METHOD AND SYSTEM FOR CONTROLLING A HYBRID ELECTRIC DRIVLINE

Abstract

A method for controlling a hybrid electric driveline 2, comprising an internal combustion engine 3 and an electric machine 5 configured in parallel for driving a propulsion member 9, comprising the steps of: driving the driveline in generator mode, where the electric machine provides a charge current to a battery 11 and where the internal combustion engine provides positive driving torque to the propulsion member, and limiting the maximal available torque from the internal combustion engine to a predetermined torque limitation value depending on the rotational speed of the internal combustion engine.

Claims

1. A method for controlling a hybrid electric driveline, comprising an internal combustion engine and an electric machine configured in parallel for driving a propulsion member, comprising the following steps: driving the driveline in generator mode, where the electric machine provides a charge current to a battery and where the internal combustion engine provides positive driving torque to the propulsion member, limiting the maximal available torque from the internal combustion engine to a predetermined torque limitation value depending on the rotational speed of the internal combustion engine.

2. Method according to claim 1, characterized in that the charge current of the electric machine is decreased when the torque request to the internal combustion engine and the required torque to charge the battery is larger than the predetermined torque limitation value.

3. Method according to claim 1, characterized in that the charge current of the electric machine is decreased to zero when the torque request to the internal combustion engine and the required torque to charge the battery is larger than the predetermined torque limitation value.

4. Method according to claim 1, characterized in that the charge current of the electric machine is decreased to zero when the maximal torque of the internal combustion engine is requested.

5. Method according to claim 1, characterized in that the charge current of the electric machine is increased when a steady state torque request during more than a predetermined time is registered.

6. Method according to claim 1, characterized in that the predetermined torque limitation value is a percentage of the maximal torque of the internal combustion engine depending on the rotational speed of the internal combustion engine.

7. Method according to claim 6, characterized in that the percentage is between 70-90% of the maximal torque of the internal combustion engine.

8. Method according to claim 1, characterized in that the predetermined torque limitation value is a table depending on the rotational speed of the internal combustion engine.

9. Method according to claim 8, characterized in that the predetermined torque limitation table comprises specific torque limitation values for specific rotational speed values of the internal combustion engine.

10. A system for controlling a hybrid electric driveline in a vehicle, where the hybrid electric driveline comprises an internal combustion engine and an electric machine configured in parallel for driving a propulsion member, where the system further comprises an electronic control unit, where the electronic control unit controls the hybrid electric driveline to function in a generator mode in which the electric machine delivers a charge current to a battery and where the internal combustion engine provides positive driving torque to the propulsion member, characterized in that the electronic control unit is adapted to limit the torque delivered by the internal combustion engine to a predetermined torque limitation value in dependence of the rotational speed of the internal combustion engine.

11. Vehicle, comprising a control system according to claim 10.

12. Vehicle according to claim 11, characterized in that the vehicle is a heavy vehicle and the propulsion member is a wheel.

13. Vehicle according to claim 11, characterized in that the vehicle is a vessel or a boat and the propulsion member is a propeller.

14. A computer program comprising program code means for performing all the steps of claim 1 when said program is run on a computer.

15. A computer program product comprising program code means stored on a computer readable medium for performing all the steps of claim 1 when said program product is run on a computer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0016] The invention will be described in greater detail in the following, with reference to the attached drawings, in which

[0017] FIG. 1 shows a schematic heavy vehicle,

[0018] FIG. 2 shows a schematic vessel,

[0019] FIG. 3 shows a schematic system for controlling a hybrid electric driveline according to the invention,

[0020] FIG. 4 shows a typical torque curve for an internal combustion engine, and

[0021] FIG. 5 shows a schematic flow chart of the inventive method.

MODES FOR CARRYING OUT THE INVENTION

[0022] The embodiments of the invention with further developments described in the following are to be regarded only as examples and are in no way to limit the scope of the protection provided by the patent claims. In this description, the term vehicle is used both for land based vehicles comprising wheels and for vessels or boats.

[0023] FIG. 1 shows a schematic heavy vehicle 20 provided with an inventive system 1 for controlling a hybrid electric driveline, and FIG. 2 shows a schematic vessel 40 provided with an inventive system 1 for controlling a hybrid electric driveline. The heavy vehicle is here a truck, but the control system can be used in any heavy vehicle comprising a hybrid electric driveline, such as busses or construction equipment vehicles. The control system is further well suited for use in vessels or boats comprising a hybrid electric driveline. The system is primarily intended for boats comprising a double engine arrangement, such as an Inboard Performance System (IPS), but is also well suited for boats or vessels comprising one internal combustion engine.

[0024] FIG. 3 shows a schematic system 1 for controlling a hybrid electric driveline 2. The system 1 comprises an internal combustion engine 3, a transmission 4, an electric machine 5 and a clutch 6. The transmission is coupled to a propulsion member that propels the vehicle or vessel. In a first example, the hybrid electric driveline is used in a heavy vehicle 20. In this case, the transmission comprises a gearbox and differential that in turn drives the wheels of the vehicle. In a second example, the hybrid electric driveline is used in a boat and the transmission may comprise a reverse gear 7 and a sterndrive 8 that drives a propeller 9.

[0025] The electric machine 5 is mounted on a drive axle of the internal combustion engine, downstream of the clutch, and the internal combustion engine and the electric machine are configured as a parallel electric hybrid driveline. The electric machine may be used as an electric motor and can be used to provide additional drive torque for driving the vehicle or can be used alone, such that the driveline is powered only by electricity. The electric machine can further be used as a generator that will charge a battery 11. Depending on the size and state of charge of the battery, more or less charge current may be required.

[0026] When the vehicle is driven by the internal combustion engine and the battery needs to be charged, the electric machine will load the internal combustion engine with an additional load, i.e. with an additional torque. Depending on the torque delivered by the internal combustion engine and the required torque required to charge the battery, the combined torque may equal or exceed the maximal torque that can be delivered by the internal combustion engine. In such a situation, there is no safety margin if the driver would request additional torque, e.g. for acceleration. In a vessel using an IPS system, additional torque may be requested by the system for positioning of the vessel or for steering of the vessel. With no additional torque available, the safety of the vessel may be compromised in some driving situations.

[0027] In order to provide a safety margin when the electric machine is charging the battery, the maximal torque that the internal combustion engine is allowed to deliver is limited to a torque limitation value. The torque limitation value is a predefined value that is dependent on the rotational speed of the internal combustion engine and that provides a margin to the maximal torque that the internal combustion engine can deliver. The torque limitation value is lower than the maximal torque, and may be e.g. 20% lower than the maximal torque value.

[0028] In this way, the requested torque from the internal combustion engine is used to propel the vehicle forwards. The difference between the requested torque and the torque limitation value at a given rotational speed can then be used by the electric machine to charge the battery. If the difference between the requested drive torque to the internal combustion engine and the torque limitation value is larger than the torque needed to charge the battery, the electric machine can charge the battery as needed with the required charge current. If the difference between the requested drive torque to the internal combustion engine and the torque limitation value is smaller than the torque needed to charge the battery, the charge current to the battery is reduced such that the requested drive torque and the torque used by the electric machine equals the torque limitation value.

[0029] When a drive torque request to the internal combustion engine is higher than the torque limitation value, the charge current is limited to zero, i.e. the battery is not charged at all. In this way, the torque from the internal combustion engine is used only to propel the vehicle. With the charge current set to zero, the maximal available torque that can be delivered by the internal combustion engine may be used. In this situation, there is no need for a safety margin, and the situation will resemble an ordinary internal combustion engine without a hybrid electric driveline.

[0030] If the vehicle is driven at a steady state for a longer time period, the charge current to the battery may be increased when the torque request to the internal combustion engine has not changed significantly for a predetermined time interval, i.e. the predetermined torque limitation value is increased temporarily when a steady state torque request to the internal combustion engine is requested for a predetermined time interval. When a higher torque is requested, the torque limitation value is reset to the nominal value, and the charge current to the battery is decreased.

[0031] The torque limitation value may be selected in different ways. In one example, the torque limitation value is a set percentage of the maximal torque of the internal combustion engine. The percentage may e.g. be between 70-90% of the maximal torque of the internal combustion engine. It is also possible to assign different percentage values for different rotational speed ranges of the internal combustion engine. In one example, the torque limitation value may be 70% for a rotational speed below a first rotational speed value, e.g. below 600 rpm. The torque limitation value may be 90% between the first rotational speed value and a second rotational speed value, e.g. 1600 rpm, and may be 80% for rotational speed values above the second rotational speed value.

[0032] The torque limitation value may also be a table depending on the rotational speed value. By using a table to determine the torque limitation value, unfavourable rotational speed values may be avoided completely, e.g. critical rotational speed values at which vibrations or resonances occur. This will prevent the internal combustion engine to run at critical rotational speed values and will minimize noise from the internal combustion engine, from the driveline and/or from the vehicle.

[0033] The control system 1 is provided with an electronic control unit (ECU) 10 adapted to control the torque output from the internal combustion engine 3 and to control the charge current of the electric machine 5. The ECU 10 will communicate with other ECU's of the vehicle.

[0034] FIG. 4 shows an example of a typical torque curve M for an internal combustion engine depending on the rotational speed RPM of the internal combustion engine, where the solid line is the maximal torque that can be delivered by the internal combustion engine. The dash-dotted line is an example of torque limitation values for different rotational speeds. The dotted line is an example of a propeller torque curve for a vessel. In the shown example, the torque limitation values are determined from a table stored in the ECU 10. The safety margin for different rotational speeds varies, and is here larger for higher rotational speeds.

[0035] FIG. 5 shows a schematic flow chart of one example of the method for controlling a hybrid electric driveline in a heavy vehicle or a vessel, comprising an internal combustion engine and an electric machine configured in parallel for driving a propulsion member. The method is performed when the internal combustion engine propels the vehicle, and when the electric machine is used to charge a battery.

[0036] In step 100, the driveline is driven in generator mode, where the electric machine provides a charge current to a battery and where the internal combustion engine provides positive driving torque to the propulsion member.

[0037] In step 110, the maximal available torque from the internal combustion engine is limited to a predetermined torque limitation value depending on the rotational speed of the internal combustion engine.

[0038] The invention is not to be regarded as being limited to the embodiments described above, a number of additional variants and modifications being possible within the scope of the subsequent patent claims.

REFERENCE SIGNS

[0039] 1: Control system [0040] 2: Driveline [0041] 3: Internal combustion engine [0042] 4: Transmission [0043] 5: Electric machine [0044] 6: Clutch [0045] 7: Reverse gear [0046] 8: Sterndrive [0047] 9: Propeller [0048] 10: Electronic control unit [0049] 11: Battery [0050] 12: Wheel [0051] 20: Vehicle [0052] 21: Vessel