Actuator for flaps in gas-carrying pipes, especially in exhaust systems, of internal combustion engines

Abstract

Drive for flaps in gas-carrying pipes, in particular in exhaust systems, of internal combustion engines, with a housing in which an electric motor is housed, the drive shaft of which drives an output shaft via at least one gear stage designed as a worm gear, which is subject to a return force, characterized in that the output shaft (23) is subject to the force of at least one return spring (27) arranged in the housing (1), and that the return force is sufficient to overcome the friction between the gear parts (18, 19) of the worm gear (33) and to return the output shaft (23) to its initial position.

Description

[0001] The invention relates to a drive for flaps in gas-carrying pipes, in particular in exhaust systems, of internal combustion engines according to the preamble of claim 1.

[0002] Such drives are used, for example, for exhaust flaps in combustion engines. The exhaust flaps are mounted on flap shafts so they can be pivoted from an open position towards a closed position. An electric motor drives the flap shaft via a spur gear and the output shaft. Such spur gears have a high efficiency. The rotation angle of the output shaft is limited by stops, against which counter-stops strike in the respective end positions. This often results in a considerable noise upon impact.

[0003] The output shaft is biased towards its starting position by a return spring, which, in the event of a malfunction, ensures that the output shaft, and thus the exhaust flap, returns to its initial or closed position. This results in the counter-stops striking the stop hard, which poses a risk of damage to drive components.

[0004] German patent DE 10 2008 052 846 A1 describes an exhaust flap actuator for a motor vehicle, which can be used for various vehicle types. Elements such as damping or coupling elements, for example made of elastomer or designed as a spring, can be interposed between the actuator and the exhaust flap. As a torsion spring, it ensures that the exhaust flap rests securely against its end stop and, if necessary, dampens vibrations. The spring compensates for play in the cable and also dampens rattling noises caused by the cable.

[0005] US Patent 2009 / 0018750A1 discloses a fuel injection system for internal combustion engines. The system comprises a housing with a throttle shaft, an electric motor, a worm drive, and a spring. The spring assists the throttle shaft in returning to its original position after it has been rotated by the motor. Due to the arrangement of the worm drive as the throttle shaft's actuator, the motor rotates it in both directions. Only in the closing direction is the spring, previously compressed in the opening direction, assisted.

[0006] DE 10 2006 041 562 A1 and DE 103 21 653 B3 each describe an identical actuating device for an internal combustion engine. These actuating devices do not require springs in or on the drive mechanism.

[0007] DE 600 10 019 T2 describes a servo valve with worm drives. In this design, a worm shaft is subject to a return force provided by a spring. The worm shaft is the input shaft. The worm wheel is mounted on the output shaft. The output shaft is not subject to any return force.

[0008] German patent DE 10 2005 033 601 A1 discloses an actuator for an exhaust gas flap. The actuator has a drive unit housed in a casing. The drive unit incorporates a worm gear. Neither the worm shaft nor the output shaft carrying the worm gear is subject to a return force. A coil spring acts directly on the valve flap shaft.

[0009] The invention is based on the objective of designing the generic drive in such a way that it ensures quiet operation in a cost-effective and compact design.

[0010] This problem is solved according to the invention in the generic drive with the characterizing features of claim 1.

[0011] The drive according to the invention is characterized by the fact that the gear stage is a worm gear. In contrast to a spur gear, the worm gear has a lower efficiency, but this is offset by significant advantages. High friction exists between the worm and the worm wheel of the worm gear, which offers the advantage that the output shaft, and thus the flap, can be held in the respective position, thereby allowing the current supplied by the electric motor to be correspondingly low. The drive itself does not need to be mechanically particularly robust. In the event of a malfunction, the output shaft or the flap is slowly returned to its initial position by a return spring, which is due to the high friction between the worm and the worm wheel of the worm gear. The high friction results in these gear components rotating back slowly.This prevents a hard impact between the stops and counter-stops at the end of the return stroke, thus eliminating impact noise. Furthermore, there is no risk of damaging any parts of the drive. The worm gear allows for very quiet operation, making the drive particularly suitable for applications where low noise levels are critical. Since the worm gear requires minimal installation space, the drive unit has a very compact design.

[0012] It is advantageous if the electric motor is arranged horizontally within the housing. This position of the electric motor contributes to a compact design.

[0013] It is advantageous if the worm gear of the worm drive is rotationally fixed to a coaxial gear of a second gear stage. This places the worm gear and the gear on the same axis, contributing to a compact design. It is particularly advantageous if the worm gear and the gear are formed as a single unit.

[0014] The gear is advantageously meshed with another gear that is fixed to the output shaft. These two gears form the second gear stage, which drives the output shaft from the electric motor. In this configuration, the drive according to the invention is advantageously designed as a two-stage unit. This reduces the number of gear components required to reduce the speed of the worm gear to the speed of the output shaft. This contributes to the compact design of the drive.

[0015] Since the flap is only pivoted back and forth between a closed position and a maximum open position, it is advantageous to design the gear on the output shaft as a gear segment.

[0016] The output shaft is advantageously subjected to the force of at least one return spring, preferably a coil spring. This return spring, for example, returns the output shaft and thus the flap to its initial position in the event of a malfunction.

[0017] To minimize the space required for the return spring, it is advantageously located in the area between the housing base and the worm gear. If the return spring extends below the worm gear, the worm gear serves at least partially as a cover for the return spring.

[0018] It is advantageous if the return spring is at least partially covered by a disc, which protects the return spring.

[0019] The disc is advantageously connected in a rotationally fixed manner to the gear wheel located on the output shaft, preferably formed in one piece with it.

[0020] However, it is also possible to mount the disc rotatably on the output shaft so that it remains in its covering position when the gear rotates.

[0021] Simple detection of the rotation angle of the output shaft and thus the pivot position of the flap is ensured if the drive is equipped with a position detection device for the output shaft.

[0022] Further features of the invention emerge from the further claims, the description and the drawings.

[0023] The invention will be explained in more detail with reference to an embodiment shown in the drawings. Fig. 1 in plan view a drive according to the invention, Fig. 2 the drive according to the invention according to Fig. 1 in perspective view, Fig. 3. Make a cut along line AA in Fig. 1, Fig. 4. Make a cut along line BB in Fig. 1, Fig. 5 a cut along line CC in Fig. 1.

[0024] The actuator described below is designed for exhaust flaps of internal combustion engines, in particular for throttling the exhaust stream of a diesel engine. These actuators can, of course, be used generally for flaps in gas-carrying pipes; that is, the actuator is not limited to use with exhaust flaps.

[0025] The drive unit has a polygonal housing 1 with side walls 2 to 8. Advantageously, the side walls are flat. They are arranged so that they surround the drive components with minimal spacing, thus saving space. Side wall 2 connects at an obtuse angle to side wall 3, which in turn transitions at an obtuse angle into side wall 4. It lies parallel to the opposite side wall 8, which, for example, is longer than side wall 4 and connects at a right angle to side wall 2.

[0026] Parallel to side wall 2 lies side wall 6, which is, however, significantly shorter than side wall 2. Side wall 6 is connected to side walls 4 and 8 via side walls 5 and 7, which adjoin it at obtuse angles. Side walls 2 to 8 are advantageously of the same height and are connected to each other by a base 9, which is advantageously formed integrally with side walls 2 to 8.

[0027] Adjacent to the side wall 2, an electric motor 10 is arranged horizontally in the housing 1. Its longitudinal axis lies parallel to the side wall 2 and to the base 9.

[0028] An axially projecting bearing 11, 12 is provided on each of the end faces of the motor housing of the electric motor 8, which is supported by a stator 13, 14. The stators 13, 14 project from the housing base 9 and are advantageously formed integrally with it ( Fig. 5) As can be seen from Fig. If the result is 5, the housing 1 can be closed by a cover 15 which advantageously has supports 16, 17 on its inside that partially overlap the bearings 11, 12 from above. Thus, the electric motor 10 is perfectly supported in the housing by the bottom supports 13, 14 and the covers-side supports 16, 17.

[0029] Inside the housing 1, a drive shaft 18 protrudes from the housing of the electric motor 10, running parallel to the base 9 and designed as a worm gear. Its axis lies approximately at the level of the transition between the side walls 3 and 4 of the housing 1 ( Fig. 1) The worm 18 meshes with a worm wheel 19, which is provided at approximately half the height of the housing 1 and is located a short distance from the side wall 4 of the housing 1. The worm wheel 19 is rotatably mounted on an axle 20 that runs perpendicular to the base 9. In the exemplary embodiment, it projects inwards from the housing cover 15 ( Fig. 3) It has straight teeth and a significantly smaller diameter than the worm gear 19. In the exemplary embodiment, the gear 21 is formed integrally with the worm gear 19. However, the gear 21 can also be a separate gear component from the worm gear 19, which is rotationally fixed to the worm gear 19.

[0030] The gear 21 is engaged with a gear segment 25 of a transmission element 22, which is fixedly mounted on an output shaft 23. Its lower end is supported in a bottom-mounted bearing 24 ( Fig. 3 and Fig. 4) stored.

[0031] The gear 25 is advantageously integrally connected to a semicircular disk 26, which is axially offset from the gear 25 and located near the housing base 9. The segmented disk 26 partially covers a coil spring 27, which loads the output shaft 23 in one direction of rotation. The output shaft 23 is non-rotatably connected to an exhaust flap shaft (not shown) of an exhaust system.

[0032] The spiral spring 27 is attached at one end to the housing 1 and at the other end to the output shaft 23.

[0033] The gear 25 can be designed not only in a segmented form but also in a ring-shaped form, unlike the illustrated embodiment. However, since the exhaust flap only pivots between a closed position and a fully open position, the segmented design of the gear 25 is sufficient. The gear segment 25 is fixed to the output shaft 23 by means of a hub 28. A magnetic ring 29 is embedded in the hub 28 and is part of a position detection device 30, which reliably detects the rotational position of the output shaft 23 and thus the pivoting position of the exhaust flap.

[0034] Any suitable sensor, such as Hall effect sensors, can be used. The sensor 31 is mounted on a circuit board 32, which is positioned in the area above the disk 26, a short distance from the electric motor 10, and is appropriately secured in the housing. The circuit board 32 carries the electrical / electronic components required for the operation of the drive.

[0035] The worm 18 and the worm gear 19 form a first gear stage 33. This worm gear stage enables a high reduction ratio, so that the high speed of the electric motor 10 can be reduced to a sufficiently low speed in just one gear stage. The gear 21, which is rotationally fixed to the worm gear 19, meshes with the segmented gear 25, forming a second gear stage 34. The gear 21 has a significantly smaller diameter than the gear segment 25, resulting in a further high reduction ratio. Thus, in just two gear stages 33 and 34, the speed of the worm 18 is reduced to the speed of the output shaft 23 for pivoting the throttle valve. This requires only a few gear components, contributing to a very compact design of the drive. The circuit board 32 extends over the disk 26 to near the hub 28 of the gear segment 25.This overlap also contributes to the compact design of the drive. The printed circuit board 32 is located very close to the electric motor 10, so that little installation space is required for the printed circuit board. The printed circuit board 32 widens from the housing side wall 8 toward the output shaft 23. Approximately at the level of the disk 26, in a top view according to . Fig. As seen in Figure 1, the circuit board 32 continues in the form of a narrow arm that extends close to the hub 28 and on which the sensor 31 is arranged. The width of this protruding circuit board arm is smaller than the diameter of the hub 28, so that the circuit board 32 does not require any additional installation space.

[0036] The gear stages 33, 34 are arranged so that a straight line 35 connecting the longitudinal axes of the axle 20 and the output shaft 23 is at an acute angle to the axis 36 of the electric motor 10 ( Fig.1) In this way, the gear stages 33, 34 are located within the housing 1 in a space-saving manner. The housing side walls 4 to 6 are arranged at such an angle to each other that they surround the gear stages 33, 34 with only a small distance, which contributes to the compactness of the housing 1.

[0037] To pivot the exhaust flap from the open position to a closed position, the electric motor 10 is actuated. The output shaft 23 is rotated against the force of the coil spring 27 via the gear stages 33 and 34. The rotation of the output shaft 23, and thus the pivoting range of the exhaust flap, can be easily detected via the magnetic ring 29 and the sensor 31. As soon as the desired pivoting range of the exhaust flap is reached, the electric motor 10 receives only enough current to hold the exhaust flap in this position. This current is low because there is high friction between the worm gear 18 and the worm wheel 19, which helps to hold the output shaft 23 and thus the exhaust flap. In this way, the exhaust flap can be pivoted to any desired intermediate position. To close the exhaust flap again, the worm gear 18 is driven in the opposite direction, which rotates the output shaft 23 accordingly.In this case, the spiral spring 27 supports the rotary movement of the output shaft 23 or the pivoting back of the exhaust flap.

[0038] It is possible to limit the rotational path of the toothed segment 25 by means of stops. These stops can interact with counter-stops fixed to the housing in such a way that the stop position is maintained both in the closed position and in the fully open position of the exhaust flap. This allows the exhaust flap to be pivoted reliably and quickly between the closed and fully open positions.

[0039] The electric motor 10 does not need to be reversible in its direction of rotation because the output shaft 23 is always loaded toward the closed position of the exhaust flap via the spiral spring 27. The spiral spring 27 has such a high restoring force that it overcomes the frictional and inhibiting forces between the individual gears of the two-stage transmission. The electric motor 10 is only switched on when the exhaust flap is to be opened. To pivot the exhaust flap back, the electric motor 10 is switched off. The spiral spring 27 rotates the gear segment 25 back toward its original position. The worm 18 of the electric motor 10 is accordingly rotated back via the gear stages 33, 34.

[0040] In the illustrated and described embodiment, the gearbox is designed as a two-stage unit. However, the described drive is not limited to this configuration. Since high reduction ratios can be achieved with a worm gear, the second gear stage can be omitted if the reduction provided by the worm gear alone is sufficient. In this case, the worm wheel 19 directly drives the output shaft 23 and is fixed to the output shaft 31. Such a single-stage gearbox design results in a particularly compact drive unit.

Claims

[1] Drive for flaps in gas-carrying pipes, in particular in exhaust systems, of internal combustion engines, with a housing in which an electric motor is accommodated, the drive shaft of which drives an output shaft via at least one gear stage designed as a worm gear, which output shaft is subject to a return force, characterized by that the output shaft (23) is under the force of at least one return spring (27) arranged in the housing (1), and that the return force is sufficient to overcome the friction between the gear parts (18, 19) of the worm gear (33) and to return the output shaft (23) to its starting position. [2] Drive according to claim 1, characterized by that the electric motor (10) is arranged horizontally in the housing (1). [3] Drive according to claim 1 or 2, characterized bythat the worm wheel (19) of the worm gear (33) is connected in a rotationally fixed manner to a coaxial gear wheel (21) of a second gear stage (34), preferably formed in one piece with it. [4] Drive according to claim 3, characterized by that the gear (21) is in engagement with another gear (25) which is non-rotatably mounted on the output shaft (23). [5] Drive according to claim 4, characterized by that the gear (25) on the output shaft (23) is designed as a gear segment. [6] Drive according to one of claims 1 to 5, characterized by that the output shaft (23) is under the force of at least one spiral spring (27) as a return spring. [7] Drive according to one of claims 1 to 6, characterized by that the return spring (27) is located in the area between the housing base (9) and the worm wheel (19). [8] Drive according to one of claims 1 to 7, characterized bythat the return spring (27) is at least partially covered by a disc (26). [9] Drive according to claim 8, characterized by that the disc (26) is connected in a rotationally fixed manner to the gear (25) seated on the output shaft (23), preferably being formed integrally therewith. [10] Drive according to one of claims 1 to 9, characterized by that a position detection device (30) is provided for the output shaft (23).

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