Experimental sample for diagnosis of hydraulic drive pumps of agricultural equipment by pressure pulsation coefficient

. It is well known that often hydraulic pumps are resource-limiting components of the units in whose design they are included, and the condition of the hydraulic pump determines the performance and efficiency of the entire unit. The purpose of the work was to develop a prototype of a diagnostic tool that provides monitoring of the technical condition of hydraulic pumps during operation. An analysis of the tools produced by the Federal Scientific Agro-Engineering Center VIM for diagnosing the technical condition of hydraulic pumps of agricultural machinery was carried out. The material of research was a prototype of a tool for diagnosing the technical condition of hydraulic units, which was based on the method of amplitude-phase characteristics for rapid assessment of the technical condition of pumps during operation. On the base of our research we came to conclusions that for further development of the technology and subsequent implementation of the presented prototype in the process of diagnosing hydraulic pumps by pulsation coefficient it is necessary to increase the controllability of hydraulic systems of agricultural machinery by installing diagnostic points for connecting pressure sensors. Also together with manufacturers of hydraulic units, develop criteria for nominal, permissible, limit states, characterized by both the supply coefficient KQ and the pulsation coefficient ɛ .


Introduction
Agricultural machinery with hydraulic implements is widely used in various types of agricultural, transport and industrial works throughout the year, which makes it possible to increase labour productivity, reduce the prime-cost of production and ultimately increase profits for the owners.Safety largely depends on the technical condition of hydraulic pumps operation, timing and quality of work performed.
It is often when hydraulic pumps are resource-limiting components of the units in whose design they are included, and the condition of the hydraulic pump determines the performance and efficiency of the entire unit.The importance of diagnosing hydraulic units is evidenced, for example, by the fact that according to National State Standard 20793-2009, when the internal-combustion engine (IС engine) reaches 1000 engine hours, motor maintenance (MM-3) is carried out, which are combined with resource diagnostics (RD) to obtain initial information on predicting the residual resource including the hydraulic pump [1,2].
It should be noted that due to the rapid development of microelectronics and its widespread implementation in all spheres of human activity, it has become possible to develop modern automated computerized tools for diagnosing agricultural machinery and hydraulic units.Such diagnostic tools allow us not only to assess the current condition of hydraulic units, but also to accumulate operational and diagnostic data for subsequent analysis, which ultimately helps to increase the level of operational reliability of equipment, reduce the prime-cost of production and the cost of ownership of equipment.
The purpose of the work was to develop a prototype of a diagnostic tool that provides monitoring of the technical condition of hydraulic pumps during operation.

Materials and methods
The material of research was a prototype of a tool for diagnosing the technical condition of hydraulic units, which was based on the method of amplitude-phase characteristics for rapid assessment of the technical condition of pumps during operation.The State National Standards and other technical documents were used for this research.

Results and discussion
Of the wide variety of methods for diagnosing the technical condition of hydraulic pumps of agricultural machinery, the static-parametric method is used to a greater extent (National State Standard 14658-86, National State Standard 29015-91, Diagnosis of hydrodrives 12-20.2004)[3,4,5].
This method is based on estimating the values of the pump volumetric flow coefficient (KQ) at minimum (  ) and nominal (  ) pressures, using the formula (1): In this case using the built-in flow meter the flow coefficient (KQ) is determined, the diagnostician compares the obtained value with standard data (specified in the passport of the unit manufacturers) and limit state criteria.For example, in RTM 70.0001.246-84(Technical guidance material) the values for reducing the supply coefficient KQ for pumps of the following hydraulic systems are indicated: for the attachment at least 0.4, for steering control -0.6, and in Gear pumps with fluid power drives.Technical requirements 1831-2008 (clauses 3, 5, 6) the criterion for the limiting state of a gear pump is to reduce KQ by more than 20% of the nominal value, which depending on the design of the pump is about 0.92...0.94 [6,7].
For the practical implementation of this method of evaluating hydraulic drive pumps both in the field and under stationary conditions the Federal Scientific Agro-Engineering Center VIM has developed and produces various diagnostic tools: hydraulic stands, throttles-flow meters.The most widely used tools for equipping repair and service enterprises and farms in the agro-industrial complex are a set of tools for diagnosing the hydraulic drive KI-5473 (a) with a throttle-flow meter DR-90, as well as the stand KI-28097M (b) used for runningin and incoming quality control of repairs (Fig. 1, a and b) [8,9].With all the advantages of the static-parametric method for assessing the technical condition of pumps and especially the main thing as the high accuracy of the method, it is also necessary to note the disadvantages that are associated with the high labour intensity of the diagnostic process as well as:  a need to disconnect the pressure hydraulic line to create a pressure difference and determine the volumetric flow;  installation of an additional drain hydraulic line into the tank;  human factor in determining the technical condition;  impossibility of monitoring the technical condition during the operation of agricultural machinery.There is a method of amplitude-phase characteristics for diagnosing hydraulic drive pumps, which is applicable for assessing the general technical condition and localizing faults.The technical condition is assessed by analyzing the amplitude of pressure fluctuations in the form of a pulsation coefficient (ɛ), which is determined by the formula (2) [10,11]: where Pmax and Pmin are the maximum and minimum pulsation amplitudes, Pa.Theoretically, for hydraulic pumps there is a dependence of the pulsation coefficient ɛ on both operating parameters and the technical condition of the pump.Most often, it is the volumetric efficiency that determines the technical condition of the pump, namely the degree of fluid leakage as a result of deformation or natural wear of the unit.Thus, continuous measurement of pulsation parameters will make it possible to determine the technical condition of the pump and prevent the operation of worn-out units leading to inefficient consumption of drive power and low performance of hydraulic actuators, which will lead to saving time and funds when operating machines and will also avoid serious breakdowns and failure out of order (failures of 2-3 groups).
The coefficient ɛ is determined by analyzing the signals of the pressure sensor on the oscilloscope screen, however largely due to the imperfection of the measuring and counting devices used and the high labour intensity, the applicability of this method in practice is quite low.As part of the scientific and research works in laboratory 11.1 at the Federal Scientific Agro-Engineering Center VIM, to calculate the required pulsation coefficient ɛ as well as measure and calculate parameters important for diagnostics based on the widely used Arduino platform as the Arduino MEGA board with the ATmega2560 microcontroller, a prototype pulsation counter-indicator was created.The Arduino platform is a convenient and modern way to control and automate technological processes that have been widely implemented in industry recently.High performance, reliability, low price, free and convenient environment for developing and programming devices on Arduino base have allowed them to become widespread in techniques and science.
A prototype pulsation counter-indicator can be used to evaluate:  pulsation coefficient ɛ and the associated supply coefficient KQ characterizing the nominal and limiting states of pumps during their operation;  counting the number of operating and idle cycles performed by the pump to determine the degree of consumption of the gamma-percentage time to failure specified by the manufacturer;  temperature of the working fluid;  signaling the need for servicing at the moment of exhaustion of the assigned life of the pump or an unacceptable change in its operating properties;  prevention of emergency situations such as leakage of working fluid, overheating.
Measuring pressure pulsation parameters will allow us to determine the technical condition of pumps and save time and funds when diagnosing them and will also allow us to avoid operating in extreme technical condition.Fig. 2 shows a graphical interpretation of the results of staged experiments to assess the technical condition of the GP-32 pump (gear pump) at stand KI-28256 (stand for diagnosing and testing hydraulic units).The prototype of a device for monitoring pump operation based on ATmega2560 is shown in Fig. 3  A high-speed pressure sensor with a voltage output of 0...5 V, 100 MPa is connected to the analog inputs of the microcontroller (MC).The sensor is installed in the pressure line of the pump.The MC at high speed measures pressure pulsations in the pressure line with a frequency of over 1 kHz.
The device automatically calculates such parameters as average pressure value, maximum pressure pulsation value, minimum pressure pulsation value, pulsation coefficient ɛ.All measured and calculated data are transferred to the PC in the form of an automatically filled table.
The diagram of the developed prototype of the pulsation counter and the appearance of the counter display is presented in Fig. 4 and 5. Due to this device, it is possible to carry uot an experiment to determine the dependence of the pulsation coefficient on the hydraulic efficiency of the pump, the speed of rotation of the pump shaft, the pressure developed by the pump, the oil temperature and the environment.The process of monitoring the performance of the pump in the hydraulic system of the machine is also significantly simplified, the cost is reduced and the control equipment is simplified.In the future, it is possible to create electronic self-diagnosis devices for hydraulic systems, built directly into the pump, and transmitting data about the operation of this unit to the on-board information and control system of the machine.This will allow continuous monitoring and prevent ineffective operation of the machine or its failure by identifying a pump malfunction.
When conducting experiments, analog signals from sensors are additionally recorded in the form of oscillograms on the PC with a high frequency and high resolution using a parallelconnected recorder L-CardE-14-140 M. It allows us to verify the accuracy of the measurements of the ADCs built into the microcontroller and the correctness of the programmed algorithms and correct setup of equipment.Data from the recorder is decrypted manually and, if necessary (inconsistencies), adjustments are made to the microcontroller program.
In order to carry out experiments, a prototype device for measuring pressure pulsations and a PC are installed on a stand of the Federal Scientific Agro-Engineering Center VIM with a power of 15 kW (Fig/ 6).The GP-32 pump was installed.Using the throttle, the required operating pressure is set, and the speed is set using a frequency converter.The stand instruments display the operating parameters of the process, including power and torque developed by the electric motor, oil temperature in the stand tank, oil temperature in the drain line, oil consumption in the drain line.Pressure pulsations are measured using a domestically produced high-speed pressure sensor RTM-M3-100-0.25%with a ratio metric output analog signal of 0.5...4.5 V (Fig. 7), which significantly simplifies the connection circuit to the inputs of the ADC MC.Using a flow meter in the stand, it is possible to determine the volumetric efficiency developed by the pump under various operating modes.Stand equipment also allows us to smoothly adjust process parameters.
Also, during the experiments, measuring equipment and algorithms for processing sensor signals are tested.For example, the selection of parameters of electronic noise filters for signals measured by the analog inputs of the microcontroller.During the experiment, the pressure in the hydraulic system changes stepwise uses a throttle.Parameters are automatically recorded: pressure, temperature, rotation speed.The flow coefficient KQ corresponding to these parameters is measured manually using a flow meter.Using stand equipment, the oil temperature, power and torque on the pump shaft are determined.At the same time, time is monitored in order to determine the dynamics of changes in the measured parameters.The following are automatically calculated: pulsation coefficient ɛ; average pressure Pav, the value is displayed with 2 decimal places; the value of the pump temperature and its increase per second T and ∆T are calculated with an accuracy of 0.05 ºС.The data is written to a txt file in the form of a table, convenient for further processing by third-party software.
Production tests carried out of the presented prototype showed the possibility of reliably assessing the diagnosis of hydraulic pumps based on the pulsation coefficient, and the greatest effect was obtained when assessing the limiting technical condition, which consists in minimizing labour time and efficiency in identifying faults up to 5 times in comparison with the Dr-90 throttle-flow meter.The components that are widely available in the Russian Federation, which can significantly reduce the prime-cost of the final product with the subsequent implementation of the development has been used.The collected information can also be used for economic calculation and assessment of the costs of operating hydraulic units of machines, as well as possible repair costs in the event of failure of units, to calculate the economic feasibility of carrying out maintenance to prevent failures of high groups and associated equipment downtime, to evaluate the real cost of operating equipment, taking into account the wear and tear of hydraulic units.At the same time, the low cost of electronic components of counters, indicators and sensors will make it possible to introduce such calculation systems into a wide range of agricultural machinery [12].

Conclusion
On the base of our research we believe that for further development of the technology and subsequent implementation of the presented prototype in the process of diagnosing hydraulic pumps by pulsation coefficient, it is necessary:  increase the controllability of hydraulic systems of agricultural machinery by installing diagnostic points for connecting pressure sensors;  together with manufacturers of hydraulic units, develop criteria for nominal, permissible, limit states, characterized by both the supply coefficient KQ and the pulsation coefficient ɛ.

Fig. 1 .
Fig. 1.Tools for diagnosing hydraulic drive units using the static-parametric method produced by the Federal Scientific Agro-Engineering Center VIM: a -KI-5473; b -KI-28097M

Fig. 2 .
Fig. 2. General view of the dependence of the values of the pulsation coefficient and the flow coefficient on the technical condition of the pump.

Fig. 3 .
Fig. 3. Prototype of pressure pulsation measurement device on the Mega 2560 module: 1 -MC Mega 2560; 2 -OLED display with all necessary information displayed; 3 -boost DC-DC-converter for powering sensors; 4 -terminal blocks for connecting sensors, external devices, buttons; 5programmable controller for setting the level, set point, settings, navigation in the menu; 6programmable button; 7 -device power switch; 8 -external battery to ensure autonomous operation