JP2005306110A - Road surface condition sensing control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a road surface condition sensing device of a preliminarily working type for suppressing the number of sensing runs of the friction coefficient of the road surface, in a vehicle equipped with a function to sense the friction coefficient of the road surface. <P>SOLUTION: The road surface condition sensing device of a vehicle is equipped with a wheel rotating speed sensing means (step S11) to sense the rotating speed of each wheel, a frequency analyzing means (step S11) to subject the vehicle rotating speed sensed by the sensing means to a frequency analysis, and a road surface condition change judging means (step S16) to judge the arrival of the sensing timing of the road surface condition on the basis of the analytical result analyzed by the frequency analyzing means. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle including a road surface state detection control device that detects a change in road surface state while the vehicle is traveling.

  In recent years, various traveling controls have been performed in order to improve the traveling performance of vehicles. For example, there is a case where control is performed to change the front / rear and left / right driving force ratios according to road surface conditions. In such a case, means for accurately detecting the road surface condition is required.

  The road surface condition can be considered as a change in the friction coefficient of the road surface, but the friction coefficient cannot be directly grasped as a state quantity of the vehicle. Therefore, the invention of Patent Document 1 is configured to apply an additional driving force to a wheel, detect a wheel slip point from a change in wheel speed, and obtain a friction coefficient from various forces applied to the wheel at the slip point. Yes.

Further, the invention of Patent Document 2 shows that when an additional driving force is generated on a certain wheel, a braking force is generated on another wheel to prevent the vehicle from feeling acceleration and deceleration, and the wheel when the wheel slips. The road surface friction coefficient is estimated from the time change of the speed.
JP 2001-171504 A JP 2001-354129 A

  According to the invention of Patent Document 1, slip is generated in the wheel to be detected for the friction coefficient, and the speed change of the wheel at that time is detected. Therefore, the actual road surface friction coefficient can be detected with high accuracy. Further, according to the invention of Patent Document 2, it is possible to prevent acceleration / deceleration that occurs when a driving force is applied to detect a friction coefficient.

  However, since a driving force for generating slip on the wheels has to be added, the burden on the driving system increases. Further, since the road surface condition changes every moment during traveling, conventionally, a driving force is regularly added, and a braking force for suppressing acceleration due to the driving force must be applied to the wheels via a brake. Also, the load on the braking system increases. In other words, since the brakes are applied regularly, there is a problem that the brake pads are easily worn out, and repeated braking is likely to cause a phenomenon that the friction surface of the brake becomes hot and the friction decreases. It was.

  The present invention has been made paying attention to the above technical problem, and an object of the present invention is to provide means for optimizing the detection timing of a road surface state in order to avoid repeated braking.

  In order to solve the above technical problem, the present invention is characterized in that a change in road surface condition is detected prior to a full-scale road surface friction coefficient. More specifically, according to the first aspect of the present invention, in the road surface condition detecting device for a vehicle, a wheel rotational speed detecting means for detecting a rotational speed of the wheel, and a frequency analysis of the wheel rotational speed detected by the wheel rotational speed detecting means. And a road surface state change determination unit that determines arrival of a road surface state detection timing based on an analysis result analyzed by the frequency analysis unit.

  The invention according to claim 2 is the control device according to claim 1, wherein the road surface state change determination means further includes a road surface friction coefficient high / low determination means.

  Further, the invention according to claim 3 is the case where the intensity of the specific frequency region of the wheel rotation speed detected by the road surface state change determining means is not less than a first predetermined value and not more than a second predetermined value. The control device according to claim 1, wherein the road surface state is determined to have changed from a high friction coefficient state to a low friction coefficient state.

  According to a fourth aspect of the present invention, when the intensity of the specific frequency region of the wheel rotation speed detected by the road surface state change determining means is not less than a third predetermined value and not more than a fourth predetermined value. The control device according to claim 1, wherein the road surface state is determined to have changed from a low friction coefficient state to a high friction coefficient state.

  Further, the invention according to claim 5 is a friction coefficient detection that selects a wheel having the smallest gain in the frequency domain as a target for detecting the road surface friction coefficient when the road surface state change determining means determines that the road surface state has changed. 5. The control device according to claim 1, further comprising a selection unit.

  According to the first aspect of the present invention, the change of the road surface condition is detected prior to the accurate detection of the road surface friction coefficient. That is, if the road surface state does not change, it is not necessary to perform a road surface friction coefficient detection operation by applying an additional driving force. Therefore, it is not necessary to repeat the detection operation of the road surface friction coefficient at a constant period, and the burden on the drive system and the control system can be reduced.

  According to any one of claims 2 to 4, it is determined whether or not the road surface state has changed according to the gain in a specific frequency region of the rotational speed of the wheel. Therefore, since the road surface state can be detected without applying additional driving force or braking force to the wheels, the road surface state can be continuously detected.

  Furthermore, according to the invention of claim 5, it is possible to select a wheel that is considered to have the smallest friction coefficient among the four wheels, and it is possible to accurately perform vehicle motion control following this control.

  Next, the present invention will be described using specific examples. FIG. 3 is a schematic view of a four-wheel drive four-wheel drive vehicle targeted by the present invention. The four-wheel drive vehicle shown here is premised on a front engine front wheel drive vehicle, and the engine 1 is connected to a transaxle 2 including a transmission (transmission) and a transfer and a front differential. The front differential is connected to the front wheels 5 and 6 via the drive shaft 4. In addition, a rear differential 8 is connected to the transfer via a propeller shaft 7, and the rear differential 8 is connected to rear wheels 10 and 11 via a drive shaft 9.

  The wheels 5, 6, 10, and 11 have rotational speed sensors 14, 15, 16, and 17 that detect their rotational speeds, and brake mechanisms 18, 19, and 20 that brake the wheels 5, 6, 10, and 11, respectively. , 21 are provided.

  Further, a steering device 1 for steering the front wheels 5 and 6 is provided. The front wheel steering device 13 includes a steering wheel and a steering linkage, a hydraulic actuator, a steering angle sensor, and the like, depending on the operation of the steering wheel. The front wheels 5 and 6 are steered. A steering mechanism 12 is connected to the rear wheels 10 and 11 so as to control each of the rear wheels 10 and 11 by steering, and the rear wheels 10 and 11 are controlled by a command from the steering device 13 via the ECU 100. It is configured to perform steering.

  These rotational speed sensors 14, 15, 16, 17 and brake mechanisms 18, 19, 20, 21 are connected to the ECU 100. Further, the differential 8 and the steering mechanism 12 are also connected to the ECU 100. That is, the ECU 100 is configured to control the entire vehicle.

  The transaxle 2 has a friction engagement device for controlling the torque distribution ratio to the front and rear wheels by the differential action of the transfer, and the torque distribution ratio to the left and right front wheels 5, 6 by the differential action of the front differential. A friction engagement device (not shown) for controlling is provided, and the rear differential 8 is a friction engagement device (not shown) for controlling the torque distribution ratio with respect to the left and right rear wheels 10 and 11 by the differential action. ) Is provided. Accordingly, these friction engagement devices are configured so that different driving forces can be applied to the front wheels 5 and 6 and the rear wheels 10 and 11, respectively. By utilizing such a function, the road surface state or the road surface friction coefficient is detected from the driving force when the slip occurs and the rotational speeds of the wheels 5, 6, 10, and 11 as described below.

  The rotational speed is detected by rotational speed sensors 14, 15, 16, and 17. The detected rotation speed signal is subjected to signal processing by the ECU 100, and a road surface condition or a road surface friction coefficient is estimated. Based on the estimation result, the braking force of the brakes 18, 19, 20, and 21 is changed, and the braking force is applied to the wheels 5, 6, 10, and 11 independently.

  Incidentally, the driving force for detecting the road surface friction coefficient and the braking force for suppressing the occurrence of yawing accompanying the addition of the driving force are repeatedly applied at regular intervals. That is, braking is repeatedly applied to the wheels 5, 6, 10, 11 and the brake mechanisms 18, 19, 20, 21. In order to suppress this repeated braking, it is conceivable to optimize the application timing of the braking force. FIG. 1 is a flowchart showing an example of control in a case where a road surface state detects a change from a high friction coefficient road surface to a low friction coefficient road surface in order to optimize the addition timing of the braking force.

  First, frequency analysis of the signals of the rotational speed sensors 14, 15, 16, and 17 attached to the wheels 5, 6, 10, and 11 is performed to calculate the frequency spectrum of the detection signals of the rotational speed sensors 14, 15, 16, and 17. . For this frequency analysis, FFT (Fast Fourier Transform) or the like can be used.

  The frequency spectrum of the signals of the rotational speed sensors 14, 15, 16, and 17 has a property that the intensity of a specific region on the frequency spectrum changes when the road surface state changes. Therefore, the gain G that is the intensity of the specific region is detected (step S11). Then, it is determined whether or not the gain G, which is the intensity, is greater than a predetermined value G1 (step S12). If the determination in step S12 is negative, that is, if it is determined that no change in the road surface condition has occurred, this routine is exited.

  On the other hand, if the determination in step S12 is affirmative, that is, if the road surface state has changed and the gain of a specific region of the spectrum has increased, whether or not the gain G is smaller than a predetermined value G2 greater than a predetermined value G1. Judgment is made (step S13). If a negative determination is made in step S13, that is, if it is determined that the gain has increased due to a factor other than a change in road surface condition such as noise or disturbance, the routine is exited.

  If the determination in step S13 is affirmative, that is, if it is determined that the gain G is smaller than G2 and the cause of the increase in the gain G is not an influence of noise or disturbance but a change in road surface condition, The counter value is incremented (step S14).

  Next, it is determined whether or not the counter value is equal to or greater than a predetermined value N (step S15). That is, it is determined whether the gain G has exceeded the threshold value N times. If the determination in step S15 is affirmative, that is, if the gain G exceeds the predetermined value G1 N times, the process proceeds to step S16, where it is determined that the high road surface friction coefficient state has changed to the low road surface friction coefficient state. The On the other hand, if a negative determination is made in step S15, this routine is exited.

  In the above steps, the change from the high road surface friction coefficient state to the low road surface friction coefficient state is detected, but it is also possible to change from the low road surface friction coefficient state to the high road surface friction coefficient state. The control contents in this case will be described based on the flowchart of FIG.

  First, frequency analysis of the signals of the rotational speed sensors 14, 15, 16, and 17 attached to the wheels 5, 6, 10, and 11 is performed to calculate the frequency spectrum of the detection signals of the rotational speed sensors 14, 15, 16, and 17. . For this frequency analysis, FFT (Fast Fourier Transform) or the like can be used.

  Then, the gain G of the specific area is detected (step S21). Then, it is determined whether or not the gain G is smaller than a predetermined value G3 (step S22). If the determination in step S22 is negative, that is, if it is determined that no change in the road surface condition has occurred, this routine is exited.

  On the other hand, if the determination in step S22 is affirmative, that is, if the road surface condition has changed and the gain in a specific region of the spectrum has decreased, whether or not the gain G is smaller than a predetermined value G4 smaller than a predetermined value G3. Judgment is made (step S23). If a negative determination is made in step S23, that is, if the gain G is smaller than G4 and it is determined that the gain is decreased due to a factor other than a change in road surface condition such as noise or disturbance, the routine is exited.

  If the determination in step S23 is affirmative, that is, if the cause of the increase in the gain G is not the influence of noise or disturbance but a change in road surface condition, the counter value is incremented (step S24).

  Next, it is determined whether or not the counter value is equal to or greater than a predetermined value N (step S25). That is, it is determined whether the gain G has exceeded the threshold value N times. If the determination in step S25 is affirmative, that is, if the gain G exceeds the predetermined value G1 N times, the process proceeds to step S26, where it is determined that the high road surface friction coefficient state has changed to the low road surface friction coefficient state. The On the other hand, if a negative determination is made in step S25, the routine is exited.

  Next, the change of the frequency spectrum accompanying the change of the road surface state will be described. FIG. 4 is a diagram when the detection signals of the rotation speed sensors 14, 15, 16, and 17 are subjected to frequency analysis by FFT. When the road surface state is the low road surface friction coefficient (μ) state, the gain near the frequency f (Hz) is not increased, but the frequency f (Hz) is increased as the road surface state becomes the high road surface friction coefficient state. The nearby gain increases. In order to capture this, threshold values G1 and G2 that are larger than G1 are set, and it is determined that the road surface friction state has changed when it is larger than G1 and smaller than G2 (see FIG. 5).

  Similarly, when the road surface state changes from the high road surface friction coefficient state to the low road surface friction coefficient state, the gain near the frequency f (Hz) decreases. Accordingly, threshold values G4 and G3 that are larger than G4 are set, and it is determined that the road friction state has changed when G4 is larger than G4 and smaller than G3 (see FIG. 6).

  Therefore, a change in the road surface state is detected prior to accurate detection of the road surface friction coefficient. That is, if the road surface state does not change, it is not necessary to perform a road surface friction coefficient detection operation by applying an additional driving force. Therefore, it is not necessary to perform a road surface friction coefficient detection operation at a constant cycle, and the burden on the drive system and the control system can be reduced.

  Further, it is determined whether or not the road surface state has changed according to the gain in a specific frequency region of the rotational speed of the wheel. Therefore, since the road surface state can be detected without applying additional driving force or braking force to the wheels, the road surface state can be continuously detected.

  Next, processing when a change in road surface condition is detected as a result of the above detection control will be described. When a change in road surface condition is detected in only one wheel in a four-wheel drive vehicle such as in the above embodiment, a driving force is applied only to the detected one wheel to detect a road surface friction coefficient and to apply a driving force. A braking force is applied to the other wheels so as to suppress the accompanying yawing.

  Further, when a change in road surface condition is detected in either the left or right wheel of either the front wheel or the rear wheel, a driving force is applied to the determined left and right wheels of the front wheel or the rear wheel to detect the road surface friction coefficient. Further, when a change in road surface condition is detected on both the front wheels and the rear wheels, the driving force is applied to the wheel having the smallest gain G among all the wheels to detect the road surface friction coefficient. The braking force is applied to the other wheels so as to suppress the occurrence of yawing accompanying the driving force application.

  Therefore, it is possible to select the wheel that is considered to have the smallest friction coefficient among the four wheels, and the vehicle motion control following this control can be accurately performed.

  In the above specific example, the case where four-wheel steering is performed with a four-wheel drive vehicle has been described, but the present invention can also be applied to the case where four-wheel steering is performed with a front wheel drive vehicle, so-called FF vehicle. In this case, when a change in the road surface condition is detected with only one wheel, the driving force is applied to only the detected wheel to detect the road surface friction coefficient and the driving force is applied, as in the previous embodiment. A braking force is applied to the other wheels so as to suppress the accompanying yawing.

  On the other hand, when a change in the road surface condition is detected by a plurality of wheels, in this embodiment, a driving force is applied to the driven wheel, i.e., both the front and rear wheels, and the road surface friction coefficient Perform detection.

  Furthermore, the present invention can also be applied to the case where four-wheel steering is performed in an in-wheel motor vehicle. In this case, as in the case of the four-wheel drive, it is possible to select the wheel that is considered to have the smallest friction coefficient among the four wheels, and the vehicle motion control following this control can be performed accurately.

  In addition, this invention is not limited to the said Example. In the above embodiment, a vehicle having a front-wheel drive four-wheel steering device has been described. However, the present invention can also be applied to a vehicle having a rear-wheel drive four-wheel steering device. In the above embodiment, a four-wheel drive vehicle, a so-called FF vehicle, or a vehicle having an in-wheel motor on all four wheels has been described. The present invention can be applied. In other words, any vehicle that can apply braking force to at least the front wheels or the rear wheels independently and can detect the rotational speed of each wheel independently may be used.

  Here, the relationship between each of the above-described specific examples and the present invention will be briefly described. The predetermined value G1 corresponds to the “first predetermined value” in claim 2, and the predetermined value G2 corresponds to the “first This corresponds to “a predetermined value of 2.” Further, the predetermined value G3 corresponds to a “fourth predetermined value” in claim 3, and the predetermined value G4 corresponds to a “third predetermined value” in claim 4.

  Further, the functional means in step S11 or step S21 corresponds to “wheel rotational speed detection means” and “frequency analysis means”, and the functional means in step S16 or step S26 corresponds to “road surface state change determination means”. . Further, the functional means of steps S12 and S13 corresponds to the “means for determining that the friction coefficient state is low” in claim 2, and the functional means of steps S22 and S23 is the “high friction coefficient state” in claim 3. Corresponds to “means for determining whether or not”.

It is a flowchart which shows the example of control for detecting the change from high micro to low micro. It is a flowchart which shows the example of control for detecting the change from low micro to high micro. This is one form of a vehicle to which the present invention is applied, and is a case of four-wheel steering with four-wheel drive. It is a figure which shows the relationship between the magnitude | size of (mu), and the frequency spectrum of wheel vibration. It is a figure which shows the magnitude of the threshold value when detecting the change from high micro to low micro. It is a figure which shows the magnitude of the threshold value when detecting the change from low micro to high micro.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 5, 6, 10, 11 ... Wheel, 14, 15, 16, 17 ... Rotational speed sensor 18, 19, 20, 21 ... Brake mechanism, 22, 23, 24, 25 ... Drive motor, 101 ... Motor ECU, 100 ... ECU.

Claims (5)

In a vehicle road surface condition detection device,
Wheel rotation speed detection means for detecting the rotation speed of the wheel;
A frequency analysis means for analyzing the frequency of the wheel rotation speed detected by the wheel rotation speed detection means;
A road surface state detection control device comprising road surface state change determination means for determining arrival of a road surface state detection time based on an analysis result analyzed by the frequency analysis means.   The road surface state detection control device according to claim 1, wherein the road surface state change determination unit further includes a road surface friction coefficient high / low determination unit.   When the strength of the specific frequency region of the wheel rotation speed detected by the road surface state change determining means is not less than the first predetermined value and not more than the second predetermined value, the road surface state is lowered from the high friction coefficient state. The road surface state detection control device according to claim 1, wherein the road surface state detection control device determines that the friction coefficient state has changed.   When the strength of the specific frequency region of the wheel rotation speed detected by the road surface state change determining means is not less than the third predetermined value and not more than the fourth predetermined value, the road surface state is increased from the low friction coefficient state. The road surface state detection control apparatus according to claim 1 or 3, wherein it is determined that the friction coefficient state has been changed.   When the road surface state change determining unit determines that the road surface state has changed, the vehicle further includes a friction coefficient detection / selection unit that selects a wheel having the smallest gain in the frequency domain as a target of road surface friction coefficient detection. The road surface condition detection control device according to any one of claims 1 to 4, wherein

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