SU787724A1 - Stand for recording characteristics of pneumatic engines - Google Patents

Description

The invention relates to mechanical engineering hydraulics, and more particularly to stands for testing pneumatic motors, and can be used in organizations involved in the design and manufacture of pneumatic motors.

A known stand for characterization of pneumatic motors, containing a source of compressed air connected through the pressure line through the control valve with the tested pneumatic motor, which is kinematically connected to the braking device and speed sensor, and flow-15 measures [1].

A disadvantage of the known stand is a drop in the accuracy of measuring costs due to a change in the pressure value of the ambient temperature.

The purpose of the invention is to improve the accuracy of measurements.

This goal is achieved by the fact that the stand is equipped with two heat exchangers and a constant pressure valve installed 25 in series between the control valve and the pneumatic motor, and the flow meter is installed between the heat exchangers and is made in the form of a JQ nozzle operating at a supercritical pressure ratio.

In FIG. 1 is a schematic diagram of a stand for taking characteristics of pneumatic motors; in FIG. 2 circuit diagram of the electrical part of the stand.

The stand for characterizing the pneumatic motors contains a source of 10 compressed air connected by a pressure line 2 through an adjustment valve 3 with the tested pneumatic motor 4, which is kinematically connected to the brake device 5 and the speed sensor 6. Between the control valve 3 and the pneumatic motor 4 heat exchangers 7 and 8 and a constant pressure valve 9 are installed. The nozzle 10, operating on a supercritical pressure ratio, acts as a flow meter and is located between the heat exchangers 7 and 8.

The constant pressure valve 9 is provided with a screw. 11 adjustment, the pressure in front of the pneumatic motor 4 is measured by a pressure gauge 12.

The force developed by the pneumatic motor 4, through the braking device 5 is transmitted to the dose meter 13 and then in the gauge 14 of the overpressure is converted into an electrical signal. An absolute pressure sensor 15 is installed in front of the nozzle 10, which produces a signal proportional to the mass flow rate of the air passing through the nozzle 10.

The speed sensor 6 is connected 5 to the frequency converter 16.

In addition, the stand includes multiplication and division blocks 17 and 18, plotters 19-21, as well as a device 22 for temporary loading of the brake device 10.

Stand for characterization of pneumatic motors works as follows.

Air from compressed air source 1 through pressure line 2, control valve 3 and nozzle 10, passing through heat exchangers 7 and 8, which maintain a constant air temperature before and after nozzle 10, flows into pneumatic motor 4, bringing it into rotation. The magnitude of the nozzle 10 is selected so that in the entire measuring range the pressure ratio before the last and before the pneumatic motor 4 is supercritical. **

The pressure value in front of the motor motor 4 is set by the adjustment screw 11 when the load changes from the side of the brake device 5, set by the time-loading device 22, and is maintained by the valve 9 by changing the passage section of the control valve 3. The rotation speed of the air motor 4 is measured by the speed sensor 6 and is converted into a voltage proportional to the speed of rotation n by the frequency converter 16.

The mass air flow G through the nozzle 10 at a supercritical outflow and a constant temperature in front of it, supported by the heat exchanger 7, is proportional to the absolute value of the pressure in front of the nozzle 10, which is measured by the absolute pressure sensor 15 and converted by it to a voltage proportional to the mass flow rate.

The moment M, developed by the pneumatic motor 4, is transmitted to the brake device 5, measured by the pressure in the month-50 dose 13 and converted by the gauge 14 overpressure, the pressure into voltage is proportional to the moment M.

The power Nf supplied to the pneumatic motor 4 is determined by the formula 55

N _r ± b _o 'G, where. o'PIR _P m1%) J

- disposable work; m is the indicator of polytropy;

P _SL - pressure drain pneumomotor 4;

-R _PRL - pressure in front of the pneumomotor 4;

θΛΛΛ “air density at a pressure of P _{P / A} and a constant temperature of the air supported by the heat exchanger 8.

Since the outflow of air through the pneumatic motor 4 is fast, the process of its expansion is close to adiabatic and ° \ ^p nJ I.

where K is the adiabatic index (for air, K = 1.4).

Since the air temperature in front of the pneumatic motor 4 is constant, then 6o ⁼ £ (Pn * D and at P _{L (L} = const, C _about = const. Therefore, at P _pm = const the voltage is proportional to M _g .

Stresses = Kd η and u _r = K _% M, where u and Kt are constant coefficients for a given stand, are entered at the input of the multiplication unit 17, at the output of which voltage Vd is formed. = Kd · Ν _Μ , where Kd is constant for a given stand coefficient, Ν _Μ - air motor power 4.

Stresses Пд and Ug - К _а <N _r (Kg coefficient constant for a given stand and pressure Р _{П (Л} ) are entered at the input of division unit 18, at the output of which voltage = Ί is formed, ^{where κ} * '

- Efficiency of the pneumatic motor 4.

The irradiated voltages U d, U3, and Bh are fed to the graph plotter inputs ^U 5 _ * 4 'Vo and ₅ points 19-21 to obtain, respectively, characteristics at various constant values of P _{P (L} : M = M (u) ₍ ' N _M = N _h (n) and η - η (μ).

The download speed of the brake device 5, i.e. changes in the rotational speed η of the pneumatic motor 4 is controlled by the setting of the time load device 22.

The invention allows to automate the process of graphical processing of experimental data using equipment commercially available by the domestic industry, and the implementation of the flow meter in the form of a jet operating at a supercritical pressure ratio increases the accuracy of measurements and eliminates errors in processing experimental data.

Claims (1)

1. Bashta TM, Zaichenko I. 3., Ermakov A.V., Khaimovich E.M. Volumetric hydraulic actuators. M., Mechanical Engineering, 1969, p. 276, Fig.2. 142 H};