RU2554383C1 - Diagnostic method of cylinder-piston group of internal combustion engine - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: invention relates to technical diagnostics and can be used for determination of a technical state of a cylinder-piston group of individual cylinders in an internal combustion engine by initiation of pressure inside a deactivated cylinder and calculation of its change rate at operation of the engine at minimum idle rotation speed. The proposed method consists in the fact that pressure inside the deactivated cylinder is measured by a pressure sensor on the engine operating at minimum idle rotation speed; with that, for assessment of the state of a "piston-rings-sleeve" connection of the cylinder-piston group the measurement of pressure in the engine cylinder and calculation of its change rate as per it is made as per a turning angle of a crankshaft by means of an angular movement sensor that is installed opposite a gear rim of the flywheel.

EFFECT: proposed method allows performing an assessment of the state of the "piston-rings-sleeve" connection of the cylinder-piston group of the engine along the whole working surface of the cylinder, detecting different failures and forecasting residual life of the engine.

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Description

The invention relates to the field of technical diagnostics and can be used to determine the technical condition of the cylinder-piston group (CPG) of individual cylinders in an internal combustion engine by indicating the pressure inside the cylinder and calculating its rate of change when the engine is running at the minimum idle speed.

The closest technical solution, selected as a prototype, is a method for diagnosing an internal combustion engine, published on the Internet on October 29, 2009 (Analysis of a waveform of pressure in a cylinder http://old.quantexlab.ru).

The known method is based on obtaining a waveform of pressure in a disabled cylinder by installing a pressure sensor in it on a running engine and analyzing the pressure at its characteristic points.

The disadvantage of this method is the inability to assess the pairing “piston-ring-sleeve” of the CPG over the entire working surface of the cylinder liner due to the lack of reference to the angular movement of the crankshaft when measuring pressure inside the cylinder, as well as calculating the rate of change.

Thus, in order to evaluate the “piston-ring-sleeve” coupling of the CPG over the entire working surface of the cylinder, in addition to measuring pressure by the angle of rotation of the crankshaft, it is necessary to take into account the rate of change.

The inventive method allows to obtain a new technical result compared with the prototype, which consists in a qualitative assessment of the coupling of the piston-ring-sleeve CPG along the entire working surface of the cylinder liner.

To achieve the specified technical result, the following set of essential features is used:

- in the method of diagnosing the CPG, as well as in the prototype, the pressure measurement in the disconnected cylinder of the working engine is carried out by installing a pressure sensor in it;

- pressure measurement inside the cylinder by the angle of rotation of the crankshaft is carried out using an angular displacement sensor;

- calculation according to the oscillogram of the rate of change of pressure is carried out by differentiating the function of changing the pressure inside the cylinder by the angle of rotation of the crankshaft.

The essence of the method lies in the fact that the measurement of pressure inside a disabled cylinder running at a minimum idle speed of the engine and the calculation of the rate of change is carried out using a pressure sensor, while to increase the accuracy and reliability of assessing the state of the pairing “piston-ring-sleeve” CPG pressure measurement in the engine cylinder is carried out according to the angle of rotation of the crankshaft using an angular displacement sensor, which is installed opposite the gear ring of the flywheel.

Figure 1 presents the structural diagram of the measuring device.

Figure 2 presents a graph of the pressure inside the cylinder by the angle of rotation of the crankshaft.

The structural diagram of the measuring device consists of a pressure sensor 1, which is installed in place of a spark plug for gasoline engines or in place of nozzles in diesel engines, an angular displacement sensor 2 of the crankshaft mounted opposite the gear ring of the flywheel, and a measuring device 3, which registers the pressure inside the cylinder by the angle of rotation of the crankshaft shaft and calculating the rate of change of pressure over the entire working surface of the cylinder liner.

The measuring device 3 is equipped with an indicator, which reflects a graph of the pressure inside the cylinder by the angle of rotation of the crankshaft. A marker is installed on the flywheel next to the ring gear, corresponding to the position of the piston of the first cylinder at top dead center (TDC) at the moment when the angular displacement sensor is opposite this marker. The sensor generates a TDC signal, which is a clock signal for reading the pressure in the cylinder by the angle of rotation of the crankshaft. Figure 2 shows a graph of the pressure inside the cylinder by the angle of rotation of the crankshaft.

The graph clearly shows the change in pressure inside the cylinder along the angle of rotation of the crankshaft. Here you can highlight the characteristic points for assessing the state of the CPG. P1 - inlet pressure. For gasoline engines with a closed throttle, the intake pressure is lower than atmospheric. It characterizes the tightness of the intake tract and the condition of the cylinder liner. For diesel engines, this parameter is slightly higher, that is, the pressure is closer to atmospheric due to the lack of a throttle valve, however, even with it you can evaluate the tightness of the intake tract.

Pressure P2 characterizes the tightness of the cylinder, the state of the valves. For gasoline engines, it is in the range of 10-14 kg / cm ² depending on the degree of compression, for diesel engines it is in the range of 24-28 kg / cm ² .

Pressure P3 is below atmospheric and characterizes the condition of the piston rings and cylinder liner. When the piston moves to the top dead center on the compression stroke, part of the air charge goes into the oil pan through the ring leaks, therefore, on the expansion stroke when the piston moves down due to this leakage and the oil wedge, a short-term vacuum is created in the lower part of the piston rings until the exhaust valve opens. This vacuum characterizes how well the piston rings compact the over-piston space. If the rings are worn, coked or broken along with the baffles on the piston, the rarefaction P3 will increase due to the fact that the leakage on the compression stroke will increase, and when the piston moves down on the expansion stroke, the oil wedge at the bottom of the rings will prevent the air charge from flowing from the sump to nadporshnevoe space and therefore the vacuum will increase.

From the graph of the pressure in the cylinder, you can also calculate the rate of pressure change over the entire working surface of the cylinder liner. This parameter allows you to evaluate the condition of the piston-ring-sleeve pair according to the angle of rotation of the crankshaft from the bottom to the top dead center of the piston. Together with the pressure of the end of compression, this parameter increases the reliability of assessing the state of the engine’s CPG (it can detect chips, seizures on the surface of the cylinder). To calculate the rate of change of pressure inside the cylinder, it is necessary to differentiate the function of pressure change in the indicator diagram.

where V _p (φ) is the rate of change of pressure in the cylinder, MPa / deg. p.c.

- производная функции изменения давления по углу поворота коленчатого вала; $$P_{\varphi }^{\text{'}\text{'}}$$

- the derivative of the function of changing the pressure with respect to the angle of rotation of the crankshaft;

- дифференциал функции изменения давления по углу поворота коленчатого вала. $$\frac{dp}{d\varphi }$$

- differential pressure change function by the angle of rotation of the crankshaft.

For this, numerical methods of differentiation are used. The indicator diagram is divided into small intervals (figure 2), corresponding to the angular displacement of the crankshaft, equal to the distance between adjacent teeth of the flywheel. At each such site, the rate of change of pressure is calculated.

- отношение разности давлений P i-го и P i-1-го, МПа, к разности угловых перемещений φ i-го и φ i-1-го, угол п.к.в.Where $$\frac{\Delta p}{\Delta \varphi }$$

- the ratio of the pressure difference P i-th and P i-1-st, MPa, to the difference of the angular displacements φ i-th and φ i-1-th, the angle p.c.

Knowing the reference diagrams of pressure changes by the angle of rotation of the crankshaft inside the cylinder and the calculated rate of pressure changes, it is possible to evaluate the state of the CPG with high accuracy and reliability, identify various malfunctions and predict the remaining engine life.

The rapid growth of microelectronics allows us to abandon the traditional needle gauge devices that allow you to control individual indicators in the diagnostic process. Today, there is a huge list of microcontrollers that allow real-time monitoring of various processes, including measurement, and processing of pressure indicator diagrams in the engine cylinder depending on the angle of rotation of the crankshaft. Low cost and small dimensions of microcontrollers allow you to create miniature diagnostic devices with a color graphic display, button control, the ability to transmit diagnostic information over long distances.

Claims (1)

A method for diagnosing a cylinder-piston group of an internal combustion engine, namely, that the pressure inside the disconnected cylinder is measured by a pressure sensor running at a minimum engine idle speed by means of an indication, characterized in that to increase the accuracy and reliability of the evaluation of the piston-ring mating condition “sleeve” of the cylinder-piston group, the pressure in the cylinder is measured by the angle of rotation of the crankshaft and the calculation of its rate of change is carried out by di derivations pressure change function according to the formula:
$$\frac{dp}{d\phi }=P_{\phi }^{\text{'}\text{'}}=V_p(\phi ),$$

where V _p (φ) is the rate of change of pressure in the cylinder, MPa / deg. p.c.
$$P_{\varphi }^{\text{'}\text{'}}$$

- the derivative of the function of changing the pressure with respect to the angle of rotation of the crankshaft;
$$\frac{dp}{d\varphi }$$

- differential pressure change function by the angle of rotation of the crankshaft;
using an angular displacement sensor installed opposite the flywheel ring gear, which divides the indicator diagram into intervals corresponding to the angular displacement of the crankshaft, equal to the distance between adjacent teeth of the flywheel, and at each such section, the rate of change of pressure is calculated by the formula:
$$\frac{\Delta P}{\Delta \phi }=\frac{P_i-P_i{}_{-\mathrm{one}}}{{\phi }_i-{\phi }_{i-\mathrm{one}}}=V_{pi}({\phi }_i),$$

Where $$\frac{\Delta P}{\Delta \varphi }$$

- the ratio of the pressure difference P i-th and P i-1-st, MPa, to the difference of the angular displacements φ i-th and φ i-1-th, the angle p.c.
according to the results of determining the change in pressure and the rate of change, they judge the technical condition of the cylinder-piston group of the engine.

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