Method for engaging a positive shift element to realize a gear in an automatic transmission, wherein at least one further friction shift element is involved in the gear to be engaged

Abstract

Method for engaging a positive shifting element to realize a gear in an automatic transmission, wherein at least one further friction shifting element is involved in the gear to be engaged and a shifting element not involved in the gear to be engaged and serving as a synchronizing shifting element is controlled in order to synchronize the engaging positive shifting element, characterized in that the further friction shifting element involved in gear engagement is closed and then opened in a defined manner or brought into slip in order to ensure the engagement of the positive shifting element.

Description

[0001] The present invention relates to a method for engaging a positive shifting element for realising a gear in an automatic transmission, wherein at least one further friction shifting element is involved in the gear to be engaged, according to the preamble of patent claim 1.

[0002] During gear engagement processes in automatic transmissions, in which a positive-locking shift element to be engaged must be synchronized and at least one other friction shift element is involved, according to the prior art, a shift element not involved in the gear to be engaged and serving as a synchronizing shift element is also activated in order to synchronize the positive-locking shift element being engaged. If the positive-locking shift element is engaged, a disadvantageous torque is generated on the positive-locking shift element, even though the synchronizing shift element is already disengaged. This can lead to the inability to push the claw of the positive-locking shift element to the end stop.

[0003] Comparable procedures are known from the documents DE 10 2009 028 305 A1 and DE 10 2009 000 253 A1.

[0004] The present invention is based on the object of specifying a method for engaging a positive shifting element to realize a gear in an automatic transmission, wherein at least one further friction shifting element is involved in the gear to be engaged and a shifting element not involved in the gear to be engaged and serving as a synchronizing shifting element is controlled in order to synchronize the engaging positive shifting element, by the implementation of which the torque on the engaging positive shifting element is reduced after the synchronizing shifting element has been disengaged.

[0005] This object is achieved by the features of patent claim 1. Further embodiments and advantages of the invention emerge from the subclaims.

[0006] Accordingly, a method is proposed for engaging a positive shifting element to implement a gear in an automatic transmission, wherein at least one further friction shifting element is involved in the gear to be engaged and a shifting element not involved in the gear to be engaged and serving as a synchronizing shifting element is controlled in order to synchronize the engaging positive shifting element, within the scope of which a further friction shifting element involved in gear engagement is closed and then opened in a defined manner or brought into slip in order to ensure the engagement of the positive shifting element.

[0007] In this process, an additional frictional shift element not directly required for synchronization but involved in gear engagement is brought to its current transmission limit plus a pressure offset, so that the differential speed in this shift element is zero. Depending on the engagement time of the claw of the engaging positive shift element, the pressure on the additional frictional shift element is reduced so that slippage can occur at this shift element. This reduces the torque on the claw of the engaging positive shift element to be engaged, allowing the claw to be pushed through to the end stop.

[0008] If the end stop is detected by a corresponding sensor, the additional friction switching element is fully closed. If no sensor is provided to detect the end stop, the additional friction switching element is fully closed after a specified period of time following the start of the pressure reduction.

[0009] The invention is explained in more detail below with reference to the attached figure, which shows the pressure curve at the engaging positive-locking switching element, at the further friction-locking switching element, at the synchronizing switching element and at a third switching element involved as a function of time, as well as the differential speed at the engaging positive-locking switching element and the torque curve at the engaging positive-locking switching element according to the prior art and according to the method according to the invention as a function of time.

[0010] In the attached figure, curve A represents the temporal progression of the pressure at a third shifting element involved in the gear; this shifting element is already engaged. Curve B represents the temporal progression of the pressure at the further frictionally engaged shifting element involved in the gear, with curve C representing the temporal progression of the pressure at the synchronizing shifting element and curve D representing the temporal progression of the pressure at the engaging positive-locking shifting element. Furthermore, curve E represents the temporal progression of the differential speed at the engaging positive-locking shifting element, with curves F and G representing the temporal progression of the torque at the engaging positive-locking shifting element according to the prior art and the method according to the invention.

[0011] At time t_0, the engagement of the positive-locking shift element is initiated. For the purpose of synchronizing the positive-locking shift element, a synchronizing shift element that is not required for the gear to be engaged is filled and closed at time t_1 (curve C). At the same time t_1, the pressure of another frictionally engaged shift element that is not directly required for synchronization but is involved in gear engagement is increased (curve B), bringing it to its current transmission limit plus a pressure offset, whereby the differential speed in this shift element is zero. This pressure is maintained until time t_2.

[0012] Between time t_1 and time t_2, the pressure at the synchronizing switching element increases and the differential speed of the claw of the engaging positive-locking switching element is reduced.

[0013] At time t_2, the pressure in the additional friction shift element is reduced so that slippage can occur at this shift element. Subsequently, at time t_3, the pressure at the engaging positive shift element is increased to engage the positive shift element. Time t_2 can be determined either via the synchronization duration of the positive shift element or based on the signals from a position sensor that detects the position of the claw of the positive shift element.

[0014] The differential speed of the claw of the engaging positive-locking shift element is further reduced and reaches zero at time t_4, when the pressure on the other friction shift element reaches a minimum. This reduces the torque on the engaging claw of the engaging positive-locking shift element (curve G) compared to the prior art (curve F), allowing the claw to be pushed through to the end stop. The synchronizing shift element is deactivated.

[0015] The additional friction switching element is fully closed when the end stop of the claw of the positive-locking switching element is detected by a corresponding sensor; in the example shown in the attached figure, this occurs at time t_5. If no sensor is provided to detect the end stop, the additional friction switching element is fully closed after a predetermined period of time following the beginning of the pressure reduction in the additional friction switching element, increasing the torque on the claw of the positive-locking switching element. Reference symbol A temporal progression of the pressure on a third switching element involved in the gear B temporal progression of the pressure on the other frictional switching element involved in the gear C temporal progression of the pressure at the synchronizing switching element D temporal progression of the pressure on the positive-locking switching element to be switched on E temporal progression of the differential speed at the positive switching element to be engaged F Time course of the torque at the positive switching element to be engaged according to the state of the art G temporal course of the torque at the positive switching element to be engaged according to the present invention

Claims

[1] Method for engaging a positive-locking switching element to realize a gear in an automatic transmission, wherein at least one further friction switching element is involved in the gear to be engaged and a switching element not involved in the gear to be engaged and serving as a synchronizing switching element is controlled in order to synchronize the positive-locking switching element to be engaged, characterized by , that the further friction switching element involved in engaging the gear is closed and then opened in a defined manner or brought into slippage in order to ensure the engagement of the positive-locking switching element. [2] Method for switching on a positive locking switching element, according to claim 1, characterized by, that the further friction switching element involved in gear engagement is brought to its current transmission limit plus a pressure offset, so that the differential speed in this switching element is zero, whereby, depending on the engagement time of the claw of the engaging positive-locking switching element, the pressure on the further friction switching element is reduced, such that slippage can occur on the further friction switching element, whereby the torque on the claw to be engaged of the engaging positive-locking switching element is reduced and a pushing of the claw to the end stop is made possible. [3] Method for switching on a positive locking switching element, according to claim 2, characterized by, that the time of the pressure reduction on the further friction switching element is determined either via the synchronization period of the positive locking switching element or on the basis of the signals of a position sensor that detects the position of the claw of the positive locking switching element. [4] Method for switching on a positive locking switching element, according to claim 2, characterized by , that the further friction switching element is completely closed when the end stop of the claw of the positive locking switching element is detected by a corresponding sensor. [5] Method for switching on a positive locking switching element, according to claim 2, characterized by , that the further friction switching element is completely closed after a predetermined period of time following the start of the pressure reduction in the further friction switching element.

Images