EP0754347B1 - Protective device against thermal overload for a small high-heat-load electric motor - Google Patents

Abstract

PCT No. PCT/DE95/00464 Sec. 371 Date Oct. 7, 1996 Sec. 102(e) Date Oct. 7, 1996 PCT Filed Apr. 5, 1995 PCT Pub. No. WO95/27302 PCT Pub. Date Oct. 12, 1995A device for protecting a fractional-horsepower motor from overheating. The motor is intended to accommodate a high heat load. Its power supply accommodates a make-or-break switch. A bimetal component opens the switch once a certain temperature has been attained. The bimetal component is mounted on a support. The switch, the bimetal component, and its support are electrically connected in series. There is a specific ratio between the electrical impedance and heat capacity of the bimetal component and those of its support, and they are extensively in surface-to-surface contact.

Description

The invention relates to a protective device against heat overload Small electric motor for high thermal resilience, especially equipped with a stator made of permanent magnet material and one an electrically powered one Winding rotor and used as a short-term motor for motor vehicle equipment parts, the one switched into the motor feed circuit Interrupter contact, the contact at certain by a bimetallic element Warming - preferably suddenly, e.g. like a snap disk - Is actuated opening, which on a one-part or multi-part support part is held, the interrupter contact, the bimetallic element and the supporting part are arranged in electrical series connection and the bimetal element and the support part with respect to the respective electrical resistance and the respective Heat storage capacity have certain relationships to each other and spatially roughly parallel overlapping assignment to each other are arranged.

Small electric motors of the type in question are used in large numbers for various additional functions built into motor vehicles, e.g. For the automatic raising and lowering of windows, the adjustment of the seats, for roof adjustment, convertible top drives, drive motors for pneumatic and hydraulic pumps and antenna drives. These as DC permanent magnet motors Trained drives work with a nominal operating voltage of 12 or 24 volts, they are usually a gearbox with one downstream high gear ratio. Although for the most part only for short periods of time are turned on, they must be considerable during these short periods Provide services. Because such engines are in a normal operating phase by blocking the driven object within the prescribed Distance due to too frequent operation or incorrect operation mechanical overloads to a standstill exist the risk of the motor overheating, especially its rotor winding and its commutator brushes or their brush guides.

For these and similar purposes of such small engines there is also the demand for small size and light weight, which is why the requested service can only be provided with an operating load that predominantly in the range between P2 max. and the short-circuit or standstill load lies, which is especially true for so-called short-term rotor motors. Other critical circumstances for the operation of such small engines in motor vehicles consist in that outside temperature and battery voltage deviate greatly are subject to, application temperature ranges are from -40 ° C up to + 80 ° C, and operating voltage ranges are between 9 and 15 volts or between 18 and 30 volts. In addition, if there is a blockage, the coverage ratio must be met Carbon brushes for collector fins are taken into account, e.g. in a typical window motor with 10-groove anchor in overlapping conditions of 2 slats a total resistance of 0.479 ohms result and with 4 slats overlap a resistance value of 0.385 Ohm. This results in a constant operating voltage of e.g. 13 volts and an ambient temperature of + 25 ° C that corresponds to the at blocking conditions given the initial blocking currents of 27.1 A for 2 slats and 33.7 A for 4 slats. Through the partially bridged winding parts with 4 slats overlap result due to the lower armature resistance and the lower in the circuit lying mass higher temperature change speeds and from it shorter time constants.

This results in a temperature range from -40 ° C to + 80 ° C then at operating voltages of 13 volts and due to the different coverage ratios on the collector and the changes in resistance via the Temperature gradients of the copper winding blocking currents from 36.7 to 45.6 A. at an ambient temperature of -40 ° C and from 27.1 to 33.7 A at a Ambient temperature of + 25 ° C and from 22.7 to 28.5 A at an ambient temperature from + 80 ° C.

The following example results for the protective device in the example above Requirements for blocking:

At ambient temperature + 25 ° C: An initial blocking current at 13 V of 27.1 up to 33.7 A in a time greater than 4 seconds / less than 10 seconds.

An initial blocking current at 9 V of 18.3 - 23.4 A in a time less than 30 Seconds, i.e. within the time constant of the motor related to the Operation before the permissible limit temperatures of the winding or Carbon brushes can be achieved.

At an ambient temperature of -40 ° C an initial blocking current at 15 V of 42.3 to 52.6 A can be switched off in times of less than 12 seconds.

At 9 volts, an initial blocking current of 25.4 to 31.6 A must be smaller at times 45 seconds.

At + 80 ° C ambient temperature, an initial blocking current at 15 V of 26.4 to 32.4 A should be switched off in times greater than 2 seconds to be sufficient long operating time when the window lift system is difficult to operate to be able to ask.

The protective device must therefore in the entire ambient temperature range and Operating voltage range currents from 15.7 to 52.6 A when blocked as Master switching currents and at the same time have sufficiently long operating times in the Provide heavy-duty operation close to the closing moment.

The above circumstances result in a thermally unprotected motor of this type can only be operated in short-circuit mode for about 20-30 seconds can, without damaging the winding or other components, because Winding temperatures of e.g. greater than 300 ° C or carbon brush temperatures higher than 200 ° C lead to destruction. With conventional protective devices The short-circuit operating times can be based on the known principle of thermal switches increase, however, the entire operating temperature range and the entire operating voltage range is insufficiently covered will. Compromises have to be made here with regard to the permissible ones Operating time in heavy-duty operation at + 80 ° C or when securing the case of locking at the lowest ambient temperature of -40 ° C and undervoltage from 9 - 11 V. Mostly compromises are chosen that about higher thermal sensitivity and higher current sensitivity very short operating times in heavy load operation at high ambient temperatures allow for short-circuit strength in the low ambient temperature range at - 40 ° C and undervoltage. The motors are then usually in terms of their usable torque at room temperature and increased ambient temperatures can be used to a limited extent (overprotected).

Known protective devices which counteract overheating in the event of malfunction or in the event of mechanically impaired operation work with temperature and current-dependent switching elements, in particular bimetal elements (here also to read for trimetals etc.), which have different thermal expansion coefficients due to the parallel connection of metal layers Warming assume a change in shape, which are used as part of this protective device to operate an interrupter contact. Such bimetallic elements and their possible uses in the present case are known. Such bimetals react to any heating, to the ambient temperature (outside temperature) and also to self-heating due to current flow (so-called current heat I ² R). They also react to an increase in the ambient temperature at the installation site of the protective device by generating heat in the overloaded components, which acts as return heat over the time constant of the motor and shortens the holding times and extends the pause times until a thermal equilibrium is reached. The supply of heat or the obstruction of heat discharge can moreover take place by means of components which are connected in a heat-conducting manner and / or are arranged in a heat-radiating assignment and which serve as heat stores.

In a first presentation of known type, the bimetallic element is made by thermally conductive connection with a brush or its then metallic Cooker heat supplied, the order of magnitude of the heating of the Corresponds to the armature winding of the motor and therefore with high heat load the motor, for example in the event of a short circuit, supplies heat to the bimetal element, if its previously in the switch-on phase, in particular in the phase of Open contacts after the motor has been switched on specifically, generated electricity heat drops, so that a quick return of the bimetallic element in the Switch-on position of the interrupter contact and thus the renewed current application the engine is decelerated. An example of this is the DE-PS 2811503 referenced.

Other ideas include the supply of heat from a heat store on the bimetal element not only from the point of view of heat conduction, but also below that of heat radiation up to heat flow a. For example, a known protective device - EP 0 226 663 A1 - works with Spacers made of a material with a positive temperature coefficient (PTC), which should act on a bimetal element in the aforementioned sense the broad surface of which, however, is more vertical, so that the influence of heat radiation is rather to be regarded as minor. In the context of EP 0 104 809 B1, for example. the arrangement of a coiled heating element has become known extends more or less parallel to a bimetal element and that - too because of the mention of the influence of the distance between the heating element and Bimetal element - primarily heating the bimetal element Heat radiation should cause.

GB-PS 936801 mentions that a parallel to a bimetallic element electrical connection specifically resistive and thus heat-storing is formed and thus as a heating element for the bimetallic element serves. This should be done over an extended section, at least engages over a portion of the bimetallic element and with it intimately Contact is there. From this, the idea of a heat transfer can rather be conceived Remove heat conduction and less by heat radiation.

For the bimetallic elements of the type in question here is on the DE-OS 3401968 including the statements made there regarding the prior art and referenced for the relevant purposes.

Show protective devices of the type in question according to the prior art the tendency that the switch-off duration (pause time) after the first shutdown (thermal overload-related termination of the normal Switching on (switching on or holding time started) in the following Switching cycle becomes shorter in the event of an overload. Only if it persists Blocking results in a slight increase in pause times, so that initially, caused by the winding heating, an increasing ratio when the duty cycle (ED) is reached. The switch-on or hold times increase, the pause times remain approximately in the subsequent switching cycles constant and then increase slightly when there is feedback in the control loop achieved by increasing the ambient temperature at the protective device becomes. This increases the ratio of the on-time to the off-time, so that there is increasing heating in the winding or in the carbon brush. A long-lasting accident, especially considering the extreme situations, lowest ambient temperature of -40 ° C and lowest operating voltage from e.g. 9 V, therefore does not exclude a damaging risk of overheating from, whereby it should only be pointed out for clarification that low noise working and cheap to manufacture carbon brush guides made of plastic, consist of polyamide with a heat resistance of approx. 200 ° C.

Further protective devices are known from US-A-4 086 558 and EP-A-0 090 491.

By using protective devices with higher current sensitivity However, the risk of thermal overload can be reduced then there are restrictions in the service life of the engines at the highest Operating temperatures of + 80 ° C and short-term overloads.

The invention has for its object that by means of a protective device of the type in question achievable protective effect by limiting the brush and winding temperature increases even in the event of long-term malfunction To improve the overload condition of the motor while maintaining the Service life of the motors in the entire service temperature range and To improve the operating voltage range for the usable short-term overload condition.

Based on a protective device with the features mentioned at the beginning This object is achieved according to the invention by dimensioning the conditions the electrical resistance values and the heat storage capacity of the bimetal element alone and trained as a large-area heat radiator and arranged support part such that the on a first by normal switching on of the motor and the first heat overload cut-off have a certain holding time If the overload continues and the current is constant, switch on following cycles increasingly shorter duty cycle result. If the Despite the falling blocking current, the motors have almost constant duty cycles until the feedback due to an increase in the ambient temperature at the installation site the protective device takes effect and a thermal equilibrium state is achieved with a low duty cycle (ED).

According to the invention, the ratios of the heat storage capacity - the resistance materials provided here are in the range of the specific heat capacity of 0.095 kcal / kg grd. and 0.114 kcal / kg grd. and with weights from 8,600 kp / m ³ to 7,900 kp / m ³ , so that the masses are at least approximately comparable in relation to their heat storage capacity - and the choice of the ratio of the electrical resistance and the mass of the support part as heat storage to electrical resistance and mass of the bimetal is decisive for the fact that in the switching cycles following the first hold time (first switch-on interval), with continuously sustained overload, the switch-on times become increasingly shorter until thermal equilibrium is reached and the ratio of switch-on duration to switch-off duration increases. This behavior in particular means that a steady state of equilibrium can be achieved without overshoot of the brush and the winding temperatures, and preferably in such a way that after the first, as long as possible holding time, the following pause time is less than or equal to 15 seconds and the second holding time is not less than 0.7 seconds. The limitation of the switch-off duration in this scope is recommended because the user of the motor or the object driven thereby tends to assume a real error.

The switching temperature difference (Delta K) between the effectively reached final temperature of the bimetal switching element and the fixed switch-back temperature of the switching element increases with increasing current load the superimposed hysteresis of the thermal feedback. By the specifically dimensioned Heat storage or the aforementioned relationships of heat storage capacity and electrical resistance of the support part as a heat store on the one hand and the bimetallic element can be achieved with one and the same Protective device covered a wide range of different sensitivities can be. The current / time tripping characteristics that can be achieved are very high steep and result in long first holding times at high current and high ambient temperature as well as high current sensitivity in the holding time range of 30 Sec., For short-term engines with high temperature change speeds and therefore low time constants are very important (e.g. at ambient temperature -40 ° C and the lower limit voltage of 9 V).

Such a protective device of the type according to the invention is particularly notable characterized in that the support part as a flat heat radiator essentially parallel to the surface and partially covering a small distance from at least one of the two broad areas of the bimetallic element is arranged so that the Ratio of the heat storage capacity (masses) of the supporting part to the bimetallic element greater than / equal to 1.5: 1 to 3.5: 1 and that the ratio of the electrical Resistance from support to bimetal element greater than / equal to 4: 1 to 8: 1 is.

In a further preferred embodiment or procedure, the support part is as Heat storage adapted to the aforementioned conditions, and defined zones for the determination by specific shaping of certain areas electrical resistance and thermal conductivity. To this A zone can be formed in particular by one or more cutouts be formed in the support member.

The support part can be formed in one or more parts and adjacent to only extend one of the wide areas of the bimetallic element, but it can also between corresponding sections, the bimetal element on both sides of the Take up wide areas between them.

In a practically preferred embodiment, the bimetal element is in the form of a broad surface Snap disc element with an inwardly projecting root for fixing provided on a fastening end that is cranked out of the plane of the supporting part and with one of the fixed contact parts carried by a terminal lug outwardly protruding tongue formed by the heat-dependent Snap movement of the bimetallic element moving contact part carries. Here the support part has a root and adjoining areas of the bimetallic element large covering web and two at its end areas striving in the same direction, one of which is shorter in the to the other end of the leg, bent, then the fastening end flows, while the other leg is longer formed in a connecting lug transforms. The protective device can be a bimetallic element and Have support part enveloping housing, which by means of the individual parts and Connections holding base is closable.

Figur 1

eine schematische Seitenansicht;

Figur 2

eine schematische Stirnansicht, von der den Anschlußfahnen abgewandten Seite her und

Figur 3

eine Draufsicht etwa senkrecht zur flächigen Erstreckung von Bimetallelement und Tragteil.

The invention is explained below with reference to the embodiment shown in the drawing. Show it

Figure 1

a schematic side view;

Figure 2

is a schematic front view, from the side facing away from the terminal lugs and

Figure 3

a plan view approximately perpendicular to the planar extent of the bimetallic element and supporting part.

The exemplary protective device shown overall with 1 in the three representations has a base 2, which all components of the protective device holds and serves to attach a housing, not shown, which in plugged-in state of the components with the exception of those emerging from the base Includes lugs 4 and 5.

A flat support part 3 passes through the base 2 and opens out into the Terminal lug 4, and a further terminal lug 5 passes through the base 2 and carries the fixed at an angled to the other flag 4 end portion Contact part 7 of a total of 6 breaker contact.

A movable contact part 8 is on an outward on the fixed contact part 7 to directed tongue 9 of a bimetallic element designed as a snap disk 10 attached, which in turn over a root area protruding into the interior of the ring 11 with a fastening end 12 which is bent to the ring plane of the supporting part 3 is fixed thereon, for example by spot welding or the like. permanent attachment.

The support part 3 is in its area facing away from the connecting lug 4 with a Web 15 provided, the transverse to the longitudinal direction of the connecting lugs 4 and 5 over the width of the flat bimetallic element 10 partially covering its wide area is guided and projecting legs at right angles at both ends, one of which 13 directed towards the terminal lug 5 and then bent at right angles opens into the cranked fastening end 12, while the other Leg 14 passes straight into the connecting lug 4. This one in particular area of interest of the flat support part 3, which is relatively closely adjacent assigned to the bimetallic element 10 and part of it broadside is arranged overlapping, emphasizes hatching in the drawing. The support part 3 forms a heat store, between the and the bimetallic element 10 heat transfer takes place primarily through heat radiation.

The bimetallic element 10 is in terms of its mass and its electrical Resistance specified much further than the supporting part, so that this as Heat storage with regard to its heat storage capacity or its mass and its electrical resistance to be adapted to the bimetal element can, in a ratio of 1.5: 1 to 3.5: 1 in terms of mass Support part as heat storage to mass bimetal element and in the ratio of 4: 1 to 8: 1 with regard to the electrical resistance of the supporting part to electrical Resistance bimetallic element. A corresponding adjustment option lets through recesses and recesses, as in the web 15 of the support part 3 16 shown. The formed by this recess 16 in the web 15 Rod-shaped zones 17 and 18 determine in addition to the electrical resistance also the thermal conductivity, so that the heat flow from the support member 3 over the cranked fastening end 12 in the root region 11 of the bimetal element 10 or vice versa can also be influenced.

Between the connecting lugs 4 and 5, which are not shown in the feed circuit Motor winding are switched on, the break contact 6, the Bimetallic element 10 and the support member 13 in an electrical series connection, see above that in the case of motor power supply the aforementioned parts of the Protective device flows through, the targeted in the above ratio electrically resistive components bimetallic element 10 and support part 3 themselves warm up and again store heat in the above ratio. At Overloading the motor opens the bimetallic element 10 due to its heat-dependent Deformation of the break contact 6 and thus interrupts the Current flow through the motor winding and the protective device. The heat application of the bimetallic element is due to the heat storage influenced in such a way that, in the case of previous high overload, e.g. at high operating voltage and the resulting high current, the following first pause time is extended and that the subsequent stopping times are shorter and the following pause times despite the falling current the winding heating remains approximately the same, so that the duty cycle (ED) becomes shorter without first having engine heat returned through the Anchor heating is needed. With increasing engine warming with continued Overload, the switch-on times become shorter and the pause times longer until a thermal equilibrium is reached. This Equilibrium is achieved with an extremely low duty cycle of typically reached below 5%, so that the resulting winding temperatures and Carbon brush temperatures very low values, e.g. typically 150 - 180 ° C winding temperature and 135 - 170 ° C coal temperature.

Claims (10)

1. A protective device (1) to protect a small electric motor from overloading due to heat for high thermal loadability, especially equipped with a stator made from permanent magnetic material and an electrically-supplied rotor with windings being utilised as a short-time service motor in automotive equipment, having a contact-breaker assembly (6) switched in the motor supply circuit, the contact being opened on reaching a certain temperature, preferably immediately, e.g. in the manner of a snap-ring, by a bimetallic element (10), which is fitted to a one-or multi-part carrier unit (3), the contact-breaker assembly (6), the bimetallic element (10) and the carrier unit (3) being electrically arranged in series, and the bimetallic element (10) and the carrier unit (3) having a certain relationship with each other with regard to the respective electrical resistances and the respective heat storage capacities, and being spatially arranged to be located parallel and overlapping over a wide area, characterised by the provision of the relationships of the electrical resistance values and the heat storage capacities of the bimetallic element (10) alone and of the attached carrier unit (3), formed as a wide-surface heat radiator, in such a way that an increasingly short operating time results via a first normal activation of the motor and the first stop-time determined by the heat overload shutoff on cessation of the overload and with constant current for the following switching cycles, and has an increasing relationship between shutoff time and activation time.
2. A protective device according to claim 1,
   characterised in that on cessation of the motor overload, the switching cycle consequences which are additional to the shutoff time reach a transient end heating state without exceeding the brush and winding temperature.
3. A protective device according to claim 2,
   characterised in that the operating time is not less than 0.7 seconds and the shutoff time is less than or equal to 15 seconds in the transient state.
4. A protective device according to claims 1 to 3,
   characterised in that the carrier unit (3) is arranged as a flat heat radiator, substantially area-parallel and partially overlapping, located close to one of the two wide-area contacts of the bimetallic element (10), and that the ratio of the heat storage capacity, i.e. mass, of the carrier unit (3) to the bimetallic element (10) is greater than or equal to 1.5:1 to 3.5:1, and that the ratio of the electrical resistances of carrier unit (3) to the bimetallic element (10) is greater or equal to 4:1 to 8:1.
5. A protective device according to claims 1 to 4,
   characterised in that the carrier unit (3), as a result of targeted shaping of certain areas, has defined zones (17,18) for determination of the electrical resistance and the heat storage capacity of the carrier unit (3).
6. A protective device according to claim 5,
   characterised in that the shaping of the zones is defined by one or more recesses (16).
7. A protective device according to claims 1 to 6,
   characterised in that the bimetallic element (10) is formed as a wide-area snap-ring element with an inwardly-facing root (11) for fixing to an attachment end (12) hollowed out of the plane of the carrier unit (3), and with a tongue (9) extending outwards from the fixed contact (7), supported via a connection lug (5), which supports the moveable contact (8), the latter being moved by the heat-dependent snap-action of the bimetallic element (10).
8. A protective device according to claims 1 to 7,
   characterised in that the carrier unit (3) has a web (15) which extensively covers the root (11) and connected areas of the bimetallic element (10), and also has at an end region two equiaxially-braced arms, of which one (13) is shorter, and ends in a hollowed-out connecting end (12) facing the other arm end (14), whereas the other arm (14) is longer, and merges into a connecting lug (4).
9. A protective device according to claims 6 to 8,
   characterised in that the web (15) of the carrier unit (3) is brought into a recess (16).
10. A protective device according to claims 1 to 9,
    characterised in that the connecting lugs (4,5) are held in a socket (2), onto which the housing embracing the bimetallic element (10) and the carrier unit (3) can be placed.

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