Method and device for operating a drive system for a motor vehicle including an acceleration monitoring system

Abstract

A method for operating a drive system including a drive engine for a motor vehicle, including carrying out an acceleration monitoring of the motor vehicle; switching to an alternative monitoring when a signal, which is relevant for the acceleration monitoring and for which a substitute signal exists, does not exist or has failed, and when a driver input which is below a predefined threshold value is specified, and/or a braking intent is specified.

Claims

1. A method of operating an engine of a motor vehicle, the method comprising: obtaining, by processing circuitry, inputs identifying whether a braking request is present and identifying driver-input drive requests; cyclically performing, by the processing circuitry, an acceleration monitoring that includes checking whether there is an unintentional acceleration of the motor vehicle, wherein the acceleration monitoring is performed by executing an algorithm that: defines to determine whether the unintentional acceleration is present using a primary check based on signals of a first sensor that indicates a longitudinal acceleration of the vehicle when no fault is detected in the first sensor and its output signals, and without using a secondary check; defines to determine whether the unintentional acceleration is present using the secondary check based on signals of a second sensor in response to satisfaction of a first condition that (a) a fault is detected in the first sensor or its output signals and (b) the inputs indicate that the braking request is present; defines to determine whether the unintentional acceleration is present using the secondary check in response to satisfaction of a second condition that (a) the fault is detected in the first sensor or its output signals and (b) the inputs indicate that an identified driver-input drive request is below a predefined threshold value; defines to determine whether the unintentional acceleration is present using the secondary check in response to satisfaction of a third condition that (a) the fault is detected in the first sensor or its output signals and (b) an unintentional acceleration is indicated to be present by the primary check using a substitute vehicle longitudinal acceleration value that is obtained by reconstructing the longitudinal acceleration of the vehicle using a signal of a third sensor; and defines that the unintentional acceleration is not present, independent of the secondary check, in response to a combination of (a) the fault being detected in the first sensor or its output signals, (b) no braking request being indicated to be present by the inputs, (c) the identified driver-input drive request not being below the predefined threshold value, and (d) the unintentional acceleration being indicated not to be present by a result of the primary check using the substitute vehicle longitudinal acceleration value; and modifying, by the processing circuitry, an operation of the engine in response to a result of the acceleration monitoring being that the unintentional acceleration is present.

2. The method as recited in claim 1, wherein the secondary check is not performed when there is a combination of conditions that (a) a result of the primary check using the substitute signal is obtained without detection of the unintentional acceleration, the driver-input drive request is not below the predefined threshold value, and the braking request is not present.

3. The method as recited in claim 1, wherein the secondary check includes comparing a speed of the engine to a value which is dependent on driver input.

4. The method as recited in claim 1, wherein the secondary check includes comparing of a torque of the engine to a value which is dependent on driver input.

5. The method as recited in claim 1, wherein the third sensor is a wheel speed sensor on a primary or secondary axle.

6. A drive system of a motor vehicle, the drive system comprising: a first sensor, output signals of which indicate a longitudinal acceleration of the vehicle; a second sensor; a third sensor; an engine; and processing circuitry; wherein: the processing circuitry is configured to obtain inputs identifying whether a braking request is present and identifying driver-input drive requests; the processing circuitry is configured to cyclically perform an acceleration monitoring that includes checking whether there is an unintentional acceleration of the motor vehicle; the acceleration monitoring is performed by executing an algorithm that: defines to determine whether the unintentional acceleration is present using a primary check based on signals of the first sensor when no fault is detected in the first sensor and its output signals, and without using a secondary check; defines to determine whether the unintentional acceleration is present using the secondary check based on signals of the second sensor in response to satisfaction of a first condition that (a) a fault is detected in the first sensor or its output signals and (b) the inputs indicate that the braking request is present; defines to determine whether the unintentional acceleration is present using the secondary check in response to satisfaction of a second condition that (a) the fault is detected in the first sensor or its output signals and (b) the inputs indicate that an identified driver-input drive request is below a predefined threshold value; defines to determine whether the unintentional acceleration is present using the secondary check in response to satisfaction of a third condition that (a) the fault is detected in the first sensor or its output signals and (b) an unintentional acceleration is indicated to be present by the primary check using a substitute vehicle longitudinal acceleration value that is obtained by reconstructing the longitudinal acceleration of the vehicle using a signal of the third sensor; and defines that the unintentional acceleration is not present, independent of the secondary check, in response to a combination of (a) the fault being detected in the first sensor or its output signals, (b) no braking request being indicated to be present by the inputs, (c) the identified driver-input drive request not being below the predefined threshold value, and (d) the unintentional acceleration being indicated not to be present by a result of the primary check using the substitute vehicle longitudinal acceleration value; and the processing circuitry is configured to modify an operation of the engine in response to a result of the acceleration monitoring being that the unintentional acceleration is present.

7. A non-transitory computer-readable medium on which are stored instructions that (1) are executable by a processor of a motor vehicle that includes an engine, a first sensor that outputs signals that indicate a longitudinal acceleration of the vehicle, a second sensor, and a third sensor, and (2) when executed by the processor, cause the processor to perform a method of operating the engine of the motor vehicle, the method comprising: obtaining inputs identifying whether a braking request is present and identifying driver-input drive requests; cyclically performing an acceleration monitoring that includes checking whether there is an unintentional acceleration of the motor vehicle, wherein the acceleration monitoring is performed by executing an algorithm that: defines to determine whether the unintentional acceleration is present using a primary check based on signals of the first sensor when no fault is detected in the first sensor and its output signals, and without using a secondary check; defines to determine whether the unintentional acceleration is present using the secondary check based on signals of the second sensor in response to satisfaction of a first condition that (a) a fault is detected in the first sensor or its output signals and (b) the inputs indicate that the braking request is present; defines to determine whether the unintentional acceleration is present using the secondary check in response to satisfaction of a second condition that (a) the fault is detected in the first sensor or its output signals and (b) the inputs indicate that an identified driver-input drive request is below a predefined threshold value; defines to determine whether the unintentional acceleration is present using the secondary check in response to satisfaction of a third condition that (a) the fault is detected in the first sensor or its output signals and (b) an unintentional acceleration is indicated to be present by the primary check using a substitute vehicle longitudinal acceleration value that is obtained by reconstructing the longitudinal acceleration of the vehicle using a signal of the third sensor; and defines that the unintentional acceleration is not present, independent of the secondary check, in response to a combination of (a) the fault being detected in the first sensor or its output signals, (b) no braking request being indicated to be present by the inputs, (c) the identified driver-input drive request not being below the predefined threshold value, and (d) the unintentional acceleration being indicated not to be present by a result of the primary check using the substitute vehicle longitudinal acceleration value; and modifying an operation of the engine in response to a result of the acceleration monitoring being that the unintentional acceleration is present.

8. A method of operating an engine of a motor vehicle, the method comprising: obtaining, by processing circuitry, inputs identifying whether a braking request is present and identifying driver-input drive requests; cyclically performing, by the processing circuitry and while no fault is detected in a first sensor that indicates a longitudinal acceleration of the vehicle and in its output signals, a primary acceleration monitoring that includes checking whether there is an unintentional acceleration of the motor vehicle based on the signals of the first sensor; upon occurrence of a fault in the first sensor or in its signals: determining, by the processing circuitry and based on the inputs, that at least one of the braking request is present and a driver-input drive request identified by the inputs is below a predefined threshold value; and responding to the determination that the at least one of the braking request is present and the driver-input drive request identified by the inputs is below the predefined threshold value by performing, by the processing circuitry, a secondary acceleration monitoring that includes checking whether there is an unintentional acceleration of the motor vehicle based on signals of a second sensor; and modifying, by the processing circuitry, an operation of the engine in response to a result of the secondary acceleration monitoring being that the unintentional acceleration is present, wherein the processing circuitry is configured to also modify the operation of the engine whenever a result of the primary acceleration monitoring, performed while no fault is detected in the first sensor and its output signals, is that the unintentional acceleration is present.

9. A method of operating an engine of a motor vehicle, the method comprising: cyclically performing, by the processing circuitry and while no fault is detected in a first sensor that indicates a longitudinal acceleration of the vehicle and in its output signals, a primary acceleration monitoring that includes checking whether there is an unintentional acceleration of the motor vehicle based on the signals of the first sensor; respond to an occurrence of a fault in the first sensor or in its signals by: continuing, by the processing circuitry, performance of the primary acceleration monitoring using signals of a second sensor, instead of the first sensor, by reconstructing the longitudinal acceleration of the vehicle using the signals of the second sensor; obtaining, by the processing circuitry, a result of the primary acceleration monitoring using the signals of the second sensor that indicates that the unintentional acceleration of the motor vehicle is present; in response to the result, performing, by the processing circuitry, a secondary acceleration monitoring that includes checking whether the unintentional acceleration of the motor vehicle is present based on signals of a third sensor; and in response to a result of the secondary acceleration monitoring indicating that the unintentional acceleration of the motor vehicle is present, modifying, by the processing circuitry, an operation of the engine.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Specific embodiments are described in greater detail in the following with reference to the figures.

(2) FIG. 1 shows a schematic representation of a drive system for a motor vehicle.

(3) FIG. 2 shows a flow chart for illustrating a monitoring function for operating the drive system including an alternative monitoring system.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

(4) FIG. 1 shows a schematic representation of a drive system 1 including a drive engine 2 including an output shaft 3 which is coupled via a clutch 4 and a transmission 5 to a drive shaft 6 for driving drive wheels 7. Drive engine 2 may be designed as an internal combustion engine, in particular as an air-guided internal combustion engine, and may be operated by an engine control unit 10.

(5) Engine control unit 10 may be coupled to an accelerator pedal 11 in order to receive a piece of information regarding an accelerator pedal position which specifies a driver input, e.g., in the form of a driver-input torque desired by the driver. During regular operation, the driver input resulting from the accelerator pedal position is converted, in engine control unit 10, into a set point torque according to torque path functions, and the set point torque is specified to control output stages, corresponding to a fuel injection quantity for controlling fuel injectors of internal combustion engine 2.

(6) A monitoring function which may carry out an acceleration monitoring of the torque path functions is provided. In an acceleration-based monitoring, a check is carried out to determine whether the acceleration of the motor vehicle, in which drive system 1 is utilized, does not exceed (or does so by no more than a tolerance value) a permissible acceleration. For this purpose, an actual vehicle longitudinal acceleration which is measured and made available as a longitudinal acceleration signal, e.g., with the aid of an acceleration sensor 12 (inertial sensor), is compared with the permissible acceleration. The permissible acceleration may be calculated from the driver input, the requirements of driver assistance systems and external control units, braking torques, a rotational acceleration of drive train 6 and wheels 7, which is calculated from measured rotational speeds, and tractional resistances. If an increase results, from which it may be inferred that an unintentional acceleration of the motor vehicle is taking place, an alternative monitoring is switched to or an error response operating mode is engaged.

(7) It may be provided that the monitoring function is carried out on the basis of a substitute signal if a signal required for the acceleration monitoring fails. As substitute signals for the monitoring-relevant signals, i.e., the longitudinal acceleration signal for the vehicle longitudinal acceleration and the speed signal for the vehicle speed, which are determined with the aid of the signal from acceleration sensor 12, the substitute acceleration signal may be used, which results from the wheel speed of a secondary axle 14, i.e., a non-driven wheel axle, or the substitute speed signal may be used, which results from the wheel speed of secondary axle 14. For this purpose, a wheel speed sensor 13 may be provided on secondary axle 14 in order to measure a wheel speed or wheel acceleration. Wheel speed sensor 13 may be situated at the drive wheels or on a secondary axle 14 which is not driven.

(8) In addition, a brake pedal 14 or any other type of device may be provided in order to communicate a braking intent to control unit 10.

(9) In control unit 10, both the acceleration monitoring as well as the alternative monitoring is carried out, and control for the error operation mode is carried out. The method for operating the acceleration monitoring system is schematically represented in the flow chart in FIG. 2.

(10) The following description relates to a method which is based on a conventional acceleration monitoring of the motor vehicle. The acceleration monitoring is based on a comparison between an actual and a permissible acceleration using a torque-based, acceleration-based and/or power- or energy-based conversion.

(11) In step S1, the acceleration monitoring is carried out in a conventional manner. If an error is detected therein, an error operation mode is engaged, which provides for, e.g., an emergency operation or a shutoff of engine system 1.

(12) In step S2, a check is carried out within the scope of the acceleration monitoring to determine whether a signal, which is relevant for the acceleration monitoring, is faulty or has failed. If a sensor, such as, e.g., acceleration sensor 12, has failed (alternative: Yes), the longitudinal acceleration signal originally provided for determining the vehicle acceleration on the basis of the vehicle longitudinal acceleration is not available and the method is continued with step S3; otherwise (alternative: No) the method returns to step S1.

(13) If a signal, which is relevant for the acceleration monitoring, has failed, then, instead, a vehicle acceleration of the vehicle may be derived from wheel speed sensor 13, which is provided as a substitute acceleration signal, and so there is no need to automatically switch to the error operation mode. The vehicle acceleration in the form of the substitute acceleration signal may be fairly precisely determined from wheel speed sensor 13 for the cases in which the motor vehicle moves on a level road section and the wheels are not blocked by brakes. For travel on uphill grades and downhill grades, however, the vehicle acceleration calculated from the wheel speeds differs from the vehicle longitudinal acceleration determined by acceleration sensor 12, since the acceleration components caused by gravity are also included in the substitute acceleration signal which is ascertainable from the wheel speeds. In order to safely and robustly monitor for unintentional acceleration despite these differences between the longitudinal acceleration signal and the substitute acceleration signal, which was ascertained as a substitute, an adaptation of the monitoring method is necessary.

(14) The vehicle acceleration, which is established as a substitute acceleration signal via wheel speed sensor 13, generally corresponds, during travel on a level road section, to the actual vehicle longitudinal acceleration. If an impermissible acceleration is then detected in the acceleration monitoring system on the basis of the vehicle acceleration determined from the alternatively ascertained substitute acceleration signal, it must be assumed that the acceleration is actually unintentional and the alternative monitoring must be carried out. However, it is not possible to establish that traveling is taking place on a level road section based solely on the substitute acceleration signal.

(15) If the vehicle is traveling on a downhill grade, the substitute acceleration signal is greater than the longitudinal acceleration signal would be, provided an acceleration sensor is available and functional, due to the additionally acting component of gravity due to the downhill grade. Therefore, it cannot be differentiated whether there is an impermissible acceleration in the horizontal or on a slight downhill grade, or if there is error-free operation and on a steeper downhill grade. Since travel on a level road section and travel on a downhill grade may not be differentiated on the basis of the substitute acceleration signal, a switch to the alternative monitoring takes place independently thereof when an impermissible acceleration is detected.

(16) When the substitute acceleration signal indicates lower vehicle acceleration than the longitudinal acceleration signal during travel on an uphill grade, an impermissible acceleration may be detected only with a delay. If the vehicle acceleration indicated by the substitute acceleration signal is only so great that the overall acceleration during travel on the uphill grade is less than or equal to the vehicle acceleration which would result in the case of an identical driver input in a case of error-free operation during travel on a level road section, the vehicle acceleration cannot be detected. If the impermissible absolute value is greater, then only the absolute value which exceeds the permissible acceleration during travel on a level road section may result in an error detection, which is possibly greatly delayed.

(17) A high unintentional acceleration may also be detected during travel on an uphill grade, since the component of the acceleration resulting from gravity is significantly less than the component of the actual acceleration of the motor vehicle. Therefore, when an impermissible acceleration occurs on an uphill grade and, due to the use of a substitute acceleration signal, cannot be detected, or may only be detected after a long delay, it may be assumed that the resultant acceleration is low enough that the driver may respond thereto in a timely manner by discontinuing the actuation of the accelerator pedal or by actuating the brakes, without a safety-critical state being reached.

(18) For this purpose, a check is carried out in step S3 to determine whether the acceleration monitoring based on the substitute signal results in an error. If this is the case (alternative: Yes), the error operation mode is engaged in step S4 and appropriate measures are implemented. Otherwise, the method is continued with step S5.

(19) In step S5, a check is carried out to determine whether the driver is specifying a driver input which is less than a predefined threshold value, or is specifying a braking intent. If this is the case (alternative: Yes), the method is continued with the error operation mode being engaged in step S4. Otherwise (alternative: No), the method is continued with step S6. Since a compensation of an unintentional acceleration by a brake actuation during travel on an uphill grade cannot be reliably differentiated from a normal braking operation during travel on a level road section, a switch to the alternative monitoring always takes place in the event of a braking intent by the driver.

(20) The monitoring function therefore provides that the monitoring function is carried out on the basis of the substitute signal when a signal, which is relevant for the acceleration monitoring and for which a substitute signal exists, has failed. If an error is detected in this case or if a driver input which is below a predefined threshold value is detected, or if an actuation of brake pedal 14 is detected, a switch to the alternative monitoring takes place.

(21) In step S6, the alternative monitoring is exited again. In this way, the alternative monitoring may be exited again when the monitoring function does not detect an erroneous acceleration of the motor vehicle on the basis of the substitute acceleration signal, and a greater driver input is present.

(22) As compared to the previous monitoring method, in which the alternative monitoring is always switched to when an error occurs, in the method described above, the alternative monitoring is necessarily switched to significantly less often in the event of a failure of a signal which is relevant for the acceleration monitoring and for which a substitute signal exists. In addition, the method may be carried out cyclically, so that an alternative monitoring which has already been engaged may be exited again when the acceleration monitoring system no longer reports that a limit has been exceeded, and a driver input which is above the predefined threshold value is present, and a braking intent is not present.