Method for increasing comfort when reversing in a motor vehicle comprising an automatic transmission

Abstract

Method for increasing comfort when reversing in a motor vehicle comprising an automatic transmission, characterized in that it includes the following steps: Detecting a reversing process; Initializing a motor torque limit to a predefined initial value (m_1) that corresponds to the current turbine torque or the value of an active motor torque limit; Reducing the motor torque within a specified time to a target value, which is determined depending on the target motor torque and the progress of the reversal of the direction of rotation; Maintaining the torque reduction at the target value for as long as the reversing process continues or until a defined phase of filling the force-closing switching element is reached; and Increasing the permissible engine torque up to the target engine torque depending on the target engine torque and a timer that is started when the accelerator pedal position exceeds a predetermined threshold or when the gear engagement process is completed.

Description

[0001] The present invention relates to a method for increasing comfort when reversing in a motor vehicle comprising an automatic transmission, according to the preamble of claim 1.

[0002] In current technology, excessive engine torque is often permitted during reversing from reverse to drive and vice versa, while the shift elements involved are not yet fully engaged. This can occur throughout the entire phase between the opening of the disengaging shift element and the secure transmission of the clutch. This results in a rapidly increasing engine and turbine speed, which in turn leads to reduced comfort, excessive friction in the shift elements, and potentially damage to them. A general engine torque limitation in first gear, reverse, and neutral would be possible, but would have disadvantages in other driving situations, such as improved acceleration performance in situations without reversing.

[0003] During a reversing operation, various engine torque limiters are typically active, which restrict the engine torque either when engaging a gear or depending on the current gear. These limiters do not adequately meet all requirements for torque limitation during reversing. For example, despite a general engine torque limiter, the current transmission capacity of the switching elements involved in reversing could be temporarily exceeded due to incomplete fluid flow from the switching elements; a reversal of the direction of rotation during reversing is not considered in current engine torque limiters.

[0004] From EP 0 931 686 A1 a method for controlling a motor vehicle transmission system with a multi-gear transmission driven by a motor is known, in which the motor torque is limited to a predetermined value when starting off if the vehicle speed falls below a predetermined value.

[0005] Furthermore, DE 37 35 246 A1 of the applicant discloses a drive unit for a motor vehicle comprising a drive motor, a transmission, and at least one vehicle drive axle, as well as a control unit for the drive motor, wherein the control unit controls the actuator of the throttle valve or the injection pump and / or the ignition timing adjustment device, at least depending on the position of the accelerator pedal. It is provided that, depending on a predetermined gear ratio in the transmission, the power of the drive motor is limited by means of motor intervention so that a defined torque at the transmission output shaft is not exceeded.

[0006] Further methods for increasing comfort when reversing in a motor vehicle are known from documents DE 10 2004 011 113 A1 and US 2015 / 0 337 877 A1.

[0007] The present invention is based on the objective of providing a method for increasing comfort when reversing in a motor vehicle comprising an automatic transmission.

[0008] This problem is solved by the features of claim 1. Further embodiments and advantages of the invention are set out in the dependent claims.

[0009] Accordingly, a procedure for increasing comfort when reversing in a motor vehicle, including an automatic transmission, is proposed, comprising the following steps: Detecting a reversing process;

[0010] Initializing a motor torque limit to a predefined initial value that corresponds to the current turbine torque or the value of an active motor torque limit;

[0011] Reducing the engine torque within a specified time to a target value, which is determined depending on the target engine torque and thus on the driver's request and the progress of the reversal of the direction of rotation;

[0012] Maintaining the torque reduction at the target value for as long as the reversing process continues or until a defined phase of filling the force-shooting switching element is reached; and

[0013] Increasing the permissible engine torque up to the target engine torque depending on the target engine torque and a timer that is started when the accelerator pedal position exceeds a predetermined threshold or when the gear engagement process is completed.

[0014] The permissible engine torque can be increased gradually, for example, by ramping up the torque. Furthermore, the target torque limit can be updated at predetermined intervals based on the current driver input and the progress of the reversal of rotation.

[0015] A reversing process and the associated change in direction of rotation are detected by evaluating speed signals from the speed sensors located in the vehicle's transmission and provided as a flag by the transmission control unit for the torque limitation according to the invention. To determine whether a defined phase of filling the force-closing switching element has been reached, the filling status pointer of the force-closing switching element is monitored.

[0016] According to the invention, the progress of the reversal of rotation is determined by evaluating the magnitude and sign of the measured or calculated output speed. Alternatively, the progress of the reversal of rotation can be determined by evaluating the magnitude and sign of the measured longitudinal vehicle acceleration. Another possibility for determining the progress of the reversal of rotation is to evaluate the magnitude and sign of the measured turbine speed. Furthermore, the progress of the reversal of rotation can be determined by evaluating the magnitude and sign of the speed difference to the synchronous speed.

[0017] The phases for filling the power-operated switching element can include the rapid filling phase, the filling equalization phase, or a pressure ramp required for gear changes.

[0018] According to a further development of the invention, the method is carried out when the speed of the vehicle falls below a predetermined threshold.

[0019] Furthermore, according to further embodiments, the target value of the engine torque limitation can additionally be determined depending on the transmission oil temperature and / or on the measured or calculated temperature of the force-closing switching element and / or on the coefficient of friction of the lining of the force-closing switching element.

[0020] As part of further training, it is proposed to provide an entry ramp in the transition from an active motor torque limit before the reversing process to the specified initial value of the motor torque limit during reversing, either time-controlled or dependent on the target motor torque.

[0021] Furthermore, in drive mode D, either first or second gear can be engaged for reversing, with the gear being determined by the driving strategy. For example, first gear is engaged when a high level of sportiness is selected or when a trailer is detected.

[0022] The inventive concept of situational engine torque limitation, independent of engine intervention, offers the advantage that the vehicle can still be rocked free off-road by reversing. Furthermore, the vehicle's starting performance is not reduced, and a deliberate revving of the engine in neutral is not prevented.

[0023] The invention is explained in more detail below with reference to the accompanying figures. These show: Fig. 1: a diagram of the possible time profiles of the motor torque, the pressure of the force-closing switching element, the pressure of the opening switching element, the transmission capability of the opening switching element and the transmission capability of the force-closing switching element according to the state of the art; Fig. 2: a diagram of the time profiles of the motor torque, the pressure of the force-closing switching element, the pressure of the opening switching element, the transmission capacity of the opening switching element and the transmission capacity of the force-closing switching element according to the invention; and Fig. 3: a flowchart to illustrate the process of the method according to the invention.

[0024] In the attached Fig. 1 and Fig. 2 Curve A represents the time course of the motor torque, curve B represents the time course of the pressure of the force-closing switching element, curve C represents the time course of the pressure of the opening switching element, curve D represents the time course of the transmission capability of the opening switching element and curve E represents the time course of the transmission capability of the force-closing switching element.

[0025] According to the state of the art and with reference to Fig. 1. If the reversing process begins at time t_1, the motor torque is not limited depending on the reversing process, so that at the beginning of the gear engagement at time t_3 the motor torque assumes a high value, so that in the later course until the end of the gear engagement at time t_5 there are fluctuations in the motor torque, which can lead to damage to the force-closing switching element and negatively affects comfort.

[0026] According to the invention and with reference to Fig. 2. Upon detection of a reversing process at time t_1, the engine torque is limited to a predetermined initial value m_1, and subsequently reduced at time t_2 to a target value m_2, which is determined at predetermined time intervals depending on the target engine torque, and thus on the driver's request and the progress of the reversal of rotation. At a later time t_3, the gear is engaged, and thus the filling process of the force-closing shift element begins.

[0027] According to the invention, the target value m_2 is maintained until the reversing process is completed or until a defined phase of filling the force-closing switching element is reached, which in the example shown occurs at time t_4. As shown Fig. As can be seen in Figure 2, this prevents fluctuations in the motor torque. From time t_4 to time t_5, the motor torque is increased gradually, whereby at time t_5 the force-closing switching element is fully closed and the motor torque assumes the value of the target motor torque.

[0028] In the example shown, the increase of the permitted engine torque up to the target engine torque depends on the target engine torque and a timer that is started when the accelerator pedal position exceeds a predetermined threshold.

[0029] The steps of the inventive method are described using the following examples: Fig.Figure 3 illustrates: After the detection of a reversing process, the motor torque limit is initialized to a predetermined initial value, which corresponds to the current turbine torque or the value of a motor torque limit active according to further functions, followed by a defined reduction of the motor torque to a target value, which is determined synchronously depending on the target motor torque and the progress of the direction reversal, i.e. the differential speed.

[0030] When the reversing process is complete, which can be determined, for example, by querying a flag in the transmission control unit or when a defined phase of filling the force-closing shift element is reached, the engine torque is increased up to the target engine torque depending on the target engine torque and a timer that is started when the accelerator pedal position exceeds a predetermined threshold or when the gear engagement process is completed. Reference sign A time course of the motor torque B. Time course of the pressure of the force-closing switching element C Time course of the pressure of the opening switching element D time course of the transmission capability of the opening switching element E time course of the transmission capability of the force-closing switching element

Claims

[1] Method for increasing comfort when reversing in a motor vehicle comprising an automatic transmission, characterized by that it includes the following steps: Detecting a reversing process; Initializing a motor torque limit to a predefined initial value (m_1) that corresponds to the current turbine torque or the value of an active motor torque limit; Reducing the motor torque within a specified time to a target value, which is determined depending on the target motor torque and the progress of the reversal of the direction of rotation; Maintaining the torque reduction at the target value for as long as the reversing process continues or until a defined phase of filling the force-closing switching element is reached; and Increasing the permissible engine torque up to the target engine torque depending on the target engine torque and a timer that is started when the accelerator pedal position exceeds a predetermined threshold or when the gear engagement process is completed. [2] Method according to claim 1, characterized by that the increase in the permissible engine torque up to the target engine torque occurs in a ramp-like manner. [3] Method according to claim 1 or 2, characterized by , that the target value of the torque limitation is updated at predetermined time intervals based on the current driver request and the progress of the direction reversal. [4] Method according to claim 1, 2 or 3, characterized by , that a reversing process and the associated reversal of the direction of rotation are detected by evaluating speed signals from the speed sensors present in the transmission of the vehicle and are provided as a flag by the transmission control for the torque limitation according to the invention. [5] Method according to any of the preceding claims, characterized by , that the status pointer of the filling of the force-closing switching element is monitored to determine whether the defined phase of filling the force-closing switching element has been reached. [6] Method according to any of the preceding claims, characterized by , that the progress of the reversal of rotation is determined by evaluating the magnitude and sign of the measured or calculated output speed, or that the progress of the reversal of rotation is determined by evaluating the magnitude and sign of the measured longitudinal vehicle acceleration, or that the progress of the reversal of rotation is determined by evaluating the magnitude and sign of the measured turbine speed, or that the progress of the reversal of rotation is determined by evaluating the magnitude and sign of the speed difference to synchronous. [7] Method according to any of the preceding claims, characterized by , that the rapid filling phase, the filling equalization phase or a pressure increase ramp required for gear changes are used as phases for filling the force-closing switching element. [8] Method according to any of the preceding claims, characterized by that it is carried out when the vehicle's speed falls below a predetermined threshold. [9] Method according to any of the preceding claims, characterized by , that the target value of the engine torque limitation is additionally determined depending on the transmission oil temperature and / or the measured or calculated temperature of the force-closing switching element and / or the coefficient of friction of the lining of the force-closing switching element. [10] Method according to any of the preceding claims, characterized by, that in the transition from an active motor torque limit before the reversing process to the specified initial value (m_1) of the motor torque limit during reversing, a time-controlled or target motor torque-dependent entry ramp is provided.

Images