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THE FILE TRANSMISSION GEAR SELECTION
OF THE BASIC PARAMETERS
1, Reasonable choice of module:
Modulus is an important gear basic parameters, the greater the modulus, the greater the tooth thickness, the bending strength of gear is also greater, and its greater carrying capacity. Instead modulus smaller tooth thickness will be thinner, the bending strength of gear will be smaller. The low profile of the gear, due to the low rotational speed, torque, and gear of the relatively large bending stress, so need to choose a larger module in order to ensure its strength. And high-speed file gear, due to the high-speed, torque small gear bending stress is relatively small, so to ensure that the bending strength of gear under the premise of the general selection of the smaller module, so that gear teeth can be increased in order to obtain larger degree of overlap, so as to achieve the purpose of reducing noise.
In a modern gearbox design, the file selection module gear is different. For example, a transmission gear of a file to the five-gear gear module are: 3.5; 3; 2.75; 2.5; 2; to change over the past modulus or modulus of the same can not be the situation of Latin America.
2, a reasonable selection of pressure angle:
When a gear module and set the number of teeth, the gear diameter is determined, and the gear tooth involute base circle depends on the size, the size of the base circle and under pressure angle. For the same pitch circle of gear, if its pitch circle a different pressure angle, base circle is different. When the greater the pressure angle, the base circle diameter of the smaller, more curved involute, tooth root of the tooth will thicken, increase the tooth surface radius of curvature, which can increase the tooth bending strength and contact strength. When reducing the pressure angle, the base will become larger diameter, involute tooth profile will change some of the straight, thinning of the tooth root, tooth smaller radius of curvature, making the tooth bending strength and contact intensity will decrease, but decrease with the pressure angle, to increase the contact ratio gears, reducing the stiffness of the tooth, and can reduce the entry and exit load at the time of engagement, all of which are beneficial to reduce noise. There-fore, low profile gear, often larger pressure angle in order to meet the strength requirements; and regular use of high-speed file smaller gear pressure angle in order to meet the requirements of its lower noise.
For example: a gear module 3, the number of teeth of 30, when the pressure angle of 17.5 degrees for the circular tooth thickness of the base to 5.341; when the pressure angle of 25 degrees, the tooth thickness of the base circle to 6.716; its base circle to increase the tooth thickness 25%, so increase the pressure angle to increase their flexural strength.
3, A reasonable selection of Helix Angle:
Compared with the straight gear, helical gear drive with a smooth, coincidence degree, the impact is small and the advantages of small noise. As a result of the present with synchronous transmission, and transmission will no longer be a direct mobile gear meshing with another gear, but with all the gears are meshing, so that'll bring convenience to the use of helical gear, so to bring the gearbox synchronizer Most of the use of helical gear.
Helical gear as a result of the characteristics of the entire tooth width decision not to enter the mesh at the same time all but one end of first gear into the mesh, with the drive gear along the tooth width direction mesh gradually until all the teeth have wide access to mesh, so the actual meshing helical gear spur the region than the large. When the tooth when a certain width, the contact ratio of helical gear with helix angle increases. Carrying capacity is also stronger, have better stability. In theory, the better helix angle, but the helix angle increases, the axial force will also increase, so that reduces the transmission efficiency.
In the modern design of the gearbox, in order to ensure smooth gear drive, low noise and less impact, all . Files for°gear should choose a larger helix angle, generally about 30 high-speed gear as a result of the higher speed, for a smooth, low impact, low noise, so the use of small modulus, large helical angle; and low-profile gear module using the larger, smaller helix angle.
4, The perspective of a reasonable modification is selected:
With good conditions for the lubrication of the hardened gear is generally believed that the main danger is in the cycle under alternating stress, the fatigue crack Dedendum gradual expansion of the tooth root fracture caused by the failure. Failure in the gear transmission is a part of this. In order to avoid a broken tooth, should be to maximize the tooth root bending strength, and the use is changed, and can achieve this objective. Under normal circumstances, the greater the coefficient, the smaller values tooth, tooth bending stress on the smaller, the higher the bending strength of teeth.
In the hardened gear, the tooth surface pitting failure is one of the reasons off. Increased engagement angle, can reduce the inter-tooth contact stress and maximum slip rates, can greatly increase the ability of anti-pitting. And increased engagement angle, it must have a gear shift is introduced, thereby enhancing contact strength of tooth surface can improve the flexural strength of tooth roots, so as to enhance the effect of the carrying capacity of gears. However, for helical gear drive, variable coefficient is too large, and will total tooth length of the contact line, but to reduce its carrying capacity. At the same time, the greater the coefficient, as a result of tooth to tip increases, the thickness of the tip will be smaller, which will affect the strength of the top teeth.
Therefore, in the design of a modern gearbox, the majority of all reasonable use of gear shift is the angle in order to maximize its advantages. Mainly in the following design criteria:
low profile for the gear pair, the driving gear of the coefficient should be larger than the passive gear shift coefficient, and pair of high-speed profile, the driving gear of the coefficient should be less than passive coefficient gear.
gear with the modification coefficient increased gradually stalls xiajiang. This is because low-grade zones as a result of low rotational speed, torque, and gear for high intensity, so the need to use more of the modification coefficient da.
The total of the gear profile shift coefficient is positive (of the anglel shift as amended), and increased with the stalls and gradually decreased. The smaller the total coefficient, a pair of pair of tooth root of the thickness of the total will be thin, tooth root becomes weak, the lower the bending strength, but decreased as a result of the stiffness of the tooth, easy to absorb shock and vibration, so can reduce the noise. And tooth contact ratio will increase, which bear a single tooth at the time of maximum load Dedendum recent focus distance, the reduced bending moment, which is equivalent to increase the strength of the tooth root, which as a result of thinning and weakened tooth root strength offset factor. Therefore, the greater the overall coefficient, the higher the strength of the tooth root, but the noise may increase. Thus high-speed gear to choose a smaller file of the total coefficient, and low-profile gear must be chosen larger coefficient
5, to improve tip high coefficient:
Top gear in the transmission of high quality factor, the impact of focusing on adaptation, in the main impact of helical gear contact ratio face. Coincidence degree by the end of the formula, we can see that when the number of teeth and meshing certain angle, the tooth tip is affected by tooth pressure angle coefficient of the top high impact factor the greater the high-tip, round tip the greater the pressure angle, contact ratio is The greater and ore stable drive. However, the high coefficient the greater the tip, the thickness of the top teth will become thin, thus affecting the strength tip. At the same time, at least not from the tooth root formula, the high coefficient the greater the tip, at least not the root will increase the number of gear, otherwise, they would have a root cutting. As a result, guarantees of non-root tip-cut and sufficient strength, increased tooth top high coefficient of coincidence degree for the increase is significant.
Top gear in the transmission of high quality factor, the impact of focusing on adaptation, in the main impact of helical gear contact ratio face. Coincidence degree by the end of the formula, we can see that when the number of teeth and meshing certain angle, the tooth tip is affected by tooth pressure angle coefficient of the top high impact factor the greater the high-tip, round tip the greater the pressure angle, contact ratio is The greater and more stable drive. However, the high coefficient the greater the tip, the thickness of the top teeth will become thin, thus affecting the strength tip. At the same time, at least not from the tooth root formula, the high coefficient the greater the tip, at least not the root will increase the number of gear, otherwise, they would have a root cutting. As a result, guarantees of non-root tip-cut and sufficient strength, increased tooth top high coeff-icient of coincidence degree for the increase is significant.
The above is from the module, pressure angle, helix angle, coefficient and a high coefficient of this addendum to an independent analysis of the five aspects of gear design trends. In fact between the various para-meters are inter-related, involved with each other, the choice of transmission parameters, it is necessary to take into account their strengths and weaknesses, but also consider the relationship between them, so in order to maximize their strengths and avoid weaknesses to improve transmission performance.
變速箱各檔齒輪基本參數(shù)的選擇
1、合理選用模數(shù)
模數(shù)是齒輪的一個(gè)重要基本參數(shù),模數(shù)越大,齒厚也就越大,齒輪的彎曲強(qiáng)度也越大,它的承載能力也就越大。反之模數(shù)越小,齒厚就會(huì)變薄,齒輪的彎曲強(qiáng)度也就越小。對(duì)于低速檔的齒輪,由于轉(zhuǎn)速低、扭矩大,齒輪的彎曲應(yīng)力比較大,所以需選用較大的模數(shù),以保證其強(qiáng)度要求。而高速檔齒輪,由于轉(zhuǎn)速高、扭矩小,齒輪的彎曲應(yīng)力比較小,所以在保證齒輪彎曲強(qiáng)度的前提下,一般選用較小的模數(shù),這樣就可以增加齒輪的齒數(shù),以得到較大的重合度,從而達(dá)到降低噪聲的目的。
在現(xiàn)代變速箱設(shè)計(jì)中,各檔齒輪模數(shù)的選擇是不同的。例如,某變速箱一檔齒輪到五檔齒輪的模數(shù)分別是:3.5;3;2.75;2.5;2;從而改變了過(guò)去模數(shù)相同或模數(shù)拉不開的狀況。
2、合理選用壓力角
當(dāng)一個(gè)齒輪的模數(shù)和齒數(shù)確定了,齒輪的分度圓直徑也就確定了,而齒輪的漸開線齒形取決于基圓的大小,基圓大小又受到壓力角的影響。對(duì)于同一分度圓的齒輪而言,若其分度圓壓力角不同,基圓也就不同。當(dāng)壓力角越大時(shí),基圓直徑就越小,漸開線就越彎曲,輪齒的齒根就會(huì)變厚,齒面曲率半徑增大,從而可以提高輪齒的彎曲強(qiáng)度和接觸強(qiáng)度。當(dāng)減小壓力角時(shí),基圓直徑就會(huì)變大,齒形漸開線就會(huì)變的平直一些,齒根變薄,齒面的曲率半徑變小,從而使得輪齒的彎曲強(qiáng)度和接觸強(qiáng)度均會(huì)下降,但是隨著壓力角的減小,可增加齒輪的重合度,減小輪齒的剛度,并且可以減小進(jìn)入和退出嚙合時(shí)的動(dòng)載荷,所有這些都有利于降低噪聲。因此,對(duì)于低速檔齒輪,常采用較大的壓力角,以滿足其強(qiáng)度要求;而高速檔齒輪常采用較小的壓力角,以滿足其降低噪聲的要求。
例如:某一齒輪模數(shù)為3,齒數(shù)為30,當(dāng)壓力角為17.5度時(shí)基圓齒厚為5.341;當(dāng)壓力角為25度時(shí),基圓齒厚為6.716;其基圓齒厚增加了25%左右,所以增大壓力角可以增加其彎曲強(qiáng)度。
3、合理選用螺旋角
與直齒輪相比,斜齒輪具有傳動(dòng)平穩(wěn),重合度大,沖擊小和噪聲小等優(yōu)點(diǎn)?,F(xiàn)在的變速箱由于帶同步器,換檔時(shí)不再直接移動(dòng)一個(gè)齒輪與另一個(gè)齒輪嚙合,而是所有的齒輪都相嚙合,這樣就給使用斜齒輪帶來(lái)方便,因此帶同步器的變速箱大多都使用斜齒輪。
由于斜齒輪的特點(diǎn),決定了整個(gè)齒寬不是同時(shí)全部進(jìn)入嚙合的,而是先由輪齒的一端進(jìn)入嚙合,隨著輪齒的傳動(dòng),沿齒寬方向逐漸進(jìn)入嚙合,直到全部齒寬都進(jìn)入嚙合,所以斜齒輪的實(shí)際嚙合區(qū)域比直齒輪的大。當(dāng)齒寬一定時(shí),斜齒輪的重合度隨螺旋角增加而增加。承載能力也就越強(qiáng),平穩(wěn)性也就越好。從理論上講,螺旋角越大越好,但螺旋角增大,會(huì)使軸向分力也增大,從而使得傳遞效率降低了。
在現(xiàn)代變速箱的設(shè)計(jì)中,為了保證齒輪傳動(dòng)的平穩(wěn)性、低噪聲和少?zèng)_擊,所有齒輪都要選擇較大的螺旋角,一般都在30°左右。對(duì)于高速檔齒輪由于轉(zhuǎn)速較高,要求平穩(wěn),少?zèng)_擊,低噪聲,因此采用小模數(shù),大螺旋角;而低速檔齒輪則用較大模數(shù),較小螺旋角。
4、合理選用正角度變位
對(duì)于具有良好潤(rùn)滑條件的硬齒面齒輪傳動(dòng),一般認(rèn)為其主要危險(xiǎn)是在循環(huán)交變應(yīng)力作用下,齒根的疲勞裂紋逐漸擴(kuò)張?jiān)斐升X根斷裂而失效。變速箱中齒輪失效正是屬于這一種。為了避免輪齒折斷,應(yīng)盡量提高齒根彎曲強(qiáng)度,而運(yùn)用正變位,則可達(dá)到這個(gè)目的。一般情況下,變位系數(shù)越大,齒形系數(shù)值就越小,輪齒上彎曲應(yīng)力越小,輪齒彎曲強(qiáng)度就越高。
在硬齒面的齒輪傳動(dòng)中,齒面點(diǎn)蝕剝落也是失效原因之一。增大嚙合角,可降低齒面間的接觸應(yīng)力和最大滑動(dòng)率,能大大提高抗點(diǎn)蝕能力。而增大嚙合角,則必須對(duì)一副齒輪都實(shí)行正變位,這樣既可提高齒面的接觸強(qiáng)度,又可提高齒根的彎曲強(qiáng)度,從而達(dá)到提高齒輪的承載能力效果。但是,對(duì)于斜齒輪傳動(dòng),變位系數(shù)過(guò)大,又會(huì)使輪齒總的接觸線長(zhǎng)度縮短,反而降低其承載能力。同時(shí),變位系數(shù)越大,由于齒頂圓要隨之增大,其齒頂厚度將會(huì)變小,這會(huì)影響齒頂?shù)膹?qiáng)度。
因此在現(xiàn)代變速箱的設(shè)計(jì)中,大多數(shù)齒輪均合理采用正角度變位,以最大限度發(fā)揮其優(yōu)點(diǎn)。主要有以下幾個(gè)設(shè)計(jì)準(zhǔn)則:
l 對(duì)于低速檔齒輪副來(lái)說(shuō),主動(dòng)齒輪的變位系數(shù)應(yīng)大于被動(dòng)齒輪的變位系數(shù),而對(duì)高速檔齒輪副,其主動(dòng)齒輪的變位系數(shù)應(yīng)小于被動(dòng)齒輪的變位系數(shù)。
l 主動(dòng)齒輪的變位系數(shù)隨檔位的升高而逐漸下降。這是因?yàn)榈蜋n區(qū)由于轉(zhuǎn)速低、扭矩大,齒輪強(qiáng)度要求高,因此需采用較da的變位系數(shù)。
l 各檔齒輪的總變位系數(shù)都是正的(屬于角變位修正),而且隨著檔位的升高而逐漸減小??傋兾幌禂?shù)越小,一對(duì)齒輪副的齒根總的厚度就越薄,齒根就越弱,其抗彎強(qiáng)度就越 低,但是由于輪齒的剛度減小,易于吸收沖擊振動(dòng),故可降低噪聲。而且齒形重合度會(huì)增加,這使得單齒承受最大載荷時(shí)的著力點(diǎn)距齒根近,使得彎曲力矩減小,相當(dāng)于提高了齒根強(qiáng)度,這對(duì)由于齒根減薄而消弱強(qiáng)度的因素有所抵消。所以總變位系數(shù)越大,則齒根強(qiáng)度越高,但噪聲則有可能增大。因此高速檔齒輪要選擇較小的總變位系數(shù),而低速檔齒輪則必須選用較大的總變位系數(shù)。
5、提高齒頂高系數(shù)
齒頂高系數(shù)在傳動(dòng)質(zhì)量指標(biāo)中,影響著重合度,在斜齒輪中主要影響端面重合度。由端面重合度的公式可知,當(dāng)齒數(shù)和嚙合角一定時(shí),齒頂圓壓力角是受齒頂高系數(shù)影響的,齒頂高系數(shù)越大,齒頂圓壓力角也越大,重合度也就越大,傳動(dòng)也就越平穩(wěn)。但是,齒頂高系數(shù)越大,齒頂厚度就會(huì)越薄,從而影響齒頂強(qiáng)度。同時(shí),從最少不根切齒數(shù)公式來(lái)看,齒頂高系數(shù)越大,最少不根切齒數(shù)就會(huì)增加,否則的話,就會(huì)產(chǎn)生根切。因此,在保證不根切和齒頂強(qiáng)度足夠的情況下,增大齒頂高系數(shù),對(duì)于增加重合度是有意義的。
因此在現(xiàn)代變速箱的設(shè)計(jì)中,各檔齒輪的齒頂高系數(shù)都選擇較大的值,一般都大于1.0,稱為細(xì)高齒,這對(duì)降低噪聲,增加傳動(dòng)平穩(wěn)性都有明顯的效果。對(duì)于低速檔齒輪,為了保證其具有足夠的齒根彎曲強(qiáng)度,一般選用較小的齒頂高系數(shù);而高速檔齒輪,為了保證其傳動(dòng)的平穩(wěn)性和低噪聲,一般選用較大的齒頂高系數(shù)。
以上是從模數(shù)、壓力角、螺旋角、變位系數(shù)和齒頂高系數(shù)這五個(gè)方面去獨(dú)立分析齒輪設(shè)計(jì)趨勢(shì)。實(shí)際上各個(gè)參數(shù)之間是互相影響、互相牽連的,在選擇變速箱的參數(shù)時(shí),既要考慮它們的優(yōu)缺點(diǎn),又要考慮它們之間的相互關(guān)系,從而以最大限度發(fā)揮其長(zhǎng)處,避免短處,改善變速箱的使用性能。
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2009級(jí)汽車服務(wù)工程(1)班
指導(dǎo)教師及職稱
?講師
學(xué)??? 院
工學(xué)院?
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20? 年? 月? 日
畢業(yè)論文
(設(shè)計(jì))題目
防后溜手動(dòng)汽車變速箱設(shè)計(jì)
選題來(lái)源
□結(jié)合科研課題?? 課題名稱: ?
□生產(chǎn)實(shí)際或社會(huì)實(shí)際??????????■其他???
選題性質(zhì)
□基礎(chǔ)研究????? ■應(yīng)用研究???? □其他
題目完成形式
□畢業(yè)論文????? ■畢業(yè)設(shè)計(jì)???? □提交作品,并撰寫論文
研究?jī)?nèi)容
在現(xiàn)有摩擦式離合器工作的基礎(chǔ)上,增加安全性結(jié)構(gòu),研究一種單向超速離合器,如采用楔形片或單向鎖止?jié)L珠,將其安裝于發(fā)動(dòng)機(jī)飛輪壓板與摩擦片兩者的外緣,使兩者之間只能單向相對(duì)運(yùn)動(dòng),將普通離合器改造成一種“自由”與“單向”相結(jié)合的“混合離合器”,具備單向鎖定的同時(shí)又不影響離合器本身的工作性質(zhì)和效應(yīng)。經(jīng)過(guò)這樣改進(jìn)設(shè)計(jì)的摩擦式離合器完全不影響其原本的使用效果,同時(shí)增加了可防止汽車在上坡的時(shí)候由于重力作用向后反轉(zhuǎn)而出現(xiàn)溜車現(xiàn)象的安全措施。
主要要求:
1. 設(shè)計(jì)思路清晰,方案正確,方法科學(xué);
2. 結(jié)構(gòu)完整,布局合理可靠,具有一定的實(shí)用性和安全性;
3. 設(shè)計(jì)說(shuō)明書書寫結(jié)構(gòu)合理,設(shè)計(jì)過(guò)程和步驟完整,計(jì)算嚴(yán)謹(jǐn)正確,行文條理清晰、通順;格式、字?jǐn)?shù)、排版符合畢業(yè)設(shè)計(jì)的要求。
4. 圖紙工作量和質(zhì)量符合本科畢業(yè)設(shè)計(jì)的要求。
注:此表如不夠填寫,可另加附頁(yè)。
主要中文參考資料與外文資料
1. 國(guó)內(nèi)外有關(guān)摩擦式離合器的安全性改進(jìn)設(shè)計(jì)的方法和技術(shù),相應(yīng)的產(chǎn)品及其發(fā)展情況;
2. 機(jī)械設(shè)計(jì)理論相關(guān)、機(jī)械設(shè)計(jì)手冊(cè),機(jī)械傳動(dòng)手冊(cè),機(jī)械制造工藝辭典及相關(guān)資料;
3. 現(xiàn)代機(jī)電控制及機(jī)電一體化等相關(guān)的書籍。
4. 維普資料網(wǎng)、中文期刊網(wǎng)、各類網(wǎng)站等,了解相關(guān)的設(shè)計(jì)內(nèi)容。
工作進(jìn)度安排
第一階段 2012-12-11至2012-12-31 選定畢業(yè)設(shè)計(jì)題目、下達(dá)任務(wù)書
第二階段 2013-01-01至2013-01-13 撰寫開題報(bào)告、開題論證
第三階段 2013-02-24至2013-04-01調(diào)查、收集資料、論文提綱及論文寫作
第四階段 2013-04-02至2013-04-13 論文中期檢查表
第五階段 2013-04-15至2013-04-28 提交初稿
第六階段 2013-05-01至2013-05-06 論文修改、提交正稿
第七階段 2013-05-07至2013-05-15 論文評(píng)閱
第八階段 2013-05-16至2013-05-26 論文答辯
要求完成日期:20?12 年?5 月?5日??????? 指導(dǎo)教師簽名:? ??????????????????????
審查日期:20??? 年??? 月??? 日??????????? 專業(yè)委員會(huì)主任簽名: ?????????????????
批準(zhǔn)日期:20??? 年??? 月??? 日??????????? 學(xué)院指導(dǎo)委員會(huì)簽名(公章):??????????
接受任務(wù)日期:20??? 年??? 月??? 日? ??????學(xué)生本人簽名:???????? ???????????????
注:簽名欄必須由相應(yīng)責(zé)任人親筆簽名。此表可從教務(wù)處網(wǎng)站下載中心下載。
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湖南農(nóng)業(yè)大學(xué)全日制普通本科生
畢業(yè)論文(設(shè)計(jì))開題報(bào)告
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學(xué)生姓名
學(xué)??? 號(hào)
年級(jí)專業(yè)及班級(jí)
2009級(jí)汽車服務(wù)工程(1)班
指導(dǎo)教師及職稱
講師
學(xué)??? 院
工學(xué)院
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20??? 年???? 月???? 日
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畢業(yè)論文(設(shè)計(jì))題目
防后溜手動(dòng)汽車變速箱設(shè)計(jì)
文獻(xiàn)綜述(選題研究意義、國(guó)內(nèi)外研究現(xiàn)狀、主要參考文獻(xiàn)等,不少于1000字)
選題研究意義
隨著社會(huì)的進(jìn)步,我們生活水平的提高,汽車變的不在遙遠(yuǎn),開始走進(jìn)千家萬(wàn)戶。在市場(chǎng)上,由于手動(dòng)擋汽車相對(duì)同配置的自動(dòng)擋汽車要便宜實(shí)惠不少,所以手動(dòng)擋汽車被廣泛的消費(fèi)者所喜愛,特別是男性車主。但是由于操作相對(duì)復(fù)雜,換擋頻頻出現(xiàn)。尤其是在上坡起步時(shí) 容易熄火或者溜車。容易造成交通堵塞,更嚴(yán)重的是可能發(fā)生意外交通事故。因此,如何防止坡上后溜或熄火帶來(lái)的麻煩、降低駕駛的勞動(dòng)強(qiáng)度,一直是駕駛手動(dòng)檔車友的困惑和亟待解決的問(wèn)題。
改造現(xiàn)有摩擦式離合器的結(jié)構(gòu),增加防后溜的方向鎖定機(jī)構(gòu),從而使車輛在上坡的時(shí)候可以類似自動(dòng)檔汽車,不會(huì)向后滑行,駕駛者不用擔(dān)心后滑,也不容易熄火,操作離合器將變得非常簡(jiǎn)單輕松,駕馭隨心,大大降低駕駛的勞動(dòng)強(qiáng)度和緊張程度,有利于車流暢通,同時(shí)有效降低交通事故隱患。
防后溜手動(dòng)變速箱的設(shè)計(jì)是在摩擦式離合器基礎(chǔ)上進(jìn)行安全性的改造既不影響離合器本身的功能性能,同時(shí)大大提高了汽車行駛的安全性能,成本較低,效果顯著,便于推廣,可明顯節(jié)約消費(fèi)者的用車成本。對(duì)于我們學(xué)習(xí)汽車專業(yè)的學(xué)生來(lái)說(shuō),這既是一次專業(yè)實(shí)驗(yàn)的鍛煉,加強(qiáng)了對(duì)專業(yè)理論知識(shí)和實(shí)踐技能的掌握,同時(shí)又加強(qiáng)了動(dòng)手能力,拓展了創(chuàng)新思維。
國(guó)內(nèi)外研究現(xiàn)狀
??? 在采用離合器的傳動(dòng)系統(tǒng)中,早期離合器的結(jié)果形式是錐形摩擦離合器。錐形摩擦離合器傳遞扭矩的能力,比相同直徑的其他結(jié)構(gòu)形式的摩擦離合器要大。但是,其最大的缺點(diǎn)是從動(dòng)部分的轉(zhuǎn)動(dòng)慣量太大,引起變速器換擋困難。而且這種離合器在接合時(shí)也不夠柔和,容易卡住。
次后,在油中工作的所謂濕式的多片離合器逐漸取代了錐形摩擦離合器。但是多片濕式摩擦離合器的片與片之間容易被油粘?。ㄓ绕涫窃诶涮煊鸵鹤儩鈺r(shí)更容易發(fā)生),導(dǎo)致分離不徹底,造成換擋困難。所以它又被干式所取代。多片干式摩擦離合器的主要優(yōu)點(diǎn)是由于接觸面數(shù)多,故接合平順柔和,保證了汽車的平穩(wěn)起步。但因片數(shù)較多,從動(dòng)部分的轉(zhuǎn)動(dòng)慣量較大,還是感到換擋不夠容易。多年的實(shí)踐經(jīng)驗(yàn)使人們逐漸趨向于采用單片干式摩擦離合器。它具有從動(dòng)部分轉(zhuǎn)動(dòng)慣量小,散熱性好,結(jié)構(gòu)簡(jiǎn)單,調(diào)整方便,尺寸緊湊,分離徹底等優(yōu)點(diǎn)。而且只要在結(jié)構(gòu)上采取一定措施,也能使其接合平順。因此,它得到了極為廣泛的應(yīng)用。
??? 如今,單片干式摩擦離合器在結(jié)構(gòu)設(shè)計(jì)方面也相當(dāng)完善:采用具有軸向彈性的從動(dòng)盤,提高了離合器的接合平順性;離合器中裝有扭轉(zhuǎn)減振器,防止了傳動(dòng)系統(tǒng)的共振,減少了噪音;以及采用了摩擦較小的分離桿機(jī)構(gòu)等。另外,采用了膜片彈簧作為壓簧,可同時(shí)兼起到分離杠桿的作用,使離合器結(jié)構(gòu)大為簡(jiǎn)化,并顯著地縮短了離合器的軸向尺寸。膜片彈簧和壓盤的環(huán)行接觸,可保證壓盤上的壓力均勻。由于膜片彈簧本身的特性,當(dāng)摩擦片磨損時(shí),彈簧的壓力幾乎沒(méi)有改變,且可減輕分離離合器時(shí)所需要的踏板力。為了提高離合器的傳扭能力,在重型汽車上多采用多片干式離合器。次外,近年來(lái)由于多片濕式離合器在技術(shù)上的不段改善,在國(guó)外的某些重型牽引汽車和自卸車上又開始采用多片濕式離合器,并有不斷增加的傾向。與干式離合器相比,由于用油泵進(jìn)行強(qiáng)制制冷的結(jié)果,摩擦表面的溫度較低(不超過(guò) 93℃)。因此,允許起步時(shí)長(zhǎng)時(shí)間地打滑或用高檔起步而不致燒損摩擦片,具有良好的起步能力。
??? 為了實(shí)現(xiàn)離合器的自動(dòng)操縱,有自動(dòng)離合器。采用自動(dòng)離合器時(shí)可以省去離合器踏板,實(shí)現(xiàn)汽車的“雙踏板”操縱。與其他自動(dòng)傳動(dòng)系統(tǒng)(如液力傳動(dòng))相比,它具有結(jié)構(gòu)簡(jiǎn)單,成本低廉及傳動(dòng)效率高的優(yōu)點(diǎn)。因此,在歐洲小排量汽車上曾得到廣泛的應(yīng)用。但是在現(xiàn)有自動(dòng)離合器的各種結(jié)構(gòu)中,離合器的摩擦力矩的力矩調(diào)節(jié)特性還不夠理想,使用性能不盡完善。例如,汽車以高檔低速上坡時(shí),離合器往往容易打滑。因此必須提前換如低檔以防止摩擦片的早期磨損以至燒壞。這些都需要進(jìn)一步改善。
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主要參考文獻(xiàn)
1、吉林大學(xué)汽車工程編著,陳家瑞主編,汽車構(gòu)造,上下冊(cè)。(第五版)北京,人民交通出版社
2、王望予主編,汽車設(shè)計(jì),北京,機(jī)械工業(yè)出版社,2004
3、徐石安, 肖德炳,劉惟信. 離合器(汽車設(shè)計(jì)). 北京,人民交通出版社1981
4、劉惟信主編. 離合器設(shè)計(jì). 北京. 清華大學(xué)出版社, 2003
5、張洪欣,汽車設(shè)計(jì),北京:機(jī)械工業(yè)出版社1995
6、余志生主編. 裝載機(jī)理論. 第3版. 北京: 機(jī)械工業(yè)出版社, 2000
7、機(jī)械工程手冊(cè)、電機(jī)工程手冊(cè)編輯委員會(huì)編. 機(jī)械工程手冊(cè): 第3卷專用機(jī)械卷. (第2版)北京: 機(jī)械工業(yè)出版社, 1997
8、劉惟信主編. 機(jī)械最優(yōu)化設(shè)計(jì). 北京: 清華大學(xué)出版社, 1994
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注:此表如不夠填寫,可另加頁(yè)。
研究方案(研究目的、內(nèi)容、方法、預(yù)期成果、條件保障等)
一 、研究?jī)?nèi)容
在現(xiàn)有摩擦式離合器工作的基礎(chǔ)上,增加安全性結(jié)構(gòu),研究一種單向超速離合器,如采用楔形片或單向鎖止?jié)L珠,將其安裝于發(fā)動(dòng)機(jī)飛輪壓板與摩擦片兩者的外緣,使兩者之間只能單向相對(duì)運(yùn)動(dòng),將普通離合器改造成一種“自由”與“單向”相結(jié)合的“混合離合器”,具備單向鎖定的同時(shí)又不影響離合器本身的工作性質(zhì)和效應(yīng)。經(jīng)過(guò)這樣改進(jìn)設(shè)計(jì)的摩擦式離合器完全不影響其原本的使用效果,同時(shí)增加了可防止汽車在上坡的時(shí)候由于重力作用向后反轉(zhuǎn)而出現(xiàn)溜車現(xiàn)象的安全措施。
二、實(shí)施方案
了解各類離合器的工作原理的基礎(chǔ)上,查閱和搜索各類關(guān)于離合器的資料,提出解決的創(chuàng)新構(gòu)想和思維。在指導(dǎo)老師的設(shè)計(jì)方案指導(dǎo)下,在理論上完全可以實(shí)現(xiàn)既定的創(chuàng)新改造功能,確定實(shí)施方案。
三、預(yù)期成果
1. 熟悉汽車底盤的組成結(jié)構(gòu),掌握摩擦式離合器工作原理和結(jié)構(gòu)原理;改進(jìn)設(shè)計(jì)現(xiàn)有離合器結(jié)構(gòu),增加附加鎖向裝置、聯(lián)接機(jī)構(gòu)、保護(hù)機(jī)構(gòu),實(shí)現(xiàn)預(yù)定設(shè)計(jì)方案效果;試驗(yàn)檢驗(yàn)及試驗(yàn)結(jié)果分析;
2.設(shè)計(jì)圖紙1套,設(shè)計(jì)說(shuō)明書1份
四、條件保障
工學(xué)院現(xiàn)有相關(guān)的實(shí)驗(yàn)室、實(shí)驗(yàn)器材和加工設(shè)備一應(yīng)俱全,還有一貫以來(lái)提供大學(xué)生科技創(chuàng)新的專用實(shí)驗(yàn)室,滿足設(shè)計(jì)和改造的需要。在技術(shù)方面,有具備多年創(chuàng)新指導(dǎo)工作經(jīng)驗(yàn)的專業(yè)老師導(dǎo)。作指
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進(jìn)程計(jì)劃(各研究環(huán)節(jié)的時(shí)間安排、實(shí)施進(jìn)度、完成程度等)
第一階段 2012-12-11至2012-12-31 選定畢業(yè)設(shè)計(jì)題目、下達(dá)任務(wù)書
第二階段 2013-01-01至2013-01-13 撰寫開題報(bào)告、開題論證
第三階段 2013-02-24至2013-04-01調(diào)查、收集資料、論文提綱及論文寫作
第四階段 2013-04-02至2013-04-13 論文中期檢查表
第五階段 2013-04-15至2013-04-28 提交初稿
第六階段 2013-05-01至2013-05-06 論文修改、提交正稿
第七階段 2013-05-07至2013-05-15 論文評(píng)閱
第八階段 2013-05-16至2013-05-26 論文答辯
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論證小組意見
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????????????????????????????? 組長(zhǎng)簽名:
??????????????????????????????????????????????? 20??? 年?? 月?? 日
專業(yè)委員會(huì)意見
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??????????????????????????????專業(yè)委員會(huì)主任簽名:
??????????? ???????????????????????????????????20?? 年?? 月?? 日
注:1.此表可用黑色簽字筆填寫,也可打印,但意見欄必須相應(yīng)責(zé)任人親筆填寫。
2.此表可從教務(wù)處網(wǎng)站下載中心下載。