JP3779423B2 - Ground load control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a grounding load capable of temporarily increasing the grounding load by generating an inertial force in the vertical direction on the vehicle body by an extension acceleration of an actuator that actively changes a vertical relative distance between the vehicle body and an axle. More particularly, the present invention relates to a contact load control device that can contribute to shortening of the braking distance.
[0002]
[Prior art]
It is well known that if the tire is locked during braking, the maneuverability will be lost, especially on road surfaces where the grip of the tire is significantly reduced, such as icy roads and gravel roads, where braking is possible within the range where the tire does not lock. It is important. Based on this viewpoint, the correlation between the slip ratio (λ = (Vv−Vw) / Vv) representing the ratio of the difference between the vehicle speed Vv and the tire circumferential speed Vw to the vehicle speed and the grip force F of the tire is used. An anti-lock brake system (ABS) that automatically prevents tire locking by keeping the slip ratio within a range where a high grip force can be obtained is already installed in many commercial vehicles.
[0003]
[Problems to be solved by the invention]
However, since the grip force F of the tire is given by the product (F = μW) of the friction coefficient μ between the tire and the road surface and the vertical load W applied to the ground contact surface of the tire, the limit of the braking force is essential. It is determined by the wheel load of the vehicle. Therefore, it has been extremely difficult in the conventional ABS to prevent the tire from being locked and to further shorten the braking distance.
[0004]
The present invention has been devised to solve such problems of the prior art, and a main object of the present invention is to provide a contact load control device capable of further shortening the braking distance. It is in.
[0005]
[Means for Solving the Problems]
In order to achieve such an object, in the present invention, when it is determined from the slip ratio during braking that the tire has a tendency to lock, an extension acceleration is generated in the actuator that connects the vehicle body and the tire, and at that time , In the one that temporarily increases the apparent wheel load by the reaction force of the vertical inertia force acting on the vehicle body, it has an anti-lock brake system whose operation timing is determined based on the slip rate of the tire, The slip ratio for executing the ground load increase control is set to a value lower than the slip ratio at which the operation of the antilock brake system is executed. In this way, the increase in the ground load due to the reaction force of the vehicle body inertia force generated by the extension acceleration of the actuator is instantaneous, and it is considered that the slip ratio increases again while the actuator is contracted. First, by increasing the grounding load control, the lock limit is increased and a greater braking force is applied to reduce the vehicle speed, and then the anti-lock brake system can be linked to the lock suppression action, so the braking distance can be shortened. It becomes possible.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration of the present invention will be described in detail with reference to embodiments shown in the accompanying drawings.
[0007]
FIG. 1 schematically shows a schematic configuration of a main part of an active suspension device to which the present invention is applied. The tire 1 is supported by upper and lower suspension arms 2 and 3 so as to be movable up and down with respect to the vehicle body 4. A hydraulic actuator linear actuator 5 is provided between the lower suspension arm 3 and the vehicle body 4.
[0008]
The linear actuator 5 is of the cylinder / piston type, and the hydraulic pressure supplied from the variable displacement hydraulic pump 9 to the upper and lower oil chambers 7 and 8 of the piston 6 inserted in the cylinder is controlled by the servo valve 10. As a result, a vertical thrust is generated in the piston rod 11, whereby the relative distance between the center (axle) of the tire 1 and the vehicle body 4 can be freely changed.
[0009]
The oil discharged from the pump 9 is stored in an accumulator 12 for removing pump pulsation and securing the oil amount in a transient state, and then individually to each actuator 5 with respect to the actuator 5 provided on each wheel. It is supplied via a provided servo valve 10.
[0010]
An unload valve 13, an oil filter 14, a check valve 15, a pressure adjustment valve 16, an oil cooler 17, and the like are connected to this hydraulic circuit as in a known active suspension system.
[0011]
The servo valve 10 continuously controls the hydraulic pressure and direction applied to the hydraulic actuator 5 by providing a control signal generated from an electronic control unit (ECU) 18 to the solenoid 10a via the servo valve driver 19. A load sensor 20 provided at a connection portion between the vehicle body 4 and the piston rod 11, a stroke sensor 21 provided between the vehicle body 4 and the lower suspension arm 3, and a sprung for detecting vertical acceleration on the vehicle body side. Control is performed according to the following control algorithm based on signals obtained by processing the signals of the acceleration sensor 22 and the unsprung acceleration sensor 23 for detecting the vertical acceleration on the tire side by the ECU 18.
[0012]
Next, the control algorithm will be described with reference to FIG. First, signals from the vehicle speed sensor 27 and the wheel speed sensor 28 are input to the slip ratio calculating means 29 to calculate the slip ratio λ during braking (step 1), and then the relationship between the grip force F and the slip ratio λ. Referring to a predetermined map 30 (see FIG. 3), the presence / absence determination of the tire having the slip ratio value λw at which the grip force exceeds the slip ratio value at which the grip force exhibits the maximum value Fmax and the grip force starts to decrease is performed (see FIG. 3). Step 2). Thus, it is determined whether or not the tire is locked. Then, according to this determination, the temporary target load is internally determined with reference to the input signals to the target load calculation unit 24 of the sprung acceleration sensor 22 and the unsprung acceleration sensor 23 provided in the suspension device of the tire that tends to be locked. (Step 3), the deviation between this value and the signal (actual load) of the load sensor 20 is calculated (Step 4), and after this difference is processed by the stabilization calculation unit 25, the displacement limit comparison calculation unit 26 The command value given to the servo valve driver 19 is adjusted with reference to the signal of the stroke sensor 21 so that the control is performed within the stroke limit of the actuator 5 (step 5). Based on the adjusted signal, the servo valve 10 is driven so that the target load and the actual load are equal to generate an extension acceleration in the actuator 5, and an inertial force in a direction that increases the tire ground contact load is generated in the vehicle body . (Step 6). As a result, the grip force of the tire temporarily increases (see FIG. 4), so that the lock limit is raised and the braking distance is shortened.
[0013]
FIG. 4 conceptually shows the tire contact load (= grip force) distribution, the contact load in the static load range is represented by a solid circle, and the contact load increased by the stroke control of the actuator 5 is expressed in two points. It is represented by a chain line circle. FIG. 4 illustrates the case where the ground load on the rear wheel side is increased, but it goes without saying that the actuators corresponding to the wheels determined to have a large locking tendency are individually controlled.
[0014]
In particular, in a vehicle equipped with an ABS whose operation timing is determined based on the slip ratio λ, the slip ratio λw for executing the above-described contact load increase control is set to a value lower than the slip ratio λa for executing the ABS operation. This should be set (see FIG. 3). In this way, when the actuator 5 is extended to generate acceleration, it is necessary to contract the actuator 5 once in order to generate acceleration again, but it is considered that the slip ratio increases again during this time. First, after the lock limit is temporarily increased by the acceleration of the actuator 5 and the braking force is sufficiently applied, the lock can be suppressed by the ABS.
[0015]
On the other hand, the contact load when driving on rough roads with flapping tires may tend to decrease compared to flat roads, and the relationship between grip force F and slip ratio λ So they are different from each other. Therefore, sufficient braking force cannot be obtained if the above control is executed at a slip ratio corresponding to a flat road on a bad road. A method for dealing with this inconvenience will be described below with reference to FIG.
[0016]
First, road noise is detected with a microphone provided in the vicinity of the tire of the vehicle body (step 11), and a sound pressure value in a specific frequency region is extracted from the road noise through a frequency analysis circuit and a bandpass filter (step 12). Next, a road surface condition that is currently running is determined with reference to a database in which the relationship between the sound pressure value and the vehicle speed and the road surface condition is mapped in advance (step 13). Based on the determination result, a road surface condition prepared in advance is determined. The optimum slip ratio map is selected from the F-λ characteristic map corresponding to (see FIG. 6) (step 14). By determining the above-mentioned lock tendency based on the slip ratio value obtained in this way, it is possible to execute the contact load increase control at the optimum timing according to the road surface condition.
[0017]
Next, the principle of the present invention will be described. In the model of FIG.
M2: Unsprung mass M1: Unsprung mass Z2: Unsprung coordinate Z1: Unsprung coordinate Kt: Spring constant of tire Fz: Actuator thrust, where the downward direction is positive, the motion of unsprung mass M2 and unsprung mass M1 Each equation is given by the following equation. However, the * mark in the formula represents the first derivative, and the ** mark represents the second derivative.
M2 ・ Z2 ^** = −Fz
M1 ・ Z1 ^** + Kt ・ Z1 ＝ Fz
[0018]
Therefore, the tire ground contact load W is given by the following equation.
W = -Kt · Z1 = -Fz + M1 · Z1 ^**
= M2 ・ Z2 ^** + M1 ・ Z1 ^**
[0019]
That is, since the ground load W is the sum of the sprung inertia force and the unsprung inertia force, the inertial force of the sprung mass or the unsprung mass is changed by controlling the expansion / contraction acceleration of the actuator 5. As a result, the ground load W can be changed. Therefore, the ground load W can be temporarily increased for each tire by controlling the extension acceleration of the actuator 5. When the suspension stroke is 200 mm and a thrust of 1 ton is generated in the actuator 5, it can be operated for about 0.2 seconds.
[0020]
In general, in order to save energy consumption of the actuator, a suspension spring that supports the vehicle weight and a damper for generating a damping force are used in combination (see FIG. 8).
When Ks is the spring constant of the suspension spring and C is the damping coefficient of the damper, the equations of motion for the sprung mass M2 and the unsprung mass M1 are given by the following equations, respectively.
M2 ・ Z2 ^** + C ・ (Z2 ^* −Z1 ^* ) + Ks ・ (Z2−Z1)
= -Fz
M1 ・ Z1 ^** + C ・ (Z1 ^* -Z2 ^* )
+ Ks · (Z1−Z2) + Kt · Z1 = Fz
[0021]
Therefore, the tire ground contact load W is given by the following equation.
W = -Kt · Z1
= -Fz + M1 · Z1 ^** + C · (Z1 ^* -Z2 ^* )
+ Ks · (Z1-Z2)
= M2 ・ Z2 ^** + M1 ・ Z1 ^**
[0022]
That is, it can be seen that the ground load W can be changed by controlling the expansion / contraction acceleration of the actuator, as described above.
[0023]
In the above embodiment, an actuator using a hydraulically driven cylinder device is shown. However, this may be achieved by using other electric thrust generating means such as a linear motor or a voice coil, a cam mechanism, The same effect can be obtained even if acceleration is generated using the spring means.
[0024]
In addition, the sensor used can be simplified without departing from the scope of the present invention. For example, the position detection signal can also be obtained by second-order integration of the output difference between the unsprung and unsprung acceleration sensors, so the stroke sensor can be eliminated, and the actual measured values of both the unsprung and unsprung weights can be used. Since the force generated by the actuator can be obtained by calculating the output values of the unsprung and unsprung acceleration sensors, the load sensor can be eliminated. Furthermore, a state estimator can be configured based on signals from the load sensor and the displacement sensor, and both unsprung and sprung accelerations can be obtained indirectly. Needless to say, the ECU can be realized by any of digital, analog, and hybrid.
[0025]
【The invention's effect】
As described above, according to the present invention, it is possible to increase the generation limit of the grip force of the tire that is likely to be locked by dynamically increasing the contact load, and therefore it is possible to prevent the tire lock without reducing the braking force. possible and on Do that, when increased again slip rate while the actuator is contracted can be the vehicle speed as compared with the prior art is to operate the anti-lock braking system in a state with a reduced Therefore, a great effect can be brought about in shortening the braking distance.
[Brief description of the drawings]
FIG. 1 is a schematic system configuration diagram of an active suspension device to which the present invention is applied.
FIG. 2 is a control flow diagram of the present invention.
FIG. 3 is a graph conceptually showing an example of a relationship between grip force and slip rate.
FIG. 4 is a conceptual ground load distribution map during sudden braking.
FIG. 5 is a control flow diagram of another embodiment of the present invention.
FIG. 6 is a graph conceptually showing another example of the relationship between grip force and slip ratio.
FIG. 7 is a model diagram for explaining the principle of the present invention.
FIG. 8 is a model diagram of a general active suspension system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Tire 2 Upper suspension arm 3 Lower suspension arm 4 Car body 5 Actuator 6 Piston 7/8 Oil chamber 9 Hydraulic pump 10 Servo valve 11 Piston rod 12 Accumulator 13 Unload valve 14 Oil filter 15 Check valve 16 Pressure adjustment valve 17 Oil cooler 18 Electronic control unit (ECU)
19 servo valve driver 20 load sensor 21 stroke sensor 22 sprung acceleration sensor 23 unsprung acceleration sensor 24 target load calculation unit 25 stabilization calculation unit 26 displacement limit comparison calculation unit 27 vehicle speed sensor 28 wheel speed sensor 29 slip rate calculation unit 30 map

Claims (1)

An actuator that actively changes the vertical relative distance between the vehicle body and the axle, and a ground load control that generates an inertial force in the vertical direction on the vehicle body by the extension acceleration of the actuator and applies the reaction force to the tire ground load means and, and a slip rate calculating means of each tire at the time of braking, the slip rate calculating means ground contact load control device slip ratio that perform vertical load increase control of the tire at the time exceeds a predetermined value to output Because
An anti-lock brake system whose operation timing is determined based on the slip ratio of the tire is provided, and the contact load increase control is executed to a value lower than the slip ratio at which the operation of the anti-lock brake system is executed. A contact load control device characterized in that a slip ratio is set .

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