BRUSHLESS DC MOTOR

Abstract: A brushless D. C. motor is disclosed having two bifilar winding wire pairs (P1, P3 and P2, P4) with each bifilar pair forming alternate windings. Each winding (P1 to P4) is switched by a transistor (T1-T4) which has a back poled diode (45) connected in parallel therewith. A control circuit sequences energization of single windings with each winding energized being in a different bifilar pair than the next preceding energized winding whereby when a transistor is switched off the other winding of the bifilar pair and the associated back poled diode protect the transistor and provide an energy conserving/heat eliminating path for the induced current. Each winding is further formed of a pair of subwindings having an angle of separation therebetween approximately half the angular separation between adjacent windings.

Description: This invention concerns a bifilar wound brushless DC motor according to the pre-characterising part of claim 1. Such a motor is known from DE-0S-25 27 744. The object of the present invention is to provide a construction of motor of the known kind which permits the generation of an angularly narrower magnetic pole with higher torque per ampere, and in addition permits a more compact winding configuration. This object is achieved by the combination claimed in claim 1. An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, wherein:- FIG. 1 is an exploded view of a motor including rotor and stator assemblies; FIG. 2 schematically illustrates the sequence of winding the bifilar winding pairs on the stator core; FIG. 3 shows the poles established by energizing the windings sequentially; FIG. 4 shows a logic circuit for controlling the energizing of the windings; FIG. 5 is a timing diagram of the input signals to the circuit of FIG. 4; and FIG. 6 shows the motor windings circuit including switching transistors and back poled protection diodes. FIG. 1 is an exploded view of the principal parts of the motor. The rotor includes a ring 17 of magnetically permeable metal with a ring 18 of permanent magnet material bonded to the interior cylindrical surface of ring 17. The ring 18 of magnetic material has formed therein four permanent magnet poles of 90° intervals with like poles being 180° apart. The metal ring 17 is pressed into the housing 20 to constrain the housing 20 and rings 17, 18 to rotate in unison. The stator 22 includes a core lamination/winding assembly 23 and a base 24 which are interconnected by three bolts 25. Housing 20 has a depending central shaft (not shown) which extends through a sleeve 26 and is secured by a nut 27. The sleeve 26 is pressed into the inner races of bearings 29 to permit the rotor to rotate freely about stator 22 with the ring 18 of magnetic material surrounding the stator core lamination/winding assembly 23. The individual winding leads 31 and the common lead 32 extend from the terminal stator slot locations through a slotted opening 33 in base 24. The motor winding comprises two bifilar winding wire pairs which are wound through slots 34 in the periphery of the core laminations 35 in accordance with the sequence of steps shown in FIG. 2, and which are thereafter compressed or crushed to reduce their volume and potted in epoxy 37. FIG. 2 shows the steps used in winding the two bifilar winding wire pairs on the stator with the stator slot locations indicated by the numbers 1 through 16 about the periphery of the ring 36 which represents a bottom view of the core lamination stack. Steps 1, 3, 5 and 7 show the winding locations of the phase 1 (P1) and phase 3 (P3) bifilar winding wire pair and steps 2, 4, 6 and 8 illustrate the winding locations of the phase (P2) and phase 4 (P4) biflar winding wire pair. With reference to step 1, the P1/P3 wires are wound with the initial half of the turns through slots 1 and 5, the final half of the turns through slots 2 and 6 and the lead being finally terminated in slot 5. The termination in slot 5 places the P1/P3 wires in position to start the next sequence of windings using this winding wire pair in step 3. Referring now to step 2, the winding wire bifilar pair composed by phase 2 (P2) and phase 4 (P4) winding wires are wound with the first half of the first winding turns through slots 3 and 7 (starting from slot 3), the second half of the first winding turns through slots 4 and 8 and terminating at slot 7 in preparation for step 4 when the next winding of P2/P4 is initiated. In step 3 the P1/P3 pair is wound with the initial half of the winding turns between slots 5 and 9, the second half of the winding turns between slots 6 and 10 and terminating at slot 9. At step 4 biflar pair P2/P4 is wound with the initial half of the turns between slots 7 and 11, the final half of the turns between slots 8 and 12 and terminates at slot 11. During step 5 the P1/P3 pair is wound to form a subwinding of half the turns using slots 9 and 13 followed by a subwinding of half the turns using slots 10 and 14 and terminating at slot 13. Using the P2/P4 bifilar pair in step 6 the initial half number of turns are formed using slots 11 and 15, the final half number of turns use slots 12 and 16 and the wire pair is terminated through slot 15. The final winding of wire pair P1/P3 is wound by halves using slots 13 and 1 and thereafter using slots 14 and 2 with the wires finally extending through slot 1. Accordingly the P1/P3 wires both start and terminate the four winding set by passing through slot 1. Finally in step 8 the subwinding of the P2/P4 wire pair are wound in slots 15 and 3 followed by 16 and 4 and terminate through slot 3 whereby these wire pairs both start and end by passing through slot 3. Although shown separately in figure 2, it is to be understood that both bifilar winding wire pairs are wound on the same stator, so that the final result is the combination of steps 7 and 8. FIG. 3 shows the induced magnetic pole patterns created by energizing the winding phases P1 through P4. By cyclically energizing the windings in the sequence P1, P2, P3, P4 the pole pattern processes in a counterclockwise direction in 45° increments with each winding phase change. Similarly a clockwise procession would be established by a cyclical P4, P3, P2, P1 energisation sequence. FIG. 4 schematically illustrates the circuit for energizing the bifilar winding phases using a pair of trains of clock pulses H1 and H2 (FIG. 5) which are 45° out of phase with one another. The true and complement values of the H1 and H2 input signals are generated using inverters with the various combinations of input signals being decoded by open collector AND gates 41, 42, 43 and 44. The 2 bit decode of H1 and H2 signals yield the 4 unique combinations which respectively activate windings P1, P2, P3 or P4 in the proper sequence. As shown in FIG. 5 the combination of input signals or pulses gives a P1, P3, P4 phase sequence. FIG. 6 illustrates the circuit for controlling the energization of the windings wherein transistors T1, T2, T3 and T4 function as switches for turning on and turning off the current flow to windings P1, P2, P3 and P4 respectively. Each of the switching transistors T1 through T4 has respectively connected in parallel therewith a reverse poled diode 45. Also connected between the input voltage +V and ground in parallel with the windings P1 through P4 is a capacitance 46. During operation, the motor windings are sequenced by energising the lines 51, 52, 53 and 54 singly in that order. When T1 has been on causing a current to flow through winding P1 and is then turned off, current flow ceases between node A and ground. Since transistor T3 is turned off, the reverse poled diode 45 in parallel with transistor T3 permits the induced current to flow through coil P3. It will be noted that the induced current flows in the opposite direction (upward through P3 as viewed in Fig. 6). As a result the voltage as node A is limited and transistor T1 is protected. Thus, the diode 45 in parallel with T3 protects T1 when T1 turns off. The induced back EMF charges the capacitor 46. When another winding is turned on, the capacitor 46 discharges through that winding. The ability of winding P3 to conduct a reverse flow of current to the power supply not only conserves energy otherwise wasted, but also reduces the heat dissipation problems occasioned by the dissipation of energy through a resistance. Since the sequence of energized windings causes windings to be consecutively energized in different bifilar winding pairs, as shown, alternately between the two bifilar pairs, the diode protection of the switching transistors is fully effective and the induced current in the closely coupled and reverse wired other bifilar winding of the pair produces a torque in the same direction that assists the desired operation.

Claims: 1. A bifilar wound brushless DC motor including a rotor (17, 18), a stator (22) having a plurality of bifilar winding wire pairs (P1, P3 and P2, P4) arranged in a series of equi-angularly disposed bifilar windings (Fig. 2) mounted around the periphery of the stator with adjacent bifilar windings formed by coiling from different bifilar winding wire pairs and the bifilar winding wire pairs each forming a plurality of equi-angularly disposed bifilar windings with at least one intervening bifilar winding formed from a different bifilar winding wire pair, and a plurality of similar winding circuits (Fig. 6) connected in parallel to a potential source (+V) and each including a respective winding wire (P1 to P4), switch means (T1, T3) for energising the associated winding wire (P1 to P4), diode means (45), each respectively connected in parallel with the associated switch means to permit a reverse flow of current through the associated winding wire that by-passes the switch means connected in parallel thereto, the motor further having switch control means (Fig. 4 and 5) arranged to cyclically and individually energise the winding wires in such a sequence that first one winding wire (P1, P2) of each bifilar pair (P1, P3 and P2, P4), and then the other winding wire (P3, P4) of each bifilar pair are energised in succession (P1, P2, P3, P4) to provide a precession of induced magnetic poles around the stator, characterised in that each of the bifilar windings is formed of two bifilar sub-windings which overlap one another and have axes of symmetry separated by an angle half the angular separation between the axes of adjacent bifilar windings. 2. The motor of claim 1, wherein each of the switch means comprises a respective transistor (T1 to T4). 3. The motor of claim 1 or 2, wherein there are two bifilar winding wire pairs (P1, P3 and P2, P4) with successively adjacent bifilar windings formed by coiling from alternate ones of the bifilar winding wire pairs. 4. The motor of any preceding claim, wherein the switch control means comprises two bistable input signals (Fig. 5) and circuit means (Fig. 4) for decoding the bistable input signals into four mutually exclusive signals (51 to 54) respectively connected to the switch means (T1 to T4).

Inventors: BURKE, MICHAEL JOSEPH, COLLINS, DAVID WHINERY
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1980
Main classification: H02P6
IPC codes: H02P6, H02K29