An Electronic Brake Control System (EBCS) is often included as standard equipment on new vehicles. When actuated, the EBCS is operative to modulate the pressure applied to the vehicle wheel brakes. A typical EBCS includes a plurality of solenoid valve mounted within a control valve body and connected to the vehicle hydraulic brake system between the brake master cylinder and the individual wheel brake cylinders. The solenoid valves usually are normally open, or isolation, valves and normally closed, or dump, valves. Proportional solenoid valves also can be included. The valve body further includes one or more accumulators for the temporary storage of brake fluid during an operating cycle of the EBCS.
An EBCS further includes an electronic control module which has a microprocessor. The microprocessor is electrically connected to the pump motor, a plurality of solenoid coils associated with the solenoid valves, and wheel speed sensors for monitoring the speed and deceleration of the vehicle wheels. The microprocessor also is typically electrically connected to the brake light switch and receives a signal from the switch when the vehicle brakes are applied. Additionally, the EBCS may include one or more accelerometers which also are connected to the microprocessor. The microprocessor includes a memory portion which stores control algorithms for each mode of operation of the EBCS. The control algorithms comprise a set of instructions for the microprocessor which control the operation of the EBCS. The control module is usually mounted upon the valve body. The assembled valve body, motor and control module form a compact unit which is often referred to as an electro-hydraulic control unit.
Another mode of operation provides Traction Control (TC). If the microprocessors detect excessive slip of a driven wheel when the wheel brakes are not applied, the EBCS will apply the brakes to the slipping wheel and thereby transfer more engine torque to the non-slipping wheel.
Referring now to FIG. 1, there is shown a partial sectional view of a typical EBCS solenoid valve 10 mounted upon an EBCS control valve body 11. The control valve body includes a plurality of internal passages (not shown) that communicate with the valve 10. The valve 10 is a digital valve, that is, it is either open or closed. The particular valve 10 shown in FIG. 1 is a normally open valve, however, the following discussion also applies to normally closed valves. The valve 10 includes an axially shiftable armature (not shown) which is biased in an upward direction by a spring (not shown) such that a ball valve
(not shown) is maintained in a normally open position. The ball valve cooperates with a valve seat member 15 which is mounted in the valve body 11. The armature and ball valve are slideably disposed within a valve sleeve 16 having a closed end.
The solenoid coil 20 is of conventional design, comprising a winding 24 formed from multiple turns of an insulated magnet wire having a round cross section, such as #28 ? magnet wire. The magnet wire is helically wound upon a plastic bobbin 26. The bobbin 26 has a cylindrical center portion 28 that terminates in upper and lower flanges, 30 and 32, respectively. A pair of terminal pin supports 34 extend in an axial direction from the top of the bobbin 26. Each of the supports 34 is molded over a terminal pin 36. An end 38 of the coil winding wire is wound around the base of each of the terminal pins 36 and soldered thereto. The pins 36 are electrically coupled to via a printed circuit board (not shown) to the EBCS microprocessor.
The bobbin can include an annular ring formed upon an inner surface of the bore and spaced from the ends of the bore. The annular ring forms a stepped bore within the sleeve with the steps positioning at least one of the first and second flux rings within the bore. Alternately, the bobbin can include an least one axially extending rib formed upon an inner surface of the bore and spaced from the ends of the bore. The rib positions at least one of the first and second flux rings within the bore.
The invention further contemplates that the coil and flux rings are received within a flux casing with at least one of the flux rings secured to the flux casing. In the preferred embodiment, the flux rings are pressed into the ends of the flux casing to retain the coil and flux rings within the flux casing.
For electronic brake control systems being currently developed, vehicular solenoid valve can be energized for long periods of time. The energized coils generate heat that must be conducted away from the coils to avoid overheating. Conventional coil bobbins typically have air gaps and low-pressure contacts between the bobbins and the metal parts of the other components of the control system. Accordingly, current units have poor heat conduction properties. Therefore, a coil assembly having improved heat conduction properties would be desirable.
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