Cylindrical cover attached encoder apparatus

This application is a continuation of U.S. application Ser. No. 12/230,919, filed Sep. 8, 2008, which is a continuation of U.S. application Ser. No. 11/905,835, filed Oct. 4, 2007, now abandoned, which is a continuation of U.S. application Ser. No. 11/649,803, filed Jan. 5, 2007, now abandoned, which is a continuation of U.S. application Ser. No. 11/439,992, filed May 25, 2006, now abandoned, which is a continuation of U.S. application Ser. No. 10/959,084, filed Oct. 7, 2004, now abandoned.

The present invention relates to an encoder apparatus, or more specifically an encoder that is included in the encoder apparatus as one of its components, wherein the encoder apparatus may be mounted on a rotational member in the automotive vehicle (such as between the outer and inner races of the wheel bearing unit on the driving shaft or driven shaft) for detecting the number of revolutions of the rotational member.

One example of the conventional encoder apparatus that may be mounted on a rotational member in the automotive vehicle by pressing the encoder apparatus into the rotational member for detecting the number of revolutions of the rotational member is disclosed in Japanese patent application as now published under No. 62(1987)-25267, for example, wherein the encoder apparatus includes an encoder in the form of a magnetic signal generator ring.

As described in the above document, the magnetic signal generator ring is based on a synthetic resin material that is mechanically strong enough to avoid any possible damages that might occur on the ring as it is pressed into the rotational member, and includes an annular synthetic resin magnet that is buried around the outer peripheral surface of the ring. The synthetic resin magnet takes the form of a multipole magnet having S polarities and N polarities magnetized alternately at equal intervals in the circumferential direction.

As the encoder apparatus is mounted on the rotational member in the manner described above, the encoder in the encoder apparatus may be placed to face opposite the sensor that is located adjacently to the encoder outside it.

As the rotational member on which the encoder apparatus is mounted is thus rotating at the number of revolutions that is changing every moment, the encoder may magnetically produce pulses each of which represent the respective ever-changing number of revolutions and the sensor may detect the ever-changing number of revolutions by responding to each of the pulses.

In the conventional encoder apparatus described above, however, there is a risk that some extraneous matter such as stones might enter the area between the encoder in the encoder apparatus and the sensor located to face opposite the encoder outside it. So that, said extraneous matter such as stones might be engaged between the encoder and the sensor, and thus it causing damages on the encoder.

The side of the encoder facing opposite the sensor is magnetized as described above, acting as the magnetized surface having alternate N polarities and S polarities appear at equal intervals. If this magnetized surface may be damaged by the extraneous matter such as stones which entering the area between the encoder and sensor, the sensor would not be able to detect the number of revolutions correctly because the encoder would fail to function properly. Thus, this presents a serious disadvantage.

Another example of the conventional encoder apparatus that includes an encoder known as the annular encoder is disclosed in Japanese patent application as now published under No. 2001-241435, wherein the encoder apparatus may be mounted on a rotational member, such as between the inner and outer races of the bearing unit rotating relative to each other, so that it can detect the number of revolutions. In this conventional encoder apparatus, the encoder is covered by a nonmagnetic cover on the side thereof facing opposite the sensor in order to avoid that the damages might occur on the encoder as described above. Other examples of the encoder apparatus are disclosed in Japanese patent applications as now published under No. H5 (1993)-249126, No. H11 (1999)-303879, and No. 2002-286739, respectively.

For those recent years, the encoder apparatus that may be mounted on a rotational member on the automotive vehicle by pressing the encoder apparatus into the rotational member for detecting the ever-changing number of revolutions for the rotational member has more often been used with the FF (front engine, front drive) vehicle in particular, in which the encoder apparatus is mounted on the drive shaft and the like, and is used under the more severe running or ambient conditions.

In order to avoid that any damages occur on the encoder in the encoder apparatus when it is mounted on the rotational member by pressing it into the rotational member, there are demands for the encoder apparatus that includes an encoder that is mechanically strong enough to permit the encoder to withstand any severe or vigorous ambient or running conditions, thereby protecting the encoder from such damages more securely.

In order to solve the problems associated with the prior art encoder apparatus as described above, the present invention proposes to provide a cylindrical cover-attached encoder apparatus that includes a magnetic metal-based body having the cylindrical shape, a magnetic rubber-based encoder having the cylindrical shape and formed around the cylindrical portion of the magnetic metal-based cylindrical body, and a nonmagnetic material-based cover having the cylindrical shape and mounted on the magnetic rubber-based encoder for covering the outer peripheral surface of the cylindrical portion of the encoder.

It may be understood that as the cylindrical cover-attached encoder apparatus according to the present invention includes the magnetic rubber-based cylindrical encoder that may be formed around the cylindrical portion of the magnetic metal-based cylindrical body, it can have the improved mechanical strength that enables the encoder apparatus to be mounted on the rotational member without causing any damages on the encoder in the encoder apparatus when the encoder apparatus is pressed into the rotational member.

It may also be understood that as the magnetic rubber-based cylindrical encoder has its outer peripheral side covered by the nonmagnetic material-based cover, it can be protected from any unfavorable ambient conditions outside it, and it can withstand any severe or vigorous running or ambient conditions for an extended period of the time without causing any damages, even when it is used under such conditions.

The cylindrical encoder that constitutes one component of the cylindrical cover-attached encoder apparatus according to the present invention may be any type of the encoder that is known to any person skilled in the relevant art. For example, the cylindrical encoder may be formed by preparing ferrite magnetic powders (such as strontium ferrite powder, barium ferrite powder and the like) or rare earth magnetic powders (such as a combination of neodymium, iron and boron, a combination of samarium, iron and nitrogen and the like), adding any of the above powders to elastic element such as synthetic rubber or synthetic resin, mixing them together, and molding the mixture into the cylindrical shape by using the vulcanizing, molding process. Then, said molded cylindrical shape may be magnetized so that S polarities and N polarities can appear alternately at equal intervals in the circumferential direction thereof. Finally, the multipole encoder having the cylindrical shape can be obtained. This cylindrical encoder may then be attached to the magnetic metal-based cylindrical body by using any adhesive medium.

It should be noted that the ferrite magnetic powder or rare earth magnetic powder and the elastic element such as synthetic rubber or synthetic resin may preferably have the composition ratio range of between 70% and 95% by weight.

The synthetic rubber that may be based on the encoder may include NBR, H-NBR, ACM, AEM, FKM, EPDM and the like.