УДК 681.5.015:658.786 SIMULINK SOFTWARE FEATURES FOR MODELLING A SMALL-SIZE LOADER

Computer simulation as a tool to determine the loading for implements and hydraulic drives of small-size loaders has been considered in the paper. A number of lifting mechanism design models has been built; their strengths and shortcomings have been analysed. It has been proposed to alter the machine’s hydraulic drive design as well as to redesign the arm and the levelling mechanism to improve reliability of a small-size loader.


Introduction
High performance of a loader largely depends on the design of the hydraulic drive. In heavy loading operations the hydraulic drive of the working equipment operates 80-85% of the total length of the working cycle. The turn-on fre-quency of the hydraulic drive is 600-900 per hour. Hydraulic drive is the main actuating device for the working equipment of all road and construction machines in general and particularly loaders. Therefore, engineers are constantly working on its improvement. This makes the topicality of the presented paper.

Analysis of Publications
Basic principles of mathematical modelling of hydraulic drives used in road and construction machines were discussed in paper [1]. The drawback of this method is the calculation of road and construction machines' hydraulic drive loads in the form of static values that do not consider the workflow dynamics of modern machines. In papers [2][3][4] MATLAB 6 and Solid-Works computer modelling features for dynamic processes in hydraulic drive loading were described.

Purpose and Tasks
The purpose of the paper is to develop a computer model of the hydraulic drive and to analyse the model in terms of improving the reliability and performance of the loader.
The tasks include: 1) overview of software packages applied for computer-aided design of hydraulic drives; 2) design of the loader components and determination of their parameters; 3) development of a computer model of the hydraulic drive; 4) optimization of both the hydraulic drive parameters and working equipment designs.

Hydraulic Drive Models for Road and Construction Machines
The aim of computer modelling is to reduce both the expenses needed for numerous experiments and the hydraulic drive design time. The paper deals with the analysis of three different hydraulic drive CAD-systems (FLOW-3D, SIMULINK and COSMOSFloWorks). SIM-ULINK was selected for modelling due to its following advantages: simplicity, user friendly interface, block modelling system.
A two-module machine with a process module «Т16МГ Universal loader» with the bucket capacity of 0.165 m 3 was chosen as an object of the study. The mathematical model of the loader's working equipment with three joint coordinates was applied for the analysis. It was built on the basis of Lagrange equation of the second type.
With the help of Simulink blocks the hydraulic drive models were built: models with one, two, four hydraulic cylinders, a model of the existing machine. A model of the loader's working equipment is composed of a hydraulic pump, hydraulic cylinders and a crossbeam. It simulates the operation of the hydraulic drive when the lifting arm is being raised with the load.
A model with one hydraulic cylinder is composed of a single-acting cylinder with a return spring ( Figure 1). a b Fig. 1 Pressure curve (а) and cylinder rod travel The curve shows that at T = 0.04 sec (time of operation) compression begins at the inlet of the pump, and at T = 0.05 sec it is removed. The value of the feed pressure  1 drops rapidly. The pressure chart for the  2 cylinder piston side does not show such a rapid change. Pressure almost did not change in the  3 cylinder rod side. This can be explained by the fact that the outage of the hydraulic pump operation was short.  The machine implements model simulates the operation of the hydraulic drive at lifting the loader arm with a full bucket. The beam (arm) travel curves as well as the angles of the beam position relative to the horizon in radians are displayed on the oscilloscopes. In developing this model of the hydraulic drive some assumptions were made: -the loader arm was taken as an absolutely rigid (nondeformable) beam placed perpendicular to the longitudinal axis of the loader; -the hydraulic cylinders were placed so that when the arm is raised, the piston cavity is working; -the sum of the arm's weight and the loader's maximum load carrying capacity was taken as the cargo weight in the model.
Another purpose of the research was to study the effect of the arm speed on the working processes. The influence of the pump feed changes on the hydraulic drive operation was studied. The load is in the centre of the beam. The following pumps were used here: Gear Pump-32, Gear Pump-46, Gear Pump-67, Gear Pump-98 ( Figure 3). The obtained values show that with increasing the hydraulic pump feed the arm lifting speed rises, though the amplitude of the beam angle oscillations also increases ( Table 1). а b Fig. 3. Angle curve (а) and crossbeam travel curve (b) with a НШ-32 pump The obtained values show that at increasing the hydraulic pump feed the arm lifting speed rises, though the amplitude of the beam angle oscillations also increases (Table 1). In the model the arm is lifted while the bucket is fully loaded. The centre of gravity of the bucket (beam) is displaced to the right edge at a distance of 1/3 from the right edge of the bucket. This may be due to the heterogeneity of the material being developed, such as construction waste. The parameters of the loading process were analysed with changes of displacements zb and za depending on the increase of the hydraulic cylinder piston area ( Figure 4). The curves given above show that when the piston area was increased, the difference between the displacement coordinates zb and za was decreased from 0.0028 m to 0.001m at T = 0.1 s. Since the smallest difference between the values zb and za is 0.001m was observed in this latter case, it is advisable to use the hydraulic cylinder of D=125 mm ( The analysis of the research data proved that increased weight of cargo does not significantly affect the arm lifting speed in these operating modes. However, the use of hydraulic cylinders with a piston diameter of D = 125 mm with the given cargo weight compensates for the overload caused by the centre-of-gravity shift, since the value of the za-zb difference in this case is the smallest.

Conclusion
The computer model analysis of the loader drive system showed that in order to increase the efficiency of the existing design of the loader it is necessary: -to change the position of the hydraulic cylinders which lift the arm in such a way that a piston cavity will become the working cavity of the hydraulic cylinder when lifting the arm; -to replace a Gear Pump-32 pump with a Gear Pump-67 pump in order to increase the arm lifting speed; -when using a loader to move nonhomogeneous materials, for example construction wastes, it is advisable to provide a Gear Pump-67 hydraulic pump and hydraulic cylinders with a diameter of a piston D = 125 mm as parts of the hydraulic drive system. This is due to the nonuniform distribution of the material in the loader bucket. As a result, there is a tilt of the frame and hydraulic cylinders. Whereas, when the power on the hydraulic cylinder rods increases, the lifting capacity of the hydraulic drive increases, too. Therefore, it is advisable to increase the strength characteristics of the loader frame or to change the design of the frame. With such a layout of the hydraulic drive we can use the frame design ( Figure 5).

Fig. 5. Proposed design of a loader implement
Its advantage is that in case of implements tilting, the main load is concentrated not on the hydraulic drive but on the steel structure of the arm.