Vehicle

Abstract

A vehicle (1) comprises: steering wheels (111, 112, 113) that are steered on the basis of a turning operation or a turning command; a steering mechanism (12) that steers the steering wheels; and a control device (13) that can operate the steering mechanism (12) separately from or in addition to the turning operation or the turning command. The control device (13) operates the steering mechanism (12) separately from or in addition to the turning operation or the turning command so that when the total lateral acceleration obtained by combining at least revolution-induced lateral acceleration induced by revolution of the vehicle and rotation-induced lateral acceleration induced by rotation of the vehicle is changing together with the turning of the vehicle based on the turning operation or the turning command, total lateral acceleration in which peaks are suppressed by the rotation-induced lateral acceleration combined with the revolution-induced lateral acceleration is generated.

Description

vehicle

[0001] The present invention relates to a vehicle.

[0002] 2. Description of the Related Art A vehicle is known in which, when a driver operates a steering device, the front wheels are steered and the rear wheels are steered as an auxiliary to turn the vehicle. Such a vehicle is disclosed, for example, in Patent Document 1.

[0003] In the vehicle disclosed in Patent Document 1, the front wheels are mechanically connected to the steering wheel, and the rear wheels are connected to an actuator. When the driver operates the steering wheel, the front wheels are steered and the rear wheels are assisted by the actuator. The steering angle of the rear wheels is calculated by a vehicle motion control device installed in the vehicle. The vehicle motion control device calculates a target value for the yaw motion of the vehicle and calculates a first target rear wheel steering angle so that the vehicle has desired yaw motion characteristics. The vehicle motion control device calculates a target value for the lateral motion of the vehicle and calculates a second target rear wheel steering angle so that the vehicle has desired lateral motion characteristics. The vehicle motion control device calculates a final rear wheel steering angle by adding together the calculated first target rear wheel steering angle and second target rear wheel steering angle.

[0004] Japanese Patent Application Publication No. 11-91608

[0005] In the vehicle of Patent Document 1, the rear wheels are steered based on parameters of both the yaw motion and the lateral motion of the vehicle. According to the vehicle of Patent Document 1, it is possible to control two vehicle motions, namely the yaw motion and the lateral motion. Furthermore, according to this vehicle, by appropriately setting each parameter, it is possible to easily tune the vehicle motion characteristics even for different vehicle models.

[0006] On the other hand, in addition to the dynamic characteristics, a vehicle is also required to have a good ride quality that is perceived by the occupants. Examples of indicators of a vehicle's ride quality include the ride comfort, responsiveness to operation, and enjoyment of the vehicle. Here, if the vehicle's dynamic characteristics are set, it is considered that the ride quality perceived by the occupants is also set. For example, if the vehicle's dynamic characteristics are made sporty, it is considered that a driver who prefers sporty vehicles will find the ride enjoyable. However, the impressions that people have of vehicle dynamics vary. Therefore, the ride quality of a vehicle does not necessarily match the vehicle's dynamic characteristics.

[0007] An object of the present invention is to optimize the physical quantity of load applied to an object at any position on a vehicle, thereby increasing the degree of freedom in designing vehicle characteristics.

[0008] The present inventor has studied the ride quality of a vehicle. One example of when a vehicle occupant feels the vehicle's behavior is when the vehicle is turning. Therefore, the present inventor conducted an experiment to investigate the physical quantities loaded on the driver when the vehicle is turning. In the experiment, a rear-wheel non-steering vehicle was used, in which the front wheels were steered by a test driver and the rear wheels were not steered. The test driver drove the vehicle straight at a predetermined speed and then operated the steering device a predetermined amount. After operating the steering device a predetermined amount, the test driver maintained the operation amount of the steering device for a while and continued to turn the vehicle. An IMU (Inertial Measurement Unit) was installed in the vehicle near the driver's seat to measure various physical quantities.

[0009] 2 is a graph showing changes in various physical quantities when a rear-wheel non-steerable vehicle turns. Graph (A) shows the vehicle speed, graph (B) shows the steering device operation amount, and graph (C) shows the yaw rate measured by the IMU. In graph (D), the solid line shows the lateral acceleration measured by the IMU, and the dashed line shows the lateral acceleration obtained by multiplying the yaw rate measured by the IMU by the velocity.

[0010] Referring to graph (A), in this experiment, the vehicle speed was maintained at a roughly constant value when traveling straight and when turning. Referring to graphs (B) and (C), for a while after the start of measurement, the test driver drove the vehicle straight without operating the steering device. During this time, the yaw rate measured by the IMU was substantially zero. From the time the test driver began to operate the steering device until the amount of operation reached a predetermined amount, i.e., while the test driver was operating the steering device, the yaw rate measured by the IMU increased linearly. Thereafter, while the test driver maintained the amount of operation of the steering device at a predetermined value, the yaw rate measured by the IMU remained substantially constant.

[0011] As shown by the dashed line in graph (D), the lateral acceleration calculated by multiplying the yaw rate measured by the IMU by the velocity increased linearly while the test driver operated the steering device, similar to graph (C). Thereafter, the lateral acceleration calculated by multiplying the yaw rate measured by the IMU by the velocity remained substantially constant. Meanwhile, as shown by the solid line in graph (D), while the test driver operated the steering device, the lateral acceleration actually measured by the IMU increased sharply and then decreased sharply. Thereafter, while the test driver maintained a predetermined steering amount, the lateral acceleration measured by the IMU, shown by the solid line, remained substantially constant, equal to the lateral acceleration calculated by multiplying the yaw rate measured by the IMU by the velocity, shown by the dashed line. After the experiment, the inventor interviewed the test driver about the ride quality of the vehicle. The test driver informed the inventor that his head shook while operating the steering device, making it difficult to drive.

[0012] The present inventor further studied vehicle ride quality to clarify the ride quality felt by test drivers. The inventor focused on lateral acceleration measured by an IMU, which showed a change in value different from other physical quantities. The inventor analyzed the motion of a vehicle during a turn and conducted a detailed study of the lateral acceleration measured by the IMU. Note that in this specification, the phenomenon in which the lateral acceleration measured by the IMU increases or decreases to produce a peak during a turning transition when the steering device is operated is referred to as a lateral acceleration spike.

[0013] FIG. 3 is a schematic diagram showing the movement of a vehicle when turning. For example, suppose that vehicle 100 turns from a certain position at a constant speed and with a constant turning radius. In this case, the vehicle performs uniform circular motion, tracing a circular trajectory centered on point C1, and after completing one revolution, returns to the original position in the original attitude. In other words, the vehicle performs revolution around point C1. Meanwhile, while the vehicle revolves around point C1, the attitude of the vehicle, i.e., the traveling direction, changes from moment to moment. If the vehicle returns to the original position in the original attitude after one revolution, the vehicle rotates once on its axis during one revolution. The inventors have conducted a more detailed study of the revolution and rotation of a vehicle when turning.

[0014] Assuming that the vehicle turns by rotating once on its axis while revolving around one revolution, consider a case in which a vehicle at a constant speed turns with a certain revolution radius and a certain rotation radius. Referring to the dashed line in graph (D) of Figure 2, the lateral acceleration obtained by multiplying the yaw rate measured by the IMU by the velocity is the acceleration component of centrifugal force. Therefore, the lateral acceleration obtained by multiplying the yaw rate measured by the IMU by the velocity, shown by the dashed line, can be considered to be the lateral acceleration caused by the revolution. In fact, the lateral acceleration obtained by multiplying the yaw rate measured by the IMU by the velocity increases linearly once the vehicle begins to turn and remains constant while the vehicle is making a steady turn (uniform circular motion).

[0015] Here, it is considered that the driver of a turning vehicle is primarily subjected to lateral acceleration resulting from the sum of lateral acceleration due to the vehicle's revolution and lateral acceleration due to its rotation. When a vehicle turns so that it rotates once per revolution, the angular velocity of the revolution and the angular velocity of the rotation can be considered to be equal. Since lateral acceleration is calculated as the product of angular velocity and vehicle speed, it depends on the angular velocity if the vehicle speed is constant. If the lateral acceleration due to revolution, shown by the dashed line in graph (D) of Figure 2, increases linearly, then the lateral acceleration due to rotation will also increase linearly, and the combined lateral acceleration, shown by the solid line, will also increase linearly.

[0016] The inventors have focused on the fact that lateral acceleration spikes occur during the period when the steering device is operated, i.e., during the turning transition period. It is believed that immediately after the steering device is operated, the front wheels are steered and the vehicle begins to rotate. Meanwhile, it is believed that a short period of time is required between the steering device operation and the start of the vehicle's revolution. In other words, it is believed that the vehicle's rotation begins before the vehicle's revolution. As a result, during the turning transition period, the driver is first subjected to the lateral acceleration due to the vehicle's rotation, followed by the lateral acceleration due to the vehicle's revolution. Based on this, the inventors have concluded that the lateral acceleration spike during the turning transition period shown in graph (D) exhibits a different tendency from other physical quantities due to the influence of the lateral acceleration due to the vehicle's rotation.

[0017] Based on the above, the inventors have concluded that the lateral acceleration spikes that appear during the turning transition shown by the solid line in graph (D) are caused by lateral acceleration due to rotation. The inventors have also conceived the following invention, believing that if this lateral acceleration due to rotation can be controlled, it will be possible to variably adjust the ride quality of the vehicle as perceived by passengers and the lateral acceleration applied to cargo loaded in the vehicle.

[0018] (1) A vehicle of the present invention includes a steering wheel that is steered based on a turning operation or a turning command, a steering mechanism that steers the steering wheel, and a control device that can operate the steering mechanism separately from or in addition to the turning operation or turning command. When a total lateral acceleration that is a combination of at least the revolution-induced lateral acceleration due to the revolution of the vehicle and the rotation-induced lateral acceleration due to the rotation of the vehicle changes as the vehicle turns based on the turning operation or turning command, the control device operates the steering mechanism separately from or in addition to the turning operation or turning command so as to generate a total lateral acceleration whose peak is suppressed by the rotation-induced lateral acceleration combined with the revolution-induced lateral acceleration.

[0019] In the above vehicle, when the total lateral acceleration is changing, the peak of the total lateral acceleration is suppressed by controlling the rotation-induced lateral acceleration, which is one of the revolution-induced lateral acceleration and the rotation-induced lateral acceleration included in the total lateral acceleration. That is, the peak of the lateral acceleration spike is suppressed by controlling the rotation-induced lateral acceleration during a turning transition. The above vehicle controls the rotation-induced lateral acceleration to a desired value while suppressing the peak of the lateral acceleration spike during a turning transition. This allows, for example, optimization of the ride quality felt by passengers in a vehicle carrying passengers. Furthermore, in a vehicle carrying cargo, optimization of the lateral acceleration applied to the cargo. Therefore, the above vehicle allows optimization of the physical quantity applied to an object at any position on the vehicle, thereby increasing the degree of freedom in designing vehicle characteristics.

[0020] (2) In the vehicle of (1) above, when the total lateral acceleration is changing as the vehicle turns, the control device operates the steering mechanism to generate a total lateral acceleration whose peak is suppressed by the rotation-induced lateral acceleration, which is a value that is less than the peak of the non-additionally controlled rotation-induced lateral acceleration that would occur due to the rotation of the vehicle if the steering mechanism were not operated separately from or in addition to a turning operation or the turning command, in absolute value.

[0021] In the above vehicle, when the vehicle specifications, driving conditions, measurement conditions, etc. are all the same, the total lateral acceleration generated during a turning transition is reduced compared to a vehicle in which the auxiliary steering mechanism is not activated. Furthermore, the direction of the controlled rotation-induced lateral acceleration can be either toward the inside or outside of the turn. Therefore, with the above vehicle, the physical quantity applied to an object at any position on the vehicle can be optimized, increasing the degree of freedom in designing vehicle characteristics.

[0022] (3) A program of the present invention is used in the vehicle control device described in (1) or (2) above. The program causes a computer to function as a steering mechanism operating unit that operates a steering mechanism, and when a total lateral acceleration, which is the sum of at least the revolution-induced lateral acceleration resulting from the revolution of the vehicle and the rotation-induced lateral acceleration resulting from the rotation of the vehicle, changes in association with a turning operation or a turning command, the steering mechanism operating unit operates the steering mechanism separately from or in addition to a turning operation or a turning command so as to generate a total lateral acceleration whose peak is suppressed by the rotation-induced lateral acceleration combined with the revolution-induced lateral acceleration.

[0023] Hereinafter, each configuration and terminology of the present invention will be explained.

[0024] A "vehicle" is, for example, a vehicle in which people ride. The vehicle may be, for example, a vehicle that carries cargo. The vehicle can, for example, carry at least one of people and cargo. The vehicle includes, for example, seats for accommodating passengers. The seats may be, for example, seats or standing seats. The vehicle includes, for example, at least one seat. The location of the seats is not particularly limited. The vehicle includes, for example, a front seat. The vehicle includes, for example, a rear seat located behind the front seat. The vehicle may be, for example, a manually driven vehicle that runs by operation of a driver, or an automatically driven vehicle that runs without operation of a driver. The vehicle may be, for example, a vehicle that can switch between manual driving and automatic driving. The vehicle may be, for example, an engine vehicle or an electric vehicle. In other words, the power source of the vehicle is not particularly limited.

[0025] For example, a vehicle may have at least one "steering wheel." A vehicle may have multiple steering wheels, for example. In the case of a human-driven vehicle, the steering is performed, for example, by the driver operating the steering mechanism. That is, the steering wheels are steered, for example, based on the driver's turning operation. In the case of an autonomous vehicle, the steering wheels are steered, for example, based on a turning command from a control device. The turning command is, for example, a command transmitted to turn the vehicle at a predetermined turning radius. The turning command is, for example, input to the steering mechanism to turn the vehicle. When a vehicle has multiple steering wheels, at least some of the multiple steering wheels may be steered based on a turning operation. At least some of the multiple steering wheels may be steered based on a turning command. The steering wheels may be, for example, front wheels or rear wheels of the vehicle. For example, the steering wheels may be positioned so that at least a portion is located forward of the center of gravity of the vehicle, or at least a portion is located rearward of the center of gravity of the vehicle. For example, the steering wheels may be positioned so that at least a portion is located on the center of gravity of the vehicle. The steering wheel may be provided, for example, at the center of the vehicle in the left-right direction. Multiple steering wheels may be provided. When the vehicle has multiple steering wheels, for example, one steering wheel may be provided so that at least a portion thereof is located to the left of the center of the vehicle in the left-right direction, and another steering wheel may be provided so that at least a portion thereof is located to the right of the center of the vehicle in the left-right direction.

[0026] The steering wheel may be, for example, a primary steering wheel steered to turn the vehicle. The steering wheel may also be an auxiliary steering wheel steered to control rotation-induced lateral acceleration. The steering wheel may be steered to control rotation-induced lateral acceleration in addition to turning the vehicle. That is, the steering wheel may be, for example, both primary and auxiliary steering. The steering wheel steered based on a turning operation or a turning command may be the same as or different from the steering wheel steered to control rotation-induced lateral acceleration. When a vehicle has multiple steering wheels, for example, some of the multiple steering wheels may be primary steering wheels and some may be auxiliary steering wheels. For example, some of the multiple steering wheels may be primary steering wheels and some may be both primary steering wheels and auxiliary steering wheels. For example, some of the multiple steering wheels may be auxiliary steering wheels and some may be both primary steering wheels and auxiliary steering wheels. For example, some of the multiple steering wheels may be both auxiliary steering wheels and some may be both primary steering wheels and auxiliary steering wheels. For example, all of the multiple steering wheels may be both primary steering wheels and auxiliary steering wheels.

[0027] The "steering mechanism" is, for example, mechanically connected to the steering wheel. In this case, the steering mechanism is, for example, a steering device. The steering mechanism operates, for example, based on a turning operation by a driver. The steering mechanism may be, for example, electrically connected to the steering wheel. The steering mechanism steers, for example, the steering wheel by electronic control. In this case, the steering mechanism is, for example, a steer-by-wire system. The steering mechanism operates, for example, based on a turning command from a control device. The steering mechanism is, for example, mechanically connected to at least one steering wheel. The steering mechanism may be, for example, electrically connected to at least one steering wheel. The steering mechanism may include, for example, a main steering mechanism that steers the steering wheel based on a turning operation or a turning command, and an auxiliary steering mechanism that steers the steering wheel to control the rotation-induced lateral acceleration. The steering mechanism is steered, for example, based on a rotation-induced lateral acceleration control command transmitted from the control device. The rotation-induced lateral acceleration control command is, for example, a command transmitted to control the rotation-induced lateral acceleration.

[0028] The "control device" operates a steering mechanism separately from a turning operation or a turning command, for example, when the total lateral acceleration is changing due to the turning of the vehicle based on a turning operation or a turning command. A specific explanation will be given below. Assume that the vehicle has multiple steering wheels. For example, when one steering wheel (first steering wheel) is steered based on a turning operation or a turning command to turn the vehicle, the control device operates a steering mechanism that steers another steering wheel (second steering wheel) to generate a total lateral acceleration with a reduced peak. In this case, the steering mechanism that steers the other steering wheel is steered separately from the turning operation or turning command. As an example, when the front wheels are steered (primary steering) based on a turning operation or a turning command and the vehicle is turning, the control device operates a steering mechanism that steers the rear wheels (auxiliary steering) to control the rotation-induced lateral acceleration.

[0029] The control device may operate the steering mechanism in addition to a turning operation or a turning command, for example, when the total lateral acceleration is changing due to the turning of the vehicle based on a turning operation or a turning command. Specifically, for example, when a certain steered wheel (first steered wheel) is steered based on a turning operation or a turning command to turn the vehicle, the control device operates a steering mechanism that steers the steered wheel (first steered wheel) so as to generate a total lateral acceleration with a reduced peak. In this case, the steering mechanism that steers the steered wheel (first steered wheel) is steered not only by the turning operation or the turning command but also to control the spin-induced lateral acceleration. As an example, when the front wheels are steered (primary steering) based on a turning operation or a turning command and the vehicle is turning, the control device additionally operates a steering mechanism that steers the front wheels (primary steering and auxiliary steering) to control the spin-induced lateral acceleration.

[0030] The control device controls the steering angle of the steering wheels to generate a peak-suppressed total lateral acceleration at, for example, a peak suppression position of the vehicle. The peak suppression position is, for example, the position of a person or cargo loaded in the vehicle. The peak suppression position is, for example, a position overlapping with a seat of the vehicle in a top view. When multiple people are riding in the vehicle, the peak suppression position may be, for example, the position of the target person or cargo, or may be between the people (or cargo). In short, the peak suppression position is, for example, a position at which the rotation-induced lateral acceleration is controlled. The peak suppression position overlaps, for example, with any position on the vehicle in a top view. The peak suppression position may be, for example, located at the center of the vehicle in the left-right direction, or may be located to the left or right of the center. The peak suppression position may be, for example, located at the center of the vehicle in the front-rear direction, or may be located forward or rearward of the center.

[0031] The control device controls the turning angle of the steered wheels to control the spin-induced lateral acceleration, for example, based on at least the turning angle of the steered wheels steered based on a turning operation or a turning command. The control device may control the turning angle of the steered wheels to control the spin-induced lateral acceleration, for example, based on the turning angle of the steered wheels steered based on a turning operation or a turning command and other factors. The other factors may be, for example, the vehicle speed, lateral acceleration, yaw rate, etc.

[0032] The control device controls the turning angle of the steered wheels to control the rotation-induced lateral acceleration, for example, during at least a portion of a period during which the total lateral acceleration is changing. The control device controls the turning angle of the steered wheels to control the rotation-induced lateral acceleration, for example, when the total lateral acceleration is increasing as the vehicle turns. The total lateral acceleration is increasing, for example, when the vehicle starts to turn from a stopped or straight-traveling state, or when it starts to accelerate or turn with a smaller turning radius from a steady turning state, etc. The control device may also control the turning angle of the steered wheels to control the rotation-induced lateral acceleration when the total lateral acceleration is decreasing as the vehicle turns. The total lateral acceleration is decreasing, for example, when the vehicle starts to move straight or stop from a steady turning state, or when it starts to decelerate or turn with a larger turning radius from a steady turning state, etc. In other words, the control device controls the turning angle of the steered wheels to control the rotation-induced lateral acceleration during a turning transition period during which the total lateral acceleration is changing, for example.

[0033] The control device includes, for example, an acquisition unit and a steering mechanism operation unit. The acquisition unit acquires, for example, a total lateral acceleration from an acceleration measuring device. The acquisition unit acquires, for example, a yaw rate from the acceleration measuring device. The steering mechanism operation unit calculates the revolution-induced lateral acceleration and the rotation-induced lateral acceleration based on, for example, the total lateral acceleration and the yaw rate acquired by the acquisition unit.

[0034] "Total lateral acceleration" refers to the lateral acceleration that occurs at the peak suppression position due to, for example, a turning of the vehicle. The total lateral acceleration is measured, for example, by an acceleration measuring device that measures acceleration. The acceleration measuring device is, for example, an acceleration sensor. The total lateral acceleration includes, for example, at least the rotation-induced lateral acceleration and the revolution-induced lateral acceleration. The total lateral acceleration may also include lateral accelerations other than the rotation-induced lateral acceleration and the revolution-induced lateral acceleration. The other accelerations are, for example, lateral accelerations caused by the roll motion of the vehicle.

[0035] The total lateral acceleration changes, for example, during a turning transition. The total lateral acceleration increases and then decreases, for example, so that a peak appears during the turning transition. The direction of the total lateral acceleration may be, for example, toward the inside of the turn or toward the outside of the turn. That is, the total lateral acceleration increases or decreases in absolute value during, for example, a turning transition. The peak of the total lateral acceleration appears, for example, between the time the vehicle starts turning and the time it reaches a steady state of turning. The peak of the total lateral acceleration appears, for example, between the time the vehicle goes from a steady state of turning to a straight state of traveling. In other words, the peak of the total lateral acceleration appears, for example, while the turning radius or yaw rate of the vehicle changes. The total lateral acceleration does not substantially change, for example, during a steady state of turning.

[0036] The total lateral acceleration is the lateral acceleration that occurs when the vehicle is making a normal turn, for example. The total lateral acceleration is not the lateral acceleration that occurs when the vehicle is drifting, for example. In other words, a normal turn refers to a turn in which the direction of the steering wheels steered based on a turning operation or a turning command substantially coincides with the turning direction of the vehicle. The peak value of the total lateral acceleration may be set appropriately depending on, for example, the vehicle concept, or may be set according to the preferences of the vehicle occupants.

[0037] "Non-additional control rotation-induced lateral acceleration" refers to the lateral acceleration caused by the rotation of the vehicle when, for example, steering the steering wheels based solely on a turning operation or a turning command and turning without steering to control the rotation-induced lateral acceleration. Non-additional control rotation-induced lateral acceleration occurs, for example, during a turning transition. The peak value of non-additional control rotation-induced lateral acceleration is greater than the peak value of the total lateral acceleration that occurs when, for example, steering is performed to control the rotation-induced lateral acceleration. The non-additional control rotation-induced lateral acceleration is compared with the total lateral acceleration that occurs when, for example, steering is performed to control the rotation-induced lateral acceleration. The comparison between the non-additional control rotation-induced lateral acceleration and the total lateral acceleration that occurs when steering to control the rotation-induced lateral acceleration is performed under the same conditions. The same conditions mean that various parameters that affect lateral acceleration, such as the vehicle specifications, driving conditions, and measurement location, are the same. During a turning transition, the change per unit time of the non-additional control rotation-induced lateral acceleration is greater than, for example, the revolution-induced lateral acceleration measured or calculated under the same conditions. The non-additional control rotation-induced lateral acceleration depends, for example, on the change per unit time of the vehicle's yaw rate. The non-additional control rotation-induced lateral acceleration depends, for example, on the distance between the vehicle's rotation center and the position where the non-additional control rotation-induced lateral acceleration is measured. The non-additional control rotation-induced lateral acceleration is set based, for example, on the change per unit time of the yaw rate and the distance between the rotation center and the position where the non-additional control rotation-induced lateral acceleration occurs. The peak value of the non-additional control rotation-induced lateral acceleration is not particularly limited. The non-additional control rotation-induced lateral acceleration is, for example, stored in advance in a storage device.

[0038] "Rotation-induced lateral acceleration" refers to the lateral acceleration caused by, for example, a vehicle rotating around its rotation center. The rotation-induced lateral acceleration is measured, for example, at the same position (peak suppression position) as the position where the total lateral acceleration is measured. The rotation-induced lateral acceleration occurs, for example, during a turning transition. The rotation-induced lateral acceleration does not substantially occur, for example, during a steady-state turning period. The rotation-induced lateral acceleration depends, for example, on the distance between the vehicle's rotation center and the peak suppression position. The rotation-induced lateral acceleration is calculated, for example, based on the distance between the vehicle's rotation center and the peak suppression position.

[0039] "Revolution-induced lateral acceleration" refers to the lateral acceleration caused by, for example, a vehicle rotating around its center of revolution. Revolution-induced lateral acceleration is calculated, for example, based on the yaw rate measured by a yaw rate measuring device at the same position where the total lateral acceleration occurs. Revolution-induced lateral acceleration is calculated, for example, by multiplying the measured yaw rate by the speed. Revolution-induced lateral acceleration often occurs later than rotation-induced lateral acceleration, for example, during a turning transition. Revolution-induced lateral acceleration occurs at a substantially constant value, for example, during a steady-state turning period.

[0040] According to the present invention, it is possible to optimize the physical quantity of load applied to an object at any position on a vehicle, thereby increasing the degree of freedom in designing vehicle characteristics.

[0041] Fig. 1(A) is a schematic diagram showing the structure of a vehicle of this embodiment, Fig. 1(B) is a graph showing various lateral accelerations when the vehicle of this embodiment turns, Fig. 2 is a graph showing changes in various physical quantities when a rear-wheel non-steered vehicle turns, and Fig. 3 is a schematic diagram showing the motion of the vehicle when turning.

[0042] A vehicle according to an embodiment of the present invention will be described below with reference to the drawings. Note that the embodiment described below is merely an example. The present invention should not be construed as being limited in any way by the embodiment described below.

[0043] 1A is a schematic diagram showing the structure of a vehicle according to this embodiment. The vehicle 1 is a manned vehicle that is driven by a driver. The vehicle 1 includes three steerable wheels 111, 112, and 113, a steering mechanism 12, and a control device 13.

[0044] The two steering wheels 111, 112 are located in front of the center in the longitudinal direction of the vehicle 1. The steering wheel 111 is located to the left of the center in the transverse direction of the vehicle 1, and the steering wheel 112 is located to the right of the center in the transverse direction. The two steering wheels 111, 112 can be steered left and right. The other steering wheel 113 is located behind the two steering wheels 111, 112. The steering wheel 113 is located behind the center in the transverse direction of the vehicle 1. The steering wheel 113 is located in the center in the transverse direction of the vehicle 1. However, the steering wheel 113 may be offset from the center of the vehicle 1 in the transverse direction.

[0045] The steering mechanism 12 includes a main steering mechanism 121 and an auxiliary steering mechanism 122. The main steering mechanism 121 is operated by the driver to steer the two steered wheels 111, 112. The main steering mechanism 121 includes a steering device, a steering shaft, a tie rod, a turning angle sensor, etc. In other words, the two steered wheels 111, 112 are steered based on a turning operation by the driver. The auxiliary steering mechanism 122 is electrically connected to the steered wheel 113. The auxiliary steering mechanism 122 steers the steered wheel 113 based on instructions from the control device 13. The auxiliary steering mechanism 122 includes an actuator, etc. that steers the steered wheel 113. In other words, in the vehicle 1, the two steered wheels 111, 112, which are the front wheels, are steered mechanically, and the steered wheel 113, which is the rear wheel, is steered by electronic control.

[0046] The control device 13 operates the auxiliary steering mechanism 122 to control the turning angle of the steered wheel 113 relative to the turning angle of the steered wheels 111, 112. The control device 13 is electrically connected to a turning angle sensor in the main steering mechanism 121. The control device 13 is electrically connected to an actuator in the auxiliary steering mechanism 122. The control device 13 receives a signal indicating the turning angle of the steered wheels 111, 112 from the turning angle sensor. The control device 13 controls the actuator based on the received signal indicating the turning angle. The control device 13 controls the ratio of the turning angle of the steered wheel 113 relative to the turning angle of the steered wheels 111, 112 by controlling the actuator.

[0047] The control device 13 includes a processor such as a CPU (Central Processing Unit). The control device 13 performs various controls by having the processor read and execute one or more programs recorded in a nonvolatile memory. The nonvolatile memory may be provided, for example, inside the control device 13 or outside the control device 13.

[0048] 1B is a graph showing various lateral accelerations when the vehicle of this embodiment turns. The vertical axis represents lateral acceleration, and the horizontal axis represents time. The solid line represents total lateral acceleration, the dashed-dotted line represents rotation-induced lateral acceleration, and the dashed line represents revolution-induced lateral acceleration. The graph shows the transition of each lateral acceleration when a vehicle traveling straight starts to turn, makes a steady turn, and then continues traveling straight again. Note that the speed of vehicle 1 is constant when traveling straight and when turning.

[0049] Time t: 0 to t1 While the vehicle is traveling straight, no rotation-induced lateral acceleration, no revolution-induced lateral acceleration, and no total lateral acceleration occurs.

[0050] Time t: t1 to t2 From the time the vehicle 1 starts turning until it reaches a steady turn, i.e., during the turning transition period, the rotation-induced lateral acceleration increases linearly with time. However, as time passes, the rotation-induced lateral acceleration reaches a constant value P2 and then decreases. The rotation-induced lateral acceleration becomes zero at time t2, i.e., when the steady turn begins. In other words, the rotation-induced lateral acceleration increases and decreases during the turning transition period. The revolution-induced lateral acceleration increases linearly with time. The revolution-induced lateral acceleration increases more slowly than the rotation-induced lateral acceleration. The revolution-induced lateral acceleration continues to increase until time t2 is reached. The total lateral acceleration increases with time and decreases after reaching a peak P1. The total lateral acceleration continues to decrease until time t2 is reached.

[0051] Time t: t2 to t3 While the vehicle 1 is making a steady turn, no rotation-induced lateral acceleration occurs. The revolution-induced lateral acceleration is substantially constant. The total lateral acceleration is substantially the same value as the revolution-induced lateral acceleration.

[0052] Time t: t3 to t4 During the transitional period from when the vehicle turns steadily to when it continues straight, the increase and decrease in the lateral accelerations described above for the time t: t1 to t2 are reversed.

[0053] When the total lateral acceleration, which is at least the sum of the revolution-induced lateral acceleration and the rotation-induced lateral acceleration, is changing as the vehicle 1 turns (i.e., t: t1 to t2, t3 to t4), the control device 13 operates the auxiliary steering mechanism 122 to generate a total lateral acceleration whose peak P1 is suppressed by the rotation-induced lateral acceleration combined with the revolution-induced lateral acceleration.

[0054] In this way, the control device 13 controls the turning angle of the steered wheels 113 to control the rotation-induced lateral acceleration. This allows the control device 13 to generate a total lateral acceleration with a suppressed peak P1. The extent to which the value of the rotation-induced lateral acceleration is controlled is set appropriately. However, preferably, when the total lateral acceleration is changing, the control device 13 operates the auxiliary steering mechanism 122 to generate a total lateral acceleration with a suppressed peak P1 by the rotation-induced lateral acceleration whose absolute value is P2, which is less than the peak of the non-additionally controlled rotation-induced lateral acceleration that would occur due to the rotation of the vehicle if the ratio of the turning angle of the steered wheels 111 and 112 to the turning angle of the steered wheels 111 and 112 were not controlled.

[0055] 1: Vehicle 111, 112, 113: Steering wheels 12: Steering mechanism 121: Main steering mechanism 122: Auxiliary steering mechanism 13: Control device

Claims

1. A vehicle comprising: a steering wheel that is steered based on a turning operation or a turning command; a steering mechanism that steers the steering wheel; and a control device capable of operating the steering mechanism separately from or in addition to the turning operation or the turning command, wherein when a total lateral acceleration, which is the sum of at least the revolution-induced lateral acceleration caused by the revolution of the vehicle and the rotation-induced lateral acceleration caused by the rotation of the vehicle, is changing due to the turning of the vehicle based on the turning operation or the turning command, the control device operates the steering mechanism separately from or in addition to the turning operation or the turning command so as to generate a total lateral acceleration whose peak is suppressed by the rotation-induced lateral acceleration combined with the revolution-induced lateral acceleration.

2. A vehicle as described in claim 1, wherein, when the total lateral acceleration is changing as the vehicle turns, the control device operates the steering mechanism so as to generate the total lateral acceleration whose peak is suppressed by the rotation-induced lateral acceleration, which has an absolute value that is less than the peak of the non-additionally controlled rotation-induced lateral acceleration that would be caused by the rotation of the vehicle if the steering mechanism were not operated separately or in addition to the turning operation or turning command.

3. A program used in a vehicle control device as described in claim 1 or 2, which causes a computer to function as a steering mechanism operating unit that operates the steering mechanism, and the steering mechanism operating unit operates the steering mechanism separately from or in addition to the turning operation or turning command so as to generate the total lateral acceleration whose peak is suppressed by the rotation-induced lateral acceleration combined with the revolution-induced lateral acceleration when a total lateral acceleration, which is the sum of at least the revolution-induced lateral acceleration caused by the revolution of the vehicle and the rotation-induced lateral acceleration caused by the rotation of the vehicle, changes in conjunction with the turning of the vehicle based on the turning operation or turning command.

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