【導(dǎo)讀】推土機(jī)在國(guó)民經(jīng)濟(jì)與國(guó)家建設(shè)事業(yè)中，占據(jù)重要的地位。它廣泛應(yīng)用于鐵道建筑工程、至于人煙稀少，工作面狹窄，可能完成任務(wù)的。與提高，是大有可為的。因此我們從國(guó)家建設(shè)事業(yè)出發(fā)，選擇了履帶式推土機(jī)液壓系統(tǒng)的設(shè)。計(jì)，是大有前景的?？捎糜谄秸麍?chǎng)地，堆積松散材料，清除作業(yè)地段內(nèi)的障礙物等。在實(shí)際使用中，如果運(yùn)距過長(zhǎng)，由于土壤漏失的影響，所用時(shí)間占比例增大，同樣也會(huì)使推土機(jī)生產(chǎn)率降低。為宜；大型推土機(jī)的運(yùn)距一般不應(yīng)超過150m；推土機(jī)的經(jīng)濟(jì)運(yùn)距為50～80。這種推土機(jī)通用性好，廣泛應(yīng)用于各類土方工程的施工作業(yè)，是目前。他們均屬于特殊條件下使用的專用推。作可靠等優(yōu)點(diǎn)，所以推土機(jī)均采用柴油機(jī)為動(dòng)力裝置。目前大中型推土機(jī)采用這種傳動(dòng)方式較為普遍。和電纜的限制，它的使用范圍受到很大制約。稱為直鏟式推土機(jī)。稱活動(dòng)式鏟刀推土機(jī)或角鏟式推土機(jī)。產(chǎn)量已有1萬臺(tái)以上。推土機(jī)的可靠性和使用壽命。

　　

【正文】 上海 交通大學(xué)畢業(yè)設(shè)計(jì) 31 附錄 A HYDRAULIC SYSTEM INDUSTRIAL HYDRAULIC CIRCUIT The purpose of the pump is , of course , to give pressure to the oil 。 in other words , to give power to the machine ,the purpose of the values is to control the flow of oil and to apply the power when and where it may be needed . To illustrate as simply as possible how this is acplished in a ― circuit ‖ , that is , in the rum of oil from the reservoir , through the pump , the valves , the valves , the driven unit , and back to the reservoir references are made to the diagrams shown in Figs 11 and . First , get the general idea of the circuit from Fig , (omitting the feeding mechanism ) , then a clear understanding of the operation of the speedcontrol and reverse valves (Fig ) , after whi8ch it should not be difficult to understand the details of including the feed mechanism . The diagram in shows speedcontrol valve open (speed controlpiston) pulled out , permitting the exhaust through V port (9) to the reservoir . through R1 to the intake port (1) in the valve , out through (3) to the righthand end of the cylinder , and forces the piston out of the cylinder and down through (4) , across the spool through port (2) , and on down through the V port (9) to the reservoir . The instant the valve is changed , the flow of oil through the valve is reversed (as shown in ) , and the piston travels in the opposite direction . Referring to a in (which is an enlargement ) of the valve in , oil from the reservoir ( and pump) , through R1 to (1) to (3) to the cylinder , pushers the piston to the left 。 oil on the other side of the piston escapes from the cylinder down through (4)to (2) to (9) to R2 to the reservoir . Notice that the oil can enter (1) but cannot enter (5) because it is stopped by the land (11) ,also that it cannot get through (12) because it is stopped by the land (13) . In b() the valve is shown shifted to the left . This merely closes (1) and opens (5) . oil flows now through R1 to (5) to (4) to the left side of the cylinder , and at the same time the oil on the right side of the cylinder exhausts through (3) to (2) to (9) to R2 to the reservoir . Note that , as in a , the oil can flow on as stated 。 elsewhere it is shut off by the lands on the valve plunger . Referring to the speedcontrol plunger , the V port (9) is simply a notch cut in the side . Rotating the plunger a slight amount serves to reduce the size of the port , and of course , the amount of oil that can pass through the port , and consequently the speed of the driven piston in the cylinder and therefore of the sliding worktable . when the V port (9) and the table remains stationary 。 oil from the pump bypassing through the exhaust line (12) and the space (14) . This is the way to stop the table , instead of shutting off (9) entirely ,since it avoids forcing the oil through the relief valve . It will be noted (Fig .) that ,with the plunger pushed way in and the power traverse stopped , the oil which fills the cylinder and the pipe line is pushed by the piston back an forth from one side of the piston to the other through the pipe line . To understand this more easily , refer to a , same figure , and imagine this line is openas in c . Then as the table is moved from right to left , the oil will flow from the cylinder through (4) to (10) through (15) through the rest of (10) and on up through (3) to the cylinder . When the stroke is reversed an the table is moved left to right , the oil be reversed an well flow from (3) to (10) through the space (15) and up through the rest of (10) to (4) , thence to the left end of the cylinder . FLUID POWER PUMPS . Every fluidpower system used one or more pumps to pressurize the hydraulic fluid . The fluid under pressure , in turn performs work in the out put section of the fluidpower system . Thus , the pressurized fluid may be used to move a piston in a cylinder or to turn the shaft of a hydraulic motor . 曹小平 履帶式推土機(jī)液壓系統(tǒng)設(shè)計(jì) 32 The purpose of pump in a fluidpower system is to pressurize the fluid so that work may be performed . Some fluidpower system use low pressurize100pis or les to do work . W here a large work output is required , high pressures1000pis or moremay be used . So we find that every modern fluidpower system used at least one pump to pressurize the fluid . 1. Types of pumps Three types pumps find use in fluidpower Systems : 1). Rotary , 2). Reciprocating , and 3). Centrifugal pumps . Simple hydraulic systems may use but one type of pump . The trend is to use pumps with the most satisfactory characteristics for the specific tasks involved . In matching the characteristics of the pump to the requirements of the hydraulic system , it is not unusual to find two types of pumps in series . For example , a centrifugal pump may be used to supercharge a reciprocating pump , or a rotary pump may be used to supply pressurized oil for the controls associated with a reversing variabledisplacement reciprocating pump . 2. Rotary pumps These are built in many different designs and are extremely popular in modern fluidpower system . The most mon rotarypump . Each type has advantages that make it most suitable for a given application . SpurGear pumps . These pumps () have two mating gears are turned in a closely fitted casing . Rotation of one gear , the driver , causes the second , or follower gear , to turn . The driving shaft is usually connected to the upper gear of the pump 。 When the pump is first started , rotation of gears forces air ort the casing and into the discharge pipe . This removal of air from the pump casing produces a partial vacuum on the sucti