Method for performing shifts in a dog clutch element

Abstract

A method performs shifts in a dog clutch element of a transmission system in a hybrid vehicle. The vehicle has an input shaft being connected to a crankshaft of an internal combustion engine, an output shaft being connected indirectly to driven wheels, an electric machine which is in engagement with the input shaft, and an automatic transmission connected between the input and output shafts. The transmission has a dog clutch element for the releasable coupling of two transmission elements. During a desired shifting of the dog clutch element, the torque of the input shaft is adapted via the electric machine, and therefore a reduced load prevails in the region of the dog clutch element and the latter can be disengaged, after which the internal combustion engine is set to a desired target rotational speed, and after which the dog clutch element is engaged when the target rotational speed is reached.

Claims

1. A method for performing shifts in a dog clutch element of a transmission system of a hybrid vehicle, the hybrid vehicle having driven wheels, an internal combustion engine with a crankshaft, an input shaft connected to the crankshaft, an output shaft connected at least indirectly to the driven wheels, an electric machine being in engagement with the input shaft, and an automatic transmission or a transmission which is shiftable in an automated manner between the input shaft and the output shaft, the transmission having the dog clutch element for a releasable coupling of two transmission elements, which comprises the steps of: during a desired shifting of the dog clutch element, a torque of the input shaft is adapted via the electric machine, and therefore a reduced load prevails in a region of the dog clutch element and the dog clutch element is disengaged; subsequently braking or accelerating the internal combustion engine to a desired target rotational speed via the electric machine; and subsequently engaging the dog clutch element when or shortly before the desired target rotational speed is reached.

2. The method according to claim 1, which further comprises controlling/regulating a shifting operation of the dog clutch element via at least one control unit for the transmission and the electric machine and integrated in the transmission system.

3. The method according to claim 1, which further comprises reducing the load on the dog clutch element to zero before disengagement.

4. The method according to claim 1, which further comprises determining the desired target rotational speed at the output shaft.

5. The method according to claim 1, which further comprises providing each of the input shaft and the output shaft with one rotational speed sensor, wherein the rotational speed sensor supplies a sensed rotational speed to a control unit integrated in the transmission system.

6. The method according to claim 1, which further comprises disposing an inclination sensor in the transmission system, the inclination sensor supplying its sensed data to a control unit integrated in the transmission system.

7. The method according to claim 1, wherein the transmission used is a differential converter transmission having an overdrive, and a change in a transmission ratio of the transmission is switched on via the dog clutch element.

8. The method according to claim 1, which further comprises using a gas engine as the internal combustion engine in the hybrid vehicle.

9. The method according to claim 1, wherein the input shaft is connected directly or via a torsional vibration damper to the crankshaft of the internal combustion engine.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The sole attached FIGURE shows a vehicle arranged in principle or the drive train thereof in a variant with which the method according to the invention can be carried out.

DESCRIPTION OF THE INVENTION

(2) In the illustration of the FIGURE, a drive train 1 of a vehicle 2, not illustrated in its entirety, can be seen in highly schematized form. The vehicle 2 is intended to be designed here as a hybrid vehicle, in particular as a commercial vehicle. The vehicle 2 can particularly preferably be a bus.

(3) The drive train 1 of the hybrid vehicle 2 comprises an internal combustion engine 3 and an electric machine 4. The latter is part of a transmission system which, in addition to a transmission 5 and the electric machine 4, also has a control unit 6 and a frequency converter 7 for activating the electric machine 4, and an energy accumulator device 8, for example a battery or supercapacitors or a combination thereof. An input shaft 9 of the transmission system connects a crankshaft of the internal combustion engine 3 to the electric machine 4 and the transmission 5. An output shaft 10 of the transmission provides the drive of driven wheels 11 of the hybrid vehicle 2, which wheels are likewise indicated here. In the exemplary embodiment illustrated here, the transmission 5 is intended to be designed as an automatic transmission in the form of a differential converter transmission 12 which has what is referred to as an overdrive 13 connected downstream of said differential converter transmission 12. Depending on the engaged gear of the differential converter transmission 12, said overdrive 13 can be brought into at least two different shifting positions in order thereby once again to change the transmission ratio prevailing at the output shaft 10. Said shifting of the overdrive 13 typically takes place via dog clutch elements, wherein one such dog clutch element 14 with two dogs is indicated purely by way of example in the region of the overdrive 13.

(4) In addition, the transmission system comprises a rotational speed sensor 15 which is connected to the input shaft 9, and a rotational speed sensor 16 which is connected to the output shaft 10. Furthermore, an inclination sensor 17 is installed in the transmission system. All of the sensors 15, 16, 17 supply data to the control unit 6 of the transmission system and assist said control unit in controlling or regulating the operations within the transmission 5.

(5) The input shaft 9 is ideally connected here to the crankshaft of the internal combustion engine 3 via a torsional vibration damper. A shiftable clutch can likewise be provided in principle in the region between the input shaft 9 and the crankshaft. However, the design functions particularly simply and efficiently if a shiftable clutch is omitted in the region of the input shaft 9. The internal combustion engine 3 can be any desired internal combustion engine 3. The latter will frequently be designed as a diesel engine in the sphere of commercial vehicles. However, it can also be configured as a different type of internal combustion engine, for example as a gas engine. In respect of activation, in particular such gas engines are highly complex and substantially more difficult to precisely activate than, for example, these diesel engines are. The method below is suitable for both variants. In particular, however, an extremely simple, efficient and effective shifting of the dog clutch element 14 can be achieved even with the gas engine which can be difficult to activate.

(6) If, via a data bus system 18, which can be designed in particular as a CAN bus, a shifting requirement now arrives at the control unit 6 of the transmission system, or is generated by the latter itself, then at this time loads typically prevail in the region of the dog clutch element 14, and therefore the latter cannot be simply disengaged, in particular since an inadvertent disengagement of the individual dogs is prevented by suitable undercuts in the normal situation. Starting from the control unit 6 of the transmission system, the electric machine 4 can now be activated via the frequency converter 7 in such a manner that the load in the region of the dog clutch element 4 is reduced and ideally becomes zero. For this purpose, the internal combustion engine 3 is braked via the electric machine 4, for example in the generator mode. Energy arising in the process migrates via the frequency converter 7 into the energy accumulator device 8. If an increase in the torque or the rotational speed of the internal combustion engine 3 is necessary in order to reduce the load, this can likewise take place via the electric machine 4, in this case then in motor mode. The electrical power necessary for this purpose originates in turn from the energy accumulator device 8.

(7) The desired torque or the desired rotational speed of the input shaft 9 can therefore be set solely on the basis of the transmission system, and without having to intervene in the motor controller of the internal combustion engine 3. The transmission system therefore as it were creates its idealized conditions by engagement with the electric machine 4 on the input shaft 9 itself. The desired rotational speed can be monitored via the rotational speed sensor 15. In the ideal case, only a very small moment, or preferably no longer any torque at all, now prevails between the dogs of the dog clutch element 14. The latter can then be simply disengaged. The target rotational speed, and here preferably the target rotational speed in the region of the output shaft 10, which can be sensed by the rotational speed sensor 16, can now be set in turn via the electric machine 4. For this purpose, in turn, for example in the motor mode of the electric machine 4, the internal combustion engine 3 is accelerated or, in the generator mode thereof is braked. This ultimately leads to the desired target rotational speed of the output shaft 10. At said target rotational speed, the dog clutch element 14 or the two dogs thereof is then engaged again, which in turn can take place in a load-free manner without a significant difference in rotational speed, and therefore overall an extremely rapid and efficient shifting is possible. As is also customary in previous dog clutch elements, the dog clutch element 14 can have mechanical synchronization devices which permit engagement even when there are already differences in rotational speed. However, by means of the described method, said differences in rotational speed can be significantly minimized, and therefore the engagement is possible in an extremely rapid and efficient manner. In particular, friction losses are minimized, which leads to improved utilization of energy, on the one hand, and to reduced wear, on the other hand.

(8) The dog clutch element 14 can therefore be used in all operating situations of the transmission system and therefore of the hybrid vehicle 2, which constitutes a decisive advantage over the conventional use. The use takes place here extremely rapidly and efficiently, and therefore a very rapid and use-optimized shifting is possible. Furthermore, the driving comfort is increased by means of the shortened shifting time.