Abstract:
An engine crankcase gas blow-by sensor. In a closed crankcase ventilation system, crankcase gases are caused to flow through a venturi which includes high pressure and low pressure taps. The high and low pressure taps are coupled to a differential pressure transducer which produces an output that is proportional to the volumetric flow of crankcase gases through the venturi. The use of a venturi in conjunction with a differential pressure sensor offers a low resistance path for the flow of crankcase gases and allows continuous monitoring of blow-by without exceeding the operating pressure limitations of various oil seals. Such a sensor is particularly suited for closed crankcase ventilation (ccv) systems, as it doesn&#39;t require venting of crankcase gases to the atmosphere, but works well in open crankcase ventilation systems also.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 08/816,274, Mar. 13, 1997 (now abandoned, which is a continuation-in-part of U.S. patent application Ser. No. 08/564,429, filed Nov. 29, 1995 now U.S. Pat. No. 5,686,868. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to engine crankcase gas blow-by sensors and, more particularly, to an engine crankcase gas blow-by sensor using a venturi and a differential pressure transducer to measure volumetric flow of blow-by gases. 
     BACKGROUND OF THE INVENTION 
     Ideally, the pressure within an internal combustion engine crankcase should be maintained at a level equal to or slightly less than atmospheric pressure to prevent external oil leakage through the various gasketed joints, such as that between the valve cover and the cylinder head. As is well known, in an internal combustion engine, a so-called blow-by gas is emitted in the crankcase as a result of leaks of intake air-fuel mixture and combustion gases through the clearances around piston rings, during the compression, combustion and/or exhaust cycles. Because of these blow-by gases, the crankcase pressure will inherently rise, promoting leakage of oil from the crankcase. Originally, the crankcase pressure was vented to the atmosphere through a breather in order to solve this problem. 
     More recently, environmental considerations have dictated that the blow-by gases in the crankcase be vented back to the combustion chamber rather than being released to the atmosphere. Such closed crankcase ventilation (CCV) systems recycle the blow-by gas by burning these gases together with the intake air-fuel mixture. 
     Heavy duty and high horsepower internal combustion engines run under severe and sometimes adverse conditions, where engine downtime is expensive and service is not always available. A good method of checking an engine&#39;s “health” is to periodically, or preferably continuously, monitor the flow of crankcase blow-by gases. The greater the quantity of blow-by gases escaping around the pistons, the poorer the condition of the engine. Therefore, sensing of the amount of blow-by gas in an engine can detect catastrophic failures (i.e. an instantaneous increase in the amount of blow-by gas) or monitor engine wear over time in order to predict when the engine will require an overhaul (i.e. a slowly increasing amount of blow-by gas). 
     A good way to measure the volume of blow-by gas entering the crankcase is to measure the pressure of such gases in the crankcase. However, closed crankcase ventilation systems do not allow any of the crankcase gases to be vented through an orifice, which would be required in order to measure the crankcase pressure. There is therefore a need for an alternative way to measure the amount of blow-by gas entering the engine crankcase and to collect this data for making determinations of engine health. The present invention is directed toward meeting this need. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an engine crankcase gas blow-by sensor. In a closed crankcase ventilation system, crankcase gases are caused to flow through a venturi which includes high pressure and low pressure taps. The high and low pressure taps are coupled to a differential pressure transducer which produces an output that is proportional to the volumetric flow of crankcase gases through the venturi. The use of a venturi in conjunction with a differential pressure sensor offers a low resistance path for the flow of crankcase gases and allows continuous monitoring of blow-by without exceeding the operating pressure limitations of various oil seals. Such a sensor is particularly suited for closed crankcase ventilation (ccv) systems, as it doesn&#39;t require venting of crankcase gases to the atmosphere (but will also work well on open systems). 
     In one form of the invention, an internal combustion engine is disclosed, comprising at least one cylinder; at least one piston slidingly disposed within the at least one cylinder in order to define a combustion chamber above the piston; an air intake system operable to supply air to the combustion chamber; a crankcase coupled to the at least one cylinder, wherein an interior of the crankcase is in fluid communication with an interior of the at least one cylinder below the at least one piston, wherein combustion gases which blow-by the at least one piston may enter the crankcase; a venturi having an inlet port and an outlet port, wherein the inlet port is coupled to the crankcase interior and the outlet port is coupled to the air intake system such that gas within the crankcase may flow through the venturi; a high pressure tap extending from an exterior of the venturi to an interior of the venturi; a low pressure tap extending from the venturi exterior to the venturi interior; and a sensor coupled to the venturi and operative to measure a differential pressure between the high pressure tap and the low pressure tap. 
     In another form of the invention, an engine crankcase gas blow-by sensor is disclosed, comprising an engine crankcase operative to contain blow-by gases; an air intake system; a venturi having an inlet port and an outlet port, wherein the inlet port is coupled to an interior of the engine crankcase and the outlet port is coupled to the air intake system such that gas within the crankcase may flow through the venturi; a high pressure tap extending from an exterior of the venturi to an interior of the venturi; a low pressure tap extending from the venturi exterior to the venturi interior; and a sensor coupled to the venturi and operative to measure a differential pressure between the high pressure tap and the low pressure tap. 
     In another form of the invention a method of evaluating performance of an internal combustion engine is disclosed, comprising the steps of: (a) routing at least a portion of blow-by gases within a crankcase of the engine through a venturi having a high pressure tap and a low pressure tap; (b) measuring a pressure differential between the high pressure tap and the low pressure tap; and (c) outputting a signal that is proportional to the measured pressure differential. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a cross-sectional view of a preferred embodiment of the venturi of the present invention. 
     FIG. 1 b  is an end view of the venturi of FIG.  1 . 
     FIG. 2 is a top plan view of the venturi of FIG. 1 with the differential pressure transducer mounted thereon. 
     FIG. 3 is a cross-sectional view of the venturi and differential pressure sensor of FIG.  2 . 
     FIG. 4 is an end view of the venturi and differential pressure sensor of FIG.  2 . 
     FIG. 5 is a graph of differential pressure as a function of the flow transfer function of the venturi of FIG.  2 . 
     FIG. 6 is a graph of the voltage output signal of the differential pressure sensor of FIG. 2 as a function of air flow through the venturi. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     Hereinafter, when expressions such as “above” and “below” are used, it will be assumed that the piston is so oriented that its axis is vertical and the crankcase is positioned below the piston. This hypothesis is merely intended to simplify the description and therefore does not imply that the piston is in fact oriented in this way when it is mounted in an internal combustion engine. 
     The present invention involves the sensing of crankcase blow-by gases by measuring the volumetric flow of such gases rather than the prior art method of measuring the pressure of these gases. Volumetric flow of the blow-by gases is accomplished by routing a portion of these gases through a venturi which has high pressure and low pressure taps therein. A differential pressure sensor is then attached to the high and low pressure taps in order to measure the pressure differential between the taps. This differential pressure is related to the volumetric flow of blow-by gases through the venturi, and hence the volumetric flow of blow-by gases around the engine pistons. Both instantaneous measurement of this volumetric flow, as well as historical trend analysis, provide useful information in determining the health of the engine as well as to predict future needs for service. The sensor will therefore yield data suitable for trend analysis to aid diagnostics and prognostics, and can be used to avoid catastrophic failure. 
     Referring to FIG. 1 a , a cross-sectional view of a preferred embodiment venturi of the present invention is illustrated and indicated generally at  10 . The venturi  10  includes a generally cylindrical venturi body  12  having an inlet port  14  and an outlet port  16  attached thereto. The inlet port  14  includes a hose connection nipple  18  while the outlet port  16  includes a hose connection nipple  20 . Crankcase gases (such as those communicated to the engine head through the engine pushtubes) may thus be routed to the venturi  10  via a suitable hose (not shown), and crankcase gases exiting the venturi  10  may be routed back to the air intake of the engine (such as an inlet of an engine turbocharger) via a second suitable hose (not shown). The venturi  10  is preferably formed from aluminum, steel or an injection molded engineering thermoplastic, or any other suitable material. 
     The dimensions of the venturi  10  will vary depending upon the engine size with which the venturi is associated. The dimensions given for the venturi  10  of FIG. 1 a  are preferred for use with a K50 diesel engine manufactured by the Cummins Engine Company of Columbus, Ind. Because the venturi effectively amplifies the flow rate of crankcase gases through the venturi, different venturi sizes will be appropriate for different size engines. 
     In the preferred embodiment of FIG. 1 a , the venturi  10  has an inlet port  14  internal diameter of  1  inch. The outlet port  16  also has an internal diameter of 1 inch. The venturi throat  22  has an internal diameter of 0.425 inches. Dimensions for the other portions of the venturi  10  are illustrated in FIG. 1 a . A high pressure tap  24  is formed from the exterior surface of the venturi body  12  to the inlet bore  26  which extends through the inlet port  14 . Similarly, a low pressure tap  28  is formed from the exterior surface of the venturi body  12  to the venturi throat  22 . 
     Referring to FIG. 2, a differential pressure sensor  30  is coupled to the venturi body  12  by means of four screws  32  which bore into the body  12 . The differential pressure sensor  30  is preferably a variable capacitive on ceramic differential pressure sensor such as a model P604 manufactured by Kavlico of Moorepark, Calif., but any type of differential pressure sensor may be utilized in the present invention. 
     As illustrated in the cross-sectional view of FIG. 3, the differential pressure sensor  30  is mounted to the venturi body  12  such that the high pressure tap  24  is aligned with the inlet  34  to the high pressure side of the differential pressure sensor  30 . Similarly, the low pressure tap  28  communicates with the inlet  36  of the low pressure side of the differential pressure sensor  30 . The differential pressure sensor  30  is preferably of the wet-dry type, therefore the low pressure side of the sensor includes a filter element  38  in order to prevent liquid, such as uncombusted fuel and oil, to enter the low pressure side of the differential pressure sensor  30 . The output of the differential pressure sensor  30  is a voltage which is proportional to the differential pressure across the high pressure tap  24  and the low pressure tap  28 . This output voltage is supplied to a multi-pin electrical connector  40 . The connector  40  additionally accepts the input voltage which is used to power the differential pressure sensor  30 . 
     The venturi  10  of FIG. 1 a  is capable of flowing in excess of  50  actual cubic feet per minute (ACFM) air or crankcase gas, although the flow rate will be approximately 26 ACFM maximum for the model K50 engine for which the venturi  10  was designed. A flow rate of 26 ACFM results in approximately 30 inches of water pressure differential developed across the pressure taps  24  and  28 . 
     This is illustrated in the graph of FIG. 5 which illustrates the differential pressure developed across the pressure taps  24  and  28  of the venturi  10  as a function of gas flow through the venturi  10 . This graph illustrates that the transfer function of gas flow vs. differential pressure for the venturi  10  is not linear. 
     The combination venturi body  12  and differential pressure sensor  30  is preferably mounted in a substantially vertical orientation in order to allow gas to run out of the venturi in order to prevent build-up and contamination within the differential pressure sensor  30 . Such build-up will change the measured pressure and result in inaccuracies in the measurement of crankcase gas flow. The differential pressure sensor  30  is mounted to the venturi body  12  by means of an appropriate sealing gasket which forms an airtight seal between the differential pressure sensor  30  and the high pressure tap  24  and low pressure tap  28 . 
     Referring to FIG. 6, it can be seen that the output voltage of the differential pressure sensor  30  is a non-linear function of media volumetric flow, which tracks the actual differential pressure developed across the high and low pressure taps of the venturi. The input voltage to the differential pressure sensor  30  is 5.0+/−5% VDC. Because the sensor  30  is ratiometric to the input voltage, the output voltage illustrated in FIG. 6 assumes a 5.0 VDC input voltage. It will be appreciated by those skilled in the art that the transfer function of FIG. 6 allows an engine monitoring system to determine the flow-rate of crankcase gases through the venturi by monitoring the output voltage of the differential pressure sensor  30 . This information may be used in different ways by the engine monitoring system. For instance, the output voltage of the differential pressure sensor  30  may be monitored for an instantaneous increase of blow-by gas flow, indicative of a catastrophic failure within the engine. The amount of instantaneous increase necessary to signal a catastrophic failure may be made a calibratable threshold point within the engine monitoring system and is dependent upon engine size. Upon the sensing of such an instantaneous increase in blow-by gas flow, an indicator light may be used to alert the driver of the situation. The output voltage of the differential pressure sensor  30  may also be used to record crankcase gas flow rate over time in order to chart the wear of the engine and hence predict when the engine will require an overhaul. The engine monitoring system may use a filtered linear projection in order to determine at what time the engine blow-by gases have increased to the point where maximum performance is no longer available from the engine. Appropriate servicing can then be scheduled for the vehicle prior to that time. 
     It will therefore be appreciated by those skilled in the art that the present invention allows useful measurement of engine crankcase blow-by which was previously unavailable in closed crankcase ventilation systems. Measurement of such blow-by gases can provide information to signal catastrophic failures within the engine as well as to predict when major engine servicing will be required in the future. Such information may be used to minimize downtime of the engine and to prevent expensive catastrophic engine failure. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.