Abstract
A method for operating a serial-parallel hybrid powertrain of a motor vehicle has the steps of mechanically decoupling the internal combustion engine from the wheels of the motor vehicle, accelerating the motor vehicle from a first speed to a second speed by means of the second electric machine, and increasing the speed n of the internal combustion engine from a first rotational speed to a second rotational speed. Increasing the speed of the internal combustion engine from the first rotational speed to the second rotational speed always takes place as a function of the increase in the speed of the motor vehicle from the first speed to the second speed. A motor vehicle may have such a serial-parallel hybrid powertrain.
Claims
1. A method for operating a serial-parallel hybrid powertrain of a motor vehicle, the powertrain having an internal combustion engine, a first electric machine that is mechanically coupleable to the internal combustion engine, and a second electric machine that is mechanically coupleable to at least one wheel of the motor vehicle, the method having the following steps: mechanically decoupling the internal combustion engine from the wheels of the motor vehicle, accelerating the motor vehicle from a first speed to a second speed by means of the second electric machine, increasing a rotational speed of the internal combustion engine from a first rotational speed to a second rotational speed, as a function of the increase in the speed v of the motor vehicle from the first speed to the second speed; and accelerating the motor vehicle is from the second speed to a third speed, wherein the rotational speed of the internal combustion engine at the second speed is initially reduced and then subsequently increased once again, such that the reduction in the rotational speed takes place more rapidly than the increase in the rotational speed.
2. The method according to claim 1, wherein the increase in the rotational speed takes place in proportion to the increase in the speed.
3. The method according to claim 1, wherein, in the reduction of the rotational speed, the speed of the internal combustion engine is reduced from the second rotational speed to the first rotational speed or a higher rotational speed n than the first rotational speed.
4. The method according to claim 1, wherein the subsequent increase in the speed of the internal combustion engine takes place in such a way that, at the third speed, the internal combustion engine has the second rotational speed.
5. The method according to claim 1, wherein the reduction in the rotational speed n takes place abruptly.
6. The method according to claim 1, wherein the first rotational speed and the second rotational speed are selected in such a way that the second rotational speed is at least 130% of the first rotational speed.
7. The method according to claim 1, wherein the first rotational speed is selected in such a way that it is at least 200% of an idle speed of the internal combustion engine.
8. A motor vehicle having a serial-parallel hybrid powertrain, the hybrid powertrain having an internal combustion engine, a first electric machine that is mechanically coupleable to the internal combustion engine, and a second electric machine that is mechanically coupleable to at least one wheel of the motor vehicle, wherein the motor vehicle is designed for carrying out a method according to claim 1.
9. The motor vehicle according to claim 8, wherein the internal combustion engine is designed to provide constant internal combustion engine power in the rotational speed range between the first rotational speed and the second rotational speed.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) A method according to the invention and a motor vehicle according to the invention are explained in greater detail below with reference to the drawings, which schematically show the following:
(2) FIG. 1 shows a top view of one preferred embodiment of a serial-parallel hybrid powertrain according to the prior art,
(3) FIG. 2 shows a speed-rotational speed diagram of one preferred sequence of the method according to the invention,
(4) FIG. 3 shows a speed-rotational speed diagram of an alternative, preferred sequence of the method according to the invention,
(5) FIG. 4 shows a rotational speed-torque diagram of a preferred first process control of the method according to the invention,
(6) FIG. 5 shows a rotational speed-torque diagram of a preferred second process control of the method according to the invention, and
(7) FIG. 6 shows a side view of one preferred embodiment of a motor vehicle according to the invention having a serial-parallel hybrid powertrain.
(8) Elements having identical functions and operating principles are provided with the same reference numerals in each of FIGS. 1 through 6.
DETAILED DESCRIPTION OF THE INVENTION
(9) FIG. 1 schematically shows one preferred embodiment of a serial-parallel hybrid powertrain 1 according to the prior art, in a top view. The powertrain has an internal combustion engine 3 that is mechanically coupled to a first electric machine 4 via a single-speed nonshiftable first transmission 9. The first electric machine 4 is preferably controllable via a power electronics system (not illustrated) of the serial-parallel hybrid powertrain 1. In addition, the powertrain 1 has a second electric machine 6 that is mechanically coupled to a drive axle 8 of the powertrain 1 via a single-speed nonshiftable second transmission 10. The second electric machine 6 is preferably controllable via a power electronics system (not illustrated) of the serial-parallel hybrid powertrain 1. The internal combustion engine 1 is mechanically coupleable or decoupleable to/from an intermediate stage of the second transmission 10 via a separating clutch 11. In addition, the powertrain 1 has a battery 7 that is electrically coupled to the first electric machine 4 and the second electric machine 6. Electrical current that is generated by the first electric machine 4 and/or the second electric machine 6 is thus storable in the battery 7, and electrical current is providable by the battery 7 for operating the first electric machine 4 and/or the second electric machine 6.
(10) FIG. 2 schematically shows one preferred sequence of the method according to the invention in a speed-rotational speed diagram. The diagram illustrates carrying out the method during an acceleration operation of a motor vehicle 2 (see FIG. 6) from a first speed v.sub.1 to an end speed v.sub.E. In this exemplary embodiment, the internal combustion engine 3 is mechanically decoupled from the second transmission 10, and thus from the drive axle 8, by means of the separating clutch 11. At the first speed v.sub.1 the internal combustion engine 3 has a first rotational speed n.sub.1. Upon acceleration of the motor vehicle 2, a rotational speed n of the internal combustion engine 3 is increased in proportion to the speed v of the motor vehicle 2, so that at a second speed v.sub.2 the internal combustion engine 3 has a second rotational speed n.sub.2, the second rotational speed n.sub.2 being greater than the first speed n.sub.1. Upon reaching the second speed v.sub.2, the rotational speed n is abruptly reduced to the first rotational speed n.sub.1, and upon further acceleration to a third speed v.sub.3 is again increased in proportion to the speed v, so that at the third speed v.sub.3 the internal combustion engine once again has the second rotational speed n.sub.2. This operation is repeated until the end speed v.sub.E is reached. It may be optionally provided that the rotational speed n is reduced to an end rotational speed n.sub.E upon reaching the end speed v.sub.E. By varying the rotational speed n of the internal combustion engine, the operation of a conventional powertrain having a multispeed transmission, in the present case a five-speed transmission, is simulated. Occupants of the motor vehicle 2 thus experience a familiar driving experience, so that acceptance by the occupants for the serial-parallel hybrid powertrain 1 is improved.
(11) FIG. 3 schematically shows another, alternative preferred sequence of the method according to the invention in a speed-rotational speed diagram. The diagram illustrates carrying out the method during an acceleration operation of a motor vehicle 2 (see FIG. 6) from a first speed v.sub.1 to an end speed v.sub.E. In this exemplary embodiment, the internal combustion engine 3 is mechanically decoupled from the second transmission 10, and thus from the drive axle 8, by means of the separating clutch 11. At the first speed v.sub.1 the internal combustion engine 3 has a first rotational speed n.sub.1. Upon acceleration of the motor vehicle 2, a rotational speed n of the internal combustion engine 3 is increased in proportion to the speed v of the motor vehicle 2, so that at a second speed v.sub.2 the internal combustion engine 3 has a second rotational speed n.sub.2, the second rotational speed n.sub.2 being greater than the first rotational speed n.sub.1. Upon reaching the second speed v.sub.2, the rotational speed n is abruptly reduced to a third rotational speed n.sub.3, the third rotational speed n.sub.3 being greater than the first rotational speed n.sub.1. Upon further acceleration to a third speed v.sub.3, the rotational speed n is once again increased in proportion to the speed v, so that at the third speed v.sub.3 the internal combustion engine again has the second rotational speed n.sub.2. Upon reaching the third speed v.sub.3, the rotational speed n is abruptly reduced to a fourth rotational speed n.sub.4, the fourth rotational speed n.sub.4 being greater than the third rotational speed n.sub.3. Upon further acceleration to a fourth speed v.sub.4, the rotational speed n is once again increased in proportion to the speed v, so that at the fourth speed v.sub.4 the internal combustion engine again has the second rotational speed n.sub.2. Upon reaching the fourth speed v.sub.4, the rotational speed n is abruptly reduced to a fifth rotational speed n.sub.5, the fifth rotational speed n.sub.5 being greater than the fourth rotational speed n.sub.4. Upon further acceleration to a fifth speed v.sub.5, the rotational speed n is once again increased in proportion to the speed v, so that at the fifth speed v.sub.5 the internal combustion engine again has the second rotational speed n.sub.2. Upon reaching the fifth speed v.sub.5, the rotational speed n is abruptly reduced to a sixth rotational speed n.sub.6, the sixth rotational speed n.sub.6 being greater than the fifth rotational speed n.sub.5. Upon further acceleration to an end speed v.sub.E, the rotational speed n is once again increased in proportion to the speed v, so that at the end speed v.sub.E the internal combustion engine has a seventh rotational speed n.sub.7, which in the present example is greater than the second rotational speed n.sub.2 and less than the sixth rotational speed n.sub.6. It may optionally be provided that the rotational speed n is reduced to an end rotational speed n.sub.E upon reaching the end speed v.sub.E. The end rotational speed n.sub.E may, for example, be greater than the fifth rotational speed n.sub.5. The operation of a conventional powertrain having a multispeed transmission, in the present case a five-speed transmission, is simulated by varying the rotational speed n of the internal combustion engine in this way. Occupants of the motor vehicle 2 thus experience a familiar driving experience, so that acceptance by the occupants for the serial-parallel hybrid powertrain 1 is improved.
(12) FIG. 4 schematically shows a preferred first process control of the method according to the invention over multiple phases in a rotational speed-torque diagram. The internal combustion engine 3 drives the first electric machine 4 as a generator. Starting from a first rotational speed n.sub.1 and a maximum torque M.sub.max, in a first phase 12 the rotational speed n of the internal combustion engine 3 is increased to the second rotational speed n.sub.2. The torque M is hereby reduced at constant or essentially constant internal combustion engine power. Upon reaching the second rotational speed n.sub.2, in a second phase 13 the torque is abruptly reduced by reducing the load on the internal combustion engine 3. The first electric machine 4 continues to operate under full load upon reaching the second rotational speed n.sub.2. In a third phase 14, the rotational speed n of the internal combustion engine 3 decreases to the first rotational speed n.sub.1 due to the power deficit. The power of the first electric machine 4 is now provided by the inertia of the internal combustion engine 3. After reaching the first rotational speed n.sub.1, in a fourth phase 15 the internal combustion engine 3 is once again operated under full load, so that the starting point at the maximum torque M.sub.max and the first rotational speed n.sub.1 is again reached. Upshifting of a virtual gear and subsequent upshifting to a virtual higher gear are simulated in this way.
(13) FIG. 5 schematically shows a preferred second process control of the method according to the invention over multiple phases in a rotational speed-torque diagram. The second process control differs from the first process control in that in the second phase 13, the load variation of the internal combustion engine 3 no longer takes place abruptly, but instead occurs continuously according to so-called down-ramping. Likewise, in the fourth phase 15 the load increase on the internal combustion engine 3 no longer takes place abruptly, but instead occurs continuously according to so-called up-ramping. Knocks in the powertrain 1 may thus be avoided, and the robustness of the method may be increased. During the second process control, the third phase 14 is therefore shorter than during the first process control.
(14) FIG. 6 schematically shows one preferred embodiment of a motor vehicle 2 according to the invention having a serial-parallel hybrid powertrain 1 and wheels 5, in a side view. The powertrain 1 has an internal combustion engine 3, a first electric machine 4, a second electric machine 6, and a battery 7. The powertrain 1 is preferably designed according to a known powertrain 1 from FIG. 1, the motor vehicle 2 according to the invention being designed and configured for carrying out the method according to the invention. For this purpose, for example the method steps may be stored in a memory unit (not illustrated) of an engine control device (not illustrated). The engine control device is designed for controlling the powertrain 1 and for reading out the memory unit.
LIST OF REFERENCE NUMERALS
(15) 1 powertrain 2 motor vehicle 3 internal combustion engine 4 first electric machine 5 wheel 6 second electric machine 7 battery 8 drive axle 9 first transmission 10 second transmission 11 separating clutch 12 first phase 13 second phase 14 third phase 15 fourth phase M torque M.sub.max maximum torque n.sub.1 first rotational speed n.sub.2 second rotational speed n.sub.3 third rotational speed n.sub.4 fourth rotational speed n.sub.5 fifth rotational speed n.sub.6 sixth rotational speed n.sub.7 seventh rotational speed n.sub.E end rotational speed n.sub.L idle speed n.sub.max maximum rotational speed v speed v.sub.1 first speed v.sub.2 second speed v.sub.3 third speed v.sub.4 fourth speed v.sub.5 fifth speed v.sub.E end speed
