Method and gear change control device for shift point control in automatic transmissions

Abstract

Method for shift point control in automatic transmissions in motor vehicles with an internal combustion engine, in which upshifts and downshifts are triggered by means of an electronic control unit via shift characteristics stored therein, wherein in overrun mode of the internal combustion engine an immediate downshift (RS) is triggered by means of the electronic control unit independently of a currently relevant shift characteristic as a function of a reactivation speed (N_WE) and a shift delay time (t_SV_DU), characterized in that the shift delay time (t_SV_DU) is the respective empirically determined and stored delay time during a gear change starting with a shift sequence up to the reversal of the speed due to the interruption of traction of a clutch responsible for the current gear (gear X).

Description

[0001] The invention relates to a method and a gear change control device for shift point control in automatic transmissions.

[0002] Methods and gearshift control devices for shift point control in automatic transmissions are already known in principle. The publications DE 10 2005 057 805 A1, DE 10 2008 023 805 A1, and DE 10 2007 060 161 A1 also disclose shift point control systems that have characteristic curves with different upshift and downshift hystereses to largely avoid rapid switching back and forth between two gears, and that execute shifts deviating from the characteristic curves as needed.

[0003] Normally, a dedicated shift map with shift characteristics for gearshift control is stored for many operating situations, depending on the driver's input or the recognition of a specific driving situation. Generally, the downshift is determined with a certain hysteresis depending on the required upshift during acceleration. However, if the vehicle is subsequently decelerated, the shift point may be so low that, under certain circumstances, a possible fuel-saving overrun cut-off of the drive engine (particularly of an internal combustion engine) is deactivated. According to the methods cited above as state of the art, measures are already being taken to prevent the resulting unnecessary fuel consumption that occurs in some operating situations.

[0004] For further information on the state of the art, please refer to DE 43 29 916 A1.

[0005] The object of the invention is to further improve a method of the type mentioned at the outset with a view to reducing fuel consumption.

[0006] This object is achieved according to the invention by the subject matter of patent claim 1. Advantageous developments of the invention are contained in the dependent claims.

[0007] In already known shift point controls for electronically controlled automatic transmissions in motor vehicles, upshifts and downshifts are generally triggered by means of an electronic control unit via shift characteristics stored therein, depending on a power requirement value and the vehicle speed.

[0008] According to the invention, in the preferably unfired overrun mode of an internal combustion engine present in the motor vehicle as a drive motor, an immediate downshift is triggered by means of the electronic control unit independently of the stored shift characteristics depending on a re-engagement speed and / or a specific shift delay time.

[0009] The reactivation speed is the minimum required engine speed to remain in overrun cutoff (e.g., approximately 850 rpm) or to switch from unfired to fired overrun mode. The reactivation speed is transmitted from the engine control unit to the electronic control unit and can vary depending on various operating parameters, such as the engine speed gradient, the engine braking torque, the air conditioning system operation, the number of on-board electrical consumers activated, and / or the steering angle.

[0010] The specific shift delay time specified here is the delay time during a gear change, beginning with a gear change command until the engine speed reversal due to the interruption of traction of a clutch responsible for the current gear. The shift delay times are determined empirically and stored either in the electronic control unit itself or in another unit connected to it for shift sequence control.

[0011] The invention is based on the following considerations: To optimize fuel consumption, the upshift points must be set very low in the fuel-optimal lower load range. The base coasting shift point is set correspondingly low, taking into account a hysteresis to prevent shifting.

[0012] From a fuel consumption perspective, it is expedient to keep the combustion engine in overrun cut-off when decelerating the vehicle.

[0013] Currently, the switching points are determined and validated empirically with considerable effort, and are still not suitable for all driving situations and for all available engine versions (e.g. market-specific engine application Japan).

[0014] According to the invention, a function was developed to dynamically calculate the coasting downshift points, taking into account the deceleration gradient, the shift delay time, and the re-engagement speed. The predicted shift delay times are transmitted from the shift sequence control for the transmission actuators. The variable predicted re-engagement speed for the current gear X and gear X-1 comes from the engine control unit. This value can vary depending on various parameters (e.g., idle speed, deceleration gradient, air conditioning, consumers, steering angle, etc.). Furthermore, individual country variants may differ in the basic application due to country-specific emissions requirements (e.g., the Japanese variant).

[0015] The invention achieves the following advantages: • Greater robustness with reduced application and security effort. • Cost reduction through the ability to serve various markets and vehicle derivatives with a single application. • Optimization of consumption values.

[0016] The drawing illustrates an embodiment of the invention. It shows the functional components required to trigger an early downshift deviating from the specified shift characteristics.

[0017] Typically, a known electronic control unit (transmission control unit) (and therefore not specifically illustrated here) receives, in particular, the vehicle speed, the engine speed N, and a power demand value, for example, the accelerator pedal position specified by the driver, as input signals. The electronic control unit has a functional module, in particular in the form of a software program module, for implementing the method according to the invention. The electronic control unit issues commands to control actuators of an automatic transmission to carry out gear changes. Using the functional module for shift point control, which is available in the form of hardware and software, the control unit generally triggers upshifts and downshifts via stored shift characteristics depending on the power demand value and the vehicle speed.

[0018] According to the invention, an immediate downshift RS from a current gear X to gear X-1 is performed by means of the functional module in the electronic control unit in the preferably unfired overrun mode of the internal combustion engine, regardless of a currently relevant shift characteristic curve, depending on a reactivation speed N_WE and / or a shift delay time t_SV_DU. The reactivation speed N_WE is a required speed of the internal combustion engine for switching from unfired to fired overrun mode. The shift delay time t_SV_DU is the delay time during a gear change, beginning with a gear change command until the speed reversal due to the interruption of traction of a clutch responsible for the current gear X.

[0019] Preferably, the immediate downshift RS is triggered when a virtually determined engine speed N_v (gear X) reaches a predetermined minimum permissible target reversing speed N_ZU, wherein the target reversing speed N_ZU is a target speed within a defined safety margin dN_T of the re-engagement speed N_WE transmitted by the engine control unit of the internal combustion engine. In addition to the engine speed N (gear X) of the internal combustion engine for the current gear X, the electronic control unit also receives the empirically determined stored shift delay time t_SV_DU as information. The virtual engine speed N_v (gear X) is determined as a function of the shift delay time t_SV_DU, preferably by subtracting a speed offset dN_Offset from the current engine speed N (gear X), which is calculated by multiplying the gradient -dN / dt of the current engine speed N (gear X) by the shift delay time t_SV_DU.

[0020] For the sake of completeness, the figure also shows the total shift delay time t_SV_SE for the entire gearshift process, from the gearshift command to the end of the shift. The speed curve N (gear X-1) of the new gear is also shown. The speed drop -dN_SV is caused by the shift delay time t_SV_DU.

[0021] Finally, we would like to point out the special feature of double or multiple downshifts: The shift delay times of single comfort downshifts with large deceleration gradients are too long to ensure the minimum target reversing speed even for several consecutive shifts. Accordingly, multiple downshifts are implemented with faster shift speeds if necessary.

[0022] After an immediate downshift carried out by the invention, an upshift suppression is preferably activated for a predetermined time in order to prevent oscillations.

Claims

[1] Method for shift point control in automatic transmissions in motor vehicles with an internal combustion engine, in which upshifts and downshifts are triggered by means of an electronic control unit via shift characteristics stored therein, whereby in overrun mode of the internal combustion engine an immediate downshift (RS) is triggered by means of the electronic control unit independently of a currently relevant shift characteristic depending on a re-engagement speed (N_WE) and a shift delay time (t_SV_DU) characterized by that the shift delay time (t_SV_DU) is the empirically determined and stored delay time during a gear change starting with a shift sequence until the speed reversal due to the interruption of the traction of a clutch responsible for the current gear (gear X). [2] Method according to claim 1, characterized bythat the reactivation speed (N_WE) is a required speed of the combustion engine for switching from unfired to fired overrun mode or for maintaining the overrun cut-off. [3] Method according to one of the preceding claims, characterized by that the immediate downshift (RS) is triggered when a virtually determined engine speed (N_v (gear X)) reaches a predetermined minimum permissible target reversing speed (N_ZU), wherein the target reversing speed (N_ZU) is a target speed at a defined safety distance from the reactivation speed (N_WE) transmitted by the engine control of the internal combustion engine. [4] Method according to claim 3 characterized bythat the electronic control unit receives the empirically determined stored shift delay time (t_SV_DU) as information in addition to the engine speed (N (gear X)) of the internal combustion engine for the current gear (gear X) and that the virtual engine speed (N_v (gear X)) is determined depending on the shift delay time (t_SV_DU). [5] Method according to claim 4 characterized by that the virtual engine speed (N_v (gear X)) is calculated by subtracting a speed offset (dN_Offset) from the current engine speed (N (gear X)), which is determined depending on the gradient (-dN / dt) of the current engine speed (N (gear X)) and the shift delay time (t_SV_DU). [6] Method according to one of the preceding claims, characterized by that the reset speed (N_WE) is variable depending on different operating parameters. [7] Gear change control device for carrying out the method according to one of the preceding claims with an electronic control unit which has a correspondingly programmed function module.

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