GB2213946A - Engine testing method and system therefor - Google Patents

Abstract

The performance of an automotive engine 12 is tested by accelerating the engine while imposing a predetermined load 28 on the engine and measuring the rotational speed of the engine. Rotational speed data per unit time of said engine is measured during acceleration thereof after it has started to operate, and rotational acceleration of the engine is calculated by processing said rotational speed data. The calculated rotational acceleration is compared with rotational accelerations of a normal engine and engines with intentionally given troubles e.g. ignition phase lagging or leading, timing belt lagging or leading, spark plug failure or compression leakage, and whether the performance of the engine is acceptable or not is determined, and if unacceptable the cause of a trouble of the engine is estimated, based on the result of the comparison. A cylinder 44 maintains tension in endless driving belt 18 being reduced by vibration. <IMAGE>

Description

ENGINE TESTING METHOD AND SYSTEM THEHEFOH The present invention relates to an engine testing method and system therefor, and more particularly to a method of and system for testing an engine-completed on a production line for determining the performance of the engine by accelerating the engine while imposing a predetermined inertial load thereon and t.lculat- ing the rotational acceleration of the engine at the time, and comparing the the calculated rotational acceleration with rotational acceleration data which have been measured with respect to a normal engine and engines with various troubles, so that the performance of the engine being tested can be determined easily and within a short period of time, and the cause of a trouble can be estimated for the engine which has been judged as being troubled.

Automotive engines assembled on a production line are tested or inspected in various ways in a testing process so that the performance of such engines can be checked before being mounted on automobiles. In the engine test, each engine is accelerated while a predetermined load is being imposed thereon to provide various data based on which the engine performance will be judged.

According to one engine test mode, the rotational speed of an engine being tested is measured while the engine is being operated under a given load to ascertain the char acteristics of the engine. Typical examples of such an engine test are disclosed in Japanese Laid-Open Patent Publications Nos. 55-468 and 56-63231, for example.

In the disclosed engine test, a flywheel having a certain mass of inertia is coupled to the crankshaft of an engine to be tested, and the engine is accelerated while giving the engine an inertial load through the flywheel.

During acceleration, pulses each produced when a spark plug of the engine is energized are counted to detect the rotational speed of the engine.

After the tested engine starts being operated, a time period consumed before the engine speed goes up to a predetermined speed is determined, and the operation and characteristics of the engine are estimated based on the measured time period. If the engine speed does not reach the predetermined speed within a reference period of time, then the engine being tested is found to be in trouble.

This engine testing method has however proven unsatisfactory in that the characteristics of the engine when it is raced are only qualitatively determined, but the output power of the engine cannot be quantitatively judged.

U.S. Patent No. 4,169,371 (corresponding to British Patent No. 1,538,929) discloses an engine testing process in which pulses produced by an ignition coil are differentiated for quantitatively measuring the output characteristics of an engine, such as acceleration, torque, and the like. The cause of a trouble of such a tested engine cannot however be clearly indicated by the results of the measurement, but should be determined in a different process. Therefore, the disclosed testing method is inefficient.

The present invention provides a method of testing the performance of an engine by accelerating the engine while imposing a predetermined load on the engine and measuring the rotational speed of the engine, said method comprising the steps of: measuring rotational speed data per unit time of said engine during acceleration thereof after it has started to operate; calculating rotational acceleration of the engine by processing said rotational speed data; comparing the calculated rotational acceleration with rotational accelerations of a normal engine and engines with intentionally given troubles; and determining whether the performance of the engine is acceptable or not, and/or estimating the cause of a trouble of the engine if the performance of the engine is not acceptable, based on the result of the comparison.

The method may further comprise the steps of: keeping at a constant level the tension of a belt for transmitting rotation of the crankshaft of the engine to a rotatable shaft supporting a flywheel having a predetermined mass of inertia; representing the rotational speed of said rotatable shaft by a pulse train produced by an encoder coupled to said rotatable shaft; and measuring the rotational speed data per unit time of said engine from said pulse train.

The method may further comprise the steps of: sampling the rotational speed data per unit time of said engine with a data logger at predetermined time intervals and transferring the sampled rotational speed data to arit,imetic processing means; processing the rotational speed data to calculate a rotational acceleration in a predetermined speed zone with said arithmetic processing means; and comparing the rotational acceleration with the rotational accelerations of the normal engine and the engines with intentionally given troubles in said predetermined speed zone.

Additionally, the method may further comprise the step of: measuring beforehand rotational accelerations of an engine with an ignition phase deviation, an engine with a timing belt phase deviation, and an engine with a spark plug failure in the predetermined speed zone.

The present invention also provides system for testing an engine, comprising: a flywheel for imposing an inertial load on the crankshaft of the engine; speed detecting means coupled to said flywheel for detecting the rotational speed of the flywheel, first memory means for storing rotational speed of the engine produced from said speed detecting means; second memory means for storing reference engine rotational acceleration data; and comparator means for comparing rotational acceleration data of the engine calculated from the rotational speed data obtained from said first memory means with the reference engine rotational acceleration data obtained from said second memory means to determine whether said engine is normal or not.

Preferably, said first memory means comprises a data logger which is supplied with data on a rotational condition of the engine.

The system may further include an encoder coupled to said flywheel and an analog-to-digital converter for converting an output signal from said encoder to a digital signal and applying the digital signal to said data logger.

Optionally, said rotational condition of the engine supplied to said data logger is represented by a signal indicating the opening of a throttle valve of the engine.

The system may further include third memory means for storing data on rotational accelerations of engines with intentionally given troubles, and wherein said comparator means compares the data stored in said third memory means and the rotational acceleration data of said engine.

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings, in which: FIG. 1 is a perspective view of a system according to the present invention comprising an engine testing apparatus, with a measuring unit shown in block form, used for carrying out an engine testing method according to the present invention; FIG. 2 is a flowchart of a procedure of the engine testing method of the invention; FIG. 3 is a graph showing rotational speeds of an engine tested according to the engine testing method; FIG. 4 is a graph illustrating, at an enlarged scale, data shown in FIG. 3; FIGS. 5(a) and 5(b) are graphs showing data produced by processing the rotational speed data of FIG. 3 for determining rotational acceleration;; FIG. 6 is a graph showing the manner in which rotational acceleration is calculated from the rotational speed data of FIG. 5(b); FIGS. 7(a) and 7(b) are graphs of rotational acceleration data measured of a normal engine and troubled engines; and FIG. 8 is a graph showing rotational speed curves measured of a plurality of engines.

FIG. 1 shows the system of the present invention comprising an engine testing apparatus, generally designated by the reference numeral 10, used for carrying out an engine testing method according to the present invention.

An engine 12 such as an automotive engine is conveyed into a position above the testing apparatus 10 by a conveyor means (not shown) and secured in position by a clamp means (not shown) while being suspended above the testing apparatus 10. The engine 12 has a crankshaft 14 on which a crankshaft pulley 16 is mounted. The crankshaft pulley 16 is operatively coupled to the testing apparatus 10 by means of an endless belt 18.

The testing apparatus 10 will be described in detail below. A first pulley 26 is mounted on a rotatable shaft 24 supported by bearings 22a, 22b mounted on a support base 20. A flywheel 28 is attached to one end portion of the shaft 24 fot imposing a predetermined inertial load on the engine 12. A support member 32 is angularly movably supported on a support shaft 30 fitted over the rotatable shaft 24, and a second pulley 34 is rotatably mounted on the distal end of the support member 32, the second pulley 34 having two sheaves 36a, 36b. The sheave 36a is operatively coupled to the crankshaft pulley 16 by the belt 18. Another endless belt 38 is trained around the sheave 36b and the first pulley 26.Therefore, rotative power from the engine 12 is transmitted through the belt 18 to the second pulley 34 from which it is transmitted through the belt 38 to the shaft 24 rotating with the first pulley 26, thus rotating the flywheel 28. The engine 12 is therefore rotated while the inertial load of the flywheel 28 is being applied to the engine 12. The rotational speed of the engine 12 at the time is detected as a train of pulses generated by an encoder 40 mounted on the end of the shaft 24 and applied to a measuring unit 42. The frequency of the generated pulses corresponds to the rotational speed of the engine 12.

A cylinder 44 mounted on the support base 20 serves to prevent the belt 18 from being slackened due to vibration produced when the engine 12 is in operation. More specifically, zone cylinder 44 has a rod 46 coupled to the base end of the support member 32 through a pin. By operating the cylinder 44, the support member 32 is tilted about the support shaft 30 in the direction of the arrow A to tension the belt 18 that is trained around the second pulley 34 on the distal end of the support member 32 and the crankshaft pulley 16 of the engine 12. Therefore, the rotational speed of the engine 12 can accurately be detected by the encoder 40.

The measuring unit 42 is constructed as follows: The encoder 40 has an output terminal coupled to a frequency-to-voltage (F/V) converter 48 which converts the frequency of the pulses from the encoder 40 to a voltage proportional to the pulse frequency. The output terminal of the F/V converter 48 is connected to a first memory means comprising, for example, a data logger 52 through an analog-to-digital (A/D) converter 50.

An output signal from the F/W converter 48 is thus converted to dic tal data which are sampled by the data logger 52. The data logger 52 is connected to a data processing computer 54 serving as an arithmetic means for processing the sampled data. To the data processing computer 54, there are connected a keyboard 56, a CRT display 58, a floppy disc unit 60, and a line printer 62.

The data processing computer 54 is supplied with various parameters representing the conditions of the engine 12, e.g., data on the temperature of an engine coolant, the temperature of engine lubricating oil, the pressure under which lubricating oil is circulated through the engine, and the like, which are measured by various respective sensors.

The data processing computer 54 is controlled by a sequencer 64 which also controls a throttle actuator 68 through a throttle controller 66. The engine 12 has a throttle valve 70 which can be opened and closed by the throttle actuator 68. A signal indicative of the opening of the throttle valve 70 is applied through the throttle controller 66 and an A/D converter 72 to the data logger 52. A voltage comparator 74 applies a signal for half opening the throttle valve 70 to the throttle controller 66 when the output voltage from the F/V converter 48 exceeds the constant level of a reference signal.

An engine testing method according to the present invention, which is carried out by a system comprising the testing apparatus 10 and the measuring unit 42, will be described below.

FIG. 2 shows a procedure of the engine testing method of the invention. The engine testing method will be described with reference to FIGS. 1 and 2.

A signal for half opening the throttle valve 70 is sent to the throttle controller 66 under the control of the sequencer 64 to operate the throttle actuator 68 to half open the throttle valve 70. Then, the engine 12 is started and warms up for a predetermined period of time. Various parameters indicating the initial conditions of the engine 12, e.g., the temperature of an engine coolant, the pressure under which engine lubricating oil is circulated, the temperature of engine lubricating oil, and the like, are sent from sensors or measuring devices (not shown) to the data processing computer 54. The values of these parameters are displayed on the CRT display 58 and printed by the line printer 62.

If the initial conditions of the engine 12 are normal in a step 1 (FIG. 2), then the sequencer 64 sends a signal for fully opening the throttle valve 70 of the engine 12 to the throttle controller 66. The throttle controller 66 operate the throttle actuator 68 to fully open the throttle valve 70 in a step 2. Data indicating the opening of the throttle valve 70 are transferred via the A/D converter 72 to the data logger 52. As the opening of the throttle valve 70 increases, the rotational speed of the engine 12 also increases. Rotative power of the engine 12 is transmitted from the crankshaft pulley 16 via the belt 18, the second pulley 34, the belt 38, and the first pulley 26 to the shaft 24, and an inertial load of the flywheel 28 is imposed on the engine 12. The rotational speed of the engine 12 during this time is detected as a pulse train by the encoder 40. The encoder 40 is designed to issue 150 pulses per revolution, for example, of the engine 12.

The pulse train is converted to the reciprocal of the periodic time thereof1 i.e., a voltage proportional to the frequency of the pulse train, by the F/V converter 48.

The output voltage from the F/V converter 48 corresponds to the number of revolutions of the engine per unit time, and is converted to digital data indicative of the number of revolutions per unit time by the A/D converter 50. The digital rotational speed data are thereafter sampled and stored by the data logger 53.

After the engine testing process has started, the data logger 53 successively stores the rotational speed data introduced from the A/D converter 50 into a first memory area thereof (not shown) per 1 msec. At the same time, the data on the opening of the throttle valve 70 are applied from the throttle controller 66 to the A/D converter 72, which converts the data to digital data that are successively stored in the memory area of the data logger 52 per 5 msec., for example.

The number of revolutions per unit time of the engine 12 and the opening of the throttle valve 70 are continued for 4 seconds, for example. Therefore, 400 points of data on the rotational speed of the engine 12 and 800 points of data on the opening of the throttle valve 70 are sampled and stored by the data logger 52 during the above measuring time.

Then, the above data measurement is repeated a required number of times in a step 4. It is sufficient for the data measurement to be repeated three times. The data on the number of revolutions per unit time of the engine and the data on the opening of the throttle valve 70, thus obtained, are then transferred from the data logger 52 to the data processing computer 54 and stored therein.

The data transferred to the data processing computer 54 are processed for graphic display, and displayed on the CRT display 58 as engine rotational speed and throttle valve opening curves as shown in FIG. 3. The curve 80 in FIG. 3 indicates a time-dependent change of the opening [%] of the throttle valve 70, and the curve 82 indicates a timedependent change of rke number of revolutions per unit time, here [rpm], of the engine 12. The curves 80, 82 are plotted based on data measured three times.

The data shown in FIG. 3 are cr - e data and hence are not suitable for use as a basis for a data analysis because the rotational speed of the engine fluctuates dependent on the successive power strokes of the cylinders of the engine.

Therefore, the rotational speed data are processed by the data processing computer 54 in a step 5 automatically based on a program read in the data processing computer 54.

In FIG. 3, the rotational speed data before the throttle valve 70 is fully opened, i.e., prior to a time to, are neglected, and only the rotational speed data after the time to are used as effective. This is because the time required for the throttle valve 70 to be fully opened varies from measurement to measurement, and one measurement result and another measurement result would not accurately be compared if such time differences were involved. Therefore, only the effective rotational speed data will be processed by the data processing computer 54.

FIG. 4 shows a portion, at an enlarged scale, of the curve 82 representing the rotational speed shown in FIG.

3. There are 10 points of rotational speed data in each zone of 10 msec. In each zone, the average value of the maximum and minimum rotational speeds is calculated. More specifically, the average value Meant of the minimum rotational speed Minl and the maximum rotational speed Maxl in a zone I1 of 10 msec. is calculated. Likewise, average values Mean2, ... are calculated in respective zones 12 ... . The average values Meant, Mean2, ... are used as representing the rotational speeds in the respective zones I,, 12 ...

Through the above calculations, the rotational speed data shown in FIG. 3 are converted to rotational speed data shown in FIG. 5(a).

Then, the rotational speed data shown in FIG. 5(a) are filtered by a soltware-implemented digital filter in the data processing computer 54 to remove unwanted rotational speed components, thereby producing rotational speed data represented by a smooth curve as shown in FIG. 5(b).

Rotational acceleration is then calculated from the rotational speed data which are thus finally processed, in the following manner (step 6): Rotational accelerations are determined in predetermined rotational speed zones, i.e., an initial rotational speed zone: 1200 - 2000 rpm, and successive 500-rpm rotational speed zones: 2000 - 2500 rpm, 2500 - 3000 rpm, 3000 - 3500 rp, and 3500 - 4000 rpm.

At this time, the rotational acceleration in the zone of 2000 - 2500 rpm, for instance, is determined as follows: The rotational speed data a corresponding td 2000 rpm, ,the rotational speed data b, c which are before and after the rotational speed data a by times da, the rotational speed data a1 corresponding to 2500 rpm, and the rotational speed data bl, c1 which are before and after the rotational speed data a1 by times Aa are picked up, and the following values are calculated:

where At, is the time interval between the data a and the data al. The average of these calculated values is used as the rotational acceleration of the zone 2000 - 2500 rpm.

The rotational accelerations of the other zones are similarly determined. Then, the rotational acceleration from 2000 rpm to 4000 rpm is determined by averaging the rotational accelerations which have been calculated as described above with respect to the 500-rpm rotational speed zones.

In this manner, the rotational accelerations of the initial rotational speed zone 1200 - 2000 rpm and the rota tional speed zone 2000 - 4000 rpm are calculated. These rotational accelerations are calculated based on the rota tional speed data which have been measured three times in the step 4.

The data processing computer 54 stores, in a second memory means, rotational acceleration data, as reference data, which have been measured beforehand with respect to a normal engine and also stores in a third memory means rotational acceleration data which have been measured beforehand with respect to engines with various intentionally given troubles, in the same manner as described above. As shown in FIG. 7(a), the reference data are plotted as a graph on the CRT display 58. The graph of FIG. 7(a) has a horizontal axis marked with IG+5, IG-5, VT+1, VT-1, PG&num;1, and TC which are representative of intentionally given troubles. For example, data on the mark IG+5 are obtained by adjusting a plurality of engines to have the ignition phase of spark plugs leading by 5 , calculating rotational acceleration data in the rotational speed zone 2000 - 4000 rpm with respect to these engines, and plotting the calculated rotational acceleration data. Each of the vertical lines drawn across the plotted data indicates a range of + 3s from the average of the rotational acceleration data where o is the standard deviation. In this range, the data are relia ble taken into consideration measuring errors produced when the rotational accelerations are determined as the reference data and also errors produced when the data are processed.

The range may be established dependent on the causes of troubles, the characteristics of the engines, or the number and accuracy of zone data. The data indicated by NORMAL in FIG. 7(a) are reference data similarly obtained with respect to a normal engine. The range of + 3O from the average of the rotational acceleration data of the normal engine is specially indicated as a region S which will be used for determining whether the performance of a tested engine is acceptable or not, as described later. FIG. 7(b) shows-'sim- ilar reference data for the rotational speed zone 1200 2000 rpm.

The rotational acceleration obtained by the aforesaid data processing is supplied from the data processing computer 54 and displayed on the CRT display 58 with the reference data of FIG. 7(a), the displayed rotational acceleration data being indicated at TEST in FIG. 7(a). A step 7 of FIG. 2 then compares the rotational acceleration with the reference data to determine whether the acceleration performance of the engine 12 is acceptable or not. Since the rotational acceleration data (TEST) fall within the range S in of FIG. 7(a) in the illustrated embodiment, the engine 12 is judged as being normal. If, however, the rotational acceleration data (TEST) fall within the range indicated by IG+5, then the engine is determined as being troubled, and the cause of the trouble is estimated as being the leading ignition phase in a step 8.The same comparison and judgment are carried out with respect to the rotational speed range 1200 - 2000 rpm shown in FIG. 7(b). Based on the combined analysis for both the rotational speed zones or ranges, the performance of the engine 12 being tested can be determined more reliably.

Whether the engine 12 is acceptable or not can be judged in a very short period of time by displaying the graphs of FIGS. 7(a) and 7(b) on the CRT display 58 through the operation of the keyboard 56 by the operator. The data on the rotational speed of the engine 12 and the data on the opening of the throttle valve 70, which are obtained in the step 3 of FIG. 2 are stored in the memory in the data processing computer 54. These data can be displayed on the CRT display 58 in desired ways, for example, by superposing the rotational speed curves and throttle valve opening curves of other engines, as shown in FIG. 8. It can therefore be understood that the performance of an engine can be tested in various different manners.

With the present invention, as described above, the number of revolutions per unit time of an engine is measured, and the measured rotational speed data are processed to calculate a rotational acceleration. The calculated rotational acceleration is compared with rotational acceleration data of a normal engine and engines with intentionally given troubles. Therefore, it is possible to determine whether performance of the engine is acceptable or not, based on objective criteria without relying upon empir ical personal judgment. Moreover, the cause of a trouble of an engine which is found to be troubled can be estimated at the same time.Since the rotational acceleration of an engine is proportional to the output torque of the engine, the judgment of the tested engine is not limited to a quali tative approach, but quantitative data with respect to acceleration performance and output torque, for example, can be obtained. The measured rotational speed data are immedi ately displayed by being processed by the means which have calculated the rotational speed data. Consequently, the engine test can quickly and easily be performed, and the efficiency of the test is greatly increased.

The preferred embodiment of the present invention can provide an engine testing method and system therefor for measuring the output characteristics of an engine being tested, determining whether the performance of the engine is acceptable or not, and estimating the cause of a trouble if the engine is found to be troubled, by measuring beforehand data of the rota tional accelerations of a normal reference engine and engines with various troubles which have been caused intentionally, and comparing the data with an åcceleration measured of the engine being tested.

Although a certain preferred embodiment has been shown and described, it should be understood that many changes and-modifications may be made therein without departing from the scope of the appended claims.

Claims (11)

CLAIMS.

1. A method of testing the performance of an engine by accelerating the engine while imposing a predetermined load on the engine and measuring the rotational speed of the engine, said method comprising the steps of: measuring rotational speed data per unit time of said engine during acceleration thereof after it has started to operate; calculating rotational acceleration of the engine by processing said rotational speed data; comparing the calculated rotational acceleration with rotational accelerations of a normal engine and engines with intentionally given troubles; and determining whether the performance of the engine is acceptable or not, and/or estimating the cause of a trouble of the engine if the performance of the engine is not acceptable, based on the result of the comparison.

2. A method according to claim 1, further colaprising the steps of: keeping at a constant level the tension of a belt for transmitting rotation of the crankshaft of the engine to a rotatable shaft supporting a flywheel having a predetermined mass of inertia; representing the rotational speed of said rotatable shaft by a pulse train produced by an encoder coupled to said rotatable shaft; and measuring the rotational speed data per unit time of said engine from said pulse train.

3. A method according to claim 1 or 2, further comprising the steps of: sampling the rotational speed data per unit time of said engine with a data logger at predetermined time intervals and transferring the sampled rotational speed data to arithmetic processing means; processing the rotational speed data to calculate a rotational acceleration in a predetermined speed zone with said arithmetic processing means; and comparing the rotational acceleration with the rotational accelerations of the normal engine and the engines with intentionally given troubles in said predetermined speed zone.

4. A method according to claim 3, further comprising the step of: measuring beforehand rotational accelerations of an engine with an ignition phase deviation, an engine with a timing belt phase deviation, and an engine with a spark plug failure in the predetermined speed zone.

5. A system for testing an engine, comprising: a flywheel for imposing an inertial load on the crankshaft of the engine; speed detecting means coupled to said flywheel for detecting the rotational speed of the flywheel; first memory means for storing rotational speed of the engine produced from said speed detecting means; second memory means for storing reference engine rotational acceleration data; and comparator means for comparing rotational acceleration data of the engine calculated from the rotational speed data obtained from said first memory means with the reference engine rotational acceleration data obtained from said second memory means to determine whether said engine is normal or not.

6. A system according to claim 5, wherein said first memory means comprises a data logger which is supplied with data on a rotational condition of the engine.

7. A system according to claim 6, further including an encoder coupled to said flywheel and an analog-to-digital converter for converting an output signal from said encoder to a digital signal and applying the digital signal to said data logger.

8. A system according to claim 6 or 7, wherein said rotational condition of the engine supplied to said data logger is represented by a signal indicating the opening of a throttle valve of the engine.

9. A system according to claim 5, further including third memory means for storing data on rotational accelerations of engines with intentionally given troubles, and wherein said comparator means compares the data stored in said third mem ory means and the rotational acceleration data of said engine.

10. A method of testing the performance of an engine substantially as hereinbefore described with reference to the accompanying drawings.

11. A system for testing an engine substantially as hereinbefore described with reference to the accompanying drawings.