DRIVING ASSISTANCE CONTROL APPARATUS OF VEHICLE

Abstract

A driving assistance control apparatus of a vehicle includes a blind area detector, a driving operation detector, and an electronic control unit. The blind area detector is configured to detect the presence or absence of a blind area as seen from the vehicle in a traveling direction of the vehicle. The driving operation detector is configured to detect driving operation of the driver. The electronic control unit is configured to perform automatic deceleration control of the vehicle based on detection of the presence of the blind area by the blind area detector. The electronic control unit is configured to start the automatic deceleration control, by referring to the driving operation of the driver after detection of the presence of the blind area by the blind area detector.

Claims

1. A driving assistance control apparatus of a vehicle, comprising: a blind area detector configured to detect a presence or absence of a blind area as seen from the vehicle in a traveling direction of the vehicle; a driving operation detector configured to detect driving operation of a driver; and an electronic control unit configured to perform automatic deceleration control of the vehicle based on detection of the presence of the blind area by the blind area detector, wherein the electronic control unit is configured to start the automatic deceleration control, by referring to the driving operation of the driver after detection of the presence of the blind area by the blind area detector.

2. The driving assistance control apparatus according to claim 1, wherein the electronic control unit is configured to start the automatic deceleration control when braking operation or steering operation of the driver is detected after detection of the presence of the blind area.

3. The driving assistance control apparatus according to claim 1, wherein the electronic control unit is configured to start the automatic deceleration control when a predetermined time elapses after detection of the blind area.

4. The driving assistance control apparatus according to claim 1, further comprising: a risk presentation device configured to present a risk of sudden emergence of an object from the blind area, to the driver, when the blind area is detected.

5. The driving assistance control apparatus according to claim 4, wherein the risk presentation device is configured to visually indicate the risk of sudden emergence of the object, the risk presentation device being configured to express that the risk of sudden emergence of the object becomes higher with passage of time.

6. The driving assistance control apparatus according to claim 1, wherein the electronic control unit is configured to assume that an object suddenly emerges from the blind area, and enters a traveling path of the vehicle, and calculate an entry region of the object within the traveling path, the electronic control unit is configured to set a target deceleration based on a relative distance between the entry region and the vehicle, the electronic control unit is configured to perform the automatic deceleration control so that an actual deceleration of the vehicle becomes substantially equal to the target deceleration.

7. The driving assistance control apparatus according to claim 6, wherein the electronic control unit is configured to apply braking force to the vehicle so as to compensate for a difference between the target deceleration and a deceleration applied by braking operation of the driver, when the automatic deceleration control is performed.

8. The driving assistance control apparatus according to claim 6, wherein the electronic control unit is configured to set the target deceleration, based on a relative distance between the entry region and a target position set ahead of the entry region, and a target vehicle speed of the vehicle when the vehicle reaches the target position, the target position and the target vehicle speed being set as a position and a vehicle speed at which the vehicle speed can be reduced to be substantially equal to 0 by a time when the vehicle reaches the entry region from the target position.

9. The driving assistance control apparatus according to claim 8, wherein the electronic control unit sets the target deceleration, based on a virtual spring potential, which is a spring potential obtained by modeling braking force applied to the vehicle as repulsion from the object, during deceleration operation performed by a model driver so as to decelerate the vehicle from a given vehicle speed to the target vehicle speed while the vehicle is moving from a given position to the target position.

10. The driving assistance control apparatus according to claim 1, further comprising an accelerator pedal reaction force controller that applies reaction force to an accelerator pedal of the vehicle, during execution of the automatic deceleration control by the electronic control unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Features, advantages, and technical and industrial significance of exemplary embodiments of the present disclosure will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

[0020] FIG. 1A is a schematic view of a vehicle on which a driving assistance control apparatus of a vehicle as a preferred embodiment of the present disclosure is installed;

[0021] FIG. 1B is a block diagram showing the configuration of a system in the driving assistance control apparatus as one embodiment of the present disclosure;

[0022] FIG. 2A is a schematic view useful for explaining a situation where driving assistance is carried out by the driving assistance control apparatus of the vehicle as the embodiment of the present disclosure;

[0023] FIG. 2B is a schematic view useful for explaining a situation where driving assistance is carried out by the driving assistance control apparatus of the vehicle as the embodiment of the present disclosure;

[0024] FIG. 2C is a flowchart illustrating a routine executed in the driving assistance control apparatus as the embodiment of the present disclosure;

[0025] FIG. 3A is a view schematically showing an example of a risk display indicating the presence of a potential risk (sudden emergence of a pedestrian, or the like, from a blind area) visually presented to the driver, after detection of the blind area, during traveling of the vehicle, in the driving assistance control apparatus of the vehicle as the embodiment of the present disclosure;

[0026] FIG. 3B is a display presented during execution of automatic deceleration control, and a display presented at the completion of the automatic deceleration control, in the driving assistance control apparatus as the embodiment of the present disclosure;

[0027] FIG. 3C is a view schematically showing an example (right side) of a display presented when a pedestrian, or the like, actually comes out from a blind area, after detection of the blind area, in the driving assistance control apparatus of the vehicle as the embodiment of the present disclosure;

[0028] FIG. 4A is a view schematically showing an example of changes of a display of a potential risk, deceleration of the vehicle, and the vehicle speed, with respect to time, according to the routine of FIG. 2C, in the case where, after detection of a blind area, driving operation performed by the driver in view of the blind area is detected before a predetermined time elapses;

[0029] FIG. 4B is a view schematically showing an example of changes of a display of a potential risk, deceleration of the vehicle, and the vehicle speed, with respect to time, according to the routine of FIG. 2C, in the case where, after detection of a blind area, no driving operation performed by the driver in view of the blind area is detected over a predetermined period of time;

[0030] FIG. 5A is a schematic view of a situation where automatic deceleration control is performed in the driving assistance control apparatus of the present disclosure, which view is useful for explaining a target position and a target speed referred to in determination of a target deceleration for use in control;

[0031] FIG. 5B is a schematic view of a virtual spring potential obtained by modeling braking force applied to the vehicle in decelerating operation when a model driver reduces the vehicle speed from a given speed to a target vehicle speed during movement of the vehicle from a given position to a target position, as repulsion from a pedestrian, or the like, the virtual spring potential being referred to in determination of a target deceleration during automatic deceleration control; and

[0032] FIG. 5C is a view schematically illustrating an example of predicted positions of the vehicle referred to in determination of a target deceleration under automatic deceleration control.

DETAILED DESCRIPTION OF EMBODIMENTS

[0033] Referring to FIG. 1A, in a vehicle 10, such as an automobile, in which a driving assistance control apparatus as a preferred embodiment of the present disclosure is incorporated, right and left front wheels 12FR, 12FL, right and left rear wheels 12RR, 12RL, a drive system (a part of which is shown in FIG. 1A), a steering device 30 for controlling the steering angle of the front wheels (a steering device for rear wheels may be further provided), and a braking system 40 that generates braking force in each wheel, are installed. The drive system generates braking/driving force in each wheel (of only the rear wheels, since the vehicle is a rear-wheel-drive vehicle, in the embodiment shown in FIG. 1A), according to depression of an accelerator pedal by the driver. The drive system is configured to transmit drive torque or rotational force, from an engine and/or an electric motor (not shown, the drive system may be a hybrid drive system having both an engine and an electric motor), to the rear wheels 12RR, 12RL, via a transmission (not shown), and a differential gear unit 28, in a normal mode. A power steering device may be employed as the steering device 30. The power steering device transmits rotation of a steering wheel 32 operated by the driver, to tie rods 36R, 36L, while boosting or increasing its torque by means of a booster 34, so as to turn the front wheels 12FR, 12FL.

[0034] The braking system 40 is an electronically controlled, hydraulic braking system of a type in which a braking pressure in a wheel cylinder 42i (i=FR, FL, RL, RR) mounted in each wheel, namely, braking force in each wheel, is adjusted by a hydraulic circuit 46 that communicates with a master cylinder 45 that is operated in response to depression of a brake pedal 44 by the driver. The hydraulic circuit 46 is provided with various valves (such as a master-cylinder cut valve, hydraulic pressure holding valve, and a pressure reduction valve) for selectively communicating the wheel cylinder of each wheel with the master cylinder, oil pump, or an oil reservoir (not shown). In normal operation, the pressure of the master cylinder 45 is supplied to the respective wheel cylinders 42i, in response to depression of the brake pedal 44. As will be described later, when automatic deceleration control is performed after detection of a blind area, the above-indicated various valves are actuated, based on a command of an electronic control unit 60, so that the brake pressure in the wheel cylinder of each wheel is controlled to be equal to its target pressure, based on a detection value Pbi (i=FR, FL, RR, RL) of a corresponding pressure sensor. The braking system 40 may be of a type that pneumatically or electromagnetically applies braking force to each wheel, or any type known to those skilled in the art.

[0035] In the vehicle 10 in which the driving assistance control apparatus as the preferred embodiment of the present disclosure is used, a vehicle-mounted camera 70, a radar device 72, etc. are provided for detecting the circumstances surrounding the vehicle, so as to detect another vehicle around the vehicle, obstacle, pedestrian, or the like (e.g., bicycle), road width, building, and so forth. Further, a GPS system (car navigation system) 74 may be provided which communicates with a GPS satellite, and obtains various kinds of information, such as the circumstances surrounding the own vehicle, and positional information.

[0036] Operation control of each part of the vehicle and operation control of the driving assistance control apparatus according to the present disclosure are performed by the electronic control unit 60. The electronic control unit 60 may include a microcomputer and a drive circuit of normal types. The microcomputer has CPU, ROM, RAM, and input/output port device, which are connected to each other via a bidirectional common bus. The configuration and operation of each part of the driving assistance control apparatus of the present disclosure, which will be described later, may be realized by operation of the electronic control unit 60 according to programs. The electronic control unit 60 receives detection values from various sensors, which are used as parameters for the driving assistance control of the present disclosure performed in manners as described later. For example, the electronic control unit 60 receives items of information s1-s3 from the vehicle-mounted camera 70, radar device 72, GPS system 74, etc., depression amount θb of the brake pedal, steering angle δ, detection value ax of a longitudinal G sensor 65, wheel speeds Vwi (i=FR, FL, RR, RL), and so forth. The electronic control unit 60 outputs a control command for presenting risk indication to the driver, a control command representing a control amount for use in the automatic deceleration control, etc., to corresponding systems or devices. Although not illustrated in the drawings, the electronic control unit 60 may receive various parameters needed for various controls to be performed in the vehicle of this embodiment, for example, various detection signals, such as the yaw rate γ from a gyro sensor 62 and/or the lateral acceleration Yg, and may output various control commands to the corresponding systems or devices.

[0037] In the system configuration of the driving assistance control apparatus according to the present disclosure, as shown in FIG. 1B, an environment recognizing unit, a display-system interface unit, a potential risk predicting unit, an assistance execution determining unit, and a coordination control unit are constructed. The environment recognizing unit recognizes the circumferences surrounding the vehicle, based on information of the camera, sensor, etc. If the environment recognizing unit detects the presence of a blind area as seen from the own vehicle, the information is given to the display-system interface unit, potential risk predicting unit, and the assistance execution determining unit. In the display-system interface unit, a process or routine of presenting risk indication on a display mounted in the vehicle is executed, in a manner as described later. In the potential risk predicting unit, a target deceleration for use in automatic deceleration control, and a control amount that achieves the target deceleration, are calculated, using a driver model that models driving behavior of a model driver, based on the positional information of the blind area and conditions (such as the vehicle speed) of the own vehicle, in a manner as described later. The assistance execution determining unit monitors driving operation of the driver, in a manner as described later, after receiving information on the presence of the blind area, and determines the timing of the automatic deceleration control. If execution of the automatic deceleration control is determined, the information is given to the coordination control unit. The coordination control unit determines a control command, based on the control amount for the automatic deceleration control determined by the potential risk predicting unit, and driving operation (braking operation) of the driver, and transmits the control command to a brake control system. Also, the assistance execution determining unit may execute control for increasing reaction force of the accelerator pedal in a manner as described later, during execution of the automatic deceleration control.

[0038] In operation of the driving assistance control apparatus of the present disclosure, if a parked vehicle around a side strip of a road or a corner of a building is detected, during traveling of the vehicle (own vehicle), and the presence of a blind area behind the parked vehicle or building (ahead of the vehicle or building as seen from the own vehicle) is recognized, as schematically depicted in FIG. 2A, FIG. 2B, a possibility that a pedestrian, or the like, may suddenly emerge or come out from the detected blind area is assumed, as a potential risk, and automatic deceleration of the own vehicle is carried out in preparation for the potential risk. However, if the apparatus immediately executes the automatic deceleration control, simply because of detection of the blind area, the intention or operation of the control of the apparatus may not be understood by the driver, or the intention or operation of the control of the apparatus may not accord with the intention of the driver. As a result, the driving operation of the driver may not be reflected by the vehicle behavior, and the driver may feel strange or uncomfortable about the control operation of the apparatus. Thus, under the driving assistance control performed by the apparatus of this embodiment, the automatic deceleration control is not immediately executed, at the time when the presence of the blind area is detected or recognized, but the presence of the potential risk is presented to the driver, and driving operation of the driver is monitored. Then, if the driver starts braking operation or steering operation in an attempt to avoid the potential risk, the apparatus may also start the automatic deceleration control, in accordance with the driver's operation. Also, if the driver does not perform braking operation or steering operation, even after a lapse of a predetermined time from detection of the blind area, the automatic deceleration control may be performed.

[0039] Referring to FIG. 2C, in a control routine of the driving assistance control performed by the apparatus of this embodiment, the circumstances surrounding the vehicle are initially monitored by the environment recognizing unit, during traveling of the vehicle, and detection of a blind area is carried out (step S1). The circumstances surrounding the vehicle may be monitored in any manner, using devices, such as the vehicle-mounted camera 70, radar device 72, and the GPS system 74, for collecting information on the surroundings of the vehicle. Then, if a parked vehicle, an obstacle, a corner of a building, a blind intersection (i.e., an intersection with poor visibility), or the like, is recognized, based on the information obtained by the camera, and other devices, it may be determined that there exists a blind area behind it.

[0040] If the presence of the blind area is determined, time T representing an elapsed time from the determination is reset, or set to 0 (T=0) in step S2. While the elapsed time T is being measured (steps S2-S5), attention-seeking indication for presenting a potential risk due to the presence of the blind area to the driver is started (step S3), and monitoring of the driving operation of the driver is performed (step S4). In the attention-seeking indication operation, visual indication for calling the driver's attention to sudden emergence of a pedestrian, or the like, as shown in FIG. 3A by way of example, is presented on a display (not shown) located in the vicinity of the dashboard in front of the driver's seat, for example. In this case, it is preferable to emphasize or highlight the indication by increasing the brightness or blinking speed of the display, as time elapses from immediately after detection of the blind area, so as to express gradual increase of the degree of the potential risk. With this arrangement, the driver shares information that the apparatus recognizes the presence of the potential risk, and the intention of the apparatus for control is transmitted to the driver.

[0041] In the step (step S4) of monitoring the driving operation of the driver, depression of the brake pedal by the driver or manipulation of the steering wheel by the driver is monitored, as driving operation of the driver for avoiding a potential risk. For example, it may be determined that the driving operation for avoiding the potential risk has been performed, when the amount θb of depression of the brake pedal has exceeded a predetermined value θth, or the amount of change of the steering angle δ of the steering wheel has exceeded a predetermined angle δo in a such a direction that the vehicle moves away from the blind area.

[0042] If the driver's driving operation for avoiding the potential risk is detected in this manner, automatic deceleration control is executed in a manner as described later, in response to the detection (step S6). Also, if no driving operation for avoiding the potential risk is performed, irrespective of the attention-seeking indication or display, automatic deceleration control is executed based on determination of the apparatus, when the elapsed time T exceeds the predetermined value Tth. During execution of the automatic deceleration control, an indication to the effect that the deceleration control is being performed may be displayed in a given portion of the dashboard in front of the driver's seat, for example, as illustrated on the left-hand side in FIG. 3B. Then, when the automatic deceleration control ends, an indication of the end of the control may be presented, as illustrated on the right-hand side in FIG. 3B.

[0043] Further, during execution of the automatic deceleration control, control for applying reaction force to the accelerator pedal against depression of the accelerator pedal may be performed, so as to prevent useless acceleration of the vehicle, and inform the driver of the fact that the deceleration control is being executed by the apparatus. More specifically, during execution of the automatic deceleration control, reaction force F as expressed below may be applied to the accelerator pedal, in such a direction as to make the accelerator pedal stroke P equal to 0.

F=−Ka.Math.P  (1)

In the above expression (1), Ka is a positive coefficient. Namely, the reaction force F increases as the accelerator pedal stroke P increases.

[0044] Referring to FIG. 4A and FIG. 4B, the flow of control as described above will be summarized. If a blind area is detected during traveling of the vehicle, T is reset to 0, and attention-seeking indication or display is started. The indication is gradually emphasized by increasing the brightness or blinking speed I of the display with time, so that the driver can recognize and grasp the potential risk detected by the apparatus with higher reliability. Then, if driving operation of the driver is detected, as shown in FIG. 4A, the automatic deceleration control is executed from that point in time, so that a deceleration “a” is applied to the vehicle, and the vehicle speed V is reduced. On the other hand, if the elapsed time T after detection of the blind area reaches Th, as shown in FIG. 4B, the automatic deceleration control is executed from that point in time, even in the absence of driving operation of the driver, so that a deceleration “a” is applied to the vehicle, and the vehicle speed V is reduced.

[0045] If a pedestrian, or the like, actually emerges or comes out from the blind area, during execution of the above control routine or after completion of the automatic deceleration control, deceleration control may be performed by an AEB system, or braking operation or steering operation of the driver himself/herself may be expected. In this case, the attention-seeking indication may be converted from indication of a potential risk to indication of actual occurrence of the risk (sudden emergence of a pedestrian, or the like).

[0046] As explained above with reference to FIG. 2A and FIG. 2B, the automatic deceleration control performed in the apparatus of this embodiment is control for predicting a risk or possibility that a pedestrian, or the like, may suddenly come out from a blind area, when the presence of the blind area is detected, and decelerating the vehicle in advance, in a condition where sudden emergence of the pedestrian, or the like, has not been detected. In fact, a model driver is expected to predict a risk of sudden emergence of a pedestrian, or the like, when he/she finds a blind area, under the situations illustrated in FIG. 2A, FIG. 2B, and decelerate the vehicle, even in a condition where no pedestrian, or the like, has been found, so as to avoid contact with a pedestrian, or the like, with higher reliability when the pedestrian, or the like, actually suddenly emerges from the blind area. The automatic deceleration control of this embodiment may be said to be control that simulates driving of the model driver as described above.

[0047] Under the automatic deceleration control, brake control assistance is performed based on a potential risk prediction driver model. In this case, a brake control assistance system includes the environment recognizing unit, potential risk prediction driver model unit, and assistance execution determining unit, as shown in FIG. 1B. The potential risk prediction driver model sets a deceleration calculated from optimization of a potential function that can simulate decelerating operation of a model driver, and an evaluation function defined by a risk evaluation term using the potential function and an operation amount term used for control, as a target deceleration. The calculated target deceleration is converted into a pedal stroke amount. Then, coordination control is performed by comparing the pedal stroke amount entered by the driver with the pedal stroke amount entered by the assistance system, and selecting the larger one of the pedal stroke amounts. The selected pedal stroke amount is then received by the vehicle.

[0048] 1. Environment Recognizing Unit When an environment recognition sensor (camera) detects a parked vehicle, space behind an object, a blind intersection with no signal, or the like, the environment recognizing unit assumes that a pedestrian, or the like, who is currently invisible will suddenly emerges in front of the vehicle, and transmits a flag indicating the assumption to the potential risk prediction driver model unit.

[0049] 2. Potential Risk Prediction Driver Model When the control flag is transmitted from the environment recognizing unit to the potential risk prediction driver model unit, the potential risk prediction driver model unit calculates the target deceleration.

[0050] A repulsion potential function of a hypothetical pedestrian is defined as follows.

[00001]$\begin{array}{cc}\mathrm{Uped}=\frac{1}{2}.Math.{\mathrm{Kped}\left(\mathrm{Xst}-\mathrm{Xe}\left(t\right)\right)}^2.Math..Math.\left(\mathrm{Xst}\prec X\left(t\right)\prec \mathrm{Xfin}\right).Math.& \left(1\right)\end{array}$

where, Kped denotes a spring constant of the repulsion potential of the hypothetical pedestrian, and Xst and Xfin denote the minimum X coordinate and the maximum X coordinate, respectively, between which the repulsion is received, and also denote the deceleration start position and the deceleration ending position (see FIG. 5B).

[0051] [Method of Calculating Spring Constant] In traveling space, where the sum of the potential energy produced by a virtual spring and kinetic energy is conserved, the spring constant Kped of the repulsion potential of the hypothetical pedestrian is expressed as follows.

[00002]$\begin{array}{cc}\mathrm{Kped}=\frac{m\left(V^2.Math.\min -{V\left(t\right)}^2\right)}{{\left(\mathrm{Xst}-\mathrm{Xe}\left(t\right)\right)}^2-{\left(\mathrm{Xst}-\mathrm{Xfin}\right)}^2}& \left(2\right)\end{array}$

Here, the spring constant Kped is not constant. The spring constant Kped is characterized by changing for each sampling period, according to the own vehicle position Xe and the approaching velocity V.

[0052] Vmin, Xfin in the above equation (2) are obtained from the following equations (3), (4).

[00003]$\begin{array}{cc}V.Math..Math.\min =a_{\max }\left(-{\tau }_x+\sqrt{{\tau }_x^2+\frac{2.Math.\left(\tilde{X}.Math.\mathrm{ped}-\mathrm{Xfin}\right)}{a_{\max }}}\right)& \left(3\right)\\ \mathrm{Xfin}=-V.Math..Math.\min .Math..Math.{\tau }_x-\frac{V^2.Math.\min }{2.Math.a_{\max }}+\tilde{X}.Math.\mathrm{ped}& \left(4\right)\end{array}$

[0053] The coordinate position Xfin, at which the brake control based on the potential risk prediction driver model ends, changes according to the position Yped of the hypothetical pedestrian calculated based on a lateral interval Ypass between the own vehicle and the parked vehicle (see FIG. 5A). In the above equation (4), τx indicates a response time (recognition time) of the AEB, and a.sub.max indicates the maximum acceleration of the AEB. Namely, it is necessary to reduce the vehicle speed to Vmin at the operating position of Xfin, so as to avoid a collision through operation of the AEB when a pedestrian suddenly emerges in front of the vehicle.

[0054] [Method of Calculating Target Deceleration of Potential Risk Prediction Driver Model] The target deceleration ax* is determined by optimizing trade-off between the repulsion potential Uped with the hypothetical pedestrian at the predicted position of the own vehicle indicated by the following equation (5), and the magnitude of the target deceleration ax*.

[00004]$\begin{array}{cc}{X}_{\mathrm{px}}\left(i_x,j_x\right)=\mathrm{Xe}\left(t\right)+V\left(t\right).Math.t_{\mathrm{px}}\left(j_x\right)+\frac{1}{2}.Math.a_x\left(i_x\right).Math.{t_{\mathrm{px}}\left(j_x\right)}^2& \left(5\right)\end{array}$

Here, the evaluation function is given by the following equation (6).

[00005]$\begin{array}{cc}{a}_x^{*}\left(t\right)={\min }_{a_{\mathrm{px}}\left(i_x\right)}.Math.\underset{j_x.Math.1}{\overset{\mathrm{Nx}}{.Math.}}.Math.\left(\mathrm{Uped}\left(X_{\mathrm{px}}\left(i_x,j_x\right)\right)+r_x.Math.a_x^2\right)& \left(6\right)\end{array}$

[0055] In this connection, restrictions on the target deceleration are expressed by 0≦a.sub.x(ix)≦a.sub.xmax. In the above equation (6), a deceleration at which the total value of Uped that expresses the risk within a predicted time as indicated by Eq. (7) below and the total value of the target deceleration are minimized is determined.

t.sub.px(j.sub.x)=Δt.sub.pxj.sub.x(j.sub.x=0,1,2, . . . ,N.sub.x)  (7)

[0056] The target deceleration ax* of the potential risk prediction driver model is converted into the pedal stroke amount by Eq. (8) below.

P.sub.b-s=−K.sub.ffaa.sub.x*−K.sub.fbPa(a.sub.x*−a.sub.x)−K.sub.fbP-V(V*−V)+b  (8)

where Kffa is an acceleration FF gain, KfbPa is an acceleration FB proportional gain, KfbPV is a velocity FB proportional gain, and b is a play of the stroke.

[0057] While the above description is concerned with the embodiment of the present disclosure, many modifications and changes can be easily made by those skilled in the art. It would be apparent that the present disclosure is not limited only to the illustrated embodiment, but may be applied to various apparatuses or systems without departing from the concept of the present disclosure.