Method and control device for operating a belt drive

Abstract

Method for operating a belt drive (1) with an elastic belt (10) connecting a drive machine to a unit to be driven, wherein a variable influencing the belt drive is obtained continuously or at a given time; and an operating variable of the belt drive is determined simultaneously as a function of the received variable influencing the belt drive, wherein the variable influencing the belt drive includes air humidity, wherein the air humidity is determined by monitoring an actuating element for activating and / or deactivating a windscreen wiper; and where the operating variable is a belt pretension (σ eR ) of the elastic belt (10), which depends at least on the air humidity.

Description

[0001] The invention relates to a method and a control device for operating a belt drive with an elastic belt which connects a drive machine, in particular a drive machine of a motor vehicle, to an assembly to be driven.

[0002] Belt drives are used, for example, in motor vehicles to connect a drive engine to one or more driven components, such as a water pump, an air conditioning compressor, a starter generator, and other auxiliary components. The coupling is achieved by means of an elastic belt and depends on the belt pretension of the elastic belt.

[0003] In the current state of the art, the belt pretension of belt drives such as auxiliary and timing drives is designed for the worst-case operating scenario with regard to belt length, slippage, belt pretension variation, and damping of a non-adjustable tensioner. However, such a constant belt pretension can lead to increased friction (consumption) and increased wear on the belt and bearings of driven components, such as generator bearings.

[0004] Therefore, belt tensioners have been developed that allow adjustment of the belt pretension depending on the wear of the elastic belt. For example, DE 102 25 268 A1 describes a tensioning device for a traction drive that has an electronic actuator that sets a predetermined, constant belt pretension depending on an operating parameter of the traction drive. DE 10 2012 020 967 A1 discloses a method in which a constant belt pretension is determined depending on the course of a movement variable.

[0005] However, when using a constant belt pretension, an unnecessarily high belt pretension is selected in many operating conditions to ensure that slippage is sufficiently prevented even in a critical operating condition.

[0006] Furthermore, with a fixed belt pretension, the elastic behavior of the belt, spring decoupling elements, and the spring-assisted tensioning system create an oscillating system during start-up, which generates, in some cases, very high dynamic strand forces due to resonance effects. These strand forces can be minimized by temporarily changing / increasing the pretension via the tensioning system. This reduces the reaction forces in the belt and in the pulley bearings, thus reducing slippage during excitation. This, in turn, results in longer service life for the belt and the support bearings.

[0007] DE 10 2009 045 880 A1 relates to a method for operating a belt drive, wherein the belt tension depends on the current state of the belt drive or on the current load of the belt drive. Similar methods are also described in DE 11 55 199 A1, DE 199 59 21 A1, and DE 10 2004 020 459 A1.

[0008] The object of the present invention is to provide a method and a control device for operating a belt drive as well as a device for determining a belt pretension, which at least partially overcome the above-mentioned disadvantages.

[0009] This object is achieved by the method according to the invention for operating a belt drive according to claim 1 and the control device according to the invention for operating a belt drive according to claim 5.

[0010] According to a first aspect, the invention relates to a method for operating a belt drive with an elastic belt which connects a drive machine to a unit to be driven, wherein a variable influencing the belt drive is obtained continuously or at a given time; and an operating variable of the belt drive is determined simultaneously as a function of the received variable influencing the belt drive, wherein the variable influencing the belt drive includes air humidity, wherein the air humidity is determined by monitoring an actuating element for activating and / or deactivating a windscreen wiper; and wherein the operating variable is an adjustable belt pretension of the elastic belt, which depends at least on the air humidity.

[0011] According to a second aspect, the invention relates to a control device for operating a belt drive with an elastic belt which connects a drive machine to a unit to be driven, which is designed to to obtain a variable influencing the belt drive continuously or at a given time; and to determine an operating variable of the belt drive simultaneously as a function of the received variable influencing the belt drive, wherein the variable influencing the belt drive includes air humidity, wherein the air humidity is determined by monitoring an actuating element for activating and / or deactivating a windscreen wiper; and wherein the operating variable is an adjustable belt pretension of the elastic belt, which depends at least on the air humidity.

[0012] Further advantageous embodiments of the invention emerge from the subclaims and the following description of preferred embodiments of the present invention.

[0013] The present invention relates to a method for operating a belt drive with an elastic belt that connects a drive motor to a driven unit, in particular a driving pulley of the drive motor to a driven pulley of the driven unit. The belt drive can be a toothed belt drive, for example a primary belt drive between a crankshaft and a camshaft of the drive motor, or a V-ribbed belt drive, for example a secondary belt drive between the camshaft and one or more auxiliary units. The drive motor can be a drive engine of a motor vehicle, for example an internal combustion engine such as a gasoline engine or a diesel engine, or an electric motor.The unit to be driven can be a generator, an air conditioning compressor, a power steering pump, a fan, one or more mechanical bearings, one or more pumps, for example for secondary air injection, a starter generator or another auxiliary unit of a motor vehicle.

[0014] According to the method, a humidity and, if applicable, one or more other variables influencing the belt drive, which are described in detail below, are measured continuously or at a specified time. Subsequently, an operating variable of the belt drive, which is described in detail below, is determined simultaneously as a function of the obtained humidity and, if applicable, one or more other variables influencing the belt drive.

[0015] With the aid of the method according to the invention, reliable operation of the belt drive can be made possible.

[0016] In some embodiments, the variable influencing the belt drive can be an operating state of the belt drive or an environmental condition of the belt drive, or can contain the operating state of the belt drive and / or the environmental condition. The operating variable is then a belt pretension of the elastic belt to be adjusted, which depends on the operating state of the belt drive or the environmental condition of the belt drive. The belt pretension can thus be adjusted during operation of the belt drive depending on the operating state of the belt drive and / or the environmental condition. Due to the possibility of actively influencing the belt pretension, for example, with small wrap angles of the driving and / or driven pulleys, e.g.At wrap angles of less than 180°, at low speeds of the driving pulley, or in high humidity, a reduction in slip in the belt drive is possible by increasing the belt pretension as needed. This enables, at best, slip-reduced, and in particular slip-free, operation of the belt under all load conditions, without the elastic belt being unnecessarily stressed by a consistently increased belt pretension. This can lead to friction-minimized operation of the belt drive, whose CO 2 -potential is 0.5 - 1% in the so-called New European Vehicle Cycle (NEDC).

[0017] In some embodiments, the operating state of the belt drive may be an operating state of the drive machine, an operating state of the unit to be driven, a request for a predetermined operating state of the unit to be driven, an operating state of the elastic belt or another operating state of the belt drive or may include at least one of these.

[0018] The operating state of the prime mover can be a speed, a torque, a driving mode of the prime mover, for example a sporty or a fuel-efficient (Eco) driving mode, and / or another operating state of the prime mover, or can include at least one of these. For example, at low speeds and high torques of the prime mover, rotational irregularities may occur in the prime mover, increasing the risk of slippage. At higher speeds, the rotational irregularities decrease and the risk of slippage decreases. Consequently, the belt pretension can be determined such that it decreases with increasing speeds. An engine map-based determination of the belt pretension can therefore be carried out.

[0019] The operating state of the driven unit can include a switched-off state and one or more switched-on states of the driven unit. In the switched-on state, the driven unit can be operated under partial load or at full load. The belt pretension can then change, for example, at a time of a state change or shortly before the time of the state change, for example between 1 ms and 1000 ms, in particular between 10 ms and 500 ms, for example by increasing or decreasing in steps. The operation of the driven unit, for example an air conditioning compressor and / or a generator, in particular under partial load or at full load, has different effects on a load on the elastic belt, which influences the risk of slippage. Therefore, a lower belt pretension can be determined when the driven unit is switched off than when it is switched on.The belt pretension can therefore increase with increasing load on the belt, preferably in steps.

[0020] In the case of a starter-generator, the operating mode of the prime mover and the operating mode of the driven unit can be a starter-generator operating mode, for example, a recuperation mode or a generator mode. For engines with belt starter-generators (BSGs), the belt pretension can be adjusted to a recuperation mode, a start and restart, and the BSG's engine boost functions.

[0021] The requirement for a predefined operating state of the driven unit can, for example, be the requirement for the driven unit to be switched on. The requirement can, for example, be based on a change in the operating state of the prime mover, for example an acceleration, a change in engine temperature, by actuating a control element, for example an air conditioning system, or another change in one or more parameters. The activation of the driven unit, for example an air conditioning compressor and / or a generator, often leads to uneven loading of the elastic belt, which causes slip peaks. Therefore, when activation of an auxiliary unit is requested, an increased belt pretension can be determined, whereby such slip peaks can be reduced or even avoided.

[0022] In some embodiments, the ambient condition may be or include at least one of air pressure, ambient temperature, road surface, or other ambient condition.

[0023] For example, increased humidity, such as during rain, can increase the risk of slippage compared to lower humidity in dry weather. Therefore, the belt pretension can be set to increase with increasing humidity. Furthermore, at temperatures below 0°C, a layer of frost can form on the belt, which in turn increases the risk of slippage. Therefore, the belt pretension can be increased accordingly during the start-up phase of the belt drive.

[0024] In some embodiments, the variable influencing the belt drive can be obtained continuously during operation of the belt drive. The belt drive is in operation, for example, when the elastic belt is moving or when the drive motor is not stationary and / or a speed of one of the pulleys is not equal to 0 rpm. The variable influencing the belt drive can, for example, be measured with the aid of a sensor or provided by an engine control unit of the motor vehicle, wherein the engine control unit receives this variable from a sensor or extracts it from a characteristic map. The belt pretension to be adjusted can then be determined continuously as a function of the obtained variable influencing the belt. In this way, the variable influencing the belt can be obtained and, at the same time, the belt pretension to be adjusted can be determined.By continuously determining the belt pretension, it can be dynamically updated to enable optimal operation.

[0025] For example, the current speed of the drive motor can be continuously supplied by the engine control unit, and the belt pretension to be adjusted can be continuously adjusted to the speed. When the speed increases, the belt pretension to be adjusted can be decreased, and when the speed decreases, it can be increased.

[0026] Alternatively or additionally, humidity can be continuously monitored, for example, by measuring it or by monitoring the actuation of an actuator to activate or deactivate a windshield wiper. Depending on the humidity, the belt pretension can then be adjusted accordingly, particularly by increasing it with increasing humidity. The belt pretension can be increased by up to 20% compared to a map-based normal value for the belt pretension.

[0027] In some embodiments, the belt pretension can be varied at a time of a change in the operating state of the belt drive or before the time of the change in the operating state of the belt drive. For example, the belt pretension can be varied between 1 ms and 1000 ms, in particular between 10 ms and 500 ms, before the time of the change in the operating state of the belt drive. For example, the belt pretension can be increased before a unit such as the air conditioning compressor or the generator is activated.

[0028] In some embodiments, the variable influencing the belt drive can be obtained at the predetermined time at the start of operation of the belt drive and / or during operation of the belt drive. For example, the predetermined time can be a time at which a predetermined condition is met, such as a start time of the drive motor or a time at which the driven pulley begins to rotate (start of operation of the belt drive). The belt pretension to be set can then be determined for a predetermined period of time after the start of operation or after the predetermined time depending on the obtained variable influencing the belt. The predetermined period of time can, for example, be in a range of 2 seconds to 10 minutes or, alternatively, be 20 to 10,000 cumulative engine revolutions from an engine start or from a start of operation of the belt drive.

[0029] For example, an outside temperature can be measured during engine start-up. If the temperature is below 0°C, a belt pretension increased by a specified value can be determined for a period of 10 seconds to 5 minutes, or alternatively, from 100 to 10,000 cumulative engine revolutions. The period for which the belt pretension is increased and / or the specified value can vary with temperature, in particular, increasing as temperature decreases. By adjusting the specified belt pretension, slip can be reduced below a threshold and belt service life can be increased.

[0030] In some embodiments, the belt pretension to be adjusted, determined as described above, can be adjusted. The belt pretension to be adjusted can be controlled or regulated. For example, an engine map-driven active control of the belt pretension or a regulation of the belt pretension to a map-based setpoint can be performed. This can prevent the occurrence of slippage and thus reduce belt wear as much as possible in all operating conditions.

[0031] To adjust the belt pretension, for example, speed differences between a crankshaft of the prime mover and the driven unit can be detected and, if the speed differences are above a predefined threshold, the belt pretension can be controlled accordingly. Alternatively, the belt pretension can be adjusted by increasing the belt pretension until it falls below a predefined slip threshold. The predefined slip threshold can, for example, be 3% slip or less. The belt pretension can also be controlled or regulated in other ways. Through targeted active adjustment of the belt pretension, the risk of slippage can be significantly reduced and thus the service life of the belt drive, especially of the elastic belt, can be increased.

[0032] The variable influencing the belt drive can also be a position of a belt tensioner of the belt drive, which is obtained at a time when the belt drive is out of operation, i.e. when the belt drive is in particular at a standstill, or when the drive machine is in particular at a standstill. The position of the belt tensioner is preferably a position of a tensioning roller of an adjustable belt tensioner. It can be determined depending on the shape of the belt tensioner from a state of an actuator, for example an electric motor or another actuator. The operating variable can then comprise a control signal for an indicator for indicating a wear state of the elastic belt and / or a control signal for requesting emergency operation of the belt drive.

[0033] Depending on the position of the belt tensioner, a change in the length of the elastic belt compared to an original length of the elastic belt can be determined and the operating size can be determined depending on the change in length.

[0034] The change in length can be determined while the drive machine, in particular the drive machine of a motor vehicle, is at a standstill, in particular when the speed of the output pulley is 0 rpm.

[0035] For example, belt quality or wear progression can be derived from the change in length. Depending on the belt quality or wear progression, a monitoring signal can then be generated as an operating variable to indicate the belt quality or wear progression to the user. For example, if the belt quality falls below a limit, a warning signal can be issued. This enables wear detection and, depending on this, an active display of a replacement interval for the elastic belt. This allows a preventative belt replacement to be indicated if it is foreseeable that otherwise specified time or mileage intervals can no longer be met, thus eliminating the need for rigid replacement intervals that must take critical operation into account.In addition, an error message can be issued in the event of extreme wear (due to a belt failure expected in the short term), for example as a result of damage caused by a stone grinding through the belt drive or as a result of a manufacturing defect in the elastic belt.

[0036] Additionally or alternatively, depending on the belt quality or the progression of wear, control signals for initiating engine emergency measures can be determined as an operating variable, particularly in the event of high wear or a high wear rate. For example, a maximum or minimum speed can be limited, an engine torque can be limited, particularly at speeds with high rotational irregularities, a dynamic limitation can be initiated when consumers (for example, a generator, an air conditioning system, or another driven unit) are switched on or off, a different automatic transmission shift program can be selected, an automatic start-stop function can be suppressed, and / or the like.

[0037] The described belt quality monitoring can be combined with the method described above for determining or adjusting the belt pretension of an elastic belt within a belt drive. This allows the service life of the elastic belt to be extended through reliable monitoring and variable belt pretension.

[0038] The present invention further relates to a control unit for operating a belt drive with an elastic belt that connects a drive motor to a driven unit. The belt drive can be designed as described in detail above. The control unit is designed to receive a variable influencing the belt drive continuously or at a predetermined time and to simultaneously determine an operating variable of the belt drive as a function of the received variable influencing the belt drive. The belt drive is designed, in particular, to carry out the above-described inventive method for operating a belt drive.

[0039] The control unit can be, for example, an engine controller. The control unit can have a processor, in particular a microprocessor, for executing the above-described method for operating a belt drive. The control unit can also have a memory, for example a data memory, in which limit values ​​and parameters and information necessary for executing the above-described method for operating the belt drive can be stored. Furthermore, the control unit can have a data input for receiving measurement data, operating state information, and / or other parameters, and a data output for outputting the operating variable and other information.

[0040] A device for determining the belt pretension of an elastic belt connecting a drive machine to a driven unit can comprise an adjustable belt tensioner and a device built into the belt tensioner for determining the belt pretension of the elastic belt. The belt tensioner can, for example, have a tension pulley whose position can be adjusted by means of an actuator. The device for determining the belt pretension of the elastic belt can be a device for detecting the current required by an electric actuator, an integrated load cell, a piezo element, a device for measuring the belt's natural frequency in airborne sound, or another device suitable for determining the belt pretension.

[0041] With an adjustable belt pretension and a device which, due to its design, can measure the static belt pretension at any time, new functions become possible for an auxiliary drive or timing drive system, for example the detection of belt length changes due to wear over the running time as a result of a change in the position of the belt tensioner when the engine is not running, an engine map-driven active control of the belt pretension or control to a map-based setpoint and / or slip compensation.

[0042] Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings. Fig. 1 is a schematic representation of a belt drive known from the prior art; Fig. 2 is a flowchart of a first known method for adjusting a belt pretension; Fig. 3 a schematic relationship between a speed and the belt pretension; Fig. 4 a schematic relationship between activation of an air conditioning compressor and the belt pretension; Fig. 5 a schematic relationship between a windscreen wiper setting and the belt pretension; Fig. 6 is a flowchart of a second known method for adjusting a belt pretension; and Fig. 7 shows a schematic relationship between an outside temperature and the belt pretension.

[0043] Fig. 1 shows, by way of example, a schematic, highly simplified representation of a belt drive 1 of a motor vehicle, as is known from the prior art. The belt drive 1 has an elastic belt 10 in the form of a revolving V-ribbed belt, which partially wraps around a driving pulley 11, which is fixedly coupled to a crankshaft of a drive engine (not shown), a first driven pulley 12, which is coupled to an air conditioning compressor (not shown), and a second driven pulley 13, which is coupled to a starter-generator (not shown), thus connecting the driving pulley, the first driven pulley 12, and the second driven pulley 13 to one another. The belt drive 1 further has a tensioning pulley 14 of an adjustable belt tensioner, which is also partially wrapped by the belt.To adjust the belt pretension, the position of the tensioning pulley 14 can be varied, resulting in a change in the belt pretension. The arrangement of the components of the belt drive in . Fig. 1 may vary and other and / or additional ancillary units may be integrated into the belt drive.

[0044] Fig. 2 shows a flow chart of a first known method 2 for adjusting a belt pretension of an elastic belt of a belt drive, for example the one shown in Fig. 1 shown belt drive 1.

[0045] At 20, an operating state of the belt drive or an environmental condition of the belt drive is continuously determined during operation of the belt drive.

[0046] At 21, a belt pretension is dynamically determined depending on the operating state of the belt drive and / or the ambient conditions of the belt drive.

[0047] At 22 the specific belt pretension is then set.

[0048] For example, a crankshaft speed is received by an engine control unit as the operating state of the belt drive. The belt pretension is then determined depending on the speed. For this purpose, a characteristic map can be used, for example, that indicates a relationship between the crankshaft speed and the belt pretension. An example of such a relationship is shown schematically in Fig. 3. As can be seen from Fig. 3, the belt pretension σ eR with increasing speed first slowly, then faster and then slower again until a minimum belt pretension σ eR , min However, other belt tension versus speed curves can also be used to determine the pretension.

[0049] It can also detect whether a driven unit, in this case the air conditioning compressor, is activated or not, and determine the belt pretension depending on the detected result. As in Fig. 4, the belt pretension σ eR with the air conditioning compressor deactivated until time t akt , at which the air conditioning compressor is activated, a value σ eR,norm and from time t akt when the air conditioning compressor is activated, a value σ eR , add Instead of at time t akt The belt pretension can also be adjusted 10 ms to 500 ms before the time t akt raised to safely avoid slippage when switching on the driven unit.

[0050] In one embodiment of the invention, the position of an actuating element for actuating a windshield wiper is detected, which reflects air humidity. The belt pretension is then determined depending on the position of the actuating element. As shown in Fig. 5, the actuating element can have four different positions x o , X1 , x 2 , x 3 with the windscreen wiper in position x o of the actuating element is deactivated and in position x 3 is operated at maximum speed. The belt pretension σ eR increases gradually with the change of the position of the actuating element from position x o , in which the windscreen wiper is deactivated and the humidity is low, to position x 3 in which the windscreen wiper moves at maximum speed and the humidity is high.

[0051] For example, the belt pretension can be determined depending on the condition of the air conditioning compressor and the humidity.

[0052] Fig. 6 shows a flow chart of a second known method 3 for dynamically adjusting a belt pretension of an elastic belt of a belt drive, for example the one shown in Fig. 1 shown belt drive 1.

[0053] At 30, an operating state of the belt drive or an environmental condition of the belt drive is determined at the beginning of the operation of the belt drive.

[0054] At 31, a belt pretension is determined depending on the operating state of the belt drive and / or the ambient conditions of the belt drive.

[0055] At 32, the specific belt pretension is then adjusted dynamically.

[0056] For example, at the beginning of the belt drive's operation, an outside temperature is determined. The belt pretension is then determined depending on the outside temperature. As shown in Fig. 7, the belt pretension σ eR at temperatures T 1 ≥ 0°C at time t 0 , which indicates the start of operation of the belt drive, to a belt pretension σ eR,norm and then remains constant. At temperatures -10 °C < T 2 < 0°C the belt pretension increases at t 0 to a 10% of the belt pretension σ eR,norm increased belt pretension and drops after 1 min at t 1 on the belt pretension σ eR,norm . At temperatures T 2 ≤ -10 °C the belt pretension increases at t 0 to a 20% of the belt pretension σ eR,norm increased belt pretension and drops after 2 min at t 2 on the belt pretension G eR,norm .

[0057] The first and second methods can be combined in any way. For example, the belt pretension can be determined depending on the humidity and the outside temperature. Other combinations are also possible. List of reference symbols 1 belt drive 10 elastic straps 11 driving pulley 12 first driven pulley 13 second output pulley 14 Tension pulley 2 first method for dynamically adjusting a belt pretension 20 Determining an operating state or an environmental condition continuously during operation of the belt drive 21 dynamic determination of a belt pretension 22 Adjusting the specific belt pretension 3 second method for dynamically adjusting a belt pretension 30 Determining an operating state or environmental condition at the start of belt drive operation 31 Determining a belt pretension 32 dynamic adjustment of the specific belt pretension σ eR , σ eR,norm , σ eR,add , σ eR,min Belt pretensions n speed t, t akt , t 0 , t 1 , t 2 Times X SW , X 0 , X 1 , X 2 , X 3 Positions of an actuating element for a windscreen wiper T 1 , T 2 , T 3 Temperatures

Claims

[1] Method for operating a belt drive (1) with an elastic belt (10) which connects a drive machine to a unit to be driven, wherein a variable influencing the belt drive is obtained continuously or at a given time; and an operating variable of the belt drive is determined simultaneously as a function of the received variable influencing the belt drive, wherein the variable influencing the belt drive includes air humidity, wherein the air humidity is determined by monitoring an actuating element for activating and / or deactivating a windscreen wiper; and where the operating variable is a belt pretension (σ eR ) of the elastic belt (10), which depends at least on the air humidity. [2] The method according to claim 1, wherein the variable influencing the belt drive is continuously maintained during operation of the belt drive (1); and the belt pretension to be adjusted is continuously determined depending on the obtained variable influencing the belt. [3] Method according to claim 1 or 2, wherein the belt pretension also depends on the operating condition of the belt drive and the belt pretension is adjusted at a time of a change in the operating state of the belt drive or before the time of the change in the operating state of the belt drive. [4] The method according to claim 1, wherein the variable influencing the belt drive at the start of operation (t 0 ) of the belt drive (1) and / or during operation of the belt drive; and the belt pretension to be set is determined for a specified period after the start of operation and / or after the specified time depending on the obtained variable influencing the belt. [5] Control device for operating a belt drive (1) with an elastic belt (10) which connects a drive machine to a unit to be driven, which is designed to to obtain a variable influencing the belt drive continuously or at a given time; and to determine an operating variable of the belt drive simultaneously as a function of the received variable influencing the belt drive, wherein the variable influencing the belt drive includes air humidity, wherein the air humidity is determined by monitoring an actuating element for activating and / or deactivating a windscreen wiper; and where the operating variable is a belt pretension (σeR ) of the elastic belt (10), which depends at least on the air humidity.

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