Method and control apparatus for operating a vehicle drive train

Abstract

A method for operating a vehicle drive train (1) comprising a prime mover (2), transmission (3), and comprising a driven end (4) may include limiting, during a demand for engaging a form-locking shift element (A, F) of the transmission (3) when a rotational speed of the driven end (4) is close to zero, a rate of change of a transmission input torque present at the form-locking shift element (A, F) to a value. Below the value, forces present at the form-locking shift element (A, F) during an engagement process are less than a load limit. Above the value, irreversible damage to the form-locking shift element (A, F) occurs.

Claims

1. A method for operating a vehicle drive train (1) comprising a prime mover (2), a transmission (3), and comprising a driven end (4), the method comprising: limiting, during a demand for engaging a form-locking shift element (A, F) of the transmission (3) when a rotational speed of the driven end (4) is zero, a rate of change of a transmission input torque at the form-locking shift element (A, F) to a value, wherein below the value, one or more forces at the form-locking shift element (A, F) during an engagement process are less than a load limit, and wherein above the value, irreversible damage to the form-locking shift element (A, F) occurs.

2. The method of claim 1, further comprising varying, in the presence of the demand to engage the form-locking shift element (A, F), a torque at the form-locking shift element (A, F), an actuation force of the form-locking shift element (A, F) in the engagement direction, and a differential speed between shift-element halves (10, 11) of the form-locking shift element (A, F) in order to transfer the form-locking shift element (A, F) into an engaged operating condition.

3. The method of claim 1, further comprising adjusting, during the engagement process, a differential speed between shift-element halves (10, 11) of the form-locking shift element (A, F) to a value within a speed range, the shift-element halves (10, 11) being brought into engagement with each other in a form-fitting manner within the speed range, the speed range encompassing a zero point.

4. The method of claim 1, further comprising adjusting, during the engagement process and before a positive engagement between shift-element halves (10, 11) of the form-locking shift element (A, F), a torque at the form-locking shift element (A, F) to a value greater than a threshold value, wherein, above the threshold value, a tooth-on-tooth position between the shift-element halves (10, 11) does not occur.

5. The method of claim 1, further comprising adjusting, during the engagement process and before a positive engagement between shift-element halves (10, 11) of the form-locking shift element (A, F), an actuation force at the form-locking shift element (A, F) to a value less than a threshold value, wherein, below the threshold value, a tooth-on-tooth position between the shift-element halves (10, 11) does not occur and the form-locking shift element (A, F) is transferable into an engaged operating condition.

6. The method of claim 1, further comprising adjusting, during the engagement process and when the shift-element halves (10, 11) of the form-locking shift element (A, F) are positively engaged, a torque at the form-locking shift element (A, F) to a value less than a threshold value, wherein, below the threshold value, flank clamping between the shift-element halves (10, 11) does not occur.

7. The method claim 1, further comprising adjusting, during the engagement process and when shift-element halves (10, 11) of the form-locking shift element (A, F) are positively engaged, an actuation force at the form-locking shift element (A, F) to a value greater than a threshold value, wherein, above the threshold value, flank clamping between the shift-element halves (10, 11) does not occur and the form-locking shift element (A, F) is transferable into an engaged operating condition.

8. The method of claim 1, wherein the transmission (3) comprises further shift elements (B, C, D, E), the further shift elements (B, C, D, E) being friction-locking shift elements, wherein a torque at the form-locking shift element (A, F) is varied by selective actuation of the further shift elements (B, C, D, E).

9. The method of claim 1, wherein a torque at the form-locking shift element (A, F) is varied by adjusting the transmission input torque.

10. A control unit for operating a vehicle drive train (1) that comprises a prime mover (2), a transmission (3), and a driven end (4), the transmission (3) comprising at least one form-locking shift element (A, F), the control unit configured for: limiting, during a demand for engaging the form-locking shift element (A, F) when a rotational speed of the driven end (4) is zero, a gradient of a progression of a transmission input torque at the form-locking shift element (A, F) to a value, wherein, below the value, one or more forces at the form-locking shift element (A, F) during an engagement process are less than a load limit, and wherein, above the value, irreversible damage to the form-locking shift element (A, F) occurs.

11. The control unit of claim 10, wherein the control unit carries out the method of claim 1 on a control side.

12. A computer program comprising program code stored on a non-transitory computer-readable medium with software instructions to carry out the method of claim 1 when executed on a control unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred refinements result from the dependent claims and the following description. An exemplary embodiment of the invention is explained in greater detail with reference to the drawing, without being limited thereto. Wherein:

(2) FIG. 1 shows a schematic of a vehicle drive train having a prime mover, a transmission, and a driven end;

(3) FIG. 2 shows a shift logic, in table form, of the transmission shown in FIG. 1;

(4) FIGS. 3a-3e each show various, highly schematic views of different operating conditions of a form-locking shift element between a completely disengaged condition and a completely engaged condition; and

(5) FIG. 4a-4f each show highly schematic views of various operating conditions of a form-locking shift element whose dog elements have different lengths.

DETAILED DESCRIPTION

(6) Reference will now be made to embodiments of the invention, one or more examples of which are shown in the drawings. Each embodiment is provided by way of explanation of the invention, and not as a limitation of the invention. For example, features illustrated or described as part of one embodiment can be combined with another embodiment to yield still another embodiment. It is intended that the present invention include these and other modifications and variations to the embodiments described herein.

(7) FIG. 1 shows a schematic view of a vehicle drive train 1 having a prime mover 2, a transmission 3, and a driven end 4. The prime mover 2 is, in one embodiment, an internal combustion engine. The transmission 3 is an automatic transmission, in which multiple gear stages “1”-“9” (FIG. 2) for forward travel and at least one gear stage “R” (FIG. 2) for travel in reverse are implementable. Depending on the particular configuration of the vehicle drive train 1, the driven end 4 has one, two, or more drivable vehicle axles to which the torque of the prime mover 2 is applicable via the transmission 3. The transmission 3 includes a first hydraulically actuatable shift element A, a second hydraulically actuatable shift element B, a third hydraulically actuatable shift element C, a fourth hydraulically actuatable shift element D, a fifth hydraulically actuatable shift element E, and a sixth hydraulically actuatable shift element F. Hydraulically actuatable shift elements A-F are actuated during a ratio change in the transmission 3, i.e., during upshifts or downshifts. The ratio changes are to be carried out essentially without an interruption of tractive force, in combination with a high level of ride comfort and at a desired level of performance. The term “performance” is understood to mean, in each case, a ratio change in the transmission 3 that is implemented within a defined operating time.

(8) In order to be able to carry out the particular demanded gear shift to the desired extent, the shift elements A-F are selectively acted upon according to shift sequences stored in a transmission control unit and a shift pressure corresponding to the particular shift sequence.

(9) The transmission 3 has a transmission input shaft 5 and a transmission output shaft 6. The transmission output shaft 6 is connected to the driven end 4. In the present case, a torsion damper 7 and a hydrodynamic torque converter 8, as a starting component, having an associated torque converter lockup clutch 9 are arranged between the transmission input shaft 5 and the prime mover 2.

(10) In addition, the transmission 3 includes a first planetary gear set P1, a second planetary gear set P2, a third planetary gear set P3, and a fourth planetary gear set—P4. The first planetary gear set P1 and the second planetary gear set P2, which are preferably minus planetary gear sets, form a shiftable front-mounted gear set. The third planetary gear set P3 and the fourth planetary gear set P4 represent a main gear set. The third shift element C, the fourth shift element D, and the sixth shift element F of the transmission 3 are brakes, while the first shift element A, the second shift element B, and the fifth shift element E are separating clutches.

(11) Selective shifting of the gear stages “1”-“R” is implementable via the shift elements A-F according to the shift logic represented in greater detail in FIG. 2. In order to establish a power flow in the transmission, three of the shift elements A-F are to be transferred into or held in an engaged operating condition essentially simultaneously in each gear stage.

(12) The first shift element A and the sixth shift element F are, in this case, form-locking shift elements without additional synchronization. As a result, in the case of the transmission 3, as compared to transmissions including only friction-locking shift elements, drag torques caused by disengaged friction-locking shift elements are reduced.

(13) As is known, form-locking shift elements are generally transferable out of a disengaged operating condition into an engaged operating condition only within a very narrow range of differential speeds between the shift-element halves to be brought into an operative connection with one another in a form-locking manner, where the range encompasses the synchronous speed. If the synchronization of a form-locking shift element to be engaged cannot be carried out with the aid of additional structural embodiments, the synchronization is implemented via an appropriate actuation of the further friction-locking shift elements contributing to the gear shift and/or an engine override. During such an engine override, for example, the drive torque made available by the prime mover 2 is varied in the coasting condition as well as in the traction operation of the vehicle drive train 1 to the extent necessary for the synchronization. This also applies for the actuation of the friction-locking shift elements during the carrying-out of demanded traction or coasting shifts.

(14) FIGS. 3a-3e each show two shift-element halves 10, 11 of the form-locking shift element A, F in various operating conditions. FIG. 3a shows the completely disengaged operating condition of the form-locking shift element A, F, in which there is no positive engagement between the first shift element half 10 and the second shift element half 11, and in which the shift-element halves 10, 11 are spaced apart from one another in the axial direction x.

(15) The first shift element half 10 has a first dog element 10A and the second shift element half 11 has a second dog element 11A. The dog elements 10A, 11A are brought into engagement with one another in a form-locking manner depending on the particular current application via axial displacement of the first shift-element half 10 relative to the second shift-element half 11 and/or of the second shift-element half 11 relative to the first shift-element half 10 in order to transmit a torque present at the form-locking shift element A, F to the desired extent.

(16) In the presence of an appropriate demand to engage the form-locking shift element A, F, an appropriate actuation force is applied in the engagement direction at the particular displaceable shift-element half 10, 11. As a result, the axial distance between the end faces 10B, 11B of the dog elements 10A, 11A facing one another is increasingly reduced.

(17) If the differential speed between the shift-element halves 10, 11 is too great, the dog elements 10A, 11A cannot be brought into engagement with one another in a form-locking manner. In such a case, a rattling occurs, during which the dog elements 10A, 11A glide off of one another, at their adjacent end faces 10B, 11B, in the circumferential direction of the shift element halves 10, 11 to the extent shown in FIG. 3b. Such a rattling is undesirable, however, since it causes irreversible damage in the area of the dog elements 10A, 11A as the period of operation increases.

(18) For this reason, the differential speed between the shift-element halves 10, 11 is adjusted to values within a differential speed window, which encompasses the synchronous speed of the form-locking shift element A, F, via appropriate actuation of the particular friction-locking shift elements B-E contributing to the operating condition change in the transmission 3. Within this differential speed window, the dog elements 10A, 11A of the shift-element halves 10, 11 can be brought into engagement with each other in a form-locking manner to the desired extent.

(19) It should be noted, however, that the positive engagement to be established is preventable by a so-called tooth-on-tooth position between the shift-element halves 10, 11. The tooth-on-tooth position, as represented in FIG. 3c, is characterized in that the dog elements 10A, 11A rest against one another at their end faces 10B, 11B, and the differential speed between the shift-element halves 10, 11 is zero. During such a tooth-on-tooth position of the form-locking shift element A, F, the static friction between the end faces 10B, 11B of the dog elements 10A, 11A is so great that the torque present at the form-locking shift element A, F is transmitted via the form-locking shift element A, F without the tooth-on-tooth position being released or unmeshed.

(20) In order to release the tooth-on-tooth position, it is advantageous if the actuation force acting on the form-locking shift element A, F in the engagement direction is reduced and/or the torque present at the form-locking shift element A, F is increased. The static friction between the end faces 10B, 11B of the dog elements 10A, 11A is lowered via the reduction of the engagement force. Simultaneously, by raising the torque present at the form-locking shift element A, F, the static friction between the end faces 10B, 11B is overcome and the differential speed between the shift-element halves 10, 11 increases to an extent that enables the positive engagement between the dog elements 10A, 11A to be established.

(21) FIG. 3d shows an operating condition of the form-locking shift element A, F, in which a positive engagement between the shift-element halves 10, 11 is present with a partial overlap of the dog elements 10A, 11A. Such an operating condition is present during a disengagement process as well as during an engagement process of the form-locking shift element A, F.

(22) The torque acting on the shift element A, F and the coefficients of friction of the flanks 10C, 11C yield a static friction force, which acts between the flanks 10C, 11C. If the actuation force acting on the shift-element halves 10, 11 in the disengagement direction or in the engagement direction of the form-locking shift element A, F is too low in relation to the static friction force between the flanks 10C, 11C of the dog elements 10A, 11A, flank clamping occurs. During flank clamping, the relative axial actuating movement between the shift-element halves 10, 11 in the engagement direction or in the disengagement direction is zero, and so the demanded operating condition change of the form-locking shift element A, F does not take place. In order to prevent or release such a flank clamping, the actuation force acting on the shift element A, F, for example, is raised and/or the particular torque present at the form-locking shift element A, F is reduced to the extent necessary for this purpose.

(23) The completely engaged operating condition of the form-locking shift element A, F is represented in FIG. 3e, in which the full overlap between the dog elements 10A, 11A in the axial direction x is present.

(24) FIGS. 4a-4f each show a representation of the form-locking shift element A, F corresponding to FIG. 3a. In the case of the shift element A, F, the dog elements 10A, 11A of the shift-element halves 10, 11, which are arranged next to one another in the circumferential direction of the shift-element halves 10, 11, each have a different length in the axial direction x. In the following, the first dog element 10A has a longer dog element 10A1 and a shorter dog element 10A2, and the second dog element 11A has a longer dog element 11A1 and a shorter dog element 11A2.

(25) This embodiment of the form-locking shift elements A, F offers the advantage that the positive engagement between the shift-element halves 10, 11 can be established at higher differential speeds between the shift-element halves 10, 11 than is the case with the embodiment of the form-locking shift elements A, F represented in FIGS. 3a-3e. However, the embodiment of the form-locking shift element A, F according to FIGS. 4a-4f is less robust against rattling as compared to the embodiment of the form-locking shift element A, F according to FIGS. 3a-3e.

(26) The shift element A, F can have further operating conditions, due to the combination of the longer dog elements 10A1, 11A1 and the shorter dog elements 10A2, 11A2, in addition to the operating conditions of the form-locking shift element A, F described with reference to FIGS. 3a-3e. The further operating conditions will be described in greater detail in the following description of FIGS. 4a-4f.

(27) Initially, the completely disengaged operating condition of the shift element A, F is represented in FIG. 4a. FIG. 4b shows the operating condition of the form-locking shift element A, F during a rattling operation. During the rattling operation, the shift-element halves 10, 11 glide off of one another at the end faces 10B1, 11B1 of the longer dog elements 10A1, 11A1 in the circumferential direction. Therefore, the positive engagement between the shift-element halves 10, 11 cannot be established. This rattling operation is prevented or ended to the extent described with reference to FIG. 3b by reducing the differential speed between the shift-element halves 10, 11.

(28) Moreover, FIG. 4c and FIG. 4d each show a tooth-on-tooth position, which prevents the establishment of the positive engagement between the shift-element halves 10, 11. In the operating condition of the form-locking shift element A, F represented in FIG. 4c, the tooth-on-tooth position is between the end faces 10B1, 11B1 of the longer dog elements 10A1, 11A1. In contrast thereto, the tooth-on-tooth position between the shift-element halves 10, 11 in the operating condition of the form-locking shift element A, F represented in FIG. 4d is between the end faces 11B1 of the longer dog elements 11A1 of the shift-element half 11 and the end faces 10B2 of the shorter dog elements 10A2 of the shift-element half 10.

(29) Regardless of the particular tooth-on-tooth position between the shift-element halves 10, 11, the tooth-on-tooth positions are released or prevented in the way described with respect to FIG. 3c.

(30) FIG. 4e shows an intermediate operating condition of the form-locking shift element A, F between the completely disengaged operating condition and the completely engaged operating condition of the form-locking shift element A, F. During this intermediate operating condition, flank clamping—described above—between the dog elements 10A1, 10A2 and the dog elements 11A1, 11A2, respectively, is possible. The flank clamping is prevented or released to the extent described with reference to FIG. 3d in order to disengage or engage the form-locking shift element A, F to the demanded extent.

(31) The completely engaged operating condition of the form-locking shift element A, F is represented in FIG. 4f.

(32) If a vehicle including the vehicle drive train 1 is at a standstill or is close to a standstill, and if, for example, a downshift is demanded by the transmission control unit, in the case of which the form-locking shift element A, F is to be transferred into the engaged operating condition, the gradient of the transmission input torque is initially limited. As a result, an excessively rapid increase of the torque present at the form-locking shift element A, F is prevented if a driver demands a starting process, as an excessively great gradient of the progression of the transmission input torque in the presence of a tooth-on-tooth position of the form-locking shift element A, F can cause damage in the area of the transmission 3.

(33) Moreover, a tooth-on-tooth position or flank clamping of the form-locking shift element A, F during the downshift and close to the standstill of the vehicle can be released without releasing the force-fit connection in the transmission 3 if the gradient of the progression of the transmission input torque is limited.

(34) During a starting process, the torque present at the form-locking shift element A, F increases, whereby a tooth-on-tooth position, which may be present, is released above a defined torque value.

(35) If the torque present at the form-locking shift element A, F has an appropriate value, the actuation force acting in the engagement direction of the form-locking shift element A, F is subsequently raised if a positive engagement of the form-locking shift element A, F is detected. As a result, a flank clamping can be released to the desired extent.

(36) If a driver-side demand to disengage the gear stage “1”-“R” currently engaged in the transmission 3 is present, all shift elements A-F of the transmission 3 are abruptly disengaged. Therefore, although the force-fit connection in the area of the transmission 3 is interrupted, this corresponds to the driver demand and, therefore, is not perceived as disruptive.

(37) Modifications and variations can be made to the embodiments illustrated or described herein without departing from the scope and spirit of the invention as set forth in the appended claims. In the claims, reference characters corresponding to elements recited in the detailed description and the drawings may be recited. Such reference characters are enclosed within parentheses and are provided as an aid for reference to example embodiments described in the detailed description and the drawings. Such reference characters are provided for convenience only and have no effect on the scope of the claims. In particular, such reference characters are not intended to limit the claims to the particular example embodiments described in the detailed description and the drawings.

REFERENCE NUMBERS

(38) 1 vehicle drive train 2 prime mover 3 transmission 4 driven end 5 transmission input shaft 6 transmission output shaft 7 torsion damper 8 hydrodynamic torque converter 9 torque converter lockup clutch 10, 11 shift-element half 10A, 10A1, 10A2 dog element 11A, 11A1, 11A2 dog element 10B, 10B1, 10B2 end face of the dog element 10C flank of the dog element 11B, 11B1, 11B2 end face of the dog element 11C flank of the dog element “1” to “9” transmission ratio for forward driving A to F shift element P1 to P4 planetary gear set “R” transmission ratio for travel in reverse