文献翻译-与循环主系统相关的附属液压传动与控制的新概念

1附录 A1与循环主系统相关的附属液压传动与控制的新概念介绍这一个论题提出一个新的概念为 与液压循环主系统相关联的附属控制. 在这项新的概念中, 我们研究多个与液压循环主系统相关联的多变位移的液压动力机的能力 ，并且所有的液压动力机能以多变的速度工作，并能驱动各种负载。液压动力机的速度在任何时候都能够被有效的改变，这是通过对速度要求的操纵来完成的，没有对其他机构产生影响。 这些液压动力机通过与液压相关的成本和能耗方面被控制这一工作的一个主要部分是与这一概念的可行性调查相关联的。这一概念包括满足驱动的要求，驱动的稳定性以及驱动负载维持在一特定速度的能力。1.背景信息:液压传动是一种流体静力学理论。这种理论已作为传递动力的方式被使用。液压传动的目的是把机械能转换为液体压力能，而有通过另外一种形式把液压能转化成机械能输出。并且还要满足驱动机械或装置的速度和转距要求。在驱动理论方面, 二个叁数对被传输的力很重要: 1) 转距= M(牛 米)2) 速度 = n(转/每分)这些机械的叁数分别与对流体静力学的下列叁数符合: 1) 压力 = P(帕)2) 流量= Q(立方米/秒)在通常的动力源中举例来说，一个内燃机或一个电动机, 在机械参数之间的关系是：P= M *w (1.1)其中: P= 功 (千瓦)M=转距(牛 米)w= 角速度(弧度/秒)因为有相同的动力来源和在效率考虑范围，传输的动力总是与动力源提供的最大力2相等，并且是常数。那么公式 (1.1) 变成: 最大功率= 转距 转速= K。 (1.2)其中: K= 常数。转距= K/转速。1转 距 转 速转矩和速度之间的关系反之亦然,也就是说，对于任何一个转矩只有一个于之符合的速度。换句话说, 在各种转速的情况,通过使转速由小到大变化，由于传递同样的功率，将使转矩从大到小发生变化。这是在考虑效率的情况下，由动力源产生的最大功率条件下分析的。在液压驱动控制中，这个理论是不同的。公式(1.1)变成: dP=Q p (1.3)其中:dp= 液压马达的压力差液压传动能够维持在一个提前设定的高压情况下。这种液压系统通过一个压力可调节的泵和一个变量马达能够改变流速。然后公式(1.3)变成:P= Q dp=Q K其中:K= 常数P; Q (1.4)从公式(1.4),根据流量(Q)，流速与流入到液压传动系统中的功率与成了比例关系。换句话说,在各种速度的条件下，根据流量(Q)来从小到大的增加速度，液压传动功率将随公式(1.3) 增加, 压力差不同的时候，转矩将总是保持最大值。液压传动的这种特性使它能以任何的速度传送相同的最大扭矩,根据不同的压力差 ,通过描述部分而不是所有的动力源的动力，这对提前设定的最大扭矩 (dp) 是足够的，并能提供所要求的各种流速(Q)。3依据液压参数的结合形式，俩个驱动概念能被定义为：1)流量传动系统(传统的系统)。2)可变压力的系统(第二单元的控制系统)2.流量传动系统(传统的系统): 这种简单的传动系统(一种输出),由主要的单元（泵）和次要的单元（马达）组成。其与流量Q相关。公式(1.1)用一种封闭的传动出示了这种关系。 测定体积流量 Q(由输入的传动速度n 1转/每分和泵位移v 1决定)导致液压马达产生一个输出速度n 2。取决于它的位移v2.因为没有阻塞元件存在，所以这一个系统是相对地有效率的。在大的工程应用中对于小输入输出系统,安装带有一种特定的油供应的液压系统是平常不过的了，叫做主要响应系统。因为动力源能够作成适应总体的能源要求，而不是用独立的动力源供应每个液压元件，因此一个循环主系统节约了重量和成本。循环主系统通过压力变量泵和与其平行连接的元件在特定的压力下运作。为了保证所有的液体在最低程度的阻力下不能通过各种元件溢流，在能量传送通道中安装密封元件是必不可少的。这可保证流量到达每个相关的元件。有在开环循环中的二个引动器表示循环主系统。 它也表示一个被三种控制阀控制的变量马达; 流量控制、方向控制、流量控制。流入马达的最大流量被流量控制阀控制；在流量控制阀下，马达被方向控制阀控制，其控制的流量范围可以达到更广。如果马达在低载状况下运行，能量更容易转换成热而损失掉。通过密封件和带载条件下工作，一部分能量转化成热而损失掉，这事实上是泵产生压力的一部分，而不是执行机构所要求的。随着输出转矩的改变压力通过执行元件也有一个减少量dp；压力的这种改变导致液体的压缩及再膨胀。这对液压系统的稳定性产生一个负面的影响，由于“液体弹簧”的作用。因此增加泵的控制时间是必要的，以便形成稳定的压力并保持系统的稳定性。3.压力控制系统:(系统用附属单元控制):寻找另一种传动概念是必要的，即没有传动系统的这些不利条件。这一种概念叫做压力控制，也叫做“附属控制”。这中附属控制系统的优点是：41) 没有限制的一些液压控制阀的并联引用。2) 能量从主要单元传递到附属单元没有堵塞。3) 能量回收为其他控制阀使用或能量返回到最初的单元没有阻塞。4) 一个固定的控制压力为了除去液体弹簧的影响力。5) 具有在任何工作点工作的能力。4.附属控制传动系统(新的观念): 有一种液压循环系统，其附属控制单元连接到循环主系统，并被一个速度控制装置固定。这种液压循环系统由以下组成：1. 变量液压马达。2. 定量齿轮泵。当液压马达在预先设置的速度压力下运转时（要求的压力），液压控制阀将达到最大的开启位置。同时作用在液压控制阀上的力是预先设定的压力。弹簧力，速度控制泵的压力取决于液压马达的速度。当液压马达的速度增加时，液压泵的压力也随之增加。液压控制阀的弹簧再次使之返回到预先设定的压力值。当速度控制泵外泄压力并且液压控制阀超出预先设定的压力值（要求的压力）时，液压控制阀开始移动到一个新的位置以减少液压马达的流量，进而减少液压马达的速度。随着液压马达的转速降低，外部速度控制泵的压力也降低，直到设定的速度压力超出速度控制泵压力和液压控制阀的压力的总和 。然后液压控制阀开始移动到一个新的位置以增加液压泵的位移以增加转速。这种动作将要重复，直到液压控制阀停止在一个平衡的位置。这个位置上作用在液压控制阀上的合力等于零。并且液压马达产生足够的转矩维持这一速度。这一速度符合要求的压力（预设的速度压力）5.结论新观念附属控制液压系统的摹拟表明液压控制系统能够在不同的单个的多边的速度下工作，还能够在速度不变的稳定条件下高精度的工作。通过运用新观念我们能够增加附属控制的下列优点：1. 把许多液压系统连结到循环主系统，所有的液压传动各自多变的速度下工作。2. 能量储存。3. 低的成本。4. 在稳定速度状态下工作，没有速度的变化。55. 液压控制驱动。致谢在这里还要再次感谢我的导师王慧,是他在百忙之中指导我收集英文资料,在翻译后又指导我进行修改.设计过程的每一部都凝结了老师辛勤的汗水,在这里再次对我的导师表示深深的感谢.6附录 B1New Concept for Hydrostatic Drive with Control of the Secondary Unit Connected to the Ring Main System.Introduction:This thesis proposes a new concept for Control of the Secondary Units Connected to the Hydraulic Ring Main System. In this new concept, we study the ability to connect more than one variable displacement hydraulic motor to the hydraulic ring main system, and all motors can work at variable speeds, and drive different loads. The speed for any hydraulic motor can be changed individually at any time through the operation to any speed required, without any effect on the other. These hydraulic motors are controlled by hydraulic means for cost consideration, and energy saving.A major part of this work is directed towards investigation of the ability of this concept to meet the requirements of the drive concept, the stability of the drives, and their ability to drive the loads maintaining the specific speed.Background information:Hydrostatic Drive is a fluid power technology, which has been used as means of transmitting power. The purpose of hydrostatic transmission is to convert mechanical power into hydraulic power, and convert it back into mechanical output power in a form, which matches the speed and torque demands of driven mechanisms or machines.In drive technology, two parameters are important to the power being transmitted: 1) Torque = M (Nm)2) Speed = n (RPM)These mechanical parameters correspond respectively to the following parameters in hydrostatic drives: 1) Pressure = P (bar)2) Flow rate = Q (m3/sec)In normal power sources e.g. a combustion engine or an electrical motor, the relation between the mechanical parameters is:P M (1.1)Where: P = Power (KW)M = Torque (Nm)7= Angular velocity (rad/sec)For the same power source and within efficiency considerations the power transmitted is constant and equal to the maximum power that can be produce by the power source, which is constant.Then equation (1.1) becomes: Pmax M K (1.2)Where: K = constantM K/M1/The relation between torque and speed is vice versa, that is, for any torque there is only one corresponding speed. In other words, in the case of variable speed, by increasing the speed from minimum to maximum speed, the torque will reduce from maximum to minimum torque for the same power being transmitted,which is the maximum power produced by the power source, after efficiency considerations.In hydrostatic drives, the story is different.The equation (1.1) becomes: dP Qp (1.3)Where: dp = pressure difference across the motorThe hydrostatic transmission is capable of maintaining a preset highpressure level in the hydraulic circuit,while changing the flow rate, by using a pressure regulated pump and a variable displacement motor.Then equation (1.3) becomes: P Q dp QKWhere: K = constantP ; Q (1.4)From the equation (1.4), the speed in terms of flow rate (Q) has proportional relation with the power input to the hydrostatic transmission. In other words, in the case of variable speed, by increasing the speed in terms of flow rate (Q), from minimum to maximum speed, the power input to the hydrostatic transmission will increase according to equation (1.3), while the torque in terms of pressure difference across the motor (dp), remains constant at the maximum value. The characteristic of hydrostatic transmission, is that it can transmit the same maximum torque at 8any speed, in terms of pressure difference across the motor (dp), by drawing part but not all of the power sources power, which is enough for the preset maximum torque (dp), and producing the required variable speed (Q).Dependent upon the couplings type of the hydraulic parameters two drive concepts can be defined: 1) Drive systems with flow coupling (conventional systems).2) Drive systems with coupling via the operating pressure (systems with control of the secondary unit).Drive Systems With Flow Coupling (Conventional Systems): The simple hydrostatic drives (one output), consist of the primary unit (pump) and the secondary unit (motor), which are interrelated by virtue of the hydraulic flow Q in (m3/sec). Fig. (1.1) shows this relationship using a closed circuit drive.The volumetric flow Q(which is determined by the input drive speed n1 in rpm and the pump displacement v1) causes the hydraulic motor to achieve an output speed n2 dependent upon its displacement v2.This system is relatively efficient because no throttling elements are present.In heavy engineering applications for multioutput circuits, it is common practice to install hydraulic systems with a central oil supply on a socalled RING MAIN SYSTEM, because the power supply unit can be sized to suit total power required, instead of using individual power packs to supply every hydraulic component. Therefore, a ring main system saves weight and cost. The ring main system operates at a constant pressure by using pressureregulated pumps and with many actuators connected in parallel. In order to ensure that all of the fluid does not flow through the actuator with the lowest level of resistance, it is necessary to install throttling elements in the energy transmission lines. These ensure that the relevant amount of flow reaches the individual actuators.There are the ring main system with two actuators in an open circuit. It also shows a variable displacement motor controlled by three types of control valves; flow control, directional control and counter balance valve. The maximum flow to this motor is limited by a flow control valve; below the flow control valve the motor is controlled by a directional control valve, which controls the direction of rotation and throttles the flow even further. If the motors tend to act as generators while lowering a load, energy is converted into heat in a counter balance valve.Through the throttling and under partially loaded conditions, a part of the power is converted into heat losses. This is in fact a part of the pressure generated by the pumps and is not required by the actuator at any flow.9With any change in output torque there is change in pressure drop dp across the actuator; this change in pressure drop causes the fluid to compress and then expand again. This has an adverse effect on the system stability due to the HYDRAULIC SPRING. Therefore it is necessary to increase the control time of the pumps to damp the pressure buildup and keep the systems stability under control.Drive Systems With Pressure Coupling (Systems With Control Of The Secondary Unit): It was necessary to look for another drive concept which did not have these disadvantages of the drive systems with flow coupling. This drive concept is called Drive Systems With Pressure Coupling also known as The Secondary Control.The advantages of the secondary control systems are: 1) Parallel operation of a number of actuators without limitation.2) Energy transfer from the primary to the secondary units without throttling.3) Energy recovery for use by other actuators or by returning the energy to the primary unit, againwithout throttling.4) A constant operating pressure in order to eliminate the influence of the hydraulic spring.5) The ability to include accumulators at any required point.The Drive System For Secondary Control (The New Concept): There are the hydraulic circuit for the secondary control unit connected to the ring mainsystem and fitted with a speed control device. The hydraulic circuit consists of: 1. Variable displacement hydraulic motor.2. Fixed displacement gear pump.When the hydraulic motor starts running under the reset speed pressure (demand pressure), the swashplate actuator will shift to the maximum opening position. At this time the force acting in the actuator are the reset speed pressure, the spring force, and the speed control pump pressure which is depend upon the hydraulic motor speed. As the hydraulic motor speed increases, the outlet speed control pump pressure increases, and acts with the swashplate actuator spring force against the preset pressure. When the speed control pump outlet pressure and swashplate actuator spring force exceed the reset speed pressure (demand pressure), the swashplate actuator will start to move in a direction to reduce the hydraulic motor displacement, to reduce the hydraulic motor speed. As the hydraulic motor speed decreases the outlet speedcontrol pump pressure decreases, until the reset speed pressure exceeds the sum of the speed control pump pressure and the swashplate actuator spring force. Then the swashplate actuator starts to move in a direction to increase the hydraulic motor displacement to increase the speed. 10This action will repeat with decay until the swashplate actuator stops at the equilibrium position, where the summing forces acting on the swashplate actuator equal zero, and the hydraulic motor produces enough torque to maintain the speed, which corresponds to the demand pressure (reset speed pressure).CONCLUSIONS.The simulation for the new concept secondary controlled hydraulic drive showed that the hydraulic drives can work at different individual vari