Method for determining belt wear in a belt drive and belt drive

Abstract

Method for determining belt wear in a belt drive, in particular in a belt-driven starter generator (3) of an internal combustion engine, which has a pulley (4) and at least one tensioning arm (8, 9) pivotably mounted on the pulley (4) and connected to a tensioning roller (6, 7), wherein a belt (5) is guided around the pulley (4) and the tensioning roller (6, 7), wherein the belt (5) is subjected to a defined torque and the angle of twist (φ) of the pulley (4) or a quantity correlated therewith is determined as a measure of belt wear.

Description

[0001] The invention relates to a method for determining belt wear in a belt drive, for example in a belt-driven starter generator of an internal combustion engine, and to a belt drive. State of the art

[0002] A belt-driven starter generator, which can be used both to start an internal combustion engine and as a generator when the engine is running, is described in DE 100 45 143 A1. The starter generator has a motor-driven pulley that is encircled by a V-belt, which is additionally placed around a crankshaft output shaft of the internal combustion engine. The starter generator is equipped with a tensioning system to ensure that the V-belt has sufficient pretension in both directions of movement. The tensioning system comprises two tensioning rollers that bear against the V-belt and are rotatably attached to a hub via lever arms. The entire tensioning system is pivotable about a pivot axis located centrally in the hub.

[0003] From DE 101 12 568 A1 it is known to determine the slip in the drive of starter generator systems and to limit the transmitted drive torques so that the slip is within a permissible value. This is also intended to limit belt wear.

[0004] DE 10 2014 217 455 A1 relates to a method for starting an internal combustion engine by means of a starter generator, which has a pulley of the starter generator, a pulley of the internal combustion engine and a belt connecting the pulleys in a torque-transmitting manner, wherein the starter generator is operated in such a way that its drive torque delivered to the pulley of the starter generator has a certain drive torque profile, so that at times an output torque is generated at the pulley of the internal combustion engine which, taking into account a transmission ratio of the belt drive, is higher than the drive torque of the starter generator. Disclosure of the invention

[0005] According to the invention, a method for determining belt wear in a belt drive and a belt drive with the features of the independent claims are proposed.

[0006] The inventive method allows the current belt wear in a belt drive to be determined. The belt drive is, for example, a belt-driven starter generator of an internal combustion engine, which can be used to start the engine and can also be used as a generator when the engine is running. The belt drive comprises a pulley and at least one tensioning arm pivotally mounted on the pulley, on which a tensioning roller is rotatably arranged, with the belt of the belt drive being guided around the pulley and the tensioning roller. The tensioning roller ensures sufficient tension in the belt.

[0007] The pulley is advantageously coupled to a drive motor, in particular an electric drive motor, which generates a torque to determine belt wear. In the case of an electric drive motor, it can also be operated as a generator.

[0008] In the method according to the invention, belt wear is detected by applying a defined torque to the belt and determining the angle of twist of the pulley that results in response to the torque. In addition to or as an alternative to the angle of twist of the pulley, a correlative parameter can also be determined. The angle of twist of the pulley—or the correlative parameter—serves as a measure of the current belt wear. As belt wear increases, the belt elongates, which also causes the angle of twist of the pulley, or the correlative parameter, to increase in response to the applied torque.

[0009] The torque used to detect belt wear is preferably applied in the form of a defined torque pulse with a fixed duration, a fixed shape, and a fixed amplitude. The torque pulse shape is, for example, at least approximately rectangular.

[0010] Knowing the current belt wear allows the maximum torque in the belt drive to be adjusted during regular operation, and in particular, limited to minimize further wear and slippage. For example, a wear-dependent torque limit can be set that must not be exceeded during belt drive operation.

[0011] The applied torque for determining belt wear is limited in both magnitude and duration. For example, the torque is applied for a maximum of one second or 0.5 seconds, with a maximum torque of 10 Nm or 5 Nm.

[0012] The torque is generated primarily via the electric motor, which is coupled to the pulley.

[0013] According to an advantageous embodiment, which relates to a belt drive with two tensioning arms rotatably mounted around the pulley of the electric motor, each with a tensioning roller, the belt is successively subjected to a torque in opposite directions. Alternatively, the tensioning arms can also be rotatably mounted about an axis that is not coaxial with the drive shaft of the electric motor.

[0014] The torques are generated in particular in immediate succession, for example within a time interval of a maximum of 2 seconds or a maximum of 0.5 seconds in opposite directions.

[0015] In response to the applied torques, the total angle of rotation of the pulley, or a quantity correlated with this angle, is determined as a measure of belt wear. By generating two torques in opposite directions, a larger overall angle of rotation, or a corresponding quantity, is achieved, which can be more accurately detected by the sensor, thus ensuring higher measurement accuracy. Advantageously, the torque in both opposite directions is the same, both in terms of magnitude and duration. Alternatively, the torques in the opposite directions can differ, with variations in magnitude and / or duration.Advantageously, the belt can be pre-tensioned in one direction before the test sequence, thus already achieving an end position in order to reduce disturbances, such as friction, and thereby increase the measurement accuracy.

[0016] Instead of, or in addition to, the angle of rotation of the pulley, the time it takes for the pulley to reach an end position corresponding to the torque can be used as a measure of belt wear. The angular rotation of the tensioning system in the belt drive, which includes at least one tensioning arm with the tensioning roller, also correlates with the angle of rotation of the pulley and can be used to determine belt wear.

[0017] According to yet another advantageous embodiment, relating to a belt drive as a starter-generator of an internal combustion engine, the applied torque is limited to a maximum value that is less than the breakaway torque of the internal combustion engine's crankshaft. This ensures that applying the torque to determine belt wear has no effect on the crankshaft position.

[0018] According to yet another advantageous embodiment, which also relates to a belt drive with a starter-generator of an internal combustion engine, the torque is applied only in defined operating conditions of the internal combustion engine, in particular when the engine is stationary. However, it can also be advantageous to determine the belt wear by applying a torque while the engine is running, especially in steady-state operating conditions of the internal combustion engine, for example, at idle.

[0019] According to yet another advantageous embodiment, a defined torque is applied multiple times to determine belt wear, and the angle of rotation of the pulley or a correlated quantity is measured. By repeatedly generating the torques and measuring the angle of rotation or the correlated quantity, the influence of statistical variations can be minimized and the accuracy of wear determination improved. Advantageously, the measurements are carried out under identical boundary conditions, in particular with the same magnitude and duration of the torques and the same operating state of the internal combustion engine, especially when the engine is switched off.

[0020] Further advantages and practical designs can be found in the additional requirements, the figure description, and the drawings. These show: Fig. 1 A schematic representation of a belt-driven starter generator coupled to the crankshaft of an internal combustion engine via a belt, shown in a first deflection of a tensioning system mounted coaxially to the starter generator, with a transmitted torque in a first direction, Fig. 2 one Fig. 1 corresponding representation, but with a transmitted torque in the opposite direction, whereby the clamping system is also opposite Fig. 1 is deflected in the opposite direction, Fig. 3 The starter generator in two representations after the application of a torque in different directions, as well as in a superimposed representation of both states to determine the angle of rotation of the pulley as a measure of the wear of the belt.

[0021] In the figures, identical components are labelled with the same reference symbols.

[0022] In the Fig. 1 and Fig. Figure 2 shows an internal combustion engine 1, which is started via a belt-driven starter generator 3 or which drives the starter generator 3 in generator operation. Fig. 1 represents the motor operating case for starting and providing motor support to the internal combustion engine, Fig. 2 the generator operation, in which the starter generator 3 is driven by the internal combustion engine 1 and generates electricity. Accordingly, a torque M is generated. RSG in the starter generator 3, the power is transmitted in different directions relative to a pulley 4.

[0023] The internal combustion engine 1 and the belt-driven starter-generator 3 are coupled via a belt 5 of the starter-generator, which is placed around a crankshaft output pulley 2 of the internal combustion engine. The starter-generator 3 further comprises the pulley 4, which is connected, in particular, to an electric motor either non-rotatably or via a gearbox, which, in the case of engine operation, according to Fig. 1 as a drive motor and in generator operation according to Fig. 2 functions as a generator.

[0024] The belt 5 is placed around the pulley 4, which is rotatably mounted. Two tension arms 8 and 9 are pivotally mounted coaxially to the pulley 4 on the starter generator 3; the pivot axis of the tension arms 8 and 9 coincides with the axis of rotation of the pulley 4. The pivotability of the tension arms 8 and 9 is independent of the rotation of the pulley 4 about its axis of rotation.

[0025] The tensioning arms 8 and 9, on their side facing away from the pulley 4, each support a tensioning roller 6 or 7, respectively. These rollers exert an inward force on the belt 5 from the outside to tension it. The tensioning forces exerted on the belt 5 by the tensioning rollers 6 and 7 are directed towards each other. The tensioning arms 8 and 9 with the tensioning rollers 6 and 7 constitute a tensioning system or belt tensioner, in which the belt 5 is subjected to a tensioning force transverse to its longitudinal extent. To generate this tensioning force, the tensioning rollers 6 and 7, and thus the associated tensioning arms 8 and 9, are pre-tensioned. This pre-tension is dimensioned such that the belt 5 is subjected to a tensioning force by the tensioning rollers 6 and 7 even when at rest.

[0026] In the exemplary embodiment, the two clamping arms 8 and 9 are pivotably mounted on the pulley 4 independently of each other and are force-coupled via a spring element 10, which is designed, for example, as a tension spring.

[0027] The belt 5 can additionally be looped around one or more auxiliary components 11 and drive them. These auxiliary components 11 include, for example, a power steering unit, the water pump, or the air conditioning system in the vehicle.

[0028] In the case of propulsion according to Fig. 1. The belt section between crankshaft output pulley 2 and pulley 4 forms the loaded side, and the belt section between pulley 4 and auxiliary unit 11 forms the slack side. In generator operation according to Fig. In contrast, the belt section between the crankshaft output pulley 2 and the pulley 4 is the slack side and the belt section between the pulley 4 and the auxiliary unit 11 is the load side.

[0029] In Fig. Figure 3 shows three individual images. The left image depicts the motor operation after the application of a defined torque, and the middle image depicts the generator operation after the torque has been applied, but in the opposite direction. The right image is a superimposition of the left and middle images, including the pulley 4 and the two tensioning rollers 6 and 7 of the belt tensioner.

[0030] The torque is applied to determine belt wear. The torque is less than the breakaway torque of the internal combustion engine. The torque is preferably applied with the engine stationary, both in motor and generator modes. The torque can be the same in terms of duration and magnitude for both motor and generator operation, but its direction is opposite. The torque is generated by actuating the electric motor connected to pulley 4. The torque duration is preferably a maximum of one second, for example, half a second. The torque magnitude is preferably a maximum of 10 Nm, for example, 5 Nm.

[0031] To determine belt wear, it is advantageous to apply a torque at regular intervals, preferably consecutively, in both opposite directions of motor and generator operation and to determine the angle of rotation of the pulley 4. A change in the angle of rotation indicates the current wear state of the belt. If reference values ​​are available, it is also possible to infer the current belt wear from the absolute values ​​of the pulley's angle of rotation.

[0032] Once belt wear has been determined, the maximum torque acting on the belt drive can be limited, if necessary, to prevent a failure of the belt drive.

[0033] In the right image of Fig. Figure 3 shows the motor and generator operating conditions superimposed when applying torques for belt wear determination, with the motor operating condition indicated by a dashed line and the generator operating condition by a solid line. The angle of rotation φ of the pulley between the motor and generator operating conditions after applying a positive or negative torque can be measured by sensors and serves as a measure of belt wear. Additionally or alternatively, another quantity correlated with the angle of rotation φ can be used, for example, the time required for the pulley 4 to reach its respective deflection.

[0034] The image on the right shows... Fig.3. In addition, the angle α that the tensioning pulley 6 of the belt tensioner travels during the transition from motor to generator operation. If necessary, this angle α can also be used to determine belt wear.

Claims

[1] Method for determining belt wear in a belt drive, in particular in a belt-driven starter generator (3) of an internal combustion engine, which has a pulley (4) and at least one tensioning arm (8, 9) pivotably mounted on the pulley (4) and connected to a tensioning roller (6, 7), wherein a belt (5) is guided around the pulley (4) and the tensioning roller (6, 7), wherein the belt (5) is subjected to a defined torque and the angle of twist (φ) of the pulley (4) or a quantity correlated therewith is determined as a measure of belt wear. [2] Method according to claim 1, characterized by, that the belt drive has two tension arms (8, 9) pivotably mounted on the pulley (4), each of which is connected to a tension roller (6, 7), wherein the belt (5) is guided around the pulley (4) and the two tension rollers (6, 7) and the belt (5) is subjected to defined torques in opposite directions, wherein the total angle of rotation (φ) of the pulley (4) or a correlative quantity is determined as a measure of belt wear. [3] Method according to claim 2, characterized by that the magnitude of the torques in both directions is the same or is in a defined ratio to each other. [4] Method according to any one of claims 1 to 3, characterized by , that in addition to or instead of the angle of rotation (φ) of the pulley (4) the time interval is determined as a measure of belt wear which the pulley (4) needs to achieve a deflection corresponding to the torque. [5] Method according to any one of claims 1 to 4, characterized by , that the belt drive is designed as a belt-driven starter generator (3) of an internal combustion engine (1), wherein the magnitude of the applied torque is less than the breakaway torque of the crankshaft of the internal combustion engine (1). [6] Method according to any one of claims 1 to 5, characterized by , that the belt drive is designed as a belt-driven starter generator (3) of an internal combustion engine (1), wherein the torque is applied only in defined operating conditions of the internal combustion engine (1). [7] Method according to claim 5 or 6, characterized by , that the torque is only applied when the internal combustion engine (1) is stationary. [8] Method according to any one of claims 5 to 7, characterized by , that depending on the determined belt wear, the level of the maximum permissible starting torque in the starter generator (3) is limited. [9] Method according to any one of claims 1 to 8, characterized by , that the belt (5) is subjected to defined torques multiple times, whereby the belt wear is determined from several measurements of the angle of rotation (φ) of the pulley (4) or a correlated quantity. [10] Belt drive, in particular belt-driven starter generator (3), with a pulley (4) and at least one pivotably mounted, pre-tensioned tensioning arm (8, 9) which is connected to a tensioning roller (6, 7), wherein a belt (5) is guided around the pulley (4) and the tensioning roller (6, 7), wherein the belt drive is configured to carry out the method according to any one of claims 1 to 9. [11] Belt drive according to claim 10, characterized by, that the belt drive has two pivotably mounted tension arms (8, 9) which are each connected to a tension roller (6, 7), wherein the belt (5) is guided around the pulley (4) and the two tension rollers (6, 7). [12] Belt drive according to claim 11, characterized by , that the two pivotably mounted clamping arms (8, 9) are connected to each other via a spring element (10). [13] Belt drive according to claim 11 or 12, characterized by , that the two tension rollers (6, 7) apply a force to the belt (5) in opposite directions.

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