HYBRID VEHICLE

Abstract

A hybrid vehicle (1) has an internal combustion engine (2) and an electric motor (3) that act on a common shaft (11). The torque exerted on the shaft (11) by the internal combustion engine (2) varies during a cycle of the internal combustion engine (2). A control unit (14) is configured to modulate the torque of the electric motor (3) such that the sum of the torques of the internal combustion engine (2) and the electric motor (3) has a smaller relative fluctuation range than the torque of the internal combustion engine (2) alone.

Description

[0001] The present invention relates to a hybrid vehicle having an internal combustion engine and an electric motor acting on a common shaft, for example to drive a chassis.

[0002] In the cylinders of an internal combustion engine, gas is compressed during the upward movement of the cylinder, so that the cylinder in question exerts a decelerating torque on the shaft, whereas during the downward movement an accelerating torque acts. For vehicle occupants, these fluctuations are perceptible as shaking, accompanied by noise. The fluctuations can partially compensate for each other if the cylinders operate out of phase, so that at the same time as a decelerating torque from one of the cylinders is exerted, an accelerating torque from at least one other acts on the shaft. While torque fluctuations can be reduced in this way, they cannot be completely suppressed; in particular, the damping of harmonics of the shaft's rotational frequency is unsatisfactory.Particularly at low rotational frequencies of the shaft, which occur when the combustion engine is started, resonance phenomena can occur, which considerably increase the extent of the disturbance for the vehicle occupants.

[0003] Since vibration compensation is traditionally more effective the larger the number of cylinders, customers associate low-vibration engine operation particularly with luxury class automobiles.

[0004] The object of the present invention is to create a hybrid vehicle whose running smoothness corresponds to an internal combustion engine with a higher number of cylinders than that of the internal combustion engine actually installed in the vehicle.

[0005] According to one aspect of the invention, the object is achieved in that, in a hybrid vehicle having an internal combustion engine and an electric motor acting on a common shaft, wherein the torque exerted by the internal combustion engine on the shaft is variable over the course of a cycle of the internal combustion engine, a control unit is arranged to modulate the torque of the electric motor such that the sum of the torques of the internal combustion engine and the electric motor has a smaller relative fluctuation range than the torque of the internal combustion engine alone.

[0006] Specifically, the vehicle according to the invention can be fitted with a conventional four-cylinder engine that is manufactured cost-effectively in large quantities, while the impression of smooth running conveyed to the occupants corresponds to a much more expensive engine with six or more cylinders.

[0007] Since road surface irregularities, in addition to the operation of the combustion engine, contribute to the vibrations and noise perceived by the occupants when the vehicle is moving, torque compensation is most effective during the engine start-up phase, before the vehicle begins to move. The control unit can therefore be configured to terminate the torque modulation of the electric motor after the engine has successfully started.

[0008] In particular, the control unit can be connected to a sensor to detect a phase angle of the shaft and can be configured to set a target value of the torque of the electric motor as a function of the detected phase angle.

[0009] In order to make the transition between operation of the combustion engine with torque compensation by the electric motor and without torque compensation as unnoticeable as possible for the occupants, the setpoint should be a product of a periodic function of the phase angle and a function that decreases monotonically with the phase angle or time.

[0010] Furthermore, when setting the target value, it should be taken into account whether the fuel injection of the combustion engine is (already) in operation or not.

[0011] To effectively dampen vibrations at the fundamental frequency, i.e., the shaft's rotational frequency, the electric motor's torque should also be the same during phases where the internal combustion engine's torque is the same, especially at top and bottom dead centers of one of its cylinders. Like the internal combustion engine's torque, it can be zero at both dead centers; however, it can also have an equal, non-zero value if the electric motor is used to push the internal combustion engine's rotation during starting.

[0012] In order to effectively dampen harmonics of the fundamental frequency, the control unit can be configured to calculate the torque exerted by the internal combustion engine on the shaft as a sum of phase angle-dependent moments resulting from gas pressures acting on cylinders of the internal combustion engine.

[0013] In order to take into account the time offset between the detection of a phase angle and the output of the corresponding setpoint value of the torque of the electric motor by the control unit, the control unit can be configured to define the setpoint value as a function of a corrected phase angle which deviates from the detected value of the phase angle by a correction value proportional to the rotational speed of the shaft.

[0014] According to a further aspect of the invention, the object is achieved by a method for operating a hybrid vehicle with an internal combustion engine and an electric motor acting on a common shaft, wherein the torque exerted by the internal combustion engine on the shaft is variable over the course of a cycle of the internal combustion engine, comprising the steps: - estimating the variation of a torque exerted by the internal combustion engine on the shaft during one cycle of the internal combustion engine; and - Modulating the torque of the electric motor so that the relative fluctuation range of the sum of the torques of the combustion engine and the electric motor has a smaller relative fluctuation range than the torque of the combustion engine alone.

[0015] The invention further relates to a computer program product comprising computer-executable instructions that enable a computer to operate as a control unit in a hybrid vehicle as described above or to carry out the method described above.

[0016] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying figures. Fig. 1 is a block diagram of a motor vehicle with a hybrid drive; Fig. 2 a block diagram of a control unit of the motor vehicle from Fig. 1; Fig. 3 schematically shows a cylinder of an internal combustion engine of the motor vehicle and the forces acting on it; and Fig. 4 shows a typical relationship between phase angle and torque exerted by the cylinder.

[0017] Fig. Figure 1 shows a block diagram of a motor vehicle 1 with a hybrid drive system comprising an internal combustion engine 2 and an electric motor 3. The internal combustion engine is depicted as an in-line engine with four cylinders 4; however, other designs are also possible. While the number n of cylinders 4 is arbitrary, the advantages of the invention are greatest with a relatively low number of cylinders n, e.g., n=4 or 5.

[0018] The cylinders 4 act on a crankshaft 5 of the internal combustion engine 2. An axis of rotation 6 of the crankshaft 5 is defined by bearings 7. Connecting rods 8 of the cylinders 4 are each rotatably connected to the crankshaft 5 at connecting rod journals 9. Viewed in the direction of the axis of rotation 6, the connecting rod journals 9 define an equilateral n-gon, in the illustrated case, n=4, a square with the axis of rotation 6 at its center, so that after every 1 / n of a revolution of the crankshaft 5, one of the cylinders 4 passes through a top (or bottom) dead center.

[0019] The crankshaft 5 is connectable via a clutch 10 to a shaft 11, which carries a rotor of the electric motor 3 and can thus be driven by both the electric motor 3 and the combustion engine 2. A manual transmission 12 supports several shift positions that couple the wheels 13 of the vehicle 1 to the shaft 11 with different gear ratios, and a neutral position in which the torque transmission between the motors 2, 3 on the one hand and the wheels 13 on the other hand is interrupted.

[0020] An electronic control unit 14 controls, in a manner known per se, the fuel supply to the cylinders 4 via injection valves 15. In order to determine the appropriate injection timing for each of the cylinders 4, the control unit 14 receives measured values ​​of a phase angle φ of the rotation of the shaft 11 from an angle sensor 16.

[0021] According to the invention, the control unit 14 also temporarily controls the electric motor 3 based on the measured values ​​of the angle sensor 16, as described in more detail below.

[0022] Fig. Figure 2 is a block diagram of the control unit 14. The control unit 14 receives as input data the phase angle φ of the shaft 11 detected by the angle sensor 16 and a measured value of the air mass flow 17 drawn in by the internal combustion engine 2. A measured value of the engine speed 18 can be measured or derived by the control unit 14 from the measured values ​​of the phase angle φ. The detected phase angle φ corresponds to different positions of the pistons in the cylinders 4 of the internal combustion engine 2, and thus to different forces F G , which exerts compressed gas in the cylinders 4 on the pistons.

[0023] Fig. 3 shows for one of the pistons 4, seen in a direction parallel to the axis 6 or 11, which results from the force F Gresulting forces at other locations in the engine 2. A piston force F K results from the force F G by correcting for inertial influences resulting from the movement of the piston and connecting rod 8. The connecting rod 8 crosses a plane passing through its pivot point 19 on the piston and the axis 11 at an angle β. The piston force F K acts perpendicular to the piston surface. However, the connecting rod can only exert a force F S in a direction deviating from the perpendicular by β, for which the following applies FS=FKcos β.

[0024] This force is to be broken down at the connecting rod pin 9 into a component F that accelerates or decelerates the rotation of the shaft 11 T , tangential to an orbit of the connecting rod pin 9 around the axis 11 and a neutral component oriented radially to the axis 11. For the tangential component, Fr=FS⋅cos γ, where γ=90°−β−φ applies.

[0025] This results in a relationship between the phase angle φ of the shaft 11 and the torque exerted on it by the cylinder 4 as in Fig. 4 is shown as curve P1: At the dead centers of the cylinder, here at φ = 0 and φ = 180°, the torque is zero. On the way from bottom to top dead center, gas trapped in cylinder 4 is compressed and thus initially counteracts the rotation more strongly the higher the pressure becomes. Shortly before reaching top dead center, the distance traveled by the piston in the cylinder becomes increasingly smaller in relation to the angle of rotation of the shaft, so that the amount of torque decreases again. On the way from top to bottom dead center, the process repeats in the opposite direction. Due to the asymmetrical curve shape, a cylinder that acts on the shaft 11 at a phase angle offset by 180° cannot compensate for these fluctuations; even if a large number of cylinders work together, there remains an unavoidable fluctuation in the torque exerted on the shaft 11 by the cylinders 4 during one revolution of the shaft 11, shown as curve P4.The dependence of this torque on the phase angle φ can be calculated based on geometric considerations as outlined above or determined empirically. By controlling the torque exerted by the electric motor 3 on the shaft 11 as a function of the phase angle φ, the control unit 14 compensates for the fluctuation of the torque exerted by the cylinders 4, ideally generating a torque P4' that is a mirror image of P4, the sum of the torques acting on the shaft 11 can be made constant, thus achieving low-noise and low-vibration operation of the shaft 11.

[0026] In order to take into account a time delay between the measurement of the phase angle φ by the sensor 16 and the generation of the compensating torque corresponding to this value of the phase angle by the electric motor 3, a correction unit 20 (see Fig.2) a correction Δφ of the phase angle φ corresponding to this time offset by multiplying the time delay by the rotational speed 18. An adder 21 adds the correction Δφ to the measured phase angle φ and transfers the result to two parallel computing units 22, 23. The computing units 22, 23 each calculate a torque of the internal combustion engine 2 to be compensated for the phase angle φ+Δφ transferred to them, taking into account the air mass flow 17, one, 22, for the case that the fuel injection of the internal combustion engine 2 is in operation, the other, 23, for the case that the fuel injection is switched off, and output a corresponding target torque signal in each case. A switch 24 receives the target torque signals and a signal representative of the operating state of the fuel injection and forwards the one of the two target torque signals that corresponds to the operating state to a weighting unit 25.

[0027] A difference unit 26 determines the deviation between the rotational speed 18 and a predetermined upper limit of the rotational speed, above which compensation of the torque of the internal combustion engine 2 by the electric motor 3 is no longer to take place. A weighting factor unit 27 supplies a weighting factor to the weighting unit 25, which, as long as the rotational speed is below the upper limit, is proportional to the difference between the rotational speed 18 and the upper limit, and is constantly zero when the rotational speed is above the upper limit. The weighting unit 25 multiplies the target torque signal by the weighting factor.

[0028] An adder 28 adds the output of the weighting unit 25 to a target torque of the electric motor 3. This target torque may be zero during starting; when the electric motor 3 serves as a starter, the torque specified here is the starting torque that the electric motor 3 must generate to start the internal combustion engine 2.

[0029] As the rotational speed 18 of the internal combustion engine 2 increases as the starting process progresses, the differential unit 26 regulates the weighting factor down until it becomes zero when the upper limit is reached and the torque compensation ends imperceptibly for the vehicle occupants. Reference symbol 1 motor vehicle 2 combustion engine 3 electric motor 4 cylinders 5 Crankshaft 6 axis of rotation 7 camps 8 connecting rod 9 connecting rod pins 10 Clutch 11 Wave 12 manual transmissions 13 wheels 14 Control unit 15 Injector 16 Angle sensor 17 Air mass flow 18 engine speed 19 Pivot point 20 correction unit 21 adders 22 computing unit 23 Computing unit 24 switches 25 weighting units 26 Differential unit 27 Weighting factor unit 28 adders

Claims

[1] Hybrid vehicle (1) comprising an internal combustion engine (2) and an electric motor (3) acting on a common shaft (11), wherein the torque (P4) exerted by the internal combustion engine (2) on the shaft (11) is variable during a cycle of the internal combustion engine (2), characterized by , a control unit (14) is arranged to modulate the torque (P4`) of the electric motor (3) such that the sum of the torques (P4, P4`) of the internal combustion engine (2) and the electric motor (3) has a smaller relative fluctuation range than the torque (P4) of the internal combustion engine (2) alone. [2] Hybrid vehicle according to claim 1, wherein the control unit is arranged to terminate the modulation of the torque of the electric motor (3) after successful starting of the internal combustion engine (2). [3] Hybrid vehicle according to claim 1 or 2, wherein the control unit (14) is connected to a sensor (16) to detect a phase angle (φ) of the shaft (11) and is arranged to set a target value of the torque of the electric motor (3) as a function of the detected phase angle (φ). [4] Hybrid vehicle according to claim 3, wherein the setpoint is a product of a periodic function of the phase angle (φ) and a function monotonically decreasing with the phase angle, the time or the rotational speed (18). [5] Hybrid vehicle according to claim 3 or 4, wherein the setpoint depends on whether the fuel injection of the internal combustion engine (2) is in operation or not. [6] Hybrid vehicle according to one of the preceding claims, in which the torque of the electric motor (3) at the top dead center and at the bottom dead center of a cylinder (4) of the internal combustion engine (2) is equal and optionally zero. [7] Hybrid vehicle according to one of the preceding claims, in which the control unit (14) is arranged to calculate the torque (P4) exerted by the internal combustion engine (2) on the shaft (11) as a sum of phase angle-dependent moments (P1) which are derived from gas pressures (F G ) result. [8] Hybrid vehicle according to claim 7, wherein the control unit (14) is arranged to establish a target value of the torque of the electric motor as a function of a corrected phase angle (φ+Δφ) which deviates from the detected value (φ) of the phase angle by a correction value (Δφ) proportional to the rotational speed of the shaft (11). [9] Method for operating a hybrid vehicle (1) with an internal combustion engine (2) and an electric motor (3) acting on a common shaft (11), wherein the torque (P4) exerted by the internal combustion engine (2) on the shaft (11) is variable during a cycle of the internal combustion engine (2), comprising the steps of: - estimating the variation of a torque (P4) exerted by the internal combustion engine (2) on the shaft (11) during a cycle of the internal combustion engine (2); and - Modulating the torque (P4`) of the electric motor (3) so that the relative fluctuation range of the sum (P4+P4') of the torques of the internal combustion engine (2) and the electric motor (3) has a smaller relative fluctuation range than the torque (P4) of the internal combustion engine (2) alone. [10] A computer program product comprising computer-executable instructions enabling a computer to operate as a control unit (14) in a hybrid vehicle (1) according to any one of claims 1-8 or to carry out the method according to claim 9.

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