Step detection method, damping force control method, and step detection device

Abstract

To determine whether a vehicle gets over a step part which is a sporadically existing projection or a recess or the vehicle is traveling on a road surface with continuous irregularities.SOLUTION: A level difference detection method for detecting a step part which is a projection or recess sporadically existing on a road surface on which a vehicle runs, includes: detecting a wheel speed of the vehicle (S1); extracting high frequency components of the wheel speed (S2); calculating a moving average value of the high frequency components (S4); and determining that there is a step part when the difference between an instantaneous value and the moving average value of the high frequency components is equal to or higher than a threshold and not determining that there is a step part when the difference is less than the threshold (S5, S6).SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a step detection method, a damping force control method, and a step detection device.

Background Art

[0002] When the relative speed between the sprung and unsprung masses on the extension side on the front wheel side of the vehicle suspension device described in Patent Document 1 exceeds a predetermined control threshold value, the damping force characteristic on the extension side of the shock absorber on the rear wheel side is fixed to a predetermined hard characteristic within a subsequent predetermined control time, thereby preventing the bounce of the unsprung mass after crossing a road surface bump.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if the damping force is simply set high after crossing the unevenness of the road surface, when the unevenness of the road surface is continuous, the shock on the sprung mass when crossing the subsequent unevenness increases, and there is a risk that the riding comfort deteriorates instead. An object of the present invention is to determine whether a vehicle has crossed a protrusion or a depression (which may be referred to as a "step portion" in the following description) that exists singly on the road surface on which the vehicle travels, or whether the vehicle is running on a road surface with continuous unevenness.

Means for Solving the Problems

[0005] According to one aspect of the present invention, a step detection method is provided for detecting a step, which is a single protrusion or depression present on the road surface on which a vehicle travels. In the step detection method, the vehicle's wheel speed is detected, the high-frequency component of the wheel speed is extracted, the moving average value of the high-frequency component is calculated, and if the difference between the instantaneous value and the moving average value of the high-frequency component is greater than or equal to a threshold, it is determined that a step exists, and if the difference is less than the threshold, it is not determined that a step exists. [Effects of the Invention]

[0006] According to the present invention, it is possible to determine whether a vehicle has driven over a single, isolated protrusion or depression, or whether it is traveling on a road surface with continuous bumps and dips. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram of an example of a vehicle suspension system according to an embodiment. [Figure 2] This is a block diagram showing an example of the controller's functional configuration. [Figure 3] This is a block diagram showing an example of the functional configuration of the step detection unit. [Figure 4] (a) and (b) are schematic diagrams illustrating examples of the operation of the step detection unit in the case of a smooth road without steps. [Figure 5] (a) and (b) are schematic diagrams illustrating examples of the operation of the step detection unit in the case of a rough road with continuous bumps and dips. [Figure 6] (a) and (b) are schematic diagrams illustrating examples of the operation of the step detection unit when a single step is present. [Figure 7] (a) is a time chart of the output of the step detection unit, (b) is a time chart schematically showing the time change of sprung mass vibration and unsprung mass vibration, and (c) to (e) are time charts schematically showing examples of damping force settings. [Figure 8] This is a flowchart of the step detection method according to the embodiment. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings. Note that the drawings are schematic and may differ from actual ones. Furthermore, the embodiments of the present invention described below are illustrative examples of devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited to the structure, arrangement, etc., of the components described below. The technical concept of the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0009] (composition) Figure 1 is a schematic diagram of an example of a vehicle suspension system according to an embodiment. The vehicle suspension system comprises damping force variable dampers 4FR, 4FL, 4RR, and 4RL interposed between the vehicle body 2 of the vehicle 1 and the right front wheel 3FR, left front wheel 3FL, right rear wheel 3RR, and left rear wheel 3RL, respectively; a controller 5; and wheel speed sensors 6FR, 6FL, 6RR, and 6RL that detect the wheel speeds of the right front wheel 3FR, left front wheel 3FL, right rear wheel 3RR, and left rear wheel 3RL, respectively.

[0010] In the following explanation, the right front wheel 3FR, left front wheel 3FL, right rear wheel 3RR, and left rear wheel 3RL may be collectively referred to as "wheel 3" or "wheels 3FR, 3FL, 3RR, and 3RL". Furthermore, the variable damping dampers 4FR, 4FL, 4RR, and 4RL are sometimes collectively referred to as "variable damping damper 4," and the wheel speed sensors 6FR, 6FL, 6RR, and 6RL are sometimes collectively referred to as "wheel speed sensor 6."

[0011] The variable damping force damper 4 is a damping force generating device that dampens the elastic motion of a coil spring provided between the unsprung mass and sprung mass of the vehicle 1, and the damping force can be changed by operating an actuator. For example, the variable damping damper 4 may be an electronically controlled damper. The electronically controlled damper has a cylinder filled with fluid, a piston that strokes within the cylinder, and orifices that control the fluid movement between fluid chambers formed above and below the piston.

[0012] The piston has orifices of multiple diameters, and when the actuator is operated, an orifice is selected from among the multiple orifices according to the control command. This makes it possible to generate a damping force corresponding to the orifice diameter. For example, if the orifice diameter is small, the movement of the piston is more easily restricted, so the damping force is high. Conversely, if the orifice diameter is large, the movement of the piston is less restricted, so the damping force is low.

[0013] Furthermore, the variable damping force damper 4 applicable to this embodiment is not limited to a configuration in which the damping force is changed by selecting the orifice diameter as described above, but various configurations of variable damping force dampers that can variably control the damping force can be employed. For example, the damping force may be controlled by placing an electromagnetic control valve on a passage connecting fluids formed above and below the piston and changing the amount of opening and closing of this electromagnetic control valve, or the damping force may be controlled by using magnetic fluid as the fluid and changing the fluidity of the fluid.

[0014] Wheel speed sensors 6FR, 6FL, 6RR, and 6RL detect the wheel speeds of the right front wheel 3FR, left front wheel 3FL, right rear wheel 3RR, and left rear wheel 3RL, respectively. Such wheel speed sensors 6 are installed in many vehicle models for control systems such as ABS (Anti-lock Braking System), TCS (Traction Control System), and ESC (Electronic Stability Control). The wheel speed sensor 6 has a gear-shaped rotor mounted on a rotating part such as the drive shaft, axle hub, or brake drum, and a sensor consisting of a coil and magnetic poles is installed on its outer circumference with a gap of about 1 mm. When the rotor rotates, the magnetic flux passing through the coil changes, generating an alternating current, and thus the rotational speed of the wheel 3 is detected.

[0015] Controller 5 is an electronic control unit (ECU) that independently controls the damping force of the variable damping dampers 4FR, 4FL, 4RR, and 4RL, which are mounted on wheels 3FR, 3FL, 3RR, and 3RL, respectively. The controller 5 includes, for example, a computer including a processor 5a and peripheral components such as a storage device 5b. The processor 5a may be, for example, a CPU (Central Processing Unit) or a MPU (Micro-Processing Unit).

[0016] The storage device 5b may include any one of a semiconductor storage device, a magnetic storage device, and an optical storage device. The storage device 5b may include memories such as ROM (Read Only Memory) and RAM (Random Access Memory) used as a main storage device, registers, and cache memories. The functions of the controller 5 described below are realized, for example, when the processor 5a executes a computer program stored in the storage device 5b.

[0017] Note that the controller 5 may be formed of dedicated hardware for executing each information processing described below. For example, the controller 5 may include a functional logic circuit set in a general-purpose semiconductor integrated circuit. For example, the controller 5 may have a programmable logic device (PLD) such as a field-programmable gate array (FPGA).

[0018] FIG. 2 is a block diagram of a functional configuration example of the controller 5. The controller 5 includes a vehicle behavior detection unit 10, a step detection unit 11, and a damping force control unit 12. The vehicle behavior detection unit 10 calculates a reference wheel speed corresponding to the vehicle body speed based on the wheel speed of the wheel 3 detected by the wheel speed sensor 6. For example, the vehicle behavior detection unit 10 may calculate the reference wheel speed by performing low-pass filter processing on the detection value of the wheel speed sensor 6.

[0019] The vehicle behavior detection unit 10 calculates the deviation of the detected values ​​of the wheel speed sensors 6FR, 6FL, 6RR, and 6RL from the reference wheel speed as fluctuations in the wheel speed of wheels 3FR, 3FL, 3RR, and 3RL, respectively. Then, based on the fluctuations in the wheel speeds of wheels 3FR, 3FL, 3RR, and 3RL, the suspension stroke speeds of wheels 3FR, 3FL, 3RR, and 3RL are estimated, thereby estimating the vehicle behavior of vehicle 1, such as sprung displacement, roll, and pitch.

[0020] Assuming that wheel 3 does not slip against the ground when the suspension strokes, the stroke speed can be calculated by multiplying the variation in wheel speed by a conversion coefficient determined according to the suspension geometry. The vehicle behavior detection unit 10 estimates the behavior of the sprung mass (vertical displacement, roll, and pitch) from the calculated stroke velocities of each of the wheels 3FR, 3FL, 3RR, and 3RL.

[0021] The step detection unit 11 detects step areas, which are single protrusions or depressions present on the road surface on which the vehicle 1 travels. The step detection unit 11 detects step areas using the wheel speed signal of the wheel 3 detected by the wheel speed sensor 6. Figure 3 is a block diagram of an example of the functional configuration of the step detection unit 11. The step detection unit 11 includes a high-pass filter (HPF) 20, an absolute value calculation unit 21, an average calculation unit 22, and a determination unit 23.

[0022] The HPF20 extracts high-frequency components (e.g., unsprung resonance frequency components) from the wheel speed signal output by the wheel speed sensor 6 by applying a high-pass filter to it. The absolute value calculation unit 21 calculates the absolute value of the extracted high-frequency components as the instantaneous value IMPt. The average calculation unit 22 calculates the moving average value IMPs of the instantaneous value IMPt. The determination unit 23 detects that the vehicle 1 has crossed the step if the difference between the instantaneous value IMPt and the moving average value IMPs exceeds the threshold Th. If the difference between the instantaneous value IMPt and the moving average value IMPs does not exceed the threshold Th, the vehicle 1 is not detected to have crossed the step.

[0023] The operation examples of the step detection unit 11 are described below. Figures 4(a) and 4(b) show the time changes of the instantaneous value IMPt and the moving average value IMPs, and the step detection results by the step detection unit 11, respectively, when driving on a flat, smooth road without steps. Figures 5(a) and 5(b) show the time changes of the instantaneous value IMPt and the moving average value IMPs, and the step detection results by the step detection unit 11, respectively, when driving on a rough road with continuous bumps. Figures 6(a) and 6(b) show the time changes of the instantaneous value IMPt and the moving average value IMPs, and the step detection results by the step detection unit 11, when a single step is present. In Figures 4(a), 5(a), and 6(a), the solid line represents the instantaneous value IMPt, and the dashed line represents the moving average value IMPs.

[0024] As shown in Figure 4(a), when driving on a flat, smooth road without any steps, no unsprung vibration occurs, resulting in minimal fluctuations in the suspension stroke length. Therefore, the high-frequency components of the wheel speed are small, and the instantaneous IMPt does not fluctuate. As a result, the difference between the instantaneous IMPt and the moving average IMPs does not exceed the threshold Th, and the step detection unit 11 does not detect any steps (Figure 4(b)). As shown in Figure 5(a), when driving on a rough road with continuous bumps and dips, unsprung vibrations continue, resulting in a large moving average IMPs. As a result, the difference between the instantaneous IMPt and the moving average IMPs does not exceed the threshold Th, and therefore the step detection unit 11 does not detect the step (Figure 5(b)).

[0025] As shown in Figure 6(a), if there is a single, isolated step, when vehicle 1 reaches the step at time t0, the instantaneous value IMPt increases, and the difference between the moving average IMPs and the instantaneous value IMPt becomes large. When the difference between the instantaneous value IMPt and the moving average IMPs exceeds the threshold Th at time t1, it is detected that vehicle 1 has crossed the step (Figure 6(b)).

[0026] Refer to Figure 2. The damping force control unit 12 sets target values ​​for the damping force of each of the variable damping force dampers 4FR, 4FL, 4RR, and 4RL for each wheel 3FR, 3FL, 3RR, and 3RL, based on the vehicle behavior estimated by the vehicle behavior detection unit 10. The damping force control unit 12 controls the variable damping force damper 4 so that its damping force reaches the target value. The damping force control unit 12 comprises a basic control unit 12a and a damping force correction unit 12b.

[0027] The basic control unit 12a calculates target damping force values ​​based on skyhook control and sets the damping force of each variable damping force damper 4 accordingly. The skyhook control theory envisions the vehicle body being suspended and fixed from the air, with the shock absorbers supported between the vehicle body and the air. By generating control command values ​​according to this theory and inputting equivalent control command values ​​to the variable damping force damper 4, the ride comfort is improved.

[0028] The damping force correction unit 12b corrects the target value of the damping force of the variable damping damper 4 when the step detection unit 11 detects that the vehicle 1 has gone over a step. In other words, it changes the setting of the damping force of the variable damping damper 4 depending on whether or not a step is detected. The following describes examples of damping force settings for the variable damping damper 4 when overcoming a step, referring to Figures 7(a) to 7(e).

[0029] Figure 7(a) shows the detection timing at which the step detection unit 11 detects that the vehicle 1 has crossed the step, similar to Figure 6(b). Figure 7(b) is a time chart schematically showing the time evolution of sprung mass and unsprung mass vibrations when vehicle 1 goes over a bump without correcting the damping force. The solid line shows the vertical acceleration of the unsprung mass vibration, and the dashed line shows the vertical acceleration of the sprung mass vibration. In the example shown in Figure 7(b), we assume that vehicle 1 crosses the step at time t1, after a period T0 has elapsed during which vehicle 1 has been traveling without crossing the step. When vehicle 1 crosses the step at time t1, a large shock is input to vehicle 1, causing the sprung mass and unsprung mass to vibrate significantly up and down. Therefore, as shown in Figure 7(a), the step detection unit 11 detects that vehicle 1 has crossed the step.

[0030] The vibrations do not subside immediately, but gradually decrease in amplitude. These continuous vibrations have a low frequency and give the occupants a floating sensation, so they need to be dampened quickly to improve ride comfort. Therefore, if the damping force correction unit 12b detects the presence of a step, it may set the target value of the damping force of the variable damping damper 4 to be higher than it would be if it did not detect the presence of a step. For example, the lower limit of the target value of the damping force of the variable damping damper 4 may be set to be higher than it would be if it did not detect the presence of a step.

[0031] Figure 7(c) is a time chart schematically showing a first example of setting the damping force of the variable damping damper 4 by the damping force correction unit 12b. For example, the damping force correction unit 12b may set the target value of the damping force of the variable damping damper 4 to be greater in the period T2, which starts at time t2, later than the time t1, when a step is detected, than in the period T0, when no step is detected. This allows for faster damping of continuous vibrations of the unsprung mass. For example, the length of the period T2 may be appropriately set to a fixed length corresponding to the mass of the wheel of the vehicle 1 and the spring constant (stiffness) of the tire. For example, it may be set to an appropriate length in advance through experiments or simulations.

[0032] However, setting the damping force too high while driving on rough roads with continuous bumps will worsen ride comfort. This is because, when driving on rough roads, the unsprung stroke is large, and if the damping force is set too high, road vibrations are directly transmitted to the sprung mass. For this reason, it is preferable to set the damping force of the variable damping damper 4 to a higher level only when driving over a single bump on a smooth road, and only after driving over the bump. Subsequently, at time t3, after period T2 has elapsed, the damping force correction unit 12b may return the target value of the damping force of the variable damping force damper 4 to the target value in period T0, when it is not determined that there is a step.

[0033] Figure 7(d) is a time chart schematically showing a second example of setting the damping force of the variable damping damper 4 by the damping force correction unit 12b. The damping force correction unit 12b may set the target value of the damping force of the variable damping damper 4 immediately after detecting the step over at time t1 to be smaller than when it is not determined that there is a step. For example, the upper limit of the target value of the damping force of the variable damping damper 4 may be set to be smaller than when it is not determined that there is a step. This makes it possible to suppress the large shock being input to the sprung mass when going over a step.

[0034] In the example shown in Figure 7(d), the target value of the damping force of the variable damping damper 4 during period T1, which begins immediately after time t1 when the step is detected, is set to be smaller than the target value during period T0 when no step is detected. For example, the length of period T1 may be appropriately set to a fixed length corresponding to the mass of the vehicle 1's wheel and the spring constant (stiffness) of the tire. Subsequently, at time t2, after period T1 has elapsed, the damping force correction unit 12b returns the target value of the damping force of the variable damping damper 4 to the target value during period T0 when no step is detected.

[0035] Figure 7(e) is a time chart schematically showing a third example of setting the damping force of the variable damping damper 4 by the damping force correction unit 12b. The damping force correction unit 12b may set the target value of the damping force of the variable damping damper 4 immediately after detecting crossing the step at time t1 to be smaller than when it is not determined that there is a step, and then set the target value of the damping force of the variable damping damper 4 thereafter to be larger than when it is not determined that there is a step.

[0036] In the example shown in Figure 7(e), the target value of the damping force of the variable damping damper 4 during period T1, which begins immediately after time t1 when the step is detected, is set to be smaller than the target value during period T0 when no step is detected. This suppresses the large shock being input to the sprung mass when the vehicle steps over a step. In period T2, which begins at time t2 after period T1 has elapsed, the target value of the damping force of the variable damping damper 4 is set higher than in period T0, when no step is detected. This allows for faster damping of continuous vibrations of the unsprung mass. At time t3, after period T2 has elapsed, the damping force correction unit 12b returns the target value of the damping force of the variable damping force damper 4 to the target value in period T0, when it is not determined that there is a step.

[0037] In addition to detecting when the vehicle 1 has driven over a step, the step detection unit 11 may also detect continuous irregularities on the road surface. For example, it may determine whether the vehicle 1 is traveling on a road with continuous irregularities (rough road). For example, the step detection unit 11 may detect continuous irregularities on the road surface when the magnitude of the moving average IMPs is greater than or equal to a threshold, or when the state in which the magnitude of the moving average IMPs is greater than or equal to a threshold continues for a predetermined period of time or longer.

[0038] When the step detection unit 11 detects continuous irregularities on the road surface, the damping force correction unit 12b does not need to set the target value of the damping force of the variable damping damper 4 when continuous irregularities are detected to a value greater than the target value when no step is detected. In other words, it may be set to a value less than or equal to the target value when no step is detected. For example, when continuous irregularities are detected, the damping force of the variable damping damper 4 after determining the presence of irregularities may be set to less than or equal to the damping force of the variable damper after determining the presence of a step (which is not a continuous irregularity) when a step is detected. This prevents the ride comfort from deteriorating due to the damping force of the variable damper 4 being set too high when driving on a road surface with continuous bumps and unevenness.

[0039] (operation) Figure 8 is a flowchart of the step detection method according to the embodiment. In step S1, the controller 5 acquires the wheel speed signal (sensor information) of wheel 3 output by the wheel speed sensor 6. In step S2, the HPF20 of the step detection unit 11 extracts the high-frequency components of the wheel speed signal by applying a high-pass filter to the wheel speed signal of the wheel 3.

[0040] In step S3, the absolute value calculation unit 21 calculates the absolute value of the extracted high-frequency component as the instantaneous value IMPt. In step S4, the averaging unit 22 calculates the moving average IMPs of the instantaneous value IMPt.

[0041] In step S5, the determination unit 23 determines whether the difference between the instantaneous value IMPt and the moving average value IMPs exceeds the threshold Th. If the difference between the instantaneous value IMPt and the moving average value IMPs does not exceed the threshold Th (step S5:N), the process ends. In this case, the determination unit 23 does not detect that the vehicle 1 has crossed the step.

[0042] On the other hand, if the difference between the instantaneous value IMPt and the moving average value IMPs exceeds the threshold Th (step S5:Y), the process proceeds to step S6. In step S6, the determination unit 23 detects that vehicle 1 has crossed the step. The process then ends.

[0043] (Effects of the embodiment) (1) The controller 5 detects any steps or depressions that are isolated protrusions or depressions on the road surface on which the vehicle 1 is traveling. The controller 5 detects the wheel speed of the vehicle 1, extracts the high-frequency component of the wheel speed, calculates the moving average value of the high-frequency component, and determines that there is a step if the difference between the instantaneous value and the moving average value of the high-frequency component is greater than or equal to a threshold, and does not determine that there is a step if the difference is less than the threshold. This allows for the distinction between steps, which are spontaneously occurring protrusions or depressions, and continuous unevenness such as that found on rough roads. Furthermore, since sensors that detect wheel speed are installed in many vehicles, steps can be detected at a low cost.

[0044] (2) The controller 5 may change the setting of the damping force of the variable damping damper 4, which is interposed between the vehicle body 2 and the wheels 3 of the vehicle 1 and can variably control the damping force, depending on whether it is determined that there is a step or not. This makes it possible to suppress the amplitude of vibrations in the sprung mass caused by the shock when vehicle 1 goes over a step, and the fluttering of the unsprung mass after vehicle 1 has gone over the step.

[0045] (3) The controller 5 may set the damping force of the variable damping damper 4 to be greater than the damping force of the variable damping damper 4 when it is determined that there is a step, after it has determined that there is a step. This helps to suppress vibrations in the unsprung mass after going over bumps. If the unsprung mass is bouncy, a floaty vibration remains after going over bumps, worsening the ride comfort, but this can be suppressed.

[0046] (4) When the controller 5 detects continuous irregularities on the road surface, it may set the damping force of the variable damping damper 4 after it has determined that there are irregularities to be present, to be less than or equal to the damping force of the variable damping damper 4 after it has determined that there are steps or uneven surfaces. This prevents the ride comfort from deteriorating due to the damping force of the variable damping damper 4 being set too high when driving on a road surface with continuous bumps and unevenness. [Explanation of Symbols]

[0047] 1...Vehicle, 2...Body, 3FL...Left front wheel, 3FR...Right front wheel, 3RL...Left rear wheel, 3RR...Right rear wheel, 4FL, 4FR, 4RL, 4RR...Variable damping force damper, 5...Controller, 5a...Processor, 5b...Memory device, 6FL, 6FR, 6RL, 6RR...Wheel speed sensor, 10...Vehicle behavior detection unit, 11...Step detection unit, 12...Damping force control unit, 12a...Basic control unit, 12b...Damping force correction unit, 20...High-pass filter (HPF), 21...Absolute value calculation unit, 22...Average calculation unit, 23...Decision unit

Claims

1. A step detection method for detecting a step, which is a single protrusion or depression present on the road surface on which a vehicle travels, The wheel speed of the aforementioned vehicle is detected, The high-frequency component of the aforementioned wheel speed is extracted, The moving average value of the aforementioned high-frequency component is calculated, If the difference between the instantaneous value of the high-frequency component and the moving average value is greater than or equal to a threshold, it is determined that the step portion exists; if the difference is less than the threshold, it is not determined that the step portion exists. A method for detecting steps, characterized by the features described above.

2. The step detection method described in claim 1 determines whether or not there is a step on the road surface on which the vehicle is traveling, A damping force control method characterized by changing the setting of the damping force of a variable damping damper, which is interposed between the vehicle body and the wheels and capable of variably controlling the damping force, between when it is determined that there is a step and when it is not determined that there is a step.

3. The damping force control method according to claim 2, characterized in that, when it is determined that there is a step, the damping force of the variable damping force damper is set to be greater than the damping force of the variable damping force damper when it is not determined that there is a step, after it has been determined that there is a step.

4. The damping force control method according to claim 3, characterized in that when continuous irregularities are detected on the road surface, the damping force of the variable damping force damper after determining the presence of irregularities is set to be less than or equal to the damping force of the variable damping force damper after determining the presence of a step when a step is determined to exist.

5. A step detection device for detecting a step, which is a single protrusion or depression present on the road surface on which a vehicle travels, A wheel speed sensor for detecting the wheel speed of the vehicle, A controller that performs the following processes: extracting the high-frequency component of the wheel speed detected by the wheel speed sensor; calculating a moving average value of the high-frequency component; determining that there is a step if the difference between the instantaneous value of the high-frequency component and the moving average value is greater than or equal to a threshold; and not determining that there is a step if the difference is less than the threshold. A step detection device characterized by comprising the following features.

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