TECHNICAL FIELD

The present invention relates to an electric power steering device, and more particularly to an electric power steering device having two electric motor systems, and a rack assist-type steering device using the same.

BACKGROUND ART

In an electric power steering device of a vehicle, a revolving direction and revolving force of a steering shaft revolved by a driver's operation of a steering wheel is detected, and an electric motor is driven to revolve in the direction same as the revolving direction of the steering shaft on the basis of the detected values, thereby generating steering assist force. In addition, an electronic control unit is included in the power steering device to control the electric motor.

In this type of the electric power steering device, a three-phase AC electric motor is used to assist steering operation, and a power conversion circuit including an inverter circuit is used to control and drive the three-phase AC electric motor. Incidentally, when the electric motor fails, the steering assist force cannot be generated, whereby there may be a high possibility that the driver's steering becomes difficult. In view of the above, in recent years, there has been proposed an electric power steering device in which a winding wound around a stator included in an electric motor and an power conversion circuit for controlling power supplied to the winding are configured in two systems so that, even if failure occurs in one of the systems, steering assist force is generated in the other system to support driver's steering.

Such an electric power steering device including the electric motor in two systems has been well known as disclosed in a number of documents. For example, JP 2007-331639 A (PTL 1) discloses an electric power steering device using the following two electric motor systems. In PTL 1, there is disclosed an electric power steering device in which a winding to be wound around a stator is configured to be two winding systems and the winding in one system to be wound around the stator is divided into two and disposed at opposing positions of 180° while the winding in the other system is also divided into two and disposed at opposing positions of 180° rotated by 90° with the winding position of one system.

CITATION LIST

Patent Literature

PTL 1: JP 2007-331639 A

SUMMARY OF INVENTION

Technical Problem

In a rack assist-type steering device using an electric power steering device, a rubber boot covers a rack case and a rack shaft. This rubber boot is damaged at times by pebbles bounced during traveling or obstacles on the road. It is assumed that, when it is traveling in the rain in this state, or traveling on a puddled road, moisture (hereinafter representatively referred to as rainwater or the like) penetrates from the damaged portion of the rubber boot. In that case, in the rack assist-type steering device, the electric motor of the electric power steering device is typically disposed at a position lower than the rack shaft or the rubber boot, that is, on the bottom side, so that the rainwater or the like that has entered the rubber boot may further enter inside the housing of the electric motor.

In the PTL 1, the winding in two systems is divided into four and wound around the stator. Accordingly, when the rainwater or the like enters inside the housing of the electric motor, the windings of both of the two systems are immersed in the rainwater, whereby there has been a possibility that an electrical short circuit phenomenon of the winding may occur in the case where coating of the winding is damaged. Note that, even in the case of the winding in two systems in which the winding of the stator is divided into two, the problem described above may occur depending on the winding position of the winding. If the electric motor fails due to the short circuit phenomenon, the steering assist force cannot be generated, whereby there may be a high possibility that the driver's steering becomes difficult.

It is an object of the present invention to provide a novel electric power steering device capable of continuing a steering assist function as much as possible even in an environment where rainwater or the like enters inside a housing of an electric motor due to breakage of a rubber boot and an electrical short circuit phenomenon occurs, and a steering device using the same.

Solution to Problem

The present invention is characterized in that a stator around which a winding is wound is vertically divided into two areas in the direction of gravity, a winding of one system is wound in the upper stator area of the stator while a winding of the other system is wound in the lower stator area of the stator, and power of the winding of one system is controlled by an electronic control means of one system while power of the winding of the other system is controlled by an electronic control means of the other system.

Advantageous Effects of Invention

According to the present invention, even if rainwater or the like enters inside a housing of an electric motor due to breakage of a rubber boot, occurrence of an electrical short circuit phenomenon is suppressed at least in the winding wound on the upper side, whereby a steering assist can be continued.

