Method of detecting belt skip in a starter system having a bisg

Abstract

A method of detecting belt slip in a starter system (10) for starting an internal combustion engine of a motor vehicle, the starter system (10) having a belt-driven integrated starter generator (11). In the event that the determined belt slip value exceeds a limit value, a control unit (20) of the motor vehicle evaluates the detection of belt slip, the belt slip value being determined to belong to a defined time window T which is opened after the internal combustion engine is started, and the belt slip value is determined to belong to the defined time window T after the internal combustion engine is started. The determination takes into account at least one acceleration value of the starter generator (11) within the time window T. The invention also relates to a motor vehicle having a control unit designed to carry out the method.

Description

Technical Field

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

[0002] In a mild hybrid system of a motor vehicle, the internal combustion engine is usually started by a belt-driven belt-integrated starter-generator (BISG), which is connected to the front-end accessory drive (FEAD) via a belt as a starting device for automatic stop-start operation. In addition, the BISG is also used to recover energy during engine operation, and the torque of the recovered energy is used to support the internal combustion engine (ICE) to improve fuel economy. On the one hand, the belt tension should be kept low to reduce parasitic friction losses. On the other hand, the belt tension should be high enough to ensure the robustness of the FEAD load transmission.

[0003] Thus, for example, the belt tension is regulated using an active two-stage tensioner that can switch between low and high belt tension. During the engine starting phase, when the torque transmitted through the FEAD is very high, the tensioner is controlled to switch to the high belt pretension position. When the engine is running, the tensioner remains in the low belt tension position to maximize fuel economy and only switches to the high belt tension position when the requested BISG torque exceeds a certain threshold.

[0004] However, FEAD slip can occur both when starting and when running the engine, which can negatively impact fuel efficiency, belt wear, and noise, vibration, and harshness (NVH) levels. Therefore, a method for detecting belt slip in such starter systems is needed.

[0005] Belt slip occurs whenever the friction between the FEAD's belt and the various pulleys is insufficient to transfer the required torque from one pulley to the other (i.e., from the BISG to the crankshaft pulley of the internal combustion engine, or vice versa). Belt slip can be caused, for example, by a defective or improperly adjusted belt tensioner, belt wear, belt elongation, contamination of the belt with fluids or materials that reduce the coefficient of friction (CoF) between the belt surface and the pulley surface. These causes can be temporary, i.e., the belt slips when wet, and after the water evaporates, the belt will work as expected again, or they can be permanent, such as belt wear.

[0006] Detecting belt slip during these events is critical to initiating countermeasures to prevent unnecessary noise (NVH) and excessive wear, as well as notifying the operator and / or bringing the system to a safe state.

[0007] Well-known solutions have some disadvantages. For example, DE 10 2007 008 858 A1 provides a method that compares the crankshaft speed with the BISG machine speed to detect belt slip when starting the engine. However, this requires a cost-intensive data bus system to provide a data stream with a high repetition rate and high resolution measurement. As an alternative cost-effective solution, a belt slip value (BSV) can be calculated from the acceleration of the BISG based on the speed of the BISG and the BISG internal resistance (based on measured current and voltage). However, depending on the internal control logic of the BISG and the power system, the BISG internal resistance may not behave as described in DE 10 2007 008 858 A1 during starting slip.

[0008] In view of the proposed prior art, there is still room for improvement in detecting belt slip in this area. Summary of the invention

[0009] The object of the present invention is to provide an improved method for detecting belt slip in a starter system with a belt-driven integrated starter generator, which method in particular avoids the above-mentioned disadvantages.

[0010] According to the invention, this object is achieved by a method having the features of claim 1 .

[0011] A method for detecting belt slip in a starter system for starting an internal combustion engine of a motor vehicle is disclosed, wherein the starter system has an integrated starter generator driven by a belt, wherein according to the invention, a control unit of the motor vehicle evaluates that belt slip has been detected in the event that a determined belt slip value exceeds a limit value, wherein the belt slip value is determined to belong to a defined time window T, which opens after the internal combustion engine is started, and the determination takes into account at least one acceleration value of the starter generator within the time window T.

[0012] Furthermore, the dependent claims disclose particularly advantageous embodiments of the invention. In another aspect, claim 10 specifies an associated motor vehicle.

[0013] It should be noted that the features and measures mentioned individually in the following description can be combined with each other in any technically reasonable manner and reveal further embodiments of the present invention. The description also particularly characterizes and specifically describes the present invention in conjunction with the accompanying drawings.

[0014] The method according to the invention serves to detect belt slip in a starter system for starting an internal combustion engine of a motor vehicle, wherein the starter 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. The motor vehicle is preferably a motor vehicle with a P0 mild hybrid system and a BISG (belt integrated starter generator). The letter P designates the position of the electric motor in the mild hybrid system, wherein in the P0 mild hybrid system the electric motor is connected to the internal combustion engine.

[0015] The present invention comprises that a control unit of a motor vehicle evaluates the detection of belt slip in the event that a determined belt slip value exceeds a limit value, wherein the belt slip value is determined to belong to a defined time window T, which opens after the internal combustion engine is started, and the determination takes into account at least one acceleration value of the starter generator within the time window T.

[0016] Therefore, the method according to the invention for detecting belt slip in such a starter system with a BISG is based on the consideration of the acceleration values ​​of the BISG. Slip when starting the engine can lead to a severe overshoot of the BISG acceleration values. However, due to interfering factors, such as engine speed fluctuations caused by pumping and ignition processes, the occurrence of belt slip cannot be reliably determined by a simple statically calibrated acceleration value of the BISG. Therefore, during engine starting, it is advantageous for the control unit to evaluate several samples of the acceleration value of the BISG within a certain time window T. The advantage of taking into account at least one acceleration value is that an overshoot of the acceleration of the BISG is always an indication of slip. The advantage of setting the time window T after starting is that a higher acceleration of the BISG that may be caused by the engine combustion does not have to be taken into account.

[0017] In a preferred embodiment of the invention, the method provides that after the internal combustion engine has been started, a time window T for slip detection is first specified. Then, the control unit repeatedly performs at least the following steps until the determined belt slip value exceeds a limit value or the time window T is exceeded: - Determine the acceleration value of the starter generator; - determining a slip number assigned to the respective determined acceleration value; - add up the slip numbers determined so far to get the belt slip value; and - Compare the belt slip value with the limit value.

[0018] For example, the acceleration value of the starter generator is determined by measuring a first speed value RPM_a within a time window T and measuring a second speed value RPM_b after a defined sampling time interval Ti_sampling has expired, wherein the acceleration value of the starter generator is calculated by (RPM_a-RPM_b) / Ti_sampling. For example, the speed value RPM_a and the speed value RPM_b are measured based on the shaft speed of the starter generator.

[0019] Preferably, the assignment between the respective acceleration value of the starter generator and the slip number is stored in the control unit or can be retrieved by the control unit from another data source. In particular, the slip number is an incremental value.

[0020] In an embodiment of the present invention, the time window T is defined by a period of time from the beginning of the engine start to before the engine ignition. The end of the time window T can be determined based on feedback of the engine ignition signal or based on a calibrated duration of the engine stop position.

[0021] In the event that the accumulated belt slip count exceeds a specified limit value, the control unit takes countermeasures, which have proven to be advantageous. The countermeasures may include, for example, reducing the BISG torque, interrupting the starting process and / or starting with a conventional starter motor. Thus, the invention can be used advantageously to avoid unnecessary noise (NVH) and prevent excessive belt wear.

[0022] The invention also comprises a motor vehicle having a starter system for starting an internal combustion engine with a belt-driven integrated starter generator and a control unit designed to carry out a method for detecting belt slip according to an embodiment of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Further advantageous embodiments of the invention are disclosed in the dependent claims and in the following description of the drawings. In the drawings: Figure 1 A schematic diagram showing the integration of a BISG into a starter system of an internal combustion engine; Figure 2A Shown are (a) a graph of the speed of the internal combustion engine and the BISG during a normal start (rpm versus time); and (b) a graph of the acceleration of the BISG during a normal start (rpm / s versus time); Figure 2B Shown are (a) a graph of the speed of the internal combustion engine and the BISG during a slip start (rpm versus time); and (b) a graph of the acceleration of the BISG during a slip start (rpm / s versus time); Figure 3shows (a) a graph of the speed value of the BISG (rpm vs. time); and (b) a graph of the acceleration of the BISG with a sampling interval Ti_sample (rpm / s vs. time); Figure 4 Example data of a lookup table showing incremental values ​​of slip numbers assigned to acceleration values; and Figure 5 A flow chart of an embodiment of a method for detecting and controlling belt slip when starting an engine according to the present invention is shown. DETAILED DESCRIPTION

[0024] In the different figures, identical components always have the same reference symbols, which is why they are usually described only once.

[0025] Figure 1 A starter system 10 for a mild hybrid system of a motor vehicle is schematically shown, which is connected to an internal combustion engine or a FEAD (not shown) via a crankshaft pulley 13. The starter system 10 has a belt-driven, belt-integrated starter generator (BISG) with a belt 15. The belt-driven integrated starter generator 11 is referred to as BISG 11 in the following. The BISG 11 is also preferably used to recover energy during engine operation and to support the internal combustion engine with the torque of the recovered energy. Therefore, the pulley 12 is also shown as an example, and the belt 15 is fed around the pulley of the BISG 11, the crankshaft pulley 13 and the pulley 12. An active tensioner 14 is provided for adjusting the belt tension, which active tensioner 14 can be switched between a position with high belt tension H and a position with low belt tension N, for example.

[0026] During the starting phase of the engine, when the torque transmitted by the FEAD is very high, the tensioner 14 is controlled to switch to the high pre-tension h position. When the engine is running, the tensioner 14 will remain in the low tension position N to maximize fuel economy and will only switch to the high tension position when the requested BISG torque is above a certain threshold. The switching is performed by a control unit of the motor vehicle, which control unit is also designed to execute the method according to the invention for detecting belt slip in the starter system 10. Such a control unit 20 is as Figure 1 , wherein a communication link 30 of the control unit 20 at least with the BISG 11 or a shaft of the BISG 11 is indicated by a dashed line. The control unit 20 is usually formed by a large number of interconnected individual components, which for the sake of simplicity are shown here as one control unit 20. In addition, there may be other communication links (not shown here) to the pulley 13, the pulley 12, etc. of the crankshaft.

[0027] The present invention provides that the control unit 20 evaluates a plurality of samples of the acceleration value of the BISG within a specific time window T during engine start. Therefore, a suitable time window for slip detection must first be determined. Figure 2A and Figure 2B It can be seen in the graph that in the initial stage of starting the engine, the slip start produces a higher acceleration of the BISG than the normal start. However, after the engine ignition begins, the combustion in the engine may cause a higher acceleration of the BISG than the acceleration of the BISG caused by belt slip. Therefore, it is necessary to define a time window after starting the engine and before the engine ignition. The end of the time window can be determined based on feedback from the engine ignition signal or based on a calibrated duration based on the engine stop position. The acceleration of the BISG within this time window T is valid for slip detection and is collected for further calculations. For example, the duration of the time window is 0.2 seconds to 0.3 seconds.

[0028] In particular, the control unit 20 calculates the acceleration of the BISG by measuring the speed of the BISG shaft twice in succession in time to obtain the values ​​RPM_a and RPM_b. For example, the speed can be measured using a speed sensor mounted on the BISG shaft or a sensorless speed measurement method based on motor current analysis, wherein these values ​​are transmitted to the control unit 20.

[0029] RPM_b is then subtracted from RPM_a, and the result is then divided by the sampling time Ti_sample (i.e. the sampling interval between two measurements) to obtain the acceleration of the BISG in the current calculation step. Thus, the calculation of (RPM_a - RPM_b) / Ti_sample is performed. Figure 3 The graph also shows the determination of these values, where Figure 3 (a) shows the measured velocity values ​​of the BISG, Figure 3 (b) shows the calculated acceleration of the BISG. Figure 3 a shows an example of a sampling interval (Ti_sample) with a duration of 0.01 seconds.

[0030] Subsequently, the accumulated slip number is calculated based on the acceleration of the BISG during the specified time window T. For example, for each calculation step, an incremental value of the slip number is calculated according to a lookup table with the acceleration of the BISG as input. Figure 4 Example data for a lookup table of stepwise increment values ​​for the slip number is given.

[0031] These steps are repeated in the time window T, i.e. they are performed one after another. The slip numbers determined in this way are accumulated in each step to obtain a belt slip value for the time window T. This belt slip value is then compared with a specified limit value used by the control unit 20. This limit value or threshold value can be static or dynamic. In case the belt slip value is above the specified limit value during a certain time window T, the control unit 20 evaluates that an excessively high belt slip has been detected.

[0032] In the event that such belt slip is detected, appropriate measures may be taken to prevent excessive belt slip. This may include, for example, reducing the BISG torque, interrupting the BISG start-up process, and / or starting using a conventional starter motor.

[0033] Figure 5 A flow chart of an embodiment of a method for detecting and controlling belt slip when starting an engine according to the present invention is shown. The method is executed by a control unit of a motor vehicle and starts in step S40. First, in step S41, it is checked whether it is necessary to start the internal combustion engine. Only in this case, step S42 determines how much time has passed since the start request. In the case where the determined time is outside the time window T for detecting belt slip, the method is terminated or canceled in step S50. However, in the case where it is determined in step S43 that the time is still in the time window T, the speed values ​​RPM_a and RPM_b of the two BISG are continuously measured in step S44. Step 44 can be completed as described above. In step S45, the acceleration of the BISG is then calculated using the calculation method (RPM_b-RPM_a) / Ti_sampling, where Ti_sampling represents the sampling interval between the two measured values ​​RPM_a and RPM_b. Figure 3a shows an example of a sampling interval (Ti_sampling) of 0.01 s. In step S46, the assigned slip number is determined for the acceleration of the BISG, and in step S47, the assigned slip numbers are summed, or the first slip number forms the starting point for the summation. The summed slip numbers 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 has not been met, the method returns to step S42 and checks in step S43 whether the elapsed time is still within the time window T. The speed of the BISG, the acceleration of the BISG and the corresponding slip number are then determined again until the comparison in step S48 shows that the belt slip value (that is, the sum of the slip numbers up to this point) exceeds the limit value. In this case, in step S49, it is considered that a belt slip is detected and countermeasures are optionally activated. In the exemplary embodiment, this includes aborting the start process by the BISG, for example using a conventional starter motor to start the engine. The method is then terminated in step S50.

[0034] List of reference numerals: 10Starter system 11 Belt Integrated Starter Generator (BISG) 12 Pulley 13 Crankshaft pulley 14 Active tensioner 15. Belt 20Control Unit 30 communication links S40-S50 Method Steps N low tension position H high tension position

Claims

1. A method for detecting belt slip in a starter system (10) for starting an internal combustion engine of a motor vehicle, the starter system (10) having an integrated starter generator (11) driven by a belt, It is characterized in that In the event that the determined belt slip value exceeds a limit value, a control unit (20) of the motor vehicle evaluates that belt slip has been detected, wherein the belt slip value is determined to belong to a defined time window T, which opens after the internal combustion engine is started, and the determination takes into account at least one acceleration value of the starter generator (11) within the time window T.

2. The method according to claim 1, It is characterized in that Setting a time window T for slip detection after starting the internal combustion engine, and The control unit (20) repeats at least the following steps until the determined belt slip value exceeds a limit value or a time window T is exceeded: - determining the acceleration value of the starter generator (11); - determining a slip number assigned to the respective determined acceleration value; - add up the slip numbers determined so far to get the belt slip value; and - Compare the belt slip value with the limit value.

3. The method according to claim 1 or 2, It is characterized in that 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 measuring a second speed value RPM_b after expiration of a defined time sampling interval Ti_sampling, wherein the acceleration value of the starter generator (11) is calculated by (RPM_a-RPM_b) / Ti_sampling.

4. The method according to claim 3, It is characterized in that The speed value RPM_a and the speed value RPM_b are measured based on the shaft speed of the starter generator (11).

5. The method according to any one of claims 2 to 4, It is characterized in that The assignment between the respective acceleration values ​​of the starter generator (11) and the slip number is stored in the control unit (20) or can be retrieved by the control unit (20) from another data source.

6. The method according to claim 5, It is characterized in that The slip number is an incremental value.

7. The method according to any one of claims 1 to 6, It is characterized in that The time window T defines a period of time from the start of starting the engine to before the engine ignites.

8. The method according to claim 7, It is characterized in that The end of the time window T is determined based on feedback of an engine firing signal or based on a calibrated duration of an engine stop position.

9. The method according to any one of claims 1 to 8, It is characterized in that In case the accumulated number of belt slips exceeds a specified limit value, the control unit initiates countermeasures.

10. A motor vehicle having a starter system (10) for starting an internal combustion engine of the motor vehicle with an integrated starter generator (11) with a belt drive, and a control unit (20) designed to execute the method for detecting belt slip according to any one of claims 1 to 9.

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