GB2485897A

GB2485897A - Electrical connecting device with contacts of different resonant frequency

Info

Publication number: GB2485897A
Application number: GB1120270.2A
Authority: GB
Inventors: Masahiro Kondo; Tetsuya Miwa
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2010-11-25
Filing date: 2011-11-24
Publication date: 2012-05-30
Anticipated expiration: 2031-11-24
Also published as: JP2012129193A; DE102011087048A1; GB2485897B; JP5810815B2; GB201120270D0; DE102011087048B4

Abstract

An electrical connecting device for connecting an electronic control device and a controlled electrical device, wherein the connecting device comprises: a male connector 1 with at least two control signal male contacts 13, 14, each with an exposed portion 130, 140 that extends outside a body of a housing 10 of the male connector; and a female connector 2 with at least two control signal female contacts 23, 24 that establish elastic electrical joints with the exposed portions 130, 140 of the corresponding control signal male contacts 13, 14. Two signal paths are formed, through which a control signal 300 is transmitted. The exposed portion 130 of one of the control signal male contacts 13 differs from the exposed portion 140 of the other control signal male contact 14 in at least one of; length, density, cross-sectional area and Youngâ s modulus. Consequently, the two control signal contacts 13, 14 have different resonant frequencies, reducing the possibility that the two signal paths are opened simultaneously when subjected to a large scale impact or vibration.

Description

I

ELECTRICAL CONNECTING DEVICE

BACKGROUND OF THE INVENTION

I Technical Field of the Invention

The present invention relates generally to an electrical connecting device designed to ensure the stability in electrical connection between an electronic control unit and an electticai device for establishing transmission of a high-frequency electric signal therebetweert.

2 Background Art

For instance, automotive vehicles are equipped with an electronic control unit which outputs an ignition control signal to an ignition device to apply a high-voltage to a spark plug to create an electric spark, thereby igniting an air-fuel mixture in a combustion chamber of an internal combustion engine.

1(5 The electronic control unit also works to output a fuel injection control signal to a fuel injection device to control an open/close operation of a fuel injection valve for spraying fuel into the combustion chamber of the internal combustion engine.

The electronic control unit and the above type of a controlled device are usually connected electrically through a wire harness that is a string of a power supply cable, a ground cable, and electric signal cables. The joint between the wire harness and each of the electronic control unit and the controlled device is achieved through male and female connectors. The male and female connectors have male and female housings which are fitted together to make electric and elastic connections between male terminals (e.g., pin contacts) and female terminals (e.g., socket contacts).

Japanese Patent First Publication No, 2002-280138 teaches mu1tIpln connectors equipped with a male and a female housing.

The male housing has formed therein a hood into which the female housing is to be fitted to make electrical connections between male contacts disposed in the hood and elastically deforinable female contacts disposed in the female housing. The multi-pin connects are designed to change physical pressure exerted on the male and female contacts to minimize the friction therebetween.

The male and female terminals of the electric connectors used in connecting with the ignition device or the fuel injection device of the automotive vehicle are usually subjected to mechanical vibrations, as generated by the internal combustion engine, which usually change in magnitude depending upon. operating conditions of the engine. For instance, the male and female terminals undergo an instantaneous strong impact when the vehicle stops or accelerates suddenly1 which may result in disconnection thereof and thereby block the transmission of electric signals between the electronic control unit and the ignition device of the fuel injection device.

Particularly, the ignition device or the fuel injection device for the internal combustion engine of the automotive vehicle is usually required to be controlled accurately in a time as short as microseconds. The high-frequency control signal such as the ignition control signal or the fuel injection control signal, as produced by the electronic control unit, therefore needs to be transmitted with very high precision to the ignition control device of the fuel injection device.

The above type of high-frequency control signal is produced in the form of a very small electric current, which may result in malfunction of the ignition device or the fuel injection device when the transmission path of the control signal is cut for a short time.

For instance, the ignition device is responsive to an on/off state of the ignition control signal to energize or deenergize an X0 ignition coil to apply a high voltage to the spark plug to ignite fuel in the internal combustion engine. An unexpected switch to the off-state of the ignition control signal arising from an instantaneous disconnection of the connectors during the transmission of the ignition control signal to the ignition device, therefore, may result in w an error in operation of the ignition coil which may lead to application of high-voltage to the spark plug to produce a spark in error.

Particularly when the pr&ignition occurs in a multi-cylinder internal combustion engine, combustion pressure which is produced in one of the cylinders where the fuel is not to be ignited may interfere with that in another of the cylinders where the fuel has been ignited correctly, which may lead to damage to the engine. It is, thus, essential to ensure the stability in transmission of the control signal free from the effects of the external vibrations or impact

SUMMARY OF' THE INVENTION

It is therefore an object of the invention to provide an electrical connecting device which is designed to ensure the stabilitj in electrical connection between an electronic control device and a controlled electrical device under the influence of physical impact or S vibration According to one aspect of the invention, there is provided an electrical connecting device for use in connecting an electronic control device and a controlled electrical device. The electrical connecting device comprises: (a) a male connector equipped with a to housing, the male connector also having at least a first control signal male contact and a. second control signal male contact which are disposed in the housing and having a first and a second exposed portion which extend outside a body of the housing; and (b) a female connector equipped with a. housing, the female connector having at least a first control signal female contact and a second control signal female contact which are disposed in the housing. The female connector is connected to the male connector to establish elastic joints of the first and second control signal female contacts to the first and second exposed pardons of the first and second control signal male contacts to form a first and a second signal transmission path through which a control signal is transmitted between the electronic control device and the controlled electric device. The first and second exposed portions are different in at least one of length, density, sectional area and Young's modulus from each other.

Specifically, the elastic joint between the first control signal male contact and the first control signal female contact defines the first signal transmission, while the joint between the second control signal metal contact and the second control signal female contact forms the second signal transmission path. The first and second exposed portions are different in at least one of lengthy density, sectional area, and Young's modulus from each other, thereby differentiating resonance frequencies of the first and second exposed portions from each other. This results in a minimized possibility that the first and second signal transmission paths are opened simultaneously when subjected to a large scale impact or vibration, thus ensuring the stability in transmitting the control signal through either of the first and second transmission paths This results in a decreased possibility of failure In operation of the controlled electrical device.

In the case where the electronic control device Is art engine control system, and the controlled electrical device is an ignition device for an internal combustion engine of an automotive four-wheeled or two-wheeled vehicle, when either of the first and second signal transmission paths is broken due to physical vibrations of the engine or impact arising from sudden acceleration or deceleration of the vehicle or a hit on an obstacle, there is a high possibility that the other of the first and second signal transmission paths is kept closed, thereby ensuring the stability in transmitting the control signal from the engine control system to the ignition device, which avoids a failure in igniting an air/fuel mixture itt the 26 engine, such as the pre-ignition.

In the preferred mode of the invention, the body of the a housing of the male connector includes one of a thick'-walled portion and a thin-walled portion in which one of the first and second control signal male contacts is disposed to differentiate lengths of the first and second exposed portions from each other, This S differentiates the resonance frequencies of the first and second exposed portions from each other.

The length of the second exposed portion may be smaller than or equal to the square root of 3./il times or greater than or equal to the square root of 1/0.9 times of the length of the first exposed portion. This causes the resonance frequency of the second exposed portion to deviate by ± 10% or more from the resonance frequency of the first exposed portion. This results in decreased possibility that the first and second signal transmission paths are opened simultaneously when subjected to the impact or vibration.

At least one of the first and second control signal male contacts is made of a fiat plate member. At least one of the first and second control signal female contacts is shaped to make a plurality of contacts with the at least one of the first and second control signal male contacts1 The female contacts serve to clip opposed surfaces of the at least one of the first and second control signal male contacts. This results in increased stability of the joints of the first and second control signal female contacts to the first and second exposed portions of the first and second control signal male contacts.

BRIEF DESCRIPTION OF' THE DRAWINGS

The present invention Will, be understood more fully from the dethiled description given hereinbelow and from the accompanying drawings of the preferred embodiments of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for the purpose of explanation and understanding only.

In the drawings: Fig. 1(a) is a longitudinal sectional view which illustrates a male connector of an electrical connecting device which is fit in an it) electronic control unit or a controlled electrical device according to the invention; Fig. 1(b) is a longitudinal sectional view which illustrates a female connector of the electrical connecting device to be coupled to the male connector of Fig. 1 (a); Fig. 2(a) is a perspective view which shows a first and a second exposed portion of pin contacts disposed in the mate connector of Fig. 1(a); Fig. 2(b) is a perspective view which shows the first and second exposed portions of Fig. 2(s) when resonate upon receiving engine vibration; Fig. 3(a) is a longitudinal sectional view which illustrates an example of the male connector of Fig. 1(a) joined to an ignition control device and a wire harness; Fig. 3(b) is a longitudinal sectional view which illustrates an example of the female connector of Fig. 1(b) joined to an electronic control unit and a wire harness; Fig. 4(a) is a time chart which demonstrates a transmitted ignition control signal, a received ignition control signal, and a secondary voltage when the electrical connecting device of Figs 1(a) and 1(b) is operating properly; Fig. 4(b) is a time chart which demonstrates a transmitted ignition control signal, a contact joint of a conventional connector, a received ignition control signal, and a secondary voltage when the connector joint is opened by an unexpected external impact or vibration; Fig. 4(c) is a time chart which demonstrates a transmitted ignition control signal, a received ignition control signal, a first contact joint, a second contact joint, arid a secondary voltage when.

the first and second connector joints are opened undesirably by an unexpected external. impact or vibration; Fig. 5(a-1) is a top view which illustrates a first modification of the male connector of Fig. 1(a); Fig. 5(a-2) is a cross sectional view, as taken along the line A-A of Fig. 5(a-1); Fig. 5(b-I)is a. top view which illustrates a second modification of the male connector of Fig. 1 (a); Fig. S(b-2) is a cross sectional view, as taken along the line A-A of Fig. 5(b-1); Fig. 5(c-1) is a top view which illustrates a third modification of the male connector of Fig. 1(a); Fig. 5(c-2) is a cross sectional view, as taken along the line A-A of Fig. 5(04); Fig. 5(a-1) is a top view which illustrates a fourth modification of the male connector of Fig. 1(a); Fig. 6(a-2) is a cross sectional view, as taken along the line A-A of Fig. 6(a-ifl Fig, 6(b-1) is a top view which illustrates a fifth modification of the male connector of Fig. 1(a); Fig. 6(b2) is a cross sectional view, as taken along the line A-A of Figs 6(b1); Fig. 6(b4) is a cross sectional view, as taken along the line B-B of Fig. 6(1,-i); Fig. 6(c-l) is a top View which illustrates a sixth modification of the male connector of Fig. 1(a); Fig. 6(c-2) is a cross sectional view, as taken along the line A-A of Fig. 6(c-1); Fig. 6(c-3) is a cross sectional view, as taken along the line B-B of Fig. 6(c4); Fig. 7(a) is a. view which illustrates an ecample of structures of the male and female contacts of Figs. 1(a) and 1(b); Fig. 7(b) is a view which illustrates the second example of structures of the male and female contacts of Figs. 1(a) arid 1(b); and Fig, 7(c) is a view which illustrates the third example of structures of the male and female contacts of Figs. 1(a) and 2(b).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers 26 refer to like parts in several views, particularly to Figs. 1(a) and 1(b), there is shown an electrical connecting device (also called an electrical connecting device) made up of a male connector I and a female connector 2 according to the first embodiment of the nVetLtOTL. The electrical connecting device is used in this embodiment to electrically connect an controlled device 3, such as an ignition device for an internal combustion engine of automotive vehicles, and an electronic control unit S mounted in the vehicle1 ?or the brevity of illustrationF'ig. 1(a) illustrates only either of the controlled device 3 or the electronic control unitS. The electrical connecting device (i.e., the male connector 1) may be mounted in either or both of the controlled device 3 and the electronic control unit 5.

The electrical connecting device is used to transmit a high-frequency control signal SIC) between the controlled device 3 and the electronic control unit 5. The male connector 1 is, as can be seen in Fig. 1(a), designed as a male plug and includes a housing (also called a male shell) in which pin contacts 11, 12, 13, and 14 are secured. The female connector 2 is, as can be seen in Fig. 1(b), designed as a female receptacle and includes a housing 20 (also called a female shell) and socket contacts 21,22,23, and 24 secured to the housing 20. The malq connector 1 is fitted in the female connector 2 to establish elastic electric connections between the pin contacts 11, 12, 13, and 14 and the socket contacts 21, 22, 23, and 24. The electrical connecting device is made up of the male 2$ connector 1 secured to either of the controlled device 3 and the electronic control unit 5, the female contact 2, and a wire harness 40

II

joined to the female connector 2.

The control signal SIC is transmitted through at least two transmission paths extending from a control signal line 300 leading to the pin contacts 13 and 14 of the male connector I to a control signal line 43 leading to the socket contacts 23 and 2401 the female connector 2. The pin connectors 13 and 14 are, as illustrated in Fig 1(a), joined together and connected to the control signal line 300.

The socket contacts 23 and 24 are each connected to the control signal line 43. The pin connector 13 has a portion 130 exposed outside the housing 10. The exposed portion 130 has a length L130, a density p, a sectional areas, and a Young's modulus E. similarly, the pin connector 14 has a portion 140 exposed outside the housing 10. The exposed portion 140 has a length a density p, a sectional areaS, and a. Young's modulus B. The exposed portions 130 and 140 are, as will be described later in detail., different in at least one of length, density, sectional area, and Young's modulus from each other.

The male connector 1 is, as described above, made up of the housing 10 and the pin contacts 11 to 14 arrayed within the housing 10. The housing 10 is cylindrical and made of an insulating resin material. The housing 10 has a bottom 100 in which fixing bases l11 121, and 131 of the pin contacts 11, 12, and 13 are insert-molded1 The pin contact 11 serves as a. power supply terminal (which will also be referred to as a power supply male contact below) and is made of a conductive flat strip which has an end protruding within the housing 10 as a power supply pin 110 and an end extending from the bottom 100 into the controlled device 3 or the electronic control unit S as a power supply wiring terminal 112+ The power supply pin 110 and the power supply wiring terminal 112 are joined integrally through the fixing base 111. The Ibdng base 111 is embedded in the bottom 100 of the housing 10.

The pin contact 12 serves as a grounding terminal (which will also be referred to as a grounding male contact below) and is made of a conductive flat strip which has an end protruding inside the housing 10 as a grounding pin 120 and an end extending from the bottom 100 into the controlled device 3 or the electronic control unit as a grounding wiring terminal 122. The grounding pin 120 and the grounding wiring terminal 122 are joined integrally through the fixing base 121. The fixing base 121 is embedded in the bottom 100 ofthehousinglO.

The pin contact 13 serves as a first control signal terminal (which will also be referred to as a first control signal male contact below) and is made of a conductive flat strip which has an end protruding inside the housing 10 as a. first control signal pin 130 (which will also be referred to as a first exposed portion) and an end extending from the bottom 100 into the controlled device 3 or the electronic control unitS as a first control signal wiring terminal 132+ The control signal pin 130 and the first control signal wiring terminal 132 are joined integrally through the fixing base 131. The ftxing base 131 is embedded in the bottom 100 of the housing 10.

* The pin contact 14 serves as a second control signal terminal (which will also be referred to as a second control signal male contact below) and is macic of a conductive flat strip which has an end protruding within the housing 10 as a second control signal pin (which will also be referked to as a second exposed portion) and an end which is bent and leads to the fixing base 131 as a second control signal terminal joint 142. The second control signal pin 140 and the second control signal terminal joint 142 are formed integrally through the fixing base 141. The fixing base 141 and the second control signal tenninal joint 142 are embedded in the bottom 100 of the housing 10, The power supply pin 110, the grounding pin 120, and the first control signal pin (it, the first exposed portion) 130 have the same length Liao which protrudes from the inner surface of the bottom 100 into an inner chamber of the housing 10.

The bottom 100 of the housing 10 has a thlnwafled portion 101 which is smaller in thickness than a major portion of the bottom 100$ The fixing base 141 of the second control signal terminal 14 is embedded in the thinwalted portion 101. The second control signal pin 140 has the length L140 which protrudes from the inner surface of the thin-walled portion 101 into the inner chamber of the housing 10. the length L140 of the second control signal pin 140 is greater than the length L,so of the first control signal pin 130.

The power supply wiring terminal 112, the çoundhg wiring terminal 122, and the control signal wiring terminal 132 are joined to a power supply terminal -B, a grounding terminal (HiD, and a control signal terminal SKI of the controlled device 3 or the electronic control unit 5.

The female connector 2 is, as illustrated in Fig. 1(b), made up of the housing 20 and the socket contacts 21 to 24 arrayed inside the housing 20. The housing 20 is cylindrical and made of an insulating resin material. The housing 20 has a bottom 200 in which fixing bases 211, 221,231, and 241 of the socket contacts 21, 22, 23, and 24 are insert-molded.

The socket contact 21 serves as a power supply terminal and is made of a conductive materiaL The socket contact 21 has an end 3,0 protruding inside the housing 20 as a power supply female contact 210 and an end extending outside the bottom 200 to the wire harness 4 as a power supply wiring terminal 212. The power supply female contact 210 and the power supply wiring terminal 212 are joined integrally through the fixing base 211. The fixing base 121 is embedded in the bottom 200 of the housing 204 The socket contact 22 serves as a grounding terminal and is made of a, conductive material4 The socket contact 22 has an end protruding within the housing 20 as a grounding female contact 220 and an end extending outside the bottom 200 to the wire harness 4 as a grounding wiring terminal 222. The grounding female contact 220 arid the grounding wiring terminal 222 are joined integrally through the fixing base 221. The fixing base 221 is embedded in the bottom 200 of the housing 204 the socket contact 23 serves as a first control signal terminal and is made of' a conductive materiaL The socket contact 23 has an end protruding within the housing 20 as a first control signal female contact 230 and an end extending outside the bottom 200 to the wire harness 4 as a first control signal wiring terminal 232. The first control signal female contact 230 and the first control signal wiring terminal 232 are joined integrally through the fixing base 231.

The fixing base 231 is embedded in the bottom 200 of the housing 20.

The socket contact 24 serves as a second control signal terminal and is made of a conductive material. The socket contact 24 has an end protruding within the housing 20 as a. second control signal female contact 240 and an end extending outside the bottom to the wire harness 4 as a second control signal wiring terminal 242. The second control signal female contact 240 and the second control signal wiring terminal 242 arc joined integrally through the fixing base 241. The fixing base 241 is embedded in the bottom 200 ofthehouslng20, The power supply female contact 210, the grounding fezna]e contact 220, the first control signal female contact 230, and the second control signal female contact 240 are so designed as to elastically clamp or clip the power supply pin 110, the grounding pin 120, the first control signal pin (i.e., the first exposed portion) 130, and the second control signal pin (i.e., the second exposed portion) when the male connector 1 is fit in the female connector 2.

The power supply wiring terminal 212 and the grounding wiring terminal 222 are joined to a power supply lIne 41 and a grounding line 42 of the wire harness 4. The first control signal wiring terminal 232 and the second control signal wiring terminal 242 are joined to the control signal line 43 of the wire harness 4. All the joints are encapsulated hermetically by a protective cover 40.

The housing 10 of the male connector 1 has a cylindrical side wall 102. The side wall 102 has barb-like protrusions 103 formed thereon. The housing 20 of the female connector 2 has a cylindrical side wall 201. The side wall 201 has hooks 202 formed on an inner edge thereof. When the male connector 1 is inserted into the female connector 2, the hooks 202 will be snap-lit on the protrusions 103 of the housing IC) to make a firm mechanical joint between the male and female connectors 1 and 2, which also ensures electrical connections of the pin contacts 11, 12, 13, and 14 of the male connector I to the socket contacts 21, 22, 23, and 24 of the female connector 2. The protrusions 103 and the hooks 202 are not limited in location and size to the ones, as illustrated in Figs. 1(a) and 1(b), The mechanical joint of the male and female connectors I and 2 may alternatively be achieved by another known means.

The housing 10 of the mate connector 1, as described above has the thim-walled portion 101 through which the pin contact 14 extends, The length L14( of the second control signal pin 140 (i.e., the second exposed portion of the pin contact 14) extending outside the thin-walled portion 101 is, therefore, different from the length Liso of the first control signal pin 130 (i.e., the first exposed pardon of the pin contact 13) extending outside the bottom 100, so that the first control signal pin 130 and the second control signal pin 140 26 have resonance frequencies different from each other.

The configuration of the pins 110, 120, 130, and 140 of the pin contacts 11, 12, 13, and 14 of the male connector 1 is not limited to the one in Fig. 1(a). Similarly, the configuration of the female contacts 210, 220, 230, and 240 of the female connector 2 is not limited to the one in Fig. 1(b)t In other words, the manner in which the pins 110, 120, 130, and 140 are engaged with the female contacts 210,220,230, and 240 is not essential in this embodiment.

Such engagement may be achieved in any known method. For instance, the pins 110, 120, 130, and 140 may be made of a flat conductive strip, while the female contacts 210, 220, 230, and 240 may be made of an elastically deformable clamp with a central slot In which the pins 110, 120, 130, and 140 are to be fit at least partially in contact abutment with two surfaces of the clamp which face each other through the slot. In this case, when the male connector I is fit in the female connector 2 to make an electrical connection between the controlled device 3 and the electronic control unit 5, each of the pin contacts 11, 12, 13, arid 14 will be held or clipped elastically by a. corresponding one of the socket contacts 21, 22, 23, and 24, thereby creating the joints between the pin contacts 11, 12, 13, and 14 and the socket contacts 21, 22, 23, and 24 which are strong enough to withstand a great mechanical impact or vibration and ensuring the stability in transmission of signals between the controlled device 3 and the electronic control wait 5.

Each of the housings 10 and 20 is, as described above, of a hollow cylindrical shape with a bottom, but may be designed to have another shape which achieves a firm mechanical fit of the male connector 1 to the female connector 2.

The beneficial advantages of the structure of the electrical connecting device of this embodiment Will be described below with reference to Figs. 2(a) and 2(b).

The pins 110, 120, 130, and 140 of the pin contacts 11, 12, 13, and 14 of the male connector I are anchored at only one end thereof to the bottom 100 of the housing lOin the form of a.

cantilever beam.

The resonance frequency of each of the pins 110 to 140 of the male connector 1 may, therefore, be derived by solving an equation of motion of a minute part of the pins 110 to 140 under the influence of force when a shear force Facts on the pin contacts 11, 12, 13, and 14 through the housing 10. A sectional area of the pin contacts lit 12, l3,and l4isdefinedasS.

The resonance frequencies fisc and fua of the liz-st control signal pin 130 and the second control signal pin 140 axe given by ( A 2 IE. I I A 1 fri.i BC) where Lisa and L14o are the lengths of the first and second control signal pins 130 and 140, n. is a number of a vibration mode, A is a constant (e.g., 1.875), . is a Young's modulus of the pin contacts 11 to 14, Xis the moment of inertia of a section of the pin contacts 11 to 14, p is the density of the pin contacts 11 to 14, and S is a sectional area of the pin contacts 11 to 14.

It is found that the resonance frequencies fiso and fzo of the first control signal pin 130 and the second control signal pin 140 are inversely proportional to the square of the lengths Lyso and L14o thereof, respectively.

For instance, in the case where the electrical connecting device is used to connect the ignition device (i.e., the controlled device 3) and an engine control unit (Le., the electronic control unit S) for a four-cylinder internal combustion engine of an automotive vehicle, the length L130 of the first control signal pin iSO is 7mm, the length L140 of the second control signal pin 140 is 8mm, vibration of 200Hz occurs while the four-cylinder internal combustion engine is running at 6000rpm, and the resonance frequency fjaq of the first control signal pin 130 is assumed to be 400Hz taking the second harmonic of rotation of the engine into account, the resonance frequency f140 of the second control signal pin 140 is 306Hz.

Specifically, the first control signal pin 130 and the second control signal pin 140, as demonstrated in Fig. 2(b), vibrate at different frequencies. Therefore, when subjected to the external mechanical impact or vibration during transmission of the control signal $10 through the male and female connectors I and 2, the elastic joint of the first control signal pin 130 and the first control signal female contact 230 and the elastic joint of the second control signal pin 140 nd the second control signal female contact 240 will not be opened siniultaneous1y The second control signal pin 140 may be either greater or less in length than the first control signal pin 130. The length 11240 of the second control signal pin 140 may be selected to be smaller than or equal to the square root of 1/1.1 times (Lee, 958%) or greater than or equal to the square root of 1/OS times (i.e., 105.4%) of the length L120 of the first control signal pin 130, so that the resonance frequency f140 of the second control signal pin 140 will deviate by ±10% or more from the resonance frequency fiao of the first control signal pin 130.

t0 The male connector I is as described above, designed to have the thinwafled portion 101 formed in the bottom 100 of the housing 10 of the male connector I to differentiate the lengths Ljso and 11140 of the first and second control signal pins 130 and 140 in order to differentiate the resonance frequencies fix and f140 of the first and second control signal pins 130 and 140. This is based on the fact that the resonance frequency of an object will change inversely proportional to the length of the object, so that the resonance frequencies.1230 and f140 of the first and second control signal pins 130 and 140 may be differentiated easily by selecting the lengths 11130 and 11140 of the first and second control signal pins 130 and 140 to be different from each other. The first and second control signal pins 130 and 140 have top ends, as can be seen from Pig. 1(a), which lie flush with each other, in other words are arrayed in alignment with each other in a direction perpendicular to the length of the pin contacts 11 to 14 (i.e., an axial direction of the male connector 1), thus eliminating the need for altering the structure of the female connector 2 in order to differentiate the resonance frequencies fiso and ff40 of the first and second control signal pins and 140+ The differentiation betweeA the resonance frequencies fiso 8 and ff40 of the first and second control signal pins 130 and 140 may alternatively be achieved by differentiating values of at least one of the density p, the sectional area S, and/or the Young's modulus E thereOf.

For example, the first and second control signal pins 130 and 140 may be configured to be different in width or thickness from each other, so that they will have different sectional areas S,30 and S.r40 which establish the different resonance frequencies 1230 and fzw+ The first and second control signal terminals 13 and 14 may alternatively be made of materials different from each other to have 16 different values of the density p or the Young's modulus E thereof.

When the first and second control signal pins 130 and 140 are designed to be different in the density p, the sectional area S, or the Young's modulus E, it will cause a difference between the resonance frequencies fiso and fjo to be smaller than when the lengths Lisa and £140 are selected to be different from each other because the resonance frequencies fiso and ff40 are, as can be seen from Eqs. 1) and 2), in proportion or inverse proportion to the square root of the density p, the sectional areaS, or the Young's modulus B. Figs. 3(a) and 3(b) demonstrate an example where the ignition device 3 (i.e, the controlled device) and the engine control system S (i.e+, the electronic control unit) are electrically coupled together through the electrical connecting device (i.e., the male and female connectors 1 and 2) and the wire harness 4.

The ignition device 3, as illustrated in Fig. a(a) receives a high-freqtlericy ignition control signal JGt in the form of the control signal 514 as oscillated and outputted by the engine control system 5. The engine control system 5 switches the control signal SKI between an on-level and an off-level. The ignition device a includes an igniter 31,an ignition coil 32, a rectifying device 33, and a spark plug 34. The igniter 31 works as a switching device which is opened or closed in response to the on-level or the off4evel of the control signal SIC. The voltage +8, as provided by a storage battery mounted in the vehicle, is inputted through the power supply line 41 to the ignition coil 32 as the primary voltage. The ignition coil 32 is responsive to the opening or closing of the igniter 31 to produce the i secondary voltage V2 higher than the primary voltage. The secondary voltage V2 is rectified by the rectifying device 33. The spark plug 3415 responsive to application of the secondary voltage V2 to produce an electric spark within the combustion chamber of the engine to ignite the air/fuel xnizthre. The housing 10 of the male connector 1 has a fitting feature 104 (e.g., a groove) formed in the side wall of the bottom 100. The fitting feature 104 engages the housing 30 of the ignition device 30 to make a mechanical joint of the male connector 1 to the ignition device 30.

The power supply wiring terminal 112 of the male connector 1 is connected to the primary winding of the ignition coil 32. the grounding wiring terniinal 122 is connected to a ground side (i.e., the source) of the igniter 3]. and a ground side of the spark plug 34.

The control signal wiring terminal 132 is connected to a drive terminal (i.e., the gate) of the igniter 31. the input terminal (i.e., the drain) of the igniter 33. is connected to the power supply wiring terminal 112 along with the primary winding of the ignition coil 32.

The male connector 1 is fit in the female connector 2. The power supply pin 110, the grounding pin 120, the first control signal pin 130, and the second control signal pin 140 are placed in electric elastic contact with the power supply female contact 210, the to grounding female contact 220, the first control signal female contact 230, and the second control signal female contact 240, respectIvely, Within the housings 10 and 20 of the male and female connectors 1 and 2. For instance7 the power supply female contact 210, the grounding female contact 220, the first control signal female contact 230, and the second control signal female contact 240 are each made of a spring member in the form of a clip to hold the power supply pin 110, the grounding pin 120, the first control signal pin 130, and the second control signal pIn 140 elastically, thereby making the transmission paths strong enough to withstand mechanical impact or vibration.

The power supply wiring terminal 212 and the grounding wiring terminal 222 are joined to the power supply line 41 and the grounding line 42, respectively. The first control signal wiring terminal 232 and the second control signal wiring terminal 242 are both joined to the control signal line 43, The ignition control signal JOt is inputted from the engine control system S to the ignition device 3 through two control signal transmission paths: the first being formed through the joint of the first control signal pin 130 and the first control signal female contact 230, and the second being formed through the joint of the second & control signal pin 140 and the second control signal female contact 240.

The controlled device.to which the male connector 1 is attached is not limited to the ignition device 3, as illustrated in Fig. 3(a), which is of an inductive discharge type using the ignition coil 32, but may be a capacitor discharge Ignition (CDI) system.

The engine control system 5 is implemented by an electronic control unit (ECU) and equipped with a power controfler (PWR CNT) SI, a central processing unit (CPU) 52 a peripheral logic circuit (LOG IC) 53 a memory (MEM) 54, and an input/output interface (1/0) 55 which are disposed inside a housing sop The engine control system 5 is coupled with the ignition device 3 through the electrical connecting device made up of the male and female connectors I and 2 and the wire harness 4.

The electrical connecting device may also be used to connect between sensors (not shown) and peripheral devices.

The male connector 1. is joined at the fitting feature 104 to the housing 50 of the engine control system 5.

The I/O interface 55 has a. power supply terminal +B connected to the power supply wiring terminal 112 and a ground 2 terminal GEl) connected to the grounding wiring terminal 122. The 1/0 interface 55 also has a control signal output terminal connected to the first control signal wiring terminal 132. The CPU 51 produces the ignition control signal. lOt based on an operating condition of the engine and outputs it to the 1/0 interface 55.

The ignition control signal IGt, as inputted to the I/O interlace 55, is outputted to the ignition device 3 through two control signal transrriissiort paths: the first being formed through the joint of the first control signal pin 130 and the first control signal female contact 230, and the second being formed through the joint of the second control signal pin 140 and the second control signal female contact 240.

The beneficial advantages of the structure of the electrical connecting device in the above example will be described below with reference to Figs. 4(a), 4(b), and 4(c).

When the engine control system 5 and the ignition device 3 as are joined through the male and female connectors 1 and 2 without being subjected to any external physical impact or vibration, the waveform of the ignition control signal JOt outputted from the engine control unitS is, as illustrated in FIg. 4(a), identicaL just with that received by the ignition device a. When the ignition control signal IGt is switched between the on and offlevel, it will cause the secondary voltage V2, as developed at the ignition coil 32 of the ignition deviceS, to be stepped up and applied to the spark plug 34 cyclically. The spark plug 34 then produces a sequence of electric sparks.

Fig. 4(b) demonstrates a äomparative example where the engine control systemS and the ignition device 3 are joined through conventional male and female connectors. When a joint of a pin contact and a socket contact of the male and female connectors through which the ignition control signal lOt is transmitted is opened by a big Impact or vibration instantaneously, so that the ignition control signal rOt is switched in the ignition device 3 undesirably to the off-level for, for example, 10pm such an instantaneous change in level of the ignition control signal LOt may appear as a long-duration noise which can't be removed by a noise filter. This will cause the secondary voltage 1⁄2 to be developed which is higher in level than required to induce the spark plug to generate the spark, which may lead to the pre-ignition where the air/fuel mixture is ignited at an incorrect timing.

Fig. 4(e) demonstrates an example where the male and female connectors 3. and 2 are subjected to a big impact or vibration.

For example, when the elastic joint (ie., a first transntission path) of the first control signal pin 130 and the first control signal female contact 230 is opened. undesirably, the elastic joint (i.e., a second transmission path) of the second control signal pin 140 and the second control signal female contact 240 is hardly opened. In other words, there is a very low possibility that the first and second transmission paths are cut simultarteously when the male and female connectors I and 2 are subjected to the impact or vibration because the resonance frequencies fist and f240 of the first and second control signal pins 130 and 140 are different from each other.

If the male and female connectors I and 2 has undergone a great degree of impact which Will break the first and second transmission paths, times when the first and second transmission paths are cut will be slightly offset from each other, so that the phase of the ignition control signal JOt will be different between when. the first transmission path is cut and when the second transmission path is cut. For instance, a difference in time between when the first transmission path is cut and when the second transmission path is cut is as short as 5ps or less, so that a resulting change in level of the ignition control signal lOt may be reduced through a noise filter to a negligible level.

Accordingly, even when the change in level of the ignition control signal JOt results in discharge from the secondary winding of the ignition coil 32, the time duration of the discharge Is very short, so that no spark is produced by the spark plug 34, thereby eliminating the possibility of the pre4gaition and ensuring the is stability in igniting the air/fuel mixture in the engine4 Modifications of the male and female connectors 1 and 2 will be described below with reference to Figs. 5(a4) to 6(c-3). Note that the same reference numbers except suffixes of lower-case letters refer to substantially the same parts.

The male connector 115, as described abov; designed to have the thin-walled portion 101 formed in the bottom 100 to make the length Luo of the first control signal pin 140 greater than the length Lisa of the first control signal pin 130 in order to differentiate the resonance frequencies fsso and fs of the first and second control signal pins 130 and 140, but may be, as illustrated in Figs. 5(a-1} and 5(a2), configured to have a housing Wa with a bottom lOOa which has formed therein a thick-walled portion lOla, The thick-walled portion lola is grea.ter in thickness than a major portion of the bottom iOOa+ The male connector Ia has a pin contact l4a (i.e., the second control signal terminal). The pin contact 14e. is macis up of a second control signal pin 140a and a ±bdng base 14 Ia, The fixing base 141a is embedded in the thick-walled portion IOta and leads to the fixing base 131 of the pin contact 13. The length of a portion of the pin contact 14 which protrudes from the thick-walled portion lOla (i.e., the length LJ4Q of the second control signal pin 140a) is, therefore, smaller than the length Lisa of the first control signal pin ISO, thereby differentiating the resonance frequencies f230 and f;40 of the first and second control signal pins 130 arid 140a.

The female connector 2 of the same structure as in Fig. 1(b) may be used as a mating connector for the male connector is, but alternatively be designed to have a recess formed in the bottom 200 to accommodate the thick-walled portion lOla to achieve a close fit of the male connector Ia in the female connector 2.

Fig. 5(b-1) arid 5(1>2) illustrates a male connector lb. The male connector lb includes two discrete housing lOb 1 and lOb2 The housing lObi has the pin contacts I Ib, 12b, and 131, (i.e., the power supply terminal, the grounding terminal, and the first control signal tenninal) disposed therein. The housing 10b2 has the pin contact 141, (i.e., the second control signal terminal) disposed therein4 The pin contact 13b includes the first control signal pin lSOb and the first control signal wiring terminal 132b. The pin contact 14b includes the second control signal pin 14Gb and the second control signal wiring terminal l42b The first and second control signal wiring terminals 132b and 142b are joined together through a connecting wire 15 and then coupled to the signal input & terminal SIC; of, for example, the controlled device S through the control signal line 300, as illustrated in Fig. 1(a). The first and second control signal wiring terminals 132b and 142b may alternatively be joined directly to the signal input terminal $10, respectively1 The housing 1GM has the bottom 100b11 The housing 10b2 has the bottom 100b2. The bottom lOObl and the bottom 100b2 are different in thickness from each other to differentiate the resonance frequencies fiaa and f140 of the first and second control signal pins 130b and 14Gb.

The male connector lb may be implemented by a combination of an existing three-pin connector and a one-pin connector which is shaped to have a. plurality of transmission paths along with the threepin connector through which the control signal Sf0 passes1 The electrical connecting device of this modification includes discrete female connectors 2b1 and 2b2 as mating connectors for the male connectors lbl and 1b2. The female connector 2W!. has the same socket contact 23 as in Fig. 1(b) which is equipped with the first control signal wiring terminal 232h (not shown). The female connector 2b2 has the same socket contact 24 as in Fig. 1(b) which is equipped with the second control signal wiring terminal 242b (not shown)1 The first and second control signal wiring terminals 232b and 242b are connected electrically to the control signal line 43.

The bottom 100b2 of the housing 10b2 in which the pin contact 14b is disposed is smaller in thickness than the bottom lOObi of the housing lObi in which th& pin contacts 1 lb, 12b, and 13b are disposed, but may conversely be designed to be greater in thickness than the bottom 100b14 The bottom lOObI of the housing lObl and the bottom 100b2 of the housing 10b2. may alternatively be designed to have the same thiclcness4 The housing lObi and the housing 101,2 are, however, different in size from each other and thus have different resonance frequencies. This differentiates the resonance frequencies fiso and 1140 of the first and second control signal pins 130b and 140b from each other.

Fig4 5(c-1) and 5(c-2) illustrate a male connector lct The male connector le, like In Fig4 1(a), has the housing 100 with the thinwaUed portion 10 Ic. The male connector to is equipped with the pin contact 14c made up of the second control signal pin 140c and the fixing base 141c. The fixing base 141c is embedded in the thin-walled portion bit and extends substantially perpendicular to the second control signal pin 140c and the lengths of the pin contacts 11, 12, and 13, thereby enhancing the resistance of the pin contacts 13 arid 14c to the impact or vibration from different directions and ensuring the reliability in connection of the pin contacts 13 and 14c to the socket contacts 23 and 24 of the female 2S contact 2, as illustrated in Fig. 1(b). The pin contact 14c is made of a flat strip. The width of the pin contact 14c, as illustrated in Fig. 5(c-1), may be oriented perpendicular to those of the pin contacts 11, 12, and 13.

Figs4 6(al) arid 6(ar2) illustrate a male connector Id The male connector Id, like in Figs. 5(1>-i) and 5(b-2), includes two discrete housing lOdi and 10d2. The housing lOdi has the pin contacts lid, 12d, and 13d disposed therein. The housing 10d2 has the pin contact 14d disposed therein. The pin contact 13d includes the first control signal pin 1 30d and the first control signal wiring terminal 132ct. The pin contact lid, 12c1, 18d, and 14d are each made of a flat strip. The width of the pin contact 14d, as illustrated in Fig. 6(a-l), may be oriented perpendicular to those of the pin contacts lid, 12d, and l3d. The pin contact 14b includes the second control signal pin 140d and the second control signal wiring terminal 142d. The first and second control signal wiring tenainals 132d and I 42b are joined together through the connecting wire 15 and then coupled to the signal input terminal 310 of, for example, the controlled device 5 through the control signal line 300, as illustrated in Fig. 1(a). The first and second control signal wiring terminals i32d and 142d may alternatively be joined directly to the signal input terminal SIC, respectively. The housing lOdi has the bottom lOOdI. The housing 10d2 has the bottom lOCd2. The bottom IQOCIl and the bottom 100d2 are different in thickness from each other to differentiate the resonance frequencies fwo and f240 of the first and second control signal pins 130d and l4Od.

The bottom lOOdi of the housing lOdi and the bottom 100d2 of the housing lOd2 may alternatively be designed to have the $2 sarrie thickness. The housing lOdl and the housing 10d2 are, however, different in size from each other and thus have different resonance frequencies. This differentiates the resonance frequencies fiso and f140 of the first and second control signal pins s 130d and 140d from each other. The structure of the male connector Id enhances the resistance of the pin contacts lad and 14d to the impact or vibration from different directions and ensuring the reliability in conneàtion of the pift àbntacts 1 3d and 14d to the socket contacts 23 and 24 of the female contact 2, as illustrated in Fig. 1(b).

The electrical connecting device of this modification includes a female connector 2d (not shown) which includes discrete housings 20d1 arid 20d2 (not shown) as mating housings for the housings lOd]. and 10d2. The housing 20d1 has the same socket contact 23 as in Fig. 1(b) which is equipped with the first control signal wiring terminal 232d (not shown) The housing 20d2 has the same socket contact 24 as in Fig. 1(b) which is equipped with the second control signal wiring terminal 242d (not shown). The first and second control signal wiring terminals 232d and 242d are connected electrically to the control signal line 43.

Figs. 6(b-l), 6(b-2), and 6(b3) illustrate a male connector le The male connector le has the housing We which is substantially square in cross section. The housing lOe has the bottom boo in which the pin contacts lie, 12; 13e, and 14d (i.e., the power supply terminal, the grounding terminal, the first control signal terminal, and the second control signal terminal) are arrayed in two rows and 8$ two columns, in other words, in a 2x2 matrix. The housing We includes the bottom WOe. The bottom lOOe has a thin-walled portion lOb in which the pin contact 14e is disposed1 The pin contacts lie, 12; and 13e are disposed in a major portion of the bottom 10Cc other than the thin-walled portion lOle. the pin contact lie is made up of the power supply pin 11 Oe and the power supply wiring terminal ii 2e. The pin contact 12e is made up of the grounding pin 12Cc and the grounding wiring terminal 122e. The pin tontact 13e is made up of the first control signal pin iSOc and IC the first control signal wiring terminal 132e. The pin contact l4e is made up of the second control signal pin 140e and the fixing base 14 Ic. The length of a portion of the pin contact 14e which protrudes from the thick-wailed portion 10Th (i.e., the length L140 of the second control signal pin 14Cc) is, therefore, greater than the length Lzaoof the first control signal pin 13Cc, thereby differentiating the resonance frequencies fzso and /140 of the first and second control signal pins 13Cc and 140e, The fixing base 14th extends perpendicular to the second control signal pin 140e and connects with the fixing base 131 e of the pin contact 13e. The fixing base 141c may be formed to have a length extending outside the bottom 10Cc and joined to the first control signal wiring terminal 132e outside the housing iCe.

The electrical connecting device of this modification includes a female connector 2e (not shown) designed to have the socket contacts (i.e., the power supply terminal, the grounding terminal, the first control signal tenninal, and the second control signal terminal) 21e, 22e, 23e, and 24e which are arrayed in a. 2'c2 matrix.

The first and second control signal wiring terminals 232e and 242e of the socket contacts 23e and 24e are connected electrically to the control signal line 43.

Figs. 6(c-1), 6(c-2), and 6(c3) illustrate a male connector 11 The male connector If, like in Figs. 6(a1) and 6(a-2), includes two discrete housing 1011 anti 1012. The housing 1011 has the pin contacts 1 11 and 121 disposed therein. The housing 1012 has the pin contacts 131 and 141 disposed therein. The contact pins 111 to 141 are each made of a flat strip. Widths of the pin contacts ill and 121 are oriented in alignment with each other in a horizontal direction, as viewed in the drawing, while widths of the pin contacts iSland 141 arc oriented in alignment with each other in a vertical direction, as viewed in the drawing. In other words, the widths of the pin contacts 1 11 and 121 are oriented in a direction different from that in which the widths of the pin contacts iSland 141 are oriented.

The housing 1012 has two bottoms 1001 and 1011 in which the pin contacts ISland 141 are disposed respectively. The bottoms 1001 and 1011 are different in thickness from each other1 For instance, the thickness of the bottom 1011 is smaller than that of the bottom 1001. This differentiates the resonance frequencies f13c7 and fs of the first arid second control signal pins 1301 and 1401.

The pin contact 151 may alternatively be disposed in the housing 1011, while the pin contact 141 may be disposed solely in the housing 1012. The first and second control signal wiring terminal 1321 and 1421 of the pin contacts 131 and 141 are both joined to the control signal line 300, as illustrated in Pig. 1(a). The first and second control signal wiring terminal I 321 and 1421 may alternatively be coupled together through the connecting wire 15.

In this case, either one of the first and second control signal wiring terminal 132f and 142f is connected to the control signal line 300.

The electrical connecting device of this modification includes a female connector 21 (not shown) which includes discrete housings 20f1 and 20f2 (not shown) as mating housings f9r the housings 1011 and 1012. The housing 20f1 has the caine socket contacts 21 and 22 as in Fig. 1(b). The housing 2012 has the same socket contacts 23 ind 24 as in Fig. 1(b).

Figs1 7(a), 7(b) and 7(c) illustrate modifications of an elastic joint of each of the power supply pin 110, the grounding pin 120, the first control signal pin 130, and the second control signal pin 140 is and a corresponding one of the power supply female contact 210, the grounding female contact 220, the first control signal female contact 230, and the second control signal female contact 240. The structures, as illustrated in Figs. 7(a) to 7(c);, may be used in the modifications of the electrical connecting devices, as described above.

In each of Figs. 7(a) to 7(c), the left-hand view illustrates, for example, the power supply pine 110 and the power supply female contact 210 before being joined together. The right-hand view illustrates the power supply pine 110 and the power supply female contact 210 after being joined together. White arrows indicate directions in which pressure acts on the joint. The power supply pin 110, the grounding pin 120, the first control signal pin 130, and the second control signal pin 140 are identical in structure with each other4 Similarly, the power supply female contact 2107 the grounding female contact 220, the first control signal female contact 230, and the second control signal female contact 240 are identical in structure with each other4 For the brevity of explanation, the following discussion will refer only to the power supply pin 110 and the power supply female contact 2104 The power supply pin. 110 and the power supply female 11) contact 210 are made of a flat conductive strip and, as described above, protrude from the bottoms 100 and 200 of the housings 10 and 20, respectively. The power supply female contact 210 in each of Figs4 7(a), 7(b), an 7(c) is designed to clip at least two opposed faces of the power supply pin 110 elastically from opposite directions.

In other words, when the tnale connector 11$ fitted in the female connector 2, the power supply pin 110 is inserted tightly into the power supply female contact 210 and then connected elastically at a plurality of points, lines or areas of contact with the power supply female contact 210. When the power supply pin 110 and the power supply female contact 210 are exposed to external impact or vibration, the power supply pin 110 will be deflected4 This causes the pressure exerted on any one of' the contact points, lines, or areas to be decreased, while the pressure on another of them will be increased4 The electrical connection of the power supply pin 11.0 arid the power supply female contact 210 is, therefore, assured at least one of the contacts points, lines, or areas4 Either one of the pressures exerted on the joint of the power supply pin 110 and the power supply female contact 210 from opposite directions works to absorb the other when the power supply pin 110 is deflected, thereby suppressing the deflection, The power supply pin 110 of the pin contact 1]. which is to be clipped by the power supply female contact 210 is, as described above, made of a flat plate member * In the example of Fig. 7(a), the power supply female contact 210 of the socket contact 21 is made of a flat strip which has a T-shapecl top end, as indicated by a broken 1ine Sides of the T-shaped top end are, as indicated by arrows7 curled in directions facing each other into a female crimp terminal into which the power supply pin 110 is to be inserted.

hi the example of lDig, 7(b), the power supply female contact 210 is made of a flat strip which is folded several times into a S' or W-shaped clip 2 Wa which forms art elastic clip through which the power supply pin 110 is to be inserted.

In the example of Fig. 7(c), the power supply female contact 210 is made of a flat strip with a T-shaped top end. The T-shaped 21) top end is rounded into a hollow cylinder 2 lOb with a slit 65.

In each of the examples of Fig. 7(a) to 7(c), when the power supply pin 110 is inserted into the power supply female contact 210, the power supply female contact 210 serves to hold opposed surfaces of the power supply pin 110 elastically.

While the present invention has been disclosed in terms of the preferred embodiments in order to facilitate better

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understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention. Therefore, the invention should be understood to include all possible embodiments and modifications to the shown embodiments which can be embodied without departing from the principle of the invention as set forth in. the appended claint For instance, the power supply pin 110 of Fig. 7(c) may alternatively be shaped into a cylinder or a polygonal column.

The bottom 100 of the housing 10 of the male connector 1, as described above, has the recess (i.e., the thin-wailed portion 101) to differentiate the lengths L230 and L140 of the first and second control signal pins 130 and 140 (iA., the first and second exposed portions of the pin contacts 13 and 14) in order to differentiate the resonance frequencies frno and fvw of the first and second control signal pins and 140, but may alternatively be designed to differentiate the lengths Lzao and L140 of the first and second control signal pins 130 and 140 from each other without having the recess formed in the bottom 100 if it is possible to alter the female connector 2 (i.e., the socket contacts 23 and 24) into a shape which ensures the stability in fitting on the male connector 1.

The male and female connectors). and 2, as described above, have the pin contacts 13 and 14 and the socket contacts 23 and 24 which are joined to create the two signal transmission paths through which the control signal SIC) passes, but may alternatively be designed to have three or more signal transmission paths. For instance, two additional transmission paths may be provided for connection with the grounding lInes 42 and 121 Four transmission paths may also be procvided two of which are connected to the grounding lines 42 and 122 and two of which are connected to the control signal lines 43 and 300