Method of starting an electric brushless rotating machine for driving an internal combustion engine

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of starting an electric brushless rotating machine and particularly to a method of starting an electric brushless rotating machine appropriated for generating a large torque at the startup stage.

[0003] 2. Description of the Related Art

[0004] A brushless motor is provided as an electric rotating machine where the energization of three-phase stator windings for driving a rotating member (referred to as a rotor hereinafter) is switched from one to another whenever the rotor rotates through 120 degrees of the electric angle. Such a conventional brushless motor has commonly a position detector element such as a Hall device for detecting the rotating position of the rotor. Recently, another type of brushless motor which includes no position detector element has been developed in response to the demand for down-sizing of the brushless motor.

[0005] For example, a brushless motor is disclosed in Japanese Patent Publication (Heisei)5-24760 where, in view of any two different phases of the three-phase stator windings being energized in a sequence, the voltage induced at the remaining not-energized phase is measured and used for calculating the rotating position of the rotor. As the brushless motor produces non of the induced voltage at the startup stage which is used for calculating the rotating position of the rotor, its rotor has slightly be driven by forced commutation. The forced commutation means that any two desired phases of the stator, e.g. U and V, are energized regardless of the position of the rotor (which is hence referred to as one-phase energization hereinafter). The position of the rotor is detected from the induced voltage and then a common procedure of the energization will follow in relation to the detected rotor position.

[0006] The positional relationship between the rotor and the stator when they stop their movement as the motor has been deenergized is determined by attracting and repulsing forces of the magnets. For example, when the motor is an outer rotor type brushless motor having three-phase stator windings, its positional relationship between the rotor and the stator is expressed by six different pausing modes, p1 to p6, shown in FIG. 13. FIG. 13 illustrates an arrangement of a primary part of the brushless motor in addition to the six pausing modes of the position relationship between the rotor and the stator of which the movement stops as the motor has been deenergized.

[0007] As shown in FIG. 12, the counter clockwise direction is the forward direction Rs of the rotor while the clockwise direction is the reverse direction Rr. The stator 100 and the rotor 200 of the brushless motor are disposed inward and outward respectively. The stator 100 has magnetic poles 300 of U, V, and W phase. The magnetic poles 300 incorporate windings. The rotor 200 has a row of permanent magnets m1, m2, m3, . . . of which the polarity alternates between N and S along the circumference.

[0008] A movement of the rotor from the initial pausing mode p1 to p6 when is driven by forced commutation between U phase and W phase without initial magnetization will be explained. When an electric current is supplied through U phase to W phase, the U phase is magnetized to positive (N) pole and the W phase is magnetized to negative (S) pole.

[0009] At the initial pausing mode p1, the magnet m2 at S is attracted by the U phase at N but repulsed by the W phase at S. This causes the rotor 200 to rotate at a maximum torque in the forward direction Rs. At the initial pausing mode p2, the U phase at N attracts the magnet m2 at S but repulses the magnet m3 at N hence allowing the rotor 200 to rotate at the maximum torque in the forward direction Rs. At the initial pausing mode p3, the attraction between the U phase at N and the magnet m2 at S is balanced with the attraction between the W phase at S and the magnet m1 at N. This permits no movement of the rotor 200.

[0010] At the initial pausing mode p4, the magnet m2 at N is attracted by the W phase at S while the magnet m1 at S is repulsed by the same. This causes the rotor 200 to rotate in the reverse direction Rr. At the initial pausing mode p5, the U phase at N attracts the magnet m3 at S but repulses the magnet m2 at N hence allowing the rotor 200 to rotate further in the reverse direction Rr. At the initial pausing mode p6, the repulsion between the U phase at N and the magnet m2 at N is balanced with the repulsion between the W phase at S and the magnet m1 at S. This permits no movement of the rotor 200.

[0011] As described, the startup torque may be generated non or too small at the initial pausing modes p3 and p6 thus disallowing the brushless motor to start up. In particular, when the brushless motor is linked to a heavy load and thus required to generate a large torque, this disadvantage will be significant. For example, the motor for starting an internal combustion engine, even if its output is great, may fail to generate a desired level of the startup torque because the friction in the engine is too high. At the initial pausing modes p4 and p5, the rotor rotates in the reverse direction and fails to generate a desired magnitude of the induced voltage needed for detecting the position of the rotor, hence inhibiting any normal energizing action. More particularly, by force commutation, the motor when remains free in the movement can be rotated in the forward direction two times out of six trials or at ⅓ of the probability.

SUMMARY OF THE INVENTION

[0012] It is hence an object of the present invention to provide a method of starting an electric brushless rotating machine which can generate a great level of the startup torque with no use of rotor position detecting elements. Another object of the present invention is to provide a method of starting an electric brushless rotating machine which can securely rotate in the right direction at high probability when the forced commutation is executed.

[0013] A first feature of the present invention is that a method of starting an electric brushless rotating machine which has a magnetic rotor and a set of first, second, and third stator windings arranged at phase intervals of 120 electric degrees to be energized in a sequence for forced commutation according to a voltage signal induced on the stator windings when the rotor is rotated, comprising the steps of, energizing the second stator winding and the first stator winding in this order for initial magnetization at the startup to rotate for the positioning of the rotor, and energizing the first stator winding and the third stator winding in this order for the forced commutation.

[0014] According to this feature, the method allows an electric brushless rotating machine to start with a maximum of the startup torque.

[0015] A second feature of the present invention is that the duration of energization for the initial magnetization is predetermined to such a length as to stabilize the position of the rotor after movement caused by the initial magnetization. As a third feature of the present invention, the duration of energization for the initial magnetization is based on the maximum of time among the time which are needed to stabilize the positions of the rotor after movement from the six positions where the rotor may be stopped spontaneously.

[0016] According to the second and third features, the electric brushless rotating machine can be minimized in the loss during the energization and its startup duration can be shortened.

[0017] A fourth feature of the present invention is that when its rotor is joined directly to the engine, the machine acts as an engine starter motor.

[0018] According to the fourth feature, the startup action can remain tuned with stability while not affected by a great power of startup friction.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]
FIG. 1 is a side view of one embodiment of an electric brushless rotating machine in the form of an engine generator system according to the present invention;

[0020]
FIG. 2 is a cross sectional view taken along the line V-V of FIG. 1;

[0021]
FIG. 3 is a schematic view of the engine generator system;

[0022]
FIG. 4 is a flowchart for controlling the startup of the engine generator system;

[0023]
FIG. 5 is a flowchart for controlling the initial magnetization;

[0024]
FIG. 6 is an explanatory view showing a fist and a second action of the initial magnetization;

[0025]
FIG. 7 is an explanatory view showing the fist and second actions of the initial magnetization;

[0026]
FIG. 8 is a flowchart for controlling the forced commutation in the first embodiment;

[0027]
FIG. 9 is a flowchart for controlling the forced commutation in the second embodiment;

[0028]
FIG. 10 is a flowchart for controlling a normal energization;

[0029]
FIG. 11 is a diagram showing a stable duration of the rotor single-phase energized at the initial pausing modes p1 to p6; and

[0030]
FIG. 12 illustrates a relationship between the stator and the rotor which are held spontaneously.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] One embodiment of the present invention will be described in mode detail referring to the relevant drawings. FIG. 1 is a side view of an electric brushless rotating machine of the embodiment in the form of an engine generator system. FIG. 2 is a cross sectional view taken along the line V-V of FIG. 1.

[0032] The engine generator system 1 includes an engine 2 and a generator 3. The generator 3 is a magnet type multi-pole power generator. The engine 2 has a crank shaft 4 thereof supported by a bearing 6 installed in a side wall 5a of a crank case 5 to extend at one end outwardly of the engine 2. A star-shaped annular iron core 7 is fixedly mounted by bolts 8 to a boss region about the crank shaft 4 of the side wall 5a of the crank case 5. The iron core 7 comprises an annular center yoke portion 7a with twenty seven projections 7b extending radially from the center yoke portion.

[0033] The projections 7b have three-phase alternate windings provided thereon thus constituting a stator 8. The iron core 7 is multi-poled for generating a large output of power and its center yoke portion 7a and projection 7b are decreased in the radial length thus contributing to the lower weight of the system.

[0034] The crank shaft 4 has a hub 9 of a forged member fitted onto the distal end thereof. The hub 9 is linked to a flywheel 10 which also acts as a rotor yoke. The flywheel 10 is a pressed member of a cup-like shape comprising a disk portion 10a and a cylinder portion 10b. The disk portion 10a is fixedly joined to the hub 9 so that the cylinder portion 10b encloses the outsides of the projections 7b of the iron core 7.

[0035] Eighteen neodymium magnets 11 having higher magnetism are circumferentially mounted on the inner side of the cylinder portion 10b of the flywheel 10 thus constituting a magnetic rotor 12 of an outer rotor type. The rotor 12 has the magnets 11 aligned tightly on the inner side of the cylinder portion 10b to have a sufficient mass and can hence function successfully as the flywheel.

[0036] A cooling fan 13 is mounted to the disk portion 10a of the flywheel 10. The cooling fan 13 has a set of blades 13b provided upright and arranged circumferentially on one side of an annular base 13a thereof. The annular base 13a is fixedly mounted to the outer side of the disk portion 10a of the flywheel 10. The cooling fan 13 is enclosed in a fan cover 14 which provides a cooling air passage 14a extending from the outer side of the flywheel 10 to the engine 2.

[0037]
FIG. 3 is a schematic view of the engine generator system 1. The generator 3 is driven by the (internal combustion) engine 2 to generate a three-phase alternating current. The alternating current output of the generator 3 is full-wave rectified to a direct current by a converter 15 which comprises a rectifying circuit having a group of semiconductor rectifier devices connected in a bridge form. The direct current output of the converter 15 is then smoothed by a capacitor smoothing circuit 16 and transferred to an inverter 17 where it is converted into an alternating current at a desired frequency by the FET bridge circuit of the inverter 17. The alternating current output of the inverter 17 is received by a demodulation filter 18 where a lower frequency component (e.g. commercial frequencies) is passed through. The alternating current passed through the demodulation filter 18 is transferred via a relay 19 and a fuse 20 to an output terminal 21. The relay 19 remains open at the startup of the engine 2 and is then closed when the engine 2 runs to a specific level.

[0038] The generator 3 in the engine generator system 1 is also used as a starter for starting the engine 2. For the purpose, the generator 3 includes a starter driver 22. A rectifying circuit 23 and a smoothing circuit 24 are provided for supplying the starter driver 22 with a current for starting the engine 2. The rectifying circuit 23 comprises a harmonic filter 231 and a converter 232. The harmonic filter 231 has a fuse 20A and is connected by the fuse 20A to the output terminal 21. The output of the generator 3 is connected to, for example, a single-phase power source 25 at 200 VAC and receives the alternating current from the source 25 for the startup action. The alternating current is transmitted to the harmonic filter 231 where its harmonic is removed off, converted to a direct current by the converter 232, and received as a power supply via the smoothing circuit 24 by the starter driver 22.

[0039] The starter driver 22 supplies the three-phase windings of the generator 3 in a predetermined sequence with the current for starting the engine 2. For sequentially supplying the windings with the current, a switching device (FET) 221, a CPU 222, and a sensorless driver 223 employing no sensor (magnetic pole detector) for detecting the location of the rotor 12. As the rotor rotates, the sensorless driver 223 measures the location of the rotor from voltage signals induced on the first, second, and third stator windings arranged at equal intervals of a 120-degree phase difference and determines the energization of the stator windings.

[0040]
FIG. 4 is a flowchart for controlling the startup of the engine generator system 1. When the generator 3 starts operating after its free pausing state, it may fail to have a desired startup torque during the forced commutation due to the negative positional relationship between the rotor and the stator. Also, the forward rotation may be interrupted. For compensation, Steps S1 and S2 conduct the first and the second action of the initial magnetization for shifting the rotor 12 to its desired location relative to the stator so that the desired startup torque is gained by the forced commutation and the forward rotation is encouraged. The initial magnetization then allows the rotor 12 to move to the desired location for gaining its maximum torque. The first and the second action of the initial magnetization are different in the energizing phase but equal in the procedure (as will be described later in more detail) . Even when the rotor and the stator remain at their free pausing state or at any positional relationship (ranging from p1 to p6 in FIG. 13), the two initial magnetizing actions can shift the rotor 12 to a desired position for producing the maximum torque. If the duration of the initial magnetization is too short, the rotor may rotate without steadiness and jog at its stop position. The energizing period for the initial magnetization will hence extend until the rotor is located with stability, i.e. substantially one second.

[0041] At Step S3, the forced commutation is carried out. The forced commutation involves single-phase energization from the positional relationship between the rotor and the stator when the maximum torque is gained after the second action of the initial magnetization. The induced voltage from the non-energized phase is measured through the forced commutation and then used for detecting the position of the rotor 12. As the position of the rotor 12 has been determined from the induced voltage detected, the procedure goes to Step S4 where a normal procedure of the energization is carried out.

[0042]
FIG. 5 is a flowchart for the initial magnetization (of both the first and the second action). At Step S10, the FET 221 is driven for energization of a predetermined phase. The first action of the initial magnetization energizes from the V phase to the U phase while the second action of the initial magnetization energizes from the V phase to the W phase. Step S11 follows where the initial value of energization duty is increased by a predetermined rate (for example, 1%). It is then examined at Step S12 whether or not the rotor 12 stops at any initial location (ranging from p1′ to p6′) in relation to the stator after a counter electromotive force is produced. When the rotor 12 remains not moved, the counter electromotive force is zero. Accordingly, the pausing of the rotor 12 at the initial location can be determined when the counter electromotive force is zero. At this step, once the counter electromotive force has been released, its value is examined whether zero or not. If no counter electromotive force has been released, it is judged “no” at the step. When “yes” at Step S12 is given, it is judged that the initial magnetization has been completed and the procedure goes to the next step. More specifically, when the first action of the initial magnetization is completed, the procedure goes to the second action of the initial magnetization. When the second action of the initial magnetization is completed, the procedure goes to the force commutation.

[0043] When it is judged “no” at Step S12, the procedure advances to Step S13 where it is examined whether the energization duty of the FET 221 exceeds an upper limit (e.g. 50%) or not. If not, the energization is carried out at the current duty (at Step S14) and the procedure returns to Step S11. When the rotor 12 fails to pause at the initial location with the duty reaching the upper limit or the counter electromotive force has not yet been released, it is judged “yes” at Step S13. This indicates a lockup state or an overloaded state and the duty is turned back to zero at Step S15 before the procedure is terminated with fail (at Step S16).

[0044] The first and the second action of the initial magnetization will be explained in more detail referring to FIGS. 6 and 7. The initial pausing modes from p1 to p6 illustrated at the left end in FIGS. 6 and 7 indicate the initial location of the rotor 200 relative to the stator 100 when the generator stops spontaneously as are identical to those p1 to p6 shown in FIG. 13. When the energization from the V phase to the U phase is carried out for conducting the first action of the initial magnetization, the polarity of the V phase is turned to N and the polarity of the U phase is turned to S. This causes the permanent magnets m2 and m3 of the rotor 200 at the initial relationship p1 to be attracted by the N pole of the V phase and the S pole of the U phase respectively. As a result, the magnetic interaction between the stator 100 and the rotor 200 is balanced thus holding the rotor 200 at the location p1′. When the positional relationship between the stator 100 and the rotor 200 is at any of the locations p2 to p6, the rotor 200 is held by the same effect at the locations p2′ to p6′. As apparent, the location p4′ among p1′ to p6′ is different from the others p1′ to p3′, p5′, and p6′.

[0045] When the energization from the V phase to the W phase is carried out for conducting the second action of the initial magnetization, the polarity of the V phase is turned to N and the polarity of the W phase is turned to S. This allows the S pole and the N pole of the rotor 200 to be repulsed and attracted respectively by the S pole of the W phase. As a result, the rotor 200 pauses with the permanent magnet m2 at S and the permanent magnet m1 at N held by the N pole of the V phase and the S pole of the W phase respectively. It is hence apparent that the pausing mode p1″ is established when the second action of the initial magnetization is carried out at any pausing mode of p1′ to p6′ determined by the first action of the initial magnetization. More particularly, all the different pausing modes p1 to p6 can be converged to the single pausing mode p1″ through the first and the second action of the initial magnetization. The positional relationship between the stator and the rotor involves the generation of a maximum of the startup torque in the revolution in the forward direction when the U and W phases are shifted to the N and S poles respectively by the succeeding forced commutation from the U phase to the W phase.

[0046] Accordingly, when the generator at the initial pausing mode p1″ is driven by the forced commutation, it starts up with its rotor and stator generating the maximum torque and can thus rotate without difficulty in the forward direction.

[0047] The duration of the first and the second action of the initial magnetization will now be explained referring to FIG. 11. FIG. 11 illustrates the duration required before the rotation of the rotor becomes stable when the stator and the rotor at any of the initial pausing modes p1 to p6 have been single-phase magnetized. If the duration of the initial magnetization is too short, the rotor may rotate unstable and create a rocking motion at its pausing location. As apparent from FIG. 11, the duration from the startup of the initial magnetization and to the rotor becoming stable is a maximum or substantially 0.7 second at the initial pausing mode p5. It is hence desired that the duration for the initial magnetization before the rotation of the rotor becomes stable is substantially one second in consideration of a generous margin.

[0048]
FIG. 8 is a flowchart showing a procedure of the forced commutation. At Step S20, the energization to a predetermined phase, e.g. from the U phase to the W phase, is conducted. Step S21 follows where the duty of PWM is gradually increased, for example, at steps of 1%. It is examined at Step S22 whether or not the current required for generating a torque of starting the engine or getting over the upper dead point for the compression exceeds an upper limit determined from the allowance for the energization (over-current).

[0049] When it is judged “yes” at Step S22 or the current exceeds the upper limit, the procedure jumps to Step S24 where the duty is reduced, for example, by 1% to protect a relevant component or switching device in the driver. At Step S25, the forced commutation is executed/continued at the 1% reduced duty.

[0050] When it is judged “no” at Step S22, the procedure moves to Step S23 for examining again whether or not the internal combustion engine has completed its full turning motion of predetermined times, for example, 10 times. When so, it is judged at Step S23 that the number of revolutions by the forced commutation is turned stable and the procedure for the force commutation is terminated before returning back to the normal energization procedure shown in FIG. 10. It is also possible to judge the rotating action from the number of revolutions per unit time instead of the foregoing predetermined number.

[0051] As the duty of PWM is gradually increased to the predetermined upper limit, the energization to any of the windings can be efficient without a redundancy of the energizing current. Also, when the duty reaches its upper limit, it can be decreased to inhibit over-current in the energization to the windings thus permitting the continuous operation.

[0052]
FIG. 9 is a flowchart showing a modification of the forced commutation. It may be necessary in respect of the capability of the switching element or the driver in the engine generator system 1 to carry out some times the forced commutation with over-currents exceeding the upper limit and overcome or climb over the upper dead point for the compression using a climb over torque. This is implemented by the modification of the forced commutation. Like steps are denoted by like numerals as those shown in FIG. 8 and will be explained in no more detail.

[0053] When it is judged at Step S22 that over-current is drawn, the procedure goes to Step S31 for increasing the count by one. It is then examined at Step S32 whether or not the count is greater than e.g. 10. When not, the procedure moves to Step S25 for carrying out the forced commutation at the duty of over-current. The forced commutation with over-current is continued until the count reaches 10. When the over-current remains (as judged “not” at Step S32), the duty is decreased by 1% at Step S33 to eliminate the over-current.

[0054]
FIG. 10 is a flowchart for the normal energization. At Step S41, the duty is increased by 1%. It is then examined at Step S42 whether or not the duty reaches its upper limit or the over-current is drawn. When not, the procedure goes to Step S43 where it is examined whether or not the number of revolution is higher than a predetermined level (for example, 800 rpm). When it is judged “yes” at Step S43 or the engine has started, the action of the stator is completed. In other words, the procedure goes to Step S44 for turning the duty to 0%. When it is judged “yes” at Step S42, the procedure advances to Step S45 for decreasing the duty by 1% to eliminate the over-current. Step S46 follows where the action is executed at the decreased duty.

[0055] While the forced commutation is carried out but not limited to after the first and the second action of the initial magnetization in the above embodiment, it may be conducted after the first action of the initial magnetization. At the initial pausing mode p4 shown in FIG. 7, the forced commutation after the first action of the initial magnetization causes a reverse of the rotation. However, the rotation can be in the forward direction with any of the initial pausing modes p1 to p3, p5, and p6. More specifically, if the forced commutation is conducted without the initial magnetization, the rotation in the forward direction can be implemented two times out of six trials as described. When the forced commutation follows the first action of the initial magnetization, the forward direction can be effected five times out of six trials thus exhibiting a higher rate of the probability.

[0056] As apparent from the foregoing description, the electric brushless rotating machine according to claims 1 to 5 can start with a maximum of the startup torque even if it is equipped with no position detector. Also, the invention allows the system to be simplified in the arrangement without declining the stability in the startup action.

[0057] Particularly as defined in claims 3 and 4, the startup action can be shortened in the duration while its energizing power is minimized in the loss.

[0058] According to claim 5 of the present invention, the startup action is commenced at a maximum of the startup torque and can thus remain tuned with stability while not affected by a great power of startup friction.

Method of starting an electric brushless rotating machine for driving an internal combustion engine

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