Method for operating a belt drive

Abstract

The invention relates to a method for operating a belt drive with a belt that connects a driving pulley and a driven pulley in a torque-transmitting manner, wherein a total slip of the belt is determined as a function of a rotational speed of the driving pulley and a rotational speed of the driven pulley (211), wherein an elongation slip of the belt is determined (212), wherein a difference between the determined total slip and the elongation slip is determined as the relevant belt slip of the belt (213), wherein, when the relevant belt slip reaches a threshold value (214), a maximum torque of the driving pulley is reduced (221) until the relevant belt slip no longer reaches the threshold value (222).

Description

[0001] The present invention relates to a method for operating a belt drive, as well as a computing unit and a computer program for carrying it out. State of the art

[0002] Electric machines can be used in motor vehicles as so-called starter generators to start the combustion engine when the electric machine is in motor mode, and to generate electricity for the vehicle's electrical system and to charge the vehicle battery when the electric machine is in generator mode. Such electric machines can be connected to the combustion engine or crankshaft via a belt to transmit torque, for example, via the combustion engine's serpentine belt (so-called belt-driven starter generators, BSG).

[0003] A boost recuperation system (BRS) can be implemented using such an electric machine. In generator mode, the electric machine absorbs drive torque and converts mechanical energy into electrical energy. In motor mode, the electric machine converts electrical energy back into mechanical energy and generates drive torque.

[0004] The power and torque transmission capacity of such belts can change due to aging, wear, temperature, or other influences. If the belt's maximum power and torque transmission limit is exceeded, this leads to a sudden increase in belt slippage and the belt slipping, preventing effective torque transmission. Methods for detecting belt slippage are known, for example, from EP 1 818 572 B1 and EP 1 522 447 B1.

[0005] DE 101 12 568 A1 relates to a method for detecting slip in the drive of generator or starter-generator systems. The three-phase generators of these systems are equipped with electronic control components such as pulse inverters or rectifier bridges. The drive torque of the three-phase generator is transmitted to it via a belt drive of an internal combustion engine. When slip is detected at a comparator stage, to which speed-dependent input variables are supplied, the maximum transmissible drive torque is determined in a torque limiting stage, and a control system adjusts the generator output power accordingly.

[0006] DE 10 2015 208 679 A1 discloses a method for measuring the slip between a drive belt and an associated pulley in a belt drive, wherein both an actual first rotational speed of the pulley measured at the pulley and a second rotational speed of the pulley corresponding to the circumferential speed of the drive belt encircling the pulley are determined by sensors, wherein the slip is determined by the difference Δn between the first and second rotational speeds and a parameter influenced by the elongation of the drive belt is determined within the belt drive and used to compensate for the elongation-induced component of the determined second rotational speed. Disclosure of the invention

[0007] According to the invention, a method for operating a belt drive, as well as a computing unit and a computer program for carrying it out, are proposed with the features of the independent patent claims.

[0008] Advantageous embodiments are the subject of the dependent claims and the following description.

[0009] The invention provides a means to reliably detect and compensate for belt slippage or rotation in the belt drive, and to operate the belt drive effectively and with minimal losses. Within the scope of the invention, a critical belt slip is determined, which serves as an evaluation parameter for reliably detecting unwanted belt slippage or rotation.

[0010] The belt of the belt drive connects a driving pulley and a driven pulley, transmitting torque. The procedure determines the total slip of the belt as a function of the rotational speed of the driving pulley and the rotational speed of the driven pulley. This total slip specifically describes the actual total slip of the belt at the current rotational speeds of the pulleys, i.e., during the current torque transmission from the driving to the driven pulley.

[0011] This total slip takes into account all components of belt slip, particularly belt slip due to wear effects, aging, and deterioration of the belt, as well as belt slip due to current environmental conditions such as the current temperature or speed of the pulleys. Furthermore, this total slip also specifically considers the so-called stretch slip, which is always present due to the specific design and characteristics of the belt drive. This stretch slip is due to the elasticity of the belt. Due to the varying forces acting on the belt as it rotates around the pulleys, a relative movement occurs between the belt and the pulleys, which is referred to as stretch slip. However, this stretch slip has no effect on the transmission of torque or on the belt's ability to transmit power or torque.

[0012] Within this procedure, the belt's elongation slip is determined, particularly as a function of a theoretical model of the belt drive or as a function of specific belt drive parameters. Specifically, the elongation slip is modeled from the determined total slip using this theoretical model. The difference between the determined total slip and the elongation slip is then defined as the relevant belt slip. The total slip is expediently determined within this procedure from the rotational speeds and diameters of the two pulleys, whereas other physical parameters of the belt drive, such as the belt's modulus of elasticity, can also be incorporated into the determination of the elongation slip.

[0013] This key belt slip describes the components of slip that are not always present, particularly belt slip due to wear effects, aging and deterioration of the belt, and current environmental conditions. Therefore, this key belt slip allows for the particularly reliable detection of unwanted belt slippage or rotation.

[0014] For this purpose, the relevant belt slip is compared with a threshold value, in particular with a permissible maximum value. Reaching or exceeding this threshold value indicates, in particular, that the belt is slipping. If the relevant belt slip reaches this threshold value, the maximum torque or torque limit of the driving pulley is reduced as part of the procedure until the relevant belt slip no longer reaches the threshold value.

[0015] This maximum torque, in particular, represents a torque limit for the torque transmitted from the driving to the driven pulley. This limit is set within the system and cannot be exceeded during operation. Specifically, the maximum torque is gradually reduced by predetermined torque values, for example, 5 Nm, until the relevant belt slip no longer reaches the threshold value. Thus, if belt slippage is detected, a new value for the maximum permissible torque of the driving pulley is determined, at which belt slippage no longer occurs. This determined value of the maximum torque is then used as the new torque limit to prevent future slippage.

[0016] If, for example, the belt slips even though the previously valid torque limit has not been reached—perhaps due to progressive aging or wear of the belt—the process automatically determines a new valid torque limit. This method thus enables efficient operation of the belt drive and effective torque transmission, taking into account wear effects, aging, abrasion, and current environmental conditions, and without distortion caused by the always-present strain slip.

[0017] According to a particularly preferred embodiment, if a condition is met after the reduction of the maximum torque, the maximum torque is increased again. This condition is met, in particular, if the belt no longer slips, especially during a predetermined time interval. In this case, increasing the maximum torque expediently serves to verify whether a more precise, higher torque limit can be found, up to which the belt can transmit torque without slipping.

[0018] The maximum torque is increased incrementally by predetermined torque values, e.g., 3 Nm, which are advantageously lower than the torque values ​​by which the maximum torque was previously reduced. This allows for a relatively rapid reduction of the maximum torque upon detection of belt slippage, enabling the belt to grip as quickly as possible. Subsequent increases of the maximum torque by comparatively small increments allow for precise adjustment to the maximum torque limit under the current belt drive conditions, up to which no belt slippage occurs.

[0019] Advantageously, the maximum torque is increased repeatedly until the relevant belt slip is within a predetermined range around the threshold value. In particular, this range characterizes the maximum possible torque transmission of the belt at which the belt still adheres to the pulleys and does not slip.

[0020] According to a preferred embodiment, the specified condition is met if the torque of the driving pulley remains below the maximum torque within a specified range of, for example, 3 Nm for a specified time interval of, for example, 1 s, and if the relevant belt slip does not reach the threshold value for the duration of the specified time interval. Advantageously, the condition is thus met if, during the specified time interval, the torque is close to the current maximum torque and no belt slippage occurs.

[0021] Preferably, the total slip S ges of the belt as a function of a difference in circumferential speed v t the driving pulley and a circumferential speed v g the driven pulley. The total slip S ges is expediently determined according to the following formula: Stotal = vt − vgvt = 1 − vgvt

[0022] Since the circumferential speeds also depend on the rotational speeds nt, n g and the diameters d t , d g The total slip S can be expressed as the slip of the pulleys. ges can also be determined as follows: Sges=1−ngdgntdt

[0023] Due to expansion slippage, a speed loss occurs between the driving pulley, which rotates faster than the belt, and the driven pulley, which rotates slower than the belt, relative to the circumferential speeds of the pulleys. The circumferential speed v g The speed of the driven pulley is less than the circumferential speed v. t the driving pulley.

[0024] As already explained, the total slip is influenced both by belt slippage due to excessive torque transmission and by the elongation slip, which is always present in an elastic belt during torque transmission, as explained below.

[0025] As the belt rotates around the pulleys, it is subjected to different forces. The tension side, i.e., the section of the belt that runs from the driven pulley to the driving pulley, is subject to the so-called tension side force F. Z exposed. The slack side, i.e., the section of the belt running from the driving pulley to the driven pulley, is the so-called slack side force F. L exposed. The tensile force F Z is greater than the slack-side force F L The tension side of the belt rotates at a higher speed than the slack side. As the belt rotates around the driven pulley, the belt or side tension decreases, releasing the so-called circumferential force F. U of the tensile force F Z on the slack force F L Conversely, the belt tension increases from the slack side tension F as the belt rotates around the driving pulley. L to the circumferential force F U on the tensile force FZ These different belt forces cause different elongations due to the elasticity of the belt.

[0026] As the belt rotates around the driven pulley, it stretches on the pulley. The stretched section of the belt is essentially pulled across the driven pulley, resulting in relative movement or sliding between the belt and the driven pulley. Conversely, as the belt rotates around the driven pulley, the section on the tension side, which is at its maximum stretch, contracts again due to the decreasing tension on the tension side. The belt essentially shrinks on the driven pulley, resulting in relative movement or sliding. These stretching and shrinking processes of the belt on the pulleys, which lead to relative movement between the belt and the respective pulley, are referred to as belt slippage.

[0027] The circumferential force F U is dependent on the difference in the stalk forces (F U =F Z -F L These belt tension forces apply equally to both pulleys, so the circumferential forces acting on both pulleys are also identical. The different belt tension forces only result in different belt elongations at the two pulleys; the effective belt tension forces, however, are transmitted equally throughout the belt. Therefore, the elongation slippage has no effect on the circumferential force and thus does not influence the torque conversion.

[0028] As already explained, the expansion slip is advantageously determined as a function of a theoretical model of the belt drive or as a function of physical quantities of the belt drive. Preferably, the expansion slip S D as determined as follows: SD=kMt

[0029] Mt is the torque of the driving pulley and k is a parameter specific to the belt drive, which can be determined, for example, by analyzing measured values.

[0030] The total slip and the expansion slip can be determined using the rotational speed n t the driving pulley can be related in particular as follows: Sges=SDnt=kMtnt

[0031] If the factor k is known, the strain slip can be conveniently modeled using this relationship.

[0032] As explained above, the parameter k can be determined by evaluating measured values, in particular from measured values ​​for total slip and power of the driving pulley. The total slip can further be expressed as follows: Sges=kMtnt=kMtωt602π=kPt602π where ω t the angular velocity of the driving pulley is and P t = Mt ω t The power output of the driving pulley. By solving this relationship, the parameter k can be expressed as follows: k=Sgesπ30Pt

[0033] For example, during the manufacturing process of a belt drive, the specific parameters for that belt drive can be determined. However, a suitable measuring range should be used in this context. A measuring range is particularly suitable when measurable power transmission occurs and there is no steep change in torque. Since P t The formula for smaller P is in the denominator. t -Values ​​inaccurate.

[0034] According to a preferred embodiment, when the relevant belt slip reaches the threshold value, the maximum torque is reduced to a value corresponding to the difference between an average torque of the driving pulley during a predetermined time interval and a predefinable torque value. For example, the average torque value of the last 100 ms can be used and reduced by a torque value of, for example, 5 Nm until the relevant belt slip no longer reaches the threshold value. For example, a first-order lag element (PT1 element) of a torque control system can be used to determine the average torque value.

[0035] According to a particularly preferred embodiment, the belt connects a pulley of an electric machine and a pulley of an internal combustion engine of a motor vehicle in a torque-transmitting manner. Depending on whether the electric machine is operated as a motor or a generator, either the pulley of the electric machine or the pulley of the internal combustion engine is used as the driving pulley. Even with worn and damaged belts that no longer possess their original maximum capacity for force or torque transmission, the present method enables optimal torque transmission between the internal combustion engine and the electric machine.

[0036] Advantageously, the electric machine is designed as a starter generator, e.g., as a belt-driven starter generator (BSG). As explained above, such a belt-driven starter generator can be used, on the one hand, to start the internal combustion engine with the electric machine during engine operation, and on the other hand, to generate electricity for an on-board electrical system and for charging a vehicle battery during generator operation.

[0037] The electric machine, designed as a starter-generator, is particularly preferred for use in a boost recuperation system (BRS) or as a so-called boost recuperation machine (BRM). Such a boost recuperation machine (BRM) can, in generator mode, absorb drive torque and convert mechanical energy into electrical energy, and in motor mode, convert electrical energy back into mechanical energy, thus generating drive torque. During operation of such a boost recuperation system, the electric machine can be used for various functions, in particular for recuperation (energy recovery during braking), for torque support (especially during starting and acceleration), for a start / stop function (allowing the combustion engine to restart after an automatic stop), and / or for coasting, for example, when rolling or driving slightly downhill.

[0038] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is, in particular in terms of programming, equipped to carry out a method according to the invention.

[0039] Implementing the process as a computer program is also advantageous, as this incurs particularly low costs, especially if the executing control unit is already used for other tasks and is therefore already present. Suitable data carriers for providing the computer program include magnetic, optical, and electrical storage devices, such as hard drives, flash memory, EEPROMs, DVDs, etc. Downloading the program via computer networks (Internet, intranet, etc.) is also possible.

[0040] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawing.

[0041] The invention is schematically illustrated in the drawing using exemplary embodiments and is described below with reference to the drawing. Brief description of the drawings Fig. Figure 1 schematically shows a belt drive of a motor vehicle with an internal combustion engine and a starter generator, which is configured to carry out a preferred embodiment of a method according to the invention. Fig. Figure 2 schematically shows a preferred embodiment of a method according to the invention as a block diagram. embodiment(s) of the invention

[0042] In Fig. Figure 1 is a schematic representation of a belt drive of a motor vehicle and is labelled 100.

[0043] A combustion engine 120 of the motor vehicle is connected to an electric machine 130 in the form of a belt-driven starter generator via a belt 110 of the belt drive 100 in a torque-transmitting manner.

[0044] The internal combustion engine 120 and the electric machine 130 each have a pulley 121 and 131 respectively, which are connected via the belt 110 to transmit torque. The pulley 121 of the internal combustion engine 120 can, for example, be designed as a crankshaft drive gear, and the pulley 131 of the electric machine 130, for example, as a drive gear of the starter generator 130.

[0045] The starter generator 130 can be operated as a motor, for example to start or assist the internal combustion engine 120, with torque being transferred from the pulley 131 of the starter generator 130 to the pulley 121 of the internal combustion engine 120. In generator mode, the starter generator 130 also transfers torque from the pulley 121 of the internal combustion engine 120 to the pulley 131 of the starter generator 130.

[0046] In order to detect and compensate for belt slippage 110 during torque transmission using the belt drive 100, a control unit 140 is provided, which is programmed in particular to carry out a preferred embodiment of a method according to the invention, as described below with regard to Fig. 2 is explained.

[0047] In Fig.Figure 2 shows a preferred embodiment of a method according to the invention schematically as a block diagram.

[0048] The following example considers the case where the starter generator 130 is motor-driven and the torque is transmitted to the internal combustion engine 120 via the belt drive 100. In this case, the pulley 131 of the starter generator 130 operates as the driving pulley, and the pulley 121 of the starter generator 120 operates as the driven pulley.

[0049] As part of the procedure, a check 210 is first carried out to determine whether the belt 110 is rotating or slipping. For this purpose, a total slip S is calculated in step 211. ges of the belt 110 as a function of a difference in circumferential speed v t the driving pulley 131 and the circumferential speed v g the driven pulley 121 is determined according to the following formula: Sges=1−ngdgntdt

[0050] Furthermore, in step 212, a stretching slip S D of the belt 110, in particular with the help of a theoretical model of the belt drive 100.

[0051] For example, the stretch slip S D , as explained above, determined using the following formula: SD=kMt

[0052] M t Here, is the torque of the driving pulley and k is a parameter specific to the belt drive, which can be determined, for example, by analyzing measured values ​​for the total slip S. ges of the belt 110 and for the power P t the driving pulley 131 is determined according to the following formula: k=Sgesπ30Pt

[0053] For example, the parameter k can be determined during the manufacturing process of the belt drive 100 and stored in the control unit 140. As explained above, a suitable measuring range should be used.

[0054] In step 213, a significant slip S of the belt 110 is determined as the difference between the total slip and the stretch slip: S=Stotal−SD

[0055] This relevant slip S is compared with a threshold value in step 214. If the relevant slip S does not reach the threshold value, there is no slippage of the belt 110. However, if the relevant slip S exceeds the threshold value, slippage of the belt 110 is detected and a compensation 220 of the slippage is carried out so that the belt 110 adheres again to the pulleys 121, 131.

[0056] In step 221, the maximum torque of the driving pulley 131 is reduced. For example, the maximum torque M is... max a value is determined which corresponds to an average value M Δt the torque of the driving pulley 131 during a given time interval Δt, e.g. during the last 100 ms, reduced by a given torque value ΔM of e.g. 5 Nm corresponds to: Mmax=MΔt−ΔM

[0057] In step 222, it is then checked whether the relevant slip S no longer exceeds the threshold value. As long as the relevant slip S exceeds the threshold value, the maximum torque value according to step 221 is again reduced by the specified torque value ΔM. If the relevant slip S is below the threshold value, the corresponding maximum torque value is retained in step 223 as the torque limit for the driving pulley 131.

[0058] After the maximum torque has been reduced to this corresponding value, a further increase 230 of the maximum torque is carried out in order to precisely determine the maximum possible torque of the driving pulley 131 at which no slippage of the belt 110 occurs.

[0059] For this purpose, step 231 checks whether a predefined condition is met, in particular whether the torque of the driving pulley 131 is within a predefined range of, for example, 3 Nm below the maximum torque for a predefined time interval of, for example, 1 s and whether, at the same time, the relevant belt slip does not exceed the threshold value for the duration of this time interval of 1 s.

[0060] If this is the case, the maximum torque in step 232 is increased by a predetermined torque value, for example, 3 Nm. Then, in step 233, it is checked whether the relevant belt slip is within a predetermined range below the threshold. As long as this is not the case, the maximum torque according to step 232 is increased by the predetermined torque value of 3 Nm each time. As soon as the relevant belt slip is within the predetermined range below the threshold, the corresponding maximum torque is used as the torque limit for the driving pulley 131 in step 234.

Claims

[1] Method for operating a belt drive (100) with a belt (110) which connects a driving pulley (131) and a driven pulley (121) in a torque-transmitting manner, wherein a total slip of the belt (110) is determined as a function of a rotational speed of the driving pulley (131) and of a rotational speed of the driven pulley (121) (211), wherein a stretching slip of the belt (110) is determined (212), wherein a difference between the determined total slip and the stretching slip is determined as the relevant belt slip of the belt (110) (213), wherein, when the relevant belt slip reaches a threshold value (214), a maximum torque of the driving pulley (131) is reduced (221) until the relevant belt slip no longer reaches the threshold value (222). [2] Method according to claim 1, wherein, if after the reduction of the maximum torque a condition is met (231), the maximum torque is increased again (232). [3] Method according to claim 2, wherein the maximum torque is increased again (232) until the relevant belt slip is within a predetermined range around the threshold value (233). [4] Method according to claim 2 or 3, wherein the predetermined condition is satisfied if the torque of the driving pulley (131) is below the maximum torque in a predetermined range for a predetermined time interval and if the relevant belt slip does not reach the threshold value (231) for the predetermined time interval. [5] Method according to one of the preceding claims, wherein the total slip of the belt (110) is determined as a function of a difference between the circumferential speed of the driving pulley (131) and the circumferential speed of the driven pulley (121) (211). [6] Method according to one of the preceding claims, wherein the elongation slip of the belt (110) is determined as a function of a theoretical model of the belt drive (100) and / or of physical quantities of the belt drive (100). [7] Method according to one of the preceding claims, wherein when the relevant belt slip reaches the threshold value (214), the maximum torque is reduced to a value which corresponds to a difference between an average value of the torque of the driving pulley (131) during a predetermined time interval and a predetermined torque value (221). [8] Method according to one of the preceding claims, wherein the belt connects a pulley (131) of an electric machine (130) and a pulley (121) of an internal combustion engine (120) in a torque-transmitting manner. [9] Method according to claim 8, wherein the electric machine (130) is a starter generator, in particular a boost recuperation machine. [10] Computing unit (140) configured to perform a method according to any of the preceding claims. [11] Computer program that causes a computing unit (140) to perform a method according to any one of claims 1 to 9 when executed on the computing unit (140). [12] Machine-readable storage medium with a computer program stored thereon according to claim 11.

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