- 解密!讓各大車企瑟瑟發(fā)抖的中保研是什么來頭?
- 學(xué)汽修選哪個專業(yè)好呢?
- 同濟大學(xué)車輛工程專業(yè)怎么樣
- 求一篇“機電技術(shù)應(yīng)用”的畢業(yè)論文!要求3000字以上!要符合實際一些的,不能太夸張了!小弟在此謝過了。
制動系統(tǒng) Braking Systems
由于字數(shù)太多所以就不全部粘貼了。
brake is a device for slowing or stopping the motion of a machine or vehicle, or alternatively a device to restrain it from starting to move again. The kinetic energy lost by the moving part is usually translated to heat by friction. Alternatively, in regenerative braking, much of the energy is recovered and stored in a flywheel, capacitor or turned into alternating current by an alternator, then rectified and stored in a battery for later use.
Note that kinetic energy increases with the square of the velocity (E = 1/2·m·v2 relationship). This means that if the speed of a vehicle doubles, it has four times as much energy. The brakes must therefore dissipate four times as much energy to stop it and consequently the braking distance is four times as long.
Brakes of some description are fitted to most wheeled vehicles, including automobiles of all kinds, trucks, trains, motorcycles, and bicycles. Baggage carts and shopping carts may h***e them for use on a moving ramp.
Some aeroplanes are fitted with wheel brakes on the undercarriage. Some aircraft also feature air brakes designed to slow them down in flight. Notable examples include gliders and some WWII-era fighter aircraft. These allow the aircraft to maintain a safe speed in a steep descent. The Saab B 17 dive bomber used the deployed undercarriage as an air brake.
Deceleration and ***oiding acceleration when going downhill can also be achieved by using a low gear; see engine braking.
Friction brakes on cars store the heat in the rotating part (drum brake or disc brake) during the brake ***lication and release it to the air gradually.
Effects on noise pollution
The action of braking for motor vehicles produces recognizable sound level emissions, varying with the specific tire types and with the roadway surface type produces considerable effect upon sound levels or noise pollution emanating from moving vehicles.[1] There is a considerable range in acoustical intensities produced depending upon the specific tire tread design and the rapidity of deceleration required to slow the vehicle.
[edit] See also
Archaic past tense of break (see brake)
Air brake (aircraft)
Air brake (rail)
Air brake (road vehicle)
Bicycle brake systems
Brake-by-wire (or electromechanical braking)
Brake lining
Brake pad
Brake shoe
Bundy tube
Disc brake
Drum brake
Electromagnetic brake
Electronic Parking Brake
Engine braking
Hand brake
Hydraulic brake
Jake brake also known as J braking
Overrun brake
Parking brake
Railway brake
Regenerative braking
Threshold braking
Trail braking
Vehicle brake
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How brakes work
Of all the systems that make up your car, the brake system might just be the most important. In the olden days it was also one of the simplest. Over the years as improvements h***e been made, the system that has evolved isn't so simple anymore... (It's also about a zillion times more reliable and safer.)
Your brakes work as hard or harder than any other part of the car, however much energy it takes to get your car up a hill, it takes at least as much energy to stop it at the bottom. Think about that for a second. Here, I'll say it again, it takes at least as much energy to get your car safely down a hill and stop it at the bottom, as it took to get your car up the hill in the first place. Your brakes do this by converting the kinetic energy to heat energy. All of this heat is generated between the friction surfaces of your brake pads and your rotors. (I am going to disregard the rear brakes for now, since the front brakes do the lion's share of the work.)
Rather than try to give you a step-by-step procedure for repairing your brakes, I'm going to try to show you how to diagnose a few of the many simple brake problems. Unfortunately, before I can do that, I h***e to talk about how the brake system works. If you already know how it works, then you probably already know what your problem is, but you might find something useful here anyway or at least I hope so.
Brakes operate on a simple hydraulic principle. (See diagram below) If a force is exerted on the piston putting pressure on the fluid confined in the left hand container, the fluid is forced out through the narrow tube at the bottom and into the right hand container, exerting a force on the second piston, forcing it to move upward.
Now this is how the force from your foot gets to the four corners of the car. If we add a lever to magnify the force ***lied to the first (master) cylinder, and maybe even a power booster unit to increase that force even more, all we h***e to do next is figure a way to use that force to slow down the wheels. Since the wheels are attached to the car, slowing them down will slow the car.
If we change the shape of the right hand container, (see below) to make something for the piston to push against, we can make it pinch something. Let's bolt a disc(Brake rotor) to the wheel, so that it rotates whenever the wheel does. We'll mount it in such a way that the edge of it is between the caliper piston and the caliper that we h***e bolted to the axle of the car.so that when the piston moves out, the disc is pinched between it and the other side of the caliper. Actually we're not quite done. As we h***e the system now, the disc and the caliper would wear out rather quickly (not to mention making horrible grinding/scraping noises). We need to put something between them to protect the surfaces. Let's call this part "Brake Pads" But wait, as we h***e drawn it, the piston only pushes on one side of the disc. We h***e to allow the caliper to slide back and forth if we want it to actually pinch the disc efficiently. Let's make an anchor post and allow the caliper to slide along it. Let's make a nice, strong mount to hold the brake pads, and secure it to the axle. Now all we h***e to do is mount the caliper assembly to some sturdy part of the car and we're in business.
Brake pads h***e two main parts, the steel backing, and the actual friction material. The backing is only there to support the friction material, which does the actual work of stopping the car. The friction material does it's job by converting the energy of motion to heat energy. This is done by the magic of friction. The friction between the pad and the disc slows down the disc, and creates heat. This heat is transferred to the pad and the disc and then (at some fixed rate) dissipated to the surrounding air. How fast that heat is radiated is determined by a simple formula, depends on mainly two factors, the temperature of the air around the parts, and the flow of air past them. 99% of the time, this cooling is more than enough to keep the brakes cool enough to work just fine.
OK, now we h***e our simple brake system. Let's see what can go wrong...
Air in the system This is usually caused by air getting into the brake fluid area, usually from the master cylinder. As the brake pads wear, the caliper pistons ride farther out of the caliper, allowing more fluid to remain in the calipers. Over time this can add up to almost as much fluid as there is in the master cylinder reservoir. If neglected, this will allow the master cylinder to pump some air into the brake lines. Air is very compressable, whereas brake fluid is not, as long as there is a solid stream of brake fluid between the master cylinder piston and the caliper piston, the brake pedal will be nice and firm. If there is air in the system, the pedal will feel spongy and will go down almost all the way to the floor, maybe all the way, depending on how much air is in the system. The standard way of dealing with air in the brake system is to perform an operation called "bleeding the brakes".
Hard brake pedal: Can be caused by bad power booster, (or loss of vacuum to the booster) seized caliper pistons, seized caliper slides, pinched brake lines, and (rarely) problems with the pedal linkage under the dash. The probable best fix is rebuilt calipers,and new pads.
Brake fade: I h***e seen too much of this, h***ing spent 5 years at the bottom of a 13 km hill with 15% grade and continuous switchbacks. Two phenomena contribute to brake fade, one is the fact that the coefficient of friction of most substances gets lower at high temperatures, and that most liquids will boil at some temperature, and that gases compress, while liquids do not. When you use the brakes to decelerate 3,000 or 4,000 or 7-8-15,000 lbs of vehicle, they get hot. Very hot. Under normal circumstances this would be no big deal, the heat that builts up in the pads, rotors, and calipers will slowly radiate back to the air flowing over them as the car continues down the road. But you aren't going down the road, you are back on the brakes, doing more decelerating for the next switchback. Instead of cooling off, your brakes are getting hotter. And hotter, and hotter. . .As the pads and rotors get hotter the friction material of the pads starts to separate. The binding agent starts to boil off from the surface of the pad, plating out on the rotor as a dark, paintlike film...coefficient of friction ***roaches zero, pedal gets hard, but no braking action. Your pupils dilate to 10 mm and your body goes into fight-or-flight mode, adrenalin courses through your system. But the car just goes faster.... You shift down, now you are standing on the brake pedal with both feet, around this time, the temperature of the brake fluid in the calipers usually reaches it's boiling point and the pedal just sinks to the floor. Your pupils reach 12 mm, your sphyncters contract to pinpoints, somehow you manage to stop the car. There is ***oke coming from behind your front wheels, maybe fire. You put out the fire and h***e lunch. After things cool off you sit in the car and try the brake pedal, it feels almost normal. Congratulations, you've just experienced, (and survived) brake fade. (You've also just flash-fried your front brakes, figure on new everything to fix it properly.)
Brake squeal: This is a high pitched squealing noise, often heard when you are going slow and are not ***lying the brakes. If it goes away as you ***ly the brakes, it could be coming from the brake wear sensors. (Also called 'squealers' by mechanics.) They are ***all bits of spring steel that are attached to the brake pads in such a way that when the pads are about 75% worn out, the sensors start to rub on the rotors, making the noise. GM invented them, and they are one of the best ideas anyone has ever had in the automotive industry. The sound is so scary that you usually go to a mechanic before any major damage is done to your rotors, and before your braking power is compromised, s***ing you money and maybe your life.
Grinding noise: Although this is one of the nastiest sounds you will ever hear, it often is the easiest to repair. The first thing you must do is learn what is making the noise. Figure out which wheel it is, then, after safely raising and supporting the car, take off the wheel & tire. Hopefully you will see a simple disc brake system, with a rotor, a caliper, and brake pads. Identify the various components. Gently rotate the brake rotor back and forth until you can identify the source of the noise. Sometimes it is just a ***all stone, tr***ed between the brake rotor and the air deflector. The faces of the rotor should be ***ooth and clean. If you see large scaly rusted places on the friction surfaces of the rotor you should replace them. Most of the time new ones cost less than you would guess. If your pads are worn out(less than 3/16 of an inch of friction material left) and you catch it in time, all you h***e to do is install new brake pads. If the surface of the rotor is damaged, you will h***e to resurface or replace it.
Brake pedal pulsation: There are a lot of things that can cause this, from out-of-adjustment wheel bearings to rotors that are bent, brake drums that are out-of-round, rusty spots on the rotors that h***e a different surface ***oothness. To determine whether the pulsation is coming from the front or the rear wheels, check to see if you can feel the pulsation in the steering wheel when the pedal is pulsating. If you can, the problem is coming from the front wheels.
Brake pull: Mostly this one comes from either a caliper piston seized or caliper slides seized. This one is dangerous! If your car tries to turn when you ***ly the brakes you could veer into oncoming traffic. What often h***ens with this one is this: the caliper piston on one side starts to seize, the other one now ***lies first, car veers away from bad part. Driver learns to compensate by steering opposite to the pull every time he brakes. A panic situation comes along, driver nails the brakes, steers away from the expected pull, but because the piston was only partially seized, it works just fine when the brakes are ***lied with vigor. There is no pull this time. It is easy to lose control of your car in situations like this, if your car pulls to one side or the other when you brake, fix it(or get it fixed) before you hurt somebody. Replace calipers and pads and service the caliper slides.
Brake grag: When you just barely touch the brake pedal and one or more wheels locks up and skids. This one most commonly comes from contaminated friction material on one or more brakes.
Pedal goes to the floor: Gotta be the scariest of them all. If you're lucky, a quick pump on the pedal will get you some braking action. On most newer cars, there will be some braking just before the pedal reaches the floor. Stop driving and check your fluid level. It might just need to be topped up to temporarily get you some braking action to get you home. Regardless, you must find out what caused it and fix it before you drive any further.
Components
Disc brakes h***e:
brake calipers
brake pads
rotors
caliper mounting hardware
Drum brakes h***e:
brake backing plates
brake drums
brake shoe self-adjusters
brake shoes
brake springs
wheel cylinders
Both types use:
Brake fluid
Steel brake lines and reinforced rubber brake hoses
Master cylinder
Power brake booster (usually)
proportioning valve
delay valve
metering valve
brake warning light
park brake cables, levers,
解密!讓各大車企瑟瑟發(fā)抖的中保研是什么來頭?
汽車檢測與維修專業(yè)是培養(yǎng)具有汽車檢測、運行、維修與技術(shù)管理能力,且具有職業(yè)崗位(群)所需的基礎(chǔ)知識和專業(yè)技能的經(jīng)過汽車維修工程師初步訓(xùn)練的高素質(zhì)技能型專門人才的一門學(xué)科。
汽車檢測與維修技術(shù)主要研究汽車故障檢測與維修、汽車使用性能檢測與維修、發(fā)動機原理與汽車理論等方面的基礎(chǔ)知識和技能,在汽車檢測與維修技術(shù)領(lǐng)域進行汽車檢測、診斷、維修、銷售、服務(wù)等。例如:車輛鑒定、評估、理賠、車輛事故查勘等。
《汽車駕駛技術(shù)》、《汽車構(gòu)造與拆裝》、《發(fā)動機系統(tǒng)診斷與修復(fù)》、《汽車傳動系統(tǒng)的檢查與修復(fù)》、《轉(zhuǎn)向與制動系統(tǒng)檢查與修復(fù)》、《汽車底盤控制系統(tǒng)診斷與修復(fù)》、《汽車電控系統(tǒng)診斷與修復(fù)》、《汽車舒適與安全系統(tǒng)診斷與檢修》、《汽車保養(yǎng)及維護》、《汽車性能檢測與評估》、《汽車綜合性能故障分析與診斷》、《汽車維修經(jīng)營與管理》、《汽車保險與理賠》部分高校按以下專業(yè)方向培養(yǎng):檢測火箭軍、4S店店長、大眾汽車、德系汽車、新能源汽車、汽車維修管理、大型客貨車駕駛、制造與裝配技術(shù)、汽車技術(shù)服務(wù)與營銷。
學(xué)汽修選哪個專業(yè)好呢?
汽車安全性一直以來都是我們關(guān)注的重點,我們在買車之前經(jīng)常被老司機提醒:“買車就要買安全的”“安全比什么配置都重要”。這也衍生到一個問題:怎么樣的車才算安全?
在全球范圍內(nèi),測試車輛安全的重要標準——碰撞測試,在C端最著名的就是C-NCAP碰撞測試。C-NCAP碰撞來源于中國汽車技術(shù)研究中心有限公司,簡稱中汽研。C-NCAP是中國第一個專業(yè)的第三方評測機構(gòu),在信息不是特別發(fā)達的階段,成為當(dāng)時老百姓判斷車輛安全性的重要參考依據(jù)。
而近年來有一個新的碰撞測試機構(gòu)異軍突起,國內(nèi)被熟知的車企好像一下子被揭了底一樣,部分車型成績之差讓人咋舌,沒錯,就是最近風(fēng)頭無兩的中保研。
中保研是由中國保險行業(yè)協(xié)會于2015年3月牽頭發(fā)起,中國汽研作技術(shù)指導(dǎo),并由行業(yè)內(nèi)八家財產(chǎn)保險公司與精友世紀公司共同出資,入股改制原“北京中保研汽車技術(shù)研究院”而來。是目前國際機構(gòu)RCAR組織(權(quán)威的國際性汽車研究機構(gòu)聯(lián)盟)在中國唯一的正式會員單位,并取得CNAS實驗室能力認可。
可以說,中保研是目前中國范圍內(nèi)最專業(yè)、可信度最高、執(zhí)行標準最嚴苛的機構(gòu),這也是為什么中保研能夠讓消費者信服的重要原因。
實際上,很多人會搞混中國汽研、中汽研、中保研三者的概念及它們之間的關(guān)系,特別是中汽研和中國汽研,如果對此沒有關(guān)注的話,很容易認為這是同一個機構(gòu),其實不然。
中國汽研,全稱:中國汽車工程研究院股份有限公司,始建于1965年3月,原名:重慶中型汽車研究所,是國家一類科研院所,主要承擔(dān)中國企業(yè)行業(yè)產(chǎn)品開發(fā)、試驗研究、質(zhì)量檢測的重要基地及技術(shù)支撐機構(gòu)。其中包括:技術(shù)服務(wù)業(yè)務(wù)包括汽車研發(fā)及咨詢和汽車測試與評價業(yè)務(wù);產(chǎn)業(yè)化制造業(yè)務(wù)包括專用汽車、軌道交通關(guān)鍵零部件、汽車燃氣系統(tǒng)及其關(guān)鍵零部件制造業(yè)務(wù)。
對于廣大消費者來說,中國汽研被大多數(shù)人認知是因為其每年發(fā)布的四大汽車行業(yè)權(quán)威測評指數(shù),包括:中國保險汽車安全指數(shù)(C-IASI)、中國汽車健康安全指數(shù)、中國智能汽車指數(shù)、中國消費者汽車駕乘指數(shù)。
C-IASI是參考美國IIHS制定測試標準,而美國IIHS標準是從80年代左右出現(xiàn),一直致力于對美國銷售的車輛進行測試,而且IIHS擁有號稱全球最嚴苛的測試標準——25%偏置碰撞,以及NCAP標準沒有的車頂強度測試、燈光測試以及兒童安全座椅測試。中國的C-IASI測試就是引進了IIHS測試方法,并且根據(jù)中國國情進行一定的調(diào)整而來,可以說C-IASI測試是中國最嚴苛的汽車安全測試。所以,C-IASI并非隨意制定出來的標準,而是有根有據(jù),對我國消費者有重要參考意義。
實際上C-NCAP和C-IASI這兩個體系并非對立,而是相輔相成的關(guān)系。兩者的數(shù)據(jù)基礎(chǔ)和測試側(cè)重點不同,不能簡單地以要求高低來直接比較,以正面碰撞項目為例,C-NCAP***用40%可變形壁障偏置碰撞與C-IASI的25%重疊不可變形壁障碰撞相比,C-IASI的測試更接近極限時的碰撞情景,更加深入挖掘車輛的極限安全能力。
這里簡單小結(jié)一下,中保研是中國汽研與保險協(xié)會合作推出,兩者共同組成我們俗稱“中保研碰撞測試”,而中汽研最著名的則是C-NCAP碰撞測試。
前文說過,中國汽研是主要承擔(dān)中國企業(yè)行業(yè)產(chǎn)品開發(fā)、試驗研究、質(zhì)量檢測的重要基地及技術(shù)支撐機構(gòu),一直以來對我國汽車發(fā)展作出重要貢獻。
在1965年前后,為了我國的軍用重型汽車和重型載貨車的,長春汽車研究所和第一汽車制造廠的技術(shù)人員、畢業(yè)生以及宜賓高壓開關(guān)廠技術(shù)人員在西南***江畔會師,開始了重型汽車研究所的創(chuàng)建工作。
1965年至1988年,汽研所獨立開發(fā)了20多種車型,諸如CQ261軍用越野車,紅巖261越野軍用牽引車、CQ30290公路載貨汽車等;1984年還開發(fā)了CD632客車、在1985年引進MTS材料實驗機。
為了更好地服務(wù)中國汽車工業(yè)的發(fā)展?1988年重慶中型汽車研究所搬遷到重慶九龍坡區(qū)陳家坪,總投資2996萬元,建筑面積4.5萬平方米。新基地有汽車側(cè)傾實驗、高低溫實驗、燈光試驗室、三坐標測量實驗室、傳動系統(tǒng)實驗室、轉(zhuǎn)向器實驗室等多個一流實驗室。
千禧年后,轉(zhuǎn)制為全民所有制企業(yè),并更名為“重慶汽車研究所”;2003年重慶汽車研究所劃轉(zhuǎn)國資委管理;2006年聯(lián)合重組并入中國通用技術(shù)(集團)控股有限責(zé)任公司。
2010年整體變更設(shè)計為“中國汽車工程研究院股份有限公司”,并于2012年在上海證交所掛牌上市。
2013年中國汽研研發(fā)和測試新基地建成并投入使用,選址位于重慶市北部新區(qū)金渝大道9號,總投資約15億元,占地550畝,為中國汽研具有國際一流、功能完善的汽車技術(shù)研發(fā)、測試評價綜合能力打下堅實基礎(chǔ)。
據(jù)2018年5月中國汽研重慶凱瑞汽車試驗設(shè)備開發(fā)有限公司***顯示,公司擁有整車、發(fā)動機、動力總成、傳動系、轉(zhuǎn)向系、制動系、新能源等方面的產(chǎn)品設(shè)備共208項,全方位保障中國汽車產(chǎn)品開發(fā)、試驗研究以及質(zhì)量檢測。
而近年來與保險行業(yè)合作開展碰撞測試的根本目的是增加我國車輛的安全性,但不可否認,中保研C-IASI是為了幫助保險機構(gòu)去認清車輛的后期維修成本,所以在中保研的測試中有一項獨特的地方:耐撞性與維修經(jīng)濟性指數(shù),代表著車輛在發(fā)生嚴重事故中需要的維修成本高低,并將此來定奪某些車輛是否需要提升保費。
用直白的話來說就是中保研為了更清晰明了判斷保費高低,他們需要一個參考標準,一個可以將極端情況考慮在內(nèi)的標準。不難發(fā)現(xiàn),中保研的利益正好與車企相反,車企想要降低成本去獲取最大利潤,而中保研要求的車身安全性則需要高成本去支撐,所以中保研的測試會更加客觀。此外,與C-NCAP不同,C-IASI測試以市面低配車型為主,不接受企業(yè)送檢,可以有效防止測試車的用料、安全配置與市售車型不一致,也就是說,中保研測試的車輛跟我們消費者買到的車輛是一樣的,進一步提升了公信力和可信度。
前文說過,C-NCAP、C-IASI、IIHS各有不同的標準,根據(jù)圖表顯示,除了碰撞測試的項目不同以外,側(cè)向碰撞實驗的速度、撞擊試驗車的重量都會有些許出入。例如,C-NCAP和C-IASI的碰撞速度都是50km/h,而IIHS則是64km/h;IIHS與C-IASI的撞擊試驗車的重量均為1500kg,C-NCAP的重量只有1400±20kg。C-IASI的測試更加接近美國IIHS這個堪稱最嚴苛的碰撞測試,車企想要獲得好成績就必須在車身安全層面下狠功夫,最后獲益的自然是消費者自身,對購車也有更強的參考意義。
從車市宏觀來看,產(chǎn)品的持續(xù)性升級和技術(shù)的進步才是正道,因此類似中保研體系的誕生是發(fā)展的必然結(jié)果。一向習(xí)慣了C-NCAP測試標準的車企,突然接受C-IASI標準的測試,難免出現(xiàn)窘態(tài),就好像一個做湘菜的廚師,要同時學(xué)會做粵菜、客家菜一樣,要求車企在安全方面做得更為全面,而不應(yīng)該只是應(yīng)試教育,得過且過。
C-IASI就像是車市的“鯰魚”,可以明顯***那些已經(jīng)慵懶的“沙丁魚”活躍起來,從消費者對C-IASI結(jié)果的高關(guān)注度來看,車企們已經(jīng)不能再忽視這一套汽車評價體系了。
從消費者角度來看,越嚴苛、越全面、越多的體系建立,可以明顯增加車輛在各個維度的安全性,舉個例子,C-NCAP需要40%偏置碰撞,而C-IASI則是25%偏置,只有兩個方面都獲得好成績,車輛才能在消費者中有較好的口碑,才能最大程度保證消費者用車安全。
回歸到根本,安全碰撞測試最核心的目的是為了讓消費者購買到更加安全的車輛,這也是中保研做碰撞測試的初心。希望在測試機構(gòu)的監(jiān)督下,車企能更注重車輛安全,消費者買到的車輛會更加安全。
本文來源于汽車之家車家號作者,不代表汽車之家的觀點立場。
同濟大學(xué)車輛工程專業(yè)怎么樣
學(xué)汽修選哪個專業(yè)好? 很多同學(xué)想知道學(xué)汽修哪個專業(yè)最吃香,以下是小編進行的相關(guān)信息的整理,希望能對同學(xué)們有所幫助。
1、汽車檢測與維修
汽車檢測與維修主要研究汽車整車、機械系統(tǒng)、傳動系統(tǒng)、制動系統(tǒng)、電氣系統(tǒng)等的構(gòu)造、故障診斷、檢測維修等方面的基本知識和技能,進行汽車的檢測、維修、評估等。例如:汽車整車的裝配,汽車故障的診斷與維修,汽車零配件的更換與保養(yǎng),二手車價值的評估等。
2、新能源汽車技術(shù)工程師
新能源汽車技術(shù)主要研究新能源汽車組成構(gòu)造、電池設(shè)計、故障診斷、維修養(yǎng)護等方面的基本知識和技能,進行新能源汽車的生產(chǎn)制造、裝配調(diào)試、檢測維修等。常見的新能源汽車有:純電動汽車、增程式電動汽車、插電式混合動力汽車、燃料電池電動汽車等。
現(xiàn)在中國的汽車越來越多,而汽修人才并沒有倍數(shù)增,汽修人才定是緊缺,拿高薪也就成為必然。但以后汽修行業(yè)的競爭也會很激烈,那就要看你汽修技術(shù)是否過硬。這個專業(yè)都很好找工作的,只要你好好干,工資肯定會讓你滿意的。
以上回答僅供參考!
求一篇“機電技術(shù)應(yīng)用”的畢業(yè)論文!要求3000字以上!要符合實際一些的,不能太夸張了!小弟在此謝過了。
車輛工程(本科類) (軌道交通)
本專業(yè)培養(yǎng)具備從事車輛工程(軌道交通)領(lǐng)域內(nèi)的設(shè)計制造、應(yīng)用開發(fā)、創(chuàng)新研究和系統(tǒng)運用維護的機-電-信息復(fù)合化人才。注重培養(yǎng)能掌握現(xiàn)代城市軌道交通、高速鐵路、磁懸浮系統(tǒng)、新交通系統(tǒng)的車輛及其驅(qū)動系統(tǒng)的基本構(gòu)造、原理和制造技術(shù),以及具有系統(tǒng)集成知識和能力的專業(yè)人才。 本專業(yè)設(shè)兩個專業(yè)方向,即車輛設(shè)計及 制造方向、軌道交通車輛電氣及信息工程方向。 本專業(yè)的主要課程有:大學(xué)英語、高等數(shù) 學(xué)、機械制圖、機械原理、機械設(shè)計、機械振動、理論力學(xué)、材料力學(xué)、工程材料、制造技術(shù)基礎(chǔ)、電工學(xué)、電子學(xué)、計算機硬件技術(shù)、軌道交通概論、自動控制原理、微機原理、軌道車輛結(jié)構(gòu)與強度、軌道車輛動力學(xué)、電氣傳動、電力電子技術(shù)、機電一體化系統(tǒng)設(shè)計、車輛制動與控制技術(shù)、動車總體技術(shù)、軌道車輛制造技術(shù)、傳感與測試技術(shù)、內(nèi)燃機原理與應(yīng)用、空氣動力學(xué)、電子測量技術(shù)與儀器、電力牽引控制系統(tǒng)、電子測量與儀器、計算機通訊與網(wǎng)絡(luò)等,課程設(shè)計、畢業(yè)設(shè)計等。 本專業(yè)培養(yǎng)的畢業(yè)生,在軌道交通行業(yè)有很大的影響,已畢業(yè)的學(xué)生主要在研究所、高校、軌道車輛制造廠及外資、合資企業(yè)工作,在當(dāng)前軌道交通被大中城市大力發(fā)展,并作為中長期發(fā)展規(guī)劃的形勢下,畢業(yè)學(xué)生有寬廣和長遠的發(fā)展前途。
機電畢業(yè)論文-實現(xiàn)變頻調(diào)速器多電機控制
[摘要]本文介紹了一種plc與變頻調(diào)速器構(gòu)成的多分支通訊網(wǎng)絡(luò),闡明了該網(wǎng)絡(luò)控制調(diào)速系統(tǒng)與一般模擬量控制調(diào)速系統(tǒng)相比的優(yōu)越性,給出了系統(tǒng)框圖及plc程序。
[關(guān)鍵詞]plc變頻調(diào)速器多電機控制網(wǎng)絡(luò)通訊協(xié)議
一、引言
以變頻調(diào)速器為調(diào)速控制器
的同步控制系統(tǒng)、比例控制系統(tǒng)和同速系統(tǒng)等已廣泛應(yīng)用于冶金、機械、紡織、化工等行業(yè)。以比例控制系統(tǒng)為例,一般的系統(tǒng)構(gòu)成如圖1所示。
工作時操作人員通過控制機(可為plc或工業(yè)pc)設(shè)定比例運行參數(shù),然后控制機通過d/a轉(zhuǎn)換模件發(fā)出控制變頻調(diào)速器的速度指令使各個變頻調(diào)速器帶動電機按一定的速度比例運轉(zhuǎn)。此方案對電機數(shù)目不多,電機分布比較集中的應(yīng)用系統(tǒng)較合適。但對于大規(guī)模生產(chǎn)自動線,一方面電機數(shù)目較多,另一方面電機分布距離較遠。***用此控制方案時由于速度指令信號在長距離傳輸中的衰減和外界的干擾,使整個系統(tǒng)的工作穩(wěn)定性和可靠性降低;同時大量d/a轉(zhuǎn)換模件使系統(tǒng)成本增加。為此我們提出了plc與變頻調(diào)速器構(gòu)成多分支通訊控制網(wǎng)絡(luò)。該系統(tǒng)成本較低、信號傳輸距離遠、抗干擾能力強,尤其適合遠距離,多電機控制。
二、系統(tǒng)硬件構(gòu)成
系統(tǒng)硬件結(jié)構(gòu)如圖2所示,主要由下列組件構(gòu)成;
1、fx0n—24mr為plc基本單元,執(zhí)行系統(tǒng)及用戶軟件,是系統(tǒng)的核心。
2、fx0n—485adp為fx0n系統(tǒng)plc的通訊適配器,該模塊的主要作用是在計算機—plc通訊系統(tǒng)中作為子站接受計算機發(fā)給plc的信息或在多plc構(gòu)成n:n網(wǎng)絡(luò)時作為網(wǎng)絡(luò)適配器,一般只作為規(guī)定協(xié)議的收信單元使用。本文作者在分析其結(jié)構(gòu)的基礎(chǔ)上,將其作為通訊主站使用,完成變頻調(diào)速器控制信號的發(fā)送。
3、fr—cu03為fr—a044系列比例調(diào)速器的計算機連接單元,符合rs—422/rs—485通訊規(guī)范,用于實現(xiàn)計算機與多臺變頻調(diào)速器的連網(wǎng)。通過該單元能夠在網(wǎng)絡(luò)上實現(xiàn)變頻調(diào)速器的運行控制(如啟動、停止、運行頻率設(shè)定)、參數(shù)設(shè)定和狀態(tài)監(jiān)控等功能,是變頻器的網(wǎng)絡(luò)接口。
4、fr—a044變頻調(diào)查器,實現(xiàn)電機調(diào)速。
在1:n(本文中為1:3)多分支通訊網(wǎng)絡(luò)中,每個變頻器為一個子站,每個子站均有一個站號,事先由參數(shù)設(shè)定單元設(shè)定。工作過程中,plc通過fx0n—485adp發(fā)有關(guān)命令信息后,各個子站均收到該信息,然后每個子站判斷該信息的站號地址是否與本站站號一致。若一致則處理該信息并返回應(yīng)答信息;若不一致則放棄該信息的處理,這樣就保證了在網(wǎng)絡(luò)上同時只有一個子站與主站交換信息。
三、軟件設(shè)計
1、通訊協(xié)議
fr—cu03規(guī)定計算機與變頻器的通訊過程如圖3所示,
該過程最多分5個階段。?、計算機發(fā)出通訊請求;?、變頻器處理等待;?、變頻器作出應(yīng)答;?、計算機處理等待;?、計算機作出應(yīng)答。根據(jù)不同的通訊要求完成相應(yīng)的過程,如寫變頻器啟停控制命令時完成?~?三個過程;監(jiān)視變頻器運行頻率時完成?~?五個過程。不論是寫數(shù)據(jù)還是讀數(shù)據(jù),均有計算機發(fā)出請求,變頻器只是被動接受請求并作出應(yīng)答。每個階段的數(shù)據(jù)格式均有差別。圖4分別為寫變頻器控制命令和變頻器運行頻率的數(shù)據(jù)格式。
2、plc編程
要實現(xiàn)對變頻器的控制,必須對plc進行編程,通過程序?qū)崿F(xiàn)plc與變頻器信息交換的控制。plc程序應(yīng)完成fx0n—485adp通訊適配器的初始化、控制命令字的組合、代碼轉(zhuǎn)換及變頻器應(yīng)答信息的處理等工作。plc梯形圖程序(部分程序)如圖5所示。
程序中通訊發(fā)送緩沖區(qū)為d127~d149;接受緩沖區(qū)為d150~d160。電機1啟動、停止分別由x0的上升、下降沿控制;電機2啟動、停止分別由x1的上升、下降沿控制;電機3啟動、停止分別由x2的上升、下降沿控制。程序由系統(tǒng)起始脈沖m8002初始化fx0n—485adp的通訊協(xié)議;然后進行啟動、停止信號的處理。以電機1啟動為例,x0的上升沿m50吸合,變頻器1的站號送入d130,運行命令字送入d135,enq、寫運行命令的控制字和等待時間等由編程器事先寫入d131、d132、d133;接著求校驗和并送入d136、d137;最后置m8122允許rs指令發(fā)送控制信息到。變頻器受到信號后立刻返回應(yīng)答信息,此信息fx0n—485adp收到后置m8132,plc根據(jù)情況作出相應(yīng)處理后結(jié)束程序。
四、變頻器制動的思路和新方法
在通用變頻器、異步電動機和機械負載所組成的變頻調(diào)速傳統(tǒng)系統(tǒng)中,當(dāng)電動機所傳動的位能負載下放時,電動機將可能處于再生發(fā)電制動狀態(tài);或當(dāng)電動機從高速到低速(含停車減速時,頻率可以突減,但因電機的機械慣性,電機可能處于再生發(fā)電狀態(tài),傳動系統(tǒng)中所儲存的機械能經(jīng)電動機轉(zhuǎn)換成電能,通過逆變器的六個續(xù)流二極管回送到變頻器的直流回路中。此時的逆變器處于整流狀態(tài)。這時,如果變頻器中沒***取消耗能量的措施,這部分能量將導(dǎo)致中間回路的儲能電容器的電壓上升。如果當(dāng)制動過快或機械負載為提升機類時,這部分能量就可能
對變頻器帶來損壞,所以這部分能量我們就應(yīng)該考慮考慮了。
在通用變頻器中,對再生能量最常用的處理方式有兩種:(1)、耗散到直流回路中人為設(shè)置的與電容器并聯(lián)的“制動電阻”中,稱之為動力制動狀態(tài);(2)、使之回饋到電網(wǎng),則稱之為回饋制動狀態(tài)(又稱再生制動狀態(tài))。還有一種制動方式,即直流制動,可以用于要求準確停車的情況或起動前制動電機由于外界因素引起的不規(guī)則旋轉(zhuǎn)。
在書籍、刊物上有許多專家談?wù)撨^有關(guān)變頻器制動方面的設(shè)計與應(yīng)用,尤其是近些時間有過許多關(guān)于“能量回饋制動”方面的文章。今天,筆者提供一種新型的制動方法,它具有“回饋制動”的四象限運轉(zhuǎn)、運行效率高等優(yōu)點,也具有“能耗制動”對電網(wǎng)無污染、可靠性高等好處。
1、能耗制動
利用設(shè)置在直流回路中的制動電阻吸收電機的再生電能的方式稱為能耗制動。
其優(yōu)點是構(gòu)造簡單;對電網(wǎng)無污染(與回饋制動作比較),成本低廉;缺點是運行效率低,特別是在頻繁制動時將要消耗大量的能量且制動電阻的容量將增大。
一般在通用變頻器中,小功率變頻器(22kw以下)內(nèi)置有了剎車單元,只需外加剎車電阻。大功率變頻器(22kw以上)就需外置剎車單元、剎車電阻了。
2、回饋制動
實現(xiàn)能量回饋制動就要求電壓同頻同相控制、回饋電流控制等條件。它是***用有源逆變技術(shù),將再生電能逆變?yōu)榕c電網(wǎng)同頻率同相位的交流電回送電網(wǎng),從而實現(xiàn)制動。
回饋制動的優(yōu)點是能四象限運行,電能回饋提高了系統(tǒng)的效率。其缺點是:(1)、只有在不易發(fā)生故障的穩(wěn)定電網(wǎng)電壓下(電網(wǎng)電壓波動不大于10%),才可以***用這種回饋制動方式。因為在發(fā)電制動運行時,電網(wǎng)電壓故障時間大于2ms,則可能發(fā)生換相失敗,損壞器件。(2)、在回饋時,對電網(wǎng)有諧波污染。(3)、控制復(fù)雜,成本較高。
3、新型制動方式(電容反饋制動)
3.1主回路原理
整流部分***用普通的不可控整流橋進行整流,濾波回路***用通用的電解電容,延時回路***用接觸器或可控硅都行。充電、反饋回路由功率模塊ig***、充電、反饋電抗器l及大電解電容c(容量約零點幾法,可根據(jù)變頻器所在的工況系統(tǒng)決定)組成。逆變部分由功率模塊ig***組成。保護回路,由ig***、功率電阻組成。
(1)電動機發(fā)電運行狀態(tài)
cpu對輸入的交流電壓和直流回路電壓νd的實時監(jiān)控,決定向vt1是否發(fā)出充電信號,一旦νd比輸入交流電壓所對應(yīng)的直流電壓值(如380vac—530vdc)高到一定值時,cpu關(guān)斷vt3,通過對vt1的脈沖導(dǎo)通實現(xiàn)對電解電容c的充電過程。此時的電抗器l與電解電容c分壓,從而確保電解電容c工作在安全范圍內(nèi)。當(dāng)電解電容c上的電壓快到危險值(比如說370v),而系統(tǒng)仍處于發(fā)電狀態(tài),電能不斷通過逆變部分回送到直流回路中時,安全回路發(fā)揮作用,實現(xiàn)能耗制動(電阻制動),控制vt3的關(guān)斷與開通,從而實現(xiàn)電阻r消耗多余的能量,一般這種情況是不會出現(xiàn)的。
(2)電動機電動運行狀態(tài)
當(dāng)cpu發(fā)現(xiàn)系統(tǒng)不再充電時,則對vt3進行脈沖導(dǎo)通,使得在電抗器l上行成了一個瞬時左正右負的電壓,再加上電解電容c上的電壓就能實現(xiàn)從電容到直流回路的能量反饋過程。cpu通過對電解電容c上的電壓和直流回路的電壓的檢測,控制vt3的開關(guān)頻率以及占空比,從而控制反饋電流,確保直流回路電壓νd不出現(xiàn)過高。
3.2系統(tǒng)難點
(1)電抗器的選取
(a)、我們考慮到工況的特殊性,***設(shè)系統(tǒng)出現(xiàn)某種故障,導(dǎo)致電機所載的位能負載自由加速下落,這時電機處于一種發(fā)電運行狀態(tài),再生能量通過六個續(xù)流二極管回送至直流回路,致使νd升高,很快使變頻器處于充電狀態(tài),這時的電流會很大。所以所選取電抗器線徑要大到能通過此時的電流。
(b)、在反饋回路中,為了使電解電容在下次充電前把盡可能多的電能釋放出來,選取普通的鐵芯(硅鋼片)是不能達到目的的,最好選用鐵氧體材料制成的鐵芯,再看看上述考慮的電流值如此大,可見這個鐵芯有多大,素不知市面上有無這么大的鐵氧體鐵芯,即使有,其價格也肯定不會很低。
所以筆者建議充電、反饋回路各***用一個電抗器。
(2)控制上的難點
(a)、變頻器的直流回路中,電壓νd一般都高于500vdc,而電解電容c的耐壓才400vdc,可見這種充電過程的控制就不像能量制動(電阻制動)的控制方式了。其在電抗器上所產(chǎn)生的瞬時電壓降為,電解電容c的瞬時充電電壓為νc=νd-νl,為了確保電解電容工作在安全范圍內(nèi)(≤400v),就得有效的控制電抗器上的電壓降νl,而電壓降νl又取決于電感量和電流的瞬時變化率。
(b)、在反饋過程中,還得防止電解電容c所放的電能通過電抗器造成直流回路電壓過高,以致系統(tǒng)出現(xiàn)過壓保護。
3.3主要應(yīng)用場合及應(yīng)用實例
正是由于變頻器的這種新型制動方式(電容反饋制動)所具有的優(yōu)越性,近些來,不少用戶結(jié)合其設(shè)備的特點,紛紛提出了要配備這種系統(tǒng)。由于技術(shù)上有一定的難度,國外還不知有無此制動方式?國內(nèi)目前只有山東風(fēng)光電子公司由以前***用回饋制動方式的變頻器(仍有2臺在正常運行中)改用了這種電容反饋制動方式的新型礦用提升機系列,到目前為止,這種電容反饋制動的變頻器正長期正常運行在山東寧陽保安煤礦及山西太原等地,填補了國內(nèi)這一空白。
隨著變頻器應(yīng)用領(lǐng)域的拓寬,這個應(yīng)用技術(shù)將大有發(fā)展前途,具體來講,主要用在礦井中的吊籠(載人或裝料)、斜井礦車(單筒或雙筒)、起重機械等行業(yè)??傊枰芰炕仞佈b置的場合都可選用。
五、結(jié)語
1、實際使用表明,該方案能夠?qū)崿F(xiàn)plc通過網(wǎng)絡(luò)對變頻調(diào)速器的運行控制、參數(shù)設(shè)定和運行狀態(tài)監(jiān)控。
2、該系統(tǒng)最多可控制變頻調(diào)速器32臺,最大距離500m。
3、控制多臺變頻器,成本明顯低于d/a控制方式。
4、隨著變頻器的增加,通訊延遲加大,系統(tǒng)響應(yīng)速度低于d/a控制方式。
參考文獻
1、韓安榮.通用變頻器及其應(yīng)用(第2版)[m].北京:機械工業(yè)出版社,
2、劉文兵(1981—)男從事過變頻器的應(yīng)用工作,現(xiàn)在臺州富凌機電制造有限公司,從事變頻器的設(shè)計與制造。
鳴謝
在論文完成之際,我真心地感謝在設(shè)計之中給予我?guī)椭能餮育埨蠋熀透魑煌拢刮胰缙谕瓿僧厴I(yè)論文,并使我終生受益。
在論文的完成過程中,系里的各位老師對我?guī)椭艽蟆T诖松畋碇x意!其他的同學(xué)也給予我許多關(guān)心和幫助,真誠地感謝他們。
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