Method for controlling a transmission of a vehicle

Abstract

Described is a method for the control of a transmission of a motor vehicle, especially an automatic transmission, with hydraulically activated shifting elements. The shifting elements are shifted to engage or disengage by means of specified pressure pattern (pkab, pkzu) which have been input into an electronic control unit. In the said method, an applied pressure (pkab) on a disengaged shifting element, by the release of a force flow generated by a holding pressure (pkab-h), is reduced to a shift pressure (pkab-sd) and a transmission input speed of rotation (nt) experiences a change dependent upon the applied pressure (pkab) on a disengaged shifting element. An adaption of the pressure pattern (pkab) of a disengaged shifting element is dependent upon the deviation of an actual release time (TLZ-T) of the change of the transmission input speed of rotation from a specified release time (TLZ) of the transmission input speed of rotation, and is designed in such a manner that, the change in speed of rotation of the transmission input speed of rotation (nt), occurs at a shifting at the preset release time (TLZ) or in a window of time incorporating that same preset release time (TLZ).

Description

[0001] The invention concerns a method for the control of a transmission of a motor vehicle in accord with the concept as more closely defined in Claim 1.

[0002] In the case of known automatic transmissions, gear shifting, is carried out by, among other names, “overrunning shifting”. In this said shifting, in the force flow of an input power train of a motor vehicle, a first force-fit clutch is opened in a specified pressure pattern. Simultaneously (or nearly so) a second clutch shifts into a second opening, this time in a slip condition, by means of an additional pressure pattern. The pressure pattern of the clutches taking part in said shifting is specified by an electronic control unit and exercised on the clutches by electro-magnetic positioning devices.

[0003] In general, where this overrunning shifting is concerned, the applied pressure on a disengaged clutch is reduced to shift-pressure by a holding pressure dependent upon the fluid filling of an engaged clutch. Because of the lessening of the shift-pressure, the power transfer capability of the disengaged clutch reduces itself on a continuing basis, and the transmission input speed of rotation begins to increasingly deviate from a synchronized speed of rotation of the prior actual gear ratio, i.e. the “old” gear position.

[0004] The time, at which the deviation of the transmission input speed of rotation from the run of the synchronized speed of rotation of the actual gear ratio occurs, is designated as a “release time” and at the same time represents that instant at which the driver, subjectively makes a change in the driving conditions of the of the motor vehicle, namely, gear shifting. This is carried out especially following a kickdown, after which the pressure applied on the disengaged clutch is reduced and a take-off drive moment reduces itself, before the true gear shift process for the achievement of the desired gear ratio, i.e., the “new” gear. The synchronization is initiated by means of an increasing power transfer capability of an engaged clutch in the automatic transmission.

[0005] For the increasing of the quality of shifting, after the release time, there is provided a control of a gradient in the transmission input speed of rotation which is dependent upon the pressure being applied to the disengaged clutch, by means of which, a time span is created for a speed of rotation change to approach a synchronized rotational speed in accord with the desired new ratio change of the transmission.

[0006] Because of the growing requests for shifting quality and the requirement for spontaneity, the demands on the functionality of the software of the automatic transmission also increase. In order to meet these demands, the consensus of the practice has now embraced the idea, of placing the release time of the transmission input speed of rotation very close to the beginning of a shift operation.

[0007] However, in achieving the above goal, a problematical situation arises, in that the said release time wanders away from a set, specified time, during the progress of operation where known automatic transmissions are concerned, as a result of tolerances, scattering, and further negative influences, such as, for instance, frictional values which change their characteristics during the time of operation, and/or ongoing component wear. As a result, ease of shifting becomes poorer and the spontaneity of the automatic transmission is impaired. Known efforts to hold the release time of the transmission input speed of rotation nearly constant, are, at least to this date, connected with considerable costs in labor and money, all leading to no satisfactory results.

[0008] Thus, it is the purpose of the present invention to make available a method, with which the release time can be so adjusted, over the life time of an automatic transmission, that the said release time approaches as nearly as possible the beginning of a shifting action and occurs at a specified time.

[0009] In accord with the invention, this purpose is achieved with a method for the control of a transmission of a motor vehicle following the principles of Claim 1 or Claim 2 of the claims of this invention.

[0010] With the aid of the invented method, in which an adaption of the pressure pattern of a disengaged shifting element, dependent on a deviation between an actual release time of the transmission input speed of rotation and a specified release time, to this effect, provision is made, that the change in rotational speed of the transmission input can be carried out, when a shift is made either at the specified release time or within a period of time including the said specified release time, in an advantageous manner, the time of the change of the transmission input speed of rotation, that is to say, the actual release time, can be held constant during the entire operational life for the transmission with the same shifting. Further this can specifically be made to occur at the start of the shifting, in order to bring about a desired high spontaneity detectable by the driver as well as achieving a good quality of shifting. Thereby, the behavior of the transmission closely approaches the driver's wish for capacity. Further, scattering and tolerances degradation caused by wear of components which would negatively affect the behavior of shifting, can be specifically compensated for over the said operational life of the transmission.

[0011] Moreover, the invented method offers the advantage, that in the case of multiple gear changes, that is, a multiplicity of sequential changes, a synchronous release time of a second shifting element of a second shifting can be adjusted to an actual synchronous time of a first shifting element. This permits that after the synchronous time of the first shifting element, no all too long a dead time exists in regard to the increase of the transmission input speed of rotation. Further, the increase of the transmission input speed of rotation at the same time is, to the sensations of a driver, the same as continual.

[0012] Further advantages and developments of the invention arise from the claims and from the following description made with the aid of the drawing, the principles of which are shown by embodiments shown in the drawing as principles. There is shown in:

[0013] FIG. 1 a simplified set of mutually corresponding, qualitative curves of the speed of rotation of a transmission with plotted pressure relations of a disengaged clutch as well as the pressure relations of an engaged clutch, and

[0014] FIG. 2 a program flow chart of an adaption-routine in accord with the invention.

[0015] The curves of FIG. 1, schematically presented, represent the speed of rotation of a transmission input, which, in this case is also the speed of rotation of a converter nt, a pressure pattern pkab of a disengaged shift element, this being, for instance, a disengaged clutch, and as well a pressure pattern pkzu of an engaged switching element this being, for instance, a engaged clutch. These named components relate to a method for the control of an automatic transmission, in the case of which, an adaption of the pressure pattern pkab of the disengaged clutch, dependent upon a deviation between an actual release time TTZ-T and a specified release time TTZ of the speed of rotation nt of the turbine wheel, is so designed, that the speed of rotation change nt of the turbine wheel is made to occur simultaneously with a gear change (shift) at the specified, preset release time TLZ.

[0016] The shifting elements are designed as hydraulically activated clutches, which, in the case of gear shifting, are shifted open or closed by means of an electronic control apparatus which regulates the pressure patterns shown by curves pkab and pkzu. With this said arrangement, a pressure pkab drops off from the release of a force flow emanating from a holding pressure pkab-h and acting on a shift-pressure pkab-sd, and the speed of rotation nt of the turbine wheel, dependent on the pressure pkab exerted on the disengaged coupling, brings about such a change.

[0017] The pre-set, specified release time TLZ, occurs after a start of the reduction of the pressure pkab, said pressure reduction being effected by the holding pressure pkab-h countering the shift pressure pkab-sd. At this time, during the adaption, the time of a shift is determined as that of the actual release time TTZ-T, at which the speed of rotation nt of the turbine wheel based on one of the actual selected transmission gear ratios, that is, the synchronized speed nt-synalt corresponding to the last selected gear, has overstepped a threshold value nt.

[0018] The threshold value nt-schwell of the turbine speed of rotation upon a power shift, lies in excess of a to-be-expected time in the characteristic pattern of the synchronous speed of rotation nt-synalt of the actual selected gear in the transmission, that is, the selected gear ratio change. When this occurs, the threshold limit appears as a series of values corresponding to the speed of rotation nt of the turbine wheel appears (in FIG. 1) as a straight line, parallel to the curve of the speed of rotation nt of the turbine wheel.

[0019] The numerical quantity of the threshold value nt-schwell is determined in accord with the desired sensitiveness of the reaction of the adaption and also with consideration of the application at the time. As a result, this quantity can lie, advantageously, in a range of from 10 r.p.m. to 50 r.p.m. Obviously, it is a matter for the judgement of the expert if this limit is to be set above the here stated range.

[0020] Referring again to FIG. 1, at a defined shift-pressure pkab-sd of a disengaged clutch, the speed of rotation nt of the turbine wheel begins to climb at a certain slope upward in the direction of a synchronized speed of rotation nt-synneu of the newly targeted gear ratio of the transmission to be achieved. As this is done, the actual release time TLZ-T, is established by means of the intersection of the said straight line of the threshold values nt-schwell with the upward inclined line of the speed of rotation of the turbine wheel nt.

[0021] In order to execute an easily operating down shifting where a gear change ratio of the transmission is done by overrunning shifting, it is necessary, before the clutch to be shifted is brought into the power flow of the output train, to fill said clutch by means of a quick-fill phase tsf. This is carried out along with a successive filling-compensation phase in such a manner that the clutch to be shifted, upon reaching a speed of rotation criterium, at a time before the synchronized speed of rotation nt-synneu of the “new” gear ratio of the transmission has achieved the necessary transmission capability. When this is so carried out, then the desired synchronization of the automatic transmission has been accomplished.

[0022] For this reason, the speed of rotation nt of the turbine wheel, by the application of the holding pressure pkab-h onto the disengaged clutch is maintained at the synchronized speed of rotation ntsynalt of the “old” gear ratio and only after the run-out of this period, is the pressure pkab, now applied to the disengaged clutch, reduced to the shift-pressure pkab-sd.

[0023] By means of the shift-pressure pkab-sd of the disengaged clutch, that is to say, the controllable operation thereof, a simultaneous control of the depicted gradient of the of the speed of rotation nt of the turbine wheel is carried out. This control enables raising the speed of rotation nt of the turbine wheel at an optional, or necessary time to the synchronized speed of rotation nt-synneu of the “new” gear selection. This synchronized speed of rotation nt-synneu of the said “new” gear selection is, in FIG. 1, that part of the curve of the speed of rotation nt of the turbine wheel, which adjoins the more central part of the curve of the speed of rotation nt at a more gradual slope, that is, with a lesser incline.

[0024] In FIG. 2 is presented a Program Flow Chart of an adaption routine for the acquiring of a constant release time TLZ of the speed of rotation nt of the turbine wheel, wherein, at a first step S1 the adaption routine begins. In a second step S2, a test is carried out, as to whether or not, a shift-command has been issued from the electronic control unit of the automatic transmission. In the case of a positive reply, then, in proceeding to Step 3, first a holding phase is introduced, in which the pressure pkab applied on the disengaged clutch is lowered to the holding pressure pkab-h by means of an offset and maintained at that pressure for a specified time-span.

[0025] In a Step 4, which follows Step 3, a shift-pressure phase is started, in which the pressure pkab applied to the disengaged clutch is decreased to the shift-pressure pkab-sd In this shift-pressure phase, there is carried out, dependent on the pressure pkab of the disengaged clutch, a control of the gradient of the speed of rotation nt of the turbine wheel, which, in the curve of the pressure pkab applied to the disengaged clutch, that is, the shift-pressure pkab-sd which is shown in FIG. 1 as a wavy line.

[0026] With the start of the shift-pressure phase, in a step S5 a monitoring of the release time, that is to say, of the actual release time TTZ-T begins. In a following step S6 the speed of rotation nt of the turbine wheel and an output speed of rotation nab is measured. The output speed of rotation nab is input into the computation of a computerized transmission input speed of rotation, which is the same as the turbine wheel speed of rotation, by means of an actual gear ratio iist in the transmission. From the computed speed of rotation of the turbine wheel, once again the threshold value nt-schwell of the speed of rotation nt of the turbine wheel, the curve of which is designed for the true release time LLZ-T, whereby the threshold value nt-schwell is greater by the off-set value than the computerized determined rotational speed of the turbine rotational speed.

[0027] In step S7 a check is made, as to whether or not the speed of rotation nt of the turbine is greater than the threshold value nt-schwell. If the answer is “yes”, the procedure is to the next step S8, wherein the actual release time TLZ-T is determined and input into a reference value for the adaption of the pressure pkab of the disengaged clutch.

[0028] If the check in the step S7 shows that the speed of rotation nt of the turbine wheel is less than the threshold nt-schwell the flow of action, with a dwell period, is returned to the step S6. Then follows anew, a measurement of the speed of rotation nt of the turbine wheel as well as the output speed of rotation nab. Next, in the step S7 which follows step S6 as before, the examination is repeated. This small loop between S6 and S7 will keep on until the criterion of the step 7 is fulfilled, or a break-off limit, such as, perhaps, a maximum number of loopings, is reached.

[0029] In embodiments of the invention, provision can be made, that instead of employing the threshold value nt-schwell for the determination of the actual release time, an applicable threshold of an acceleration impulse or an appropriate threshold of a speed of rotation gradient, or yet an applicable threshold of a measured difference between the speeds of rotation of the shifting elements may be employed.

[0030] The actual release time TTZ-T defined by the adaption routine, is in turn employed for the determination of a correction value adadruck. To carry this out, first, in a Step 9, the value of a deviation tdlz of the known, actual release time TTZ-T from the specified release time TLZ is computed. In a subsequent step S10 an adaption value is calculated by means of a specified characteristic line in the electronic control unit, based upon the deviation tdlz of the already determined release time TLZ-T from the specified release time TLZ. The specified release time TLZ, as an example, can be fed into the transmission control, as a characteristics map KF=f(Cgetr, mmot, nmot, pkuppl, . . . ).

[0031] Moreover, the possibility exists, of determining the correction value adadruck in connection with the deviation of the already determined actual release time from the specified release time TLZ by means of a characteristics map. This characteristics map presents a function of the most different operational parameters of the automatic transmission, for instance, the disengaged clutch. As this is done, in the dependency, one or more values, such as, transmission temperature Cgetr, clutch pressure Pkuppl, motor speed of rotation nmot, motor torque mmot, is incorporated into the characteristics map.

[0032] The adaption value, in the present described variant of the adaptions routine will be added or subtracted to/from the correction values retained in an adaption memory storage. Continuing with the adaption program, in a Step S11 an examination takes place of the correction value adadruck as compared in a positive as well as a negative direction against a specified maximum correction value adadruck-max.

[0033] If the evaluation of the Step 11 shows that the determined correction value adadruck is, in its amount, greater than the specified maximum correction value adadruck-max, then, for the adaption of the pressure run pkab of the disengaged clutch, as a correction value adadruck, the specified maximum correction value adadruck-max will be given and input into the adaption memory. The adaption routine then terminates.

[0034] The differentiating function, i.e. the examination in Step 11 is provided for the purpose of monitoring the adaption as to its plausibility, especially in the case of a system with some run-in time, that is a system with a history of high operating time, a one-time “drop-out” because of extraordinary operational situations of the automatic transmission not to be taken into the evaluation.

[0035] The correction value adadruck, that is, the final adaption value, leads to an increase of the shift-pressure pkab-sd of a later shifting in the amount of the correction value adadruck, if the actual release time TTZ-T of the expired shifting lies before the specified release time TLZ.

[0036] If, however, by means of the above described adaption, an actual release time TTZ-T of the evaluated but expired shifting, lies after the specified release time TLZ, then this leads to a diminution of shift-pressure pkab-sd adapted for a later shifting in the amount of the correction value adadruck, that is, by the computed adaption value.

[0037] The adaption of the pressure curve pkab of the disengaged clutch is realized by means of a change in the shift-pressure pkab-sd of the disengaged clutch. Since the holding pressure pkab-h corresponds with the shift-pressure pkab-sd, then the said change of the shift-pressure pkab-sd of the disengaged clutch can invoke a change of the holding pressure pkab-h of the disengaged clutch along with it.

[0038] In another embodiment of the invention, provision can be made, that the adaption of the pressure distribution pkab of the disengaged clutch, is so designed in dependency of the deviation of the actual release time TLZ-T of the transmission input speed of rotation nt from the specified release time TLZ, can be so arranged that the change of speed of rotation of the transmission input speed of rotation nt upon the shifting within an applicable window of time can be carried out at the specified release time TLZ.

[0039] The goal of the adaption is, in any case, to adjust the release time of the speed of rotation nt of the turbine wheel as closely as possible to that time, at which, the pressure pkab of the disengaged clutch is reduced by the holding pressure Pkabph to the shift-pressure pkab-sd, which is correspondingly, the beginning of the shifting procedure.

REFERENCE NUMBERS

[0040] adadruck Correction value

[0041] adakdruck-max Maximum correction value

[0042] Ctr-getr Transmission temperature

[0043] iist-gear Actual gear ratio of transmission

[0044] mmot Motor Torque

[0045] nmot RPM of motor

[0046] nab RPM of output shaft

[0047] nt RPM of turbine wheel

[0048] nt-schwell Set threshold value (turbine)

[0049] nt-syn-alt Synchronized RPM of turbine wheel of a current real set ratio in the automatic transmission

[0050] nt-syn-new Synchronized RPM of turbine wheel in targeted gear ratio

[0051] pkab Pressure run of a disengaged shift element

[0052] pkzu Pressure run of an engaged shift element

[0053] pkab-sd Shift pressure of a disengaged shift element

[0054] pkab-h Holding pressure

[0055] pkuppl Clutch pressure

[0056] tdlz Deviation of the actual release time from the specified set time

[0057] tf Complete compensation phase of the engaged clutch

[0058] tsf Quick full phase of the engaging clutch

[0059] TLZ release time

[0060] TTZ-T Actual release time.

[0061] S1 to s11 step of the adaption routine

Claims

1. A method for the control of a transmission of a motor vehicle, especially an automatic transmission with hydraulically activated shifting elements, which are shifted into engagement or disengagement by means of a pattern of pressure (pkab, pkzu) which is preset into an electronic control unit, wherein, a pressure (pkab) applied to a disengaged shifting element by the release of a flow of force from a holding pressure (pkab-h) is reduced to a shift-pressure (pkab-sd) and a transmission input speed of rotation (nt), which is dependent upon the pressure (pkab) applied to a disengaged shifting element, is subjected to a change, therein characterized, in that an adaption of the pressure pattern (pkab) of a disengaged shifting element, dependent upon a deviation of an actual release time (TLZ-T) of the transmission input speed of rotation (nt) from a preset release time (TLZ-), is so designed, that the speed of rotation change of the transmission input speed of rotation (nt) can occur at a given shifting at the said specified release time (TLZ).

2. A method in accord with the concept of claim 1, therein characterized, in that an adaption of the pressure pattern (pkab) of a disengaged shifting element, dependent upon a deviation of an actual release time (TLZ-T) of the transmission input speed of rotation (nt) from a preset release time (TLZ) of the transmission drive input speed of rotation is so designed, that the speed of rotation change of the transmission input speed of rotation (nt) does occur upon a given gear shifting at the said specified release time (TLZ).

3. A method in accord with claim 1 or 2, therein characterized, in that the preset release time (TLZ) occurs after a beginning of the reduction of the disengaged shifting element pressure (pkab) to the shift-pressure (pkab-sd) by means of the holding pressure (pkab-h).

4. A method in accord with claims 1 to 3, therein characterized, in that, as an actual release time (TLZ-T), the time of a shifting is determined to be that time at which the transmission input speed of rotation (nt), based on a pattern of a synchronized speed of rotation (nt-syn-alt) of the transmission input speed of rotation of an actual operating gear ratio of the transmission, oversteps a specified threshold value (nt-schwell).

5. A method in accord with claims 1 to 3, therein characterized, in that as an actual release time (TLZ-T) the time of a shifting operation is determined as that time at which an acceleration surge of the motor vehicle exceeds a preset threshold.

6. A method in accord with one of the claims 1 to 3, therein characterized, in that, an actual release time (TLZ-T) is determined as that time of a shifting operation, at which a gradient of the transmission input speed of rotation (nt) oversteps a preset threshold.

7. A method in accord with one of the claims 1 to 3, therein characterized, in that an actual release time (TLZ-T) is determined as that time of a shifting operation, at which a measured change in speed of rotation at the disengaged shifting element oversteps a preset threshold.

8. A method in accord with one of the claims 1 to 7, therein characterized, in that, by means of an adaption of the pressure pattern (pkab) of a disengaged shifting element, the shift-pressure (p-kab-sd) is changed.

9. A method in accord with one of the claims 3 to 8, therein characterized, in that by means of the adaption of the pressure pattern (pkab) of a disengaged shifting element, the holding pressure (pkab-h) of the disengaged shifting element is changed.

10. A method in accord with claim 9, therein characterized, in that the change of the holding pressure (pkab-h) is carried out dependent upon the change of the shift-pressure (pkab-sd).

11. A method in accord with one of the claims 8 to 10, therein characterized, in that the shift-pressure (pkab-sd) is increased for a later shifting operation by a correction value (adadruck), if the actual release time (TLZ-T) of the evaluated shifting occurs before the preset release time (TLZ).

12. A method in accord with one of the claims 8 to 11, therein characterized, in that the shift-pressure (pkab-sd) is diminished by a correction value (adadruck) for a later shifting operation, if the actual release time (TLZ-T) of the evaluated shifting occurs after the preset release time (TLZ).

13. A method in accord with one of the foregoing claims therein characterized, in that, upon the transition to the shift pressure (pkab-sd) a regulation of the gradient of the transmission input speed of rotation (nt) is effected as dependent upon the pressure (pkab) which is exerted on the disengaged shifting element.