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畢 業(yè) 設(shè) 計(jì)(論 文)
題目 實(shí)用微型客車設(shè)計(jì)—車架、制動系設(shè)計(jì)
畢業(yè)設(shè)計(jì)(論文)開題報(bào)告
(學(xué)生填表)
院系:車輛與動力工程學(xué)院
課題名稱
實(shí)用微型客車設(shè)計(jì)------------車架設(shè)計(jì)、制動系統(tǒng)設(shè)計(jì)
學(xué)生姓名
專業(yè)班級
課題類型
指導(dǎo)教師
職稱
課題來源
1. 設(shè)計(jì)(或研究)的依據(jù)與意義
近年來,我國客車市場相繼出現(xiàn)了高速增長、平緩調(diào)整、全面回升的發(fā)展景象:2003-2004年高速發(fā)展;2005年,隨著國家宏觀調(diào)控政策的全面施行,客車市場受到一定的抑制,銷量下滑,2007年國民經(jīng)濟(jì)穩(wěn)定快速發(fā)展,汽車行業(yè)蓬勃向上,汽車市場也走出了2005年的低迷狀態(tài),表現(xiàn)出良好的回升勢頭。,
當(dāng)然,隨著汽車技術(shù)的進(jìn)步和汽車行駛速度的提高,車架及車輛制動系統(tǒng)在車輛的安全方面占著重要的地位,車架作為汽車的承載基體,為貨車,中型及以下的客車,中高級轎車所采用;支撐著發(fā)動機(jī),離合器,變速器,轉(zhuǎn)向器,非承載式車身和貨箱等所有簧上質(zhì)量的有關(guān)機(jī)件,承受著傳給它的各種力和力矩。本設(shè)計(jì)采用邊梁式車架。要保證微型客車的良性發(fā)展必須采用低成本戰(zhàn)略。采用傳統(tǒng)技術(shù),以低的投入實(shí)現(xiàn)高的效益的增長,發(fā)展廉價(jià)的中低檔車,以適應(yīng)市場的需求,本設(shè)計(jì)采用液力制動器,由于降低成本,采用人力制動系統(tǒng),行車制動系統(tǒng)采用液力式,駐車制動采用機(jī)械式。在制動傳動機(jī)構(gòu)方面,為適應(yīng)各國和各地區(qū)制動法規(guī)的要求,制動管路必須采用雙回路傳能型式。
為保證汽車行駛的安全性,進(jìn)行車架和制動系的設(shè)計(jì)是很有必要的。
2. 國內(nèi)外同類設(shè)計(jì)(或同類研究)的概況綜述
車架有邊梁式,鋼管式等多種形式,目前國內(nèi)外采用最多的是邊梁式,而汽車制動器的種類很多,形式多樣。伴隨著汽車的研究開發(fā),汽車動力系統(tǒng)發(fā)生了很大的改變,出現(xiàn)了很多新的結(jié)構(gòu)型式和功能形式。新型動力系統(tǒng)的出現(xiàn)也要求制動系統(tǒng)結(jié)構(gòu)形式和功能形式發(fā)生相應(yīng)的改變。
(1)供能裝置的發(fā)展
氣壓制動是發(fā)展最早的一種動力制動系統(tǒng)。液壓制動是目前得到廣泛應(yīng)用的一種制動系統(tǒng),技術(shù)已經(jīng)非常成熟。目前正在發(fā)展的電液復(fù)合制動以及電子制動中使用了電機(jī)作為制動能源,人力踩制動踏板作為控制來源。
(2)控制裝置的發(fā)展
隨著清潔能源汽車和電動汽車的研究應(yīng)用,以及電子技術(shù)在汽車上面的廣泛應(yīng)用,制動系統(tǒng)的控制裝置也出現(xiàn)了電子化的趨勢,其中電制動完全改變了制動系統(tǒng)的控制和管理,會使汽車制動系統(tǒng)發(fā)生革命性的變化,它采用電子控制,可以更加準(zhǔn)確、更高效率地實(shí)現(xiàn)制動。
(3)傳動裝置的發(fā)展
電子制動是利用制動電機(jī)產(chǎn)生制動力直接作用到制動器,它的控制信號來自控制單元,用信號線傳遞制動信號和制動力信息。
(4)制動器的發(fā)展
目前汽車制動器基本都是摩擦式制動器,由于盤式制動器熱和水穩(wěn)定性以及抗衰減性能較鼓式制動器好,可靠性和安全性也好,而得到廣泛應(yīng)用。普遍應(yīng)用的液壓制動現(xiàn)在已經(jīng)是非常成熟的技術(shù),隨著人們對制動性能要求的提高,防抱死制動系統(tǒng)、驅(qū)動防滑轉(zhuǎn)控制系統(tǒng)、電子穩(wěn)定性控制程序、主動避撞技術(shù)等功能逐漸融人到制動系統(tǒng)中,需要在制動系統(tǒng)上添加很多附加裝置來實(shí)現(xiàn)這些功能,使得制動系統(tǒng)結(jié)構(gòu)復(fù)雜化,增加了液壓回路泄漏的可能以及裝配、維修的難度,制動系統(tǒng)要求結(jié)構(gòu)更加簡潔,功能更加全面和可靠,制動系統(tǒng)的管理也成為必須要面對的問題,電子技術(shù)的應(yīng)用是大勢所趨。
3. 課題設(shè)計(jì)(或研究)的內(nèi)容
微型客車的基本參數(shù)為:發(fā)動機(jī)選用JL462Q,最高車速為95km/h,最小轉(zhuǎn)彎半徑≤4.5m,乘員人數(shù)6-8人,檔位數(shù)4+1。
參照長安牌SC6331A微型客車的整體布局參數(shù)(網(wǎng)上可以查到)、亞洲牌微型客車底盤實(shí)物(車輛實(shí)驗(yàn)室整車陳列室內(nèi))、長劍牌微型轎車實(shí)物(車輛實(shí)驗(yàn)室整車拆裝室內(nèi))和有關(guān)的其他車型(查閱有關(guān)資料),完成微型客車的車架、制動系設(shè)計(jì)任務(wù)。
4. 設(shè)計(jì)(或研究)方法
(1)進(jìn)行制動系統(tǒng)的總成設(shè)計(jì)
1,制動系的結(jié)構(gòu)類型及選擇
2,制動系參數(shù)選擇及計(jì)算
3,駐車制動和應(yīng)急制動的計(jì)算
4,制動器主要零件的結(jié)構(gòu)設(shè)計(jì)
5,制動驅(qū)動機(jī)構(gòu)的選擇及計(jì)算
(2)進(jìn)行車架的總成設(shè)計(jì)
5. 實(shí)施計(jì)劃
(5-6周) 進(jìn)行調(diào)研,搜集,分析資料,完成開題報(bào)告。
(6-7周) 全組集體討論,確定總體方案。每個(gè)學(xué)生確定自己的設(shè)計(jì)內(nèi)容與繪圖數(shù)量。
(8-9周) 整理本設(shè)計(jì)內(nèi)容相關(guān)的數(shù)據(jù)資料,進(jìn)行必要的理論計(jì)算,擬說明書 草稿,搜集相關(guān)外文資料并翻譯。
(10-11周) 完成總圖設(shè)計(jì)。
(12-13周) 完成零部件圖設(shè)計(jì),并完成機(jī)繪圖。
(14-15周) 按要求整理,編寫設(shè)計(jì)說明書。
(16-17周) 審閱,評閱設(shè)計(jì)資料,答辯,評定成績。
指導(dǎo)教師意見
指導(dǎo)教師簽字: 年 月 日
研究所(教研室)意見
研究所所長(教研室主任)簽字: 年 月 日
車輛與動力工程學(xué)院畢業(yè)設(shè)計(jì)說明書
實(shí)用微型客車設(shè)計(jì)—車架、制動系設(shè)計(jì)
摘要
汽車制動系是保證汽車及駕駛者生命安全的重要部分,制動系是使行進(jìn)中的汽車減慢速度或者停止運(yùn)動。
這次我的畢業(yè)設(shè)計(jì)題目是微型客車設(shè)計(jì)---車架和制動系設(shè)計(jì)。在第二章我主要介紹了制動系的概況和設(shè)計(jì)時(shí)應(yīng)滿足的基本要求。第三章主要是制動系的類型及最后確定的方案,其中列出了幾種可供選擇的類型并進(jìn)行了分析、比較最后確定的方案如下:行車制動器:前盤后鼓,盤式制動器為通風(fēng)型浮動鉗盤式制動器,鼓式制動器為領(lǐng)從蹄式制動器。第四章主要介紹了制動系主要結(jié)構(gòu)參數(shù)的選擇并進(jìn)行了簡單的計(jì)算,是本設(shè)計(jì)說明書的核心部分,其中包括鼓式和盤式制動器主要結(jié)構(gòu)參數(shù)的選擇,例如:制動鼓內(nèi)徑、摩擦襯片寬度和包角、摩擦襯片起始角、制動盤直徑和厚度等,同時(shí)對制動力和制動力矩分配系數(shù)進(jìn)行了計(jì)算。第五章主要對駐車制動和應(yīng)急制動進(jìn)行了簡單的計(jì)算。第六章介紹的是制動器主要零件的結(jié)構(gòu)設(shè)計(jì),如制動鼓、制動蹄、制動底板和制動輪缸等。第七章包括制動驅(qū)動機(jī)構(gòu)的選擇和計(jì)算,制動管路的分路系統(tǒng)和液壓驅(qū)動機(jī)構(gòu)的設(shè)計(jì)和計(jì)算。第八章列出了車架的幾種類型,分析比較之后,最后確定選用前窄后寬的邊梁式車架,并且在這一章中對車架的彎曲強(qiáng)度進(jìn)行了計(jì)算,對車架的剛度進(jìn)行了校核。通過這一系列的分析、計(jì)算、校核等,這套設(shè)計(jì)方案是可行的。 THE DESIGN OF PRARECTICAL MINIATURE
CAR’S —THE DESIGN OF FRAME AND BRAKE SYSTEM
ABSTRACT
The brake system is an important part to keep safety for automobile, the purpose of the braking system is to slow down and stop the moving automobile.
My topic in this graduation design is the design of frame and the brake system.In second chapter we mainly introduced something about the brake system and some requests which the brake system should satisfied. The third chapter mainly introduced the type of the brake system and finally determined the plan, in this chapter we listed several kinds to choose, at last we determined the plan through analysis and compare with as follows: In traveling brake system, the former wheels are disc brake and the rear wheels are drum brake. The disc brake for ventilating fluctuation pliers disc brake, and the drum type brake for collar from foot brake. The fourth chapter mainly introduced the main design parameter’s choice and has carried on the simple computation, and this chapter is the most important part. Including drum type and disc brake main design parameter choice, For example: The brake drum inside diameter, the width, the angle and the outset angle, the diameter and thickness of the brake plate and so on, simultaneously have carried on the computation to the brake strength and the braking moment distribution coefficient. The fifth chapter mainly said the vehicle to brake on stopping and momentary through simple computation. The brake major parts structural design, like brake drum, brake shield plate or disc and brake wheel cylinder and so on were designed in the sixth chapter. Seventh chapter including applies the brake the driving mechanism choice and the computation, the brake line by-pass system and the hydraulic pressure driving mechanism design and the computation. Eighth chapter has listed the frame several kind of types, after the analysis comparison, after finally front determined selects the narrow width side beam plate frame, And has carried on the computation in this chapter to the frame bending strength, has carried on the examination to the frame rigidity. Through this a series of analysis, computation, examination and so on, this set of design proposal is feasible
KEY WORDS: brake system, drum brake, disk brake, frame
目 錄
第一章 前言…………………………………………………………......1
§1.1 汽車的誕生與世界汽車工業(yè)的發(fā)展……..…….……….…....1
§1.2 我國汽車工業(yè)的發(fā)展………….………….……………..…....2
第二章 制動系概況………………………………………………..…....4
第三章 制動系的結(jié)構(gòu)類型及選擇………………………………..…....6
§3.1 后輪鼓式制動器的選擇…………………………………........6
§3.2 前輪盤式制動器的選擇…………………………………...….9
§3.3 盤式制動器的優(yōu)缺點(diǎn)及確定的方案………………………..10
第四章 制動系參數(shù)選擇及計(jì)算…………………………………........11
§4.1 制動器主要結(jié)構(gòu)參數(shù)的選擇………………………….….....11
§4.2 制動力與制動力矩分配系數(shù)………………………………..14
第五章 駐車制動和應(yīng)急制動計(jì)算…………………………………....18
§5.1 駐車制動計(jì)算………………………………………………..18
§5.2 應(yīng)急制動計(jì)算…………………………………………..…....19
第六章 制動器主要零件的結(jié)構(gòu)設(shè)計(jì)………………………………....20
第七章 制動驅(qū)動機(jī)構(gòu)的選擇及計(jì)算………………………………....22
第八章 車架…………………………………………………………....26
第九章 總結(jié)……………………………………………………….…...33
參考文獻(xiàn)………………………………………………………….….....34
致謝………………………………………………………………...…...35
III
Brake System Service and Maintenance
The types of trouble that may develop in drum-type hydraulic braking systems include the following.
(1) Brake pedal goes to floorboard. When this happens, it means that there is no pedal reserve, since full pedal movement does not provide adequate braking. This would be a very unlikely situation with a dual-brake system. One section might fail (front or rear) but it would be rare for both to fail at the same time. If this happens, chances are the driver has been driving for some time with one section out .
(2) One brake drags. This means that the brake shoes are not moving away from the brake drum when the brakes are released.
(3) All brake drag. When all brakes drag, it may be that the brake pedal does not have sufficient play, so that the piston in the master cylinder does not fully retract.
(4) Car pulls to one side. If the car pulls to one side when the brakes are applied, this means that more braking pressure is being applied to one side than to the other.
(5) Soft, or spongy, pedal. If the pedal action is soft, or spongy, the chances are that there I is air in the system, although out-of adjustment brake shoes could cause this.
(6) Poor braking action requiring excessive pedal pressure. If the brake lining is soaked with oil or brake fluid, they will not hold well, and excessive pedal pressure is required for braking action. Improper brake-shoe adjustment or the use of the wrong brake lining could cause the same trouble.
(7) Brakes too sensitive or grab. When the brakes are too sensitive and brake hard or grab with slight brake –pedal pressure, it may be that the linings have become greasy , that the brake shoes are out of adjustment , that the wrong lining is being used and that drums are scored or rough .
(8) Noisy brakes. Brakes will become noisy if the brake linings wear so much that rivets come into contact with the brake drum, if the shoes become warped so that pressure on the drum is not uniform ,if shoe rivets become loose so that they contact the drum , or if the drum becomes rough or worn .
(9)Air in system. If air gets into the hydraulic system, poor braking and a spongy pedal will result. It is possible accidentally to plug the vent (by wrench action ) when the filler plug is removed .
(10) Loss of brake fluid. Brake fluid can be lost if the master cylinder leaks, if the wheel cylinder leaks, if the wheel cylinder leaks, if the line connections are loose, or if the line is damaged.
(11) Warning light comes on when braking (dual system). This is a signal that one of the two braking systems has failed. Both systems (rear and front) should be checked so that the trouble can be found and eliminated. It is dangerous to drive with this condition, even though braking can be achieved, because only half the wheels are being broken.
Many of the troubles on the disk in the disk type of brake system are similar to those that may be found in the drum type.
Whenever you encounter a complaint of faulty braking action, always try to analyze it and determine its cause. Sometimes, all that is necessary (in earlier drum-type brakes) is a minor brake with the self-adjuster; the brakes automatically adjust themselves to compensate for lining wear. Other brake services include addition of brake fluid, bleeding the hydraulic system to remove air, repair or replacement of master cylinder and wheel cylinders, replacement of master cylinder and wheel cylinders, replacement of brake linings, and refinishing of brake drums.
Tire service and maintenance includes periodic inflation to make sure that the tire is kept at the proper pressure, periodic tire inspection so that small damages can be detected and repaired before they develop into major defects, and tire removal, repair, and replacement.
Incorrect tire inflation can cause many types of steering and braking difficulty. Low pressure will cause hard steering, front wheel shimmy, steering kickback, and tire squeal on turns. Uneven tire pressure will tend to make the car pull to one side. For these reason, it is very important to maintain proper pressure in the tires. There are a few points you should remember when inflating tires:
(1) Don’t inflate a tire when it is hot, as, for instance, after hard driving on the highway.
(2) Always replace the cap (where used) after checking air pressure or inflating a tire.
The removal and replacement of tires are not difficult on smaller vehicles, but on large, heavy-duty applications special tools are required to remove and handle them. Air must be released from the center of the rim. A tire tool or flat stock can be used to pry one part of the bead up over the rim flange (start near the valve stem). Care must be exercised to avoid damaging the tire bead or inner tube. After the bead is started over the rim flange with the tool, the remainder of the bead can be worked out over the flange with the hands. The other bead of the tire is removed from over the same side of the rim flange in a similar manner.
In tire shops where many tires are being changed daily, special tire-changing machines are used. In these, the wheel is put into place and air pressure is used to force the tire bead away from the rim. This machine will remove a tire from a wheel rim in a few seconds. Further, it can be used to quickly install a tire on the rim.
The following cautions should be carefully observed in tire service and maintenance work:
(1) On tubeless tires, do not use tire irons to force the beads away from the rim flanges; this could damage the rim seals on the beads and cause an air leak. Instead, use a bead breaker tool.
(2) If a tire has been deflated, never inflate it while the car weight is on the tire. Always jack up the car before inflating the tire so that the tube can distribute itself around the tire evenly. If this is not done, some parts of the tube will be stretched more than other parts, and this puts a strain on the tube that might cause it to blow out.
A number of repairs can be made on tires and tubes, ranging from the patching of nail holes, punctures, or cuts to vulcanizing new tread material to the tire casing. This latter operation is known as recapping, since a new cap, or tread, is placed on the tire. Repair procedures vary according to whether the tire is or is not of the tubeless type.
With the tube type, puncture repair requires removal of the tire so that the puncture in the tube can be attached. This is done with a special kit. Patches require curing, or vulcanizing, at a temperature of around 150℃.
Tubeless-tire punctures can usually be repaired without taking the tire off the rim. One method uses a rubber plug, which is inserted, into the puncture hole along with special cement. After the cement dries and the plug is trimmed flush with the tread, the repair is complete.
Applying a patch on the inside can repair larger holes and cuts in tires. In addition, when treads have worn down, new treads can be vulcanized onto the casing provided the casing is in good condition.
Tires have two functions. First, they interpose a cushion between the road and the car wheels to absorb shocks resulting from irregularities in the road. The tires flex, or give, as bumps are encountered, thus reducing the shock effect to the passengers in the car. Second, the tires provide frictional contact between the wheels and the road so that good traction is secured. This permits the transmitting of power through the tires to the road for rapid accelerating, combats the tendency of the car to skid on turns, and allows quick stops when the brakes are applied.
Tires are of two basic types, solid and pneumatic (air filled). Solid tires have very limited usage, being confined largely to specialized industrial applications. Pneumatic tires are of two types, those using an inner tube and the tubeless type. The amount of air pressure used depends on the type of tire and operation. Passenger-car tires are inflated to about 275 to 413 KPa. Air is introduced into the tire (or inner tube) through a valve that opens when the chuck on the air hoses if applied. On the tire with an inner tube, the valve is mounted on the tube. On the tubeless tire, the valve is mounted on the wheel rim.
外文資料翻譯
翻 譯
Fig.3.5 裝備有獨(dú)立懸掛時(shí),當(dāng)車輪行駛在顛簸道路作上下的反復(fù)運(yùn)動時(shí),可以使軌跡改變,是輪胎在微小的α角度范圍內(nèi)轉(zhuǎn)動。尤其是顛簸發(fā)生在一側(cè)時(shí)可以影響側(cè)向力、方向的穩(wěn)定性和滾動阻力。
Fig.3.6 對路面的側(cè)向力Fy.w是由于軌跡的改變而產(chǎn)生的。圖中所示的是型號為175/65R 14 82 H的輪胎在充氣至1.9巴、負(fù)荷為380千克及時(shí)速80km時(shí)輪距的變化與橫向力的關(guān)系。
Fig.3.7 由畫出的輪胎軌跡的改變和外連接桿的軌跡在雙叉骨懸掛上的U點(diǎn)交匯可以進(jìn)行計(jì)算,如Fig.3.8中的圖形所示。
Fig.3.8 為方便計(jì)算出軌跡的改變的圖形可以用于雙叉骨懸掛和縱連接軸系統(tǒng)。
正如水平線先前表明的那樣,在圖中沿著C、D點(diǎn)周圍的弧直到顛簸的最高點(diǎn)W上下行程為S1和S2。然后用鉛筆一步步記錄下點(diǎn)W、U的運(yùn)動軌跡。由這種方法而畫出的連接各點(diǎn)的線可以顯示軌跡的改變和連接桿的運(yùn)動,但沒有考慮懸掛控制臂所產(chǎn)生的彈力。(參見Fig.3.18)
若是在縱向臂狀控制軸情況下,必須在D點(diǎn)的下端畫一個(gè)弧,同時(shí)必須在旋轉(zhuǎn)的懸掛控制臂狀軸上畫一條過點(diǎn)1的垂線。同時(shí),一個(gè)如Fig.3.8中的模形沿著弧和垂線運(yùn)動以決定輪距的變化。
麥克佛森支撐桿在輪槽里有個(gè)最高點(diǎn)E(Fig1.7),當(dāng)車輪行駛在顛簸道路上時(shí)較低的圓形連接點(diǎn)2 到C點(diǎn)的距離變短,當(dāng)輪胎反彈時(shí)則變長。這個(gè)模型必須考慮像這種長度的變化,它在支撐減震器中線EE方向上有個(gè)槽。經(jīng)常且必須出現(xiàn)在模型中的點(diǎn)2在D點(diǎn)周圍的弧上運(yùn)動,同時(shí)開口向上越過點(diǎn)C。應(yīng)該在畫板上做個(gè)小標(biāo)記。
若在P點(diǎn)周圍畫弧,那么雙重連接擺動軸軌跡的改變可以容易的畫出。Figure 3.12同時(shí)說明了這個(gè)和降低車尾的好處。例如,完成一較小的弧度角和較高的側(cè)面弧形力。
在全獨(dú)立懸掛情況下,P的位置決定了輪距的瞬間改變量±⊿b。如果P處在水平面上,當(dāng)雙叉骨懸掛的懸掛控制臂的長度固定不變使`該點(diǎn)在車輪受擠壓或反彈時(shí)從一邊到另一邊作水平運(yùn)動時(shí)(Fig.3.13),輪距的改變可以完全得到避免。這可以用計(jì)算、畫圖或者考慮任何彈力的模型來表明車輪運(yùn)動距離s=±70mm之間(Fig.3.18)。
Fig.3.9確定縱向連接軸軌跡的改變和外連接桿交匯于U的軌跡在Fig.3.8中表示。對于此懸掛系統(tǒng)的說明參見參考文獻(xiàn)[2]中的Fig3.32、3.157 和9.4 Fig.3.10用畫圖的方法計(jì)算麥克佛森減震器輪距的改變,減振器中心線E方向必須有個(gè)槽。
在研究兩輪一軸的汽車時(shí),輪距的改變量可以看作一個(gè)由兩平行車輪單側(cè)改變時(shí)引起車輪往復(fù)運(yùn)動距離的方程。車輪的平行運(yùn)行是必要的,因?yàn)樵谲囕嗩嶔ぴ谧罡唿c(diǎn)或最低點(diǎn)時(shí),運(yùn)動軌跡的微小改變會使測量數(shù)據(jù)失真。
用圖形表示,車輪的改變應(yīng)標(biāo)在y軸上,
Fig.3.11 Fig.3.10顯示的是麥克佛森支撐桿減震器的單輪軌跡改變和U 點(diǎn)的變化。C點(diǎn)是麥克佛森支撐桿上部的槽的中心;這個(gè)點(diǎn)在Figs 1.8和 3.139中被標(biāo)為E。
Fig.3.12降低懸掛的控制臂支點(diǎn)P可以減少雙擺動軸軌跡的改變,使車身的重心從RO1降到RO2且需要一個(gè)更寬的輪距。若車上有兩名乘客時(shí),輪胎上會產(chǎn)生負(fù)曲面效應(yīng),盡管這樣做的優(yōu)點(diǎn)是吸收更多的側(cè)面力,但缺點(diǎn)是不利于減少顛簸。
Fig.3.13 要使輪距不改變就要求車的滾動中心位于水平面上。同時(shí)還會取得較好的運(yùn)動性能。
要與軸的運(yùn)動方向一致,即上彈為正下彈為負(fù)。原點(diǎn)應(yīng)與設(shè)計(jì)重量一致,換句話說有兩個(gè)或三個(gè)體重68千克的人的重量??哲囀遣环蠈?shí)際的。
兩個(gè)輪子軌跡的改變量⊿b標(biāo)在x軸,向右表示增加,向左表示減少。需要指出的是目前軌跡處在原點(diǎn)位置。輪距在滿載或空車時(shí)的改變量⊿b可以由彈簧的彈性來界定。彈簧在彈性范圍內(nèi)從原點(diǎn)運(yùn)動距離⊿S1,從而得出一個(gè)⊿b關(guān)于⊿s的方程的曲線。
圖5.9中顯示的是一輛前輪驅(qū)動汽車的前輪彈簧的情況,用115毫米減掉80毫米就得到了反彈距離,到原點(diǎn)的距離⊿s=35mm。汽車在允許的負(fù)重范圍內(nèi),在顛簸路況行駛距離為⊿s1=92-50=42毫米。路線被顯示在Fig.3.14中;⊿s1減⊿b1=+4mm, ⊿s2-⊿b2=-8mm.在規(guī)定重量下的軌跡為:bf=1286mm.
Fig.3.14獨(dú)立懸掛系統(tǒng)中的輪距b取決于負(fù)荷。
圖3.7、3.15 和3.18 顯示的是雙叉骨懸掛系統(tǒng)和麥克佛森支撐桿系統(tǒng)輪距的改變,圖中顯而易見的是較低的改變值。正如在3.4.1章細(xì)節(jié)描述的那樣,曲線的形狀取決于重心的高低。在三座位的車型中,Rof在地面以上,當(dāng)滿載時(shí)會靈敏的下降。
若汽車制造商設(shè)計(jì)較低的重心作為標(biāo)準(zhǔn),那么重心隨后再下降則會走向反面。Rof在地面以下時(shí),方向的穩(wěn)定性會受損,尤其是寬輪胎時(shí)。
在雙叉骨懸掛系統(tǒng)中,彈簧位于控制臂的上方或下方,無論哪種情況,猛然一下的提升會使輪距變化曲線發(fā)生輕微變動。同時(shí)引起重心的輕微變化(Fig3.18)。曲線的形狀取決于裝有彈簧的汽車上的測量量。在任何情況下曲線的變化表明了正確的高度。
典型的后輪懸掛輪距的變化……..
Fig.3.15 奧迪A6、歐寶阿斯特拉、和本田雅閣的前輪距的變化曲線。其中本田是唯一裝備雙叉骨懸掛的乘用車;行使方面的優(yōu)勢顯而易見。
汽車重心高見下表,單位是mm
制動系的保養(yǎng)和維修
鼓式液壓制動系統(tǒng)所發(fā)生的故障有以下幾種類型:
(1)制動踏板移至汽車底板:發(fā)生這種情況時(shí),由于整個(gè)踏板位移,不能提供滿意的制動,意味著沒有踏板行程余量。這對于裝有雙管路的制動系統(tǒng)來說,是極不可能發(fā)生的事,(前部或后部的)一套管路可能損壞,但兩套管路同時(shí)損壞是極少見的。如果發(fā)生這種情況,駕駛員很可能在一套管路失靈的情況下已經(jīng)行駛了一段時(shí)間。
(2)一邊制動器咬死:這意味著解除制動時(shí),制動蹄片不能從制動鼓上分開。
(3)全部制動器咬死:如果所有的制動器都咬死,可能是由于踏板未能充分地起作用,致使制動總泵中的活塞不能完全返回。
(4)汽車跑偏:如果制動時(shí)發(fā)生汽車跑偏,即意味著提供的制動力一邊比另一邊要大。
(5)制動踏板發(fā)軟或如踏在海綿上:如果踩踏板時(shí),感覺發(fā)軟或像踏在海綿上,可能是系統(tǒng)中進(jìn)了空氣。不過,調(diào)整不當(dāng)?shù)闹苿犹闫矔l(fā)生這種現(xiàn)象。
(6)制動作用不佳,需加大踏板壓力:如果制動襯片被油或制動液浸漬,就會失去作用。調(diào)整不當(dāng)?shù)闹苿右r片或是使用的制動襯片有毛病均會引起同樣的問題。
(7)制動器反應(yīng)過于靈敏或猛烈:制動器過于靈敏,或輕輕踏下制動踏板,即猛然剎車,可能是襯片被油浸漬、制動片脫出、使用的是有毛病的襯片、以及制動鼓工作面擦傷或凹凸不平所至。
(8)制動噪音:制動器襯片磨損嚴(yán)重,致使鉚釘直接與制動鼓接觸;制動蹄翹曲,使其直接觸及制動鼓上的壓力不均;制動蹄上的鉚釘松動,使其直接觸及制動鼓;制動鼓凹凸不平或磨損;這些情況都會使制動器產(chǎn)生噪音。
(9)空氣進(jìn)入系統(tǒng):如果空氣進(jìn)入系統(tǒng),就會產(chǎn)生制動不良和踩下踏板不能產(chǎn)生制動力。也可能是拆卸加注口螺栓時(shí),(用扳手不當(dāng))偶然堵住排氣口所至。
(10)制動液流失:如果制動總泵滲漏,連接管松動或破損,均會使制動液流失。
(11)制動時(shí)(雙管路系統(tǒng))警示燈亮:這是兩路制動系統(tǒng)之一發(fā)生故障的信號,檢查(前后)兩個(gè)系統(tǒng)以便發(fā)現(xiàn)并排除故障。帶著這類故障行車是非常危險(xiǎn)的,即使還可實(shí)現(xiàn)制動,也僅僅是因?yàn)榘霐?shù)車輪還能夠?qū)崿F(xiàn)制動。
在盤式制動系統(tǒng)中制動盤與鼓式制動系統(tǒng)所發(fā)生的大部分故障相類似。
無論何時(shí)制動出故障,總要盡力去分析并確定其原因。有時(shí),所要做的僅僅是對制動器稍做調(diào)整,以減少襯片磨損。目前帶有自動調(diào)校裝置的制動器,可自動調(diào)整以減少襯片的磨損。制動器的其它維修工作還包括:添加制動液,排出液壓系統(tǒng)的空氣,修理或更換制動總泵和分泵,更換制動襯片和整修制動鼓工作表面。
輪胎的維修包括定期充氣,保證輪胎氣壓正常;定期檢查輪胎可以及時(shí)發(fā)現(xiàn)和修理較小的損壞,以免發(fā)展為大故障。維修還包括拆卸、修理和更換輪胎。
不適當(dāng)?shù)妮喬コ錃鈺鸲喾N類型的轉(zhuǎn)向和制動障礙。壓力低會使轉(zhuǎn)向沉重,前輪擺振,轉(zhuǎn)向回跳以及轉(zhuǎn)動時(shí)輪胎發(fā)出噪音;各輪胎壓力不均勻?qū)⒃黾悠嚺芷膬A向。由于這些原因,保持輪胎的正常氣壓是非常重要的。在給輪胎充氣時(shí),應(yīng)注意以下幾點(diǎn):
(1)輪胎在熱狀態(tài)下時(shí)不要充氣。例如,在高速公路上長途行駛之后。
(2)檢查氣壓或充氣后,應(yīng)該把輪胎氣門蓋放回原處。
在小型車輛上更換和拆卸輪胎并不困難。但是在重型車輛上,需使用專門的工具進(jìn)行拆卸和操作。開始拆卸輪胎時(shí),首先應(yīng)從內(nèi)胎中排除空氣,輪胎的輪緣一側(cè)應(yīng)推向輪輞的中心,可用輪胎工具或扁平的翹棒把輪緣的一端從輪輞輞圈上翹起。要當(dāng)心不要損壞輪胎輪緣或內(nèi)胎。當(dāng)用工具使輪緣從輪輞輞圈中脫出后,輪緣的剩余部分可用手將其扒過輞圈。再用類似的方法拆卸另一邊的輪緣。
輪胎商店每天都更換很多輪胎,所使用的是專門的輪胎更換設(shè)備。使用這種設(shè)備時(shí),只要把輪胎安裝到位,氣壓裝置就把輪緣從輞圈中壓出,這種裝置在幾秒鐘的時(shí)間內(nèi)即可將輪胎從輞圈中拆下來。此外,還可以很快地把輪胎裝入輞圈內(nèi)。維修輪胎時(shí),應(yīng)該認(rèn)真遵守下列注意事項(xiàng):
(1)維修無內(nèi)胎輪胎時(shí),不能使用撬棒強(qiáng)行把輪緣從輪輞上拆卸下來。這樣容易損壞輪緣上的輪輞止口,并造成空氣泄漏。應(yīng)該使用專門工具。
(2)如果輪胎已經(jīng)沒氣了,不要在汽車負(fù)載時(shí)給輪胎充氣。在充氣前,通常應(yīng)該用千斤頂頂起汽車,使內(nèi)胎能夠均勻地沿著輪胎的每一處擴(kuò)充起來。如果不這樣做,內(nèi)胎的某一部分就比其它部分膨脹的更多,這一部分內(nèi)胎可能就會因拉的過緊而引起爆裂。
輪胎和內(nèi)胎的維修范圍為修補(bǔ)釘子劃破的口子、破洞、或切口,以及用新的胎冠材料熱補(bǔ)外胎。后者就是大家都知道的輪胎翻新,因?yàn)槭窃谳喬ド霞恿艘粚犹ゼy。維修過程要依據(jù)是無內(nèi)胎輪胎,還是有內(nèi)胎輪胎而定。
修補(bǔ)內(nèi)胎的破口,需拆下輪胎,粘補(bǔ)內(nèi)胎破口。需用專門工具。硫化或熱補(bǔ)的溫度大約為150℃。
通常修補(bǔ)無內(nèi)胎輪胎的破口時(shí),無需將輪胎從輪輞上取下。一種方法是橡皮塞修整的與胎冠一樣高,修理工作就完成了。較大的輪胎破口和切口可用補(bǔ)胎片在內(nèi)側(cè)進(jìn)行修補(bǔ)。另外,輪胎磨損后,可在外胎上熱補(bǔ)新的胎面,使外胎翻舊如新。
輪胎有兩種功能。首先,輪胎吸收路面的沖擊。輪胎具有可彎性,也就是彈性。在遇到顛簸路面時(shí),可以減少對車上乘員的沖擊。其次,輪胎提供了車輪與路面的摩擦接觸,保證汽車穩(wěn)定行駛。輪胎的這些功能可以使汽車在突然加速時(shí)傳遞驅(qū)動力,在汽車轉(zhuǎn)彎時(shí)避免打滑,在汽車剎車時(shí)快速停車。
輪胎有兩種基本形式,實(shí)心輪胎和充氣輪胎。實(shí)心輪胎的使用范圍極為有限,僅在某些特定的工業(yè)方面應(yīng)用。充氣輪胎又分為有內(nèi)胎式和無內(nèi)胎式兩種。輪胎的充氣量取決于輪胎的種類和用途。載人轎車的輪胎充氣量為275千帕到413千帕。把導(dǎo)入空氣的橡膠軟管夾在氣門上,空氣就被打入輪胎(或內(nèi)胎)。
有內(nèi)胎式輪胎氣門是直接做在內(nèi)胎上的,無內(nèi)胎式輪胎的氣門安裝在輪轂上。
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