GB2296325A

GB2296325A - Accelerometer-based apparatus for determining engine power balance

Info

Publication number: GB2296325A
Application number: GB9523602A
Authority: GB
Inventors: Michael B Meeker; Matthew M Crass; Robert D Braun
Original assignee: Snap On Inc; Snap On Tools Corp
Current assignee: Snap On Inc
Priority date: 1994-12-20
Filing date: 1995-11-17
Publication date: 1996-06-26
Also published as: GB9523602D0; DE19543063A1; CA2162979A1

Description

1 2296325

ACCELEROKETER-BASED APPARATUS AND METHOD FOR DETERMINING ENGINE POWER BALANCE Backaround of the Invention Field of the Invention

The present invention relates to analysis of malfunctions in internal combustion engines. The invention relates in particular to analysis of the relative power contributions of individual cylinders of a multi- cylinder internal combustion engine.

Description of the Prior Art

Frequently, when a multi-cylinder internal combustion engine fails to deliver its rated power, the problem arises from the weakness or malfunctioning of one or more of the cylinders. Evidence of a malfunction may be roughness of engine operation or poor cylinder compression.

Heretofore, in order to analyze the relative power contributions of individual cylinders of a multi-cylinder internal combustion engine, a technique known as "cylinder shorting" was used. In this technique, the contribution of an individual cylinder to the overall power output of the engine is determined by "shorting," or preventing the occurrence of the ignition event of a cylinder and noting the resultant change in engine speed in rpm. An ignition event is the f iring of the spark, plug in the case of a gasoline engine, or the fuel injection, in the case of a diesel engine. If the cylinder were contributing no power, then the shorting of that cylinder would not decrease the engine speed. If, on the other hand the individual cylinder were a normal contributor to the overall power, then, when it is shorted, the speed of the engine would drop.. If each individual cylinder normally contributed a like amount to the overall engine power then, when it is shorted, each cylinder would cause the same drop in engine speed.

In modern computer-controlled engines with catalytic converters, it is difficult and potentially harmful to short out cylinders. Accordingly, alternative techniques of measuring the cylinder power balance have been developed.

2 Thus, it has been found that the speed variation ofthe engine within a single engine cycle can give an indication of the cylinder power balance. One system for determining power balance by analyzing engine speed variations over a single engine is disclosed in U.S. patent no. 4,539,841. In this system, the engine speed is sensed by use of an electromagnetic sensor positioned adjacent to the teeth on the engine flywheel or ring gear. The sensor senses the passing of the teeth of the ring gear as it is rotated and provides an alternating output, the frequency of which is proportional to the engine speed. While this permits fairly accurate monitoring of engine speed, it has the disadvantage that the installation of the sensor is very cumbersome and time consuming since the ring gear is relatively inaccessible in most engines and the electromagnetic sensor must be very precisely positioned relative to thegear teeth.

Another system for determining power balance by analyzing engine speed variations over a single engine cycle is disclosed in U.S. patent no. 5,182,512. In this system, a linearly moving external part on the engine, such as a belt, is contacted with a hand-held, rotary encoder, contact tachometer which outputs a waveform signal which, along with a signal responsive to the f iring of the number 1 cylinder, is applied to an engine analyzer processor f or display of a single engine cycle of the waveform signal on the CRT oscilloscope of the engine analyzer. But this requires the operator to hold the probe against the drive belt to obtain information. This not only occupies one of the operator I s hands, but occupies his attention to make sure 'that the probe stays on the belt, thereby preventing him from viewing the CRT screen.

It has also been known heretofore to detect other conditions occurring in one or more cylinders of an engine, such as improperly f itted parts, knocking and the like, by detecting engine vibrations with a vibration sensor. But 3 such systems typically seek to detect excessive vibration, rather than detection of cylinders which lack power contribution.

Summary of the Invention

It is a general object of the invention to provide an improved method for determining the relative power contribution by a cylinder of a multicylinder internal combustion engine which avoids the disadvantages of other power balance analysis techniques while affording additional structural and operating advantages.

An important feature of the invention is the provision of a method of the type set f orth which utilizes a probe which can be conveniently mounted at any of a number of easily accessible locations on an engine.

In connection with the foregoing feature, a further feature of the invention is the provision of a method of the type set forth, in which the probe can be fixed to the engine and need not be hand- held thereon.

A still further feature of the invention is the provision of a method of the type set forth which determines power balance by sensing engine vibrations. Yet another f eature of the invention is the provision of a method of the type set forth, which displays a waveform signal indicative of cylinder power balance. 25 Another feature of the invention is the provision of an apparatus for performing the method of the type set forth. These and other features of the invention are attained by providing apparatus for determining the relative power contribution by a cylinder of a multi-cylinder internal combustion engine having a crankshaft with an axis of rotation, the apparatus comprising: a vibration detecting circuit including a vibration sensor having an axis of sensitivity, the detecting circuit producing an electrical waveform signal as a function of detected vibrations, structure for mounting the sensor on the engine in a sensing position with the axis of sensitivity disposed in a 4 predetermined orientation neither parallel to nor perpendicular to the axis of rotation, and a display unit coupled to the detecting circuit for displaying the waveform signal.

Still further features of the invention are attained by providing a method for determining the relative power contribution by a cylinder of a multi-cylinder internal combustion engine having a crankshaft with an axis of rotation, the method comprising the steps of: providing a vibration sensor having an axis of sensitivity, mounting the sensor on the engine in a sensing position with the axis of sensitivity in a predetermined orientation neither parallel to nor perpendicular to the axis of rotation to produce an electrical waveform signal as a function of detected vibrations, and displaying the waveform signal.

The invention consists of certain novel features and a combination of parts hereinafter fully described, illustrated in the accompanying drawings, and particularly pointed out in the appended claims, it being understood that various changes in the details may be made without departing from the spirit, or sacrificing any of the advantages of the present invention.

Brief Defteription of the Dravings For the purpose of facilitating an understanding of the invention, there is illustrated in the accompanying drawings a preferred embodiment thereof, from an inspection of which, when considered in connection with the following description, the invention, its construction and operation, and many of its advantages should be readily understood and appreciated.

FIG. 1 is a diagrammatic end elevational view of an internal combustion engine, illustrating the positioning thereon of a vibration sensor in accordance with the present invention and the coupling thereof to an associated engine analyzer; and FIG. 2 is a schematic circuit diagram of the vibration detecting circuit of the preset invention.

DescriRticu Of the Preferred Embodizent Referring to FIG. 1, there is illustrated a multi cylinder internal combustion engine, generally designated by the numeral 10. The engine 10 has a crankshaft 11 on which may be mounted a flywheel 12, the crankshaft 11 being rotatable about an axis of rotation 13 in a direction indicated by an arrow 14. The flywheel 12 defines a plane P perpendicular to the axis of rotation 13. There are also illustrated in FIG. 1 imaginary circles 15, 16 and 17, all coaxial with the crankshaft 11, and which lie in planes parallel to the plane P. Also illustrated in FIG. 1 is an engine analyzer 18 with an associated CRT oscilloscope display 19. The engine analyzer 18 may be of any of a number of different types of known engine analyzers, but is preferably a digital engine analyzer of the type disclosed, for example, in U.S. patent no. 5,259,935.

The present invention includes a vibration probe assembly, generally designated by the numeral 20, which includes a housing 21, adapted to be fixed to the engine 10, as by magnetic attraction. In this regard, the housing 21 may have a portion thereof formed of a magnetized material or may have a permanent magnet affixed thereto. Other mounting means, such as bolts, clips and the like, could also be used. Referring also to FIG. 2, the vibration probe assembly 20 includes a vibration sensor 22, in the nature of an accelerometer, which is disposed within the housing 21 and has an axis of sensitivity 23 indicated by the arrow in FIG. 1, which is directed in a predetermined direction. The vibration probe assembly 20 is adapted to be coupled, as a by a cable 24, to the engine analyzer 18.

Referring in particular to FIG. 2, the vibration probe assembly 20 includes a probe circuit 25 disposed within the housing 21 and coupled by a suitable multi-conductor connector 26 to the cable 24, in a known manner. The cable 6 24 and the connector 26 include a conductor 27 which carries +12VDC voltage from the engine analyzer 18, which may be derived from the battery of the vehicle in which the engine is mounted. The conductor 27 is coupled through a resistor 28 to the accelerometer 22, which is, in turn, coupled to ground. The resistor 28 reduces the +12VDC supply to roughly +8 volts for use by the accelerometer 22 as a bias voltage. The accelerometer 22 may be of any of a number of known types, and is responsive to detected vibrations in the direction of its axis of sensitivity 23 for generating an electrical output signal indicative of those vibrations.

The output of the accelerometer 22 is supplied to an input buffer 30, which includes an amplifier 31 configured as a unity gain buf f er. More specifically, the output of the accelerometer 22 is supplied through a coupling capacitor 32, which removes the DC bias from the signal, to the non-inverting input of the amplif ier 31, which input is also connected to ground through a resistor 33. The output of the amplifier 31 is fed back to its inverting input. The conductor 27 is connected to the amplifier 31 to provide a +12VDC supply voltage, the conductor 27 being connected to ground through a capacitor 34, which provides power supply filtering. A -12VDC supply voltage is provided to the amplifier 31 over a conductor 35, which is connected to ground through a filter capacitor 36. The resistor 33 provides input loading.

The output of the amplifier 31 is supplied to a filter 40, which includes an amplif ier 41 conf igured as a unity gain inverting amplifier. More particularly, the output of the amplifier 41 is coupled to its inverting input through a parallel combination of a resistor 42 and a capacitor 43.

The output of the amplifier 31 is coupled to the inverting input of the amplifier 41 through a resistor 44. The non inverting input of the amplifier 41 is connected to ground through a resistor 45. The purpose of the f ilter 40 is to 7 remove the high frequency component of the accelerometer output signal. Unity gain is established by matching the resistance of the resistors 42 and 44. The cut-off frequency is determined by the capacitor 43 and the resistor 42. The resistor 45 is chosen to have the value of the parallel combination of the resistance of resistors 42 and 44 for impedance matching.

The output of the filter 40 is supplied to an amplifier stage 50, which includes an amplifier 51, which is preferably configured as an inverting amplifier with a gain of 50. The output of the amplifier 51 is coupled to its inverting input through a resistor 52, while the output of the amplifier 41 is coupled to the inverting input of the amplifier 51 through a resistor 53, the resistors 52 and 53 serving to determine the gain of the amplifier. The noninverting input of the amplifier 51 is coupled to ground through a resistor 54, which provides impedance matching for the ground reference. The purpose of the amplifier stage 50 is restore proper signal phase and amplify the signal to levels usable by the oscilloscope 19 of the engine analyzer 18. In this regard, the amplifier stage 50 has an output terminal 55, which is adapted to be coupled to the output conductor 56 of the connector 26 by a jumper 57.

The probe circuit 25 may also be optionally provided with an amplif ier stage 60, for the purpose of adding gain to the stage 50, should it be needed. The amplifier stage 60 includes an amplifier 61 configured as a non-inverting amplifier, which preferably has a gain of 6. The output of the amplifier 61 is coupled to its inverting input through a resistor 62, while the inverting and non-inverting inputs of the amplifier 61 are also coupled to ground through resistors 63 and 64, respectively. The non-inverting input of the amplifier 61 is also coupled to an input terminal 65, while the output of the amplifier 61 is coupled to an output terminal 66. The gain of the amplifier stage 60 is determined by the resistors 62 and 63, while the resistor 64 8 provides impedance matching. In the event that additional gain is desired, the output terminal 55 of the amplifier stage 50 is disconnected from the conductor 56 and connected to the input terminal 65 of the amplifier stage 60, while the output terminal 66 of the amplifier stage 60 is coupled to the output conductor 56 with another jumper, not shown. The extraneous conductors of the connector 26 are connected to ground.

It is a significant aspect of the invention, that it has been determined that the accelerometer 22can give a reliable indication of the relative power contributions of the several cylinders of the engine 10 if it is mounted on the engine 10 in a particular orientation, i.e., with the axis of sensitivity 23 of the accelerometer 22 oriented in is the direction of rotation of the crankshaft 11. The comparative magnitude of the vibration associated with the firing of each cylinder, as viewed on the display oscilloscope 19, is indicative of the power contribution of that cylinder. more specifically, referring to FIG. 1, the accelerometer housing 21 is positioned on the engine 10 such that the axis of sensitivity 23 is disposed in a plane which is perpendicular to the axis of rotation 13. r Preferably, the accelerometer housing 21 is positioned so that the axis of sensitivity 23 is disposed in such a plane with the portion of the axis of sensitivity 23 within the housing 21 being perpendicular to a radius of the crankshaft 11. For example, it may be positioned at the bottom of the block of engine 10 tangent to the circle 16 and intersecting radius R, or on a cylinder head, tangent to the circle 17 and intersecting radius R1. However, it will be appreciated that the accelerometer housing 21 could be positioned anywhere along a line of tangency to such a circle, such as on the side of the engine 10 along a tangent of the circle 15.

In each case, it is important that the axis of sensitivity 23 be directed in the direction of rotation of 9 the crankshaft 11, as indicated by the arrow 14. Thus, for example, referring to the accelerometer housing 21 as shown in the solid line in FIG. 1, since it is disposed on the right-hand side of the crankshaft 11, it is arranged with the axis of sensitivity 23 pointed downwardly. If, however, it were disposed on the opposite side of the block of the engine 10, it would be oriented with the axis of sensitivity 23 pointing upwardly. It will be appreciated that the invention could work if the accelerometer were arranged with its axis of sensitivity 23 pointing in the opposite direction from the direction of rotation, but in this case the polarity of the output signal would be reversed.

While, in the preferred embodiment, the accelerometer 22 is disposed on the engine 10 with its axis of sensitivity 23 lying in a plane which is perpendicular to the axis of rotation 13, the invention would still work if the axis of sensitivity 23 were inclined slightly to such a plane, but the intensity of the output signal from the accelerometer would be reduced. In general, in order to obtain acceptable results, the axis of sensitivity 23 should be inclined no more than within 200 to a plane which is perpendicular to the axis of rotation, and preferably within 1011 thereof. When the accelerometer 22 is properly oriented on the engine 10, it will generate an output signal waveform 70 which typically has peaks corresponding to the cylinders of the engine, and the relative amplitudes of these peaks give an indication of the relative power contributions by the several cylinders.

It is a significant aspect of the invention that the vibration probe assembly 20 can be simply and easily mounted on the engine 10 at any of a number of easily accessible locations, as long as it is properly oriented relative to the crankshaft. Thus, the invention can be simply and easily used under the hood of a vehicle, and leaves the operator's hands and eyes free for operating and monitoring the engine analyzer 18 and the oscilloscope 19, while at the same time permitting the operator to directly view the displayed waveform signal.

11

Claims

we Clai:

1. Apparatus for determining the relative power contribution by a cylinder of a multi-cylinder internal combustion engine having a crankshaft with an axis of rotation, said apparatus comprising: a vibration detecting circuit including a vibration sensor having an axis of sensitivity, said detecting circuit producing an electrical waveform signal as a function of detected vibrations, structure for mounting said sensor on the engine in a sensing position with said axis of sensitivity disposed in a predetermined orientation spaced from and substantially orthogonal to the axis of rotation, and a display unit coupled to said detecting circuit for displaying the waveform signal.

2. The apparatus of claim 1, wherein said vibration sensor is an accelerometer.

3. The apparatus of claim 1, wherein said structure for mounting includes a magnetic housing.

4. The apparatus of claim 1, wherein said sensor in its sensing position has its axis of sensitivity disposed approximately in a plane which is perpendicular to the axis of rotation.

5. The apparatus of claim 4, wherein the axis of sensitivity is disposed in said plane.

6. The apparatus of claim 4, wherein the axis of sensitivity is directed in the direction of rotation of the crankshaft.

7. The apparatus of claim 1, wherein said detecting circuit includes an amplifier for amplifying the waveform signal.

8. The apparatus of claim 7, wherein said amplifier includes means for selectively varying the amplification of the waveform signal.

9. The apparatus of claim 1, wherein said detecting circuit includes means for providing a DC bias voltage to said sensor.

12 is 10. The apparatus of claim 1, wherein said display unit includes a cathode ray tube oscilloscope.

11. The apparatus of claim 1, wherein said display unit includes an engine analyzer.

12. A method for determining the relative power contribution by a cylinder of a multi-cylinder internal combustion engine having a crankshaft with an axis of rotation, said method comprising the steps of: providing a vibration sensor having an axis of sensitivity, mounting the sensor on the engine in a sensing position with the axis of sensitivity in a predetermined orientation spaced from and substantially orthogonal to the axis of rotation to produce an electrical waveform signal as a function of detected vibrations, and displaying the waveform signal. 13. The method of claim 12, said sensor in its sensing position has its axis of sensitivity disposed approximately in a plane which is perpendicular to the axis of rotation. 14. The method of claim 13, wherein the axis of sensitivity is disposed in said plane. 15. The method of claim 13, wherein the axis of sensitivity is directed in the direction of rotation of the crankshaft. 16. The method of claim 12, and further comprising the step of amplifying the waveform signal before displaying it. 25 17. The method of claim 12, and further comprising the step of providing a DC bias voltage to the sensor. 18. Determinative apparatus substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.