Mobile2012.pdf

6 Mobile 2012 | Updated Solutions for Compact Excavators Bosch Rexroth AG

efficient and innovative Components for better Use of installed energy

Energy efficiency implies an increase in the productivity of mobile working machines. The basic requirements here are the reduction of power loss and the optimization of components in the hydraulic system in terms of their efficiency.

By introducing new components and working with existing components in an innovative way, it is possible to meet market requirements and customer demands that center on the improved use of installed energy, a reduction in fuel consumption, and greater overall vehicle functionality.

In the context of this topic, Bosch Rexroth presents innovative solutions with new model series while continuing to develop its existing product range in all respects.

Updated Solutions for Compact Excavators | Mobile 2012 7Bosch Rexroth AG

A boost in Productivity – Updated Solutions for Compact excavators

AbstractIt is becoming increasingly important to achieve optimum productivity in mobile applications. Especially for compact excavators (mini and midi excavators), it is crucial to make the best use of available power by keeping the hydraulics simple. Furthermore, end users tend to place exacting demands on the maneuverability and multi-purpose functions of their machines.In this context, Bosch Rexroth proposes updated flow sharing (LUDV) technology that both boosts machine productivity and enhances fine control and precision performance. With redeveloped products based on proven solutions and with 20 years of experience in the field, the company presents a new range of systems in response to the latest market requirements.

Gilles ChetailSales and Industry Sector Management Construction Machinery


Single flow sharing (lUDV) system The increasing popularity of compact excavators (mini and midi excavators) has led to a strong demand for these machines around the world. The number of machines equipped with a closed center “flow sharing” hydraulic system has also risen in recent years, especially due to the flexible ability of this technology to meet individual customer requirements, such as:

▶ Improved control and precision

▶ Better use of available engine power

▶ Compatibility with various attachments

▶ Reduced costs thanks to a simplified hydraulic circuit

Fig. 1: Compact excavator

MCR Slew Drive

GFT + A10VT Travel Drive

MHSTE Pilot Oil Supply

TH6 Command Units

RS12 Control Block

A7VO Travel Drive and Implement Hydraulic

Fig. 2: Hydraulic circuit


Bosch Rexroth was one of the first hydraulics manufactu-rers to develop and introduce this concept for compact excavators, which today enjoys great success. The soluti-on comprises a single variable pump with power control-ler and load sensing control valve with an anti-saturation function / post-compensated flow sharing (Fig. 2).

The newly updated flow sharing (LUDV) system combines the new RS12 control block – the successor to the SX12 – and a redesigned version of the proven A7VO variable pump. It offers outstanding improvement to the producti-vity of compact excavators.The revised system solution is a response to new challenges and offers:

▶ Greater productivity

▶ Reduced fuel consumption

▶ Improved operating feeling

▶ Easy control

A7Vo variable pump

The A7VO variable pump of bent-axis design (Fig. 3), available in a high-pressure version, allows a greater supply flow to the main block with same installed power.

The design of the A7VO rotary group boosts volumetric efficiency. Furthermore, the large displacement angle compared to the swashplate design provides greater efficiency for pressure levels in situations where working conditions present challenging power management requi-rements, for example digging out trenches and turning.

Optional features (Fig. 4) such as a variable margin (dif-ferential pressure setting) will be available for managing optimal flow control in relation to engine speed (the wide range of fine control for working speed is maintained independent of the engine speed), as well as powershift function (the power curve is shifted depending on the engine speed).

For compact excavators, the A7VO pump is available from 28 to 160 cm3/rev and is well suited for pressure levels of up to 350 bar. The compact pump includes a robust bearing system with a long service lifetime.

Fig. 3: A7VO variable pump

Lever Stroke

nmax

nreduced

Flow

Flow

Pres

sure

Fig. 4: Variable margin and powershift features


RS12 flow sharing (lUDV) control block

The new RS12 control block (Fig. 5) also contributes to greater efficiency thanks to the new layout of internal channels, which reduces the drop in pressure both from the P line to user ports and from user ports to the T channel. As for the SX12, the flow control in the RS12 directional block makes the machine easier to control by maintaining parameters within an optimum range independently of load pressure and ensuring the flow distribution requested by the operator no matter what combination of machine movements is being performed (Fig. 6 and 7). The four-way control system based on the closed center principle allows an even faster optimization of the control parameters of each directional valve spool when compared to conventional six-way valves. This shortens the development time for new machine models and simplifies system coordination considerably. With the help of flow sharing (LUDV), the manufacturer can also set different velocities for each actuator axis and direction of movement. In this way, better matching of the working cycle can be achieved.

Moreover, the manufacturer gains a much greater degree of flexibility for realizing additional functions, such as rotating grapple and angle blade, because the system permits the addition of a second or third auxiliary section to the circuit without an additional pump, as is required for multi-pump open center systems.

Fig. 5: RS12 main control block

Fine control

Fig. 6: Fine control

Consumer I QSoll = 80.0 L/min QRed = 61.5 L/min RATIO = 0.77

Consumer II QSoll = 50.0 L/min QRed = 38.5 L/min RATIO = 0.77

Pump Qmax = 100 L/min

Consumer I

QSoll = 80,0 l/minQRed = 61,5 l/minRATIO = 0,77

Consumer II

QSoll = 50,0 l/minQRed = 38,5 l/minRATIO = 0,77

Pump

Qmax = 100 l/min

80 60 40 20

100 80 60 40 20

80 60 40 20

Q

t

t

t

Q

Q

Fig. 7: Proportional flow sharing


Another key benefit is that the one-pump circuit allows component rationalization. The valve contains a single inlet element, and the summation power control pump regula-tor used in multi-pump circuits is replaced with a simple power control regulator, reducing the amount of pipework needed. This reduces the number of components and assembly costs.

Both the A7VO pump and RS12 control block are designed for high-pressure systems and are robust products that can be adapted to meet possibly higher pressure level requi-rements in the future. Together, they form the basis of the best system to drive and control compact excavators with greater efficiency and enhanced maneuverability.

Greater productivityThe major challenge for excavator control systems in terms of simultaneous movements is to manage the distribution of hydraulic power in the most effective way in order to avoid unexpected speed changes and drops in torque, and to maintain the optimal dynamic behavior for the machine.

It is necessary to strike the right balance between control-lability, performance, and energy efficiency. With the new system consisting of the A7VO pump and RS12 control block, Bosch Rexroth is able to provide greater efficiency while maintaining the same level of installed engine power and without compromising the performance of fine controls – indeed, performance is even better thanks to the new and improved RS12 block, as mentioned above.

In one of the first 6.5 t compact excavators to be fitted with this sytem, output power of the pump which is available for the hydraulic system was compared on current serial machine equiped with pump of swashplate design and then with A7VO pump of bent axis design. This comparison is based on same engine power with pump input power set at 32.6 KW in both cases (Fig. 8).

180

165

150

135

120

105

90

75

60

45

3060 80 100 120 140 160 180 200 220 240 250

Pressure [bar]

Flow

[L/m

in]

Input power 32.6 kW

Output power / Current 24.5 kW à 2250 rpm

Output power / New 27.3 kW à 2250 rpm

Fig. 8: Comparison of pump output power


MCR-X slew drive

On compact excavators in particular, the slew gear drive plays a decisive role in operator acceptance. Bosch Rexroth offers a low-speed, high-torque, radial piston motor of type MCR-X (160 to 820 cm3/rev) with an integrated valve block, which is designed to meet the requirements of compact excavators weighing 3 to 8 t (Fig. 10). The motor, complete with shockless cross-port relief, anti-cavitation and brake-delay valves, is supplied with an integrated multi-disc brake (Fig. 9).

The shockless cross-port relief valves limit and control the increase in pressure and prevent excessive changes in acceleration, thus preventing the machine operator from feeling any shocks; they also extend gear life (Fig. 9).

The MCR-X motor offers smooth running at low velocities thanks to improved and more intuitive proportionality, insignificant backlash, more compact installation, low operating noise in the cabin, and high pressure capability with very good volumetric and mechanical efficiency.

Furthermore, the combination of the MCR-X and the new RS12 control block boosts efficiency, especially during

fine control operation with optimized valve adjustment to manage lower meter-out pressures. Improved slew control can also be achieved thanks to the enhanced anti-cavitation performance of the new cartridge valves of RS12 main block.

The MCR-X radial piston motor represents an alternative solution to the slew drives currently used on the market, and it is also an additional possibility as part of the Rex-roth product range. It represents an optimized solution for the system controlled by the flow sharing (LUDV) technology.

Pres

sure

pre

lief

Time t

t1

L

M

A

B

X1

X2

Z

F

Fig. 9: MCR-X schematic and pressure-relief valve characteristics Fig. 10: MCR5-X slew drive motor


The Rexroth system In order to maximize the performance of machines, Bosch Rexroth provides a full range of hydraulic products that cover compact excavators weighing up to 12 t.

The 4TH5 and 4TH6N joysticks (Fig. 11), adapted for compact excavators are very successful in the market. A reduction in both operating effort and variation during lever inclination improves working conditions and driver comfort. The handgrip with integrated slider meets the high demands for ergonomic operation of auxiliary functions.

The new EC1500 handgrip (Fig. 14) completes the range and is a response to the need for a thinner shape, as expressed in Asian markets.

For the travel function, the 4TH5NR and 4TH6NR range of foot pedal controllers (Fig. 12) with integrated lever damping is an additional improvement to driving comfort. This function softens any rough operation of the levers and helps to prevent oscillations when switching back to neutral position.

The 2TH6L blade controller (Fig. 13) is now available with float position and mechanical detent features in line with the market evolution from mechanical to hydraulic opera-tion. It is also possible to install other types of handgrips from the Rexroth range, meaning that there is added flexibility for the inclusion of angle blade control.

Fig. 11: Joystick Fig. 12: Travel controller Fig. 13: Blade controller

Fig. 14: EC1500 handgrip


For some cases in which the traditional open center hydraulic system has been maintained, Bosch Rexroth can provide the AP2D double pump of swashplate design (Fig. 15); this is available for compact excavators weig-hing approximately 5 to 10 t.

The main features of AP2D are as follows:

▶ Integrated power controller with power override via third gear pump pressure

▶ Short length

▶ Optional flanged-mounted gear pump for third loop and pilot pump with a common suction port

▶ Integrated pilot oil unit with two solenoids (optional)

▶ Power override via pilot pressure (optional)

The GFT 2120 travel drive (Fig. 16) is a combination of an ultra-compact two-stage planetary gear drive with a medium-pressure hydraulic motor, available for the 7 to 10 t weight class. It is characterized by remarkable compactness and completes the product range for com-pact excavators.

The main features are as follows:

▶ Compact, space-saving two-stage planetary construction

▶ Robust bearings

▶ Integral medium-pressure hydraulic dual displacement motors

▶ Counterbalance valve and secondary relief valve integ-rated into the motor plate

▶ Integrated multi-disc parking brake

▶ High starting efficiency

▶ Easy assembly

▶ Simple oil change

▶ Low-noise running

Fig. 15: AP2D double pump

Fig. 16: GFT 2120 travel drive


The GFB 2120, the associated slew drive (Fig. 17) for the same excavator weight class (7 to 10 t), also offers remar-kable characteristics:

▶ Two-stage planetary drive with one-piece forged out-put shaft/pinion

▶ Swashplate hydraulic slew motor with integrated negative mechanical multi-disc parking brake

▶ Shockless pressure-relief valves that provide quick acceleration and smooth braking performance

▶ Anti-reaction valves integrated into the motor port plate as standard to prevent upper carriage from swinging back during braking operations

▶ Smooth and quiet operation

The AVBC series check and metering valves (Fig. 18) are the result of a close and long-standing collaboration with many major manufacturers of earth-moving equipment. These valves are used as components of lowering control devices in machines intended for object handling and are subject to the requirements of ISO 8643.

Calibration of the valve opening parameters via the main control valve is an important point in terms of compliance with ISO norms and the optimization of machine per-formance. In this sense, we are able to offer a variety of existing solutions in addition to tailored solutions for each machine.

Bosch Rexroth is a one-stop shop for components that are highly compatible with each other, offering its customers additional support in the design of machine applications.

Fig. 17: GFB 2120 slew drive Fig. 18: Check and metering valve


SummaryIncreasing market and customer requirements regarding the productivity of compact excavators call for new tech-nical solutions.

Against this background, Bosch Rexroth offers a wide range of high-performance components and systems for compact excavators from a single source to meet all needs. Furthermore, the specifications and interfaces of these systems are perfectly coordinated (Fig. 19). There are significant benefits for machine manufacturers:

▶ Simplification of the entire process, from design and assembly to global service

▶ Easy development of new concepts

▶ Faster market launch with reduced effort and expenditure

Rexroth solutions can be finely scaled in terms of power and functions. They improve both operator comfort and the maneuverability of machines, and also fulfill stringent customer requirements regarding higher productivity and lower fuel consumption.

Fig. 19: Bosch Rexroth system

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