WO2021110244A1

WO2021110244A1 - A method for controlling a hybrid powertrain system of a vehicle

Info

Publication number: WO2021110244A1
Application number: PCT/EP2019/083419
Authority: WO
Inventors: Larry Hiltunen; Viktor KARLSSON
Original assignee: Volvo Truck Corporation
Priority date: 2019-12-03
Filing date: 2019-12-03
Publication date: 2021-06-10

Abstract

The invention relates to a method (200) for controlling a hybrid powertrain system of a vehicle, comprising an internal combustion engine, an electrical propulsion system, a gearbox assembly for the internal combustion engine and the electrical propulsion system, the hybrid powertrain system being operable to provide motive power to the vehicle, and further comprising a control unit operable to set the hybrid powertrain system in an operational mode selected from a group comprising of: an internal combustion engine mode; an electrical propulsion system mode; and a combined internal combustion engine and electrical propulsion system mode; and wherein the method comprises the steps of: determining (220) a prevailing speed of the vehicle; determining (240) a requested propulsion torque; determining (260) an optimal gear stage of the gearbox assembly based on the determined prevailing speed of the vehicle and the determined requested propulsion torque; determining (280) an efficiency level of the internal combustion engine based on the determined optimal gear stage; and selecting (290) operational mode for the hybrid powertrain system based on the determined efficiency level of the internal combustion engine.

Description

A method for controlling a hybrid powertrain system of a vehicle

TECHNICAL FIELD

The invention relates to a method for controlling a hybrid powertrain system of a vehicle comprising an internal combustion engine and an electrical propulsion system. The invention further relates to a computer program, a computer readable medium, a hybrid powertrain system and a hybrid vehicle.

The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other hybrid vehicles such as buses, cars, construction equipment, working machines e.g. wheel loaders, articulated haulers, dump trucks, excavators and backhoe loaders etc.

BACKGROUND

In connection with vehicles comprising a hybrid powertrain system having an internal combustion engine (ICE) and one or more electric motors, it is generally desirable to reduce emissions by operating the vehicle using electric propulsion whenever possible. A further aim is to control the hybrid powertrain system for an optimal energy use efficiency in view of the operational circumstances of the vehicle. Occasionally, the ICE may thus be turned off or operating a low load during extensive time periods.

In addition, in some driving situations, e.g. when a hybrid vehicle operates in so-called low or zero emission zones, the hybrid vehicle may be required to have full capabilities in its full electric mode. That is, the electrical propulsion system of the hybrid vehicle may need to be dimensioned and specified so that the vehicle can operate in the same manner as a pure electrical vehicle although with the distinct difference that the range in distance can be limited. As electrical propulsion systems of hybrid vehicles generally have rechargeable batteries, such systems are also needed to be controlled in an effective manner in order to ensure that the batteries are not used in an unfavourable manner. Hence, by way of example, many hybrid vehicle systems are adapted to always use the batteries with a safety margin to the state-of-charge (SOC) limits of the batteries.

However, this reduces the energy available in the batteries, and thus also reduces the vehicle range. In fact, in some operational situations in which there is a high power demand from the vehicle, a hybrid vehicle may not have enough power to operate as expected if one or a number of batteries are on a critical low level of charge.

By way of example, WO 2014/016327 A1 discloses a method of determining power source switching for a hybrid electric vehicle based on its battery status and pollution information along the planned route. Further, the driver or the control unit of the vehicle may determine to switch to a reduced-emission running mode such as electric-only propulsion when the observed pollution is above a certain threshold.

Despite the activity in the field, there remains a need for an improved control of a vehicle hybrid powertrain system of a vehicle. In addition, it would be desirable to further improve the overall performance of the hybrid powertrain system during operation of the vehicle.

SUMMARY

An object of the invention is to move the operation of a hybrid powertrain system closer to an optimal balance between using any one of an internal combustion engine and an electrical propulsion system of the vehicle. The object is achieved by a method according to claim 1.

According to a first aspect of the invention, there is provided a method for controlling a hybrid powertrain system of a vehicle, the hybrid powertrain system comprising an internal combustion engine, an electrical propulsion system, a gearbox assembly for the internal combustion engine and the electrical propulsion system, the hybrid powertrain system being operable to provide motive power to the vehicle, and further comprising a control unit operable to set the hybrid powertrain system in an operational mode selected from a group comprising: an internal combustion engine mode; an electrical propulsion system mode; and a combined internal combustion engine and electrical propulsion system mode. The method comprises the steps of: determining a prevailing speed of the vehicle; determining a requested propulsion torque; determining an optimal gear stage of the gearbox assembly based on the determined prevailing speed of the vehicle and the determined requested propulsion torque; determining an efficiency level of the internal combustion engine based on the determined optimal gear stage; and selecting operational mode for the hybrid powertrain system based on the determined efficiency level of the internal combustion engine.

The method according to the invention allows for optimizing the use of the internal combustion engine (ICE) and the electrical propulsion system during operation of the vehicle, while avoiding that the internal combustion engine reaches an operating state where the engine efficiency is relatively low. In particular, the method allows for using a smaller ICE, in terms of engine capacity, than a conventional sized ICE for a heavy-weight vehicle. Further, the method provides for controlling the hybrid powertrain system to only operate the ICE in a vehicle speed range where the ICE can work efficiently based on the configuration of the gearbox assembly and the number of available gears. To this end, the method according to the invention allows for operating the ICE in an energy efficient state, thus providing a long range for the vehicle with low fuel consumption.

The example embodiments of the invention are based on the possibility of using a hybrid powertrain system with a smaller ICE and also on the possibility of using a relatively simple gearbox that may not necessarily have all gear stages needed to operate efficiently in all ordinary vehicle speed ranges or operate at all in all ordinary vehicle speed ranges. As such, it becomes possible to reduce the weight of the hybrid powertrain systems and provide systems with less expensive components. In other words, the method provides for controlling the hybrid powertrain system so that the vehicle may be operated as a full electric vehicle, i.e. operated in the electrical propulsion system mode, in operational conditions when the ICE is not capable of providing propulsion torque to the wheels in an efficient manner. This is rather opposite to many of the conventional hybrid powertrains systems where the ICE is generally over-dimensioned providing a safety margin to ensure that the vehicle can be operated by means of the ICE in all driving situations and independently of the prevailing vehicle speed and the magnitude of the requested propulsion torque.

If it is determined that the efficiency level of the ICE is not acceptable based on the optimal gear stage, the prevailing vehicle speed and the requested propulsion torque, the method may generally decide to operate the hybrid powertrain system in either the electrical propulsion system mode or the combined internal combustion engine and electrical propulsion system mode.

Accordingly, by providing a method of the invention, it becomes possible to operate the hybrid powertrain system in an efficient manner by determining when the efficiency level of the ICE is too low based on determining optimal gear stages, prevailing vehicle speed and requested propulsion torque of the vehicle. In other words, by providing a method according to the example embodiments, in which the operational mode for the hybrid powertrain system is based on the determined efficiency level of the internal combustion engine, it becomes possible to ensure that the hybrid powertrain system uses the ICE in its most favorable manner.

More specifically, the efficiency level of the internal combustion engine is derivable from the provisions of determining whether there is an available optimal gear stage for operating the hybrid powertrain system in the internal combustion mode based on the prevailing speed of the vehicle and the requested propulsion torque. An optimal gear stage of the gearbox assembly is determined based on the determined prevailing speed of the vehicle and the determined requested propulsion torque in order to confirm if there is at least one available gear stage of the gearbox assembly that can deliver a propulsion torque at the given vehicle speed. The method is particularly useful for vehicles with relatively small-sized ICEs where the ICE may not be used to propel the vehicle in an efficient manner at a given vehicle speed in view of the requested propulsion torque.

The provision of determining a requested propulsion torque can be obtained in several different manners. By way of example, the requested propulsion torque is determined based on an actuation of a vehicle acceleration device, such as an acceleration pedal. The requested propulsion torque may e.g. be determined based on the position of the acceleration pedal, as manipulated by a driver. In addition, or alternatively, the requested propulsion torque may be determined based on data indicative of the requested propulsion torque by means of a control unit, such as the electronic control unit. The term “requested propulsion torque”, as used herein, typically refers to propulsion torque needed for the vehicle at the present state, i.e. the torque deliverable by any one or both of the electrical propulsion system and the internal combustion engine upon a request from a driver, control unit etc. Typically, in the step of selecting operational mode for the hybrid powertrain system, the electrical propulsion system mode is always selected if the determined efficiency level of the internal combustion engine is below a threshold. As such, if the determined efficiency level of the internal combustion engine is below the threshold, the hybrid powertrain system is always operated in the electrical propulsion system mode. Hence, the control unit may either switch mode to the electrical propulsion system mode or continue to operate the hybrid powertrain system in the electrical propulsion system mode.

According to one example embodiment, the method further comprises the step of only permitting the internal combustion engine to provide motive power to the vehicle when the determined efficiency level of the internal combustion engine is above a threshold. Accordingly, the method may further comprise the step of selecting the internal combustion engine mode only when the determined efficiency level of the internal combustion engine is above such threshold.

By way of example, the threshold corresponds to an optimal internal combustion engine output torque level. The internal combustion engine output torque level typically refers to the engine output torque level at the revolution speed of the ICE. The threshold value can be a predetermined value stored in a control unit. In other words, the method can be configured to initially determine an optimal internal combustion engine output torque level to the wheels of the vehicle.

According to one example embodiment, the method further comprises the step of determining if the optimal gear stage is an available gear stage for the internal combustion engine. Typically, if there is no available gear stage for the internal combustion engine, the method may always select to operate the hybrid powertrain system in the electrical propulsion system mode.

According to one example embodiment, the method further comprises the step of determining an efficiency level of the electrical propulsion system, and thus also selecting operational mode for the hybrid powertrain system based on the efficiency level of the electrical propulsion system. Selecting operational mode based on both the efficiency level of the electrical propulsion system and the efficiency level of the internal combustion engine system provides for an even more improved method for controlling the hybrid powertrains system. The efficiency level of the electrical propulsion system may be derivable from several different parameters and/or a combination thereof, including, but not limited to the capacity of the electrical machine(s), the electrical energy storage system efficiency, a prevailing operational parameter of an energy storage system, external influence factors such as ambient temperature, the electrical energy storage system temperature and any other thermal characteristics affecting the energy efficiency. Hence, according to one example embodiment, the step of determining an efficiency level of the electrical propulsion system comprises determining any one of the prevailing capacity of the electrical machine(s), the prevailing operational parameter of the electrical energy storage system, the electrical energy storage system efficiency, the ambient temperature of the electrical propulsion system, the ambient temperature of the electrical energy storage system, the electrical energy storage system temperature. Such data relating to the efficiency level of the electrical propulsion system may be stored and updated in the control unit and/or be gathered from various types of sensors in the vehicle and in connection with the electrical propulsion system, and subsequently transmitted to the control unit and used as input data for determining the current efficiency level of the electrical propulsion system.

According to one example embodiment, the efficiency level of the electrical propulsion system is determined based on a prevailing operational parameter of an energy storage system comprised within the electrical propulsion system. The operational parameter is generally indicative of any one of a state-of-power (SOP) parameter and a state-of-charge (SOC) parameter. In this manner, it becomes possible to estimate whether the current electrical power provided by the electrical energy storage system is sufficient for providing traction power for a given time, to an upcoming event or to an upcoming charging activity, e.g. until the next charging location.

According to one example embodiment, the method further comprises the steps of determining a predicted operational condition of the electrical propulsion system and determining the operational mode for the electrical propulsion system based on the predicted operational condition of the electrical propulsion system. The predicted operational condition may be any one of: a time to a charging event and a magnitude of the charging event, a time to a discharging event and a magnitude of the discharging event, a range of a driving cycle, a required driving range, or combinations thereof. According to some example embodiments, the electrical propulsion system comprises at least two electrical machines. To safeguard operation of the vehicle in situations where the energy storage system of the electrical propulsion system is depleted, the ICE, the gearbox assembly and the electrical propulsion system may be arranged such that the ICE is connected with gears and clutches to one of the electrical machines so that the ICE can act as a generator via one of the electrical machines, while the other electrical machine is operated to provide propulsion torque to the vehicle in its normal operation.

According to one example embodiment, if the determined prevailing speed of the vehicle is below a vehicle speed threshold corresponding to a lower vehicle speed range, the method comprises the step of selecting to operate the hybrid powertrain system in the electrical propulsion system mode. In this manner, the method is configured to operate the system so as to maximize the start torque capabilities of the system. In other words, in the step of selecting operational mode for the hybrid powertrain system, the electrical propulsion system mode is selected, if the determined prevailing speed of the vehicle is below a vehicle speed threshold corresponding to a lower vehicle speed range.

According to one example embodiment, if a prevailing speed of the vehicle is above a vehicle speed threshold corresponding to a higher vehicle speed range, the method comprises the step of selecting to operate the hybrid powertrain system in the combined internal combustion engine and electrical propulsion system mode. The prevailing speed of the vehicle is typically determined by the control unit and data indicative of a decrease or increase in speed of the vehicle. In other words, in the step of selecting operational mode for the hybrid powertrain system, the combined internal combustion engine and electrical propulsion system mode is selected, if a prevailing speed of the vehicle is above a vehicle speed threshold corresponding to a higher vehicle speed range.

In some embodiments, the use of the ICE to operate the vehicle may be entirely disabled, e.g. where the vehicle is in an “electric zone”, also referred to as a “low emission zone”, i.e. an area in which regulations prohibit internal combustion engines to be operated. The positioning of the vehicle in such an area may be done e.g. by means of a global positioning system (GPS) device. Hence, according to one example embodiment, the method may further comprise the step of receiving a signal indicative of an expected low emission zone, and selecting to operate the hybrid powertrain system in the electrical propulsion system mode in response to the signal indicative of an expected low emission zone and regardless of the determined prevailing vehicle speed. According to one example embodiment, the method may further comprise the step of predicting the expected low emission zone based on geo-fencing data received at a control unit.

The method according to the example embodiments can be executed in several different manners. According to one example embodiment, the steps of the method are performed by a control unit during use of the hybrid powertrain system of the vehicle. According to one example embodiment, the steps of the method are performed in sequence. However, at least some of the steps of the method can be performed in parallel.

According to a second aspect of the present invention, there is provided a computer program comprising program code means for performing the steps of any of the example embodiments of the first aspect when the program is run on a computer. Effects and features of the second aspect of the invention are largely analogous to those described above in connection with the first aspect.

According to a third aspect of the present invention, there is provided a computer readable medium carrying a computer program comprising program code means for performing the steps of any of the embodiments of the first aspect when the program product is run on a computer. Effects and features of the third aspect of the invention are largely analogous to those described above in connection with the first aspect.

According to a fourth aspect of the present invention, there is provided a hybrid powertrain system for a vehicle. The hybrid powertrain system comprises: an internal combustion engine, an electrical propulsion system, a gearbox assembly for the internal combustion engine and the electrical propulsion system. The hybrid powertrain system is operable to provide motive power to the vehicle. The hybrid powertrain system further comprises a control unit operable to set the hybrid powertrain system in an operational mode selected from a group comprising: an internal combustion engine mode; an electrical propulsion system mode; and a combined internal combustion engine and electrical propulsion system mode.

Further, the control unit is configured to determine a prevailing speed of the vehicle, to determine a requested propulsion torque; to determine an optimal gear stage of the gearbox assembly based on the determined prevailing speed of the vehicle and the determined requested propulsion torque; to determine an efficiency level of the internal combustion engine based on the determined optimal gear stage; and to select an operational mode for the hybrid powertrain system based on the determined efficiency level of the internal combustion engine. Effects and features of the fourth aspect of the invention are largely analogous to those described above in connection with the first aspect.

Generally, the term “electrical propulsion system”, as used herein, typically refers to vehicle electrical components for providing energy (such as traction energy) and for storing energy (delivering and receiving energy). Besides the electrical components as mentioned above, an electrical propulsion system may include additional components such as the electrical energy source, including a battery unit assembly, cable(s), sensor(s), control units, battery management unit(s) etc. The electrical propulsion system is in particular configured to deliver and receive energy for providing propulsion to the vehicle, but also for performing various vehicle operations of the vehicle. One component of the electrical propulsion system is the electrical energy storage system. The electrical energy storage system is typically a battery, a number of batteries, or a plurality of battery units connected to form a battery pack. It is to be noted that the battery pack can include different types of batteries. By way of example, any one of the batteries/battery units is any one of a lithium-ion battery or sodium-ion battery. A sodium-ion battery typically includes any type of sodium iron battery or sodium ferrite battery. Also, it is to be noted that the battery pack is generally a so-called high voltage battery pack. In this context, the term “high voltage” refers to a battery pack of about 400 - 1000 volt (V). In the context of the example embodiments of the invention, the term “state of power (SOP)”, as used herein, refers to the available power at the present status of the electrical energy storage system (such as the battery pack). In particular, the SOP refers to available dischargeable or available chargeable power of the electrical energy storage system (battery pack) at the present status of the electrical energy storage system (battery pack). The SOP can be determined for different time periods. In the context of the example embodiments of the invention, the term “state of charge (SOC)”, as used herein, refers to the available capacity at the present status of the battery pack. The SOC may also include or represent the charge level of a battery cell, a single battery unit, a single battery pack, the electrical energy storage system or a combination thereof. The SOC is typically determined in percentage (%) between available capacity and rated capacity of a new battery cell or current capacity or a battery cell. The electrical propulsion system typically comprises an electrical machine/electrical motor for providing power to the vehicle; an electrical energy storage system connected to the electrical machine/electrical motor to provide power to the electrical machine/motor, the electrical energy storage system comprising a plurality of battery units connected to form a battery unit assembly. As such, the example embodiments of the invention include an electrical machine so as to permit the vehicle to propel at all speed ranges. The electrical motor can be provided in several different manners. According to one example embodiment, the electrical motor is any one of a permanent magnet synchronous machine, a brushless DC machine, an asynchronous machine, an electrically magnetized synchronous machine, a synchronous reluctance machine or a switched reluctance machine. Typically, the electrical motor is configured for driving at least a ground engaging member. Typically, the electric motor is configured for driving a pair of ground engaging members. By way of example, the ground engaging member is a wheel, a track or the like. The electrical motor can be coupled to the ground engaging members in several different manners. In one example embodiment, the electrical motor is coupled to a pair of ground engaging members by means of the gearbox assembly, a clutch and a differential, as is commonly known in the art of propulsion systems. In the context of the example embodiments of the invention, the gearbox assembly may include one or several gearbox units. While the gearbox assembly typically comprises a gearbox unit for the ICE and another gearbox unit for the electric propulsion system, i.e. for the electric machine, it may also be possible that the gearbox assembly is a common gearbox for both the ICE and the electric propulsion system. In some example embodiments, the gearbox assembly is a combination of a gearbox for the ICE and a gearbox for the electric propulsion system. In such example embodiments, the gearbox assembly is connectable to the internal combustion engine and the electrical propulsion system. However, it may also be possible that the gearbox assembly comprises individual gearbox devices for the ICE and the electric propulsion system, respectively. Further, in one example embodiment, the gearbox assembly comprises spaced-apart (i.e. separately arranged) individual gearbox devices for the ICE and the electric propulsion system, respectively. In such example embodiments, the ICE is connectable to a first gearbox device and the electric machine of the electrical propulsions system is connectable to a second gearbox device. Such configurations of the gearbox assembly can be provided in several different arrangements depending on type of vehicle etc. Moreover, the gearbox assembly typically comprises a number of gears including a neutral gear. In one example embodiment, the gearbox assembly comprises a number of gear stages for the internal combustion engine and a number of gear stages for the electrical propulsion system. Typically, although strictly not required, the gear ratios of the number of gear stages for the internal combustion engine are different than the gear ratios of the number of gear stages for the electrical machine. By way of example, the gearbox assembly comprises at least two gear stages for the electrical propulsion system, preferably three gear stages, more preferably four gear stages for the electrical propulsion system. In an example where the gearbox assembly comprises four stages for the electrical propulsion system, the gearbox assembly comprises four stages for the internal combustion engine. In one example embodiment, the gearbox assembly comprises a split gear arranged to provide additional gear stages for the internal combustion engine.

The term “internal combustion engine mode”, as used herein, typically refers to an operational mode in which all power to the wheels of the vehicle is provided by the internal combustion engine via the gearbox assembly. The term “electrical propulsion system mode”, as used herein, typically refers to an operational mode in which all power to the wheels of the vehicle is provided by the electrical machine(s) of the electrical propulsion system via the gearbox assembly. The term “combined internal combustion engine and electrical propulsion system mode”, as used herein, typically refers to an operational mode in which power to the wheels of the vehicle is provided by ICE and the electrical machine(s) via the gearbox assembly.

The control unit may include a microprocessor, microcontroller, programmable digital signal processor or another programmable device. Thus, the control unit comprises electronic circuits and connections as well as processing circuitry such that the control unit can communicate with different parts of the hybrid powertrain system such as the ICE, the electrical machine(s), the clutch, the electrical energy source, and any other parts in need of being operated in order to provide the functions of the example embodiments. Typically, the control unit may also be configured to communicate with other parts of the vehicle such as the brakes, suspension, and further electrical auxiliary devices, e.g. the air conditioning system, in order to at least partly operate the vehicle. The control unit may comprise modules in either hardware or software, or partially in hardware or software and communicate using known transmission buses such as CAN-bus and/or wireless communication capabilities. The processing circuitry may be a general purpose processor or a specific processor. The control unit typically comprises a non-transistory memory for storing computer program code and data upon. Thus, the control unit may be embodied by many different constructions.

In other words, the control functionality of the example embodiments of the hybrid powertrain system may be implemented using existing computer processors, or by a special purpose computer processor for an appropriate system, incorporated for this or another purpose, or by a hardwire system. Embodiments within the scope of the present disclosure include program products comprising machine-readable medium for carrying or having machine-executable instructions or data structures stored thereon. Such machine- readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a machine, the machine properly views the connection as a machine-readable medium. Thus, any such connection is properly termed a machine-readable medium. Combinations of the above are also included within the scope of machine-readable media. Machine- executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions. While the example embodiments of the system described above includes a control unit being an integral part thereof, it is also possible that the control unit may be a separate part of the vehicle, and/or arranged remote from the system and in communication with the system.

According to a fifth aspect of the present invention, there is provided a vehicle, comprising a hybrid powertrain system according to any one of the example embodiments mentioned above. Effects and features of the fifth aspect of the invention are largely analogous to those described above in connection with the first aspect. The vehicle is a hybrid vehicle, such as a plug-in hybrid vehicle comprising an electrical motor, wherein the electrical energy source system (such as a battery pack) is arranged to provide power to the electrical motor for providing propulsion for the hybrid, or plug-in hybrid vehicle and an internal combustion engine for providing propulsion for the vehicle.

It should be noted that the vehicle can be of a variety of alternative types, e.g. it may be a truck, e.g. a tractor for a semitrailer, a bus, a car or a working machine such as a wheel loader.

Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realizes that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present invention, wherein:

Fig. 1 is a side view of a vehicle in the form of a truck according to example embodiments of the invention;

Fig. 2 schematically illustrates parts of a hybrid powertrain system of the vehicle in Fig. 1, the hybrid powertrain system comprising an internal combustion engine and an electrical propulsion system according to example embodiments of the invention;

Fig. 3 is a flow-chart of a method according to an example embodiment of the invention, in which the method comprises a number of steps for controlling the hybrid powertrain system in Fig. 2;

Fig. 4 is a flow-chart of additional steps of the method in Fig. 3 according to an example embodiment of the invention, in which the method comprises a number of steps for controlling the hybrid powertrain system in Fig. 2. With reference to the appended drawings, below follows a more detailed description of the embodiments of the invention cited as examples. DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. The skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.

Like reference character refer to like elements throughout the description. Fig. 1 illustrates a vehicle in the form of a vehicle 5. The vehicle 5 is here a plug-in hybrid electric vehicle comprising a hybrid electric vehicle (HEV) propulsion system, more specifically a parallel hybrid system. The parallel hybrid system is here a hybrid powertrain system 100. The hybrid powertrain system comprises an electrical energy storage system (ESS), such as a battery pack, as further described below. The battery pack is typically arranged to be charged at a charging station via a charging interface (not shown) of the vehicle.

Fig. 2 schematically illustrates further details of the hybrid powertrain system 100 according to the example embodiment in fig. 1. The hybrid powertrain system 100 can be incorporated and installed in a vehicle as mentioned above in relation to fig. 1 , or in any other type of hybrid vehicle. The hybrid powertrain system 100 comprises an internal combustion engine (ICE) 29. The ICE is in this example a diesel piston engine. The ICE has a propulsion shaft 27 for transferring an engine torque to a gearbox assembly 22. In other words, the ICE is mechanically connected to the gearbox assembly 22 via the propulsion shaft. Further, in this example, the engine is disengagebly connected to the gearbox assembly by means of a clutch 28. The clutch is arranged in-between the ICE and the gearbox assembly. As illustrated in fig. 2, the clutch 28 is arranged in connection with the propulsion shaft 27, thus the propulsion shaft typically comprises a shaft portion between the ICE and the clutch and another shaft portion between the clutch and the gearbox assembly. As illustrated in fig. 2, the hybrid powertrain system 100 further comprises an electrical propulsion system 20 having an electrical machine 30 and the electrical energy storage system 34 connected to the electrical machine. The electrical propulsion system 20 is connected to the gearbox assembly 22. The electrical propulsion system 20 is configured to provide traction power to the vehicle either by itself or in combination with the ICE.

The gearbox assembly 22 is mechanically connected via a torque transmitting assembly 40 to two wheels 64 of the vehicle 5 for its propulsion. The torque transmitting assembly 40 may comprise a cardan shaft, a wheel axle and a differential gear.

As mentioned above, the electrical propulsion system 20 also comprises the electric energy storage system in the form of a battery pack 34. The battery pack is electrically connected to the electrical machine 30 via an inverter (although not shown). The battery pack 34 is connected to the electrical machine 30 to provide power to the electrical machine, thereby the electrical machine can provide traction power to one or more ground engaging members, e.g. one or more wheels 64. While the hybrid powertrain system is here arranged to provide traction power to the rear wheels 64, it may likewise be arranged to provide traction power to the front wheels, or to both the rear wheels and the front wheels depending on type of vehicle.

The gearbox assembly 22 is here adapted to provide a power split function between the ICE, the electrical propulsion system 20 and the torque transmitting assembly 40. The hybrid powertrain system 100 is arranged to operate in a number of different modes. More specifically, the system 100 is arranged to operate in a fully electric propulsion system mode, in which the ICE is turned off, the clutch 28 is disengaged, and all power to the wheels 64 is provided by the electrical machine 30 via the gearbox assembly 22, the electrical machine 30 being powered by the battery pack 34 via the inverter. In a combined internal combustion engine and electrical propulsion system mode., the clutch 28 is engaged and the ICE 29 and the electrical machine 30 are both providing power to the wheels 64 via the gearbox assembly 22. In a regenerative braking mode, a braking torque is provided by the electrical machine 30 to the wheels 64, whereby the electrical machine works as a generator and charges the battery pack via the inverter. In an internal combustion engine mode, all power to the wheels 64 is provided solely by the ICE 29. In some embodiments, power may also be provided by the ICE 29 to the electrical machine 30, which then works as a generator to charge the battery pack via the inverter.

It is understood that the example embodiments of the invention are applicable to hybrid electric vehicle propulsion systems where components are arranged differently from that of the hybrid system in fig. 2. For example, in an alternative hybrid system the ICE, the electrical machine 30 and the gearbox assembly 22 may be connected via a planet gear set.

The ICE and the electrical machine are here independently connected to the gearbox assembly 22. By way of example, the ICE is disengagebly connected to the gearbox assembly 22 by means of the clutch unit 28, as illustrated in fig. 2. Further, the electrical machine is disengagably connected to the gearbox assembly 22 by means of a so-called claw coupling (although not shown).

Furthermore, in this example, the gearbox assembly 22 comprises a number of gear stages for the electrical machine and a number of gear stages for the ICE. Typically, although strictly not required, the gear ratios of the number of gear stages for the internal combustion engine are different than the gear ratios of the number of gear stages for the electrical machine. In addition, the gearbox assembly here comprises a first reduction drive 23 for reducing the speed from the electrical motor and a second reduction drive 24 for reducing the speed from the propulsion shaft of the ICE. Also, the gearbox assembly 22 here comprises a split gear arrangement 26 arranged between the second reduction drive gearbox 24 and the propulsion shaft 27. The split gear arrangement 26 may be an optional component of the gearbox assembly 22.

Optionally, if the system is arranged to provide propulsion to a rear axle of the vehicle, the system 100 further comprises a rear suspension unit 60 arranged in-between a rear torque transmitting assembly 40 and at least one of the wheels 64. By way of example, the rear suspension unit 60 is arranged in connection with the rear torque transmitting assembly 40, which is schematically illustrated in fig. 2.

Typically, the vehicle 5 further comprises a control unit 8 arranged to send and receive control signals from each one of the ICE 29, the clutch 28, the gearbox assembly 22, the electrical machine 30, the battery pack 34. In particular, the control unit 8 is arranged in communication with the ICE 29 and the electrical propulsion system, and operable to set the hybrid powertrain system 100 in an operational mode selected from the group consisting of: the internal combustion engine mode; the electrical propulsion system mode; and the combined internal combustion engine and electrical propulsion system mode.

It is understood that the control unit 8 may be provided as a single unit, or as a plurality of units arranged to communicate with each other. For example, an engine electric control unit (ECU), a gearbox assembly ECU, a battery ECU and a HEV ECU may be arranged to control respective parts of the system and to communicate with each other. While the example embodiment described above includes a control unit being an integral part of the system 100, it is also possible that the control unit may be a separate part of the system 100 or the like.

Turning now to fig. 3, there is depicted a flowchart of a method according to example embodiments of the invention. The method is intended for controlling a hybrid powertrain system 100 as described above in relation to figs. 1 and 2. The sequences of the method are typically performed by the control unit 8, as described above in relation to the figs. 1 and 2. Thus, while referring to fig. 3, a number of steps for controlling the hybrid powertrain system in fig. 2 will now be described. The method comprises the step 220 of determining the prevailing speed of the vehicle. The prevailing speed of the vehicle is determined by the control unit during operation of the vehicle on a road. Determining the prevailing speed of the vehicle can be performed by standard measurements as is commonly known in the art. Data indicative of the prevailing speed may be temporarily stored in the control unit.

Subsequently, the control unit is arranged to perform a step 240 of determining a requested propulsion torque. The requested propulsion torque generally refers to the demanded propulsion torque from the driver of the vehicle. Hence, the demanded propulsion torque can be determined from measuring the magnitude of the actuation of the acceleration pedal of the vehicle, or from any other acceleration control device of the vehicle. By way of example, data indicative of the actuation of the acceleration control device and/or a data indicative of the position of an acceleration pedal position is transferred to the control unit 8 for further processing and for determining a corresponding requested propulsion torque based on the data received by the control unit. When the prevailing speed of the vehicle and the requested propulsion torque are determined at the control unit, the control unit proceeds to the step 260 of determining an optimal gear stage of the gearbox assembly based on the determined prevailing speed of the vehicle and the determined requested propulsion torque. Accordingly, the control unit is arranged in communication with the gearbox assembly 22 to receive data indicative of an optimal gear stage based on the demanded propulsion torque from the driver and the prevailing speed of the vehicle. Subsequently, the control unit performs the step 280 of determining an efficiency level of the internal combustion engine based on the determined optimal gear stage and the step 290 of selecting an operational mode for the hybrid powertrain system based on the determined efficiency level of the internal combustion engine. If it is determined that the efficiency level of the internal combustion engine is below a threshold, the control unit 8 is arranged to always operate the hybrid powertrain system in the electrical propulsion system mode. In this example, the threshold corresponds to an optimal internal combustion engine output torque level at the requested revolution speed of the ICE. The internal combustion engine output torque level here refers to the output level from the propulsion shaft 27. Then, the optimal gear, if present and engaged, will provide the needed drive shaft torque on the drive rear shaft 62. In other words, the control unit 8 determines that the vehicle is to be operated solely by the electrical machine of the electrical propulsion system if the efficiency level of the internal combustion engine is determined to be too low to operate in an efficient manner, i.e. below the threshold.

On the other hand, if it is determined that the efficiency level of the internal combustion engine is above the threshold, the control unit is arranged to determine that the internal combustion engine is to provide motive power to the vehicle. That is, if the efficiency level of the internal combustion engine is above the threshold, the ICE is capable of being operated in an optimal manner.

In addition, if the determined prevailing speed of the vehicle is below a vehicle speed threshold corresponding to a lower vehicle speed range, the control unit is arranged to operate the hybrid powertrain system in the electrical propulsion system mode. In other words, the control unit may be arranged to always operate the hybrid powertrain system in the electrical propulsion system mode if certain conditions are fulfilled.

In this manner, the method is capable of estimating whether the vehicle should continue to be used in the current operational mode or be switched into another operational mode based on the efficiency level of the internal combustion engine.

Furthermore, the control unit may also be arranged to take other vehicle speed ranges into consideration. Hence, by way of example, if a prevailing speed of the vehicle is above a vehicle speed threshold corresponding to a higher vehicle speed range, the control unit is arranged to operate the hybrid powertrain system in the combined internal combustion engine and electrical propulsion system mode. Such combined mode is generally selected to ensure an efficient use of the hybrid powertrain system for higher speeds.

Turning now to fig. 4, there is depicted some additional optional steps of the method according to the example embodiment described in relation to fig. 3. In other words, the method as described in fig. 4 comprises the steps 220, 240, 260, 280 and 290 as described above in relation to fig. 3. In the example embodiment illustrated in fig. 4, the step 260 of determining an optimal gear stage of the gearbox assembly 22 based on the determined prevailing speed of the vehicle and the determined requested propulsion torque also comprises the step 262 of determining if the determined optimal gear stage is an available gear stage for the internal combustion engine. Typically, if there is no available gear stage for the internal combustion engine, the method proceeds to step 290 and the control unit is arranged to always select to operate the hybrid powertrain system in the electrical propulsion system mode.

Moreover, in the example embodiment as illustrated in fig. 4, the control unit is arranged to perform the step 285 of determining an efficiency level of the electrical propulsion system 20. To this end, the step 290 of selecting operational mode for the hybrid powertrain system is also based on the efficiency level of the electrical propulsion system 20. By way of example, the efficiency level of the electrical propulsion system 20 is here determined based on the thermal characteristics of the battery pack and the capacity of the electrical machine. Other factors that may influence the efficiency level of the electrical propulsion system 20 may relate to a prevailing operational parameter of the energy storage system 34 comprised within the electrical propulsion system 20. By way of example, the operational parameter is indicative of a state-of-charge (SOC) parameter.

Typically, in the example embodiment illustrated in fig. 4, the control unit is also arranged to operate the hybrid powertrain system 100 in the electrical propulsion system mode if the vehicle approaches or enters a so-called low emission zone. The low emission zone may be detected by the control unit 8 itself, the control unit 8 in combination with a sensor and/or by means of a global positioning system of the vehicle. By way of example, the control unit 8 may be arranged to predict an expected low emission zone based on geo fencing data received by the control unit 8.

In other words, in this example, the method further comprises a step 287 of receiving a signal indicative of the expected low emission zone, and further selecting to operate the hybrid powertrain system in the electrical propulsion system mode in response to the signal indicative of the expected low emission zone and regardless of the determined prevailing vehicle speed.

Furthermore, although not illustrated in fig. 4, the method may comprise the steps of determining a predicted operational condition of the electrical propulsion system and determining operational mode for the electrical propulsion system based on the predicted operational condition of the electrical propulsion system. By way of example, the predicted operational condition is any one of: a time to a charging event and a magnitude of the charging event, a time to a discharging event and a magnitude of the discharging event, a range of a driving cycle, a required driving range, or combinations thereof.

As mentioned above, it is to be noted that the steps of the method are typically performed by the control unit 8 during use of the hybrid powertrain system. Thus, the control unit is configured to perform any one of the steps of any one of the example embodiments as described above in relation to the Figs. 1 - 4. Moreover, although the figures may show a sequence, the order of the steps may differ from what is depicted. Also, two or more steps may be performed concurrently or with a partial concurrence. Such variation will depend on the software and hardware systems chosen and on designer choice. All such variations are within the scope of the disclosure. Likewise, software implementations could be accomplished with standard programming techniques with rule-based logic and other logic to accomplish the various connection steps, processing steps, comparison steps and decision steps. Additionally, even though the invention has been described with reference to specific exemplifying embodiments thereof, many different alterations, modifications and the like will become apparent for those skilled in the art. It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. For example, although the present invention has mainly been described in relation to a truck, the invention should be understood to be equally applicable for any type of hybrid electric vehicle, in particular a bus, a car, or the like.

Claims

1. A method for controlling a hybrid powertrain system of a vehicle, the hybrid powertrain system comprising an internal combustion engine, an electrical propulsion system, a gearbox assembly for the internal combustion engine and the electrical propulsion system, the hybrid powertrain system being operable to provide motive power to the vehicle, and further comprising a control unit operable to set the hybrid powertrain system in an operational mode selected from a group comprising of: an internal combustion engine mode; - an electrical propulsion system mode; and a combined internal combustion engine and electrical propulsion system mode; and, wherein the method comprises the steps of: determining (220) a prevailing speed of the vehicle; determining (240) a requested propulsion torque; determining (260) an optimal gear stage of the gearbox assembly based on the determined prevailing speed of the vehicle and the determined requested propulsion torque; determining (280) an efficiency level of the internal combustion engine based on the determined optimal gear stage; and selecting (290) operational mode for the hybrid powertrain system based on the determined efficiency level of the internal combustion engine.

2. Method according to claim 1 , wherein in said step (290) of selecting operational mode for the hybrid powertrain system, the electrical propulsion system mode is always selected if the determined efficiency level of the internal combustion engine is below a threshold.

3. Method according to any one of the claim 1 or claim 2, further comprising the step of selecting the internal combustion engine mode only when the determined efficiency level of the internal combustion engine is above a threshold.

4. Method according to claim 2 or claim 3, wherein the threshold corresponds to an optimal internal combustion engine output torque level.

5. Method according to any one of the preceding claims, further comprising the step (262) of determining if the determined optimal gear stage is an available gear stage for the internal combustion engine. 6. Method according to claim 5, wherein in said step (290) of selecting operational mode for the hybrid powertrain system, the electrical propulsion system mode is always selected, if there is no available gear stage for the internal combustion engine. 7. Method according to any one of the preceding claims, further comprising the step

(285) of determining an efficiency level of the electrical propulsion system, and selecting operational mode for the hybrid powertrain system based on the efficiency level of the electrical propulsion system.

8. Method according to claim 7, wherein the efficiency level of the electrical propulsion system is determined based on a prevailing operational parameter of an energy storage system comprised with the electrical propulsion system, the operational parameter being indicative of any one of a state-of-power (SOP) parameter and a state-of-charge (SOC) parameter.

9. Method according to any one of the preceding claims, wherein in said step (290) of selecting operational mode for the hybrid powertrain system, the electrical propulsion system mode is selected, if the determined prevailing speed of the vehicle is below a vehicle speed threshold corresponding to a lower vehicle speed range.

10. Method according to any one of the preceding claims, wherein in said step (290) of selecting operational mode for the hybrid powertrain system, the combined internal combustion engine and electrical propulsion system mode is selected, if the prevailing speed of the vehicle is above a vehicle speed threshold corresponding to a higher vehicle speed range.

11. Method according to any one of the preceding claims, further comprising the step (287) of receiving a signal indicative of an expected low emission zone, and selecting to operate the hybrid powertrain system in the electrical propulsion system mode in response to the signal indicative of an expected low emission zone and regardless of the determined prevailing vehicle speed.

12. Method according to claim 11, further comprising the step of predicting an expected low emission zone based on geo-fencing data received at a control unit. 13. Method according to any one of the preceding claims, further comprising the steps of determining a predicted operational condition of the hybrid powertrain system and selecting operational mode for the hybrid powertrain system based on the predicted operational condition of the hybrid powertrain system, the predicted operational condition being any one of: a time to a charging event and a magnitude of the charging event, a time to a discharging event and a magnitude of the discharging event, a range of a driving cycle, a required driving range, or combinations thereof.

14. A computer program comprising program code means for performing the steps of any one of claims 1 - 13 when said program is run on a computer.

15. A computer readable medium carrying a computer program comprising program means for performing the steps of any one of claims 1 - 13 when said program means is run on a computer.

16. A hybrid powertrain system (100) for a vehicle (5), the hybrid powertrain system comprising: an internal combustion engine, an electrical propulsion system, a gearbox assembly for the internal combustion engine and the electrical propulsion system, the hybrid powertrain system being operable to provide motive power to the vehicle, and further comprising a control unit operable to set the hybrid powertrain system in an operational mode selected from a group comprising: an internal combustion engine mode; an electrical propulsion system mode; and a combined internal combustion engine and electrical propulsion system mode, wherein the control unit (8) is further configured to determine a prevailing speed of the vehicle, to determine a requested propulsion torque, to determine an optimal gear stage of the gearbox assembly based on the determined prevailing speed of the vehicle and the determined requested propulsion torque, to determine an efficiency level of the internal combustion engine based on the determined optimal gear stage, and to select an operational mode for the hybrid powertrain system based on the determined efficiency level of the internal combustion engine.

17. A vehicle (5), comprising a hybrid powertrain system according to claim 16.