Method for monitoring rotational speed in a vehicle's drivetrain

Abstract

The invention relates to a method for monitoring rotational speed in a vehicle drivetrain, comprising the steps of: receiving (210) a request to change vehicle speed; determining (220) a torque request for the vehicle drivetrain depending on the received request to change vehicle speed; determining (230) an expected change in rotational speed in the drivetrain depending on the determined torque request; determining (240) a permissible change in rotational speed in the drivetrain depending on the determined expected change in rotational speed in the drivetrain; determining (250) a permissible rotational speed in the drivetrain depending on the determined permissible change in rotational speed; comparing (260) a current rotational speed in the drivetrain with the permissible rotational speed in the drivetrain; and performing (270) a predetermined action if the current rotational speed deviates from the permissible rotational speed.

Description

[0001] The present invention relates to a method for monitoring a rotational speed in a drive train of a vehicle as well as a computing unit and a computer program for carrying out the method. Background of the invention

[0002] A vehicle's drivetrain, drive, or drive system may comprise one or more electric motors for generating torque to propel the vehicle and for recovering braking energy into electrical energy. To monitor such a drivetrain while the vehicle is moving, torque monitoring algorithms can be conventionally used, which are usually based on a correct torque estimate. Input signals to such algorithms, e.g., currents, voltages, temperatures, rotor position, and speed, can be subject to high safety loads and must usually meet stringent safety requirements. Disclosure of the invention

[0003] According to the invention, a method for monitoring a rotational speed in a drive train of a vehicle, as well as a computing unit and a computer program for implementing the method, are proposed, having the features of the independent patent claims. Advantageous embodiments are the subject of the dependent claims and the following description.

[0004] The drivetrain, or drive system, of the vehicle comprises, in particular, one or more electric motors. A request or acceleration request is received to change the vehicle speed or to perform positive or negative acceleration of the vehicle. For example, this request can be made by a driver, e.g., by pressing an accelerator or brake pedal. Furthermore, this request can also be issued, for example, by an Advanced Driver Assistance System (ADAS).

[0005] Depending on the received request to change the vehicle speed, a torque request or requested torque is determined for the vehicle's powertrain. For example, the driver's actuation of the respective pedal or the specification of the respective ADAS can be coordinated into the corresponding torque request. In addition to this torque request for the powertrain, torque requests for other vehicle components can also be determined, for example a braking system. For example, in the case of a braking request, a torque request can be determined for both the powertrain and the braking system if the entire requested torque is to be distributed between the braking system and the powertrain to recuperate braking energy into electrical energy.In particular, in the case of a request for positive acceleration to increase the vehicle speed by operating the accelerator pedal, only a torque request to the drive system can be determined.

[0006] From a safety perspective, a malfunction that results in a torque that deviates from the requested torque can be critical, as this deviation can lead to excessive acceleration or deceleration of the vehicle. In extreme cases, it can even cause the wheels to lock or spin, which can lead to vehicle instability or a hazardous situation for the vehicle. The drivetrain is expediently monitored as part of the procedure to ensure that such a malfunction can be detected and counteracted, preventing such a hazardous situation for the vehicle.

[0007] Depending on the specific torque request, an expected or anticipated speed change in the drivetrain is determined. For example, the speed of an engine output shaft and / or a transmission output shaft and / or a wheel of the vehicle can be monitored. A speed change is understood in particular as a positive or negative longitudinal acceleration of the vehicle driven by the drivetrain. The expected speed change corresponds in particular to a positive or negative longitudinal acceleration of the vehicle, taking into account the vehicle's ambient conditions, if the specific torque request is implemented accordingly.

[0008] Depending on the specific, expected speed change, a permissible or allowed speed change is determined. This permissible speed change describes, in particular, the maximum positive acceleration or deceleration rate the vehicle may experience without causing a hazardous situation. In particular, an interval or range of permissible values ​​can be defined as the permissible speed change.

[0009] Depending on the specific permissible speed change, a permissible or permitted speed of the drivetrain is determined. This permissible speed describes, in particular, a range of values ​​that the speed may assume at a specified future point in time or within a specified time interval from a current point in time, so that no dangerous situation can arise for the vehicle.

[0010] The current speed in the drivetrain is compared with the permissible speed in the drivetrain. If the current speed deviates from the permissible speed, particularly if the current speed lies outside the permissible value range, a predetermined action is taken. Such a deviation indicates a malfunction that could lead to excessive acceleration or deceleration or even to instability or a dangerous situation in the vehicle. The predetermined action can counteract this malfunction so that the vehicle can always be operated safely without endangering the vehicle, its occupants, or other road users.

[0011] The present invention provides an improved option for monitoring the drivetrain. In contrast to conventional torque monitoring algorithms, the present method does not directly monitor the torque in the drivetrain. Instead, the torque is indirectly monitored by determining a permissible acceleration and a permissible speed for the drivetrain from the requested torque. The drivetrain is thus expediently monitored based on speed or at the speed level. The safety requirements for input signals and sensors can be reduced, in particular, thereby lowering costs without compromising safety.Particularly useful for powertrain monitoring, the safety requirements for most sensors can be reduced, especially for current and voltage sensors, while only high safety requirements are expediently placed on sensors for determining rotor or speed information. Particularly useful, the present invention provides a way to combine a torque-based algorithm and an acceleration-based algorithm for powertrain monitoring. Depending on the distribution of safety loads between these two algorithms, the corresponding powertrain monitoring system can be optimized with respect to meeting the required safety requirements while simultaneously reducing sensor costs.

[0012] According to one embodiment, a maximum permissible speed change and a minimum permissible speed change are determined as the permissible speed change. These maximum and minimum permissible speed changes specify, in particular, an interval or range of permissible values, in particular around the current speed change, which the speed change may assume so that no danger to the vehicle can occur.

[0013] According to one embodiment, a maximum permissible speed and a minimum permissible speed are determined as the permissible speed. These maximum and minimum permissible speeds expediently specify an interval or value range of permissible values, in particular around the current speed, which the speed may assume so that no danger to the vehicle can arise. The maximum permissible speed is determined in particular as a function of the maximum permissible speed change. The minimum permissible speed is determined in particular as a function of the minimum permissible speed change.

[0014] According to one embodiment, the specified measure is implemented when the current speed exceeds the maximum permissible speed or falls below the minimum permissible speed. In particular, the measure is implemented when the current speed lies outside the value range specified by the maximum and minimum permissible speed.

[0015] According to one embodiment, the drive train is transferred to a safe state as a predetermined measure. For example, in this safe state, the speed and speed change in the drive train, as well as, for example, the vehicle speed and vehicle acceleration, can each be limited to a predetermined value. Furthermore, in this safe state, an error message can be output, for example, to a driver of the vehicle via a display in a dashboard area or to a vehicle manufacturer via a wireless communication connection, e.g., the Internet. Furthermore, an entry can be created in an error log, for example.

[0016] According to one embodiment, the permissible speed is determined and the current speed is compared with the permissible speed iteratively at predetermined time intervals. In particular, in each iteration step, the permissible speed for the next iteration step or for the next time interval can be determined, in particular depending on the current speed at the current iteration step. Thus, in particular, a future permissible speed can be determined.

[0017] According to one embodiment, the expected speed change in the drivetrain is determined using an equation of the vehicle's longitudinal dynamics. This longitudinal dynamics equation relates, in particular, the acceleration force acting on the vehicle to the drive torque and braking torque, as well as to the air resistance and the slope force. This equation expediently contains only the expected speed change as an unknown and can be solved for this variable.

[0018] According to one embodiment, the expected speed change in the drive train is determined in addition to the determined torque requirement M D for the powertrain further determined depending on a vehicle mass m* or a vehicle mass parameter or a generalized vehicle mass and / or a torque requirement M Bfor other vehicle components, in particular the braking system, and / or from a rolling resistance moment M R and / or of a radius r w a tire of the vehicle and / or an air resistance R Air and / or from a slope force or a climbing resistance R Climb In particular, the equation of longitudinal dynamics depending on these quantities can be expressed as follows: m*a=MD−MB−MRrW−RAir−RClimb

[0019] The equation can be solved in particular for the expected speed change or acceleration a in the drive train. The rolling resistance moment M R can also be neglected. The torque requirement M D for the drive train can be transmitted in particular in the form of a signal via a communication system or a communication bus of the vehicle. Accordingly, the torque requirement M Bfor the other vehicle components, in particular also in the form of a corresponding signal via the communication system or the communication bus. The slope force R Climb depends on the vehicle mass m* and the gradient α of a roadway or road. Depending on the gradient, the slope force can also be neglected. For the slope force R climb In particular, the following equation applies: RClimb=m*g sin α

[0020] According to one embodiment, the air resistance R Air depending on an air resistance parameter c and on a current vehicle speed v, in particular according to the following equation: RAir=c2∗v2∗sign(v)

[0021] The drag parameter c can be determined offline or in advance, especially before the vehicle is put into operation, e.g., during a development phase. In particular, the drag parameter c depends on a drag coefficient C Air , from a longitudinal airflow area A F and of an air density p Air in particular according to the following equation: c=cAir∗AF∗ρAir

[0022] According to one embodiment, the current vehicle speed v is dependent on the current rotational speed ω, on a transmission ratio T and on the tire radius r w determined, in particular according to the following equation: v=ωT∗2π∗rW

[0023] According to one embodiment, the permissible speed change, in particular the maximum permissible speed change and the minimum permissible speed change, is determined depending on a robustness parameter for compensating for varying vehicle parameters. This robustness parameter can be determined offline or in advance, in particular before commissioning of the vehicle, e.g., during the development phase. The robustness parameter depends on a friction coefficient of the vehicle's tires. The permissible speed change can, for example, be determined for a highest friction coefficient, in particular on a dry road surface. The robustness parameter can also depend, for example, on a load or loading state of the vehicle, on slippage and / or on model accuracy; however, the friction coefficient in particular has the greatest influence on the robustness parameter.

[0024] For example, the robustness parameter can be added as an offset to the expected speed change to determine the maximum permissible speed change, and subtracted from the expected speed change to determine the minimum permissible speed change. However, particular care must be taken to ensure that safety thresholds for the speed change, in particular a maximum safety threshold and a minimum safety threshold, are not exceeded or undercut, as the vehicle behavior is considered unsafe. If this were the case, the maximum safety threshold can be determined as the maximum permissible speed change, or the minimum safety threshold as the minimum permissible speed change.

[0025] According to one embodiment, the permissible speed in the drive train is further determined, in addition to the determined permissible speed change, depending on the radius of the vehicle's tire and the current speed in the drive train. In particular, in a current iteration step n, a maximum speed change difference and a minimum speed change difference can be determined for a next iteration step n+1 depending on the determined maximum permissible speed change for the next iteration step n+1, depending on the determined minimum permissible speed change for the next iteration step n+1, depending on the length or duration of an iteration step, and depending on the tire radius.Depending on these speed change differences and depending on the current speed of the current iteration step n, the maximum permissible speed and the minimum permissible speed for the next iteration step n+1 can then be determined.

[0026] A computing unit according to the invention, e.g. a control unit of a motor vehicle, is configured, in particular in terms of programming, to carry out a method according to the invention.

[0027] The implementation of a method according to the invention in the form of a computer program or computer program product with program code for carrying out all method steps is also advantageous, since this entails particularly low costs, in particular if an executing control unit is also used for other tasks and is therefore already present. Finally, a machine-readable storage medium is provided with a computer program stored thereon, as described above. Suitable storage media or data carriers for providing the computer program are, in particular, magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, and others. Downloading a program via computer networks (Internet, intranet, etc.) is also possible. Such a download can be wired or cable-based or wireless (e.g. via a WLAN network, a 3G, 4G, 5G or 6G connection, etc.).

[0028] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0029] The invention is illustrated schematically in the drawing using exemplary embodiments and is described below with reference to the drawing. Short description of the drawings Fig. 1 shows a schematic embodiment of a computing unit according to the invention, which is configured to carry out an embodiment of a method according to the invention. Fig. 2 shows an embodiment of a method according to the invention as a schematic block diagram. Fig. 3 schematically shows a diagram of a speed change plotted against a torque difference, which diagram can be determined according to an embodiment of a method according to the invention. Fig. 4 schematically shows a diagram of a rotational speed plotted against an iteration step, which diagram can be determined according to an embodiment of a method according to the invention. Fig. 5 schematically shows a diagram of a rotational speed plotted against an iteration step, which diagram can be determined according to an embodiment of a method according to the invention. Embodiment(s) of the invention

[0030] In Fig. 1 schematically depicts a computing unit, designated 100, for example, a control unit of a vehicle. Control unit 100 is configured, particularly in terms of programming, to carry out an embodiment of a method according to the invention. In the course of this, control unit 100 monitors a rotational speed in a drive train of the vehicle, which drive train may comprise one or more drive motors, for example, electric motors and / or internal combustion engines.

[0031] The control unit 100 has a communication interface 110, via which the control unit 100 is connected to a communication system of the vehicle, e.g., to a vehicle bus. The control unit 100 further has a memory unit 120, in which constants and vehicle parameters are stored, which were determined, for example, before commissioning of the control unit 100 or vehicle during a development phase. Furthermore, the control unit 100 has a sensor input 130, to which a speed sensor is connected, which can detect a current speed in the drive train. The control unit 100 further has a determination unit 140, which, within the scope of the proposed method, can determine a permissible speed for the drive train, in particular a maximum and a minimum permissible speed.For this purpose, signals and parameter values ​​145 can be transmitted from the communication interface 110, from the storage unit 120, and from the sensor input 130 to the determination unit 140. The determined permissible speed 155 is transmitted from the determination unit 140 to a comparison unit 150, which compares the current speed with the permissible speed.

[0032] Succession will be in relation to Fig. 2 explains how the permissible speed is determined. Fig. 2 an embodiment of the method according to the invention is shown as a schematic block diagram.

[0033] In a step 210, a request to change a vehicle speed is received, e.g., by actuation of a brake or accelerator pedal by a driver and / or by a command from an ADAS.

[0034] In a step 220, a torque request or a requested torque for the drive train of the vehicle is determined depending on the received request to change the vehicle speed. In the case of a braking request, for example, a torque request for a braking system of the vehicle can also be determined if the entire requested torque is to be distributed between the braking system and the drive train, e.g., to recuperate braking energy. For example, the request to change a vehicle speed can be received by the control unit 100 via the communication interface 110, and the torque request can be determined by the determination unit 140. It is also conceivable for the torque request to be determined by a further control unit of the vehicle and received by the control unit 100 or its communication interface 110 as a signal via the vehicle bus.

[0035] In a step 230, an expected or expected speed change in the drive train or an expected acceleration in the drive train is determined depending on the determined torque request, in particular by the determination unit 140. The expected speed change can be determined using the above equation (1) of the longitudinal dynamics.

[0036] In equation (2), the gradient α can be determined, for example, using a sensor on the vehicle and received by the communication interface 110. Depending on the gradient, the slope force can be neglected if necessary.

[0037] The parameters required in equations (1) to (5) are vehicle mass m*, air resistance factor C Air , Airflow area A F , air density ρ Air , transmission ratio T and tire radius r wcan each be stored in the storage unit 120 and read in by the determination unit 140 to determine the speed change. The current speed ω can be received via the sensor input 130. The equation of the longitudinal dynamics thus has, in particular, only the speed change a as an unknown and can be solved for this by the determination unit 140.

[0038] In a step 240, a permissible or allowed speed change in the drive train is determined, in particular by the determination unit 140, depending on the determined, expected speed change in the drive train. In particular, a maximum permissible speed change and a minimum permissible speed change are determined as this permissible speed change, thereby specifying, in particular, a value range or interval of permissible values ​​around the current speed change.

[0039] For example, the permissible speed change can be determined depending on a robustness parameter for compensating vehicle parameters, wherein this robustness parameter depends on a friction coefficient of the vehicle's tire. The robustness parameter can be stored in the storage unit 120 and read in by the determination unit 140 to determine the permissible speed change. The robustness parameter can also depend on a load or load state of the vehicle, on slippage, and / or on model accuracy. Furthermore, the robustness parameter can also depend on whether a vehicle standstill is requested. If a standstill is requested, the robustness parameter can be reduced to very small values, for example, to prevent the vehicle from rolling away.For example, the robustness parameter can be added as an offset to the expected speed change to determine the maximum allowable speed change and subtracted from the expected speed change to determine the minimum allowable speed change.

[0040] This determination of the permissible speed change is carried out in Fig. 3, which shows a schematic diagram in which the speed change a is plotted against the difference between the requested torque for the drive train and the requested torque for the braking system (M D -M B ). Curve 310 represents the expected speed change in the drive train for different torque differences (M D -M B ). Curve 320 represents the maximum permissible speed change and curve 330 the minimum permissible speed change. Fig. The difference 340 shown in Figure 3 between the maximum permissible speed change 320 and the expected speed change 310 at a torque difference of 0 corresponds to the robustness parameter. A maximum safety threshold 350 and a minimum safety threshold 360 can be specified, which the speed change must not exceed or fall below. If the sum of the robustness parameter and the expected speed change exceeds the maximum safety threshold 350, the maximum safety threshold 350 can be determined as the maximum permissible speed change. Accordingly, the minimum safety threshold 360 can be determined as the minimum permissible speed change if the difference between the expected speed change and the robustness parameter falls below the minimum safety threshold 360.

[0041] In a step 250, a permissible speed in the drive train is determined as a function of the determined, permissible speed change, in particular by the determination unit 140. In particular, a maximum permissible speed and a minimum permissible speed are determined as this permissible speed, which in particular predetermine a value range or interval of permissible values ​​around the current speed. In particular, the maximum permissible speed is determined as a function of the maximum permissible speed change, and the minimum permissible speed is determined in particular as a function of the minimum permissible speed change. Furthermore, the maximum and minimum permissible speeds are each determined in particular as a function of the tire radius and the current speed.

[0042] The permissible speed is determined iteratively in specified time intervals or iteration steps of 10 ms. In particular, in a current iteration step n, a maximum speed change difference ("SpeedMaxDeltaCalc") and a minimum speed change difference ("Speed-MinDeltaCalc") can be determined for a next iteration step n+1, depending on the determined maximum permissible speed change ("AllowedAccelMaxCalc") for the next iteration step n+1, on the determined minimum permissible speed change ("AllowedAccelMinCalc") for the next iteration step n+1, on the length or duration of an iteration step ("StepWidth"), and on the tire radius ("WheelRadiusPar"), in particular according to the following equations: SpeedMaxDeltaCalc(n+1)=AllowedAccelMaxCalc(n+1)∗StepWidth2π∗WheelRadiusPar SpeedMinDeltaCalc(n+1)=AllowedAccelMinCalc(n+1)∗StepWidth2π∗WheelRadiusPar

[0043] Depending on these speed change differences and depending on the current speed ("PTSpeedCalc") of the current iteration step n, the maximum allowable speed ("AllowedPTSpeedMaxCalc") and the minimum allowable speed ("AllowedPTSpeedMinCalc") for the next iteration step n+1 can then be determined, in particular according to the following equations: AllowedPTSpeedMinCalc(n+1)=max[PTSpeedCalc(n),AllowedPTSpeedMinCalc(n+1)]+SpeedMinDeltaCalc(n+1) AllowedPTSpeedMaxCalc(n+1)=min[PTSpeedCalc(n),AllowedPTSpeedMinCalc(n+1)]+SpeedMaxDeltaCalc(n+1)

[0044] This determination of the permissible speed is in Fig. 4 illustrates, where Fig. 4 shows a schematic diagram in which the speed ω is plotted against the iteration step i. Curve 410 represents the current speed, curve 420 the maximum permissible speed, and curve 430 the minimum permissible speed. The addition of the maximum permissible speed determined for the next iteration step to the current speed of the current iteration step is shown in Fig. 4 is schematically represented by arrows 441, 442, 443, and 444 for iteration steps n, (n+1), (n+2), and (n+3). Accordingly, arrows 451, 452, 453, and 454 for iteration steps n, (n+1), (n+2), and (n+3) schematically represent the subtraction of the minimum permissible speed determined for the next iteration step from the current speed of the current iteration step.

[0045] In step 260, the comparison unit 150 compares the current speed with the maximum and minimum permissible speeds. For this purpose, the determined values ​​for the maximum and minimum permissible speeds 155 are transmitted from the determination unit 140 to the comparison unit 150. If the current speed lies within this interval, this indicates fault-free operation, and no action is taken. However, if the current speed lies outside this interval, this indicates a fault that could lead to a hazardous situation for the vehicle. In this case, a predetermined action is taken in step 270, e.g., transferring the drive train to a safe state.

[0046] Such an error case is in Fig. 5 illustrates. Fig. 5 shows, according to Fig.4, a schematic diagram of the speed ω plotted against iteration step i. Curve 510 represents the expected speed, curve 520 the maximum permissible speed, and curve 530 the minimum permissible speed. Curve 540 represents the actual, current speed. For example, an error occurs at step n, represented by element 551. In step (n+1), the comparison unit 150 determines that the current speed 540 exceeds the maximum permissible speed 510, indicated by element 552. This indicates that there is an error in the drive train control system causing excessive speed. Depending on the system requirements, error filtering methods, for example, can be applied. After error filtering, the specified action is carried out in step (n+3), indicated by element 553, and the system transitions to the safe state.

[0047] The present invention thus provides a way to monitor the drive train at the speed level, whereby a permissible acceleration and a permissible speed are determined from the requested torque. In particular, high safety requirements apply to the monitoring process only for sensors that determine rotor or speed information. Safety requirements for other sensors can be reduced, thereby reducing the costs and effort for monitoring without compromising safety.

Claims

[1] A method for monitoring a rotational speed in a drive train of a vehicle, comprising the steps of: Receiving (210) a request to change a vehicle speed; Determining (220) a torque request for the vehicle's powertrain dependent on the received request to change the vehicle speed; Determining (230) an expected speed change (310) in the drive train depending on the determined torque request; Determining (240) a permissible speed change (320, 330) in the drive train depending on the determined, expected speed change (310) in the drive train; Determining (250) a permissible speed (410, 420, 510, 520) in the drive train depending on the determined permissible speed change (320, 330); Comparing (260) a current speed (540) in the drive train with the permissible speed (410, 420, 510, 520) in the drive train; and Carrying out (270) a predetermined measure (553) if the current speed (540) deviates from the permissible speed (410, 420, 510, 520). [2] Method according to claim 1, wherein a maximum permissible speed change (310) and a minimum permissible speed change (320) are determined (240) as the permissible speed change. [3] Method according to claim 1 or 2, wherein a maximum permissible speed (410, 510) and a minimum permissible speed (420, 520) are determined (140) as the permissible speed. [4] Method according to claim 3, wherein the predetermined measure is carried out when the current rotational speed (540) exceeds the maximum permissible rotational speed (410, 510) or falls below the minimum permissible rotational speed (420, 520). [5] Method according to one of the preceding claims, wherein the drive train is transferred to a safe state as a predetermined measure (270). [6] Method according to one of the preceding claims, wherein the determination (250) of the permissible speed and the comparison (260) of the current speed with the permissible speed are carried out iteratively at predetermined time intervals. [7] Method according to one of the preceding claims, wherein the expected speed change (310) in the drive train is determined using an equation of the longitudinal dynamics of the vehicle (230). [8] Method according to one of the preceding claims, wherein the expected speed change (310) in the drive train is further determined depending on one or more of the following variables: of a vehicle mass; from a torque requirement for other vehicle components; from a rolling resistance moment; of a radius of a tire of the vehicle; from air resistance; from a downhill force. [9] The method of claim 8, further comprising: Determining (230) the air resistance depending on an air resistance parameter and a current vehicle speed. [10] The method of claim 9, further comprising: Determining (230) the current vehicle speed depending on the current rotational speed, a transmission ratio and the radius of the vehicle's tire. [11] Method according to one of the preceding claims, wherein the permissible speed change (310) is determined as a function of a robustness parameter (340) for compensating vehicle parameters, wherein the robustness parameter is dependent on a friction coefficient of a tire of the vehicle. [12] Method according to one of the preceding claims, wherein the permissible rotational speed (410, 510, 420, 520) in the drive train is further determined as a function of a radius of a tire of the vehicle and of the current rotational speed in the drive train. [13] Computing unit (100) which is configured to carry out all method steps of a method according to one of the preceding claims. [14] Computer program which causes a computing unit (100) to carry out all method steps of a method according to one of claims 1 to 12 when it is executed on the computing unit (100). [15] A machine-readable storage medium having stored thereon a computer program according to claim 14.

Images