Vehicle

Abstract

A vehicle having a normalized pitch moment of inertia of 0.73 or less in a state in which a load of 60-65 kilograms, inclusive, is placed on a driver seat and / or a passenger seat, said vehicle comprising: a vehicle main body; a shaft connected to the vehicle main body; n wheels connected to the shaft; and n springs connected to the vehicle main body and the shaft and provided respectively to the n wheels, wherein a value obtained by dividing a combined spring constant of the n springs by the weight of the vehicle is 0.08 or less.

Description

vehicle

[0001] The present invention relates to vehicles.

[0002] In recent years, due to environmental concerns, there has been an increasing demand for electric vehicles, which are powered by electricity, instead of gasoline-powered vehicles. Unlike conventional vehicles, electric vehicles do not generate power by burning gasoline, but rather by using electrical energy, which allows for dramatic reductions in carbon dioxide and carbon monoxide emissions.

[0003] JP 2009-106136 A

[0004] However, vehicles with a center of gravity near the center, such as battery-powered electric vehicles, have a problem in that when low-frequency vibrations of 3 Hz or less are caused by road bumps, the vehicle body's pitch direction (the front and rear ends of the vehicle body move up and down in opposite directions) becomes large. This behavior makes the ride uncomfortable for passengers. Passengers in the passenger seat are particularly likely to feel uncomfortable due to the pitching, as they are not holding on to the steering wheel.

[0005] The smaller the normalized pitch moment of inertia, which is the normalized moment of inertia of a vehicle in the pitch direction, the more likely the above-mentioned phenomenon occurs. Compared to conventional gasoline-powered vehicles with engines mounted in the front of the vehicle, the normalized pitch moment of inertia of electric vehicles is smaller. Thus, the smaller the normalized pitch moment of inertia of a vehicle, the more likely it is to cause discomfort to passengers, especially those sitting in the passenger seat.

[0006] One embodiment of the present invention has been made in consideration of the above problems, and one of its objectives is to realize a vehicle that can provide passengers with good riding comfort and safety.

[0007] A vehicle according to one embodiment of the present invention has a normalized pitch moment of inertia of 0.73 or less when a load of 60 kilograms or more and 65 kilograms or less is applied to the driver's seat and passenger seat, and comprises a vehicle main body, a shaft connected to the vehicle main body, n wheels (n is an integer of 2 or more) connected to the shaft, and n springs connected to the vehicle main body and the shaft and provided for each of the n wheels, and the value obtained by dividing the composite spring constant of the n springs by the weight of the vehicle is 0.08 or less.

[0008] The vehicle main body is provided with a seat having a seating surface and a back surface, and a headrest attached to the seat, the back surface having a first portion provided on a side closer to the seating surface and a second portion provided on a side closer to the headrest, and a hemispherical head portion having a diameter of 20 mm is brought close to the headrest and displaced 15 mm from the position where the head portion contacts the headrest, and the first load value when the head portion is brought close to the first portion and displaced 15 mm from the position where the head portion contacts the first portion may be 0.7 times or less of a third load value when the head portion is brought close to the first portion and displaced 15 mm from the position where the head portion contacts the first portion.

[0009] The vehicle main body is provided with a seat having a seating surface and a back surface, and a headrest attached to the seat, the back surface having a first portion provided on a side closer to the seating surface and a second portion provided on a side closer to the headrest, and a first load value when a hemispherical head portion having a diameter of 20 mm is brought close to the headrest and the displacement from the position where the head portion contacts the headrest is 15 mm, and a second load value when the head portion is brought close to the second portion and the displacement from the position where the head portion contacts the second portion may be smaller than a third load value when the head portion is brought close to the first portion and the displacement from the position where the head portion contacts the first portion is 15 mm.

[0010] The boundary between the first portion and the second portion may be at a position that is 300 mm or more and 400 mm or less in vertical distance from the upper surface of the seat portion.

[0011] A value obtained by dividing the first load value by the third load value may be 0.7 or less, and a value obtained by dividing the second load value by the third load value may be 0.8 or less.

[0012] The vehicle may further include a stabilizer, and when the roll stiffness of the front wheels is defined as a value obtained by multiplying the square of the tread of the two front wheels divided by 2 by the sum of the spring constant of the spring provided for one of the two front wheels and the spring constant of the front stabilizer, and the roll stiffness of the rear wheels is defined as a value obtained by multiplying the square of the tread of the two rear wheels divided by 2 by the sum of the spring constant of the spring provided for one of the two rear wheels and the spring constant of the rear stabilizer, the value obtained by dividing the roll stiffness of the front wheels by the roll stiffness of the rear wheels may be 0.45 or less.

[0013] The vehicle may be an electric vehicle further comprising a battery.

[0014] According to the vehicle according to one embodiment of the present invention, it is possible to realize a vehicle that can provide passengers with a comfortable ride and safety.

[0015] FIG. 1 is a side view showing the appearance of a vehicle according to one embodiment of the present invention. FIG. 2 is a view showing the state of an occupant when the vehicle according to one embodiment of the present invention goes over a step. FIG. 3 is a view showing the state of an occupant when the vehicle according to one embodiment of the present invention goes over a step. FIG. 4 is a view showing test results conducted on a vehicle according to one embodiment of the present invention. FIG. 5 is a view showing an evaluation method for a headrest and a seat used in a vehicle according to one embodiment of the present invention. FIG. 6 is a view showing test results conducted on a vehicle according to one embodiment of the present invention. FIG. 7 is a view showing test results conducted on a vehicle according to one embodiment of the present invention. FIG. 8 is a front view showing the configuration of a back portion of a seat used in a vehicle according to one embodiment of the present invention. FIG. 9 is a perspective view showing the configuration of a back portion of a seat used in a vehicle according to one embodiment of the present invention. FIG. 10 is a view showing the surface hardness ratio between the headrest and the lower back portion of a seat used in a vehicle according to one embodiment of the present invention. FIG. 11 is a view showing the surface hardness ratio between a first portion and a second portion of a seat used in a vehicle according to one embodiment of the present invention.

[0016] A vehicle according to an embodiment of the present invention will be described below with reference to the drawings. However, the vehicle according to an embodiment of the present invention can be implemented in many different forms, and should not be construed as being limited to the description of the example shown below. In the drawings referred to in this embodiment, identical parts or parts having similar functions are designated by the same reference numerals, and repeated description thereof will be omitted.

[0017] In this specification, unless otherwise specified, expressions such as "α includes A, B, or C," "α includes any one of A, B, and C," and "α includes one selected from the group consisting of A, B, and C" do not exclude cases where α includes multiple combinations of A to C. Furthermore, these expressions do not exclude cases where α includes other elements.

[0018] [1. Overall Configuration] The overall configuration of a vehicle 10 according to this embodiment will be described with reference to FIG. 1 . FIG. 1 is a side view showing the exterior of a vehicle according to one embodiment of the present invention. As shown in FIG. 1 , the vehicle 10 includes a vehicle main body 100, a shaft 200, wheels 300, springs 400, and a stabilizer 500. A seat 600 and a headrest 700 are disposed in the vehicle main body 100. The seat 600 includes a seating surface 610 and a back surface 620. As will be described in detail later, in this embodiment, the normalized pitch moment of inertia of the vehicle 10 is 0.73 or less. The vehicle 10 is, for example, an electric vehicle equipped with a battery. The "normalized pitch moment of inertia" in this embodiment refers to the normalized pitch moment of inertia when a load of 60 kilograms or more and 65 kilograms or less is applied to the driver's seat and the passenger seat, respectively, assuming that passengers are seated in the driver's seat and the passenger seat. The normalized pitch moment of inertia may be 0.73 or less when the load is at least 60 kilograms or more and 65 kilograms or less. The normalized pitch moment of inertia is calculated with the above loads applied to the driver's seat and passenger seat or the floor. The loads may be applied separately to the driver's seat and passenger seat and the floor.

[0019] The shaft 200 is connected to the vehicle main body 100 via a frame or the like. The shaft 200 extends in the left-right direction relative to the traveling direction of the vehicle 10. The wheels 300 are connected to both ends of the shaft 200 and rotate around the shaft 200 as an axis. Two shafts 200 are provided at the front and rear of the vehicle main body 100. Front wheels 310 are connected to the left and right ends of the front shaft 200, respectively. Similarly, rear wheels 320 are connected to the left and right ends of the rear shaft 200, respectively. When there is no need to particularly distinguish between the front wheels 310 and the rear wheels 320, they are simply referred to as wheels 300.

[0020] The spring 400 is provided between the vehicle body 100 and the shaft 200, or between the vehicle body 100 and a frame supporting the shaft 200. In other words, the spring 400 is connected to the vehicle body 100 and the shaft 200. The spring 400 suppresses vibrations generated in the wheel 300 due to unevenness in the road surface from being transmitted to the vehicle body 100. For example, a coil spring is used as the spring 400. The spring 400 is arranged so as to be wound around a damper (or a shock absorber). However, the spring 400 and the damper may be separate.

[0021] In this embodiment, the spring constant of the spring 400 is equal to or less than a predetermined value. Specifically, the value obtained by dividing the combined spring constant of the springs 400 provided for all the wheels 300 provided on the vehicle 10 by the weight of the vehicle 10 is equal to or less than 0.08.

[0022] Specifically, in this embodiment, there are provided a left front wheel 310L, a right front wheel 310R, a left rear wheel 320L, and a right rear wheel 320R. The spring 400 provided for the front wheel 310L is referred to as spring 400FL. The spring 400 provided for the front wheel 310R is referred to as spring 400FR. The spring 400 provided for the rear wheel 320L is referred to as spring 400RL. The spring 400 provided for the rear wheel 320R is referred to as spring 400RR. The springs 400FL, 400FR, 400RL, and 400RR are connected in parallel between the road surface and the vehicle main body 100.

[0023] In the above case, the "composite spring constant" means the composite spring constant of springs connected in parallel. The spring constant of the spring 400FL is k ＦＬ , the spring constant of the 400FR spring is k ＦＲ , the spring constant of the 400RL spring is k ＲＬ , the spring constant of the 400RR spring is k ＲＲ Then, "total spring constant (k ＴＯＴＡＬ ) can be calculated using the following formula (1): ＴＯＴＡＬ = k ＦＬ +k ＦＲ +k ＲＬ +k ＲＲ (Formula 1)

[0024] In this embodiment, since there are four wheels 300, the total spring constant is calculated using the above formula (1), but if the vehicle 10 is provided with n wheels 300 (n is an integer of 2 or more), n springs 400 are also provided corresponding to the wheels 300. Therefore, the total spring constant is calculated as the composite spring constant of the n springs 400 connected in parallel.

[0025] Generally, to improve the riding comfort of the occupants, a spring with a small spring constant (i.e., a soft spring) is used as the spring 400. However, from the viewpoint of the driving performance and safety of the vehicle 10, the spring constant of the spring 400 cannot be reduced without limit. In other words, there is a lower limit to the spring constant of the spring 400 used in the vehicle 10.

[0026] In cases where it is necessary to prevent vehicle 10 from tilting or twisting due to centrifugal force when traveling around a curve, such as in a sports car, a spring with a large spring constant (i.e., a hard spring) is used as spring 400. For example, many mid-ship vehicles in which the engine is located near the center of the vehicle in the fore-and-aft direction are developed for use as sports cars. Therefore, in such mid-ship gasoline-powered vehicles, a spring with a large spring constant is used as spring 400.

[0027] The stabilizer 500 is connected to a member supporting the shaft 200 or the spring 400, or to the vehicle main body 100. The stabilizer 500 is a member that suppresses tilt in the roll direction of the vehicle main body 100 and stabilizes driving. The roll direction means the direction of rotation of the vehicle 10 around the axis corresponding to the direction of travel of the vehicle 10. The stabilizer 500 is an elastic body.

[0028] As will be described in detail later, reducing the spring constant of the spring 400 to improve the ride comfort of the occupant reduces the rigidity in the roll direction. Therefore, it is necessary to take measures to prevent the reduction in roll rigidity. One such measure is to increase the spring constant of the stabilizer 500 to increase the roll rigidity. However, if the roll rigidity of the rear wheels is increased, when a low frequency of 3 Hz or less is input to one wheel (for example, when the rear wheels go over a bump), the occupant will feel uncomfortable due to vibrations in the pitch direction. As a result, the effect of improving ride comfort will be reduced.

[0029] However, this phenomenon can be suppressed by making the roll stiffness of the front wheels greater than that of the rear wheels. In other words, the spring constants of the stabilizer 500 and the springs 400 are determined so that the ratio of the roll stiffness of the front wheels to the roll stiffness of the rear wheels (roll stiffness ratio) is equal to or less than a predetermined value. Specifically, the spring constants of the stabilizer 500 and the springs 400 are determined so that the value obtained by dividing the roll stiffness of the front wheels by the roll stiffness of the rear wheels is equal to or less than 0.45.

[0030] The details are shown in Equation 3 below, but the roll stiffness of the rear wheels is a numerical value obtained by multiplying the square of the tread of the two rear wheels 300 divided by 2 by the sum of the spring constant of the spring 400 provided for either the left or right rear wheels 300 and the spring constant of the rear stabilizer 500. Similarly, the roll stiffness of the front wheels is a numerical value obtained by multiplying the square of the tread of the two front wheels 300 divided by 2 by the sum of the spring constant of the spring 400 provided for either the left or right front wheels 300 and the spring constant of the front stabilizer 500.

[0031] Usually, when priority is given to ride comfort, the spring 400 is determined based on the weight of the vehicle 10, and the stabilizer 500 is determined to match the spring constant of the spring 400. On the other hand, when priority is given to suppressing tilting and twisting of the vehicle 10, as in a sports car, a spring with a large spring constant (i.e., a hard spring) is used as the spring 400, and a stabilizer 500 with a large spring constant is used to match that spring constant.

[0032] As will be described in detail later, in most vehicles, the roll stiffness ratio is greater than 0.45. However, in the vehicle 10 according to this embodiment, when a low-frequency road input of 3 Hz or less is input to a vehicle having a normalized pitch moment of inertia of 0.73 or less, the spring constants of the stabilizer 500 and the springs 400 are set so that the roll stiffness ratio is 0.45 or less in order to reduce discomfort to the occupants and the risk of whiplash caused by behavior in the pitch direction. This configuration is effective in both improving the ride comfort of the occupants and ensuring the roll stiffness of the vehicle 10.

[0033] The seat 600 is disposed inside the vehicle main body 100. The seat 600 is provided in the driver's seat, the passenger seat, and the rear seats. FIG. 1 shows only the seat 600 disposed in the passenger seat. The seat 600 comprises a seating surface 610 and a back surface 620. The seating surface 610 supports the buttocks of the occupant. The back surface 620 supports the back of the occupant. The seating surface 610 and the back surface 620 can be made of a cushioned material, an elastic material, or a low-resilience material. The characteristics required of the low-resilience material used as the back surface 620 will be described later.

[0034] The headrest 700 is attached to the seat 600 inside the vehicle main body 100. The headrest 700 is connected to the upper end of the back portion 620. The headrest 700 supports the head of the occupant. The headrest 700 may be made of a cushioning material, an elastic material, or a low-resilience material. The headrest 700 and the back portion 620 may be integral with each other. The characteristics required of the low-resilience material used for the headrest 700 will be described later.

[0035] 2. Normalized Pitch Moment of Inertia The influence of vibrations or shocks that the vehicle 10 receives from the road surface on an occupant will be described using Figures 2 and 3. Figure 2 is a diagram showing the state of an occupant when the vehicle according to one embodiment of the present invention goes over a step. Figure 3 is a diagram showing the state of an occupant when the vehicle according to one embodiment of the present invention goes over a step. In Figures 2 and 3, the state of the vehicle 10 is shown in the upper part of the drawing, and the state of the occupant in the state of the vehicle 10 (partially enlarged view) is shown in the lower part of the drawing.

[0036] 2 shows a state of the vehicle 10 when the rear wheel 320 of the vehicle 10 runs over an obstacle. When the rear wheel 320 runs over an obstacle, the rear wheel 320 is lifted upward so that the vehicle 10 rotates around the vicinity of the front wheel 310. This movement causes the seat 600 to be thrust forward while the vehicle 10 is tilted forward or while the vehicle 10 is tilting forward, pushing the occupant forward.

[0037] The state of vehicle 10 shown in Figure 3 is a state in which rear wheel 320 of vehicle 10 has run over an obstacle and landed on the road surface. When rear wheel 320 falls from the obstacle onto the road surface, rear wheel 320 moves downward so that vehicle 10 rotates around the vicinity of front wheel 310. This movement causes seat 600 to move downward, and the occupant in the state shown in Figure 2 is returned rearward, causing the occupant's head to collide with headrest 700. After this collision, the head bounces off headrest 700, causing a further collision. When vehicle 10 is viewed from the side as shown in Figures 2 and 3, the direction in which the front and rear ends of vehicle 10 move up and down in opposite directions, or the direction of rotation around an axis parallel to shaft 200 in the side view of vehicle 10, is called the pitch direction.

[0038] Here, the normalized pitch moment of inertia is a dimensionless value obtained by dividing the moment of inertia in the pitch direction by the distance between the mass and the point of application of force. In a side view of the vehicle 10, if the front and rear shared masses of the vehicle 10 are on the shaft 200, the normalized pitch moment of inertia is 1; if the shared masses are on the outside of the shaft 200, the normalized pitch moment of inertia is greater than 1; and if the shared masses are between the front and rear shafts 200, the normalized pitch moment of inertia is less than 1. The smaller the value of the normalized pitch moment of inertia, the faster and larger the pitch behavior in response to road surface input, resulting in a worse ride comfort.

[0039] When the normalized pitch moment of inertia is 0.73 or less, i.e., when the center of gravity of the vehicle 10 is located near the center in the longitudinal direction, the speed at which the occupant's head strikes the headrest 700 is faster than when the normalized pitch moment of inertia is greater. In particular, in the case of a vehicle 10 having a normalized pitch moment of inertia of 0.73 or less, such as an electric vehicle, the speed at which the occupant's head strikes the headrest 700 is very high, which not only increases the discomfort experienced by the occupant but also makes the occupant more susceptible to whiplash injury. It is known that gasoline-powered vehicles with forward-mounted engines have a normalized pitch moment of inertia greater than 0.73 because the center of gravity of the vehicle is located further forward than in electric vehicles. Therefore, the above-described problem is less likely to occur in such gasoline-powered vehicles.

[0040] As described above, in a vehicle 10 having a normalized pitch moment of inertia of 0.73 or less, the occupants are more likely to experience discomfort and suffer whiplash injuries than in a conventional vehicle (a vehicle having a normalized pitch moment of inertia greater than 0.73). Therefore, in the vehicle 10 described above, it is necessary to provide the occupants with a comfortable ride and to take measures to prevent whiplash injuries.

[0041] [3. Test Results] Figure 4 shows test results conducted on a vehicle according to one embodiment of the present invention. The results shown in Figure 4 were obtained for a vehicle 10 having a normalized pitch moment of inertia value of 0.73 or less. Figure 4 shows the results of a pitch behavior test, a sensory test, and a whiplash test, using the types of materials used in the spring 400, stabilizer 500, headrest 700, and back surface portion 620 as parameters. In Figure 4, Samples 1 and 2 are comparative examples, Samples 3 to 5 are examples according to this embodiment, and Sample 6 is a reference example that demonstrates the effect of the back surface portion 620 of the seat 600.

[0042] In Fig. 4, the item "Spring" indicates the type of spring 400 in Fig. 1. The item "Stabilizer" indicates the type of stabilizer 500 in Fig. 1. The item "Headrest" indicates the type of headrest 700 in Fig. 1. The item "Back portion" indicates the type of back portion 620 in Fig. 1.

[0043] The spring constant of the spring 400 depends on the weight of the vehicle 10 on which the spring 400 is installed. In order to provide a similar ride comfort even for different vehicles, the heavier the vehicle 10, the larger the spring constant of the spring 400 used. Therefore, the condition in the "Spring" section is determined by the ratio of the spring constant of the spring 400 to the weight of the vehicle 10. Specifically, as described above, the condition in the "Spring" section is determined by the value obtained by dividing the composite spring constant of all the springs 400 provided on the vehicle 10 by the weight of the vehicle 10. More specifically, "standard" in the "Spring" section means that the value obtained by dividing the composite spring constant by the weight of the vehicle 10 is greater than 0.08. "Low spring" in the "Spring" section means that the value obtained by dividing the composite spring constant by the weight of the vehicle 10 is 0.08 or less. More specifically, the "total spring constant (k ＴＯＴＡＬ The spring constant of each of the springs 400 is determined so that the weight W of the vehicle 10 satisfies the following (Equation 2): ＴＯＴＡＬ / W≦0.08 (Formula 2)

[0044] The spring constant of the stabilizer 500 depends on the spring constant of the spring 400. As described above, the spring constant of the stabilizer 500 is determined to match the spring constant of the spring 400. As an index for this, for example, the condition in the "stabilizer" category is determined by the value obtained by dividing the roll stiffness of the front wheels by the roll stiffness of the rear wheels. Specifically, as described above, "standard" in the "stabilizer" category means that the value obtained by dividing the roll stiffness of the front wheels by the roll stiffness of the rear wheels is greater than 0.45. "High stability" in the "stabilizer" category means that a stabilizer 500 with a larger spring constant than the "standard" condition is used, and that the value obtained by dividing the roll stiffness of the front wheels by the roll stiffness of the rear wheels is 0.45 or less.

[0045] More specifically, the roll stiffness of the front wheels is Fr, the roll stiffness of the rear wheels is Rr, and the spring constant of the front stabilizer 500 is k ＳＴＢ－Ｆ and the spring constant of the rear stabilizer 500 is k ＳＴＢ－Ｒ and the tread of the two front wheels 300 is T Ｆ and the tread of the two rear wheels 300 is T Ｒ Then, the spring constants of the stabilizer 500 and the spring 400 are determined so as to satisfy the following (Equation 3): Fr=(k ＦＬ or k ＦＲ +k ＳＴＢ－Ｆ ) x T Ｆ ２ / 2 Rr = (k ＲＬ or k ＲＲ +k ＳＴＢ－Ｒ ) x T Ｒ ２ / 2 (Formula 3) Fr / Rr≦0.45

[0046] Reducing the spring constant of the spring 400 improves the pitch behavior and the evaluation results of the sensory test, but reduces the roll rigidity of the vehicle 10. Increasing the spring constant of the stabilizer 500 can suppress the reduction in roll rigidity, but in order to suppress the deterioration of the evaluation results of the sensory test, the spring constant of the stabilizer 500 and the spring constant of the spring 400 are adjusted so that the roll rigidity ratio is 0.45 or less. As a result, it is possible to compensate for the reduction in roll rigidity without deteriorating the evaluation results of the sensory test.

[0047] For the items "headrest" and "back portion," "standard" or "low resilience" is displayed according to the surface hardness of each component. First, the evaluation method for these items will be explained using FIG. 5. FIG. 5 is a diagram showing an evaluation method for a headrest and a seat used in a vehicle according to one embodiment of the present invention. FIG. 5 shows a measuring device 800 and a measuring jig 840 for evaluating the characteristics of the headrest 700 and the back portion 620. For example, a mechanical force gauge or a push-pull gauge is used as the measuring device 800. The measuring device 800 includes a main body 810, a movable arm 820, and a head portion 830.

[0048] The main body 810 measures the external force acting on the head 830 and displays the measured external force in a visual manner. The movable arm 820 is a member that can move relative to the main body 810 in the direction of the arrow. The head 830 is fixed to the tip of the movable arm 820. The tip of the head 830 is approximately hemispherical, with a diameter R of 20 mm. The measuring jig 840 is a member separate from the measuring instrument 800, and is a plate-like member with a through hole 841 formed therein. The shape of the through hole 841 in a plan view is approximately the same circle as the shape of the head 830. The diameter of the circle of the through hole 841 is slightly larger than the diameter R of the hemisphere of the head 830. In other words, the through hole 841 has the function of guiding the movement direction of the head 830 when it is pressed into the test object, without creating resistance to the movement of the head 830.

[0049] The state shown in Figure 5 is one in which the tip of head unit 830 is in contact with the test object. A mark 831 is attached to head unit 830, and in this state, the distance from the top surface of measuring jig 840 to mark 831 is 15 mm. When evaluating the characteristics of headrest 700 and back surface unit 620, head unit 830 is further pressed toward the test object from the state shown in Figure 5, and the value (load value) displayed on main body unit 810 is read when mark 831 reaches the top surface of measuring jig 840. The unit of external force in this case is [N].

[0050] In the items "Headrest" and "Back portion," "standard" means that the load value obtained by the above evaluation method for the headrest 700 and back portion 620 is greater than 18 [N], and "low resilience" means that the load value obtained by the evaluation method is 18 [N] or less. In other words, "low resilience" in the items "Headrest" and "Back portion" means that the load value is 18 [N] or less when a hemispherical head portion 830 with a diameter of 20 mm is brought close to the headrest 700 or back portion 620 and the head portion 830 is displaced 15 mm from the position where it contacts the headrest 700 or back portion 620. As will be described in detail later, the portion of the back portion 620 where a low resilience material is used is the upper center portion 641 (see FIG. 8 ).

[0051] The "Pitch Behavior" item is a value indicating the behavior in the pitch direction (magnitude of vibration) when a low frequency of 3 Hz or less is input as a road surface input to a vehicle according to this embodiment (a vehicle having a normalized pitch moment of inertia value of 0.73 or less). The smaller the absolute value of the "Pitch Behavior" value, the smaller the behavior in the pitch direction, and therefore the smaller the impact transmitted to the occupants. In other words, the pitch behavior of Sample 1 is "-212.15" and the pitch behavior of Sample 3 is "-207.09", and therefore Sample 3 transmits a smaller impact to the occupants when the vehicle 10 goes over an obstacle than Sample 1.

[0052] The "sensory test" item is a numerical representation of the impression of a tester when the tester rides in each sample vehicle 10 and a low frequency of 3 Hz or less is input as a road surface input. The smaller this number, the better the ride comfort. The evaluation value of the sensory test is not used simply as an index of comfort, but is an important factor in determining whether or not a product can be shipped. It is not desirable to ship a vehicle 10 with the same specifications as a sample with a sensory test value of more than 3 as a product. Therefore, a sensory test value of 3 or less is a very important indicator.

[0053] The "whiplash" item is a result calculated based on the difference in acceleration between the occupant's head and neck during a rear-end collision. If the difference in these accelerations is small, it is marked with an "O", and if the difference in acceleration is greater than "O" but within the acceptable range, it is marked with a "△". Like the sensory test, the "whiplash" result is an important factor that determines whether or not a product can be shipped. In order to ship a product, the "whiplash" result must be "O" or "△".

[0054] The results of each sample in Figure 4 will be explained. Comparing Sample 1 and Sample 2, the difference is that Sample 1's headrest 700 is "standard," while Sample 2's headrest 700 is "low resilience." By changing the headrest 700 from "standard" to "low resilience," the sensory test score improved from "5.25" to "3.38." On the other hand, this change slightly worsened the whiplash test score, but it remained at "Fair." However, because the sensory test score is required to be 3 or less, it is undesirable to ship Sample 2 as a product.

[0055] One possible solution to further reduce the sensory test value would be to change headrest 700 to a softer one (one that reduces the load value obtained by the measurement method shown in Figure 5). However, if headrest 700 of sample 2 is made even softer, the sensory test value will decrease, but the whiplash test result will fall below the standard value (the result will be "X"). Therefore, headrest 700 of sample 2 cannot be made even softer.

[0056] Next, comparing Sample 1 and Sample 3, the difference between them is that Sample 1 has a "standard" spring 400, while Sample 3 has a "low spring" spring 400. By changing the spring 400 from "standard" to "low spring," the sensory test value improved from "5.25" to "2.5." This change did not change the whiplash test result, and the "○" rating was maintained. In other words, Sample 3 cleared the standard values ​​in both the sensory test and the whiplash test.

[0057] On the other hand, as described above, there is a lower limit to the spring constant of spring 400 from the viewpoint of the driving performance and safety of vehicle 10. Therefore, when attempting to further improve the sensory test value from sample 3, the spring constant of spring 400 cannot be made smaller than that of sample 3. Therefore, in order to make the sensory test value smaller than that of sample 3, it is necessary to change components other than spring 400.

[0058] Next, comparing Sample 3 and Sample 4, the difference is that Sample 3's headrest 700 is "standard," while Sample 4's headrest 700 is "low resilience." By changing the headrest 700 from "standard" to "low resilience," the sensory test score improved from "2.5" to "1.125." Meanwhile, the whiplash test result worsened slightly as a result of this change, but remained at "Fair." In other words, Sample 4 cleared the standard values ​​for both the sensory test and the whiplash test. Furthermore, Sample 4's sensory test score was further improved compared to Sample 3.

[0059] Next, comparing Sample 3 and Sample 5, the difference between them is that the stabilizer 500 of Sample 3 is "standard" while the stabilizer 500 of Sample 5 is "high stability." By changing the stabilizer 500 from "standard" to "high stability," both the sensory test values ​​and the whiplash test results cleared the standard values.

[0060] As described above, by changing the springs 400 from "standard" to "low springs," both the sensory test values ​​and whiplash results can satisfy the standard values. In other words, when the normalized pitch moment of inertia of the vehicle 10 is 0.73 or less, if the value obtained by dividing the composite spring constant of all springs 400 provided in the vehicle 10 by the weight of the vehicle 10 is 0.08 or less, both the sensory test values ​​and whiplash results can satisfy the standard values.

[0061] Comparing Sample 2 and Sample 6, both headrests 700 are "low resilience", but the difference between them is that the back surface 620 of Sample 2 is "standard", while the back surface 620 of Sample 6 is "low resilience". By changing the back surface 620 from "standard" to "low resilience", the sensory test value improves from "3.38" to "1.25". This change improves the whiplash test result from "△" to "◯". In other words, by changing the back surface 620 from "standard" to "low resilience", it is possible to reduce the sensory test value while improving the whiplash test result.

[0062] FIG. 6 shows the results of comparing the vehicle 10 shown in Sample 3 of FIG. 4 with other vehicles for the value (spring constant / vehicle weight) obtained by dividing the composite spring constant of all springs 400 provided on the vehicle 10 by the weight of the vehicle 10. In FIG. 6, "◯" indicates the result for the vehicle 10 shown in Sample 3 of FIG. 4. "Δ" indicates the result for the vehicle 10 shown in Sample 1 of FIG. 4. "X" indicates the result for other vehicles (including vehicles with a normalized pitch moment of inertia greater than 0.73) that are different from the sample shown in FIG. 4. As shown in FIG. 6, the "spring constant / vehicle weight" is 0.08 or less in Sample 3, while the "spring constant / vehicle weight" is greater than 0.08 in the other samples. In other words, the condition that the "spring constant / vehicle weight" is 0.08 or less is not a general condition, but a condition specific to this embodiment.

[0063] FIG. 7 shows the results of comparing the vehicle 10 shown in Sample 6 of FIG. 4 with other vehicles with respect to the ratio of the roll stiffness of the front wheels to the roll stiffness of the rear wheels (roll stiffness ratio), which is determined by the spring constant of the stabilizer 500 and the spring constant of the spring 400. In FIG. 7, "◯" indicates the result for the vehicle 10 shown in Sample 6 of FIG. 4. "Δ" indicates the result for the vehicle 10 shown in Sample 3 of FIG. 4. "X" indicates the result for other vehicles (including vehicles with a normalized pitch moment of inertia greater than 0.73) different from the sample shown in FIG. 4. As shown in FIG. 7, "Fr / Rr (roll stiffness ratio)" is 0.45 or less in Sample 6, whereas "Fr / Rr" is greater than 0.45 in the other samples.

[0064] 4. Configuration of rear portion 620 The configuration of rear portion 620 will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a front view showing the configuration of the rear portion of a seat used in a vehicle according to one embodiment of the present invention. Fig. 9 is a perspective view showing the configuration of the rear portion of a seat used in a vehicle according to one embodiment of the present invention.

[0065] As shown in FIGS. 8 and 9 , the back portion 620 includes a lower back portion 630 and an upper back portion 640. The lower back portion 630 is a portion of the back portion 620 that is closer to the seating surface 610. The upper back portion 640 is a portion of the back portion 620 that is closer to the headrest 700. As will be described in detail later, a boundary 649 between the lower back portion 630 and the upper back portion 640 is located at a vertical distance of 300 mm or more and 400 mm or less from the top surface of the seating surface 610. By positioning the boundary 649 within the above range, when an occupant sits in the seat 600, the occupant's shoulder blades face the upper back portion 640, regardless of the occupant's height. In other words, when the occupant leans against the seat 600, the occupant's shoulder blades come into contact with the upper back portion 640. The position of the boundary 649 can be selected from the above range, but for example, the position of the boundary 649 is 350 mm from the upper surface of the seat portion 610.

[0066] The lower back surface 630 includes a lower central portion 631 and lower side portions 632, 633. The lower central portion 631 supports the occupant's back. The lower side portions 632, 633 protrude forward from the lower central portion 631 and prevent the occupant's back from moving sideways. In other words, the lower side portions 632, 633 keep the occupant's back near the center of the seat 600. The lower central portion 631 and the lower side portions 632, 633 are made of the same material (e.g., polyurethane). In other words, the surface hardness of the lower central portion 631 and the surface hardness of the lower side portions 632, 633 are the same. Here, "same surface hardness" means that the load values ​​obtained by measurement using the measuring device 800 shown in FIG. 5 are approximately the same. "Approximately the same load values" means that the difference between the two measured load values ​​is within the measurement error (±5%) of the measuring device 800.

[0067] The upper back surface 640 includes an upper central portion 641 and upper side portions 642, 643. The upper central portion 641 supports the occupant's shoulder blades and shoulders. In the front-to-rear direction, the upper central portion 641 supports the occupant at approximately the same position as the lower central portion 631. The upper side portions 642, 643 protrude forward from the upper central portion 641 and prevent the occupant's shoulder blades and shoulders from moving sideways. In other words, the upper side portions 642, 643 keep the occupant's shoulder blades and shoulders near the center of the seat 600. The boundary between the upper central portion 641 and the upper side portion 642, and the boundary between the upper central portion 641 and the upper side portion 643, are curved. In other words, these boundaries are convex and curved. In other words, the inclination angle of these boundaries with respect to the horizontal plane gradually increases from the lateral ends toward the center.

[0068] The upper portions 642 and 643 are made of the same material. On the other hand, the upper central portion 641 is made of a different material from the upper portions 642 and 643. For example, polyurethane is used for the upper portions 642 and 643, and a low-resilience material is used for the upper central portion 641. In other words, the surface hardness of the upper central portion 641 is different from the surface hardness of the upper portions 642 and 643. Here, the lower back portion 630 may be referred to as the "first portion," and the upper central portion 641 may be referred to as the "second portion." If the upper portions 642 and 643 are made of a low-resilience material, like the upper central portion 641, the entire upper back portion 640 may be referred to as the "second portion."

[0069] As shown in FIG. 9 , an upper central support member 644 is provided on the rear side of the upper central portion 641. A pad hole 645 for inserting a bushing of the headrest 700 is formed in the upper central support member 644. As shown in FIG. 9 , the upper central portion 641 does not reach the pad hole 645 in the thickness direction of the rear portion 620. In other words, the pad hole 645 is surrounded by the upper central support member 644. If the upper central portion 641, which is made of a low-resilience material, were to reach the pad hole 645, for example, in the event of a rear-end collision, an occupant moving rearward could come into contact with a component such as the bushing of the headrest 700 and injure their shoulder blades or shoulders. To prevent this from occurring, the pad hole 645 is surrounded by the upper central support member 644. The upper central support member 644 is made of the same material as the lower central portion 631 and the lower portions 632 and 633. For example, the upper central support member 644 is made of polyurethane. The upper central support member 644 and the lower central portion 631 may be formed integrally or separately. Similarly, the upper central support member 644 and the upper portions 642, 643 are made of the same material. The upper central support member 644 and the upper portions 642, 643 may be formed integrally or separately.

[0070] In this embodiment, the thickness T1 of the upper central portion 641 is substantially the same as the thickness T2 of the upper central support member 644 sandwiched between the pad hole 645 and the upper central portion 641. Thicknesses T1 and T2 do not have to be completely identical; for example, the difference between thicknesses T1 and T2 may be 10% or less of either thickness. This configuration can prevent the above-mentioned phenomenon from occurring even in the event of a rear-end collision.

[0071] The load value obtained for the headrest 700 may be referred to as the "first load value." The load value obtained for the upper central portion 641 may be referred to as the "second load value." The load value obtained for the lower back portion 630 may be referred to as the "third load value." In this case, the first load value and the second load value are smaller than the third load value.

[0072] 10 is a diagram showing the ratio of the surface hardness of the headrest to the lower back surface of a seat used in a vehicle according to an embodiment of the present invention. Fig. 10 shows the ratio of the surface hardness of the headrest 700 to the surface hardness of the lower back surface 630 for the seat 600 according to the present embodiment and seats according to several comparative examples. The several comparative examples are seats that are standard equipment in different commercially available vehicles.

[0073] The vertical axis of Fig. 10 (headrest HR / lower part of back surface BA) represents the ratio of the first load value of the headrest 700 to the third load value of the lower back surface 630 measured by the method shown in Fig. 5 . In other words, the vertical axis of Fig. 10 represents the value obtained by dividing the first load value by the third load value. The smaller this ratio, the softer the surface of the headrest 700 is relative to the lower back surface 630. As shown in Fig. 10 , the ratio is greater than 0.7 in all comparative examples, whereas the ratio is 0.7 or less in the examples.

[0074] Fig. 11 is a diagram showing the ratio of the surface hardness of the first portion to the second portion of a seat used in a vehicle according to one embodiment of the present invention. The example and several comparative examples in Fig. 11 are the same as those shown in Fig. 10. Fig. 11 shows the ratio of the surface hardness of the upper central portion 641 (second portion) to the surface hardness of the lower back portion 630 (first portion) for the seat 600 according to this embodiment and the seats according to several comparative examples.

[0075] The vertical axis of Fig. 11 (upper part of back surface BA / lower part of back surface BA) represents the ratio of the second load value of the upper central portion 641 to the third load value of the lower part of back surface 630 measured by the method shown in Fig. 5 . In other words, the vertical axis of Fig. 11 represents the value obtained by dividing the second load value by the third load value. The smaller this ratio, the softer the surface of the upper central portion 641 is relative to the lower part of back surface 630. As shown in Fig. 11 , the ratio is greater than 0.8 in most comparative examples, with the exception of a few comparative examples, whereas the ratio is 0.8 or less in the examples.

[0076] 10 and 11, in the example, the value obtained by dividing the first load value by the third load value is 0.7 or less, and the value obtained by dividing the second load value by the third load value is 0.8 or less. In other words, in the seat 600 according to the example, the surface hardness of both the headrest 700 and the upper central portion 641 is softer than that of the seat installed in a commercially available vehicle, relative to the lower back portion 630. No seat with such characteristics has existed in the past.

[0077] As described above, by making the surface hardness of the headrest 700 and the upper central portion 641 softer than that of the lower back surface 630, it is possible to reduce the impact caused by the headrest 700 colliding with the occupant's head and the impact caused by the upper central portion 641 colliding with the occupant's shoulder blades and shoulders, even when the vehicle 10 vibrates in the pitch direction. Furthermore, by making the surface hardness of the lower back surface 630 harder than that of the upper central portion 641, it is possible to suppress deterioration of the results of a whiplash test in a rear-end collision of the vehicle 10 from behind. For example, as shown in FIG. 4 (comparison between Sample 2 and Sample 6), by using a low-resilience material for the headrest 700 and the back surface portion 620 (specifically, the upper central portion 641), it is possible to reduce the value of the sensory test without deteriorating the results of the whiplash test.

[0078] By using a low-resilience material for upper central portion 641, the shoulders of the occupant's body that protrude rearward are more likely to move rearward when vehicle 10 is hit from behind. At that time, headrest 700 also moves rearward together with upper central portion 641, which makes it possible to prevent the results of the whiplash test from deteriorating.

[0079] Because the surface hardness of the upper side portions 642, 643 is harder than that of the upper central portion 641, when the vehicle 10 is hit from behind, the occupant's shoulder blades and head will move rearward due to the upper central portion 641 and headrest 700, both of which are made of soft materials, but the outer sides of the occupant's shoulders will be held by the upper side portions 642, 643. This makes it possible to suppress shaking of the occupant in the left-right direction. Furthermore, because the boundary between the upper central portion 641 and the upper side portions 642 has the above-mentioned shape, it is possible to make it less likely that the occupant will notice that the surface hardness of the upper central portion 641 is different from that of the upper side portions 642.

[0080] As described above, the vehicle 10 according to this embodiment can meet the standard values ​​in both the sensory test and the whiplash test, thereby providing the occupants with a comfortable ride and safety.

[0081] The above-described embodiments of the present invention can be combined as appropriate as long as they are not mutually inconsistent. A product in which a person skilled in the art appropriately adds or deletes components or modifies the design, or adds or omits steps or modifies conditions based on each embodiment, is also included within the scope of the present invention as long as it includes the gist of the present invention.

[0082] Even if there are other effects and advantages different from those brought about by the above-mentioned embodiments, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention.

[0083] 1 to 6: Samples, 10: Vehicle, 100: Vehicle body, 200: Shaft, 300: Wheel, 310: Front wheel, 320: Rear wheel, 400: Spring, 500: Stabilizer, 600: Seat, 610: Seat surface, 620: Back surface, 700: Headrest, 800: Measuring instrument, 810: Body, 820: Movable arm, 830: Head, 831: Mark, 840: Measuring jig, 841: Through hole

Claims

1. A vehicle with a normalized pitch moment of inertia of 0.73 or less when a load of 60 kg or more and 65 kg or less is applied to the driver's seat and passenger seat, comprising: a vehicle main body; a shaft connected to said vehicle main body; n wheels (n is an integer of 2 or more) connected to said shaft; and n springs connected to said vehicle main body and said shaft and provided for each of said n wheels, wherein the value obtained by dividing the composite spring constant of said n springs by the weight of said vehicle is 0.08 or less.

2. A vehicle as described in claim 1, wherein the vehicle main body comprises a seat having a seating surface and a back surface, and a headrest attached to the seat, the back surface comprising a first portion provided on a side closer to the seating surface and a second portion provided on a side closer to the headrest, and wherein when a hemispherical head portion having a diameter of 20 mm is brought close to the headrest and the displacement of the head portion from the position where the head portion contacts the headrest is 15 mm, the first load value is 0.7 times or less of the third load value when the head portion is brought close to the first portion and the displacement of the head portion from the position where the head portion contacts the first portion is 15 mm.

3. A vehicle as described in claim 1, wherein the vehicle main body comprises a seat having a seating surface and a back surface, and a headrest attached to the seat, the back surface comprising a first portion provided on a side closer to the seating surface and a second portion provided on a side closer to the headrest, and wherein a first load value when a hemispherical head portion having a diameter of 20 mm is brought close to the headrest and the displacement from the position where the head portion contacts the headrest is 15 mm, and a second load value when the head portion is brought close to the second portion and the displacement from the position where the head portion contacts the second portion is 15 mm, are smaller than a third load value when the head portion is brought close to the first portion and the displacement from the position where the head portion contacts the first portion is 15 mm.

4. The vehicle according to claim 3, wherein the boundary between the first portion and the second portion is at a position that is 300 mm or more and 400 mm or less in vertical distance from the upper surface of the seating portion.

5. The vehicle according to claim 3, wherein the value obtained by dividing the first load value by the third load value is 0.7 or less, and the value obtained by dividing the second load value by the third load value is 0.8 or less.

6. The vehicle according to claim 1, further comprising a stabilizer, wherein the roll stiffness of the front wheels is defined as a value obtained by multiplying the square of the tread of the two front wheels divided by 2 by the sum of the spring constant of the spring provided for one of the two front wheels and the spring constant of the front stabilizer, and the roll stiffness of the rear wheels is defined as a value obtained by multiplying the square of the tread of the two rear wheels divided by 2 by the sum of the spring constant of the spring provided for one of the two rear wheels and the spring constant of the rear stabilizer, and the value obtained by multiplying the square of the tread of the two rear wheels divided by 2 by the sum of the spring constant of the spring provided for one of the two rear wheels and the spring constant of the rear stabilizer is defined as 7. The vehicle of claim 1, wherein the vehicle is an electric vehicle further comprising a battery.

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