ELECTRICAL PROTECTION SYSTEMS

Abstract: Electrical protection systems which contain a resistor and a relay in series with a load, and a PTC device which is connected in parallel with the load and in series with a coil which controls the relay. The PTC device is thermally linked to the resistor, and in consequence the relay opens if an overcurrent heats the resistor. The relay coil can be activated remotely in order to close the relay, for example by means of an RC circuit. Such protection systems can be combined with other components to provide diagnostics capability.

Description: -1- ELECTRICAL PROTECTION SYSTEMS This invention relates to electrical systems which contain positive temperature coefficient (PTC) circuit protection devices, particularly such systems in automobiles and other wheeled vehicles. PTC devices are well known. Particularly useful devices contain PTC elements composed of a PTC conductive polymer, i.e. a composition comprising an organic polymer and, dispersed or otherwise distributed therein, a particulate conductive filler, e.g. carbon black, a metal or a conductive metal compound. Such devices are referred to herein as polymer PTC, or PPTC, devices. Other PTC materials are also known, e.g. doped ceramics, but are not as generally useful as PTC conductive polymer, in particular because they have higher resistivities. PTC devices can be used in a number of different ways, and are particularly useful in circuit protection applications, in which they function as remotely resettable fuses to protect electrical components from excessive currents and/or temperatures. Components which can be protected in this way include motors, batteries, loudspeakers and wiring harnesses in automobiles. The use of PPTC devices in this way has grown rapidly over recent years, and continues to increase. Reference may be made for example to U.S. Patent Nos. 4,237,441, 4,238,812, 4,315,237, 4,317,027, 4,426,633, 4,545,926, 4,689,475, 4,724,417, 4,774,024, 4,780,598, 4,800,253, 4,845,838, 4,857,880, 4,859,836, 4,907,340, 4,924,074, 4,935,156, 4,967,176, 5,049,850, 5,089,801, 5,378,407, 5,451,919, 5,451,921, 5,645,746, 5,831,510, 5,852,397 and 5,864,281. More recently, it has been proposed to combine PTC devices with other electrical components to provide circuit protection systems which respond to faults in ways which make use of the characteristics of both the PTC device and the electrical component. Reference may be made for example to U.S. Patent Nos. 5,666,254 and 5,689,395, and to International Publication Nos. WO 97/10636, WO 97/20372, WO 98/31084, WO 98/02946, WO 98/02947 and WO 98/56014, all of which International Publications were published after the priority date of this application. PCT Publication Nos. WO 98/02946 and WO 98/02947 describe protection systems which comprise a sensor element (typically a resistor) and a circuit interruption element (typically a relay) in series with the load, and a control element (typically a PTC device in parallel with the sensor element) which links the sensor element and the circuit interruption element so that an overcurrent is detected by the sensor element, and causes a change in the control element, which in turn causes a change in (typically opens) the circuit interruption element. Depending on the arrangement of these and other components, the system can (a) latch in an open state, either with or without a trickle current to keep the PTC device in a tripped condition, or (b) reclose if the overcurrent has gone away or cycle between open and closed positions if the overcurrent remains. PCT Publication No. WO 98/56014 describes particularly useful devices for use in the protection systems of PCT Publication Nos. WO 98/02946 and WO 98/02947. In the design of electrical systems for automobiles and like complex systems, it is usual for an electronic control module (ECM) to be connected to the electrical system through a connector bar having a number of separate contacts. The normal application of modular construction principles means that the number of contacts cannot easily be changed, and competition for space dictates that the number of contacts be kept to a minimum. It is, therefore, highly desirable for each electrical system connected to a connector bar to make use of a minimum number of contacts, preferably a single contact. For example, U.S. Patent No. 5,645,746 refers to the possibility of monitoring the state of a PTC device by means of an LED or other voltage sensor; this works well, but requires the use of two positions on the connector bar. In many electrical systems, it is desirable to incorporate diagnostics which will signal the condition of the system, at least when there has been a malfunction. Particularly is this so in automobiles and like complex systems in which the occurrence of a malfunction may not be immediately apparent. We have found that the protection systems described in PCT Publication Nos. WO 98/02946 and WO 98/02947 can be modified and combined with other components to provide both fault protection and diagnostic capabilities which do not depend upon manual interaction. For brevity and convenience, protection systems of the kind disclosed in PCT Publication Nos. WO 98/02946 and WO 98/02947 are referred to herein as TLPRR systems (TLPRR being an acronym for Thermally Linked PTC device, Resistor and Relay). The first step in making use of TLPRR systems in diagnostics is to modify the TLPRR system disclosed in the earlier applications by replacing the momentary-on switch disclosed in those applications by a remotely-operated system which will activate the relay coil and thus close the relay contacts. Such a modified TLPRR system is referred to herein as a TLPRR (Mod) system. This modification can result in significant improvements even when not combined with diagnostic capabilities, and as such it forms an independent part of the present invention. Preferably the remotely- operated system comprises a resistor-capacitor (RC) network or other electrical system which occupies only a single position on a connector bar at a power distribution side. However, it is also possible to use a two-line system which activates the relay coil simply by passing a current through it for a sufficient time. Another important advantage of an RC circuit is that it can be designed to produce other useful functionality. The capacitor can be charged up by closing a switching unit at the return side of the coil (also known as low-side switching), and must have a size such that its discharge provides current to the relay coil long enough to close the relay contacts. Thereafter, the capacitor is charged up to the system voltage and acts as an open switch under normal operating conditions. If an overcurrent occurs, tripping the PTC device and opening the relay contacts, the sizes of the capacitor and the resistor will be significant factors in determining the time which will elapse before the TLPRR (Mod) attempts to reset. Thus the capacitor and resistor can be selected so as to result in a desired delay. Another important advantage of the RC network is that it protects the relay contacts if, when the system is turned on, there is a high current short circuit which sufficiently drops the system voltage to a level below the required relay activation voltage. In this case, the RC network will not have enough voltage to charge up the capacitor sufficiently to close the relay. Thus, in a first aspect, the present invention provides an electrical protection system which can be connected between an electrical power supply and an electrical load to form an operating circuit, the operating circuit having an on state and an off state and comprising a current carrying line and a return line, and which when so connected protects the circuit from overcurrents, the system having a normal operating condition and a fault condition, and comprising: a. a set of relay contacts which, when the system is so connected, is connected in series between the power supply and the load, and has: i. a closed state which permits the flow of a normal current, IN ORMAL , when the system is in the normal operating condition, and ii. an open state which permits the flow of at most a reduced current, substantially less than I NORMAL , when the system is in the fault condition; b. a resistive device which, when the system is so connected, is connected in series with the set of relay contacts and the load, and has i. a normal state, when the current in the system does not exceed the normal current, I NORMAL , by a predetermined current amount, and ii. a fault state, when the current in the system exceeds the normal current, I NORMAL , by the predetermined amount; c. a control element which comprises a series combination of i. a PTC device thermally coupled with the resistive device; and ii. a relay coil coupled with the relay contacts; the series combination being connected across the power supply, between the current carrying line and the return line, with the PTC device connected to the current carrying line and the relay coil coupled to the return line; the set of relay contacts changing from its closed state to its open state, thereby causing the system to change from its normal operating condition to its fault condition, when the resistance of the PTC device increases by a predetermined resistance amount in response to the resistive element changing from its normal state to its fault state; and d. a relay coil current supply means which enables current to be supplied to the relay coil, so that if the relay contacts are open, the only way in which they can be closed is by supplying current to the relay coil through the relay coil current supply means. As illustrated in Figure 1, this invention provides, at a power distribution side, an electrical protection system 10 which is connected between an electrical power supply V+ and an electrical load R L to form an operating circuit, the operating circuit having an on state and an off state and comprising a current carrying line 12 and a return line 14, and which when so connected protects the circuit from overcurrents, the system having a normal operating condition and a fault condition, and comprising: -5- a. a set of relay contacts 16, 17 and 18 which, when the system is so connected, is connected in series between the power supply V+ and the load R L , and has: i. a closed state which permits the flow of a normal current, IN ORMAL , when the system is in the normal operating condition, and ii. an open state which permits the flow of at most a reduced current, substantially less than I NORMAL , when the system is in the fault condition; b. a resistive device R g which, when the system is so connected, is connected in series with the set of relay contacts 16, 17 and 18 and the load R L , and has i. a normal state, when the current in the system does not exceed the normal current, I N O RMAL , by a predetermined current amount, and ii. a fault state, when the current in the system exceeds the normal current, I NORMAL , by the predetermined amount; c. a control element 20 which comprises a series combination of i. a PTC device 24 thermally coupled with the resistive device R§; and ii. a relay coil 25 coupled with the relay contacts; the series combination being connected across the power supply, between the current carrying line and the return line, with the PTC device connected to the current carrying line and the relay coil coupled to the return line; the set of relay contacts changing from its closed state to its open state, thereby causing the system to change from its normal operating condition to its fault condition, when the resistance of the PTC device increases by a predetermined resistance amount in response to the resistive element changing from its normal state to its fault state; and d. a relay coil current supply means, such as RC network 28, which enables current to be supplied to the relay coil, so that if the relay contacts are -6- open, the only way in which they can be closed is by supplying current to the relay coil through the relay coil current supply means. A TLPRR (Mod) system can advantageously be used as part of a diagnostic system, especially in an electrical system containing a connector bar 31 through which one or more of a number of electrical systems (one or more of which can be TLPRR (Mod) systems) can be separately connected to an electronic control module (ECM) 32 at the control side. The ECM, upon command V Command , can close or open a switch 34. The switch 34 controls a line 35 (called herein the "diagnostic line") which is connected to the return side of the relay coil through a series resistor R D (called herein the "diagnostic resistor"). The switch is preferably an FET, particularly an FET with certain level of diagnostics capabilities, e.g. over-voltage, over-temperature, over-current conditions, but any other type of solid state switch, or even a mechanical relay, can be used. By examining the voltage V SENSE on me diagnostic line, and knowing the system voltage delivered by the FET (or other switch), it is possible to diagnose the condition of the main load circuit. V SENSE can be sensed by the ECM 32 and indicated by an LED 36. Thus the voltage V S E NSE on ^ e diagnostic line will be one of three values, namely (1) the full system voltage (e.g. nominally 12 volts in a conventional automobile), if the main load circuit is in a normal off state; (2) an intermediate voltage (set by the relative resistances of the diagnostic resistor and of the relay coil) if the main load circuit is in a normal operating state and (3) substantially zero if (i) the relay coil has failed, (ii) there has been a fault which has caused the PTC to trip and the relay contacts to open, or (iii) there is a high current short circuit. This information can, if desired, be stored in the ECM and used for system inquiry either during assembly of an electrical system, for maintenance of a system which is in use, or to disable a faulty system by turning off the FET until the fault condition is corrected, or to indicate to a user the system fault condition by using the LED 36, for example. Thus as illustrated in Figure 1, the second aspect of this invention provides an electrical system which comprises ( 1 ) an electronic control module (ECM), (2) a switch controlled by the ECM, (3) a TLPRR (Mod) system according to the first aspect of the invention, (4) a diagnostics resistor which is connected in series between the switch and the protection system, and (5) means for determining the voltage on a line between the diagnostics resistor and the protection system, the relay coil and the relay contacts being operable by a voltage which is the system voltage minus the voltage dropped across the diagnostics resistor. The resistance of the diagnostic resistor can be for example 0.7 to 1.3 times the resistance of the relay coil. If the relay coil is designed to close the relay contacts only when the full system voltage is dropped across the coil (as will usually be the case), then the insertion of the diagnostic resistor R D will make it impossible to close the relay contacts. This difficulty can be overcome in two different ways. The first way is to use a relay coil/contact arrangement which will be operated by the residue of the system voltage which is not dropped across the diagnostics resistor R D . The second way is, as illustrated in Figure 2, to put a capacitor C D in parallel with the diagnostic resistor R D , thus creating an RC network which will enable the relay to be closed upon command. As illustrated in Figure 2, a third aspect of this invention provides an electrical system which comprises ( 1 ) an electronic control module (ECM) 32, (2) a switch 34 controlled by the ECM, (3) a TLPRR (Mod) system according to the first aspect of the invention at the power distribution side, -8- (4) an RC network 38 which is connected in series between the switch and the protection system, and (5) means for determining the voltage V SENSE on a ^ ne 35 between the RC network and the protection system. The circuitry at the control side can also be used in conjunction with other circuit configurations at the power distribution side such as illustrated in Figures 2, 3, 5-8 and 10 of PCT Publication No. WO 98/02946.

Claims: -9- CLAIMS 1. An electrical protection system which can be connected between an electrical power supply and an electrical load to form an operating circuit, the operating circuit having an on state and an off state and comprising a current carrying line and a return line, and which when so connected protects the circuit from overcurrents, the system having a normal operating condition and a fault condition, and comprising: a. a set of relay contacts which, when the system is so connected, is connected in series between the power supply and the load, and has: i. a closed state which permits the flow of a normal current, I NORMAL , when the system is in the normal operating condition, and ii. an open state which permits the flow of at most a reduced current, substantially less than I NOR M AL , when the system is in the fault condition; b. a resistive device which, when the system is so connected, is connected in series with the set of relay contacts and the load, and has i. a normal state, when the current in the system does not exceed the normal current, I NORMAL , by a predetermined current amount, and ii. a fault state, when the current in the system exceeds the normal current, I NORMAL , by the predetermined amount; c. a control element which comprises a series combination of i. a PTC device thermally coupled with the resistive device; and ii. a relay coil coupled with the relay contacts; the series combination being connected across the power supply, between the current carrying line and the return line, with the PTC device connected to the current carrying line and the relay coil coupled to the return line; the set of relay contacts changing from its closed state to its open state, thereby causing the system to change from its normal operating condition to its fault condition, when the resistance of the PTC device increases by a predetermined resistance amount in response to the resistive element changing from its normal state to its fault state; and d. a relay coil current supply means which enables current to be supplied to the relay coil, so that if the relay contacts are open, the only way in which they can -10- be closed is by supplying current to the relay coil through the relay coil current supply means. 2. A system according to claim 1 wherein the relay coil current supply means comprises a resistance capacitance (RC) network which is connected to the relay coil and which, when the relay contacts are open, can be charged up and will then supply sufficient current through the relay coil to close the relay contacts. 3. A system according to claim 1 or 2 wherein the RC network protects against high current short circuit at the turn-on of the system. 4. An electrical system which comprises (1) an electronic control module (ECM), (2) a switch controlled by the ECM, (3) a protection system as claimed in any of claims 1 to 3, (4) an RC network which is connected in series between the switch and the protection system, and (5) means for sensing the voltage on a line between the RC network and the protection system. 5. A system according to claim 4 wherein the ECM disables the system upon detecting a fault condition of the system based on the voltage sensed. 6. A system according to claim 4 or 5, further comprising an indicator for indicating a fault condition of the system. 7. A system according to any one of claims 4 to 6 wherein the switch is an FET. 8. An electrical system which comprises (1) an electronic control module (ECM), (2) a switch controlled by the ECM, -11- (3) a protection system as claimed in any one of claims 1 to 3, (4) a diagnostics resistor which is connected in series between the switch and the protection system, and (5) means for sensing the voltage on a line between the RC network and the protection system, the relay coil and the relay contacts being operable by a voltage which is the system voltage minus the voltage dropped across the diagnostics resistor. 9. A system according to claim 8 wherein the ECM disables the system upon detecting a fault condition of the system based on the voltage sensed. 10. A system according to claim 8 or 9, further comprising an indicator for indicating a fault condition of the system.

Inventors: MYONG INHO, PRESLEY WILLIAM T, MYONG, INHO, PRESLEY, WILLIAM, T.
Applicants: RAYCHEM CORP, RAYCHEM CORPORATION
Application year: 1999
Main classification: H02H3
IPC codes: G01R31, H02H3