Rotation detecting device having a terminal holding arrangement

A rotation detecting device comprising a pole formed of a ferromagnetic material, a bias magnet for applying a magnetic flux to the pole, a bobbon receiving the pole and the bias magnet in a series arrangement, a detecting coil mounted on the bobbin, terminals each having a coil connecting part connected to one end of the wire of the coil and a lead wire connecting part connected to a lead wire, a cap for covering the terminals and a portion of the bobbin holding the terminals, fixing means for fixing the terminals to the bobbin.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a rotation detecting device for detecting 
the angular displacement of a magnetic body and capable of improving the 
reliability of finishing the ends of a detecting coil. 
2. Discussion of Background 
The conventional magnetic rotation detecting device has a magnetic circuit 
comprising (1) a pole, (2) a bias magnet and (3) a detecting coil. 
A high output voltage of the detecting coil can be obtained by means such 
as (a) providing a fixed pole having a high magnetic permeability, (b) 
providing a bias magnet having a high magnetic flux density or (c) 
increasing the number of turns of the detecting coil. Generally, the means 
(c) is employed to obtain a high output voltage of the detecting coil. 
However, a very thin wire must inevitably be used for forming the detecting 
coil to increase the number of turns within a limited space and ordinarily 
a wire of 0.13 mm to 0.15 mm in diameter is used for forming such a 
detecting coil. The ends of the wire are connected to terminals for lead 
wires, for example, by soldering. If the junctions of the ends of the wire 
and the terminal is stressed locally, the coil may possibly be 
disconnected from the terminal or terminals. 
Referring to FIGS. 5, 6(A) and 6(B) showing a conventional rotation 
detecting device, there are shown a pole 1 formed of a ferromagnetic 
material, a bias magnet 2 for applying a magnetic flux to the pole 1, a 
spacer 3 for enhancing the effective magnetic flux of the bias magnet 2, a 
bobbin 4 receiving the pole 1 therein, a detecting coil 5 wound on the 
bobbin 4, the ends 5a of a wire forming the detecting coil 5, which are 
respectively wound around the connecting sections 6a of terminals 6 
provided on the bobbin 4, and lead wires 7 respectively connected to the 
lead connecting sections 6b of the terminals 6. 
Projections 4a and 4b are provided respectively at predetermined positions 
on the outer circumference of the bobbin 4. The projection 4a is engaged 
with a cap 8, and the terminals 6 are fitted respectively on the 
projection 4b. The pole 1, the bias magnet 2 and the spacer 3 are fixed in 
place by the cap 8. The lead wires 7 are connected respectively to the 
terminals 6 by putting the cap 8 on the projection 4a. The bobbin 4 
mounted with the detecting coil 5 is received in a housing 10 formed of a 
plastic material such as Nylon by injection molding. The housing 10 is 
attached to a transmission case or the like with a screw so that the 
rotation detecting device is disposed near a rotary member. The housing 10 
has a cylindrical fitting part 10a, a reduced part 10b having a diameter 
smaller than that of the fitting part 10a, an annular groove 10c for 
receiving an O-ring 11 therein, and a supporting part 10d. A locking bush 
12 is provided in the supporting part 10d of the housing 10 to prevent the 
screw fastening the housing 10 to a transmission case or the like from 
loosening. 
When the rotation detecting device is mounted on the transmission case, the 
pole 1 is located near a projection provided on the rotary member. When 
the projection of the rotary member approaches the pole 1 as the rotary 
member rotates, the magnetic lines of force of the bias magnet 2 extend 
from the bias magnet 2 through the pole 1, the rotary member, the external 
space and the spacer 3 to the bias magnet 2. Since the magnetic lines of 
force extend across the coil 5, voltage is induced in the detecting coil 5 
as the magnetic flux varies according to the variation of the distance 
between the projection of the rotary member and the pole 1. The rotating 
speed of the rotary member is calculated by using the induced voltage. 
Such an induced voltage induced in the coil of the rotation detecting 
device is used also for detecting the approach of an object. 
In assembling this conventional rotation detecting device, the connection 
of the lead wires 7 and the terminals 6 and the connection of the ends 5a 
of the wire of the coil 5 and the terminals 6 are implemented in the 
following procedure. 
(1) The lead wires 7 are fixedly connected to the lead wire connecting 
parts of the terminals 6 by crimping. 
(2) The ends of the wires of the detecting coil 5 are wound several turns 
respectively around the U-shaped coil connecting parts 6a of the terminals 
6, and then the ends of the wires of the detecting coil 5 are fixed to the 
coil connecting parts 6a by soldering. 
(3) The lead wire connecting parts 6b of the terminals 6 are placed between 
the projections 4a and 4b of the bobbin 4. 
(4) The cap 8 is put on the housing 10 so as to cover the terminals 6, the 
rear part of the bobbin 4 and the extremities of the lead wires 7. 
When the rotation detecting device is thus assembled, a clearance .DELTA.x 
in the range of 0.2 mm to 0.3 mm is formed between the rear end of the 
lead wire connecting parts 6b of the terminals 6 and the projection 4a of 
the bobbin 4, and hence the terminals 6 are movable to the left, as viewed 
in FIG. 6(B), by a distance .DELTA.x when the lead wires 7 are pulled to 
the left. Therefore, the wire of the coil 5 may possibly be broken when 
the lead wires 7 are pulled to the left if the slack of the wire between 
the coil 5 and the coil connecting parts 6a of the terminals 6 is smaller 
than the clearance .DELTA.x. Such a trouble occurs before injection 
molding and will not occur after injection molding because the terminals 6 
are fixed by the molding and the ends 5a of the wire of the coil 5 will 
not be pulled even if the lead wires 7 are pulled. 
However, in placing the assembly of the bobbin 4, the coil 5, the terminals 
6 and the lead wires 7 in a mold for injection molding, the lead wires 7, 
in general, are pulled to set the assembly accurately in the mold, which 
often causes the breakage of the ends 5a of the wire of the coil 5. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a rotation 
detecting device constructed so that no force acts on the ends of the wire 
of the coil even if the lead wires are stressed by an external force such 
as tension, capable of preventing the breakage of the wire of the coil, 
and having remarkably improved reliability. 
To achieve the object of the invention, the present invention provides a 
rotation detecting device comprising a pole formed of a ferromagnetic 
material, a bias magnet for applying a magnetic flux to the pole, a bobbin 
receiving the pole and the bias magnet in a series arrangement, a 
detecting coil mounted on the bobbin, terminals each having a coil 
connecting part connected to one end of the wire of the coil and a lead 
wire connecting part connected to a lead wire, a cap for covering the 
terminals and a portion of the bobbin holding the terminals, fixing means 
for fixing the terminals to the bobbin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the following description of the preferred embodiments of the present 
invention, parts similar to those previously described with reference to 
FIGS. 5, 6(A) and 6(B) showing the conventional rotation detecting device 
will be denoted by like reference numerals and the description thereof 
will be omitted. Only the features of the present invention will be 
described hereunder. 
Referring to FIGS. 1(A) and 1(B), a rotation detecting device comprises a 
bobbin 4, terminals 6, a cap 8, and other components which are similar to 
those of the conventional rotation detecting device. A positioning hole 6c 
is formed in the upper surface, as viewed in FIG. 1(A), namely, in the 
surface opposite the lead wire holding surface, of a terminal 6. 
A positioning projection 4c is formed in a bobbin 4 at a position 
corresponding to the positioning hole 6c of each of the terminals 6 on the 
bobbin 4 when the terminals 6 are mounted on the bobbin 4 at correct 
positions. The positioning projections 4c may be formed integrally with 
the bobbin 4 or may be separate members attached to the bobbin 4. 
In assembling the rotation detecting device, the terminals 6 are mounted on 
the bobbin 4 so that the positioning projections 4c of the bobbin 4 engage 
the positioning holes 6c of the terminals 6, respectively, and then a cap 
8 is pressed against the bobbin 4 to receive the assembly of the bobbin 4 
and the terminals 6 therein. Since the positioning projections 4c of the 
bobbin 4 engage the positioning holes 6c of the terminals 6, the terminals 
6 are held fixedly on the bobbin 4 and are unable to move relative to the 
bobbin 4 even if there is a clearance .DELTA.x between the rear end of the 
terminals 6 and projections 4a formed in the bobbin 4 and even if an 
external force is applied to lead wires 7 connected to the terminals 6 
after assembly, and thereby the accidental breakage of the wires of the 
detection coil 5 is prevented to enhance the reliability of the rotation 
detecting device. 
Referring to FIGS. 2(A) and 2(B), a rotation detecting device comprises a 
bobbin 4, terminals 6, a cap 8, and other components which are similar to 
those of the conventional rotation detecting device. A sawtooth ridge 6d 
having an upright rear end surface is formed in the central part of the 
upper surface, as viewed in FIG. 2(B) of the lead wire holding part 6b of 
each terminal 6 so as to extend along the axis of the bobbin 4. Axial 
grooves 8a respectively for receiving the sawtooth ridges 6d of the 
terminals 6 are formed in the inner circumference of the cap 8. When the 
cap 8 is put in place on the bobbin 4, the upright rear end surfaces of 
the sawtooth ridges 6d are in contact respectively with the end walls of 
the axial grooves 8a of the cap 8. 
In assembling the rotation detecting device, the terminals 6 are mounted on 
the bobbin 4 between projections 4a and 4b of the bobbin 4, and then the 
assembly of the bobbin 4 and the terminals 6 are pushed into the cap 8 as 
deep as the upright rear end surfaces of the sawtooth ridges 6d of the 
terminals 6 come into contact respectively with the end surfaces of the 
axial grooves 8a, and thereby the terminals 6 are held fixedly between the 
bobbin 4 and the cap 8. 
Thus, the second embodiment is the same in effect as the first embodiment. 
Referring to FIGS. 3(A), 3(B) and 4, a rotation detecting device comprises 
a bobbin 4, terminals 6, a cap 8, and other components which are similar 
to those of the conventional rotation detecting device. The bobbin 4 has 
two pairs of projections 4a and 4d capable of being deformed easily by a 
small pressure and formed integrally therewith at the rear end, namely, at 
the left end as viewed in FIG. 3(B), thereof. Each pair of projections 4a 
and 4d are separated from each other by a predetermined distance to form a 
U-shaped groove 4e therebetween as best shown in FIG. 4. A lead wire 7 is 
extended through the U-shaped groove 4e and is held between the pair of 
projections 4a and 4d. 
In assembling the rotation detecting device, the terminals 6 are put in 
place on the bobbin 4 between the pairs of projections 4a and 4d, and 
projections 4b, respectively. Then, the assembly of the bobbin 4 and the 
terminals 6 is pushed into the cap 8 as far as the rear end of the bobbin 
4 comes into contact with the inner bottom surface of the cap 8. As the 
assembly of the bobbin 4 and the terminals 6 is pushed into the cap 8, the 
pairs of projections 4a and 4d are bent toward the front end, namely, the 
right end as viewed in FIG. 3(B), of the bobbin 4 to press the terminals 6 
respectively against the projections 4b of the bobbin 4, and thereby the 
terminals 6 are held firmly respectively between the pairs of the 
projections 4a and 4d, and the projections 4b. 
The third embodiment is the same in effect as the first embodiment. 
Although the invention has been described with reference to preferred forms 
thereof with a certain degree of particularity, obviously many changes and 
variations are possible therein. It is therefore to be understood the 
present invention may be practiced otherwise than specifically described 
herein without departing from the scope and spirit thereof.