Method and control unit for controlling a continuously variable transmission for a vehicle

Abstract

Method for controlling a continuously variable transmission (1) for a vehicle, wherein the continuously variable transmission (1) comprises a hydrostatic unit (2) with a position control valve (3) and is designed to interact with a drive shaft (4) and an output shaft (5), wherein the hydrostatic unit (2) is adjusted when the position control valve (3) is energized in order to accelerate the vehicle, characterized in that the energization of the position control valve (3) is cyclically monitored by a safety function, wherein the safety function is designed to detect an unintended energization of the position control valve (3) that leads to an unintended acceleration of the vehicle, in order to then disconnect the transmission (1) at least from the output shaft (5) and thereby prevent an unintended acceleration of the vehicle, wherein the safety function is triggered,if at least one limit value for the current supply to the position control valve (3) is exceeded.

Description

[0001] The invention relates to a method for controlling a continuously variable transmission for a vehicle, wherein the continuously variable transmission has a hydrostatic drive with a position control valve.

[0002] In a continuously variable drive with a continuously variable transmission, an incorrect control current applied to the position control valve on the hydrostatic transmission can cause the vehicle to accelerate unintentionally from a standstill or while driving when the drivetrain is closed. The position control valve is designed to adjust the continuously variable transmission. Due to the very high adjustment speeds of the hydrostatic transmission, this acceleration is implemented almost instantly.

[0003] DE 103 03 206 A1 discloses a hydrostatic transmission operating in an open circuit. The transmission is driven by an adjustable hydraulic motor, which is adjusted for acceleration or deceleration using an electronic control system so that a desired vehicle speed corresponds to a measured vehicle speed.

[0004] From DE 10 2015 100 766 A1 a device for detecting abnormalities in a continuously variable transmission is known.

[0005] A control device for an actuating device for use in a gear unit can be found in DE 601 26 384 T2.

[0006] The object of the present invention is to create a method for controlling a continuously variable transmission that quickly detects an incorrect current application to the position control valve and prevents unwanted acceleration of the vehicle. In particular, the incorrect current application, which leads to unwanted acceleration, is to be distinguished from intended acceleration.

[0007] The object is achieved by the subject matter of patent claim 1. Preferred embodiments are the subject matter of the dependent claims.

[0008] The method according to the invention for controlling a continuously variable transmission for a vehicle is provided for a continuously variable transmission with a hydrostat, wherein the hydrostat has a position control valve. The continuously variable transmission interacts with an input shaft for drive purposes and with an output shaft for output purposes. The hydrostat is adjusted when the position control valve is energized in order to accelerate the vehicle. The energization of the position control valve is cyclically monitored by a safety function. The safety function is provided to detect an unintentional energization of the position control valve, which could lead to unintentional acceleration of the vehicle, in order to then disconnect the transmission at least from the output shaft and thereby prevent unintentional acceleration of the vehicle.The safety function is triggered if at least one limit value for the current supply to the position control valve is exceeded.

[0009] The minimum limit value for the current supply to the position control valve, which is intended to trigger the safety function, depends on vehicle and transmission parameters as well as on a large number of operating parameters of the continuously variable transmission.

[0010] The continuously variable transmission is a mechanically power-split transmission. In particular, the continuously variable transmission has up to three driving ranges, with the driving ranges being selected or adjusted via so-called range clutches. The continuously variable transmission is connected to a drive engine, in particular a diesel engine, via a so-called directional clutch. The hydrostatic drive is connected to the power flow in the transmission via a planetary gear, which is part of the continuously variable transmission. When the directional clutch and the first range clutch are engaged, the vehicle starts moving by pivoting the hydrostatic drive. The pivoting of the hydrostatic drive is realized via the position control valve arranged in the hydrostatic drive. Furthermore, the vehicle accelerates in the respective driving range by pivoting the hydrostatic drive and thus by energizing the position control valve.

[0011] During cyclic monitoring of the current supply to the position control valve, the current and / or voltage applied to the position control valve is monitored in particular. In particular, a change in the current and / or voltage can also be monitored. Preferably, the cyclic monitoring of the current supply to the position control valve takes place at intervals of 10 milliseconds. This allows a preliminary evaluation of the current supply, which selects only those currents to the position control valve that could lead to vehicle acceleration. For example, currents that would compensate for unwanted acceleration due to drivetrain inertia can be ignored.

[0012] According to a preferred embodiment, the safety function is used to monitor for unintentional vehicle start-up. The start-up monitoring function is activated when the speed of the output shaft is below a variably adjustable limit and there is a frictional connection between the drive shaft and the output shaft. Thus, the start-up monitoring function is designed to prevent unintentional acceleration of the vehicle from a standstill. The start-up monitoring function is therefore not permanently active, but is only activated when the speed of the output shaft is below the variably adjustable limit and the drive shaft is frictionally connected to the output shaft via the continuously variable transmission. Therefore, both the direction-of-drive clutch and the first range clutch must be engaged.

[0013] Preferably, the start-up monitoring is deactivated when a limit value for the accelerator pedal position is exceeded. The limit value for the accelerator pedal position provides information about whether the current to the position control valve is intended. When a driving request is entered, for example by pressing the accelerator pedal, the vehicle is accelerated by, among other things, energizing the position control valve. If the accelerator pedal is not depressed, the position control valve must not be energized either. To differentiate between intended and unintended acceleration, the limit value for the accelerator pedal position can preferably be set to 5%. Therefore, the accelerator pedal must be depressed by at least 5% to deactivate the start-up monitoring. This increases the quality of the safety function and thus the performance of the powertrain.

[0014] In particular, a debounce time of two to three cycles is provided before the safety function is triggered to further enhance the quality of the safety function. Therefore, the conditions intended to trigger the safety function must be verified over two to three cycles.

[0015] According to a preferred embodiment, the safety function is triggered when a maximum current value for energizing the position control valve is exceeded. Therefore, the following conditions must be met simultaneously to trigger the safety function: The speed of the output shaft is below a variably adjustable limit, there is a frictional connection between the input shaft and the output shaft, the current accelerator pedal position is below the limit for the accelerator pedal position, and the current current value for energizing the position control valve is above the maximum current value for energizing the position control valve.

[0016] According to a further preferred embodiment, the safety function is triggered when a maximum differential current value for energizing the position control valve is exceeded. Therefore, the following conditions must be met simultaneously to trigger the safety function: The speed of the output shaft is below a variably adjustable limit, there is a frictional connection between the drive shaft and the output shaft, the current accelerator pedal position is below the limit for the accelerator pedal position, and the maximum differential current value for energizing the position control valve has been exceeded. The differential current value is understood to mean a change in the current value over a specific period of time or over at least two cycles.

[0017] The invention includes the technical teaching that an unintentional start-up of the vehicle is detected if a limit value for the current supply to the position control valve is exceeded without the maximum differential current value being reached. A counter is then started, and the safety function is triggered when the counter has expired and the limit value for the current value of the position control valve is still exceeded. The counter describes, for example, a time interval that is passed through. In other words, a counter is started at the time the limit value for the current supply to the position control valve is exceeded, which is below the maximum limit value for the current supply to the position control valve. This case occurs when the current supply to the position control valve does not increase suddenly but slowly, i.e. the maximum differential current value is not reached.This means that the vehicle only accelerates later.

[0018] The safety function is only triggered when the counter has expired and the limit value for the current value of the position control valve is still exceeded. The counter thus implements a delay time. While the delay time is elapsed, other conditions, such as the accelerator pedal position, are evaluated preferentially. If the accelerator pedal position is below the limit value for the accelerator pedal position, additional conditions are applied that are intended to detect an unintentional start-up. In particular, only conditions that indicate a change in the output speed are applied, since otherwise no acceleration occurs.

[0019] Movement on the output shaft can be detected using various means. For example, an output speed sensor can be evaluated. The output speed sensor reliably detects movement on the output shaft once a lower threshold is reached. The lower threshold is one revolution of the output shaft per minute. To enable even earlier detection of movement on the output shaft, a sensor signal for measuring the displacement of the transmission can be evaluated additionally or alternatively. Furthermore, it is also conceivable to use additional internal speed sensors to detect movement on the output shaft, particularly speed sensors that detect a voltage change when the output shaft moves.

[0020] If the monitored limits are exceeded and the counter has expired, the safety function is triggered. In contrast, the detection of unintentional start-up is deactivated if the current supply to the position control valve falls below the limit value for the current supply to the position control valve and the counter has not yet expired.

[0021] According to a preferred embodiment, the safety function is used to monitor for unwanted acceleration of the vehicle while driving. The acceleration monitoring comprises a parameterizable evaluation function, with a current change from a last to a current cycle and a sum of the current changes in a number of elapsed cycles being provided as input variables. In other words, the check to determine whether an unwanted current change has occurred at the position control valve is carried out by monitoring the current change in consecutive cycles, which are preferably repeated every 10 milliseconds. An average permissible current change is set. If this average permissible current change is exceeded, the safety function is triggered.

[0022] In particular, acceleration monitoring is only active when there is a frictional connection between the input shaft and the output shaft, meaning both the direction clutch and the range clutch are engaged, or when the range clutch is engaged, meaning only a frictional connection between the transmission and the output shaft, but at the same time the internal speeds of the transmission are above a certain limit. If the internal speeds of the transmission are above the limit, the inertia of the rotating masses in the transmission can generate unwanted acceleration when the hydrostatic drive is energized.

[0023] The invention includes the technical teaching that the parameterizable evaluation function is generated from a variety of vehicle data. In particular, the average permissible current change depends on the number of cycles and decreases with increasing number of cycles.

[0024] In the following, embodiments of the invention are explained in more detail with reference to the drawings. Fig. 1: a simplified schematic representation of a continuously variable transmission for a vehicle which can be controlled according to a method according to the invention, Fig. 2: a diagram illustrating a parameterizable evaluation function that can be used for a method according to the invention, Fig. 3: a diagram illustrating an exemplary course of a method according to the invention, Fig. 4: another diagram illustrating an exemplary course of a method according to the invention, Fig. 5: another diagram illustrating an exemplary course of a method according to the invention.

[0025] Fig. 1 shows a continuously variable transmission 1 for a vehicle (not shown here), wherein the continuously variable transmission 1 comprises a hydrostat 2 with a position control valve 3. The continuously variable transmission 1 is drive-relatedly connected to a drive shaft 4, which is operatively connected to a drive motor (not shown here) in order to feed drive power into the continuously variable transmission 1. Furthermore, the continuously variable transmission 1 is output-relatedly connected to an output shaft 5, wherein the output shaft 5 is operatively connected to at least one drive axle (not shown here). By energizing the position control valve 3, the hydrostat 2 is adjusted, thereby accelerating the vehicle when the drive motor is operating at a substantially constant speed and with a power flow between the drive shaft 4 and the output shaft 5. Not shown in Fig. 1, a control unit that transmits signals to the transmission 1, the hydrostatic unit, and the position control valve 3. Furthermore, the control unit can also transmit signals to other sensors (e.g., speed sensors on the input shaft 4 or output shaft 5, accelerator pedal) or other control units (vehicle control computer, engine control unit, etc.).

[0026] According to Fig. 2 to Fig. 5 shows the method according to the invention in various exemplary embodiments. Regardless of the respective exemplary embodiment, the current supply to the position control valve 3 is cyclically monitored by a safety function. The safety function is intended to detect an unintended current supply to the position control valve 3, which leads to an unintended acceleration of the vehicle, in order to then disconnect the transmission 1 at least from the output shaft 5 and thereby prevent an unintended acceleration of the vehicle. The safety function is triggered when a variably selected limit value for the current supply to the position control valve 3 is exceeded.

[0027] In Fig. Figure 2 shows the curve of a parameterizable evaluation function BF. The parameterizable evaluation function BF is used to implement the method according to the invention. In this case, the parameterizable evaluation function BF represents the limit value for the current supply to the position control valve 3, which, if exceeded, triggers the safety function. According to Fig. 2, the safety function, specifically the evaluation function BF, is used to monitor for unintentional acceleration of the vehicle while driving. A current change at a control unit output is plotted on the ordinate Y, with the number of cycles plotted on the abscissa X. Thus, the evaluation of the current supply to position control valve 3 is performed based on the average maximum permitted current change at the control unit output. The maximum permitted current change at the control unit output depends on the number of last observed cycles. The evaluation function BF specifies the maximum permitted deviation values ​​across the number of cycles.

[0028] For example, a value A does not trigger the safety function because it is below the evaluation function BF and within a permissible range. In contrast, a value B triggers the safety function because it is above the evaluation function BF and within an impermissible range. A short-term, high positive current change at position control valve 3 can only lead to a brief acceleration of the vehicle due to the system's inertia (value A). In contrast, a longer-lasting positive current change at position control valve 3 is more difficult for the driver to control, making initiation of the safety function necessary (value B).

[0029] The current change from a previous cycle to a current cycle, as well as the sum of the current changes over a number of elapsed cycles, are provided as input variables for the parameterizable evaluation function BF. The parameterizable evaluation function BF is generated from a wide range of vehicle data and enables a good compromise between safety and system robustness. The course of the evaluation function BF shows that the average permissible current change depends on the number of cycles and decreases with increasing cycles.

[0030] When checking the permissible current values ​​of position control valve 3, only current values ​​at position control valve 3 that can physically lead to vehicle acceleration are considered. For example, a current change in an initial driving range below an offset current of 300 mA is not considered if the current increases from 75 mA to 250 mA within a few cycles. However, if it is determined that the maximum current change is exceeded, a threshold flag (memory signal) is set.If the threshold flag is set and the monitoring function is active, i.e. there is a frictional connection between the input shaft 4 and the output shaft 5 or at least a frictional connection between the gearbox 1 and the output shaft 5, whereby the internal speeds in the gearbox 1 must then be above a limit value, the gearbox 1 is transferred to a safe state after a parameterizable debounce time, whereby the safety function is activated.

[0031] Initiating a safe state of the transmission 1 means that the transmission 1 is disconnected at least from the output shaft 5, preferably also from the drive shaft 4, thereby preventing unwanted acceleration of the vehicle in the event of unwanted energization of the position control valve 3. Thus, by initiating the safe state of the transmission 1, the frictional connection between the drive shaft 4 and the output shaft 5 is severed.

[0032] According to Fig. 3, Fig. 4 and Fig. 5, the safety function is used to monitor for unintentional start-up of the vehicle, whereby the start-up monitoring is activated when a speed of the output shaft 5 is below a variably adjustable limit value and there is a frictional connection between the drive shaft 4 and the output shaft 5.

[0033] After Fig. 3 and Fig. 4, five diagrams are integrated into a single diagram. A time is plotted on each abscissa X. In contrast, from bottom to top along the ordinate Y, the initiation of a safe state SZ of transmission 1, an accelerator pedal position F, an electrical current I, an activity of the start-up monitoring system Ü, and finally the presence of a frictional connection K between the input shaft 4 and the output shaft 5 are plotted.

[0034] According to Fig. 3, the safety function is triggered when a maximum limit value MG for the current supply to the position control valve 3 is exceeded and, at the same time, a limit value GF for an accelerator pedal position is not exceeded. Since the start-up monitoring Ü is only active from the moment of frictional connection K between the input shaft 4 and the output shaft 5, the safety function is triggered shortly thereafter at time ZP, and after a few cycles, the safe state SZ of the transmission 1 is also initiated.

[0035] After Fig. 4, the safety function is triggered when a maximum differential current value DS for the current supply to the position control valve 3 is exceeded. The maximum differential current value DS is represented here by the sudden increase in the current supply to the position control valve 3.

[0036] According to Fig. 5, seven diagrams are combined into a single diagram. Time is plotted on the respective abscissa X. In contrast, from bottom to top along the ordinate Y, the initiation of the safe state SZ of the transmission 1, a voltage SE for detecting movement on the output shaft 5, a speed DE for detecting movement on the output shaft 5, the accelerator pedal position F, the electrical current I, the activity of the start-up monitoring Ü, and finally the presence of the frictional connection K between the input shaft 4 and the output shaft 5 are plotted.

[0037] After Fig.5, if a limit value GW for the current supply to the position control valve 3 is exceeded, an unintentional start-up of the vehicle is detected. From this point in time, a counter Z is started, whereby the safety function is triggered when the counter Z has expired and the limit value GW for the current value of the position control valve 3 is still exceeded, at the same time a limit value for an accelerator pedal position GF is not exceeded, the voltage SE for detecting a movement on the output shaft 5 is above a limit value GS and a speed DE for detecting a movement on the output shaft 5 is above a limit value GD. Therefore, the expiration of the counter Z is the time ZP at which the safety function is triggered and, after a few cycles, the safe state SZ of the transmission 1 is also initiated. Reference symbol 1 continuously variable transmission 2 Hydrostat 3 Position control valve 4 drive shaft 5 Output shaft A, B value I electrical current F Accelerator pedal position Ü Activity of the start-up monitoring K Presence of a frictional connection X abscissa Y Ordninate Z counter BF parameterizable evaluation function MG maximum limit for energizing the position control valve DS maximum differential current value for energizing the position control valve DE Speed ​​to detect movement on the output shaft GD Limit value for detecting movement on the output shaft GS limit value for detecting movement on the output shaft GW limit value for the current supply to the position control valve GF limit value for an accelerator pedal position SE Voltage to detect movement on the output shaft SZ Initiation of a safe state ZP Time to trigger the safety function

Claims

[1] Method for controlling a continuously variable transmission (1) for a vehicle, wherein the continuously variable transmission (1) has a hydrostat (2) with a position control valve (3) and is provided to cooperate with a drive shaft (4) and with an output shaft (5) in terms of drive technology, wherein the hydrostat (2) is adjusted when the position control valve (3) is energized in order to accelerate the vehicle, characterized byin that the energization of the position control valve (3) is cyclically monitored by a safety function, wherein the safety function is provided to detect an unwanted energization of the position control valve (3), which leads to an unwanted acceleration of the vehicle, in order to then separate the transmission (1) at least from the output shaft (5) and thereby prevent an unwanted acceleration of the vehicle, wherein the safety function is triggered when at least one limit value for the energization of the position control valve (3) is exceeded. [2] Method according to claim 1, characterized by that the safety function is used to monitor for unintentional start-up of the vehicle, wherein the start-up monitoring is activated when a speed of the output shaft (5) is below a variably adjustable limit value and there is a frictional connection between the drive shaft (4) and the output shaft (5). [3] Method according to claim 2, characterized by that the start-up monitoring is deactivated if a limit value for an accelerator pedal position (F) is exceeded. [4] Method according to claim 3, characterized by that the safety function is triggered when a maximum limit value (MG) for the current supply to the position control valve (3) is exceeded. [5] Method according to one of claims 3 to 4, characterized by that the safety function is triggered when a maximum differential current value (DS) for the current supply to the position control valve (3) is exceeded. [6] Method according to claim 5, characterized bythat if a limit value (GW) for the current supply to the position control valve (3) is exceeded without the maximum differential current value (DS) being reached, an unwanted start-up is detected, whereby a counter (Z) is then started, whereby the safety function is triggered when the counter (Z) has expired and the limit value (GW) for the current value of the position control valve (3) is still exceeded. [7] Method according to claim 6, characterized by that while the counter (Z) is running, at least the speed (DE) on the output shaft (5) is monitored, wherein the safety function is triggered if, after the counter (Z) has run down, at least the speed (DE) on the output shaft (5) exceeds a limit value (GD). [8] Method according to claim 1, characterized bythat the safety function is used for unintentional acceleration monitoring of the vehicle while driving, wherein the acceleration monitoring comprises a parameterizable evaluation function (BF), wherein a current change from a last to a current cycle and a sum of the current changes in a number of elapsed cycles are provided as input variables. [9] Method according to claim 8, characterized by that the parameterizable evaluation function (BF) is generated from a large number of vehicle data. [10] Method according to claim 8, characterized by that the average allowable current change depends on the number of cycles and decreases with increasing number of cycles. [11] Control device which is designed to carry out a method according to one of claims 1 to 10.

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