Drive system for hybrid vehicle with means for calculating engine torque based on motor torque

Abstract

A drive system and a method of driving a vehicle (1). The drive system includes (1) a combustion engine (2), a gear box (3), an electric machine (9), and a planetary gear. A control unit (18) has access to information concerning the moment (T.sub.el) of the electric machine (9) for driving the vehicle (1) and to calculate the moment (T.sub.1c) of the combustion engine (2) for driving the vehicle (1) at at least a first operation occasion (D.sub.1) when there is a known relation between the moment (T.sub.el) of the electric machine and the moment (T.sub.1c) of the combustion engine.

Claims

1. A drive system for a vehicle, wherein the drive system comprises a combustion engine with an output shaft, a gear box with an input shaft, an electric machine which comprises a stator and a rotor, and a planetary gear which comprises a sun wheel, a ring wheel and a planet wheel holder, wherein the output shaft of the combustion engine is connected to a first of the components of the planetary gear such that rotation of the output shaft leads to rotation of the first component, the input shaft of the gear box is connected to a second of the components of the planetary gear such that rotation of the input shaft leads to rotation of the second component, and the rotor of the electric machine is connected to a third of the components of the planetary gear such that rotation of the rotor leads to rotation of the third component; the drive system comprises a control unit which has access to information concerning the moment of the electric machine for driving the vehicle based on knowledge of the electric energy led to or from the electric machine, and the control unit calculates the moment of the combustion engine for driving the vehicle at at least a first operation occasion when there is a known relation between the moment of the electric machine and the moment of the combustion engine based on knowledge of the moment of the electric machine, wherein the control unit is configured to compare the calculated moment of the combustion engine with a demanded moment of the combustion engine at the first operation occasion, and wherein the control unit is configured to store information concerning a deviation between the calculated moment of the combustion engine and the demanded moment of the combustion engine at the first operation occasion and to use the stored information for controlling the combustion engine at a second operation occasion.

2. A drive system according to claim 1, further comprising the control unit is configured to store information concerning the deviation between the calculated moment of the combustion engine and the demanded moment of the combustion engine at different operation states of the combustion engine.

3. A drive system according to claim 2, further comprising the control unit is configured to supplement and/or update the stored information concerning the deviation between the calculated moment of the combustion engine and the demanded moment of the combustion engine during subsequent first operation occasions.

4. A drive system according to claim 1, further comprising the control unit is configured to use the calculated moment of the combustion engine for controlling the combustion engine at second operation occasions when the combustion engine supplies the demanded moment.

5. A drive system according to claim 4, further comprising the control unit is configured to use the calculated moment of the combustion engine for controlling the combustion engine at second operation occasions.

6. A drive system according to claim 1, further comprising the planetary gear comprises a coupling member configured to lock the output shaft of the combustion engine and the input shaft of the gear box in relation to each other and the control unit is configured to determine the calculated moment of the combustion engine at first operation occasions when the coupling member is in a non-locked position in which the output and input shafts are rotatable with different rotation speeds.

7. A drive system according to claim 1, further comprising the control unit is configured to determine the calculated moment of the combustion engine with assistance from a correlation which comprises the transmission ratio between the output shaft of the combustion engine and the electric machine in the planetary gear, the moment of inertia of the electric machine, the moment of inertia of the combustion engine, the acceleration of the electric machine, and the acceleration of the combustion engine.

8. A drive system according to claim 1, further comprising the output shaft of the combustion engine is connected to the sun wheel of the planetary gear, the input shaft of the gear box is connected to the planet wheel holder of the planetary gear and the rotor of the electric machine is connected to the ring wheel of the planetary gear.

9. Vehicle comprising a drive system according to claim 1.

10. A method of driving a vehicle, wherein the vehicle comprises a control unit, a combustion engine with an output shaft, a gear box with an input shaft, an electric machine which comprises a stator and a rotor, and a planetary gear which comprises a sun wheel, a ring wheel and a planet wheel holder, wherein the output shaft of the combustion engine is connected to a first of the components of the planetary gear such that rotation of the output shaft leads to rotation of the first component, the input shaft of the gear box is connected to a second of the components of the planetary gear such that rotation of the input shaft leads to rotation of the second component and the rotor of the electric machine is connected to a third of the components of the planetary gear such that rotation of the rotor leads to rotation of the third component; the method comprising the steps of providing to the control unit access to information concerning the moment of the electric machine for driving the vehicle based on gaining knowledge of the electric energy led to or from the electric machine, calculating with the control unit the moment of the combustion engine for driving the vehicle at at least a first operation occasion when there is a known relation between the moment of the electric machine and the moment of the combustion engine based on knowledge of the moment of the electric machine, comparing the calculated moment of the combustion engine with a demanded moment of the combustion engine at the first operation occasion, storing information concerning the deviation between the calculated moment of the combustion engine and the demanded moment of the combustion engine at the first operation occasion, and using the stored information for controlling the combustion engine at a second operation occasion.

11. A method according to claim 10, further comprising storing information concerning the deviation between the calculated moment of the combustion engine and the demanded moment of the combustion engine at different operation occasions of the combustion engine.

12. A method according to claim 10, further comprising supplementing and/or updating the stored information concerning the deviation between the calculated moment of the combustion engine and the demanded moment of the combustion engine during subsequent first operation occasions.

13. A method according to claim 10, further comprising using the calculated moment of the combustion engine for controlling the combustion engine at second operation occasions when the combustion engine is to supply the demanded moment.

14. A method according to claim 13, further comprising using the calculated moment of the combustion engine for controlling the combustion engine at second operation occasions.

15. A method according to claim 10, further comprising locking the output shaft of the combustion engine and the input shaft of the gear box in relation to each other with a coupling member and determining the calculated moment of the combustion engine at first operation occasions when the coupling member is in a non-locked position in which the output and input shafts are rotatable with different rotation speeds.

16. A method according to claim 10, further comprising determining the calculated moment of the combustion engine with help of a correlation which comprises the transmission ratio between the output shaft of the combustion engine and the electric machine in the planetary gear, the moment of inertia of the electric machine, the moment of inertia of the combustion engine, the acceleration of the electric machine, and the acceleration of the combustion engine.

17. A method according to claim 10, further comprising connecting the output shaft of the combustion engine to the sun wheel of the planetary gear, connecting the input shaft of the gear box to the planet wheel holder of the planetary gear and connecting the rotor of the electric machine to the ring wheel of the planetary gear.

18. A non-transitory computer program product comprising a non-volatile data storage medium on which computer code is stored and which is readable by a computer, wherein the computer program code of the computer program product causes a computer to implement a method when the computer program code is executed in the computer, the method comprising driving a vehicle, wherein the vehicle comprises a control unit, a combustion engine with an output shaft, a gear box with an input shaft, an electric machine which comprises a stator and a rotor, and a planetary gear which comprises a sun wheel, a ring wheel and a planet wheel holder, wherein the output shaft of the combustion engine is connected to a first of the components of the planetary gear such that rotation of the output shaft leads to rotation of the first component, the input shaft of the gear box is connected to a second of the components of the planetary gear such that rotation of the input shaft leads to rotation of the second component and the rotor of the electric machine is connected to a third of the components of the planetary gear such that rotation of the rotor leads to rotation of the third component; the method comprising the steps of providing to the control unit access to information concerning the moment of the electric machine for driving the vehicle based on gaining knowledge of the electric energy led to or from the electric machine, calculating with the control unit the moment of the combustion engine for driving the vehicle at at least a first operation occasion when there is a known relation between the moment of the electric machine and the moment of the combustion engine based on knowledge of the moment of the electric machine, comparing the calculated moment of the combustion engine with a demanded moment of the combustion engine at the first operation occasion, storing information concerning the deviation between the calculated moment of the combustion engine and the demanded moment of the combustion engine at the first operation occasion, and using the stored information for controlling the combustion engine at a second operation occasion.

Description

SHORT DESCRIPTION OF THE DRAWINGS

(1) In the following preferred embodiments of the invention are described, as examples, with reference to the annexed drawings, on which:

(2) FIG. 1 shows a drive line of a vehicle with a drive system according to the present invention,

(3) FIG. 2 shows the drive system in more detail and

(4) FIG. 3 shows a flow chart which shows an embodiment of a method according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(5) FIG. 1 shows a drive line for a heavy vehicle 1. The drive line comprises a combustion engine 2, a gear box 3, a number of drive shafts 4 and drive wheels 5. Between the combustion engine 2 and the gear box 3 the drive line comprises an intermediate part 6. FIG. 2 shows the components in the intermediate part 6 in more detail. The combustion engine 2 is provided with an output shaft 2a and the gear box 3 with an input shaft 3a in the intermediate part 6. The output shaft 2a of the combustion engine is coaxially arranged in relation to the input shaft 3a of the gear box. The output shaft 2a of the combustion engine and the input shaft 3a of the gear box are rotatably arranged around a common axis of rotation 7. The intermediate part 6 comprises a housing 8 which encloses an electric machine 9 and a planetary gear. The electric machine 9 comprises in a customary manner a stator 9a and a rotor 9b. The stator 9a comprises a stator core which is attached in a suitable manner on the inside of the housing 8. The stator core comprises the windings of the stator. The electric machine 9 is adapted to during certain operation states use stored electric energy for supplying drive power to the input shaft 3a of the gear box and to during other operation states use the kinetic energy of the input shaft 3 of the gear box for extracting and storing electric energy.

(6) The planetary gear is arranged substantially radially inside of the stator 9a and rotor 9b of the electric machine. The planetary gear comprises in a customary manner a sun wheel 10, a ring wheel 11 and a planet wheel holder 12. The planet wheel holder 12 carries a number of cog wheels 13 which are rotatably arranged in a radial space between the cogs of the sun wheel 10 and the ring wheel 11. The sun wheel 10 is attached on a peripheral surface of the output shaft 2a of the combustion engine. The sun wheel 10 and the output shaft 2a of the combustion engine rotate as a unit with a first rotation speed n.sub.1. The planet wheel holder 12 comprises an attachment portion 12a which is attached on a peripheral surface of the input shaft 3a of the gear box with the help of a spline joint 14. With the help of this joint, the planet wheel holder 12 and the input shaft 3a of the gear box can rotate as a unit with a second rotation speed n.sub.2.

(7) The ring wheel 11 comprises an external peripheral surface on which the rotor 9b is fixedly mounted. The rotor 9b and the ring wheel 11 constitute a rotatable unit which rotates with a third rotation speed n.sub.3.

(8) Since the intermediate part 6 between the combustion engine 2 and the gear box 3 in a vehicle is limited, it is required that the electric machine 9 and the planetary gear constitute a compact unit. The components 10-12 of the planetary gear are here arranged substantially radially inside of the stator 9a of the electric machine. The rotor 9b of the electric machine, the ring wheel 11 of the planetary gear, the output shaft 2a of the combustion engine and the input shaft 3a of the gear box are here rotatably arranged around a common axis of rotation 5. With such a design, the electric machine 9 and the planetary gear occupy a relatively small space.

(9) The vehicle comprises a locking mechanism which is movable between a first open position in which the three components 10-12 of the planetary gear are allowed to rotate with different rotation speeds, and a second locked position, in which it locks together two of the components 10, 12 of the planetary gear such that the three components 10-12 of the planetary gear rotate with the same rotation speed. In this embodiment, the locking mechanism comprises a displaceable coupling member 15. The coupling member 15 is attached on the output shaft 2a of the combustion engine with the help of a spline joint 16. The coupling member 15 is in this case arranged, secured against turning on axis 7, on the output shaft 2a of the combustion engine and is displaceably arranged in an axial direction on the output shaft 2a of the combustion engine. The coupling member 15 comprises a coupling portion 15a which is connectable to a coupling portion 12b of the planet wheel holder 12. The locking mechanism comprises a schematically shown displacement member 17 which displaces the coupling member 15 between the first free position I.sub.1 when the coupling portions 15a, 12b are not in engagement with each other and the second locked position I.sub.2 when the coupling portions 15a, 12b are in engagement with each other. In the first open position, the output shaft 2 of the combustion engine and the input shaft 3 of the gear box can rotate with different rotation speeds. When the coupling portions 15a, 12b are in engagement with each other, the output shaft 2 of the combustion engine and the input shaft 3 of the gear box will rotate with the same rotation speed.

(10) An electric control unit 18 controls the displacement member 17. The control unit 18 is also decides at which operation occasions the electric machine 9 is to work as a motor and at which operation occasions it is to work as a generator. In order to decide this, the control unit 18 can receive actual information from suitable operation parameters. The control unit 18 can be a computer with suitable software for this purpose. The control unit 18 can be one or more separate units. The control unit 18 also controls a schematically shown control equipment 19 which controls the flow of electric energy between a hybrid battery 20 and the stator 9a of the electric machine. At operation occasions when the electric machine 9 works as a motor, stored electric energy from the hybrid battery 20 is supplied to the stator 9a. At operation occasions when the electric machine works as a generator, electric energy from the stator 9a is supplied to the hybrid battery 20. The hybrid battery 20 delivers and stores electric energy with a rated voltage which is on the order of 200-800 Volt. The vehicle 1 is equipped with a motor control function 26 with which the moment T.sub.1 and rotation speed n.sub.1 of the combustion engine can be controlled. The control unit 18 has, for example, the possibility to activate the motor control function 26 when gears are engaged and disengaged in the gear box 3 in order to create a momentless state in the gear box 3.

(11) During the operation of the vehicle 1, a moment is demanded for driving the vehicle 1 by a driver via a schematically shown accelerator pedal 21. The control unit 18 determines the moment T.sub.3 which the electric machine 9 is to deliver and the moment T.sub.1 which the combustion engine is to deliver in order for the vehicle to be driven with the demanded moment T. The control unit 18 controls the control mechanism 19 such that it leads current from the hybrid battery 20 to the electric machine 9 with an amplitude and a phase such that the electric machine 9 obtains the demanded moment T.sub.3. The moment T.sub.3 which the electric machine 9 delivers for driving the vehicle 1 is supplied or received with high accuracy. The control unit 18 controls schematically shown injection members 22 in the combustion engine 2 such that fuel is injected in an amount which corresponds to the demanded moment T.sub.1. The combustion engine 2 is however often used for the operation of different assemblies in the vehicle 1. It is, inter alia, for this reason that the combustion engine 2 does not always supply the demanded moment T.sub.1, with a desired accuracy. Other such reasons are related to the components of the combustion engine which supply the fuel, the quality and temperature of the fuel.

(12) In a planetary gear there is a correlation between the moments of the sun wheel 10, the ring wheel 11 and the planet holder 12 which is defined by the number of cogs of the respective components 10-12. Since the electric machine 9 and the combustion engine 2 are each connected to one component 10, 12 of the planetary gear, it is possible to calculate the moment T.sub.1c of the combustion engine 2 with knowledge about the estimated moment T.sub.3 of the electric machine. Since the supplied moment T.sub.3 of the electric machine 9 can be determined with high accuracy, the calculated moment T.sub.1c of the combustion engine 2 corresponds to the real supplied moment of the combustion engine with high accuracy.

(13) The moment T.sub.1c of the combustion engine 2 can be calculated according to the correlation
i(J.sub.3dw.sub.3/dt+T.sub.3)=(J.sub.1dw.sub.1/dt+T.sub.1c)

(14) i=the transmission ratio between the electric machine and the combustion engine in the planetary gear,

(15) J.sub.3=The moment of inertia of the electric machine,

(16) J.sub.1=The moment of inertia of the combustion engine,

(17) T.sub.el=The estimated moment of the electric machine,

(18) T.sub.1c=The calculated moment of the combustion engine,

(19) dw.sub.el/dt=The time derivative of the angular velocity of the electric machine and

(20) dw.sub.1/dt=The time derivative of the angular velocity of the combustion engine.

(21) J.sub.3 and J.sub.1 are known quantities while dw.sub.el/dt and dw.sub.1/dt denote the acceleration of the electric motor 9 and the combustion engine 2, respectively, and can be determined as the difference in rotation speed for the respective components per time unit between two points in time. The moment T.sub.1c of the combustion engine 2 can be calculated since the other parameters in the correlation are known.

(22) T.sub.1 is thus the moment which the control unit 18 has demanded that the combustion engine 2 is to supply for driving the vehicle 1. T.sub.1c constitutes a calculated estimate of the real moment which the combustion engine supplies when driving the vehicle 1. The calculated moment T.sub.1c thus corresponds to the real moment with high accuracy. The error between the demanded moment T.sub.1 of the combustion engine and the real moment can thereby be estimated as a deviation between the demanded moment T.sub.1 and the calculated moment T.sub.1c.

(23) From observations of errors in the above mentioned moment relation, parameters in a correction model may, for example, be estimated;
T.sub.ice*=.sub.1T.sub.ice+.sub.0

(24) The parameters .sub.1 and .sub.0 are estimated by known techniques, (for example RLS), and saved for later use in the correction of moment from the combustion engine. The improved accuracy of the correction is beneficial during for example motor controlled gear shifts.

(25) FIG. 3 shows a flow chart which describes a method for driving the vehicle 1. The method starts at 30. At first operation occasions D.sub.1 of the vehicle when the coupling portions 15a, 12b are not in engagement with each other and the planetary gear is in a non-locked position, it is possible to calculate the moment T.sub.1c which the combustion engine supplies. At 31, such a first operation occasion D.sub.1 arises. Suitable such first operation occasions D.sub.1 are when the vehicle starts with a free planetary gear, when gears are shifted in the vehicle and when the vehicle is driven with a low positive or negative driving moment at the same time as the combustion engine is driven with idle running rotation speed. At 32, the supplied moment T.sub.1c of the combustion engine is calculated at at least a demanded moment T.sub.1 and at a rotation speed n.sub.1 with the help of the moment T.sub.el of the electric machine. With advantage a large number of moments T.sub.1c are calculated with a considerable spread concerning demanded moment T.sub.1 and rotation speed n.sub.1 of the combustion engine 2.

(26) At 33, the demanded moment T.sub.1 is compared with the calculated T.sub.1c. In many cases there is here a deviation since the combustion engine 2 does not always deliver a demanded moment T.sub.1 with high accuracy. Information concerning the deviation between the demanded moment T.sub.1 and the calculated moment T.sub.1c is thus with advantage determined at different moments T.sub.1 and rotation speeds n.sub.1 of the combustion engine 2. At 34, a correction model is created and a correction factor K is calculated which defines how the deviation varies with the moment T.sub.1 and rotation speed n.sub.1 of the combustion engine. Such a correction factor K can be determined according to a suitable mathematical method such as the method of least squares. Here the method can start again, at 31, if a new suitable first operation occasion D1 of the vehicle arises at which it is suitable in order to calculate the supplied moment T.sub.1c of the combustion engine 2 in order to supplement or update the correction model and the correction factor K. Otherwise the method continues, at 35, when a second operation occasion D.sub.2 arises at which the combustion engine 2 is to deliver a demanded moment T.sub.1 with a high accuracy. Such a second operation occasion D.sub.2 can be when a momentless state is to be created in the gear box 3 for the disengagement of a gear. Another such second operation occasion D.sub.2 may be when a momentless state is to be created between the sun wheel 10 and the planet holder 12 for disengagement of the coupling member 15.

(27) At 36, with the help of the demanded moment T.sub.1 and the correction factor K, the amount of fuel I is determined which is to be injected into the combustion engine 2 in order for the demanded moment T.sub.1 to be obtained with a high accuracy. With the help of such a correction model, the control unit 18 can control the injection member 22 such that it injects an amount of fuel such that the combustion engine 2 provides the demanded moment T.sub.1 with a high accuracy. The method thereafter continues at 35 at the next second operation occasion D.sub.2 which arises during the continued operation of the vehicle. Alternatively, the method continues at 31 when a new first operation occasion D.sub.1 arises at which it is suitable for calculating the supplied moment T.sub.1c of the combustion engine 2 in order to supplement or update the correction model and the correction factor K. Since the combustion engine 2 can operate certain assemblies in the vehicle intermittently or with a varying power, it is important that the correction factor is updated relatively frequently. In the above mentioned method, the correction factor K is used only at operation occasions when the combustion engine 2 must provide a demanded moment T.sub.1 with a high accuracy. It is however possible to use the correction factor at all operation occasions.

(28) The invention is in no way limited to the embodiment described on the drawings but can be varied freely within the scope of the claims. For example, a transmission with a gear ratio can be arranged between the rotor 9 and the ring wheel 11. The rotor 9 and the ring wheel 11 thus need not rotate with the same rotation speed.