Orientation control device

Abstract

A BCTU (braking control unit) determines the pitch state of a vehicle from a plurality of types of determination conditions (first to fourth tables) on the basis of the rotational speed of the vehicle wheels and the longitudinal acceleration of the vehicle during forward travel of the vehicle. After determining, through pitch state determination, that the front wheels have entered a dip in the ground, and the BCTU 31 determines that the front wheels have started to climb out of the dip in the ground during a first time threshold Xtime1 (first predetermined time) determined in advance as a time until the front wheels start to climb out of the dip in the ground, the BCTU 31 sets a first torque Tb1 for suppressing any change in pitch as a braking torque Tb to be applied to the vehicle.

Description

Attitude control device

[0001] The present invention relates to an attitude control device.

[0002] Conventionally, there are known technologies relating to attitude control for suppressing pitch changes when a vehicle travels over a depression, etc. For example, Patent Document 1 describes a brake control device that uses a vertical movement sensor to detect that the front wheels have reached a step or unevenness in the road surface while the vehicle is moving forward, estimates a delay time for brake control to estimate the time it will take for the rear wheels to reach the step or unevenness based on the vehicle speed, and, based on the estimated time, applies braking force to the rear wheels when they reach the step or unevenness, assuming that the rear wheels will move up and down in the same direction as the up and down movement of the front wheels.

[0003] Japanese Patent Application Laid-Open No. 2022-181963

[0004] However, the brake control device described in Patent Document 1 only estimates the movement of the rear wheels when the front wheels reach a step or unevenness as a trigger, and controls the rear of the vehicle to raise or lower in accordance with the estimated up and down movement of the rear wheels, but does not take into account in detail situations such as when the front or rear wheels go over or enter a depression, which may prevent the pitch change from being appropriately suppressed.

[0005] The present invention has been made in consideration of such problems, and its purpose is to provide an attitude control device that can more appropriately suppress pitch changes when a vehicle passes through a depression.

[0006] In order to achieve the above-mentioned object, the attitude control device of the present invention is an attitude control device provided on a vehicle in which front, rear, left and right wheels are suspended by suspension devices having anti-dive and anti-lift geometry, and comprises a braking device that applies braking torque to the vehicle, a wheel speed detection unit that detects the rotational speed of each wheel, a longitudinal acceleration detection unit that detects the longitudinal acceleration of the vehicle, and a braking control unit that controls the friction braking device, wherein the braking control unit, when the vehicle is traveling forward, determines the pitch state of the vehicle from a plurality of types of judgment conditions based on the rotational speed of the wheels and the longitudinal acceleration of the vehicle, and if it determines that the front wheels have started to climb the depression within a first predetermined time, which is predetermined as the time from when it determines that the front wheels have entered a depression to when the front wheels start to climb the depression based on the pitch state judgment, it performs pitch control that sets a first torque for suppressing pitch changes as the braking torque to be applied to the vehicle.

[0007] According to the attitude control device of the present invention, it is possible to more appropriately suppress pitch changes when the vehicle passes through a depression.

[0008] FIG. 1 is a schematic configuration diagram of a vehicle equipped with an attitude control device of an embodiment. FIG. 2 is an explanatory diagram of an anti-dive force and an anti-lift force. FIG. 3 is a schematic diagram of a vehicle when a front wheel descends a depression. FIG. 4 is a schematic diagram of a vehicle when a front wheel climbs a depression. FIG. 5 is a schematic diagram of a vehicle when a rear wheel descends a depression. FIG. 6 is a schematic diagram of a vehicle when a rear wheel climbs a depression. FIG. 7 is a schematic diagram showing a rebound attitude change occurring in the vehicle after the rear wheel has gone over a depression. FIG. 8 is an explanatory diagram showing an example of a time change in braking torque applied to the entire vehicle, which is set in pitch control of this embodiment. FIG. 9 is a flowchart showing an example of processing when a first torque is set in pitch control. FIG. 10 is a flowchart showing an example of processing when a first torque is set in pitch control. FIG. 11 is a flowchart showing an example of processing when a second torque and a third torque are set in pitch control. FIG. 12 is a flowchart showing an example of processing when a second torque and a third torque are set in pitch control. FIG. 13 is a flowchart showing execution determination control of pitch control.

[0009] An embodiment of the present invention will now be described with reference to the drawings. Fig. 1 is a schematic diagram of a vehicle equipped with an attitude control device according to the embodiment. An attitude control device 10 is mounted on a four-wheel vehicle (hereinafter referred to as vehicle 1) having wheels 3a to 3d on the front, rear, left and right sides of the vehicle body. Between each wheel 3a to 3d of vehicle 1 and the vehicle body, a suspension device 11 having anti-dive and anti-lift geometry is provided, which suspends each of the wheels 3a to 3d relative to the vehicle body.

[0010] Each of the wheels 3a to 3d of the vehicle 1 is equipped with a friction braking device 30a to 30d (brake device). The friction braking devices 30a to 30d are controlled by a brake control unit 31 (brake control unit, hereinafter referred to as "BCTU 31"), which allows different friction braking forces (friction braking torques) to be applied to each of the wheels 3a to 3d. The wheels 3a to 3d are driven by, for example, an electric motor or an engine. The present invention is applicable to various driving sources, such as a plug-in hybrid vehicle (PHEV) or hybrid vehicle in which the front wheels 3a, 3b and the rear wheels 3c, 3d can be driven by an electric motor and the front wheels 3a, 3b can be driven by an engine, an electric vehicle in which the wheels 3a to 3d are driven solely by an electric motor, or an engine vehicle in which the wheels 3a to 3d are driven solely by an engine, as well as to vehicles with various drive configurations, such as four-wheel drive or two-wheel drive. A plug-in hybrid vehicle is a vehicle that has an external charging function that supplies power from an external power source to an onboard power storage device to charge it, and an external power supply that supplies power from the battery to electrical appliances outside the vehicle.

[0011] The vehicle 1 is provided with a longitudinal acceleration sensor 40 (longitudinal acceleration detection unit) that detects acceleration in the longitudinal direction of the vehicle body, and wheel speed sensors 42a to 42d (wheel speed detection unit) that detect the rotational speeds of the wheels 3a to 3d. The attitude control device 10 is made up of the longitudinal acceleration sensor 40, the wheel speed sensors 42a to 42d for the wheels 3a to 3d, and the BCTU 31. In this embodiment, the detected values ​​of the longitudinal acceleration sensor 40 and the wheel speed sensors 42a to 42d are input to the BCTU 31, but they may also be input via, for example, the main control unit 20 that controls the entire vehicle.

[0012] The BCTU 31 includes input / output devices, storage devices (ROM, RAM, non-volatile RAM, etc.), a central processing unit (CPU), a timer, etc. The BCTU 31 receives input of the amount of brake pedal operation from a brake pedal sensor (not shown), and controls the braking force of the friction braking devices 30a to 30d based on the amount of brake pedal operation, etc. The BCTU 31 also receives detection information from a longitudinal acceleration sensor 40 and wheel speed sensors 42a to 42d. The BCTU 31 estimates the pitch state of the vehicle 1 based on the detection information from the longitudinal acceleration sensor 40 and the wheel speed sensors 42a to 42d of each wheel 3a to 3d, and performs pitch control by applying a braking torque Tb to the entire vehicle 1 to suppress pitch changes.

[0013] Figure 2 is an explanatory diagram of the anti-dive force and anti-lift force. First, the relationship between the anti-dive force and anti-lift force of the suspension system of the vehicle 1 and the pitch moment and roll moment will be described. As shown in Figure 3, if the distance in the vehicle longitudinal direction between the ground contact points of the front wheels 3a and 3b of the vehicle 1 and the center of gravity A of the vehicle body is a, the distance in the vehicle longitudinal direction between the ground contact points of the rear wheels 3c and 3d of the vehicle 1 and the center of gravity A is b, the height of the center of gravity A from the ground is hCG, the braking force (braking force) of the entire vehicle is F, the ratio of the braking force on the front wheel 3a / 3b side is λ, the anti-lift angle is βf, and the anti-dive angle is βr, the additional pitch moment My, which is the sum of the pitch moment generated by deceleration of the vehicle 1 and the pitch moment generated by the anti-dive and anti-lift forces of the suspension system 11, can be calculated by the following equation (1):

[0014] My=F×hCG-(λF×|tan(βf)|×a+(1-λ)F×|tan(βr)|×b) ...(1)

[0015] Here, Fig. 3 is a schematic diagram of the vehicle 1 when the front wheels 3a, 3b descend a depression. Fig. 4 is a schematic diagram of the vehicle 1 when the front wheels 3a, 3b climb a depression. Fig. 5 is a schematic diagram of the vehicle 1 when the rear wheels 3c, 3d descend a depression. Fig. 6 is a schematic diagram of the vehicle 1 when the rear wheels 3c, 3d climb a depression. Fig. 7 is a schematic diagram showing how a rebound attitude change occurs in the vehicle 1 after the rear wheels 3c, 3d go over the depression. Note that in Figs. 3 to 7, the pitch change of the vehicle 1 is depicted relatively exaggerated as an example for the purpose of explanation.

[0016] First, as shown in Fig. 3, when the front wheels 3a, 3b enter a depression and descend, a pitch change occurs in the vehicle 1 such that the front of the vehicle body descends around the center of gravity. Then, as shown by the solid arrow in Fig. 4, when the front wheels 3a, 3b begin to climb out of the depression from the bottom of the depression (see the dashed-dotted line), a pitch change occurs in the vehicle 1 such that the front of the vehicle body ascends around the center of gravity. That is, from the time the front wheels 3a, 3b begin to climb out of the depression until the vehicle passes over the depression, for example, as shown in Fig. 4, a pitch change occurs from a state in which the front of the vehicle body descends relatively to a state in which the front of the vehicle body ascends, and the driver may perceive this change in pitch rate (pitch angular velocity) as being strange.

[0017] Next, as shown in Fig. 5, when the rear wheels 3c, 3d enter a depression and descend, a pitch change occurs in the vehicle 1 such that the front of the vehicle body rises around the center of gravity. Then, as shown by the solid arrow in Fig. 6, when the rear wheels 3c, 3d start to climb up the depression from the bottom of the depression (see the dashed dotted line), a pitch change occurs in the vehicle 1 such that the front of the vehicle body drops around the center of gravity. That is, from the time the rear wheels 3c, 3d start to climb up the depression until they pass over the depression, for example as shown in Fig. 6, a pitch change occurs from a state in which the front of the vehicle body is relatively raised to a state in which the front of the vehicle body is relatively lowered.

[0018] Furthermore, as shown in Fig. 7, after the rear wheels 3c, 3d go over a depression, a rebound pitch change occurs in the vehicle 1 such that the front of the vehicle body relatively rises around the center of gravity from at least the state shown in Fig. 6 as a reaction to the pitch change shown in Fig. 6. The change from Fig. 6 to Fig. 7 causes a pitch change from a state in which the front of the vehicle body is relatively raised to a state in which the front of the vehicle body is relatively lowered, and the driver may feel this change in pitch rate as being uncomfortable. In order to suppress the pitch changes shown in Figs. 4, 5, and 7, the attitude control device 10 of this embodiment sets the braking torque to be applied to the entire vehicle 1 so as to add additional pitch moments My1, My2, and My3 that rotate the vehicle forward, as indicated by the solid arrows in the figures.

[0019] The method for determining the attitude of the vehicle 1 executed by the BCTU 31 in relation to the application of braking torque will now be described. The BCTU 31 determines the attitude of the vehicle 1 with respect to each pitch change shown in FIGS. 3 to 6 based on the total driving force, longitudinal acceleration, and wheel rotational speed of each of the wheels 3a to 3d of the vehicle 1. The attitude when the front wheels 3a and 3b enter a depression (start to descend from the depression) as shown in FIG. 3 is determined when the conditions of the first table shown in Table 1 are satisfied. The conditions of the first table are satisfied when both the total driving torque PTT of the vehicle 1 is less than a predetermined threshold XPTT and the first derivative value Xb of the longitudinal acceleration of the vehicle 1 detected by the longitudinal acceleration sensor 40 exceeds a predetermined threshold Xba1. The condition that the total driving torque PTT of the vehicle 1 is less than the predetermined threshold XPTT is set in order to exclude from the determination conditions changes in longitudinal acceleration caused by the total driving torque required for the vehicle 1 to travel.

[0020]

[0021] The posture when the front wheels 3a, 3b start climbing a depression as shown in Figure 4 occurs when the conditions of the second table shown in Table 2 are satisfied. The conditions of the second table are satisfied when all three conditions are met: the average value of the rotational acceleration of the front wheels 3a, 3b (FRwa + FLwa) / 2 exceeds a predetermined threshold value Xwa1; the absolute value of the average value of the rotational acceleration of the rear wheels 3c, 3d (RRwa + RLwa) / 2 is less than a predetermined threshold value Xwa2; and the first-order differential value Xb of the longitudinal acceleration of the vehicle 1 is less than a predetermined threshold value Xba2. The rotational accelerations FRwa, FLwa, RRwa, and RLwa are first-order differential values ​​of the wheel speeds detected by the wheel speed sensors 42a to 42d.

[0022]

[0023] 5, the posture when the rear wheels 3c, 3d enter a depression (start to descend the depression) is achieved when the conditions of the third table shown in Table 3 are satisfied. The conditions of the third table are achieved when all three conditions are satisfied: the average value (FRwa+FLwa) / 2 of the rotational acceleration of the front wheels 3a, 3b is less than a predetermined threshold value Xwa3; the absolute value of the average value (RRwa+RLwa) / 2 of the rotational acceleration of the rear wheels 3c, 3d is less than a predetermined threshold value Xwa4; and the first derivative value Xb of the longitudinal acceleration of the vehicle 1 exceeds a predetermined threshold value Xba3.

[0024]

[0025] The posture when the rear wheels 3c, 3d start climbing a depression as shown in Figure 6 occurs when the conditions of the fourth table shown in Table 4 are satisfied. The conditions of the fourth table are satisfied when all three conditions are met: the average value of the rotational acceleration of the front wheels 3a, 3b (FRwa + FLwa) / 2 exceeds a predetermined threshold value Xwa5; the absolute value of the average value of the rotational acceleration of the rear wheels 3c, 3d (RRwa + RLwa) / 2 is less than the predetermined threshold value Xwa5; and the first derivative value Xb of the longitudinal acceleration of the vehicle 1 is less than a predetermined threshold value Xba4. The threshold values ​​Xwa1 to Xwa6 and Xba1 to Xba4 are set appropriately based on experiments, analyses, etc.

[0026]

[0027] Next, pitch control according to this embodiment will be described. FIG. 8 is an explanatory diagram showing an example of the time change of the braking torque Tb applied to the entire vehicle 1, which is set by the pitch control according to this embodiment. In FIG. 8, it is assumed that the conditions of the first table are satisfied at time t1. If the conditions of the second table are satisfied (time t2) between time t1 and the elapse of a first time threshold Xtime1 (first predetermined time), the attitude control device 10 sets the braking torque Tb to a first torque Tb1 for a second time threshold Xtime2. The first torque Tb1 is a braking torque for applying the additional pitch moment My1 shown in FIG. 4 to the vehicle 1 when converted into the braking force F in the above equation (1), and is set appropriately based on experiments, analysis, and the like. The first time threshold Xtime1 is the time from when the front wheels 3a, 3b enter a depression until they start climbing the depression. The second time threshold Xtime2 is the time required to apply the additional pitch moment My1 shown in FIG. 4 to the vehicle body to suppress pitch changes.

[0028] Next, assume that the condition of the third table is met at time t3. The posture control device 10 sets the braking torque Tb to the second torque Tb2 from time t3 to the third time threshold Xtime3. The second torque Tb2 is a braking torque for applying the additional pitch moment My2 shown in FIG. 5 to the vehicle 1 when converted into the braking force F in the above equation (1), and is set appropriately based on experiments, analysis, etc. The third time threshold Xtime3 is the time for applying the additional pitch moment My2 shown in FIG. 5 to the vehicle body to suppress pitch changes.

[0029] Next, assume that the condition of the fourth table is satisfied at time t4 during the period from time t3 to the fourth time threshold Xtime4. After the fifth time threshold Xtime5 (second predetermined time) has elapsed from time t4, the posture control device 10 sets the braking torque Tb to the third torque Tb3 for the sixth time threshold Xtime6. The third torque Tb3 is a braking torque for applying the additional pitch moment My3 shown in FIG. 7 to the vehicle 1 when converted to the braking force F in the above equation (1), and is set appropriately based on experiments, analysis, etc. The fourth time threshold Xtime4 is the time from when the rear wheels 3c, 3d enter a depression to when they start to climb the depression. The fifth time threshold Xtime5 is the time from when the rear wheels 3c, 3d start to climb the depression to when the rebound pitch change described above occurs. The sixth time threshold Xtime6 is the time for applying the additional pitch moment My3 shown in FIG. 7 to the vehicle body to suppress the pitch change.

[0030] 8, the first torque Tb1, the second torque Tb2, and the third torque Tb3 are all set to the same value, but this is an example and they may be set to different values. The first time threshold Xtime1, the second time threshold Xtime2, the third time threshold Xtime3, the fourth time threshold Xtime4, the fifth time threshold Xtime5, and the sixth time threshold Xtime6 are set in advance through experiments, analysis, or the like in accordance with the vehicle specifications, and are set to shorter times as the vehicle speed increases.

[0031] In the posture control device 10 of this embodiment, if the first time threshold Xtime1 has elapsed since the condition of the first table was met (time t2) and the second table is not met, pitch control is canceled and the braking torque Tb is set to 0. In other words, after detecting that the front wheels 3a, 3b have entered a depression (the condition of the first table is met), if it is detected that the front wheels 3a, 3b have started climbing the depression within the first time threshold Xtime1 (the condition of the second table is met), the final first torque Tb1 is generated. This makes it possible to accurately detect that the front wheels 3a, 3b have entered a depression and then started climbing the depression. Furthermore, it is possible to prevent unnecessary braking torque from being generated when the condition of the second table is not met.

[0032] Furthermore, if the fourth time threshold Xtime4 has elapsed since the condition of the third table was met (time t3) and the fourth table is not met, the posture control device 10 cancels pitch control and sets the braking torque Tb to 0. In other words, after detecting that the rear wheels 3c, 3d have entered a depression (the condition of the third table is met), if the posture control device 10 detects that the rear wheels 3c, 3d have started climbing the depression within the fourth time threshold Xtime4 (the condition of the fourth table is met), it generates the final third torque Tb3. This makes it possible to accurately detect that the rear wheels 3c, 3d have entered a depression and then started climbing the depression. Furthermore, it is possible to avoid generating unnecessary braking torque when the condition of the fourth table is not met.

[0033] Next, a specific example of the pitch control will be described. Figures 9 and 10 are flowcharts showing an example of a process for setting the first torque Tb1 in pitch control. The process shown in Figures 9 and 10 is repeatedly executed by the BCTU 31 at unit time intervals (e.g., several msec) while the vehicle 1 is traveling forward.

[0034] 9, the BCTU 31 first determines whether the conditions in the first table are satisfied in step S1. If the conditions in the first table are not satisfied, the BCTU 31 proceeds to step S2 and determines whether the brake timer XT1 is not equal to the value 0. If the BCTU 31 determines that the brake timer XT1 is equal to the value 0, the BCTU 31 proceeds to step S3, sets the braking torque Tb to the value 0, and executes the processing from step S1 onwards again.

[0035] On the other hand, if the BCTU 31 determines that the conditions in the first table are satisfied and that the brake timer XT1 is not equal to 0, the BCTU 31 proceeds to step S4, counts up the brake timer XT1, and then proceeds to step S5. In step S5, the BCTU 31 determines whether the brake timer XT1 is less than the first time threshold Xtime1. If the BCTU 31 determines that the brake timer XT1 is less than the first time threshold Xtime1, the BCTU 31 proceeds to the flowchart shown in FIG. 10.

[0036] Furthermore, if the BCTU 31 determines in step S5 that the brake timer XT1 is equal to or greater than the first time threshold Xtime1, the process proceeds to step S6, where it determines whether the brake timer XT2 has a value of 0. If the BCTU 31 determines that the brake timer XT2 has a value of 0, the process proceeds to step S7, where it sets the braking torque Tb to a value of 0 and resets the brake timer XT1 to a value of 0, and then executes the processes from step S1 onwards again. If the BCTU 31 determines that the brake timer XT2 does not have a value of 0, the process proceeds to the flowchart shown in FIG.

[0037] The flowchart in Fig. 10 will be described. In step S8, the BCTU 31 determines whether the conditions in the second table are satisfied. If the BCTU 31 determines that the conditions in the second table are not satisfied, the BCTU 31 proceeds to step S9 and determines whether the brake timer XT2 is not equal to the value 0. If the BCTU 31 determines that the brake timer XT2 is equal to the value 0, the BCTU 31 again executes the processing from step S1 onward in Fig. 9.

[0038] On the other hand, if the conditions in the second table are satisfied or the brake timer XT2 is not equal to 0, the BCTU 31 proceeds to step S10, increments the brake timer XT2, and then proceeds to step S11. In step S11, the BCTU 31 determines whether the brake timer XT2 is less than the second time threshold Xtime2. If the BCTU 31 determines that the brake timer XT2 is less than the second time threshold Xtime2, the BCTU 31 proceeds to step S12, where the BCTU 31 sets the braking torque Tb to the first torque Tb1. Thereafter, the BCTU 31 again executes the processes from step S8 onward in FIG. 10. Furthermore, if the BCTU 31 determines in step S11 that the brake timer XT2 is equal to or greater than the second time threshold Xtime2, the BCTU 31 sets the braking torque Tb to 0 and resets the brake timers XT1 and XT2 to 0 in step S13. Thereafter, the BCTU 31 executes the process from step S1 onward in FIG. 9 again.

[0039] 11 and 12 are flowcharts showing an example of a process for setting the second torque Tb2 and the third torque Tb3 in pitch control. The process shown in Fig. 11 and 12 is repeatedly executed by the BCTU 31 at unit time intervals (e.g., several msec) while the vehicle 1 is traveling forward. Note that the process shown in Fig. 11 and 12 may be started after the conditions of the first table are satisfied while the vehicle 1 is traveling forward, or after the conditions of both the first table and the second table are satisfied.

[0040] 11, the BCTU 31 first determines whether the conditions in the third table are satisfied in step S20. If the conditions in the third table are not satisfied, the BCTU 31 proceeds to step S21 to determine whether the brake timer XT3 is not equal to the value 0. If the BCTU 31 determines that the brake timer XT3 is equal to the value 0, the BCTU 31 proceeds to step S22 to set the braking torque Tb to the value 0 and executes the processing from step S20 onwards again.

[0041] On the other hand, if the BCTU 31 determines that the conditions in the third table are satisfied or that the brake timer XT3 does not have a value of 0, the BCTU 31 proceeds to step S23, where it counts up the brake timers XT3 and XT4, and then proceeds to step S24. In step S24, the BCTU 31 determines whether the brake timer XT3 is less than the third time threshold Xtime3. If the BCTU 31 determines that the brake timer XT3 is less than the third time threshold Xtime3, the BCTU 31 sets the braking torque Tb to the second torque Tb2 in step S25, and repeats the processing from step S20 onwards.

[0042] Furthermore, if the BCTU 31 determines in step S24 that the brake timer XT3 is equal to or greater than the third time threshold Xtime3, the process proceeds to step S26, where it determines whether the brake timer XT4 is less than the fourth time threshold Xtime4. If the BCTU 31 determines that XT4 is less than the fourth time threshold Xtime4, the process proceeds to step S27, where it sets the braking torque Tb to 0, and then proceeds to the flowchart shown in FIG.

[0043] If the BCTU 31 determines in step S26 that the brake timer XT4 is equal to or greater than the fourth time threshold Xtime4, the process proceeds to step S28, where it determines whether both the brake timers XT5 and XT6 have a value of 0. If the BCTU 31 determines that both the brake timers XT5 and XT6 have a value of 0, the BCTU 31 sets the braking torque Tb to a value of 0 in step S29, and repeats the process from step S20 onwards. On the other hand, if the BCTU 31 determines that either one of the brake timers XT5 and XT6 has a value other than 0, the process proceeds to the flowchart shown in FIG. 12.

[0044] The flowchart of Fig. 12 will be described. In step S30, the BCTU 31 determines whether the conditions in the fourth table are satisfied. If the BCTU 31 determines that the conditions in the fourth table are not satisfied, the BCTU 31 proceeds to step S31 and determines whether the brake timer XT5 is not equal to 0. If the BCTU 31 determines that the brake timer XT5 is equal to 0, the BCTU 31 again executes the processing from step S20 onwards in Fig. 11.

[0045] On the other hand, if the conditions in the fourth table are satisfied or if the brake timer XT5 is not equal to 0, the BCTU 31 proceeds to step S32, increments the brake timer XT5, and then proceeds to step S33. In step S33, the BCTU 31 determines whether the brake timer XT5 is less than the fifth time threshold Xtime5. If the BCTU 31 determines that the brake timer XT5 is less than the fifth time threshold Xtime5, the BCTU 31 proceeds to step S34, in which the braking torque Tb is set to 0. Thereafter, the BCTU 31 again executes the processes from step S30 onward in FIG. 12 .

[0046] If the BCTU31 determines in step S33 that the brake timer XT5 is equal to or greater than the fifth time threshold Xtime5, it counts up the brake timer XT6 in step S35 and then proceeds to step S36. In step S36, the BCTU31 determines whether the brake timer XT6 is less than the sixth time threshold Xtime6. If the BCTU31 determines that the brake timer XT6 is less than the sixth time threshold Xtime6, it proceeds to step S37, sets the braking torque Tb to the third torque Tb3, and repeats the process from step S30 onward. On the other hand, if the BCTU31 determines that the brake timer XT6 is equal to or greater than the sixth time threshold Xtime6, it proceeds to step S38, sets the braking torque Tb to 0, and resets the brake timers XT3 to XT6 to 0. Then, the BCTU31 repeats the process from step S20 onward in FIG. 11.

[0047] Figure 13 is a flowchart showing pitch control execution determination control. The process shown in Figure 13 begins when the system is started and is repeated while the vehicle 1 is running. First, in step S40, the BCTU 31 determines whether the BCTU 31 or each of the friction braking devices 30a to 30d is in an abnormal (failed) state. Whether these units are abnormal can be determined using a known self-diagnosis function. If the BCTU 31 and each of the friction braking devices 30a to 30d are normal, the BCTU 31 proceeds to step S41.

[0048] In step S41, the BCTU 31 determines whether the driver's brake operation amount (operation force) exceeds a predetermined threshold XCF that has been appropriately set. The predetermined threshold XCF is a threshold value of the brake operation amount (operation force) at which pitch change can be suppressed by pitch control, and is set through experiments, analysis, etc. If the brake operation amount is equal to or less than the threshold XCF, the BCTU 31 proceeds to step S42.

[0049] In step S42, the BCTU 31 determines whether or not other driving control devices (driving safety devices) of the vehicle 1 are in an operating state (under control). The other driving control devices are driving control devices that control the braking forces of the friction braking devices 30a to 30d to improve the driving safety of the vehicle 1, and are, for example, an electric stability control system (ESC), an antilock braking system (ABS), or an automatic emergency braking system (AEB). If the other driving control devices are not in an operating state (standby state), the BCTU 31 proceeds to step S43.

[0050] In step S43, the BCTU 31 determines whether the shift position of the vehicle 1 is set to a position other than the forward driving position (D position). If the BCTU 31 determines that the shift position of the vehicle 1 is not set to the forward driving position (D position), the BCTU 31 proceeds to step S44.

[0051] In step S44, the BCTU 31 determines whether the vehicle speed V of the vehicle 1 is less than a predetermined first vehicle speed V1 or greater than a predetermined second vehicle speed V2. The first vehicle speed V1 is the minimum vehicle speed at which pitch change can be suppressed by pitch control, and the second vehicle speed V2 is greater than the first vehicle speed V1 and is the maximum vehicle speed at which pitch change can be suppressed by pitch control. The first vehicle speed V1 and the second vehicle speed V2 are set through experiments, analysis, or the like. If the BCTU 31 determines that the vehicle speed V of the vehicle 1 is less than the first vehicle speed V1 or greater than the second vehicle speed V2, it turns on pitch control in step S45 and executes this routine from the beginning.

[0052] In contrast, if the BCT31 determines that the BCTU31 and each friction braking device 30a to 30d are abnormal, if it determines that the driver's brake operation amount (operating force) exceeds an appropriately set predetermined threshold value XCF, if it determines that other driving control devices of the vehicle 1 are in an operating state, if it determines that the shift position of the vehicle 1 is set to a position other than the forward driving position (D position), or if it determines that the vehicle speed V is equal to or greater than the first vehicle speed V1 and equal to or less than the second vehicle speed V2, it turns off pitch control in step S46 and executes this routine from the beginning.

[0053] As a result, pitch control is not performed when it is difficult to perform appropriate pitch control, such as when an abnormality occurs, when the vehicle speed V is equal to or greater than a predetermined first vehicle speed V1 and equal to or less than a predetermined second vehicle speed V2, or when the vehicle is set to a position other than the forward driving position (D position), thereby preventing unstable driving control of the vehicle 1. Furthermore, pitch control is not performed when the driver's brake operation amount (operation force) exceeds a predetermined threshold XCF, so that braking of the vehicle 1 by brake operation can be prioritized. Furthermore, when another driving control device is operating, pitch control is not performed, so that the other driving control device can be prioritized.

[0054] As described above, in the attitude control device 10 of this embodiment, the BCTU 31 (brake control unit) determines the pitch state of the vehicle 1 when the vehicle 1 is traveling forward from a plurality of types of determination conditions (first to fourth tables) based on the rotational speeds of the wheels 3 a to 3 d and the longitudinal acceleration of the vehicle 1. If the BCTU 31 determines, based on the determination of the pitch state, that the front wheels 3 a, 3 b have started to climb the depression within a first time threshold Xtime1 (first predetermined time) that is predetermined as the time from when it is determined that the front wheels 3 a, 3 b have entered a depression until when the front wheels 3 a, 3 b start to climb the depression, it sets a first torque Tb1 for suppressing pitch changes as the braking torque Tb to be applied to the vehicle.

[0055] With this configuration, the pitch change of the vehicle 1 is determined based on the conditions that the front wheels 3a, 3b have entered a depression (the first table is satisfied at time t1) and that the front wheels 3a, 3b have begun climbing the depression during the first time threshold Xtime1 (the second table is satisfied at time t2). This allows for accurate determination of whether the front wheels 3a, 3b have begun climbing the depression. By setting the first torque Tb1 to the braking torque Tb, the pitch change of the vehicle 1 when the front wheels 3a, 3b are climbing the depression (while climbing the depression) can be suppressed. Therefore, the attitude control device 10 of this embodiment can more appropriately suppress pitch change when the vehicle 1 passes through a depression. Furthermore, because the pitch state of the vehicle 1 is determined using the longitudinal acceleration sensor 40 and the wheel speed sensors 42a to 42d, the attitude control device 10 can be configured at a relatively low cost compared to systems that detect whether the vehicle 1 has passed through a depression using, for example, a suspension stroke sensor, a pitch rate sensor, or a camera.

[0056] Furthermore, when the BCTU 31 determines that the rear wheels 3 c, 3 d have entered a depression based on the pitch state (the third table is established at time t3), it sets the second torque Tb2 for suppressing pitch changes as the braking torque Tb. With this configuration, pitch changes of the vehicle 1 can be suppressed when the rear wheels 3 c, 3 d have entered a depression (while descending the depression).

[0057] Furthermore, after determining that the rear wheels 3 c, 3 d have started climbing the depression based on the pitch state (the fourth table is established at time t4), the BCTU 31 sets the braking torque Tb to a third torque Tb3 for suppressing the pitch change after a fifth time threshold Xtime5 (a second predetermined time) has elapsed, which is a predetermined time until a rebound pitch change occurs after the rear wheels 3 c, 3 d have passed over the depression. With this configuration, it is possible to suppress the rebound pitch change after the rear wheels 3 c, 3 d have passed over the depression.

[0058] Furthermore, if the BCTU 31 determines that the rear wheels 3 c, 3 d have started climbing the depression (the fourth table is established, time t4) during a fourth time threshold Xtime4 (third predetermined time) that is predetermined as the time from when the rear wheels 3 c, 3 d have entered the depression based on the pitch state determination (the third table is established, time t3) until the rear wheels 3 c, 3 d start climbing the depression, the BCTU 31 sets the third torque Tb3 as the braking torque Tb after the fifth time threshold Xtime5 has elapsed. This configuration enables more accurate determination that the rear wheels 3 c, 3 d have started climbing the depression.

[0059] Furthermore, the BCTU 31 does not perform pitch control when the driver of the vehicle 1 applies a braking operation greater than a predetermined value, i.e., when the brake operation amount (operation force) exceeds a predetermined threshold value XCF. This configuration allows priority to be given to the output of braking force when the driver desires a strong braking force.

[0060] Furthermore, the BCTU 31 does not perform pitch control when the vehicle speed V is less than a predetermined first vehicle speed V1 or exceeds a predetermined second vehicle speed V2 that is greater than the first vehicle speed V1. With this configuration, pitch control is not performed in low speed ranges or high speed ranges where it is difficult to suppress pitch changes, and it is possible to prevent the vehicle's driving control from becoming unstable due to pitch control.

[0061] Furthermore, the BCTU 31 does not perform pitch control when other travel control devices are in operation. This configuration ensures that the travel safety functions of the other travel control devices are properly maintained.

[0062] Although the description of the embodiment is now complete, aspects of the present invention are not limited to this embodiment. For example, in this embodiment, friction braking devices 30a to 30d that apply friction braking torque to each of the wheels 3a to 3d are used as braking devices to apply braking torque Tb to the vehicle 1. However, any braking device may be used as long as it is capable of applying braking torque Tb to the vehicle 1. For example, a regenerative braking device including an electric motor that can apply regenerative braking force to the vehicle 1 may be used in addition to (or instead of) the friction braking devices 30a to 30d.

[0063] REFERENCE SIGNS LIST 1 vehicle 3a, 3b front wheels (wheels) 3c, 3d rear wheels (wheels) 10 attitude control device 11 suspension device 30a to 30d friction braking device (braking device) 31 brake control unit (braking control section) 40 longitudinal acceleration sensor (longitudinal acceleration detection section) 42a to 42d wheel speed sensor (wheel speed detection section) Tb braking torque Tb1 first torque Tb2 second torque Tb3 third torque V vehicle speed V1 first vehicle speed V2 second vehicle speed Xtime1 first time threshold (first predetermined time) Xtime2 second time threshold Xtime3 third time threshold Xtime4 fourth time threshold (third predetermined time) Xtime5 fifth time threshold (second predetermined time) Xtime6 sixth time threshold

Claims

1. An attitude control device provided on a vehicle whose front, rear, left and right wheels are suspended by a suspension device having anti-dive and anti-lift geometry, comprising: a braking device which applies a braking torque to the vehicle; a wheel speed detection unit which detects the rotational speed of each of the wheels; a longitudinal acceleration detection unit which detects the longitudinal acceleration of the vehicle; and a braking control unit which controls the braking device, wherein the braking control unit, when the vehicle is traveling forward, determines a pitch state of the vehicle from a plurality of types of determination conditions based on the rotational speed of the wheels and the longitudinal acceleration of the vehicle, and, when it determines, based on the pitch state determination, that the front wheels have started to climb the depression within a first predetermined time which is set as the time from when it is determined that the front wheels have entered a depression to when it is determined that the front wheels start to climb the depression, performs pitch control by setting a first torque for suppressing pitch change as the braking torque to be applied to the vehicle.

2. The attitude control device described in claim 1, characterized in that when the braking control unit determines that the rear wheels have entered a depression based on the pitch state judgment, it sets a second torque for suppressing pitch changes as the braking torque to be applied to the vehicle.

3. The attitude control device described in claim 1, characterized in that the braking control unit sets a third torque for suppressing pitch change as the braking torque to be applied to the vehicle after a second predetermined time has elapsed, which is determined in advance as the time from when it is determined that the rear wheels have started to climb a depression based on the pitch state judgment to when a rebound pitch change occurs after the rear wheels have gone over the depression.

4. The attitude control device described in claim 3, characterized in that when the braking control unit determines that the rear wheels have started climbing the depression within a third predetermined time, which is a time from when the rear wheels have entered a depression based on the pitch state judgment to when the rear wheels start to climb the depression, it sets the third torque as the braking torque after the second predetermined time has elapsed.

5. An attitude control device as described in any one of claims 1 to 3, characterized in that the braking control unit does not perform the pitch control when the vehicle speed is less than a predetermined first vehicle speed or exceeds a predetermined second vehicle speed that is greater than the predetermined first vehicle speed.

6. An attitude control device as claimed in any one of claims 1 to 3, characterized in that the braking control unit does not perform the pitch control when the driver of the vehicle applies a braking operation of a predetermined magnitude or more.

7. The attitude control device according to any one of claims 1 to 3, characterized in that the vehicle is equipped with a driving control device that controls the braking force of the braking device to improve the driving safety of the vehicle, and the braking control unit does not perform the pitch control when the driving control device is operating.

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