Method for smooth gear set engagement in dual-clutch transmissions

Abstract

Method for engaging a gear set starting from a standstill of a dual-clutch transmission with an electric machine (EM) connected to one of the gear stages, wherein only one of the two existing clutches (K1, K2) is pressurized as the active clutch, and after receiving the driver's request to drive off with a forward or reverse gear stage (D, R), in a first method step (V1), the active clutch is set to a "closed" state, while at the same time the electric machine (EM) provides an increasing torque (torque_EM) as a counter-torque to the clutch torque of the active clutch, wherein in a second method step (V2), a plateau (P) of a torque (torque_EM) of the electric machine (EM) is maintained, and in a third method step (V3), after reaching the target pressure of the active clutch, the torque (torque_EM) of the electric machine (EM) is slowly reduced,wherein in a fourth method step (V4) a constant holding torque of the electric machine is applied to compensate for vibration and noise.

Description

[0001] The invention relates to a method for wheel set application starting from a standstill in dual clutch transmissions. State of the art

[0002] Methods for operating a hybridized dual-clutch transmission drive train comprising an internal combustion engine, a dual-clutch arrangement with a first and a second friction clutch, a first sub-transmission, a second sub-transmission and an electric machine that is connected to the input of one of the sub-transmissions or that can be connected thereto are known.

[0003] Such a dual-clutch transmission drivetrain is described, for example, in DE 10 2010 044 618 A1. The powertrain includes a dual-clutch transmission with two power transmission paths, allowing gear changes without a drop in traction. The drive torque provided by the combustion engine is transferred from one power transmission path to the other through overlapping actuation without interrupting traction.

[0004] EP 2 765 338 B1 describes a method for operating a hybridized dual-clutch transmission drive train, which comprises an internal combustion engine, a dual-clutch arrangement with a first and a second friction clutch, a first partial transmission containing a plurality of gear stages, a second partial transmission containing a plurality of gear stages, and an electric machine which is connected to the input of one of the partial transmissions or is connectable thereto, wherein in a hybrid operation in which drive power from the electric machine is transmitted via one partial transmission, drive power from the internal combustion engine is transmitted via the other partial transmission, wherein the friction clutch assigned to the other partial transmission is closed and the friction clutch assigned to one partial transmission is open, a source gear stage is disengaged in one partial transmission,comprising the steps of: closing the friction clutch assigned to one partial transmission so that this friction clutch can transmit a torque corresponding to the drive torque provided by the electric machine, and disengaging the source gear stage in the one partial transmission.

[0005] Due to the response characteristics near standstill and at low speeds, the clutch must provide the torque for creeping and starting as quickly as possible, which leads to the problem because the flanks of the transmission change very quickly.

[0006] The clutch drag torque varies depending on temperature. Furthermore, there is a marginal variation between vehicles due to tolerances, so it cannot be guaranteed that the gear set is actually engaged. This leads to anomalies / complaints in subsequent situations such as creeping, starting, stationary loading, shift drum movement, etc.

[0007] In some dual-clutch transmissions, it is possible to fill both clutches at the same time to compensate for this behavior.

[0008] In other dual-clutch transmissions, it is not possible to recharge pressure while stationary. To compensate for this behavior, a static torque of the electric motor has been set, but this function cannot compensate for the influence of drag torque. Fig. 1 shows curves describing the influence of a set torque of the electric motor. Graph 2 shows whether a positive or negative torque must be set, depending on the engagement of an automatic gear. Graph 3 shows the zero line without a set torque of the electric motor, graph 4 shows a step-like position, and graph 5 shows a controlled torque curve of the electric motor.

[0009] The object of the invention is to develop a method for improved wheel set engagement near standstill in special dual-clutch transmissions. Description of the invention

[0010] The problem is solved by a method for engaging the gear set starting from the standstill of a dual-clutch transmission with an electric motor that is connected to one of the gear stages, wherein only one of the two existing clutches is pressurized as the active clutch, and after receiving the driver's request to drive off with a forward or reverse gear stage, in a first method step the active clutch is set to a "closed" state, while at the same time the electric machine provides an increasing torque as a counter-torque to the clutch torque of the active clutch, wherein in a second method step a plateau of a torque of the electric machine is maintained, and in a third method step after reaching the target pressure of the active clutch the torque of the electric machine is slowly reduced,In a fourth process step, a constant holding torque of the electrical machine is applied to compensate for vibration and noise.

[0011] The plateau is maintained for a predetermined holding time, which is determined empirically from a variety of vehicle data.

[0012] Alternatively, the plateau is determined by measuring the difference between the clutch pressure target and the actual value of the active clutch, whereby the third process step begins when the difference reaches a threshold value.

[0013] During the reduction of the torque in process step V3, the speed of the electric machine is calculated by an edge_tq function.

[0014] Each time the electric machine speed reaches a calibratable threshold or threshold gradient, the electric machine torque is frozen until the speed drops. Description of the characters Fig. 1 shows an overview of the different measures for compensating a drag torque, Fig. 2 shows the moment curve, Fig. 3 shows the pressure curve and the drag torque of the clutch in four steps, Fig. 4 to 7 show schematically the application of the torque of the electric machine, Fig. 8 shows a second variant of the method, Fig. Figure 9 shows a third variant of the procedure.

[0015] To compensate for all influences on a dual-clutch transmission without filling the clutches at standstill, an edge torque function 1 operates in four consecutive steps. Edge torque function 1 runs on a controller and is based on an edge_tq function used to control the process.

[0016] The flank torque function 1 is divided into four areas, which can be configured separately for the target level D or R. The compensation torque of the electric machine EM to be set is negative in the automatic level R, and positive in the automatic level D as in Fig. 1. In the upper part of the Fig. 1 shown automatic gear stages D and R.

[0017] In the lower part of the Fig. Figure 1 schematically shows the torque of the electric machine over time. Line 3 shows a curve without a compensation effect, line 4 shows a support function of the electric machine with a step function, and line 5 shows the inventive solution with a flank torque function 1.

[0018] The four areas are, as in Fig. 2 and Fig. 3 shown, divided.

[0019] The course of the proceedings will also be reported in the Fig. 4 to 7 clearly.

[0020] The procedure for applying a flank torque function 1 begins with the driver's request, whereby the driver engages a forward or reverse gear.

[0021] In the embodiment of the Fig. 4 to 7 a fourth gear is engaged and the clutch K2 of the dual clutch has a certain pressure to hold the fourth gear.

[0022] In the first process step V1, the engaged gear set is held in the currently present flank of the gear wheels. This is achieved by the electric motor EM.

[0023] For this purpose, the electric motor is driven at a high clock rate, which generates a high torque that counteracts the torque of the filling clutch. This process is Fig. 4. The narrower arrow pointing upwards represents the torque of the clutch K2, the wider arrow pointing downwards the counter torque of the electric machine with a torque edge_tq.

[0024] In the Fig. Figures 4 to 7 schematically show a hybridized dual-clutch transmission. This transmission features two countershafts, the output shafts 11 and 12, for setting several forward gears and one reverse gear. Drive is provided via the input shaft 10 and the two clutches K1 and K2. Typically, a loose gear is provided to implement the reverse gear R, positioned specifically for the reverse gear. Accordingly, a separate gear set, usually with an intermediate gear, is provided for the reverse gear, although this gear set is not used for any other gears. In a dual-clutch transmission, gear changes are typically achieved by switching from one clutch to the other. Accordingly, gear changes from two already engaged gears occur by changing the clutch with shortened shift intervals.When engaging reverse gear, for example when manoeuvring a vehicle, the gear change for the manoeuvre takes place between first and reverse gear.

[0025] In Fig. Figure 2 shows the first process step V1. After the forward gear D is determined, the electric motor begins to deliver torque_EM while the clutch K2 is not yet engaged and still exhibits slip in an intermediate state. The electric motor EM must be faster than the clutch—here, K2—while the gear set must be maintained in the old, currently existing direction until the clutch pressure reaches the setpoint.

[0026] In the second process step V2, the electric machine is maintained at a torque plateau P. At the beginning of the second process step V2, the status of the clutch in the control system is changed to the "closed" state, which causes the clutch pressure to build up.

[0027] The plateau P is maintained for a specific holding time even after the clutch state changes to "closed." A timer sets a holding time that allows the clutch just enough time to reach its filling state.

[0028] The status of the clutch changes at the position of the cursor A in Fig. 3 before the target pressure specified by the control system is reached, which occurs at the position of cursor B. The setting of the holding time t_H is determined by empirically determining the filling time of the clutch over many vehicles and stored in the control system.

[0029] The P plateau must be maintained until the clutch pressure reaches the target value. Otherwise, the buildup of clutch pressure and the reduction of edge_tq work in the same direction.

[0030] This situation is still in the Fig. 5. The two arrows representing the torques of the clutch and the electric machines are almost equally strong.

[0031] During process step V2, it is also possible in this first variant of the process to calculate the difference between the target and actual clutch pressure values. The timer is no longer required, as the transition from process step V2 to process step V3 is initiated when the difference between the target and actual clutch pressure values ​​is small enough. The threshold values ​​are stored in the control system beforehand.

[0032] The holding time of the plateau P can be replaced by a comparison of the target and actual clutch pressure. Due to signal noise, a corridor is required to prevent signal toggling, i.e., switching between different states.

[0033] In the third process step V3, the torque torque_EM is reduced in order to realize the shifting of the wheelset from one flank to the next flank.

[0034] The torque torque_EM, which counteracts the clutch torque, is constantly reduced so that the clutch torque gently rotates the gear set due to the now slow clock rate of the electric motor and thus applies it in the direction desired by the driver.

[0035] Fig. Figure 6 shows the schematic representation with an arrow of the electric machines, which is significantly narrower than the arrow of the clutch. During the reduction of edge_tq in process step V3, the speed of the electric machine is influenced by the edge_tq function.

[0036] The second variant is used in the Fig. 8. The upper part of the figure shows the curve of the torque edge_tq over time, with the control specification shown in graph 5. The torque of the electric machine EM follows the control curve in a dotted line.

[0037] In the lower part of the Fig. Figure 8 plots the speed ω of the electric motors over time. The shift time ts for engaging the gear is also indicated.

[0038] In the second variant of the method, the pure control via the flank torque function 1 is supplemented by a control step that regulates the duration of the plateau.

[0039] In Fig. Figure 9 illustrates the control behavior during a speed increase. The measured speed curve ω_EM_m is shown in the lower part of the figure.

[0040] Whenever the speed ω of the electric machine EM reaches a calibratable threshold or a threshold gradient, the torque ω of the electric machine EM is frozen until the speed drops—even if the gradient is too high. In the event that the speed ω of the electric machine EM does not decrease, a separate output condition is required. This output condition is stored in the control system.

[0041] This results in a smoother engagement of the gear flank in the gearbox since the torque gradient is zero under critical conditions.

[0042] The torque of the electric machine torque_EM is frozen at the time when an increase in speed is detected - as in Fig.9. Based on the speed curve or its decrease, the torque is reduced, which ensures that only the sufficient torque ratio is maintained and the gear set turns even more smoothly. Graph 15 shows the "damped speed curve" due to the control effect. The control effect is shown in graph 16.

[0043] In the fourth process step V4, a constant holding torque is applied to the electric motor to compensate for vibration and noise. This torque serves to ensure that the torque pulsations introduced into the system via the rotational irregularity of the combustion engine do not lead to noise-related anomalies.

[0044] The intermediate gear stage 13 is thus slightly applied, which counteracts the excitations from the combustion engine.

[0045] In an alternative embodiment, the function is designed as a completely adaptive control.

[0046] Empirically derived criteria are selected based on the speed and clutch pressure curves, and the torque of the electric motor EM is adjusted accordingly. This allows the electric motor to be set to the lowest possible torque level, thus optimizing efficiency. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2010 044 618 A1

[0003] EP 2 765 338 B1

[0004]

Claims

[1] Method for engaging the wheelset starting from the standstill of a dual-clutch transmission with an electric machine (EM) connected to one of the gear stages, wherein only one of the two existing clutches (K1, K2) is pressurized as the active clutch, and after receipt of the driver's request to start driving in a forward or reverse gear stage (D, R), in a first process step (V1) the active clutch is set to a state "closed", while at the same time the electric machine (EM) provides an increasing torque (torque_EM) as a counter-torque to the clutch torque of the active clutch, wherein in a second process step (V2) a plateau (P) of torque (torque_EM) of the electric machine (EM) is maintained, and in a third process step (V3) after reaching the target pressure of the active clutch the torque (torque_EM) of the electric machine (EM) is slowly reduced,wherein in a fourth process step (V4) a constant holding torque of the electric machine is applied to compensate for vibration and noise. [2] Method according to claim 1, characterized by , that the plateau (P) is held for a predetermined holding time (t_H), which is empirically determined from a variety of vehicle data. [3] Method according to claim 1, characterized by , that the plateau (P) is controlled by measurements of the difference between the clutch pressure target and actual value of the active clutch in process step (V2) and that the third process step (V3) begins when a threshold value of the difference is reached. [4] Method according to any one of the preceding claims, characterized by , that during the reduction of the torque in process step (V3) the speed of the electric machine (EM) is regulated. [5] Method according to claim 4, characterized by, that each time the rotational speed of the electric machine (EM) reaches a calibratable threshold or threshold gradient in the third process step (V3), the torque of the electric machine (EM) is frozen until the rotational speed drops.

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