US-12623651-B2 - Method and control device for operating a drive train of a motor vehicle

US12623651B2US 12623651 B2US12623651 B2US 12623651B2US-12623651-B2

Abstract

A method for operating a drive train of a motor vehicle for a reversing operation for changing from a forward gear to a reverse gear or vice versa when the motor vehicle is rolling at a speed less than a limit value, and in which a first shift element of the transmission is disengaged and a second shift element of the transmission is engaged, the method including receiving a target torque profile for a transmission output shaft for the reversing operation. The method further includes determining, based on the target torque profile for the transmission output shaft, target torque profiles for the first and second shift elements and the propulsion unit. Additionally, the method includes activating the first and second shift elements and the propulsion unit based on the respective target torque profile such that an actual torque profile follows the target torque profile for the transmission output shaft.

Inventors

Franz Lutz

Assignees

ZF FRIEDRICHSHAFEN AG

Dates

Publication Date: 20260512
Application Date: 20250206
Priority Date: 20240208

Claims (8)

1 . A method for operating a drive train ( 1 ) of a motor vehicle, the drive train ( 1 ) comprising a propulsion unit ( 2 ) and an automatic or automated transmission ( 4 ) connected between the propulsion unit ( 2 ) and a driven end ( 3 ), the method comprising: for a reversing operation for changing from a forward gear to a reverse gear or from the reverse gear to the forward gear, the reversing operation being carried out when the motor vehicle is rolling at a rolling speed less than a limit value, a first friction-locking shift element ( 5 ) of the transmission ( 4 ) being disengaged during the reversing operation and a second friction-locking shift element ( 6 ) of the transmission ( 4 ) being engaged during the reversing operation, the first friction-locking shift element ( 5 ) being a first shift element which is engaged in the forward gear and the second friction-locking shift element ( 6 ) being a second shift element which is disengaged in the forward gear for changing from the forward gear to the reverse gear, or the first friction-locking shift element ( 5 ) being one shift element which is engaged in the reverse gear and the second friction-locking shift element ( 6 ) being another shift element which is disengaged in the reverse gear for changing from the reverse gear to the forward gear: receiving a target torque profile for a transmission output shaft ( 9 ) of the transmission ( 4 ) for the reversing operation; determining, in accordance with the target torque profile for the transmission output shaft ( 9 ), a target torque profile for the first friction-locking shift element ( 5 ), a target torque profile for the second friction-locking shift element ( 6 ), and a target torque profile for the propulsion unit ( 2 ); and activating the first friction-locking shift element ( 5 ) in accordance with the target torque profile for the first friction-locking shift element ( 5 ), the second friction-locking shift element ( 6 ) in accordance with the target torque profile for the second friction-locking shift element ( 6 ), and the propulsion unit ( 2 ) in accordance with the target torque profile for the propulsion unit ( 2 ) such that an actual torque profile for the transmission output shaft ( 9 ) follows the target torque profile for the transmission output shaft ( 9 ).
2 . The method of claim 1 , wherein a time gradient of the target torque profile for the transmission output shaft ( 9 ) over time in a range defined about a zero crossing of the target torque profile is less than a limit value.
3 . The method of claim 1 , wherein determining the target torque profile for the first friction-locking shift element ( 5 ), the target torque profile for the second friction-locking shift element ( 6 ), and the target torque profile for the propulsion unit ( 2 ) comprises: determining for a first phase of the reversing operation, in which exclusively the first friction-locking shift element ( 5 ) to be disengaged for the reversing operation transmits torque, one target torque profile each exclusively for the first friction-locking shift element ( 5 ) and for the propulsion unit ( 2 ); determining for a second phase of the reversing operation, in which exclusively the second friction-locking shift element ( 6 ) to be engaged for the reversing operation transmits torque, one target torque profile each exclusively for the second friction-locking shift element ( 6 ) and for the propulsion unit ( 2 ); and determining for a third phase of the reversing operation, one target torque profile each for the first friction-locking shift element ( 5 ), the second friction-locking shift element ( 6 ), and the propulsion unit ( 2 ), wherein the first phase, the second phase, and the third phase are successive time phases, with the third phase being between the first phase and the second phase.
4 . The method of claim 3 , wherein, for the third phase: a target torque value of the first friction-locking shift element ( 5 ) which is valid at an end of the first phase and at a beginning of the third phase is stored, the target torque value of the first friction-locking shift element ( 5 ) is reduced to zero along a reduction characteristic curve from the end of the first phase to the beginning of the third phase, the target torque profile for the propulsion unit ( 2 ) is determined according to the target torque value of the first friction-locking shift element ( 5 ), the target torque profile for the second friction-locking shift element ( 6 ) is determined according to the target torque value of the first friction-locking shift element ( 5 ) and the reduction characteristic curve for the target torque value of the first friction-locking shift element ( 5 ).
5 . The method of claim 4 , wherein determining, for the first phase, the target torque profile (M K1sek-SOLL ) for the first friction-locking shift element ( 5 ) and the target torque profile (M AN-SOLL ) for the propulsion unit ( 2 ) comprises: determining, for the first phase, the target torque profile (M K1sek-SOLL ) for the first friction-locking shift element ( 5 ) based on a moment of inertia (J 1 ) acting on a secondary side of the first friction-locking shift element ( 5 ), a secondary-side angular speed ({acute over (ω)} K1sek ) of the first shift element ( 5 ), a transmission ratio (i) effective for the secondary side of the first shift element ( 5 ), a moment of inertia (J 2 ) acting on a secondary side of the second friction-locking shift element ( 6 ), a secondary-side angular speed ({acute over (ω)} K2sek ) of the second shift element ( 6 ), a transmission ratio (i 2 ) effective for the secondary side of the second shift element ( 6 ), and the target torque profile (M AB-SOLL ) for the transmission output shaft ( 9 ) using: M K1sek-SOLL =(J 1 *{acute over (ω)} K1sek )*i 1 +(J 2 *{acute over (ω)} K2sek )*i 2 −M AB-SOLL ; and determining, for the first phase, the target torque profile (M AN-SOLL ) for the propulsion unit ( 2 ) based on a moment of inertia (J AN ) at a transmission input shaft ( 10 ), an angular speed ({acute over (ω)} AN ) of the transmission input shaft ( 10 ), the moment of inertia (J 1 ) acting on the secondary side of the first friction-locking shift element ( 5 ), the secondary-side angular speed ({acute over (ω)} K1sek ) of the first shift element ( 5 ), the transmission ratio (i 1 ) effective for the secondary side of the first shift element ( 5 ), the moment of inertia (J 2 ) acting on the secondary side of the second friction-locking shift element ( 6 ), the secondary-side angular speed ({acute over (ω)} K2sek ) of the second shift element ( 6 ), the transmission ratio (i 2 ) effective for the secondary side of the second shift element ( 6 ), and the target torque profile (M AB-SOLL ) for the transmission output shaft ( 9 ) using: M AN-SOLL =(J AN *{acute over (ω)} AN )+(J 1 *{acute over (ω)} K1sek )*i 1 +(J 2 *{acute over (ω)} K2sek )*i 2 −M AB-SOLL .
6 . The method of claim 4 , wherein, for the second phase, determining the target torque profile (M K2sek-SOLL ) for the second friction-locking shift element ( 6 ) and the target torque profile (M AN-SOLL ) for the propulsion unit ( 2 ) comprises: determining the target torque profile (M K2sek-SOLL ) for the second friction-locking shift element ( 6 ) based on a moment of inertia (J 2 ) acting on a secondary side of the second friction-locking shift element ( 6 ), a secondary-side angular speed ({acute over (ω)} K2sek ) of the second shift element ( 6 ), a transmission ratio (i 2 ) effective for the secondary side of the second shift element ( 6 ), a moment of inertia (J 1 ) acting on a secondary side of the first friction-locking shift element ( 5 ), a secondary-side angular speed ({acute over (ω)} K1sek ) of the first shift element ( 5 ), a transmission ratio (i 1 ) effective for the secondary side of the first shift element ( 5 ), and the target torque profile (M AR-SOLL ) for the transmission output shaft ( 9 ) using: M K2sek-SOLL =(J 2 *{acute over (ω)} K2sek )*i 2 +(J 1 *{acute over (ω)} K1sek )*i 1 −M AB-SOLL ; and determining the target torque profile (M AN-SOLL ) for the propulsion unit ( 2 ) based on a moment of inertia (J AN ) at a transmission input shaft ( 10 ), an angular speed ({acute over (ω)} AN ) of the transmission input shaft ( 10 ), the moment of inertia (J 2 ) acting on the secondary side of the second friction-locking shift element ( 6 ), the secondary-side angular speed ({acute over (ω)} K2sek ) of the second shift element ( 6 ), the transmission ratio (i 2 ) effective for the secondary side of the second shift element ( 6 ), the moment of inertia (J 1 ) acting on the secondary side of the first friction-locking shift element ( 5 ), the secondary-side angular speed ({acute over (ω)} K1sek ) of the first shift element ( 5 ), the transmission ratio (i 1 ) effective for the secondary side of the first shift element ( 5 ), and the target torque profile (M AR-SOLL ) for the transmission output shaft ( 9 ) using: M AN-SOLL =(J AN *{acute over (ω)} AN )+(J 2 *{acute over (ω)} K2sek )*i 2 +(J 1 *{acute over (ω)} K1sek )*i 1 −M AB-SOLL .
7 . The method of claim 6 , wherein, for the third phase, determining the target torque profile (M K1sek-SOLL ) for the first friction-locking shift element ( 5 ), the target torque profile (M K2sek-SOLL ) for the second friction-locking shift element ( 6 ), and the target torque profile (M AN-SOLL ) for the propulsion unit ( 2 ) comprises: determining the target torque profile (M K1sek-SOLL ) for the first friction-locking shift element ( 5 ) based on a stored target torque (M K1sek-INI ) of the first shift element ( 5 ) and a characteristic curve (k(t)), normalized over time (t), for reducing the target torque profile of the first shift element ( 5 ) to zero using: M K1sek-SOLL =M K1sek-INI *(1−k(t)); determining the target torque profile (M AN-SOLL ) for the propulsion unit ( 2 ) the second friction locking shift element ( 6 ) based on the moment of inertia (J An ) at the transmission input shaft ( 10 ), the angular speed ({acute over (ω)} AN ) of the transmission input shaft ( 10 ), and the stored target torque (M K1sek-INI ) of the first shift element ( 5 ) using M AN-SOLL =J An *{acute over (ω)} AN +M K1sek-INI ; and determining the target torque profile (M K2sek-SOLL ) for the second friction-locking shift element ( 6 ) based on the stored target torque (M K1sek-INI ) of the first shift element ( 5 ), the moment of inertia (J 1 ) acting on the secondary side of the first friction-locking shift element ( 5 ), the secondary-side angular speed ({acute over (ω)} K1sek ) of the first shift element ( 5 ), the transmission ratio (i 1 ) effective for the secondary side of the first shift element ( 5 ), the characteristic curve (k(t)), the moment of inertia (J 2 ) acting on the secondary side of the second friction-locking shift element ( 6 ), the secondary-side angular speed ({acute over (ω)} K2sek ) of the second shift element ( 6 ), the transmission ratio (i 2 ) effective for the secondary side of the second shift element ( 6 ), and the target torque profile (M AB-SOLL ) for the transmission output shaft ( 9 ) using: [M K1sek-INI −J 1 *{acute over (ω)} K1sek ]*i 1 *(1−k(t))+[M K2sek-SOLL −J 2 *{acute over (ω)} K2sek ]*i 2 *k(t)+M AB-SOLL =0.
8 . A control unit ( 20 ) for operating a drive train ( 1 ) of a motor vehicle, the control unit ( 20 ) being configured to automatically carry out the method of claim 1 on a control side.

Description

CROSS-REFERENCE TO RELATED APPLICATION The present application is related and has right of priority to German Patent Application No. 10 2024 201 132.0 filed on Feb. 8, 2024, the entirety of which is incorporated by reference for all purposes. FIELD OF THE INVENTION The invention relates generally to a method and to a control device or unit for operating a drive train of a motor vehicle. BACKGROUND A drive train of a motor vehicle includes a propulsion unit as well as a transmission connected between the propulsion unit and a drive output. The transmission converts rotational speeds and torques and, in this way, provides the available tractive force of the propulsion unit at the driven end. Transmissions of motor vehicles which are known from practical experience and provide multiple gears include multiple shift elements. The shift elements of the transmission are form-locking shift elements such as dogs, and friction-locking shift elements such as clutches or brakes. In each engaged force-locking gear of a transmission, a first defined number of shift elements of the transmission is engaged and a second defined number of shift elements of the transmission is disengaged. When implementing a gear change from an actual gear to a target gear of the transmission, at least one previously engaged shift element of the transmission is disengaged and at least another, previously disengaged shift element of the transmission is engaged. A method and a control unit for operating a drive train of a motor vehicle are desired, specifically for carrying out a reversing operation in which a gear change from a forward gear to a reverse gear or from a reverse gear to a forward gear is to be carried out in the transmission when the motor vehicle is rolling and the rolling speed thereof is less than a limit value. In such a reversing operation, the torque provided by the propulsion unit and supplied to the transmission at the transmission input shaft is redirected such that the transmission output shaft rotates in the opposite direction of rotation during and after the reversing operation. In the process, the rotational speed and the direction of rotation are inverted in addition to the torque. Between the propulsion unit and the drive output, a drive train has a multitude of points of tooth engagement having different transmission ratios as well as elastic and/or damping assemblies. The points of tooth engagement having different transmission ratios include, for example, the automatic, or automated, transmission and an axle transmission and/or differential gear of the drive train. The elastic and/or damping assemblies include, for example, a cardan shaft and the like. When the motor vehicle rolls in a defined direction and a corresponding gear is engaged in the transmission, all points of tooth engagement have contact and the elastic assemblies are preloaded. In this way, the drive torque is constantly and smoothly transmitted in the corresponding direction of travel. In a reversing operation, the direction of the force flow is inverted. Points of tooth engagement which were previously under tension disengage and preloaded elastic components are relaxed. Then, a tensile stress is built up in an opposite direction and the points of tooth engagement come to rest against opposite tooth flanks. Elastic components are tensioned in the opposite direction of rotation. In such a reversing operation, tooth flanks can come to rest against one another in an uncontrolled manner and shafts can be tensioned in a manner which is incongruous with the spring stiffness thereof. As a result, shift shocks and/or jolts develop in the drive train during a reversing operation. DE 10 2021 212 842 A1 discloses a method for determining an operating point of a clutch device in a drive train of a motor vehicle. The operating point of the clutch device is determined, in particular in a parked state of the motor vehicle, on the basis of an operating parameter of the drive train which differs from an operating variable of an actuator of the clutch device. EP 2 927 071 B1 discloses a method for operating a drive train of a work vehicle, wherein it is determined whether the work vehicle is in an oscillating movement. According to the invention, target torques for input shafts and output shafts are to be ascertained for such an oscillating movement. There is a need for a method and for a control unit for operating a drive train of a motor vehicle by which shift shocks and/or jolts occurring during a reversing operation are reduced or entirely avoided. SUMMARY OF THE INVENTION The problem addressed by the present invention is to provide a method and a control unit for operating a transmission, which allow for a constant, smooth reversing operation. According to the invention, a target torque profile for the transmission output shaft is specified for the reversing operation. According to the specified target torque profile for the transmission output shaft, a tar