Vehicle height control device

Abstract

To provide a vehicle height control apparatus improved so as to be capable of effectively reducing longitudinal force acting on a wheel due to vertical input from a road surface, even if an equivalent inertia moment of a driving system fluctuates due to a change of a gear ratio of a transmission.SOLUTION: A vehicle height control apparatus is applied to a vehicle 20 which includes: a wheel 12 supported rotatably about a rotational axis 24 and having a tire 26; and a driving system 14 for driving the wheel by an engine 28 as a driving source via a transmission 30. A suspension arm is arranged between a wheel carrier and a vehicle body 34 such that, when viewed in a lateral direction of the vehicle, the rotational axis draws a locus 36 inclined backward with vertical displacement of the wheel. The vehicle height control apparatus includes: a vehicle height adjustment device 42; and a control device 44 for controlling the vehicle height adjustment device. The control device acquires information on an index indicating an equivalent inertia moment IP of the driving system, and controls the vehicle height adjustment device such that a vehicle height H becomes lower as the equivalent inertia moment indicated by the index becomes smaller.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vehicle height control device for a vehicle such as an automobile. [Background technology]

[0002] There is known a suspension that improves the ride comfort of a vehicle by reducing the longitudinal forces acting on the wheels due to vertical inputs from the road surface. For example, Patent Document 1 listed below describes a suspension in which suspension arms are arranged so that the rotation axis of the wheel, as viewed in the lateral direction of the vehicle, follows a trajectory that is tilted backward as the wheel moves up and down, and shock absorbers are arranged to be tilted forward.

[0003] With this type of suspension, the longitudinal forces acting on the wheels due to vertical inputs from the road surface can be at least partially offset by the longitudinal forces generated by the backward tilt of the trajectory and the longitudinal forces generated by the damping force of the shock absorber, thereby reducing the longitudinal forces on the wheels. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-40349 Summary of the Invention

[0005] [Problem to be solved by the invention] In a vehicle with a drivetrain in which the wheels are rotated by a drive source via a transmission, longitudinal vibrations caused by longitudinal forces at the wheels increase when the torsional resonance frequency of the drivetrain approaches the vertical resonance frequency of the suspension. As will be explained in detail later, the torsional resonance frequency of the drivetrain is determined by the moment of inertia and torsional rigidity of the drivetrain, and the moment of inertia of the drivetrain varies with changes in the gear ratio of the transmission. Therefore, the longitudinal forces acting on the wheels due to vertical inputs from the road surface vary with changes in the moment of inertia of the drivetrain, and therefore with changes in the gear ratio of the transmission.

[0006] The suspension described in Patent Document 1 cannot deal with fluctuations in the longitudinal forces acting on the wheels due to fluctuations in the moment of inertia of the drivetrain, and therefore cannot effectively reduce the longitudinal forces acting on the wheels due to vertical inputs from the road surface, regardless of fluctuations in the moment of inertia of the drivetrain that accompany changes in the gear ratio of the transmission.

[0007] The present invention provides an improved vehicle height control device that can effectively reduce the longitudinal forces acting on the wheels due to vertical inputs from the road surface, even if the equivalent moment of inertia of the drive system fluctuates with changes in the gear ratio of the transmission.

[0008] [Means for solving the problems and effects of the invention] According to the present invention, there is provided a vehicle height control device (10) applied to a vehicle (20) including a wheel (12) rotatably supported around a rotation axis (24) by a wheel carrier (22) and having a tire, a drive system (14) that rotates and drives the wheel via a transmission (30) by a drive source (engine 28), and a suspension arm (16) arranged between the wheel carrier and a vehicle body (34).

[0009] The suspension arm (16) is disposed so that the axis of rotation thereof, as viewed in the lateral direction of the vehicle (20), describes a trajectory (36) that tilts backward in response to the vertical displacement of the wheel (12). The vehicle height control device (10) includes a vehicle height adjustment device (42) configured to change the vehicle height, and a control device (44) that controls the vehicle height adjustment device. The control device controls an equivalent moment of inertia (I P The vehicle height adjusting device is configured to obtain information on an index (speed ratio Rt or gear stage St) indicating the equivalent moment of inertia (equivalent moment of inertia) and control the vehicle height adjusting device so that the vehicle height (H) becomes lower as the equivalent moment of inertia indicated by the index becomes smaller.

[0010] According to the above configuration, the rotation axis of the wheel describes a trajectory that is tilted backward as the wheel moves up and down, so that the longitudinal forces acting on the wheel due to vertical inputs from the road surface are at least partially offset by the longitudinal forces generated by the backward tilt of the trajectory, as will be described in detail later. The longitudinal forces acting on the wheel due to vertical inputs from the road surface vary with changes in the equivalent moment of inertia of the drivetrain, but the vehicle height control device is controlled so that the smaller the equivalent moment of inertia, the lower the vehicle height.

[0011] As will be described in detail later, the longitudinal force generated by the backward tilt of the trajectory can be changed in accordance with the fluctuation in the longitudinal force acting on the wheels that accompanies a change in the equivalent moment of inertia of the drivetrain, and therefore the longitudinal force acting on the wheels can be effectively reduced even if the equivalent moment of inertia of the drivetrain fluctuates.

[0012] [Mode of the Invention] In one aspect of the present invention, the backward tilt angle (γ) of the trajectory is determined by the first longitudinal force (F X 1) is the second longitudinal force (F X The control device (44) is set at an angle that at least partially offsets the equivalent moment of inertia (I P ) with the change of the first longitudinal force (F X The vehicle height adjusting device (42) is controlled so that a change in the backward tilt angle (γ) of the trajectory required to offset the change in 1) by a change in the second longitudinal force is achieved by a change in the vehicle height (H).

[0013] In another embodiment of the present invention, the control device (44) calculates the equivalent moment of inertia (I P ) with the change of the first longitudinal force (F X 1) is the change in the second longitudinal force (F XThe system stores a relationship between a target vehicle height (Ht) and an index (gear ratio Rt or gear St) for adjusting the vehicle height (H) to achieve a change in the backward tilt angle (γ) of the trajectory (36) required to offset the change in 2) and the target vehicle height is calculated from the relationship based on the index, and the vehicle height adjusting device (42) is controlled so that the vehicle height becomes the target vehicle height.

[0014] Furthermore, in another aspect of the present invention, the index is the gear ratio (Rt) of the transmission (30), and the above relationship is a relationship between the target vehicle height (Ht) and the gear ratio of the transmission (30) that is set so that the target vehicle height (Ht) becomes lower as the gear ratio of the transmission (30) becomes smaller.

[0015] Furthermore, in another aspect of the present invention, the transmission (30) is a multi-stage transmission, the index is a gear stage (St) of the transmission, and the relationship is a relationship between the target vehicle height (Ht) and the gear stage of the transmission, which is set so that the target vehicle height (Ht) becomes lower as the gear stage of the transmission is higher.

[0016] Other objects, other features and attendant advantages of the present invention will be readily apparent from the following description of the preferred embodiments of the present invention which will be given with reference to the accompanying drawings. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing an embodiment of a vehicle height control device according to the present invention; [Figure 2] FIG. 2 is an explanatory diagram showing wheels driven by a drive train. [Figure 3] 1A is a diagram showing an example of the relationship between the vertical displacement Z of the wheel and the longitudinal force FX1; FIG. 1B is a diagram showing an example of the relationship between the vertical displacement Z of the wheel and the longitudinal force FX2; and FIG. 1C is a diagram showing an example of the relationship between the vertical displacement Z of the wheel and the longitudinal force FX3. [Figure 4] FIG. 10 is a diagram showing a longitudinal force FXT acting on a wheel due to the inclination of the road surface. [Figure 5] FIG. 10 is a diagram showing longitudinal forces FXS acting on the wheels due to wheel slippage. [Figure 6]FIG. 10 is a diagram showing the relationship between the gain of h′(s) and the frequency (upper part) and the relationship between the phase of h′(s) and the frequency (lower part). [Figure 7] FIG. 10 is a diagram showing the relationship between the gain and frequency of the transfer function from tire deflection Z-Z0 to longitudinal force FX1 (top), and the relationship between the phase and frequency of the transfer function from deflection Z-Z0 to longitudinal force FX1 (bottom). [Figure 8] This figure shows the relationship between the gain and frequency of the transfer function from tire deflection Z-Z0 to the vertical displacement Z of the wheel (top), and the relationship between the phase and frequency of the transfer function from deflection Z-Z0 to the vertical displacement Z of the wheel (bottom). [Figure 9] FIG. 10 is a diagram showing the relationship between the gain and frequency of the transfer function from the vertical displacement Z of the wheel to the longitudinal force FX1 (upper part) and the relationship between the phase and frequency of the transfer function from the vertical displacement Z of the wheel to the longitudinal force FX1 (lower part). [Figure 10] This is a vector diagram showing the upper and lower resonance frequencies of the wheel, FX1 / Z, separated into real and imaginary parts. [Figure 11] FIG. 10 is a diagram showing the relationship between the real part of the transfer function from the vertical displacement Z of the wheel to the longitudinal force FX1 and the moment of inertia IP of the drive train. [Figure 12] FIG. 10 is a diagram showing the relationship between the target rearward tilt angle γt of the trajectory of the wheel rotation axis and the moment of inertia IP of the drive train (left half), and the relationship between the target rearward tilt angle γt of the trajectory and the target deviation ΔHt of the vehicle height (right half). [Figure 13] 1A is a diagram showing the relationship between the speed ratio Rt and the target vehicle height Ht, and FIG. 1B is a diagram showing the relationship between the gear position St and the target vehicle height Ht. [Figure 14] 4 is a flowchart corresponding to a vehicle height control program according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] [Embodiment] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0019] As shown in Figures 1 and 2, a vehicle height control device 10 according to an embodiment of the present invention is applied to a vehicle 20 including a wheel 12, a drivetrain 14, a suspension arm 16, and a shock absorber 18. The vehicle 20 may be an autonomous vehicle. The wheel 12 is rotatably supported about a rotation axis 24 by a wheel carrier 22, and has an elastically deformable tire 26, as is well known. The drivetrain 14 is configured to rotate the wheel 12 via a transmission 30 and a drive shaft 32 using an engine 28 as a drive source. The suspension arm 16 and the shock absorber 18 are disposed between the wheel carrier 22 and a vehicle body 34.

[0020] 1 shows only one suspension arm, the suspension arm may include multiple arms, links, etc., and suspension arm 16 indicates a suspension arm equivalent to multiple arms, links, etc. when viewed from the side of vehicle 20. The drive source may be any drive source known in the art other than an engine. Furthermore, in the embodiment, transmission 30 is a continuously variable transmission, but may also be a multi-stage transmission such as a gear transmission.

[0021] The suspension arm 16 is disposed between the wheel carrier 22 and the vehicle body 34 so that, when viewed laterally of the vehicle 20, the rotation axis 24 describes a locus 36 that is tilted backward at an angle γ with respect to the vertical as the wheel 12 moves up and down. The end of the suspension arm 16 on the vehicle body 34 side is positioned higher than the end on the wheel carrier 22 side. When the wheel 12 is in a neutral position for vertical displacement, the inclination angle of the suspension arm 16, i.e., the angle that the line connecting both ends of the suspension arm 16 makes with the horizontal, is β. Note that the locus 36 does not have to be a straight line, and the backward inclination angle γ of the locus 36 may be considered to be the same as the inclination angle β within the range of vertical displacement of the wheel 12 as the vehicle 20 moves.

[0022] The shock absorber 18 is disposed between the wheel carrier 22 and the vehicle body 34 in a forward tilted state, and the angle of forward tilt, i.e., the angle that the main axis of the shock absorber (not shown) makes with the vertical direction, is α. The shock absorber 18 is connected at its upper end to the vehicle body 34 via an upper support 38, and at its lower end to the wheel carrier 22. The upper support 38 functions as a spring 38A and a damper 38B.

[0023] The angle γ of the backward tilt of the trajectory 36 and the angle α of the forward tilt of the shock absorber are determined by the longitudinal force F acting on the wheel 12 at the contact point P due to the vertical input from the road surface 40. X 1 is the longitudinal force F generated by the backward tilt of the trajectory 36 X 2 and the longitudinal force F generated by the damping force of the shock absorber X 3.

[0024] For example, FIG. 3A shows the relationship between the vertical displacement Z and the longitudinal force F of the wheel 12 as the unsprung part. X 1 and the longitudinal force F X 1 is a positive value when the vertical displacement Z is positive (upward displacement). FIG. 3(B) shows the relationship between the vertical displacement Z of the wheel 12 and the longitudinal force F X 2 and the longitudinal force F X 2 is a negative value when the vertical displacement Z is positive, and is proportional to the vertical displacement Z. FIG. 3(C) shows the relationship between the vertical displacement Z of the wheel 12 and the longitudinal force F X 3 shows an example of the relationship between the longitudinal force F X 3 is a differential value of the vertical displacement Z, that is, when the upward displacement speed of the wheel 12 is positive, it becomes a negative value and is proportional to the displacement speed.

[0025] Fore-and-aft force F X 2 and F X The sum of these three is the value shown by the dashed line in Figure 3(A). X 1, the longitudinal force F X 2 and F X 3(A) and 3(C), the arrows indicate the longitudinal force FX 1 and F X This shows the direction of change in 3.

[0026] A suspension spring 42 is also disposed between the wheel carrier 22 and the vehicle body 34. In particular, in this embodiment, the suspension spring 42 is an air spring with a height adjustment function, and functions as a height adjustment device configured to change the vehicle height. Therefore, in this specification, the suspension spring 42 will be referred to as a height adjustment device 42 as needed. Note that the suspension spring is a spring such as a coil spring, and the height adjustment device may be any other height adjustment device known in the art other than the suspension spring.

[0027] The vehicle height control device 10 includes a control device 44 that controls the vehicle height adjustment device 42. The control device 44 includes a vehicle height sensor 46, a drivetrain control ECU 48, and a vehicle height control ECU 50. The ECU stands for an electronic control unit that includes a microcomputer as its main component. The vehicle height sensor 46 detects the vehicle height H as the vertical distance between a reference position (not shown) of the vehicle body 34 and the rotation axis 24.

[0028] The microcomputer of each ECU includes a CPU, ROM, RAM, a read / write nonvolatile memory (N / M), and an interface (I / F). The CPU executes instructions (programs, routines) stored in the ROM to realize various functions. Furthermore, these ECUs and sensors such as the vehicle height sensor 46 are connected to each other via a CAN (Controller Area Network) 52 so as to be able to communicate with each other.

[0029] The drivetrain control ECU 48 controls the output torque T of the drivetrain 14, and therefore the drive torque applied to the wheels 12, by controlling the output of the engine 28 and the gear ratio (gear ratio) Rt of the transmission 30. The drivetrain control ECU 48 outputs a signal indicating the gear ratio Rt of the transmission 30 to the vehicle height control ECU 50 via the CAN 52. The gear ratio Rt is calculated based on the equivalent moment of inertia I of the drivetrain 14. P is an index showing the equivalent moment of inertia I P is the product of the sum of the equivalent moments of inertia of the individual components of the transmission 30 and the square of the speed ratio Rt, and is therefore proportional to the square of the speed ratio Rt.

[0030] As will be described in detail later, a longitudinal force F acting on the wheel 12 at the contact point P due to a vertical input from the road surface 40 is X 1 is the equivalent moment of inertia I of the drivetrain 14 P Therefore, the vehicle height control ECU 50 calculates the equivalent moment of inertia I P The vehicle height control ECU 50 obtains information on the gear ratio Rt as an index indicating the equivalent moment of inertia I and controls the vehicle height adjusting device 42 so that the vehicle height H becomes lower as the equivalent moment of inertia I indicated by the index becomes smaller. P longitudinal force F due to change in X The change in the longitudinal force F generated by the backward tilt of the trajectory 36 X The vehicle height adjusting device 42 is controlled so that the change in the backward tilt angle γ of the trajectory required to compensate for the difference 2 is achieved by changing the vehicle height H.

[0031] [Principle of Vehicle Height Control Adopted in the Embodiments of the Present Invention] To facilitate understanding of the present invention and its embodiments, the principle of vehicle height control in the present invention will be described.

[0032] A longitudinal force F acting on the wheel 12 at the contact point P due to vertical input from the road surface 40 X 1 is a longitudinal force F acting on the wheel 12 due to the inclination of the road surface 40. XT (FIG. 4) and the longitudinal force F acting on the wheel due to the slip of the wheel 12. XS(Figure 5)

[0033] As shown in FIG. 4, the inclination angle of the road surface 40 is θ X The ground load of the wheel 12 is defined as W. The steady component of the vehicle speed is defined as U, the fluctuating component of the longitudinal speed of the wheel 12 is defined as ΔU, and the vertical displacement of the road surface 40 is defined as Z0. The longitudinal force F XT is expressed by the following formula (1).

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[0034] As shown in Figures 2 and 5, the driving stiffness is X The slip ratio of the wheel 12 is S X The radius (steady-state component) of the tire 26 is r0, and the fluctuation component of the rolling radius of the tire 26 is ηΔr. Here, η is the ratio of the rolling radius fluctuation amount to the vertical deformation amount of the tire. The steady-state component and fluctuation component of the rotational angular velocity of the wheel 12 are ω0 and Δω, respectively. The longitudinal force F acting on the wheel at the contact point P due to the driving torque applied to the wheel 12 is XW The front and rear spring constants of the tire 26 are K X and the Laplace operator is s. The longitudinal force F XS teeth 、 It is expressed by the following formula (2).

number

[0035] The rotational angular velocities of the drive train 14 and the wheels 12 are respectively ω P and ω T (=ω0+Δω), and the torsional rigidity of the drive shaft 32 is K P Then, the equation of motion in the rotational direction of the drive system 14 is given by the following equation (3).

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[0036] The equivalent moment of inertia of the wheel 12 is I TThen, the equation of motion in the rotational direction of the wheel is given by the following equation (4).

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[0037] From the above equations (3) and (4), the longitudinal force F XW By substituting the above equation (2), the longitudinal force F acting on the wheel 12 is calculated. X 1 is expressed by the following equation (5).

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[0038] In equation (5), h'(s) is a term of dynamic characteristics, and the term in curly brackets is a term of steady-state characteristics. The first and third terms of the steady-state characteristics are the longitudinal force F X The influence on 1 is smaller than that of the second term. Therefore, if the first and third terms are omitted, h'(s) can be expressed by the following equation (6).

number

[0039] In addition, in equation (6), ω E is the resonance frequency of the rotation of the drive system 14 expressed by the following equation (7), and ω W is the resonance frequency of the rotation of the wheel 12, which is expressed by the following equation (8): D is the torsional resonance frequency of the drive shaft 32, i.e., the anti-resonance frequency, expressed by the following equation (9), and ζ W is the damping ratio in the rotational direction of the wheel 12, expressed by the following equation (10).

number

[0040] The upper part of Fig. 6 shows an example of the relationship between the gain of h'(s) and the frequency, and the lower part of Fig. 6 shows an example of the relationship between the phase of h'(s) and the frequency. In Fig. 6, the solid line, the dashed line, and the dashed dotted line respectively represent the equivalent moment of inertia IP The values ​​are shown for 0, 0.43 and 0.60.

[0041] From Figure 6, the equivalent moment of inertia I P As the frequency band of 10 to 20 Hz increases, the gain of h'(s) increases and the phase of h'(s) lags. D It can be seen that it becomes a minimum at .

[0042] The upper part of Figure 7 shows the longitudinal force F from the deflection Z-Z0 of the tire 26. X The bottom part of Fig. 7 shows an example of the relationship between the gain of the transfer function and frequency from deflection Z-Z0 to longitudinal force F X 7 shows an example of the relationship between the phase and frequency of the transfer function to the drive train 14. In FIG. 7, the solid line, the dashed line, and the dashed dotted line respectively represent the equivalent moment of inertia I P The values ​​shown are for 0.4, 0.8 and 1.6.

[0043] From Figure 7, the equivalent moment of inertia I P As the value of Z increases, the deflection Z-Z0 to the longitudinal force F increases in the frequency range of 10 to 20 Hz. X The gain of the transfer function increases to 1, and the longitudinal force F from the deflection Z-Z0 X It can be seen that the phase lag of the transfer function to 1 increases.

[0044] The upper part of Fig. 8 shows an example of the relationship between frequency and gain of the transfer function from deflection Z-Z0 of the tire 26 to vertical displacement Z of the wheel 12, and the lower part of Fig. 8 shows an example of the relationship between frequency and phase of the transfer function from deflection Z-Z0 to vertical displacement Z of the wheel 12. It can be seen from Fig. 8 that the gain and phase of the transfer function from deflection Z-Z0 to vertical displacement Z of the wheel 12 decrease as the frequency increases.

[0045] The object to be controlled is the longitudinal force F from the vertical displacement Z of the wheel 12. X 1, the vertical displacement Z is converted into the longitudinal force F according to the following equation (11) based on the values ​​in Figures 7 and 8. XCalculate the relationship between the gain and phase of the transfer function to 1 and frequency.

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[0046] The upper part of Fig. 9 shows the relationship between the vertical displacement Z and the longitudinal force F X The bottom part of Fig. 9 shows an example of the relationship between the gain of the transfer function and frequency from vertical displacement Z to longitudinal force F X 9 shows an example of the relationship between the phase and frequency of the transfer function to the drive train 14. In FIG. 9, the solid line, the dashed line, and the dashed dotted line respectively represent the equivalent moment of inertia I P The values ​​shown are for 0.4, 0.8 and 1.6.

[0047] Based on FIG. 9, the upper and lower resonance frequencies (15 Hz) of the unsprung wheel 12 are X If 1 / Z is divided into a real part, i.e., a component proportional to the vertical displacement Z, and an imaginary part, i.e., a component proportional to the first derivative of the vertical displacement Z (vertical velocity), and displayed as a vector, Figure 10 is obtained. In Figure 10, the solid line, dashed line, and dashed line arrows respectively represent the equivalent moment of inertia I of the drive system 14. P The vectors for are 0.4, 0.8 and 1.6 are shown.

[0048] Figure 11 shows the relationship between the vertical displacement Z and the longitudinal force F based on Figure 10. X The real part of the transfer function to 1 and the equivalent moment of inertia of the drive system 14 P As can be seen from Figure 11, the vertical displacement Z is used to calculate the longitudinal force F X The real part of the transfer function to 1 is the equivalent moment of inertia I of the drivetrain 14. P increases as increases.

[0049] Vertical displacement Z to longitudinal force F X The real part of the transfer function (forward and backward force F X The longitudinal force F generated by the backward tilt of the locus 34 is required to offset the component proportional to the vertical displacement Z of the locus 34. X 2" is βZK SK The longitudinal force F generated by the backward tilt of the locus 34 per unit vertical displacement Z isX 2" is βK S Therefore, the following equation (12) holds. SK is the elastic modulus of the suspension arm in the direction along the line connecting both ends of the suspension arm 16 (for example, 1,000,000 N / m). βK SK = Vertical displacement Z to longitudinal force F X Real part of transfer function to 1 …(12)

[0050] Therefore, the vertical displacement Z is replaced by the longitudinal force F X The angle of backward tilt of the locus 36 required to cancel out the real part of the transfer function to 1, that is, the target backward tilt angle γt, is expressed by the following equation (13) based on the above equation (12). γt = β = (vertical displacement Z to longitudinal force F X (real part of transfer function to 1) / K SK …(13)

[0051] The left half of FIG. 12 is a graph showing the target rearward tilt angle γt of the trajectory 36 and the equivalent moment of inertia I of the drive train 14 based on FIG. 11. P As shown in the figure, the target rearward tilt angle γt of the trajectory 36 is proportional to the equivalent moment of inertia I of the drivetrain 14. P The right half of FIG. 12 shows the relationship between the target rearward tilt angle γt of the locus 36 and the target vehicle height deviation ΔHt. The target vehicle height deviation ΔHt is the target value of the difference between the target vehicle height Ht and a preset standard vehicle height (ΔHt=0). As shown in the right half of FIG. 12, the smaller the gear ratio Rt, the smaller the target vehicle height deviation ΔHt, and therefore the smaller the gear ratio Rt, the lower the target vehicle height Ht. Therefore, the smaller the target rearward tilt angle γt of the locus 36, and therefore the smaller the equivalent moment of inertia I of the drivetrain 14, the lower the target vehicle height Ht. P In Figure 12, the dashed line indicates the equivalent moment of inertia I P This shows how to calculate the target vehicle height Ht based on the above.

[0052] FIG. 13(A) shows the equivalent moment of inertia I P and the speed ratio Rt of the transmission 30 (IP 13A shows an example of the relationship between the gear ratio Rt and the target vehicle height Ht based on the equation (where Rt is proportional to the square of Rt). As shown in FIG. 13A, the target vehicle height Ht is lower as the gear ratio Rt is smaller.

[0053] In this embodiment, the ROM of the vehicle height control ECU 50 stores a vehicle height control program and a map corresponding to Fig. 13, i.e., a map of the relationship between the gear ratio Rt and the target vehicle height Ht. The program corresponds to the flowchart shown in Fig. 14, and the vehicle height control is executed in accordance with this flowchart.

[0054] <Vehicle height control program according to an embodiment> Next, the vehicle height control in this embodiment will be described with reference to the flowchart shown in Fig. 14. The vehicle height control according to the flowchart shown in Fig. 14 is repeatedly executed at predetermined time intervals by the CPU of the vehicle height control ECU 50 when an ignition switch (not shown) is on.

[0055] First, in step S10, the CPU reads a signal indicating the gear ratio Rt of the transmission 30 from the drivetrain ECU 48. As described above, the gear ratio Rt is calculated by multiplying the equivalent moment of inertia I of the drivetrain 14 by P It is an indicator that shows the following.

[0056] In step S20, the CPU determines the target vehicle height Ht based on the speed ratio Rt by referring to a map corresponding to FIG. 13(A).

[0057] In step S30, the CPU controls the vehicle height adjusting device 42 so that the vehicle height H detected by the vehicle height sensor 46 becomes the target vehicle height Ht.

[0058] As can be seen from the above description, according to the embodiment, the rotation axis 24 of the wheel 12 traces a backward-inclined path 36 in accordance with the vertical displacement of the wheel, so that the longitudinal force F acting on the wheel due to the vertical input from the road surface 40 is x 1 is the longitudinal force F generated by the backward tilt of the trajectory x2. The longitudinal force F acting on the wheel due to the vertical input from the road surface is at least partially offset by x 1 is the equivalent moment of inertia I of the drivetrain 14 P The vehicle height adjuster 42 is controlled so that the vehicle height becomes lower as the equivalent moment of inertia becomes smaller.

[0059] Therefore, the equivalent moment of inertia I of the drive train 14 is P The longitudinal force F acting on the wheel due to the change in x The longitudinal force F generated by the backward tilt of the trajectory according to the change of 1 x Therefore, even if the equivalent moment of inertia of the drivetrain fluctuates, the longitudinal force F acting on the wheels x 1+F x 2, thereby effectively reducing the longitudinal force input from the wheels to the vehicle body.

[0060] In particular, according to the embodiment, the angle γ of the rearward tilt of the trajectory 36 and the angle α of the forward tilt of the shock absorber 18 are set to a value that is proportional to the first longitudinal force F acting on the wheel due to the input from the road surface. x 1 is the second longitudinal force F generated by the backward tilt of the trajectory x 2 and a third longitudinal force F generated by the damping force of the shock absorber. x 3. The equivalent moment of inertia I of the drivetrain 14 is set at an angle at which the P The first longitudinal force F x The change in the second longitudinal force F x The vehicle height adjuster 42 is controlled so that the change in the rearward tilt angle γ of the trajectory required to offset the change in θ2 is achieved by changing the vehicle height H.

[0061] Therefore, the equivalent moment of inertia I of the drive train 14 is P The first longitudinal force F x The change in the second longitudinal force F xThe vehicle height can be controlled so that the backward tilt angle γ of the locus 36 changes with the change in vehicle height H by an angle necessary to offset the change in the speed ratio Rt of the transmission 30. P Even if the equivalent moment of inertia changes, the second longitudinal force can be changed by changing the angle of backward tilt of the trajectory due to a change in the vehicle height so that the change in the first longitudinal force due to a change in the equivalent moment of inertia is offset by the change in the second longitudinal force.

[0062] Also, according to the embodiment, the equivalent moment of inertia I P The first longitudinal force F x The change in the second longitudinal force F x The relationship between the target vehicle height Ht and the index (gear ratio Rt or gear St) (FIG. 13(A) or FIG. 13(B)) for achieving the change in the backward tilt angle γ of the locus 36 required to offset the change in the rearward tilt angle γ of the locus 36 by adjusting the vehicle height H, which is necessary to offset the change in the rearward tilt angle γ of the locus 36 due to the change in the rearward tilt angle γ of the locus 36 due to the change in the rearward tilt angle γ of the locus 36, is stored. Furthermore, the target vehicle height is calculated from the above relationship based on the index, and the vehicle height adjusting device 42 is controlled so that the vehicle height becomes the target vehicle height.

[0063] Therefore, by controlling the vehicle height adjusting device so that the vehicle height becomes the target vehicle height, the equivalent moment of inertia I P Even if the equivalent moment of inertia fluctuates, the second longitudinal force can be changed so that the change in the first longitudinal force accompanying the change in the equivalent moment of inertia is offset by the change in the second longitudinal force.

[0064] As mentioned above, the equivalent moment of inertia I of the drivetrain 14 P is proportional to the square of the gear ratio Rt of the transmission 30, and decreases as the gear ratio of the transmission decreases. According to the embodiment, the relationship between the target vehicle height and the index is the relationship between the target vehicle height Ht and the gear ratio Rt of the transmission (FIG. 13(A)), which is set so that the vehicle height decreases as the gear ratio of the transmission decreases. Therefore, the equivalent moment of inertia I of the drivetrain 14 changes with the change in the gear ratio of the transmission. P Even if the equivalent moment of inertia fluctuates, the vehicle height can be controlled so that the vehicle height becomes lower as the equivalent moment of inertia becomes smaller.

[0065] Furthermore, according to the embodiment, the shock absorber 18 is disposed in a forward tilted position, and the backward tilt angle γ and the forward tilt angle α of the trajectory are determined by the first longitudinal force F X 1 is the second longitudinal force F generated by the backward tilt of the trajectory. X 2 and a third longitudinal force F generated by the damping force of the shock absorber 18. X 3 at least partially offsets the longitudinal force F acting on the wheel. Therefore, compared to when the shock absorber 18 is disposed without being tilted forward, even if the equivalent moment of inertia of the drive train fluctuates, x 1+F x 2+F X 3 can be effectively reduced.

[0066] Although the present invention has been described in detail above with reference to specific embodiments, it will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments, and that various other embodiments are possible within the scope of the present invention.

[0067] For example, in the above embodiment, the equivalent moment of inertia I of the drivetrain 14 is P The relationship between the index indicating the target vehicle height Ht is the relationship between the gear ratio Rt of the transmission 30 and the target vehicle height Ht (FIG. 13(A)). However, if the transmission 30 is a multi-stage transmission, the relationship between the index and the target vehicle height Ht may be the relationship between the gear stage St of the transmission 30 and the target vehicle height Ht (variation example). In that case, the relationship between the gear stage St and the target vehicle height Ht is set so that the target vehicle height is lower the higher the gear stage, for example, as shown in FIG. 13(B).

[0068] In Fig. 13(B), the black circles indicate examples of gear positions. In a modified example, a signal indicating the gear position St is read in step S10 of Fig. 14, and the target vehicle height Ht is calculated in step S20 by referring to a map corresponding to Fig. 13(B) based on the gear position St.

[0069] The gear ratio Rt of the transmission 30 becomes smaller as the gear stage St of the transmission 30 becomes higher. Therefore, the equivalent moment of inertia IP becomes smaller as the gear stage of the transmission becomes higher. According to a modified example, the target vehicle height Ht becomes lower as the gear stage St of the transmission 30 becomes higher. Therefore, the equivalent moment of inertia I of the drivetrain 14 changes with the change in the gear stage of the transmission. P Even if the equivalent moment of inertia fluctuates, the vehicle height can be controlled so that the vehicle height becomes lower as the equivalent moment of inertia becomes smaller.

[0070] In the above-described embodiment, the shock absorber 18 is disposed in a forward-inclined state between the wheel carrier 22 and the vehicle body 34. However, the shock absorber 18 may be disposed in a non-forward-inclined state. [Explanation of symbols]

[0071] 10...Vehicle height control device, 12...Wheel, 14...Drive system, 16...Suspension arm, 18...Shock absorber, 20...Vehicle, 22...Wheel carrier, 24...Rotation axis, 26...Tire, 28...Engine, 30...Transmission, 34...Vehicle body, 36...Trajectory, 40...Road surface, 42...Suspension spring (vehicle height adjustment device), 44...Control device, 50...Vehicle height control ECU

Claims

1. A vehicle height control device applied to a vehicle including a wheel having a tire and supported by a wheel carrier so as to be rotatable about a rotation axis, a drive system that rotates and drives the wheel by a drive source via a transmission, and a suspension arm disposed between the wheel carrier and a vehicle body, The suspension arm is arranged so that, when viewed laterally of the vehicle, the axis of rotation traces a trajectory that tilts backward in accordance with the vertical displacement of the wheel, and the vehicle height control device includes a vehicle height adjustment device configured to change the vehicle height, and a control device that controls the vehicle height adjustment device, and the control device is configured to obtain information on an index that indicates the equivalent moment of inertia of the drive system, and to control the vehicle height adjustment device so that the vehicle height becomes lower as the equivalent moment of inertia indicated by the index becomes smaller.

2. In the vehicle height control device described in claim 1, the angle of the backward inclination of the trajectory is set to an angle at which a first longitudinal force acting on the wheel due to vertical input from the road surface is at least partially offset by a second longitudinal force generated by the backward inclination of the trajectory, and the control device is configured to control the vehicle height adjustment device so that the change in the angle of the backward inclination of the trajectory required to offset the change in the first longitudinal force due to the change in the equivalent moment of inertia with the change in the second longitudinal force is achieved by changing the vehicle height.

3. 3. The vehicle height control device according to claim 2, wherein the control device stores a relationship between a target vehicle height and the index for adjusting the vehicle height to achieve a change in the backward tilt angle of the trajectory required to offset a change in the first longitudinal force due to a change in the equivalent moment of inertia with a change in the second longitudinal force, and is configured to determine the target vehicle height from the relationship based on the index and control the vehicle height adjustment device so that the vehicle height becomes the target vehicle height.

4. 4. The vehicle height control device according to claim 3, wherein the index is a gear ratio of the transmission, and the relationship is a relationship between a target vehicle height and the gear ratio of the transmission, the target vehicle height being set so that the smaller the gear ratio of the transmission, the lower the target vehicle height.

5. 4. The vehicle height control device according to claim 3, wherein the transmission is a multi-stage transmission, the index is a gear stage of the transmission, and the relationship is a relationship between a target vehicle height and a gear stage of the transmission, the target vehicle height being set so that the target vehicle height becomes lower the higher the gear stage of the transmission.

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