GB2143039A - Timing apparatus for rotating parts - Google Patents

Abstract

Timing pulses having a fixed relationship to a rotating part, for example a flywheel starter ring in the case of an IC engine, have been produced by the difficult and costly method of drilling a plurality of accurately positioned holes in the flywheel, sensing their passage past a transducer and generating a pulse in response to each passage. In this invention, the pulses are generated by a microprocessor 1, and their synchronisation with the rotation of the flywheel is checked each time one of the pre-existing accurately machined teeth of the flywheel starter ring passes a transducer and their period adjusted if necessary. A second transducer produces a reference pulse once per revolution at a position representative of the top dead centre position. From these pulses a number of pulse trains synchronised with the rotation of flywheel may be produced (Channels 1 to 8). <IMAGE>

Description

SPECIFICATION Timing apparatus For a number of purposes, the need exists with internal combustion engines, and other devices having rotating parts, to produce a given number of electrical pulses per revolution, the pulses being accurately spaced from one another. The pulses must in almost all cases be synchronised, or at least have some predetermined relationship, with some fixed reference point or position within, for example, an internal combustion engine's operating cycle. In the case of such an engine, a commonly used reference position is the piston top dead centre (TDC) position for a particular cylinder, in the case of an engine having more than one cylinder.

A practical requirement in internal combustion engine development laboratories is the ability to provide timing marks in certain definite angular positions when taking diagrams to follow some operating function of the engine under test. Uses for such processing indicators can be, by way of Example, tracing the gas pressure variation within an engine cylinder throughout its cycle of operation; measuring fuel injection pipe pressures during the injection period, including noting any cycle to cycle variations; measuring fuel injector needle lifts; and measuring valve lifts, velocities or accelerations throughout their lift cycles. Such information is frequently observed on a cathode ray oscilloscope, or photographed, when accurately placed timing marks facilitate the interpretation of phenomena displayed.When observations are made it is sometimes advantageous to expand the time axis (or axis indicating the crank angle of the engine) of the diagram in orderto study the details more closely. In such cases, time markings are clearly very valuable.

When viewing such diagrams, it may be required to follow an expanded diagram in sections so it is necessary at times to rephase the starting point of the display sweep by an accurately known number of degrees.

It is has been found that it is possible to read the (for all practical purposes) instantaneous voltage or other analogous signals corresponding to (say) the pressure prevailing at that instant within an internal combustion engine cylinder, convert it to digital form and to retain its value in a suitable memory store. For this exercise to be of value, accurate determination of the crank angle is needed at the instant of reading, together with its repetition, if the value of the parameter under study is to be stored over a number of cycles, after which either the mean value or the cycle to cycle variation may be studied. By organising a large number of parameter values and crank angles the whole indicator diagram can be stored digitally and used for further analysis or even as a basis for design calculations.To enhance accuracy it is desirable to take readings at much smaller time intervals when the parameters, for example, the pressures, are changing rapidly with time.

From this it is clear that there is a real need to produce a train of timing pulses of known phase and number. Traditionally, this has been done by drilling holes, or slotting grooves, at the required angular positions in an internal combustion engine flywheel, or in a separately attached disc, and generating timing pulses by means of a suitable transducer. Sometimes more than one timing track has been necessary if separate synchronising signals have been required simultaneously. The machining to a high order or accuracy is difficult, time consuming and expensive, particularly in large engines. If, subsequently, a different set of timing intervals is required the process must be repeated.

The present invention enables the provision of a method for flexibly selecting desired operational markers or triggering points with a high degree of accuracy. The operational markers may be, but do not necessarily have to be, used in the study of an internal combustion engine.

According to a first aspect of the present invention, there is provided a method of producing a train of pulses having a predetermined relationship with the angle of rotation of a rotatable object having a plurality of separating detectable features, the relative position of the features being fixed with respect to a reference position of the object, the method comprising generating a train of pulses from a period controllable oscillator, sensing each time a feature passes a certain point during the object's rotation, determining at the passage of each feature past the point whether the train of pulses generated by the oscillator has the desired predetermined relationship, and, if the train does not have the desired predetermined relationship altering the period of the period controllable oscillator by way of correction.

The rotatable object is preferably a toothed wheel, the separately detectable features being teeth of the wheel. It is with such a case that the present invention is particularly applicable to the study of internal combustion engines, as the toothed wheel may be a starter ring of an internal combustion engine. The starter ring is always present on multi-cylinder vehicle engines. The teeth on this ring are machined to quite a high standard of accuracy by conventional gear cutting methods during production.

Again when the invention is applied to an internal combustion engine, the reference position may be representative of a piston TDC position.

The passage of a feature of the rotating object (such as a tooth of a starter ring) past a certain point may be detected by positioning a first transducer at that point. The transducer would usually be an electromagnetic one and positioned in close proximity to the tips of the gear teeth. An approximately sinusoidal voltage would be induced in the winding surrounding the permanent magnet core of this type of transducer as each tooth approaches, passes and leaves. Such transducers in themselves are well known and widely used for various timing devices. Although such an inductive magnetic transducer has been specifically mentioned, and is probably the most convenient type to use at present, other transducers such as occulting light beam, capacity type proximity pickup, magneto-striction and Hall-effect transducers may be used.

The voltage generated at the passage of each tooth can then be passed to a Schmidt trigger circuit, by means of which an accurately-shaped constant amplitude rectangular pulse output can be obtained with virtually instantaneous rises of voltage from zero to full amplitude. Thus the output of the Schmidt triggers a train of rectangular wave-form pulses whose frequency is the product of the gear wheel's rotational speed and the number of teeth used.

A second transducer may be used to detect the passage of the reference position past a certain point. The second transducer may be similar to or different from the first transducer. The second transducer can in effect be used to create a synchronisationlinitiation pulse every revolution of the rotating object. Thus a carefully positioned drilled hole or slot in an internal combustion engine flywheel may generate a single pulse per revolution as the second transducer is passed. Normaliy, this single pulse would be arranged to be at TOC, but this is not essential.Even for internal combustion engines, any position other than TDC can be used providing that the angular position of, for example, the flywheel is accurately known or that some other means, for example a proximity gauge, is used to monitor the TDC position and that appropriate adjustment is made to the generated pulse train.

The most usual predetermined relationship between the train of pulses and the angle of rotation will be one of synchronism with rotation of the reference position, for example, TDC. Once a train of pulses having a desired predetermined relationship has been produced, it is possible to derive further pulse trains having other predetermined relationships with the rotation. Pulses obtained from rotation of the reference position may also be used in this derivation.

In a particularly preferred embodiment, the period controllable oscillator comprises a microprocessorbased down counter of decrementer, the period being controlled by the value loaded into the decrementer at the start of each countdown. Thus in effect the decrementer is used as an oscillator under digital control.

The determination of whether the pulse train has the desired predetermined relationship with the rotatable object, for example, the toothed wheel, may be achieved by (a) observing when the feature (or tooth) passes the said point (b) calculating from the pulse train characteristics when the feature (or tooth) should pass or should have passed the said point if the pulse train were to have the desired predetermined relationship and (c) altering the period of the period controllable oscillator, if the result from (a) is not the same as the result from (b), by way of correction. It is particularly preferred that the period be so altered as to correct any deviation from the desired predetermined relationship by the time that the next feature (or tooth) passes the set point.

It can thus be seen that the first aspect of the invention extends to and embraces a method of producing a train of pulses having a predetermined relationship with the angle of rotation of a a toothed wheel, the relative position of the teeth of which wheel are fixed with respect to a reference position of the wheel, the method comprising generating a train of pulses from a period-controllable oscillator, sensing each time a tooth of the wheel passes a certain point during the wheel's rotation, determining at the passage of each tooth past the point whether the train of pulses has the desired predetermined relationship with the rotation of the wheel and, if the train does not have the desired predetermined relationship, altering the period of the period controllable oscillator by way of correction.

According to a second aspect of the present invention, there is provided an apparatus for producing a train of pulses having a predetermined relationship with the angle of rotation of a rotatable object having a plurality of separately detectable features, the relative position of the features being fixed with respect to a reference position of the object, the apparatus comprising a period controllable oscillator for generating a train of pulses, means for sensing each time a feature passes a certain point during the object's rotation, means for determining whether the train of pulses generated by the oscillator has the desired predetermined relationship and means for altering the period of the period controllable oscillator if the pulse train does not have the desired predetermined relationship.

It can be seen that the second aspect of the invention extends to an apparatus for producing a train of pulses having a predetermined relationship with the angle of rotation of a toothed wheel, the relative position of the teeth of which wheel are fixed with respect to a reference position of the wheel, the apparatus comprising a period controllable oscillator for generating a train of pulses, means for sensing each time a tooth passes a certain point during the wheel's rotation, means for determining whether the train of pulses generated by the oscillator has the desired predetermined relationship and means for altering the period of the period controllable oscillator if the pulse train does not have the desired predetermined relationship.

Many preferred embodiments of the second aspect of the invention correspond to preferred aspects of the first aspect of the invention, mutatis mutandis.

In a particularly preferred embodiment of the second aspect of the invention, the period controllable oscillator, the determining means and the altering means are provided by a microprocessor which may be at least a 16-bit processor. But it will be understood that other arrangements are possible: for example, the determining means and the altering means may be provided by a microprocessor or by other means and the decrementer could be provided by a separate piece of hardware.

According to a third aspect of the present invention, there is provided an internal combustion engine test apparatus including an apparatus in accordance with the second aspect of the invention and/or whose operation includes a method in accordance with the first aspect of the invention.

For a better understanding of the present invention, and to show how it may be put into effect, the following description of a preferred embodiment will now be given, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of an apparatus in accordance with the invention; Figure 2 is a partial circuit diagram of the preferred embodiment; Figure 3a is a diagram showing the variables involved in the middle of a revolutionary cycle; Figure 3b is a diagram showing the variables involved at the beginning of a revolutionary cycle; Figure 4 is a diagram illustrating the calculation of the period, measured in microprocessor decrementer time base units; and Figure 5 is a diagram showing the result of control action.

The preferred embodiment of the present invention produces a train of timing pulses accurately synchronised with each cycle of operation of an internal combustion engine. A microprocessor 1 is shown schematically in Figure 1. It has two inputs. The first is for a reference pulse which derives from a transducer located near the flywheel of the internal combustion engine adjacent a hole or a slit cut in the flywheel side or perimeter accurately phased to the TDC piston position for, for example, number 1 cylinder in the case of a multi-cylinder engine; thus a pulse is obtained once every flywheel revolution. The second input is from a further transducer positioned adjacent the path of the flywheel starter ring teeth, so that a pulse is received as each tooth passes the transducer.

By means of the microprocessor 1, a series of pulsed output signals, each in a respective channel (labelled Nos. 1 to 8) can be obtained and used to synchronise, for example, crank angle indicating marks on a cathode ray oscilloscope or otherwise operate known devices. Information obtained from channels 1 to 8 can be used for the study of event timing of engine variables, such as diesel fuel line pressures, fuel injection needle lift diagrams and so forth. If desired, the output pulses in any one of channels 1 to 8 may be used to sample signals from devices measuring continuous but variable-with-time output parameters such as pressure.

By way of example, the following pulse trains can be derived from the output of the microprocessor 1: Channel 1 720 pulses per engine revolution 2 1 pulse (at TDC) per engine revolution 3 360 pulses per engine revolution 4 A fixed timing pulse at 70"BTDC used for ignition delay studies.

(any other such fixed reference timing may be obtained).

5 Synchronisation pulses at six equally spaced times per engine revolution 6 Patterns of degree marks for use on C.R.O. indicator diagrams, for example pulse marks at 10 intervals for most of a revolution but at 5" intervals at + 20 of TDC.

7) 8) Spare channels which may be used to signal faults, for example, too large or too small time intervals between the passage of successive flywheel teeth.

The pulse trains in channels 3 to 6 can be derived from channel 1, using channel 2 in addition if necessary.

Figure 2 shows the arrangement indicated diagrammatically in Figure 1 in rather more detail. Connected across the terminals XTAL1 and XTAL2 of the TMS 9995 microprocessor lisa 12 MHz crystal determining the operational frequency of the microprocessor. Other frequencies can be used if desired. Signals from the TDC reference transducer are fed to the terminal of the device marked REF and pulses from the flywheel starter ring tooth transducer are fed to the RING input. Pulses from REF and RING inputs pass through respective inverting buffers to pins marked INT1 and INT4/EC.

As the "on-board" memory of the microprocessor 1 is limited, the microprocessor 1 is connected to a TMS 2516 Erasable Programmable Read-Only Memory (EPROM)2 as shown in Figure 2 via address bus, data bus and control signals. A 74LS374 output storage buffer 3, which leads to output channels 1 to 8, is driven from the data bus.

The preferred embodiment of the invention is based around an oscillator on board the TMS9995 microprocessor 1. The on-chip decrementer performs as a period controllable oscillator in that the frequency of down counts to zero (or zero points) is determined by the value loaded into the period register. At each zero point the microprocessor output changes to a new value, that is to say the output either goes from low to high or goes from high to low. Thus the zero points coincide with the transition points of the output pulse train and so, by varying the value loaded into the period register of the decrementer, the characteristics of the output pulse train can be varied.

Each time a zero point occurs, a software counter is incremented. It is required that the contents of this counter at a given moment should correspond to the actual crank angle at that moment.

In the following analysis of operation of the preferred embodiment, the following terms are used: M Total number of engine flywheel (starter ring) teeth (10. . .200) m Current flywheel tooth number under consideration (1. . .M) N Total number of zero points (and therefore an output transition points) per flywheel revolution; in this case, 720 n Current number of times that the decrementer has counted to zero so far in the current revolution (0.. .719) nm The value of n at tooth m TM Decrementer reload counter value (1. . .hFFFF) A Starter ring tooth spacing in degrees (1.. .100) E Angular error in degrees at current position (0. . .10) em Erroreattooth m in unitsofn T Previous flywheel tooth period in decrementer time base units (10. ..hFFFF) dm Offset of reference position from first tooth position (in units of n) Dm current decrementercontents at tooth m Note 1:(a.. .b), when referring to a number, means that the number can have a value from a to b.

Note 2:hNNNN refers to a number in hexadecimal. hFFFF equals 6553510.

It will be understood that M is a constant for a given starter ring. But this number is treated as a variable, so that different starter rings can be used. It is possible for the microprocessor to be programmed to measure M for a given flywheel starter ring.

in the operation of the preferred embodiment, at each tooth m, the actual value of the crank angle (in units of n - that is to say, there are 720 units per revolution) is observed. Also at each tooth m, the "set point value". of the crank angle, that is to say the calculated value of what the crank angle should be, is obtained.

This is also done in units of n. From the actual value of the crank angle and the set point value of the crank angle, the error in the crank angle em is calculated. From this, a new decrementer reload value TM' is then derived to determine the value loaded into the period register after each zero point until the next tooth n+1 is reached.

The key formula which controls the new decrementer reload countervalue TM' is: TM'= T 2A- (I) This formula will now be derived. First, a word about angular units. The angular units used in the calculation are, as mentioned above, units of n. In the present case, there are 720 (that is to say N) such units per revolution and so each unit n can be regarded, in steady state rotation of the flywheel, as a half degree.

The relationships between of the variables used in the derivation can be seen in Figures 3a and 3b. Figure 3a shows the relationship between flywheel teeth and output pulses during the middle of a revolution and Figure 3b shows the relationship between flywheel teeth pulses and a pulse resulting from the reference position. The actual value for the crank angle (in units of n) is equal to the number of accumulated zero points nm and a fraction of the downcount currently underway: Actual value

The set point value (or calculated value) of the crank angle is derived from knowing the current flywheel tooth number m, the total number of flywheel teeth M and the offset between the TDC (reference) position pulse and the first flywheel tooth pulse dm N Setpointvalue = (m + dm). M (3) Now, the error em is the difference between the setpoint value and the actual value and is:

We thus have a value of em for the error at tooth m and it now has to be shown how this is used in the calculation of the new decremental reload counter value, which sets the new period of the period controllable oscillator.

First, it is true that the total number of decrements carried out by the decrementer during one flywheel revolution will be TM.N, as there are TM decrements between each zero point. It is also true that the number of decrements per revolution is given by M.T as there are T decrements per tooth m. Therefore TM.N TM.N=M.T ..TM=M.T N But A = 360 (by definition) M ..A A = N as N = 720 TM ..TM=T 2A The above derivation of TM shows that, for zero error, TM is inversely related to 2A, which is the space in between the teeth in units of n. But to correct an error em, the new decrementer reload countervalue TM', is given by TM'= T 2A-em which is equation (1).

Viewed another way, as N/M is the number of zero points between successive teeth if there is no error, as N/M = 2A and can therefore replace 2A in formula 1, it will be apparent that the number of zero points after tooth m, at which error em was detected, should be (N/M-em) by way of correction. Hence the denominator on the right hand side of equation 1 is (N/M - em) or (2A-em).

In equation 1, we have values for A (= N/2M) and em (see equation 4). To be able to calculate TM', we additionally need to be able to calculate T. T is the time period in decrementer time base units between tooth m - 1 and tooth m and is measured by accumulating the number of down counts to zero that occur in the interval (and multiplying this by TM) and also taking into account the fractions at each end. T is given by T = Dim~1 + (nm-nm-i). TM Dm In practice, as is shown in Figure 4, equation 5 is implemented as a series of additions of TM at each zero point. This is done for speed as an addition takes only 16% of the time required for a multiplication in the microprocessor.

It is now possible to calculate the new decrementer reload countervalue TM', and hence the new period of the period controllable oscillator, to compensate for error em recognised at tooth m. The correction principle is shown in Figure 5. Here, the line ABC is the required true relationship between the crank shaft angle (and hence flywheel angle) and time. However, by way of example, the relationship during the passage time between teeth m- 1 and m may in fact be along the line ab which would continue without correction to c. At the pulse due to the passage of tooth m the error em is recognised to adjust the period of the period controllable oscillator such that the correct crank angle/time relationship is reached at point C by the time tooth m+1 is reached.

Thus it is possible to establish the required output pulse train accurately phased with the TDC reference marker pulse. In addition, this can be achieved regardless ofthe engine's mean operating speed and possible instantaneous cyclical speed variation, which is the consequence of the varying instantaneous torques characteristic of the reciprocating internal combustion engine.

It is possible to make an estimate of the maximum error involved in steady state running conditions, that is to say ignoring any interruptions in the operation of the decrementer and ignoring arithmetic truncation errors. The maximum error is determined by the quantum value and is given by Maximum time error = 0.5 x 1.333 x 10-6x 720s M where M is the number of flywheel teeth.

With 100 flywheel teeth say, the maximum time error can be calculated to be 4.8 microseconds. At an engine speed of 3200 RPM this corresponds to an angular error of 0.15". This error is reduced proportionally at lower engine speeds. If an uprated microprocessor with a 16 MHz crystal were used, the error would be reduced to 0.12".

At several stages during the operation of the microprocessor, the downcount of the decrementer is interrupted. The TMS 9995 microprocessor has a multi-level interrupt facility and the routines to which control temporarily passes during each interrupt is now described, by way of example.

Interrupt level zero - System set-up Interrupt Level 0 Copy program from EPROM area h1000 to microprocessor on-chip RAM area hF000 Calculate N/M and store for future use I Load decrementer with hFFFF and set going I Set interrupt mask to 4 to enable flywheel starter ring tooth (4), decrementer (3) and reference/TDC mark (1) routines I Idle Interrupt Level 1 - when reference/TDC pulse arrives Interrupt level 1 I Save current flywheel tooth number m as M I clear m I Return Interrupt Level 3 - when decrementer reaches zero Interrupt level 3 I I Output next data word to eight channel output latch I Increment output counter n I In n=N (i.e. if n=720) then reset n to 0 for start of next revolution I Reload decrementer with latest value of TM' I I return Interrupt Level 4 - when pulse from flywheel starter ring tooth arrives Interrupt Level 4 Disable all other routines 1 Save current decrementer value (Dm) and current n for subsequent error analysis I Enable all other routines I Calculate error em Calculate tooth period T calculate new decrementer reload counter value TM' I Limit TM' to within 10.. .h7FFF I Return

Claims (22)

1. A method of producing a train of pulses having a predetermined relationship with the angle of rotation of a rotatable object having a plurality of separately detectable features, the relative position of the features being fixed with respect to a reference position of the object, the method comprising generating a train of pulses from a period controllable oscillator, sensing each time a feature passes a certain point during the object's rotation, determining at the passage of each feature past the point whether the train of pulses generated by the oscillator has the described predetermined relationship and, if the train does not have the desired predetermined relationship, altering the period of the period controllable oscillator by way of correction.

2. A method as claimed in Claim 1, wherein the rotatable object is a toothed wheel, the separately detectable features being teeth of the wheel.

3. A method as claimed in Claim 2, wherein the toothed wheel is a starter ring of an internal combustion engine.

4. A method as claimed in Claim 3, wherein the reference position is representative of a piston top dead centre position.

5. A method as claimed in any one of Claims 1 to 4, wherein the period controllable oscillator comprises a microprocessor-based decrementer, the period being controllable by the value loaded into the decrementer at the start of each down count.

6. A method as claimed in any one of Claims 1 to 5, wherein the passage of a feature past a certain point is detected by a first transducer.

7. A method as claimed in any one of Claims 1 to 6, wherein the passage of the reference position past a certain point is detected by a second transducer.

8. A method as claimed in Claim 6 or 7, wherein the or each transducer is an inductive magnetic transducer.

9. A method as claimed in Claim 6 or 7, wherein the or each transducer is an occulting light beam, capacity type proximity pick-up, magneto-striction or Hall-effect transducer.

10. A method as claimed in any one of Claims 1 to 9, wherein the predetermined relationship is synchronism of the train of pulses with rotation of the reference position.

11. A method as claimed in any one of Claims 1 to 10 wherein one or more further trains are derived from the train of pulses having the predetermined relationship.

12. A method as claimed in Claim 11, wherein pulses obtained from rotation of the reference position are also used in the derivation of the said one or more further trains.

13. A method as claimed in any one of Claims 1 to 12, wherein the determination of whether the train has the desired relationship is achieved by (a) observing when the feature passes the said point, (b) calculating when the feature should pass or should have passed the said point if the pulse train were to have the desired predetermined relationship and (c) altering the period of the period controllable oscillator, if the result from (a) is not the same as the result from (b), by way of correction.

14. A method as claimed in Claim 13, wherein the period is so altered as to correct any deviation from the desired predetermined relationship by the time that the next feature passes the said point.

15. A method of producing a train of pulses having a predetermined relationship with the angle of rotation of a toothed wheel, the relative position of the teeth of which wheel are fixed with respect to a reference position of the wheel, the method comprising generating a train of pulses from a periodcontrollable oscillator, sensing each time a tooth of the wheel passes a certain point during the wheel's rotation, determining at the passage of each tooth past the point whether the train of pulses has the desired predetermined relationship with the rotation of the wheel and, if the train does not have the desired predetermined relationship, altering the period of the period controllable oscillator by way of correction.

16. An apparatus for producing a train of pulses having a predetermined relationship with the angle of rotation of a rotatable object having a plurality of separately detectable features, the relative position of the features being fixed with respect to a reference position of the object, the apparatus comprising a period controllable oscillator for generating a train of pulses, means for sensing each time a feature passes a certain point during the object's rotation, means for determining whether the train of pulses generated by the oscillator has the desired predetermined relationship and means for altering the period of the period controllable oscillator if the pulse train does not have the desired predetermined relationship.

17. An apparatus for producing a train of pulses having a predetermined relationship with the angle of rotation of a toothed wheel, the relative position of the teeth of which wheel are fixed with respect to a reference position of the wheel, the apparatus comprising a period controllable oscillator for generating a train of pulses, means for sensing each time a tooth passes a certain point during the wheel's rotation, means for determining whether the train of pulses generated by the oscillator has the desired predetermined relationship and means for altering the period of the period controllable oscillator if the pulse train does not have the desired predetermined relationship.

18. An apparatus as claimed in Claim 16 or 17 wherein the period controllable oscillator, the determining means and the altering means are provided by a microprocessor.

19. An apparatus as claimed in Claim 18 wherein the microprocessor is a 16-bit processor.

20. A method of producing a train of pulses substantially as herein described.

21. An apparatus substantially as herein described with reference to Figures 1 to 5 of the drawings.

22. An internal combustion engine test apparatus including an apparatus as claimed in any one of Claims 16 to 19 and 21 and/or whose operation includes a method as claimed in any one of Claims 1 to 15 and 20.