Brushless motor incorporating an integrated circuit having a one-chipped peripheral circuit

Abstract: A brushless motor having accommodated within a case of said motor by having mounted on a substrate (25), rotor revolution detection sensors (7A - 7C, 8 and 8A) and a monolithic integrated circuit (40) which includes an inverter (2) for rotatingly driving a rotor, drive circuits (3, 6) for driving the inverter (2), a power source circuit (4) for supplying a power required by each circuit, circuits (9, 10, 11, 12 and 13) for controlling the revolution number of the rotor and a protection circuit (5) for protecting the inverter (2) from an excess current.

Description: BACKGROUND OF THE INVENTION The present invention relates to a motor which is suitable for application to the motor for driving a fan for a room air conditioner or the like, and, more particularly, to a brushless motor incorporating an inverter which enables variable speed control. Recently, as shown in "Japan Radio Newspaper" on March 22, 1990, a high-voltage one-chipped three-phase inverter (hereinafter referred to as a one-chip three-phase inverter) has been developed which controls revolution number of a motor by utilizing a direct power source voltage that is obtained by rectifying and smoothing a commercial AC voltage of 100 (V). The one-chip three-phase inverter is extremely small as compared with the conventional inverter and can be stored in a motor. As shown in Fig. 1A, this three-phase one-chip inverter has such a device structure that polysilicon is used as the base and the area of each phase is divided at high withstanding voltage by dielectric dividing means or by an SiO 2 phase so that a circuit of one phase is formed in each area. The circuits in the two-dotted line of Fig. 2 are integrated on the one-chip. Fig. 1B is a plane view showing the layout of each element of the one-chip three-phase inverter. As is clear from this diagram, this one-chip three-phase inverter comprises, in a one-chipped integrated circuit, six switching transistors 2 as main elements, a diode 1 for turning off the switching transistors 2 connected between the collector and the emitter of each of the switching transistors 2, a logic circuit 6 for forming a switching signal for turning on and off each of the switching transistors 2, a drive circuit 3 for on- and off-driving each switching transistor with this switching signal, an excess current protection circuit 5 for preventing the integrated circuit from being destroyed by an excess current by detecting a current that flows through the switching transistors 2, and an internal power source 4. The integrated circuit element of the one-chip three-phase inverter has the dimensions of a 4.3 mm length and a 5.8 mm width. In the one-chip three-phase inverter explained above, a lateral Insulated Gate Bipolar Transistor (IGBT) has been developed and employed as the switching transistor 2 to have substantially reduced areas as compared with the conventional power MOSFET. At the same time, a high-speed diode has been newly developed and employed that can be realized in the same process as that of the lateral IGBT, so that an inverse recovery current is reduced substantially thereby to reduce substantially the switching loss of the switching transistors 2 due to an inverse recovery current Further, a power source circuit is incorporated in the one-chip three-phase inverter to require only one external power source for driving the switching transistors 2 that form the power element. The excess current protection circuit 5 is also incorporated in the one-chip three-phase inverter to be able to prevent the integrated circuit from being destroyed by an excess current that is generated by a short-circuiting of a load or the like. Further, the inverter frequency is set to 20 KHz which is higher than an audio frequency so that noise of the motor can be reduced substantially. Fig. 2 is a block diagram showing a brushless motor that uses the one-chip three-phase inverter as described above. 7A, 7B and 7C designate Hall device sensors, 8 a sensor amplifier, 9 a revolution number signal formation circuit, 10 a speed correction circuit, 11 a pulse width modulation (PWM) signal formation circuit, 12 a start current limit circuit, 13 an oscillation circuit 14 a stator, 15 the above-described one-chip three-phase inverter, and 16 an external power source. Referring to Fig. 2, when a commercial AC voltage of 100 (V) is applied to the external power source 16, a DC power source voltage (VI) is applied to each circuit from the external power source 16. By applying a voltage (VZ) for a signal, the oscillation circuit 13 is started. When a speed command is given to the speed correction circuit 10 from an external circuit, the drive circuit 3 on- and off- drives each of the switching transistors 2 sequentially according to signals generated from the logic circuit 6. Then, a current flows to each coil provided in the stator 14 in a predetermined direction, so that a rotor not shown starts rotation to start the motor. When the motor is started, the start current limit circuit 12 controls the PWM signal formation circuit 11 based on the result of a detection by the excess current protection circuit 5 so that the start current flowing through each switching transistor 2 is not excessive, thereby to adjust the duty ratio of the PWM signal. Assume that the switching transistors 2 are expressed as Q 1 , Q 2 , Q 3 , Q 4 , Q 5 and Q 6 and the diodes 1 to be connected to these switching transistors 2 are expressed as D 1 , D 2 , D 3 , D 4 , D 5 and D 6 . Then, the collectors of the switching transistors Q 1 to Q 3 are connected to the + terminal of the external power source 16 and the emitters of the switching transistors Q 4 to Q 6 are connected to one terminal of the external power source 16. The emitter of the switching transistor Q 1 and the collector of the switching transistor Q 4 are connected to the first coil provided in the stator 14. Similarly, the emitter of the switching transistor Q 2 and the collector of the switching transistor Q 6 are connected to the second coil, and the emitter of the switching transistor Q 3 and the collector of the switching transistor Q 6 are connected to the third coil. The drive circuit 3 turns on the switching transistors Q 1 , Q 2 and Q 3 sequentially at an electrical angle of every 120 degrees, and turns on the switching transistors Q 4 , Q 5 and Q 6 sequentially by chopping with a PWM signal at an electrical angle of every 120 degrees. The driving timings of the switching transistors Q 1 to Q 6 are shown as Q 1 to Q 6 in Fig. 3. In Fig. 3, the switching transistor Q 4 is turned on and off at the same cyde and the same duty ratio as those of the PWM signal during the period from the latter half of the on-period of the switching transistor Q 2 to the former half of the on-period of the switching transistor Q 3 , the switching transistor Q 5 is turned on and off at the same cyde and the same duty ratio as those of the PWM signal during the period from the latter half of the on-period of the switching transistor Q 3 to the former half of the on- period of the switching transistor Q 1 , and the switching transistor Q 6 is turned on and off at the same cycle and the same duty ratio as those of the PWM signal during the period from the latter half of the on-period of the switching transistor Q 1 to the former half of the on-period of the switching transistor Q 2 . As described above, when the motor starts, the Hall device sensors 7A, 7B and 7C detect the rotation of the rotors, and generate rotor position signals of an electrical angle of 180-degree width, with phase difference of an electrical angle 120 degrees at a rotor rotation electrical angle of 360 degrees. These rotor position angles are amplified and waveform-shaped by the sensor amplifier 8 which has been adjusted to a predetermined gain. These signals are then supplied to the logic circuit 6 of the one-chip three-phase inverter 15, and one of the rotor position signals, for example the rotor position signal generated in the Hall device sensor 7A, is supplied to the revolution number signal formation circuit 9 so that a revolution number signal representing the revolution number of the rotor is formed by the frequency or cyde of the rotor position signal. The revolution number signals are supplied to the speed correction circuit 10 and compared with the revolution number based on the speed command supplied from the outside, so that a speed correction signal is formed in accordance with the difference between the revolution numbers. The duty ratio of the PWM signal outputted from the PWM signal formation circuit 11 is controlled by the speed correction signal. In order to improve the precision of revolution number detection, until three revolution number signals obtained from the Hall device sensors can be inputted into the revolution number signal formation circuit 9. The logic circuit 6 forms a commutation signal (switching signal) for sequentially turning on and off the switching transistors Q 1 to Q 3 with an electrical angle 120 degrees and a deviated phase of every 120 degrees from the three-phase rotor position signals supplied from the sensor amplifier 8, and a switching signal having the same cyde and the same duty ratio as those of the PWM signal supplied from the PWM signal formation circuit 11 of the timings explained in Fig. 3 in accordance with this commutation signal, and sends these signals to the drive circuit 3. By the above arrangement, a current conduction time of each coil provided in the stator is controlled in accordance with the duty ratio of the PWM signal that has been corrected by the speed correction signal from the speed correction circuit 10, and the rotor revolution number is controlled to be consistent with the revolution number according to the external speed command. When the rotor revolution number has changed, the cycles of the Hall device sensors 7A, 7B and 7C also change accordingly. As described above, the rotor revolution number is determined by the duty ratio of the PWM signal, and the revolution number ofthe motor can be changed by changing the duty ratio. Fig. 4 is an exploded perspective view showing one example of the conventional motors incorporating a one-chip three-phase inverter, based on the circuit structure shown in Fig.2. 17 designates an upper case, 18 a stator core, 19 a coil, 20 an aperture, 21A, 21B and 21C supporting members, 22 a shaft, 23A and 23B bearings, 24 a rotor, 25 a printed wiring panel, 26 a peripheral circuit, 27A, 27B and 27C screws, 28 lead wires, 29 a lower case, 30A, 30B, 30C and 30D openings, 31 a drawing duct, 32 an opening, 33 a screw and 34A, 34B and 34C screw holes. Referring to Fig. 4, the cylindrical stator core 18 having the coil 19 wound up by an internal slot is engaged inside the upper case 17. The opening 20 is provided at the center of the upper surface of the upper case 17, and an edge portion is formed at the lower end of the external periphery of the opening 20. The four screw holes 34A, 34B, 34C and 34d (which is not shown because it is located at the rear side) are provided at equal intervals at the edge portion. The bar-shaped supporting members 21A, 21B and 21C which stretch downward are fixed at equal intervals at the external periphery of the lower surface of the stator core 18. The rotor 24 is covered with a ferrite magnetic material having the thickness of about 2 mm on the peripheral surface, and the shaft 22 passing through the center of the rotor 24 is integrated. The bearings 23a are fixed to the shaft 22 at a portion above the rotor 24, and the bearings 23B are also fixed to the lower end of the shaft 22. The printed wiring substrate 25 having the shaft 22 pierced through it is provided between the rotor 24 and the bearings 23B. The lower case 29 is provided with the opening 32 at the center of the bottom and the drawing duct 31 which pierces through the side. The lower case 29 is also provided with the edge portion which stretches externally at the upper side, and the openings 30A, 30B, 30C and 30D are provided at equal distance at the edge portion. On the upper surface of the printed wiring substrate 25, a circuit conductor pattern for the circuit structure shown in Figs. 6 or 8 is formed and the peripheral circuits 26 induding the sensor amplifier 8 and the revolution number signal formation circuit 9, together with the Hall device sensors 7A, 7B and 7C and the one-chip three-phase inverter 15, are mounted and the terminal of the circuit conductor pattern is guided to the lower surface of the printed wiring substrate 25, with the lead wires 28 connected to the terminal. The rotor 24, together with the shaft 22, is inserted into the inside of the stator core 18, and the bearings 23A are fixed to the upper surface of the inside of the upper case 17. When the rotor 24 is fixed, the upper portion of the shaft 22 stretches to the outside through the opening 20 of the upper case 17. The printed wiring substrate 25 is fixed to the supporting members 21A, 21B and 21C which stretch to below the stator core 18, by the screws 27A, 27B and 27C. The lower case 29 is fixed to the upper case 17 so as to cover the printed wiring substrate 25 and the stator core 18, by matching the screw holes 34A, 34B, 34C and 34D (not shown) at the edge portion of the upper case 17 with the openings 30A, 30B, 30C and 30D at the edge portion of the lower case 29 respectively and by fastening screws 33 to the screw holes 34A, 34B, 34C and 34D through the openings 30A, 30B, 30C and 30D. In this case, the bearings 23B at the lower end of the shaft 22 are fixed within the opening 32 of the lower case 29 and the lead wires 28 are guided to the outside from the inside of the lower case 29 through the drawing duct 31. Fig. 5 shows a partially extended view of the room air conditioner using the above-described motor as a fan motor. The room air conditioner comprises an indoor unit 35 disposed within a room, an outdoor unit 36 disposed outside the room and a pipe connected between these units. A tangential floor fan 38A and a propeller fan 38B are provided in the indoor unit 35 and the outdoor unit 36 respectively. The above-described motor can be used as drive motors 39A and 39B for driving the fans 38A and 38B respectively. Usually, the three-phase inverter of the motor has about the same size as that of motor body. However, since a one-chip three-phase inverter is incorporated in the above motor, the control section of the outdoor unit 36 can be made compact by that amount and the outdoor unit 36 itself can be made compact accordingly. This also applies to the indoor unit 35. A high-power device such as a switching transistor within the one-chip three-phase inverter is a heating unit, and therefore it has a problem that the properties of the one-chip three-phase inverter are deteriorated resulting in its reduced reliability when the one-chip three-phase inverter is heated to a high temperature. Accordingly, it is necessary to provide a heat radiation fan in the one-chip three-phase inverter. However, as explained in Fig. 4, not only the one-chip three-phase inverter 15 and the Hall device sensors 7A, 7B and 7C, their peripheral circuits 26 are also mounted in a large number on the printed wiring substrate 25, so that there has been no space to provide a heat radiation fan in the one-chip three-phase inverter 15 according to the prior art. As a result, about 20 (W) has been a limit to the output of the motor. In GB 2 150 364 A a DC brushless motor is shown in which a drive circuit is installed. All the parts of the drive circuit except for a Hall IC are made as a single IC. As the Hall IC a monolithic integrated circuit using Hall effect is proposed. The housing of the integrated circuit of the drive circuit is substantially integral with the base plate which forms a main part of the stator. The base plate can directly contact a metallic yoke for heat dissipation. In "Three phase control and drive IC for brushless motor", Phil Davies, Mike Null ; Electronic Engineering ; Nov. 1986 an intelligent power IC which after control, drive, electronic commutation and protection features is described which can reduce parts count, board space and design time for motor control and drive circuits. In DE 38 42 588 A1 a brushless motor is disclosed in which power semiconductors are mounted or a disk shaped cooling body. The cooling body is disposed in parallel to a disk shaped circuit board comprising electronic components by means of a spacer in order to provide sufficient space between the disks for the electronic components. Both disks have a central hole for receiving a rotor axis. SUMMARY OF THE INVENTION It is an object of the present invention to provide a motor which solves the above problems and which realizes a high output by making it possible to radiate heat from a three-phase inverter integrated circuit incorporated in the motor. In order to achieve the above object, there is provided a brushless motor according to claim 1. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a partial cross sectional diagram of the integrated circuit of the one-chip three-phase inverter; Fig. 1B is a plan view showing the layout of the integrated circuit of Fig. 1A; Fig. 2 is a block diagram showing the circuit system of the motor using a one-chip three-phase inverter; Fig. 3 is a diagram for explaining the operation of the motor in Fig. 2; Fig. 4 is an exploded perspective view of the motor in Fig. 2; Fig. 5 is a configuration diagram of the room air conditioner; Fig. 6 is a block diagram of the peripheral circuits incorporated into an integrated circuit; Fig. 7 is a diagram showing an embodiment of the peripheral circuits incorporated into an integrated circuit for the motor according to the present invention; Fig. 8 is an exploded perspective view of the motor. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 6 is a block diagram showing the circuit configuration of Fig. 6 and Fig. 7 is an exploded perspective view thereof. In Figs. 6 and 7, 15' designates a three-phase inverter, 21D and 21E supporting members, 40 a monolithic integrated circuit, and 41 a heat radiation panel, and portions corresponding to those in Figs. 2 and 4 are placed with the same symbols to omit a duplicated explanation. Fig. 6 will be explained first. According to the prior art technique explained above, only the three-phase inverter 15' encircled by a two-dot line is integrated into a circuit in one chip to form the one-chip three-phase inverter. In the present embodiment, however, this three-phase inverter 15' and its peripheral circuits induding the revolution number signal formation circuit 9, the speed correction circuit 10, the PWM signal formation circuit 11, the start current formation circuit 16 and the oscillation circuit 13 are all set into a high withstand voltage monolithic integrated circuit on the same basis which are encircled by a broken line, as explained in Fig. 1A. The size of the monolithic integrated circuit 40 is larger than that of the device of the conventional one-chip three-phase inverter 15 by about only 10%. Therefore, a package of the same shape and the same size as those of the package for the conventional one-chip three-phase inverter 15 can be used as the package for storing the device of the monolithic integrated circuit 40. A gain adjusting device such as a resistor 8a is provided in the sensor amplifier 8 for adjusting a gain, so that the gain can be adjusted at the time of assembling the motor. The Hall integrated circuit incorporated in the sensor amplifier may be used instead of the Hall device sensors 7A, 7B and 7C. In this case, a sufficiently high gain of the Hall integrated circuit can be obtained to avoid the need for the gain adjusting resistor 8a. The excess current protection circuit 5 of the present invention prevents the integrated circuit from being destroyed by an excess current which is generated due to a short-circuiting of the load or the like. The excess current protection circuit 5 detects a rising time (dv/dt) of a current from the stator and stops the system when the detected value is within a predetermined time by regarding it as an excess current. If the detected time exceeds the predetermined time, the start current limit circuit 12 is started. The current of the stator may be detected directly to start the start current limit circuit 12. The circuit diagram in this case is shown in Fig. 8. The only difference between Fig. 6 and Fig. 8 is a difference of an input signal to the start current limit circuit 12. Figs. 7 shows one embodiment of the motor according to the present invention. When the above-described monolithic integrated circuit 40 is used, the number of parts to be mounted on the printed wiring substrate 25 and the mounting area can be reduced to about 1/20 and about 1/2 respectively as compared with those on the printed wiring substrate according to the prior art technique. In the present embodiment, it is assumed that the printed wiring substrate 25 is formed in a half-disk shape and heat radiation means for the monolithic integrated circuit 40 are formed at the remaining half-disk portion. To be more specific, the printed wiring substrate 25 is formed in a half-disk shape and is fixed to the supporting members 21A and 21D of the stator core 18, and a half-disk shape heat radiation panel 41 made of aluminum faces the printed wiring substrate 25 and is fixed to the supporting members 21B and 21E of the stator core 18. The printed wiring substrate 25 is mounted with the Hall device sensors 7A, 7B and 7C and the sensor amplifier 8 for supplying outputs of these sensors. On the heat radiation panel 41, the monolithic integrated circuit 40 shown in Fig. 6 is mounted such that the heat sink at the rear side of the monolithic integrated circuit 40 is brought into close contact with the heat radiation panel 41. Each of the pins of the monolithic integrated circuit 40 is connected to a predetermined terminal of the circuit conductor pattern on the printed wiring substrate 25. As described above, the three-phase inverter and its peripheral circuits are integrated into a monolithic integrated circuit which is accommodated in a package of the same shape and the same size as those of the package for the conventional one-chip three-phase inverter. Therefore, it is possible to reduce the number of parts mounted on the printed wiring substrate 25 and the space occupied, and the heat radiation material made of an aluminum panel can be mounted on the portion corresponding to the space reduced by the monolithic integrated circuit 40. Accordingly, heat radiation effect of the monolithic integrated circuit 40 can be obtained sufficiently. As a result the output capacity of the motor can be increased to about 50 (W) from the conventional capacity of about 20 (W). Further, since the number of parts mounted on the printed wiring substrate 25 is reduced, the number of solderings is also reduced, with an improved reliability of the circuit system mounted on the substrated. In this case, the number of solderings becomes about 1/100 of that of the prior art technique.

Claims: A brushless motor having accommodated in a case: (a) a rotor (24); (b) a stator (19); (c) a revolution detection means (7A-7C, 8 and 8A) for detecting revolution of said rotor (24); (d) a substrate (25) having mounted thereon said revolution detection means (7A-7C. 8 and 8A); and (e) an integrated circuit (40) including an inverter (2) for rotatingly driving said rotor (24), a drive circuit (3, 6) for driving said inverter (2), a power source circuit (4) for supplying a power which is required by each circuit. circuits (9-13) for controlling the revolution number of said rotor (24), and a protection circuit (15) for protecting said inverter (2) from an excess current; said revolution detection means being connected to said integrated circuit (40); said integrated circuit (40) being mounted on a heat radiation means (41) which, together with said substrate (25), forms a disk shape having a hole for receiving a rotor axis (22).

Inventors: ARAKAWA NORIAKI, ISII MAKOTO, KAWAGUCHI YASUTSUGU, ARAKAWA, NORIAKI, ISII, MAKOTO, KAWAGUCHI, YASUTSUGU
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1991
Main classification: H02P6
IPC codes: H02K29, H02P6, H02K11