Solenoid coil attachment mechanism

A solenoid coil attachment mechanism includes a coil assembly with a wire end that projects from the coil assembly and an extending elongated leg that includes a latching mechanism. A carrier has a wall with an opening receiving the leg of the coil assembly and has a wire guide that is funnel shaped, has an open end and receives the end of the wire. A circuit board is attached to the carrier and the wire end is soldered directly to the circuit board.

TECHNICAL FIELD 
The present invention relates to a solenoid coil attachment mechanism and 
more particularly, to a mechanism for attaching control devices to the 
solenoid coils that are used with a hydraulic modulator for onboard 
vehicle system controls. 
BACKGROUND OF THE INVENTION 
Present state-of-the-art hydraulic modulator and electronic control unit 
(ECU) assemblies typically used in on-board vehicle control of braking and 
intelligent chassis control systems are known to include integrated 
solenoid valves. These valves are a key component in providing the 
necessary level of hydraulic control that serves the function of directing 
fluid flow to the brake and/or suspension systems. The hydraulic controls 
enable outputs from the ECU to change vehicle operating parameters. 
Exemplary systems include anti-lock braking systems (ABS), traction 
control systems (TCS) and intelligent ride control systems (ICS) that 
operate through the vehicles chassis systems. One of the latest designs on 
the market utilizes solenoid valves with sealed hydraulic valve bodies and 
separately removable solenoid coil assemblies. This system is disclosed in 
U.S. Pat. No. 5,845,672, which is commonly assigned. 
Numerous other design variations of these types of valve and coil 
assemblies have been created in attempts to minimize cost, minimize 
package size, and maximize design for manufacture. Previous designs have 
included coil terminals that are individually welded to lead frames with 
built in compliance to provide the coil with sufficient "float" to take up 
manufacturing tolerances. Other designs use rigid terminals that are 
wave-soldered directly to a standard circuit board and the coil case is 
allowed to float. Still other designs have coil wires that are directly 
wave soldered to a circuit board and are supported by a plastic housing to 
limit travel and float. The goal in all cases is to minimize stresses on 
the connection between the solenoid coils and the circuit board. Since the 
operating environment is onboard a vehicle, vibratory inputs are commonly 
encountered. A complicating factor in designing the solenoid/control board 
interface is that the assembly of the unit tends to become more difficult 
as features are added to address the goal of limiting stresses on the 
connection. Accordingly, a need continues to exist for a solenoid coil 
attachment mechanism that is easily assembled while protecting the 
assembly from vibratory inputs while in service. 
SUMMARY OF THE INVENTION 
A goal of the present invention resides in addressing the concurrent needs 
for simplified assembly and robust service in a solenoid coil attachment 
mechanism through the concept of a "coil pack" assembly. A separate 
carrier is employed, and the solenoid coils are pre-attached to the 
carrier before assembly to the control system. This design avoids 
expensive insert molding techniques. The arrangement also advantageously 
permits the coil pack to be installed in one relatively simple operation 
on the main circuit board assembly line, which can greatly simplify the 
design and cost of the final system assembly operation. 
A solenoid coil attachment mechanism according to the invention includes a 
coil assembly with a wire end that projects from the coil assembly and an 
extending elongated leg that includes a latching mechanism. A carrier has 
a wall with an opening receiving the leg of the coil assembly and has a 
wire guide that is funnel shaped and that receives and guides the end of 
the wire. Preferably, a circuit board is attached to the carrier and the 
coil wire end is soldered directly to the circuit board.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings, illustrated in FIG. 1 is a coil pack assembly 10 
as used in the presently preferred embodiment of the invention. The 
plastic carrier 11 provides a housing for twelve individual solenoid coils 
although the number of coils will vary according to the application. The 
individual coil assemblies 16 snap into one of two initial positions by 
pushing the latches 17 through rectangular holes 30 that are formed in the 
surface 31 of the carrier 11. Each coil assembly 16 includes two latches 
17 and comprises a plurality of turns of wire wound on a bobbin. The 
latches 17 each comprise a flexing elongated leg that extends from the 
coil assemblies 16. The latches 17 are shown in a secondary initial 
position in FIG. 1 for clarity, but would normally be in a shipping 
position for the assembly of coil pack 10 prior to engagement with the 
assembled control circuit board. 
Referring to FIG. 2A along with FIG. 1, the initial snap position of the 
coil assemblies 16 is referred to as the shipping position. Here the coil 
assemblies 16 are suspended by the outboard tab 32 of the latch 17 which 
operates as a catch. There are two coil wires ends 18 for each coil 
assembly 16. One end 18 is visible in FIG. 2A and both of the ends 18 are 
visible in FIG. 1. Ends 18 are the termination ends of the main coil 
windings 24 projecting from the coil assembly 16 and are located just 
below the surface of the carrier funnels 14 when the unit is oriented in 
the shipping position. The typical coil wire, including the ends 18, is 28 
or 30 gauge. When the terminal ends are cut, they undergo a coining 
operation to remove any burrs on the cut ends. The ends are also 
preferably tin or solder plated in preparation for future assembly 
operations. 
In FIG. 2B, the circuit board 21 is located on top of the carrier by two 
pins 12 and is snapped onto the carrier 11 and is held in location by the 
four tabs 13 that are located around the edges of the carrier 11. A skirt 
15 is provided on the carrier 11 to assist in initially locating the 
coils. The shipping position of the coil assemblies 16 within the coil 
pack 10 allows preassembly with the carrier 11 for unitary transport to 
the location of the process that effects marriage of the coil pack 10 with 
the control circuit board 21. 
The coil assemblies 16 are placed into the solder position shown in FIG. 2C 
by being moved relative to the carrier 11 and toward the circuit board 21 
by applying a force (either manually or through automatic assembly 
equipment), to the coil assemblies 16 . At this point the spring 19, which 
is carried by or formed as part of the carrier 11, pre-engages the ends of 
coil cases 23 to provide a sufficient biasing force so that the inboard 
tabs 33 operate as catches to hold the coil assemblies 16 in position. 
While the coil assemblies 16 are being moved into the solder position, the 
small discharge end of the wire guide funnels 14 at the face 34 assures 
that the fragile coil wires 18 are always sufficiently in line with the 
relevant solder holes 40 on the circuit board 21 so that no binding will 
be sustained. To ensure wire alignment the discharge openings in the 
funnels 14 are significantly smaller than the solder holes 40 in the 
circuit board. In the prior art, separate terminals are employed at the 
ends of the coil wire 18 (either soldered or wrapped) to give additional 
rigidity to the termination. Use of such terminals is avoided in this 
embodiment of the present invention. 
Even though the coil wires are quite small in diameter, with the present 
invention, by leading the ends 18 into the large end of the wire guide 
funnels 14 with smooth, gradually sloping sides toward a relatively small 
discharge opening, the system locates the ends 18 accurately with respect 
to the circuit board 21. This provides for an efficient manufacturing 
process and allows for the total elimination of the separate terminal 
pieces themselves. An insulator 20 is used on a portion of the wire to 
isolate the wire from the case 23 of coil assembly 16 and from the springs 
19. Optionally, as shown in FIG. 4, bosses 43 can be molded directly on 
the top surface of spool, that are sufficiently high so that the wires 
cannot touch either the case 23 or spring 19 as it is being installed. 
Once the coil assemblies 16 are located in the solder position, the wire 
ends 18 project a sufficient amount through the circuit board 21 so that 
conventional processing techniques such as wave soldering may be employed 
to connect the ends 18 to the appropriate circuit. When the coil assembly 
16 is mated with the corresponding hydraulic modulator valve 26, as shown 
in FIG. 2D, the coil assemblies 16 are moved toward the circuit board 21 
and the wire ends 18 are partially buckled within the funnels 14 to allow 
slack for coil movement as alignment occurs with the mating valve 
assemblies. This provides for the part-to-part variation of valve spacing 
due to normal manufacturing tolerances. Additional compliance may be added 
to the wire ends 18 by preforming an optional coil 44 as shown in FIG. 4. 
When the coil assemblies 16 are mated with the valves 26, the inboard tabs 
33 separate from the wall 31 and the valves hold the coil assemblies in 
alignment. The valve 26 is of the type disclosed in U.S. Pat. No. 
5,845,672 which is commonly assigned and is specifically incorporated 
herein by reference. The use of the present concept, with the coil 
assemblies 16 pre-assembled into a separate carrier 11 before assembly to 
the circuit board 21 simplifies the final coil-to-circuit board assembly 
process. 
FIG. 4 shows the molded plastic coil carrier 11 removed to reveal the 
details and the location of the finger springs 19. Springs 19 are first 
attached to the coil carrier 11 by pressing the four openings 35 of the 
springs over corresponding projections 42 on the carrier 11 as shown in 
FIG. 3. The springs 19 are formed as two separate components. Each of the 
separate spring assemblies 36 includes a main body with twelve branches, 
two of which engage each coil assembly 16. These springs provide multiple 
functions. First, they are used to keep the coils 16 locked against the 
tabs 17 when the assembly is in the solder position. Thus, the carrier 11 
may be fully turned over and the coil wire ends 18 are held in the correct 
position for wave soldering 22. Second, the springs serve to push the 
coils 16 against the base 37 of the valve 26 as shown in the installed 
position of FIG. 2D. The installed position refers to the state when the 
entire ECU assembly is mated with the hydraulic portion of the ICS. When 
the coil assembly 16 and valve 26 are mated, the magnetic coupling path is 
optimized since a close surface contact is assured directly between the 
coil case 23 and the valve body flange 37. 
Third, the springs also serve to stabilize the valve coil assemblies 16 
from any typical underhood vibration effects which may be experienced in 
normal driving conditions. In particular, the installed spring force is 
sufficiently high so that the coils 16 are kept firmly in place even 
though vibrational forces operate in an attempt to separate the coil 
assemblies 16 from the valve body flanges 37. This minimizes any fatigue 
on the coil wire ends 18 and assures a constant magnetic coupling. This 
becomes important during an ABS stop when there may be high levels of 
underhood vibrations generated from a high coefficient surface, at the 
same time that consistent valve performance is required. Although multiple 
leaf-type springs are shown in this particular design, either single coil 
springs sufficiently sized to act on the top of each coil case 23 or 
multiple small coil springs contained in individual pockets in the carrier 
and acting on opposite sides of the top of the coils case 23 (neither 
concept shown) could be used to provide the same spring function as the 
multiple leaf spring. 
FIG. 5 shows details of the funnel 14. The general shape is that of a 
truncated round conical section with openings at both ends so that the 
wire ends 18 may pass through. The terminal end of the funnel 14 away from 
the wall 31 has a face 34 that is used to rest directly on the circuit 
board 21 as shown in FIG. 2D. The soldering flow channels designated 38 
and 39 are positioned in the face 34 and intersect at the opening in the 
face 34. This geometry, coupled with a sufficient size, allows solder to 
flow onto the back side of the circuit board solder holes 40 facilitating 
optimum solder joint quality. 
In summary, the present invention utilizes a coil pack concept for 
pre-assembly of coil assemblies to a carrier minimizing the time and 
effort required to install the coils on the main circuit board assembly 
line. A low cost, all-plastic carrier with associated built-in features, 
pilot pins and clips is used for easy, precise circuit board mounting. 
Cone shaped wire guide funnels are used, and external guides in the 
carrier assembly make the installation of individual coils efficient for 
design for manufacture. A latch arrangement is built into the coil bobbin 
that has a double catch feature. The first catch provides a shipping 
position and the second catch provides a solder position. A series of 
springs act against each coil case to pre-load the coils against the 
bobbin latch(es), against the valve body flange for optimized consistent 
magnetic coupling, and against the valve body flange to eliminate any 
relative motion between the coil and valve body in order to alleviate 
concerns for fatigue of the coil attachment wires. Additionally, a solder 
well feature is used at the end of each wire guide funnel to promote good 
solder penetration to assure consistent product quality. Thus, the 
solenoid coil attachment mechanism of the present invention provides a 
robust and highly efficient means of attaching solenoid valve coils 
directly to an electronic controller circuit board.