Hub unit with pulse rotor and cover mounted sensor for sensing rotational speed

A pulse rotor is externally supported and secured on a cylindrical face section formed on a hub. The amount by which this pulse rotor projects from an outer ring member is regulated when the pulse rotor is fitted onto the cylindrical face section for supporting. A sensor is provided on the inside of a cover which covers the open end section of the outer ring member. The axial positional relationship between the cover and the outer ring member is uniformly maintained by means of an engaging projection formed on the radially outer peripheral surface of the cover. The distance between the axial end surface of the sensor and the axial end surface of the outer ring member is controlled to a specified value by this means. As a result, the distance between the pulse rotor and the sensor is precisely controlled.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a hub unit for sensing rotational speed, 
and, in particular, to a hub unit which is installed in a built-in 
Antilock Brake System (ABS) or Traction Control System (TCS) and is used 
to support the wheels of the automobile in a freely rotatable manner with 
respect to a suspension system and to sense the speed of rotation of the 
wheels. 
2. Description of the Prior Art 
The wheels of an automobile are supported in a freely rotatable manner 
through a suspension device, and it is essential that the speed of 
rotation of the wheels be sensed in order to control an Antilock Brake 
System (ABS) or Traction Control System (TCS). Conventionally, a hub unit 
for sensing rotational speed, as shown in FIG. 13, has been used for this 
purpose. 
This hub unit for sensing rotational speed comprises a hub 3, an inner ring 
or race member 4, a nut 6, an outer ring or race member 9, and a plurality 
of rolling members 10. 
The hub 3 is provided with an axially outer end (the left end in FIG. 13) 
having a flange section 1 for securing the wheel, a middle section and an 
axially inner end section (the right end section in FIG. 13). 
A radially outwardly facing inner ring track 2a is formed on the radially 
outer peripheral surface of the middle section of the hub 3. The inner 
ring member 4 is externally secured or fitted on the radially outer 
peripheral surface of the middle section of the hub 3 and provided with a 
radially outwardly facing inner track 2b on its radially outer peripheral 
surface. 
The nut 6 is placed in threaded engagement with the male threaded section 
formed on the radially outer peripheral surface of the inner end section 
of the hub 3. The nut 6 is tightened to press against the axially inner 
end surface of the inner ring member 4, and the inner ring member 4 is 
secured to the radially outer peripheral surface of the hub 3 in a 
specified position. 
The outer ring member 9 is provided with a mounting section 7 on its 
radially outer peripheral surface to provide support on a suspension 
device (omitted from the drawing) and a plurality of inwardly facing outer 
ring tracks 8a, 8b are formed on the radially inner peripheral surface of 
the outer ring member 9. 
The rolling members 10 are provided between the hub 3 and the outer ring 
member 9, and between the inner ring member 4 and the outer ring member 9. 
The hub unit for sensing rotational speed is thus comprised of the hub 3, 
the inner ring or race member 4, the nut 6, the outer ring or race member 
9, and the plurality of rolling members 10 to support the hub 3 in a 
freely rotatable manner on the inside of the outer ring member 9 which is 
supported on the suspension system. 
The nut 6 is formed with a irregular section 11 on the axially inner end 
surface thereof. The irregular section 11 of the nut 6 functions as a 
pulse rotor which generates a pulse as the hub 3 rotates. 
A cover 12 is mounted at an axially inner end section (the right end 
section in FIG. 13) with an opening of the outer ring member 9 and covers 
the opening of the outer ring member 9. A sensor 13 is secured to the 
cover 12. The axially outer end surface (the left end surface in FIG. 13) 
of the sensor 13 faces the irregular section 11 of the nut 6. 
Through the rotational speed sensing hub unit described above, a wheel 
secured to the flange section 1 provided on the axially outer face section 
of the hub 3 is supported in a freely rotatable manner by the suspension 
system which supports the outer ring member 9. 
The output of the sensor 13 varies according to the rotation of the wheel. 
The frequency of the variation of the output of the sensor 13 is 
proportional to the rotational speed of the wheel. For this reason, the 
rotational speed of the wheel is obtained by inputting the output signal 
from the sensor 13 to a controller (not shown). The ABS and the TCS are 
then suitably controlled according to the desired speed of rotation. 
A distance 1 between the part which functions as the pulse rotor on the 
rotational speed sensing hub unit (the irregular section 11 formed on the 
axially inner end surface of the nut 6 in the example shown in FIG. 13) 
and the axially outer end surface of the sensor 13 must be precisely 
controlled to a suitable value for accurate sensing of the rotational 
speed. 
The nut 6 which functions as the pulse rotor in FIG. 13 plays the role of 
securing the inner ring member 4 to the radially outer peripheral surface 
of the hub 3. This nut 6 must be firmly tightened on a male threaded 
section 5 of the radially outer peripheral surface of the inner end 
section of the hub 3. For this reason it is difficult to precisely control 
the positional relationship between the nut 6 and the hub 3 and the outer 
ring member 9. 
Specifically, a suitable value for the distance 1 is an extremely small 
value of less than 1 mm. For this reason, the distance 1 cannot be 
maintained if the positional relationship between the nut 6 and the hub 3 
and the outer ring member 9 deviates by even a very small amount. If the 
distance 1 exceeds a suitable value, there is concern that the ABS and TCS 
cannot perform adequately. 
In particular, in the structure shown in FIG. 13, there is no method for 
determining whether or not the distance 1 after the hub unit is assembled 
is the correct value other than by checking the output of the sensor 13. 
However, the distance 1 cannot be adjusted during assembly. For this 
reason, highly precisely fabricated parts are required for the hub to 
maintain a suitable value for the distance 1, resulting in the high cost 
of manufacturing the hub unit. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide, with due consideration to 
the drawbacks of such conventional devices, a rotational speed sensing hub 
unit in which the distance between the pulse rotor and the sensor is 
always kept appropriate for accurate sensing of the rotational speed. 
In the rotational speed sensing hub unit of the present invention, the 
distance between a pulse rotor and a sensor is maintained at a suitable 
value even when the high precision of the structural parts is not rigidly 
controlled. 
The sensor is provided at a specified positional relationship with respect 
to the cover on the inside of a cover which is supported at a specified 
positional relationship with respect to an outer ring member, and a pulse 
rotor is externally secured on a cylindrical face section formed at the 
axially inner end section of the hub so as to regulate the positional 
relationship between the hub and the pulse rotor. When the axial 
positional relationship between the hub and the pulse rotor is regulated, 
with a specific positional relationship maintained between the outer ring 
member and the hub, a suitable distance is maintained between the pulse 
rotor and the sensor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Now referring to FIGS. 1 to 3 which show a first embodiment of a hub unit 
for sensing rotational speed according to the present invention, a hub 3 
is provided with an axially outer end section (the left end section in 
FIG. 1 and FIG. 2) having a flange section 1 for securing a wheel, a 
middle section 3a and an axially inner end section 3b (the right end 
section in FIG. 1 and FIG. 2). 
The flange section 1 is formed on the radially outer peripheral surface of 
the axially outer end section (the left end section in FIG. 1 and FIG. 2) 
of the hub 3. 
A radially outwardly facing inner ring track 2a and a step section 14 are 
formed on the radially outer peripheral surface of the middle section of 
the hub 3. An inner ring member 4 having a radially outwardly facing inner 
ring track 2b on its radially outer peripheral surface is externally 
secured on the radially outer peripheral surface of the hub 3 adjacent to 
the step section 14. One end surface of the inner ring member 4 (the left 
end surface in FIG. 1) is abutted to the step section 14. 
Although the inner ring track 2a is directly formed on the radially outer 
peripheral surface of the hub 3 in FIG. 1, the inner ring track 2a can be 
formed on another inner ring member not integral to the hub 3 as shown in 
FIG. 13, so that this another inner ring member and the inner ring member 
4 are externally secured or fitted on the hub 3. 
A male threaded section 5 is formed on the axially inner end section of the 
hub 3, and a nut 6 is screwed onto this threaded section 5 and firmly 
tightened. The inner ring member 4 is secured to a specified part of the 
radially outer peripheral surface of the hub 3 by the nut 6 which applies 
pressure against an axially inner end surface 4a thereof. 
A mounting section 7 is formed on the radially outer peripheral surface of 
the axially inner end section of an outer ring member 9. The outer ring 
member 9 is secured to the suspension system by the mounting section 7. 
Also, a pair of radially inwardly facing outer ring tracks 8a, 8b are 
formed on the radially inner peripheral surface of the outer ring member 
9. The outer ring tracks 8a, 8b are opposed to the inner ring tracks 2a, 
2b, respectively. 
A plurality of rolling members 10, 10 are provided between the pair of 
inner ring tracks 2a, 2b and the pair of outer ring tracks 8a, 8b. As a 
result, the hub 3 freely rotates on the inside of the outer ring member 9. 
A sealing material 15 is provided between the radially inner peripheral 
surface of the outer ring member 9 and the radially outer peripheral 
surface of the hub 3 to partly define the space in which the plurality of 
rolling members 10 are accommodated. 
A cylindrical face section or end portion 16 in which there is 
substantially no change in thickness in an axial direction is formed on 
the axially inner end section of the hub 3, such that the cylindrical face 
end portion 16 is placed further in the axially inner side than the male 
threaded section 5 to project from the axially inner end surface of the 
nut 6. 
A pulse rotor 17 is externally fitted on and supported by the cylindrical 
face section 16. As a matter of course, the outer diameter of the 
cylindrical face section 16 is smaller than the diameter of the male 
threaded section 5 at the bottom of the thread grooves. 
The pulse rotor 17 is provided with an annular and inwardly radially 
extending flange main section 18 which is formed with an irregular section 
on the axially inner end surface 18a thereof. An axially outer end surface 
18b of flange section 18 faces nut 6. A cylindrical section 19 is formed 
and connected to the radially outer peripheral edge of the main section 
18. The cylindrical section 19 has an axially outer open section which 
opens outwardly (to the left side in FIG. 1 and FIG. 2). 
A circular hole 20 is formed in the center section of the main section 18. 
The center section of the main section 18 with this circular hole 20 is 
externally secured or fitted onto the cylindrical face section 16. At the 
same time, the axially outer open end section of the cylindrical section 
19 is externally secured or fitted onto the radially outer peripheral 
surface of the axially inner end section of the inner ring member 4. As a 
result, the pulse rotor 17 is secured on the hub 3. 
Incidentally, the cylindrical section 19 may be omitted. 
The radially outer peripheral edge of the axially inner end surface of the 
cylindrical face section 16, after being inserted into the circular hole 
section 20, can be caulked in a radially outward direction. As a result, 
the main section 18 is prevented from coming loose from the hub 3. 
The axially inner end section of the outer ring member 9 has an opening 9a 
which is closed by a cover 21. A sensor 13 which may be, for example, a 
magnetic type sensor, is maintained on the inside of the cover 21. 
However, in the case where a unit comprising alternating N and S 
electrodes is disposed around the circumference of the pulse rotor 17 in 
place of the irregular section 11, a semiconductor sensor or a Hall device 
sensor, or the like, is used as the sensor 13. 
The cover 21 is fabricated from a metal plate by a drawing process and has 
an opening in the axially outer end thereof. A flange-shaped engaging 
projection 22 is formed closer to the opening circumferentially on a 
section of the radially outer peripheral surface of the cover 21. The 
outer diameter of the opening of the cover 21 is the same as or slightly 
larger than the inner diameter of the opening at the axially inner end 
section of the outer ring member 9. As a result, the edge section of the 
cover adjacent to the opening is freely interposed in the axially inner 
end open section of the outer ring member 9 until the engating projection 
22 reaches the axially inner end surface 9b of the outer ring member 9. 
In order that the sensor 13 is supported and secured in a 
positionally-controlled state on the inside of the cover 21, the 
peripheral wall of the cover 21 is partly crimped to oppose a pair of 
recessed grooves 23 formed on the radially outer peripheral surface of the 
main body of the sensor 13. This prevents the sensor 13 from slipping out 
of place inside the cover 21. 
Accordingly, the distance D between the axially outer surface of the 
engaging projection 22 and the axially outer end surface of the sensor 13 
is maintained at a present distance without any deviation. As required, a 
plate-shaped backing is interposedly maintained between te back surface of 
the cover 21 and the end surface of the sensor 13 so that any backlash of 
the sensor 13 inside the cover 21 is prevented. 
The rotational speed sensing hub unit of the present invention with the 
above-described configuration senses the rotational speed of the wheel 
secured to the flang section 1 of the hub 3, with the wheels of the 
vehicle supported in a freely rotatable manner on the suspension system in 
the same manner as with a conventional unit. 
In particular, in the rotational speed sensing hub unit of the present 
invention in the state where the pulse rotor 17 is secured to the hub 3, 
the mutal positonal relationship between the pulse rotor 17 and the hub 3, 
specifically, the distance d from the axially inner end surface 9b of the 
outer ring member 9 to the axially inner end surface 18a of the pulse 
rotor 17, is freely adjustable. The adjustment of the distance d is 
performed by changing the depth of the fitting engagement between the 
cylindrical face section 16 formed on the axially inner end section of the 
hub 3 and the circular hole section 20 formed at the center of the main 
section 18 of the pulse rotor 17, and the depth of the fitting engagement 
between the open end section of the cylindrical section 19 of the pulse 
rotor 17 and the inner ring member 4. 
In addition, the distance D between the outside surface of the 
flange-shaped engaging projection 22 formed on the radially outer 
peripheral surface of the cover 21 and the axially outer end surface of 
the sensor 13 remains in the present state with substantially no deviation 
as outlined above. Accordingly, the positional relationship between the 
axially outer end surface of the sensor 13, which is securely maintained 
on the cover 21, and the axially inner end surface of the outer ring 
member 9 is normally fixed in the state where the axially outer end 
section of the cover 21 is secured to the axially inner end section of the 
outer ring member 9. In addition, the positional relationship between the 
hub 3 and the outer ring member 9 in the assembled state through the 
plurality of rolling members 10 is normally fixed. 
Accordingly, it is possible to set at a suitable value the distance between 
the axially inner end surface of the pulse rotor 17 and the axially outer 
end surface of the sensor 13 through the steps that the depth of the 
fitting engagement at the two abovementioned engaging positions is 
regulated, that a specific positional relationship of the pulse rotor 17 
with respect to the hub 3 is set, and that the cover 21, which maintains 
and secures the sensor 13, is then secured to the outer ring member 9. 
Specifically, the distance between the axially inner end surface of the 
pulse rotor 17 and the axially outer end surface of the sensor 13 is the 
difference between the distance D between the axially outside surface of 
the projection 22 formed on the radially outer peripheral surface of the 
cover 21 and the axially outer end surface of the sensor 13, and the 
distance d from the axially inner end surface of the outer ring member 9 
to the axially inner en surface of the pulse rotor 17 (=D-d). The distance 
D is fixed, while minute adjustments of the distance d are freely made 
through measuring the distance d. For this reason, precise control is 
possible in setting the distance between the axially inner end surface 
(the right end surface in FIG. 1 and FIG. 2) of the pulse rotor 17 and the 
axially outer end surface (the left end surface in FIG. 1 and FIG. 2) of 
the sensor 13, so that adjustment is not required after assembly. As also 
shown in FIG. 2, a gap G is provided between a radial shoulder 5a of the 
axially inner end section 5 of the hub and the face 18b of the flange 
section 18 of the pulse rotor 17. 
In addition, in the case of the embodiment shown in the drawings, the pulse 
rotor 17 is securely set at two positions, specifically, the position 
where the circular hole section 20 engages the cylindrical face section 16 
and the position where the cylindrical section 19 engages the inner ring 
member 4. For this reason the pulse rotor 17 is reliably prevented from 
inclining. Because the pulse rotor 17 cannot incline, the distance between 
the irregular section 11 of the pulse rotor 17 and the end surface of the 
sensor 13 is fixed to a constant value during the rotation of the hub 3, 
and a stable output can be obtained. 
The rotational speed sensing hug unit of the present invention provides 
improved reliability for the ABS and TCS by means of accurate rotational 
speed detection, because the distance between the pulser rotor and the 
sensor can be precisely adjusted. 
In a second embodiment of the present invention shown in FIG. 4 to FIG. 7, 
the cover 21 is reliably supported by the outer ring member 9, and, if 
required, the cover 21 can be removed from the outer ring member 9. 
A plurality of arc-shaped projections 24 is formed in a plurality of 
positions (four positions are shown in the drawings) on the axially inner 
open end section of the outer ring member 9. The flange-shaped engaging 
projection 22 formed closer to the opening circumferentially on the 
radially outer peripheral surface of the cover 21 is held down by caulking 
portions 24a of the arc-shaped projections 24 for engagement after the 
axially outer end section of the cover 21 is inserted into the opening in 
the axially inner end of the outer ring member 9. As a result, the cover 
21 cannot be easily separated from the outer ring member 9. 
A plurality of indented sections 25 is formed in a plurality of positions 
(four positions are shown in the drawings) on the axially inner end 
surface of the outer ring member 9. The tip of a tool such as a 
screwdriver or the like can be passed through the indented sections 25 and 
freely inserted between the engaging projection 22 and the end surface of 
the outer ring member 9, so that the support of the cover 21 for the outer 
ring member 9 can be released. Accordingly, this embodiment provides 
reliable support for the outer ring member 9 by the cover 21, and also 
provides convenience that the expensive sensor 13 once used can be reused 
in another hub unit. 
An O-ring 26 prevents the entry of extraneous material or rainwater inside 
the cover 21. In addition, the sensor 13 is supported inside the cover 21 
by friction or by an adhesive. 
A third embodiment of the present invention shown in FIG. 8 to FIG. 12 
exhibits the same type of effects as the second embodiment. An indented 
groove 27 for engagement is formed on the radially inner peripheral 
surface of the axially inner end section of the outer ring member 9. Also, 
a dike-shaped projection 28 for engagement with the groove 27 is formed on 
the radially outer peripheral surface of the axially outer end section of 
the cover 21 closer to the opening than the flange-shaped engaging 
projection 22. A plurality of notches 29 is formed at a plurality of 
positions (threee postions in the example shown in the drawings) on the 
axially inner end edge of the cover 21. By the presence of these notches 
29, the outer diameter of the dike-shaped projection 28 can be reduced. A 
generally annular plate spring 30 whit a cutout is provided in the groove 
as an elastic backup for the dike-shaped projection 28. As a result, the 
cover 21 reliably engages the outer ring member 9 by the engaging indented 
groove 27 and the dike-shaped projection 28. 
The function of the indented sections 25 formed for tool operation in the 
axially inner end surface of the outer ring member 9 is the same as in the 
second embodiment.