Method for Determining Air Filter Condition

Technical Field

[0001] This invention relates generally to transport refrigeration systems and, more particularly, to a method of using a manifold absolute pressure sensor to determine the condition of an engine air filter.

Background of the Invention

[0002] In transport refrigeration systems, such as are used in truck trailers and refrigerated containers, a diesel engine is provided to drive certain components such as the compressor and the generator for the refrigeration system. [0003] While operating in high altitude conditions, the inadequacy of air to the engine when more power is called for may cause the engine to stall. This problem is commonly addressed by the use of a manifold absolute pressure (MAP) sensor in the air intake system and using it to control the power required by the unit, which in turn would prevent the engine from stalling.

[0004] A separate, and unrelated problem is that of the intake air filter being clogged after extensive use. This problem has generally been addressed by the use of a so called "filter minder", which is a simple visual pressure indicator which shows when an air filter is plugged and needs to be cleaned or replaced.

Disclosure of the Invention

[0005] In accordance with one aspect of the invention, the "filter minder" device can be eliminated by selective use of the MAP in such a way as to measure the air pressure in the air intake manifold before and after starting the engine in order to determine the condition of the filter.

Brief Description of the Drawings

[0006] FIG. 1 is a schematic illustration of an engine and associated air system in accordance with the prior art.

[0007] FIG. 2 is a flowchart indicating the method of determining a filter condition in accordance with the present invention.

Detailed Description of the Invention

[0008] Fig. 1 is a schematic illustration of an engine and its air intake system in accordance with the prior art. The engine 11 is typically a diesel engine for driving components of a self-contained refrigeration system of the type installed in a refrigerated truck trailer or a refrigerated container 10.

[0009] The air intake system 12 includes, in serial flow relationship, an air filter 13, an air intake manifold 14 and an air inlet hose 16 for delivering ambient air to the engine 11 for purposes of supporting combustion therein. [0010] In order to accommodate operation of the engine 11 at high altitude conditions, a MAP (manifold absolute pressure) sensor 17 is provided in the air intake manifold 14. The sensor 17 determines the air pressure inside the intake manifold 14 and automatically controls the unit power requirement of the engine 11 if the pressure in the air intake manifold 14 indicates that there will not be sufficient air to properly support combustion when normal power demands are placed on the engine 11.

[0011] Separate and independent from the MAP sensor 17 is a filter minder sensor 18 which shows the pressure in the intake manifold 14 and provides a visual indication of that pressure to indicate to the observer whether the air filter 13 is plugged. That is, if it is plugged, the pressure in the intake manifold 14 will be below its normal level.

[0012] In accordance with the present invention, the filter minder sensor 18 can be eliminated, and the MAP sensor 17 may be used in a unique way in order to perform the function of determining the condition of the air filter 13 in accordance with the method as shown in Fig. 2.

[0013] Before the engine 11 is started, the unit power is turned on as shown in block 19. The MAP sensor 17 then senses the pressure within the air intake manifold 14, and that pressure P ₁ is recorded as shown in block 21. That pressure, which is indicative of the ambient pressure as indicated in block 22, is then applied to control unit power requirement of the engine 11 if the pressure is below a predetermined level as indicated in block 23. That concludes what is the normal function of the MAP sensor 17.

[0014] After the engine is started as shown in block 24, another MAP sensor pressure P ₂ is taken within the air intake manifold 14 as shown in block 26. In block 27, the pressure P ₂ is subtracted from the pressure Pi to obtain a pressure difference P _D , and in block 28 the pressure difference P _D is compared with a predetermined reference P _ref . If P _D is determined to be less than P _ref , then the filter is determined to be acceptable as shown in block 29. If it is greater than P _ref , then the computer indicates that the filter should be replaced as shown in block 31. [0015] While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.