Precision to increase power
16 July 2010
The combination of FEM (finite element method) simulation and latest production techniques has seen one range of hydraulic systems satisfy demands for efficiency, reliability and reduced noise.
The application example was developed in collaboration with the ELASIS research centre in Lecce and concerns the fan drive hydraulic system used to cool the engine compartment of the new Wheel Loader range by Fiat Kobelco. Marzocchi gear pumps from jbj Techniques.
Marzocchi - leader in the micro-pumps sector, apply all their ‘micro-hydraulics’ experience to the whole new product range.
The two main areas of gear pumps and motors are the ALP and ALM range utilising aluminium flanges and covers, and the GHP and GHM range of gear pumps and motors utilising cast iron flanges and covers ideal for high pressure applications and to the Mobile market.
R & D has applied the latest FEM simulation techniques that, together with the new tools for the experimental mechanics, have produced specific product optimisation aimed at satisfying current market demands for top efficiency, reliability and reduced noise levels.
The R & D department equipped with the latest testing equipment have analysed mechanical, hydraulic, acoustic and vibration criteria for performance and durability in the toughest working conditions. This has resulted in the optimisation of the compensation geometry (used to balance the dynamic thrust caused by pressure in gear vanes), gear profiles and the undercut drain on the bushings in order to increase product reliability and reduce noise levels. These innovations were transferred to the production department by a wide-scale renewal of the run-in and test benches.
The current Marzocchi production range varies between 0.19 and 200.3 cm3/rev (0.0104 – 12.223 in3/rev) and it is divided into 8 groups according to gear size (0.25, 0.5, 1P, 1, 2, 3, 3.5, 4). Within each group, the different displacements are obtained by changing the gears width.
A wide range of flange, shaft and coupling configurations is available; these components can also be manufactured according to customer specifications.
The cast iron versions exist in groups 1, 2 and 3. Maximum operating pressure depends on pump displacement and type: it varies on an average between 230 bar (3300 PSI) on aluminium models and 280 bar (4100 PSI) for cast iron versions. All products can also be supplied with Viton seals and special versions are available for temperatures between -40°C and +120°C (-40°F / +248°F).
Mono-directional and bi-directional motors are divided into three families (1,2,3) covering a range of displacements between 2.8 and 87 cm3/rev (0.17 / 53.1 in3/rev). The maximum working pressures for the motors are similar to those established for the pumps and they can deliver torque up to 250 Nm and power up to 60 kW.
The run-in is the last stage of the manufacturing process and it is one of the most important operations because it permits the optimisation and check of the product efficiencies.
During run-in in tests, increasingly higher pressure levels are created; the gears, inflected by the hydraulic load, act as tools machining the pump body, thus creating the best tolerances among the parts. This process is performed under computer control.
The definition of the gradual increase of the pressure is particularly important because it establishes the machining speed of the material by the gears and thus the particles dimension; these particles must be small enough not to interfere with the running of the product under testing and its future performance. Each motor of each group has a personalised pressure ramp in order that no contaminating material remains in the circuit and the pump is able to attain maximum performance levels immediately.
Reversible motors and pumps are subject to run-in procedure on both rotations. After this process product efficiencies are measured at fixed parameters.
Test data is automatically recorded to provide updated statistics on product performances, supplied on customer request.
After the run-in for gear motors another specific test follows on a dedicated test-bench, where the relative operating conditions must be reproduced:
• under braking, when the energy of the fluid is transferred to the shaft to overcome the resisting torque
•under counter pressure, when the fluid passes through the motor with the shaft free to turn without load
•under braking the stress distribution is similar to that which exists on the pumps: if maximum pressure exists at the inlet, and discharge pressure exists at the outlet, compensation seals and rotating parts are subjected to the maximum stress according to resisting torque.
•under counter-pressure inlet and outlet are under the same conditions: at maximum pressure the stress on the rotating parts is zero, while the flanges, body and external seals are subjected to the maximum stress. A typical motor’s working conditions are between these two situations: part of the energy is transferred to the shaft and part is used, for example, by another motor connected in series.
Therefore, on the Marzocchi motors test bench, the final control is divided in three phases:
Braking phase:at an established rotation speed a resisting torque is applied to the motor shaft. The application of this torque creates a variation in the fluid’s inlet speed and pressure; the test-bench control system stabilises the motor in fixed conditions in which running parameters are acquired, such as volumetric and mechanical performances and draining flow rate.
Counter-pressure phase:a fixed amount of oil goes through the motor without any resisting torque applied to the shaft; the outlet line is kept closed and therefore a bilateral pressure is established. The drain flow rate is measured at these conditions.
Start-up phase: without any resisting torque applied to the shaft, the start up torque is determined by measuring the minimum inlet pressure at which the motor starts running.
In the case of bi-directional motors, the three phases are performed for both rotations.
After this test the motor is delivered to the customer perfectly run-in and controlled: its extreme reliability makes it suitable for use even under extreme conditions.
The following application example was developed in collaboration with the ELASIS research centre in Lecce and concerns the fan drive hydraulic system used to cool the engine compartment of the new Wheel Loader range by Fiat Kobelco.
To make motor maintenance easier (model W270LB Evolution is mounted with a Cummins 6 cylinder, 10.8 litre direct injection diesel, 202 kW turbo air after-cooler), the rear section of the vehicle can be opened. This incorporates the fan directly connected to the Marzocchi gear motor and the air conveyor, so permitting bilateral access to the radiant mass. The rotation direction of the fan is reversible, providing perfect self-cleaning action of the radiators.
This operation can be activated using an appropriate switch located in the cabin on the control dashboard.
The fan is driven by aluminium reversible motor (type ALM2BK1-R-20-T4-T-H, 14.1 cm3/rev displacement), equipped with support bearing and specific seals for wide temperature range.
The aluminium fan (weighs 7 kg) takes in hot hair from the engine compartment and therefore the hydraulic motor working temperature is approximately 70° - 80°C (158° - 176°F).
The hydraulic motor is also subjected to vibration due to the wide swings of the rear side of the machine, when the bucket is rapidly moving. Under extreme conditions, acceleration up to 7g possible.
Normally the motor performs with an inlet pressure of 200 bar and 50 bar in outlet pressure. To ensure the best temperature control, the fan rotation speed is independent of the motor running speed.
For the project validation the hydraulic motor was subjected to an internal Marzocchi approval procedure (to which all new/special products are subject) and to a test performed directly by the customer.
Internal approval includes various endurance tests in which the components are checked on the test benches in the R & D department: they are subject to on-off pressure cycles at the maximum allowed pressure. Periodically, an inspection is made in order to check the components conditions.
Where necessary, tests have been performed with similar operating condition of the final application: same pressure cycles, temperature, oil type, etc.
Once the endurance test has been completed, a comparison is made between the initial and final product performances and a deep analysis of each component is performed to identify any possible failure. No failure and no performance degradation higher than the internal specifications must occur to validate the project.
The test performed by ELASIS is composed of a first cycle under continuous pressure at 210 bar (3050 PSI) at a temperature of 110°C (230°F), followed by a second cycle at pulsating pressure (0 - 210°C) at the same temperature conditions.
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