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动力输出总成的设计（720转-分）

拖拉机动力输出总成的设计（720转-分）【优秀拖拉机动力课程毕业设计含3张CAD图纸】

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动力输出轴--文献翻译.doc

封皮.doc

开题报告.doc

拖拉机动力输出总成的设计（720转-分）.doc

摘要.doc

装配图.dwg

大齿轮.dwg

高速轴.dwg

动力输出总成的设计（720转/分）

摘要

动力输出轴是拖拉机的重要工作部件,动力输出主要用于拖拉机在行进中输出发动机动力以驱动农机具,如割草机、喷药机等。动力输出总成的设计是基于减速增扭的原理。动力从变速箱引出，再进过一对大小齿轮减速，转速减小的同时，扭矩成比例的增加。动力输出没有标准的设计过程，主要根据变速器和减速器的设计，确定齿轮的传动类型、传动关系、受力分析、建立数学模型。依据传统的设计方法，本着半经验半理论的设计原则通过类比的方法，参考已有车型的动力输出的设计过程，然后验算零件的强度和机械应力情况，最后确定了采用半独立式的动力输出机构方案，动力直接从发动机的曲轴引出，这种输出类型现在被广泛使用，特别受到欧美的青睐。本次设计采用的主动的直齿滑动齿轮啮合，主动齿轮可以在高速轴上滑动，以提供啮合和分离的选择。这种设计最大的优点是结构简单，便于安装和维修。

而且为了避免动力输出轴头在高速旋转下危及人身的事故发生，本次设计专门设计了动力输出轴保护罩，保证外露的高速旋转部件不会伤害人，提高了使用的安全性。

关键词：动力输出轴，半独立式，主动齿轮，从动齿轮

POWER TAKEOFF SHAFT DESIGN（720r/min）

ABSTRACT

Power take off shaft is an important part of the tractor, PTO shaft provides a means to drive the machines that are being towed by the tractor, Take mower and manure spreaders for example.

The PTO shaft operates on the principle of reducing the PTO shaft speed, before the drive from the transmission is applied. At the same time ,the PTO shaft increases the torque ,for when speed is lost through gears, torque is gained in the same proportion . According to the design of the transmissions in consideration of the simplicity and reliability. According to the traditional mean of design, part experience and theory and analogism. We firstly chose gear type, make selection of the gear parameter, then establish the mathematic model dose the type of the being.

In this thesis, we dose semi-independent type. This type of PTO shaft is popular not only in our country, but also in Europe. The merit of this type is outstanding, We choose spur gear to transmit the drive.the driving gear can be slid along the splines on the internal end of shaft and into mesh with driven gear. The means of this type is easy for fixing and mending.

To avoid the accident of the wound from the revolving of the end of PTO shaft, the shaft and universal joint of PTO should be guarded by commercially available shields ,which cover moving part, so it will improve the softy.

Key words：PTO shaft, semi-independent, driving gear, driven gear

第一章绪论........ .. .. .. .. .. ........................1

§1.1拖拉机发展概述............................1

§1.2动力输出总成的概述............................3

§1.3拖拉机工作速度匹配...........................5

§1.4 动力输出轴的转速配置...........................5

§1.5动力输出轴性能...........................6

第二章动力输出总成齿轮主要参数的确定... .. .. .. .. .....8

§2.1 齿轮的概述.... .. .. .. .. .......................8

§2.2 方案一设计.. .. ................................8

§2.2.1 方案一齿轮计算 . ................... ......8

§2.2.2 方案一轴设计......................... .....9

§2.3 方案二设计.. ............... .. ...............12

§2.3.1 方案二齿轮设计...................... ......12

§2.3.2 齿轮变位设计...................... ........ 15

§2.3.3 齿轮重合度的设计...................... ....17

第三章动力输出总成轴承的计算......................19

§3.1 轴承的概述.. .. .. .. ...........................19

§3.2 轴承的计算.................................19

第四章轴的校核计算................................21

§4.1 高速轴设计.... .. .. .. .........................21

§4.2 低速轴设计.... .. ..............................23

第五章花键的计算...................................26

§5.1 低速轴花键设计. ... ............................26

§5.2 高速轴花键设计.................................27

§5.3 连轴器花键设计........................ ........ 28

第六章控制机构设计.................................30

§6.1 自锁弹簧的设计.... .. .........................30

§6.2 操纵机构位置的设计.............................31

第七章动力输出轴的加工方法.......................34

第八章使用与保养......................35

第九章结论.........................................37

参考文献...............................................38

致谢...................................................40

第一章绪论

§1.1 拖拉机发展概述

　国外拖拉机的技术发展趋势，是广泛采用高新技术，提高拖拉机性能、可靠性、操作方便性、舒适性、安全性及外观质量等。

　　1、降低振动、噪声及发动机排放污染

　　拖拉机前驱动桥采用液压悬架，以大幅度降低拖拉机的振动；小型拖拉机采用小缸径柴油机代替单缸柴油机，使柴油机结构尺寸缩小、噪声降低。此外，发达国家还对拖拉机发动机的排放规定了严格的标准，并分期实施。

　　2、完善性能，满足农田与运输作业要求

　　如完善拖拉机的传动系统，采用先进的换挡装置，满足农机具不同作业速度需要；采用前后桥驱动与制动、前后动力输出轴以及可变速的后动力输出轴，以适应配置不同农具的动力配套需要；另外，静液压驱动的拖拉机也日趋增多。

　　3、提高可靠性

　　如将拖拉机平均故障时间(MTBF)提高到300h以上；广泛采用子午线轮胎，大中型拖拉机普遍应用宽断面子午线轮胎，较大地提高拖拉机的附着性能和耐磨性能；完善液压悬挂系统，提高农机具悬挂的方便性。在大中型拖拉机上广泛采用负荷传感的闭环液压控制系统、电子液压悬挂系统；将液压力输出增至3-4组，每组单独操作；拖拉机设置前、后三点悬挂，普遍采用快速挂接装置等。

参考文献

[1] 程悦荪.拖拉机设计.北京：中国农业机械出版社，1981,43-67

[2] 吉林工业大学拖拉机教研室编.拖拉机构造.北京：机械工业出版社，1974,90-99

[3] 文农.底盘设计.北京：机械工业出版社，1981.67-89

[4] 《拖拉机编辑部》.拖拉机设计和计算.上海：上海科学技术文献出版社,45-67

[5] 孙恒模主编.机械原理（第六版）.北京：高等教育出版社，2001,67-87

[6] 濮良贵、纪名刚.机械设计（第七版）北京：高等教育出版社，2001, 184-234

[7] 林建兴，曹曼玲,刘鸿文.简明材料力学.北京：高等教育出版社，1995，67-90

[8] 第一机械工业部机械研究院农业机械研究所编.农业机械设计手册.北京：机械工业出版社，1973，12-67

[9] 侯洪生.机械工程图学.北京：科学出版社，2003，67-120

[10] 全国拖拉机标准化技术委员会秘书处，中国一拖集团有限公司，洛阳拖拉机研究所编.拖拉机柴油机设计标准手册.北京：中国标准化出版社，45-70

[11] 吉林工业大学，北京农机学院，洛阳农机学院，湖北农机学院，镇江农机学院，河北工学院合编.拖拉机底盘结构设计图册.北京：机械工业出版社，67-90

[12] 东北大学《机械零件设计手册》编写组编，蔡春源主编.机械零件设计手册，1145-1340

[13] 机械电子工业部洛阳拖拉机研究所主编.拖拉机设计手册.北京：机械工业出版社，1994.

45-87

[14] 王昆，何小柏，汪信远.机械设计机械设计基础课程设计.北京：高等教育出版社，2005，119-197

[15] 姜勇.AUTO CAD 高级教程 .北京：人民邮电出版社，1994，8-70

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内容简介：: 车辆与动力工程学院毕业设计说明书 1 Power takeoff shaft The power takeoff shaft usually called simply the power takeoff ,provides a means to drive the machine that are being towed by the tractor .the engine power of the tractor is being used not only to pull or carry the machine ,but also to operate it .typical exampled of machines that are power driven are mowers .,balers ,combine.potato harvests ,and manure spreader .the PTO provides a very useful source of power .and the alternative would be to fit an engine to each of these machine .this is ,of course done where the power required to drive the machine may be greater than the tractor can be supply. Generally most machines can be powered by the tractor . Power take off shaft are calssifily according to their location of the tractor,type of the drive .rotation speed ,and method of control . Most tractor are equipped with a rear PTO.some of them have a front PTO ,ROW-tractor use both a rear and a side PTO . AS to the type of drive, power take off shaft are classed as transmission drive .live ,semi-independent ,and ground-speed type ,the transmission drive PTO IS driven from the tractor transmission and so it will stop rotating whenever the engine clutch is disengage . The live PTO is driven from the engine crankshaft through the clutch driving member irrespective of the position of the clutch .the semi-independent PTO WILL continue to operate while the driver is shifting gears , but is incapable of being engaged or disengaged while the tractor is moving .the ground-speed PTO has its speed proportional to the ground speed of the tractor .such A PTO finds application on row-crop tractors to operate machine .such as mounted drills .whose working rate must be in synchronism with the ground speed of the tractor . nts车辆与动力工程学院毕业设计说明书 2 The power takeoff are standardized at 540 and 1000rpm (AT nominal engine speed )the spined ends of PTO shaft of all tractor are of one and same size and are arranged at one and the same level relative to the tractor support surface .when the PTO Shaft is not used ,its end is covered by a guard stamped from sheet steel. Power takeoff shaft may be control by either mechanical or hydraulic means Live PTO shaft can be engage or disengage on the run by hydraulic or complex mechanical means. When the PTO is disengage , sun gear brake is released and planet carrier is applied. In this case ,PTO shaft is held stationary and the planet gear transmit rotation from the internal gear to the sun gear . When the PTO is engaged. sun gear brake is applied and planet carrier is released. The planet gears now have to walk around the sun gear .as the planet gears roll around the sun gear.they carry the planet carrier around with them .thus driving the PTO shaft which is rigidly connected the planer carrier. When the PTO is not used the PTO control lever is placed into its neutral (central) position. In this case.both the sun gear and the planet carrier brakes are released. Toothed clutch 1 inserted into the PTO driving line makes it possible to have either independent or ground-speed power takeoff. The clutch is operated by a control lever and can be placed into three different positions. When the clutch is shifted all the way forward (to the left .as shown in Fig.165a), drive shaft 9(see Fig.164) of the PTO nit is connected to the transmission main(output) shaft to obtain ground-speed power takeoff. If the clutch is moved all the way backward (to the right .as shown in Fig.165b). the drive shaft of the PTO unit will be connected to the engine crankshaft, and so power takeoff will be independent. With the clutch in its neutral (central) position . no drive is transmitted to the PTO unit. nts车辆与动力工程学院毕业设计说明书 3 To place the clutch into the “ GROUND-SPEED PTO” position, one should disengage the engine clutch, whereas placing it into the “ LIVE PTO”position required that the engine should be stopped. THE HYDRAULICALLY CONTROLLED PTO UNIT (Fig.166) includes a planetary gear set and a self-contained hydraulic system. The unit is contained in a case that is attached to the rear axle housing of the tractor. The reduction gear set of the PTO unit comprises drive gear 3 carried on shaft 1 and driven gear 9 and hydraulic clutch 10 that are mounted on PTO shaft 5. The shafts are supported by ball bearings housed in bores in the PTO case. Drive gear shaft 1 is driven from the engine crankshaft, and so the unit provides splined to its shaft and is in constant mesh with a hub that is freely supported by ball bearings on the PTO shaft. The connection between the driven gear and the PTO shaft is effected by hydraulic clutch 10 similar to those described in Section 11.4. The clutch comprises a series of driving and driven discs accommodated in a drum that is splined to the PTO shaft. The clutch driving discs are made of steel and equipped with cermet linings. These discs are splined on to the drive gear hub. The clutch driven discs of plain steel are arranged alternately between the driving discs and are splined into the clutch drum. Inside the clutch drum, there is annular space 12 that plays the part of a hydraulic cylinder, into which fits piston 11. The piston is sealed in the annular space of the clutch drum by a cast-iron ring on the outside and a rubber ring on the inside and is loaded by a series of springs 14. To engage the clutch and hence the PTO shaft, oil is delivered under pressure into the annular space in the clutch drum. This causes the piston to move against spring pressure and tightly compress the pack of the clutch discs , thus connecting the PTO shaft to the driven gear of the reduction gear set. To disengage the clutch ,the annular space nts车辆与动力工程学院毕业设计说明书 4 in its drum is connected to a return line leading to oil sump 7. Now, release springs 14 force the piston to expel the oil contained in the annular space and release the clutch discs. The piston carries a series of pins which ,at the end of the return stroke of the piston ,bring pressure to bear against the discs of brake 13 thus stropping the PTO shaft. Oil is let in and out of the clutch through passages drilled in the shaft. The hydraulic system of the PTO unit includes oil pump 4, oil intake filter 8, a valve arrangement ,and oil lines. The valve arrangement includes pressure regulator valve 15 and PTO control valve 4 (Fig.167) that are carried in a common housing bolted to the front wall of the PTO case. The pressure regulator valve maintains a constant pressure (1 Mpa) irrespective of the delivery of the oil pump. The PTO control valve is essentially a ball valve loaded by two springs and operated by a plunger and an eccentric held to the shaft of PTO control lever8. When the PTO shaft is engaged ,the control valve also doubles as a relief valve. With PTO control lever in the “ OFF” position (Fig.167a). the eccentric on the control lever shaft releases the control valve plunger, which relieves the ball valve of spring pressure. In this case ,oil pump 5 draws oil from the oil sump of the PTO case through oil intake filter 1 and delivers via the discharge line to both valves of the valve arrangement . Since PTO control valve 4 is relieved of spring pressure ,the oil flows past it and return to the sump, some oil going through passage 3 drilled in the PTO shaft to lubricate the friction discs of hydraulic cultch 2. When the PTO control lever is placed into the “ ON” position (Fig.167b),the eccentric turns and depress the control valve plunger. As the plunger is depressed , it compresses both control valve springs which,in turn, push the valve against its seat. This closes the oil nts车辆与动力工程学院毕业设计说明书 5 return passage to the sump. Since there is no escape route open to the oil ,the pressure in the system goes up ,and the oil is forced into annular space 6 of the clutch and causes the cultch piston to the PTO shaft. The oil pressure will rise to 1 Mpa ,at which point pressure regulator valve 7 will come into operation to maintain this pressure invariable. To make the clutch engage smoothly ,the PTO control lever should be operated slowly. designated person responsible for safety. Therefore, the owner was not in compliance with Title 8 Program. (As of July 1, 1991 the State of California requires all employers to have a written seven point injury prevention program: designated safety person responsible for implementing the program; m California Code of Regulations 3203 - Injury and Illness Prevention ode for ensuring employee compliance;hazard communication; hazard evaluation through periodic inspections; injury investigation procedures; intervention process for correcting hazards; and a health and safety program.) INCIDENT On December 22, 1991 at approximately 8:00 a.m. a 30 year old male Portuguese farm laborer was driving a farm tractor which was pulling a dairy feed wagon. The power take off unit at the rear of the tractor was driving the feed dispensing auger system inside the feed wagon. (A power take off unit (P.T.O.) is an extension of the tractor transmission shaft used to power implements with the tractor engine.) This is a common method of feeding the dairy cows by using the auger to mix the feed and push the cattle feed out. The P.T.O. was apparently not functioning correctly, and the employee left the tractor engine idling and climbed off the tractor to check the attachment. The employee was standing next to the P.T.O. when he turned to reach up and pull the hydraulic lever on the rear of the tractor which engages nts车辆与动力工程学院毕业设计说明书 6 or disengages the P.T.O. At this time his left shirt sleeve was caught on the rotating shaft of the P.T.O. The employee was wound around the P.T.O shaft as it rotated. The rotation of the shaft wedged him into the metal frame around the P.T.O. shaft and sheared his arm almost completely off. He also hit his head on the metal frame, receiving a 2 centimeter laceration on his scalp near the back of his head, and a cervical fracture. The tractor engine stalled at this time because it was idling at low speed and jammed by the body of the farm laborer. He lost consciousness for an unknown length of time; when he regained consciousness he called for help and was found by co- workers. Employees at the dairy called the local ambulance service and then disconnected the P.T.O shaft in order to extricate the injured workers arm. At this time his left arm almost completely detached about half way between his shoulder and elbow, remaining connected only by skin and muscle. The ambulance crew immobilized his spine, splinted his arm, gave oxygen, started an I.V. and transported him to the emergency department of the local hospital. He was stabilized and transferred four hours later by helicopter to a microsurgery medical center 200 miles from the incident to have his arm reattached. Because of the extensive damage and loss of tissue to his arm, reattachment was not attempted and the arm was surgically amputated approximately six inches below his shoulder. Currently, the employee is in rehabilitation and is planning to return to work at the dairy. PREVENTION STRATEGIES 1. The shaft and universal joints of the P.T.O. should be guarded by commercially available shields which cover moving parts. This P.T.O. was not shielded at the time of the incident, which is a violation of California law* and recognized safety practice, in this case leading directly to the amputation of the workers nts车辆与动力工程学院毕业设计说明书 7 arm. At the time of our investigation, the dairy owner had purchased and installed guards on the P.T.O. of the involved tractor. If the P.T.O. shaft had been guarded at the time of the incident, the workers sleeve would have not been caught and he would not have lost his arm. * California Code of Regulations T8 3440 (subparagraph c) requires that all P.T.O. units and drivelines be guarded. 2. All equipment should be checked prior to beginning daily work activities. This allows the worker to make sure that all equipment is working correctly, before any work is initiated. A regular check of the tractor and feed wagon prior to its use would have identified the problem of the malfunctioning P.T.O. The worker could then have had this fixed before trying to use it. 3. The design of the tractor permitted the driver to reach behind while still in the seat to pull the lever for the P.T.O. Therefore, he should not have tried to reach the lever from the ground. Because he was standing near to the rotating shaft while he was attempting to adjust the P.T.O. he came into contact with the rotating shaft. If he had remained in the seat this would not have occurred. 4. Workers should disconnect the power source and wait for all machine movement to stop before servicing equipment.* If the employee needed to leave the tractor, he should have turned the tractor engine off prior to leaving the tractor seat. He would not have come into contact with the rotating P.T.O. shaft if he had complied with this regulation. Note: * (California Code of Regulations T8 3441 Paragraph a (subsection c) requires that power sources be disconnected and machine movement stopped before servicing equipment) 5. This worker had only been working at this dairy for 3 months nts车辆与动力工程学院毕业设计说明书 8 although he had worked at different dairies for approximately 10 years. Since he had begun working at this dairy, he had received no safety training related to equipment or job tasks or hazard identification*. If he was trained on how to recognize and avoid hazards he might not have lost his arm. Note: * California Code of Regulations T8 3383 (subparagraph b) requires workers to receive safe operating and servicing instructions at the time of their initial assignment. 6. This incident occurred because loose clothing worn by the worker was caught in the rotating P.T.O. shaft. If the worker had better fitting clothing this incident would not have occurred*. The owner of the dairy was wearing a loose shirt at the time of this investigation, which indicates that he still did not recognize this as a hazard. This is an inexpensive and relatively simple way of preventing machinery entanglement. Note: * California Code of Regulations T8 3383 (subparagraph b) requires that loose clothing that could be entangled in machinery should not be worn. nts车辆与动力工程学院毕业设计说明书 9 动力输出轴动力输出通常被简称为 PTO 轴。它提供一种途径去驱动农机具工作。牵引力不仅仅用来牵引农机具，而且用来操纵控制它。典型的机械例子就是割草机，打包机，联合收割机和施肥散布机。动力输出轴提供了一个非常有用的能量源，根据农机具的不同选用不同的轴头。动力输出所提供的动力可能比直接从拖拉机引出的动力要强劲。动力输出总成的分类，根据 PTO 轴在拖拉机上位置的不同，驱动方式和控制方式的不同进行分类的。根据驱动方式的不同拖拉机动力输出分成非独立式的，独立式的，半独立式的和同步式的。非独立式的它的动力直接从变速箱传递过来的，在离合器分离的时候， PTO 轴就会停止工作。独立式 PTO 轴就是它的动力直接来源于发动机曲轴，它的工作情况和离合器的工作没有联系。半独立式 PTO 轴，在齿轮换档时候，仍然能工作，但是在拖拉机运动时，它是没有办法进行啮合和分离的。同步式 PTO轴，它的速度和轮子的转速成比例。最好的例子就是播种机，它的工作速度必须和拖拉机的移动成比例 PTO 轴的轴头按标准分为 1000r/min 和 540r/min 两种类型。所有的拖拉机尽量做成这两种标准，这样有利于维修和替换。当动力输出轴不工作时候，它通常用铁制的轴头保护罩，保护轴头免受伤害。 PTO 的分离和啮合可以通过机械力或者液压的方式控制。 PTO 箱体一般被安装在 PTO 总成箱体里。一般是由主动齿轮，从动齿轮组成的，从动齿轮可以在低速轴的中间滑动，和主动齿轮啮合。这种啮合必须在拖拉机停车的情况下进行。独立式的 PTO 可以通过液压和复杂的机械控制其工作， PTO 总成包括中心轮，太阳轮和行星轮，行星轮被放置在行星架上。还有两种鼓式刹车片，一种是作用在行星齿轮上的，另一种是作用在太阳轮上的，太阳齿轮的轮毂被牢牢的固定在刹车片上，刹车片通过球轴承被安装在 PTO 轴上，刹车片被固定在轴上。钢制的刹车片上装有摩擦衬套，刹车片一端用销钉固定，另一端和曲轴，调整螺栓连接。通过其对动力输出进行控制。在 PTO 轴没有啮合的情况下，中心轮的刹车片被释放，行星轮的刹车片工作。这样的话 PTO 轴不旋转，中心轮和太阳轮之间的旋转通过行星轮的旋转而进行的。当 PTO 轴啮合时，控制太阳轮的刹车片工作，而行星轮的刹车片被释放，行星齿轮现在不得不绕着太阳轮旋转，当行星齿轮绕着太阳轮旋转的同nts车辆与动力工程学院毕业设计说明书 10 时，行星齿轮架也跟着旋转，因为行星齿轮架和 PTO 轴是固结的，所以行星架带动 PTO 轴一起旋转。当 PTO 轴不工作的时候， PTO 轴不使用的时候。PTO 控制杆必须放在中间位置，太阳齿轮和行星齿轮的刹车片被同时释放。牙式离合器被装入 PTO 的传动链中，这样使得它有可能成为独立式和同步式的兼容体。离合器通过控制杠杆工作，杠杆有三个位置，离合器换档向前，PTO 轴被连接到变速器的输出轴，这样就获得了与轮速成比例的转速。如果离合器的控制杆件向后运动， PTO 轴就和发动机曲轴直接相连，因此发动机就获得了独立输出。如果在中间位置，没有动力传输到 PTO 总成上。当离合器放置在同步档位上时，我们应该先断开离合器，若要进入“独立式”的工作模式，也要求发动机停机。液压控制的 PTO 总成的齿轮机构包括在轴上的主动齿轮和被动齿轮，液压离合器。液压离合器被安装在 PTO 轴上， PTO 轴通过球轴承安装在箱体上，一轴的动力是直接由发动机曲轴传递过来的，因此这种 PTO 轴总成提供了一种独立的动力输出。主动齿轮和从动齿轮属于常啮合类型，从动齿轮固定在轮毂上，轮毂通过球轴承安装在 PTO 轴上。从动齿轮和 PTO 轴的连接是通过液力离合器连接的，液力离合器有一系列主动盘和从动盘构成，从动盘被铆接到到齿轮轮毂上，离合器的主动盘是由钢铁制成的，内部安装有耐磨衬套，这些主动盘被安装在主动齿轮轮毂上，离合器的从动盘也是有钢铁压铸而成的。为了使离合器工作 PTO 轴工作，液压油在压力的作用下，被压入离合器空腔，这就使得活塞移动，顶开预紧弹簧，继而压紧离合器盘片，连接 PTO 轴和从动盘总成。在 PTO 轴不工作的时候，环状空腔和回油管相连，回油管道把油流到到外部油箱 ,这种情况下，回位弹簧把环状空腔里的油排出来。释放盘片，在活塞回程的最后一段，活塞带走了一系列用于产生盘片压力的销子，最终 PTO 轴停止转动，油通过轴上的油道流出离合器。液力 PTO 总成包括液压泵，进油滤清器，多种阀门和油路。其中阀门包括调压阀和 PTO 控制阀门。 PTO 控制阀被放置在一个箱体上。这个箱体被螺栓固定在 PTO 箱体的前部。无论油泵输出的油压大小，调压阀使得输出的液压油保持一个恒定的油压。 PTO 控制阀本质上受弹簧力作用的球阀控制，通过PTO 控制杆件上的偏心机构调节。当 nts车辆与动力工程学院毕业设计说明书 11 PTO 轴工作时，控制阀还可以当作减压阀来使用。当 PTO 控制杆件在“ OFF”位置上时，控制机构上的偏心器释放控制阀的活塞，这个活塞本用来减小球阀的弹簧力的。在这种情况下，油泵把油从油箱中抽取出来，油通过滤清器、油管到多路阀中，因为控制阀较小了弹簧力，所以液压油流过控制阀经过轴上的油道又流回到油箱里。而一些液压油经过轴上的油道润滑部件。当 PTO 控制杆件在“ ON”的位置时，偏心器压下控制柱塞，当柱塞被压下，他们共同压缩弹簧，同时使阀体顶压阀座，这样就切断了回油的线路，此时，管路中的压力升高，液压油进入离合器，压紧盘片，使从动盘和 PTO轴一起转动，当油压上升到 1Mpa 时，油压保持不变，使得液力离合器顺利工作。一名农场工人在奶牛场饲养奶牛，他驾驶一辆拖拉机 ,拉着一车饲料 . 在拖拉机后部旋转的轴头用来混合饲料 , 轴头连接了拖拉机和牵引件，并且在高速旋转，没有保护罩加以保护 . 工人下了拖拉机，检查动力输出轴 ,此时，拖拉机空转及轴仍然转动 . 当他拉过了轴拉杠杆时候，拖拉机轴头卷住了他的衬衫袖子 . 轴裹住手臂 ,手臂被撕开 ,几乎完全被卷进去 ,他的脖子被打断 . 工人存活 ,但失去了他的手臂 . 这怎么可能伤得到预防 ? 一切的动力输出都要加装安全保护罩 . 检查设备 ,然后用它 . 关闭电源 ,等待机器停止，再操纵。为工人提供安全训练 . 在操纵机器时，不要穿着宽松的衣服 . 背景 121991 加州职业安全与健康管理局 (cal/osha)民政厅公布了保护项目 ,一个奶牛场员工留下了 PTO 轴被截去了手臂 . 事件发生时 ,奶牛场的工人正开着拖拉机的牛饲料车皮 . 事件发生四天后牧场主人通知世界卫生组织，此时，nts车辆与动力工程学院毕业设计说明书 12 世界卫生组织进行了一次调查 ,在短短数天 . 一位护士在医院采访受伤工人。在 1992 年 1 月 2

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