50 Mobile 2003 Backhoe Loaders Bosch Rexroth AG

Application Center Backhoe Loaders

Head: Philippe Fillon

Bosch Rexroth AG
Mobile Hydraulics
91 bd. Irène Joliot Curie
69634 Vénissieux, France
Telephone: +33 (4) 78 78 - 52 47
Facsimile: +33 (4) 78 78 - 52 71
E-Mail: philippe.fillon@boschrexroth.fr
Bosch Rexroth AG Backhoe Loaders Mobile 2003 51

New Developments for Backhoe Loaders

The backhoe loader is an all-round

machine suitable for many different
applications. Employing a tractor as
its base, it unites the functions of an
excavator and a loader. Robust and
easy to operate as you would expect,
its hydraulic system is rated for medi-
um pressure.
As development of this machine type
has advanced, so too have the require-
ments and demands placed on it. To-
day, attention must be paid more than
ever before to efficiency and control-
lability. Besides, ergonomic operation,
fuel economy, reduced exhaust and
noise emission are expected. A satisf-
actory emergency operation is man-
datory. Figure 1: Backhoe loaders
These targets can only be achieved
with a modern hydraulic drive system.
The new option that are now available
1.1 Horse power control or
form even better systems, that cover
torque limiting
the whole range from basics to bench-
As long as a hydraulic pump without
mark performance.
power controlling device is conside-
red, the decision on the pump’s dis-
1. Power management placement is based on the corner po-
wer (power at maximum displace-
concepts ment and pressure) taken up. This
Only in few cases the power available corner power should not exceed po-
from the Diesel engine is sufficient to wer available from the diesel engine
drive the hydraulic pump used for the because otherwise the engine will
implements at full displacement Figure 2: Variable displacement pump stall. Not using all the power available
A10VSO74DFLR/31 with flow con-
against the maximum pressure level. instead results in insufficient machine
trol device
A variable displacement pump in con- performance.
junction with the adequate control of- The pump’s power controlling device
fers the possibility to manage the in- swash plate design for medium pres- restricts the torque taken up and en-
stalled power. Depending on the desi- sure levels, can be selected with diffe- ables installation of pumps regardless
red quality of control the commonly rent regulator options. of their corner power. This permits
applied A10VO axial piston pump in larger flows of oil at lower pressures

Authors:
Philippe Fillon BRFD
Detlef van Bracht BRM-AK/VMH3
Helmut Funk BRM-MC/EVL
52 Mobile 2003 Backhoe Loaders Bosch Rexroth AG

Pressure - better exhaust emission behavior, pressure drop in the control line as
p i.e. meeting the most stringent of soon as its opening pressure is attai-
emission standards ned, thus influencing the flow regula-
Eckleistung
Corner power – maximum handling convenience tor in such a way that the pump
swivels into position. Note, that once
- no overloading of diesel engine
the horse power control is active the
- no stalling of diesel engine flow regulator becomes a remote pres-
- machine easier to control sure controller. The flow rate is redu-
The A10VO standard horse power ced as the pump swivels into position,
Q (Vg) increasing the opening pressure (con-
control (DFLR, see also figure 4) li-
Flow
mits the pumps discharge pressure trol pressure) and thus keeping pump
Figure 3: Flow control allows a wide
depending on it’s displacement. The drive torque constant.
utilization of the available power
horse power control valve (or torque
limiter) is a pressure relief valve con- T ~ VG • p ⇒ P ~ T • n ~ Q • p = const.
nected to the swivel cradle via two sp-
rings. Its opening pressure is therefore 1.2 Dual horse power control or
governed by the position of the swivel dual torque limiting
cradle: When delivery from the It is in a backhoe loader’s nature to be
A10VO variable displacement pump used either as excavator or loader. Sin-
is low, opening pressure is high, when ce nearly all diesel engine power can
pump delivery is high, opening pres- be used for the implement hydraulic
sure is low. The valve is piloting the when excavating, but only partial die-
flow regulator (or in cases that flow sel engine power when loading - here
sharing (LUDV) blocks are used a se- the power basically has to be shared
Figure 4: Schematic of the A10VO DFLR between the transmission and imple-
parated regulator) and limits pressure
in the LS-line. Since the control oil is ment hydraulic -, the possibility to
delivered through a nozzle, the power shift between a high and a low setting
and smaller flows of oil at higher pres-
regulating valve is able to generate a is highly desirable (figure 5).
sures (see Figure 3), thus preventing
the diesel engine from being overloa-
ded or even stalled. This also produces
significant advantages in terms of ma- Torque
chine behavior: engine characteristic torque
available
– greater handling power as a result of high pump
setting
higher corner power
transmission
- faster working speeds through low pump
setting
higher oil flow rates
- higher forces through higher pump pump
pressures only

– better utilization of diesel engine

output low high engine
- greater fuel economy idle idle speed

- lower noise emission

Figure 5: Power distribution on the dual horse power control
Bosch Rexroth AG Backhoe Loaders Mobile 2003 53

– Excavation ⇒ implement hydraulic hoe loader. Whereas setting the stan-

only ⇒ high power setting dard power regulator demanded a
Loader Backhoe
– Loading ⇒ implement hydraulic compromise between excavator and
smaller larger loader operation, the advantages of
plus driving ⇒ low power setting orifice orifice
power control are now utilized to the
This capability is fairly easily achieved
full extent for both operating modes.
by the dual horse power control (figu- DFR1
Moreover, it is possible to adjust the
re 7). By utilizing the power control
power output setting to the particular
valves dependency on the rate of con-
diesel engine speed (diesel engine po-
trol oil flow it is possible to modify
wer output). This is, for example, wel-
the power output setting. Increasing
LR comed in residential areas where ma-
the rate at which control oil is deliver-
chines may only be operated at redu-
ed to the power control valve raises
ced speed for noise reasons.
pressure in the control line and incre-
ases the power output setting (also re-
Loader Backhoe
fer to section 1.1 Standard power con-
trol). Delivering a lower rate of cont-
rol oil flow will bring pressure down
and reduce the power output setting.
By feeding back the LS-pressure sig- DFR1
nals over different orifice sizes the
control oil flow can be influenced (wi-
thin limits). Using a
– Larger orifice ⇒ higher setting ⇒
Backhoe operation LR

– Smaller orifice ⇒ lower setting ⇒

Loader operation
Figure 5
dual horse power control is simply
and cost effective achieved.
In some loader operating conditions, Bagger
Backhoe
for example lifting the loader boom at p
machine standstill, or only to leave the
machine operator the last choice full
diesel engine power could be applied
to the implement hydraulic. For these
Lader
cases dual horse power control is avai- Loader
lable in the option as electrical
shiftable (figure 6 and 7).
Regardless, which type of dual horse
power control is used, the setting can Q
now be controlled inside limits, i.e. Figure 6: Dual horse power control allows
the A10 variable displacement pump adjusted working behavior
takes up the power available to it - to
meet the operating status of the back-
54 Mobile 2003 Backhoe Loaders Bosch Rexroth AG

1.3 Speed sensing power control Speed controlled diesel engines are
The latest development on cost effec- commonly used in backhoe loaders,
tive controls of the A10VO is the EK i.e. the drop of diesel engine speed re-
control electro-proportional displace- flects the load on it. Detecting the po-
ment control (figure 8). The pumps sition of the gas pedal or the stroke of
displacement is governed by an elec- the injection pump via an angle sensor
tric current applied to the controls so- WS equals the power available. Sen-
lenoid. It’s unique design is compact sing the actual diesel engine speed
and directly connected via a pilot (with sensor type ID) equals the load
spool to the pump’s displacement on the diesel engine. Both signals are
control cylinder. It acts like an adjus- Figure 9: Control unit RC2-2 compared and processed in a control
table maximum displacement stop. In unit (RC2-2) determining the utiliza-
case of total electric power loss the tion of the diesel engine power.
The diesel engine is overloaded if the
drop of engine speed is too high. In
X
this case, the control unit reduces the
solenoid current of the A10VO’s EK
controller bringing the pump to a
smaller displacement. This in turn re-
B duces the load on the diesel engine al-
lowing it to recover.
If the drop of diesel engine speed is
Figure 10: Variable displacement pump
A10VO EK.D with electro- too low, the diesel engine power is not
proportional flow regulation fully utilized. The control unit will in-
crease the solenoid current of the
pump will automatically return to A10VO’s EK control bringing the
S L1 L maximum displacement, ensuring oil pump to a larger displacement. This
flow to steering unit and braking devi- will increase the load on the diesel en-
1
ses - Fail Save! Combination with flow gine using all the power that is avai-
EK and pressure control are optional, al- lable.
lowing the use of LS- or flow sharing
pump swivel angle
α/αmax

(LUDV) mobile blocks. As the current

applied is determining the pumps ma-
ximum displacement, flow and pres-
sure control still can control the
pumps displacement from maximum
to minimum. This allows a speed-sen-
0
I/Imax 1 sing load limiting control (figure 11).
control current

Figure 8: Functional principle of the A10VOEK

Bosch Rexroth AG Backhoe Loaders Mobile 2003 55

The power taken up by the implement

hydraulic is automatically adjusted to
control unit
the power that is available regardless
RC2-2
what power is used by the gearbox
control block
(see also figure 12), whereas with SX14
(dual) horse power the controller set-
ting is always a compromise. Tests
have proven that therefore, especially
in loader operation, even a smaller si-
angle of rotation
zed pump with EK control can lead to WS
machine performance set out by a lar-
ger sized pump with (dual) horse po- speed sensor ID
wer control. Besides,
– automatic compensation of weak
diesel engines
- tolerances
- low idle
- high altitude operation
– automatic compensation of load ta-
variable displacement
ken up by other components, for diesel engine pump A10VO...EK.D./53
gear
example gear pumps, air conditio-
ning compressors, alternators, etc. Figure 11: Load limiting control
– programmable machine operation
modes
Torque

– diagnosis feature engine characteristic torque

available

become state of the art and all bene- transmission

fits of (dual) horse power controlled
pumps are further improved.
The new EK control of A10VO pumps
hydraulic
combines the strength of the electro-
nics (controlling) with the strength of
hydraulics (power transmission). It’s low high engine
unique and cost effective design and idle idle speed
the concept of speed sensing without
Figure 12: Power distribution with load limiting control
any electronic pressure transducer will
bring the power management in back-
hoe loaders into the next generation.
56 Mobile 2003 Backhoe Loaders Bosch Rexroth AG

2. A10VO flow control - constant displ. A10 variable displ.

pump /DFR
the link to flow sharing - p corner power p corner power
(LUDV), LS control
blocks
In addition to the capability to mana-
ge the power, the variable displace-
ment pump in conjunction with LS or
Q Q
flow sharing (LUDV) systems enables
to benefit fully from the advantages Figure 13: Flow regulated pumps (right) adjust their flow rate to the requirements in contrary
to fixed displacement pumps (left)
provided by the pumps flow control
over a fixed displacement pump. The
main difference between a system This produces the following direct ad-
with a flow-controlled variable displa- vantages for backhoe loaders:
cement pump and an otherwise iden- – better fuel economy
tical system with fixed-displacement
– lower operating costs
pump lies in the fact that a system
with flow-controlled variable adjust- – environmentally friendly
ment pump delivers just as much oil – lower cooling capacity requirement
as is required whereas in a system – smaller radiator
with fixed-displacement pump the – smaller tank and thus less fluid
flow of oil is governed by the pump
– exposure of fluid to lower tempera-
drive speed and pump size. In the lat-
tures
ter case, excess oil flow must be
– longer service life Figure 14: Flow regulated variable displace-
throttled back against pump pressure, ment pump A10VO DFR/52
resulting in high amounts of energy The enhanced utilization of primary
being lost in the form of heat (see fi- energy provides more power at partial
gure 13). load for the travel drive in loader
mode.
Flow control in pumps means:
Oil flow delivered = oil flow required
⇒ This means no energy is lost
through excess flows of oil.
Bosch Rexroth AG Backhoe Loaders Mobile 2003 57

3. Flow sharing (LUDV) professional operator who said ãthe Today with the flow sharing (LUDV)
machine is so easy to operate that no- giving to the backhoe loader a con-
technology body will need me anymore“. trollability comparable to modern ex-
The load sensing flow sharing Obviously this operator will still be cavators it is probably the opportunity
(LUDV) concept improves the stan- needed because the performances of to improve also the way the control is
dard Load sensing by giving to the sy- the machine being improved in such a made by using remote controls and
stem an independence to the load va- drastic way by the flow sharing locate them in the armrests of the
riations but also to the flow availabili- (LUDV) means that he will be able to seats to come closer to the excavators
ty. perform quicker and better. ergonomy.
This possibility is obviously a break There are two main possibilities to
through in the attempt to make the What are the next improvements that control a valve with remote controls :
machines more user friendly and operators will expect from their ma- – hydraulic controls
more performant. chines ? – electronic controls
The other field of improvement is the
Since 1997 thousands of machines ergonomy and the comfort; at that
The choice between these two techno-
equipped with the flow sharing point it is interesting to consider what
logies depends on many factors. These
(LUDV) device of the SX14 have been other machines are competing against
are among others:
delivered to the market. The best the back hoe loaders.
– costs packaging
compliment we’ve had was given by a The 7 tons wheeled excavator in com-
bination with a small /medium loader – space available to run pipes
is probably the classic alternative to a – remote controls as option or serie
backhoe loader, if one looks at the – type of functions to be controlled
controls used on those machines, it – number of functions to be cont-
will be very obvious that in the com- rolled
fort and ergonomical department the
Since its creation the SX14 our flow
backhoe is still lacking a little bit of it,
sharing (LUDV) valve was available
with its long, out of reach, huge dis-
with mechanical and hydraulic con-
placement levers, it is certainly not the
trols. In the meantime it is available as
best reference as far as operators com-
well with electronic control.
Figure 15: Flow sharing control block SX14 fort is concerned.
The today’s controls of the backhoe
loaders are an heritage of what the
machine was in the past : a tractor to
which some attachments were added
later on. The levers directly mounted
on the valves were in this respect the
best and probably only solution .
Also because of the lack of controlla-
bility and the impossibility to perform
several movements simultaneously
there was little improvement to be ex-
Figure 16: Cross sectional view across one pected by only changing the type of Figure 17: Flow sharing control block SX14
section of the control block SX14 control. with electronic pilot control
58 Mobile 2003 Backhoe Loaders Bosch Rexroth AG

4. Joysticks-control - 4THF5 for light duty (see data sheet:

RE64557) with electric detents for
With regards to the joysticks Rexroth
float & return to dig on the loader
has in its range all necessary joysticks
side.
in hydraulic or in electronic version:

In hydraulic version :
– 4TH6 for heavy duty applications
– 4TH5 for light duty applications for
the excavator operation (RE 64555)
Figure 23: Joystick EC4000 with up to 3 pro-
portional and up to 9 switch out-
puts

Figure 21: Joystick 4THF5 Because a joystick can only control 2

axis and the backhoe loader control
In electronic version : requires a minimum of 5 proportio-
The THE5 family (see data sheet nal functions : Boom, arm, bucket,
RE 29881). slew, telescopic, Rexroth has created
Figure 18: Joystick 4TH6
– 4THE5 power control joystick the EC4000 handle that provides 3
proportional electrical roller or up to
– 4THES5 signal joystick
9 on off switches, this handle is avai-
– 4THEC5 CAN bus signal joystick lable on any of the Rexroth joysticks
hydraulic or electronic version.

As said previously there are basically

two main solutions for remote cont-
rol. In addition, there are many pos-
sible combinations between all types
Figure 19: Joystick 4TH5
of controls (mechanical, hydraulic,
electrical on/off, electrical proportio-
– 4THF6 for heavy duty (see data
nal) which allow individual solutions
sheet: RE 64553)
of the vehicle designer.
Figure 22: Joystick 4THES5, THE5, THEC5

Figure 20: Joystick 4THF6

Bosch Rexroth AG Backhoe Loaders Mobile 2003 59

5. Steering units
Today in backhoe loaders hydrostatic
steering units of types Open Center -
Non Reaction or Closed Center - Non
Reaction are used. These components
represent from a system point of view
the best technical solution to the re-
quirements for „steering“.
High axial loads and the dynamic
operating conditions for backhoe loa-
ders lead to a requirement for corres-
pondingly high control pressures. For
backhoe loaders there are also stan-
dards and guidelines governing the
ability to steer the machine - also re-
quirements for emergency steering Figure 24: Power steering units from BRM-MC product segment
with the power steering unit functio-
ning as hand pump.
P
So as to fulfill the requirements it can
be necessary to that the power stee- advanteges
ring units be fitted that have reduced – better control performance
effectiveness ratio for emergency use. caused in optimized control
edges and special dumping
Our LAGU power steering units with – especialy for using with
chamber switch-off and LAGZ power LD
A10VO
steering units with rotor set switch-off tech. datas
have been developed for these appli- – pressure control delta-p: 7 or
10 bar
cation requirements. – Flow range: till 160 l/min
In servo operation the LAGU and – Pressure range: 250 bar
LAGZ units operate indistinguishably
from other power steering units. EF CF
In emergency operation however the Figure 25: Priority valve LPS - series 11: LPS 160R11/LD...
volume delivered is automatically re-
duced. This causes the effort on the
steering wheel to be reduced by ap- hout steering sensors and signal con- connected at the priority valves, and
prox. 50% compared to the well- nections. those can be given lower rankings.
known conventional power steering Such following consumers could be:
unit. The supply to closed center – power - Operating functions with pressures
steering units is provided by a fixed or up to 250 bar
As well as power steering units, Rex- variable displacement pump through - Power assisted braking, trailer brake
roth also supplies auxiliary individual a priority valve. The priority valve valves
components for equipping power provides supply to the power steering
- Fan drive
steering circuits. This includes priori- unit on an as-needed basis, since it is
activated by the LS signal. - Control oil supply
ty valves in variety of liter capacities,
Further hydraulic consumers can be - Infeed functions
and steering columns with and wit-
60 Mobile 2003 Backhoe Loaders Bosch Rexroth AG

The 160 liter priority valves are opti- ons, which are available now, will not
mized in respect of their control be- only further improve efficiency and
havior in use with variable pumps at controllability but also opens new op-
the control edges and in the damping portunities for future backhoe
of the control piston. loaders.
Where necessary this is also available
for smaller priority valves. The power management concept of
As well as valves for fitting into the pi- speed sensing based on an electro-
pework, Rexroth also offers priority proportional displacement controlled
valves for up to 80 l/min nominal vo- A10VO EK guarantees optimum die-
lume flow for attachment to either sel engine power utilization at any
power steering units or to gear time without overloading or stalling.
pumps. In conjunction with SX14 flow sha-
ring (LUDV) technology the full hy-
draulic power can be controlled at
operator’s convenience enabling him
to operate the backhoe loader even
Figure 27: Alternative steering system better and quicker.

The next improvements allowed by

of a modular system concept for the flow sharing (LUDV) are : the
equipping the most diverse variety of increase of speed and the improve-
Figure 26: Steering column - ment of the ergonomy, there are also
vehicles with alternative steering sys-
type LAB with sensor
tems. some possibilities to make simpler,
Applicable regulations for steering more cost effective and more flexible
The standard steering columns are equipment, such as ECE-R79, are in- option controls. Flow sharing (LUDV)
also part of our accessories range. At corporated into the development. technology also offers the possibility
this point we would like to mention In this we aim at improvements in er- of dispensing with a priority valve in
our steering sensors. They deliver a gonomics and convenience, which in hydrostatic steering systems, provided
digital signal and an analog signal. the end will lead to higher loading ra- that the maximum operating pressure
Rotation direction sensing is contai- tes and to reduced strain on the driver. of the implement hydraulics does not
ned in the next development step and exceed the maximum operating pres-
at that time will be tested in functio- sure of the steering system.
nal samples. 6. Summary At the end of the day, decision upon
Based on proven technology - steering the hydraulic system will be based on
The objective is to offer the steering unit LAG, flow sharing (LUDV) block cost of products compared to the ope-
sensor in future in alternative steering SX 14, joy sticks 4 TH, variable displa- rating cost and performance.
systems. cement pump A10VO -Rexroth can Optimum machine utilization keeps
offer a large variety of products to be operating costs down, also making
In the figure 27 you can see the con- used in backhoe loaders. These pro- this system an attractive option com-
cept of external volume flow amplifi- ducts are under constant development pared with the costs of the technically
cation by the power steering unit as to adapt the hydraulics components inferior fixed displacement pump sy-
an example of an alternative steering even better for the optimum utilizati- stem.
system. It is part of the development on in backhoe loaders. The new opti-
Bosch Rexroth AG Backhoe Loaders Mobile 2003 61