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QY12
汽车起重机
下车
系统
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QY12汽车起重机下车系统设计,QY12,汽车起重机,下车,系统,设计
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Truck crane hydraulic systemTechnical status and development trend Miralbs R.,Castejn LOne, industry background(1.1) the development trend of foreign engineering truck craneThe past 20 years the worlds construction crane industry produced very big change. RT ( cross-country wheel crane ) and AT ( all terrain crane ) the rapid development of product, broke original products and the pattern of the market, in the economic development and the fierce competition in the market impact, leading to world market further towards integration. As with RT and AT counter products, automobile crane new technology, new products are also constantly developing. In recent years auto crane in Britain, the United States market revival, enabling people to generate new understanding of automobile crane. A few years ago, some industry had predicted, the RT and AT product rise will lead to automobile crane recession. Japan automobile crane is increasingly prevalent throughout the world, and more recently, grove, Terex, Linc. Belt, Tokuma Yasuke and other companies automobile crane product development, has the idea to challenge. With all types of engineering crane technology mutual infiltration and competition, automobile lifting the opportunity to continue to occupy a space for one person in the world market.Foreign crane from the overall situation, the leading domestic 10 20 years ( different types of different products ). Along with the economic development speed smoothly, construction crane to the intelligent, high-performance, flexible, adaptable, multi-functional direction. The following 25t basically is production, products to the high value added, large tonnage, Sumitomo Construction machinery, the Tadahino and Kato company in 1989 has introduced 360t truck crane. Sumitomo Construction Machinery in the 90s the development of 80t 250t total of 4 kinds of AT products. TADANO also in 90 time in succession to launch 100t 550t total of 6 kinds of large AT product. Kato company developed NK5000 type 500t truck crane. Supporting industries and domestic different:1, get off the main diesel engine power is more than 300kW, and the matching of torque converter and automatic gearbox, 12 tons of drive steering bridge and off-road tires. In 2,: high strength material, large torque of the lifting mechanism, a rotating mechanism, slewing bearing. 3, hydraulic system: variable pump, a variable motor, an electromagnetic reversing valve and main valve, balance valve, suspension system, hydraulic lock valve, hydraulic cylinder and standard pipe fittings. 4, intelligent control system: limiter display control, memory communication and single cylinder sequential telescopic automatic control.( 1.2) the development trend of domestic engineering truck craneDomestic engineering machinery products for nearly ten years with the technology introduction, digestion, absorption, had great progress, product performance, reliability, appearance has greatly improved, but compared with the foreign engineering machinery, still put in bigger difference.China engineering crane industry in 94 99 years is the development of the trough, 5 years in the industry several major manufacturers, bitter Liannei Gong, active organization variant and replacement, in product appearance. From 99 years since, with economy construction is new round started, construction crane market competition pattern produces tremendous change, the enterprise constantly adjust train of thought, newer idea, changeover mechanism, enhance core competitiveness, product development efforts, to develop the market. Product focus from 8t to 16t, 12t, 25t, 50t 25t large tonnage development, the fastest growth rate, yield is renovated ceaselessly, basic dominant. 50t products due to the requirement of wide, technology mature gradually, also enter the market in large quantities. The end of the twentieth Century domestic main products automobile crane for the 8t, 12t, 16t, 20t, 25t, 35t, 50t, 65t, 80t, l00t, 125t. The overall style is:Get off with the head and half head two different styles, for many years a half head car because of overall layout of convenience and price factors have been widely adopted. But in recent years with the improvement of material conditions, peoples living conditions and quality improvement, convenient operation, comfortable, reliable users gradually become a focus, large and medium tonnage to the head direction.The car is manipulated from the traditional mechanical operation to the hydraulic and electro-hydraulic proportional direction, lifting arm from the traditional three section to the four section, five section of the direction of development, product lifting performance and lifting height has been greatly improved, product appearance and reliability are greatly improved.After joining WTO, while the domestic market ( especially with Kit ) got bigger impact, but also bring us new technology applications, so that domestic host and supporting enterprise more clearly recognize the gap, to learn more about the domestic products are fatal problems, forcing domestic host and supporting enterprises to carry on technological innovation and technical progress.After several years of efforts, the domestic crane manufacturers have made great progress. Known as China the first hanging QY300 wheeled hydraulic truck cranes Puyuan success off the assembly line in 2004 in. It represents the Chinese automobile crane manufacturing at the highest level. To fill Chinas independent research and production of the product blank, broke this kind of product entirely dependent on imports of the convention. Chinas crane industry to shorten the gap with foreign countries, but the gap is still very great, a lot of manufacturers mainly rely on the purchase of foreign backward technology, lack of independent research and development ability. It makes people feel worried.Two, domestic and foreign automobile crane hydraulic system new technology( 2.1 ) on truck crane hydraulic system security problems research 2.1.1 The generation of intelligent overload limiter of crane in automobile application.The third generation of microcomputer overload limiter ( XT), with independent intellectual property rights of domestic electromechanical integration device. The device is composed of a main machine part and a sensor part, microcomputer control, modular structure. Installation and commissioning of all the key operation, large screen LCD dot matrix display, in the setting of parameters and the display is very concise, do not adjust any potentiometer, the debugging is simple and intuitive, friendly interface. Limiter adopts digital and large scale integrated circuit, reducing the failure, increases the capacity of resisting disturbance, thereby improving reliability; when the crane is more than the rated capacity or stroke, can automatically alarm and cut off the crane to the dangerous movement of the loop, but allows it to move towards a safe direction; system of automatic fault detection, the results showed; low power ( power consumption less than 10W), digital circuit using all the CMOS chip; a black box function, automatic recording overload time and then the operational parameters; data and parameters of all Chinese characters display graphics presentation, numerical accuracy, convenient operation, stick out a mile, no operator is required to memorize the password prompt; setting function, prevent parameter error setting; good generality, without altering the host circumstances, as long as the software changes, can meet various types of heavy machinery; machine memory a plurality of rated load curve, satisfy various working continuously alarm calls; the sensor drift and drift can carry out automatic regulation and compensation with sound and light alarm function. The technique has been used in many domestic manufacturers of large crane crane above, good results.2.2.2 heavy machine load sensing system analysisLoad sensing system can be divided into two categories: pump control load sensing system and valve control load sensing system, the former must use of variable pump, the latter can be used for quantitative pump. At present our country by the introduction of Japan, Germany technology used is the valve load sensing system. Valve load sensing system principle:Valve load sensing system is composed of a pump, load sensing control valve ( valve ) and settable orifice ( valve port of the valve ). Pump to provide the oil flowing through the settable orifice, to form the load pressure is applied to the actuator. Load sensing control valve for receiving a load pressure sensor signal, through the pressure compensation function of settable orifice pressure difference between the ends basically unchanged, and the system pressure just above the load pressure of a pressure differential. Thus, both the flow through the orifice flow only with the throttle opening is proportional to the area and are independent of load, guarantees the implementation of mechanism motion speed regulation and good stability; and reduce the system stream pressure loss, improves the efficiency of the system. Load sensing control valve as the load sensing system core components, has many kinds of structure types. In Kato, Tadahino and Liebherr crane control valve load sensing system, employs a constant difference wins flow valve type, the priority valve type and its combination form.The constant difference overflow valve and the priority valve pressure compensation principle diagram. As shown in the picture, when settable orifice ( valve valve ) FC in an open position, the constant difference overflow valve and RC or the priority valve PF balance, FC pressure difference between the ends of Pt ( Po, Pr or P1 - Pr ) on the valve plug produced by the hydraulic force and valve spring force will keep balance. From the pump working fluid ( Po ) part directly or through the valve port H1 to FC branch, another part of the remaining oil through the valve port H2 to tank or by-pass ( Pz ). If the FC branch load pressure of Pr with the actuator load increases ( decreases ), the valve core is shifted to the right ( left ), decrease (increase ) the valve opening H2 and increase (decrease) the valve opening H1, the results of system pressure Po and preferred branch pressure Pl increases ( decreases ), then the valve core to balance in a new valve export position. Because the spring design is weaker, and the valve core balance position displacement amount is very small, thus playing the turtle force changes are negligible, thus ensuring and spring force balance valve throttle pressure difference across the FC will basically remain unchanged. At the same time, the system pressure is only slightly higher than the load pressure. On the constant difference overflow valve, pressure Po above the load pressure Pr a constant value, namely the spring set valve throttle pressure difference between the ends of the priority valve of Pt, Pt priority branch pressure P1=Pr+; Po system pressure slightly higher than the pressure of P1 and P2 branch of the larger.2.1.3 heavy machine limited stop protectionCrane motor control contactors are often dense on-off, therefore prone to breakdown. When the crane is in the process of operation required for accurate localization or emergency stop, because if the contact welding leads the crane refused to stop, there may be a collision accident. In order to solve this problem, propose a crane lifting mechanism refused to stop protection design.From three aspects to solve this problem, it is a contactor contact welding leads to the action logic, which can increase a middle relay to judge; second is to avoid the contactor, relay competition leads to protection false start, therefore refused to stop protection setting short delay, which requires a time relay; third is once contactor refused to jump, by the general circuit breaker shunt tripping action execution protection.From the perspective of crane electrical, prevent to stop are key measures to monitor whether the brake contactor contact welding. QRIS type lifting mechanism control cabinet adopts non stop protection circuit diagram design.The design of circuit is composed of three parts. The first is to monitor, made with brake contactor K07 coil is connected in parallel with the intermediate relay, K07 and K1 under normal circumstances is the synchronization action. If the K7 due to contact welding cannot release, so both movement is inconsistent, it will start delay time link.Second links, namely time delay is borrowed from the original design in the K03 time relay, consists of parallel K7 normally closed contact and a normally open contact of the control K07. K7, K07 parallel contact under normal conditions is always connected, stopping only when the K7 contact occurs when welding condition and connection to disconnect. K03 time relay is energized immediately attracted, power-off time delay time delay release, 0.6s, so long as the control circuit on electric, K03 immediately. And the main controller S40. At the start, stop switch process, even though the K7, K07 contact action of competition, instantaneous disconnection coil circuit, K03 time delay closing of the normally closed contact remained disconnected, so K7, K07 parallel contact access K03 coil loop does not influence the normal work of K03.In an access of parallel contacts before, only in the main controller to rise or fall 3 Block 2 block, due to acceleration level contactor K42 electric, K42 normally closed contacts open, K03 power release, the normally closed contact of the time delay closing, accelerating stage contactor K41 can attract, resection of third level dynamic resistance. In the master control down 2 blocks a block 0, a rise of 1 block when switching between the master controller, 17, 18 and 19, 20 contacts are disconnected, accelerating stage contactor K42 cannot attract, K03 may not power off, the normally closed contact also does not work, namely K03 in lifting mechanism for starting and stopping phase is actually not working. And refused to stop protection is working in crane stopping and starting stage, so can be used in K03 does not work all the time be borrowed for refusing to stop protection work, therefore, in the K03 loop of the coil is inserted in the parallel contacts. Once the K7 contact welding leads the crane refused to stop, parallel contact immediately disconnect, the K03 relay is de-energized, the normally closed contact of the 0.6s delay after the closure, connect to the main circuit breaker Q0 shunt trip coil YA - OFF, bringing the total tripping the circuit breaker, lift brake power-off brake, achieve the purpose of non stop protection.The third link is non stop protection starting point, which consists of a K03 time delay closing of the normally closed contact of the normally open contact, K7, K07 normally closed contact with the total circuit breaker shunt trip coil connected in series. Main breaker just closing moment, K07 normally closed contact has not yet been disconnected, so we must in the series circuit access K7 normally open contact, otherwise it will cause shunt trip coil gets electricity, making the total circuit breaker tripping just closing immediately. K07 normally closed contact role is to prevent the K03 in the execution of the original design features, i.e. delayed resection third starting resistance, resulting in a total circuit breaker tripping. Because of the crane is accelerated stage, K07 normally closed contact is disconnected, so the shunt trip coil K03 will normally closed contacts closed and electricity, resulting in incorrect trip.If the crane braking contactor before starting K7 contact is welded, so a total circuit breaker Q0 because the shunt contact is opened, so that the K03 is in an off state, K03 normally closed contacts closed, normally open contact, while the K7 K07 normally-closed contacts are closed, so the shunt trip coil gets electricity, so just close general circuit breaker tripping prevent crane in immediately, not braking condition start, eliminate accident hidden danger.For the maintenance of safety, the original design of lifting mechanism control power conversion switch Q3 by diode instead of quadrupole, so Q3 disconnected, cut off the lifting control circuit and circuit breaker shunt tripping circuit connection, ensure the lifting control circuit power. Q3 can use HZ5 - 10 type quadrupole combined switch.By the use of the original design of the time relay, crane lifting mechanism of non stop protection only needs to add an intermediate relay, and a diode switch to quadruple combination switch, costs less.( 2.2) crane electronic control technologyIn order to improve the construction crane operation efficiency, reduce labor intensity, prevent accidents, ensure the personal and equipment safety, using a variety of control device. Manipulation and control has become the important problem of crane.To solve the problem by manipulation and control, machinery and hydraulic pressure is not enough, because the steering and control is actually the problem of information processing. Mechanical and hydraulic information processing capacity is low, the control performance is poor, must introduce information processing capability, good control performance of the electronic technology. The current engineering crane electronic control device used for one one overview.2.2.1 load torque limitIn order to prevent the excessive loads caused by the tilting and the folding arm and other accidents, the construction crane is arranged on the load moment limiter.Microcomputer control of torque limiter principle as shown on the 3. It is composed of a suspension arm angle, length, weight, leg span detection device, microcomputer control device, display, alarm and executive mechanism.The basic working principle, composed of a detection device by a sensor arm length, angle, legs cross torque signal, sent as a microcomputer control device. Microcomputer control device calculates in the current circumstances, the maximum weight allowed hoisting crane, and the crane hoisting weight sensor detects the actual comparison, if the actual lifting weight to allow lifting weights 90%, then the computer system by a display and a buzzer sends out the alarm, to remind operators of careful operation. When the ratio reached 100%, a microcomputer system by a display and a buzzer to instruct operators to stop the current task and by performing a mechanism to restrict the crane only safe operation direction, stop all the dangerous operation.2.2.2 The force sensing systemHoisting operation, operation personnel eyes often can not be correctly estimated lifting weight, especially the pilot hydraulic control, reduces the operating force in operation when load changes, load lifting falling situation, drivers do not feel, in building structure hoisting and installation of machinery equipment was operating difficulties. Therefore, in some crane adopts electronic sensing system.Device a force sensing system, due to a negative force feedback, the driver on the control lever can be perceived hanging weight size, contribute to the high precision micro manipulation. At the same time can be avoided due to excessive lifting, hoisting swing and other causes of person and equipment accident.The basic principle is to detect the hoisting motor pressure, through the controller sends the control signals, to control the electro-hydraulic proportional valve to produce the corresponding hydraulic, acting on the reverse force on the piston, allowing manipulation of rod produces the load force feeling.The force sensing system can be achieved by reverse power setting device, according to a drivers personal characteristics and job types to set the counter force, when think that do not need, also can be opposite force sensing system for lifting.2.2.3 anti collision controlConstruction crane in narrow site work, need to control its operation range, namely limit crane rotation and degree and a movable arm telescopic and variable range.Often used to teach again means to control, the operating personnel according to the allowable working range operation again, the crisis system down its trajectory, the way of setting the scope of work. Also available ultrasonic obstacle detection device to realize real collision control.In order to prevent collision high-pressure line, cause electric shock caused by accidents and power supply failure, with close to the high voltage line automatic alarm device,Detection device usually adopts spherical electrode, through electrostatic induction, detection grid acoustic intensity, then the weak signal preamplifier, through the sensitivity equipment for processing and gets the power distance, and the control baseline comparison, the output of the corresponding control signal.2.2.4 lifting control deviceIn high-rise building and the viaduct s construction, in order to improve the working efficiency, shorten time limit for a project, so that the operation is simple and improves the safety, often using the following lifting control device of automatic level - mobile control device.In the lifting operation is often required in every level of mobile crane, usually by the driver operating the technology, driver visual hoisting height, while manipulating the amplitude and lifting the two handles, and observed around, operation difficulty is quite big. Automatic level control device using mobile, simply manipulation of luffing jib of a joystick, can be stable, rapid high precision horizontal movement.Automatic level control device consisting of the mobile. Composed of sensors, control device and control microcomputer electro-hydraulic conversion execution device. The sensor includes : a detection arm angle detector for or jib angle; rotary encoder testing live drum or side drum rotation quantity; pressure detector detection for arm control valve pilot control pressure, as a feedback input control microcomputer; engine speed sensor detection engine speed, according to the engine speed to vary the gain of the system. From the main arm angle can be calculated on the main arm pivot point height, in order to maintain the level of mobile crane hoisting drum can calculate the required amount of rotation, to control the rotation of a spool, and a rotary encoder is measured by the actual amount of rotation reel comparison is made with modified. Pressure feedback and according to the engine speed to change had beneficial purposes, in order to get a high accuracy stable level mobile. The device adopts manual priority principle, main hoisting drum manipulation, automatically switching from automatic to manual, when suddenly encountered an obstacle avoiding.In addition to prevent lifting of side, produces a lifting swing caused by collision and rollover, arm folding and other accidents, the hoisting center follow control mechanism,just click reel joystick button, can achieve hoisting center automatic following. There are rotating emergency-stopping and rotary suspension conversion control device.2.2.5 multiplex signal transmission deviceIn the single cab off-road crane, a technically difficult problems is how the relative motion between upper and lower transmitting large amount of control information ( up to several dozen ). Cab in the car, and the engine, transmission, steering, braking and leg in the car, how to manipulate and to control them, the solution is to try to hydraulic control signal to electrical control signals, at the same time in order to reduce pathways, a pathway that transfer the multiplex signal, this would require the use of computer and electronic technology.In addition to the introduction of the electronic control device, and many control device.In the engine, pump and valve control : the need for adaptation to load changes and multiple hydraulic actuators which act at the same time composite operation of the power control, achieve high loading speed and reduce the speed, and engine power match, give full play to the engine power; microcomputer operation when the engine and pump control, and is independent of the load and at the same time act ten no mutual interference, depends only on the handle to control speed control, to improve its maneuverability; load sensing compensation energy saving control, reducing the fuel consumption. Currently these also uses lots of hydraulic control, can be expected in the future will be excellent control performance of electronic control is replaced by. In addition. These control systems are mostly engine, pump and valve controlled separately, the future is expected to achieve joint control.In all terrain crane and cross-country crane, many using the computer controlled automatic transmission.In addition, there are electronic surveillance and automatic fault diagnosis device. In short, can be said to manipulate and control, crane within the information processing has become the focus of further development of crane. Although there are still a lot of electronic control for the body, for example, the sensor technology and the electrohydraulic conversion technology storage are not mature enough, microcomputer control system, including electromagnetic radiation interference, temperature, humidity, vibration and impact caused by environmental interference, do electronic control probability of surviving a certain problem, but electronic control is not resist technology trends, machine integrated telecommunication engineering machinery product upgrading of the inevitable development direction.Three, look to the futureThe crane control system is mainly mechanical hydraulic control, with electro hydraulic proportional control technology and electronic technology in the control system of the increasingly large and its superiority, electro-hydraulic control will be the main development trend. With the hydraulic components, computer technology and the continuous development of information technology, intelligent hydraulic crane coming. Then the giants can replace people to do more work, for human development to estimate the role. 汽车式起重机液压系统 技术现状与发展趋势 Miralbs R.,Castejn L1 行业背景1.1国外工程汽车起重机的发展趋势近20年世界工程起重机行业发生了很大变化。RT(越野轮胎起重机)和AT(全地面起重机)产品的迅速发展，打破了原有产品与市场格局，在经济发展及市场激烈竞争冲击下，导致世界市场进一步趋向一体化。为与RT和AT产品抗衡，汽车起重机新技术、新产品也在不断发展。近年来汽车起重机在英、美等国市场的复兴，使人们对汽车起重机产生新的认识。几年前某些工业界人士曾预测，RT和AT产品的兴起将导致汽车起重机的衰退。日本汽车起重机在世界各地日益流行，以及最近格鲁夫、特雷克斯、林克贝尔特、德马泰克等公司汽车起重机的产品进展，已向上述观念提出挑战。随着工程起重机各机种间技术的相互渗透与竞争，汽车起重机会在世界市场中继续占有一席之地。国外工程起重机从整体情况分析，领先国内1020年(不同类型产品有所不同)。随着国外经济发展速度趋于平稳，工程起重机向智能、高性能、灵活、适应性强、多功能方向发展。25t以下基本上不生产，产品向高附加值、大吨位发展，住友建机、多田野和加藤公司曾于1989年相继推出360t汽车起重机。住友建机在90年代开发出80t250t共4种AT产品。多田野也在90年代相继推出100t550t共6种特大型AT产品。加藤公司则研制成NK5000型500t汽车起重机。行业配套也与国内有所不同：1、下车主要是300kW以上柴油大功率发动机，与之配套的液力变矩器和自动换档变速箱、12吨级驱动转向桥及越野轮胎。 2、上车：高强度材料、大扭矩的起升机构、回转机构、回转支承。3、液压系统：变量泵、变量马达、电磁换向先导阀及主阀、平衡阀、悬挂系统阀、液压锁、液压缸及管路标准配套件。4、智能控制系统：力限器显示控制、记忆通讯及单缸顺序伸缩自动控制。1.2国内工程汽车起重机的发展趋势 国内工程机械产品近十年来随着技术的引进、消化、吸收，有了长足的进步，产品性能、可靠性、外观都有较大幅度的提高，但同国外工程机械比较来看，还存在较大差距。 国内工程起重机行业在9499年是发展低谷，5年中行业几个主要的生产厂家，苦练内功，积极组织产品变型和换代，在产品外观上下功夫。从99年以来，随经济建设新一轮启动，工程起重机市场竞争格局发生巨大变化，各企业不断调整思路、更新观念、转换机制、提高核心竞争力，努力开发产品，开拓市场。产品重心也从8t、12t向16t、25t、50t中大吨位发展，25t增速最快，产量不断翻新，基本占据主导地位。50t产品由于需求面较广，技术逐渐成熟，也大批量进入市场。20世纪末期国内主要产品系列汽车起重机为8t、12t、16t、20t、25t、35t、50t、65t、80t、l00t、125t。整体技术风格是：下车有全头和半头两种不同风格，多年来半头车因总体布置的方便性及价格因素一直被广泛采用。但近年来随着物质条件的改善，人们的生活条件和质量提高，操作方便、舒适、可靠逐渐成为用户关注的焦点，中大吨位向全头方向发展。 上车操纵从传统的机械操作向液比例和电液比例方向发展，起重吊臂也从传统的三节向四节、五节方向发展，产品的起重性能和起重高度有了较大提高，产品的外观和可靠性有了较大幅度提高。加入世贸组织后，虽然国内市场(特别是配套件)受到了较大冲击，但同时也给我们带来新技术的应用，使国内主机和配套件企业更清晰认识到差距，更多地了解国产产品存在的致命问题，迫使国产主机和配套件企业不得不进行技术创新和技术进步。经过几年的努力，国内起重机厂家取得了巨大进步。被誉为神州第一吊的QY300轮式液压汽车起重机2004年在中联浦沅成功下线。它代表了中国汽车起重机制造的最高水平填补了我国自主研制生产该类产品的空白，打破了此类产品完全依赖进口的惯例。缩短了我国起重机行业与国外的差距，但差距还很大，很多厂家主要还是靠购买国外的“落后”技术，缺乏自主研发能力。这让国人感到担忧。2 国内外汽车起重机液压系统新技术2.1关于汽车起重机液压系统安全问题的诸多研究2.1.1. 代智能超载限制器在汽车起重机中的运用第三代微电脑超载限制器(XT一 型)，是具有自主知识产权的国产机电一体化装置。该装置由主机部分和传感器部分组成，微电脑控制，模块化结构。安装调试全部采用按键操作、大屏幕液晶点阵显示，在参数设置及显示上非常简明，不用调整任何电位器，使调试变得简单直观，界面友好。限制器采用了数字和大规模集成电路，减少了故障，增加了抗干扰能力，从而提高了可靠性；当起重机超过额定起重量或超行程时，能自动报警并切断起重机向危险方向运动的回路，但允许其向安全方向动作；系统故障自动检测，结果显示；低功耗(整机功耗小于10W)，数字电路全部采用CMOS芯片；黑匣子功能，自动记录超载时间及当时的各工况参数；数据及参数显示全部图形汉字提示，数值准确，直观方便，操作人员一目了然，无需操作人员熟记提示符；密码设定功能，防止参数误设定；通用性好，在不改变主机的情况下，只要修改软件，就能够满足各种类型重机机械的要求；机内存储了多组额定载荷曲线，满足了各种工况无级报警要求；对传感器的“温度漂移”和“零点漂移”可进行自动调节补偿；具有声光报警功能。该技术现已被国内很多起重机厂家用于大型起重机上面，效果良好。2.1.2 重机负荷传感系统分析负荷传感系统可分为两大类：泵控负荷传感系统和阀控负荷传感系统，前者必须采用变量泵，后者可用于定量泵。目前我国所引进的日本、德国技术常用的是阀控负荷传感系统。阀控负荷传感系统的原理： 阀控负荷传感系统是由泵、负荷传感控制阀(压力补偿阀)和可变节流口(换向阀阀口)等组成。泵提供的工作油液流经可变节流口后，形成负载压力作用于执行机构。负荷传感控制阀接受负载压力传感信号，通过压力补偿作用保持可变节流口两端压差基本不变，并使系统压力仅高于负载压力一个压差。这样，既使得流过节流口的流量仅与节流口开度面积成正比而与负载大小无关，保证了执行机构运动速度良好的调节性和稳定性；又减少了系统激流的压力损失，提高了系统效率。 负荷传感控制阀作为负荷传感系统的核心元件，有多种结构类型。在加藤、多田野和利勃海尔汽车起重机阀控负荷传感系统中，采用了定差胜流阀式、优先分流阀式及其组合形式。当可变节流口(换向阀阀口)FC处于某一开度位置， 定差溢流阀及RC或优先分流阀PF达到平衡状态时，FC两端压差Pt(PoPr或P1Pr)对阀芯所产生的液压作用力与阀芯左端弹簧力将保持平衡。来自泵的工作油液(Po)一部分直接或经阀口h1去FC支路，另一部分剩余油液经阀口h2去油箱或旁通支路(Pz)。若FC支路负载压力Pr随执行机构负载增加(减小)时，阀芯右移(左移)，减小(增大)阀口h2和增大(减小)阀口h1，结果系统压力Po和优先支路压力Pl增加(减小)，于是阀芯重新平蘅在一个新的阀口位置处。由于弹簧设计得较弱，且阀芯平衡位置变化的位移量很小，因此弹鳖力的变化可以忽略不计，从而保证与弹簧力相平衡的换向阀节流口FC两端压差将基本上保持不变。同时，系统压力仅略高于负载压力。对定差溢流阀而言，系统压力Po高于负载压力Pr一个定值，即由弹簧设定的换向阀节流口两端压差Pt对优先分流阀而言，优先支路压力P1=Pr+Pt;系统压力Po则略高于支路压力P1与P2中的大者。2.1.3 重机的拘停保护起重机电动机的控制接触器常常是密集通断的，因此易发生触头熔焊故障。当起重机在运行过程中需要准确定位或紧急停止时，如果因触头熔焊导致起重机拒停，就有可能发生碰撞事故。为解决这个问题，提出一个起重机升降机构拒停保护设计。从三个方面着手解决这个问题，其一是接触器触头熔焊导致其动作不合逻辑，这可增加一个中间继电器来判断；其二是为避免接触器、继电器动作竞争导致保护误起动，为此拒停保护设置短暂延时，即需要一个时间继电器；第三是一旦接触器拒跳时，由总断路器分励脱扣动作执行保护。 从电气角度看，防止起重机拒停的关键措施是监视制动器接触器触头是否熔焊。这个设计电路由三个环节构成。第一个是监视环节，由与制动器接触器K07线圈并联的中间继电器构成，K07与K1 正常情况下是同步动作的。如果K7因触头熔焊不能释放，那么两者动作就不一致，这就将起动延时环节。第二环节，即延时环节是借用原设计中的K03时间继电器，由并联的K7 常闭接点和K07常开接点控制。K7、K07 并联接点在正常情况下总是接通的，只有在停止时K7触头发生熔焊的情况下并联接点才断开。K03时间继电器通电立即吸合，断电延时释放，延时0.6s，因此只要控制电路一得电，K03立即吸合。而且主令控制器S40 。在起动、停止的切换过程中，即使K7、K07 接点动作竞争，瞬时断开 线圈回路，K03延时闭合的常闭接点仍保持断开，因此K7、K07 并联接点接入 K03线圈回路不会影响K03 的正常工作。在未接入并联接点前，只有在主令控制器转到上升2挡或下降3挡后，因加速级接触器K42得电，K42常闭接点断开，K03才断电释放，其常闭接点延时闭合，使加速级接触器K41能够吸合，切除第3级起动电阻。在主
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