Engine control method and engine control device

Abstract

Provided is an engine control method in which, in a series hybrid vehicle that in response to a requested output charges a battery by driving an electric generator with an engine and supplies electric power from the battery to a drive motor for traveling, the engine is started when the requested output is greater than or equal to a start threshold value and the engine stops when the requested output is less than or equal to a stop threshold value, said method comprising: a detection step for detecting vibration or noise of the vehicle; a level determination step for determining the level of background noise, on the basis of the vibration or noise which has been detected; and an output adjustment step for changing, in accordance with the level of the background noise which has been determined, the speed or compression ratio of the engine which has been started.

Description

Engine control method and engine control device

[0001] The present invention relates to an engine control method and an engine control device for a series hybrid vehicle.

[0002] A known engine control method for a series hybrid vehicle is to determine whether to start the engine depending on the level of background noise. This is based on the technical idea that when road noise is high, the engine noise is inconspicuous, so the engine is operated to generate electricity, and when road noise is low, the engine noise is conspicuous, so the engine is not operated. JP 7140300 B2 discloses a method of estimating the level of road noise using a road noise value quantified using the angular velocity of the vehicle's wheels or a parameter correlated thereto, and determining whether the background noise of the vehicle is high based on the road noise value.

[0003] However, the method of the above document, which uses the angular velocity of the wheels and the like as parameters, makes it difficult to accurately estimate the magnitude of road noise, and as a result, there is a risk of erroneous judgment of the background noise state.

[0004] Therefore, an object of the present invention is to provide a control method that can accurately estimate the state of background noise.

[0005] According to one aspect of the present invention, there is provided an engine control method for a series hybrid vehicle in which the engine drives a generator to charge a battery in accordance with a required output, and the battery supplies electric power to a drive motor for running, the method including: starting the engine when the required output is equal to or greater than a start threshold; and stopping the engine when the required output is equal to or less than a stop threshold. The method includes a detection step of detecting vibration or noise of the vehicle, a level determination step of determining a background noise level based on the detected vibration or noise, and an output adjustment step of changing the engine speed or compression ratio after start-up in accordance with the determined background noise level.

[0006] FIG. 1 is a diagram illustrating the configuration of a series hybrid vehicle in which an engine control method according to an embodiment of the present invention is executed. FIG. 2 is a block diagram illustrating the functions of a controller that executes processing related to the engine control method. FIG. 3 is a block diagram illustrating the functions of a road surface determination unit according to the first embodiment. FIG. 4 is a diagram illustrating a process for processing a longitudinal acceleration detection value. FIG. 5A is a flowchart illustrating processing for setting a deactivation flag. FIG. 5B is a flowchart illustrating processing for clearing a deactivation flag. FIG. 6 is a flowchart illustrating processing for setting a start flag. FIG. 7 is a flowchart illustrating processing for setting a stop flag. FIG. 8 is a diagram illustrating an example of a map that determines a start threshold and a stop threshold. FIG. 9 is a diagram illustrating an example of the relationship between road surface level and engine speed. FIG. 10A is a time chart when control according to a reference example is executed. FIG. 10B is a time chart when control according to the first embodiment is executed. FIG. 11 is a block diagram illustrating the functions of a road surface determination unit according to a second embodiment. FIG. 12 is a time chart illustrating an example of the effect of control according to the second embodiment. FIG. 13 is a time chart illustrating another example of the effect of control according to the second embodiment. Fig. 14 is a time chart when control according to Modification 1 is executed. Fig. 15 is a time chart when control according to Modification 2 is executed. Fig. 16 is a time chart when control according to Modification 3 is executed. Fig. 17A is a time chart when control according to the second embodiment is executed. Fig. 17B is a time chart when control according to Modification 4 is executed. Fig. 18 is a time chart when control according to Modification 7 is executed.

[0007] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0008] First Embodiment FIG. 1 is a block diagram illustrating a configuration common to a series hybrid vehicle (hereinafter also simply referred to as "vehicle 100") to which an engine control method according to this embodiment is applied.

[0009] As shown in Fig. 1, the vehicle 100 is configured as a so-called series hybrid vehicle, including an engine (internal combustion engine) 1, a generator 2, a battery 3, an electric drive motor 4, a gear 5, an axle 6, wheels 7, and a controller 50. That is, in the vehicle 100, a required output P ｒ In response to this, the engine 1 drives the generator 2 to charge the battery 3, and the battery 3 supplies electric power to the drive motor 4 for running the vehicle.

[0010] The engine 1 is mechanically connected to a generator 2 via a speed increaser (not shown), and the generator 2 is connected to a battery 3 so as to be able to transmit and receive electricity.

[0011] The drive motor 4 is mechanically coupled to an axle 6 via a gear 5, and the axle 6 is mechanically coupled to wheels 7. The drive force (or regenerative force) of the drive motor 4 is transmitted to the wheels 7 via the gear 5 and the axle 6. Therefore, the rotational speed of the wheels 7 (i.e., the acceleration or deceleration of the vehicle 100) is adjusted by the drive force (or regenerative force) of the drive motor 4.

[0012] In particular, the vehicle 100 of this embodiment is equipped with a mechanical brake that brakes the vehicle 100 in response to operation of the brake pedal mounted on the vehicle 100, as well as a regenerative brake that generates braking force by regenerating the drive motor 4 in accordance with the amount of depression of the accelerator pedal mounted on the vehicle 100 when the amount of depression is reduced.

[0013] The controller 50 is a computer programmed to control the vehicle 100, including the processes related to the engine control method according to this embodiment. More specifically, the controller 50 is configured by providing a hardware configuration including a central processing unit (CPU), a read-only memory (ROM), a random access memory (RAM), and an input / output interface (I / O interface) with a program for executing the processes that constitute the in-vehicle actuator control method. The controller 50 may be implemented by installing the program on a single piece of computer hardware, or by distributing the program across multiple pieces of computer hardware. As a specific example, the functions of the controller 50 may be implemented by various computers, such as a battery controller, a vehicle controller, and a motor controller, installed in the vehicle 100.

[0014] The controller 50 executes the engine control method using as input various parameters received from various sensors or other controllers (not shown). Specifically, the controller 50 receives a detected value of the state of charge (SOC) of the battery 3 (hereinafter also referred to as "battery SOC"), a detected value of the rotational speed of the wheels 7 (hereinafter also referred to as "wheel speed w"), a detected value of the steering angle with respect to a steering wheel mounted on the vehicle 100 (hereinafter also referred to as "steering angle θ"), a detected value of longitudinal acceleration (the ratio of acceleration in the forward or backward direction of the vehicle 100 to the acceleration of gravity) (hereinafter also referred to as "longitudinal acceleration detected value"), a flag indicating the operation of a vehicle dynamics control (VDC) system (hereinafter also referred to as "VDC operation flag f"), and a time-series ... ｖｄｃ "), a flag indicating the operation of the TCS (Traction Control System) (hereinafter referred to as "TCS operation flag f ｔｃｓ "), a flag indicating whether or not the ABS (Anti-lock Brake System) is activated (hereinafter referred to as "ABS activation flag f ａｂｓ "), a flag indicating the validity of CAN (Controller Area Network) communication (hereinafter referred to as "CAN valid flag fｃａｎ "), a flag indicating that a mechanical brake mounted on the vehicle 100 is being operated (brake pedal operation) (hereinafter referred to as "brake pedal operation flag f ｂ "), an estimated value of the rotation speed of the drive motor 4 (hereinafter referred to as "motor rotation speed N ｍ "), and the amount of operation of an accelerator pedal mounted on the vehicle 100 (hereinafter also referred to as "accelerator pedal opening APO") are acquired as inputs.

[0015] In this embodiment, the accelerator opening APO determines the magnitude of the output (mainly the power consumed by the running of the vehicle 100) required of the vehicle 100 (particularly the drive motor 4). In particular, in this embodiment, the controller 50 executes powering control, which requests a positive drive force from the drive motor 4, when the accelerator opening APO is equal to or greater than a predetermined value, and executes regenerative control, which requests a negative drive force (i.e., regenerative braking force) from the drive motor 4, when the accelerator opening APO is less than the predetermined value. In other words, when the accelerator opening APO is equal to or greater than the predetermined value, the output required of the vehicle 100 is a positive value, and when the accelerator opening APO is less than the predetermined value, the output required of the vehicle 100 is a negative value. In the following description, for the sake of simplicity, the output (positive or negative value) required of the vehicle 100 will be referred to as the "required output P ｒ "

[0016] 2 is a block diagram illustrating the functions of the controller 50. As shown in the figure, the controller 50 includes a vehicle speed calculation unit 20, a target driving force calculation unit 22, a road surface determination unit 24, a sound and vibration start determination unit 26, a start / stop flag setting unit 27, and a target power generation operating point setting unit 28.

[0017] The vehicle speed calculation unit 20 calculates the motor rotation speed N ｍ The vehicle speed calculation unit 20 calculates the vehicle speed v of the vehicle 100 based on the above. The vehicle speed calculation unit 20 outputs the calculated vehicle speed v to the target driving force calculation unit 22 and the road surface determination unit 24.

[0018] The target driving force calculation unit 22 calculates the vehicle speed v and the accelerator opening APO (required output P ｒ ), the target value of the driving force to be set to the driving motor 4 (hereinafter referred to as the "target motor torque Tｍ The target driving force calculation unit 22 calculates the calculated target motor torque T ｍ and outputs the signal to the road surface determination unit 24 and the drive motor 4 (more specifically, to a motor inverter not shown).

[0019] The road surface determination unit 24 sets the road surface level Le based on the detected longitudinal acceleration value.

[0020] Here, the road surface level Le is a parameter that indexes the state of background noise of the vehicle 100 while the vehicle 100 is traveling. In particular, the road surface level Le is set as an estimated value (hereinafter also referred to as the "road noise value") that quantifies the degree of roughness of the road surface calculated from the longitudinal acceleration detection value by processing described below. More specifically, the road surface level Le in this embodiment is configured as "0" to "3" by leveling the magnitude of the road noise value in predetermined stages. A smooth, non-undulating paved road or the like is set to level 0, and the higher the road noise value, the rougher the road surface becomes. For example, a road surface with many irregularities such as tortoiseshell cracks is set to level 3, a road surface with undulations or unevenness that would cause the shock absorber to bottom out is set to level 2, and a road surface with undulations or unevenness that does not cause bottoming out is set to level 1. In this embodiment, road surfaces of levels 0 to 1 may be referred to as good roads, road surfaces of level 2 as slightly rough roads, and road surfaces of level 3 as rough roads.

[0021] The process of setting the road surface level Le by the road surface determination unit 24 will be described in detail below.

[0022] Fig. 3 is a block diagram showing the functions of the road surface determination unit 24. As shown in the figure, the road surface determination unit 24 includes a filter processing unit 241, an exponential average calculation unit 242, a moving average calculation unit 243, and a road surface level setting unit 244. Fig. 4 is a diagram showing the process of processing the longitudinal acceleration detection value.

[0023] The filter processing unit 241 performs band-pass filtering to extract vibrations in a frequency band correlated with the road noise value from the longitudinal acceleration detection value ("sensor input signal" in FIG. 4). As a result, vibrations such as those shown in "after band-pass filtering" in FIG. 4 are extracted. Noise is included at this stage. Note that, although filtering using a band-pass filter is performed in this embodiment, other filtering methods, such as a low-pass filter or a high-pass filter, may be used as long as they are capable of extracting vibrations in a frequency band correlated with the road noise value.

[0024] The exponential average calculation unit 242 calculates the exponential average value of the extracted acceleration in order to remove noise from the vibration extracted by the filter processing unit 241 .

[0025] To eliminate the influence of frequent changes in road surface conditions, the moving average calculation unit 243 calculates the moving average value of the acceleration calculated by the exponential average calculation unit 242. This smooths out the vibrations as shown in "smoothing" in FIG.

[0026] The road surface level setting unit 244 determines the road surface level based on the moving average value calculated by the moving average calculation unit 243. In this embodiment, the vibration is smoothed using the exponential average and the moving average, but the smoothing method is not limited to this. For example, an increase rate limiter process can be used to forcibly convert an input signal of a predetermined value or more into a constant value.

[0027] It should be noted that a steering angle correction unit may be provided between the filter processing unit 241 and the exponential average calculation unit 242. Because the road noise value also changes depending on the steering angle of the steering wheels, the road surface level can be determined more accurately by correcting the value after band-pass filtering in accordance with the magnitude of the steering angle. Specifically, a map showing the relationship between the steering angle, the steering angle change rate, and the amount of change in road noise is stored in advance in the controller 50, and the amount of change in road noise is calculated by searching the map using the detection value of a steering angle sensor (not shown), and then this is used for correction.

[0028] Returning to FIG. 2, the sound vibration start determination unit 26 receives the road surface level Le and the vehicle speed v as inputs, and determines the required output P at which the engine 1 should be started in accordance with the magnitude of the road surface level Le. ｒ The value of the starting threshold P ｒ＿ｓｔｈ ") or the required output P ｒ The value of the stop threshold P ｒ＿ｅｔｈ In particular, in the estimated state determination process of this embodiment, when the sound vibration start determination process should be executed, the deactivation flag f ｎｏ is set to "0", and if it should not be executed, it is set to "1". Details of the sound vibration start determination process will be explained below. In this embodiment, when the vehicle 100 is started (when the ignition switch is turned on), the deactivation flag f ｎｏ It is assumed that the initial value of is set to either "0" or "1".

[0029] 5A and 5B are flowcharts illustrating the sound vibration start determination process. In particular, FIG. 5A shows a process for determining whether the sound vibration start control is activated by setting a deactivation flag f ｎｏ 5B is a flowchart illustrating the determination of setting the deactivation flag f to "1" (deactivation flag setting determination). ｎｏ 10 is a flowchart illustrating a determination to clear the deactivation flag (deactivation flag clear determination).

[0030] First, in the deactivation flag setting determination shown in FIG. 5A, in step S100, the sound vibration start determination unit 26 determines the control unit distance d ｕ Here, the control unit distance d ｕ is the distance traveled by the vehicle 100 during a preset calculation period Δt (for example, 10 ms). That is, the control unit distance d ｕ is defined as a value obtained by multiplying the vehicle speed v by the calculation period Δt, and is a variable amount that varies depending on the magnitude of the vehicle speed v.

[0031] In step S110, the sound vibration start determination unit 26 calculates a road surface determination cumulative travel distance D. Specifically, first, the sound vibration start determination unit 26 acquires the total travel distance of the vehicle 100 from the start of the vehicle 100 (for example, the timing when the ignition switch is turned on) to the current control cycle. Then, the sound vibration start determination unit 26 calculates the distance traveled by the vehicle 100 from the start of the vehicle 100 to the current control cycle. More specifically, the sound vibration start determination unit 26 multiplies the number of controls from the start to the current by the control unit distance d ｕ The road surface judgment cumulative travel distance D is calculated by multiplying the above equation by .times. ...

[0032] In step S120, the sound vibration start determination unit 26 calculates the rough road travel cumulative distance D ｂａ Specifically, the sound vibration start determination unit 26 calculates the control unit distance d ｕ By multiplying this, the cumulative distance traveled on rough roads D ｂａ Ask for.

[0033] Then, in step S130, the sound vibration start determination unit 26 calculates the rough road continuation rate R ｂｃ Specifically, the sound vibration start determination unit 26 calculates the rough road travel cumulative distance D ｂａ Divide by the road surface judgment cumulative travel distance D to obtain the rough road continuation rate R ｂｃ Ask for.

[0034] Next, in step S140, the sound vibration start determination unit 26 determines whether the vehicle 100 has traveled a predetermined specified distance D _ｔｈ After driving for a period of time, the rough road continuation rate R ｂｃ is a predetermined rough road continuation rate threshold R ｂｃ_ｔｈ Specifically, the sound vibration start determination unit 26 determines whether the control unit distance d ｕ Multiply by the specified driving distance D _ｔｈ Then, the sound vibration start determination unit 26 calculates the specified traveling distance D _ｔｈ During the control period, the rough road continuation rate R ｂｃ is the rough road continuation rate threshold R ｂｃ_ｔｈ It is determined whether the rough road continuation rate threshold R ｂｃ_ｔｈis set to an appropriate value from the viewpoint of determining whether or not erroneous judgments continue in determining whether the road on which the vehicle 100 is traveling is a "bad road" or a "good road" (a judgment based on the road surface level Le).

[0035] In particular, the rough road continuation rate threshold R ｂｃ_ｔｈ is set from the viewpoint of determining whether enabling the operation of the sound vibration start control will result in a longer operation time of the engine 1 and a decrease in fuel efficiency. More specifically, it is assumed that if the erroneous determination that the vehicle 100 is traveling on a "bad road" is maintained for a certain period of time or more and the operation of the sound vibration start control is enabled (a state in which the engine 1 is easy to start or difficult to stop), the battery SOC will rise and the engine 1 will be started and stopped frequently. Therefore, the bad road continuation rate threshold R ｂｃ_ｔｈ is set to a suitable value from the viewpoint of preventing such a situation.

[0036] Then, the sound vibration start determination unit 26 determines the specified traveling distance D _ｔｈ Ratio of bad roads over the entire ｂｃ is the rough road continuation rate threshold R ｂｃ_ｔｈ If it is determined that the number is equal to or greater than the number, the process proceeds to step S150, and the deactivation flag f ｎｏ On the other hand, if the result of the determination is negative, the sound vibration start determination unit 26 proceeds to step S160 and sets the deactivation flag f ｎｏ This routine ends while maintaining the above.

[0037] The sound vibration start determination unit 26 sets the deactivation flag f ｎｏ In the control cycle after the value of "1" is changed from "0", the road surface judgment cumulative travel distance D calculated in step S110 is preferably reset to 0. As a result, in a scene where the vehicle 100 travels a relatively long distance from the start, the road surface judgment cumulative travel distance D becomes a large value, and the bad road travel cumulative distance D ｂａ The rough road continuation rate R is obtained by dividing the above by the road surface judgment cumulative travel distance D. ｂｃ As a result, the rate of change of the rough road continuation rate R ｂｃTherefore, the accuracy of the erroneous determination based on the above can be further improved.

[0038] Next, the deactivation flag clearing determination shown in FIG. 5B will be described.

[0039] First, in step S200, the sound vibration start determination unit 26 sets the deactivation flag f ｎｏ The sound vibration start determining unit 26 then determines whether the deactivation flag f ｎｏ On the other hand, if the sound vibration start determining unit 26 determines that the deactivation flag f is not "1" (determines that the flag is "0"), the routine ends. ｎｏ If it is determined that the value is "1", the process proceeds to step S210 and thereafter.

[0040] In step S210, the sound vibration start determination unit 26 determines the specified traveling distance D _ｔｈ The good road continuation rate R ｇｃ is a predetermined good road continuation rate threshold R ｇｃ_ｔｈ Specifically, the noise / vibration start determining unit 26 determines whether the specified mileage D _ｔｈ Then, the sound vibration start determination unit 26 calculates the specified traveling distance D _ｔｈ During the control period, the good road continuation rate R ｇｃ is the threshold value R for the good road continuation rate ｇｃ_ｔｈ It is determined whether or not the value is equal to or greater than this value.

[0041] Here, the good road continuation rate R ｇｃ is the cumulative distance traveled on good roads D ｇｃ This is the value obtained by dividing the road surface judgment cumulative travel distance D. ｇｃ is the number of times the road surface level Le is set to any one of "0" to "1" and the control unit distance d ｕ It can be calculated by multiplying the good road continuation rate R ｇｃ 1 (corresponding to the total road surface judgment cumulative travel distance D) to obtain the bad road continuation rate R ｂｃ Furthermore, the good road continuation rate threshold R ｇｃ_ｔｈ is the deactivation flag f ｎｏThis is set to a suitable value from the viewpoint of determining that the road is still in a good condition based on the road surface level Le to the extent that the above condition can be satisfied (i.e., determining that the road is not being judged as being on a bad road based on an erroneous judgment).

[0042] In particular, the good road continuation rate threshold R ｇｃ_ｔｈ is a deactivation flag f that is set in order to prevent the noise and vibration start control from being executed based on the above-mentioned erroneous bad road judgment. ｎｏ is set to a suitable value from the viewpoint of preventing a situation in which the engine 1 does not operate even in a necessary scene due to the fact that the value is set to "1" indefinitely.

[0043] Then, the sound vibration start determination unit 26 determines the specified traveling distance D _ｔｈ The continuation rate of good roads is R ｇｃ is the threshold value R for the good road continuation rate ｇｃ_ｔｈ If it is determined that the number is equal to or greater than the number, the process proceeds to step S220, and the deactivation flag f ｎｏ is set to "0" and the routine ends. That is, in this case, the sound vibration start control is switched from the disabled state to the enabled state. On the other hand, if the result of the above determination is negative, the sound vibration start determination unit 26 proceeds to step S230 and sets the deactivation flag f ｎｏ This routine ends while maintaining the above.

[0044] Returning to FIG. 2, the sound vibration start determination unit 26 determines whether the set deactivation flag f ｎｏ is output to the start / stop flag setting unit 27.

[0045] The start / stop flag setting unit 27 sets the battery SOC and the deactivation flag f ｎｏ , and the target motor torque T ｍ is input, and a start flag f for starting the engine 1 is set. ｓｔ (Normal start flag f ｕｓｔ and rough road start flag f ｂｓｔ ) and a stop flag f ｅｎ (Normal stop flag f ｕｅｎ and a bad road stop flag f ｂｅｎ ) is set.

[0046] FIG. 6 is a flowchart illustrating the start flag setting process.

[0047] First, in steps S300 and S310, the start / stop flag setting unit 27 sets the normal start threshold P ｒ＿ｓｕｔｈ and rough road starting threshold P ｒ＿ｓｂｔｈ Set.

[0048] Here, the normal start threshold P ｒ＿ｓｕｔｈ is a required output P that defines the start timing determined from the viewpoint of operating the engine 1 at an operating point with the best possible operating efficiency (an operating point close to the optimal fuel consumption point) while maintaining the battery SOC within an appropriate range. ｒ Therefore, the normal start threshold value P ｒ＿ｓｕｔｈ is the required output P ｒ , vehicle speed v, and battery SOC are prepared in advance in the form of a map having these as variables.

[0049] On the other hand, the rough road starting threshold P ｒ＿ｓｂｔｈ is the normal start threshold P within the range where the battery SOC does not exceed the appropriate range. ｒ＿ｓｕｔｈ The required output P that defines the start timing is determined from the viewpoint of making it easier to start the engine 1 compared to when ｒ That is, the rough road starting threshold P ｒ＿ｓｂｔｈ is the normal starting threshold P ｒ＿ｓｕｔｈ The required output P is set to the following value: ｒ , vehicle speed v, and battery SOC are prepared in advance in the form of a map having these as variables.

[0050] Next, in step S320, the start / stop flag setting unit 27 sets the deactivation flag f ｎｏ Then, the start / stop flag setting unit 27 determines whether the deactivation flag f ｎｏ If it is determined that the value is "1" (if the sound vibration start control is disabled), the process proceeds to step S330.

[0051] In step S330, the start / stop flag setting unit 27 determines the required output P ｒ is the normal starting threshold P ｒ＿ｓｕｔｈ Then, the start / stop flag setting unit 27 determines whether the required output Pｒ is the normal starting threshold P ｒ＿ｓｕｔｈ If it is determined that the value is equal to or greater than the start flag f ｓｔ Normal start flag f ｕｓｔ is set and this process ends.

[0052] On the other hand, the start / stop flag setting unit 27 sets the deactivation flag f ｎｏ If it is determined that the value is "0" (if the sound vibration start control is enabled), the process proceeds to step S340.

[0053] In step S340, the start / stop flag setting unit 27 determines the required output P ｒ is the rough road starting threshold P ｒ＿ｓｂｔｈ Then, the start / stop flag setting unit 27 determines whether the required output P ｒ is the rough road starting threshold P ｒ＿ｓｂｔｈ If it is determined that the value is equal to or greater than the start flag f ｓｔ As a rough road start flag f ｂｓｔ is set and this process ends.

[0054] According to the start flag setting process described above, when the sound and vibration start control is enabled, the required output P ｒ is the normal starting threshold P ｒ＿ｓｕｔｈ A rough road starting threshold P ｒ＿ｓｂｔｈ When the above occurs, the start flag f ｓｔ (Rough road start flag f ｂｓｔ ) will be set.

[0055] FIG. 7 is a flowchart illustrating the stop flag setting process.

[0056] First, in steps S400 and S410, the start / stop flag setting unit 27 sets the normal stop threshold P ｒ＿ｅｕｔｈ and rough road stopping threshold P ｒ＿ｅｂｔｈ Set.

[0057] Here, the normal stop threshold P ｒ＿ｅｕｔｈ is the required output P that determines the timing of stopping the engine 1 (stopping power generation) so that the battery SOC can be sufficiently secured. ｒ The normal stop threshold Pｒ＿ｅｕｔｈ is the required output P ｒ , vehicle speed v, and battery SOC are prepared in advance in the form of a map having these as variables.

[0058] On the other hand, the rough road stopping threshold P ｒ＿ｅｂｔｈ is the required output P that defines the timing to stop the engine 1 so that it is more difficult to stop the engine 1 while maintaining the battery SOC within an appropriate range. ｒ That is, the rough road stopping threshold P ｒ＿ｅｂｔｈ is the normal stopping threshold P ｒ＿ｅｕｔｈ The required output P is set to the following value: ｒ , vehicle speed v, and battery SOC are prepared in advance in the form of a map having these as variables.

[0059] In step S420, the start / stop flag setting unit 27 sets the start flag f ｓｔ As a rough road start flag f ｂｓｔ Then, the start / stop flag setting unit 27 determines whether the rough road start flag f ｂｓｔ If it is determined that the setting is made, the process proceeds to step S440, and if it is determined that the setting is not made, the process proceeds to step S430.

[0060] In step S430, the start / stop flag setting unit 27 determines whether the vehicle 100 is currently traveling on a rough road. Specifically, the start / stop flag setting unit 27 determines that the vehicle 100 is traveling on a rough road if the road surface level Le set at the current control timing is "2", and otherwise determines that the vehicle 100 is traveling on a good road.

[0061] If the start / stop flag setting unit 27 determines that the vehicle 100 is currently traveling on a bad road, it proceeds to step S440, whereas if it determines that the vehicle 100 is currently traveling on a good road, it proceeds to step S450.

[0062] In step S440, the start / stop flag setting unit 27 determines the required output P ｒ is the rough road stopping threshold P ｒ＿ｅｂｔｈ Then, the start / stop flag setting unit 27 determines whether the required output P ｒ is the rough road stopping threshold P ｒ＿ｅｂｔｈ If it is determined that the value is equal to or less than the stop flag fｅｎ and a rough road stop flag f ｂｅｎ (step S460), and then the process ends. ｒ is the rough road stopping threshold P ｒ＿ｅｂｔｈ If it is determined that the value is not less than the stop flag f ｅｎ This process ends without setting

[0063] In step S450, the start / stop flag setting unit 27 determines the required output P ｒ is the normal stopping threshold P ｒ＿ｅｕｔｈ Then, the start / stop flag setting unit 27 determines whether the required output P ｒ is the normal stopping threshold P ｒ＿ｅｕｔｈ If it is determined that the value is equal to or less than the stop flag f ｅｎ Normal stop flag f ｕｅｎ (step S470), and then the process ends. ｒ is the normal stopping threshold P ｒ＿ｅｕｔｈ If it is determined that the value is not less than the stop flag f ｅｎ This process ends without setting

[0064] According to the stop flag setting process described above, the start flag f ｓｔ As a rough road start flag f ｂｓｔ is set (rough road starting threshold P ｒ＿ｓｂｔｈ When the engine 1 starts, the stop flag f ｅｎ and a rough road stop flag f ｂｅｎ is set (the rough road stopping threshold P ｒ＿ｅｂｔｈ On the other hand, the start flag f ｓｔ Normal start flag f ｕｓｔ When the normal start threshold P ｒ＿ｓｕｔｈ When the engine 1 is started, the bad road stop flag f is set depending on whether the road surface when the engine 1 is stopped is a "bad road" or a "good road." ｂｅｎ Or normal stop flag f ｕｅｎ is set.

[0065] In FIG. 8, the normal start threshold P ｒ＿ｓｕｔｈ , rough road starting threshold P ｒ＿ｓｂｔｈ , normal stop threshold Pｒ＿ｅｕｔｈ , and the rough road stopping threshold P ｒ＿ｅｂｔｈ According to the map shown in FIG. 8, the rough road starting threshold P ｒ＿ｓｂｔｈ is the low / medium vehicle speed range (vehicle speed v is greater than the second vehicle speed threshold v _ｔｈ２ In the following region), the rough road starting threshold P ｒ＿ｓｂｔｈ and the rough road stopping threshold P ｒ＿ｅｂｔｈ is the normal starting threshold P ｒ＿ｓｕｔｈ and normal stop threshold P ｒ＿ｅｕｔｈ In particular, the rough road starting threshold P is set to a value lower than the SOC intermediate range where changes in the battery SOC are easily tolerated (a range where the battery SOC is unlikely to deviate from the appropriate range even if it changes). ｒ＿ｓｂｔｈ and the rough road stopping threshold P ｒ＿ｅｂｔｈ is the normal starting threshold P ｒ＿ｓｕｔｈ and normal stop threshold P ｒ＿ｅｕｔｈ In other SOC regions, the rough road starting threshold P ｒ＿ｓｂｔｈ (Rough road stopping threshold P ｒ＿ｅｂｔｈ ) and normal start threshold P ｒ＿ｓｕｔｈ (Normal stop threshold P ｒ＿ｅｕｔｈ ) are preferably set to approximately the same value. This makes it possible to suppress overcharging or overdischarging of the battery 3 caused by the execution of the noise and vibration start control, or frequent starting and stopping of the engine 1 caused by the battery SOC fluctuating within and out of the appropriate range.

[0066] In addition, the rough road starting threshold P ｒ＿ｓｂｔｈ and normal start threshold P ｒ＿ｓｕｔｈ is set to have a smaller value as the battery SOC decreases. ｒ＿ｅｂｔｈ and normal stop threshold P ｒ＿ｅｕｔｈ is set to take a larger value as the battery SOC increases.

[0067] Returning to FIG. 2, the start / stop flag setting unit 27 sets the start flag f ｓｔ and stop flag f ｅｎ is output to the target power generation operating point setting unit 28.

[0068] The target power generation operating point setting unit 28 sets the start flag f ｓｔ , stop flag f ｅｎand the road surface level Le as inputs to set the operating point of the engine 1. Specifically, the target power generation operating point setting unit 28 sets the start flag f ｓｔ and stop flag f ｅｎ When starting the engine 1, the target rotation speed N of the engine 1 is set to N. ｅ and target torque T ｅ At this time, the target rotation speed N ｅ is set according to the road surface level Le. The higher the road surface level Le, that is, the rougher the road surface, the higher the rotation speed is set. For example, as shown in FIG. 9, when the road surface level Le is "0", the engine 1 is not started so RPM1 = 0 [rpm], and as the road surface level Le increases from there to "1, 2, 3", RPM2, RPM3, RPM4 (RPM2 < RPM3 < RPM4) are set. However, RPM2 to 4 are set to rotation speeds at which the engine sound becomes smaller than the background noise at each road surface level Le. Note that RPM2 to 4 may also be set to values ​​on the fuel efficiency optimum line, which is an operating line connecting the operating points with the highest fuel efficiency to obtain each output. Furthermore, the cases where the road surface level Le is "0" and "1" are collectively considered to be good roads, and the target rotation speed N ｅ may be set to 0 [rpm].

[0069] Then, the target power generation operating point setting unit 28 sets the target rotation speed N ｅ and target torque T ｅ are output to the generator 2 (particularly, the inverter of the generator 2, not shown) and the engine 1 (particularly, the engine controller, not shown), respectively.

[0070] Next, the effects of this embodiment will be described with reference to Figures 10A and 10B. Figure 10A is a time chart when the control according to the above-mentioned document is executed (hereinafter also referred to as "reference example"), and Figure 10B is a time chart when the control according to this embodiment is executed. In the figure, the solid line indicates engine noise, and the dashed line indicates background noise. In both charts, the vehicle is traveling on a good road from time T0 to time T1, traveling on a rough road surface from time T1 to time T2, and traveling on a slightly rough road surface from time T2 onwards.

[0071] In the reference example, the vehicle is traveling on a good road from time T0 to time T1, so the engine 1 is not operating and no engine noise is generated. The engine 1 operates at time T1, but the engine noise is masked by background noise from the rough road surface. From time T2 onwards, the road surface becomes slightly rough and the level of background noise drops. However, the target rotation speed N of the engine 1 ｅ Since the difference is constant, the engine noise becomes louder than the background noise, and masking by the background noise is no longer possible (hatched portion in FIG. 10A).

[0072] 10A. However, when the road surface changes to a slightly rough road at time T2, that is, when the road surface level Le changes, the target engine speed Ne changes from RPM4 for a rough road to RPM3 for a slightly rough road, and the engine speed decreases. This also reduces the engine noise, so that the engine noise is masked by the background noise.

[0073] In this embodiment, the target rotation speed Ne of the engine 1 is changed according to the road surface level Le so that the engine noise is smaller than the background noise at each road surface level Le. As a result, even if the road surface level Le changes after the engine is started, the engine noise is masked by the background noise and is less likely to be transmitted to the occupants. In other words, quietness can be ensured.

[0074] As described above, in this embodiment, in a series hybrid vehicle 100 in which the engine 1 drives the generator 2 to charge the battery 3 in accordance with a required output and the battery 3 supplies power to the drive motor 4 for running, an engine control method is provided in which the engine 1 is started when the required output is equal to or greater than a start threshold and stopped when the required output is equal to or less than a stop threshold. This method includes a detection step of detecting vibration or noise of the vehicle 100, a level determination step of determining the level of background noise based on the detected vibration or noise, and a step of controlling the engine rotation speed N after starting according to the determined background noise level. ｅ and an output adjustment step of changing the output of the engine. As a result, the engine noise is masked by the background noise and is less likely to be transmitted to the passengers.

[0075] In this embodiment, the level determination step estimates road surface roughness from vibration or noise, and determines to which of a plurality of preset road surface levels (road surface roughness levels) Le the estimated road surface roughness belongs, thereby enabling the level of background noise to be estimated with high accuracy.

[0076] In this embodiment, the level determination process involves filtering to extract vibrations of frequencies correlated with road noise from the vibration or noise detection signal, followed by smoothing to smooth the extracted vibrations, and then estimating the road surface roughness based on the vibrations after the smoothing process. This allows the influence of noise and the like to be eliminated, making it possible to estimate the road surface level Le with high accuracy.

[0077] In this embodiment, the engine speed is increased as the background noise level increases in the output adjustment process, thereby ensuring quietness at various road surface levels Le.

[0078] Second Embodiment A second embodiment of the present invention will be described. This embodiment differs from the first embodiment in the configuration of the road surface determination unit 24. The following description will focus on the differences from the first embodiment.

[0079] 11 is a block diagram showing the functions of the road surface determination unit 24 in this embodiment. The filter processing unit 241, exponential average calculation unit 242, moving average calculation unit 243, and road surface level setting unit 244 are the same as those in the first embodiment. In addition to the above configuration, this embodiment also includes a second exponential average calculation unit 245, a gain setting unit 246, an integrating unit 247, and a correction necessity determination unit 248.

[0080] The second exponential average calculation unit 245 receives as input the detection signals of a suspension acceleration sensor provided near the suspension mounting portion of the vehicle body, calculates the exponential average value of the detection signals, and outputs the calculation result to the correction necessity determination unit 248. The suspension acceleration sensor detects the amount of suspension fluctuation according to the road surface condition.

[0081] The gain setting unit 246 uses the detection signal of the vehicle speed sensor as an input value and sets a gain using a pre-stored table in which gains for each vehicle speed are set. The magnitude of the gain is set to 0 when the vehicle speed is 50 km / h, for example, and increases in the negative direction as the vehicle speed increases and increases in the positive direction as the vehicle speed decreases. The set gain is output to the integrating unit 247.

[0082] The integrating unit 247 calculates a threshold value by multiplying the gain output from the gain setting unit 246 by a preset constant, and outputs the calculation result to the correction necessity determining unit 248. The constant here is a negative value, for example, −5 [dB].

[0083] The correction necessity determination unit 248 compares the average exponent value calculated by the second exponent average calculation unit 245 with the threshold value calculated by the accumulator 247, and determines that correction is necessary if the average exponent value is equal to or greater than the threshold value, and determines that correction is not necessary if the average exponent value is smaller than the threshold value. The correction here refers to the correction of the calculation result of the exponent average calculation unit 242.

[0084] If no correction is required, the calculation result of the exponential average calculation unit 242 is output as is to the moving average calculation unit 243 .

[0085] If correction is necessary, a predetermined value (e.g., −300 dB) is subtracted from the calculation result of the exponential average calculation unit 242. The predetermined value here is set to a value large enough to cancel out the influence of a sudden large vibration input. Note that the correction is not limited to this subtraction, and may be replaced with, for example, the previously calculated value.

[0086] FIG. 12 is a time chart illustrating an example of the effect of the control according to this embodiment. In the figure, the solid line indicates engine speed, and the dashed line indicates background noise. The road surface conditions are similar to those in FIG. 10B, with a good road from timing T0 to timing T1, a rough road surface from timing T1 to timing T2, and a slightly rough road surface from timing T2 onward. However, a sudden large vibration is input while traveling on a good road (period A in the figure). The sudden large vibration can be caused, for example, by passing over a manhole or by passing over a step such as a road joint.

[0087] If a large vibration is input while traveling, the vibration will affect the calculation results of the exponential average calculation unit 242. Therefore, without the correction according to this embodiment, the road level setting unit 244 may determine that the road surface is rough or slightly rough. However, after passing a manhole or the like, the road surface level returns to the original level Le, so even if the engine 1 is started in response to a sudden large input, it will be stopped again soon. With such a short engine operating time, the amount of power generation will also be small, and the fuel required to start the engine will be wasted.

[0088] In this regard, in the control according to this embodiment, the correction necessity determination unit 248 determines whether or not correction is necessary for the calculation result of the exponential average calculation unit 242, based on the magnitude of vibration calculated by the second exponential average calculation unit 245, and executes the correction in the case of a sudden input. Since the effect of the sudden input is canceled out by the correction, the engine 1 remains stopped during period A when a sudden vibration is input due to passing through a manhole, etc., as shown in Figure 12.

[0089] Fig. 13 is a time chart for explaining another example of the effect of the control according to this embodiment. In the figure, the solid line indicates the engine speed, and the dashed line indicates background noise. Fig. 13 shows cases where the vehicle travels on the same road at different speeds, with the upper part representing a case where the vehicle travels at a low speed and the lower part representing a case where the vehicle travels at a high speed. Note that the terms "stopping speed" and "high speed" used here refer to low and high speeds in terms of the relative relationship between the two vehicle speeds.

[0090] In the figure, the solid line indicates the engine speed, and the dashed line indicates background noise. The road surface conditions are good from time T0 to time T1, rough from time T1 to time T2, and good from time T2 onwards.

[0091] As explained in the first embodiment, when the vehicle is traveling at low speeds, engine 1 is stopped while the vehicle is traveling on a good road, and when the road surface becomes rough, engine 1 is started, and when the vehicle passes the rough road and returns to a good road, engine 1 is stopped.

[0092] In contrast, at high vehicle speeds, the time required to pass over a rough road surface (timing T1 - timing T2) is shorter than at low vehicle speeds. This time is shorter as the vehicle speed increases. In such cases, if the engine 1 is started when the vehicle reaches a rough road surface, as in the case of low vehicle speeds, and then stopped when the vehicle passes the rough road surface and becomes a smooth road, the engine operating time becomes shorter, making it difficult to generate electricity and potentially resulting in a deterioration in fuel efficiency. However, according to this embodiment, the threshold value used by the correction necessity determination unit 248 decreases as the vehicle speed increases, making it easier to correct the calculation result of the exponential average calculation unit 242. In other words, at high vehicle speeds, the increase in vibration due to a rough road surface is smoothed out by the correction. As a result, the engine 1 will not start even when the vehicle reaches a rough road surface.

[0093] As described above, in this embodiment, when the level of an input detection signal exceeds a threshold in the level determination step, the road surface roughness is estimated using the detection signal input immediately before the input detection signal or a signal with a preset level instead of the input detection signal. This makes it possible to distinguish sudden large inputs, such as when passing through a manhole or a bump in the road, from background noise, and to avoid the engine 1 stopping shortly after starting.

[0094] In this embodiment, the magnitude of the threshold value increases as the vehicle speed increases, thereby making it possible to appropriately determine whether a vibration should be distinguished from background noise or whether the vibration should be treated as background noise.

[0095] Next, modifications of the above-described embodiment will be described. Each of the modifications described below also falls within the scope of the present invention, just like the first and second embodiments. Furthermore, the first and second embodiments may be combined with each of the modifications as appropriate.

[0096] [Variation 1] The road surface determination unit 24 may be provided with a timer function, so that when the engine speed is changed in response to a change in the road surface level Le, the current engine speed is maintained for a predetermined time after the change in the engine speed, where the predetermined time is about several seconds.

[0097] 14 is a time chart when control according to this modification is executed. The solid line in the figure indicates engine speed, and the dashed line indicates background noise. The road surface conditions are as follows: good road from time T0 to time T1, rough road from time T1 to time T2, and slightly rough road from time T2 onwards. It is assumed that the road surface before time T0 was rough or slightly rough, and changed to good road at time T0.

[0098] During the period B between timing T0 and timing T1, the background noise increases due to the sudden input, but the engine remains stopped because the predetermined time Tth has not yet elapsed since the engine was stopped at timing T0. Also, at timing T2, the road surface changes from rough to slightly rough, causing the engine speed N ｅDuring periods C and D after the decrease in the engine speed N ｅ Since the predetermined time Tth has not yet elapsed since the engine was lowered, the engine is still stopped.

[0099] As described above, in this modified example, the engine rotation speed N ｅ When the engine speed N is changed, the engine speed N ｅ When road conditions change frequently, changes in engine noise in response to these changes may cause discomfort to the occupants, but this modification can prevent this.

[0100] [Modification 2] The engine speed N ｅ The function of maintaining the above for a predetermined time may be operated only when the background noise level increases, and may not be operated when the background noise level decreases.

[0101] 15 is a time chart when control according to this modification is executed. In the figure, the solid line indicates engine speed, and the dashed line indicates background noise. The road surface conditions are as follows: rough road surface from time T0 to time T1, good road surface from time T1 to time T2, and slightly rough road surface from time T2 onwards. It is assumed that the road surface was good before time T0 and changed to a rough road surface at time T0.

[0102] After the road surface becomes rough at timing T1 and the engine 1 is started, if the road surface changes to a good road at timing T1 before the predetermined time Tth has elapsed, the engine will be stopped. Then, even if the road surface changes to a slightly rough road at timing T2 before the predetermined time Tth has elapsed after the engine has been stopped, the engine 1 will not start, but will start at timing T3 after the predetermined time Tth has elapsed. In other words, if the situation allows the engine noise to be reduced, it will be reduced immediately, and if the engine noise becomes louder, it will be increased after the predetermined time Tth has elapsed.

[0103] As described above, in this modified example, the engine rotation speed N ｅThe prohibition of the change of the engine speed N is executed only when the background noise level increases, and when the background noise level decreases, the prohibition of the change of the engine speed N is executed even within a predetermined period. ｅ In the control of the first modification, even if the road is switched to a good road at timing T1, the engine 1 continues to operate until the predetermined time Tth has elapsed. In contrast, in this modification, the engine 1 is stopped immediately after the road is switched to a good road. This reduces the discomfort caused by frequent changes in engine sound and makes it possible to extend the time during which the engine sound is quiet.

[0104] [Modification 3] The road surface level Le may be further subdivided. For example, the above-mentioned road surface level Le of "2" to "3" may be subdivided into four levels of "2.0", "2.5", "3.0", and "3.5". Then, in order to suppress frequent changes in the engine speed, a background noise level threshold Thn is set, and the noise levels are divided into a group of noise levels equal to or less than the background noise level threshold Thn and a group of noise levels greater than the background noise level threshold Thn. The engine speed N ｅ Set.

[0105] Figure 16 is a time chart when control according to this modified example is executed. In the figure, the solid line indicates the engine speed, and the dashed line indicates background noise. The road surface level is "3.5" from timing T0 to timing T1, "3.5" from timing T1 to timing T2, "2.0" from timing T2 to timing T3, and "2.5" from timing T3 onwards. The background noise level threshold Thn is set to a value between the background noise when the road surface level is "2.5" and the background noise when the road surface level is "3.0".

[0106] In this case, the road surface level Le is divided into a group of "3.0" and "3.5" and a group of "2.0" and "2.5." The "2.0" and "2.5" groups are considered to be slightly rough road surfaces, and the "3.0" and "3.5" groups are considered to be rough road surfaces. The engine speed on a rough road surface is RPM1, and the engine speed on a slightly rough road surface is RPM2.

[0107] The engine speed RPM1 for a rough road surface is set so that the engine sound is smaller than the smallest background noise level that belongs to a rough road surface. In other words, it is set to an engine speed at which the engine sound is loud enough to be masked by the background noise when the road surface level Le is "3.0." On the other hand, the engine speed RPM2 for a somewhat rough road surface is set so that the engine sound is smaller than the smallest background noise level that belongs to a somewhat rough road surface. In other words, it is set to an engine speed at which the engine sound is loud enough to be masked by the background noise when the road surface level Le is "2.0." This makes it possible to generate electricity while maintaining quietness.

[0108] If further subdivision is made, for example, if the levels belonging to each group of rough road surfaces and slightly rough road surfaces are divided into three or more stages, each group may be further divided into small groups by providing multiple background noise level thresholds Thn, and the engine speed may be set for each small group. In this case as well, the engine speed for each small group is set so that the engine noise is quieter than the background noise with the smallest level within each small group.

[0109] As described above, in this modified example, in the level determination step, the background noise levels are divided into a plurality of groups using at least one threshold value, and in the output adjustment step, the engine rotation speed N corresponding to the lowest background noise level in the group is determined. ｅ This allows power generation to be performed while maintaining quietness.

[0110] [Modification 4] When the road surface level Le changes, that is, when the background noise level changes, the engine rotation speed N ｅ When the change in the background noise level is less than the threshold change amount Thr rpm, the engine rotation speed N ｅ The change threshold value Thr rpm can be set arbitrarily, and is determined based on the relationship between the magnitude of background noise at each road surface level Le and the engine sound, and the engine rotation speed N ｅ The setting should be made appropriately taking into consideration the engine noise that is transmitted to the passengers when the vehicle is running smoothly.

[0111] Engine speed N when road surface level Le is "2.5"ｅ is RPM1, engine speed N when "3.0" ｅ is RPM2, engine speed N when "3.5" ｅ When RPM is 3, the engine speed N according to the change in road surface level Le ｅ If the power generation time is changed, there is a risk of missing an opportunity to generate power. This will be explained with reference to FIG. 17A.

[0112] FIG. 17A shows the change in the engine speed N in response to the change in the road surface level Le as in the second embodiment. ｅ 1 is a time chart showing the results when the engine speed is changed. The solid line in the figure shows the engine speed, and the dashed line shows the background noise. The road surface level Le is "3.0" from time T0 to time T1, "2.5" from time T1 to time T2, and "3.5" from time T2 onwards.

[0113] At timing T1, the road surface level Le changes from "3.0" to "2.5", and the engine speed N ｅ At the timing T2 after that, the road surface level Le is changed to "3.5", but the engine rotation speed N ｅ Since the predetermined time Tth has not elapsed since the engine rotation speed N ｅ is maintained at RPM 1. Then, at timing T3 after the predetermined time Tth has elapsed, the engine 1 starts and power generation begins. In other words, between timing T2 and timing T3, the background noise increases and the engine 1 can be started, but power generation is not possible.

[0114] 17B is a time chart when the control according to this modification is executed. ｅ Same as FIG. 17A except:

[0115] As shown in FIG. 17B, when the road surface level Le is "3.0", the engine speed N ｅ RPM2 and engine speed N at "2.5" ｅ Since the difference between the engine speed N and the engine speed RPM1 is less than the change amount threshold Thr rpm, in this modified example, the engine speed Nｅ As a result, the counting of the predetermined time Tth after the change in the engine speed Ne starts at time T0, and the predetermined time Tth has passed by time T2 when the road surface level Le changes to "3.5", so it is possible to start the engine 1 at time T2 and generate electricity.

[0116] As described above, in this modified example, when the level of background noise changes in the output adjustment process, the engine rotation speed N ｅ When the change in the background noise level is less than the threshold change amount Thr rpm, the engine rotation speed N ｅ This will ensure opportunities for power generation.

[0117] [Variation 5] Any other detection parameter correlated with the magnitude of road noise may be used as the detection parameter for calculating the road noise value, instead of or in addition to the acceleration of the vehicle 100. Examples of such detection parameters include angular acceleration of the tires, running noise detected directly using a microphone or the like, and road surface conditions (grain size and unevenness) detected directly using an in-vehicle camera, a laser displacement meter, or the like.

[0118] In the above-described embodiments and modifications, the engine speed is changed to mask the engine sound with background noise, but the compression ratio may be changed instead of or in addition to the engine speed. The compression ratio can be changed using, for example, a known variable compression ratio mechanism.

[0119] The lower the engine speed Ne, the quieter the engine sound, and the higher the engine speed Ne, the louder the engine sound. In this case, "quiet" and "loud" refer to sound pressure.

[0120] Therefore, in each of the above embodiments and modifications, the engine speed Ne is reduced when the background noise is low, and the engine speed Ne is increased when the background noise is high, thereby masking the engine sound with the background noise.

[0121] On the other hand, the compression ratio has a weaker correlation with engine noise than the engine speed. However, the compression ratio does correlate with the frequency of engine noise, and the lower the compression ratio, the lower the frequency of engine noise tends to be.

[0122] The human ear tends to be less sensitive to low-frequency sounds. In other words, even if the sound pressure of the engine noise is the same, the lower the frequency, the more likely it is to be masked by background noise. Therefore, by lowering the compression ratio as the road surface level Le becomes lower, i.e., the smaller the background noise, and by raising the compression ratio as the background noise becomes louder, it is possible to make it more difficult for the engine noise to reach the passengers.

[0123] [Variation 7] In each of the above-described embodiments and variations, the allowable positions (also referred to as noise thresholds) for good roads and slightly rough road surfaces, and the noise thresholds for slightly rough road surfaces and rough road surfaces, are the same whether the road surface level changes from good (smooth) to bad (rough) or vice versa. In contrast, in this variation, a hysteresis characteristic is imparted to the noise thresholds. Specifically, the down-side noise threshold Thbgndown, which is the noise threshold when the road surface level changes from a rough level to a smooth level, is larger than the up-side noise threshold Thbgnup, which is the noise threshold when the road surface level changes from a smooth level to a rough level.

[0124] 18 is a time chart when the noise threshold value according to this modification is used. When the road noise value exceeds the upper noise threshold Thbgnup at timing T1 while traveling on a good road, the controller 50 determines that the road surface has become somewhat rough and starts the engine 1. When the road noise value falls below the lower noise threshold Thbgndown at timing T2, the controller 50 stops the engine 1, even if the road noise value is above the upper noise threshold Thbgnup, as shown in the figure. If the lower noise threshold Thbgndown is the same magnitude as the upper noise threshold Thbgnup, the controller 50 determines that the road surface remains somewhat rough and does not stop the engine 1. However, according to this modification, the controller 50 stops the engine 1 as described above.

[0125] As described above, according to this modification, the boundary values ​​between the road surface roughness levels have a hysteresis characteristic, and the boundary value when changing from a rough level to a smooth level is set higher than the boundary value when switching from a smooth level to a rough level. This increases the frequency with which the engine 1 stops when the road noise level decreases, thereby further improving quietness.

[0126] Although the embodiments of the present invention have been described above, the above embodiments merely illustrate some of the application examples of the present invention, and it is not intended that the technical scope of the present invention be limited to the specific configurations of the above embodiments.

Claims

1. An engine control method for a series hybrid vehicle in which an engine drives a generator to charge a battery in accordance with a required output, and power is supplied from the battery to a drive motor for driving, which starts the engine when the required output is equal to or greater than a start threshold, and stops the engine when the required output is equal to or less than a stop threshold, the engine control method comprising: a detection step for detecting vibration or noise of the vehicle; a level determination step for determining the level of background noise based on the detected vibration or noise; and an output adjustment step for changing the engine speed or compression ratio after starting in accordance with the determined level of background noise.

2. An engine control method as described in claim 1, wherein the level determination step estimates road surface roughness from the vibration or noise, and determines to which of a plurality of pre-set road surface roughness levels the estimated road surface roughness belongs.

3. An engine control method as claimed in claim 2, wherein the level determination step comprises performing a filtering process to extract vibrations of a frequency correlated with road noise from the detection signal of the vibration or noise, and a smoothing process to smooth the extracted vibrations, and estimating the road surface roughness based on the vibrations after the smoothing process.

4. An engine control method as claimed in claim 3, wherein in the level determination process, when the level of the input detection signal becomes equal to or above a threshold value, the road surface roughness is estimated using the detection signal input immediately before the input detection signal, or a signal of a preset level, instead of the input detection signal.

5. An engine control method according to claim 4, wherein the magnitude of the threshold value is larger as the vehicle speed is higher.

6. An engine control method as claimed in claim 1, wherein, when the engine speed or the compression ratio is changed in response to a change in the level of the background noise, changes to the engine speed or the compression ratio are prohibited for a predetermined period of time after the change.

7. An engine control method as claimed in claim 6, wherein the prohibition of changes to the engine speed or compression ratio during the specified period is executed only when the level of the background noise has increased, and when the level of the background noise has decreased, changes to the engine speed or compression ratio are permitted even within the specified period.

8. An engine control method as described in claim 6, wherein in the output adjustment process, when the level of the background noise changes and the amount of change in the engine speed in response to the change in level becomes less than a threshold value, the engine speed before the change in the level of the background noise is maintained.

9. An engine control method as claimed in claim 2, wherein the boundary values ​​between each level of the road surface roughness are given a hysteresis characteristic, and the boundary value when changing from a rough level to a smooth level is made higher than the boundary value when switching from a smooth level to a rough level.

10. An engine control method as described in claim 1, wherein in the level determination step, the background noise levels are divided into a plurality of groups based on at least one threshold value, and in the output adjustment step, the engine speed is set according to the lowest background noise level within the group.

11. The engine control method according to claim 1, wherein in the output adjustment step, the engine speed is increased as the level of the background noise increases.

12. An engine control device for a series hybrid vehicle in which an engine drives a generator to charge a battery in accordance with a required output, and power is supplied from the battery to a drive motor for driving, which starts the engine when the required output is equal to or greater than a start threshold, and stops the engine when the required output is equal to or less than a stop threshold, the engine control device including: a detection unit that detects vibration or noise of the vehicle; a level determination unit that determines the level of background noise based on the detected vibration or noise; and an output adjustment unit that changes the engine speed or compression ratio after start-up in accordance with the determined level of background noise.

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