Electric power steering apparatus

1. An electric power steering apparatus including an electric motor for outputting assist torque to a steering wheel of a vehicle, and a control unit for controlling the driving of said electric motor,

said control unit comprising:

a power main body including a bridge circuit composed of a plurality of semiconductor switching elements for switching a current supplied to said electric motor in accordance with torque assisting said steering wheel;

a control main body that generates a drive signal to control said bridge circuit based on the steering torque of said steering wheel;

a metal substrate that is composed of a plurality of insulating layers and a plurality of conductor layers having wiring patterns respectively formed thereon, said insulating layers and said conductor layers being laminated on a metal plate;

connector terminals that are made of an electrically conductive material and are arranged in a peripheral portion of said metal substrate; and

metal elements that have one end portions welded to said conductor layers of said metal substrate on which said power main body is mounted, and the other end portions welded to said connector terminals.

2. The electric power steering apparatus as set forth in claim 1 , wherein said metal substrate is composed of said insulating layers and said conductor layers alternately laminated one over another, with adjacent ones of said conductor layers being connected with one another by metal columns.

3. The electric power steering apparatus as set forth in claim 2 , wherein said metal substrate has metal substrate side welding pad portions, to which said metal elements are bonded by welding, formed on a surface of an outermost one of said conductor layers, and said metal substrate side welding pad portions and at least one of said conductor layers adjacent to said outermost conductor layer are connected to each other through welding metal columns.

4. The electric power steering control apparatus for a vehicle as set forth in claim 3 , wherein said metal substrate has areas of welding between said metal elements and said metal substrate side welding pad portions located in opposition to said welding metal columns.

5. The electric power steering apparatus as set forth in claim 1 , wherein said welding is laser welding.

6. The electric power steering apparatus as set forth in claim 5 , wherein said laser welding is YAG welding using a wavelength of 532 nanometers or below.

7. The electric power steering apparatus as set forth in claim 1 , wherein said metal elements is made of copper or a copper alloy of high conductivity.

8. The electric power steering apparatus as set forth in claim 1 , wherein said plurality of metal elements are mounted in advance on one side surface of an insulation sheet.

9. The electric power steering apparatus as set forth in claim 8 , wherein said insulation sheet is made of an insulation material of high thermal conductivity.

10. The electric power steering apparatus as set forth in claim 8 , wherein said insulation sheet has metal substrate side holes formed at locations in opposition to said metal substrate side welding pad portions, and connector terminal side holes formed at locations in opposition to said connector terminals to which said metal elements are bonded by said welding.

11. The electric power steering apparatus as set forth in claim 8 , wherein said insulation sheet is made of a material with a high laser beam transmission factor.

12. The electric power steering apparatus as set forth in claim 8 , wherein said metal substrate side holes and said connector terminal side holes are formed by irradiating thereto a first laser beam, and said metal elements are welded to said the metal substrate side welding pad portions and said connector terminals by irradiating a second laser beam to said metal substrate side holes and said connector terminal side holes.