1. Field of the Invention
The present invention generally relates to an electronic control unit of a kind required to have a waterproof structure suitable for use in an automobile and, more particularly, to the electronic control unit equipped with at least one electrical input/output connector having a plurality of terminal members adapted to be connected directly with a printed circuit board.
2. Description of the Prior Art
The electrical plug-in connector assembly providing for the input and output of one or both of an electrical power and electrical signals to the separate device has long been well known, which is generally made up of a plug-in connector and a socket connector for receiving the plug-in connector. While the plug-in connector assembly is available in various types, the present invention makes use of the type comprising the plug-in connector having a plurality of terminal sheaths and the socket connector having a corresponding number of connector terminals which are connected at one end to a printed circuit board by means of soldering and which are, when the plug-in connector is plugged into the socket connector, engaged or plugged into the associated terminal sheaths to establish electric circuits between the connector terminals and the terminal sheaths.
In this particular type of the plug-in connector assembly, it is well understood that whenever the plug-in connector is plugged in or removed from the socket connector, a compressive or tensile load act on the printed circuit board, respectively. Where the socket connector is fixed in position with the connector terminals electrically connected directly with the printed circuit board through electrical joints formed by, for example, soldering, repeated application of the alternating compressive and tensile loads to the printed circuit board will eventually result in degradation of the reliability of the printed circuit board. Accordingly, it is a general practice to mount the plug-in connector and the printed circuit board separately on a housing of the electronic control unit in order to secure a highly reliable electronic control unit.
In the structure in which the socket connector and the printed circuit board are fixed separately in the housing of the electronic control unit, the tensile load which would be brought about when the plug-in connector is removed from the socket connector will not be transmitted to the printed circuit board. However, the difference between the coefficient of thermal expansion of a material for the connector terminals in the socket connector and that of a material for the printed circuit board is apt to allow thermal stresses to develop at the solder joints which eventually leads to material fatigue at the solder joints. Once this occurs, breakage is likely to result in at one or some of the solder joints.
FIG. 4 illustrates one of the conventional methods of accomplishing an electrical connection between one of the connector terminals and the printed circuit board. As shown therein, a control unit housing 100 is made of a synthetic resin and has a connector casing 101 and a circuit casing 103 formed integrally therewith with a partition wall intervening therebetween. The connector casing 101 has a socket defined therein so as to open upwardly for receiving a plug-in connector not shown. The illustrated socket connector also includes a plurality of straight connector terminals, only one of which is shown by 102, that are fixed in position by interference fit or insert-molding so as to extend through the partition wall of the control unit housing 100. The straight connector terminals 102 thus have one end positioned inside the socket in the connector casing 101 and the opposite end positioned inside the circuit casing 103. A printed circuit board 105 is housed within and secured to the circuit casing 103 by means of a plurality of set screws, only one of which is shown by 104, that are screwed into an inwardly protruding peripheral portion 106 integral with the circuit casing 103. Those ends of the straight connector terminals 102 within the circuit casing 103 are pierced through corresponding holes in the printed circuit board 105 and are then soldered at 102a to circuit elements on the printed circuit board 105.
According to the connection shown in FIG. 4, the connector terminals 102 are simple in shape and can easily and accurately soldered to the printed circuit board 105. However, considering that the control unit housing 100 including the circuit casing 103 is made of the synthetic resin whereas the connector terminals 102 are made of, for example, brass having a good conductivity, each time the ambient temperature inside a space h delimited between the wall of the circuit casing 103, a part of which concurrently serves as the partition wall between the connector casing 101 and the circuit casing 103, and the printed circuit board 105 undergoes change, the solder joints 102a tends to be pulled laterally due to the peripheral portion 106 and, hence, the circuit casing 103 having a larger coefficient of thermal expansion, which would eventually results in failure of some or all of the solder joints 102a to conduct an electrical current therethrough.
In order to avoid the problem inherent in the structure shown in and described with reference to FIG. 4, an attempt has largely been made to provide each connector terminal of the socket connector with a deformable portion. By way of example, as shown in FIG. 51 the use is made of a connector subassembly 200 comprising a connector casing 201, separate from and independent of the circuit casing 103, and a plurality of connector terminals 202, that are fixed in position by interference fit or insert-molding so as to extend through a wall of the connector casing 201. The connector terminals 202 are so bent into a generally L-shaped configuration as to define the deformable portion so that in the assembled condition, neither the compressive load nor the tensile load will be transmitted to the solder joints 202a.
The connector subassembly 200 of the structure described above is fixedly secured to the circuit casing 103 with the connector terminals 202 extending into the circuit casing 103 through one or more perforations defined in a wall of the circuit casing 103 and then soldered at 202a to the printed circuit board 105 in a manner similar to that described in connection with the structure of FIG. 4. As is the case with the structure shown in FIG. 4, the printed circuit board 105 is supported within the circuit casing 103 by means of a plurality of set screws 104 screwed into the inwardly protruding peripheral portion 106 integral with the circuit casing 103.
In the structure shown in and described with reference to FIG. 5, change in dimension due to the difference in coefficient of thermal expansion between the connector terminals 202 and the control unit housing 100, which change tends to be brought about by change in ambient temperature inside the circuit housing 103, can be effectively absorbed by the resiliency of the deformable portion of each connector terminal 202. Consequently, no external force can be transmitted to the solder joint 202a to thereby avoid the possibility of electrical disconnection between the connector terminals 202 and the corresponding circuit elements on the printed circuit board 105.
To complete the control unit housing 100, however, the structure shown in FIG. 5 requires the use of the separate casings 103 and 201 which tends to increase the cost of manufacture. In addition, where the waterproof design is required, the use of the separate casings 103 and 201 requires a seal to be employed between these casings. Accordingly, not only does the cost of manufacture increase additionally, but also the use of the waterproof seal may constitute a cause of reduction in reliability. Where the fluid tightness is of an paramount importance, the electronic control unit should have the connector casing as a unitary part of the control unit housing 100 together with the circuit casing 103.
However, another problem will arise if the connector casing 201 is formed integrally with the control unit housing 100 together with the circuit casing 103, which will now be discussed with reference to FIG. 6.
The control unit housing 100 shown in FIG. 6 has the partition wall dividing it into the connector casing 101 and the circuit casing 103, both of which is a unitary part of the control unit housing 100. When it comes to press-fitting of the L-shaped connector terminals 202 across the partition wall, the socket in the connector casing 101 has such a limited capacity that each connector terminal 202 cannot be passed through the partition wall with its opposite ends positioned on respective sides of the partition wall. Accordingly, it would be a reasonable way to insert each connector terminal 202 from the interior of the circuit casing 103 instead of from the socket in the connector casing 201, in which case a wall portion of the circuit casing 102 confronting the partition wall must be set back a distance, indicated by L2, to provide an extra space to accommodate an end portion of each connector terminal 202 that is passed through the partition wall. The set-back distance L2 is as a matter of design equal to or greater than the length L1 of that end portion of the respective connector terminal 202, rendering the control unit housing 100 as a whole to be bulky in size.
In addition, alignment of the tip of that end portion of each connector terminal 202 with a corresponding perforation in the partition wall is indeed difficult to achieve and even the slight misalignment would require readjustment in position of the connector terminals 202 relative to the respective perforations in the partition wall. This complexity indeed increases the cost of manufacture.
Although the connector terminals 202 may be insert-molded together with the control unit housing 100 during the molding of the latter, a complicated and expensive mold would be required in such case, adding cost to the final product.
Also, considering a top surface area of the circuit casing 103 on one side of the partition wall opposite to the connector casing 201 defines a support base on which a hydraulic unit (not shown) including a hydraulic pump and a plurality of electronically controlled control valves is fixedly mounted, the provision of the set-back distance L2 results in a considerable reduction in efficiency of maximum utilization of the available space. In addition, since the structure shown in FIG. 6 requires the connector terminals 202 to be press-fitted into the corresponding apertures in the partition wall from the interior of the circuit casing 103, it is impossible to reduce the size of a portion where the connector terminals 202 are fixed even though they can be formed to have the same shape as the corresponding socket terminals in the plug-in connector, and a problem associated with reduction in physical strength of the partition wall would also occur if the connector terminals 202 are spaced a small pitch between the neighboring members of them.
U.S. Pat. No. 5,452,948, issued Sep. 26, 1995 to Cooper et al. discloses the electronically controlled hydraulic unit comprising, as reproduced in FIG. 6, the idea of bending coil leads or terminals, extending respectively from each of a plurality of electromagnetic coils, to provide resiliency so that the solder joints between circuit elements on a coil printed circuit board and the coil terminals can be substantially immune from being stressed when a compressive load is applied to the coil in a direction parallel to the coil terminals.
More specifically, referring to FIG. 7, Cooper et al. U.S. Patent discloses an electronically controlled hydraulic unit comprising a coil mounting housing 300 including a peripheral side wall 301 and a connector casing 302 both formed integrally therewith. Electromagnetic coils 303 each having a pair of coil terminals 306 are each seated on a respective coil mounting seat 304 having a snap-in, hold-down projection 305. The coil terminals 306 of each of the electromagnetic coils 303 are soldered at a free end thereof to circuit elements on a coil printed circuit board 307, but have a generally intermediate portion thereof bent to provide resiliency so that the solder joint will not be stressed when a compressive load is applied to the respective coil 303 in the direction parallel to the coil terminals 306 during mounting of the respective coil 303 onto the coil mounting housing 300.
The coil mounting housing 300 has a plurality of staking pins 308 protruding upright from a sealing rim extending inwardly from the bottom of the peripheral side wall 301. These staking pins 308 are, after the coil printed circuit board 307 has been mounted in the coil mounting housing 300 with its peripheral portion resting on the sealing rim through a sealing member 309, bent over to hold the printed circuit board securely in place. An electronic control unit printed circuit board 311 having a number of control elements 31 mounted thereon is positioned beneath the coil mounting housing 300 and is supported by connecting legs 312, which extend downwardly from a socket connector 302 and are then soldered to the electronic control unit printed circuit board 311, and also by pins 313 having one end fixed to the coil printed circuit board 307 so as to extend downwardly therefrom and soldered to the electronic control unit printed circuit board 311. After the component parts have been assembled, a lower cover 314 is secured from below to the coil mounting housing 300 to thereby maintain sealing integrity between the coil printed circuit board 307 and the coil mounting housing 300.
In this known electronically controlled hydraulic unit, the coil printed circuit board 307 is electrically connected with the electromagnetic coils 303 through the coil terminals 306 and is securely connected to the coil mounting housing 300 through the sealing member 309. On the other hand, the electronic control unit printed circuit board 311 are electrically and mechanically connected with the terminal legs 312 and the pins 313, respectively. Since the lower cover 314 when secured from below to the coil mounting housing 30 encloses the electronic control unit printed circuit board 311 in a substantially hermetic fashion, the various component parts can be fluid-tightly sealed.
According to Cooper et al. U.S. Patent, the coil terminals so bent as to provide resiliency appear effective to avoid the possibility of the solder joints from being stressed. However, the bending of the coil terminals for this purpose is required either before or after the coil terminals have been pierced under interference fit through the coil mounting seats. In either case, it has been found that some of the coil terminals are apt to deviate from the design dimension when they are bent and, therefore, alignment of the coil terminals with corresponding perforations in the coil printed circuit board appears to be difficult to achieve without complicated and time-consuming procedures.
In general, soldering is the most inexpensive and effective means for connecting connector terminals in an electrical connector with a printed circuit on a printed circuit board. However, the resultant solder joints have been found sensitive to external stresses such as, for example, thermal stresses generated in the circuit board or the like which would be brought about by change in ambient temperature.