The invention relates to a sensor holder for a sensor unit. The invention also relates to a sensor assembly comprising such a sensor holder and to a method for manufacturing such a sensor holder.

As know from WO-A-2012/046122, motorcycles often comprise a sensor unit for sensing the rotation speed of the front wheel, including an impulse ring coupled in rotation to the front wheel and a sensor mounted in a sensor holder arranged between one of the branches of the fork of the motorcycle and the wheel, around an axle of the front wheel. The sensor holder generally comprises a central spacer mounted axially around the axle, and which comprises a radial washer adapted to sustain an axial mounting load exerted, for example, by a screwed element. The sensor holder generally also includes a plastic portion in which a mounting space for a sensor is provided. The mounting space is formed on a limited angular sector of the plastic portion extending around the spacer. On a side of the mounting space, the plastic portion comprises a flange facing the wheel and which is provided with a hole in which the sensor is inserted, in order to be firmly held with respect to the impulse ring.

In some applications where radial compactness is needed, the hole for receiving the sensor is located close to the spacer, in such a way that the mounting space is therefore in the same axial direction as the spacer. In such a case, the plastic portion is difficult to manufacture by injection molding, because some parts of the injection tooling should be moved in order to extract the manufactured plastic portion. The injection tooling would therefore be relatively expensive.

The aim of the invention is to provide a new sensor holder, whose structure allows using a simpler and less expensive manufacturing tooling.

To this end, the invention concerns a sensor holder for holding a sensor adapted to sense the rotation speed of a rotatable element with respect to a non-rotatable element, the sensor holder including a housing for receiving the sensor, and a spacer which comprises a central tubular portion for accommodating a shaft around which the rotatable element rotates, and a washer for sustaining an axial mounting load. This sensor holder is characterized in that the tubular portion and the washer of the spacer are two distinct parts.

Thanks to the invention, the sensor holder can be manufactured by plastic injection molding without using complex injection tooling, because the washer does not prevent the plastic part from being easily extracted. According to further aspects of the invention which are advantageous but not compulsory, such a sensor holder may incorporate one or several of the following features:

The washer is mounted inside a radial surface of the plastic part against a lateral surface of the tubular portion.

Said radial surface comprises inwardly extending bosses adapted to exert an elastic force against an outer radial surface of the washer.

The housing is provided in a flange of the plastic portion.

The flange comprises a threaded bore for screwing a bolt inserted in a fastening flange of the sensor.

The invention also concerns a sensor assembly comprising a sensor holder as mentioned here-above, a bearing and a sensor unit comprising a sensor mounted in said sensor holder and an impulse ring coupled in rotation to one of the rings of the bearing.

According to an optional advantageous aspect, a cylindrical sensing element of the sensor is inserted in the housing, whereas the sensor is fastened to the sensor holder by a bolt screwed in the threaded bore in the flange.

The invention also concerns a method for manufacturing a sensor holder as mentioned here-above. This method is characterized in that it comprises the following steps:

a) over-moulding the plastic portion on the tubular portion of the spacer, b) mounting the washer in the plastic portion, against a lateral surface of the tubular portion.

According to further aspects of the invention which are advantageous but not compulsory, such a method may incorporate one or both of the following features:

- At step b), the washer is hot press fitted in the plastic part.

At step a), a mounting area for the washer is provided in the plastic part.

The invention will now be explained in correspondence with the annexed figures. In the annexed figures:

figure 1 is an exploded perspective view of a sensor assembly and a sensor holder according to the invention,

figure 2 is a partially exploded perspective view of the sensor holder of figure 1 , a washer of the sensor holder being remote,

figure 3 is a sectional view along a longitudinal axis, of the sensor holder in the configuration of figure 1 .

The sensor holder 1 represented on figures 1 to 3 is designed to be mounted on a non-shown fork for a front wheel of a motorcycle. Sensor holder 1 is designed to hold a sensor 2 belonging to a sensor unit A for sensing the rotation speed of the front wheel of the motorcycle. Sensor unit A comprises sensor 2 and an impulse ring 3, which is coupled in rotation with a rotatable element, such as a rotatable outer ring 40 of a bearing 4 which allows rotation of the front wheel around a rotation axis X-X'. Axis X-X' also forms a central axis for sensor holder 1.

Sensor holder 1 and sensor 2 are non-rotatable with respect axis X-X' and are fixed with respect to a non-rotatable inner ring 42 of bearing 4. Sensor holder 1 and sensor 2 are also fixed, by non-shown fastening means, to the fork of the motorcycle. Sensor holder 1 , sensor unit A and bearing 4 form a sensor assembly 100.

In a variant, sensor assembly 100 may be mounted on another type of vehicle.

In this description, the terms "axial", "radial", "axially", "radially" refer to axis X-X'. A direction is axial when this direction is parallel to axis X-X'. A direction is radial when this direction is perpendicular to axis X-X' and secant with axis X-X'. A surface is axial when it is perpendicular to axis X-X' and radial when this surface belongs to a cylinder that surrounds axis X-X' at a constant radial distance.

Sensor holder 1 comprises a spacer 5 which includes a tubular portion 51 for accommodating a non-shown shaft and a washer 53. Washer 53 permits to sustain axial mounting loads during the mounting of sensor holder 1 in the fork of a motorcycle.

Sensor holder 1 comprises a plastic portion 7 in which tubular portion 51 and washer 53 are mounted. Plastic portion 7 is preferably over-moulded on spacer 5. Plastic portion 7 comprises a mounting space 71 for accommodating sensor 2. Mounting space 71 is formed on a limited angular sector extending around spacer 5. On a side of mounting space 71 opposed to washer 53, plastic portion 7 comprises a flange 73 designed to face a non-shown wheel of the motorcycle, and which is provided with a housing 75 for receiving a cylindrical sensing element 22 of sensor 2. Flange 73 also includes a threaded bore 731 , in which a bolt 24, which is inserted in a fastening flange 26 of sensor 2, is screwed in order to firmly hold sensor 2 in sensor holder 1 with respect to impulse ring 3.

In the example, housing 75 is located close to a central area of plastic portion 7, which is superimposed to tubular portion 51 , as it may be the case in some specific applications requiring radial compactness. Mounting space 71 is therefore axially aligned with washer 53 and with housing 75. This produces a part which is difficult to manufacture by plastic injection molding, as it may need mobile injection tooling and mobile die parts to allow extraction of the manufactured plastic part 7.

To avoid such an issue, spacer 5 is made of two distinct metallic parts, namely washer 53 and tubular portion 51 . Washer 53 is removable from tubular portion 51. Washer 53 is mounted in a mounting area formed by a radial surface 77 and an axial surface 78 of plastic portion 7. Washer 53 is in contact with an axial lateral surface 510 of tubular portion 51. Axial surface 78 is axially aligned with lateral surface 510. Radial surface 77 comprises inwardly extending bosses 79 adapted to exert an elastic force against an outer radial surface 530 of washer 53.

The two-part structure of spacer 5 permits to manufacture sensor holder 1 in the following way: in a first step, plastic portion 7 is over-moulded on tubular portion 51 , in a plastic injection moulding operation. The mounting area formed by radial and axial surfaces 77 and 78 is obtained during this step. This step can be performed without using complex injection tooling, because washer 53 does not prevent the extraction of injection tooling along axis X-X'.

In a second step, washer 53 is mounted against lateral surface 510 in plastic portion 7, as represented by arrow F1 on figure 2. Washer 53 is preferably hot press-fitted in plastic portion 7 just after the plastic injection of plastic part 7. Washer 53 can be manufactured in an independent process.