Vehicular sound effect generating apparatus

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicular sound effect generating apparatus according to an embodiment of the present invention;

FIG. 2A is a diagram showing a measured gain characteristic curve;

FIG. 2B is a diagram showing a gain characteristic curve which is an inversion of the measured gain characteristic curve;

FIG. 2C is a diagram showing a corrected gain characteristic curve;

FIG. 2D is a diagram showing a gain characteristic curve with enhanced gains in a certain frequency range;

FIG. 2E is a diagram showing the inverted gain characteristic curve with enhanced gains in the certain frequency range;

FIG. 3A is a diagram showing waveform data stored in a waveform data memory of the vehicular sound effect generating apparatus;

FIG. 3B is a diagram showing a sine wave which is generated by referring to the waveform data memory;

FIG. 4 is a diagram showing the frequency characteristics of sound pressure levels before and after they are corrected;

FIG. 5 is a diagram showing the waveform of engine pulses;

FIG. 6 is a diagram showing weighting gain characteristic curves that are set in a sound pressure adjuster;

FIG. 7 is a flowchart of an operation sequence of the vehicular sound effect generating apparatus shown in FIG. 1;

FIG. 8 is a diagram showing rotational frequency changes on a motor vehicle powered by a six-cylinder engine with a manual transmission (MT motor vehicle); and

FIG. 9 is a diagram showing rotational frequency changes on a motor vehicle powered by a six-cylinder engine with an automatic transmission (AT motor vehicle).

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows in block form a vehicular sound effect generating apparatus 101 according to an embodiment of the present invention.

As shown in FIG. 1, the vehicular sound effect generating apparatus 101, which is mounted on a motor vehicle, basically comprises a section in the form of an ECU (Electronic Control Unit) 121 serving as a general control means, a speaker 14 serving as an output means, and a clutch switch 122 for generating a clutch signal Cs when a clutch pedal 120 is depressed.

The clutch switch 122 comprises a normally closed switch having a fixed terminal grounded and another fixed terminal connected to a power supply of +12 [V] through a resistor 124. While the driver of the motor vehicle is depressing the clutch pedal 120, i.e., when the driver is disengaging the clutch or partly engaging the clutch, the clutch switch 122 has its movable contact kept out of contact with the fixed terminals and hence is open. While the clutch switch 122 is being open, a clutch signal Cs of +12 [V] is supplied from the clutch switch 122 to a sound pressure adjuster 70 of the ECU 121. When the ECU 121 is supplied with the clutch signal Cs of +12 [V], it recognizes that the motor vehicle incorporating the vehicular sound effect generating apparatus 101 is a motor vehicle with a manual transmission.

Before the ECU 121 is supplied with the clutch signal Cs of +12 [V], the ECU 121 recognizes according to a default setting that the motor vehicle incorporating the vehicular sound effect generating apparatus 101 is a motor vehicle with an automatic transmission, and controls the generation of a sound effect accordingly.

The section in the form of the ECU 121 is mounted in the dashboard of the motor vehicle, and basically has a waveform data table 16 for storing waveform data in one cyclic period, a reference signal generating means 18 for generating a reference signal Sr which has a harmonic (harmonic signal) Sh based on an engine rotation frequency fe of the motor vehicle by successively reading waveform data from the waveform data table 16, and a control means 201 for generating a control signal Sc2 based on the reference signal Sr.

The speaker 14 serves to apply sounds to a passenger in a passenger position 29 such as a driver seat or a front passenger seat. The speaker 14 is fixedly disposed on a panel in each of front doors on the opposite sides of the motor vehicle or on each of kick panels on the opposite sides of the motor vehicle, i.e., door-side inner panel surfaces alongside of a driver leg space. The speaker 14 may alternatively be disposed beneath the center of the dashboard.

The speaker 14 transduces a control signal Sd that is output from the control means 201 of the ECU 121 through a D/A converter 22 into a sound effect in the form of an acoustic signal, and outputs the sound effect. An output amplifier (not shown) is connected between the D/A converter 22 and the speaker 14, and has a gain variable by the passenger.

The reference signal generating means 18 has an input port connected to a series-connected circuit comprising a frequency detector 23 such as a frequency counter or the like for detecting the frequency of engine pulses Ep which are measured by a Hall-effect device or the like when the output shaft of the engine mounted on the motor vehicle rotates, and a multiplier 26 for outputting a harmonic signal Sh which has a frequency (sixth harmonic frequency) 6fe that is six times the engine rotation frequency fe (fundamental frequency) detected by the frequency detector 23. The multiplier 26 may multiply the engine rotation frequency fe by an integer such as 2, 3, 4, 5, 6, . . . or a real number such as 2.5, 3.3, . . . . The frequency detector 23 is included in a running state detecting means 200.

Between the speaker 14 and the passenger position (front-seat passenger position) 29, there are provided inherent acoustic characteristics (sound-field characteristics, frequency transfer characteristics, or sound-field gain characteristics) C00 due to the passenger cabin structure of the motor vehicle, the materials used in the passenger cabin of the motor vehicle, etc. The sound-field gain characteristics C00 have complex disturbances such as peaks and dips in the responses thereof because of the passenger cabin structure, the materials used, etc.

The sound-field gain characteristics C00 are obtained as gain frequency characteristics (hereinafter simply referred to as gain characteristics or frequency characteristics) representing the ratio of the amplitude (magnitude) to frequency of a signal that is output from a microphone which serves as a sound detecting means disposed in the front seat passenger position 29, or specifically at the position of an ear of the passenger in the front seat passenger position 29, when the frequency of a sine-wave signal having a constant amplitude that is applied as the control signal Sd to the speaker 14 is continuously varied from lower to higher frequencies. The frequency of a sine-wave signal, which is referred to above, is not the engine rotation frequency, but the frequency of an acoustic signal.

Stated otherwise, the sound-field gain characteristics C00 represent gain characteristics obtained at the front seat passenger position 29 when the reference signal generating means 18 and the D/A converter 22 are directly connected to each other, without the control means 201 interposed therebetween, and the frequency of a sine-wave signal having a constant amplitude that is generated by the reference signal generating means 18 is continuously varied from a lower frequency such as several tens [Hz] to a higher frequency such as 1 [kHz]. The gain represented by the gain characteristics C00 changes depending on the frequency of the reference signal Sr from the speaker 14 to the front seat passenger position 29. More strictly, the gain represented by the gain characteristics C00 changes depending on the frequency of the reference signal Sr from the reference signal generating means 18 to the front seat passenger position 29.

FIG. 2A shows a gain characteristic curve C00, actually measured in a frequency range from about 30 [Hz] to about 970 [Hz], which represents sound-field characteristics from the position of the speaker 14 to the front seat passenger position 29, or more exactly to the ears of the passenger. The horizontal axis of FIG. 2A represents frequencies [Hz] and the vertical axis gains [dB]. It can be seen from FIG. 2A that gain characteristic curve C00 has complex disturbances such as peaks and dips.

The reference signal Sr is generated as follows: The waveform data table 16 is stored in a memory.

As schematically shown in FIGS. 3A and 3B, the waveform data table 16 comprises instantaneous value data stored as waveform data at respective addresses, the instantaneous value data representing a predetermined number (N) of instantaneous values into which the waveform of a sine wave in one cyclic period is divided at equal intervals along a time axis (=phase axis). The addresses (i) are indicated by integers (i=0, 1, 2, . . . , N-1) ranging from 0 to (the predetermine number-1). The alphabetical letter A shown in FIGS. 3A and 3B is represented by 1 or any desired positive real number. Therefore, the waveform data at the address i is calculated as A sin(360°×i/N). Stated otherwise, one cycle of sine waveform is divided into N sampled values at sampling points spaced over time, and data generated by quantizing the instantaneous values of the sine wave at the respective sampling points are stored as waveform data at respective addresses, which are represented by the respective sampling points, in the memory.

The reference signal generating means 18 generates a reference signal Sr, which comprises a sine-wave signal having a frequency corresponding to the frequency of the harmonic signal Sh, when the reference signal generating means 18 reads the waveform data from the waveform data table 16 while changing the readout address period depending on the period of the harmonic signal Sh that is applied to the reference signal generating means 18.

The control means 201 acoustically changes the reference signal Sr into a control signal Sc2 and outputs the control signal Sc2. The control means 201 comprises a sound field adjuster 51 and the sound pressure adjuster 70, each serving as an acoustic correcting means.

As one of the acoustic correcting means, the sound field adjuster 51 functions as a filter whose gain characteristics (having a horizontal axis representing frequencies and a vertical axis representing gains) are represented by a gain characteristic curve (inverted gain characteristic curve) Ci00 shown in FIG. 2B which is an inversion of the gain characteristic curve C00 shown in FIG. 2A that changes depending on the frequency of the reference signal Sr from the speaker 14 to the front seat passenger position 29.

The inverted gain characteristic curve Ci00 is such a gain characteristic curve that it has an increased gain level at frequencies where acoustically less transmissive dips are present in the gain characteristic curve C00 shown in FIG. 2A and a reduced gain level at frequencies where acoustically more transmissive peaks are present in the gain characteristic curve C00 shown in FIG. 2A. The inverted gain characteristic curve Ci00 is expressed by an equation (transfer function) as Ci00=B/C00 where B represents a reference value.

If the sound pressure adjuster 70 has a gain 1, i.e., 0 [dB], then the reference signal generating means 18 of the vehicular sound effect generating apparatus 101 generates a reference signal Sr having a constant amplitude in a frequency range from 30 [Hz] to 970 [Hz], the corrective gain characteristic curve Ci00 of the sound field adjuster 51 and the sound-field gain characteristic curve C00 are multiplied, producing gain characteristics C1 according to which sounds having a flat sound pressure level in the frequency range are heard at the front seat passenger position 29, as indicated by a gain characteristic curve C1 in FIG. 2C.

Therefore, when the cyclic period of the engine pulses Ep changes or remains constant as the passenger accelerates or decelerates the motor vehicle or keeps the motor vehicle running at a constant speed, the reference signal generating means 18 generates a sine-wave reference signal Sr whose frequency increases, decreases, or remains constant substantially in real time, depending on the harmonic signal Sh having a sixth-harmonic frequency 6 fe produced by the multiplier 26 from the engine rotation frequency fe that is detected by the frequency detector 23.

The reference signal Sr is converted into a control signal Sc1 that has been corrected by the gain characteristic curve Ci00 of the sound field adjuster 51. If the gain characteristic curve of the sound pressure adjuster 70 changes 0 [dB] regardless of frequency ranges, i.e., remains flat, then the sound effect output from the speaker 14 is prevented from changing depending on the frequency at the front seat passenger position 29 due to the vehicle cabin acoustic characteristics C00. Therefore, flat gain vs. frequency characteristics are available at the front seat passenger position 29. The sound effect generated at the front seat passenger position 29 is thus made linear depending on the engine rotational speed (six times the engine rotation frequency fe), or stated otherwise depending on the state of the noise source.

FIG. 4 shows actual frequency characteristics of sound pressure levels at the front seat passenger position 29 before and after they are corrected. To make the sound effect more linear in achieving the frequency characteristics shown in FIG. 4, the reference signal Sr or the control signal Sc is generated so as to have its amplitude increasing in proportion to the engine rotation frequency fe.

As shown in FIG. 4, a corrected characteristic curve 40 has its sound pressure level [dBA] changing more linearly depending on the engine rotation frequency fe than an uncorrected characteristic curve 39 having complex disturbances such as dips and peaks.

The process, referred to above for generating at the front seat passenger position 29 the sound effect which changes linearly as the engine rotation frequency fe increases or the motor vehicle is accelerated, will be referred to herein as a sound field adjusting process or a flattening process.

The sound field adjuster 51 provides a joint gain characteristic curve Ci00eh by joining a gain characteristic curve Ceh having increased gains in a certain frequency range, e.g., a frequency range from 300 [Hz] to 450 [Hz], for example, as indicated by the solid line in FIG. 2D, and the gain characteristic curve Ci00, as shown in FIG. 2E. The joint gain characteristic curve Ci00eh shown in FIG. 2E has higher gains, i.e., produces higher sound pressure levels, in the frequency range from 300 [Hz] to 450 [Hz] than the inverted gain characteristic curve Ci00 shown in FIG. 2B.

The sound field adjuster 51 may provide a gain characteristic curve Ceh′ indicated by the dotted line in FIG. 2D at the front seat passenger position 29 for thereby reducing gains or lowering sound pressure levels in the above frequency range. The process referred to above for emphasizing an acoustic signal only at desired frequencies is referred to as a frequency emphasizing process.

The vehicular sound effect generating apparatus 101 also has a frequency change detector 68 for determining a frequency change Δaf [Hz/sec] per unit time of the engine rotation frequency fe, in order to operate the sound pressure adjuster 70 as the other acoustic correcting means. The frequency change detector 68 is included in the running state detecting means 200.

The sound pressure adjuster 70 has gain characteristics 72 (output gain characteristics, acoustic correcting characteristics, or gain characteristic curve(s)), which will be described in detail below, depending on the frequency change Δaf. The sound pressure adjuster 70 corrects the control signal Sc1 supplied from the sound field adjuster 51 according to the gain characteristics 72, and outputs a corrected control signal Sc2 through the D/A converter 22 to the speaker 14 near a front seat.

FIG. 5 shows the waveform of engine pulses Ep. For determining a frequency change Δaf, the frequency change detector 68 determines the difference Δf (Δf=f2−f1) between the frequencies of two successive pulses, i.e., the frequency f1 of a preceding pulse (preceding frequency) and the frequency f2 of a following pulse (present frequency), which are successively detected by the frequency detector 23. The frequency change detector 68 multiplies the difference Δf by the present frequency f2 to determine a frequency change Δaf (Δaf=Δf×f2) [Hz/sec] per unit time of the engine rotation frequency fe, i.e., to determine an acceleration.

It is known in the art that the frequency change Δaf has a different value depending on which gear position the transmission of the motor vehicle is in. Specifically, the frequency change Δaf is greater when the transmission is in a lower gear position and is smaller when the transmission is in a higher gear position.

Generally, the sound level of the sound effect depending on the frequency change Δaf should preferably be greater in a lower gear position than in a higher gear position. The sound level of the sound effect should preferably be lower when the motor vehicle cruises at a constant speed or is decelerated. Furthermore, the sound level of the sound effect should preferably be lower such that it will not produce uncomfortable sounds when the engine is raced or operates on kickdown with the frequency change exceeding a frequency level for full throttle opening at the first gear position.

FIG. 6 shows weighting gain characteristic curves 72 that are set as acoustic correcting characteristic curves in the sound pressure adjuster 70 in view of the above considerations.

As shown in FIG. 6, the weighting gain characteristic curves 72 include a weighting gain characteristic curve 72at that is applied to an AT vehicle with an automatic transmission and weighting gain characteristic curves 72mt1, 72mt2 that are applied to an MT vehicle with a manual transmission.

According to the weighting gain characteristic curve 72at applied to the AT vehicle, the weighting gain Y is set to 0 [dB] at a frequency change X2 (see FIG. 9) for full throttle opening at the first gear position, and is progressively smaller up to a frequency change X0 (see FIG. 9) for full throttle opening at the fourth gear position as the frequency change Δaf becomes smaller from the frequency change X2 for full throttle opening at the first gear position. Specifically, a larger sound effect is produced when the vehicle is accelerated at a lower gear position, and a smaller sound effect is produced when the vehicle is accelerated at a higher gear position. The weighting gain Y is minimum when the vehicle is cruising or decelerated. When the engine is raced or operates on kickdown with the frequency change Δaf exceeding the frequency change X2 for full throttle opening at the first gear position, the weighting gain Y is quickly lowered so as not to produce an uncomfortable sound effect.

According to the weighting gain characteristic curves 72mt1, 72mt2 applied to the MT vehicle, the weighting gain Y is set to 0 [dB] at a frequency change X3 (see FIG. 8) for full throttle opening at the first gear position, and is progressively smaller up to a frequency change X1 (see FIG. 8) for full throttle opening at the fourth gear position as the frequency change Δaf becomes smaller from the frequency change X3 for full throttle opening at the first gear position. As with the AT vehicle, a larger sound effect is produced when the vehicle is accelerated at a lower gear position, and a smaller sound effect is produced when the vehicle is accelerated at a higher gear position. The weighting gain Y is minimum when the vehicle is cruising or decelerated. When the engine is raced or operates on kickdown with the frequency change Δaf exceeding the frequency change X3 for full throttle opening at the first gear position, the weighting gain characteristic curve 72mt1 with the weighting gain Y being quickly lowered so as not to produce an uncomfortable sound effect or the weighting gain characteristic curve 72mt2 with the weighting gain Y remaining unchanged can be selected. Normally, the weighting gain characteristic curve 72mt1 is selected.

The vehicular sound effect generating apparatus 101 is basically constructed as described above. A process, performed by the vehicular sound effect generating apparatus 101, of automatically setting how a sound effect is to be generated depending on whether the motor vehicle is fitted with a manual transmission or an automatic transmission will be described below with reference to a flowchart shown in FIG. 7.

In step S1, a battery, not shown, is connected to the ECU 121. In step S2, the ECU 121 detects a clutch signal Cs.

In step S3, the ECU 121 determines whether the voltage of the clutch signal Cs exceeds a threshold voltage of 10 [V] or not. If the voltage of the clutch signal Cs is equal to or lower than 10 [V], then the ECU 121 judges that the motor vehicle is fitted with an automatic transmission. Then, in step S4, the ECU 121 operates in an AT vehicle mode, i.e., generates a control signal Sc2 by acoustically changing the control signal Sc1 according to the weighting gain characteristic curve 72at applied to the AT vehicle which is set as the default setting in the sound pressure adjuster 70.

If the clutch signal Cs of +12 [V] is not detected, therefore, the vehicular sound effect generating apparatus 101 generates a sound effect weighted by the weighting gain characteristic curve 72at (see FIG. 6) applied to the AT vehicle which is written in advance in a memory such as an unillustrated EEPROM or the like.

If the voltage of the clutch signal Cs exceeds the threshold voltage of 10 [V] in step S3, then the ECU 121 determines whether the voltage of the clutch signal Cs in excess of the threshold voltage of 10 [V] has continued for a predetermined period of time or not in step S5. If the voltage of the clutch signal Cs in excess of the threshold voltage of 10 [V] has not continued for the predetermined period of time, then the ECU 121 judges that the voltage of the clutch signal Cs has been caused by noise, and continues to operate in the AT vehicle mode in step S4. If the voltage of the clutch signal Cs in excess of the threshold voltage of 10 [V] has continued for the predetermined period of time, then the ECU 121 judges that the clutch signal Cs of +12 [V] is detected because the clutch switch 122 is opened by the clutch pedal 120 depressed by the driver, and that the motor vehicle is fitted with a manual transmission instead of an automatic transmission in step S6.

The ECU 121 switches from the weighting gain characteristic curve 72at applied to the AT vehicle which is stored in the memory to the weighting gain characteristic curve 72mt1 (see FIG. 6) applied to the MT vehicle which is also stored in the memory such as an EEPROM.

If the clutch signal Cs of +12 [V] is detected continuously for the predetermined period of time, the vehicular sound effect generating apparatus 101 operates in an MT vehicle mode and generates a sound effect weighted by the weighting gain characteristic curve 72mt1 applied to the MT vehicle.

According to the embodiment described above, the vehicular sound effect generating apparatus 101 has the waveform data table 16 for storing waveform data in one cyclic period, the reference signal generating means 18 for generating a reference signal Sr by successively reading waveform data from the waveform data table 16, the running state detecting means 200 for detecting a running state of the vehicle, the control means 201 having the sound pressure adjuster 70 as an acoustic correcting means storing the weighting gain characteristic curves 72 as acoustic correcting characteristic curves depending on the frequency change Δaf [Hz/sec] which represents the running state of the vehicle, i.e., a time-dependent change of the engine rotation frequency fe in the present embodiment, for generating a control signal Sc2 by acoustically changing the reference signal Sr depending on the frequency change Δaf detected by the running state detecting means 200, and the speaker 14 as an output means for outputting the control signal Sc2 as a sound effect.

The control means 201 has a transmission determining means (steps S2, S3, S5) for determining whether the transmission on the vehicle is a manual transmission or an automatic transmission. Depending on the transmission determined by the transmission determining means, the control means 201 automatically changes the weighting gain characteristic curves 72 as acoustic correcting characteristic curves stored in the sound pressure adjuster 70. Specifically, the control means 201 determines whether the transmission on the vehicle is a manual transmission or an automatic transmission depending on whether the clutch signal Cs of +12 [V] has continued for a predetermined period of time or not. Therefore, the vehicular sound effect generating apparatus 101 is of a relatively simple arrangement and can generate an appropriate sound effect depending on whether the transmission on the vehicle is a manual transmission or an automatic transmission.

The control means 201 of the ECU 121 stores in its ROM the weighting gain characteristic curve 72at applied to an AT vehicle with an automatic transmission and the weighting gain characteristic curves 72mt1, 72mt2 applied to an MT vehicle with a manual transmission. The vehicular sound effect generating apparatus 101 can thus be manufactured and maintained at a relatively low cost because it does not need to have different ECUs operable respectively for AT and MT vehicles of the same type.

As shown in FIG. 6, the gain Y for the frequency change X3 for the automatic transmission when the engine is raced, which corresponds to the frequency change X3 for the manual transmission upon full throttle opening at the first gear position, is set to a value smaller than the gain Y of 0 [dB] for the frequency change X3 for the manual transmission for full throttle opening at the first gear position. Therefore, an appropriate sound effect is generated for the frequency change X3 for the manual transmission upon full throttle opening at the first gear position. Since a small sound effect is generated for the frequency change X3 for the automatic transmission when the engine is raced, which corresponds to the frequency change X3 for the manual transmission upon full throttle opening at the first gear position, the passengers are preventing from having an odd feeling about the sound effect generated in the vehicle cabin.

When the frequency change Δaf of the engine rotation frequency fe is greater than the frequency change X2 as a predetermined threshold, the weighting gain characteristic curves 72mt1, 72mt2 for the manual transmission are set to values greater than the weighting gain characteristic curve 72at for the automatic transmission. Consequently, when the frequency change Δaf of the engine rotation frequency fe is greater than the frequency change X2 for the automatic transmission upon full throttle opening at the first gear position, the MT vehicle with the manual transmission can generate a larger sound effect than the AT vehicle with the automatic transmission.

The clutch signal Cs of +12 [V] is produced each time the clutch pedal 120 is depressed. Therefore, the frequency change Δaf in excess of the value Y=X3 at the time the clutch signal Cs is generated is recognized as a transition state rather than an accelerated state, and the weighting gain Y is adjusted on the weighting gain characteristic curve 72mt1 wherein the weighting gain Y is reduced or the weighting gain characteristic curve 72mt2 wherein the weighting gain Y is not increased, but remains constant. Therefore, the sound pressure which makes the passengers feel odd about the sound effect can be reduced.

Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.

Vehicular sound effect generating apparatus

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CPC

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