Method for detecting belt slippage in a start system with BISG

Abstract

A method for detecting belt slippage in a starting system (10) for starting an internal combustion engine of a motor vehicle, the starting system (10) comprising a belt-driven integrated starter-generator (11). A control unit (20) of the motor vehicle evaluates belt slippage as detected when a determined belt slip value exceeds a limit value, wherein the belt slip value is determined for a defined time window T, which opens after the internal combustion engine has been started, and this determination takes into account at least one acceleration value of the starter-generator (11) within the time window T. A motor vehicle equipped with a control unit for carrying out the method is also included.

Description

[0001] The invention relates to a method for detecting belt slip in a starting system for starting an internal combustion engine of a motor vehicle according to the preamble of claim 1. The invention further relates to a motor vehicle having a control unit for carrying out the method.

[0002] In automotive mild hybrid systems, the internal combustion engine is often started with a belt-driven integrated starter generator (BISG) connected to the front-end accessory drive (FEAD) via a belt as a starting device for automatic stop-start operation. Furthermore, the BISG is also used during engine operation to recuperate energy and assist the internal combustion engine (ICE) with the torque from the recuperated energy, thus improving fuel consumption. On the one hand, the belt tension should be kept low to reduce parasitic friction loss. On the other hand, the belt tension should be high enough to ensure robust FEAD load transfer.

[0003] Therefore, for example, an active two-stage tensioner is used to adjust the belt tension. It can switch between low and high belt tension. During the engine start-up phase, when the torque transmitted via the FEAD is very high, the tensioner is controlled to switch to the high belt pre-tension position. While the engine is running, the tensioner remains in the low belt tension position to maximize fuel consumption and only switches to the high belt tension position when the requested BISG torque exceeds a certain threshold.

[0004] However, slippage can occur in the FEAD during both starting and running the engine, negatively impacting fuel efficiency, belt wear, and NVH levels. Therefore, there is a need for methods to detect belt slippage in such a starting system.

[0005] Belt slippage occurs whenever the friction between the belt and the individual pulleys of the FEAD is insufficient to transfer the required torque from one pulley to the other, i.e., in this case, from the BISG to the crankshaft pulley of the internal combustion engine or vice versa. This can be caused, for example, by a defective or incorrectly adjusted belt tensioner, belt wear, belt elongation, contamination of the belt with liquids or materials that reduce the coefficient of friction (CoF) between the belt surface and the pulley surface, etc. These causes can be temporary, i.e., the belt slips when wet, for example, and after the water evaporates, it functions as intended again, or they can be permanent, e.g., when the belt is worn, etc.

[0006] Detecting belt slippage during these events is critical to initiate countermeasures to protect against unwanted noise (NVH) and excessive wear, and to inform the driver and / or bring the system into a safe state.

[0007] Known solutions have some disadvantages. For example, DE 10 2007 008 858 A1 discloses a method in which a comparison between the crankshaft speed and the BISG engine speed is performed during engine start-up to detect belt slip. However, this requires a cost-intensive data bus system that delivers a data stream with a high repetition frequency and high-resolution measurement. As an alternative, cost-effective solution, the belt slip value (BSV) can be calculated from the BISG acceleration based on the BISG speed and the BISG internal resistance (based on measured current and voltage). However, depending on the internal control logic of the BISG and the power supply system, the BISG internal resistance may not exhibit the behavior described in DE 10 2007 008 858 A1 during start-up slip.

[0008] JP 2001-165 019 A discloses a method for detecting belt slip in a starting system for starting an internal combustion engine of a motor vehicle. This starting system comprises a belt-driven integrated starter-generator and a control unit. The control unit detects belt slip when a determined belt slip value exceeds a limit value, wherein the belt slip value is determined within a defined time window that opens after the internal combustion engine is started. The belt slip value is determined within the time window using at least one acceleration value of the starter-generator.

[0009] Given the state of the art, belt slip detection in this area still offers room for improvement.

[0010] The invention is based on the object of providing an improved method for detecting belt slip in a starting system with a belt-driven integrated starter generator, which in particular avoids the aforementioned disadvantages.

[0011] According to the invention, the object is achieved by a method having the features of claim 1.

[0012] By setting a time window T for slip detection after starting the internal combustion engine, and the control unit repeatedly carrying out at least the following steps until a determined belt slip value exceeds a limit value or the time window T is exceeded, the steps comprising determining an acceleration value of the starter generator, determining a slip number which is assigned to the respectively determined acceleration value, summing the slip numbers thus determined so far to a resulting belt slip value, and comparing the belt slip value with the limit value, a belt slip can be determined in a simple manner.

[0013] Further, particularly advantageous embodiments of the invention are disclosed in the subclaims. In a further aspect, claim 9 specifies a corresponding motor vehicle.

[0014] It should be noted that the features and measures listed individually in the following description can be combined with one another in any technically reasonable manner and demonstrate further embodiments of the invention. The description further characterizes and specifies the invention, particularly in conjunction with the figures.

[0015] The method according to the invention is used to detect belt slip in a starting system for starting an internal combustion engine of a motor vehicle, wherein the starting system has a belt-driven integrated starter generator. The motor vehicle is typically a so-called mild hybrid vehicle in which at least one electric motor supports the operation of the internal combustion engine. Preferably, it is a motor vehicle with a P0 mild hybrid system having a BISG (Belt Integrated Starter Generator). The letter P indicates the position of the electric motor in the mild hybrid system, wherein in a P0 mild hybrid system, the electric motor is connected to the internal combustion engine.

[0016] The invention includes that a control unit of the motor vehicle evaluates a belt slip as detected if a determined belt slip value exceeds a limit value, wherein the belt slip value is determined in accordance with a defined time window T which opens after a start of the internal combustion engine, and this determination takes into account at least one acceleration value of the starter generator within the time window T.

[0017] The inventive method for detecting belt slip in such a starting system with BISG is therefore based on taking into account a BISG acceleration value. Slip during engine start-up leads to a significant overshoot of the BISG acceleration value. However, due to disturbing factors such as engine speed fluctuations due to pumping and ignition processes, the occurrence of belt slip cannot be reliably determined using a simple, statically calibrated BISG acceleration value. It is therefore advantageous for the control unit to evaluate several samples of the BISG acceleration value within a specific time window T during engine start-up. Taking into account at least one acceleration value has the advantage that an overshoot of the BISG acceleration is always an indication of slip.The definition of a time window T after starting has the advantage that higher BISG accelerations that could be caused by combustion in the engine are not taken into account.

[0018] In a preferred embodiment of the invention, the method provides that a time window T is first defined for slip detection after the combustion engine has started. The control unit then repeatedly performs at least the following steps until a determined belt slip value exceeds a limit or the time window T is exceeded: - Determining an acceleration value of the starter generator; - Determining a slip number which is assigned to the acceleration value determined in each case; - Summing up the slip values ​​determined so far to obtain a resulting belt slip value; and - Comparison of the belt slip value with the limit value.

[0019] For example, an acceleration value of the starter-generator is determined by measuring a first speed value RPM_a within the time window T and a second speed value RPM_b after a defined sampling interval Ti_Sample. The acceleration value of the starter-generator is calculated as (RPM_a - RPM_b) / Ti_Sample. The speed values ​​RPM_a and RPM_b are measured, for example, based on the shaft speed of the starter-generator.

[0020] It is preferably provided that the association between a respective acceleration value of the starter-generator and a slip factor is stored in the control unit or can be retrieved by the control unit from another data source. In particular, the slip factor is an incremental value.

[0021] In one embodiment of the invention, the time window T is defined by a period of time between the start of cranking and before the ignition of the engine. The end of the time window T can be determined based on the feedback of an engine ignition signal or a calibrated duration based on the engine stop position.

[0022] It has proven advantageous for the control unit to initiate countermeasures if the accumulated belt slip exceeds the specified limit. These countermeasures may include, for example, reducing the BISG torque, interrupting the starting process, and / or using a conventional starter motor for cranking. The invention can therefore be advantageously used to prevent unwanted noise (NVH) and excessive belt wear.

[0023] The invention also encompasses a motor vehicle having a starting system for starting an internal combustion engine of the motor vehicle with a belt-driven integrated starter generator and a control unit designed to carry out a method for detecting belt slippage according to an embodiment of the invention.

[0024] Further advantageous embodiments of the invention are disclosed in the dependent claims and the following description of the figures. Fig. 1 a schematic representation of the integration of a BISG into a starting system for an internal combustion engine, Fig. 2A (a) a diagram of the speed of the combustion engine and BISG at normal start (rpm over time); and (b) a diagram of the acceleration of BISG at normal start (rpm / s over time), Fig. 2B (a) a diagram of the speed of the combustion engine and BISG during slip start (rpm over time); and (b) a diagram of the acceleration of BISG during slip start (rpm / s over time), Fig. 3 (a) a graph of speed values ​​of BISG (rpm over time); and (b) a graph of acceleration of BISG (rpm / s over time) at the sampling interval Ti_sample, Fig. 4 exemplary data of a lookup table for the incremental value of the slip number assigned to acceleration values, and Fig. 5 a flowchart of an embodiment of the method according to the invention for detecting and controlling belt slippage when starting an engine.

[0025] In the different figures, identical parts are always provided with the same reference symbols, which is why they are usually only described once.

[0026] Fig. 1 schematically shows a starting system 10 for a mild hybrid system of a motor vehicle, which is connected to an internal combustion engine or FEAD (not shown) via a crankshaft pulley 13. The starting system 10 has a belt-driven integrated starter generator 11 (Belt Integrated Starter Generator - BISG) with a belt 15. The belt-driven integrated starter generator 11 is referred to below as BISG 11. The BISG 11 is preferably also used during engine operation to recuperate energy and assist the internal combustion engine with the torque from the recuperated energy. Thus, a pulley 12 is also shown by way of example, and the belt 15 is guided around the pulleys of the BISG 11, the crankshaft pulley 13, and the pulley 12.To adjust the belt tension, an active tensioner 14 is provided, which can, for example, switch between a position with high belt tension H and a position with low belt tension N.

[0027] During the engine start-up phase, when the torque transmitted via the FEAD is very high, the tensioner 14 is controlled to switch to the high preload position h. While the engine is running, the tensioner 14 remains in the low-voltage position N to maximize fuel consumption and only switches to the high-voltage position when the requested BISG torque is above a certain threshold. The switching is carried out via a control unit of the motor vehicle, which is also designed to carry out the method according to the invention for detecting belt slip in the start-up system 10. Such a control unit 20 is shown schematically in Fig. 1, wherein the communication connection 30 of the control unit 20 at least to the BISG 11 or its shaft is indicated by dashed lines. The control unit 20 is typically formed by a plurality of interconnected individual components, which, for the sake of simplicity, are shown here as a single control unit 20. Furthermore, there may be additional communication connections to the crankshaft pulley 13, to the crankshaft pulley 12, etc., which are not shown here.

[0028] The invention provides that the control unit 20 evaluates several samples of the BISG acceleration value within a specific time window T during engine start-up. Therefore, a suitable time window for slip detection must first be determined. From the diagrams of the Fig. 2A and Fig. Figure 2B shows that the slip start generates a higher BISG acceleration during the initial phase of engine cranking than the normal start. However, after the engine begins to fire, combustion in the engine could cause an even higher BISG acceleration than that caused by belt slip. Therefore, it is necessary to define a time window after the start of cranking and before the engine fires. The end of the time window can be determined based on the feedback of the engine ignition signal or a calibrated duration based on the engine stop position. BISG accelerations within this time window T are valid for slip detection and are collected for further calculations. The duration of a time window is, for example, 0.2 to 0.3 seconds.

[0029] In particular, a BISG acceleration is calculated by the control unit 20 by measuring the BISG shaft speed twice in succession to obtain the values ​​RPM_a and RPM_b. The speed can be measured, for example, using a speed sensor mounted on the BISG shaft or using a sensorless speed measurement method based on motor current analysis, with these values ​​being transmitted to the control unit 20.

[0030] Then, RPM_b is subtracted from RPM_a and the result is divided by the sampling time Ti_Sample, i.e., the sampling interval between two measurements, to obtain the BISG acceleration in the current calculation step. Thus, the calculation is (RPM_a - RPM_b) / Ti_Sample. The determination of these values ​​is also shown in the diagrams of the Fig. 3, where Fig. 3 (a) the measured BISG speed values ​​and Fig. 3 (b) shows the calculated BISG accelerations. In Fig. Figure 3a shows an example of a sampling interval (Ti_Sample) with a value of 0.01s.

[0031] Subsequently, the accumulated slip factor is calculated based on the BISG acceleration during the specified time window T. For this purpose, for example, an incremental value of the slip factor is calculated from a lookup table at each calculation step, using the BISG acceleration as input. An example of lookup table data for the stepwise incremental value of the slip factor is shown in Fig. 4 given.

[0032] These steps are performed repeatedly within the time window T, i.e., sequentially. The slip values ​​thus determined are accumulated at each step to obtain a resulting belt slip value for the time window T. This belt slip value is then compared with a specified limit value, which is used by the control unit 20. This limit value or threshold can be either static or dynamic. If the belt slip value exceeds the specified limit value during a specific time window T, the control unit 20 considers excessive belt slip to have been detected.

[0033] If such belt slippage is detected, appropriate measures can be taken to prevent excessive belt slippage. This may include, for example, reducing the BISG torque, interrupting the BISG start process, and / or using a conventional starter motor for cranking.

[0034] Fig. 5 shows a flowchart for an embodiment of the method according to the invention for detecting and monitoring belt slippage when starting an engine. The method is carried out by a control unit of a motor vehicle and starts in step S40. It first checks in step S41 whether a request to start the internal combustion engine is present. Only if this is the case is it determined in step S42 how much time has passed since the start request. If the determined time lies outside the time window T for detecting belt slippage, the method is ended or aborted in step S50. If, however, it is determined in step S43 that the time is still within the time window T, the two BISG speed values ​​RPM_a and RPM_b are measured consecutively in step S44. This can be done as previously described.In step S45, the BISG acceleration is then calculated using the calculation method (RPM_b - RPM_a) / Ti_Sample, where Ti_Sample represents the sampling interval between the two measurements RPM_a and RPM_b. In . Fig.3a shows an example of a sampling interval (Ti_Sample) with a length of 0.01 s. In step S46, the slip factor associated with this BISG acceleration is determined and summed in step S47, or the first slip factor forms the starting point for the summation. The summed slip factors form the belt slip value, which is compared with a limit value in step S48 (belt slip value > limit value?). The limit value can be static or dynamic. If the condition is not yet met, the method returns to step S42 and checks in step S43 whether the elapsed time is still within the time window T. BISG speeds, BISG acceleration, and associated slip factor are then determined again until the comparison in step S48 shows that the belt slip value, i.e., the slip factors summed up up to that point, exceed the limit value. Then, in step S49, belt slippage is considered to be detected and optional countermeasures are initiated.In this exemplary embodiment, this involves aborting the starting process using BISG and, for example, using a conventional starter to crank the engine. The method is then terminated in step S50. List of reference symbols 10 Start System 11 Belt-driven integrated starter generator (BISG) 12 pulley 13 Crankshaft pulley 14 active tensioners 15 belts 20 Control unit 30 Communication connection S40-S50 process steps N position for low voltage H position for high voltage QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2007 008 858 A1

[0007] JP 2001-165 019 A

[0008]

Claims

[1] Method for detecting belt slip in a starting system (10) for starting an internal combustion engine of a motor vehicle, the starting system (10) comprising a belt-driven integrated starter generator (11), a control unit (20) of the motor vehicle evaluates a belt slip as detected when a determined belt slip value exceeds a limit value, wherein the belt slip value is determined in accordance with a defined time window T which opens after a start of the internal combustion engine, and this determination takes into account at least one acceleration value of the starter generator (11) within the time window T, characterized by , that a time window T is defined for the slip detection after the combustion engine has started, and the control unit (20) repeatedly carries out at least the following steps until a determined belt slip value exceeds a limit value or the time window T is exceeded: - Determining an acceleration value of the starter generator (11); - Determining a slip number which is assigned to the acceleration value determined in each case; - Summing up the slip values determined so far to obtain a resulting belt slip value; and - Comparison of the belt slip value with the limit value. [2] Method according to claim 1, characterized bythat at least one acceleration value of the starter generator (11) is determined by measuring a first speed value RPM_a within the time window T and a second speed value RPM_b after expiry of a defined time sampling interval Ti_Sample, wherein the acceleration value of the starter generator (11) is calculated by (RPM_a - RPM_b) / Ti_Sample. [3] Method according to claim 2, characterized by that the speed values RPM_a and RPM_b are measured based on the shaft speed of the starter generator (11). [4] Method according to one of the preceding claims, characterized by that the association between a respective acceleration value of the starter generator (11) and a slip number is stored in the control unit (20) or can be retrieved by the control unit (20) from a further data source. [5] Method according to claim 4, characterized by that the slip number is an incremental value. [6] Method according to one of the preceding claims, characterized by that the time window T defines a period of time between the start of starting and before the ignition of the engine. [7] Method according to claim 6, characterized by that the end of the time window T is determined based on the feedback of an engine ignition signal or a calibrated duration based on the engine stop position. [8] Method according to one of claims 1 to 7, characterized by that the control unit initiates countermeasures if the accumulated belt slip number exceeds the specified limit. [9] Motor vehicle, comprising a starting system (10) for starting an internal combustion engine of the motor vehicle with a belt-driven integrated starter generator (11) and a control unit (20) which is designed to carry out a method for detecting belt slippage according to one of claims 1 to 8.

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