Motorized mobility device with filter unit for electromagnetic interference

Abstract

Motor-driven mobility device (25) comprising: a DC motor assembly (1) comprising: a stator, a rotor (3) rotatably arranged in the stator, the rotor (3) comprising a commutator (7), a first brush (9a) and a second brush (9b) arranged stationary relative to the rotor (3), wherein the first and second brushes (9a, 9b) are configured to cooperate with the commutator (7) when the rotor (3) rotates, a first cable (11a) connected to the first brush (9a) and a second cable (11b) connected to the second brush (9b), an electrically conductive motor housing (13) which accommodates the stator, the rotor (3), the first and second brushes (9a, 9b), and the first and second cables (11a, 11b), and an electromagnetic interference filter unit (15; 15') comprising a printed circuit board (15a) having a first ground layer (15b) electrically connected to the motor housing (13), wherein a capacitor (19) is mounted on the printed circuit board (15a) and has a first terminal (19a) electrically connected to the first cable (11a), a second terminal (19b) electrically connected to the second cable (11b), and a third terminal (19c) electrically connected to the first ground layer (15b).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to motorized mobility devices such as motorized wheelchairs. BACKGROUND

[0002] Motorized mobility devices can be powered by direct current (DC) electric motors. In some cases, mobility devices can also include one or more actuators, for example, to move a seat driven by a corresponding DC motor.

[0003] DC motors have a rotor fitted with an electromagnet that is supplied with a direct current via fixed brushes that are in electrical contact with a commutator attached to the rotor shaft and electrically connected to the rotor windings.

[0004] The interaction between the rotating commutator and the fixed brushes creates sparks that can lead to electromagnetic interference (EMI) problems. SUMMARY

[0005] Electromagnetic interference filters can be used to reduce EMI problems. Such filters can comprise one or more capacitors, or inductors and capacitors in an LC filter configuration. Ferrite material can also be used to reduce electromagnetic emissions. However, none of these solutions may be sufficiently efficient, or, in the case of ferritic material, a large amount of ferrite mass would be required.

[0006] In view of the above, it is a general object of the present disclosure to provide a motorized mobility device that solves or at least mitigates the problems in the prior art.

[0007] A motor-driven mobility device is therefore provided, comprising: a DC motor assembly, comprising: a stator, a rotor rotatably arranged in the stator, the rotor comprising a commutator, a first brush and a second brush arranged stationary relative to the rotor, the first and second brushes being configured to cooperate with the commutator when the rotor rotates, a first cable connected to the first brush and a second cable connected to the second brush, an electrically conductive motor housing accommodating the stator, the rotor, the first and second brushes, and the first and second cables, and an electromagnetic interference (EMI) filter unit comprising a printed circuit board (PCB) having a first ground layer electrically connected to the motor housing, a capacitor mounted on the PCB and having a first terminal,which is electrically connected to the first cable, a second terminal electrically connected to the second cable, and a third terminal electrically connected to the first ground layer.

[0008] It has been found that using a capacitor with three or more terminals, with a third, or grounded, terminal, reduces emissions very effectively. Using a PCB further simplifies installation.

[0009] According to one embodiment, the capacitor has a fourth terminal electrically connected to the first ground layer.

[0010] The PCB can be mounted on an end bell wall of the motor housing.

[0011] According to one embodiment, the PCB comprises a second ground layer, wherein the first ground layer is a first exposed layer of the PCB provided on a first side of the PCB, and the second ground layer is a second exposed layer of the PCB provided on a second side of the PCB facing the motor housing, and the PCB comprises a plurality of vias electrically connecting the first ground layer to the second ground layer.

[0012] The vias provide a low impedance electrical contact between the capacitor and the motor housing.

[0013] The PCB may, for example, comprise at least 10, such as at least 20, at least 30, or at least 40 passes.

[0014] One embodiment includes fasteners, wherein the fasteners extend through metallized through holes in the PCB and press the second ground layer against the motor housing.

[0015] The fastenings can be screws.

[0016] The fixings ensure that the entire second ground layer is in full mechanical and therefore electrical contact with the motor housing, or in the case of an electrically conductive filler, as will be described in more detail, with the electrically conductive filler.

[0017] According to one embodiment, the motor housing has a flat surface on which the PCB is mounted.

[0018] According to one example, the PCB may be flexible so that it follows the curvature of the motor housing when attached to the motor housing.

[0019] One embodiment includes an electrically conductive filler having a curved first surface disposed in mechanical contact with the motor housing, the curved first surface having a shape that follows a curvature of the motor housing, and a flat second surface, the PCB being mounted on the flat second surface.

[0020] According to one embodiment, the PCB is arranged within the motor housing.

[0021] The electrically conductive filler piece may have a convex surface that bears against an inner surface of the motor housing.

[0022] Alternatively, the PCB may be mounted on an outer surface of the motor housing, or on the electrically conductive filler, which may be attached to the outer surface of the motor housing. The electrically conductive filler may have a concave surface that rests against an outer surface of the motor housing.

[0023] According to one embodiment, the first cable and the second cable extend through a corresponding cable passage opening in the PCB.

[0024] According to one embodiment, the capacitor is a multilayer ceramic capacitor.

[0025] According to one embodiment, the capacitor is an X2Y® capacitor.

[0026] According to one embodiment, the motorized mobility device is a motorized wheelchair.

[0027] In principle, all terms used in the claims are to be interpreted according to their usual technical meaning, unless expressly defined otherwise herein. All references to "an / an / the element, device, component, means, etc." are to be understood as referring to at least one instance of the element, device, component, means, etc., unless expressly stated otherwise. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Specific embodiments of the inventive concept will now be described by way of example with reference to the accompanying drawings, in which: Fig. Figure 1 schematically shows a cross-section of an example of a DC motor assembly; Fig. Figure 2 shows an example of an EMI filter unit of the DC motor assembly; Fig. 3A a view along section AA in Fig. 2 represents; Fig. 3B a view along section BB in Fig. 2 is; Fig. 4 is another example of an EMI filter unit; and Fig. 5 is a side view of an example of a mobility device. DETAILED DESCRIPTION

[0029] The inventive concept is explained in more detail below with reference to the accompanying drawings, which show exemplary embodiments. However, the inventive concept may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments serve as examples to make this disclosure comprehensive and complete, and to clearly convey the scope of the inventive concept to those skilled in the art. Like reference numerals refer to like elements throughout the specification.

[0030] Fig. 1 schematically shows a cross-section of an example of a DC motor assembly 1 for a motorized mobility device such as a motorized wheelchair.

[0031] The DC motor assembly 1 includes a stator (not shown) and a rotor 3.

[0032] The rotor 3 is rotatably mounted within the stator. The rotor 3 is arranged to interact electromagnetically with the stator.

[0033] The rotor 3 includes a commutator 7. The commutator is electrically connected to the rotor windings.

[0034] The DC motor assembly 1 includes a first brush 9a and a second brush 9b arranged to be in direct mechanical contact with the commutator 7. The brushes 9a, 9b are configured to cooperate with the commutator 7 when the rotor 3 rotates.

[0035] The DC motor assembly 1 includes a first cable 11a electrically connected to the first brush 9a and a second cable 11b electrically connected to the second brush 9b.

[0036] The first cable 11a is arranged to be connected to a first pole, for example the positive pole, of a direct current source, and the second cable 11b is arranged to be connected to a second pole, for example the negative pole, of the direct current source.

[0037] When the rotor 3 rotates, the polarity of the voltage at the commutator, and thus at the rotor windings, is alternately reversed by the brushes 9a, 9b.

[0038] The DC motor assembly 1 comprises an electrically conductive motor housing 13. The motor housing 13 can be made, for example, of metal or a conductive cross-linked polymer material.

[0039] The stator, the rotor 3, the commutator 7, the first brush 9a, the second brush 9b, the first cable 11a, and the second cable 11b are arranged within the motor housing 13.

[0040] The motor housing 13 may have a circular or substantially circular cross-sectional shape along its inner circumference.

[0041] The DC motor assembly 1 further includes an electromagnetic interference (EMI) filter unit 15. The EMI filter unit 15 is configured to reduce electromagnetic emissions from the DC motor assembly 1.

[0042] Fig. 2 shows a close-up view of the Fig. EMI filter unit 15 shown in Figure 1.

[0043] The EMI filter unit 15 includes a printed circuit board (PCB) 15a.

[0044] The PCB 15a has a first side defining a first ground layer 15b. The first ground layer 15b is an exposed layer forming an outermost surface of the PCB 15a on the first side.

[0045] The PCB 15a has a second side opposite the first side. The second side defines a second ground layer 15c. The second ground layer 15c is an exposed layer opposite the motor housing 13.

[0046] The first ground layer 15b and the second ground layer 15c form a ground plane.

[0047] The first ground layer 15b and the second ground layer 15c are electrically connected.

[0048] The PCB 15a includes metallized through-holes 15d that extend through the PCB 15a from the first side to the second side. The metallized through-holes 15d therefore have inner surfaces lined with metal.

[0049] The metallized vias 15d are in electrical contact with the first ground layer 15b and the second ground layer 15c.

[0050] The metallized through holes 15d may be threaded.

[0051] The DC motor assembly 1 includes mounts 17a, 17b arranged in each of the metallized through-openings 15d. The mounts 17a, 17b are electrically conductive. The mounts 17a, 17b can be made of metal, for example.

[0052] The fastenings 17a, 17b can be metal screws, for example. The metal screws can engage with the threaded, metallized through-holes 15d and / or with the motor housing 13.

[0053] According to the example, the fasteners 17a, 17b extend through the metallized through-openings 15d and into the motor housing 13. The first ground layer 15b and the second ground layer 15c are thus in electrical contact with the motor housing 13 via the fasteners 17, 17b.

[0054] The DC motor assembly 1 may include flexible elements such as spring washers provided between the mounting heads and the first ground layer 15b. This ensures that the mountings 17a, 17b press the PCB against the motor housing 13 over time, during thermal cycles that cause expansion and contraction of components of the EMI filter unit 15.

[0055] The PCB 15a includes cable through-holes through which a respective one of the first cable 11a and the second cable 11b is routed. The motor housing 13 also includes through-holes aligned with a respective one of the cable through-holes of the PCB 15a. The first cable 11a and the second cable 11b are thereby routed out of the motor housing 13. The first cable 11a and the second cable 11b can be soldered to the PCB 15a.

[0056] The EMI filter unit 15 further comprises a capacitor 19. The EMI filter unit 15 may comprise a single capacitor 19 or a plurality of capacitors 19 connected in series and / or parallel.

[0057] Capacitor 19 is a surface-mount capacitor. Capacitor 19 can be soldered to PCB 15a.

[0058] The capacitor 19 may be a multilayer ceramic capacitor.

[0059] The capacitor 19 may preferably be an X2Y® capacitor.

[0060] The capacitor 19 has a first terminal electrically connected to the first cable 11a and a second terminal electrically connected to the second cable 11b. The capacitor 19 also includes a third terminal electrically connected to the first ground layer and thus to the motor housing 13.

[0061] The capacitor 19 may include a fourth terminal electrically connected to the first ground layer 15b.

[0062] According to the Fig. In the example shown in Figure 2, the EMI filter unit 15 is mounted on the inside of the motor housing 13.

[0063] According to the Fig. In the example shown in Figure 2, the DC motor assembly 1 includes an electrically conductive filler piece 21. The filler piece 21 may be made, for example, of metal or a conductive polymer material. The filler piece 21 has a curved first surface 21a that has a shape that follows a curvature of the motor housing. In the example in Fig. 2, the first surface 21a follows the curvature of an inner surface of the motor housing 13. The first surface 21a is convex. The first surface 21a is arranged in mechanical contact with the motor housing 13.

[0064] The filler piece 21 has a planar second surface 21b. The PCB 15a is mounted on the planar second surface 21b. The fasteners 17a, 17b press the PCB 15a against the planar second surface 21b, and the curved first surface 21a is pressed against the inner surface of the motor housing 13.

[0065] According to a variation, the motor housing 13 may be provided with a planar surface, for example, a planar inner surface on which the PCB 15a is mounted. In this case, no filler piece is required.

[0066] Fig. 3A is a sectional view of the PCB 15a along lines AA in Fig. 2. In particular, the first side with the first ground layer 15b is shown. The first terminal 19a, the second terminal 19b, the third terminal 19c, and the fourth terminal 19d of the capacitor 19 are visible. The PCB 15a includes a plurality of vias 23 that extend through the PCB 15a and electrically connect the first ground layer 15b to the second ground layer 15c. The vias 23 can, for example, be evenly distributed along the periphery of the PCB 15a.

[0067] Fig. 3B is a sectional view of the PCB 15a along lines BB in Fig. 2.

[0068] Fig. Figure 4 illustrates a variation of the DC motor assembly 1, with a similar EMI filter unit 15' as the EMI filter unit 15 described above. However, according to the example, the EMI filter unit 15' is mounted on the outer surface of the motor housing 13 via the electrically conductive filler piece 21'. The curved surface 21a' is pressed against the outer surface of the motor housing 13. The first surface 21a' is concave. Alternatively, the motor housing 13 could have an outer surface portion that is concave, and in this case, the PCB could be mounted directly onto the outer surface portion without the need for the filler piece.

[0069] Fig. 5 shows an example of a motor-driven mobility device 25.

[0070] The motorized mobility device 25 may, for example, be a motorized wheelchair.

[0071] The motor-driven mobility device 25 comprises drive wheels 27.

[0072] The motorized mobility device 25 may include a seating system 29 and one or more actuators (not shown) arranged to change the position / attitude of the seating system 29.

[0073] The motorized mobility device 25 includes one or more DC motor assemblies 1 as described herein. The DC motor assemblies 1 may, for example, be configured to drive a respective drive wheel 27. According to some examples, a DC motor assembly 1 may be configured to drive an actuator for changing the position / attitude of the seating system 29.

[0074] The motorized mobility device 25 includes a battery (not shown). The first cable 11a and the second cable 11b of the DC motor assembly 1 can be connected directly or indirectly to the battery to supply power to the first brush 9a and the second brush 9b, and thus to the rotor 3.

[0075] The inventive concept has been described above primarily with reference to a few examples. However, it will be clear to those skilled in the art that, within the scope of the inventive concept as defined in the appended claims, other embodiments than those described above are also possible.

Claims

[1] Motor-driven mobility device (25) comprising: a DC motor assembly (1) comprising: a stator, a rotor (3) rotatably arranged in the stator, the rotor (3) comprising a commutator (7), a first brush (9a) and a second brush (9b) arranged stationary relative to the rotor (3), wherein the first and second brushes (9a, 9b) are configured to cooperate with the commutator (7) when the rotor (3) rotates, a first cable (11a) connected to the first brush (9a) and a second cable (11b) connected to the second brush (9b), an electrically conductive motor housing (13) which accommodates the stator, the rotor (3), the first and second brushes (9a, 9b), and the first and second cables (11a, 11b), and an electromagnetic interference filter unit (15; 15') comprising a printed circuit board (15a) having a first ground layer (15b) electrically connected to the motor housing (13), wherein a capacitor (19) is mounted on the printed circuit board (15a) and has a first terminal (19a) electrically connected to the first cable (11a), a second terminal (19b) electrically connected to the second cable (11b), and a third terminal (19c) electrically connected to the first ground layer (15b). [2] The motor-driven mobility device (25) according to claim 1, wherein the capacitor (19) has a fourth terminal (19d) electrically connected to the first ground layer (15b). [3] A motor-driven mobility device according to claim 1 or 2, wherein the printed circuit board (15a) comprises a second ground layer (15c), wherein the first ground layer (15b) is a first exposed layer of the printed circuit board (15a) provided on a first side of the printed circuit board (15a), and the second ground layer (15c) is a second exposed layer of the printed circuit board (15a) provided on a second side of the printed circuit board (15a) facing the motor housing (13), and wherein the printed circuit board (15a) comprises a plurality of vias (23) electrically connecting the first ground layer (15b) to the second ground layer (15c). [4] Motor-driven mobility device (25) according to claim 3, comprising fasteners (17a, 17b), wherein the fasteners (17a, 17b) extend through metallized through-openings (15d) in the printed circuit board (15a) and press the second ground layer (15c) against the motor housing (13). [5] Motor-driven mobility device (25) according to one of the preceding claims, wherein the motor housing (13) has a flat surface on which the printed circuit board (15a) is mounted. [6] Motor-driven mobility device (25) according to claim 1 or 2, comprising an electrically conductive filler piece (21; 21') having a curved first surface (21a; 21a') arranged in mechanical contact with the motor housing (13), the curved first surface (21a; 21a') having a shape that follows a curvature of the motor housing (13), and a flat second surface (21b), the printed circuit board (15a) being mounted on the flat second surface (21b). [7] Motor-driven mobility device (25) according to one of the preceding claims, wherein the printed circuit board (15a) is arranged within the motor housing (13). [8] Motor-driven mobility device (25) according to one of the preceding claims, wherein the first cable (11a) and the second cable (11b) extend through a corresponding cable passage opening in the printed circuit board (15a). [9] Motor-driven mobility device (25) according to one of the preceding claims, wherein the capacitor (19) is a multi-layer ceramic capacitor. [10] Motor-driven mobility device according to one of the preceding claims, wherein the capacitor (19) is an X2Y® capacitor. [11] A motorized mobility device (25) according to any one of the preceding claims, wherein the motorized mobility device (25) is a motorized wheelchair.

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