Device comprising an electromechanical relay in an electrical load circuit and an electrical control circuit, and a method for operating such a device

Abstract

Device with an electromechanical relay (14) in an electrical load circuit (10, 11) and an electrical control circuit (18, 19), wherein the relay (14) has a contact bridge (30) that can be displaced electromechanically against the force of a return spring (29), such that after activation of the control circuit (18, 19) with the contact bridge (30) a connection is established at contact points (30, 31 and 33, 34) between load contacts (25, 26) of the relay (14) for switching the load circuit (10, 11) of a consumer (1), and in the event of a relay malfunction after deactivation of the control circuit (18, 19) the contact bridge (30) “sticks” at the contact points (30, 31 and 33, 34) and the load circuit (10, 11) does not open, wherein The relay malfunction with a “sticky” contact bridge (30) is detected using a detection device (15, 16) and the electrical control circuit (18, ) is then activated as a countermeasure.19) is activated with successive pulses (35) for a corresponding "free shaking" of the contact bridge (30) until its release and reset with opening of the load circuit (10, 11), characterized in that the control frequency of the successive pulses (35) is adapted to the mechanical resonance of an armature (27) with contact bridge (30) of the relay (14), wherein the armature (27) is displaceable by a controlled magnetic coil (24), is designed with the contact bridge (30') as a spring-mass system and is optimized for high vibration amplitude, and the contact bridge (30') is designed as a double disc spring (36).

Description

The invention relates to a device with an electromechanical relay in an electrical load circuit and an electrical control circuit according to the preamble of claim 1. A commonly known relay features a contact bridge that can be moved electromechanically against the force of a return spring, such that, after activation of the control circuit, a connection is established between the relay's load contacts at contact points, thus switching the load circuit of a consumer. Typically, the load contacts and a solenoid coil, which can be excited by the control circuit, are fixed to a relay housing. The contact bridge is usually mounted as a contact ring on an armature that is attracted by the excited solenoid coil. For the relay to function properly, the force of the return spring is sufficient to return the armature to its initial position after the control circuit is deactivated, thereby releasing the contact bridge from the load contacts and interrupting the load circuit. Relays are known in various designs, such that the contact bridge can be a single piece or multiple pieces, and in particular, can also be designed with a contact spring tongue. All these different designs are to be understood here as encompassing the term "contact bridge." It is well known that relays can malfunction, where, after the control circuit is deactivated, the contact bridge "sticks" at the contact points, preventing the load circuit from opening. The reason for this "relay sticking" is usually that an arc occurs during switching operations, and the heat released welds the metal contacts of the relay together, preventing subsequent opening by the return spring. In this case, a disadvantage arises with electrical devices not designed for continuous operation: there is a risk of overheating, potentially leading to damage. For example, if the electrical device is an electric intake air preheater (heater) for an internal combustion engine in a commercial vehicle, which can be switched via a relay, there is a risk that the heating elements will melt due to overheating, be drawn into the engine with the intake air, and damage it. A relay with a "relay adhesive" is usually irreparable and must be replaced. Such a replacement is complex and, especially in the case of a relay used in a mobile application, for example, in the intake air preheater of a commercial vehicle, cannot be carried out immediately. To mitigate this problem, elaborate and costly measures are already known: for example, oversized relays or several relays connected in series in a redundant circuit are used. Furthermore, a "short-circuit circuit" with a second relay is known, which ensures that an overcurrent fuse trips in the event of a fault. Monitoring systems and functions to inform operating personnel are also known. Furthermore, it is known (DE 19 54 65 53 C1) to determine the switching state of a consumer by measuring the voltage value at a battery of a vehicle's electrical system, since every switching of a consumer in the electrical system generates a slight voltage jump. Furthermore, it is known (DE 10 2007 011 456 A1) to drive a fuel pump in a direction of delivery changed from the normal delivery direction for a certain period of time after detecting that it is blocked, in order to remove the blockage. Furthermore, DE 37 19 298 A1 describes a method for releasing the contacts of a stuck relay, one contact of which is stationary and the other contact of which is located on the ferromagnetic relay armature. By applying an electrical voltage to the winding, the ferromagnetic relay armature is attracted with its contact towards the stationary contact. When the relay coil is de-energized and the relay is intact, the contact of the ferromagnetic relay armature falls away again, thus separating the two contacts. Furthermore, US 2006 / 0114635A1 discloses a method in which the relay adhesion fault is detected by recording the properties of the circuits involved and a release process is actively triggered based on the recorded properties. The purpose of the invention is to quickly restore a relay to working order using a simple and cost-effective measure with a "relay adhesive". This problem is solved by the features of claim 1. Advantageous embodiments are the subject of the dependent claims relating thereto. According to the invention, a detection device is used to identify the relay malfunction with a "sticky" contact bridge, and as a countermeasure, the electrical control circuit is then activated with successive pulses to "shake free" the contact bridge until it is released and reset with the opening of the contact circuit. In such a temporary relay repair by "vibrating" the contacts, the fact is exploited that even with welded contacts, the armature inherently possesses a residual degree of freedom of movement. It has been shown that by jerkily activating the armature with successive pulses, it is usually possible to cause the system to oscillate and sometimes even to separate the welded contacts through the resulting force amplitudes, thus restoring the undisturbed relay function. Such an internal relay repair is usually possible if the drive frequency of the successive pulses is matched to the mechanical resonance of the armature with its contact bridge. The resonance frequency obviously depends on the type of relay used and can be easily determined experimentally. The "freeing" method of oscillation at the resonant frequency is regularly successful when the relay's armature and contact bridge are designed as a spring-mass system, since the spring then provides at least one degree of freedom. A simple and cost-effective solution is to design the contact bridge as a double disc spring (in addition to the usual return spring). In principle, the aforementioned temporary relay repair by "shaking" is possible in all electrical load circuits, but especially for heating systems in a DC load circuit. This is particularly relevant for an electric intake air preheater (heater) of an internal combustion engine in a commercial vehicle, since, as already described, there is a risk of engine damage due to melted heating elements in the event of overheating. This advantageously prevents overheating and, at least for further switching operations until the relay can be replaced, restores its proper function. To initiate the "freezing" procedure, it is first necessary to detect a "relay sticking." This can be done using a detection device in a known manner by measuring the voltage and / or the load current. After deactivating the control circuit, the load current should not be interrupted and / or the battery voltage should not rise. In this case, the detection device sends an error signal indicating a "relay sticking" to the control unit. The detection device, along with the measuring element, can optionally be integrated into the control unit. The control unit sends both the control signals for error-free switching on / off of the relay and, in the event of an error signal, the impulses for "shaking free" the contact bridge. In a further embodiment, after a successful self-repair by "shaking" the contact bridge, a warning signal, in particular a yellow light, is sent to the operator. This warning signal indicates that the relay needs to be replaced, as such a self-repair cannot be repeated indefinitely. Therefore, after a predetermined number of successful self-repairs by "shaking," the self-repair function can be completely deactivated or the relay can no longer be activated. In the event that a provisional self-repair by shaking was unsuccessful, this should be indicated to the operator by an appropriate warning signal, in particular by a red light. Furthermore, a method for an in-system repair of a relay with a "sticky contact bridge" using the aforementioned devices is claimed. The invention is further explained with the aid of a drawing. Figure 1 shows a schematic top view of an electric intake air preheater and the associated circuit arrangement, Figure 2 shows a section through a relay of a first embodiment used in the circuit according to Figure 1, and Figure 3 shows a relay corresponding to Figure 2 of a second embodiment. Fig. 1 shows a schematic representation of an intake air preheater 1 with the associated electrical circuit arrangement 2. The intake air preheater 1 is located in an (not shown) intake duct of an internal combustion engine of a commercial vehicle and essentially consists of a ring-shaped housing part 3 which lies transversely in the intake duct and a resistance element as a heating element 4 . The heating element 4 consists of meander-shaped heating fins 5, which are spaced apart in nine layers above each other, each electrically insulated laterally in the housing part 3 and are connected with their fin ends 6 and 7 to associated electrical connections 8, 9 on the housing part 3. The intake air preheater 1 is located in the load circuit (negative line 10 and positive line 11) of a battery 12 in the vehicle electrical system of the commercial vehicle. After the battery 12, a fuse 13 and subsequently a (schematically represented) relay 14 are arranged in the positive line 11, two specific embodiments of which are shown in Fig. 2 and Fig. 3. Furthermore, a current meter 15 is schematically shown in the positive line 11, with which the current load current is measured and a corresponding load signal is sent via a line 16 to a control unit 17 (ECU). The electrical control unit 17 is connected to a control circuit (negative line 18 and positive line 19) in which the relay 14 with its respective control contacts 20 and 21 is located. Furthermore, a (schematically indicated) warning lamp 22 is connected to the control unit 17. Figure 2 shows a longitudinal section through the relay 14 (first embodiment) with further details: A magnetic coil with control contacts 20, 21 is arranged on one wall of a relay housing 23, projecting into the housing. Load contacts 25, 26 are arranged on both sides of this for connecting the negative line 10 and the positive line 11 of the load circuit. In the relay housing 23, an armature 27 is also arranged, which is attracted to the magnetic coil 24 when it is energized in a controlled manner and can be moved towards it (arrow 28). The armature 27 is held in the illustrated initial position by a return spring 29, which acts as a compression spring in the area around the solenoid coil 24. A contact bridge 30, which points towards the load contacts 25, 26, is mounted on the armature 27 and forms a contact ring around the solenoid coil 24 and the return spring 29. When the magnetic coil 24 is activated, the armature 27 brings the contact bridge 30 into contact at contact points 31, 32 and 33, 34, thereby establishing an electrical connection between the load contacts 25, 26 and thus closing the load circuit for the heating function of the intake air preheater 1. Fig. 3 shows a second embodiment of a relay 14' which has largely the same structure as the relay 14 of Fig. 2, so that identical elements are marked with the same reference numerals (with a line). The difference in the second embodiment lies in the fact that, unlike in the first embodiment, the contact bridge 30 is not designed as a simple rigid contact ring, but as a spring element in the form of a double disc spring 36, so that the armature 27' and the contact bridge 30' form a spring-mass system and allow higher vibration amplitudes. The illustrated arrangement is controlled as follows: To activate the heating function of the intake air preheater 1, the control circuit (lines 18, 19) of the control unit 17, and thus the relay 14, 14', is activated, and the load circuit (lines 10, 11) is closed. In this state, contact points 31, 32 and 33, 34, or 31', 32' and 33', 34', are in contact with each other. After deactivation of the control unit 17 to switch off the intake air preheater 1, these contact points are released during normal operation by the return of the armature 27, 27' and the contact bridge 30, 30' due to the force exerted by the return spring 29. However, due to the relatively high load current, in a relay malfunction the contact points can weld together, so that the contact bridge 30 , 30' “sticks” to the load contacts 25 , 26 and thus the load circuit no longer opens after deactivation of the control circuit.This creates the risk that the heating fins 5 of the intake air preheater 1 will at least partially melt due to an impermissibly long current flow, and that fin fragments will be drawn into the internal combustion engine, potentially causing significant damage. Since the current does not rise to an impermissibly high level when the contact bridge is "stuck," the fuse 13 does not yet trip. To prevent the aforementioned scenario, the load current is measured (current meter 15) and the corresponding current signal is fed to the control unit 17. If, after deactivation of the control circuit (lines 18, 19), a load current signal is still present at the control unit 17 via line 16, this is a criterion for a "sticky" contact bridge 30, 30'. The control unit 17 then switches to a repair mode, whereby the control circuit is subjected to successive pulses (indicated by pulse sequence 35). This is intended to set the armature 27, 27' with the contact bridge 30, 30' into corresponding vibrations and "shake off" the contact bridge, so that the armature 27, 27' with the contact bridge 30, 30' is returned to its original position by the spring force of the return spring 29, 29', thus opening the load circuit. If a repair is successfully performed by "shaking" the device free, the measured load current signal (line 16) returns to zero and the repair mode ends. A successful repair can then be indicated by warning light 22. The repair mode can also be time-limited, so that it, or the controlling function, is also deactivated if the repair is unsuccessful. This can also be indicated by (another) warning light, if necessary. Repairing a "stuck" contact bridge 30, 30' is faster and more successful if the drive frequency for the pulse sequence 35 is adapted to the mechanical resonance of the armature with contact bridge. The success rate is further increased if, as in the second relay design 14' according to Fig. 3, the armature 27' with the contact bridge 30' is designed as a spring-mass system, which is specifically excited to relatively large resonant vibrations with relatively high vibrational energy relative to the load contacts 25, 26. For this purpose, the contact bridge 30' here consists of a double disc spring 36. The above measure allows for a temporary self-repair of the relay by shaking it free, which at least prevents engine damage and / or vehicle breakdown. Since such a self-repair cannot be repeated indefinitely, the repair mode or the heating function will be forcibly deactivated after a fixed number of successful self-repairs. Before this occurs, it is advisable to replace relay 14, 14'. Reference symbol list 1 Intake air preheater 2 Electrical circuit arrangement 3 Housing part 4 Heating element 5 Heating fins 6 Fin end 7 Fin end 8 Electrical connection 9 Electrical connection 10 Negative wire 11 Positive wire 12 Battery 13 Fuse 14 Relay 15 Ammeter 16 Wire 17 Control unit 18 Negative wire 19 Positive wire 20 Control contact 21 Control contact 22 Warning lamp 23 Relay housing 24 Solenoid coil 25 Load contact 26 Load contact 27 Armature 28 Arrow 29 Return spring 30 Contact bridge 31 Contact point 32 Contact point 33 Contact point 34 Contact point 35 Pulse sequence 36 Double disc spring. Reference symbol list 1 Intake air preheater 2 Electrical circuit arrangement 3 Housing part 4 Heating element 5 Heating fins 6 Fin end 7 Fin end 8 Electrical connection 9 Electrical connection 10 Negative wire 11 Positive wire 12 Battery 13 Fuse 14 Relay 15 Ammeter 16 Wire 17 Control unit 18 Negative wire 19 Positive wire 20 Control contact 21 Control contact 22 Warning lamp 23 Relay housing 24 Solenoid coil 25 Load contact 26 Load contact 27 Armature 28 Arrow 29 Return spring 30 Contact bridge 31 Contact point 32 Contact point 33 Contact point 34 Contact point 35 Pulse sequence 36 Double disc spring

Claims

Device with an electromechanical relay (14) in an electrical load circuit (10, 11) and an electrical control circuit (18, 19), wherein the relay (14) has a contact bridge (30) that can be displaced electromechanically against the force of a return spring (29), such that after activation of the control circuit (18, 19) with the contact bridge (30) a connection is established at contact points (30, 31 and 33, 34) between load contacts (25, 26) of the relay (14) for switching the load circuit (10, 11) of a consumer (1), and in the event of a relay malfunction after deactivation of the control circuit (18, 19) the contact bridge (30) “sticks” at the contact points (30, 31 and 33, 34) and the load circuit (10, 11) does not open, wherein The relay malfunction with a “sticky” contact bridge (30) is detected using a detection device (15, 16) and the electrical control circuit (18, ) is then activated as a countermeasure.19) is activated with successive pulses (35) for a corresponding "free shaking" of the contact bridge (30) until its release and reset with opening of the load circuit (10, 11), characterized in that the control frequency of the successive pulses (35) is adapted to the mechanical resonance of an armature (27) with contact bridge (30) of the relay (14), wherein the armature (27) is displaceable by a controlled magnetic coil (24), is designed with the contact bridge (30') as a spring-mass system and is optimized for high vibration amplitude, and the contact bridge (30') is designed as a double disc spring (36). Device according to claim 1, characterized in that the electrical consumer (1) is a heating system in a DC load circuit (10, 11, 12). Device according to claim 2, characterized in that the heating system is an electric intake air preheater (1) of an internal combustion engine, in particular in a motor vehicle. Device according to one of claims 1 to 3, characterized in that the detection device detects a “sticky” contact bridge (30) after a predetermined deactivation of the control circuit (18, 19) by measuring (15) the load current and / or the voltage, and in the event of such a relay malfunction, a corresponding error signal (line 16) is sent to or generated in a control unit (17). Device according to claim 4, characterized in that the control unit (17) generates both the predetermined activation signals for error-free switching on / off of the relay (14) and, in the event of an error signal, emits the pulses (35) for "shaking free" the contact bridge (30). Device according to one of claims 1 to 5, characterized in that after successful self-repair by "shaking free" the contact bridge (30) a warning signal, in particular by a yellow warning lamp (22), is given to an operator. Device according to one of claims 1 to 6, characterized in that after a fixed number of successful self-repairs by "shaking free" the contact bridge (30) the self-repair function is switched off or its activation is prohibited. Device according to one of claims 1 to 5, characterized in that a time threshold, in particular with a timer in the control unit (16), can be preset, after which, in the event of unsuccessful self-repair, a warning signal, in particular by a red lamp, is given to an operator. Method for an in-system repair of a relay (14) with a “sticky” contact bridge (30) using a device according to claims 1 to 8.

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