Control of a drive unit of a hybrid vehicle and hybrid vehicle

Abstract

Method for controlling a drive unit (3, 203) of a hybrid vehicle (1, 201) comprising an internal combustion engine (5, 205), a first electric machine (9, 209), a second electric machine (11, 211) and an accumulator (13, 213), wherein the drive unit is operable for propelling the hybrid vehicle in the following three operating modes: a purely electric operation in which a drive torque is generated by means of the second electric machine (11, 211) while the internal combustion engine (5, 205) is switched off; a series hybrid operation in which the drive torque is generated by the second electric machine (11, 211) and the internal combustion engine (5, 205) drives the first electric machine (9, 209) to generate electrical energy; a parallel hybrid operation in which a drive torque is produced by means of the internal combustion engine (5, 205), the procedure exhibits: Controlling the drive unit in series hybrid operation such that the internal combustion engine operates at a point of operation (93) based on a combined efficiency (η) VKM × η EM1 ) is operated, which depends on the efficiency (η VKM ) of the internal combustion engine and of the efficiency (η EM1 ) of the first electric machine depends, where serial hybrid operation is carried out, if both a driving speed (55) is below a driving speed threshold (65) and a target drive power (57) and / or a target drive torque is above an electrical operating threshold (67), where serial hybrid operation is further carried out, if the target drive power (57) and / or the target drive torque is above a vehicle speed-dependent parallel hybrid operation threshold (69).

Description

[0001] The present invention relates to a method for controlling a drive unit of a hybrid vehicle and a hybrid vehicle with a drive unit and a drive unit control unit configured to execute the control method.

[0002] A hybrid vehicle's drive system can comprise various drive units for powering a drive wheel, such as an internal combustion engine and one or more electric motors. These different drive units can be controlled in various ways.

[0003] German patent application DE 10 2013 001 095 A1 discloses a method for operating a hybrid drive system, wherein the hybrid drive system comprises an internal combustion engine connectable to a first axle of the motor vehicle, a first electric motor also connectable to the first axle, and a second electric motor connectable to a second axle of the motor vehicle. The electrical energy used to operate the second electric motor is generated by the first electric motor, which is driven by the internal combustion engine with an increase in its power output, or is taken exclusively from an electrical energy storage device.

[0004] European patent EP 1 074 087 B1 discloses a control method and a device for the internal combustion engine of an electric hybrid vehicle, wherein an electric motor or motor / generator is arranged between the engine and the continuously variable or automatic transmission, and wherein the hybrid vehicle has a battery and associated control elements. A control device maintains the power output of the internal combustion engine substantially along an ideal operating line when the speed of the engine changes. A second electric motor may also be provided, and the torque output of the second electric motor can be varied by means of a system control.

[0005] German patent application DE 10 2012 103 292 A1 discloses a method for operating an electric drive train of a vehicle, wherein at least two electric motors, each operatively connected to a drive axle, and a control device are provided, wherein a driver-requested torque for motor or generator operation is determined, and wherein a required total power of the electric drive train is determined at a given output speed, and wherein the power outputs of the individual electric motors are determined, and wherein the resulting power losses of the individual electric motors are minimized on the basis of stored power loss maps for the individual electric motors.

[0006] German patent application DE 10 2009 019 485 A1 discloses a drive train comprising a first electric motor and a planetary gear set, and vehicles incorporating this drive train. The drive train includes a first electric machine, which can be operated in motor or generator mode, and a planetary gear set with a speed-changing device. The planetary gear set has an input and an output side, and the first electric machine, in motor or generator mode, engages the speed-changing device to control it, thus establishing a gear ratio in the planetary gear set. The gear ratio of the planetary gear set is influenced by the first electric machine, which also determines the operating point of the internal combustion engine. The internal combustion engine is operated close to its optimal efficiency.In purely electric mode, the second electric machine operates as a motor, while the first electric machine either idles or is used as an auxiliary drive. A portion of the mechanical energy generated by the combustion engine is converted into electrical energy by the first electric machine and directly transferred to the second electric machine. Acceleration is assisted by the second electric machine. During deceleration, the energy storage system can be charged by recuperating braking energy.

[0007] The translation of European patent DE 602 23 850 T2 discloses a method for operating a drive system of a hybrid vehicle, wherein the hybrid vehicle comprises an internal combustion engine, a first electric motor / generator, a planetary gear mechanism, and a second electric motor / generator. A ratio between a first torque generated by the internal combustion engine at the vehicle axles and a second torque generated by the second electric motor at the vehicle axles at each gear position of the transmission is changed from a first ratio when both the internal combustion engine and the second electric motor are operating normally to a second ratio when either the internal combustion engine or the second electric motor is malfunctioning.

[0008] German patent application DE 10 2007 054 368 A1 discloses a control architecture for selecting an optimal mode or gear ratio and drive speed for a hybrid powertrain system comprising an internal combustion engine, a first and a second electric motor, and an electromechanical transmission that can be selectively operated to transmit torque between them and can be operated in several modes with fixed gear ratios and continuously variable modes. For each permissible operating range condition, preferred operating conditions and preferred costs are determined, and a preferred operating range condition is selected based on these.Cost structure information, entered into a strategic management facility segment and used in an optimization segment, preferably includes operating costs generally determined based on factors related to vehicle driving characteristics, fuel economy, emissions, and battery life for the specified torque range. Furthermore, costs in fuel and electrical energy consumption pertaining to the specific operating point of the powertrain system for the vehicle are allocated and assigned. The optimal operating costs can be determined by calculating a total powertrain system loss, which includes an expression based on the engine power loss driven by fuel economy and exhaust emissions, plus losses in the mechanical system, losses in the electrical system, and heat losses.

[0009] DE 103 93 594 T5 describes a drive system for a two-engine hybrid vehicle, comprising: an internal combustion engine, a clutch, a stepped transmission, a drive shaft, a brake system and drive wheels, wherein the drive system further comprises a main engine, a rotor shaft of the main engine connected to an output shaft of the stepped transmission, an auxiliary engine, wherein a rotor shaft of the auxiliary engine is connected to a crankshaft of the internal combustion engine by means of a drive mechanism, wherein the main engine and the auxiliary engine are electrically connected to a traction battery, and with an overall vehicle control system that automatically puts the drive system into operation in the following operating modes: 1.1.) When the vehicle is in a low-speed driving condition, the system operates in a purely electric drive mode in which the combustion engine is not running and only the main engine drives the drive shaft, or the system operates in a series drive mode in which the combustion engine only drives the auxiliary engine, which generates electrical energy, and the generated electrical energy is supplied to the main engine via the traction battery to drive the drive shaft; 2.) When the vehicle is in a full acceleration state, the system operates in a parallel drive mode in which both the combustion engine and the main engine drive the vehicle simultaneously; 3.) When the vehicle is in a braking and deceleration state, the system operates in an energy recovery mode in which the main engine is controlled to brake and generate electrical energy, and the traction battery is recharged; 4.) if the vehicle is in the middle of a gear shift, the system operates in an auxiliary drive mode in which the main engine provides auxiliary power to the vehicle during the shifting process, 5.) if the vehicle is in a standby / stop state, the system operates in a standby / stop mode in which the internal combustion engine stops operating, and 6.) if the vehicle is in a normal driving state, the system operates in a normal driving mode in which the internal combustion engine independently powers the vehicle.

[0010] EP 2 097 304 B1 describes a method for controlling the hybrid drive of a motor vehicle, which hybrid drive comprises the following components: an internal combustion engine, an axle drive transmission, at least one electric machine, at least one clutch, at least one energy storage device, and at least one driven axle. In the simplest case, the hybrid drive to be controlled consists of an internal combustion engine, an electric machine arranged in series and capable of operating as a motor and generator, a single-stage (i.e., non-shiftable) reduction gear, and a differential as the axle drive transmission for one driven axle. However, the hybrid drive to be controlled can also comprise several electric machines in a complex arrangement, several clutches, and several – in particular two – driven axles.

[0011] In current technology, the control of different drive units of a hybrid vehicle does not always necessarily lead to energy-efficient operation.

[0012] One object of the present invention is to provide a control method for a drive unit of a hybrid vehicle and a hybrid vehicle, wherein various drive units of the hybrid vehicle are controlled in a consumption-optimized and energy-efficient and / or emission-reducing manner in order to generate a requested drive torque or a requested drive power.

[0013] The problem is solved by the subject matter of the independent claims, which relate to a method for controlling a drive unit of a hybrid vehicle and to a hybrid vehicle itself. The dependent claims specify particular embodiments of the present invention.

[0014] According to a first aspect of the present invention, a method for controlling a drive unit of a hybrid vehicle is provided, comprising an internal combustion engine, a first electric machine, a second electric machine and an accumulator, wherein the drive unit is operable in the following three operating modes for driving the hybrid vehicle: a purely electric operation in which a drive torque is generated by means of the second electric machine while the internal combustion engine is switched off; a series hybrid operation in which the drive torque is generated by the second electric machine and the internal combustion engine drives the first electric machine to generate electrical energy; a parallel hybrid operation in which a drive torque is generated by means of the internal combustion engine.

[0015] The procedure exhibits the following characteristics: Controlling the drive system in series hybrid operation such that the internal combustion engine is operated at an operating point based on a combined efficiency that depends on the efficiency of the internal combustion engine and the efficiency of the first electric machine.

[0016] Considering the combined efficiency of the first electric motor and the combustion engine in series operation leads, as explained below, to a CO2-optimized series hybrid operation. Furthermore, the explanation of the various operating thresholds will clarify the distinction between the three operating modes. This distinction can then extend beyond the optimization of series operation to a holistically optimized "overall operation" of the hybrid vehicle.

[0017] In principle, beyond the three operating modes mentioned above, further operating modes are conceivable, such as those relating to the recuperation of braking energy during deceleration phases. The three operating modes listed here are, in particular, the essential operating modes relating to the generation of propulsion or drive power.

[0018] The method can be implemented, for example, in software and / or hardware and can, in particular, be loaded into and executed by an engine control unit. The internal combustion engine can, for example, be a diesel engine or a gasoline engine. The internal combustion engine can also include a fuel tank containing fuel. The fuel can be supplied to the combustion chambers of the internal combustion engine, in particular via injection pumps and a valve. Depending on the amount of fuel supplied per unit of time, the output power of the internal combustion engine can be controlled.

[0019] The first electric machine can be operated in either electromotive or generator mode. The second electric machine can also be operated in either electromotive or generator mode.

[0020] The internal combustion engine, the first electric motor, and the second electric motor can, for example, have similar maximum output power ratings, differing by less than 30%. The maximum output torques of the various drive units can differ, for example, depending on the transmission and / or gear ratio design. In this case, the second electric motor might provide the highest maximum output torque, the internal combustion engine a medium maximum output torque, and the first electric motor the lowest maximum output torque. This allows the second electric motor to be advantageously used as a traction motor, i.e., operated in electric motor mode.

[0021] The drive system can further include a main clutch between the internal combustion engine and a drive wheel. Optionally, a gearbox can be arranged between the main clutch and the internal combustion engine. In other embodiments, a gearbox is omitted, and a fixed gear ratio (e.g., i = 2.8) can be maintained between an output shaft of the internal combustion engine and the drive wheel. In these embodiments, a specific vehicle speed can thus correspond to a specific rotational speed of the internal combustion engine.

[0022] Optionally, a first coupling can be provided between the first electric machine and an output shaft of the internal combustion engine in order to be able to optionally decouple the first electric machine in certain operating conditions or operating modes.

[0023] Furthermore, a second coupling can optionally be provided between the second electric machine and the drive wheel in order to decouple the second electric machine from the drive wheel in certain operating conditions or in certain operating modes and also to decouple it from the output shaft of the internal combustion engine.

[0024] In purely electric operation, the main clutch can be open and the second clutch (if present) can be closed (i.e., in the coupled state).

[0025] In series hybrid operation, the main clutch can be open, and the first clutch (if present) and the second clutch (if present) can also be closed. Series hybrid operation can be performed with or without load point boosting. This means the internal combustion engine can be controlled in such a way that its output power is higher than the target drive power, so that the excess power can also be used to charge the battery.

[0026] In parallel hybrid operation, the main clutch is closed, and the first clutch (if present) and the second clutch (if present) are open, unless load point boosting is performed. In parallel hybrid operation with load point boosting via the first electric machine, the main clutch can be closed, the first clutch can be closed, and the second clutch (if present) can be open.

[0027] Alternatively, in parallel hybrid operation, a load point increase can also be achieved via the second electric machine, whereby in such a case the main clutch is closed, the first clutch (if present) is open and the second clutch (if present) is closed.

[0028] The efficiency of an internal combustion engine can be determined, for example, using a specific fuel consumption (e.g., fuel mass consumed divided by energy produced, e.g., measured in g / kWh). The lower the specific fuel consumption, the higher the efficiency of the internal combustion engine. Specific fuel consumption can be determined, for example, as a function of, and / or dependent on, the engine's rotational speed and torque or power output. Lines of equal specific fuel consumption (so-called iso-lines) can be plotted, for example, in a coordinate system that plots the engine's rotational speed against its torque and / or power output. Iso-curves for different output power outputs can also be plotted in the same coordinate system.

[0029] During series operation, the internal combustion engine drives the first electric motor, which generates electrical energy in generator mode. This generated electrical energy is then supplied to the second electric motor to drive the drive wheel. Considering the efficiency of the first electric motor accounts for losses incurred in converting the mechanical energy supplied by the internal combustion engine into electrical energy. The operating point of the internal combustion engine, determined based on the combined efficiency of the first electric motor and the internal combustion engine, may differ from the operating point determined solely based on the efficiency of the internal combustion engine.In particular, the operating point obtained based on the combined efficiency can be shifted to higher engine speeds and / or lower torques of the internal combustion engine for a given target drive power and / or target drive torque. This allows the hybrid vehicle or its drive system to be operated more energy-efficiently and, in particular, with optimized CO2 emissions in series hybrid mode.

[0030] The operating point can be an extreme point of the combined efficiency for a given target power and / or a given target torque. The extreme point can specify the argument(s) (e.g., speed and torque) at which the combined efficiency reaches an extremum (e.g., minimum or maximum). If the efficiency is represented, for example, based on specific fuel consumption, the point(s) of the argument(s) (e.g., speed and torque) at which the combined efficiency reaches a maximum can be determined. Thus, in some embodiments, a simple procedure for determining the operating point is provided. The efficiencies of the internal combustion engine and the first electric machine may have been previously determined experimentally and / or by simulation, and in particular, they may have been determined over all possible operating ranges.

[0031] Controlling the drive system in series hybrid operation can further include retrieving the operating point from a predefined operating point curve, where the operating point curve defines the operating points for a plurality of target power and / or target torque values. The operating points are determined by a plurality of extreme points of the combined efficiency for the majority of the target power and / or target torque values. The operating point curve can, for example, be determined on a test bench and can be stored in the engine control unit of the hybrid vehicle. This further simplifies the process.

[0032] The combined efficiency can be the product of the efficiency of the internal combustion engine and the efficiency of the first electric motor. The target power can correspond to a target drive power or to the sum of a target drive power and a target load point boost power. This allows for energy-efficient and CO2-optimized series operation with or without load point boosting.

[0033] Purely electric operation can be carried out if the driving speed (or rotational speed of the drive wheel) is below a driving speed threshold (or rotational speed threshold) and / or a target drive power and / or a target drive torque is below an electric operation threshold.

[0034] The vehicle speed threshold can be determined by a gear ratio between the internal combustion engine and the drive wheel, and it can also be determined by a gear ratio available from an optional transmission. Below the vehicle speed threshold, particularly with a fixed gear ratio between the output shaft of the internal combustion engine and the drive wheel, the engine speed may be too low to provide sufficient drive torque.

[0035] The electric operating threshold can be, for example, an electric operating power threshold or an electric operating torque threshold. The electric operating threshold can, for example, be determined based on the efficiency of the internal combustion engine, whereby energy-inefficient low-load operating points of the internal combustion engine are replaced by purely electric operation. The electric operating threshold can also be determined based on the capacity of the battery, whereby the electric operating threshold can increase with increasing battery capacity. Other dependencies are possible.This ensures reliable operation, in particular by preventing the internal combustion engine from operating at low load points with energy-inefficient efficiencies, by preventing excessive strain on the accumulator, and by preventing the internal combustion engine from being used to drive the drive wheel at excessively low speeds.

[0036] Series hybrid operation can be performed if both the vehicle speed is below the vehicle speed threshold and the target drive power and / or target drive torque are above the electric operation threshold. Since the main clutch is open in series operation, the speed and / or torque of the internal combustion engine can be adjusted independently of the vehicle speed so that the internal combustion engine operates at a permissible, and in particular optimal, operating point to drive the first electric motor to generate electrical energy. This energy is then used by the second electric motor to apply the target drive power or torque to the drive wheel in electric mode.

[0037] Series operation can also be performed if the target drive power and / or target drive torque is above a vehicle speed-dependent parallel hybrid operating threshold. This parallel hybrid operating threshold can be, for example, a parallel hybrid operating torque threshold or a parallel hybrid operating power threshold. The parallel hybrid operating threshold can, for example, represent the maximum power or torque that can be generated by the internal combustion engine (optionally including "boost" support from the first electric motor and / or the second electric motor). In particular, with a fixed gear ratio between an output shaft of the internal combustion engine and the drive wheel, the parallel hybrid operating threshold can be dependent on the vehicle speed. The parallel hybrid operating threshold can, for example, increase linearly with the vehicle speed. Other dependencies are possible.This allows the drive unit to be operated reliably and the target drive power and / or target drive torque to be reliably generated at the drive wheel.

[0038] Parallel hybrid operation can be implemented if the vehicle speed is above the vehicle speed threshold, the target drive power and / or torque is below the vehicle speed-dependent parallel hybrid operation threshold, and the target drive power and / or torque is above the electric operation threshold. This allows for clear transitions between the different operating modes. In particular, parallel hybrid operation can preferably be implemented whenever the aforementioned conditions are met. Fuel consumption studies have shown that in virtually all cases where parallel hybrid operation is possible due to the constraints imposed by the internal combustion engine, parallel hybrid operation is more fuel-efficient and CO2-optimized than series hybrid operation.

[0039] The electrical operating threshold can, for example, have a constant value for driving speeds below the driving speed threshold, which may be higher than a different value for the electrical operating threshold for driving speeds above the driving speed threshold. Other embodiments are possible.

[0040] The parallel hybrid operating threshold can be defined as the sum of the maximum drive power and / or drive torque achievable by the internal combustion engine, taking into account any optional boost support from the first electric motor and / or the second electric motor. In other embodiments, the parallel hybrid operating threshold can be defined as the maximum torque achievable by the internal combustion engine.

[0041] In parallel hybrid operation, the first and / or second electric motors can contribute at least partially to the drive torque and / or drive power, in addition to the maximum power and / or maximum torque of the internal combustion engine. This modification is also known as "boost." This allows parallel operation to easily be extended to higher drive power and / or drive torque.

[0042] According to a second aspect of the present invention, a hybrid vehicle is provided which comprises a drive unit comprising an internal combustion engine, a first electric machine, a second electric machine and an accumulator, wherein the drive unit can be operated in the following three operating modes for driving the hybrid vehicle: a purely electric operation in which a drive torque is generated by means of the second electric machine while the internal combustion engine is switched off; a series hybrid operation in which the drive torque is generated by the second electric machine and the internal combustion engine drives the first electric machine to generate electrical energy; a parallel hybrid operation in which a drive torque is generated by means of the internal combustion engine,

[0043] Furthermore, the hybrid vehicle has a drive control unit configured to execute a method according to one of the preceding embodiments.

[0044] Embodiments of the present invention will now be explained with reference to the accompanying drawings. The invention is not limited to the illustrated or described embodiments. Fig.Figure 1 schematically illustrates a hybrid vehicle according to an embodiment of the present invention, which is equipped to perform a method according to an embodiment of the present invention; Fig. Figure 2 schematically illustrates a hybrid vehicle according to another embodiment of the present invention, which is equipped to perform a method according to an embodiment of the present invention; Fig. 3 illustrates curves of the in Fig. 1 or Fig. 2 illustrated hybrid vehicles in parallel hybrid operation provided torque and power; Fig. Figure 4 schematically illustrates a method for controlling a drive unit of a hybrid vehicle according to an embodiment of the present invention; Fig. Figure 5 illustrates different operating modes of the in Fig. 1 and Fig.2 illustrated hybrid vehicles which are used in a method according to an embodiment of the present invention; Fig. Figure 6 illustrates fuel consumption in various operating modes, as described by the models in Fig. 1 and Fig. 2 illustrated vehicles, and Fig. Figure 7 illustrates curves representing efficiencies considered in embodiments of the present invention.

[0045] The Fig.A schematically illustrated hybrid vehicle 1 has a drive unit 3 and a drive unit control 6, which is configured to perform a method for controlling the drive unit 3 of the hybrid vehicle 1 according to an embodiment of the present invention. The drive unit 3 comprises an internal combustion engine 5 with several cylinders 7, a first electric machine (also referred to as a generator) 9, a second electric machine (also referred to as a traction machine) 11, and an accumulator 13, which is connected to both the first electric machine 9 and the second electric machine 11 via power supply cables (and power electronics) not illustrated.

[0046] The drive unit 3 can be operated in three operating modes to power the hybrid vehicle 1. First, in purely electric mode, in which a driving torque (which, for example, is applied to the drive wheels 15) is generated by the second electric machine 11, while the internal combustion engine 5 is switched off (i.e., no fuel is supplied to it from a tank not shown). Second, the drive unit 3 can be operated in series hybrid mode, in which the driving torque is generated by the second electric machine 11 and the internal combustion engine 5 drives the first electric machine 9 to generate electrical energy, which in turn is supplied to the second electric machine 11 (either directly or via the battery 13).Thirdly, the drive unit 3 can be operated in a parallel hybrid mode in which a drive torque is generated by means of the internal combustion engine 5 and in particular the second electric machine 11 and / or the first electric machine 9 are switched off.

[0047] In the Fig.In the illustrated hybrid vehicle 1, the drive unit 3 further comprises a main clutch K0 (17) and a transmission 19, both of which are arranged between the internal combustion engine 5 and a wheel drive train 21. The wheel drive train 21 is mechanically connected to the drive wheels 15 via a differential 25 with an associated differential ratio 23. The first electric machine 9 is connected to an output shaft 31 of the internal combustion engine 5 via a first clutch K1 (27) and a first transmission element 29, the output shaft 31 being mechanically connected to an input shaft 32 of the transmission 19. An output shaft 33 of the transmission 19 is connected to the main clutch K0 (17). The second electric machine 11 is connected to the wheel drive train 21 via a second transmission element 35 and a second clutch K2 (37).

[0048] In hybrid vehicle 1, a series-parallel hybrid concept is implemented. By scaling the battery 13 (also referred to as HV battery) with respect to energy content and / or power (discharging and charging power), hybrid vehicle 1 can be configured as a hybrid electric vehicle (HEV) as well as a plug-in hybrid electric vehicle (PHEV). The first electric machine 9 (also referred to as EM1) is dimensioned, for example, with respect to power and torque such that, taking into account the gear ratio 29 from the internal combustion engine 5 to the first electric machine 9, every possible internal combustion engine operating point (also referred to as operating point) can be set in series operation. The second electric machine 11 (also referred to as electric drive motor EM2) is, for example,Regarding the power dimensioning, it is based on the power dimensioning of the internal combustion engine 5, meaning it can provide a similar maximum power.

[0049] For parallel hybrid operation, the gear ratios from the internal combustion engine to the drive wheel 15 can be provided in various ways or configurations (e.g., stepped or continuously variable), whereby at least one overdrive gear ratio is provided here with, for example, a typical gear ratio from the internal combustion engine 5 to the drive wheel 15 of, for example, i = 2.8, which means that if the output shaft 31 of the internal combustion engine 5 rotates 2.8 times, the drive wheel 15 rotates once.

[0050] The reduction ratios of the traction motor EM2 and the generator EM1 can, for example, be implemented as a spur gear stage or via a (braked) planetary gear set. The parallel power path (shaft 33) can be decoupled from the drive wheel 15 via the main clutch K0. The traction motor EM2 and the generator EM1 can (optionally) each be decoupled via the second clutch 37 (also designated K2) and the first clutch 27 (also designated K1) to reduce drag losses. All clutches K0, K1, and K2 can be designed, for example, as friction-fit multi-plate clutches and / or positive-locking jaw clutches. The generator EM1 can operate primarily or exclusively as a generator, it can be used to start the internal combustion engine, or it can be used in parallel hybrid operation to provide boost support to the internal combustion engine 5.Pure electric operation (EV operation) and recuperation can be carried out via the drive motor EM2 (i.e. the second electric machine) while the main clutch K0 is open and the second clutch K2 is closed.

[0051] Table 1 below lists the different operating modes in which the drive unit 3 can be operated, together with the respective coupling states of the main coupling K0, the first coupling K1 and the second coupling K2. Table 1: Operating mode K0 K1 K2 EV operation open any closed Recuperation open any closed Serial hybrid operation with and without load point elevation open closed closed Parallel hybrid operation without load point increase closed open open Parallel hybrid operation with load point increase via EM1 closed closed open Parallel hybrid operation with load point boosting via EM2 closed open closed

[0052] Thus, the drive unit 3 can be operated in purely electric mode (EV mode), in series hybrid mode, and in parallel hybrid mode. Both series hybrid mode and parallel hybrid mode can be operated with or without load point boosting, as shown in Table 1 above.

[0053] The direct connection of the second electric machine 11 (EM2) to the drive wheel 15 enables efficient electric drive and efficient recuperation.

[0054] During series hybrid operation, the maximum combustion engine power can be used to propel the vehicle even at very low vehicle speeds and / or wheel speeds, since in this case the main clutch K0 is open and therefore the speed of the combustion engine 5 can be optimally adjusted independently of the vehicle speed. From purely electric operation (EV operation), a very smooth and traction-neutral start-up of the combustion engine can be achieved via the first electric motor 9 (generator EM1) with the main clutch K0 open.

[0055] If an additional load point increase is required in parallel operation, the necessary regenerative operation for generating electrical power to charge the battery can be carried out either via the second electric machine 11 (traction motor EM2) or the first electric machine 9 (generator EM1). In parallel hybrid operation without the need for an additional load point increase, the following applies: Fig. In the illustrated hybrid vehicle 1, to minimize drag losses, the second electric machine 11 (traction motor EM2) and the first electric machine 9 (generator EM1) are decoupled by opening the second clutch 37 (K2) and opening the first clutch 27 (K1).

[0056] The selection of all-electric hybrid operation, series hybrid operation and parallel hybrid operation can take into account the respective efficiencies of the powertrain components for the purpose of minimizing consumption.

[0057] Fig. Figure 2 illustrates a hybrid vehicle 201 according to a further embodiment of the present invention, wherein structurally and / or functionally similar or identical components are in Fig. 1 and Fig. 2 are designated by reference numerals that are identical in their last two positions. For simplification, the following description sometimes uses the reference numerals from both. Fig. 1 and Fig. 2 are given, each separated by a comma.

[0058] The Fig. The illustrated hybrid vehicle 201 can be understood as a “simplified” system topology without the possibility of decoupling the drive motor EM2 and generator EM1, and without a gearbox (stepped or continuously variable), so that only an overdrive transmission from the internal combustion engine 205 to the drive wheel 215 can be present.

[0059] In electric mode, the main clutch K0 is open. The internal combustion engine and electric generator EM1 are stationary (speed = zero). The driving request is provided by the electric drive motor EM2, drawing electrical power from the high-voltage battery. Hybrid driving operation can be configured in series and parallel modes. In series hybrid mode, the main clutch K0 is open. The speed of the internal combustion engine is freely adjustable. The mechanical power of the internal combustion engine is converted into electrical power by the generator EM1. This electrical power is used to recharge the high-voltage battery as needed and is also used by the drive motor EM2 to provide the driving request.

[0060] In parallel hybrid operation, the main clutch K0 is closed. The speed of the internal combustion engine is coupled to the wheel speed via the overdrive transmission. When required, the mechanical power of the internal combustion engine is used to recharge the high-voltage battery via the generator EM1 and is also transmitted mechanically directly to the wheel to respond to driving demands.

[0061] In parallel hybrid operation without the need for an additional load point increase, the generator EM1 can be decoupled to minimize drag losses (with a loss of dynamics acceptable to the driver, e.g., during cruise control and / or adaptive cruise control operation). In a further embodiment, the first coupling 227 can also be omitted.

[0062] Fig.Figure 3 illustrates, for parallel hybrid operation in a coordinate system with an abscissa 43, which illustrates the rotational speed of the internal combustion engine 5, 205, and with an ordinate 45, which indicates the power and / or torque applied to the input shaft 32 of the transmission 19 or an output shaft 233, a power 47 of the internal combustion engine 5, 205, a system power 49, a torque 51 of the internal combustion engine 5, 205, and a system torque 53 of the respective entire drive unit 3, 203. The system power 49 and the system torque 53 are defined taking into account electric boost support by the generator EM1 (and / or the traction motor EM2). Power and torque requirements (i.e., target powers orTarget torques) above the combustion engine full load can thus be represented in parallel hybrid operation up to the defined system power 49 and up to the defined system torque 53 via a combined combustion and electric motor operation with corresponding electrical power extraction from the accumulator (HV battery) 13, 213.

[0063] The Fig. 1 and Fig. The two illustrated drive unit controls 6, 206 are designed to carry out a method 38 for controlling the drive unit 3, 203 of the hybrid vehicle 1, 201 according to an embodiment of the present invention, which is schematically shown in Fig. 4 is illustrated.

[0064] First, in process step 39 of process 38, the drive unit 3, 203 is provided, comprising the first electric machine 9, 209, the second electric machine 11, 211, the internal combustion engine 5, 205, and an accumulator 13, 213. The drive unit 3, 203 can be operated in the following three operating modes to drive the hybrid vehicle 1, 201: a purely electric operation in which a drive torque is generated by means of the second electric machine while the internal combustion engine is switched off; a series hybrid operation in which the drive torque is generated by the second electric machine and the internal combustion engine drives the first electric machine to generate electrical energy; and a parallel hybrid operation in which a drive torque is generated by means of the internal combustion engine.

[0065] In a further process step 41, the drive unit 3, 203 is controlled in series hybrid operation such that the internal combustion engine 5, 205 is operated at an operating point based on a combined efficiency which depends on the efficiency of the internal combustion engine 5, 205 and on the efficiency of the first electric machine 9, 209.

[0066] Based on the definition of in Fig. The different operating modes (i.e., purely electric operation, series hybrid operation, and parallel hybrid operation) for propelling the hybrid vehicle 1, 201 can be visualized in a diagram of available drive power (and / or target drive power) versus vehicle speed (or drive wheel speed), as shown in Figure 3. Fig. 5 is shown. On the abscissa 55 in Fig.5 represents the speed of the hybrid vehicle, and ordinate 57 represents the (available) drive power. Pure electric operation (EV operation) is performed in sections 59 and 60, series hybrid operation in section 61, and parallel hybrid operation in section 63. Curve 64 represents the driving resistance during constant-speed driving on a level surface. Fig. The diagram shown in Figure 5 can be represented analogously as available drive torque (instead of drive power) versus vehicle speed or wheel speed.

[0067] Purely electric operation is carried out in area 59 if the driving speed is below a driving speed threshold 65 and the drive power (target drive power) is below an electric operation power threshold 67.

[0068] Furthermore, purely electric operation is carried out in range 60 if the driving speed is above the driving speed threshold 65 and the drive power (target drive power) is below a further electric operation power threshold 68, which is smaller (e.g. 3 kW) than the electric operation power threshold 67.

[0069] Parallel hybrid operation in range 63 is performed if the vehicle speed is above the vehicle speed threshold 65, the target drive power is below the vehicle speed-dependent parallel hybrid operation power threshold 69, and the target drive power is above the further electric operation threshold 68. The parallel hybrid operation power threshold 69 is defined here as the sum of the maximum output power 71 of the internal combustion engine 5, 205 and the boost support of the first electric machine 9, 209 and / or the boost support of the second electric machine 11, 211. In range 73, a boost is therefore provided in parallel hybrid operation by means of the first electric machine EM1 and / or the second electric machine EM2.

[0070] Series hybrid operation is performed in range 61 if both the vehicle speed is below the vehicle speed threshold 65 and the target drive power is above the electric operation power threshold 67. Furthermore, series hybrid operation is performed in range 61 if both the vehicle speed is above the vehicle speed threshold 65 and the target drive power is above a vehicle speed-dependent parallel hybrid operation power threshold 69.

[0071] The electric operation is limited with regard to the maximum drive power output for minimizing consumption by the electric operation threshold 67 and by the further electric operation threshold 68 (here e.g.: up to approx. 49 km / h, approx. 15 kW drive power; from approx. 49 km / h approx. 3 kW drive power).

[0072] Parallel hybrid operation is initiated as soon as a minimum rotational speed of the internal combustion engine 5, 205 is exceeded, taking into account the gear ratio of the internal combustion engine 5, 205 to the drive wheel 15, 215. In an exemplary embodiment, the overdrive gear ratio from the internal combustion engine 5, 205 to the drive wheel 15, 215 is i = 2.8, resulting in a rotational speed of the internal combustion engine 5, 205 of approximately 1200 rpm at a vehicle speed of approximately 49 km / h. From this speed onwards, the internal combustion engine is able to automatically generate the drive torque or drive power.Parallel hybrid operation is limited with respect to maximum drive power output by the maximum load of the internal combustion engine and, taking into account the electric boost support from generator EM1 and / or traction motor EM2, by the system power (here by the parallel hybrid operation power threshold 71 (without boost) or 69 (with boost)). Above the electric operation power threshold 67 and above the parallel hybrid operation power threshold 69, series hybrid operation is used. The maximum drive power output of series hybrid operation is limited by the dimensioning of the second electric machine 11, 211 (traction motor EM2) by line 75. Thresholds 67, 68, 69, 71, and 65 can be determined for optimal fuel consumption and / or CO2 emissions.

[0073] The derivation of a CO2-optimized hybrid operating strategy is based on a comparison of conventional, purely combustion-engine propulsion with intermittent electric-combustion-engine driving. In hybrid operation (series and / or parallel), in addition to recuperation, the increased fuel consumption due to load point increases, as well as the energy input for electric driving and engine start-up processes, must be taken into account. Electric driving is then only permitted within an energetically efficient range, where the overall efficiency is higher than in purely combustion-engine operation, despite the multiple, lossy energy conversions.

[0074] The transition from electric to hybrid driving mode occurs when the driver's desired drive power, derived from the pedal input, exceeds a predetermined value. This power threshold, which also depends on wheel speed and vehicle speed, is determined using a mathematical optimization procedure that considers the efficiencies of all powertrain components for various driving cycles to optimize fuel consumption.

[0075] For the in Fig. 2. In the exemplary embodiment shown and taking into account typical component efficiencies, a limiting drive power of approximately 15 kW for electric operation can be achieved up to approximately 49 km / h, and a limiting drive power of approximately 3 kW for electric operation can be achieved from 50 km / h onwards, without the present invention being limited to these values ​​and limits.

[0076] In parallel hybrid operating states, an equivalent series hybrid operating state can generally also be represented. However, for typical implementation examples, it becomes apparent for a wide variety of driving requirements that, considering all powertrain component efficiencies, series operation usually exhibits lower efficiency compared to parallel hybrid operation, as shown in Fig. Figure 6 illustrates this. In hybrid operation, parallel hybrid operation should therefore be preferred over series hybrid operation, if possible, due to its higher efficiency.

[0077] Fig. Figure 6 illustrates fuel consumption in mass per unit of time as a function of speed and load point increase. This applies to almost all types of speed and load point increase shown in Fig.As shown in Figure 6, parallel hybrid operation requires less fuel per unit of time than series hybrid operation. Parallel hybrid operation is represented by area elements 77, and series hybrid operation is illustrated by area elements 79. Only at relatively low speeds and relatively high load point increases does parallel hybrid operation show a higher fuel consumption per unit of time than series hybrid operation.

[0078] In series hybrid operating conditions, the speed of the internal combustion engine is freely adjustable due to the open main clutch K0. (The speed of the electric generator EM1 is mechanically coupled to the speed of the internal combustion engine. The speed and torque of the electric drive motor EM2 are mechanically coupled to the wheel speed and the wheel torque requested by the driver.) The mechanical power of the internal combustion engine is converted into electrical power via the generator EM1. This electrical power is used to recharge the high-voltage battery as needed (load point increase, P). LPA ) and used by the EM2 drive motor to propel the vehicle (P EM2, elektrisch ).

[0079] The CO2-optimized series hybrid operation takes into account the optimal combined efficiency of the internal combustion engine and the electric generator EM1. In this CO2-optimized series hybrid operation, the operating points of the internal combustion engine are typically shifted to higher speeds compared to its optimal efficiency, since the electric generator EM1 typically reaches its optimum efficiency at higher speeds than the internal combustion engine. In principle, the following relationship can be used, for example, to determine the fuel-efficient speed of the internal combustion engine in series hybrid operation, depending on the required charging power to the high-voltage battery, the required electrical power at the drive motor EM2 to represent the driving requirements, and the efficiencies of the internal combustion engine and the electric generator EM1: nVKM,CO2−opt.(PLPA+PEM2,electric,ηVKM,ηEM1)=max(ηVKM×ηEM1)(PLPA+PEM2,electric)

[0080] This refers to n VKM,CO2-opt the CO2-optimized speed of the internal combustion engine, η VKM the efficiency of the internal combustion engine, η EM1 the efficiency of the first electric machine, P LPA the load point increase capacity, and P EM2,elektrisch the electrical power supplied to the second electric machine.

[0081] The efficiencies are measured at the point (P). LPA + P EM2,elektrisch ) taken.

[0082] Fig.Figure 7 illustrates, in a coordinate system with abscissa 81, which indicates the rotational speed of the internal combustion engine 5, 205, and with ordinate 83, which indicates the torque provided by the internal combustion engine 5, 205, lines 85 represent the same specific fuel consumption, and dashed lines 87 represent different total output powers, that is, the powers generated by the internal combustion engine 5, 205. Line 89 illustrates the fuel-optimized efficiency of the internal combustion engine 5, 205 alone, and line 91 illustrates an operating point curve obtained by optimizing the fuel consumption of a combined efficiency, where the combined efficiency depends on the efficiency of the internal combustion engine 5, 205 and on the efficiency of the first electric machine 9, 209. In particular, the combined efficiency is determined by a product of these two efficiencies, as shown in the equation above.

[0083] To find the operating point of the internal combustion engine 5, 205 in series hybrid operation at a (given) target power, the intersection of the operating point curve 91 with the line 87 corresponding to the desired target power is located. If, for example, the target power is 20 kW (which could correspond, for example, to the sum of a target drive power of 15 kW at the drive wheel 15 and a load point increase of 5 kW for charging the battery), then the intersection of the corresponding curve 87 with the operating point curve 91 results in operating point 93, which defines a speed of approximately 2200 rpm and a torque of approximately 77 Nm. The torque and speed corresponding to operating point 93 are then set at the internal combustion engine 5, 205 by means of a suitable fuel supply. For this purpose, the drive unit control 6, 206 outputs control signals 8, 208 to the internal combustion engine 5, 205.Further control signals 10, 210 are output to the first electric machine 9, 209 and further control signals 12, 212 are output to the second electric machine 11, 211 for its control. The drive unit control 6, 206 can also output control signals 14, 214 for the main clutch K0 (17), the first clutch K1 (27) and the second clutch K2 (37) and control signal 4 to the gearbox 19. If, starting from operating point 93, a requested target power changes upwards or downwards, the operating point is shifted along the operating point line 91, as indicated by the arrows.

[0084] The operating point adjustment of the internal combustion engine in series hybrid operation under changing driving requirements is preferably carried out along line 91 of the optimal combined ICE-EM1 efficiency. The operating point adjustment of the internal combustion engine in series operation should preferably only be carried out along line 91 of the optimal combined ICE-EM1 efficiency.

[0085] The presented method for developing a CO2-optimal operating strategy may, for some embodiments, result in the following basic guidelines, for example: • EV operation can preferably take place up to approximately 50 km / h and a maximum drive power of approximately 15 kW. • In hybrid mode, parallel operation can be preferred over series hybrid operation due to its higher efficiency, if possible (here, parallel hybrid operation is possible from approx. 49 km with an internal combustion engine speed >≈ 1200 rpm at v1000, i=2,8 = 41.4 km / h). • In parallel hybrid operation, the transition to series hybrid operation can occur when torque requirements exceed the full load of the internal combustion engine or, alternatively, the full system load. • The VKM operating point adjustment in series hybrid operation can preferably be carried out along the line of the optimal combined VKM-EM1 efficiency. List of reference symbols 1 hybrid vehicle 3 Drive unit 5 Internal combustion engine 6 Drive unit control 7 cylinders 8 Control signal 9 first electric machine 10 Control signal 11 second electric machine 12 Control signal 13 Accumulator 14 Control signal 15 drive wheel 17 Main clutch K0 19 gearboxes 21 Wheel drive train 23 Differential translation 25 Differential 27 first clutch K1 29 Translation element 31 Output shaft internal combustion engine 32 Input shaft gearbox 33 Output shaft gearbox 35 Translation element 37 second clutch K2 38 procedures 39th procedural step 41st step of the process 43 Abscissa 45 ordinates 47 Internal combustion engine power 49 System performance 51 Internal combustion engine torque 53 System torque 55 Abscissa 57 ordinates 59, 60 areas of purely electrical operation 61 Serial hybrid operation area 63 Area of ​​parallel hybrid operation 64 Driving resistance during constant speed driving 65 Speed ​​limit 67 Electrical operating threshold 68 more electric operating thresholds 69 Parallel hybrid operation threshold 71 Maximum output power of the internal combustion engine 73 Boost area 75 upper limit for serial hybrid operation 77 Area with regard to parallel hybrid operation 79 Area regarding serial hybrid operation 81 Abscissa 83 ordinates 85 Specific Consumption Isolines 87 power isolines 89 Curve of fuel consumption-optimal efficiency of the internal combustion engine 91 Operating point curve 93 Operating point

Claims

[1] Method for controlling a drive device (3, 203) of a hybrid vehicle (1, 201) comprising an internal combustion engine (5, 205), a first electric machine (9, 209), a second electric machine (11, 211) and an accumulator (13, 213), wherein the drive device for driving the hybrid vehicle is operable in the following three operating modes: a purely electric operation in which a drive torque is produced by means of the second electric machine (11, 211) while the internal combustion engine (5, 205) is switched off; a serial hybrid operation in which the drive torque is produced by means of the second electric machine (11, 211) and the internal combustion engine (5, 205) drives the first electric machine (9, 209) to generate electrical energy; a parallel hybrid operation in which a drive torque is generated by means of the internal combustion engine (5, 205), the method comprising: Controlling the drive device in serial hybrid operation such that the internal combustion engine is at an operating point (93) based on a combined efficiency (η VKM × η EM1 ) which depends on the efficiency (η VKM ) of the internal combustion engine and the efficiency (η EM1 ) of the first electric machine, where serial hybrid operation is carried out, if both a driving speed (55) is below a driving speed threshold (65) and a target drive power (57) and / or a target drive torque is above an electric operation threshold (67), wherein the serial hybrid operation is further carried out, if the target drive power (57) and / or the target drive torque is above a driving speed-dependent parallel hybrid operation threshold (69). [2] Method according to claim 1, wherein the operating point (93) is an extreme point of the combined efficiency for a given target power (87) and / or a given target torque. [3] Method according to claim 1 or 2, wherein controlling the drive device (3, 203) in serial hybrid operation comprises: Retrieving the operating point (93) from a predetermined operating point curve (91) which defines operating points for a plurality of target powers and / or target torques, wherein the operating points are defined by a plurality of extreme points of the combined efficiency (η VKM × η EM1 ) are given for the majority of the target powers and / or target torques. [4] A method according to any one of the preceding claims, wherein the combined efficiency (η VKM × η EM1 ) is the product of the efficiency of the internal combustion engine and the efficiency of the first electric machine. [5] Method according to one of the preceding claims, where the purely electrical operation is carried out, if the driving speed (55) is below a driving speed threshold (65) and a target drive power (57) and / or a target drive torque are below an electric operation threshold (67), whereby the purely electrical operation is also carried out, if a target drive power (57) and / or a target drive torque are below a further electric operation threshold (68). [6] Method according to the preceding claim, where parallel hybrid operation is carried out, if both the driving speed (55) is above the driving speed threshold (65), a target drive power (57) and / or a target drive torque is below the driving speed-dependent parallel hybrid operation threshold (69), and a target drive power (57) and / or a target drive torque is above a further electric operation threshold (68). [7] Method according to one of the preceding claims 1 or 6, wherein the parallel hybrid operation threshold (69) is given as the sum of the drive torques that can be generated at most by the internal combustion engine (5, 205) and taking into account a boost support of the first electric machine (9, 209) and / or the second electric machine (11, 211). [8] Method according to one of the preceding claims, wherein in parallel hybrid operation the first electric machine (9, 209) and / or the second electric machine (11, 211) additionally contribute to the drive power at least temporarily. [9] Hybrid vehicle (1, 201), comprising: a drive device (3, 203) comprising an internal combustion engine (5, 205), a first electric machine (9, 209), a second electric machine (11, 211) and an accumulator (13, 213), wherein the drive device for driving the hybrid vehicle is arranged in the following three Operating modes: a purely electric operation in which a drive torque is generated by means of the second electric machine while the internal combustion engine is switched off; a serial hybrid operation in which the drive torque is provided by the second electric machine and the internal combustion engine drives the first electric machine to generate electrical energy; a parallel hybrid operation in which a drive torque is generated by the internal combustion engine, wherein the hybrid vehicle further comprises a drive device control (6, 206) which is designed to carry out a method according to one of the preceding claims, where serial hybrid operation is carried out, if both a driving speed (55) is below a driving speed threshold (65) and a target drive power (57) and / or a target drive torque is above an electric operation threshold (67), wherein the serial hybrid operation is further carried out, if the target drive power (57) and / or the target drive torque is above a driving speed-dependent parallel hybrid operation threshold (69).

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