Drive train with thermal overload protection

Abstract

Drive train (10), comprising a drive element (14), an output element (16) and a thermal overload protection device (12), wherein the thermal overload protection device (12) is designed such that below a critical temperature there is a connection between the drive element (14) and the output element (16) and above the critical temperature the drive element (14) and the output element (16) are mechanically decoupled from one another, wherein the thermal overload protection device (12) comprises at least one thermal protection element (20), characterized in that the volume of the thermal protection element (20) decreases above the critical temperature.

Description

[0001] The present invention relates to a drive train.

[0002] State-of-the-art overload clutches, which are arranged in the load flow of a drive, act on torque overload, so that they trigger in the event of a mechanical overload. When a preset limit torque is reached, they decouple a drive element from an output element and thus prevent damage. For example, such known overload clutches have shear pins that break in the event of a mechanical overload, i.e. when the preset limit torque is reached or exceeded. Slipping overload clutches are also known. Such clutches can have balls that transmit the torque and, above a certain torque, are pressed out of their seat against a spring force, causing disengagement. Alternatively, such clutches can transmit the torque using frictional engagement, whereby an overload causes slipping between frictionally connected torque transmission elements.If the drivetrain is exposed to critical operating conditions during operation, such as thermal stress, a component of the drivetrain, particularly a bearing or gearing, may fail before the preset torque limit is reached. This can lead to drivetrain failure despite the overload clutch, since the overload clutch only triggers when the preset torque limit is reached.

[0003] FR 1 061 450 A describes a device for coupling rotating parts, comprising a drive element and an output element connected to each other by heat-sensitive intermediate elements which interrupt the coupling as soon as the device exceeds a certain limit temperature.

[0004] DE 27 36 636 A1 discloses a coupling which has a safety element which is sensitive to temperature increases.

[0005] It is therefore an object of the present invention to provide a drive train with a protective mechanism that effectively prevents failure even under critical operating conditions.

[0006] The problem is solved by a drive train comprising a drive element, an output element, and a thermal overload protection device. The thermal overload protection device is designed such that below a critical temperature, a connection exists between the drive element and the output element, and above the critical temperature, the drive element and the output element are mechanically decoupled from one another. The thermal overload protection device comprises at least one thermal protection element, wherein the volume of the thermal protection element decreases above the critical temperature. For example, there is a positive and / or non-positive connection between the drive element and the output element.

[0007] The thermal overload protection function can be provided via the thermal fuse element. The at least one thermal fuse element can act in the circumferential direction or in the axial direction. In particular, several fuse elements are provided, which, for example, have different directions of action.

[0008] In particular, the fuse element is thermally reversible. As soon as the temperature drops below the critical temperature, the fuse element returns to its original state.

[0009] The basic idea of the invention is that the transmission of motion from the input element to the output element depends on the ambient temperature in the drive train. The thermal overload protection device therefore interrupts the transmission of torque via the drive train if the temperature is too high, which could potentially cause damage to the drive train. The mechanical decoupling above a critical temperature prevents safety-critical blocking, thereby preventing damage to the drive train. It ensures that the components of the drive train are not weakened by the thermal load to such an extent that they are damaged by the acting forces before the torque overload protection device is reached. In general, the thermal overload protection device therefore protects the drive train from overheating, which can occur, for example, if there is a lack of lubrication.This creates a cost-effective way to effectively protect a powertrain. The critical temperature can correspond to the tempering temperature of a metal or the melting temperature of a plastic.

[0010] In particular, it is a drive train of a motor vehicle.

[0011] The input element, the output element, and the thermal overload protection device can be part of a transmission. A torque to be transmitted can be applied to the input element, for example, from a motor vehicle engine.

[0012] The drive element and the output element can be configured such that a torque from the drive element can be transmitted to the output element. The drive element can preferably transmit a torque to the output element, which converts the torque and transmits it to at least one further element, for example, to a wheel of the motor vehicle.

[0013] The transmission of torque from the drive element to the output element can be achieved via a positive and / or non-positive connection via the thermal overload protection.

[0014] According to one embodiment, the overload protection device is designed as a thermal clutch, in particular as a thermal overload clutch. In this respect, it can assume an open position in which no torque is transmitted, and a closed position in which torque is transmitted. Furthermore, the thermal clutch ensures that it can react quickly to changing temperatures, so that the thermal clutch triggers when the critical temperature is reached or exceeded.

[0015] During normal operation of a motor vehicle, the temperature in the area surrounding the drivetrain is preferably below the critical temperature. However, in the event of malfunctions or errors during operation, such as a lack of lubrication, the temperature can rise above the critical temperature. This is also referred to as a critical operating condition.

[0016] A fluid, such as a lubricating or gear oil, is typically used in the transmission to reduce friction and dissipate heat loss in the drivetrain environment. In demanding environmental conditions, higher-viscosity fluids such as lubricating greases are also used to further protect components from dirt, for example.

[0017] To mechanically decouple the drive element and the output element above the critical temperature, the thermal fuse element can be designed in such a way that it changes its mechanical properties above the critical temperature. For example, the fuse element loses strength above the critical temperature, so that it becomes flexible or bends.

[0018] The safety element can be designed as a bolt, particularly a threaded bolt, or as a spring. Such safety elements are particularly simple and cost-effective to manufacture, thus reducing manufacturing and repair costs for the thermal overload protection device if the thermal overload protection device has been triggered.

[0019] According to a further aspect of the invention, the safety element can be designed such that it breaks above the critical temperature and a predefined force. Thus, the drive train has a thermal predetermined breaking point due to the thermal overload protection, since the thermal overload protection breaks above the critical temperature.

[0020] For example, the at least one securing element comprises a shape memory alloy so that it always returns to its original shape when the temperature drops below the critical temperature.

[0021] The at least one thermal fuse element can be arranged between the drive element and the output element. The at least one thermal fuse element can thereby ensure a mechanical, in particular positive-locking, connection between the drive element and the output element. In particular, the at least one thermal fuse element is arranged in the radial direction between the drive element and the output element.

[0022] The at least one safety element can alternatively act in the axial direction on the drive or output element. For example, in a claw clutch, the at least one thermal safety element can act axially against at least one claw, which attempts to self-decouple via a spring element, in particular a disc or coil spring.

[0023] Alternatively, the spring element can be omitted if at least one claw has bevels so that it self-aligns due to the drive power if the thermal overload protection is triggered.

[0024] In particular, above the critical temperature, the torque flow in the drive train is mechanically interrupted. This can provide the advantage of protecting drive train components, particularly from mechanical overload. In this respect, the thermal overload protection device protects against mechanical overload by mechanically interrupting the torque flow.

[0025] A further advantage of the invention is that when repairing the drive, only the thermal fuse element needs to be replaced if it was damaged or destroyed when the thermal overload protection device was triggered. This keeps the costs and labor required for the repair low.

[0026] The thermal fuse element may comprise a plastic, a metal, or an expansion material, in particular consisting of one of these materials. Furthermore, the thermal fuse element may consist of a combination of two or more of these materials.

[0027] According to one embodiment, the drive train can have an overload protection unit to decouple in the event of both thermal and mechanical overload. For example, the thermal overload protection can be designed such that the drive and output elements are mechanically decoupled not only above a critical temperature, but also below a critical temperature above a predefined force or torque. This can ensure that safety-critical blocking does not occur in the event of either thermal or mechanical overload. A force at which the safety element breaks below the critical temperature is preferably greater than a force at which the safety element breaks above the critical temperature.

[0028] According to a further embodiment of the invention, the drive train can have at least one thermal overload protection device and additionally at least one mechanical overload protection device, for example, a torque overload protection device. The overload protection unit then comprises, in addition to the thermal overload protection device, the mechanical overload protection device, in particular the torque overload protection device.

[0029] Preferably, the drive element is a shaft. However, the drive element can also be designed as a drive pinion, a piston, or the like.

[0030] The output element can be designed as a hub. Alternatively, the output element can also be designed as a pinion, a shaft, such as a crankshaft, or something similar.

[0031] The above describes the use of the overload protection device for an application in a motor vehicle. However, the overload protection device can also be used in many other areas, for example, in pumps, tool spindles, or other power-carrying components.

[0032] Further features and advantages of the invention will become apparent from the following description and the accompanying drawings, to which reference is made. In the drawings: - Fig. 1 a schematic sectional view of a drive train according to the invention with a thermal overload protection device according to a first embodiment, - Fig. 2 a schematic sectional view of a drive train according to the invention with a thermal overload protection device according to a second embodiment, and - Fig. 3 a schematic sectional view of a drive train according to the invention with a thermal overload protection device according to a third embodiment.

[0033] Fig. Figure 1 schematically shows a cross-section through a drive train 10 for transmitting torque. For example, this is a drive train of a motor vehicle, i.e., a motor vehicle drive train.

[0034] The drive train 10 has a thermal overload protection device 12, a drive element 14 and an output element 16. The drive element 14 according to the Fig. 1 is designed as a shaft, whereas the output element 16 is designed as a hub.

[0035] The thermal overload protection device 12 forms a thermal coupling 18, in particular a thermal overload coupling, which is provided between the drive element 14 and the output element 16.

[0036] In the embodiment shown, the thermal overload protection device 12 comprises a thermal safety element 20, which acts in the radial direction between the drive element 14 and the output element 16. The drive element 14 is non-positively connected to the output element 16 via the thermal safety element 20, wherein a positive connection can be present between the drive element 14 and the safety element 20, as well as between the output element 16 and the safety element 20. The thermal safety element 20 is also arranged between the drive element 14 and the output element 16, in particular in the radial direction.

[0037] The thermal fuse element 20 is designed as a spring 22, in particular as a key. Both the drive element 14 and the output element 16 each have a receptacle 24, 25 in which the fuse element 20 is positively received, in particular can engage, so that a torque can be transmitted from the drive element 14 to the output element 16.

[0038] In the event of a thermal overload, particularly when a critical temperature is exceeded, the safety element 20, designed as a spring 22, can change its mechanical properties. Due to its changed mechanical properties, the spring 22 can lose strength, causing the resulting shear forces to at least partially shear off the spring 22. This causes the thermal clutch 18 to trigger, mechanically interrupting the torque transmission. Consequently, the drive element 14 and the output element 16 are mechanically decoupled. This prevents damage to other elements of the drive train 10, which are connected, for example, to the output element 16.

[0039] Alternatively, the securing element 20 can be designed as a bolt 26, which also changes its mechanical properties above the critical temperature. For example, the bolt 26 loses strength, causing it to break if a (pre-)determined force acts on the bolt 26.

[0040] To repair the coupling 18 or the thermal overload protection device 12 after reaching or exceeding the critical temperature, it is sufficient to replace the safety element 20. This makes repair in the event of a thermal overload particularly simple and cost-effective.

[0041] Alternatively or additionally, the securing element 20 is provided to change its volume above the critical temperature. The securing element 20 can reversibly return to its original shape, for example, due to a shape memory alloy, so that repair is not necessarily required.

[0042] Regardless of the type of safety element 20, the thermal overload protection 12 ensures that a torque flow via the drive and output elements 14, 16, i.e. in the drive train 10, is mechanically interrupted if the critical temperature has been reached or exceeded.

[0043] Fig. 2 shows a section of a drive train 10 according to a second embodiment in a sectional view.

[0044] In the Fig. In the embodiment shown in Figure 2, the drive element 14 and the output element 16 are each designed as a flange hub, which are arranged, for example, at a shaft end not shown.

[0045] The thermal overload protection device 12 has the thermal safety element 20, which in the embodiment shown is designed as a bolt 26, in particular as a shear pin. The drive element 14 and the output element 16 each have at least one bore 28, 30. The safety element 20 is arranged within the bores 28, 30. As a result, the drive element 14 and the output element 16 are non-positively connected to one another, so that a torque can be transmitted from the drive element 14 to the output element 16. A hardened sleeve 32, 33 can optionally be arranged within the bores 28, 30.

[0046] The securing element 20 has a material weakening 34, for example, a notch, that serves as a predetermined breaking point. If the securing element 20 loses strength due to thermal overload, it can break along the predetermined breaking point.

[0047] The Fig. However, the thermal fuse element 20 shown in Figure 2 can also be designed such that it breaks along the predetermined breaking point in the event of mechanical overload.

[0048] Fig. Figure 3 shows a portion of a drive train 10 according to a third embodiment, which includes a claw clutch 36. The input element 14 and the output element 16 are each configured as claws 38 with helical teeth, the teeth meshing during proper operation. The input element 14 and the output element 16 can be connected to a shaft 40, 42 in a force-fitting manner by shrinking or in a form-fitting manner by means of a key or the like.

[0049] The drive element 14 and the output element 16 are held in engagement with each other by a thermal safety element 20. The safety element 20 is arranged on the output element 16 and acts on the output element 16 in the axial direction. The safety element 20 can also be arranged at other positions in the drive train 10, for example, upstream of the drive element 14, as long as the drive element 14 and the output element 16 are positively engaged by the safety element 20.

[0050] In general, the axial direction is the direction along which the shafts 40, 42 extend.

[0051] The axial direction therefore defines the axis of rotation of the drive and output elements 14, 16.

[0052] The Fig. The drive train 10 shown in Figure 3 has a retaining element 44. The retaining element 44 can be shrunk onto the shaft 42 or connected to it in some other way. The output element 16 and the retaining element 44 are movable relative to one another, in particular, the output element 16 is movable in the axial direction.

[0053] The securing element 20 is arranged between the output element 16 and the holding element 44. The holding element 44 has a recess 46 in the axial direction.

[0054] During normal operation of the drive train 10, particularly when the temperature in the drive train is below the critical temperature, the securing element 20 is arranged partly in the recess 46 and partly outside the recess 46. The securing element 20 presses the output element 16 against the input element 14, so that they are held in toothed engagement, i.e., in positive engagement. Fig. 3, the drive train 10 is shown in a state during normal operation.

[0055] If the temperature within the drive train 10 rises above the critical temperature, the retaining element 20 can change its volume and optionally its mechanical properties, for example, lose strength or break. This allows the output element 16 to disengage from the toothed engagement with the input element 14 and move axially on the retaining element 44, which simultaneously serves as a guide element.

[0056] In particular, in the mechanically decoupled state, the output element 16 moves back and forth between the drive element 14 and a stop 48 of the holding element 44 on the holding element 44. When the output element 16 abuts the stop 48, the drive element 14 and the output element 16 are completely mechanically decoupled.

[0057] Due to the helical toothing of the claws shown, no spring element is necessary to decouple the drive element 14 and the output element 16 from each other; in this case, the clutch 18, 36 is automatically relieved due to the acting torque.

[0058] Furthermore, the securing element 20 can also be designed as a spring that presses the output element 16 into the coupled position. The spring force decreases with increasing temperature, so that the clutch 18, 36 automatically disengages due to the acting torque. The spring can be made of an expandable material.

[0059] However, alternative design options are also conceivable in which the mechanical decoupling of drive element 14 and output element 16 is supported by a spring element. For example, this is a tension spring that actively decouples the output element 16 if the securing element 20 changes its mechanical properties so that the tensile force exceeds the holding force of the securing element 20.

[0060] The output element 16 does not necessarily have to be mounted on the holding element 44; it can also be mounted directly on the shaft 42 in a sliding manner.

[0061] In an alternative embodiment, the drive element 14 can be slidably mounted and the output element 16 can be fixed in position with respect to the axial direction or longitudinal direction of the drive train 10.

[0062] In general, the securing element 20 is located in Fig. 3 shown embodiment is not in the power flow.

[0063] The thermal overload protection device 12 can be used to establish a mechanical connection between the drive element 14 and the output element 16.

Claims

[1] Drive train (10), comprising a drive element (14), an output element (16) and a thermal overload protection device (12), wherein the thermal overload protection device (12) is designed such that below a critical temperature there is a connection between the drive element (14) and the output element (16) and above the critical temperature the drive element (14) and the output element (16) are mechanically decoupled from one another, wherein the thermal overload protection device (12) comprises at least one thermal protection element (20), characterized by that the volume of the thermal fuse element (20) decreases above the critical temperature. [2] Drive train (10) according to claim 1, characterized by that the overload protection device is a thermal coupling (18) which is arranged between the drive element (14) and the output element (16). [3] Drive train (10) according to one of the preceding claims, characterized bythat the thermal fuse element (20) is designed as a bolt (26) or a spring (22). [4] Drive train (10) according to one of the preceding claims, characterized by that the thermal fuse element (20) breaks above a critical temperature and a predefined force. [5] Drive train (10) according to one of the preceding claims, characterized by that above the critical temperature a torque flow in the drive train (10) is mechanically interrupted. [6] Drive train (10) according to one of the preceding claims, characterized by that the drive element (14) is designed as a shaft and the output element (16) as a hub.

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