GB2070354A

GB2070354A - Electronically commutating motor

Info

Publication number: GB2070354A
Application number: GB8039256A
Authority: GB
Original assignee: Philips Gloeilampenfabrieken NV
Current assignee: Koninklijke Philips NV
Priority date: 1979-12-12
Filing date: 1980-12-08
Publication date: 1981-09-03
Also published as: NL7908925A; DE3045673A1; JPS5694995A; CA1163314A; FR2471693A1; FR2471693B1; GB2070354B

Abstract

A brushless motor has two Hall elements arranged at a tangential angle which is smaller than the phase difference d which is necessary between the energizing signals in order to obtain a correct energization of the motor. The energizing circuit is provided with a combining circuit for linearly combining the signals obtained from the Hall elements in order to obtain signals with a phase difference equal to d.

Description

SPECIFICATION Electric machine with electronic commutation The invention relates to an electric machine with electronic commutation.

Such an electric machine is known from Netherlands Patent Application 7,503,046, which has been laid open to public inspection. This known machine comprises a rotor which at least partly consists of a permanent-magnet material which rotor co-operates with at least two stationarily arranged stator coils, which machine is equippedwith at least two magneto-sensitive elements arranged on a common substrate, for example Hall elements, for supplying signals which vary substantially sinusoidally with the rotor position in order to energize the stator coils as a function of the rotor position via an energizing circuit, the magneto-sensitive elements being arranged at a tangential angle relative to the rotor axis, which angle is smaller than the phase difference which is necessary between the energizing signals for the stator coils in order to obtain a correct energization of said stator coils.

In conventional electronically commutating machines the magneto-sensitive elements are arranged at an angle corresponding to the phase angle of the machine, i.e. electrically at 120 in the case of a three-phase machine and at 90 in the case of a two orfour-phase machine. In accordance with the said Patent Application the drawbacks of this, such as mounting and interconnecting two separate parts, are overcome by mounting the two magnetosensitive elements together on one substrate and having this co-operate with a disk which is mounted on the rotor shaft and is provided with two concentric magnetically coded tracks.A disadvantage of this is that, since said tracks should be arranged near each other, there is a substantial amount of leakage, so that the Hall elements receive little flux and should be mounted very closely to the disk but no so close as to prevent free rotation of the disk. Moroever, such a magnetically-coded disk is highly disadvantageous from an economic point of view.

It is the object of the invention to provide an electric machine which does not have this drawback.

According to the present invention there is provided an electric machine with electronic commutation, having a rotor which at least partly consists of a permanent magnetic material, at least two fixedly mounted stator coils which co-operate with the rotor, at least two magneto-sensitive elements arranged on a common substrate for supplying signals which vary substantially sinusoidally with the rotor position in order to energize the stator coils as a function of the rotor position via an energizing circuit, the magneto-sensitive elements being arranged at a tangential angle relative to the rotor axis, which angle is smaller than the phase difference cp which is necessary between the energizing signals for the stator coils in order to obtain a correct energization of said stator coils, wherein the energizing circuit includes a combining circuit for linearly combining the signals supplied by the at least two magneto-sensitive elements, in order to obtain at least two energizing signals having a mutual phase difference which is substantially equal to cp.

The invention is based on the recognition that from two phase-shifted substantially sinusoidal signals two signals with another phase difference can be derived by linearly combining said signals and that this enables the magneto-sensitive elements to be arranged at comparatively small tangential angles relative to the rotor axis.

A first embodiment of the invention concerns a two-phase orfour-phase machine and is characterized in that the combining circuit supplies a signal which is proportional to the sum of the signals supplied byte two magneto-sentive elements and a signal which is proportional to the difference of the signals supplied by the two magneto-sensitive elements.

This embodiment has the advantage that the phase difference between said combined signals is independent of the tangential angle within the defined limit of being smaller than B at which the two magneto-sensitive elements are arranged.

In general, such a linear combination, which also enables phase differences other than 90 to be realized, may be characterized in that the combining circuit supplies a first signal C, which satisfies the equation C = A + KB and a second signal D, which satisifes the equation D = A - KB, where A is the signal supplied by a first one of the magnetosensitive elements, B is the signal supplied by a second one of the magneto-sensitive elements, and K is a predetermined constant which is such that the phase difference between the signals C and D is equal to ((.

A drawback of this combining method may be that in general the amplitudes of the combination signals C and Dare not equal. An embodiment of the machine in accordance with the invention which does not have said drawback may be characterized in that the combining circuit supplies a first signal C, which satisfies the equation C = A -- kB, and a second signal D, which satisfies the equation D = B - kA, where A is the signal supplied by a first one of the magneto-sensitive elements, B is the signal supplied by a second one of the magneto-sensitive elements, and k is a predetermined constant which is such that the phase difference between the signals C and D is equal to ((.

Avery simple embodiment of the last-mentioned machine may further be characterized in that the energizing circuit comprises a first comparator, of which a first input is connected to a first one of the magneto-sensitive elements, of which an output is connected to the series connection of a first one of the stator coils and a first resistor, and ofwhich a second input is connected to the junction between said first stator coil and said first resistor, a second comparator, of which a first input is connected to a second one of the magneto-sensitive elements, of which an output is connected to the series connection of a second one of the stator coils and a second resistor, and of which a second input is connected to the junction between the second stator coil and said second resistor, and a third resistor, which is included between the junction of the first stator coil and the first resistor and the junction of the second stator coil and the second resistor In the case of a three-phase machine in accordance with the invention the first resistor may be a variable resistor.

The present invention will now be explained and described in more detail, by way of example, with reference to the accompanying drawings, in which: Figure l is a schematic elevation of a three-phase electronically commutating motor which is equipped with Hall-elements in a conventional manner, Figure 2 represents a sectional view of the motor of Figure 1 in more detail, Figure 3 shows an electric machine in accordance with the invention, Figure 4 is a vector diagram to illustrate the operation of a two-phase motor made in accordance with the present invention, Figure 5 is a vector diagram to illustrate a first general embodiment of an electric machine, for example a motor, in accordance with the invention, Figure 6 is a vector diagram to illustrate another embodiment of an electric machine, for example a motor, in accordance with the invention, Figure 7 is a vector diagram to illustrate an alternative of the embodiment described with reference to Figure 6, Figure 8 is a circuit for realizing the linear com bination described with reference to Figure 4, Figure 9 represents a circuit for realizing the linear combinations described with reference to Figures 6 and7, Figure 10 is a vector diagram to illustrate the linear combination in the case of a three phase motor, Figure ii represents an embodiment of a combining circuit for realizing the combination method described with reference to Figure 10, and Figure 12 represents a combination method in which the signals produced by the magnetosensitive elements are triangular shape.

Figure 1 is a schematic elevation of a three-phase motor with electronic commutation equipped with Hall elements in a conventional manner and Figure 2 in a greater detail represents a sectional view of the motor of Figure 1 taken on the line ll-ll. The motor comprises a shaft 1 on which a bell-shaped rotor housing 2 is secured, which on the inner circumference is provided with an annular permanent magnet 3. The stator body 4 carries a lamination assembly 5 on which three stator coils 6,7 and 8 are arranged.

On the stator body 4 a support 9 is mounted on which the Hall elements 10 and 11 are arranged at an angle of 120 , which elements detect the field of the permanent-magnet ring 3 and via a circuit which is also mounted on said support, energize the stator coils 6,7 and 8 as a function of the rotor position.

Figure 3 illustrates an embodiment of an electric machine in accordance with the present invention in which the Hall elements 10 and 11 are disposed at a tangential angle which is less than the phase difference 0 between the energizing signals for the stator coils in order to obtain a correct energization of the stator coils. For the sake of simplicity only the stator lamination assembly of this motor is shown, the remainder of the construction of the motor being similar to that shown in Figure 2. The two Hall elements 10 and 11 are arranged close to each other - at an angle a relative to the rotor axis - so that by means of film techniques they can be accommodated on one substrate together with the required electronics or they can even be incorporated in one integrated circuit together with the required electronics.Nevertheless it is found possible to realize the correct phase differences between the energizing signals for the stator coils by generating linear combinations of the signals from the Hall elements 10 and 11, provided that said signals are substantially sinusoidal.

This is illustrated in Figure 4 by means of a vector diagram for a two-phase (or four-phase) motor. The signals A and B from the hall elements 10 and 11 respectively the sum C of these signals A and B and the difference D of said signals A and B are represented as vectors in this Figure. It is found that generating the linear combinations: C = A+B and D = A-B yields two signals with a phase difference of 90. For these combinations, this is independent of the angle a between the Hall elements. In general it is possible to generate any phase difference between the signals C and D by means of the linear combinations: C = A+KB and D = A-KB where K is a constant factor which depends on the angle o and the desired phase difference between the signals C and D.

If it is required - for example when the two Hall elements 10 and 11 are disposed symmetrically relative to the mid-point between two stator poles, as is shown in Figure 3 - that the vector C is situated exactly between the vectors A and B in view of the correct commutation instants, then it is for example possible to generate the following linear combinations; C A+B D = A-KB Figure 5 shows such a vector diagram for a phase difference of 120 between the signals C and D. This diagram is self-explanatory.

In the case of the combination methods described with reference to the vector diagrams of Figures 4 and 5 the amplitudes of the signals C and Dare not equal when the amplitudes of the signals A and B are equal. When the signals C and D solely switch the stator excitation at their zero passages, this is not a problem. However, if the signals C and Dare employed as energizing signals for the stator coils, as the case may be after amplification, then it may be necessary to amplify the two signals to the same amplitude by adapting the gain factors of said amplifier. A combination method which does not have this drawback is described with reference to Figure 6.

Figure 6 represents the vector diagram associated with the following linear combinations: C=B-KA D = A-KB In the case of this linear combination the amplitudes of the signals C and Dare equal if the amplitudes of the signals A and B are also equal. In the vector diagram of Figure 6 the factor K has been selected so that when the vectors A and B are situated at -1/2a and +ȧ respectively, the vectors C and D are sitated at + 120 and +240 respectively. The third phase-signal E for a three-phase motor is obtained in known manner by inverting the sum of the signals C and D (E = -C-D). It is also possible to employ the attenuated sum of the signals A and B.

Figure 7 represents the vector diagram of an alternative method of realizing the combination described with reference to Figure 6 in order to obtain a three-phase signal. The factor K is then selected so that the vectors C and D are situated at 60 and 300 respectively and the vector E = -(C + D) is consequently situated at 1800.

The linear combinations described can simply be realized by means of operational amplifiers, which may be integrated together with the Hall elements 10 and 11.

Figure 8 shows an example of a circuit for realizing the linear combination described with reference to Figure 4. The circuit comprises a summing amplifier 12 having a gain factor G1, to which the signals A and B from the Hall elements 10 and 11 are applied.

The output signal G1 (A+B) may be applied directly across a stator coil 6' of a two-phase motor. The signals A and B are further more applied to a differential amplifier 17 with a gain factor G2. The output signal G2 (A-B) is then 90" out of phase with the output signal G1 (A+B) and may be applied directly to the other stator coil 7'. By a suitable adjustment of the gain factors G1 and G2 relative to each other the amplitudes of the two output signals can be equalized.

The amplitude ratio of the signals G1 (A+B) and G2 (A- B) is of less significance when these signals are employed as switching signals, for example when the outputs of the amplifiers 12 and 17 are connected to the stator coils 6' and 7' via switching transistors T1 and T2 respectively instead of directly, as is represented by the dashed connections in Figure 8.

By means of the circuit of Figure 8 it is also possible to realize other linear combinations of the signals A and B in order to realize phase differences other than 90 between the output signals, employing the linear combinations discussed with reference to Figures 4 and 5. For this purpose the factors K may for example be realized in the amplifiers 12 and 17 for example by means of operational amplifiers known from analogue computing technology.

Figure 9 shows an example of a circuit for realizing the linear combinations A-KB and B-KA discussed with reference to Figures 6 and 7. It comprises an operational amplifier 18, which amplifies the signal A by a factor G and the signal B by a factor -KG, so that an output signal G(A-KB) is obtained, which may be applied directly to a stator coil 6 of a three-phase motor. A second operational amplifier 19 amplifies the signal B by a factor G and the signal A by a factor -KG, so that a signal G(B-KA) - which in the case of a suitable choice of the factor K differs 1200 in phase with the signal G(A-KB) - is obtained, which may be applied directly to the coil 7 of the three-phase motor. The third phase can be obtained by inverting the sum of the output signals, which yields the signal G(K-1) (A+B).This signal - as is shown in Figure 9 - can also be realized by means of a third amplifier 20 having a gain factor (K-1 )G, to which the signals A and B are applied. The output signal may then be applied directly to the third stator coil 8.

As is known, a three-phase motor may also be energized by three signals having a phase difference of 60 relative to each other instead of by three signals having a phase difference of 1200 relative to each other, if one of the stator coils is energized with opposite polarity or, viewed from the winding sense, from the opposite direction, which in the diagram of Figure 7 for example means that the vector E is shifted through 1800, so that the vectors C, D and E are situated at 60 relative to each other.If, as is illustrated by the vector diagram of Figure 10, two signals C and D with a phase difference of 60C are generated by a suitable choice of the factor K, the third phase E is obtained by taking the difference E = D - C of the signals D and C. If in the circuit of Figure 9 the factor K is selected so that a phase difference of 60" exists between the output signals of amplifiers 18 and 19, the third stator coil 8 may be energized with the third phase E by including it between the outputs of the amplifiers 18 and 19, as is represented by the dashed line in Figure 9. Amplifier 20 may then be dispensed with. Stator coil 7 should then be energized (or wound) in a reverse sense in comparison with the situation with the signals at 120".

The linear combinations C = B-KA and D = A-KB can simply be realized by allowing cross-talk with a factor K to occur between an amplifier for the signal A and an amplifier for the signal B. This is utilized in the circuit of Figure 11. In this circuit the current through the stator coil 6 or 7 is sensed by including a resistor 21 and 22 respectively, both for example having a resistance value Ro. The current through the stator coil 6 or 7 is controlled by an amplifier 23 and 24 respectively, which compares the signals A and B, in this case a voltage, with the voltage across the resistors 21 and 22 respectively. The currents through the coils 6 and 7 are then AaRo and B,Ro respectively, which when the Hall elements 10 and 11 are arranged in a conventional manner (Figure 1) exhibit a phase difference of for example 120'. If a phase difference of 60 is selected, the third stator coil 8 may simply be included between the outputs of the amplifiers 23 and 24. However, if the Hall elements 10 and 11 are arranged at a smaller angle o.

(Figure 3), the phase difference between the currents through the coils 6 and 7 can still be made 60 (or, if desired, 120' or other phase differences) by combining the signals A and B, in the present case very simply by including a cross-talk resistor 25 with a resistance value R1 between the junction of the coil 6 and resistor 21 and the junction of coil 7 and resistor 22. Through resistor 21 a currentA!Roflows, through resistor 22 a current BiRo, and through resistor 25 a current (A- B)R1,so that through stator coil 6 a current 16 = P(A-KB) flows and through stator coil 7 a current 17 = P(B-KA), where P = (Ro + R1)/RoR1 and K = Ro,(Ro + R1).By a suitable choice of K, which can be determined by experiment, for example by using a variable resistor for the resistor 25, it is again possible to obtain the correct phase difference.

In particular when the signals from the Hall elements are used for switching, instead of for analogue energization (as is for example shown as an alternative in Figure 8), the waveform of the signals A and B generated by the Hall elements 10 and 11 less critical. This can be demonstrated by means of Figure 12, in which Figures 12a and 1 2b represent the signals A and B as triangular voltage waveforms. Figure 1 2c represents the sum of said signals A and B and Figure 1 2d the difference of said signals A and B. It is found that also in this case the zero passages of the combinations A + B and A - B are shifted through a quarter of the period of the signals A and B, i.e. through 903, relative to each other. Other shifts are possible with other combinations.

Especially when the signals from the Hall elements 10 and 11 and the linear combinations thereof are employed as analogue energizing signals for the stator coils, it may occur in practice that the form andlor the strength of the magnetization of the permanent-magnet rotor is not suitable to produce suitable signals in the Hall elements. A suitable solution is then to arrange an additional magnetic disk on the rotor shaft, with which disk the Hall elements co-operate. The advantage that the two elements can be arranged near each other is then maintained, whilst the drawback of the known motor with magnetically-coded disk mentioned in the introduction does not occur.

Claims

1. An electric machine with electronic commutation, having a rotor which at least partly consists of a permanent magnetic material, at least two fixedly mounted stator coils which co-operate with the rotor, at least two magneto-sensitive elements arranged on a common substrate for supplying signals which vary substantially sinusoidally with the rotor position in order to energize the stator coils as a function of the rotor position via an energizing circuit, the magneto-sensitive elements being arranged at a tangential angle relative to the rotor axis, which angle is smaller than the phase difference (p which is necessary between the energizing signals from the stator coils in order to obtain a correct energization of said stator coils, wherein the energizing circuit includes a combining circuit for linearly combining the signals supplied by the at least two magneto-sensitive elements, in order to obtain at least two energizing signals having a mutual phase difference which is substantially equal to q.

2. An electric machine as claimed in Claim 1, adapted as a two-phase or a four-phase machine, wherein the combining circuit is arranged to supply a signal which is proportional to the sum of the signals supplied by the at least two magnetosensitive elements and a signal which is proportional to the difference of the signals supplied by the two magneto-sensitive elements.

3. An electric machine as claimed in Claim 1, wherein the combining circuit is arranged to supply a first signal C, which satisfies the equation C = A + KB, and a second signal D, which satisfies the equation D = A - KB, where A is the signal supplied by a first one of the magneto-sensitive elements, B is the signal supplied by a second one of the magnetosensitive elements, and K is a predetermined constant which is such that the phase difference between the signals C and D is equal to q.

4. An electric machine as claimed in Claim 1, wherein the combining circuit is arranged to supply a first signal C, which satisfies the equation C = A KB, and a second signal D, which satisfies the equation D = B - KA, where A is the signal supplied by a first one of the magneto-sensitive elements, B is the signal supplied by a second one of the magnetosensitive elements, and K is a predetermined constant which is such that the phase difference between the signals C and D is equal to q.

5. An electric machine as claimed in Claim 4, wherein the energizing circuit comprises a first comparator, of which a first input is connected to a first one of the magneto-sensitive elements, of which an output is connected to the series connection of a first one of the stator coils and a first resistor, and of which a second input is connected to the junction between said first stator coil and said first resistor, a second comparator, of which a first input is connected to a second one of the magnetosensitive elements, of which an output is connected to the series connection of a second one of the stator coils and a second resistor, and of which a second input is connected to the junction between the second stator coil and said second resistor, and a third resistor, which is included between the junction of the first stator coil and the first resistor and the junction of the second stator coil and the second resistor.

6. An electric machine as claimed in Claim 6, wherein the third resistor is a variable resistor.

7. An electric machine as claimed in Claim 3,4, 5 or 6, wherein the machine is a three-phase machine having three stator coils and the combining circuit is adapted to supply signals with an electrical phase difference of 60 to a first one and second one of said stator coils and wherein the third one of said stator coils is included in delta arrangement between the first and second stator coil.

8. An electric machine as claimed in any one of the preceding Claims. wherein the energizing circuit is at least partly incorporated in an integrated circuit together with the two magneto-sensitive elements.

9. An electric machine constructed and arranged to operate substantially as hereinbefore described with reference to Figures 3 to 12 of the accompanying drawings.