JP2001011585A - Steel sheet for motor driven power steering motor core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the loss torque of a motor by controlling the hysteresis loss of the subject steel sheet per frequency in the case of being magnetized to the maximum magnetic flux density to the value equal to or below a specified one. SOLUTION: Steel, e.g. contg., by weight, 0.0020% C, 0.50% Si 0.25% Mn, 0.01% P, 0.20% Al and 0.0020% N is melted, is hot-rolled and is thereafter pickled. After that, this steel is cold-rolled and is subjected to finish annealing at 750 to 950 deg.C for 1 min in a 10% hydrogen - 90% nitrogen atmosphere. As a result, the hysteresis loss per Hz of frequency in the case of being magnetized to the maximum magnetic flux density of 1.5 T can be controlled to <=0.10 J/kg, and when an EPS motor is produced by using this steel sheet, the loss torque can remarkably be reduced. For obtaining this steel sheet, a common method may be used. Namely, molten steel is subjected to degassing treatment to control its compsn. to the prescribed one, and this is successively subjected to casting, hot rolling and cold rolling to control its sheet thickness to a prescribed one, and after that, final annealing is controlled so as to regulate the hysteresis loss to a prescribed one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for an electric power steering motor core in a power steering system of an automobile.

[0002]

2. Description of the Related Art A power steering system of an automobile is a device that consumes 3 to 5% of the energy consumed by the automobile and consumes a lot of energy along with an air conditioner. In the conventional power steering system, steering is assisted by hydraulic pressure. However, in this system, since the hydraulic pump is constantly driven by the engine, there is a problem that energy is consumed even when the vehicle travels straight. To eliminate this waste,
2. Description of the Related Art An electric power steering (hereinafter, abbreviated as EPS) system that assists steering by a motor has been developed. The EPS system supplies current to the motor and assists power only when steering assistance is required, such as when cornering, so fuel efficiency is improved by about 2 to 3% compared to hydraulic systems.

[0003]

By the way, such a problem is solved.
In the EPS system, a PM motor using a permanent magnet is used from the viewpoint of small size and high torque, and the SPCC material is used as the core material from the viewpoint of cost. But,
In the PM motor, a relatively large loss torque is generated after steering, so that a time delay occurs before the vehicle enters a straight-ahead state after turning, so that the steering feeling is inferior to the hydraulic system.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a steel sheet which has low loss torque and is excellent for use in an electric power steering motor core.

[0005]

The above object is achieved by a steel plate for an electric power steering motor core, wherein the hysteresis loss per 1 Hz frequency is 0.10 J / kg or less when magnetized to a maximum magnetic flux density of 1.5 T. Is done.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a result of the present inventors' study on a material suitable for an EPS motor core material, that is, a material having a low loss torque, the loss torque is determined by mechanical loss represented by bearing loss and hysteresis dependent on hysteresis of the core material. Was found to be due to losses.

[0007] Among them, it is effective to reduce the rolling resistance of the bearing to reduce the mechanical loss. However, the reduction of the rolling resistance has almost reached the limit at present, and the further reduction of the mechanical loss is practically impossible. Near impossible. Then, reduction of loss torque by reduction of hysteresis loss was examined.

Hereinafter, the process leading to the present invention will be described based on experimental results.
And will be described in detail. Loss torque and hysteresis loss
To investigate the relationship, C: 0.0020% by weight, Si: 0.50% by weight
%, Mn: 0.25%, P: 0.01%, Al = 0.20%, N = 0.0020%
The steel containing was melted in a laboratory, hot rolled, and then pickled. Then the thickness
Cold rolled to 0.50mm, 10% H_Two-90% N _TwoAtmosphere 750-95
Performing a finish annealing at 0 ° C for 1 minute allows magnetic
Hysteresis loss per 1 Hz frequency
Was changed from 0.04 to 0.15 J / kg. Also ratio
As a comparison material, it is conventionally used as EPS motor core material.
Hysteresis loss 0.17J / kg (iron loss W15 / 50 = 11W / kg),
0.5mm-thick SPCC material (C: 0.015%, Si: 0.01%, Mn: 0.
15%, P: 0.01%, Al = 0.04%, N = 0.0020%).
Using these, an EPS motor with 300W output and 8 poles is manufactured
Lost by running the motor idling at a frequency of 1 Hz.
The measurement of luk was performed. The permanent magnet uses ferrite.
Used.

FIG. 1 shows the sample material thus obtained.
The relationship between the hysteresis loss per 1 Hz frequency and the loss torque ratio when magnetized to 1.5T is shown. Note that the hysteresis loss was calculated from the iron loss at 50 and 60 Hz obtained by the 25 cm Epstein method by the two-frequency method. Further, the loss torque ratio indicates a loss torque ratio of the test material when the loss torque of the comparative material (SPCC material) is set to 1.

As shown in FIG. 1, the loss torque ratio of the sample decreases as the hysteresis loss decreases. Especially hysteresis loss 0.10
When J / kg or less, the loss torque ratio of the test material is 0.6 or less. If the loss torque ratio is 0.6 or less, there is no problem in the steering characteristics, so the upper limit of the hysteresis loss is 0.10 J /
kg. From the viewpoint of further reducing the loss torque, it is more preferably 0.08 J / kg or less.

In the present invention, any method may be used to reduce the hysteresis loss. For example, in this experiment, by increasing the finish annealing temperature, the crystal grain size of the steel sheet was coarsened and the hysteresis loss was reduced.In the component of FIG. 1, the hysteresis loss was 0.10 J / kg by increasing the finish annealing temperature to 800 ° C or more. The following has been achieved:

Next, the manufacturing method will be described. In the present invention, any steel plate may be used as long as the hysteresis loss is within a predetermined range. As a manufacturing method for obtaining a steel sheet, a general steel sheet manufacturing process can be applied.
That is, the molten steel blown in the converter is degassed and adjusted to a predetermined component, and subsequently casting and hot rolling are performed. The finish annealing temperature and the winding temperature at the time of hot rolling do not need to be particularly defined, and may be normal. In addition, hot-rolled sheet annealing after hot-rolling may be performed, but is not essential. Next, after a predetermined sheet thickness is obtained by one cold rolling or two or more cold rolling steps including intermediate annealing, the final annealing is controlled so as to have a predetermined hysteresis loss, for example.

However, the method of controlling the hysteresis loss may be any method other than the control of the annealing temperature.

[0014]

[Example] Molten steel blown in a converter was degassed, adjusted to the components shown in Table 1, cast, heated to 1200 ° C for 1 hour, and then hot-rolled to a thickness of 2.0 mm. The hot rolling finishing temperature was 800 ° C. The winding temperature was 700 ° C. Thereafter, cold rolling was performed to a sheet thickness of 0.50 mm, and annealing was performed in a 10% H ₂ -90% N ₂ atmosphere under the finish annealing conditions shown in Table 1.

Here, the hysteresis loss was calculated by the two-frequency method from the iron loss of 50 and 60 Hz obtained by the 25 cm Epstein method, and evaluated by the hysteresis loss per 1 Hz frequency when magnetized up to 1.5T. Table 1 also shows the magnetic properties of each steel sheet.

[0016]

【table 1】

In Table 1, the No. 5 comparative steel is the same as the conventional EPS.
Iron loss W15 / 50 = 11W / used as motor core material
kg (hysteresis loss: 0.17 J / kg), SPCC material with a thickness of 0.5 mm. The loss torque ratio shows the loss torque ratio when the loss torque of No. 5 comparative steel (SPCC material) is set to 1.

From Table 1, it can be seen that steel sheets having a low loss torque ratio can be obtained from the steels of the present invention Nos. 1 to 4 in which the hysteresis loss is controlled within the range of the present invention.

On the other hand, the comparative steels No. 5 to No. 7 have a high loss torque ratio because the hysteresis loss is out of the range of the present invention.

[0020]

As described above, according to the present invention, a steel plate having a low loss torque can be obtained, and a steel plate for an electric power steering motor core which is effective in reducing the loss torque of an EPS motor can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a relationship between a hysteresis loss and a loss torque ratio.

Continuing on the front page (72) Inventor Takashi Samukawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Yoshihiko Ono 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Stock In-company (72) Inventor Yasushi Yasushi 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term (reference) 5H002 AA03 AA09

Claims (1)

[Claims] 1. A steel sheet for an electric power steering motor core, wherein a hysteresis loss per 1 Hz of a frequency when magnetized to a maximum magnetic flux density of 1.5 T is 0.10 J / kg or less.