DE3907017C2 - Pressure operated electrical switch, in particular brake light switch - Google Patents

Description

The present invention relates to a pressure operated, elec trical switch, especially a pneumatic / electrical and / or hydraulic / electric brake light switch for power vehicles, consisting of a housing with a pressure medium chamber and a switching chamber and one of these chambers tight separating, elastic membrane, being in the pressure middle chamber opens a pressure medium inlet, within the switching chamber a switching device with at least one with electri rule connected connecting elements semiconductor switching element is ordered, and wherein the membrane for driving the half conductor switching element cooperates with the switching device kendes switching part carries.

Known brake light switches have a pressure change against moving membrane a metallic contact part, wel ches with fixed counter contacts for closing and opening of a circuit interacts. This occurs at high currents however disadvantageously a high wear of the contact parts due to contact erosion due to arcing, causing the scarf ter has only a short lifespan. In addition, the appearance of switching arcs or sparks, especially in motor vehicles gene also disadvantageous in that it disturbs the Radio reception can be caused.  

From DE-OS 29 32 482 is the type described above appropriate switch known, in which the actual circuit is switched contactless by a semiconductor switching element. However, this is for driving the semiconductor switching element Mechanical contact is still necessary, which is why at the Membrane as a switching part BEFE an electrical resistance element Stigt is, which when pressurized to the system two fixed contacts is brought that it lei the contacts tend to connect with each other. The fact that the resistance value of the Resistance element decreases with increasing pressure, should harmonic switching of the semiconductor switching element he be enough. However, mechanical contacting also leads here - albeit to a somewhat lesser extent - to the above be written disadvantages in terms of life and the Interference with radio reception. In addition, the known switches on other disadvantageous properties. The mechanical contact leads due to sparking not only to shorten the life of the switch and for interference with radio reception, but also for increased thermi losses when operating the switch. Thermal losses also arise from the ver as a semiconductor switching element turned power transistor. Draw such transistors by a small thermal resistance and a large one permissible power loss. To the through the thermal Ver pleasure power of the power transistor and through the spark to dissipate heat, the switch needs one large cooling surface. It therefore has a large number of cooling fins on. These cooling fins increase the size of the switch and thus show an unfavorable mass-performance ratio of the scarf ters on.

A collision sensor is known from DE 38 14 582 A1 to protect yourself from collision damage  moving units, z. B. mobile robots and guide gear be the robot, in the expected danger area on moveable Chen units or stationary obstacles. On the base plate of a housing in the form of a cylinder with a straight circular truncated cone is open at the top attached to this sensor a Hall element isolated in the center. A preferably flexible elastic sensor is with a cylindrical Bar magnets firmly connected by a socket. One with the The cylindrical sleeve, which is connected by a thread, has a Stop with it on the edge of the circular truncated cone of the housing sits, the magnet being such a distance from the Hall element has that when the magnet is deflected from the central axis a switching function is carried out by the Hall element. The The sleeve is firmly enclosed in the housing and the sleeve eating spiral spring, the ends of which are on the cylindrical part of the housing ses and the sleeve are fixed, elastically fixed to the housing. A suitability of this collision sensor for pneumatic / electri cal and / or hydraulic / electrical switch is DE 38 14 582 A1  not to be removed.

The present invention is based on the object a switch of the known prior art to improve the type described so that an occurrence of light arcs or sparks is excluded. Beyond that too an improvement in the mass-performance ratio or specific (related to the volume) performance of the scarf ters, especially by minimizing its performance losses can be achieved. Such losses in performance occur both Spark discharge as well as by the thermal effect of the electrical Current on.

According to the invention this object is achieved in that the Switching device together with the switching part without contact  has acting sensor element and the semiconductor Schaltele ment at least one power train designed as a TEMP-FET has sistor on a cooler held in the housing sheet metal is attached and its gate connection with the output a multivibrator is connected.

The invention can thus be based entirely on a mechanical Contacting can be dispensed with, so that a spark or light arcing is absolutely excluded. In addition, with the training the switch according to the invention the possibility of a surprisingly high performance increase and size reduction connected. This improvement in mass-to-performance ratio as well as the efficiency of the switch and the reduction its power consumption is expressed by the significantly reduced adorned necessary cooling surface, which also assembly brings technical advantages.

With a switch according to the invention, it is particularly advantageous liable if the sensor element is a Hall element, and preferred assign a digital switching Hall sensor, and the switching part Is permanent magnet.

Further advantageous features of the invention are in the sub claims and the following description included.

Based on the accompanying drawings, the Invention are explained in more detail by way of example. Here demonstrate:

Fig. 1 shows a longitudinal section through an inventive switch,

Fig. 2 is an exploded view of the switch according to Fig. 1,

Fig. 3 is a partial section along the line III-III in Fig. 1 and

Fig. 4 is a circuit diagram of the switching device of the switch according to the invention.

The switch according to the invention shown in FIGS. 1 and 2, for example designed as a brake light switch 2 , consists of a preferably metallic housing 4 with a pressure medium chamber 6 and a switching chamber 8 . These two chambers 6 , 8 are separated from one another in a pressure-tight manner by an elastic membrane 10 arranged in the housing 4 . In the pressure medium chamber 6 opens a Druckmit teleinlaß 12 , the connection pipe 14 with a line, not shown, of a pressure system, for. B. a braking system is connectable. Arranged inside the switching chamber 8 is a switching device 16 which has at least one semiconductor switching element 18 ( FIGS. 3 and 4) which is electrically connected to pin-shaped connecting elements 20 leading to the outside. The membrane 10 carries in its central region, which is elastically movable in the direction of the longitudinal axis 22 of the housing by pressure changes occurring in the pressure medium chamber 6 , a switching part 24 which cooperates with the switching device 16 to control the semiconductor switching element 18 .

According to the invention, the switching device 16 has a sensor element 26 which interacts without contact with the switching part 24 , which is a digitally switching Hall sensor 28 in the exemplary embodiment of the invention shown. In this case, the switching part 24 arranged on the membrane 10 is a permanent magnet 30 . In this case, the Hall sensor 28 of the switching chamber 8 is disposed within half such that the Perma nentmagnet spaced 30 at unpressurized pressure medium chamber 6 from the Hall sensor 28 and pressurized fluid chamber 6 by the moving thereby the diaphragm 10 at a small distance the Hall Sensor 28 is opposite, whereby this changes its digital output size. The further operation of the switching device 16 is explained in more detail below.

According to the invention, the membrane 10 is connected in one piece to a sealing ring 32 arranged inside the housing 4 . This sealing ring 32 extends from the outer circumference of the membrane 10 axially into an annular chamber 34 , which - as can be seen in particular in FIG. 2 - from a housing peripheral wall 36 , an adjoining this housing end wall 38 , one is formed by the end wall 38 approximately parallel to the peripheral wall 36 annular web 40 and an end face 42 of an insert part 44 arranged in the switching chamber 8 . The annular web 40 and the end face 42 of the insert part 44 are spaced apart in the axial direction approximately by the material thickness of the membrane 10 , which it has in its area which adjoins the sealing ring 32 radially inwards (see FIG. 1). .

The membrane 10 is essentially circular-disk-shaped and cup-shaped and has in its central region an extension 46 projecting into the switching chamber 8 , in the end region of which the permanent magnet 30 is arranged. Due to the curvature of the membrane 10 , its central region is arched axially elastically with the permanent magnet 30 when the pressure medium chamber 6 is pressurized in the direction of the arrow 48 ( FIG. 2), so that the permanent magnet 30 comes into the immediate vicinity of the Hall sensor 28 . The permanent magnet 30 is either detachably attached to the neck 46 , z. B. clipped, or molded non-detachably into the material of the membrane 10 or the approach 46 , z. B. vulcanized.

In the example shown, the extension 46 of the membrane 10 is rectangular in cross section, the permanent magnet 30 being arranged in the region of a side surface of the extension 46 . The membrane 10 is advantageously held in the housing 4 in such a manner that it cannot rotate, that the permanent magnet 30 is always aligned in a defined, radial direction. For this purpose, the membrane 10 has in its outer circumferential area an axial, pin-shaped positioning projection 50 which engages in a form-fitting manner in a receiving recess 52 of the insert part 44 .

The insert part 44 according to the invention consists of an annular body 54 facing the membrane 10 with a central through-opening 56 for the shoulder 46 of the membrane 10, as well as two molded onto the annular body 54 on its side facing away from the membrane 10 , in the axial direction parallel to one another and to one another holding arms 58 extending diametrically opposite one another. A circuit board 60 carrying the switching device 16 is fastened between these holding arms 58 . The circuit board 60 expediently sits with its edge regions in longitudinal grooves of the holding arms 58 . In its area facing the ring body 54 , the circuit board 60 carries the Hall sensor 28 . Due to the central arrangement of the projection 46 of the membrane 10 , the circuit board 60 is arranged according to the invention offset parallel to the longitudinal longitudinal axis 22 of the housing in such a way that the permanent magnet 30 covers the Hall sensor 28 in the axial direction when the membrane 10 is pressurized, the Hall sensor 28 is arranged lying in a recess 62 of the circuit board 60 in the plane of the board.

According to Fig. 3 and 4 are according to the invention as two power transistors 64 formed semiconductor switching elements 18 are provided. These power transistors 64 are connected in parallel ( FIG. 4) and attached to a cooling plate 66 held in the housing 4 and connected via connecting wires 68 to the switching device 16 ( FIG. 3). So-called TEMP-FETs are particularly suitable as power transistors 64 . According to Fig. 2 and 3, the heat sink 66 suitably made of a, the circuit board 60 surrounding, concentric to the longitudinal center axis 22 of the annular disc member 70 and from the inner periphery of the annular disc member 70 of substantially extending parallel to the circuit board 60 holding tab 72. One of the power transistors 64 is fastened on both surfaces of the holding tab 72 , lying over the entire surface, optionally with the interposition of a mica layer. The annular disk part 70 of the cooling plate 66 is held between an annular step 74 of the housing 4 and an annular end face 76 of a cap-shaped housing closure part 78 ( FIGS. 1 and 2). The closure part 78 is sealed against the housing 4 by a sealing ring 80 . Since, according to the invention, the electrical connection elements 20 are held on the closure part 78 and are connected to the circuit board 60 via connection wires 82 , it is expedient if the closure part 78 is made of an insulating material, e.g. B. a suitable plastic.

The power transistors 64 are excellently cooled via the cooling plate 66 , the housing 4 and cooling fins 84 provided on the latter. Should an inadmissibly high heating nevertheless occur, the TEMP-FET used have integrated temperature sensors for automatic shutdown in the event of overtemperature. This is explained in more detail below.

The closure part 78 has, in a manner known per se, an external thread 86 for fastening an electrical plug connector part.

The switching device 16 according to the invention will be described below with reference to FIG. 4. The semiconductor switching elements 18 or power transistors 64 designed as a TEMP-FET each have the connections Gate G, Drain D and Source S. Drain D of each power transistor 64 is connected to one connection element 20 and source S to the other connection element 20 , so that switching through the power transistors 64 by driving the gate G results in a conductive connection between the connection elements 20 , whereby one or more Incandescent lamps 88 (brake light bulbs) are switched on.

According to the invention, the Hall sensor 28 is connected on the output side to the base of a transistor 92 , via whose emitter-collector path a switch-on signal via a line 94 and preferably via diodes 96 , 98 , 100 and a resistor 102 to the gate connections G of the power transistors 64 is given, whereby the power transistors 64 turn on, ie turn on the lamps 88 via their drain-source path DS.

Since in the case of seven incandescent lamps 88 connected in parallel, each with 21 W at switch-on torque, there is only an extremely low cold resistance of only 0.2 Ω in the consumer circuit, a very high switch-on current occurs and, as a result, a very high switch-on power. For example, if the current conductivity of the power transistors 64 is limited to approximately 25 A by the gate voltage, which is necessary in order to achieve short-circuit strength up to 30 V, the voltage drop across the seven incandescent lamps 88 is 0.2 Ω × 25 A = 5 V. The remaining voltage of 30 V - 5 V = 25 V is present at the transistors 64 , which results in a power loss of 25 V × 25 A = 625 W. It follows from this that the lamps 88 hardly heat up, while the transistors 64 switch off after a very short time in the ms range due to their integrated temperature fuse. The higher the ambient temperature and thus the housing temperature of the transistors, the faster the switch-off.

Since the built-in power transistors 64 Tempe ratursensoren 64 a a certain thyristor characteristic possess the transistors blank 64 for a temperature-induced or over-current induced shutdown only through switch again when its gate G has been previously reset. It is therefore provided according to the invention that a multivibrator 106 , preferably formed from IC elements with external RC circuitry, is activated via the transistor 92 and a line 104 controlled by the Hall sensor 28 and transistors 64 via the gate terminals G of the power transistors 64 the diodes 98 and 100 as well as the opponent stood 102 the switch-on signal superimposed pulses with a certain frequency, which reset the power transistors 64 on the one hand and then switch through again. The firing caused another turn on the lamps 88, whose resistance has so far increased only insignificantly, so again because of the still inadmissible high inrush current, the integrated temperature sensors 64 a, the power transistors 64 turn off. This described process is repeated until the lamp resistance caused by the pulse-like lamp current caused thereby has increased so much that the current no longer exceeds the switch-off limit of the power transistors 64 or the temperature sensors 64 a. In this case, the operating state has been reached and the lamps 88 remain on until the pressure within the pressure medium chamber 6 of the brake light switch 2 according to the invention drops when the brake pedal is released and the Hall sensor 28 thereby changes its output signal, which also means that the transistor 92 is switched off . the power transistors 64 and lamps 88 leads.

In an advantageous development of the invention it is provided that within a certain on-time of z. B. 2 ms, the gate connections G of the power transistors 64 are controlled with an increased voltage, which affects the temperature sensors to switch off only at a higher current, ie the higher the gate signal, the higher the switch-off current and vice versa. For example, B. the gate signal 6 , 8 V, the power transistors 64 switch due to the temperature sensors 64 a z. B. at 10 A. But if the gate voltage on z. B. 4.8 V reduced, the shutdown z. B. already at 6 A. For this purpose, the gate terminals G according to the invention a Zener diode 108 with a Zener voltage of z. B. 6.8 V upstream, which thus the gate voltage to 6.8 V and thus the DS cut-off current to z. B. 10 A specifies. About a timer consisting of a resistor 110 and a capacitor 112 is after a certain period of time that can be determined by appropriate selection of the RC combination of z. B. 2 ms preferably via IC elements 114 , 116 and preferably via two transistors 118 , 120 connected in series, a second Zener diode 122 connected in parallel to the first Zener diode 108 , where the second Zener diode 122 with z. B. 4.8 V has a lower Zener voltage than the first Zener diode 108 . The second zener diode 122 thus reduces the gate voltage of the power transistors 64 to z. B. 4.8 V and thus defines the operating state of the switching device 16 according to the invention by the cut-off current of the power transistors 64 z. B. 6 A. The turn-off current which is too high at the moment of switch-on is permissible because the transistors 64 are still cold at the moment of switch-on. By the described measures according to the invention, the cut-off current is reduced when the transistors 64 have warmed up. This measure is particularly advantageous in that the lamps 88 also heat up more quickly as a result of the increased current when the switch is turned on, as a result of which they are brought to their operating temperature more quickly, in which their higher resistance defines the operating current.

The switching device 16 according to the invention is advantageously also absolutely insensitive to short circuits in the lamp circuit. For this purpose, according to the invention, the input of an inverting IC element 128 is connected to the connection element 20 leading to the lamps 88 via a line 124 and preferably via a resistor 126 . The output of this IC element is connected via a base resistor 130 to the base of a transistor 132 , the emitter of which is connected to ground, and the collector of which is connected via a line 134 directly to the gate terminals G of the power transistors 64 . Since the lamps 88 are grounded, the ground is also supplied to the IC element 128 via the line 124 due to a short circuit in the lamp circuit, which thereby turns on the transistor 132 . In this way, the transistor 132 directly connects ground via its line 134 to the gate connections G of the power transistors 64 , as a result of which they switch off. An inadmissibly high short-circuit current through the power transistors 64 is consequently absolutely ruled out by the invention.

Claims (17)

1. Pressure-actuated, electrical switch, in particular pneumatic / electrical and / or hydraulic / electrical brake light switch for motor vehicles, consisting of a housing with a pressure medium chamber and a switching chamber and a chamber separating these chambers from each other, elastic membrane, wherein in the Druckmit telkammer a pressure medium inlet opens, a switching device with at least one semiconductor switching element connected to electrical connecting elements is arranged within the switching chamber, and the membrane carries a switching part which interacts with the switching device to actuate the semiconductor switching element, characterized in that the switching device ( 16 ) has a contactless arrangement with the switching part ( 24 ) cooperating sensor element ( 26 ) and the semiconductor switching element ( 18 ) has at least one designed as a TEMP-FET power transistor ( 64 ) on a in the housing ( 4 ) held cooler Lech ( 66 ) is fixed and its gate terminal (G) is connected to the output of a multivibrator ( 106 ). 2. Switch according to claim 1, characterized in that the sensor element ( 26 ) is a Hall element, preferably as a digitally switching Hall sensor ( 28 ), and the switching part ( 24 ) is a permanent magnet ( 30 ). 3. Switch according to claim 1 or 2, characterized in that the membrane ( 10 ) is integrally connected to a chambered inside the housing ( 4 ) arranged sealing ring ( 32 ). 4. Switch according to claim 3, characterized in that the sealing ring ( 32 ) of the membrane ( 10 ) is seated in a ring-shaped chamber ( 34 ) by a housing peripheral wall ( 36 ), one of these closing housing end wall ( 38 ), an annular web ( 40 ) extending from the end wall ( 38 ) approximately parallel to the peripheral wall ( 36 ), as well as an end face ( 42 ) of an insert part ( 44 ) arranged in the switching chamber ( 8 ). 5. Switch according to one of several of claims 2 to 4, characterized in that the membrane ( 10 ) is substantially circular disc-shaped and cup-like arched and in its central region has a projection ( 46 ) projecting into the switching chamber ( 8 ), in the end region of the permanent magnet ( 30 ) is arranged. 6. Switch according to claim 5, characterized in that the permanent magnet ( 30 ) on the projection ( 46 ) releasably attached, for. B. clipped, or in the material of the membrane ( 10 ) or the approach ( 46 ) is molded insoluble. 7. Switch according to claim 5 or 6, characterized in that the permanent magnet ( 30 ) is arranged laterally on the preferably rectangular cross-section ( 46 ) of the membrane ( 10 ), the membrane ( 10 ) in a defined orientation of the permanent magnet ( 30 ) is held in the housing ( 4 ) in a rotationally fixed manner. 8. Switch according to claim 7, characterized in that the membrane ( 10 ) has in its outer peripheral region an axial, pin-shaped positioning projection ( 50 ) which engages in a receiving recess ( 52 ) of the insert part ( 44 ). 9. Switch according to one or more of claims 4 to 8, characterized in that the insert ( 44 ) from a membrane ( 10 ) facing ring body ( 54 ) with a central through opening ( 56 ) for the approach ( 46 ) of the membrane ( 10 ) and two holding arms ( 58 ), which adjoin the annular body ( 54 ) on its side facing away from the membrane ( 10 ) and extend in the axial direction parallel to one another and diametrically opposite, a circuit board ( 60 ) between the holding arms ( 58 ) ) is attached, which carries the Hall sensor ( 28 ) in its area facing the ring body ( 54 ). 10. The switch of claim 9, characterized in that the circuit board (60) is arranged offset laterally to the housing longitudinal center axis (22), wherein the Hall sensor (28) in a marginal recess (62) of the board (60) the board level is arranged lying. 11. Switch according to claim 9 or 10, characterized in that the cooling plate ( 66 ) from a circuit board ( 60 ) enclosing an annular disc part ( 70 ) and one from the inner circumference of the annular disc part ( 70 ) substantially parallel to the circuit board ( 60 ) extending retaining tab (72), wherein one of the power transistors (64) is fixed completely supported on both surfaces of the retaining tab (72). 12. Switch according to claim 11, characterized in that the annular disc part ( 70 ) of the cooling plate ( 66 ) between an annular step ( 74 ) of the housing ( 4 ) and an annular end face ( 76 ) of a cap-shaped, preferably via a sealing ring ( 80 ) sealing part ( 78 ) sealed against the housing ( 4 ) is held. 13. Switch according to claim 12, characterized in that the electrical connection elements ( 20 ) are held on the closure part ( 78 ) consisting of an insulating material and are connected to the circuit board ( 60 ) via connecting wires ( 82 ). 14. Switch according to one or more of claims 1 to 13, characterized in that the Hall sensor ( 28 ) is connected on the output side to the base of a transistor ( 92 ), the emitter with positive potential and the collector via a line ( 94 ) with the gate terminals (G) of the power transistors ( 64 ) are connected. 15. Switch according to one or more of claims 1 to 14, characterized in that the gate connections (G) of the power transistors ( 64 ) is preceded by a Zener diode ( 108 ) with a certain Zener voltage of preferably 6.8 V. . 16. Switch according to claim 14 or 15, characterized in that with the collector of the transistor ( 92 ) is also a timing element formed from a resistor ( 110 ) and a capacitor ( 112 ) is connected, which preferably via a transistor ( 118 ) with the Base of a transistor ( 120 ) is connected, via the emitter-collector path, a second Zener diode ( 122 ) is connected in parallel to the first Zener diode ( 108 ), the second Zener diode ( 122 ) preferably with 4 .8 V has a lower Zener voltage than the first Zener diode ( 108 ). 17. Switch according to one or more of claims 14 to 16, characterized in that the connecting element ( 20 ) leading to the lamps ( 88 ) via a line ( 124 ) and preferably via a resistor ( 126 ) with the input of an inverting IC Link ( 128 ) is connected, which is connected on the output side to the base of a transistor ( 132 ), the emitter of which is connected to ground and the collector of which is connected to the gate connections (G) of the power transistors ( 64 ).