Apparatus and method for monitoring sliding state of piston

The present application is a 35 U.S.C. §§371 national phase conversion of PCT/JP2009/061394, filed Jun. 23, 2009, which claims priority of Japanese Patent Application No. 2008-165101, filed Jun. 24, 2008, the contents of which are incorporated herein by reference. The PCT International Application was published in the Japanese language.

The present invention relates to an apparatus and a method for monitoring a sliding state of a piston ring.

Conventionally, in order to prevent burning of a piston in an engine during operation, there are attempts to measure a thickness of a film of lubricating oil. One of the methods of measuring a thickness of an oil film is a method of measuring a capacitance of a gap between a sliding surface of a piston ring in a cylinder liner and the piston ring by use of a detection electrode, which is provided on the sliding surface of the piston ring, and then calculating an oil film thickness of a lubricating oil.

For example, as a prior art document that discloses a capacitance-detection-type film thickness measuring technique as described above, Patent Document 1 as shown below is set forth.

Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2007-107947

However, the aforementioned conventional technique requires an electronic circuit that, in order to measure the capacitance, is used for the purposes such as supplying charging electricity to the detection electrode, detecting the period of time for charging, and discharging the electricity charged in the detection electrode. This increases the cost of the apparatus.

Furthermore, the aforementioned technique requires that a through-hole be bored in the cylinder and cylinder liner by machining, and that a detection electrode be installed at a forward end portion (a sliding surface of the piston ring) of the through-hole. Therefore, the detection electrode is installed at much expense in time and effort. In addition, there is a possibility of an occurrence of combustion gas leakage through the through-hole. Consequently, there is a demand for development of a technique that detects a sign of burning of a piston by a less expensive and simpler method.

The present invention has been achieved in view of the aforementioned problems, and has objects as follows:

(1) To detect a sign of burning of a piston by use of an apparatus less expensive than conventional apparatuses.

(2) To detect a sign of burning of a piston by a method of installing a sensor simpler than conventional methods.

To achieve the above objects, the present invention adopts the following.

A first apparatus for monitoring a sliding state of a piston ring according to the present invention includes: a temperature sensor that detects a temperature at a predetermined site of a cylinder liner; a rotation sensor that detects a rotation of an engine; a temperature data collection portion that obtains, based on a detection result of the temperature sensor and a detection result of the rotation sensor, temperature data on the predetermined site when a piston ring passes; and a piston ring rotation state determination portion that detects a rotation of the piston ring based on the temperature data and determines a sign of burning of a piston based on a state of the rotation.

A second apparatus for monitoring a sliding state of a piston ring according to the present invention is the above first apparatus for monitoring a sliding state of a piston ring, including: a plurality of temperature sensors in a cross-section orthogonal to a reciprocating direction of the piston, in which the piston ring rotation state determination portion detects a rotation of the piston ring based on an average value of pieces of temperature data on the temperature sensors.

A third apparatus for monitoring a sliding state of a piston ring according to the present invention is the above second or third apparatus for monitoring a sliding state of a piston ring, in which the piston ring rotation state determination portion acquires a cycle of varying temperature based on the temperature data and detects the cycle as a cycle of rotation of the piston ring.

On the other hand, a first method for monitoring a sliding state of a piston ring includes: a temperature detection step of detecting a temperature at a predetermined site of a cylinder liner; an engine rotation detection step of detecting a rotation of an engine; a temperature data collection step of collecting, based on a detection result of the temperature and a detection result of the rotation, temperature data on a predetermined site when a piston ring passes the predetermined site; a piston ring rotation detection step of detecting a rotation of the piston ring based on the temperature data; and a determination step of determining a sign of burning of a piston based on a detection result of the rotation of the piston ring.

A second method for monitoring a sliding state of a piston ring according to the present invention is the above first method for monitoring a sliding state of a piston ring, in which the temperature detection step detects temperatures at a plurality of sites in a cross-section orthogonal to a reciprocating direction of the piston, the temperature data collection step acquires temperature data on the plurality of sites; and the piston ring rotation detection step detects a rotation of the piston ring based on an average value of the temperature data.

A third method for monitoring a sliding state of a piston ring according to the present invention is the above first or second method for monitoring a sliding state of a piston ring, in which the piston ring rotation detection step acquires a cycle of varying temperature based on the temperature data obtained in the temperature data collection step, and detects the cycle as a cycle of rotation of the piston ring.

According to the present invention, a rotation of a piston ring is detected based on a temperature at a predetermined site of the cylinder liner, and a sign of burning of a piston is determined based on a state of the rotation. Thereby, it is possible to detect a sign of burning of a piston by an apparatus less expensive than apparatuses using a conventional technique of detecting a capacitance.

FIG. 1 is a block diagram showing a structure of an apparatus for monitoring a sliding state of a piston ring according to one embodiment of the present invention.

FIG. 2A is a cross-sectional view showing a positional relationship between an arrangement of temperature sensors 1 a , 1 b , 1 c , and 1 d and fitting clearances A of piston rings p 1 in the embodiment of the present invention.

FIG. 2B is a cross-sectional view showing a positional relationship between an arrangement of temperature sensors 1 a , 1 b , 1 c , and 1 d and fitting clearances A of piston rings p 1 in the embodiment of the present invention.

FIG. 3 is a diagram schematically showing changes in temperature measurement data detected by the temperature sensors in the embodiment of the present invention.

FIG. 4 is a diagram showing a relationship between a thickness of an oil film and a rotation of a piston ring in the embodiment of the present invention.

Hereunder is a description of one embodiment of the present invention with reference to the drawings.

FIG. 1 is a block diagram showing a structure of an apparatus for monitoring a sliding state of a piston ring according to one embodiment of the present invention. The present apparatus for monitoring a sliding state of a piston ring includes: four temperature sensors 1 a , 1 b , 1 c , and 1 d ; a rotary encoder 2 ; a temperature data collection portion 3 ; and a piston ring rotation state determination portion 4 . As shown in the figure, the apparatus for monitoring a sliding state of a piston ring has an engine S as its monitoring target.

First, the engine S as the monitoring target will be described. The engine S has a known structure, in which a reciprocating piston P is contained with reciprocable in a cylinder liner s 1 having a cylindrical shape. The piston P is a cylindrical member. A piston ring p 1 fits into each groove formed in a circumferential surface of the piston P. The piston ring p 1 is a metal member generally formed in a ring shape, a part of which is cut away from the necessity of being fit into the groove of the piston P. In the present specification, the cut-away portion in the piston ring p 1 is referred to as a fitting clearance.

Of the constituent elements that constitute the present apparatus for monitoring a sliding state of a piston ring, the four temperature sensors 1 a , 1 b , 1 c , and 1 d and the rotary encoder 2 are previously provided in the engine S in order to control the engine S. That is, the four temperature sensors 1 a , 1 b , 1 c , and 1 d and the rotary encoder 2 are not additionally provided to detect a sliding state of the piston rings p 1 provided on the piston P with respect to the cylinder liner s 1 (to be more correct, a piston ring sliding surface s 2 that is a surface of the cylinder liner s 1 ).

The four temperature sensors 1 a , 1 b , 1 c , and 1 d are, for example, thermistors, thermocouples, or resistance thermometers. They are buried in the cylinder liner s 1 at regular intervals in its circumferential direction. That is, the temperature sensors 1 a , 1 b , 1 c , and 1 d measure temperatures at four points in the circumferential direction of the cylinder liner s 1 , and output them to the temperature data collection portion 3 .

FIGS. 2A and 2B are cross-sectional views showing a positional relationship between an arrangement of the temperature sensors 1 a , 1 b , 1 c , and 1 d and the fitting clearances A of the piston rings p 1 . FIG. 2A shows a cross-section of the cylinder liner s 1 in a direction parallel to the reciprocating direction of the piston P. FIG. 2B shows a cross-section of the cylinder liner s 1 in a direction vertical to the reciprocating direction of the piston P. As shown in FIGS. 2A and 2B , the temperature sensors 1 a , 1 b , 1 c , and 1 d are arranged at four points (four points spaced 90° away from each other in the circumferential direction of the cylinder liner s 1 ) in a predetermined orthogonal cross-section (arrangement cross-section) in the reciprocating direction of the piston P. The piston rings p 1 provided on the piston P reciprocatingly passes the arrangement cross-section of the temperature sensors 1 a , 1 b , 1 c , and 1 d arranged as described above, with the reciprocating movement of the piston P in the cylinder liner s 1 .

The rotary encoder 2 is a rotation sensor that detects a rotation of the engine S. In a state where the engine S is in rotation (operation), the rotary encoder 2 outputs a pulse signal corresponding to the rotation state to the temperature data collection portion 3 and the piston ring rotation state determination portion 4 . The pulse signal indicates an operational state of the engine S and also indicates a crank angle of the engine S, that is, a position of the piston P (a position of the piston ring p 1 ) in its reciprocating movement.

Based on the pulse signal that is input from the rotary encoder 2 , the temperature data collection portion 3 takes in and stores temperature detection signals that are input from the temperature sensors 1 a , 1 b , 1 c , and 1 d . That is, the temperature data collection portion 3 takes in, at the time when the piston ring p 1 passes the aforementioned arrangement cross-section, the temperature detection signals that are input from the temperature sensors 1 a , 1 b , 1 c , and 1 d . Thereby, the temperature data collection portion 3 obtains a temperature of the cylinder liner s 1 for each of the temperature sensors 1 a , 1 b , 1 c , and 1 d at the time when the piston ring p 1 passes the arrangement cross-section, and then generates and stores (accumulates) data indicative of these temperatures (temperature data). Furthermore, the temperature data collection portion 3 supplies the temperature data to the piston ring rotation state determination portion 4 in response to the request from the piston ring rotation state determination portion 4 .

Based on the temperature data and the pulse signal that is input from the rotary encoder 2 , the piston ring rotation state determination portion 4 determines the rotation state of the piston ring p 1 with the engine S being in operation. In the piston ring sliding surface s 2 , the portions that face the fitting clearances A are higher in temperature than the portions other than the fitting clearances A due to an influence of the combustion gas. Therefore, based on a difference in temperature between the fitting clearance portions and the portions other than the fitting clearances, the piston ring rotation state determination portion 4 determines the rotation state (for example, the number of rotations or the rotation speed) of the of the fitting clearances A, and outputs the determination result to an external engine control apparatus (not shown in the figure).

Next is a detailed description of an operation of the present apparatus for monitoring a sliding state of a piston ring with a structure as described above, with reference to FIG. 3 to FIG. 4 .

When the engine S is set in operation, the piston P and the piston rings p 1 reciprocate in the cylinder liner s 1 . The piston rings p 1 reciprocate in the cylinder liner s 1 while rotating about the piston P. That is, the piston rings p 1 are attached to the piston P in a state of being fitted into ring-like grooves formed in the circumferential surface of the piston P, and hence are not completely fixed to the piston P. Therefore, the piston rings p 1 rotate in a specified direction due to an influence of friction between the cylinder liner s 1 and themselves or the like.

With the piston ring p 1 rotating about the piston P, the fitting clearance A of the piston ring p 1 rotates about the piston P accordingly. The temperature data collected by the temperature data collection portion 3 via the temperature sensors 1 a , 1 b , 1 c , and 1 d is as shown in FIG. 3 . That is, because the fitting clearance A of the piston ring p 1 rotates, the temperature sensors 1 a , 1 b , 1 c , and 1 d have a highest temperature when the fitting clearance A passes. Furthermore, because the temperature sensors 1 a , 1 b , 1 c , and 1 d are spaced at 90° from each other in the circumferential direction of the cylinder liner s 1 , the time at which the temperature is highest is different among the temperature sensors 1 a , 1 b , 1 c , and 1 d.

Furthermore, in a state where a lubricating effect by the lubricating oil is favorable, that is, in a state where an oil film with a proper thickness is formed between the piston ring p 1 and the cylinder liner s 1 , the friction between the piston ring p 1 and the cylinder liner s 1 is favorably reduced. Therefore, because the piston ring p 1 rotates with a substantially constant cycle of rotation, the detection cycle for the aforementioned highest temperature (that is, the cycle of rotation of the fitting clearance A) coincides with a substantially constant cycle of rotation similar to the cycle of rotation of the piston ring p 1 .

FIG. 4 is an experiment result showing a relationship among a velocity of the engine S (an engine speed) V, an oil film thickness L of the lubricating oil between the piston ring p 1 and the cylinder liner s 1 , and a piston ring rotation index (an index indicative of the number of rotations of the piston ring p 1 per day) N. They were measured over the period of approximately one month from Dec. 8, 2007 to Jan. 9, 2008 (the experiment was suspended from December 16 to December 20). The oil film thickness L in this experiment was measured by a capacitance-type film thickness measurement apparatus. Pulse-like lines in the vertical direction reflect an influence by the fitting clearance A of the piston ring p 1 .

As shown in FIG. 4 , in the period from December 8 to December 16, that is, in a state where the engine S is operated at the specified engine speed V and the oil film thickness L is sufficiently secured, the piston ring rotation index N indicates comparatively large values. In contrast to this, in a state where the oil film thickness L is relatively small while, as is the case for December 20 and later, the engine speed V is substantially similar in value to that in the period from December 8 to December 16, the piston ring rotation index N is more decreased compared with that in the period from December 8 to December 16. That is, the piston ring p 1 rotates favorably in the case where the oil film thickness L is sufficient. On the other hand, as the oil film thickness L becomes thinner, the piston ring p 1 rotates more and more slowly and stops in the end.

In this manner, the rotation of the piston ring p 1 has a correlation with the oil film thickness L of the lubricating oil. Therefore, measuring the rotation of the piston ring p 1 instead of measuring the oil film thickness L enables detection of a sign of a production of burning of the engine S resulting from thinning of the oil film thickness L. Furthermore, it is possible to detect the rotation of the piston ring p 1 as a rotation of the fitting clearance A, as shown in FIG. 3 .

That is, in the apparatus for monitoring a sliding state of a piston ring according to the present invention, the temperature data collection portion 3 collects and stores the temperature data shown in FIG. 3 for the temperature sensors 1 a , 1 b , 1 c , and 1 d . Then, based on the temperature data on the temperature sensors 1 a , 1 b , 1 c , and 1 d that is stored in the temperature data collection portion 3 , the piston ring rotation state determination portion 4 detects a cycle in which the highest temperature is generated (that is, the cycle of rotation of the fitting clearance A).

As shown in FIG. 3 , in the detection result of each of the temperature sensors 1 a , 1 b , 1 c , and 1 d , the highest temperature appears regularly with the passage of the fitting clearance A. On the other hand, the piston ring rotation state determination portion 4 acquires a cycle in which the highest temperature is generated for each of the temperature sensors 1 a , 1 b , 1 c , and 1 d , and regards their average value as a cycle of rotation of the fitting clearance A. Furthermore, the piston ring rotation state determination portion 4 determines whether this cycle of rotation is not more than a predetermined threshold value or not, so that the piston ring rotation state determination portion 4 detects a sign of burning of the engine S. At this time, if the cycle of generation of the highest temperature is not more than the threshold value, the piston ring rotation state determination portion 4 concludes that there is a sign of burning in the engine S, and outputs an alarm to the outside.

As has been described above, according to the present embodiment, the cycle of rotation of the fitting clearance A is detected based on the temperature data on the temperature sensors 1 a , 1 b , 1 c , and 1 d so that a sign of burning of the engine S is determined. Therefore, it is possible to detect a sign of burning of the piston by a method less expensive and simpler than conventional methods.

The present invention is not limited to the above embodiment. For example, modifications as follows are conceivable.

(1) While the four temperature sensors 1 a , 1 b , 1 c , and 1 d are provided in the above embodiment, the number of the temperature sensors may be other than four.

(2) While the four temperature sensors 1 a , 1 b , 1 c , and 1 d are provided in one cross-section orthogonal to the reciprocating direction of the piston P in the above embodiment, temperature sensors may be provided in a plurality of cross-sections orthogonal to the reciprocating direction of the piston P.

(3) While the position of the fitting clearance A is detected, to thereby detect the rotation of the piston ring p 1 in the above embodiment, the present invention is not limited to this. The rotation of the piston ring p 1 may be detected by another method.

The present invention detects a rotation of a piston ring based on a temperature at a predetermined site of a cylinder liner, and determines a sign of burning of a piston based on a state of the rotation. As a result, it is possible to detect a sign of burning of a piston by an apparatus less expensive than apparatuses using a conventional technique of detecting a capacitance.

1 a , 1 b , 1 c , 1 d : temperature sensor, 2 : rotary encoder (rotation sensor), 3 : temperature data collection portion, 4 : piston ring rotation state determination portion, S: engine, P: piston, p 1 : piston ring, s 1 : cylinder liner