Motor-driven power steering device

• US 6,805,017 B2
• Filed: 02/14/2002
• Issued: 10/19/2004
• Est. Priority Date: 06/19/2000
• Status: Expired due to Term

• Current Assignee: NKS Company Limited
• Original Assignee: NSK Limited
• Inventors: Ohshima, Masamichi, Chikaraishi, Kazuo
• Primary Examiner(s): Pecci, David A.
• Assistant Examiner(s): Van Pelt, Bradley J.
• Application Number:
  US10/049,602
• Publication Number:
  US 20020112555A1
• Time in Patent Office: 978 Days
• Field of Search: 743/88.PS, 744/96, 744/98, 745/00, 744/25, 744/39, 744/46, 744/43, 74D/IG.10, 464/30, 298/93, 180/444, 180/443, 427/287, 427/486
• US Class Current: 74/388.0PS
• CPC Class Codes: B62D 5/0409 Electric motor acting on the steering column
• CPC Class Codes: B62D 5/043 characterised by clutch means between driving element, e.g. motor, and driven element, e.g. steering column or steering gear
• CPC Class Codes: F16D 1/0835 due to the elasticity of the ring or sleeve
• CPC Class Codes: F16D 7/021 with radially applied torque-limiting friction surfaces F16D7/022 takes precedence
• CPC Class Codes: F16H 1/16 comprising worm and worm-wheel
• CPC Class Codes: F16H 55/06 Use of materials; Use of treatments of toothed members or worms to affect their intrinsic material properties coatings for lubrication F16H57/041; producing gear wheels from plastics or substances in a plastic state B29D15/00; heat treatment C21D9/32; electrolytic surface treatment C25D; heating by electromagnetic field H05B6/00
• CPC Class Codes: Y10T 74/19828 Worm

Abstract

An electric power steering apparatus can correspond to high output ability, and has a power transmission mechanism of an electric driving section capable of achieving predetermined slip torque in spite of change of operating temperature. Also, a resin gear for power transmission is formed by joining a core metal and a resin with strong bonding force, and has preferable heat-dissipation property. This joining is performed by way of chemical bond according to composite molding technique or adhesive.

Claims

1. An electrical power assisted steering apparatus provided with a torque limiter having a ring member formed with a plurality of radially outwardly curved projections for applying elastic force mounted between a worm wheel and an output shaft, wherein said output shaft is made of iron material, a gear portion of said worm wheel is made of synthetic resin material, and a core metal portion of said worm wheel is made of aluminum material which has a specific gravity smaller than that of said iron material of the output shaft and which has a coefficient of linear thermal expansion larger than that of said iron material of the output shaft, and wherein the gear portion and the core metal portion are fixedly joined, whereby a change in spacing between said worm wheel and said output shaft as a result of differential thermal expansion therebetween operates to change a limit torque of said torque limiter from a lower value under high temperature to a higher value under low temperature.

2. An electrical power assisted steering apparatus according to claim 1, wherein said gear portion and said core portion are joined by way of chemical bond according to a composite molding technique.

3. An electrical power assisted steering apparatus according to claim 1, wherein the outer peripheral surface of the core metal portion is formed with irregularities for strengthening the joining between said core metal portion and said resin gear portion.

4. An electrical power assisted steering apparatus according to claim 3, wherein the outer peripheral surface of the core metal is toothed to provide said irregularities.

5. An electrical power assisted steering apparatus comprising:

a worm wheel formed with an axial through hole at a center thereof,

an output shaft fitted in the axial through hole of said worm wheel, and

a torque limiter comprising a ring member formed with a plurality of radially outwardly curved projections for applying elastic force;

wherein said output shaft is made of iron material, a gear portion of said worm wheel is made of synthetic resin material, and a core metal portion of said worm wheel is made of aluminum material which has a specific gravity smaller than that of said iron material of the output shaft, and which has a coefficient of linear thermal expansion larger than that of said iron material of the output shaft,

said gear portion and said core metal portion being fixedly joined,

wherein said ring member of said torque limiter comprises a substantially cylindrical thin metal member made of spring steel and formed with a plurality of radially outwardly curved projections, the substantially cylindrical thin metal member being press-fitted on the output shaft with said projections being in pressure contact with an inner peripheral surface defining said axial through hole of said worm wheel, and

whereby a limit torque of said torque limiter will vary based upon an operating temperature of said steering apparatus.

6. An electrical power assisted steering apparatus according to claim 5, wherein said gear portion and said core portion are joined by way of chemical bond according to a composite molding technique.

7. An electrical power assisted steering apparatus according to claim 5, wherein the outer peripheral surface of the core metal portion is formed with irregularities for strengthening the joining between said core metal portion and said resin gear portion.

8. An electrical power assisted steering apparatus according to claim 7, wherein the outer peripheral surface of the core metal is toothed to provide said irregularities.

9. An electrical power assisted steering apparatus comprising:

a housing made of aluminum;

an input shaft rotatably supported in said housing and connected at one end to a steering wheel;

an output shaft rotatably supported in said housing and connected at one end to said input shaft and at the other end to a steering gear box, the output shaft being made of iron material;

an electric motor for steering assistance;

a gear mechanism for transmitting rotation of said motor to said output shaft, the gear mechanism being received in said aluminum housing and including a worm gear rotated by said motor, and a worm wheel with an axial throughhole formed in a center thereof, in which said output shaft is fitted, the worm wheel being engaged with said worm gear;

said worm wheel comprising a core metal portion made of aluminum material which has a specific gravity smaller than that of said iron material of the output shaft and a coefficient of linear thermal expansion larger than that of said iron material of the output shaft, and an outer peripheral annular gear portion made of synthetic resin material and fixedly joined onto an outer peripheral surface of said core metal portion; and

a torque limiter comprising a substantially cylindrical thin metal member made of spring steel and formed with a plurality of radially outwardly curved projections, the substantially cylindrical thin metal member being press-fitted on the output shaft with said projections being in pressure contact with an inner peripheral surface defining said axial throughhole of said worm wheel.

10. An electrical power assisted steering apparatus according to claim 9, wherein said gear portion and said core portion are joined by way of chemical bond according to a composite molding technique.

11. An electrical power assisted steering apparatus according to claim 9, wherein the outer peripheral surface of the core metal portion is formed with irregularities for strengthening the joining between said core metal portion and said resin gear portion.

12. An electrical power assisted steering apparatus according to claim 11, wherein the outer peripheral surface of the core metal is toothed to provide said irregularities.