Abstract:
A method of operating a transmission device comprising friction-locking and form-locking shift elements for obtaining different gear ratios. A shift request for engaging a shift element undergoes a time delay dependent upon an operating state prior to a time of engagement of the shift element. A rotational speed differential between halves of the shift element lies within a rotational speed differential window required for the engagement procedure is assigned to the time of engagement. A gradient of the transmission input speed is ascertained at the time of the shift request, and the actual gradient is subsequently monitored and compared with the gradient that existed at the time of the shift request. If an absolute deviation greater than a threshold value is ascertained, the time delay is changed or an actuation of another shift element to be disengaged is varied such that the deviation is reduced below the threshold value.

Description:
This application is a National Stage completion of PCT/EP2010/054313 filed Mar. 31, 2010, which claims priority from German patent application serial no. 10 2009 002 203.1 filed Apr. 6, 2009. 
     FIELD OF THE INVENTION 
     The invention relates to a method for operating a transmission device comprising a plurality of friction-locking and form-locking shift elements. 
     BACKGROUND OF THE INVENTION 
     In automatic transmissions known from practical applications, which comprise friction-locking shift elements and form-locking shift elements for obtaining different gear ratios, the shift command for engaging a form-locking connection by applying force is triggered by a transmission control or transmission software implemented in the transmission control with a certain time delay before the synchronization point of the form-locking shift element is reached. 
     The time delay is influenced to a considerable extent by the operating temperature of the transmission oil, inter alia, in particular when the form-locking shift elements of automatic transmissions are hydraulically actuated. 
     The time delay that is required, in a particular case depending on the operating state, or the time period between the time of the shift request and the engagement time of the form-locking shift element, is preferably determined empirically and, during operation of an automatic transmission, is determined as a function of the gradient of a transmission input speed or an equivalent rotational speed parameter. 
     This approach should ensure that events which delay implementation of the shift command such as signal transit times, hydraulic delays, covering the distance to engage the form-locking connection, and the like, are taken into account to the extent that a rotational speed differential between the halves of the shift elements of the form-locking shift element to be engaged lies within a predefined rotational speed differential window at the engagement time, wherein all of the rotational speed differentials encompassed by the rotational speed differential window represent a precondition for comfortable engagement of the form-locking shift element. 
     Document DE 197 56 637 A1 makes known a shift device for connecting components of a transmission rotating at different speeds and at least one shift group, wherein the shift device is actuated by a control fluid. A unit containing valves, shift cylinder pistons, and shift elements is provided for each shift group of the transmission. Pulse-operated 2/2 directional control valves are used as the triggering valves. A position-measuring system is used to determine the actual position of the piston relative to the shift cylinder of a shift element. When gears are meshed to form a torque-transferring connection, the shift force and shifting time are adjusted in order to attain variable synchronization times and faster shifting times. 
     The above-described transmission devices have the problem, however, in that spontaneous changes in the gradient of the transmission input speed or the equivalent rotational speed parameter that results, for example, from a great change in the gas pedal position of a vehicle or strong braking of the vehicle by the driver cannot be taken into account to a desired extent after the time of the shift request to engage a form-locking shift element. 
     This is due to the fact that the gradient that exists at the time of the shift request no longer corresponds to the actual gradient, and the engagement time of the form-locking shift element determined at the time of the shift request across the selected time period no longer coincides with the point of time at which the rotational speed differential of the form-locking shift element lies within the rotational speed differential window required for comfortable engagement of the form-locking shift element. If the form-locking shift element is then engaged outside of the desired rotational speed differential window, shifting noises are produced that affect driving comfort, and torque reactions occur in the drive train, which can be perceived by a driver in the form of jerks. 
     DE 102 44 023 A1 shows such a method for operating a transmission device comprising a plurality of fiction-locking and form-locking shift elements for obtaining different gear ratios. 
     SUMMARY OF THE INVENTION 
     The problem addressed by the present invention is therefore that of providing a method for operating a transmission device comprising a plurality of friction-locking and form-locking shift elements for obtaining different gear ratios, with which shifting that involves at least one form-locking shift element and affect driver comfort are easily prevented. 
     In the method for operating a transmission device comprising a plurality of friction-locking and form-locking shift elements for obtaining different gear ratios, a shift request to engage a form-locking shift element undergoes a time delay dependent upon an operating state prior to an engagement time of the form-locking shift element. At the engagement time, a rotational speed differential between the halves of the shift elements of the form-locking shift element lies within a rotational speed differential window required for the engagement procedure. 
     According to the invention, a gradient of the transmission input speed or an equivalent rotational speed parameter is ascertained at the time of the shift request, and the actual gradient is subsequently monitored and compared with the gradient that existed at the time of the shift request, wherein, if an absolute deviation greater than a threshold value is ascertained, the period of time is changed. 
     This means that, given a predefined deviation between the gradient at the shift request time and an actual gradient of the transmission input speed or the equivalent rotational speed parameter, action is taken to remain within the time period—which was calculated in advance or selected depending on the operating state—between the generation of the shift request and the engagement time of the form-locking shift element or the engagement of the form-locking shift element by correcting the gradient, or to vary the engagement speed of the form-locking shift element, and to be able to easily engage the form-locking shift element with a high level of shifting comfort at a rotational speed differential that lies within the rotational speed differential window. 
     Given a positive deviation between the actual gradient and the gradient that existed at the time of the shift request for a downshift, the time period is shortened in an advantageous variant of the method according to the invention, wherein the rotational speed differential between the halves of the shift elements of the form-locking shift element that is present after expiration of the shortened time period lies at least approximately within the rotational speed differential window. It is thereby easily ensured that the requested shifting can be carried out with a high level of comfort. 
     Given a negative deviation between the actual gradient and the gradient that existed at the time of the shift request for a downshift, the time period is extended in a variant of the method according to the invention, wherein the rotational speed differential between the halves of the shift elements of the form-locking shift element that is present after expiration of the extended time period lies at least approximately within the rotational speed differential window, and shifting with a high level of comfort is ensured. 
     The time period between the time of the shift request for a downshift and the engagement time of the form-locking shift element can be adjusted in a manner dependent upon the operating state by varying the actuating force of the form-locking shift element, in order to perform shifting with a high level of comfort. 
     If the intention according to the request is to shorten the time period, the actuating force of the form-locking shift element is easily increased, in one variant of the method according to the invention. 
     If the intention is to extend the time period to ensure that shifting is carried out with a high level of comfort, the actuating force of the form-locking shift element is reduced, in a further variant of the method. 
     The actuating force is varied by changing the control current when the form-locking shift element is actuated electrically, while the actuating force can be varied by changing the actuating pressure when the form-locking shift element is actuated pneumatically or hydraulically. 
     Alternatively, it is also possible to vary the actuating force by applying a counter-pressure that counteracts the actuating pressure when the form-locking shift element is actuated hydraulically. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and advantageous developments of the invention will become apparent from the claims and the embodiments, the principle of which is described with reference to the drawing; for the sake of clarity, the same reference characters are used for components having the same design and function in the description of the embodiments. 
       They show: 
         FIG. 1  a gearwheel pattern of a transmission device comprising a plurality of friction-locking and form-locking shift elements for obtaining different gear ratios; 
         FIG. 2  a shift pattern of the transmission device according to  FIG. 1 ; and 
         FIG. 3  a plurality of alternative graphs of various operating state parameters of the transmission device according to  FIG. 1  during a downshift. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a gearwheel pattern of a transmission device  1  or a multi-stage transmission, which is basically known from the unpublished German patent application DE 10 2008 000 429.4 which belongs to the applicant. The transmission device  1  comprises a drive shaft  2  and an output shaft  3  which, in the installed state in a vehicle, is connected to an output drive of the vehicle, while the drive shaft  2  is operatively connected to a drive motor. 
     The transmission device  1  also comprises four planetary gear sets P 1  to P 4 , wherein the first and second planetary gear sets P 1 , P 2 , which are preferably in the form of minus planetary gear sets, form a shiftable, input-side gear set, while the third and fourth planetary gear sets P 3 , P 4  are the main gear set. The transmission device  1  also comprises six shift elements A to F, of which shift elements C, D and F are designed as brakes, and the shift elements A, B and E are designed as shifting clutches. 
     Using the shift elements A to F, selective shifting of nine forward gears “ 1 ” to “ 9 ” and one reverse gear “R” can be attained using the shift logic presented in greater detail in  FIG. 2 ; to obtain a gear ratio in the transmission device  1  or to establish power flow in the transmission device  1 , three shift elements must be moved into an engaged operating state or held there simultaneously in every case except for the fourth transmission ratio step “ 4 ”. 
     The shift elements A and F are designed as form-locking shift elements in the present case, to reduce drag torques produced by disengaged, friction-locking shift elements during operation of the transmission device  1  as compared to transmission devices comprising only friction-locking shift elements. Since form-locking shift elements can be transferred from a disengaged operating state to an engaged operating state with a desired level of comfort in general only within a very narrow rotational speed differential band or rotational speed differential window encompassing the synchronous rotational speed, the synchronization of a form-locking shift element to be engaged is supported and ensured without additional structural embodiments due to the method according to the invention, which is described in greater detail in the following. 
     The variants of the method according to the invention described below are advantageous in the case of downshifts in particular, in which a friction-locking shift element is disengaged and a form-locking shift element is engaged in the powerflow of the transmission device  1 , wherein the form-locking shift elements A and F of the transmission device  1  under consideration can be in the form of claw clutches designed with or without additional synchronization. 
     The mode of operation of different variants of the method according to the invention is explained in greater detail in the following with reference to the graphs of a plurality of operating state parameters of the transmission device  1  according to  FIG. 1 , which are plotted as a function of time t in  FIG. 3 . 
     In the courses of operating states which form the basis for the graphs of the operating state parameters of the transmission device  1  presented in  FIG. 3 , the fifth transmission ratio step “ 5 ” is engaged in the transmission device  1  in every case at a point of time T 0 . To obtain the fifth transmission ratio step “ 5 ”, the shift elements A, B and E are held in the engaged state, while the shift elements C, D and F are disengaged. 
     At a point of time T 1 , a shift request is generated for a downshift from the fifth transmission ratio step “ 5 ” to the fourth transmission ratio step “ 4 ”, which is why a shift course SV abruptly drops from the level of the fifth transmission ratio step “ 5 ” to the level of the fourth transmission ratio step “ 4 ”. 
     To carry out the requested downshift from the fifth transmission ratio step “ 5 ” to the fourth transmission ratio step “ 4 ”, the friction-locking shift element B must be disengaged or disengaged from the power flow of the transmission device  1 , and the form-locking shift element F must be engaged in the power flow of the transmission device  1  or transferred from the disengaged operating state to the engaged operating state thereof. The friction-locking shift element B is therefore acted upon up to point of time T 1  with an actuating pressure p_B that corresponds to the engagement pressure value at which the shift element B is fully engaged, while the form-locking shift element F is acted upon with a pressure value of the actuating pressure p_F_ein that is substantially equal to 0. 
     At point of time T 1 , a transmission input speed or an equivalent turbine rotational speed n_t corresponds to a synchronous rotational speed n_t_syn(“ 5 ”) of the fifth transmission ratio step “ 5 ”, thereby resulting in a rotational speed differential n_diff_F at the rotational speed level n_diff_F(“ 5 ”) in the region between the halves of the shift elements of the form-locking shift element F. 
     At point of time T 1 , at which the shift request for the downshift from the fifth transmission ratio step “ 5 ” to the fourth transmission ratio step “ 4 ” takes place, the actuating pressure p_B drops abruptly from the engagement pressure level to a first intermediate pressure value p_B 1  and remains substantially at this pressure level until point of time T 2 . Next, the actuating pressure p_B of the friction-locking shift element B is reduced to a second intermediate pressure value at which the shift element B transitions into a slip mode. 
     Reducing the transmission capability of the friction-locking shift element B causes the turbine rotational speed n_t to increase in the direction of the synchronous rotational speed n_t_syn(“ 4 ”) of the fourth transmission ratio step “ 4 ” at the point of time T 3  at which the shift element B is acted upon with the second intermediate pressure value p_B 2 , starting at the rotational speed level of the synchronous rotational speed n_t_syn(“ 5 ”) of the turbine rotational speed n_t. In turn, this causes the rotational speed differential n_diff_F of the form-locking shift element F to decrease, starting at point of time T 3 , in the direction of the synchronous rotational speed n_diff_F(“ 4 ”) which is equal to 0. At a point of time T 4 , the actuating pressure p_F_ein of the form-locking shift element F is raised to an engagement pressure level and is left at this pressure level. 
     The gradient of the turbine rotational speed n_t is determined at the point of time T 1 . At the same time, monitoring of the actual gradient of the turbine rotational speed n_t is started and is permanently compared to the gradient at shift request time T 1 . If an absolute deviation greater than a threshold value is determined, one of the actions described below is taken to change a time period t 1  determined depending on the operating state at the shift request time T 1  in a manner that ensures a high level of shifting comfort, or to decrease a deviation between the gradient of the turbine rotational speed n_t at the shift request time T 1  and an actual operating time below the predefined threshold value. 
     The time period t 1  extends between the engagement time T 1  and a shifting time T 5  of the form-locking shift element F determined depending on the operating state at time T 1  as a function of the gradient of the turbine rotational speed n_t and occurrence of events that delay the shift request, such as a signal transit time, hydraulic delays, covering the distance to engage the form-locking shift element, and the like, wherein the point of time T 5  varies greatly depending on the temperature of the transmission oil given the form-locking shift element F which is actuated hydraulically in the present case. The time period t 1  is determined via computation using a model of the transmission device  1 , or is read from an empirically determined characteristic map. 
     In a first variant of the operating state course which is used as the basis for the graphs of the operating state parameters of the transmission device  1  according to  FIG. 1 , the turbine rotational speed n_t increases at a point of time T 6  due, for example, to a spontaneous change in actuation of the gas pedal by the driver, with a steeper gradient in the direction of the synchronous rotational speed n_t_syn(“ 4 ”) than at point of time T 1 . At a point of time T 7 , the deviation between the gradient at the shift request time T 1  and the actual gradient of the turbine rotational speed n_t is greater than the predefined threshold value. The engagement speed of the form-locking shift element F is increased temporarily by raising the actuating pressure p_F_ein starting at the point of time T 7  along the single-dot-dash line, and the shift element is engaged at a point of time T 8  which occurs prior to the predefined engagement time T 5  of the form-locking shift element F. The rotational speed differential n_diff_F of the form-locking shift element at the point of time T 8  corresponds at least approximately to the synchronous rotational speed n_diff_F(“ 4 ”) which lies within the predefined rotational speed differential window, within which the requested shifting can be carried out with high shifting quality. 
     Alternatively, in a further variant of the method according to the invention, at the point of time T 7  at which a positive deviation between the actual gradient and the gradient of the turbine rotational speed n_t determined at the shift request time T 1  exists, the transmission capability of the friction-locking shift element B to be disengaged is raised temporarily along the four-dot-dash line from the second intermediate pressure value p_B 2  to a higher, third intermediate pressure value p_B 3 . As a result, the actual gradient of the turbine rotational speed n_t is reduced, and the rotational speed differential n_diff_F of the form-locking shift element F reaches the synchronous rotational speed n_diff_F(“ 4 ”) at the shifting time T 5  determined at shift request time T 1 , wherein the actuating pressure p_B is reduced to substantially 0 at the point of time T 5  at which the downshift has been completed. 
     If, at the point of time T 6 , a negative deviation is determined between the actual gradient of the turbine rotational speed n_t and the gradient of the turbine rotational speed n_t determined at the shift request time T 1 , which is triggered, for example, by actuation of the vehicle brake by the driver while friction-locking shift element B is partially engaged, or because the driver spontaneously lifts his foot off of the gas pedal, an engagement speed of the form-locking shift element F is reduced between the points in time T 7  and T 5  by temporarily lowering the actuating pressure p_F_ein of the form-locking shift element F, which is depicted graphically in  FIG. 3  by the two-dot-dash line, and the form-locking shift element F is not engaged until a point of time T 9  at which the turbine rotational speed n_t has reached the synchronous rotational speed n_t_syn(“ 4 ”) of the fourth transmission ratio step “ 4 ”. As a result, the time period t 1  determined at the shift request time T 1  is adapted or extended in a manner dependent upon the operating state by varying the actuating force of the form-locking shift element F, in order to carry out the requested shifting with the desired shifting quality which preferably remains consistently high. 
     If the form-locking shift element F is designed with a so-called dual-acting piston which can be acted upon in the region of a first effective area with the actuating pressure p_F_ein in the closing direction of the form-locking shift element F, and in the region of a second effective area with a counter-pressure p_F_aus that acts in the opening direction of the form-locking shift element F, the actuating force of the form-locking shift element F is reduced in the closing direction by temporarily increasing the counter-pressure p_F_aus of the form-locking shift element F along the three-dot-dash line between the points in time T 7  and T 5 , and the form-locking shift element F is fully engaged at the point of time T 9  to the same extent as in the above-described temporary reduction of the actuating pressure p_F_ein of the form-locking shift element F. 
     In the variant of the method according to the invention that was just described, the form-locking shift element is acted upon with the counter-pressure p_F_aus between the points in time T 0  and T 4  at the disengagement pressure level of the form-locking shift element F, while the actuating pressure p_F_ein which acts in the engagement direction is substantially equal to 0. At the point of time T 4  the counter-pressure p_F_aus is reduced from the disengagement pressure level to substantially 0, while the actuating pressure p_F_ein of the form-locking shift element F is raised from 0 abruptly to the engagement pressure level of the form-locking shift element F. 
     Between the points in time T 7  and T 5 , the actuating pressure p_F_ein of the form-locking shift element F is left at the engagement pressure level, while the counter-pressure p_F_aus of the form-locking shift element is raised in this time window to an intermediate pressure level, as indicated by the three-dot-dash line, and is lowered back to 0 at the point of time T 5  in order to extend the time period t 1  to the extent described above to the point of time T 9 , and to be able to carry out the requested downshift with high shifting quality. 
     The graphs of the operating state parameters of the transmission device  1  shown using solid lines in  FIG. 3  represent the course of the operating state of the transmission device  1  that occurs when a downshift is requested from the fifth transmission ratio step “ 5 ” to the fourth transmission ratio step “ 4 ” and it is determined that an absolute deviation between the actual gradient of the turbine rotational speed n_t and the gradient of the turbine rotational speed n_t determined at shift request time T 1  is not greater than the predefined threshold value. The dash-dotted plots of the operating parameters p_F_ein, p_F_aus and p_B occur when the above-described variants of the method according to the invention are implemented if it is determined that an absolute deviation exists between the actual gradient of the turbine rotational speed n_t and the gradient of the turbine rotational speed n_t determined at the shift request time T 1 . The objective in each case is to always carry out the requested downshift with the same high level of shifting quality. 
     The time period t 1  determined at the shift request time T 1  is shortened, extended, or is left at the specified value in order to guarantee the desired shifting quality in every case. 
     Depending on the particular application, it is also possible to carry out the above-described actions for attaining a desired shifting quality, i.e. vary the actuating force of the form-locking shift element F or increase the transmission capability of the friction-locking shift element B to be disengaged, in a suitable manner simultaneously and in a harmonized manner to attain the desired shifting quality. 
     REFERENCE CHARACTERS 
     
         
           1  transmission device 
           2  drive shaft 
           3  output shaft 
         “ 1 ” to “ 9 ” gear ratio for forward driving 
         A to F shift element 
         n_diff_F rotational speed differential of the form-locking shift element F 
         n_diff_F(“ 5 ”) rotational speed differential of the form-locking shift element F 
         n_diff_F(“ 4 ”) synchronous rotational speed of the form-locking shift element F 
         n_t turbine rotational speed 
         n_t_syn(“ 5 ”) synchronous rotational speed of the turbine rotational speed 
         n_t_syn(“ 4 ”) synchronous rotational speed of the turbine rotational speed 
         p_B actuating pressure of the friction-locking shift element B 
         p_B 1  first intermediate pressure value 
         p_B 2  second intermediate pressure value 
         p_B 3  third intermediate pressure value 
         p_F_aus counter-pressure 
         p_F_ein actuating pressure 
         P 1  to P 4  planetary gear set 
         SV shift course 
         T 0  to T 9  discrete point of time 
         t time 
         t 1  time period