阅读说明：本技术 一种基于多智能体的互联空气悬架协同控制系统及控制方法 (Interconnected air suspension cooperative control system and control method based on multiple intelligent agents ) 是由 孙丽琴 曾帅 徐亦航 杨梁 耿国庆 张佳 赵文 章国栋 徐忠堂 苏春 郝守刚 于 2021-09-18 设计创作，主要内容包括：本发明公开了一种基于多智能体的互联空气悬架协同控制系统及控制方法,在整车受到路面激励后利用气压传感器获取空气弹簧的内部气压,利用速度传感器获取车辆的簧上及簧下质量速度,将上述信息发送至中央控制单元,经中央控制单元计算得到车辆四轮位置处的目标悬架力。将阻尼、互联、车高三个悬架力的输出机构视为三个慎思型的智能体并结合所需悬架力的大小和各自的动作成本制定三者的协同控制策略对整车的目标悬架力进行分配输出,输出的悬架力将反馈作用于整车。本发明可有效解决三个悬架力输出机构耦合度高,难以协同的问题,同时降低系统因电磁阀开闭过于频繁产生的能耗。(The invention discloses an interconnected air suspension cooperative control system and a control method based on multiple intelligent agents. The output mechanisms of the damping, interconnection and vehicle height suspension forces are regarded as three deliberate intelligent bodies, and a cooperative control strategy of the three is formulated by combining the magnitude of the required suspension force and the respective action cost to distribute and output the target suspension force of the whole vehicle, and the output suspension force is fed back to act on the whole vehicle. The invention can effectively solve the problems of high coupling degree and difficult cooperation of three suspension force output mechanisms and simultaneously reduce the energy consumption of the system caused by the frequent opening and closing of the electromagnetic valve.)

1. An interconnected air suspension cooperative control system based on multiple intelligent agents is characterized by comprising an information acquisition unit, a central control unit, a vehicle height intelligent agent, interconnected intelligent agents, a damping intelligent agent and suspension force output mechanisms corresponding to the three intelligent agents; the information acquisition unit is used for acquiring basic information of the vehicle and inputting the basic information into the central control unit, and the central control unit calculates the target suspension force F of the whole vehicle in the current state according to the information acquired by the information acquisition unit₁(ii) a The action cost of the vehicle height intelligent body, the interconnection intelligent body and the damping intelligent body distributes target suspension force, the high intelligent body, the interconnection intelligent body and the damping intelligent body correspondingly output control commands to the vehicle height adjusting mechanism, the interconnection adjusting mechanism and the adjustable damping shock absorber, the vehicle height adjusting mechanism, the interconnection adjusting mechanism and the adjustable damping shock absorber receive the corresponding control commands and execute actions, the three suspension force output mechanisms distribute and output the target suspension force, and the suspension force output by the system is fed back to act on the whole vehicle.

2. The interconnected air suspension cooperative control system based on multiple intelligent agents as claimed in claim 1, wherein the vehicle height intelligent agent, the interconnected intelligent agent and the damping intelligent agent determine the working start and stop of the intelligent agent according to a cooperative working strategy, and control three suspension force output mechanisms to distribute and output target suspension force.

3. The multi-agent based interconnected air suspension cooperative control system as claimed in claim 1, wherein the information collection unit comprises an air pressure sensor and a speed sensor, the air pressure sensor is used for measuring the internal air pressure of the air spring when being excited by the road surface; the speed sensor is used for measuring the sprung mass speed and the unsprung mass speed of the whole vehicle.

4. An interconnected air suspension cooperative control method based on multiple intelligent agents is characterized by comprising the following steps:

step 1: calculating and outputting the target suspension force F of the whole vehicle in the current state according to the information acquired by the information acquisition unit₁；

Step 2: constructing a vehicle height intelligent agent, an interconnection intelligent agent and a damping intelligent agent, and respectively calculating the action cost J of the vehicle height intelligent agent, the interconnection intelligent agent and the damping intelligent agent₁、J₂、J₃；

And step 3: based on the target suspension force, a cooperative working strategy of the vehicle height intelligent body, the interconnection intelligent body and the damping intelligent body is set, and working rules among the vehicle height intelligent body, the interconnection intelligent body and the damping intelligent body are determined according to the cooperative working strategy.

5. The multi-agent-based interconnected air suspension cooperative control method as claimed in claim 4, wherein the working rules among the agents based on the cooperative working strategy are as follows:

step 3.1: according to the change of air spring inflation and deflation, the vehicle height force F of the vehicle height adjusting mechanism is set_HThe regulation range A is as follows:

ΔP_HdiS₀≤F_H≤ΔP_HciS₀

wherein, Δ P_HdiAnd Δ P_HciThe air pressure change values of the air spring caused by inflation and deflation are respectively; s₀Is the effective area of the air spring;

step 3.2: setting the interconnection force F of the interconnection adjusting mechanism according to the change of the air spring inflation and deflation_IThe regulation range B of (1) is:

0≤F_I≤ΔP_IS₀

wherein, Δ P_IThe air pressure change value of the air charging and discharging air spring caused by interconnection is obtained;

step 3.3: if the damping coefficient c is lower than the set damping coefficient, setting the damping force F of the adjustable damping shock absorber for the whole adjustable damping shock absorber system_DThe regulation range C is as follows:

c_minf_d≤F_D≤c_maxf_d

wherein f is_dFor the dynamic travel of the vehicle suspension, c ∈ [ c ]_min c_max]，c_min c_maxThe minimum and maximum values of the damping coefficient, respectively;

step 3.4: when target suspension force F₁When the adjustment range A of the vehicle height adjusting mechanism is exceeded, each suspension force output mechanism cannot bear the load independently, at the moment, the three intelligent bodies are all started, and the suspension force is output together according to the action cost ratio under the current working condition of each intelligent body so as to meet the requirement of the whole vehicle;

step 3.5: when target suspension force F₁The magnitude of the suspension force is within the adjusting range A of the vehicle height adjusting mechanism, the suspension force requirement can be met only by adjusting the vehicle height, at the moment, the interconnected intelligent body and the damping intelligent body are closed, only the vehicle height intelligent body is opened, and the vehicle height adjusting mechanism is adjusted to independently output the suspension force;

step 3.6: when target suspension force F₁When the adjustment range B of the interconnection adjusting mechanism is reduced, the vehicle height intelligent body is closed, the interconnection intelligent body and the damping intelligent body are opened, and the suspension force is output according to the action cost ratio of the interconnection intelligent body and the damping intelligent body under the current working condition;

step 3.7: when target suspension force F₁When the damping force is further reduced to the adjusting range C of the adjustable damping shock absorber, the requirement of the suspension force can be met only by adjusting the damping force. At the moment, the vehicle height intelligent body and the interconnected intelligent body are closed, only the damping intelligent body is opened, and the adjustable damping vibration attenuation is independently adjustedThe machine outputs a suspension force.

6. The multi-agent-based interconnected air suspension cooperative control method as claimed in claim 4, wherein the action cost J of the vehicle-height agent₁Expressed as:

wherein, t_ciAnd t_diRespectively representing the charging and discharging time of a vehicle height electromagnetic valve; i is left to {1, 2, 3, 4} refers to the air charging and discharging pipelines of the air spring at the four positions of front left, front right, back left and back right, E_HAnd the power of the high charging and discharging electromagnetic valve of the vehicle is shown.

7. The multi-agent-based interconnected air suspension cooperative control method as claimed in claim 4, wherein the action cost J of interconnected agents₂Expressed as:

wherein, t_iIndicating the opening time of the interconnected solenoid valves; i belongs to {1, 2, 3, 4} to indicate four electromagnetic valves in the front, back, left and right interconnected pipelines, E_IRepresenting the power of the interconnected solenoid valves.

8. The multi-agent-based interconnected air suspension cooperative control method as claimed in claim 4, wherein the action cost J of the damping agent₃Expressed as:

wherein, T_sRepresents the opening time of the damper; i is left-front and right-frontRear left and rear right dampers, V_DAnd I_DRespectively representing the supply voltage and current of the adjustable damping shock absorber.

9. The multi-agent-based interconnected air suspension cooperative control method as claimed in claim 4, wherein the information collected by the information collection unit comprises: air pressure P inside air spring_iSprung mass velocityAnd unsprung mass velocity

10. The multi-agent-based interconnected air suspension cooperative control method as claimed in claim 9, wherein the target suspension force F in the current state of the whole vehicle is calculated₁The method comprises the following steps:

based on the internal pressure P of the air spring_iAnd effective area S of air spring₀Calculating to obtain the air spring force required by the whole vehicle: f_s＝P_i×S₀；

Based on sprung mass velocityUnsprung mass velocityAnd calculating the damping coefficient c of the damper to obtain the damping force required by the whole vehicle:

target suspension force required for the entire vehicle: f₁＝F_s+F_d。

Technical Field

The invention relates to the field of interconnected air suspension control, in particular to a cooperative control system and a control strategy among three suspension force output mechanisms of an interconnected air suspension.

Background

The air suspension system is one of important systems for safe running of the vehicle, and can effectively relieve local impact of a road to the vehicle. The interconnected air suspension is used as a derivative structure of the air suspension, can further improve the driving smoothness and the road-friendly type of a vehicle, and is one of the main characteristics of the interconnected air suspension with three suspension force output mechanisms, namely vehicle height, interconnection and damping.

However, the three suspension force output mechanisms have high coupling degree, especially the interconnection part and the vehicle height part, and both achieve the purpose of changing the air spring force by charging and discharging the air spring through the opening and closing electromagnetic valve, so that the opening and closing frequency of the electromagnetic valve is easy to be too frequent, the service life of the electromagnetic valve is shortened, and the overall energy consumption of the system is increased.

National patent CN202010594863.1 proposes an interconnected air suspension cooperative control system based on MPC model predictive control. Although the cooperative control of the three suspension force output mechanisms is realized, a control system is too complex, and the contradiction between interconnection and the inflation and deflation of the vehicle height in the vehicle running process is not considered.

The national patent CN108839532B proposes a control method for timely adjusting the interconnection state of the interconnected air suspension according to the air pressure, but also ignores how to cooperatively control the vehicle height while adjusting the interconnection state.

Although the control method of the interconnected air suspension has been greatly developed under the efforts of numerous scholars, the contradiction between interconnection and vehicle height in the aspects of inflation and deflation is not fundamentally solved. Therefore, there is a need for improvements to existing interconnected air suspension control systems.

Disclosure of Invention

In order to solve the defects in the prior art, the invention provides an interconnected air suspension cooperative control system and a control method based on multiple intelligent agents.

The technical scheme adopted by the invention is as follows:

an interconnected air suspension cooperative control system based on multiple intelligent agents comprises an information acquisition unit, a central control unit, a vehicle height intelligent agent, an interconnected intelligent agent, a damping intelligent agent and suspension force output mechanisms corresponding to the three intelligent agents; the information acquisition unit is used for acquiring basic information of the vehicle and inputting the basic information into the central control unit, and the central control unit calculates the target suspension force F of the whole vehicle in the current state according to the information acquired by the information acquisition unit₁(ii) a Vehicle height agent, interconnection agent andthe action cost of the damping intelligent body distributes the target suspension force, the high intelligent body, the interconnection intelligent body and the damping intelligent body correspondingly output control commands to the vehicle height adjusting mechanism, the interconnection adjusting mechanism and the adjustable damping shock absorber, the vehicle height adjusting mechanism, the interconnection adjusting mechanism and the adjustable damping shock absorber receive the corresponding control commands and execute actions, the three suspension force output mechanisms distribute and output the target suspension force, and the suspension force output by the system is fed back to act on the whole vehicle.

Further, the vehicle height intelligent agent, the interconnection intelligent agent and the damping intelligent agent determine the working start and stop of the intelligent agent according to a cooperative working strategy, and control the three suspension force output mechanisms to distribute and output the target suspension force.

Further, the information acquisition unit comprises an air pressure sensor and a speed sensor, wherein the air pressure sensor is used for measuring the internal air pressure of the air spring when being excited by the road surface; the speed sensor is used for measuring the sprung mass speed and the unsprung mass speed of the whole vehicle.

An interconnected air suspension cooperative control method based on multiple intelligent agents comprises the following steps:

step 1: calculating and outputting the target suspension force F of the whole vehicle in the current state according to the information acquired by the information acquisition unit₁；

Step 2: constructing a vehicle height intelligent agent, an interconnection intelligent agent and a damping intelligent agent, and respectively calculating the action cost J of the vehicle height intelligent agent, the interconnection intelligent agent and the damping intelligent agent₁、J₂、J₃；

And step 3: based on the target suspension force, a cooperative working strategy of the vehicle height intelligent body, the interconnection intelligent body and the damping intelligent body is set, and working rules among the vehicle height intelligent body, the interconnection intelligent body and the damping intelligent body are determined according to the cooperative working strategy.

Further, the working rules between agents based on the collaborative working policy are as follows:

step 3.1: according to the change of air spring inflation and deflation, the vehicle height force F of the vehicle height adjusting mechanism is set_HThe regulation range A is as follows:

ΔP_HdiS₀≤F_H≤ΔP_HciS₀

wherein, Δ P_HdiAnd Δ P_HciThe air pressure change values of the air spring caused by inflation and deflation are respectively; s₀Is the effective area of the air spring;

step 3.2: setting the interconnection force F of the interconnection adjusting mechanism according to the change of the air spring inflation and deflation_IThe regulation range B of (1) is:

0≤F_I≤ΔP_IS₀

wherein, Δ P_IThe air pressure change value of the air charging and discharging air spring caused by interconnection is obtained;

step 3.3: if the damping coefficient c is lower than the set damping coefficient, setting the damping force F of the adjustable damping shock absorber for the whole adjustable damping shock absorber system_DThe regulation range C is as follows:

c_minf_d≤F_D≤c_maxf_d

wherein f is_dFor the dynamic travel of the vehicle suspension, c ∈ [ c ]_min c_max]，c_min c_maxThe minimum and maximum values of the damping coefficient, respectively;

step 3.4: when target suspension force F₁When the adjustment range A of the vehicle height adjusting mechanism is exceeded, each suspension force output mechanism cannot bear the load independently, at the moment, the three intelligent bodies are all started, and the suspension force is output together according to the action cost ratio under the current working condition of each intelligent body so as to meet the requirement of the whole vehicle;

step 3.5: when target suspension force F₁The magnitude of the suspension force is within the adjusting range A of the vehicle height adjusting mechanism, the suspension force requirement can be met only by adjusting the vehicle height, at the moment, the interconnected intelligent body and the damping intelligent body are closed, only the vehicle height intelligent body is opened, and the vehicle height adjusting mechanism is adjusted to independently output the suspension force;

step 3.6: when target suspension force F₁When the adjustment range B of the interconnection adjusting mechanism is reduced, the vehicle height intelligent body is closed, the interconnection intelligent body and the damping intelligent body are opened, and the suspension force is output according to the action cost ratio of the interconnection intelligent body and the damping intelligent body under the current working condition;

step (ii) of3.7: when target suspension force F₁When the damping force is further reduced to the adjusting range C of the adjustable damping shock absorber, the requirement of the suspension force can be met only by adjusting the damping force. At the moment, the vehicle height intelligent body and the interconnected intelligent body are closed, only the damping intelligent body is opened, and the adjustable damping shock absorber is independently adjusted to output the suspension force.

Further, the action cost J of the vehicle height agent₁Expressed as:

wherein, t_ciAnd t_diRespectively representing the charging and discharging time of a vehicle height electromagnetic valve; i is left to {1, 2, 3, 4} refers to the air charging and discharging pipelines of the air spring at the four positions of front left, front right, back left and back right, E_HAnd the power of the high charging and discharging electromagnetic valve of the vehicle is shown.

Further, the action cost J of the interconnected agents₂Expressed as:

wherein, t_iIndicating the opening time of the interconnected solenoid valves; i belongs to {1, 2, 3, 4} to indicate four electromagnetic valves in the front, back, left and right interconnected pipelines, E_IRepresenting the power of the interconnected solenoid valves.

Further, the action cost J of the damping agent₃Expressed as:

wherein, T_sRepresents the opening time of the damper; i is left to {1, 2, 3, 4} refers to the damper at four positions, front left, front right, back left and back right, V_DAnd I_DRespectively representing the supply voltage and current of the adjustable damping shock absorber.

Further, the information collected by the information collecting unit includes: air (a)Spring internal pressure P_iSprung mass velocityAnd unsprung mass velocity

Further, calculating the target suspension force F of the whole vehicle in the current state₁The method comprises the following steps:

based on the internal pressure P of the air spring_iAnd effective area S of air spring₀Calculating to obtain the air spring force required by the whole vehicle: f_s＝P_i×S₀；

Based on sprung mass velocityUnsprung mass velocityAnd calculating the damping coefficient c of the damper to obtain the damping force required by the whole vehicle:

target suspension force required for the entire vehicle: f₁＝F_s+F_d。

The invention has the beneficial effects that:

the invention constructs an interconnected air suspension cooperative control system based on a multi-agent theory. The output mechanisms of the three suspension forces of damping, interconnection and vehicle height are regarded as three deliberate intelligent bodies, and a cooperative control strategy of the three is formulated by combining the magnitude of the required suspension force and the respective action cost (energy consumption) cost to distribute and output the target suspension force of the whole vehicle, and the output suspension force is fed back to act on the whole vehicle. The problem that three suspension force output mechanisms are high in coupling degree and difficult to cooperate can be effectively solved, and energy consumption of the system caused by the fact that the electromagnetic valve is opened and closed too frequently is reduced.

Drawings

FIG. 1 is a block diagram of a multi-agent based interconnected air suspension cooperative control system;

fig. 2 is a schematic diagram of a target suspension force distribution method of the whole vehicle.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

As shown in FIG. 1, the invention provides an interconnected air suspension cooperative control system based on multiple intelligent agents, which comprises an air pressure sensor, a speed sensor, a central control unit, a vehicle height adjusting mechanism, an interconnected adjusting mechanism and an adjustable damping shock absorber. The air pressure sensor is used for measuring the internal air pressure of the air spring when the air spring is excited by a road surface. The speed sensor is used for measuring the sprung mass speed and the unsprung mass speed at the four-wheel positions of the whole vehicle. The central control unit is used for integrating information collected by the air pressure sensor and the speed sensor so as to calculate the target suspension force of the whole vehicle. The method comprises the steps of constructing a vehicle height intelligent body, an interconnection intelligent body and a damping intelligent body, distributing target suspension force according to the action cost of the vehicle height intelligent body, the interconnection intelligent body and the damping intelligent body respectively, outputting control commands to a vehicle height adjusting mechanism, an interconnection adjusting mechanism and an adjustable damping shock absorber by the high intelligent body, the interconnection intelligent body and the damping intelligent body correspondingly, receiving the corresponding control commands by the vehicle height adjusting mechanism, the interconnection adjusting mechanism and the adjustable damping shock absorber and executing the actions, distributing and outputting the target suspension force by the three suspension force output mechanisms, and applying feedback of the suspension force output by a system to the whole vehicle. Specifically, the vehicle height adjusting mechanism is used for controlling the opening and closing of an air spring air charging and discharging electromagnetic valve. The interconnection regulating mechanism is used for controlling the opening and closing of the interconnection electromagnetic valve. The adjustable damping shock absorber is used for controlling the damping force of the interconnected air suspension system.

The invention also provides a multi-agent-based interconnected air suspension cooperative control method based on the control system, which comprises the following steps:

step 1: central controlThe control unit calculates and outputs a target suspension force F under the current state of the whole vehicle according to information collected by the air pressure sensor and the speed sensor₁. The step 1 is specifically as follows:

step 1.1: the central control unit measures the air pressure P in the air spring according to the air pressure sensor_iAnd effective area S of air spring₀Calculating to obtain the air spring force F required by the whole vehicle_s。

F_s＝P_i×S₀

Step 1.2: the central control unit is based on the sprung mass velocity measured by the velocity sensorAnd unsprung mass velocityAnd calculating the damping force F required by the whole vehicle by combining the damping coefficient c of the damper_d。

Step 1.3: the central control unit sums the air spring force and the damping force required by the whole vehicle to obtain the target suspension force F required by the whole vehicle₁。

F₁＝F_s+F_d

Step 2: constructing a vehicle height intelligent agent, an interconnection intelligent agent and a damping intelligent agent, and distributing target suspension force according to the action cost of the vehicle height intelligent agent, the interconnection intelligent agent and the damping intelligent agent respectively; calculating the action cost J of the vehicle height agent, the interconnection agent and the damping agent respectively₁、J₂、J₃. The method comprises the following specific steps:

step 2.1: according to the power E of the electromagnetic valve for charging and discharging air of the vehicle height_HCalculating the action cost J of the intelligent vehicle height body₁。

In the formula, t_ciAnd t_diRespectively representing the charging and discharging time of a vehicle height electromagnetic valve; and i belongs to {1, 2, 3, 4} to refer to the air charging and discharging pipelines of the air spring at four positions of front left, front right, rear left and rear right.

Step 2.2: according to the power E of the interconnected solenoid valves_ICalculating the action cost J of the interconnected agent₂。

In the formula, t_iIndicating the opening time of the interconnected solenoid valves; and i belongs to {1, 2, 3, 4} to indicate the electromagnetic valves in the front, the rear, the left and the right interconnected pipelines.

Step 2.3: according to the supply voltage V of the adjustable damping vibration absorber_DAnd current I_DCalculating the action cost J of the damping intelligent agent₃。

In the formula, T_sRepresents the opening time of the damper; i ∈ {1, 2, 3, 4} refers to dampers at four positions front left, front right, rear left, and rear right.

Wherein, vehicle height intelligent agent cost J₁Cost > interconnect agent J₂Cost > damping agent J₃(ii) a The higher the cost, the greater the suspension force that can be provided.

And step 3: based on the target suspension force, a cooperative working strategy of the vehicle height intelligent body, the interconnection intelligent body and the damping intelligent body is set, and working rules among the vehicle height intelligent body, the interconnection intelligent body and the damping intelligent body are determined according to the cooperative working strategy.

The cooperative working strategy is as follows:

step 3.1: according to the change of air spring inflation and deflation, the vehicle height adjusting mechanism has a vehicle height force F_HIn an adjustment range A of：

ΔP_HdiS₀≤F_H≤ΔP_HciS₀

Wherein, Δ P_HdiAnd Δ P_HciThe air pressure change values of the air spring caused by inflation and deflation are respectively.

Step 3.2: according to the change of air spring inflation and deflation, the interconnection force F of the interconnection adjusting mechanism_IThe regulation range B of (1) is:

0≤F_I≤ΔP_IS₀

wherein, Δ P_IThe air pressure change value of the air charging and discharging air spring caused by interconnection.

Step 3.3: if the damping coefficient c is equal to [ c ∈ ]_min c_max]For the entire adjustable damping vibration absorber system, the damping force F of the adjustable damping vibration absorber_DThe regulation range C is as follows:

c_minf_d≤F_D≤c_maxf_d

wherein f is_dFor the running stroke of the vehicle suspension, c_min c_maxRespectively the minimum and maximum values of the damping coefficient.

Step 3.4: when the target suspension force F is as shown in FIG. 2₁When exceeding vehicle height adjustment mechanism's control range A, each suspension power output mechanism can not undertake alone, and three intelligent agent all open this moment, and action cost (energy consumption) ratio under the current operating mode of each is according to exports the suspension power jointly in order to reach whole car demand.

Step 3.5: when target suspension force F₁The size of the suspension force is within the adjusting range A of the vehicle height adjusting mechanism, and the requirement of the suspension force can be met only by adjusting the vehicle height. At the moment, the interconnected intelligent bodies and the damping intelligent bodies are closed, only the vehicle height intelligent body is opened, and the vehicle height adjusting mechanism is adjusted to output the suspension force independently.

Step 3.6: when target suspension force F₁And reducing the adjustment range to the adjustment range B of the interconnection adjusting mechanism. At the moment, the vehicle height intelligent body is closed, the interconnection intelligent body and the damping intelligent body are opened, and the suspension force is output according to the action cost (energy consumption) ratio of the interconnection intelligent body and the damping intelligent body under the current working condition.

Step 3.7: when target suspension force F₁When the damping force is further reduced to the adjusting range C of the adjustable damping shock absorber, the requirement of the suspension force can be met only by adjusting the damping force. At the moment, the vehicle height intelligent body and the interconnected intelligent body are closed, only the damping intelligent body is opened, and the adjustable damping shock absorber is independently adjusted to output the suspension force.

The above embodiments are only used for illustrating the design idea and features of the present invention, and the purpose of the present invention is to enable those skilled in the art to understand the content of the present invention and implement the present invention accordingly, and the protection scope of the present invention is not limited to the above embodiments. Therefore, all equivalent changes and modifications made in accordance with the principles and concepts disclosed herein are intended to be included within the scope of the present invention.