Modular LS Valves

Modular LS Valves

Contents To start the presentation, I would like to provide nal section flow rates of 85 l/min (M4-15 up to 150
you with an overview of the whole product con- l/min). The M4-12 provides all the essential func-
struction kit for the new M4-12 valve series com- tionality of the directional valve section familiar
0. Introduction
prising the inlet and end elements and also the from the size 15, complemented by the appropri-
1. M4-12 integrated valve concept
individual sandwich sections with the various ac- ate input and output elements, but is a completely
2. M4-12 valve section
tuation systems. This will be followed by a detailed new and independent design.
2.1 Design and function
review of the functional design and the character- The modular principle focuses on function units for
2.2 Valve Characteristics
istics of the M4-12 valve section. The information valve actuation which can be used for both sizes
3. Series M4 valve actuation controls
provided will then focus on the various valve ac- 12 and 15:
3.1 Electro-hydraulic pilot module
tuating systems (mechanical, hydraulic and electro- • The mechanical override manual actuation
3.2 Manual Valve Operation
hydraulic) with particular emphasis on the electro- system is available as both a directly
4. Electro-hydraulic LUDV
hydraulic pilot module. All the actuation units are connected and automatically latching/
5. Fazit
designed for adaptation to both nominal sizes, delatching unit.
namely the M4-12 and M4-15. Using the appli- • A die-cast aluminium cover is provided on
0. Introduction cation example „Electro-hydraulic LUDV“, the one side for the hydraulic actuation control.
LS sandwich valves have become extremely impor- presentation will conclude with an assessment of This is manufactured from the same blank as
tant in mobile hydraulics in terms of the large the technical features and benefits which accrue the electro-hydraulic cover and features an
number of applications which they cover and the from effectively applying electro-hydraulic systems. identical connection pattern for the valve
volumes sold each year. The applications extend section.
from those for which large numbers of units are
required, such as truck mounted cranes, tele-
1. M4-12 integrated valve concept • The electro-hydraulic actuation control unit
(„pilot module“), also provided on one side,
The new M4-12 LS sandwich valve series, a high-
handlers, backhoe-loaders etc., to special mobile is available both with and without integrated
pressure design (up to 420 bar), complements the
machines which are manufactured in very small electronics, and also a number of further
already existent series M4-15 at the lower end of
numbers. The requirements resulting from this application-specific options.
the capacity spectrum, and is designed for nomi-
spectrum with regard to the target costs which
have to be achieved on the one hand, and, on the
other, the wide range of functions that have to be
catered for, can only be reconciled on the basis of
a cogent integrated concept for the product. The
required approach consists of clearly defining the
market position with defined target applications
and functions, a modular design concept devel-
oped on this basis and a correspondingly derived
structure for product manufacturing and logistics.
The following paper is limited to a technical ap-
praisal of the new M4 family of LS valves. It de-
scribes the newly developed basic concept and also
the design features of the essential function units.
This new M4 family is, in fact, made up of the
standard M4-15 valve size currently in production
and earmarked for future modification, combined
with a completely newly developed M4-12 size.
Dr. Christoph Latour,
Rexroth Hydraulics
Lohr
Phone +49 (0) 93 52 18-38 89
Fax +49 (0) 93 52 18-29 16 Fig. 1: M4-12 valve concept
E-mail: christoph.latour@rexroth.de

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Detailed information regarding the actuation con-

trols is provided in section 3 of this paper.

In addition, the two nominal sizes 12 and 15 can

be adapted to one another in a block via a central
inlet element.
The designs already developed and those at the plan-
ning stage together form a modular valve family.

Fig. 1 provides a summary of the overall concept

for the M4-12, showing the main functional units
(input elements OC/CC, valve sections with the
various actuation controls and end cover).

2. M4-12 valve section

Fig. 2: Main cross section through valve section M4-12
2.1 Design and function
The M4-12 section shown in Fig. 2 essentially con-
tains all the functions usually found in LS valves, H = 110 mm x L = 125 mm x W = 46 mm. esis components in the pilot valve, and the me-
but has been completely redesigned in relation to Through the employment of ductile cast iron chanical friction components of the section,
the arrangement and design of the various com- (GGG 50), the maximum working pressures amounts to approx. 4 l/min. This control quality is
ponents: lie at pP = 350 bar and pA/B = 420 bar. sufficient for many mobile hydraulic applications,
The steady-state volume flow signal characteris- but the valve hysteresis can be further improved
• The hydraulic, mechanical and electro- tic produced with barometric, electro-hydraulic by the position control system for the main spool
hydraulic actuation control kits are described actuation control as shown in Fig. 3 indicates the which is likewise incorporated in the actuation
in detail in section 3 of this paper. control quality of the valve. control concept.
• The secondary valves employed take the form A further criterion governing the control quality of
of direct-acting shock anti-cavitation valves Electrical power output modulation is performed the valve is the pressure compensator character-
which are provided with a fixed, non- on the basis of a PWM signal with a clock rate of istic which indicates the influence of changing
adjustable pressure setting. The advantage of approx. 150 Hz. In the case of the standard spool pump ∆p values with a fixed command value in-
these valves compared with pilot-controlled indicated here with a rated volume flow of put, such as occur with parallel operation of vari-
versions lies in their extremely compact 85 l/min (∆p = 10.5 bar), a metering orifice ∆p of ous sections (Fig. 4).
construction. There is also an improvement in 9 bar produces a maximum volume flow of 72 l/min,
the accessibility and interchangeability of the while a metering orifice ∆p of 12 bar produces With the current configuration of the M4-12, there
secondary valves thanks to the radial position 100 l/min. The electrical control range lies between is a maximum volume flow deviation of approx.
of the pressure port and the axial position of 0.4 and 0.73 A. The maximum hysteresis which oc- 0.03 l/min/bar. This means that, in the parallel
the tank port. curs, comprising magnetic and mechanical hyster- mode, any change in the pump ∆p produces a
• The diameters of the pressure compensator
and the main spool are identical as compared
with the M4-15 and the M4-12 design
provides the same arrangement with springs
at both spool ends. The pressure differential
at the metering orifice of the main spool can,
as is also the case with the M4-15, be varied
between 9, 10.5 and 12 bar using a
maximum of 2 adjustment washers which can
be inserted at the pressure compensator
spring.
• The LS pressure reducing valves have been
simplified in terms of their mechanical design.
• As a result of the modified arrangement of
the components in the sandwich valve
section, the unit offers excellent overall
compactness, with a rated volume flow of
85 l/min accommodated within dimensions of
Fig. 3: Volume flow/signal characteristic M4-12

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variation of approx. 3 l/min of the section volume trols take on particular significance. The constantly chambers of the main spool. As this system
flow per 100 bar at the maximum valve actuation growing interest in electro-hydraulic actuation has no position balancing, the positioning of
position. In order to achieve such a small volume controls in particular, with its range of options, the main spool always requires a closed-loop
flow deviation, the flow forces which occur at the means that a clearly structured and modular ac- position control circuit which, in the case of
pressure compensator spool under the high hy- tuation control concept is imperative. valves of this type, is implemented in the form
draulic power levels involved must be reduced by of an integrated electronic control together
geometric shape optimisation of the pressure com- 3.1 Electro-hydraulic pilot module with the power supply system for the on/off
pensator spool. valves.
The development work begins with the need to
• In the case of Variant 2, the four pulse-
define the most suitable functional principle for the
modulated on/off valves are replaced by a
electro-hydraulic actuator. As summarised in Fig. 5,
3. Valve actuation controls there are currently three basic types of electro-hy-
proportional-action 4/3 directional throttle
valve. In the case of this type, too, a closed-
for the M4 series draulic actuation and pilot control which have be-
loop control circuit is required for the main
come established in mobile hydraulic applications.
When it comes to covering the wide range of ap- spool, and this again is incorporated in an
plications mentioned at the beginning while at the integrated electronic control system.
• In the case of Variant 1, four pulse-modulated
same time complying with the predetermined cost • In the case of the barometric pilot control
2/2-way on/off valves are arranged in a
objectives, the selected functional principles and system with two pressure reducing valves,
Wheatstone bridge and, with each switching
the mechanical design of the valve actuating con- which for example may take the form of
cycle, meter an oil volume into the pilot oil
separate screw-in cartridge valves, the
generated pilot pressure acts directly against
the correspondingly dimensioned springs of
the main spool, so offering the possibility of
proportional positioning without the need of
closed-loop position control.
A general advantage of the barometric pilot con-
trol system as compared with the closed-loop po-
sition-controlled variant lies in the fact that an
integrated electronic system with closed-loop po-
sition control and/or position monitoring only has
to be provided if the functionalities of the inte-
grated electronics (e.g. CAN bus link, user-pro-
grammable functions etc.) are also actually used
in the application.
In addition, the stand-alone barometric pilot con-
trol units can be adapted at relatively low cost to
other valve series. In the case of the pilot modules
Fig. 4: Pressure compensator characteristic, M4-12 with closed-loop position control, this is extremely
expensive owing to the large number of predefined
interfaces.
For the reasons mentioned, the new modular con-
cept of the electro-hydraulic pilot module for the
entire M4 valve family has been based on pressure
reducing valve technology.
The functionalities summarised in Fig. 6 can be il-
lustrated on the basis of the overall module de-
sign:
• The on/off and proportional options are
available in the form of various connector and
power supply versions for pure electro-
hydraulic actuation control without integrated
electronics.
• In addition, an integrated electronic control
with CAN bus, PWM or voltage input can be
selected for the proportional pilot control,
whereby this variant is again available with or
Fig. 5: Types of electro-hydraulic actuation control without a position sensor for the main spool.

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• With an integrated position sensor, the range With conventional wiring of a mixed analogue/ The disadvantages in terms of expenditure and
of options available increases to include that digital system, all the system components such as possible malfunction can be significantly mini-
of a pure closed-loop position control circuit the electrical command unit, sensors and the pi- mised with a system solution involving an inte-
for improving the transfer properties of the lot valves of the control block, are each connected grated CAN bus-capable valve electronics module
valve, zero position monitoring of the main by individual wires to the controller, which in this and individual components with a CAN interface
spool for safety-relevant functions, or both case also contains the drivers for the pilot valves. (Fig. 9). With the daisy chain wiring system of the
options combined. On the one hand, the amount of wiring required control block, only one cable is required for the
as a result is very high, and on the other the dan- power supply and CAN bus interconnection of the
Fig. 7 provides an overview of the functional and ger of wire damage and/or contact faults at the entire control block. All the information and the
mechanical design of the pilot module with its large number of plug-in connectors is considerable. requisite electrical power are transmitted from
most important functional units: section to section, and the need for complicated
individual wires leading to and from the pilot valve
• The so-called multi-cover for mounting and is eliminated.
modifying the two pilot valves, the position
sensor and the electronics enclosure takes the
form of a die-cast aluminium component. All
the machining variants for the options
mentioned, and also for the hydraulic
actuation control system, are applied to one
and the same blank.
• The established standard units MH-DRE2 and
-WE2 serve as the pilot valves.
• An LVDT sensor is used for position measur-
ing, with actuation control and evaluation
(oscillator/demodulator) being performed
with the aid of digital electronics.
• The digital on-board electronics is based on
16-bit technology and feature a flash
program memory and also an EEPROM for
storing the parameters. As a result, the
electronics can be freely programmed and
parameterised via a CAN bus or an RS232
interface. In addition, the electronic control
contains the driver output stages for
actuation of the pilot valves with pure pulse
width modulation. Fig. 6: Functions of the electro-hydraulic pilot module
• The module housing is split in two and
consists of a GRP injection moulding for
covering the pilot valves. This cover also
serves as the mounting element for the actual
electronics cover in which the PCBs are
integrated. Per module there is a total of 2
AMP Super-Seal plug-in connectors, with 4
and 5 pins respectively. The reason for
providing 2 connectors per electronics
module lies in the fact that, with CAN bus
actuation control, the so-called „daisy chain“
wiring system was selected with which the
CAN bus line can be wired from section to
section (as a „chain“).
The advantages of the daisy chain wiring system
are explained in the next two figures (Fig. 8 and
Fig. 9).

Fig. 7: Electro-hydraulic pilot module

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To summarise, it can be said that, with the exist-

ing design of the electro-hydraulic pilot module for
the M4 valve family, a large number of application-
specific functions can be provided.

3.2 Manual lever operation

Aside from the electro-hydraulic valve actuation
control unit, there is also a mechanical system with
a manual lever available in two versions which can
likewise be adapted to the two sizes of M4-12 and
15. Version 1 is the so-called latch/delatch lever
in which the mechanical connection between the
valve main spool and the manual lever is gener-
ated by a clutch device if the main spool is being
hydraulically or electro-hydraulically actuated. The
advantage of this is that, compared with the fixed-
Fig. 8: Wiring for a mixed analogue/digital system connection versions, the valve hysteresis is reduced
and, when the spool is actuated or displaced, the
lever cannot be used to override the position.
In the permanently connected version 2, the clutch
assembly is replaced by a positive mechanical lock-
ing arrangement between the lever and spool.

Both variants are provided in the same housing

and feature the same lever assemblies (die-cast
aluminium). Aside from the mechanism described,
there is also a stroke limiting device either at one
or both ends (with integrated electronics: on the
A side) incorporated in the manual lever housing.

Fig. 9: Valve block with CAN bus pilot module and daisy chain wiring

Fig. 10: Manual lever actuation, M4-12 & 15

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4. Electronic LUDV
The function of load pressure-independent flow
distribution (LUDV), the purpose of which is to
prevent an under-saturated system with high load-
pressure service motions coming to a standstill, is
required in many applications in which motions are
frequently performed simultaneously. The current
state of the art takes the form of hydraulic LUDV
control blocks featuring a special circuit compris-
ing a pressure compensator and metering orifice
for performing this operation by purely hydraulic
means. The function-related disadvantages of this
system are that (1) due to the principle involved,
there is no individual LS pressure cut-off function
per valve axis, and (2) as the system undergoes
under-saturation and then recovers, the motions
are initially decelerated, and then re-accelerated,
at a ratio which cannot be influenced. Moreover,
in purely hydraulic LUDV systems, the pressure Fig. 11: Electronic LUDV (saturated system)
differentials at the pressure compensator spools
decrease significantly under high levels of starva-
tion, so that flow distribution using the LUDV prin-
ciple - below an under-saturation point 25% -
stops operating reliably owing to the increasing
influence brought to bear by interference phenom-
ena such as spring and flow forces.
One possibility of avoiding these functional impair-
ments lies in combining an electronic LUDV with
an electro-hydraulic LS valve (Figs. 11 and 12).

Here, a variable reflecting the maximum volume

flow which can be delivered by the pump (e.g.
obtained by measurement of the engine speed) is
compared with the total volume flow delivered by
the sections (command value signals of the valve
sections) in a controller. If this sum is greater than
the maximum possible pump flow rate, the system
is in a state of under-saturation and the individual
Fig. 12: Electronic LUDV (under-saturated system)
command value signals of the valves are reduced.
Overall, this reduction of the individually de-
manded section flow rates ensures avoidance of
system under-saturation as viewed in the physical
sense. The full pump ∆p remains available!
The individual ratio with which the individual sec-
tion flows are reduced or returned to the satura-
tion condition is freely selectable with such a sys-
tem. Fig. 13 provides a typical overview of the
possibilities for individual flow reduction taking the
example of two sections which, for the sake of sim-
plicity, both deliver the same volume flows.

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The simplest case is that both sections are reduced

at the same ratio in proportion to the degree of
under-saturation, as is the case with hydraulic
LUDV systems. If, however, certain functions are to
receive a 100% priority, the possibility exists of only
reducing the less important actuators down to-
wards zero flow. As the degree of under-satura-
tion increases, the flow serving the priority actua-
tor is also then automatically reduced. In the last
shown case, each individual actuator is reduced at
an individual ratio (here: 0.5 x for section 1, and
2 x for section 2), and then subsequently a maxi-
mum value is defined for flow reduction of one
section (e.g. not below 25% for section 2).

All in all, the possibilities of individual and section-

dependent reduction and increase in flow are un-
limited.

5. Summary
Fig. 13: Individual flow reduction with an electronic LUDV system Due to the extension of valve series M4-15 by the
new size M4-12, a new M4 valve family has been
created, which, in conjunction with the modular
valve actuation system that can be adapted to both
sizes, features a high degree of functional
modularity.

Especially the new electro-hydraulic pilot module

is suitable for realising solutions that are tailored
to specific applications.

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