Patent Publication Number: US-2021179109-A1

Title: Tire noise test method, vehicle and control device

Description:
TECHNICAL FIELD 
     The invention relates to a tire noise test method, a vehicle and a control device. This application claims priority from Japanese Patent Application No. 2018-127058 filed in Japan on Jul. 3, 2018. The entire disclosure of this earlier application is herein incorporated by reference. 
     BACKGROUND ART 
     Conventionally, a tire noise test method is classified into two categories, i.e., a bench noise test and an actual vehicle noise test. In the bench noise test, as described in Patent Document 1, for example, a simulated road surface of the drum is brought into contact with the tire, and the noise generated by the tire is measured while the drum is being rotated. On the other hand, in the actual vehicle noise test, the noise generated by the tires is measured while the vehicle is put into actually travelling. 
     PRIOR ART DOCUMENT 
     Patent Document 1: JP2013-134213A 
     SUMMARY OF THE INVENTION 
     Problem 
     In the case of an actual vehicle noise test, since the vehicle is put into actual driving, it is possible to acquire more realistic tire noise data than the bench noise test. However, the conventional actual vehicle noise test involves a problem of inefficiency due to the necessity for involvement of a human driver for driving the vehicle. 
     It is therefore an object of the invention to provide a tire noise test method, a vehicle and a control device that are efficient in actual vehicle noise test. 
     Solution 
     The characteristic features of the invention are as follows. 
     According to one aspect of the invention, there is provided a tire noise test method to be conducted while a vehicle is travelling automatically, comprising steps of: 
     operating a control unit when the vehicle reaches a predetermined position or reaches a predetermined speed, for putting the vehicle into coast-traveling with a prime mover of the vehicle in a non-driving state; and 
     operating a measuring unit for measuring the tire noise during the coast-traveling of the vehicle. 
     According to another aspect of the present invention, there is provided a vehicle adapted for conducting a tire noise test during an automatic driving of the vehicle, comprising: 
     a prime mover; and 
     a control unit adapted to be operated, when the vehicle reaches a predetermined position or reaches a predetermined speed, for putting the vehicle into coast-traveling with the prime mover in a non-driving state. 
     According to still another aspect of the invention, there is provided a control device for automatically driving a vehicle and carrying out a tire noise test, wherein: 
     the control device is operated when the vehicle reaches a predetermined position or reaches a predetermined speed, for putting the vehicle into coast-traveling with a prime mover of the vehicle in a non-driving state. 
     Technical Effect 
     In accordance with the invention, it is possible to provide a tire noise test method, a vehicle and a control device that are efficient in an actual vehicle noise test. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view showing an example of the test course in the tire noise test method according to one embodiment of the invention. 
         FIG. 2  is a plan view showing the measurement zone shown in  FIG. 1 . 
         FIG. 3  is a graph showing an example of the measurement results of the tire noise in the tire noise test method according to one embodiment of the invention. 
         FIG. 4  is a block diagram showing an example of the vehicle for use in the tire noise test method according to one embodiment of the invention. 
         FIG. 5  is a flowchart showing the procedures of the tire noise test method according to one embodiment of the invention (Flow  1 ). 
         FIG. 6  is a flowchart showing the procedures of the tire noise test method according to one embodiment of the invention (Flow  2 ). 
         FIG. 7  is a flowchart showing an operation example 1 during the coast-traveling of the vehicle in the tire noise test method according to one embodiment of the invention. 
         FIG. 8  is a flowchart showing an operation example 2 during the coast-traveling of the vehicle in the tire noise test method according to one embodiment of the invention. 
         FIG. 9  is a block diagram showing an example of the control unit in the tire noise test method according to one embodiment of the invention. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     Embodiments of the invention will be described below with reference to the drawings. 
     (Outline of the Test Course) 
       FIG. 1  is a plan view showing an example of a test course  1  in the tire noise test method according to an embodiment of the present invention.  FIG. 2  is a plan view of a measuring zone  5  shown in  FIG. 1 . In the present disclosure, the terms “right side” and “left side” refer to the right side and the left side, respectively, as seen from the vehicle  10  shown in  FIG. 1 . 
     The test course  1  shown in  FIG. 1  is used for an actual vehicle noise test. In the actual vehicle noise test, the vehicle  10  travels round the test course  1 , for example, in a counterclockwise direction. As shown in  FIG. 2 , the vehicle  10  includes a tire  10   a  to be subjected to a noise test, and a vehicle body  10   b  to which the tire  10   a  is attached. The vehicle  10  is adapted to be driven automatically. In the present disclosure, the term “automatic driving” means the state of the vehicle  10  travelling under the control by a control device or the like (for example, a control unit  19  or an external device as shown in  FIG. 4  to be described later) for controlling acceleration, steering and control of the vehicle  10  without human involvement. For example, the vehicle  10  is autonomously driven at level  4  of automation as defined by the MLIT (Ministry of Land, Infrastructure, Transport and Tourism) in Japan. 
     As shown in  FIG. 1 , the test course  1  may be an oval track including straight and corner sections. The test course  1  shown in  FIG. 1  includes a speed maintenance zone  2 , an acceleration zone  3 , a coast-traveling zone  4 , and a cruising zone  6 . 
     The speed maintenance zone  2  has a position P 1  as the start point and a position P 2  as the end point, as shown in  FIG. 1 . The speed maintenance zone  2  includes a corner section. Further, the speed maintenance zone  2  is provided with an inclination angle (bank). In the speed maintenance zone  2 , the vehicle  10  travels the outer side of the corner in the speed maintenance zone  2  and travels by utilizing the centrifugal force to maintain a constant speed (e.g., 60 km/h). 
     The acceleration zone  3  starts at the position P 2  and ends at a position P 3 , as shown in  FIG. 1 . The acceleration zone  3  includes a straight section. In the acceleration zone  3 , the vehicle  10  accelerates and travels, for example, at a predetermined acceleration rate. 
     The coast-traveling zone  4  has the position P 3  as a start point and a position P 4  as an end point, as shown in  FIG. 1 . The coast-traveling zone  4  includes a straight section. The coast-traveling zone  4  further includes a measuring zone  5  as shown in  FIG. 1 . 
     As shown in  FIG. 1 , the measuring zone  5  has a position P 5  as the start point and a position P 6  as the end point. In the measuring zone  5 , the noise generated by the tire  10   a  of the vehicle  10  shown in  FIG. 2  is measured. The measuring zone  5  is provided, as shown in  FIG. 2 , with measuring devices  5 R and  5 L. The measuring devices  5 R and  5 L are located on both sides in the width direction of the road surface  5   a . The measuring devices  5 R and  5 L are, for example, microphones capable of collecting the noise of the tire  10   a . The lengths of the measuring zone  5 , i.e., the distance from the position P 5  to the position P 6 , and the location of the measuring devices  5 R and  5 L, are appropriately set based, for example, on suitable tire noise test standards. 
     For example, in the tire noise test defined by ECE R117, as shown in  FIG. 2 , the length of the measuring zone  5  is set to be 20 m. The measuring devices  5 R and  5 L are arranged in the center of the measuring zone  5 . The measuring devices  5 R and  5 L are arranged at a height 1.2 m from the road surface  5   a . In addition, the measuring device  5 R is installed at a position 7.5 m to the right of the widthwise center line O of the road surface  5   a  of the measuring zone  5 . The measuring device  5 L, in turn, is installed at a position 7.5 m to the left of the widthwise center line O of the road surface  5   a  of the measuring zone  5 . The measuring devices  5 R and  5 L are adopted to collect noise generated by the tire  10   a  of the vehicle  10  on the right side and the left side of the vehicle  10 , respectively. 
     Here, by the time the vehicle  10  reaches the position P 3  which is the starting point of the coast-traveling zone  4 , the prime mover of the vehicle  10  is put into a non-driving state. By putting the prime mover of the vehicle  10  to the non-driving state by the time the vehicle  10  reaches the position P 3 , the noise of the vehicle  10  generated other than the tire  10   a  is reduced in the measuring zone  5 . Under such control, the measuring devices  5 R and  5 L shown in  FIG. 2  can accurately collect the noise generated by the tire  10   a.    
     The cruising zone  6  shown in  FIG. 1  has a start point at the position P 4 , and an end point at the position P 1 . The cruising zone  6  includes a straight section and a corner section. In the cruising zone  6 , the vehicle  10  puts the prime mover of the vehicle  10  into the driving state again. The vehicle  10  may travel along the cruising zone  6  at any appropriate speed. 
     The cruising zone  6  includes a position P 7 . The position P 7  is a standby position for other vehicles  10 , when there are two or more vehicles  10  on the test course  1 . 
     While the vehicle  10  is traveling along the cruising zone  6 , the measuring devices  5 R and  5 L shown in  FIG. 2  may collect background noise. The background noise is the noise other than that generated by the tire  10   a  to be measured. The background noise mainly includes the noise generated in the surrounding environment of the test course  1 . 
     If the background noise is greater than a predetermined value, the test may be discontinued. 
     (Outline of the Test) 
       FIG. 3  is a graph showing an example of tire noise measurement results in the tire noise test method according to the embodiment of the present invention. In  FIG. 3 , the abscissa represents the speed of the vehicle  10 , while the ordinate represents the noise generated by the tire  10   a.    
       FIG. 3  shows an example of measuring the noise of the tire  10   a  when the reference speed is 80 km/h. The plots “Left” shown in  FIG. 3  are the data collected by the measuring device  5 L shown in  FIG. 2 . Similarly, the plots “Right” shown in  FIG. 3  are the data collected by the measuring device  5 R shown in  FIG. 2 . 
     For example, in the tire noise test according to ECE R117, the noise of the tire  10   a  when the vehicle  10  is travelling along the measuring zone  5  is measured at nine different speeds within the range of the reference speed ±10 km/h. If the reference speed is 80 km/h, as shown in  FIG. 3 , the noise of the tire  10   a  is measured while the vehicle  10  travels along the measuring zone  5  at different speeds of 72, 74, 76, 78, 80, 82, 84, 86 and 88 [km/h]. Such measurements provide  18  plots, as shown in  FIG. 3 . Further, from thus obtained  18  plots, a correlation equation is calculated to indicate the correlation between the speed of the vehicle  10  and the noise of the tire  10   a . In addition, the noise of the tire  10   a  at the reference speed of 80 km/h is calculated from the calculated correlation equation. Thus, as shown in  FIG. 3 , the noise of the tire  10   a  at the reference speed of 80 km/h is calculated to be 70.3 dB. 
     Here, when the vehicle  10  travels once along the measuring zone  5  shown in  FIG. 1 , two plots “Left” and “Right” are obtained by the measuring devices  5 R and  5 L shown in  FIG. 2 . For example, when the vehicle  10  travels once along the measuring zone  5  shown in  FIG. 1  at the speed of 80 km/h, two plots “Left” and “Right” at 80 km/h in  FIG. 3  are obtained. This means that, if  18  plots are to be obtained as shown in  FIG. 3 , the vehicle  10  must travel 9 times round the test course  1  shown in  FIG. 1 , at respectively different speeds between 72 km/h and 88 km/h shown in  FIG. 3 . 
     There may arise increased difference between the Left plot and the Right plot at the same speed. This, for example, is due to the fact that, as seen in the width direction of the road surface  5   a  shown in  FIG. 2 , the distance from the vehicle  10  to the measuring device  5 R is different from the distance from the vehicle  10  to the measuring device  5 L. In this instance, the noise of the tire  10   a  measured by the measuring devices  5 R and  5 L shown in  FIG. 2  cannot be used because of the low reliability of the data. Thus, in the tire noise test, it is necessary for the distance from the vehicle  10  to the measuring device  5 R to be same as the distance from the vehicle  10  to the measuring device  5 L in the width direction of the road surface  5   a  shown in  FIG. 2 . In other words, in the tire noise test, it is necessary for the vehicle  10  to travel along the vicinity of the center line O of the road surface  5   a  shown in  FIG. 2 . 
     [Function and Configuration of the Vehicle] 
       FIG. 4  is a block diagram showing an example of the vehicle  10  that may be used in the tire noise test method according to the embodiment of the present invention. The vehicle body  10  is provided on the vehicle body  10   b  with a prime mover  11 , a transmission  12 , a braking device  13 , a steering device  14 , a battery  15 , a sensor unit  16 , a communication unit  17 , a memory unit  18 , and a control unit  19 . 
     The prime mover  11  provides rotational power for rotating the tire  10   a . Examples of the prime mover  11  include a combustion engine, an electromotor, and a combination of a combustion engine and an electromotor. The combustion engine provides rotational power with fuel such as gasoline or light oil. The combustion engine may be, but is not limited to, a gasoline engine using gasoline as fuel, a diesel engine using light oil or the like as fuel, or the like. The electromotor provides rotational power by electric energy supplied from a power source including a storage battery, a fuel cell, or the like. However, the prime mover  11  may be any device capable of providing rotational power for rotating the tire  10   a.    
     In the case of a gasoline engine, the prime mover  11  includes, for example, a fuel injection valve, a cylinder, a piston, a spark plug, a crankshaft, an intake manifold, intake valves, and the like. The intake valve is adapted to supply air to the cylinder via the intake manifold. The fuel injection valve is adapted to inject fuel into the cylinder via the intake manifold. When fuel and air are supplied to the cylinder, the piston compresses the fuel and air mixture in the cylinder. As the air-fuel mixture is compressed in the cylinder, the spark plug generates an electric spark to explode and burn the air-fuel mixture compressed in the cylinder. As the fuel or air-fuel mixture explodes and burns in the cylinder, the crankshaft generates rotational power. This rotational power is transmitted to the tire  10   a  via the transmission  12 . 
     In the case of a diesel engine, the prime mover  11  includes, for example, a fuel injection valve, a cylinder, a piston, a crankshaft, an intake valve, and the like. The intake valve is adapted to supply air to the cylinder. When the intake air is supplied into the cylinder, the piston compresses the air in the cylinder. As the air in the cylinder is compressed to a temperature above the ignition point, the fuel injection valve injects fuel into the cylinder to self-ignite the fuel. As the fuel self-ignites in the cylinder and explodes and burns, the crankshaft generates rotational power. This rotational power is transmitted to the tire  10   a  via the transmission  12 . 
     The transmission  12  is provided in a path for transmitting rotational power between the prime mover  11  and the tire  10   a . The transmission  12  shifts the rotational speed of the prime mover  11  based on the control of the control unit  19  and transmits it to the tire  10   a . Further, the transmission  12  puts the tire  10   a  into a predetermined state based on the control of the control unit  19 . The predetermined state includes a drive state capable of traveling forward, a reverse state capable of traveling backward, a neutral state in which the tire  10   a  is disengaged from the prime mover  11 , and a parking lock state in which the tire  10   a  is restrained in a stopped state. 
     The braking device  13  includes a brake  13 A and a brake  13 B. The brake  13 A is a brake for decelerating the vehicle  10 . For example, the brake  13 A is a hydraulic brake. The brake  13 A serves to reduce the rotational speed of the tire  10   a  based on the control of the control unit  19 . The brake  13 B is a brake for stopping the vehicle  10 . For example, the brake  13 B is a mechanical brake. The brake  13 B serves to stop the rotation of the tire  10   a  based on the control of the control unit  19 . 
     The steering device  14  is adapted to adjust the steering angle of the tire  10   a . By adjusting the steering angle of the tire  10   a  by means of the steering device  14 , the traveling direction of the vehicle  10  is adjusted. 
     The battery  15  is, for example, in the form of a lithium ion battery. The battery  15  is adapted to supply electric power to the components in the vehicle  10 . The battery  15  may include a main battery that supplies electric power to the prime mover  11  and the like, and an auxiliary battery that supplies electric power to the sensor unit  16  and the like. In this instance, the auxiliary battery may supply electric power to the components of the vehicle  10  after the prime mover  11  has been put into a non-driving state by the control unit  19 , as described hereinafter. 
     The sensor unit  16  is adapted to detect information regarding the surrounding environment of the vehicle  10 . The sensor unit  16  is adapted to output the detected information to the control unit  19 . The sensor unit  16  includes, for example, at least one of a GPS (Global Positioning System), a speed sensor, an IMU (Inertial Measurement Unit), an obstacle sensor, a camera, and the like. 
     If the sensor unit  16  is configured to include a GPS, for example, it serves to detect the position of the vehicle  10 . The sensor unit  16  then outputs the detected position of the vehicle  10  to the control unit  19 . 
     If the sensor unit  16  is configured to include a speed sensor, for example, it serves to detect the speed of the vehicle  10 . The sensor unit  16  then outputs the detected speed to the control unit  19 . 
     If the sensor unit  16  includes an IMU, for example, the sensor unit  16  serves to detect the posture and acceleration of the vehicle  10 . The sensor unit  16  then outputs the detected posture and acceleration to the control unit  19 . The IMU may be configured to include an acceleration sensor and a gyro sensor. 
     If the sensor unit  16  includes an obstacle sensor, for example, the sensor unit  16  serves to detect an obstacle within a predetermined region, in the traveling direction of the vehicle  10 . The obstacle sensor may be configured to include a laser. In this instance, the obstacle sensor detects the presence of an obstacle by projecting a laser beam in the traveling direction of the vehicle  10  and detecting the laser beam reflected by the obstacle. 
     If the sensor unit  16  includes a camera, for example, the sensor unit  16  serves to capture an image of the road surface on which the vehicle  10  travels. The sensor unit  16  then outputs the captured image to the control unit  19 . 
     The communication unit  17  serves to wirelessly communicate with an external device. The communication unit  17  includes, for example, a wireless communication module corresponding to any appropriate wireless communication standards. Examples of the wireless communication standards include wireless LAN, 2G (2nd Generation), 3G (3rd Generation), 4G (4th Generation), LTE (Long Term Evolution), WiMAX (Worldwide Interoperability for Microwave Access) and PHS (Personal Handy-phone System). Further, the communication unit  17  may be configured to include a communication module corresponding to any appropriate standards for road-to-vehicle communication. 
     The memory unit  18  may be comprised of a semiconductor memory, a magnetic memory, or the like. The memory unit  18  serves to store various kinds of information and a program for operating the control unit  19 . The memory unit  18  may also function as a work memory. 
     The memory unit  18  serves to store the map data of the test course  1  shown in  FIG. 1 . The map data may be three-dimensional data. The map data includes, for example, topographical information on the road surface on which the vehicle  10  can travel, position information regarding the positions P 1  to P 7 , and position information regarding the center line O of the road surface  5   a  shown in  FIG. 2 . Further, the memory unit  18  serves to store the speed of the vehicle  10  for performing the tire noise measurement, that is, the speed of the vehicle  10  at the position P 5  which is the starting point of the measuring zone  5  shown in  FIG. 1 . For example, the memory unit  18  is adapted to store nine different speeds between 72 km/h and 88 km/h, as shown in  FIG. 3 . 
     The control unit  19  is a processor that controls and manages the entire vehicle  10 , including each functional block of the vehicle  10 . The control unit  19  may be comprised of a processor, such as a CPU (Central Processing Unit) that executes a program defining a control procedure or a dedicated processor specialized in processing each function. 
     The control unit  19  is adapted to receive starting instruction for testing the tire noise from an external device, via the communication unit  17 . The external device is comprised, for example, of a wireless communication device installed in an operation base station that is provided around the test course  1  shown in  FIG. 1 . When the control unit  19  receives the starting instruction, the vehicle  10  is located, for example, at the position P 7  of the test course  1  shown in Fig. 
     Upon receipt of the starting instruction, the control unit  19  puts the prime mover  11  into a driving state. As an example of processing for putting a gasoline-fueled engine as the prime mover  11  into a driving state, the control unit  19  turns on the ignition. For example, turning on the ignition includes that the control unit  19  outputs a driving signal to the fuel injection valve of the prime mover  11  as an engine and causes the fuel injection valve to inject fuel into the cylinder or the intake manifold. Further, if the prime mover  11  is a gasoline engine, turning on the ignition includes that the control unit  19  supplies an electric current to the spark plug of the engine to generate electric spark by the spark plug, and to explode and burn fuel or mixing in the cylinder. 
     When the prime mover  11  is put into the driving state, the control unit  19  controls the transmission  12  to put the tire  10   a  into the driving state and automatically drives the vehicle  10 . The control unit  19  then suitably controls the steering device  14  and the like, based on the detection results of the sensor unit  16  during the automatic driving of the vehicle  10 . 
     After the automatic driving has been started, based on the detection result of the sensor unit  16 , the control unit  19  serves to detect that the vehicle  10  enters into the speed maintenance zone  2  shown in  FIG. 1 . For example, based on the GPS detection results obtained by the sensor unit  16 , the control unit  19  detects the position of the vehicle  10 . Further, when the detected position of the vehicle  10  and the position P 1  stored in the memory unit  18  substantially coincide with each other in the traveling direction of the vehicle  10 , the control unit  19  allows the vehicle  10  to enter into the speed maintenance zone  2  shown in  FIG. 1 . 
     When the control unit  19  detects that the vehicle  10  is entering into the speed maintenance zone  2  shown in  FIG. 1 , the control unit  19  is operated to control so that the speed of the vehicle  10  is maintained at a constant speed. For example, the control unit  19  controls the vehicle  10  so as to travel along the outer side of the corner section of the speed maintenance zone  2  shown in  FIG. 1 , such that the speed of the vehicle  10  is maintained at a constant speed. 
     After the vehicle  10  enters the speed maintenance zone  2  shown in  FIG. 1 , the control unit  19  can detect that the vehicle  10  enters the acceleration zone  3  shown in  FIG. 1  based on the detection results of the sensor unit  16 . For example, the control unit  19  detects the position of the vehicle  10  based on the detection results of the GPS included in the sensor unit  16 . Further, when the detected position of the vehicle  10  and the position P 2  stored in the memory unit  18  substantially coincide with each other in the traveling direction of the vehicle  10 , the control unit  19  detects that the vehicle  10  is entering the acceleration zone  3  shown in  FIG. 1 . When the control unit  19  detects that the vehicle  10  is entering the acceleration zone  3  shown in  FIG. 1 , the control unit  19  suitably controls the prime mover  11  and the like to accelerate the vehicle  10 , for example, at a predetermined acceleration rate. 
     The control unit  19  puts the prime mover  11  into a non-driving state when the vehicle  10  arrives at a predetermined position or reaches a predetermined speed while the vehicle  10  is accelerating. As an example of the process of putting the prime mover  11  into a non-driving state, if the prime mover  11  is a combustion engine, the control unit  19  turns off the ignition. For example, turning off the ignition includes that the control unit  19  outputs a stop signal to the fuel injection valve of the prime mover  11 . Further, when the prime mover  11  is a gasoline engine, turning off the ignition includes that the control unit  19  stops the electric power supply to the spark plug. In the present disclosure, even after the prime mover  11  has been put into a non-driving state, the battery  15  supplies electric power to the components of the vehicle  10  except the prime mover  11 . 
     Here, the predetermined position is, for example, the position P 3  shown in  FIG. 1 . For putting the prime mover  11  into a non-driving state based on the arrival of the vehicle  10  at a predetermined position, the control unit  19  first detects the position of the vehicle  10  based on the detection results of the GPS included in the sensor unit  16 . The control unit  19  then puts the prime mover  11  into non-driving state when the detected position of the vehicle  10  and the position P 3  stored in the memory unit  18  substantially coincide with each other in the traveling direction of the vehicle  10 . The control unit  19  may put the prime mover  11  into the non-driving state at a time point of arrival at the position P 3  or may put the prime mover  11  into the non-driving state before arriving at the position P 3 . When the control unit  19  does not determine that the detected position of the vehicle  10  and the position P 3  stored in the memory unit  18  substantially coincide with each other, that is, when the vehicle  10  has not reached the position P 3 , the control unit  19  sets the vehicle  10  to continue acceleration. 
     Further, the predetermined speed is the speed calculated based on the speed of the vehicle  10  to be subjected to the noise measurement of the tire  10   a . For example, the predetermined speed is calculated by adding the speed of the vehicle  10  at the position P 5  which is the starting point of the measurement zone  5  shown in  FIG. 1 , and the speed amount (hereinafter, also referred to as “speed reduction amount”) of the vehicle  10  that has been decreased while the vehicle  10  travels from the position P 3  to the position P 5  shown in  FIG. 1 . The details of the calculation method of the predetermined speed will be described hereinafter. For putting the prime mover  11  into a non-driving state based when the vehicle  10  reaches a predetermined speed, the control unit  19  first detects the speed of the vehicle  10  based on the detection results of the speed sensor included in the sensor unit  16 . Further, the control unit  19  puts the prime mover  11  into non-driving state when the detected speed of the vehicle  10  reaches a predetermined speed. 
     When the prime mover  11  is put into a non-driving state, the control unit  19  controls the transmission  12  to put the tire  10   a  in a neutral state of disconnecting the tire  10   a  from the prime mover  11  and causes the vehicle  10  to coast. By such control, the vehicle  10  coasts in the coast-traveling zone  4  shown in  FIG. 1 . Further, in the measuring section  5  in the coast-traveling zone  4 , the vehicle  10  puts the prime mover  11  in a non-driving state, so that the noise of the vehicle  10  generated from other than the tire  10   a  is reduced. By such control, the measuring devices  5 R and  5 L shown in  FIG. 2  can accurately collect the noise of the tire  10   a.    
     The control unit  19  may calculate the speed reduction amount in order to calculate the predetermined speed to be used for the next tire noise measurement during the coast-traveling along the coast-traveling zone  4  shown in  FIG. 1 . As an example of the calculation of the speed reduction amount, first, the control unit  19  detects the speed of the vehicle  10  at the point P 2  shown on  FIG. 1 , where the coast-traveling is started, based on the detection results of the GPS and the speed sensor included in the sensor unit  16 . The control unit  19  then detects the speed of the vehicle  10  at the position P 5  shown in  FIG. 1 , which is the starting point of the measurement zone  5 , based on the detection results of the GPS and the speed sensor included in the sensor unit  16 . Further, the control unit  19  calculates the speed reduction amount by subtracting the speed at the position P 5  shown in  FIG. 1  from the speed at the position P 3  shown in  FIG. 1 . For example, the control unit  19  calculates the speed reduction amount by the following Equation (1); 
         VR=VP 3 −VP 5  (1)
 
     wherein, VR is the speed reduction amount, VP 3  is the speed of the vehicle  10  at the position P 3  shown in  FIG. 1 , and VP 5  is the speed of the vehicle  10  at the position P 5  shown in  FIG. 1 . The control unit  19  stores the calculated speed reduction amount in the memory unit  18 . 
     The control unit  19  carries out a control during the coast-traveling so that, as seen in the width direction of the road surface  5   a  shown in  FIG. 2 , the distance between the vehicle  10  and the measuring device  5 R shown in  FIG. 2  and the distance between the vehicle  10  and the measuring device  5 L are equal to each other. The details of this processing will be described below with reference to [Processing Example 1 during Coast-traveling]. Further, when the control unit  19  detects an obstacle present within a predetermined area in the traveling direction of the vehicle  10  during the coast-traveling, the control unit  19  decelerates the vehicle  10 . The details of this processing will be described below with reference to [Processing Example 2 during Coast-traveling]. 
     The control unit  19  during the coast-traveling can detect that the vehicle  10  arrives at the position P 4  shown in  FIG. 1 , based on the detection results of the sensor unit  16 . For example, the control unit  19  detects the position of the vehicle  10  based on the detection results of the GPS included in the sensor unit  16 . Further, when the detected position of the vehicle  10  and the position P 4  stored in the memory unit  18  substantially coincide with each other in the traveling direction of the vehicle  10 , the control unit  19  detects that the vehicle  10  reached the position P 4  shown in  FIG. 1 . When the vehicle  10  arrives at the position P 4  which is the end point of the coast-traveling zone  4  shown in  FIG. 1 , the control unit  19  puts the prime mover  11  into the driving state again. When the prime mover  11  is put into the driving state again, the control unit  19  controls the transmission  12  to put the tire  10   a  into the driving state and automatically drive the vehicle  10 . By such control, the vehicle  10  automatically travels along the cruising zone  6  shown in  FIG. 1 . 
     The control unit  19  may feedback the measurement results during the automatic operation in the cruising zone  6  shown in  FIG. 1 . As an example of such feedback, the control unit  19  may calculate the predetermined speed to be used in the next tire noise measurement. 
     As an example of calculating the predetermined speed, first, the control unit  19  extracts from the memory unit  18  one speed at which the noise measurement of the tire  10   a  has not yet been performed. This extracted speed may be the (predetermined) speed of the vehicle  10  at the position P 5 , which is the starting point of the measuring zone  5  shown in  FIG. 1 , for the next tire noise measurement. Next, the control unit  19  adds the extracted speed of the vehicle  10  and the current speed reduction amount stored in the memory unit  18 , to calculate a predetermined speed to be used for the next tire noise measurement. For example, the control unit  19  calculates the predetermined speed to be used for the next tire noise measurement, based on the following Equation (2): 
         VNP 3= VNP 5+ VR   (2)
 
     wherein, VNP 3  is a predetermined speed used for the next tire noise measurement, VNP  5  is the speed extracted by the control unit  19 , for which the noise measurement of the tire  10   a  has not yet been performed, i.e., VNP  5  may be the speed of the vehicle  10  for the next tire noise measurement, at the position P 5  that is the starting point of the measuring zone  5  shown in  FIG. 1 , and VR is the speed reduction amount calculated by the above Equation (1). 
     In the above example of calculation of the predetermined speed, the control unit  19  calculates the acceleration rate of the vehicle  10  in the acceleration zone  3  shown in  FIG. 1 , so that the speed of the vehicle  10  upon the next tire noise measurement becomes the calculated predetermined speed at the position P 3  shown in  FIG. 1 . By such control, in the next tire noise measurement, the speed of the vehicle  10  can reach the predetermined speed when the vehicle  10  arrives at the position P 3  shown in  FIG. 1 . 
     Here, the speed reduction amount may be generated due to friction between the tire  10   a  and the road surface. The surface shape of the tire  10   a  varies depending on the type of the tire  10   a . Thus, the speed reduction amount may change depending upon the type of the tire  10   a . Even in such a case, according to the present embodiment, the predetermined speed can be automatically calculated depending upon the type of the tire  10   a , under the control by means of the control unit  19  described above. By such control, according to the present embodiment, the tire noise test can be efficiently executed. Further, by such control, the noise of the tire  10   a  at a desired speed can be measured. 
     [Processing Example 1 During Coast-Traveling] 
     Next, explanation will be made of Processing Example 1 of the control unit  19  during the coast-traveling. 
     The control unit  19  carries out a control during the coast-traveling so that, as seen in the width direction of the road surface  5   a  shown in  FIG. 2 , the distance between the vehicle  10  and the measuring device  5 R shown in  FIG. 2  and the distance between the vehicle  10  and the measuring device  5 L shown in  FIG. 2  are equal to each other. As an example of such control, the control unit  19  may control the vehicle  10  to travel near the center of the road surface  5   a  in the measurement zone  5  shown in  FIG. 2 . Hereinafter, this control example will be described. 
     During the coast-traveling, the control unit  19  determines whether or not the distance from the center line O of the road surface  5   a  to the vehicle  10  is within a predetermined range in the width direction of the road surface  5   a  shown in  FIG. 2 . For example, first, the control unit  19  detects the position of the vehicle  10  based on the detection results of the GPS included in the sensor unit  16 . The control unit  19  then acquires the position of the center line O of the road surface  5   a  shown in  FIG. 2  from the memory unit  18 . The control unit  19  further determines whether or not the distance from the center line O of the road surface  5   a  to the vehicle  10 , as seen in the width direction of the road surface  5   a  shown in  FIG. 2 , is within a predetermined range, based on the detected position of the vehicle  10  and the acquired position of the center line O. The predetermined range may be set based on the distance between the measuring devices  5 R and  5 L shown in  FIG. 2 . 
     If the control unit  19  does not determine that the distance from the center line O of the road surface  5   a  to the vehicle  10  is within a predetermined range, the control unit  19  controls the steering device  14  to adjust the steering angle of the tire  10   a  according to that distance. By such control, the vehicle  10  according to the present embodiment can travel more accurately near the center of the road surface  5   a  than, for example, when the driver actually drives the vehicle  10 . Since the vehicle  10  travels near the center of the road surface  5   a  with high accuracy, the measuring devices  5 R and  5 L shown in  FIG. 2  can measure the noise of the tire  10   a  with higher accuracy. 
     [Processing Example 2 During Coast-Traveling] 
     Next, explanation will be made of Processing Example 2 of the control unit  19  during the coast-traveling. 
     The control unit  19  determines whether or not an obstacle is present within a predetermined region in the traveling direction of the vehicle  10 , based on the detection result of the obstacle sensor included in the sensor unit  16 . When the control unit  19  determines that an obstacle is present within the predetermined region in the traveling direction of the vehicle  10 , the control unit  19  controls the brake  13 A to decelerate the vehicle  10 . While the vehicle  10  is decelerating, if the obstacle is an animal, for example, it would be possible for the animal to escape away from the vehicle  10 . By such control, the safety of the vehicle  10  during the coast-traveling can be ensured. When the control unit  19  determines that an obstacle is present within the predetermined region in the traveling direction of the vehicle  10 , the control unit  19  may also control the brakes  13 A and  13 B to stop the vehicle  10 . 
     The control unit  19  also determines whether or not abnormal situation has occurred in the vehicle  10 . An example of abnormal situation in the vehicle  10  is failure of a component related to the travelling of the vehicle  10  (e.g., the steering device  14 ). Upon occurrence of abnormal situation in the vehicle  10 , it may not be possible for the vehicle  10  to maintain the automatic driving. Thus, when the control unit  19  detects occurrence of abnormal situation in the vehicle  10 , the control unit  19  controls the brake  13 A to decelerate the vehicle  10 . The control unit  19  further controls the brake  13 B to stop the vehicle  10 . By such control, the safety of the vehicle  10  during the coast-traveling can be more reliably ensured. 
     [Operation of the Vehicle] 
       FIG. 5  is a flowchart showing the process flow of the tire noise test method according to an embodiment of the invention (Flow No. 1).  FIG. 6  is a flowchart showing the process flow of the tire noise test method according to the embodiment of the present invention (Flow No. 2). For example, when the control unit  19  receives the test starting instruction from an external device via the communication unit  17 , the control unit  19  starts the process shown in  FIG. 5 . The vehicle  10  is located at the position P 7  of the test course  1  shown in  FIG. 1  at the start of the process shown in  FIG. 5 . 
     The control unit  19  puts the prime mover  11  into a driving state (step S 10 ). When the prime mover  11  is put into the driving state, the control unit  19  controls the transmission  12  to put the tire  10   a  into the driving state (step S 11 ), thereby allowing an automatic driving of the vehicle  10 . 
     The control unit  19  detects that the vehicle  10  enters the speed maintenance zone  2  shown in  FIG. 1  (step S 12 ). When the control unit  19  detects that the vehicle  10  enters the speed maintenance zone  2 , the control unit  19  carries out a control to maintain the speed of the vehicle  10  at a constant speed (step S 13 ). 
     The control unit  19  detects that the vehicle  10  enters the acceleration zone  3  shown in  FIG. 1  (step S 14 ). When the control unit  19  detects that the vehicle  10  enters the acceleration zone  3 , the control unit  19  appropriately controls the prime mover  11  and the like to accelerate the vehicle  10  (step S 15 ). 
     Based on the detection results of the sensor unit  16 , the control unit  19  determines whether or not the vehicle  10  reaches the position P 3  shown in  FIG. 1  as a predetermined position (step S 16 ). If the control unit  19  determines that the vehicle  10  reaches the position P 3  shown in  FIG. 1  as the predetermined position (step S 16 : Yes), the control unit  19  proceeds to the process of step S 17  shown in  FIG. 6 . On the other hand, if the control unit  19  does not determine that the vehicle  10  reaches the position P 3  shown in  FIG. 1  as the predetermined position (step S 16 : No), the control unit  19  returns to the process of step S 15 . 
     In the process of step S 17  shown in  FIG. 6 , the control unit  19  puts the prime mover  11  into a non-driving state. When the prime mover  11  is put into the non-driving state, the control unit  19  controls the transmission  12  to put the tire  10   a  into the neutral state (step S 18 ), thereby allowing the coast-traveling of the vehicle  10 . By such control, the vehicle  10  coasts in the coast-traveling zone  4  shown in  FIG. 1 . 
     During the coast-traveling, the control unit  19  calculates the speed reduction amount (step S 19 ) based, for example, on Equation (1) above, and stores it in the memory unit  18 . Further, while the vehicle  10  is traveling in the measuring zone  5  shown in  FIG. 1 , the noise generated by the tire  10   a  is collected by the measuring devices  5 R and  5 L shown in  FIG. 2 . 
     Based on the detection results of the sensor unit  16 , the control unit  19  determines whether or not the vehicle  10  reaches the position P 4 , which is the end point of the coast-traveling zone  4  shown in  FIG. 1  (step S 20 ). If the control unit  19  determines that the vehicle  10  reaches the position P 4  which is the end point of the coast-traveling zone  4  shown in  FIG. 1  (step S 20 : Yes), the control unit  19  proceeds to the process of step S 21 . On the other hand, if it is not determined that the vehicle  10  reaches the position P 4  which is the end point of the coast-traveling zone  4  shown in  FIG. 1  (step S 20 : No), the control unit  19  performs the process of step S 20  again. 
     In the process of step S 21 , the control unit  19  puts the prime mover  11  into the driving state. When the prime mover  11  is put into the driving state, the control unit  19  controls the transmission  12  to put the tire  10   a  into the driving state (step S 22 ), thereby allowing the vehicle  10  to travel automatically. By such control, the vehicle  10  travels automatically the cruising zone  6  shown in  FIG. 1 . 
     The control unit  19  determines whether or not to end the test (step S 23 ). For example, the control unit  19  determines that the test has been completed when it is determined that the noise measurement of the tire  10   a  has been performed at each speed stored in the memory unit  18 . If the control unit  19  determines that the test has been completed (step S 23 : Yes), the control unit  19  ends the processes shown in  FIGS. 5 and 6 . On the other hand, if the control unit  19  does not determine that the test has been completed (step S 23 : No), the control unit  19  proceeds to the process of step S 24 . 
     In the process of step S 24 , the control unit  19  feeds back the measurement results. For example, the control unit  19  may calculate a predetermined speed to be used in the process of the next step S 16  shown in  FIG. 5 , based on the above Equation (2) and the speed reduction amount calculated in the process of step S 19 . In other words, the control unit  19  may calculate the predetermined speed for the next tire noise test method, based on the above Equation (2) and the speed reduction amount calculated when the one tire noise test method has been carried out. In this instance, in the process of the next step S 16  shown in  FIG. 5 , the control unit  19  may determine whether or not the speed of the vehicle  10  reaches a predetermined speed based on the detection results of the sensor unit  16 . In the process of the next step S 16  shown in  FIG. 5 , if the control unit  19  determines that the speed of the vehicle  10  reaches the predetermined speed (step S 16 : Yes), the control unit  19  proceeds to the process of step S 17  shown in  FIG. 6 . On the other hand, if the control unit  19  does not determine that the speed of the vehicle  10  reaches the predetermined speed in the process of the next step S 16  shown in  FIG. 5  (step S 16 : No), the control unit  19  returns to the process of step S 15  shown in Fig. 
     The control unit  19  may determine whether or not the vehicle  10  reaches the predetermined speed in the first process of the step S 16  shown in  FIG. 5 . In this instance, if the control unit  19  determines that the vehicle  10  reaches the predetermined speed (step S 16 : Yes), the control unit  19  proceeds to the process of step S 17  shown in  FIG. 6 . On the other hand, if the control unit  19  does not determine that the vehicle  10  reaches the predetermined speed (step S 16 : No), the control unit  19  returns to the process of step S 15  shown in  FIG. 5 . 
     [Operation Example 1 During the Coast-Traveling] 
       FIG. 7  is a flowchart showing an operation example 1 during the coast-traveling of the vehicle  10  in the tire noise test method according to the embodiment of the present invention. For example, the control unit  19  starts the process shown in  FIG. 7  after execution of the process of step S 18  shown in  FIG. 6 . Further, the control unit  19  ends the process shown in  FIG. 7  before execution of the process of step S 21  shown in  FIG. 6 . 
     The control unit  19  detects the position of the vehicle  10  based on the detection results of the GPS included in the sensor unit  16  (step S 30 ). Further, the control unit  19  acquires the position of the center line O of the road surface  5   a  shown in  FIG. 2 , from the memory unit  18  (step S 31 ). 
     The control unit  19  determines whether or not the distance from the center line O of the road surface  5   a  to the vehicle  10  is within a predetermined range in the width direction of the road surface  5   a  shown in  FIG. 2  (step S 32 ). If the control unit  19  determines that the distance from the center line O of the road surface  5   a  to the vehicle  10  is within a predetermined range (step S 32 : Yes), the control unit  19  returns to the process of step S 30 . On the other hand, if the control unit  19  does not determine that the distance from the center line O of the road surface  5   a  to the vehicle  10  is within a predetermined range (step S 32 : No), the control unit  19  proceeds to the process of step S 33 . 
     In the process of step S 33 , the control unit  19  controls the steering device  14  to adjust the steering angle of the tire  10   a  according to the distance from the center line O of the road surface  5   a  to the vehicle  10 . The control unit  19  returns to the process of step S 30  after the process of step S 33 . 
     [Operation Example 2 During the Coast-Traveling] 
       FIG. 8  is a flowchart showing an operation example 2 during the coast-traveling of the vehicle  10  in the tire noise test method according to the embodiment of the present invention. For example, the control unit  19  starts the process shown in  FIG. 8  after execution of the process of step S 18  shown in  FIG. 6 . Further, the control unit  19  ends the process shown in  FIG. 8  before execution of the process of step S 21  shown in  FIG. 6 . The control unit  19  may execute the process shown in  FIG. 8  in parallel with the process shown in  FIG. 7 . 
     The control unit  19  determines whether or not an obstacle is present within a predetermined region in the traveling direction of the vehicle  10 , based on the detection results of the obstacle sensor included in the sensor unit  16  (step S 40 ). If the control unit  19  determines that an obstacle is present within the predetermined region in the traveling direction of the vehicle  10  (step S 40 : Yes), the control unit  19  proceeds to the process of step S 41 . On the other hand, if the control unit  19  does not determine that an obstacle is present within the predetermined region in the traveling direction of the vehicle  10  (step S 40 : No), the control unit  19  proceeds to the process of step S 42 . 
     In the process of step S 41 , the control unit  19  controls the brake  13 A to decelerate the vehicle  10 . While the vehicle  10  is decelerating, if the obstacle is an animal, for example, it would be possible for the animal to escape away from the vehicle  10 . 
     In the process of step S 42 , the control unit  19  determines whether or not abnormal situation has occurred in the vehicle  10 . If the control unit  19  determines that abnormal situation has occurred in the vehicle  10  (step S 42 : Yes), the control unit  19  proceeds to the process of step S 43 . On the other hand, if the control unit  19  does not determine that abnormal situation has occurred in the vehicle  10  (step S 42 : No), the control unit  19  returns to the process of step S 40 . 
     In the process of step S 43 , the control unit  19  controls the brake  13 A to decelerate the vehicle  10 . Further, the control unit  19  controls the brake  13 B to stop the vehicle  10  (step S 44 ). 
     The control unit  19  may control the brakes  13 A and  13 B to stop the vehicle  10  in the process of step S 41 . 
     As described above, in the test method for the tire  10   a  according to the present embodiment, when the vehicle  10  arrives at the position P 3  shown in  FIG. 1  as a predetermined position or reaches the predetermined speed, the prime mover  11  is put into a non-driving state. By such control, it is possible to provide an efficient tire noise test method in the actual vehicle noise test, as described below. 
     For a comparative example, it is assumed that the driver drives the vehicle  10  and performs a tire noise test. In the comparative example, it is further assumed that the prime mover  11  is a combustion engine that uses gasoline as fuel. In the comparative example, it is required for the driver to determines that the vehicle  10  reaches the position P 3  by visually recognizing the position P 3  shown in  FIG. 1 , or to determine that the vehicle  10  reaches a predetermined speed while the driver visually recognizes the speedometer of the vehicle  10 . That is, in the comparative example, the driver determines when to turn off the ignition. Thus, in the comparative example, it may not be possible to turn off the ignition at the correct timing. If the ignition cannot be turned off at the correct timing, the tire noise test cannot be performed efficiently. 
     On the other hand, in the present embodiment, the control unit  19  of the vehicle  10  determines whether the vehicle  10  reaches the position P 3  or the predetermined speed. By such control, according to the present embodiment, the ignition can be turned off at an accurate timing, and the tire noise test can be efficiently executed. 
     Further, in the comparative example, it is required to train the driver. In the comparative example, since training of the driver is required, it may be inevitable that the cost of performing the tire noise test increases. 
     In contrast, according to the present embodiment, it is not necessary to train the driver. Thus, according to the present embodiment, it is possible to suppress increase in cost for carrying out the tire noise test as compared to the comparative example. 
     The tire noise test method according to the present invention is not limited to the specific configurations shown in the above-described embodiments, and variations and modifications may be made without departing from the scope of claims. 
     In the above embodiment, the tire noise test method has been described as being executed by the vehicle  10 . However, a device different from the vehicle  10  may be used for allowing the tire noise test method to be carried out by the vehicle  10 .  FIG. 9  shows an example of the control device  20  in the tire noise test method according to the embodiment of the present invention. The vehicle  10 A shown in  FIG. 9  includes a control device  20 . The control device  20  may automatically drive the vehicle  10 A to carry out the tire noise test. The control device  20  shown in  FIG. 9  includes a sensor unit  16 , a communication unit  17 , a memory unit  18 , a control unit  19 , and a battery  21 . The battery  21  is, for example, a lithium ion battery. The battery  21  supplies power to the components in the control device  20 . When the vehicle  10 A reaches a predetermined position or reaches a predetermined speed, the control unit  19  of the control device  20  shown in  FIG. 9  causes the vehicle  10 A to coast in a non-driving state of the prime mover  11  of the vehicle  10 A. 
     In the above embodiment, the tire noise test method has been described as being carried out by the control unit  19  included in the vehicle  10 . However, the tire noise test method by the vehicle  10  may be carried out based on the instruction from another control device arranged outside the vehicle  10 . In this instance, the control unit  19  of the vehicle  10  carries out the tire noise test method based on the instruction from another control device arranged outside the vehicle  10 , via the communication unit  17 . 
     In the above embodiment, the vehicle  10  has been described as including the control unit  19 . However, in addition to the control unit  19 , the vehicle  10  may also include an auxiliary control unit for monitoring the control unit  19 . In this instance, the auxiliary control unit may determine whether or not abnormal situation has occurred in the vehicle  10  while the vehicle  10  is coast-traveling. Further, if the auxiliary control unit detects occurrence of abnormal situation in the vehicle  10 , the auxiliary control unit may control the brakes  13 A and  13 B to stop the vehicle  10 . By such control, the safety of the vehicle  10  can be ensured even upon occurrence of abnormality in the control unit  19 . 
     In the above embodiment, the control unit  19  has been described an example of detecting the position of the vehicle  10  based on the detection results of the GPS included in the sensor unit  16 . However, the detection results of the sensor unit  16  for detecting the position of the vehicle  10  are not limited to the detection results of the GPS sensor. For example, the control unit  19  may detect the position of the vehicle  10  based on the combination of the detection results of any component included in the sensor unit  16  or the detection results of any component. 
     In the above embodiment, an example of detecting the position of the vehicle  10  based on the detection results of the sensor unit  16  has been described. However, the method of detecting the position of the vehicle  10  is not limited to this. For example, the control unit  19  may detect the position of the vehicle  10  by road-to-vehicle communication. The road-to-vehicle communication is a two-way communication between the vehicle  10  and the communication device installed in the test course  1  shown in  FIG. 1 . In this example, by communicating with the communication device at the position P 3  shown in  FIG. 1 , via the communication unit  17 , the control unit  19  may detect that the position of the vehicle  10  is the position P 3 . 
     In the above embodiment, the tire noise test defined by ECE R117 has been referred to as an example of the tire noise test standard. However, the tire noise test method of the present disclosure may be used for a tire noise test of any standard. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, it is possible to provide a tire noise test method, a vehicle and a control device that are efficient in actual vehicle noise test. 
     REFERENCE NUMERALS 
     
         
         
           
               1 : Test course 
               2 : Speed maintenance zone 
               3 : Acceleration zone 
               4 : Coast-traveling zone 
               5 : Measuring zone 
               5   a : Road surface 
               5 R,  5 L: Measuring device 
               6 : Cruising zone 
               10 ,  10 A: Vehicle 
               10   a : Tire 
               10   b : Vehicle body 
               11 : Prime mover 
               12 : Transmission 
               13 ,  13 A,  13 B: Braking device 
               14 : Steering device 
               15 : Battery 
               16 : Sensor unit 
               17 : Communication unit 
               18 : Memory unit 
               19 : Control unit