GB2328752A

GB2328752A - A device for angular measurement and angular coordination.

Info

Publication number: GB2328752A
Application number: GB9818744A
Authority: GB
Inventors: Karl Ott; Helmut Denz; Klaus Walter
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1997-08-30
Filing date: 1998-08-27
Publication date: 1999-03-03
Anticipated expiration: 2018-08-27
Also published as: GB9818744D0; GB2328752B; DE19737999A1; DE19737999B4

Abstract

A device is described for the rotation angle measurement and angular coordination of a rotatable element (10, figure 1) wherein, utilizing influenceable properties of a sensor arrangement (12, figure 1), a property produced or influenced by the rotatable element, for example a magnetic property, is detectable. This associated sensor arrangement is constructed such that it emits a signal which is clearly dependent upon the angular position and prior to its further processing is converted into a pulse-width modulated signal (19, figure 2). From the pulse duty factor of this pulse-width-modulated signal a following calculating device determines the actual angular position. In a further embodiment such a device is used for rotation angle measurement and angular coordination in an internal combustion engine comprising an absolute camshaft sensor 24 and a crankshaft incremental sensor 20, a clearly defined angular coordination between camshaft angle and crankshaft angle can also be determined by the associated control device 30 of the internal combustion engine.

Description

- 1 A Device for Angular Measurement and Angular Coordination 2328752

The invention relates to a device for angular measurement and angular coordination, in particular for the angular measurement of the camshaft and/or crankshaft provided in an internal combustion engine in accordance with the preamble of the Main Claim.

Prior Art

Devices for contactless measurement of the angle of rotation of a rotatable element for example a shaft of an internal combustion engine, are already known in large numbers. Some of these devices permit the determination of the prevailing absolute angle. In such absolute angle pick-up systems, the prevailing angular position can be detected at any time following the switchirWon of the device even without the rotation of the shaft. DE-OS 195 43 562 has for example disclosed such an absolute angle pick-up system in a plurality of different embodiments.

In these known devices for the angular measurement of a rotating shaft, a disc which is magnetically polarised is fixed on the rotating shaft. The resultant magnetic field, which rotates with the shall is evaluated with the aid of a sensor operating on the basis of the Hall principle or magnetoresistive principle and comprising two separate sensor elements. By means of a suitable connection and supply of voltages mutually offset in phase, a sensor output signal can be obtained which, both in the case of the use of Hall elements and magnetoresistive elements, is substantially linearly dependent upon the rotation angle of the shaft. Such a sensor can thus be used as absolute sensor since a characteristic output voltage is obtained in accordance with the angular position.

Other devices for the angular measurement of rotating shafts, in particular in an internal combustion engine for measuring the angular position of the camshaft or crankshaft, are described for example in Patent Application DE-P 196 24 194. In these angular measurement devices a gear wheel is connected to the shaft such that it rotates at the same angular speed. This gear wheel is scanned with the aid of an inductive sensor which emits an output signal characteristic of the angular marks. If the angular marks are uniform, it is only possible to determine the rotation speed of the shaft, whereas if characteristic angular marks or teeth are provided or if the arrangement of the angular marks represents a specific code, specific angular positions can be recognised by evaluating the consecutive signals dependent upon the angular marks moving past the sensor.

In the device disclosed in DE P 196 24 194, the signal processing takes place in that!the output signal supplied by the sensor and processed into a square-wave signal is converted into a pulse-width-modulated signal by suitable modulation. This pulse-width-modulated signal is output with a fixed frequency. Here the rotation speed information is contained in the pulse duty factor of the pulse-widthmodulated signal. In this embodiment the rotation speed signal is output asynchronously to the actually occurring signal edges of the inductive sensor.

Advantages of the Invention

Claims

The device according to the invention for angular measurement and angular coordination comprising the features of Claim 1 has the advantage that a possibility is provided of determining the angular position of a stationary or rotating shaft where the angle output advantageously can take place in a fixed period duration. This advantage is achieved by means of a device according to the invention for angular measurement and angular coordination comprising the combination of features of Claim 1 wherein the sensor output signal is processed into a pulse-width- modulated signal. - 3 Further advantages of the invention are achieved by means of the measures described in the sub-claims. Here it is particularly advantageous that an angular coordination between two rotating shafts can also be determined. A particularly advantageous application in this respect consists in determining the angular coordination between a crankshaft and a camshaft of an internal combustion engine. In such a case, advantageously the angular position of the camshaft can be measured by means of an absolute angle pick-up while the angle and speed of the crankshaft are measured by means of a conventional segmental or incremental wheel. Advantageously, it is also possible to determine the angular coordination between two shafts if the two shafts are connected to one another via a gear or a known transmission ratio. P Drawing An exemplary embodiment of the invention is illustrated in the drawing and will be explained in detail in the following description. In particular, Figure 1 is a section through a rotation angle measuring arrangement on a rotatable shaft schematically illustrating the sensor arrangement, Figure 2 illustrates an associated evaluating circuit, and Figure 3 illustrates the curve of the output signal of the sensor plotted over the rotation angle. Figure 4 illustrates the parts of an internal combustion engine necessary for the explanation of the invention, in particular of the pick-up arrangement for determining the position of the crankshaft and camshaft, and Figure 5 illustrates a signal curve for the pick-up arrangement according to Figure 4 plotted over the time t and the angle cc. Description 4 Figure 1 illustrates a shaft 10 rotatable by the angle a, for example the camshaft of an internal combustion engine which at one end bears a permanent magnet 11 as co-rotatable element. a is the angle to be measured. The magnetic field lines B of the magnet 11 are detected with the aid of a sensor arrangement 12. This sensor arrangement 12 consists of two sensor elements 12a, 12b, for example Hall elements or magnetoresistive elements, which are mutually offset by a specified angle, in particular approximately 90 The voltage supply for the sensor elements and the signal evaluation take place via the evaluating circuit illustrated in Figure 2. In this evaluating circuit, which like the sensor arrangement illustrated in Figure 1 is already known in principle firom DE-OS 195 43 562, a voltage- regulated oscillator 13 followed by low-pass filter 14 generates a first sinusoidal alternating current 11 which is supplied to the first sensor element 12a. The sensor element 12b is supplied with an alternating current 12 formed in the phase shift device 15 and offset in phase for example by +90'. Depending upon their position in the magnetic field, the two sensor elements 12a and 12b supply output voltages U 1, U2 which are added in the block 16 and further processed in the phase comparator 17. An output voltage U, the level of which is proportional to the rotation angle a, occurs at the output of a following low-pass filter 18. This output voltage U is plotted over the rotation angle a in Figure 3. The angular position a can always be clearly determined from this output voltage U, the angle evaluation being effected by means of the later described conversion into a pulse-width-modulated signal S2. This conversion can take place in an electronics unit 19 forming part of the sensor or in a following control device. Figure 4 provides a rough overview of the (parts necessary) to explain the application according to the invention of the device for angular measurement and angular coordination in an internal combustion engine. Here 20 designates a pickup disc which is rigidly connected to the crankshaft 21 and rotates therewith. The - 5 pick-up disc 20 is provided on its surface with a number of regular angular marks 22. A reference mark 23 is formed by the absence of two angular marks. A second pick-up disc referenced 24 is connected to the camshaft 25 and comprises for example two magnetic zones 26, 27 which generate a homogeneous magnetic field B. The crankshaft 21 and the camshaft 25 are connected to one another via the schematically illustrated connection 28. Normally the crankshaft rotates at twice the speed of the camshaft. The pick-up disc 20 is scanned with the aid of a sensor 29 which emits a signal S 1 to the control device 30 of the internal combustion engine. The angular position of the camshaft is determined by means of the sensor 31 which is designed as an absolute sensor, comprises the sensor elements 32, 33 and corresponds for example to the sensor 12 in Figure 1. A sensor operating in accordance with the magnetoresistive or Hall principle can be used as sensor. The pick-up disc 25 can also be designed in a different manner. What is important is that the magnetic field rotating with the camshaft is evaluated by the fixed sensor 31 which supplies the signal S2 to the control device 30. In addition to the signals S1 and S2, the control device 30 is supplied via corresponding inputs with flu-ther input variables required for the control and regulation of the internal combustion engine, for example an ignition input signal 34 and fluther signals from sensors 35 not indicated in detail. At the output end the control device 30 makes available signals for ignition and injection for corresponding components of the internal combustion engine not designated in detail, the associated outputs of the control device being referenced 36 and 37. The control device 30 comprises an input- and output circuit 38, 39, a central processor unit 40 and a memory 4 1. The central processor unit performs the required calculations. 6 The evaluating circuit according to Figure 2 normally forms part of the sensor 3 1 but in principle can also be integrated in the control device. A further signal processing circuit, which forms a pulse-width-modulated signal firom the angleproportional sensor output voltage U, can likewise form part of the sensor or control device. As it is fimdainentally known how a pulse-width-modulated signal S2 is produced from an angleproportional voltage U, this will not be discussed in detail at this point. What is important is that the control device, or the central processor of the control device, determines the angular position from the pulse- w'dth in I -modulated signal, and i a flirther embodiment of the invention also determines the angular coordination between the two shafts, for example the crankshaft 21 and the camshaft 25. In the following a process will firstly be described in which the instantaneous angular position of a rotating shaft, for example the camshaft 21 of an internal combustion engine, is determined. In this process it is also possible to determine the angular position at a speed of zero, i.e. when the internal combustion engine is stationary, since the sensor 31 is an absolute sensor. Thus even when the engine is stationary or is commencing rotation, it is possible to trigger activities which require an angular coordination. Such activities consist for example of sequential injection, direct injection or ignition, which can be triggered by the control device as soon as it has knowledge of the instantaneous angular position. In the following a process will be described wherein the angular coordination between two rotating shafts is determined. Here an application can consist in determining the angular coordination between a crankshaft and a camshaft of an internal combustion engine. This process is of particular interest if it allows the recording of a camshaft adjustment or if mutual plausibility of the signals is necessary. Furthermore, an adaptation of the angular reference point of the first shaft (camshaft) can be determined if this is permanently coupled to the second shaft (crankshaft) and the first shaft occupies a defined position. In this way tolerances of the sensor system can be compensated. The procedure can be explained on the basis of the signals shown in Figure 5. Here the signal S2 represents the pulse-width-modulated output signal of the camshaft sensor 31 which is designed as an absolute angle sensor. The signal S 1 represents the processed output signal of the sensor 20. This sensor has the form of an incremental angle sensor and supplies the crankshaft signal.

1.

Process for determining the (camshaft) angle of a shaft A control device detects the edge changes of the input signal per interrupt and stores the time entries t, in a ring memory. At any time t the instantaneous angle is determined in accordance with the following process. In particular, here it is possible to update the angle in a fixed time frame:

The instantaneous angle (camshaft) at the time. is determined in accordance with:

a-ill = K (.rj-To) + c&,,, where and Ti = -co:

T:

T: period, T= (ti-t-ti-3) constant offset pulse duty factor ao,l: reference angle (camshaft) "high" phase of S2.

The angle at any time t between t, andtj+2also results from: a, = Cti,l + ((t-tj)/(ti-ti-2)) (a-j,l-aj-2,1).

8 Additionally, the signal can be checked for plausibility:

T = T,,,11:E AT where T,,,,,: set period duration AT: permissible deviation.

2.

Angular coordination between the first shaft and a second shaft (camshaft and crankshaft):

A control device detects the edge changes of the input signal of the first and second shaft per interrupt and stores the time entries tj and tz, in a respective ring memory. At any time t the angular coordination between the two shafts at the time t. can be determined by the following process. In particular, here it is possible to update the angle in a fixed time frame.

Between two shafts connected to one another via a given transmission ratio, where cc,,, (see above) and a2(ti) = CC1.12 = Wj-tZi) / (tZi-tZj-l)) (OCj,2-aj-1,2) where CCAC Oti,2: (ai,2-ai-1,2):

tzi:

the following angular coordination occurs:

Cli-1-2 = CCAti) - ai,l.

angle of shaft 2 at time tj angular position at last increment or segment angular length of last increment or segment on shaft 2 time entries at edges of shaft 2 In the case of a camshaft adjustment, this angular coordination represents the adjustment angle of the camshaft relative to the crankshaft. If the camshaft occupies a defined reference position, via the coordination which then exists it is possible to determine the reference point of the camshaft a,,, (see above).

If the device according to the invention for angular measurement and angular coordination is used as described in the foregoing in association with the evaluation of the position of the crankshaft and/or camshaft (21, 25) or the camshafts in an internal combustion engine, various functional improvements can be achieved depending upon the type of the internal combustion engine. For example, a quick start of the internal combustion engine is possible as immediately following start-up the precise engine position can be obtained at a speed of n-o. A rapid and reliable start detection is also possible. Immediately following the start of rotation "engine rotating" can be detected. Simple and rapid synchronisation is possible immediately after the start detection. In this way early cylinder-con-ect injections can be triggered. A sequential fuel injection (SEFI) can thus be obtained even from a speed of n = 0.

A reduced software outlay can be obtained compared to current internal combustion engines. The speed- and phase sensor diagnosis is simplified. Speed sensor emergency operation is possible as a simple, reliable and fast emergency synchronisation can take place. In the event of an accident, reliable and rapid under-speed detection is possible and available for the switching off of the electric fuel pump, ignition and injection. Rotation-direction detection suppresses ignition- and injection outputs in the event of engine stalling.

In internal combustion engines with variable camshaft adjustment this can be evaluated with the aid of the system according to the invention. Diagnosis of the camshaft adjustment is possible by referring to the measurement results. In a simple version it is possible to design an internal combustion engine with no speed - sensor in which the drive pulses are formed as in speed sensor emergency operation. A fast start is also possible mi the case of fuel direct injection with a socalled common rail. The sensor system used is of a relatively simple construction.

Claims 1. A device for the rotation angle measurement and angular coordination of a rotatable element wherein, utilizing influenceable properties of a sensor arrangement a property produced or influenced by the rotatable element is detectable, which sensor arrangement emits a signal clearly dependent upon the angular position, characterised in that this signal is converted into a pulse-width modulated signal, from the pulse duty factor of which a calculating device determines the actual angular position.

2. A device according to Claim 1, characterised in that the influenceable property is of a magnetic nature.

3. A device according to Claim 1 or 2, characterised in that the sensor arrangement comprises two sensor elements which operate in accordance with the Hall principle and/or magnetoresistive principle, that the sensor elements are supplied with currents mutually offset in phase by 90', and that the output voltages of the sensor elements are added and processed in a phase comparator and a following low-pass filter to form an angle-proportional output voltage.

4. A device according to one of the preceding claims, characterised in that the rotatable element is the camshaft of an internal combustion engine and the calculating device is the control device, or central processor unit of the control device, of an internal combustion engine.

5. A device according to one of the preceding claims, characterised in that the calculating device detects the edge change of the PWM-signal per interrupt and stores the time entries t., and the instantaneous angle aj, l at the time 12 tj is determined in accordance with the following equation:

aj,l = K (-rj-TO) + Cco,l where Tj = (tj-tj-,)/T.

6. A device according to Claim 5, characterised in that the angle at any time t between tj and. is calculated in accordance with the following equation:

cc, = aj.1 + W-t)j-tjJ) (aj,l-C&j.2.1).

7.. A device according to Claim 5 or 6, characterised in that a plausibility check takes place in that it is checked whether the period duration is equal to a set period duration a permissible deviation and if not an error is recognised.

8. A device according to one of the preceding claims, characterised in that the angular coordination between the rotating part and a further rotating part, in particular the angular coordination between the camshaft and the crankshaft of an internal combustion engine, is determined.

9. A device according to Claim 8, characterised in that the control device detects the edge changes of the two input signals per interrupt, stores the time entries tj and t7, and determines the angular coordination between the two shafts in accordance with the following equation:

CCAti) = al.2 + Mi-tZi) / (tZi-tZi-J) (CCj.2-aj-1,2) where angle of the shaft 2 at the time tj angular position at the last increment or segment (CCi,2-ai-1,2): angular length of the last increment or segment on the shaft 2 time entries at the edges of the shaft 2.

a2(ti):

ao:

tzi:

10. A device according to Claim 9, characterised in that the angular calculation is updated in a fixed time frame.

11. A device according to one of the preceding claims, characterised in that the calculated angular positions and angular coordinations are processed to optimise the functions of the internal combustion engine.

12. t A device for the rotation angle measurement and angular coordination of a rotatable element substantially as hereinbefore described with reference to the accompanying drawings.