Method For Operating A Hybrid Vehicle

Abstract

A hybrid vehicle is operated with a combustion engine, an electric machine and a gear unit. The vehicle has a first electrical system and a second electrical system as a vehicle electrical system. The first electrical system, which is operated at a higher voltage level than the second electrical system, operates the electric machine, an electrical energy storage device, an energy converter that transmits electrical power at least from the first electrical system into the second electrical system. An alternator is not used in the second electrical system. The first electrical system is a part of a transmission system that together with the components that are coupled to the transmission system is controlled by a transmission control unit. During power generation by the electric machine the energy supply of the second electrical system has a higher priority than a motor-mode support of the drive by the electric machine.

Claims

1-12. (canceled)

13. A method of operating a hybrid vehicle, the method comprising: operating the vehicle with a combustion engine, an electric machine and a gear unit, the gear unit being connected to the combustion engine by way of an input shaft; the vehicle having a first electrical system, a second electrical system being an onboard vehicle electrical system that has a lower voltage level than the first electrical system; operating the first electrical system at a higher voltage level than the second electrical system; operating with the first electrical system the electric machine, an electrical energy storage device, and an energy converter; transmitting electrical power at least from the first electrical system into the second electrical system, and operating the second electrical system without using an alternator; configuring the first electrical system as part of a transmission system, and controlling the transmission system, together components that are coupled to the transmission system, with a transmission control unit; generating power with the electric machine; and during a power distribution, assigning an energy supply of the second electrical system a higher priority than a motor-mode drive of the input shaft by the electric machine.

14. The method according to claim 13, which comprises: determining an average durations of traction phases of the hybrid vehicle; determining an average electrical energy requirement by the second electrical system; and effecting the motor-mode support of the drive of the input shaft by the electric machine only when and as long as a prevailing capacity of the electrical energy storage device is equal to or greater than a sum of the average electrical energy requirement of the second electrical system during the average durations and a specified residual capacity of the electrical energy storage.

15. The method according to claim 14, which comprises determining the average duration and/or the average electrical energy requirement as a moving average value.

16. The method according to claim 13 which comprises supplying the second electrical system with electrical energy from the first electrical system and the energy converter so long until a minimum capacity of the electrical energy storage device is achieved, the minimum capacity being a capacity that is required to start the combustion engine by way of the electric machine.

17. The method according to claim 16, which comprises supplying the second electrical system with electrical energy from a battery in the second electrical system after the minimum capacity of the electrical energy storage device is achieved.

18. The method according to claim 13, wherein the voltage level of the first electrical system lies below 60 V direct current voltage, and the voltage level of the second electrical system is either 12 V or 24 V direct current voltage.

19. The method according to claim 18, wherein the voltage level of the first electrical system is 48 V direct current voltage.

20. The method according to claim 13, wherein the electric machine is a permanently excited synchronous electrical machine having embedded magnets.

21. The method according to claim 13, further comprising: providing, as part of the transmission system, a hydrodynamic, wear-free sustained-action brake; as long as the required braking torque is smaller than a generator-mode torque of the electric machine, braking exclusively by way of the electric machine and providing a braking torque that exceeds the maximum generator-mode torque of the electric machine by the hydrodynamic, wear-free sustained-action brake.

22. The method according to claim 13, which comprises, during a braking operation of the hybrid vehicle, increasing switchback rotational speeds of the gear unit.

23. The method according to claim 13, which comprises, during a coasting mode of the hybrid vehicle wherein no braking or acceleration is required, operating the electric machine in a generator mode with a low torque.

24. The method according to claim 13, which comprises operating the electric machine in a generator mode as a primary braking unit for the combustion engine so as to increase an exhaust gas temperature of the combustion engine if such an increased exhaust gas temperature is required.

Description

[0023] In the drawings:

[0024] FIG. 1 illustrates a principal representation of a hybrid vehicle in a system suitable for the implementation of the method in accordance with the invention; and

[0025] FIG. 2 illustrates a diagram of the driving velocity and similar hereto of the charge level of the electrical energy storage device over time.

[0026] In the representation of FIG. 1, a hybrid vehicle 1 is schematically indicated. Said hybrid vehicle is operated by a combustion engine 2, for example a diesel engine or also a gas engine. Said combustion engine is connected by means of an input shaft 3 to a transmission system 4 that comprises and controls all the functions of the hybrid drive system other than the combustion engine 2. This transmission system 4 is connected by means of an output shaft 5 to two indicated driven wheels 6. Part of said transmission system 4 is in this case an electric machine 7 as well as a gear unit 8, for example an automatic gear unit having a differential converter. The gear unit 8 may comprise a hydrodynamic retarder T.sub.9 as a wear-free sustained-action brake. A further part of said transmission system 4 is the electrical control unit. A transmission control unit 9 is present for this purpose and is connected by means of a bus system 10, preferably a CAN bus, to a vehicle control unit that is not illustrated. A further part of the transmission system 4 is a frequency converter 11 that serves to control the electric machine. The transmission system 4 further comprises an electrical energy storage device 12 that hereafter will also be designated as a hybrid battery. The electrical energy storage device 12 does not therefore have to be designed as a battery. Said electrical energy storage device may also be configured for example in the form of capacitors.

[0027] As a further part of said transmission system 4, an energy converter 13, preferably a DC/DC converter, is present. Said energy converter converts the electrical energy from the voltage level of a first electrical system 14 that is for example 48 V to the voltage level of a second electrical system 15 that particularly represents the vehicle electrical system of said hybrid vehicle 1 inclusive of its load consumer 17, only one such load consumer being indicated in the drawing. This vehicle electrical system 15 of the hybrid vehicle may function in particular at a voltage level of 24 V when used in a commercial vehicle. In addition to the load consumers 17 of the vehicle electrical system, said vehicle electrical system also comprises with a battery 18 that for the purpose of distinction from the hybrid battery 12 shall hereafter be designated as a vehicle battery.

[0028] This system of the hybrid vehicle 1 may be used In the method in accordance with the invention in particular for the primary provision of electrical energy for the second electrical system 15 by means of the first electrical system 14 and the electric machine 7 that is coupled thereto. In order to implement the prioritization of the power supply of the second electrical system 15, it may now particularly be that for specific driving situations of said hybrid vehicle 1 modes of operation are chosen that safeguard the electrical power supply of the second electrical system 15 that hereafter will also be designated as the vehicle electrical system 15. In the representation of FIG. 2, the charge level SOC (State of Charge) is plotted over time t with reference to two diagrams that are arranged synchronized one above the other in the lower half of the diagram, wherein the driving velocity v given for example in km/h of said hybrid vehicle 1 is plotted over the same time axis t. The upper curve of the driving velocity v indicates an increase in the driving velocity v which is followed by a constant driving velocity during a time interval designated as T.sub.1. A deceleration of the hybrid vehicle 1 subsequently occurs. The velocity of said hybrid vehicle decreases and then remains at 0 for a specific time period. Subsequently, a further traction phase occurs during a time interval T.sub.2 and in turn said vehicle is braked and brought to a standstill. In addition, a further time interval T.sub.3 having a third traction phase is represented. The final velocities achieved are therefore in each case different.

[0029] In the lower half of the diagram shown in FIG. 2, the charge level SOC of the hybrid battery 12 is shown. Said charge level fluctuates during the individual time intervals. Before time interval T.sub.1 begins and the hybrid vehicle 1 is stationary, a specific energy requirement of the vehicle electrical system 15 exists that is supplied from the hybrid battery 12 by means of the DC/DC converter 13. The charge level SOC of said hybrid battery therefore decreases. At the beginning of the traction phase during time interval T.sub.1, a so-called boost operation B occurs during which the electric machine 7 provides electrical power to the input shaft 3 of the gear unit 8 in addition to power provided by the combustion engine 2. Said boost operation occurs so long until a limit SOC.sub.L of the charge level limit SOC of said hybrid battery 12 is achieved. Subsequently, the boost operation B is switched off and the hybrid vehicle 1 is accelerated only by means of the combustion engine 2. Notwithstanding this operation, an energy requirement of the vehicle electrical system 15 occurs during the time interval T.sub.1 and during the tractive operation that is being performed, said energy requirement being supplied from the hybrid battery, with the result that the charge level of said hybrid battery 12 further decreases. This electrical energy requirement of the vehicle electrical system is designated with the reference letter E in the representation. The hybrid vehicle 1 is decelerated at the end of time interval t.sub.1. Electrical energy may hereby be recovered via deceleration by means of the electric machine 7 in the generator mode, said recovery being designated as recuperation. The charge level SOC of the hybrid battery 12 hereby increases. While the hybrid vehicle 1 is subsequently at a standstill, a further specific energy requirement for the vehicle electrical system 15 arises with the result that the charge level SOC of the hybrid battery 12 once again decreases but at an appropriately smaller gradient. Subsequently, the traction phase occurs during the time interval T.sub.2. The same sequence that has been described above essentially repeats itself here. This sequence repeats itself cyclically during the operation of said hybrid vehicle 1.

[0030] In practice, the limit value of the charge state SOC.sub.L , up to which limit value the electrical machine 7 may operate in a motor mode, is of such a value that a moving average value over the time intervals T.sub.1 to T.sub.3 is determined in order to predict what may be expected during the subsequent traction phase as a time interval T for the tractive operation. The more such time intervals T are present, the more exact the predictions will be. Furthermore, by means of generating the moving average, outliers are either not strongly considered or excluded. At the same time, it is likewise determined, preferably by means of observation over a longer operating period of the hybrid vehicle 1, what the average energy requirement E of the vehicle electrical system 15 is. It is hereby possible to predict an average energy requirement E during the expected subsequent time interval T of the traction. In any case, it is necessary for this requirement to be supplied from said hybrid battery 12. Furthermore, the hybrid battery 12 must not be discharged to below a specified charge limit in order to for example avoid draining said hybrid battery. It is also considered expedient to select said charge limit such that it is possible to restart the combustion engine 2 by means of the electric machine 7, for example if the driver parks the hybrid vehicle 1 at the end of the traction phase, in other words the hybrid battery 12 may once again be recharged without the use of a recuperation process until it is possible to restart said hybrid vehicle. Based on these considerations, the limit value SOC.sub.L is itself calculated from the sum of these required capacities with the result that the boost operation B may only occur so long either until the acceleration phase of the traction phase ends or until the prevailing charge level SOC of the hybrid battery 12 reaches this limit value SOC.sub.L. The boost operation is then terminated and the further acceleration or rather further movement of the vehicle occurs exclusively by means of the combustion engine 2.

[0031] An approximate continuous electric power supply of the vehicle electrical system 15 by means of the first electrical system 14 of the hybrid system and as a result by means of the hybrid battery 12 is hereby safeguarded. Only in exceptional circumstances, or if the estimation of the expected traction period T is actually much shorter than the actual traction phase, is it possible for situations to arise wherein the hybrid battery 12 reaches a lower specified limit of its charge level SOC, which should not be undershot in order to avoid draining said hybrid battery and/or to safeguard the durability of said hybrid battery. The electric power supply of the vehicle electrical system 15 by means of the energy converter 13 is then terminated. In these situations, the energy supply of the vehicle electrical system 15 may be provided by the vehicle battery 18. In regular operation, these situations occur comparatively seldom with the result that clear safeguarding the vehicle battery 18 is possible and has only to be applied sporadically.

[0032] The total energy supply of said vehicle 1 and in particular the energy supply of the vehicle electrical system 15 or rather the load consumer 17 of said vehicle electrical system is thus provided in the exemplary embodiment illustrated in the drawing by means of the electric machine 7. This electric machine 7 that is designed in particular as a permanently excited electric machine and having embedded magnets comprises in this case a much greater degree of efficiency than offered by conventional alternators.

[0033] In addition, classic alternators are connected to the combustion engine by means of a belt configuration. Belt drives have, inter alia, the disadvantage that they decrease the overall efficiency.

[0034] Therefore, it is possible in the case of such a system of a mild hybrid system, wherein said mild hybrid system prioritizes the power supply to the vehicle electrical system by means of said hybrid battery 12 and said electric machine 7, to achieve a considerably greater degree of efficiency than is possible with conventional alternators. Although the boost performance of said hybrid system is marginally limited, a substantial advantage with respect to the total energy requirement is nevertheless achieved. This then applies particularly if a comparatively higher electrical energy requirement of the vehicle electrical system is present, as is the case particularly for commercial vehicles such as buses for example.

[0035] Aside from the outright recuperation that is used in the representation of FIG. 2 for increasing the charge level SOC of said hybrid battery 12, other methods and possibilities that are described at the beginning of the above description may be used in order to charge the hybrid battery 12 as far as possible in all conceivable situations without additional fuel consumption. For this purpose, the application of the electric machine 7 may for example be provided as a primary brake in all conceivable situations that require more or less heavy braking. Furthermore, an increased generator mode of the electric machine 7 during consistently high rotational speeds may be safeguarded for example by means of increasing the rotational speeds of the reset points in the gear unit 8 in order thus to further improve the energy yield of the electric machine.

[0036] On balance, a very advantageous mild hybrid system results that by means of prioritizing the electric power supply of the vehicle electrical system 15 enables a particularly energy efficient operation of the hybrid vehicle 1 that comprises said mild hybrid system.