Method for modulating torque by means of vehicle propulsion motor

Abstract

A method for modulating the torque of a vehicle propulsion motor driven by a first circulating current, a second circulating current and a third circulating current which are mutually shifted by an electrical angle of 120 degrees and are applied according to a rotating magnetic field of a rotor comprises applying pulse width modulation voltage pulses to a switching device, respectively, the current generator is used for generating the first circulating current, the second circulating current and the third circulating current; and adding a phase shift to the first circulating current, the second circulating current, and the third circulating current relative to the rotating magnetic field, or causing amplitude modulation in the first circulating current, the second circulating current, and the third circulating current.

Description

Technical Field

[0001] The disclosure herein relates to a method of modulating torque output by a vehicle propulsion motor, and in particular, to a method of modulating torque output by a vehicle propulsion motor powered by circulating currents having evenly spaced phase differences. Background Art

[0002] Although internal combustion engines have been dominant as a power source for vehicles in the field of transportation machinery in the past, vehicles with internal combustion engines are currently increasingly being replaced by vehicles with electric motors. The use of electric motors not only effectively suppresses carbon dioxide emissions, but also contributes to driving performance, such as excellent acceleration from low speed areas.

[0003] Typically, a motor for propelling a vehicle utilizes a permanent magnet synchronous motor in which a rotor has a permanent magnet and a stator has a coil. The motor does not include a commutator, but generates a current synchronized with a rotating magnetic field and applies the current to the coil, so that the motor generates torque. Optimization of current control suppresses torque fluctuations, and thus enables the vehicle to run smoothly.

[0004] Japanese Patent Publication No. 2013-150498 and Japanese Patent Publication No. 2022-048802 disclose related technologies. Summary of the invention

[0005] In conventional vehicle propulsion motors, smooth torque output without pulsation has been pursued, for example, based on appropriate current control using an inverter circuit. These motors can give the driver a smooth ride that is hardly produced by an internal combustion engine. However, the inventors have found that eliminating torque pulsation is not always profitable, but rather appropriate fluctuations in torque output are quite beneficial in certain aspects, such as restoring traction on any rough road (e.g., deep sand).

[0006] The following disclosure relates to a method for achieving torque fluctuations similar to torque ripples generated by an internal combustion engine.

[0007] A method for modulating the torque of a vehicle propulsion motor driven by a first circulating current, a second circulating current, and a third circulating current that are mutually shifted by an electrical angle of 120 degrees and applied according to a rotating magnetic field of a rotor is provided, comprising: applying pulse width modulated voltage pulses to switching devices respectively to generate the first circulating current, the second circulating current, and the third circulating current; and adding a phase shift to the first circulating current, the second circulating current, and the third circulating current relative to the rotating magnetic field, or causing amplitude modulation in the first circulating current, the second circulating current, and the third circulating current. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a diagram showing an example of torque fluctuation of driving force of a conventional internal combustion engine.

[0009] Figure 2 is a graph showing an example of three-phase AC current applied to a vehicle propulsion motor and output torque.

[0010] Figure 3 is a graph showing an example of torque modulated by adding a phase shift to an applied current.

[0011] Figure 4 is a graph showing an example of torque modulated by adding modulation to the applied current.

[0012] Figure 5 is a circuit diagram showing an example of a circuit for generating an alternating current.

[0013] Figure 6 is a diagram schematically illustrating an example of a pulse width modulated voltage pulse and an alternating current generated thereby.

[0014] Figure 7 is a diagram schematically illustrating another example of a pulse width modulated voltage pulse and an alternating current generated thereby.

[0015] Figure 8 is a circuit diagram showing another example of a circuit for generating an alternating current.

[0016] Fig. 9 An example of a method for modulating the voltage pulses is shown.

[0017] Fig.10 is a circuit diagram schematically illustrating yet another example of pulse width modulated voltage pulses and the alternating current generated thereby. DETAILED DESCRIPTION

[0018] Hereinafter, exemplary embodiments will be described with reference to the accompanying drawings.

[0019] For example, in a four-stroke gasoline engine, when the crankshaft rotates twice, the cylinder completes four cycles of intake, compression, combustion and exhaust. In these cycles, only the combustion cycle generates torque, while the other cycles serve as resistance. Although two or more cylinders are usually combined in such a way as to distinguish these crank angles and thus avoid overlapping of these combustion cycles, the resulting composite torque T E Shows cyclic fluctuations, such as Figure 1 as shown in the example.

[0020] In a conventional vehicle propulsion motor, circulating currents that are mutually offset by, for example, 120 electrical degrees are sequentially applied to three sets of coils in order to generate a rotating magnetic field that is synchronized with the rotation of the rotor. When a sign wave AC current is used as the circulating current and is appropriately adjusted, the motor can generate a magnetic field such as Figure 2 The essentially pulsation-free torque T M In conventional vehicle propulsion motors, pulsation-free torque generation has been pursued in view of noise and vibration reduction.

[0021] The embodiments described below implement a vehicle propulsion motor having a modulated torque similar to the torque ripple of an internal combustion engine.

[0022] In three-phase sign wave operation, when the applied current is synchronized with the rotation of the rotor, the generated torque follows the following equation:

[0023]

[0024] Where Kt represents the torque coefficient, I0 represents the total applied current, and φ represents the electrical angle.

[0025] Although the three terms on the right hand side each produce a cyclically fluctuating torque, the sum of these terms cancels out the fluctuations to provide a substantially pulsation-free torque, as Figure 2 If a small phase shift or lag θ relative to the rotating magnetic field is added to the applied current, the torque generated will follow the equation:

[0026]

[0027] Even in the summation, the fluctuations do not cancel, resulting in a generated torque T with a cyclic modulation M ,like Figure 3 as shown in the example.

[0028] Alternatively, the generated torque T can be achieved by adding amplitude modulation to the applied current I0 M Similar modulation. Figure 4 An example of this is shown in the figure. Although the above modulation torque usually appears as Figure 3 The signed waveform shown is, however, based on amplitude modulation of current I0, an arbitrary waveform may be implemented to reflect the modulation.

[0029] Still alternatively, frequency modulation may also result in a modulation of the generated torque, however, it may result in a dropout in the result and frequency modulation may therefore only be suitable for eg short-term modulation.

[0030] refer to Figure 5, a specific means for modulating the torque generated by the vehicle propulsion motor will be described below. The circuit 1 is provided with a power source 3 and three sets of switching devices S1, S2, S3, the output ends of which are respectively connected to the input ends of the coil 5. Insulated gate bipolar transistors are respectively suitable for the switching devices S1, S2, S3, but this example is not exhaustive.

[0031] When the width modulated voltage pulse P is input to the gates of the switching devices S1 , S2 , S3 , the corresponding output terminals output circulating currents C1 , C2 , C3 . Figure 6 An example of the relationship between the voltage pulse P and the output wave C is shown, where a symbol wave is output. By changing the pulse width modulation, an arbitrary waveform can be obtained. Figure 7 In the example shown, a distorted sign wave is output. It will be readily understood that if the input voltage pulse P is delayed, the resulting output wave C also exhibits a corresponding delay, and more specifically, a phase shift can be added to the circulating current relative to the rotating magnetic field. In addition, by modulating the input voltage pulse P, the amplitude of the output wave C can be modulated.

[0032] For the modulation of the voltage pulse P, for example Figure 8 The circuit shown is applicable. Specifically, for the respective gates of the switching devices S1, S2, S3, an external circuit for modulation is connected, and a wave for modulation is input to the respective circuits, thereby modulating the input voltage pulse P. In this example, the basic voltage pulse P is common to the basic voltage pulse P of the prior art, and modulation is generated only by applying the modulation wave M to the added circuit. For the added circuit, the grounded emitter circuits D1, D2, D3 shown in the drawings may be applicable, but this example is not exhaustive.

[0033] Alternatively, the basic voltage pulse P can be premodulated. Fig. 9 An example is shown in which the logic operation device A outputs a modulated voltage pulse P M By applying a voltage pulse P M Enter into e.g. Figure 6 In the circuit shown, the width of the output wave C can be modulated.

[0034] Still alternatively, Fig.10 As shown in the example, circuit C M can be added to the output stage of the switching devices S1, S2, S3 so that the width of the output wave C is increased by the circuit C M operation to modulate.

[0035] According to an embodiment of the present invention, the torque generated by the vehicle propulsion motor can be modulated with a simple structure. The modulated torque is conducive to the recovery of traction under certain road conditions. The modulated torque is similar enough to the fluctuating torque of the internal combustion engine and does not cause discomfort to the driver who is accustomed to the conventional vehicle, and the driver may prefer it. Whether the generated torque is kept constant or modulated can be easily selected by the on-off control on the added circuit. The driver of the vehicle can choose to use the modulated / unmodulated torque according to the road conditions by operating the switch at hand or under the automatic control of the vehicle.

[0036] While certain exemplary embodiments have been described above, modifications and variations of the embodiments will occur to those skilled in the art in light of the above teachings.

Claims

1. A method for modulating torque of a vehicle propulsion motor, the vehicle propulsion motor being driven by a first circulating current, a second circulating current and a third circulating current shifted by 120 electrical degrees from each other and applied according to a rotating magnetic field of a rotor, the method comprising: applying pulse width modulated voltage pulses to the switching devices respectively to generate the first circulating current, the second circulating current and the third circulating current; as well as A phase shift is added to the first circulating current, the second circulating current, and the third circulating current with respect to the rotating magnetic field, or an amplitude modulation is induced in the first circulating current, the second circulating current, and the third circulating current.

2. The method according to claim 1, further comprising: A hysteresis is added to the voltage pulses relative to the rotating magnetic field to generate the phase shift.

3. The method according to claim 1, further comprising: A cyclic modulation is added to the pulse width of the voltage pulses to generate the amplitude modulation.

4. The method according to claim 1, further comprising: Modulation is added to the gains of the generated first, second and third circulating currents to generate the amplitude modulation.

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