Method for the shift control of a transmission

Abstract

Method for shift control of a transmission arranged in a drive train (1) of a motor vehicle between a drive motor (AM) and an output, the method comprising the following steps: - Determining a vehicle speed (13) based on a rotational speed detected in the drive train (1) of the motor vehicle, - Determining the vehicle speed (14) based on a detected longitudinal and lateral acceleration of the motor vehicle, - Comparing the independently determined vehicle speeds (13, 14), and - Activating a shift lock of the transmission if the independently determined vehicle speeds (13, 14) differ from each other by more than a defined limit value.

Description

The present invention relates to a method for controlling the shifting of a motor vehicle transmission according to the type defined in more detail in claim 1. The invention further relates to a control unit for carrying out the method and a corresponding computer program. In automated manual and automatic transmissions, gear changes are controlled, among other things, based on the vehicle's speed. This speed is usually determined by measuring the rotational speed of the drivetrain, which can be the wheel speed of the vehicle's drive wheels or the transmission output speed. However, under certain driving conditions, there can be discrepancies between the calculated vehicle speed and the actual vehicle speed. If a gear change were initiated based on the calculated speed under these conditions, the discrepancy could lead to a transmission malfunction. DE 692 19 650 T2 discloses a gear-shift control method for an automatic vehicle transmission. DE 698 30 030 T2 discloses a method for controlling an automatic vehicle transmission during wheel slippage. From DE 10 2015 207 293 A1, a method for controlling gear changes in a motor vehicle transmission is known, in which gear changes are prevented by a shift lock when a specific driving condition of the vehicle is detected. To detect the driving condition, a longitudinal motion parameter of the vehicle is determined by two independent measurements. A locking brake is recognized as a driving condition, and the shift lock is activated if the independently determined longitudinal motion parameters differ significantly. The longitudinal motion parameters are determined, firstly, by measuring the wheel speeds of the drive wheels or a transmission output speed, and secondly, by an acceleration sensor. However, this approach presents the problem that the driving condition for a transmission shift control based on longitudinal movement parameters cannot be determined with sufficient accuracy in all driving situations. Against this background, the present invention aims to present an improved method for the shift control of a motor vehicle transmission, by which a driving state of the motor vehicle can be determined more precisely and the associated shift control of the transmission can be executed more accurately. Furthermore, a corresponding control unit and a computer program for carrying out the method are to be specified. This problem is solved by the patent claims. From a process engineering perspective, this problem is solved by the features of claim 1. A control unit and a computer program product are also the subject of the further independent patent claims. Advantageous further developments are the subject of the dependent claims as well as the following description and the drawings. Features described in connection with the method are intended to also apply in connection with the control unit and the computer program product according to the invention, and vice versa, so that mutual reference can always be made to the disclosure of the individual aspects of the invention. According to the present invention, a method for controlling the shifting of a transmission arranged in the drivetrain of a motor vehicle between a drive motor and an output shaft is provided. The method comprises the following steps: - Determining a vehicle speed based on a rotational speed detected in the drivetrain of the motor vehicle, - Determining the vehicle speed based on a detected longitudinal and lateral acceleration of the motor vehicle, - Comparing the independently determined vehicle speeds, and - Activating a shift lock of the transmission if the independently determined vehicle speeds differ from each other by more than a defined limit value. In other words, the inventive method for controlling the transmission to determine the vehicle speed takes into account not only the rotational speeds present in the drive train and the longitudinal acceleration of the motor vehicle, but also the lateral acceleration of the motor vehicle. Due to the lack of lateral forces on locked vehicle wheels during braking, rotation around the vehicle's vertical axis can occur. If this happens, calculating the vehicle speed from a measured longitudinal acceleration with sufficient accuracy is not possible. By taking into account the lateral acceleration acting on the vehicle during a wheel lock-up, the accuracy of the acceleration-dependent vehicle speed calculation can be increased, or the difference between the acceleration-dependent vehicle speed and the actual vehicle speed during a wheel lock-up can be reduced accordingly. Considering the vehicle speed calculated in this way allows for more precise transmission control, particularly the activation or deactivation of a transmission shift lock. A wheel lockup is a driving condition of a motor vehicle in which the vehicle's wheels lock up while the vehicle is still moving. During a wheel lockup, no rotational speed can be detected at the vehicle wheels or the transmission output shaft. The defined threshold is set so that an impending wheel lockup is clearly recognizable when this threshold is exceeded. Since the lateral acceleration of the vehicle is taken into account when determining the acceleration-dependent vehicle speed, the resulting vehicle speed corresponds almost exactly to the actual vehicle speed. Therefore, the point in time at which the activated shift lock can be deactivated can also be determined with high accuracy. The proposed method determines the speed-dependent vehicle speed independently of, and in parallel with, the acceleration-dependent vehicle speed. "Independently" means that the speed-dependent vehicle speed is determined based on values ​​or signals that have no influence on the determination of the acceleration-dependent vehicle speed, and vice versa. "In parallel" means that the determination of the speed-dependent vehicle speed and the determination of the acceleration-dependent vehicle speed are carried out simultaneously. The transmission can be an automated manual transmission, a planetary gear automatic transmission, or a dual-clutch transmission. It can also be a so-called range transmission. The vehicle can be a passenger car or a commercial vehicle, such as a truck or a bus. By means of the inventive design of a method for the shift control of a transmission, incorrect shifting during a locking brake operation of a motor vehicle can be reliably prevented. According to one embodiment of the invention, the vehicle speed, which is dependent on rotational speed, is determined by measuring the wheel speed or the rotational speed measured at a transmission output shaft. The wheel speed can be measured using at least one wheel speed sensor located in the vehicle's drivetrain, which, for example, can be an integral part of a brake control system. Alternatively or additionally, the rotational speed of the transmission output shaft can be measured using a speed sensor located in the transmission. The longitudinal and lateral acceleration of the vehicle is preferably detected using an inertial sensor. This inertial sensor can be designed as a so-called 3-axis acceleration sensor. By using a 3-axis acceleration sensor, the lateral acceleration of the vehicle can be detected in addition to the longitudinal acceleration. This allows the calculation of the vehicle speed to be optimized and more accurately matched to the actual vehicle speed. Mathematically, this can be described as follows: where vx is the longitudinal speed, vy is the lateral speed, αx is the longitudinal acceleration, αy is the lateral acceleration, and ψ̇z is the rotation rate about the vehicle's vertical axis. According to a further embodiment of the invention, the vehicle speed is additionally determined using position data of the vehicle. This position data can be received from a satellite system. Alternatively or additionally, the vehicle speed can be determined using motion data of the vehicle, which can be obtained from the vehicle's environmental sensors. These sensors can include, for example, a camera, radar, LI-DAR, an ultrasonic sensor, and / or other devices for detecting objects in the vehicle's vicinity. The vehicle speed determined in this way can then be used to verify the plausibility of the acceleration-dependent vehicle speed. The invention further relates to a control unit configured to carry out the method according to the invention. The control unit comprises means that serve to carry out the method according to the invention. These means are hardware-related and software-related. The hardware-related means are data interfaces for exchanging data with the powertrain components involved in carrying out the method according to the invention. For this purpose, the control unit is also connected to necessary sensors and, where necessary, to other control units, for example, an engine control unit, in order to receive the decision-relevant data and / or forward control commands. The hardware-related means of the transmission control unit further comprise a processor for data processing and a memory for data storage.The software-related means consist of program modules for carrying out the method according to the invention. The solution according to the invention can also be embodied as a computer program product which, when running on a processor of a control device, instructs the processor by means of software to carry out the associated process steps relating to the invention. In this context, a computer-readable medium on which a computer program product described above is stored and retrievable is also part of the subject matter of the invention. To illustrate the invention, a drawing with exemplary embodiments is included in the description. In this drawing: Fig. 1 shows a schematic representation of a drive train with a control unit for carrying out the method according to the invention, and Fig. 2 shows a diagram in which vehicle speed is shown over time. Figure 1 shows a schematic representation of a drive train 1 of a motor vehicle, which is a commercial vehicle, such as a truck or a bus. This drive train 1 has a drive unit which can be coupled to the drive side of a transmission via an intermediate starting clutch 3 on its output side. On the output side, the transmission is then connected to other output components, well known to those skilled in the art, as well as to the vehicle wheels of the commercial vehicle. The motor vehicle's drive unit can be designed as an internal combustion engine. Alternatively, the drive unit can include an electric motor in addition to an internal combustion engine and thus be designed as a hybrid drive. The transmission is preferably an automatic or automated transmission in which friction-fit and / or positive-fit switching elements are closed to shift a gear. The drivetrain 1 can be disengaged either by opening the starting clutch 3 or by shifting the transmission to neutral. When drivetrain 1 is disengaged, the internal combustion engine is disconnected from the output shaft. The drive train 1 is also equipped with a compressed air system, only a part of which is shown schematically here. The compressed air system includes a pressure generator that produces compressed air and supplies it to the system. The pressure generator functions like a compressor and is permanently connected to the drive unit. The compressed air system also includes at least one compressed air reservoir for temporarily storing compressed air. The compressed air system serves, at least in part, to operate a pneumatic braking system for the drive train 1. The vehicle's brakes are designed as wheel brakes, which are actuated via the compressed air system. The vehicle also includes a control system 2, in which several different control units are interconnected via a data bus system 5, for example, a CAN bus system. Among other things, the data bus system 5 includes an engine control unit (ECU), a transmission control unit (TCU), and a brake control unit (BCU). The engine control unit (ECU) controls the drive unit, the transmission control unit (TCU) controls the transmission and—possibly indirectly via another control unit—also the starting clutch 3, and the brake control unit (BCU) controls the pneumatic braking system. The transmission control unit (TCU) can communicate bidirectionally with the transmission, the engine control unit (ECU), and the brake control unit (BCU). The data bus system 5 supplies the control units with the data relevant to them.The control units are able to receive and process sensor signals and, depending on the results, output control or data signals. For example, the transmission control unit (TCU) comprises a processor 6 and storage means 7 for storing and retrieving parameters, signals, and information, as well as a computer program 11, which is configured to execute a method for shift control of a transmission according to the present invention. Furthermore, the transmission control unit (TCU) has at least one receiving interface 8 configured to receive all relevant data from existing sensors. The transmission control unit (TCU) also has a data processing unit 9 for processing and evaluating the received data or the information contained in the received data, and a transmitting interface 10 through which corresponding signals for controlling powertrain components can be output. The powertrain 1 has an acceleration sensor 12 for determining the vehicle acceleration.The acceleration sensor 12 can be configured as a 3-axis acceleration sensor, which can detect acceleration along the vehicle's longitudinal axis, as well as acceleration along the vehicle's transverse axis and acceleration along the vehicle's vertical axis. The acceleration sensor 12 can, for example, be located in the transmission control unit (TCU). The transmission control unit (TCU) controls the operation of the transmission using driving condition data and driver input data. A shift strategy stored in the TCU as a computer program determines the respective shift reactions, in particular a gear change from the current gear to a target gear, or a temporary interruption of power transmission in the drivetrain. The driving condition data used can include, in addition to the determined road surface condition, the current driving resistance, the current vehicle inclination, the current vehicle mass, the current vehicle speed, the current vehicle acceleration, the current engine torque, the current engine speed, and other values. This data can be provided, at least in part, by the engine control unit (ECU) and suitable sensor devices. Driver input data can be signaled, for example, by actuating a control element, detected by sensors, and transmitted directly or indirectly to the transmission control unit (TCU). The control element can be, for example, an accelerator pedal, brake pedal, or a switch for manually activating coasting mode. Control system 2 receives data from a navigation system. The navigation system provides topographic data about the area surrounding the vehicle's current position and about the area at a defined distance in front of the vehicle's current position. The vehicle's current position can be determined using a satellite positioning system, such as GPS or GLONASS. The control units are connected to corresponding components of the powertrain 1 via data transmission links 4. These data transmission links 4 between the control units and the powertrain components can be implemented, for example, by one or more electronic bus systems. The inventive method for shift control of the transmission, which is arranged in the drive train 1 between the drive motor AM and the output, will now be explained in more detail with reference to the diagram shown in Fig. 2. The inventive shift control method provides that, in a first determination, a rotational speed in the drive train 1 of the motor vehicle is detected, whereby the rotational speed can be the wheel speed of the motor vehicle's drive wheels or the output speed of the transmission. A vehicle speed 13 is then calculated from this rotational speed. In a second determination running in parallel, a vehicle acceleration in the longitudinal direction and a vehicle acceleration in the lateral direction are detected by means of the acceleration sensor 12. A vehicle speed 14 is then calculated from the detected acceleration values. The vehicle speeds 13 and 14 determined in this way are then compared. If the vehicle speeds 13 and 14 differ only slightly, gear changes in the transmission continue to be carried out normally. However, if a significant deviation between the vehicle speeds 13 and 14 is detected, a shift lock is activated, thus blocking gear changes in the transmission. A significant deviation between the speed-dependent vehicle speed 13 and the acceleration-dependent vehicle speed 14 occurs when wheel lock-up is detected, i.e., when the vehicle's wheels lock up due to the application of the vehicle's braking system, even though the vehicle is still moving. This is evident from the vehicle speed curves 13 and 14 shown in Fig. 2.Between times t1 and t2, the vehicle speed 13, determined from the rotational speed recorded in the drive train 1, drops abruptly due to a wheel lock-up. Between times t2 and t3, no rotational speed is recorded for determining the vehicle speed, resulting in a vehicle speed of 0 km / h and thus a standstill of the vehicle during this period. Since the vehicle speed 14, determined based on acceleration, deviates significantly from 0 km / h during this period, a shift lock activated in the transmission prevents gear changes. This reliably prevents an erroneous engagement of the starting gear based on the speed-dependent vehicle speed 13. Depending on the actual vehicle speed, an engaged starting gear would, upon closing of the starting clutch 3 (which is open for engaging the starting gear), lead to damage to the transmission or even cause the vehicle to skid. Between times t3 and t4, the anti-lock braking is terminated, causing the speed-dependent vehicle speed 13 to approach the acceleration-dependent vehicle speed 14 again. At time t4, the speed-dependent vehicle speed 13 corresponds approximately to the acceleration-dependent vehicle speed 14, and the shift lock in the transmission is released. An activated shift lock can be deactivated as soon as the difference between the acceleration-dependent and speed-dependent vehicle speeds falls below a defined threshold. Based on the vehicle speed currently present at the time the braking maneuver is detected and the vehicle deceleration recorded by the acceleration sensor 12, the time until the vehicle comes to a complete stop can be determined. After this determined time has elapsed, the shift lock can be deactivated, and gear changes can be permitted again. However, the shift lock remains in effect until this time has elapsed. Since the vehicle's deceleration is determined by considering both longitudinal and lateral acceleration, the time until the vehicle comes to a complete stop, and thus the time until the shift lock is deactivated, can be precisely determined. Using the inventive method for controlling the transmission, incorrect shifting during a wheel lock-up of a motor vehicle can be reliably prevented. Reference sign 1 Powertrain 2 Control system 3 Starting clutch 4 Connection 5 Data bus system 6 Processor 7 Storage device 8 Receive interface 9 Data processing unit 10 Transmit interface 11 Computer program product 12 Acceleration sensor 13 Speed-dependent vehicle speed 14 Acceleration-dependent vehicle speed ECU Engine control unit TCU Transmission control unit BCU Brake control unit

Claims

Method for shift control of a transmission arranged in a drive train (1) of a motor vehicle between a drive motor (AM) and an output, the method comprising the following steps: - Determining a vehicle speed (13) based on a rotational speed detected in the drive train (1) of the motor vehicle, - Determining the vehicle speed (14) based on a detected longitudinal and lateral acceleration of the motor vehicle, - Comparing the independently determined vehicle speeds (13, 14), and - Activating a shift lock of the transmission if the independently determined vehicle speeds (13, 14) differ from each other by more than a defined limit value. Method according to claim 1, characterized in that the determination of the speed-dependent vehicle speed (13) is carried out on the basis of a detected wheel speed or a speed detected at a transmission output. Method according to claim 1, characterized in that the longitudinal and lateral acceleration is detected using an inertial sensor to determine the acceleration-dependent vehicle speed (14). Method according to claim 3, characterized in that the longitudinal and lateral acceleration is detected to determine the acceleration-dependent vehicle speed (14) using a 3-axis acceleration sensor (12). Method according to one of claims 1 to 4, characterized in that the vehicle speed of the motor vehicle is additionally determined on the basis of position data of the motor vehicle, wherein the position data of the motor vehicle is received from a satellite system. Method according to one of claims 1 to 5, characterized in that the vehicle speed of the motor vehicle is additionally determined on the basis of movement data of the motor vehicle, which are recorded by means of an environment sensor of the motor vehicle. Method according to one of claims 1 to 6, characterized in that an activated shift lock is deactivated when a difference between the acceleration-dependent vehicle speed and the speed-dependent vehicle speed falls below a defined limit value. Transmission control unit (TCU) of a transmission which is configured to perform a method for shift control of a transmission according to any one of claims 1 to 7. Computer program product comprising program code means stored on a computer-readable data carrier for carrying out a method for shift control of a transmission according to any one of claims 1 to 7, when the computer program product is executed on a computer or on a control unit (TCU) according to claim 8.

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