GB2159955A

GB2159955A - Electronic speed measurement of a reciprocating internal-combustion engine

Info

Publication number: GB2159955A
Application number: GB08502902A
Authority: GB
Inventors: Franz Butscher
Original assignee: MTU Friedrichshafen GmbH; MTU Motoren und Turbinen Union Friedrichshafen GmbH
Current assignee: Rolls Royce Solutions GmbH
Priority date: 1984-06-05
Filing date: 1985-02-05
Publication date: 1985-12-11
Also published as: DE3420870A1; FR2566912A1; JPS60262056A; GB8502902D0; ES8505789A1; IT8423839A0; ES536926A0

Abstract

The actual speed of rotation of a reciprocating internal-combustion engine is determined from a number of instantaneous speed measurements which are each carried out electronically over equal fractions of one crankshaft revolution. As shown, the passage of each tooth on a gearwheel 11 past a sensor 13 produce a pulse which is used to gate a counter 16 receiving pubs from a generator 20. The resulting counts are fed in and stepped through an array 23 of memory locations dimensioned (e.g. twice the number of gear wheel teeth for a four stroke engine) so that after each instantaneous speed measurement the arithmetic mean can be formed from the results of all the instantaneous speed measurements of the last crankshaft revolution corresponding to one working cycle of the reciprocating internal-combustion engine. This results in a very accurate value for the actual speed of rotation. Moreover, deviations from a prevailing speed level are detected immediately. <IMAGE>

Description

SPECIFICATION Electronic speed measurement of a reciprocating internal combustion engine The invention relates to a method of determining the speed of rotation actual value of a reciprocating internal-combustion engine, in which during each revolution of its crankshaft a plurality of instantaneous speed measurements are carried out electronically, the speed actual value being formed from a number of measurements by forming the arithmetic mean value of the measurement results.

Electronics have made it possible to determine the speed of rotation of an engine even when it has completed only a small part of one revolution.

In the case of uniformly rotating engines this has the advantage that it is at once possible to derive corresponding control actions from the measurement result of the speed desired value. However, it is a disadvantage with reciprocating internal-combustion engines that because of the different working cycles the speed of rotation fluctuates considerably during one revolution and, therefore, from a plurality of individual speed measurements it is necessary once more to form an average speed actual value. Consequently, the advantageous rapidity of response of electronic speed measurement is for the most part lost.

Patent Specification EP-A-0067804 discloses a method of measuring speed, in which at predetermined positions of the crankshaft the respective instantaneous value of the speed of rotation is determined or in which, at all times for a given crankshaft angle travelled representing only part of one revolution of the crankshaft, an average value for the speed of rotation is determined. In the first case, it is thus possible to determine only a speed proportional value and not a precise average actual value. In the second case, it is firstly necessary to await the termination of the measured section before a value is obtained. This value also represents only a proportional value for the actual speed of rotation prevailing.

The subject of the invention is a method of forming an accurate speed actual value, from the plurality of instantaneous values obtained during one revolution of the crankshaft and at the same time to detect as quickly as possible any deviation from this speed actual value.

According to the invention the speed actual value is determined continuously after each instantaneous speed measurement from the results of all the instantaneous speed measurements of the previous number of crankshaft revolutions corresponding to one working cycle of the internalcombustion engine.

This method allows the influence of irregular torque on the formation of the speed actual value to be entirely eliminated. Recurrent irregularities, for example non-uniform ignition pressures of the individual cylinders, do in fact enter into consideration. However, if they have not varied relative to their last measured value, at the instant of their occurrence they do not cause any alteration to the speed actual value because only the value last measured is replaced by a new value. Therefore, no control operation is thereby triggered. However, if variations in the speed of rotation take place, for example as a result of a change in the load, this immediately causes a measurable variation in the average value, when the next instantaneous measurement occurs, and it is thus possible, for example, for the variation to be displayed or a control operation can be triggered.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, of which: Figure 1 shows a schematic arrangement of an electronic speed measurement device; and Figure 2 shows a schematic illustration of the storage of counter results.

Basically, to carry out the method according to the invention all known possibilities for electronic speed measurement can be used to determine the instantaneous speed values. Figure 1 illustrates the preferred way of using a pulse pick-up 13 to determine the tooth frequency of a gearwheel 11 on the crankshaft 12 of an internal-combustion engine.

The number of teeth of the gearwheel 11 determines the number of instantaneous speed measurements per revolution of the crankshaft 12. The pulses generated are converted in known manner in a Schmitt trigger 14 into pulses 15 of a rectangular shape and are fed to a counter 16. The pulses 19 of a pulse generator 20 are counted in the counter 16, which pulses are kept at a stable frequency by a quartz crystal 18 and which arrive between two incoming positive flanks of the pulses 15 in the counter 16. The number of the pulses 19 countered in each case is inversely proportional to the instantaneous speed of rotation of the internalcombustion engine. The second positive flank of the pulse stops the counting process in the counter 16 and simultaneously triggers an interrupt in a processor 21.The processor 21 reads out via a data bus 22 the count result from the counter 16 and stores it in a readiwrite memory 23. The number of storage locations in this read/write memory 23 is equal to the product of the number of teeth of the gearwheel 11 and the revolutions of the crankshaft, which correspond to one working cycle of the reciprocating internal-combustion engine.

If, for example, the gearwheel 11 has thirty-one teeth and the internal-combustion engine is of four-stroke type, the read- /write member 23 should comprise thirty-one times two = sixty-two storage locations.

After each newly registered count result, the processor 21 forms the arithmetic mean from the reciprocal values of all the registered count results and by multiplication with a constant the average speed of the last two revolutions is calculated. This value is displayed as a speed actual value or, for regulating the speed of rotation, it is compared continuously with a predetermined speed desired value and, depending thereon, the fuel supply to the internal-combustion is adjusted.

Figure 2 illustrates the storage of two consecutively entering count results in the read/write memory 23. In accordance with the example chosen, the readlwrite memory has sixty-two storage locations 101 to 162. In the left-hand diagram, the count results 201 to 262 are stored at these storage locations and, in fact, the count result 205 has just entered and has been allocated the storage location 101.

In the right-hand diagram, the new count result 204 is stored at storage location 101 and all the remaining already stored results are moved on. The old count result 204 is discarded.

Claims

1. A method of determining the speed of rotation actual value of a reciprocating internal-combustion engine, in which during each revolution of its crankshaft a plurality of instantaneous speed measurements are carried out electronically, the speed actual value being formed from a number of measurements by forming the arithmetic mean value of the measurement results, wherein the speed actual value is determined continuously after each instantaneous speed measurement from the results of all the instantaneous speed measurements of the previous number of crankshaft revolutions corresponding to one working cycle of the internal-combustion engine.

2. A method of determining the speed of rotation actual value of a reciprocating internal combustion engine substantially as herein described with reference to and as shown in the accompanying drawings.