GB2509132A

GB2509132A - Sound generation of an electric motor in an automotive vehicle

Info

Publication number: GB2509132A
Application number: GB1223181.7A
Authority: GB
Inventors: Jeremy Greenwood; David White
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2012-12-21
Filing date: 2012-12-21
Publication date: 2014-06-25
Also published as: GB201223181D0

Abstract

An embodiment of the present invention relates to an electric motor (1) for an automotive vehicle. The electric motor (1) has a rotor (2), a stator and a plurality of windings (4) for energising the motor (1). A generating means is provided for supplying current to at least one of the windings (4). The generating means is operable to supply current comprising a sound-producing waveform to induce vibrations to produce sound. An embodiment of the present invention relates to a related method; and to a motor vehicle.

Description

SOUND GENERATION

TECHNICAL FIELD

The present invention relates to sound generation and particularly, but not exclusively, to sound generation in an electric motor. The present invention also relates to a method of generating sound, and to an automotive vehicle.

BACKGROUND

Electrically-powered vehicles produce virtually no sound when stationary and at low vehicle speed. Some countries are introducing legislation that requires the fitment of an exterior sound system on electric vehicles to overcome this. These systems are designed to work when the vehicle is stationary and at low speed, and to produce a sound to warn that the vehicle is moving or about to move. At higher speeds these systems may turn off due to other sound sources becoming dominant.

Such a system produces warning sounds designed to alert pedestrians and other vulnerable road users to the presence of an electric vehicle such as a hybrid electric vehicle (HEy), a plug-in hybrid electric vehicle (PHEV), or an all-electric vehicle (EV) travelling at low speeds.

A typical known system is described in US5,635,903, which discloses a simulated sound generator for use in an electric passenger vehicle in which motive power for the vehicle is supplied by electricity. The generator comprises an electrically-powered drive motor for driving wheels of the electric vehicle; a start sensor for detecting starting of the electric vehicle and ignition operation of the drive motor; a speed sensor for detecting the running speed of the electric vehicle; an accelerator opening sensor for detecting a degree of opening of the accelerator of the electric vehicle; a simulated sound selector device for outputting simulated sound selection information based on starting information from the start sensor, speed information from the speed sensor and accelerator degree of opening information from the accelerator opening sensor; a simulated sound source device for producing a simulated sound based on the simulated sound selection information from the simulated sound selector device; and a sound level switcher device for selecting the sound level of the simulated sound from the simulated sound source device based on the starting information, the speed information and the accelerator degree of opening information, wherein simulated sounds depending on operating conditions of the electric vehicle are produced.

The disadvantage of this type of system is that it is complicated and expensive. Moreover the sound produced depends on the speed of the electric motor, so that less sound is produced when the vehicle is stationary or moving at low speeds.

At least in certain embodiments, the aim of embodiments of the invention is to provide an automotive vehicle electric drive motor having sound generation capabilities. Another aim of embodiments of the invention is to provide such a motor which can generate sound independent of its rotational speed, for example when the motor is not rotating so that sound can be generated by a stationary vehicle.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to an electric motor; a method of operating an electric motor; and an automotive vehicle. The present invention also relates to a method of generating sound.

According to an aspect of the present invention, there is provided an electric motor comprising a rotor, a stator, a plurality of windings for energising the motor, and generating means for supplying current to at least one of the windings, the generating means being operable to supply current comprising a sound-producing waveform to induce vibrations to produce sound. The generating means is configured to supply said sound-producing waveform to one or more of the windings. The sound-producing waveform can promote the production of sound by the electric motor. At least in certain embodiments, the sound-producing waveform can produce sound independently of the operating speed of the electric motor. The interaction between the rotor and the stator in response to the supplied sound-producing waveform can induce vibrations which result in sound being produced. The sound can be produced by the motor and/or adjacent components.

The motor can be disposed within a casing. The casing can be a dedicated casing for the electric motor. Alternatively, the casing can be shared with another component or assembly.

For example, the motor can be disposed within a transmission casing (such as the bell-housing), an engine casing or a differential casing. The fluctuations in the magnetic field in response to variations in the sound-producing waveform can cause the casing to contract and/or expand. By controlling the sound-producing waveform, the frequency and/or magnitude of the resulting vibrations of the casing can be controlled to produce a sound which is audible to humans (typically in the range 20 to 20,000 Hz). The generated sound can be tuned by appropriate control of the sound-producing waveform.

The generating means can comprise a signal generator for generating the sound-producing waveform. The signal generator can be configured to generate a sound-producing waveform which induces vibrations and thereby generates a sound. By calibrating the signal generator, the resulting sound can be tuned to provide an audible indication that the motor is active. In use, the sound can be generated when the motor is stationary (i.e. the rotor is stationary) or when the motor is moving (i.e. the rotor is rotating). At least in certain embodiments, the sound generated as a result of the sound-producing waveform applied to the motor can be independent of the rotational speed of the rotor. The sound-producing waveform could be modified based on the rotational speed of the rotor to provide an audible indication of the operating speed of the rotor. For example, the frequency and/or amplitude of the sound-producing waveform could be modified in proportion to the rotational speed of the rotor.

The signal generator could also be configured to generate a sound-reducing waveform for reducing the generation of unwanted noise from the motor. The interaction of the sound-producing waveform and the sound-reducing waveform can be used to tune the sound output from the motor (for example to suppress/amplify sound at different frequencies, as appropriate). The relative magnitude of the sound-reducing waveform and the sound-producing waveform could be varied under different operating conditions, for example different rotor speeds.

The generating means can comprise a drive generator for supplying current comprising a drive waveform for affecting rotation of the rotor. The drive waveform can be applied to affect rotation of the rotor. The drive waveform can be supplied to one or more of the windings in sequence to drive the rotor. The generating means can be configured to generate the sound-producing waveform and the drive waveform simultaneously. The generating means can be configured to superimpose the sound-producing waveform onto the drive waveform. The generating means can be configured to control or modify the sound-producing waveform independently of the drive waveform. The sound-producing waveform can thereby be controlled to vary the sound produced independently of the operating speed of the motor (i.e. the rotational speed of the rotor).

The generating means can be configured to supply the sound-producing waveform without the drive waveform. Thus, the electric motor can produce sound even when it is not operating to deliver torque. The electric motor could, for example, be a traction motor which can continue to rotate whilst the vehicle is coasting or being driven by another power source (such as an internal combustion engine). By applying the sound-producing waveform without the drive waveform, the electric motor can continue to produce sound in this scenario. The sound-producing waveform can also be applied when the electric motor is operating as a generator, for example to recharge batteries.

The drive generator and the signal generator can be integrated into a single control system.

For example, the drive generator and the signal generator can be incorporated into the motor inverter, which outputs a current having an amalgamated waveform (comprising or consisting of said sound-generating waveform and the drive waveform) to the at least one winding. For example, a generator could be configured to output a current comprising both the sound-producing waveform and the drive waveform. Alternatively, the drive generator and the signal generator could be separate generators.

The generating means can comprise a control unit, for example comprising control circuitry, for supplying the sound-producing waveform and/or the drive waveform to one or more of said windings.

The drive generator can be configured to supply a drive waveform comprising either alternating current (AC) or direct current (DC) to at least one of the windings. When the sound-producing waveform is superimposed on the drive waveform, vibrations are induced producing sound. The signal generator can be configured to generate a sound-producing waveform comprising one or more of the following: a variable current; a pulsating current; and an alternating current (AC). The sound-producing waveform could, for example, comprise: a sinusoidal waveform, a square waveform or a triangular waveform.

The motor can be a traction motor operable to output a tractive force to propel the vehicle.

Alternatively, the motor could be configured to actuate an ancillary system, such as an engine starter motor, an electric fan motor, a windscreen wiper motor or the like.

The motor can be a switched reluctance motor whose stator is constituted by a plurality of pole pieces, each of which is provided with a respective one of the windings. Alternatively, the motor can be an induction, permanent magnet or other synchronous or non-synchronous motor. The motor could be an axial flux motor or a radial flux motor.

The casing can partially or completely surround the stator. At least in certain embodiments, the stator can be fixedly coupled to the casing. The deflection of the stator in response to the sound-producing signal can cause the casing to vibrate.

The motor may comprise a control unit for controlling the supply of the drive waveform and the sound-producing waveform to one or more of the windings.

The drive waveform can comprise a holding current supplied to one of said windings to prevent the motor from rotating. The sound-producing waveform can be supplied at the same time as the holding current to induce vibrations, for example in the casing, thereby producing sound when the motor (and hence the vehicle) is stationary.

The generating means can be configured to supply the drive waveform to each of the windings in sequence to affect rotation of the rotor. The generating means can optionally supply the sound-producing waveform to one or more of the windings at the same time. This results in the casing vibrating, thereby producing sound, when the motor (and hence the vehicle) is moving.

The generating means can be configured to inhibit the sound-producing waveform, for example when the rotor speed (and hence the vehicle speed) reaches a predetermined value. In this way, the sound produced by vibration of the casing can be terminated, for example when the vehicle is moving sufficiently quickly for it to generate a warning sound, such as tyre sound.

Advantageously, the generating means can be configured to apply, to one or more of the windings, a residual current on which the signal is superimposed.

In a further aspect of the present invention, there is provided a motor vehicle comprising an electric motor as described herein.

In a still further aspect of the present invention, there is provided a control unit for supplying current to an electric motor, the control unit being configured to supply current comprising a sound-producing waveform for inducing vibrations in a casing of the electric motor to produce sound. The control unit can also be configured to supply a drive waveform to affect rotation of the electric motor. The control unit can be configured to provide independent control of the sound-producing waveform and the drive waveform. Thus, the sound produced by the sound-producing waveform can be at least substantially independent of the rotational speed of the electric motor. The control unit can comprise a microprocessor for providing automated control of the drive waveform and the sound-producing waveform.

In a yet still further aspect of the present invention, there is provided a method of generating sound in an electric motor comprising a rotor, a stator, a plurality of windings for energising the motor, and generating means for supplying current to at least one of the windings, the method comprising supplying a sound-producing waveform to at least one of the windings to induce vibrations to produce sound. The electric motor can be an electric traction motor for providing a tractive force to propel a vehicle.

The method can comprise supplying a drive waveform for controlling rotation of the rotor at the same time as supplying the sound-producing waveform. The method can control the supply of the sound-producing waveform independently of the drive waveform. The drive waveform can comprise a holding current to hold the rotor stationary. The supply of the sound-producing waveform at the same time as the holding current can induce vibrations which produce sound when the rotor is stationary.

The drive waveform can be supplied in sequence to the windings to affect rotation of the rotor. The sound-producing waveform can be selectively supplied to each of the windings to induce vibrations which produce sound when the rotor is rotating.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. For example, features described with reference to one embodiment are applicable to all embodiments, unless such features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:-Figure 1 is a schematic view of a switched reluctance (SIR) drive motor for an automotive vehicle; and Figures 2 to 4 illustrate how sound is generated by the motor under various operating conditions.

DETAILED DESCRIPTION OF AN EMBODIMENT

Referring to the drawings, Figure 1 shows a switched reluctance (SR) motor 1 having a rotor 2 mounted within a plurality of stator pole pieces 3 (only one of which is shown), each of which is provided with a stator winding 4. A casing 5 surrounds the stator pole pieces 3. The motor 1 has wound field coils as in a DC motor for the stator windings 4. The rotor 2, however, has no magnets or coils attached. The rotor 2 becomes aligned as soon as the opposite pole pieces 3 of the stator become energised. A current is supplied to the stator windings 4 by a generator 6. The supplied current comprises a drive waveform which controls the rotation of the rotor 2. Specifically, when power is delivered to the stator windings 4, the magnetic reluctance of the rotor 2 creates a force that attempts to align the rotor poles with the powered windings. In order to maintain rotation, adjacent windings are energised in turn.

This type of motor can be relatively noisy in operation, and considerable work has been undertaken to develop a quieter motor. The invention is based on a proposal to control the motor to generate a sound which can provide an audible indication of the presence of the vehicle (when the vehicle is stationary and/or moving). The attraction between the stator pole pieces 3 and the rotor 2 can slightly distort the casing 5. It has been recognised by the inventor(s) that applying a variable current having suitable characteristics to the stator windings 4 can cause fluctuations in the magnetic field. These fluctuations can cause the casing 5 to vibrate in and out in sympathy, thereby generating a sound. The current supplied to the stator windings 4 can comprise a (variable) sound-producing waveform which is superimposed on the drive waveform. The sound-producing waveform and the drive waveform can be generated by the generator 6. The sound can be turned on and off by modifying the motor drive system switching characteristics.

Figure 2 is a graph of applied voltage against time, and illustrates how the motor 1 can be controlled to generate sound when the motor is not rotating and the vehicle is stationary. It is well established that applying current to a particular stator winding 4 has the effect of locking the motor in a fixed position, a useful feature prior to driving off. This is shown in the first part A of Figure 2, where the drive waveform is a steady-state holding current (designated here as winding n) applied to the winding 4 of one of the stator pole pieces 3. The generator 6 is configured to superimpose sound-producing waveform on the drive current supplied to the active stator winding 4 and this is shown in the second part B of Figure 2. The sound-producing waveform induces vibrations in the casing 5 which cause sound to be generated.

Significantly, the sound-producing waveform can be superimposed on the steady-state holding current to generate sound even when the motor 1 is stopped. The resulting sound is related to the sound-producing waveform. For example, a sine wave will produce a tone while a square wave or combination of sine waves may produce a sound reminiscent of a conventional IC engine. The steady-state holding current and the sound-producing waveform are applied to the stator winding 4 that is aligned with one of the rotor blades to avoid unintended movement. If a small movement is permissible, the steady-state and variable currents can be applied irrespective of motor rotational position. The steady-state current may, of course, be zero.

Figure 3 is a graph of applied voltage against time, and illustrates how the motor 1 can be controlled to generate sound when the motor is rotating and the vehicle is moving slowly. In this scenario, the drive waveform is a series of drive pulses supplied to three of the stator windings 4 (designated in Figure 3 as windings n, n+1 and n±2). These pulses are square wave pulses as shown in the first part C of Figure 3 and provide the normal drive to the motor 1. When sound is required, the generator 6 superimposes the sound-producing waveform on the active stator windings in turn, and this is shown in the second part D of Figure 3. The remaining stator windings 4 are also provided, in turn, with drive waveforms and the superimposed sound-producing waveforms. Although the drive waveform in the present embodiment is illustrated with reference to a square waves, it will be apparent that, alternatively, complex waveforms could be used. A complex waveform could, for example, be used for efficiency reasons or for suppression of unwanted sound.

This is likely to introduce a distortion to the required sound relating to the rotational effect of the motor 1, and the application of the sound with the impressed rotational component. If this is a problem, then the sound-producing waveform may be applied to one or more fixed stator pole pieces by applying a residual drive waveform on which the sound-producing waveform can be superimposed. Figure 4 shows this, with the drive waveform (a residual DC signal in the present example) and superimposed sound-producing waveform applied to only one of the stator windings 4 (designated here as winding n), as designated by the part E of Figure 4.

This is less electrically efficient than the arrangement of Figure 3 but may produce advantages in the generated sound quality.

Control circuitry (not shown) is provided for controlling the application of the drive waveform and the sound-producing waveform to either a single winding 4 or to all of the windings 4 in turn. The sound-producing waveform could, for example, be applied to one or more active windings 4. The control circuitry can also operate to control the generator 6 to inhibit the sound-producing waveform when the motor speed (and hence the vehicle speed) reaches a predetermined value.

After the vehicle reaches a predetermined speed of about 15 to 20 mph, the sound-producing waveform is inhibited as sound generation is no longer required because the vehicle is moving sufficiently quickly for the tyre sound generated and wind noise to be loud enough to warn pedestrians and road users of the vehicle's presence. This can be accomplished manually, but it is preferable for it to be done automatically once the predetermined speed has been reached.

The main advantage of the system described herein is that, at least in certain embodiments, it can avoid the problems of previous solutions that utilise a separate generator and sounder, or fix the sound to the rotational speed of the motor. The system described herein allows the sound produced to be independent of rotational speed of the rotor. For example, the technique described herein can be used to produce sound when the traction motor is stationary. Equally, the sound produced can be varied without changing the rotational speed of the rotor. At least in certain embodiments of the present invention, the expense of a separate sound generation system can be avoided. Note also that combining the sound and drive functions ensures that a fault condition of drive without the attendant sound is very much reduced in probability.

The generator 6 has been described herein as supplying current comprising a combination of the drive waveform and the sound-producing waveform. For example, a motor drive inverter used to drive the motor could also implement the superimposed signal to control the output of sound from the motor. If the control function is an analogue system, sound could be injected into the analogue circuitry so that sound is generated that way. If the control function is carried out by a microprocessor/DSP running a control algorithm (e.g. a space vector), the control algorithm could be modified to generate the sound as part of the waveform generation process. In a modified embodiment, separate generators could be provided for supplying the respective drive and sound-producing waveforms.

Furthermore, the motor 1 described herein has a casing associated therewith. However, the motor 1 could be integrated into the vehicle transmission and could, for example, be located inside the transmission bell housing. In such an arrangement, the sound-producing waveform could be tailored to use the natural resonance of the bell housing.

Although the invention has been described as applicable to a SR motor, it will be apparent that it could work on a permanent magnet (PM) motor, an induction motor or other synchronous motor or non-synchronous motor.

Further aspects of the present invention are outlined in the following numbered paragraphs.

1. An electric motor comprising a rotor, a stator, a plurality of windings for energising the motor, and generating means for supplying current to at least one of the windings, the generating means being operable to supply current comprising a sound-producing waveform to induce vibrations and produce sound.

2. An electric motor as described in paragraph 1, wherein the sound-producing waveform is operable to induce vibrations and produce sound independently of the rotational speed of the rotor.

3. An electric motor as described in paragraph 1, wherein the generating means is operable to supply current also comprising a drive waveform for affecting rotation of the rotor.

4. An electric motor as described in paragraph 3, wherein the generating means is configured to generate the sound-producing waveform and the drive waveform simultaneously; or to superimpose the sound-producing waveform on the drive waveform.

5. An electric motor as described in paragraph 3, wherein the generating means is configured to control the sound-producing waveform independently of the drive waveform.

6. An electric motor as described in paragraph 3, wherein the drive waveform comprises a holding current for holding the rotor stationary, the sound-producing waveform being maintained to induce vibrations to produce sound.

7. An electric motor as described in paragraph 3, wherein the generating means is configured to supply the drive waveform to the windings in a predefined sequence to affect rotation of the rotor, the sound-producing waveform being maintained to induce vibrations to produce sound.

8. An electric motor as described in paragraph 1, wherein the generating means is configured to inhibit the sound-producing waveform when the motor speed reaches a predetermined value.

9. An electric motor as described in paragraph 1, wherein the generating means is configured to supply a sound-producing waveform comprising one or more of the following: a variable current, a pulsating current, and an alternating current (AC).

10. An electric motor as described in paragraph 1, wherein the motor is a switched reluctance motor whose stator is constituted by a plurality of pole pieces, each of which is provided with a respective one of the windings.

11. An electric motor as described in paragraph 1 comprising a casing, wherein the sound-producing waveform induces vibrations in the casing to produce said sound.

12. A motor vehicle comprising an electric motor as described in paragraph 1.

13. A motor vehicle as described in paragraph 12 wherein the electric motor is a traction motor for outputting a tractive force to drive the motor vehicle.

14. A motor vehicle as described in paragraph 13 wherein the electric motor is disposed inside one of the following casings: an engine casing, a transmission casing or a differential casing.

15. A control unit for supplying current to an electric motor, the control unit being configured to supply current comprising a sound-producing waveform for inducing vibrations to produce sound.

16. A method of generating sound in an electric motor for powering an automotive vehicle, the electric motor comprising a rotor, a stator, a plurality of windings for energising the motor, and generating means for supplying current to at least one of the windings, the method comprising supplying a sound-producing waveform to at least one of the windings to induce vibrations to produce sound.

17. A method as described in paragraph 16, wherein the method comprises supplying a drive waveform for affecting rotation of the rotor at the same time as supplying the sound-producing waveform.

18. A method as described in paragraph 17, wherein the drive waveform comprises a holding current to hold the rotor stationary, thereby inducing vibrations to produce sound when the rotor is stationary.

19. A method as described in paragraph 17, wherein the drive waveform and the sound-producing signal are selectively supplied to each of the windings to induce vibrations to produce sound when the rotor is rotating.

Claims

CLAIMS: 1. An electric motor comprising a rotor, a stator, a plurality of windings for energising the motor, and generating means for supplying current to at least one of the windings, the generating means being operable to supply current comprising a sound-producing waveform to induce vibrations and produce sound.
2. An electric motor as claimed in claim 1, wherein the sound-producing waveform is operable to induce vibrations and produce sound independently of the rotational speed of the rotor.
3. An electric motor as claimed in claim 1 or claim 2, wherein the generating means is operable to supply current also comprising a drive waveform for affecting rotation of the rotor.
4. An electric motor as claimed in claim 3, wherein the generating means is configured to generate the sound-producing waveform and the drive waveform simultaneously; or to superimpose the sound-producing waveform on the drive waveform.
5. An electric motor as claimed in claim 3 or claim 4, wherein the generating means is configured to control the sound-producing waveform independently of the drive waveform.
6. An electric motor as claimed in any one of claims 3, 4 or 5, wherein the drive waveform comprises a holding current for holding the rotor stationary, the sound-producing waveform being maintained to induce vibrations to produce sound.
7. An electric motor as claimed in any one of claims 3, 4 or 5, wherein the generating means is configured to supply the drive waveform to the windings in a predefined sequence to affect rotation of the rotor, the sound-producing waveform being maintained to induce vibrations to produce sound.
8. An electric motor as claimed in any one of the preceding claims, wherein the generating means is configured to inhibit the sound-producing waveform when the motor speed reaches a predetermined value.
9. An electric motor as claimed in any one of the preceding claims, wherein the generating means is configured to supply a sound-producing waveform comprising one or more of the following: a variable current, a pulsating current, and an alternating current (AC).
10. An electric motor as claimed in any one of the preceding claims, wherein the motor is a switched reluctance motor whose stator is constituted by a plurality of pole pieces, each of which is provided with a respective one of the windings.
11. An electric motor as claimed in any one of the preceding claims comprising a casing, wherein the sound-producing waveform induces vibrations in the casing to produce said sound.
12. A motor vehicle comprising an electric motor as claimed in any one of the preceding claims.
13. A motor vehicle as claimed in claim 12 wherein the electric motor is a traction motor for outputting a tractive force to drive the motor vehicle.
14. A motor vehicle as claimed in claim 13 wherein the electric motor is disposed inside one of the following casings: an engine casing, a transmission casing or a differential casing.
15. A control unit for supplying current to an electric motor, the control unit being configured to supply current comprising a sound-producing waveform for inducing vibrations to produce sound.
16. A method of generating sound in an electric motor for powering an automotive vehicle, the electric motor comprising a rotor, a stator, a plurality of windings for energising the motor, and generating means for supplying current to at least one of the windings, the method comprising supplying a sound-producing waveform to at least one of the windings to induce vibrations to produce sound.
17. A method as claimed in claim 16, wherein the method comprises supplying a drive waveform for affecting rotation of the rotor at the same time as supplying the sound-producing waveform.
18. A method as claimed in claim 17, wherein the drive waveform comprises a holding current to hold the rotor stationary, thereby inducing vibrations to produce sound when the rotor is stationary.
19. A method as claimed in claim 17, wherein the drive waveform and the sound-producing signal are selectively supplied to each of the windings to induce vibrations to produce sound when the rotor is rotating.
20. An electric motor substantially as hereinbefore described with reference to the accompanying drawings.
21. A motor vehicle substantially as hereinbetore described with reference to the accompanying drawings.