Electric motor and electric power steering device using same

Patent metadata

Field	Value
Publication number	US-10312768-B2
Application number	US-201715600471-A
Country	US
Kind code	B2
Filing date	May 19, 2017
Priority date	May 23, 2016
Publication date	Jun 4, 2019
Grant date	Jun 4, 2019

Abstract

An electric motor is provided which is designed to minimize a risk of corrosion or stress corrosion cracking of parts thereof and reduce mechanical vibration or noise. The electric motor includes an output shaft, a bearing which retains the output shaft, a frame, and a biasing member. The biasing member is made of austenite stainless steel and disposed between the bearing and a bottom wall of a bearing housing to elastically press the output shaft in a lengthwise direction thereof for eliminating mechanical noise arising from vibration of a rotor. The frame has a coating formed on an outer surface thereof for avoiding erosion thereof. The coating is not formed at least on a portion of the frame which faces the biasing member in order to induce sacrificial corrosion of the frame, which decelerates the corrosion of the biasing member to eliminate a risk of the stress corrosion cracking thereof.

First claim

What is claimed is:

1. An electric motor which drives a given target comprising: a cylindrical casing which has a first end and a second end opposed to the first end; a first frame which is made of metallic material containing aluminum and covers the first end of the cylindrical casing, the first frame having a first recess and a first hole formed therein, the first recess being formed in a middle portion of the first frame which faces the cylindrical casing, the first hole communicating between one of surfaces of the first frame which is farther away from the cylindrical casing and a first bottom wall that is a bottom of the first recess; a second frame which is made of metallic material containing aluminum and covers the second end of the cylindrical casing to define a storage chamber between itself and the first frame in the cylindrical casing, the second frame having a second recess formed in a middle portion thereof which faces the cylindrical casing; an annular stator which is disposed in the storage chamber coaxially with the cylindrical casing, the annular stator being held from rotating relative to the cylindrical casing; a winding wound around the stator; a first bearing which is mounted in the first recess with an outer wall thereof fit in a first inner wall that is a cylindrical inner wall of the first recess; a second bearing which is mounted in the second recess with an outer wall thereof fit in a second inner wall that is a cylindrical inner wall of the second recess; a shaft which has a given length with a first end portion and a second end portion and is retained by the first frame and the second frame to be rotatable, the first end portion passing through the first hole to connect with the target and having an outer wall fit in an inner wall of the first bearing so that the first end portion is retained by the first bearing, the second end portion having an outer wall fit in an inner wall of the second bearing, so that the second end portion is retained by the second bearing; a rotor which has an outer wall facing an inner wall of the stator and an inner wall fit on an outer wall of the shaft, so that the rotor is rotatable together with the shaft; a biasing member which is made of austenite stainless steel and disposed between the first bottom wall and the first bearing or between a second bottom wall that is a bottom wall of the second recess and the second bearing, the biasing member urging the shaft through the first bearing or the second bearing in an axial direction of the shaft; and a coating which is disposed on an outer surface of the first frame or the second frame, wherein the outer surface of the first frame or the second frame includes a coating-occupied area where there is the coating and a coating-unoccupied area where there is not a coating, the coating-unoccupied area being provided on at least a portion of the outer surface of the first frame or the second frame which faces the biasing member.

2. An electric motor as set forth in claim 1 , wherein the second frame has formed therein a second hole which communicates between a surface of the second frame which is farther away from the casing and the second bottom wall, wherein the shaft has the second end portion inserted into the second hole, and further comprising a magnet, a magnetic flux, and a control unit, the magnet being secured to an end of the second end portion of the shaft, the magnetic flux sensor being arranged on an opposite side of the second frame to the casing and so working to measure a magnetic flux, as produced by the magnet and output a signal indicative thereof, the control unit working to control electric power delivered to the winding based on the signal outputted from the magnetic flux sensor to control rotation of the rotor.

3. An electric motor as set forth in claim 1 , wherein the first bearing includes a first inner cylinder, a first outer cylinder, and a plurality of first balls, the first inner cylinder having an inner wall fit on the outer wall of the shaft and being held from moving relative to the shaft, the first outer cylinder having an outer wall fit in the first inner wall of the first recess and being movable relative to the first frame, the first balls being disposed between the first inner cylinder and the first outer cylinder to permit the first inner cylinder and the first outer cylinder to rotate relative to one another, wherein the second bearing includes a second cylinder, a second outer cylinder, and a plurality of second balls, the second inner cylinder having an inner wall fit on the outer wall of the shaft and being held from moving relative to the shaft, the second outer cylinder having an outer wall fit in the second inner wall of the second recess and being movable relative to the second frame, the second balls being disposed between the second inner cylinder and the second outer cylinder to permit the second inner cylinder and the second outer cylinder to rotate relative to one another, and wherein the biasing member is placed in contact with the first outer cylinder or the second outer cylinder.

4. An electric motor as set forth in claim 1 , wherein the first frame is made of a discrete member separate from the casing, and further comprising a first sealing member disposed between the first frame and the casing to create a liquid-tight seal between the first frame and the casing.

5. An electric motor as set forth in claim 1 , wherein the second frame is made of a discrete member separate from the casing, and further comprising a second sealing member disposed between the second frame and the casing to create a liquid-tight seal between the second frame and the casing.

6. An electric motor as set forth in claim 1 , wherein the biasing member is implemented by one of a coiled wave spring, a disc spring, a coil spring, and a wave washer.

7. An electric motor as set forth in claim 1 , wherein the coating is made of one of an anodic oxide coating, a cation electrodeposition coasting, and a plated coating.

8. An electric power steering device for a vehicle comprising: an electric motor which includes (a) a cylindrical casing which has a first end and a second end opposed to the first end, (b) a first frame which is made of metallic material containing aluminum and covers the first end of the cylindrical casing, the first frame having a first recess and a first hole formed therein, the first recess being formed in a middle portion of the first frame which faces the cylindrical casing, the first hole communicating between one of surfaces of the first frame which is farther away from the cylindrical casing and a first bottom wall that is a bottom of the first recess, (c) a second frame which is made of metallic material containing aluminum and covers the second end of the cylindrical casing to define a storage chamber between itself and the first frame in the cylindrical casing, the second frame having a second recess formed in a middle portion thereof which faces the cylindrical casing; (d) an annular stator which is disposed in the storage chamber coaxially with the cylindrical casing, the annular stator being held from rotating relative to the cylindrical casing; (e) a winding wound around the stator; (f) a first bearing which is mounted in the first recess with an outer wall thereof fit in a first inner wall that is a cylindrical inner wall of the first recess; (g) a second bearing which is mounted in the second recess with an outer wall thereof fit in a second inner wall that is a cylindrical inner wall of the second recess; (h) a shaft which has a given length with a first end portion and a second end portion and is retained by the first frame and the second frame to be rotatable, the first end portion passing through the first hole to connect with a targe

Assignees

• Denso Corp

Inventors

• Tomizawa Hiroki
• Isogai Koji

Classifications

• F16C33/82

  Arrangements for electrostatic or magnetic action against dust or other particles · CPC title

• F16C33/76

  of ball or roller bearings · CPC title

• H02K11/33

  Drive circuits, e.g. power electronics (H02K11/38 takes precedence) · CPC title

• H02K7/1004

  with pulleys · CPC title

• F16C19/54

  Systems consisting of a plurality of bearings with rolling friction (spindle bearings F16C35/08) · CPC title