller diesel engines
since they are now protected against
stalling.
Vehicle Entering a Slope
A vehicle traveling at full speed on plain ground enters an uphill slope.
This obviously requires an increased tractive effort. The working points in
the three dimensional diagram are:
1
Vehicle traveling at max. speed on plain ground: The pump is at full
stroke and delivers maximum flow. The established pressure level
corresponds to the vehicle’s drive resistance (rolling-, air
resistance) in this operation condition.
2
Entering the slope causes the tractive effort to increase. This
yields increasing hydraulic system pressure. The diesel engine lugs
due to increased power requirement. The pressure sensing rotary
group swivels back and balances hydraulic and engine power
according to the increased system pressure.
Accelerating Vehicle
A vehicle, e.g. a wheel loader, accelerating on plain ground shows a
certain characteristic travel path within this diagram. The working
points at the different states are:
Vehicle Getting into Stall Mode
Another typical situation is a vehicle driving at medium speed and getting
stalled out. This may be for instance a loader entering a pile of gravel with
its shovel.
1
At standstill, the engine runs at low idle. The DA pump stays at
zero flow at this stage.
1
2
Slightly pushing the accelerator pedal causes the engine to
speed up. The DA pump senses the increased engine speed
and starts to build up pressure. However, due to the vehicle’s
friction, it does not yet move.
Driving at medium speed across a plain ground yields a certain
pressure level that delivers the necessary tractive effort to overcome
all drag.
2
Touching the first gravel increases the required tractive effort. The
system pressure goes up. At the same time the pressure sensitive
DA-pump already reduces the flow to not overload the engine.
3
4
The vehicle overcomes the sticking forces and starts to move.
3
Steadily pushing the accelerator pedal speeds up the engine.
The DA pump continuously increases its stroke and thus
delivers increased flow. The vehicle speeds up.
Fully digging into the pile of gravel further increases the system
pressure. The engine sees increased loading. This loading leads to
an engine speed decrease.
4
If the system pressure exceeds preset values (given by hydraulic
component’s pressure rating), the DA-pump’s pressure cut-off
function reduces the pump’s flow rate. The pump adjusts its
displacement to maintain full system pressure (i.e. maximum tractive
effort) without heating up the system.
5
Approaching maximum speed, the pressure slightly decreases
again since there is no further acceleration necessary. The
vehicle only needs to overcome the frictional drag forces.
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Rexroth Automative Drive and Anti Stall Control | Options and Service
The Options
The Service
Rexroth application engineers are ready to assist you in
the right selection of components and controls that
best suit for your application. All pumps equipped
with the Automotive Drive and Anti-Stall Control are
factory set and fully tested according to specification to
meet your engine and application requirements.
Servo Override Controls
The Automotive Drive and/or Stall Control can be combined with all servo displacement controls. This allows both enjoying
the ease of operation of an automotive drive when operating on the road and the load independent precision of servo
displacement control in the working mode. Frequently used servo displacement controls with Automotive Drive and/or Anti
Stall Control (DA) are mechanical proportional (HW), hydraulical proportional (HD) or electrical proportional (EP). See the
Rexroth A4VG and A10VG pump data sheets RA/RE 92 003 and RA/RE 92 750 for reference.
The DA-pumps offer various options of override controls for specific braking and inching functions:
Brake pressure inching valve
Rotary inching valve for low speed operations
Rexroth Power Brakes with integrated inching valve
The brake pressure inching valve works simultaneously
with the service brake. This is therefore the best solution
when inching shall support the service brake to reduce
brake pad wear.
Application example: To slow down a wheel loader, the
operator pushes down the brake pedal. Pushing gently
means hydrostatic braking only, pushing harder means
hydrostatic and service braking simultaneously.
The pump’s control device is hydraulically connected with
the service brake circuit. Increasing pressure in the service
brake system causes the transmission pump to destroke.
Rotary Inching Valve is the preferred solution when
inching shall be separated from braking. This is typically
the case when certain operations require high engine
speeds while the travel speed is very low.
Application example: Sweeping machines when the brush
system requires full hydraulic oil flow from the implement
pump while the travel speed is low.
The pump’s control device is hydraulically connected to the
remotely installed rotary inching valve. The inching valve
in turn is mechanically operated by either a hand lever or a
pedal. Pushing the lever or pedal and thus increasing the
angle of the rotary inching valve’s lever causes the transmission pump to destroke.
If the vehicle includes a hydraulic power brake system, inching
can be realized cost effectively by using the Rexroth power
brake valve LT 31 with integrated inching function (see technical
data sheet RE 66 227). The function is similar to the version
with brake pressure inching valve described on the far left.
Rexroth Power
Brake Valve LT31
with integrated
inching function