Circuit arrangement for controlling a system and system with a circuit arrangement

Abstract

Circuit arrangement (100) for controlling a system (2), in particular a lumbar support with at least two air cushions (4,6), comprising - at least four actuators (8a, 8b, 10a, 10b) each with at least one actuating element (26), wherein each actuating element (26) is adjustable between a first position and a second position, - at least one supply voltage path (44a, 44b, 44c, 44d) and one ground path (46), which form at least four current paths (11a, 11b, 11c, 11d) between them, wherein the at least four actuators (8a, 8b, 10a, 10b) for actuating the actuating element (26) are integrated in a circuit between the supply voltage path (44a, 44b, 44c, 44d) and the ground path (46) such that two actuators (8a, 8b, 10a, 10b) can be switched and energized in pairs in series in one of the current paths (11a, 11b, 11c, 11d), and - electronic switching elements (48, 50, 52) for supplying current to none of the current paths (11a, 11b, 11c, 11d) or to one of the current paths (11a, 11b, 11c, 11d), - a current control circuit (54) which is integrated in the circuit between the actuators (8a, 8b, 10a, 10b) which can be connected in pairs in series, wherein the current control circuit (54) includes a current source (58) and wherein a bypass circuit (60) for the current source (58) is integrated in the current control circuit (54).

Description

[0001] The invention relates to a circuit arrangement for controlling a system, in particular a lumbar support with at least two air cushions, and to a system with such a circuit arrangement.

[0002] To increase seating comfort, systems known as lumbar supports are used, which are particularly pneumatically adjustable and integrated into a seat, for example a vehicle seat in a motor vehicle. To adjust the backrest of the seat, the system comprises several air cushions that can be filled and deflated with air to change the contour of the seat or backrest. For ventilation or venting, the air cushions are typically connected to a pneumatic pump and to the atmosphere via supply lines, with valves for opening and closing arranged in the supply lines. The valves themselves are each adjusted by actuators, usually using electromagnets.

[0003] Furthermore, actuators based on wires made of shape memory alloys, so-called SMA elements (Shape Memory Alloy), are used. In these, an actuator's control element is actuated by applying current to the SMA element. If a supply voltage is applied to an actuator or its SMA element, power is supplied to it and the actuator is activated. The supplied power must be kept within a very narrowly defined range to ensure reliable activation of the actuator while still avoiding thermal overload and thus permanent damage to the SMA element. In practical use, however, this is often problematic because the supply voltage, particularly in the automotive sector, is subject to large fluctuations, and if applied directly to the SMA elements, too much power is supplied.Furthermore, the supplied power should usually be varied depending on the ambient temperature, so that at higher ambient temperatures a lower power is supplied than at lower ambient temperatures, in order to avoid thermal overload of the SMA element.

[0004] To ensure reliable functionality of the SMA elements and actuators, it is known, for example, to integrate the actuators into a circuit arrangement having a control unit that performs a variety of tasks, in particular measuring the supply voltage and the ambient temperature using temperature sensors integrated into the control unit. The SMA elements are controlled using pulse width modulation, with the duty cycle of the pulse width modulation—i.e., the ratio of pulse width to period duration—being adjusted depending on the measured supply voltage and temperature. Another possibility is to use a current source controlled by a control unit to adjust the current flowing through the SMA elements, or to use temperature-dependent current sources, whereby one current source must be available for each actuator.

[0005] For example, US 2015 / 0 251 179 A1 describes a circuit arrangement with multiple actuators, each with a movable control element. DE 11 2014 006 722 T5 and DE 10 2008 021 444 A1 disclose SMA valves and actuators, respectively, whose control elements are actuated by SMA wires.

[0006] US 2011 / 0 227 388 A1 discloses an adjustment device for a seat, with at least one fluid chamber arranged in the seat, which is inflatable for adjusting the seat, and with a valve arrangement comprising a check valve and a 3 / 2-way valve, which is connected to the fluid chamber.

[0007] The known circuit arrangements and methods are therefore complex and expensive, particularly due to the required components such as the control unit, temperature sensors, or power sources. Furthermore, a large number of components are required, for example, one power source per actuator. Furthermore, due to the resulting power loss in the power sources, which must necessarily be dissipated into the environment to prevent overheating of the circuit and its components, a compact design is not possible, although this is desirable, especially for use in a vehicle seat.

[0008] It is therefore an object of the invention to propose a circuit arrangement for controlling a system, in particular a lumbar support, as well as a system with such a circuit arrangement, in which the aforementioned disadvantages are avoided without restricting the functionality.

[0009] The first-mentioned object is achieved by a circuit arrangement for controlling a system, in particular a lumbar support with at least two air cushions, with the features according to claim 1. The circuit arrangement comprises at least four actuators, each with at least one actuating element, wherein each actuating element is adjustable between a first position and a second position. Furthermore, the circuit arrangement comprises at least one supply voltage path and a ground path, which form at least four current paths between them, wherein the at least four actuators for actuating the respective actuating element are integrated between the supply voltage path and the ground path in a circuit or the circuit arrangement in such a way that two actuators can be connected in pairs in series into one of the current paths and can be supplied with current.To deactivate all possible current paths or to activate one of the current paths, the circuit arrangement comprises electronic switching elements for applying current to none of the current paths or to one of the current paths connecting two actuators in series.

[0010] In order to avoid thermal overload of the actuators or the SMA elements, the circuit arrangement further comprises a current control circuit which is integrated in the circuit between the actuators which can be connected in series in pairs.

[0011] The current control circuit also includes a current source. To further reduce thermal stress on the power source and prevent overheating of the power source's electronic components, a bypass circuit for the current source is integrated into the current control circuit. This ensures that only a portion of the total current flows through the power source itself, while the other portion flows through the bypass. This reduces power loss in the power source, allowing the use of inexpensive electronic components, such as inexpensive and simple transistors, in the power source. In the simplest case, the bypass circuit itself requires only a resistor as a component and is therefore also very cost-effective (bypass resistor).

[0012] With the help of the electronic switching elements, the current path through which current is to flow is selected, i.e., a current path is activated and a switch is made between the multiple current paths. Depending on which of the current paths is activated and thus has current flowing through it, two of the actuators are supplied with current together, in other words simultaneously, and their control elements are each moved from their first position to their second position. By activating different current paths, two different actuators can be activated, thus creating multiple switching states in the system. If all current paths are inactive, i.e., no current flows through the circuit, all actuators are inactive.

[0013] The flexible connection of the actuators in pairs into a current path allows two of the actuators required for controlling the system or for executing a function of the system to be activated simultaneously without the need for a large number of components.

[0014] The at least four current paths are preferably formed in that a circuit integrated in the circuit arrangement comprises a parallel circuit having at least two parallel strands, wherein in each of the at least two parallel strands at least two actuators are arranged in series, and in that the at least two parallel strands of the parallel circuit can be connected or are connected to one another via a further strand in such a way that an actuator arranged in a first parallel strand can be connected in series with an actuator arranged in a second parallel strand.

[0015] In other words: The two parallel strands of the parallel circuit each form a current path with two actuators, a first and a second, connected in series, i.e. two current paths that run between the supply voltage path and the ground path.

[0016] The additional strand connects the two parallel strands between the two actuators in such a way that a first actuator of the first parallel strand can be connected in series with a second actuator of the second parallel strand to form a third current path, and a first actuator of the second parallel strand can be connected in series with a second actuator of the first parallel strand to form a fourth current path. The two actuators, each forming a common current path, can be supplied with current together and thus activated together.

[0017] If the system is a lumbar support with two air cushions, two actuators are active at the same time to carry out a function or to adjust the contour of the seat using the lumbar support. Each actuator is assigned to one of the two air cushions or to a valve provided for filling or emptying the respective air cushion. For example, with the "FORWARD" function, both air cushions are filled at the same time and therefore the two actuators that allow air to enter the air cushion are active, i.e. they are each assigned to the valve that allows air to be supplied in its open position. With the "BACKWARD" function, on the other hand, both air cushions are deflated at the same time and therefore the two actuators that allow air to escape from the air cushion are active, i.e. they are each assigned to the valve that allows air to be released in its open position.In the "UP" function, an upper air cushion is inflated and a lower air cushion is deflated simultaneously. Therefore, the actuator that allows air to escape from the lower air cushion and the actuator that allows air to enter the upper air cushion are both active. In the "DOWN" function, however, a lower air cushion is inflated and an upper air cushion is deflated simultaneously. Accordingly, the actuator that allows air to escape from the upper air cushion and the actuator that allows air to enter the lower air cushion are both active.

[0018] In a preferred embodiment, each actuating element of an actuator is assigned an SMA element for actuating the actuator in a stroke direction. The SMA elements for actuating the actuating element are integrated into the circuit between the supply voltage path and the ground path in such a way that two SMA elements, i.e., two actuators, can be connected in pairs in series into one of the current paths and supplied with current. Thus, actuators controlled by SMA elements are integrated into the circuit arrangement.

[0019] The electronic switching elements preferably comprise a diode circuit comprising a plurality of diodes and / or one or more transistors, with at least one diode being assigned to each actuator. The activation of the respective current path is primarily controlled by the electronic switching elements, in particular the diode circuit and the transistors, thus eliminating the need for a cost-intensive and space-consuming control unit. In particular, at least two diodes are assigned to each actuator.

[0020] The current control circuit specifically includes a pulse-width modulation (PWM) generator that generates a pulse-width modulated signal with a fixed frequency and a fixed duty cycle to continuously switch the current flow in the respective active current path on and off. Due to the thermal inertia and fast switching frequency of the PWM generator, the power supplied to the SMA element is equivalent to a constant power supply. In other words, the power supplied to the SMA element has the same thermal power as a constant power supply.

[0021] As a cost-effective variant, an astable multivibrator is preferably used as a pulse width modulation generator.

[0022] Particularly when using an astable multivibrator with a constant duty cycle as a pulse-width modulation generator, the current control circuit includes a temperature-dependent current source. This ensures that the power supplied to the SMA element remains constant during changes in the supply voltage or fluctuates, but changes during temperature fluctuations, i.e., lower power at higher temperatures and higher power at lower temperatures. This helps prevent thermal overload of the SMA elements.

[0023] The second object is achieved by a system, in particular a pneumatically adjustable lumbar support, having the features of claim 8. The system comprises at least two air cushions, each of which is connected to a pump via a supply line for filling with air and to the atmosphere for emptying. Furthermore, the system comprises valves that are arranged in each supply line and / or in a line between the air cushion and an atmosphere connection or an opening to the atmosphere or that themselves have the opening to the atmosphere, wherein each valve is adjustable between an open position, in which the valve opens the supply line or releases the atmosphere connection, and a closed position, in which the valve closes the supply line or the atmosphere connection. The system further comprises a circuit arrangement for controlling the valves, in which circuit arrangement the valves oractuators controlling the valves are integrated. The circuit arrangement comprises at least four actuators, each with at least one actuating element, wherein each actuating element is adjustable between a first position and a second position. Furthermore, the circuit arrangement comprises at least one supply voltage path and one ground path, which form at least four current paths between them, wherein the at least four actuators for actuating the respective actuating element are integrated between the supply voltage path and the ground path in a circuit or the circuit arrangement in such a way that two actuators can be connected in pairs in series to one of the current paths and can be supplied with current. To deactivate all possible current paths or activate one of the current paths, the circuit arrangement comprises electronic switching elements for supplying current to none of the current paths or to one of the current paths connecting two actuators in series.Furthermore, the circuit arrangement comprises a current control circuit which is integrated in the circuit between the actuators which can be connected in series in pairs, wherein the current control circuit comprises a current source and a bypass circuit for the current source is integrated in the current control circuit.

[0024] The system or lumbar support is integrated in particular into a backrest of a seat, for example a vehicle seat in a motor vehicle, in order to adjust or set the contour of the backrest. To adjust the lumbar support and thus to set a desired seat contour, the air cushions are filled with different volumes of air or at least partially emptied, which is achieved by controlling the valves in the circuit arrangement. In a system with two air cushions, there are a total of four active and one inactive functions that can be executed by the circuit arrangement. In the "OPEN" function, a first, upper air cushion is filled and a second, lower air cushion is emptied. To fill the first, upper air cushion, a valve assigned to the first air cushion and arranged in the supply line between the first air cushion and the pneumatic pump is opened.To deflate the second, lower air cushion, a valve assigned to the second air cushion and located between the second air cushion and the atmosphere is opened at the same time. The two other valves, i.e. the valve located in the supply line between the first air cushion and the atmosphere and the valve located in the supply line between the second air cushion and the pneumatic pump, remain closed during this time. The other functions "DOWN", "FORWARD" and "BACKWARD" are achieved in a similar way by controlling the respective valves or actuators assigned to the valves in pairs, as will be explained in more detail below using the exemplary embodiment. For all four active functions, two of the valves or actuators can be switched into a common current path and are thus actuated or in their active position.

[0025] In particular, each valve is assigned an actuator with a control element, wherein the control element of the actuator closes a valve opening of the valve in the first or closed position and opens the valve opening of the valve in the second or released position. The valves or actuators are integrated into the circuit arrangement of the system in the manner described above.

[0026] Preferably, at least two valves or at least two actuators of the circuit are assigned to each air cushion, with two valves or actuators assigned to a first air cushion and two valves or actuators assigned to a second air cushion each being arranged in a parallel branch of the circuit. This allows the system's four active functions to be implemented cost-effectively and with minimal effort, without having to accept any significant functional limitations.

[0027] Further advantageous embodiments of the system are specified in the subclaims.

[0028] The invention will be explained in more detail below with regard to further features and advantages based on the description of exemplary embodiments and with reference to the accompanying drawings. Each of these drawings shows a schematic diagram: Fig. 1 a system, for example a lumbar support, with two air cushions and four valves, each controlled by an actuator, Fig. 2 a cross-section of a valve with an actuator, Fig. 3A - 3E different switching states of the lumbar support adjustment system, Fig. 4 a circuit arrangement according to the present invention, Fig. 5 a circuit diagram of an astable multivibrator, Fig. 6 a circuit diagram of a current source.

[0029] The Fig. The system 2 shown in Figure 1 is a pneumatically adjustable lumbar support that is housed in a vehicle seat (not shown) to adjust the contour of the backrest. The system 2 has a plurality of air cushions, for example two air cushions, namely a first, upper air cushion 4 and a second, lower air cushion 6. The air cushions 4, 6 are each connected to a pump 16 via a supply line 18a, 20a in order to fill the air cushions 4, 6 with air. A valve 12a, 14a, which is preferably designed as a 2 / 2-way valve, is arranged in the supply lines 18a, 20a between the pump 16 and the air cushion 4, 6. To empty the air cushions 4, 6, they are connected via lines and valves 12b, 14b to an atmosphere connection 18b, 20b or via an opening to the atmosphere, wherein the valves 12b, 14b are again preferably designed as 2 / 2-way valves.In a respective closed position of the valves 12a, 12b, 14a, 14b, the supply lines 18a, 20a, or the atmosphere connections 18b, 20b, are each closed, so that an air volume present in the air cushions 4, 6 is enclosed in a gas-tight manner. In a respective release position of the valves 12a, 12b, 14a, 14b, the respective supply line 18a, 20a, or the respective atmosphere connection 18b, 20b, is open, and the air cushions 4, 6 can be filled with air or emptied.

[0030] Depending on the inflation level of the two air cushions 4, 6, the lumbar support and thus the contour of the backrest can be adjusted. The first, upper air cushion 4 is inflated against pre-pressure by opening valve 12a and deflated to atmosphere by opening valve 12b. The second, lower air cushion 6 is inflated against pre-pressure by opening valve 14a and deflated to atmosphere by opening valve 14b.

[0031] The valves 12a, 12b, 14a, 14b are each actuated by an actuator 8a, 8b, 10a, 10b, as in Fig. 2 is shown in principle using valve 12a as an example. The other valves 12b, 14a, 14b and actuators 8b, 10a, 10b are designed accordingly. To control the valves 12a, 12b, 14a, 14b and the actuators 8a, 8b, 10a, 10b, the system 2 comprises a circuit arrangement, which is described in more detail below and into which the valves 12a, 12b, 14a, 14b and the actuators 8a, 8b, 10a, 10b are integrated. Each air cushion 4, 6 is assigned two valves 12a, 12b, 14a, 14b or two actuators 8a, 8b, 10a, 10b, wherein the two valves 12a, 12b or actuators 8a, 8b assigned to the first air cushion 4 and the two valves 14a, 14b or actuators 10a, 10b assigned to the second air cushion 6 are each arranged in a parallel branch of the circuit.

[0032] The valve 12a comprises according to Fig. 2 a pressure-tight valve housing 22 with a valve opening 24 and a media connection (not shown) for connecting an air cushion 4, 6, as well as a pressure connection (not shown) for connecting the pneumatic pump or an atmosphere connection or opening (not shown). Arranged within the valve housing 22 is the actuator 8a, which has an actuating element 26 that is movable perpendicular to a circuit board 28. The actuating element 26 is essentially cylindrical and has a sealing element 30 at its upper end for sealing the valve opening 24. A guide 38 is provided to guide the actuating element 26, in particular its upper end section. A lower end section of the actuating element 26 can additionally be guided within a bore (not shown) in the circuit board 28.To actuate the actuating element 26, the actuator 8a has a wire-shaped SMA element 32, which is fixed in a central section to the actuating element 26 and at both ends to the circuit board 28. In the de-energized state, the SMA element 32 has its greatest length. When current is applied to the SMA element 32, it shortens, the actuating element 26 is moved in the stroke direction 34 into its second position, and the valve opening 24 is opened. When the SMA element 32 is no longer supplied with current, it cools down until it transforms from the austenite phase to the martensite phase upon falling below the transformation temperature and thus lengthens again. As a result, the SMA element 32 no longer exerts any force on the actuating element 26, which is moved in the return direction opposite to the stroke direction into its first position, and the valve opening 24 is closed again by the sealing element 30.To reset the actuating element 26, a reset element 36 is attached to it, which in this example is a spring that concentrically encloses the actuating element 26.

[0033] To supply power to the actuator 8a, or more precisely, the SMA element 32, the latter is housed in the circuit arrangement. The power and signal lines required for operation are connected to the valve 12a via an interface 42.

[0034] One in Fig. 1 illustrated system 2 with four valves 12a, 12b, 14a, 14b, which are each actuated by an actuator 8a, 8b, 10a, 10b and thus their respective valve opening is released or closed by the respective actuating element of the actuator 8a, 8b, 10a, 10b, usually has four active and one inactive switching state, which in the Fig. 3A to 3E are shown schematically. In the inactive switching state ( Fig. 3A), none of the valves 12a, 12b, 14a, 14b or none of the actuators 8a, 8b, 10a, 10b are actuated, or none of the actuators 8a, 8b, 10a, 10b are energized, so that all valve openings are closed. As a result, the air volume present in both air cushions 4, 6 remains unchanged.

[0035] In the Fig. In the switching state shown in Figure 3B, the actuators 8a, 10b are actuated, thus opening the valves 12a, 14b. If the system 2 is controlled in this way, the "OPEN" function is realized, i.e., the first, upper air cushion 4 is inflated and the second, lower air cushion 6 is deflated. For this purpose, a current path 11a of the circuit arrangement, which connects the actuators 8a, 10b in series, is activated and energized, so that the control elements of the actuators 8a, 10b are actuated.

[0036] In the Fig. In the switching state shown in Figure 3C, the actuators 8a, 10a are actuated, thus opening the valves 12a, 14a to perform the "FOR" function, i.e., both the first, upper air cushion 4 and the second, lower air cushion 6 are filled with air. For this purpose, a current path 11b connecting the actuators 8a, 10a in series is closed and current flows through it, so that the control elements of the actuators 8a, 10a are actuated.

[0037] Fig. 3D shows the switching state for the function “AB”, in which a current path 11c connecting the actuators 8b, 10a in series is closed and thus the valves 12b, 14a are opened in order to empty the first, upper air cushion 4 and to fill the second, lower air cushion 6.

[0038] In the Fig. In the switching state shown in Figure 3E, the actuators 8b, 10b are actuated, thus opening the valves 12b, 14b. For this purpose, a current path 11d connecting the actuators 8b, 10b in series is activated and current flows through it, so that the control elements of the actuators 8b, 10b are actuated. This implements the "RETURN" function, i.e., both air cushions 4, 6 are deflated.

[0039] The four current paths 11a, 11b, 11c, 11d are formed in the circuit arrangement in that the circuit comprises a parallel circuit having two parallel strands, wherein in each of the at least two parallel strands, at least two actuators 8a, 8b or 10a, 10b are arranged in series, namely the actuators 8a, 8b assigned to the first air cushion 4 in a first parallel strand and the actuators 10a, 10b assigned to the second air cushion 6 in a second parallel strand. By applying current to one of the current paths 11b, 11d formed by one of the parallel strands, the "FOR" and "BACK" functions can be performed.Furthermore, the at least two parallel strands of the parallel circuit can be connected or interconnected via a further strand in such a way that an actuator 8a, 8b arranged in a first parallel strand can be connected in series with an actuator 10a, 10b arranged in a second parallel strand, represented by the current paths 11a, 11c, in order to be able to execute the functions "UP" and "DOWN".

[0040] In Fig. 4 shows a circuit arrangement 100 for controlling the system 2, for example a pneumatically adjustable lumbar support with two air cushions 4, 6 according to the present invention. The circuit arrangement 100 comprises, as already described, four actuators 8a, 8b, 10a, 10b, each with at least one actuating element 26, which is adjustable between a first position and a second position in order to open or close a valve opening. The four actuators 8a, 8b, 10a, 10b are integrated in the circuit between supply voltage paths 44a, 44b, 44c, 44d and a ground path 46, which form the four possible current paths 11a, 11b, 11c, 11d between them. To execute one of the functions, two of the at least four actuators 8a, 8b, 10a, 10b are each connected in accordance with the Fig. 3B to 3E, they are connected in pairs and in series to one of the current paths 11a, 11b, 11c, 11d and supplied with current. In other words: To perform a desired function, two of the actuators 8a, 8b, 10a, 10b are activated by current flowing through or activating the current path 11a, 11b, 11c, 11d assigned to the respective function.

[0041] The selection or activation of the respective current path 11a, 11b, 11c, 11d and thus of the two actuators 8a, 8b, 10a, 10b, which are to be actuated in order to open the respectively assigned valves 12a, 12b, 14a, 14b, is carried out by electronic switching elements integrated into the circuit arrangement 100. Each actuating element 26 of each actuator 8a, 8b, 10a, 10b is assigned an SMA element 32 for actuating it in a stroke direction (see Fig. 2), wherein the SMA elements 32 for actuating the actuating element 26 are integrated in the circuit between the supply voltage path 44a, 44b, 44c, 44d and the ground path 46 and can be supplied with current.

[0042] The electronic switching elements comprise a diode circuit 48 with a plurality of diodes 50, in this case eight diodes 50, for activating or closing one of the current paths 11a, 11b, 11c, 11d, with two diodes assigned to each actuator 8a, 8b, 10a, 10b. Furthermore, the electronic switching elements comprise a plurality of transistors 52, in this case two transistors 52. Activation of one of the current paths 11a, 11b, 11c, 11d is thus carried out solely by the electronic switching elements 48, 50, 52, thus eliminating the need for an additional control unit, thus saving costs.

[0043] In order to avoid thermal overload of the actuators 8a, 8b, 10a, 10b or their SMA elements by supplying too high a power due to fluctuating supply voltage, the circuit arrangement 100 has a current control circuit 54 which is integrated in the circuit between the actuators 8a, 8b, 10a, 10b, which can be connected in series in pairs, or between the actuators 8a, 8b assigned to the first, upper air cushion 4 and the actuators 10a, 10b assigned to the second, lower air cushion 6.

[0044] The current control circuit 54 comprises a pulse width modulation generator, in this case an astable multivibrator 56, and a temperature-dependent current source 58. Furthermore, a bypass circuit 60 with an ohmic resistor R_Bypass is integrated in the current control circuit in order to thermally relieve the current source 58 itself.

[0045] Fig. Figure 5 shows a circuit diagram of the astable multivibrator 56, which is used here as a PWM generator, as this represents a cost-effective option. The PWM generator generates a pulse-width modulated signal with a fixed frequency and a fixed duty cycle. This continuously switches the current flow on and off. With a duty cycle of 25%, for example, this means that the current is on for 25% of the time and off for 75% of the time. The frequency and duty cycle of the astable multivibrator 56 are fixed by the dimensioning of the resistors R1, R2, R3, and R4, as well as the capacitors C1 and C2. Pulse width modulation reduces the average power supplied to the SMA elements, thus preventing thermal overload of the SMA elements.

[0046] In order to take into account fluctuations in the supply voltage, as already mentioned, a temperature-dependent current source 58 is additionally integrated in the current control circuit 54, which Fig. 6 has a corresponding design. The transistor Q1 is in amplifier mode, ie it is only opened until the current I flowing through a resistor R_mess SMA creates a voltage drop as large as the (forward) forward voltage of a transistor Q2. This causes the transistor Q2 to begin conducting and feedback via Q3, so that a certain current I SMA Thus, by dimensioning R_mess, the current I SMAat a constant ambient temperature. R2 is chosen to be very high-impedance. Since the forward voltage of transistor Q2 is temperature-dependent, a temperature-dependent adjustment of the current I can also be achieved by selecting the appropriate transistor Q2. SMA reached.

[0047] If the entire current I SMAflow through the transistor Q1, it would heat up considerably due to the resulting power loss. This could be avoided, for example, by making the housing of the transistor Q1 sufficiently large to dissipate the resulting power loss to the environment. However, since a space-saving design is particularly desirable in a vehicle seat and such heat-resistant transistors are also expensive, a bypass circuit 60 is integrated into the current control circuit 54. By connecting R_Bypass in parallel to the current source 58, it is achieved that only a portion of the current I SMA flows through transistor Q1. The other part of the current I SMAflows through the bypass circuit 60, so that a portion of the resulting power loss is also dissipated via the resistor R_Bypass. This reduces the power loss of transistor Q1, allowing a space-saving and cost-effective transistor variant to be selected.

[0048] In summary, the circuit arrangement 100 can be constructed using a combination of the "H-arrangement" of the actuators 8a, 8b, 10a, 10b and the current control circuit 54, with few and inexpensive components such as diodes, transistors, resistors, and capacitors, without any limitations in functionality. The circuit arrangement 100 can be used regardless of the size of the supply voltage. Furthermore, a precisely defined current I SMA , which flows through the actuators 8a, 8b, 10a, 10b, and thus set a temperature-independent performance of the actuators 8a, 8b, 10a, 10b. List of reference symbols 2 systems 4 first, upper air cushion 6 second, lower air cushion 8, 8a, 8b Actuators first, upper air cushion 10, 10a, 10b Actuators second, lower air cushion 11a, 11b, 11c, 11d current path 12, 12a, 12b valves 12, 14a, 14b valves 16 Pump 18a, 20a supply line 18b, 20b atmosphere 22 valve housing 24 Valve opening 26 Control element 28 circuit board 30 sealing element 32 SMA element 34 Stroke direction 36 Reset element 38 leadership 42 Interface 44a, b, c, d supply voltage path 46 Ground path 48 electronic switch elements 50 diodes 52 transistors 54 Current control circuit 56 astable multivibrator 58 Power source 60 Bypass 100 circuit arrangement

Claims

[1] Circuit arrangement (100) for controlling a system (2), in particular a lumbar support with at least two air cushions (4, 6), comprising - at least four actuators (8a, 8b, 10a, 10b) each having at least one actuating element (26), each actuating element (26) being adjustable between a first position and a second position, - at least one supply voltage path (44a, 44b, 44c, 44d) and one ground path (46), which form at least four current paths (11a, 11b, 11c, 11d) between them, wherein the at least four actuators (8a, 8b, 10a, 10b) for actuating the actuating element (26) are integrated in a circuit between the supply voltage path (44a, 44b, 44c, 44d) and the ground path (46) in such a way that two actuators (8a, 8b, 10a, 10b) can be connected in pairs in series into one of the current paths (11a, 11b, 11c, 11d) and can be supplied with current, and - electronic switching elements (48, 50, 52) for supplying current to none of the current paths (11a, 11b, 11c, 11d) or to one of the current paths (11a, 11b, 11c, 11d), - a current control circuit (54) which is integrated in the circuit between the actuators (8a, 8b, 10a, 10b) which can be connected in series in pairs, wherein the current control circuit (54) comprises a current source (58) and wherein a bypass circuit (60) for the current source (58) is integrated in the current control circuit (54). [2] Circuit arrangement (100) according to claim 1, wherein the at least four current paths (11a, 11b, 11c, 11d) are formed in that the circuit comprises a parallel circuit having at least two parallel strands, wherein in each of the at least two parallel strands at least two actuators (8a, 8b; 10a, 10b) are arranged in series, and that the at least two parallel strands of the parallel circuit can be connected or are connected to one another via a further strand in such a way that an actuator (8a, 8b) arranged in a first parallel strand can be connected in series with an actuator (10a, 10b) arranged in a second parallel strand. [3] Circuit arrangement (100) according to one of the preceding claims, wherein each actuating element (26) is assigned an SMA element (32) for actuating it in a stroke direction, wherein the SMA elements (32) for actuating the actuating element (26) are integrated in the circuit between the supply voltage path (44a, 44b, 44c, 44d) and the ground path (46) in such a way that two SMA elements (32) can be connected in pairs in series into one of the current paths (11a, 11b, 11c, 11d) and can be supplied with current. [4] Circuit arrangement (100) according to one of the preceding claims, wherein the electronic switching elements (48, 50, 52) comprise a diode circuit (48) having a plurality of diodes (50) and / or one or more transistors (52), wherein at least one diode (50) is assigned to each actuator (8a, 8b, 10a, 10b). [5] Circuit arrangement (100) according to one of the preceding claims, wherein the current control circuit (54) comprises a pulse width modulation generator. [6] Circuit arrangement (100) according to claim 5, wherein the pulse width modulation generator is an astable multivibrator (56). [7] Circuit arrangement (100) according to one of the preceding claims, wherein the current control circuit (54) comprises a temperature-dependent current source. [8] System (2), in particular a pneumatically adjustable lumbar support, with at least two air cushions (4, 6), which are each connected to a pump (16) via a supply line (18a, 20a) for filling with air and each connected to the atmosphere for emptying, wherein in each supply line (18a, 20a) and / or between the air cushion (4, 6) and an atmosphere connection (18b, 20b) a valve (12a, 12b, 14a, 14b) is arranged, which can be switched between an open position in which the valve (12a, 12b, 14a, 14b) opens the supply line (18a, 20a) or releases the atmosphere connection (18b, 20b) and a closed position in which the valve (12a, 12b, 14a, 14b) closes or closes the atmosphere connection (18b, 20b), is adjustable, and with a circuit arrangement (100) for controlling the valves (12a, 12b, 14a, 14b) comprising - at least four actuators (8a, 8b, 10a, 10b) each having at least one actuating element (26), each actuating element (26) being adjustable between a first position and a second position, - at least one supply voltage path (44a, 44b, 44c, 44d) and one ground path (46), which form at least four current paths (11a, 11b, 11c, 11d) between them, wherein the at least four actuators (8a, 8b, 10a, 10b) for actuating the actuating element (26) are integrated in a circuit between the supply voltage path (44a, 44b, 44c, 44d) and the ground path (46) in such a way that two actuators (8a, 8b, 10a, 10b) can be connected in pairs in series into one of the current paths (11a, 11b, 11c, 11d) and can be supplied with current, - electronic switching elements (48, 50, 52) for supplying current to none of the current paths (11a, 11b, 11c, 11d) or to one of the current paths (11a, 11b, 11c, 11d), and - a current control circuit (54) which is integrated in the circuit between the actuators (8a, 8b, 10a, 10b) which can be connected in series in pairs, wherein the current control circuit (54) comprises a current source (58) and a bypass circuit (60) for the current source (58) is integrated in the current control circuit (54). [9] System (2) according to claim 8, wherein each valve (12a, 12b, 14a, 14b) is assigned an actuator (8a, 8b, 10a, 10b) and the actuating element of the actuator (8a, 8b, 10a, 10b) closes a valve opening (24) of the valve (12a, 12b, 14a, 14b) in the first position and releases the valve opening (24) of the valve (12a, 12b, 14a, 14b) in the second position. [10] System (2) according to one of claims 8 or 9, wherein at least two actuators (8a, 8b; 10a, 10b) are assigned to each air cushion (4, 6), wherein in particular two actuators (8a, 8b) assigned to a first air cushion (4) and two actuators (10a, 10b) assigned to a second air cushion (6) are each arranged in a parallel branch of the circuit. [11] System (2) according to one of claims 8 to 10, wherein the at least four current paths (11a, 11b, 11c, 11d) of the circuit arrangement (100) are formed in that the circuit comprises a parallel circuit having at least two parallel strands, wherein in each of the at least two parallel strands at least two actuators (8a, 8b; 10a, 10b) are arranged in series, and that the at least two parallel strands of the parallel circuit can be connected or are connected to one another via a further strand in such a way that an actuator (8a, 8b) arranged in a first parallel strand can be connected in series with an actuator (10a, 10b) arranged in a second parallel strand. [12] System (2) according to one of claims 8 to 11, wherein each actuating element (26) of the circuit arrangement (100) is assigned an SMA element (32) for actuating it in a stroke direction, wherein the SMA elements (32) for actuating the actuating element (26) are integrated in the circuit between the supply voltage path (44a, 44b, 44c, 44d) and the ground path (46) in such a way that two SMA elements (32) can be connected in pairs in series into one of the current paths (11a, 11b, 11c, 11d) and can be supplied with current. [13] System (2) according to one of claims 8 to 12, wherein the electronic switching elements (48, 50, 52) of the circuit arrangement (100) comprise a diode circuit (48) having a plurality of diodes (50) and / or one or more transistors (52), wherein at least one diode (50) is assigned to each actuator (8a, 8b, 10a, 10b). [14] System (2) according to one of claims 8 to 13, wherein the current control circuit (54) comprises a pulse width modulation generator, wherein the pulse width modulation generator is in particular an astable multivibrator (56). [15] System (2) according to one of claims 8 or 14, wherein the current control circuit (54) comprises a temperature-dependent current source.

Images