WO2008080678A2

WO2008080678A2 - Method for determining an angle of rotation of a shaft

Info

Publication number: WO2008080678A2
Application number: PCT/EP2007/062150
Authority: WO
Inventors: Uwe Kassner
Original assignee: Robert Bosch Gmbh
Priority date: 2006-12-27
Filing date: 2007-11-09
Publication date: 2008-07-10
Also published as: WO2008080678A3; DE102006061577A1

Abstract

The invention relates to a method for determining an angle of rotation of a shaft, particularly of a crankshaft of an internal combustion engine, wherein the shaft is connected to a transmitter wheel (1) having teeth (3) and tooth gaps (4) with asymmetrical pitch. The transmitter wheel (1) is associated with at least one differential transmitter (6), comprising two transmitter elements (7, 7'). The differential transmitter (6) generates an output signal (A1), which is a difference of signals of both transmitter elements (7, 7'). The output signal (A1) is a square wave signal, which can assume a first or a second value, wherein an increment of the angle of rotation of the shaft is associated with a change between the first and the second values. Additionally to the output signal (A1) of the differential transmitter, a further signal of a transmitter element (7', 6') is used for determining the angle of rotation of the shaft.

Description

description

Title Method for determining a rotation angle of a shaft

State of the art

The present invention relates to a method, a device and a computer program for determining a rotational angle of a shaft, in particular a crankshaft of a

Internal combustion engine, wherein the shaft is connected to a donor gear with teeth and tooth gaps with an asymmetric pitch and the encoder wheel at least one differential sensor comprising two donor elements is assigned, wherein the differential encoder generates an output signal which is a difference of signals of the two donor elements, wherein the off - A signal is a square wave signal, which can assume a first value or a second value, wherein a change between the first and the second value, an increment of the rotation angle is assigned.

For the control of internal combustion engines, the determination of the crankshaft angle is of central importance. Solutions known in the art in particular use incremental encoders on the crankshaft and / or camshaft. Customary are encoder discs with incremental markers, comprising teeth and tooth spaces, which enable the motor position to be determined in conjunction with the signals from the crankshaft and camshaft.

Such encoder systems allow for an absolute position determination of the crankshaft by a non-uniform arrangement of the incremental marks. A typical implementation is a donor wheel with 60 minus 2 teeth, so 58 teeth and a Geberradlücke of 2 teeth.

A disadvantage of such a gap is the lack of increments for the exact determination of the crankshaft angle within the gap. Within the gap, an extrapolation of the crankshaft angle is made by the engine control, which, however, is subject to errors due to the nonuniformity of the crankshaft angular velocity. Modern working methods of internal combustion engines place higher demands on the accuracy, in particular especially for determining the position of injections, both in gasoline engines and diesel engines.

An avoidance of the encoder wheel gap is possible by an asymmetrical division of the incremental marks and thus an asymmetrical division of the teeth into tooth gaps. Instead of one

Provide Geberradlücke, while the pitch between teeth and tooth gaps is changed over one or more tooth / tooth gap pairs. To increase the accuracy in detecting this change, the teeth and gullets are usually already made asymmetrical and the asymmetry in the area replacing the previous giver wheel gap is e.g. just turned around. If, for example, the teeth extend over a crankshaft angle degree of 4 ° and tooth gaps over a crankshaft angle of 2 °, the gear wheel gap is replaced by a reversal of this ratio, ie by teeth of, for example, 2 ° and tooth gaps of, for example, 4 °.

With the evaluation of the falling tooth flanks stands for a motor control a signal every 6 °

Crankshaft angle also available in the former gap and in addition, a designated position of the encoder wheel is detected by an evaluation of the ratio of tooth to gap time.

The additional evaluation of the ratio of tooth to gap time is hampered by the typical today execution of the crankshaft angle encoder. As a rule, these sensors are so-called differential sensors. The signal processing in this case comprises a suitable subtraction of spatially separated donor elements. The main advantage over a so-called single-encoder with only one encoder element is a significantly improved reproducibility of the encoder signal. Improved reproducibility means one

Reduction of statistical errors in the acquisition and sampling of incremental marks of the sender wheel. All changes in the magnetic field due to external interference fields or air gap changes of the encoder wheel to the encoder in the case of a single encoder affect the switching threshold of the encoder, but cancel each other out at the differential transmitter. The differential sensor is therefore more robust with respect to the mounting positions and with respect to external magnetic fields. The differential sensor switches in the middle of the tooth or the tooth gap at the zero crossing of the differential signal. In this case, an asymmetrically divided encoder wheel generates an asymmetrical output signal only once during the transition from tooth to gap division to another tooth to gap division. This is an evaluation in the engine control only at the beginning and at the end of the changed tooth pitch replacing the previous gear wheel gap, a ratio of tooth to gap time unequal to one is available. When recording the remainder of the encoder wheel, the tooth-to-gap time is approximately the same despite the asymmetrical tooth pitch.

Disclosure of the invention

An object of the present invention is to enable a higher accuracy in the detection of the tooth to gap times of a sensor wheel.

This problem is solved by a method for determining a rotational angle of a shaft, in particular a crankshaft of an internal combustion engine, wherein the shaft is connected to a donor gear with teeth and tooth gaps with an asymmetric pitch and the encoder wheel at least one differential encoder is associated with two encoder elements, wherein the differential encoder produces an output signal which is a difference of signals of the two encoder elements, the output signal being a square wave signal comprising a first signal

Value or a second value, wherein a change between the first and the second value, an increment of the rotation angle of the shaft is assigned, wherein in addition to the output signal of the differential encoder, a further signal of a donor element is used to determine the rotation angle of the shaft.

The first value and the second value are usually referred to as high or low, so at the output of the differential sensor is based on a known square wave signal. A period of the output signal, ie a change from high to low and until the next change from high to low or vice versa from a low to high change until the next low to high transition means that one tooth and one tooth gap of the encoder wheel on the encoder have been passed. In the usual division, in which tooth and tooth gap each include 6 °, this means that an increment of 6 ° was swept by the sender wheel. In this case, a change from the first to the second value or a change between high and low or vice versa is thus associated with an increment of 3 ° in a differential sensor. The further signal of a donor element for determining the angle of rotation of the

Shaft may be one of the signals of the encoder elements of the differential sensor, or be a signal of an additionally associated with the encoder wheel donor element. This additional signal of a single encoder allows a more accurate evaluation of the tooth to tooth gap times for the absolute position determination of the crankshaft. - A -

The above-mentioned problem is also solved by an arrangement for determining a rotational angle of a shaft, in particular a crankshaft of an internal combustion engine, comprising at least one encoder and a donor gear with teeth and tooth gaps with an asymmetric pitch, wherein the shaft is connected to the encoder wheel and the differential - Encoder with two encoder elements is assigned to the encoder wheel, wherein the differential encoder generates an output signal which is a difference of signals of the two encoder elements, wherein the output signal is a square wave signal, which can assume a first value or a second value, wherein a change an increment of the angle of rotation of the shaft is assigned between the first and the second value, wherein the arrangement provides a further signal of a transmitter element. The further signal of a transmitter element for determining the angle of rotation of the shaft can be one of the signals of the transmitter elements of the differential sensor, or a signal of an additional transmitter element assigned to the transmitter wheel.

The above-mentioned problem is also solved by an encoder for use in an arrangement for determining a rotation angle of a shaft, in particular a crankshaft of an internal combustion engine, comprising two encoder elements, wherein the encoder comprises a circuit which provides an output signal which is a difference of signals of the both donor elements is, wherein in addition to the output signal, which is a difference of signals of the two donor elements, a signal of one of the donor elements is provided.

The problem mentioned at the outset is also solved by a computer program with program code for carrying out all steps according to a method according to the invention, when the program is executed in a computer.

Brief description of the drawings

Hereinafter, an embodiment of the present invention will be explained in more detail with reference to the accompanying drawings. Showing:

Fig. 1 is a sketch of a sensor wheel with associated encoder;

2 shows a development of a sensor wheel with a Geberradlücke and a settlement of a sensor wheel with asymmetric pitch. 3 shows an evaluation circuit for a differential sensor;

4 shows a development of a transmitter wheel with asymmetrical pitch and output signals of a single-encoder and a differential transmitter;

5 shows an exemplary embodiment of an evaluation circuit according to the invention;

6 shows an inventive arrangement of two encoders.

Embodiments of the invention

1 shows a sketch of a known donor wheel 1, which is connected to a crankshaft, not shown here, of an internal combustion engine and rotates about an axis 2 during a rotation of the crankshaft. The sender wheel 1 has encoder wheel marks (markings), which are formed by an alternating arrangement of teeth 3 and tooth spaces 4. Of the

Distance between successive pairs of teeth 3 and tooth spaces 4 is 6 °. The teeth 3 and the tooth gaps 4 may extend over an equal angular range of 3 °, but may also be divided asymmetrically, for example by a tooth 3 covering an angular range of 2 ° and a tooth gap 4 covering an angular range of 4 °. A donor wheel gap 5 is formed by creating a donor wheel gap 5 at an angle of 12 ° by omitting a tooth 3.

The encoder wheel 1 is assigned a transmitter 6. The encoder 6 comprises two encoder elements 7, which may be, for example, Hall elements, inductive sensors or the like. The encoder elements 7 supply electrical signals via signal lines 8, of which a difference signal is formed in an evaluation logic unit 9 which is transmitted via a signal line 10 to an unillustrated control unit of the internal combustion engine. The passage of teeth 3 and tooth gaps 4 on the transmitter elements 7 generates voltage changes at outputs of the transmitter elements 7, which are passed on to the evaluation logic 9 via the signal lines 8. The encoder elements 7 are arranged offset in the circumferential direction of the encoder wheel 1, so that a

Tooth 3 or a tooth gap 4 with a rotation of the encoder wheel 1 offset in time initially passed to one of the two encoder elements 7 and then to the other of the two encoder elements 7. Instead of providing a Geberradlücke 5 in the encoder wheel 1, it is known to make an asymmetrical pitch of the encoder wheel. Thus, there are one or more pairs of teeth 3 with tooth space 4, which, although together cover an angle of 6 ° on the encoder wheel 1, in which the distribution of tooth 3 to tooth gap 4 but changed. For example, if the division tooth to tooth gap each 3 °, so each tooth 3 covers an angle of 3 ° on the encoder wheel 1 and each

Tooth gap 4 covers an angle of 3 ° on the encoder wheel 1, so a designated mark can be brought about by e.g. a pair of tooth 3 and tooth space 4 have a different distribution, for example in that a tooth extends over an angle of 2 ° and the associated tooth gap 4 extends over an angle of 4 °. Such markings can also be arranged several times in succession for more reliable recognition.

2 shows in the upper illustration a development of a sender wheel 1 with a gap 5 and in the lower illustration a development of a sender wheel 1 with an asymmetrical division. The developments are each as lines for labeling the teeth 3 and

Tooth gaps 4 shown. In the upper illustration of FIG. 2, the Geberradlücke 5 can be seen, which extends over an angle of 9 °. The teeth 3 and the tooth gaps 4 each extend over an angle of 3 °, so that the distance between like flanks of the teeth 3 is 6 °. Under similar flanks is understood in reference to an electrical square wave signal in each case a tooth edge 3, which lie with respect to the direction of rotation of the encoder wheel 1 on the same tooth side, so for example in a settlement, as shown in Fig. 2, all tooth flanks on the right side of the teeth 3 lie.

In the lower part of Fig. 2, a sender wheel 1 is shown with an asymmetrical pitch. The division of tooth 3 to tooth gap 4 is here 2: 1, so a tooth extends over a

Angular segment of 4 °, a tooth gap over an angular segment of 3 ° on the encoder wheel 1. Instead of a tooth gap here two pairs of teeth 3 'and tooth gaps 4' are provided, in which the pitch is 1: 2, ie in which the teeth 3 ' extend over an angular segment of 2 °, and the tooth spaces 4 'extend over an angular segment of 4 °.

The two consecutive pairs of teeth 3 'and tooth gaps 4' with the pitch changed from the remaining 58 pairs of teeth 3 and tooth spaces 4 is referred to here as the symmetry gap 11. 3 shows a block diagram of the circuit of an evaluation unit for processing the signals of a transmitter 6. The transmitter 6 is delimited by a dashed line in FIG. 3 from the other circuit elements. The encoder 6 comprises, as shown in FIG. 1, two encoder elements 7, which are each connected to connection lines 8 and 8 'to a differential amplifier 11. The output signal of the differential amplifier 11 is via a high-pass filter

13 is supplied to a first input of a Schmitt trigger 14 and to a second input of the Schmitt trigger 14 via a second high-pass filter 12, which is connected to ground via a capacitor 15. At the output of the Schmitt trigger 14 is a signal that the base 15 of a transistor 16 is supplied. At the collector 17 of the transistor 16 is an output signal. The emitter 19 of the transistor 16 is connected to ground, parallel to

Emitter-collector path, so between ground and collector 17 of the transistor 16, a protective diode 18 is connected. At the output Q is an amplified and filtered difference signal of the two encoder elements 7 at. The circuit shown in FIG. 3 is accommodated together with the encoder 6 in a common housing, which is indicated schematically by a rectangle 20 surrounding the circuit. In the upper part of the circuit, the power supply unit 21 is shown, comprising a voltage generating unit 21, which is connected via a first protective diode 23, which is connected to a supply voltage Vs, and a second protective diode 24, which is connected to ground. is supplied with voltage.

Fig. 4 shows the development of the encoder wheel with asymmetrical pitch of FIG. 2, the

Settlement is referred to here as line A. Shown below is the associated output signal S of a single-encoder, ie a transmitter, which includes only one encoder element 7. Shown below is the output signal D of the differential encoder 6 with two encoder elements 7 as shown in FIG. 1. Among the three lines A, S and D are marked with rectangles tooth times to gap times.

The differential sensor 6 switches in the middle of a tooth 3 or the middle of a tooth gap 4 at the zero crossing of the differential signal. In this respect, the rising or falling edges of the output signal D of the differential sensor 6 are respectively arranged in the middle of the teeth 3 or tooth gaps of the line A. In contrast, a single-encoder switches with only one

Encoder element 7 in each case at a tooth flank, ie a transition between tooth 3 and tooth space 4, so that the lines A and S in Fig. 2 have identical edges. Accordingly, an asymmetrically divided encoder wheel 1 generates an asymmetrical output signal only once during the transition from tooth to gap division to another tooth-to-gap division. Below the line for the output signal of the differential sensor 6 respectively rectangles for clarifying the tooth to gap times are shown. Non-hatched rectangles 25 represent the ratio of the high to low values for the region of the graduation according to FIG. 4, in which the teeth 3 extend over an angle of 4 ° and tooth gaps 4 extend over an angle of 2 ° extend. In the following embodiment, teeth 3 are each the value

"High" assigned, gullets each the value "Low". Depending on the circuit of the evaluation unit, this can also be reversed. In this case, the respective polyline of the output signal is symmetrical to the polyline shown here. In the transition to an altered asymmetric division, this is in Fig. 4 at the transition of the division with teeth which extend over an angle of 4 °, and tooth gaps, which extend over an angle of 2 °, ie teeth 3 and tooth gaps 4th On teeth which extend over an angle of 2 ° and tooth gaps extending over an angle of 4 °, these are the teeth 3 'and tooth gaps 4' in Fig. 4, the time ratio of the high to low changes - Values. The transition is indicated in FIG. 4 by an arrow with reference symbol A. FIG. 4 shows the changed ratio of high to low values by a rectangle 26. The subsequent pair of tooth 3 'and tooth space 4' also has a pitch in which the tooth 3 'extends over 2 ° and the tooth gap 4' extends over 4 °. Despite the changed pitch, the output signal D of the differential sensor 6 again has a symmetrical ratio of the high to low values as before. When renewed transition to another division, this is shown in Fig. 4 by an arrow B, the output signal D of the differential sensor 6 again has a changed

Division of the high to low values, this is represented by a hatched rectangle with the reference numeral 27.

The differential sensor 6 thus initially supplies a symmetrical output signal even with an asymmetrical division. Only at the transition from an asymmetric division to another asymmetric division does the ratio of the high to low values of the output signal change. The ratio of high to low values is not exactly 1, since the instantaneous acceleration of the crankshaft due to the discontinuous operation of the internal combustion engine is taken into account, so there are fluctuations of the crankshaft speed above the crankshaft angle even in stationary operation of the internal combustion engine.

To increase the robustness of the detection of the tooth to gap time and thus the entire crankshaft angle detection, the signal processing according to the invention for the crankshaft angle, as shown in FIGS. 5 and 6, is now used. Both embodiments combine the advantages of a single-encoder with its exact detection of the tooth-to-space ratio with the good reproducibility of the signal processing of the differential sensor. The additional signal processing can be implemented in the integrated circuit arrangements that contain the actual sensor elements and the previous signal processing, or in the engine control unit.

In Fig. 5, the circuit of FIG. 3 is shown further simplified. Represented are encoder elements 7 and 7 ', which are each connected via here as individual lines shown signal lines 8 with a subtraction element 28. To the difference-forming element 28, at the output in principle the same signal as applied to the differential amplifier 11 of FIG. 3, a switching logic 29 connects. At the output A1 of the switching logic 29, the signal Q is shown in FIG. 3. 5 is so far identical to the circuit of FIG. 3. The signal of the donor element 7 'is now fed to a further evaluation unit 30, at the output A2, the signal of the donor element 7' as in a single Encoder is present. At the output A1, therefore, the difference signal of the encoder elements 7 and 7 ', at the output A2 is only the signal generated by the encoder element 7'. The differential sensor 6 is simultaneously used by this supplement as a single-encoder one of the donor elements, here the donor element T. Signal processing for the signal present at the output A1 takes place in a motor control device (not shown in detail) with processing methods known per se. In addition, the signal of the output A2 is now also transmitted to the engine control unit. There, with suitable timers, as e.g. are contained in microcontrollers, determined by timing the ratio of tooth to gap time for each tooth-and-space pair. Thus it can be determined directly for each tooth, from which area of the asymmetrical tooth pitch the signal originates.

In an alternative embodiment, the encoder wheel 1, two encoders 6 and 6 'assigned. The encoder 6 is a differential sensor as previously shown. The encoder 6 'is a single-encoder, so contains only one encoder element 7. The differential sensor 6 ensures the reproducibility of the Geberraderfassung. The single-encoder 6 'allows, as in the embodiment shown above, an accurate detection of the tooth to gap time. The signal processing in an evaluation logic 31 takes place in principle as shown in FIG. 5 on the basis of the circuit elements 28, 29, 30. At the outputs A1 and A2 of the evaluation logic 31, the signals are as shown with reference to the embodiment of FIG. It should be noted that the sig- nale out of phase, which depends on the arrangement of the two encoders 6 and 6 'on the circumference of the encoder wheel 1.

Claims

claims

1. A method for determining a rotational angle of a shaft, in particular a crankshaft of an internal combustion engine, wherein the shaft with a transmitter wheel (1) with teeth (3) and tooth spaces (4) is connected with an asymmetric pitch and the encoder wheel (1) at least one differential Encoder (6) comprising two encoder elements (7, 7 ') is assigned, wherein the differential encoder (6) generates an output signal (Al), which is a difference of signals of the two encoder elements (7, 7'), wherein the Output signal (Al) is a square wave signal, which can take a first value or a second value, wherein an alternation between the first and the second value, an increment of the rotation angle of the shaft is assigned, characterized in that in addition to the output signal (Al) of the Differential encoder another signal of a donor element (7 ', 6') is used to determine the angle of rotation of the shaft.

2. The method according to claim 1, characterized in that the further signal is a signal of one of the encoder elements (7 ') of the differential encoder (6).

3. The method according to claim 1, characterized in that the further signal is a signal of an additional donor wheel associated with the donor element (6 ').

4. Arrangement for determining a rotational angle of a shaft, in particular a crankshaft of an internal combustion engine, comprising at least one encoder (6) and a transmitter wheel (1) with teeth (3) and tooth spaces (4) with an asymmetrical pitch, wherein the shaft with the encoder wheel (1) is connected and the differential encoder (6) with two encoder elements (7, 7 ') associated with the encoder wheel (1), wherein the differential encoder (6) generates an output signal (Al), which is a difference of signals the two encoder elements (7, 7 ') is, wherein the output signal is a square wave signal, which can assume a first value or a second value, wherein a change between the first and the second value, an increment of the rotation angle of the shaft is assigned, characterized in that the arrangement provides a further signal of a donor element (6 ', 7').

5. Arrangement according to claim 4, characterized in that the further signal is a signal of one of the encoder elements (7 ') of the differential encoder (6).

6. Arrangement according to claim 4, characterized in that the further signal is a signal of an additional donor wheel (1) associated with the transmitter element (6 ').

7. encoder (6) for use in an arrangement for determining a rotation angle of a

Shaft, in particular a crankshaft of an internal combustion engine, comprising two transmitter elements (7, T), wherein the transmitter (6) comprises a circuit which provides an output signal (Al) which is a difference of signals of the two transmitter elements (7, 7 ') , characterized in that in addition to the output signal (Al), which is a difference of signals of the two encoder elements, a signal (A2) of one of the encoder elements (7 ') is provided.

8. A computer program with program code for performing all the steps according to one of claims 1 to 3, when the program is executed in a computer.