METHOD FOR HEATING A GEARBOX FOR A WORKING MACHINE

Abstract

The present invention relates to a method for heating a transmission (1) for a working machine having a plurality of hydraulically actuated shifting elements (8; 9; 10; 11; 12; 13). The method involves the sending (III) of a closing signal for closing shifting elements (8; 9; 10; 11; 12; 13) in order to block the transmission (1). In addition, the method entails pulsed actuation (V) for opening and closing of at least one of the closed shifting elements (8; 9; 10; 11; 12; 13) while the transmission (1) remains blocked. Furthermore, the present invention relates to a control unit which is designed to carry out such a method, and to a transmission for a working machine with such a control unit.

Claims

1. A method for heating a transmission (1) for a working machine having a plurality of hydraulically actuated shifting elements (8; 9; 10; 11; 12; 13), the method comprising: sending (III) a closing signal for closing shifting elements (8; 9; 10; 11; 12; 13) of the transmission (1) in order to block the transmission (1); and pulsed actuation (V) to open and close at least one of the closed shifting elements (8; 9; 10; 11; 12; 13) while the transmission (1) remains blocked.

2. The method according to claim 1, wherein the pulsed actuation (V) consists in actuating the shifting element (8; 9; 10; 11; 12; 13) with a number of pulsed cycles for opening and closing the shifting element (8; 9; 10; 11; 12; 13), wherein a pulse duration of the actuation decreases as the number of cycles increases.

3. The method according to claim 1, further comprising: detecting (III) a temperature; and determining a number of cycles for opening and closing the shifting element (8; 9; 10; 11; 12; 13) as a function of the temperature detected.

4. The method according to claim 1, comprising: checking (VI) for a power transmission request through the transmission (1); recognizing no power transmission request; and continuing the pulsed actuation (V) of the shifting element (8; 9; 10; 11; 12; 13).

5. The method according to claim 1, wherein the shifting elements include driving direction clutches (8, 9, 10) and sending (III) the closing signal involves sending the closing signal to all the driving direction clutches (8, 9, 10) to engage a rotation direction of a transmission drive output (7) of the transmission (1), and sending (III) the closing signal to all the driving range clutches (11, 12, 13) to engage a rotation speed of the transmission drive output (7) of the transmission (1).

6. The method according to claim 5, wherein the pulsed actuation (V) is carried out by the pulsed actuation of only one of the shifting elements (8; 9; 10; 11; 12; 13) of the transmission (1).

7. The method according to claim 1, wherein the transmission (1) comprises a hydrodynamic torque converter (2) which, together with the shifting element (8; 9; 10; 11; 12; 13), is configured to be supplied with hydraulic fluid from a hydraulic source, and wherein the method comprises an actuation (IV) for accelerating a drive mechanism (5) which is mechanically functionally connected to the torque converter (2) in order to heat the hydraulic fluid.

8. The method according to claim 1, comprising checking (I) whether the transmission (1) is at a standstill and/or checking whether a calibration of one of the shifting elements (8; 9; 10; 11; 12; 13) should be carried out.

9. A control unit (6) configured to carry out the method according to claim 1.

10. A transmission (1) for a working machine having a plurality of hydraulically actuated shifting elements (8; 9; 10; 11; 12; 13) and the control unit (6) according to claim 9 for actuating the plurality of hydraulically actuated shifting elements (8; 9; 10; 11; 12; 13).

Description

BRIEF DESCRIPTION OF THE FIGURES

[0020] FIG. 1 shows schematically a transmission for a working machine according to an embodiment of the present invention.

[0021] FIG. 2 shows schematically a flow chart of a method for heating the transmission of FIG. 1, according to an embodiment of the present invention.

[0022] FIG. 3 shows schematically signals for the pulsed actuation of the shifting elements in the transmission of FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS

[0023] FIG. 1 shows schematically a transmission 1 for a working machine according to an embodiment of the present invention. The transmission 1 comprises a hydrodynamic torque converter 2, a driving direction change assembly 3, and a driving range assembly 4. In addition, the transmission 1 comprises a drive input mechanism 5 and a control unit 6. The drive input mechanism 5, in this embodiment, is in the form of an internal combustion engine. In an alternative embodiment, the drive input mechanism 5 is in the form of an electric motor. The drive input mechanism 5 is mechanically functionally connected to the torque converter 2, which, in this embodiment, is in the form of a Fttinger converter. The converter 2 comprises a pump wheel, which is mechanically functionally connected with the drive input mechanism 5. A turbine wheel is mechanically functionally connected to the pump wheel, which, in the present embodiment, is mechanically functionally connected to the driving direction change assembly 3.

[0024] The driving direction change assembly 3 is designed to engage a rotation direction of the transmission output 7. For that purpose, the driving direction change assembly 3 comprises shifting elements, each in the form of a clutch. A first clutch 8 serves to engage a forward driving direction with a first gear ratio. A second clutch 9 also serves to engage a forward driving direction, but with a gear ratio different from that produced by the clutch 8. A third clutch 10 serves to engage a reverse driving direction. The driving direction change assembly 3 is mechanically functionally connected to the driving range assembly 4. By means of the driving range assembly 4, different rotation speeds can be produced at the drive output 7 of the transmission 1. For this, the driving range assembly 4 has a first clutch 11, a second clutch 12, and a third clutch 13, each of which can engage different gear ratios and hence different rotation speeds at the drive output 7. Thus, by means of the transmission 1 of this embodiment, by virtue of the three driving range clutches 11, 12, 13, a total of six driving ranges in the forward direction, namely one via the forward clutch 8 or, alternatively, via the forward clutch 9, and three driving ranges in the reverse direction, namely via the reversing clutch 10, can be engaged.

[0025] In the present embodiment, all the clutches 8, 9, 10, 11, 12, and 13 of the transmission 1 are in the form of frictional disk clutches. All the clutches 8, 9, 10, 11, 12, and 13 can be actuated hydraulically, in this embodiment, by means of oil. For the hydraulic actuation of the clutches 8, 9, 10, 11, 12, and 13 a hydraulic sump (not shown) is provided, from which hydraulic fluid is drawn and delivered to the clutches 8, 9, 10, 11, 12, and 13 for their operation. The hydrodynamic torque converter 2 too is connected to the hydraulic sump in order to draw hydraulic fluid from and return it to the sump as required for its operation.

[0026] In addition, the transmission 1 comprises the control unit 6, which is connected electronically to the clutches 8, 9, and 10 of the driving direction change assembly 3 and to the clutches 11, 12, and 13 of the driving range assembly 4. Likewise, the torque converter 2 and the drive input mechanism 5 are also connected electronically to the control unit 6. By means of the control unit 6 the clutches 8, 9, 10, 11, 12, and 13, the torque converter 2, and the drive input mechanism 5 can be actuated and controlled. The control unit 6 is designed to carry out the method for heating the transmission 1 described below with reference to FIGS. 2 and 3.

[0027] In a first step I, the control unit 6 determines whether the method for heating the transmission 1 should be carried out. For that, in the present embodiment, it is checked whether the working machine is at a standstill. If so, then, in this embodiment, the method is carried out. Furthermore, in step I, the control unit 6 checks whether any of the clutches 8, 9, 10, 11, 12, and 13 should be calibrated. In that case too, in the context of the present invention, the method is carried out. If, in step I, it is determined that the method for heating the transmission 1 should indeed be carried out, the process advances to step II.

[0028] In step II, a starting temperature is now determined. In this embodiment, in step II, the control unit 6 determines, by means of a temperature sensor (not shown), the starting temperature in the transmission 1. Depending on the starting temperature determined, in step II, a number of opening and closing cycles of the shifting elements 8, 9, 10, 11, 12, and 13 is established. The lower the starting temperature, the larger is the number of cycles for opening and closing the shifting elements. If the starting temperature is above a limit value, i.e., if at the beginning of the method the transmission 1 is warmer than a certain limit value, it is established that the transmission does not need to be heated. In that case, the method does not carry out any heating of the transmission. On the other hand, if, in step II, it is found that the starting temperature is lower than the limit value, the opening and closing cycle number of the shifting elements is determined. In this embodiment, the temperature is determined by a temperature sensor provided in the transmission 1. The process then advances to step III.

[0029] In step III, in this embodiment, the control unit 6 sends out a closing signal to all the clutches in the transmission, i.e., to the driving direction change clutches 8, 9, and 10 and to the driving range clutches 11, 12, and 13. In this embodiment, the driving range clutches 11, 12, and 13 are closed first, since, in these, there is no rotation speed difference and therefore no load on the clutches. Thereafter, the driving direction change clutches 8, 9, and 10 are closed. In this, it is important that the closing clutch elements should not slip for too long since that could result in thermal overloading. Accordingly, in this case, the primary rotation speed at the clutch must be monitored. If this is not brought down to zero in an acceptable time, the closing attempt is interrupted and, after a certain waiting time, a further closure is attempted. In this embodiment, the driving range change clutches 8, 9, and 10 are closed at the same time so that there is a power branching between clutches being controlled. By closing the clutches 8, 9, and 10, the turbine of the hydrodynamic converter 2 is brought to a standstill and blocked. If now all the clutches 8, 9, 10, 11, 12, and 13 of the transmission are locked, there are no longer any rotation speed differences in the transmission 1. The transmission 1 is blocked.

[0030] Since the pump wheel of the torque converter 2 is driven by the drive input mechanism 5, in a subsequent step IV, the control unit 6 initiates a pumping of oil from the hydraulic sump through the torque converter 2. Owing to the rotation speed difference between the pump wheel and the turbine wheel in the converter 2, the temperature of the oil flowing through the converter 2 is increased due to hydrodynamic friction. Thereby, the oil in the hydraulic sump used to actuate the shifting elements 8, 9, 10, 11, 12, and 13 is also heated.

[0031] In the next step V, the clutches 8, 9, 10, 11, 12, and 13 of the transmission 1 are now actuated in alternation in pulses by the control unit 6 in order to open and close them. During this, always only a single clutch at a time is opened by the control unit 6. Thus, in step V, in this embodiment, in alternation one clutch 8, 9, 10 of the driving direction change assembly 3 and then one clutch 11, 12, 13 of the driving range assembly is actuated. In FIG. 3, the actuation pulses for opening and closing the clutches 8, 9, 10 of the driving direction change assembly 3 are shown at the top and the actuation pulses for opening and closing the driving range clutches 11, 12, 13 of the driving range assembly 4 are shown at the bottom.

[0032] As shown in FIG. 3, the clutch 8 of the driving direction change assembly 3 is first actuated in a pulse in order to be opened and then closed. The opening pulse is denoted in FIG. 3 with the index 8. Then, the control unit 6 actuates the clutch 11 of the driving range assembly 4 to open and close it. The pulse for opening the cutch 11 is denoted in FIG. 3 by the index 11. Following the pulsed actuation of the clutch 11, in the next step, the clutch 9 of the driving direction change assembly 3 is pulse-actuated, as indicated by the index 9 in FIG. 3. After that, the clutch 12 of the driving range assembly 4 is pulse-actuated to open and close it. Thereafter, the clutch 10 of the driving direction change assembly 3 is pulse-actuated, before the control unit 6 actuates the clutch 13 of the driving range assembly 4. Now, a first cycle of the pulsed actuation of all the clutches 8, 9, 10, 11, 12, and 13 of the transmission 1 has been completed. In this embodiment, a second and a third cycle of actuating all the clutches are carried out by the control unit 6 in a corresponding manner, as shown in FIG. 3. In this embodiment, the pulse duration, for example, the time during which each clutch is opened, is equal for all the clutches within a cycle. As shown in FIG. 3, however, the pulse duration for all the clutches decreases as the cycle number increases. This means that the pulse duration for the second cycle is shorter than the pulse duration for the first cycle. In turn, the pulse duration for the third cycle is shorter than the pulse duration for the second cycle.

[0033] In this embodiment, once the number of cycles of pulsed opening and closing of the clutches 8, 9, 10, 11, 12, and 13 of the transmission 1, established in step II, has been completed, in step VI, the control unit 6 checks whether the driver of the working machine has issued a command to start up the vehicle. If no such command, i.e., a request for power transmission through the transmission 1, is recognized, the method returns to step V and continues the pulsed actuation of the clutches 8, 9, 10, 11, 12, and 13 in the manner described. Otherwise, the method returns to step I.

INDEXES

[0034] 1 Transmission [0035] 2 Hydrodynamic converter [0036] 3 Driving direction change assembly [0037] 4 Driving range assembly [0038] 5 Drive mechanism [0039] 6 Control unit [0040] 7 Drive output [0041] 8, 9, 10 Driving direction change clutch [0042] 11, 12, 13 Driving range clutch [0043] I Check whether transmission heating is necessary [0044] II Detection of temperature and determination of number of cycles [0045] III Blocking of the transmission [0046] IV Actuation of torque converter [0047] V Pulsed actuation of shifting elements [0048] VI Checking for a power transmission request