JP3687465B2 - Suspension system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a suspension system that performs various types of estimation processing and control / determination processing based on a resonance frequency included in a vibration frequency component of a running tire.
[0002]
[Prior art]
An example of a service scan pension system is disclosed, for example, in JP-A-6-297923. In this suspension system, the tire air pressure is indirectly detected by calculating a resonance frequency component depending on the tire air pressure from the tire rotation speed signal. In addition, the resonance frequency varies depending on the wear state in addition to the tire air pressure as described above, but the present applicant has found that the resonance frequency also varies depending on the temperature, and the resonance frequency is maintained while maintaining the tire at a predetermined temperature. A method for measuring the above was proposed previously (Japanese Patent Laid-Open No. 11-237319).
[0003]
[Problems to be solved by the invention]
However, when using an unused tire and measuring the resonance frequency over a long period of time with the atmospheric temperature at the time of measurement and the air pressure of the tire being constant, as the elapsed time from the time of tire manufacture increases, It has been experimentally clarified that the measured resonance frequency increases. Therefore, in the suspension system that detects the air pressure of the previous tire, the estimation error of the tire air pressure increases as the elapsed time from the tire manufacture increases.
[0004]
In such a tire pressure detection system, when the tire is viewed as one spring, the spring constant and the tire air pressure are in a constant relationship, and the tire spring constant and the tire resonance frequency are in a constant relationship. The suspension system that uses this relationship directly or indirectly includes vehicle vibration control such as shock absorber damping force control, air suspension spring constant control, and VSC (Vehicle). Examples include vehicle mobility control such as Stability Control (ABS) control, ABS (Antilock Brake System) control, and BA (Brake Assist) control. In all these suspension systems, with the temporal characteristic change of tire material not considered.
[0005]
Accordingly, the present invention has been made to solve such problems, and an object of the present invention is to provide an optimal suspension system that takes into account changes in the characteristics of tire materials over time.
[0006]
[Means for Solving the Problems]
Suspension system according to claim 1, the determination and storage means for storing the temporal characteristic change of tire material, time elapsed after the tires using the characteristics change (days, months, years, etc.) determining means for, and control means for controlling the vehicle braking, and correcting means for correcting the control processing by the control means based on the time elapsed after the determined tire mounted to the judgment means, the amount of depression of the brake pedal (speed) And a brake pedal depression amount (speed) detecting means for detecting .
[0007]
Furthermore, the control device is a brake assist device, and increases the brake assist force when the depression amount (speed) detected by the brake pedal depression amount (speed) detection means exceeds a predetermined threshold value. The correction unit performs the correction to decrease the threshold value as the time passage detected by the determination unit increases.
[0008]
Storage Hand stage, or grasp the temporal characteristic change of the tire material in advance experimentally or the like based on the transition state of the resonance frequency of the tire was adjusted to prescribed air pressure, temporal characteristic change of the tire The state of is memorized . In the determination means, for example, the passage of time after tire mounting is determined based on the transition state of the resonance frequency. Then, the correction means, in consideration of the time course of the tire is grasped by the judgment means, a control process executed in the control unit (vehicle motility control) is corrected to be optimum.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0010]
First, prior to the description of the embodiment of the present invention, the first and second reference examples will be described. These reference examples include a detection unit that detects a signal including a vibration frequency component of a tire when the vehicle is traveling, an extraction unit that extracts a resonance frequency component of the tire based on a signal detected by the detection unit, and an extraction unit. And a correction unit that corrects the resonance frequency extracted based on the characteristic change of the tire material with time, and an estimation unit that estimates the tire air pressure based on the resonance frequency corrected by the correction unit. Is.
[0011]
These reference examples also include a description of techniques leading to the present invention. The tire air pressure is estimated based on the relationship between the tire air pressure and the tire resonance frequency while taking into account the change in the tire characteristics over time. In these reference examples, the extracted resonance frequency is corrected based on the change in characteristics of the tire material over time, and the tire air pressure is estimated by the estimation means based on the corrected resonance frequency.
[0012]
First, changes with time in tire vibration characteristics will be described. FIG. 1 is a diagram showing a method for experimentally measuring the vibration characteristics of a tire. The tire 10 is set in the thermostat 2 in a state of being suspended from above by a rope 12. The temperature in the thermostat 2 is maintained constant, and the temperature of the tire itself is also maintained constant. An acceleration sensor 14 is fixed to the tread portion 10 a of the tire 10 with an adhesive or the like, and the acceleration sensor 14 is connected to an FFT analyzer 16.
[0013]
In this state, the tire 10 is vibrated by hitting the tread portion 10a of the tire 10 with a hammer (not shown). The vibration of the tire 10 is detected by the acceleration sensor 14, and the detected acceleration signal is input to the FFT analyzer 16, and the FFT analyzer 16 analyzes a frequency component included in the input acceleration signal. Then, the gains of the respective frequency components are compared, and the frequency having the maximum value is set as the resonance frequency fr.
[0014]
In this way, the resonance frequency fr of the tire 10 is detected. FIG. 2 shows a detection result when the resonance frequency fr of the tire 10 is detected over time by the same measurement method. During this time, the tire 10 was stored unused, and the resonance frequency fr was measured under the same conditions of the air pressure, the atmospheric temperature, and the atmospheric pressure in the tire 10. As shown in FIG. 2, even when the resonance frequency fr is measured under the same conditions as described above, the measured resonance frequency fr gradually increases with the passage of time. It is presumed that this is caused by a change in characteristics of the tire material over time. Although FIG. 2 shows an increasing tendency at a substantially constant rate, the results of the same measurement using different types of tires are as shown in FIG. 3, and the resonance frequency fr is increasing with time. However, there were some differences depending on the material and structure of the tire.
[0015]
Therefore, a first reference example of a suspension system in consideration of such a change in tire characteristics over time will be described below.
[0016]
FIG. 4 shows a suspension system that estimates the tire air pressure. Each vehicle wheel is equipped with a tire 101, and each tire 101 is provided with a rotational speed sensor 102 that detects the rotational speed of the opposite tire. It has been. The rotational speed sensor 102 includes a gear 102a that rotates together with the tire 101, and a pickup coil 102b, and an AC signal having a period corresponding to the rotational speed of the tire 101 is output from the pickup coil 102b. In addition, a day counter 104 that counts the number of days elapsed after the tire is mounted is provided. The day counter 104 starts counting the number of days when a start switch (not shown) that starts counting is pressed. The AC signal and the day count value output from the pickup coil 102b are input to the control device 100, and a predetermined control process described later is performed. The result of this control processing is given to the display unit 103, and the display unit 103 individually displays the air pressure of the tire 101 attached to each wheel, or turns on an alarm lamp indicating a tire whose air pressure has dropped.
[0017]
Here, the process of estimating the tire air pressure performed in the control device 100 will be described with reference to the flowchart of FIG. Note that this flowchart is activated when a condition for enabling the tire air pressure estimation process to be executed is satisfied. As a condition that the estimation process can be performed, for example, a situation where the vehicle is traveling straight on a relatively flat road surface at a constant vehicle speed can be cited.
[0018]
First, the process proceeds to step 102 (hereinafter “step” is referred to as “S”), and the detection result of the rotation speed sensor 102 is read. In the subsequent S104, a signal including the vibration component of the wheel is extracted from the detection result of the rotation speed sensor 102. Then, frequency analysis calculation (FFT calculation) is performed on the extracted signal.
[0019]
In the subsequent S106, the number N of FFT calculations is incremented. In the next S108, it is determined whether the number N of calculations is greater than or equal to the reference value No. If “No”, the current routine is terminated.
[0020]
If “Yes” is determined in S108, the process proceeds to S110, where an averaging process for averaging the FFT calculation results is performed, and the average value of the gain of each frequency component is calculated. In S112, the moving average process is performed on the average value of the gain of each frequency component. That is, the gain Y (n) of the nth frequency is calculated as an average value of the gains Y (n + 1) and Y (n−1) of the n + 1th and n−1th frequencies. In subsequent S114, the frequency at which the maximum value is obtained from each gain calculated in S112 is set as the resonance frequency fr.
[0021]
In subsequent S116, the correction value fd for the resonance frequency fr obtained in S114 is set according to the count value of the day counter 104 based on the map of FIG. The map in FIG. 6 is a map obtained by experimentally examining and learning the situation in which the resonance frequency of the tire changes over time, and mapping the results. Here, as a learning result, a map corresponding to two types of tires indicated by a solid line and a dotted line is provided, and a suitable map corresponding to the type of tire is selected by operating a setting switch indicating the type of tire. .
[0022]
In the subsequent S118, a frequency obtained by subtracting the correction value fd from the resonance frequency fr set in S114 is newly set as the resonance frequency fr. Then, the process proceeds to S120, and the air pressure P of the tire 101 corresponding to the resonance frequency fr updated in S118 is set (estimated) based on the map shown in FIG.
[0023]
By executing the tire air pressure estimation process in this way, it is possible to perform a more accurate estimation process that takes into account the change in characteristics of the tire material over time.
[0024]
When a new tire is mounted, the resonance frequency of the tire 101 adjusted to the specified pressure at this time is stored as the initial value fo, and the tire air pressure is set to the specified pressure during subsequent vehicle inspections. Immediately after the adjustment, the estimation process shown in FIG. 5 is executed. Thereby, by comparing the resonance frequency fr before correction set in S114 at this time with the initial value fo, from the magnitude of the deviation (corresponding to the correction value fd) using the map of FIG. It is also possible to grasp the time lapse situation (days, months, etc.) after wearing the tire.
[0025]
A second reference example will be described.
[0026]
Here, a suspension system that performs damping force control of a shock absorber as vehicle vibration control will be described. This system includes a learning unit that learns a change in characteristics of a tire material over time, a determination unit that determines the passage of time after the tire is mounted, a control unit that controls the vibration of a vehicle, and a tire learned by the learning unit. Compensation means for correcting the control processing (vehicle vibration control) by the control means based on the change in characteristics of the material over time and the time elapsed after the tire mounting determined by the determination means. In this reference example, the learning means learns the state of the characteristic change with time of the tire, and the judgment means judges the passage of time after the tire is mounted. Then, in consideration of the tire characteristic change state grasped by the learning means and the judgment means, correction is performed so that the control processing (vehicle vibration control) executed by the control means is optimized by the correction means.
[0027]
FIG. 8 schematically shows a shock absorber with variable damping force. The upper end side of the piston rod 220 constituting the shock absorber 200 is connected to a vehicle body (not shown) as a spring, and the lower end side of the main body 210 is connected to a suspension member as an unspring. A control valve for changing the damping force is housed inside the main body 210 of the shock absorber 200. By changing the valve opening amount of the control valve by an actuator 230 fixed to the vehicle body, the maximum value (hard) Can be switched continuously from the lowest value (soft). The control device 240 performs drive control of the actuator 230 based on the detection result of the rotation speed sensor 250 that detects the rotation speed of the wheel.
[0028]
The control process of the actuator 230 implemented by the control apparatus 240 is demonstrated along the flowchart of FIG.
[0029]
First, in S202, the resonance frequency fr is set by the same processing as S102 to S114 in FIG. 5 described above, and in subsequent S204, the correction value fd for the resonance frequency fr obtained in S114 based on the map in FIG. Is set according to the count value of the day counter 104. In the subsequent S206, a frequency obtained by subtracting the correction value fd from the resonance frequency fr set in S204 is newly set as the resonance frequency fr.
[0030]
In subsequent S208, the hardness of the unsprung system formed by the tire and the bush is calculated based on the obtained resonance frequency fr. This is to serve as a basis for judging changes in tire and bush characteristics. The resonance frequency fr is a value inherent to the elastic modulus k1 of the bush and the elastic modulus k2 of the tire, and the calculation of the unsprung hardness can be easily obtained by calculating back the resonance frequency fr.
[0031]
In subsequent S210, it is determined whether or not the hardness of the tire and the bush calculated in S208 is harder than a predetermined level. If the unsprung hardness is high, the process proceeds to S212, and in order to cancel the hardness on the spring, the required damping force value of the shock absorber 200 is set to the soft side by a predetermined value from the present, and the unsprung hardness is soft. If so, the process proceeds to S214, and the required damping force value is set to the hardware side by a predetermined value from the current value.
[0032]
In S216, the actuator is driven according to the damping force requirement value set in S212 or S214.
[0033]
By variably controlling the damping force of the shock absorber in this way, it is possible to carry out a suitable damping force variable control that takes into account changes in characteristics of the tire material over time.
[0034]
Such unsprung vibration control includes air suspension spring constant control, and as implemented in S204 and S206, the resonance frequency fr is set in consideration of changes in the tire material over time. A correction process may be performed, and a specific description is omitted.
[0035]
An embodiment of the present invention will be described.
[0036]
Here, a case where the present invention is applied to a suspension system equipped with a brake assist device that generates a larger braking force during emergency braking will be described.
[0037]
FIG. 10 schematically shows the configuration of the brake assist device. The support part of the brake pedal 310 is provided with a stroke sensor 320 that detects the amount of depression of the brake pedal 310. Based on the detection result of the stroke sensor 320, the control device 300 determines whether or not emergency braking is performed. On the other hand, the brake booster 330 is provided with a solenoid valve 340 for introducing air into the booster. Under the control of the control device 300, air is introduced into the booster via the solenoid valve 340, so that the brake assist is performed. It has a structure that increases its power.
[0038]
Of the control processes performed by the control device 300, the determination process for determining the brake assist start timing will be described with reference to the flowchart of FIG.
[0039]
First, in step S302, the depression amount L of the brake pedal 310, which is the detection result of the stroke sensor 320, is read. In step S304, the depression speed VL of the brake pedal 310 is calculated from the time displacement of the depression amount L.
[0040]
In subsequent S306, an elapsed time after tire mounting or tire manufacturing is determined. As an example of this determination, the resonance frequency fr immediately after being adjusted to the specified pressure as described above is detected, and the elapsed time is determined from the deviation from the initial value fo .
[0041]
In subsequent S308, based on FIGS. 12A and 12B, threshold values Lth and VLth corresponding to the elapsed time determined in S306 are set. By executing S308, the threshold values Lth and VLth are set so as to become smaller as the elapsed time increases in consideration of the change in characteristics of the tire material over time.
[0042]
In subsequent S310, it is determined whether or not the depression amount L of the brake pedal 310 is larger than the threshold value Lth. If “Yes”, it is determined that the emergency braking state in which the brake pedal 310 is largely depressed and the process proceeds to S312. Immediately start the brake assist. As a result, the solenoid valve 340 is controlled to be opened by the control device 300, the atmospheric pressure is introduced into the brake booster 330, and the assist force of the brake is increased.
[0043]
On the other hand, if “No” in S310, the process proceeds to S314, where it is determined whether the depression speed VL of the brake pedal 310 is greater than the threshold value VLth. If “Yes”, the brake pedal 310 is depressed quickly. In this case as well, it is determined that the emergency braking state is set, and the process proceeds to S312 to start the brake assist.
[0044]
By performing such determination processing, the threshold values Lth and VLth are set to smaller values as the elapsed time after tire mounting or tire manufacturing becomes longer, so that the brake assist is started earlier. be able to.
[0045]
【The invention's effect】
As described above, the suspension system according to the present invention includes the time-dependent characteristic change of the tire material stored by the storage means, and the time course after the tire mounting determined by the determination means using this characteristic change. Basically, a correction means for correcting the control processing by the control means is provided. Here, the control device is a brake assist device, and increases the brake assist force when the depression speed detected by the brake pedal depression speed detection means exceeds a predetermined threshold value. As the passage of time detected by the means increases, the above-described correction for reducing the threshold value is performed. By doing so, it is possible to optimize the control (brake assist control) by the control means.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a method for experimentally measuring the vibration characteristics of a tire.
FIG. 2 is a diagram showing a state of change in resonance frequency over time.
FIG. 3 is a diagram showing a state of change in resonance frequency over time.
FIG. 4 is a block diagram schematically showing a suspension system for estimating tire air pressure.
FIG. 5 is a flowchart showing tire pressure estimation processing;
FIG. 6 is a map showing a result of learning a relationship between a count value (days) and a correction value.
FIG. 7 is a map showing the relationship between resonance frequency and tire air pressure.
FIG. 8 is a configuration diagram schematically showing a configuration of a shock absorber damping force control apparatus;
FIG. 9 is a flowchart illustrating an example of operation control of an actuator that changes a damping force.
FIG. 10 is a block diagram schematically showing a configuration of a brake assist device.
FIG. 11 is a flowchart showing a process for determining a brake assist start timing.
12A is a map that defines the relationship between the elapsed time and the threshold of the depression amount, and FIG. 12B is a map that defines the relationship between the elapsed time and the threshold of the depression speed.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Tire, 102 ... Rotational speed sensor, 100 ... Control apparatus 104 ... Days counter, 200 ... Shock absorber 210 ... Main body, 220 ... Piston rod, 230 ... Actuator 240 ... Control apparatus, 250 ... Rotational speed sensor, 300 ... Control apparatus 310 ... Brake pedal, 320 ... Stroke sensor 330 ... Brake booster, 340 ... Solenoid valve

Claims (2)

Storage means for storing changes in the tire material over time;
Determining means for determining timing elapsed after tires or after tire manufacture on the basis of the temporal characteristic change of tire material stored by said storage means, and control means for controlling the vehicle braking, determined by the previous SL determining means Correction means for correcting the control processing by the control means based on the elapsed time after the tire is mounted, and a brake pedal depression amount detection means for detecting the depression amount of the brake pedal,
The control device is a brake assist device, and increases the brake assist force when the depression amount detected by the brake pedal depression amount detection unit exceeds a predetermined threshold value.
It said correction means, suspension system wherein according to the elapsed time detected is increased by the determination means, you and performs correction to reduce the threshold. Storage means for storing changes in the tire material over time;
Determining means for determining timing elapsed after tires or after tire manufacture on the basis of the temporal characteristic change of tire material stored by said storage means, and control means for controlling the vehicle braking, determined by the previous SL determining means Correction means for correcting the control processing by the control means based on the elapsed time after the tire is mounted , and brake pedal depression speed detection means for detecting the depression speed of the brake pedal,
The control device is a brake assist device, and increases the brake assist force when the depression speed detected by the brake pedal depression speed detection means exceeds a predetermined threshold value,
It said correction means, suspension system wherein according to the elapsed time detected is increased by the determination means, you and performs correction to reduce the threshold.

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