活塞零件機械加工工藝及其夾具設(shè)計【粗鏜銷孔定位夾具】
活塞零件機械加工工藝及其夾具設(shè)計【粗鏜銷孔定位夾具】,粗鏜銷孔定位夾具,活塞零件機械加工工藝及其夾具設(shè)計【粗鏜銷孔定位夾具】,活塞,零件,機械,加工,工藝,及其,夾具,設(shè)計,粗鏜銷孔,定位
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附件1：外文資料翻譯譯文
優(yōu)化活塞行動改進的發(fā)動機性能
(奧托循環(huán)或優(yōu)化熱引擎或最優(yōu)控制)
MICHAEL MOZURKEWICH和 R. S. BERRY
伊利諾伊州，芝加哥大學化學系和，詹姆斯法朗克研究所，
由R.斯蒂芬莓果， 1980年12月29日
摘要 利用有限時間熱力學方法發(fā)現(xiàn)奧托循環(huán)的優(yōu)先時間路徑及摩擦和熱滲漏。 最優(yōu)性由工作的最大化定義每個周期; 系統(tǒng)被控制在一個固定的空間內(nèi)，因此便能獲得最大動力。 結(jié)果是每一個近正弦的發(fā)動機改善了大約10%的效率(第二定律效率)。有限時間熱力學是引伸常規(guī)熱力學相關(guān)原則上橫跨主題的整個間距，從最抽象的水平到廣泛的應(yīng)用。 方法是根據(jù)廣義熱力學的創(chuàng)立(1)為包含時間或?qū)υ谙拗浦械臈l件估計在系統(tǒng)之內(nèi)(2)和在產(chǎn)生對應(yīng)于那些廣義潛力的極值的最佳路徑的計算。
迄今為止，有限時間熱力學的工作集中于較為理想化的模型(2-7)和存在性定理(2)，且全部集中在抽象方面。這項工作是希望作為一個步驟連接在實用的有限時間熱力學方面涌現(xiàn)了的抽象熱力學概念，工程學方面的課題，一臺實用機器的設(shè)計的原則。
在這個報告中，我們用接近理想的奧多周期來研究內(nèi)燃機模型，但由于頻率限制使得在實際的發(fā)動機中是以二主要損失的形式存在。 我們通過“控制”時間改善活塞運動來優(yōu)化發(fā)動機的性能。 結(jié)果，沒有進行一項詳細的工程學研究，我們能夠通過受活塞的時間路徑的影響和優(yōu)化活塞行動獲得效率的改善來估計了解是怎么損失的。
模 型
我們的模型是基于標準的四沖程奧托循環(huán)。這包括進氣沖程、壓縮沖程、作功沖程和排氣沖程。 我們在這里簡要地描述這個模型和發(fā)現(xiàn)優(yōu)化活塞行動的使用方法及基本特點。 在別處將給一個詳細的介紹。
我們假設(shè)，壓縮比、空燃比、燃油消耗率和時間全部是固定的。這些制約因素有兩個目的。首先，他們利用減少優(yōu)化問題來找到活塞運動。 并且，他們保證在這分析沒考慮的性能準則與那些是為一個實用的發(fā)動機做比較的。 放松這些限制中的任一個可能進一步改善性能。
我們采取的損失是熱滲漏和摩擦。 這兩個是依靠效率來影響系統(tǒng)的時間反應(yīng)。 熱泄漏假設(shè)是圓筒的瞬間表面和與在工作流體和墻壁之間的溫差比例(即，牛頓熱耗)。 由于這個溫度區(qū)別最大是在作功沖程，熱滲漏是只包含在這個沖程中。摩擦力與活塞速度成正比，對應(yīng)于潤滑良好的金屬表面；因此，摩擦損失也直接與速度正方形有關(guān)。 這些損失在所有沖程中是不同樣的。高壓在作功沖程使它的摩擦系數(shù)高于在其他沖程。 進氣沖程得益于。
我們優(yōu)選的作用是確定每循環(huán)的最大功率。 由于燃料消費和周期是固定的，這也與最大化效率和平均功率是等效的。
在尋找優(yōu)選的活塞行程時，我們首先分離了有能量和無能量的沖程。 非特指，但確定的時間t是指作功沖程中無能量沖程剩下的時間。 循環(huán)的兩個部分優(yōu)選以一個限制時間和然后結(jié)合找到每循環(huán)的總工作量。 時間t的作功沖程后來變化了，并且這個過程會被重覆，直到凈工作量達到最大值。
采取一個簡單形式來描述無能量沖程的最佳活塞運動。在每個沖程的大多數(shù)時間，由于摩擦損失與速度的二次方成比例，最宜的運動取決于速度常數(shù)。 在沖程的末期，活塞以允許的最大效率加速并且減速。 由于摩擦損失在進氣沖程較高，與其他兩個相比，這個最佳的解決辦法是把更多的時間分配到這個沖程?；钊俣扰c作用時間的關(guān)系顯示在圖1中。
由于熱泄漏的出現(xiàn)，作功沖程更難優(yōu)選。問題是通過使用最優(yōu)控制理論的變化技術(shù)解決的 (8)。利用實際情況的非線性的微分方程產(chǎn)生活塞的運動方程式。 這些都是實際數(shù)值。整個循環(huán)運動的結(jié)果顯示在圖1上。
圖1 活塞速度與作用時間的關(guān)系，從作功沖程開始。
最大允許的加速度是2 x 104 m/sec2。
活塞行動的不對稱的形狀在作功沖程中的摩擦和熱泄漏損失之間交替出現(xiàn)。在沖程初氣體是熱的，能產(chǎn)生高效率，并且散熱率高。在作功沖程中得益于活塞速度高。這個沖程被選出，氣體冷卻率和熱泄漏相對于摩擦損失減少。 結(jié)果，當作功沖程進行時，最佳路徑的移動速度更低。
解決的辦法在加速度和上首先獲得了極大的加速度然后迅速減速。后者情況以“收費公路”解決方案在其他環(huán)境下產(chǎn)生一個交叉結(jié)果 (9)。在這些速度之間以最高效率進行加速和減速，使系統(tǒng)盡量的在它的最佳的向前和向后速度操作下盡可能延長。 這樣，系統(tǒng)花費同樣多時間盡可能沿它的最佳路徑移動。
結(jié) 果
計算的參量從參考10中獲取，在給定的摩擦系數(shù)下，通過參考10中的變量調(diào)整摩擦損失的大小。 那些參量在表1中給出。一些典型的情況下的計算結(jié)果見表2，但在一個標準近正弦運動下，他們與常規(guī)奧托循環(huán)的發(fā)動機相比有同一壓縮比。為了優(yōu)化發(fā)動機使第一列的常規(guī)發(fā)動機最大值，活塞加速度被限制在5 x 10 m3/sec2內(nèi)，使得有效利用率ε (有用功與可逆功的比率，也稱第二定律效率)稍微提高。 如果發(fā)動機的活塞允許有4個時間的加速度，有效率將增加9%；如果加速度是不受強制的，有效率比以前將增加11%。
表1 發(fā)動機參數(shù)*
發(fā)動機參數(shù)：
壓縮比=8
在最小容積的活塞位置=1厘米
位移= 7 cm
汽缸直徑(b) = 7.98 cm
汽缸容量(v) = 400 cm3
周期(t) = 33.3毫秒/3600轉(zhuǎn)每分鐘
熱力學參量：
壓縮沖程 作功沖程
最初的溫度 333K 2795K
摩爾氣體 0.0144 0.0157
恒定熱容量
容量 2.5R 3.35R
汽缸壁溫度(T) = 600 K
可逆循環(huán)的動能 (WR)= 435.7 J
可逆的能力(WR/I)= 13.1千瓦
損失條件：
摩擦系數(shù)(a) = 12.9 kg/sec
熱泄漏系數(shù)(K)= 1305 千克/ (度/sec3)
每循環(huán)的時間損耗和摩擦損失的能量= 50 J
表2 結(jié)果(所有能量單位用焦耳)
t'，在作功沖程上所用的時間；WP在作功沖程完成的工作量；WT，每循環(huán)的凈工作量；WF，摩擦損失的能量；WQ，工作中的熱泄漏損失的能量；
Q，熱泄漏；TF，作功沖程結(jié)束時的溫度；ε，有效利用率。
這些改善是顯而易見的，但不是最有利的。如果傳統(tǒng)發(fā)動機的總損失是保持大約固定的常數(shù)，但是減少高于80%的熱耗和低于60%的摩擦損失，有效利用率獲得提高，到達傳統(tǒng)發(fā)動機有效利用率的17%以上。
當潤滑油流過發(fā)動機的最高溫度附近時，在這個分析過程中的改善的主要來源是熱耗的減少。 這就是為什么在較大的摩擦力下改善發(fā)動機的熱泄漏和降低摩擦損失比發(fā)動機使用更好的絕緣材料要好，。
最后，在相應(yīng)時間內(nèi)為優(yōu)化發(fā)動機和為它的傳統(tǒng)對應(yīng)部分，它是指導研究活塞運動的最佳路徑的方法?；钊奈恢煤妥饔脮r間的關(guān)系顯示在圖2上
在結(jié)束時，強調(diào)在這工作中說明了一個熱力學的系統(tǒng)非傳統(tǒng)的優(yōu)化被方法。而不是控制熱效率、熱容量、傳熱、摩擦系數(shù)、冷卻水溫度，或者熱力發(fā)動機的其他通常參量，我們控制了發(fā)動機容量時間路徑。
圖2 在作功、排氣、進氣和壓縮沖程中
優(yōu)化的(□)和傳統(tǒng)的(○)活塞運動比較；
最佳路徑的最大加速度被限制在2 x 104 m3/sec2
參考文獻：
1、王遂雙等主編．《汽車電子控制系統(tǒng)的原理與維修》．北京：北京理工大學出版社．1998
2、弈其文主編．《上海帕薩特B5轎車故障診斷手冊》．遼寧：遼寧科學技術(shù)出版社．2003
3、楊怡主編．《汽車電子控制技術(shù)》．北京：機械工業(yè)出版社．1999
附件2：外文原文
Engine performance improved by optimized piston motion
(Otto cycle/optimized heat engines/optimal control)
MICHAEL MOZURKEWICH AND R. S. BERRY
Department of Chemistry and the James Franck Institute,
The University of Chicago, Chicago, Illinois 60637
Contributed by R. Stephen Berry, December 29, 1980
ABSTRACT The methods of finite-time thermodynamics are used to find the optimal time path of an Otto cycle with friction and heat leakage. Optimality is defined by maximization of the work per cycle; the system is constrained to operate at a fixed frequency,so the maximum power-is obtained. The result is an improvement of about 10% in the effectiveness (second-law efficiency) of a conventional near-sinusoidal engine.
Finite-time thermodynamics is an extension ofconventional thermodynamics relevant in principle across the entire span of the subject, from the most abstract level to the most applied. The approach is based on the construction of generalized thermodynamic potentials (1) for processes containing time or rate conditions among the constraints on the system (2) and on the determination of optimal paths that yield the extrema corresponding to those generalized potentials.
Heretofore, work on finite-time thermodynamics has concentrated on ratheridealized models (2-7) and on existence theorems (2), all on the abstract side of the subject. This work is intended as a step connecting the abstract thermodynamic concepts that have emerged in finite-time thermodynamics with the practical, engineering side of the subject, the design principles of a real machine.
In this report, we treat a model of the internal combustion engine closely related to the ideal Otto cycle but with rate constraints in the form ofthe two major losses found in real engines. We optimize the engine by "controlling" the time dependence of the volume-that is, the piston motion. As a result, without undertaking a detailed engineering study, we are able to understand how the losses are affected by the time path of the piston and to estimate the improvement in efficiency obtainable by optimizing the piston motion.
THE MODEL
Our model is based on the standard four-stroke Otto cycle. This consists of an intake stroke, a compression stroke, a power stroke, and an exhaust stroke. Here we briefly describe the basic features of this model and the method used to find the optimal piston motion. A detailed presentation will be given elsewhere.
We assume that the compression ratio, fuel-to-air ratio, fuel consumption, and period of the cycle all are fixed. These constraints serve two purposes. First, they reduce the optimization problem to finding the piston motion. Also,they guarantee that the performance criteria not considered in this analysis are comparable to those for a real engine. Relaxing any of these constraints can only improve the performance further.
We take the losses to be heat leakage and friction. Both of these are rate dependent and thus affect the time response of the system. The heat leak is assumed to be proportional to the instantaneous
surface of the cylinder and to the temperature difference between the working fluid and the walls (i.e., Newtonian heat loss). Because this temperature difference is large only on the power stroke, heat loss is included only on this stroke. The friction force is taken to be proportional to the piston velocity, corresponding to well-lubricated metal-on-metal sliding;thus, the frictional losses are directly related, to the square ofthe velocity. These losses are not the same for all strokes. The high pressures in the power stroke make its friction coefficient higher than in the other strokes. The intake stroke has a contribution due to viscous flow through the valve.
The function we have optimized is the maximum work per cycle. Because both fuel consumption and cycle time are fixed, this also is equivalent to maximizing both efficiency and the average power.
In finding the optimal piston motion, we first separated the power and nonpower strokes. An unspecified but fixed time t was allotted to the power stroke with the remainder of the cycle time given to the nonpower strokes. Both portions of the cycle were optimized with this time constraint and were then combined to find the total work per cycle. The duration t of the power stroke was then varied and the process was repeated until the net work was a maximum.
The optimal piston motion for the nonpower strokes takes a simple form. Because of the quadratic velocity dependence of the friction losses, the optimum motion holds the velocity constant during most of each stroke. At the ends of the stroke, the piston accelerates and decelerates at the maximum allowed rate. Because the friction losses are higher on the intake stroke, the optimal solution allots more time to this stroke than to the other two. The piston velocity as a function of time is shown in Fig.1.
The power stroke was more difficult to optimize because ofthe presence of the heat leak. The problem was solved by using the variational technique of optimal control theory (8). The formalism yields the equation of motion of the piston as a fourthorder set of nonlinear differential equations. These were solved numerically. The resulting motion is shown in Fig. 1 for the entire cycle.
The asymmetric shape of the piston motion on the power stroke arises from the trade-off between friction and heat leak losses. At the beginning of the stroke the gases are hot, capable of yielding high efficiency, and the rate of heat loss is high. It is therefore advantageous to make the velocity high on this part of the stroke. As work is extracted, the gases cool and the rate of heat leakage diminishes relative to frictional losses. Consequently the optimal path moves to lower velocities as the power stroke proceeds.
The solutions were obtained first with unlimited acceleration and then with limits on acceleration and deceleration. The latter situation yields a result familiar in other contexts under the name of "turnpike" solution (9). The system tries to operate as long as possible at its optimal forward and backward velocities, by accelerating and decelerating between these velocities at the maximum rates. In this way, the system spends as much time as possible moving along its best or turnpike path.
RESULTS
Parameters for the computations were taken from ref. 10 or, in the case of the friction coefficient, adjusted to give frictional losses of the magnitude cited in ref. 10. Those parameters are given in Table 1. The results of the calculations of some typical cases are given in Table 2, where they are compared with the conventional Otto cycle engine having the same compression ratio but a standard near-sinusoidal motion. The effectiveness ε(the ratio of the work done to the reversible work, also called the second-law efficiency) is slightly higher for the optimized engine whose piston-acceleration is limited to 5 x 103 m/sec2 ，the maximum of the conventional engine of the first row. If the piston is allowed to have 4 times the acceleration of the conventional engine, the effectiveness increases 9%; if the acceleration is unconstrained, the improvement in effectiveness goes up to 11%.
These values are typical, not the most favorable. If the total losses of the conventional engine are held approximately constant but shifted to correspond to about 80% larger heat loss and about 60% smaller friction loss, the gain in effectiveness goes up, reaching more than 17% above the effectiveness of the corresponding conventional engine.
The principal source of the improvement in use of energy in this analysis is in the reduction of heat losses when the working fluid is near its maximum temperature. This is why the improvement is greater for engines with large heat leaks and low friction than for engines with relatively better insulation but higher friction.
Finally, it is instructive to examine the path of the piston in time, for the optimized engine and for its conventional counterpart. The position of the piston as a function of time is shown for these two cases in Fig. 2.
In closing, emphasize the unconventional approach to optimizing a thermodynamic system illustrated by this work. Instead of controlling heat rates, heat capacities, conductances, friction coefficients, reservoir temperatures, or other usual parameters of thermodynamic engines, we have controlled the time path of the engine volume.
References:
1, double, such as editor-in-chief Wang. "Automotive electronic control systems and maintenance of the principle." Beijing: Beijing Institute of Technology Press. 1998
2, Yi-Qi-wen, editor-in-chief. "Shanghai Passat B5 sedans manual fault diagnosis." Liaoning: Liaoning Science and Technology Press. 2003
3,yangyi, editor. "Automotive electronic control technology." Beijing: Mechanical Industry Press. 1999
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