汽车整车性能计算

6汽车总体性能计算6.1汽车动力性计算6.1.1汽车各档车速计算各挡车速的计算公式如下：(km/h)(6-1)式中r——汽车滚动半径，r=0.279m；n——发动机转速〔r/min〕；ig——汽车变速器的传动比,=3.17；=2.158；=1.469；=1；i0——主减速器的传动比，i0=5.01。代入相关参数所得结果见表6-1。表6-1汽车各档车速n(r/min)Ua1(km/h)Ua2(km/h)Ua(km/h)Ua4(km/h)10006.622919.7287414.2917720.9946112007.9474911.6744817.1501225.1935314009.2720713.6202320.0084829.39246160010.5966515.5659822.8668333.59138180011.9212317.5117225.7251937.79030200013.2458119.4574728.5835441.98922220014.5703921.4032231.44189468949723.3489634.3002550.38707260017.2195525.2947137.1586054.58599280018.5441427.2404640.0169658.78491300019.8687229.1862142.8753162.98383320021.1933031.1319545.73367675178833.0777048.5920271.38168360023.8424635.0234551.4503775.58060380025.1670436.9691954.3087379.77952400026.4916238.9149457.1670883.97844420027.8162040.8606960.02544881407842.8064462.8837992.37629460030.4653744.7521865.7421496.57521480031.7899546.6979368.60050100.77413500033.1145348.6436871.45885104.973056.1.2汽车行驶阻力计算汽车行驶阻力包括：滚动阻力、空气阻力、加速阻力和爬坡阻力。1〕滚动阻力滚动阻力计算公式：Ff=Gf(N)〔6-2〕式中G——汽车重力,G=14250N；f——滚动阻力系数,f=0.015。2〕空气阻力空气阻力计算公式：(N)〔6-3〕式中CD——汽车的空气阻力系数,CD=0.52；A——汽车的迎风面积A=2.726；Ua——汽车各档车速(km/h)。代入相关参数有：所以，汽车的行驶阻力所得结果见表6-2。表6-2汽车各档行驶阻力(Ff+Fw)1(Ff+Fw)2(Ff+Fw)3(Ff+Fw)4216.67595220.06369227.37518243.15261217.96337222.84171233.37026256.08976219.48487226.12483240.45536271.37912221.24044229.91304248.63047289.02069223.23009234.20635257.89559309.01446225.45381239.00475268.25073331.36045227.91161244.30824279.69588356.05864230.60349250.11684292.23105383.10905233.52944256.43052305.85623412.51166236.68947263.24930320.57143444.26648240.08358270.57318336.37664478.37351243.71176278.40215353.27187514.83275247.57402286.73622371.25711553.64420251.67035295.57538390.33236594.80785256.00077304.91964410.49763638.32372260.56525314.76899431.75292684.19180265.36382325.12344454.09822732.41208270.39646335.98298477.53353782.98457275.66317347.34761502.05886835.90927281.16396359.21734527.67420891.18619286.89883371.59217554.37956948.815316.1.3汽车驱动力计算发动机转矩的拟合公式：〔6-4〕汽车驱动力计算公式：(N)〔6-5〕式中r——汽车行驶时的滚动半径,r=0.279m；n——发动机曲轴转速〔r/min〕；——汽车变速器各挡传动比；——传动系效率，=89.376%；——汽车主减速器传动比。各档驱动力的计算结果见表6-3。表6-3汽车的各档驱动力FtⅠFtⅡFtⅢFtⅣ2539.554151728.819511176.84702801.121182863.938231949.646281327.16885903.450543137.181732135.658731453.79179989.647233363.452842289.694391558.647391061.026133546.853472414.545681643.636521118.881223691.419282512.959871710.629311164.485583801.119632587.639171761.465221199.091373879.857642641.240631797.952961223.929863931.470162676.376221821.870561240.211413959.727772695.612781834.965331249.125483968.334762701.472061838.953871251.840623960.929202696.430671835.522081249.504483941.082842682.920121826.325141243.243803912.301212663.326821812.987531234.164423878.023532639.992041797.103021223.351273841.622782615.211981780.234661211.868393806.405672591.237681763.914801200.758893775.612632570.275101749.645101191.044993752.417832554.485071738.896461183.728023739.929182545.983331733.109141179.788383741.188302546.840491733.692621180.185586.1.4汽车驱动力-行驶阻力平衡图及最高车速确实定汽车稳速行驶时驱动力、行驶阻力平衡。即：(N) 〔6-6〕驱动力行驶阻力平衡图见图6-1。图6-1汽车驱动力-行驶阻力平衡图行驶阻力曲线(Ff+Fw-Ua)与四档驱动力曲线(FtⅣ-Ua)的交点所对应的车速即为汽车的最高行驶车速。由图4-1知汽车的最高车速为：109km/h。设计误差为：=3.8%≦5%，因此满足要求。6.1.5汽车加速能力计算1〕加速度的计算〔6-7〕式中a——汽车各挡加速度；——汽车旋转质量转换系数；——驱动力〔N〕；——风阻力〔N〕；m——汽车质量〔kg〕。并有：〔6-8〕式中——变速器的速比——=，其中为飞轮转动惯量，=0.04；——=，其中为车轮转动惯量，=0.03。计算结果如表6-4。表6-4汽车旋转质量换算系数3.172.1581.46911.43191.216281.116321.07将表6-4数值带入式6-7中便可求出汽车各档下的加速度，所得结果见表6-5和图6-2。表6-5汽车各档加速度Ua1Ua2Ua3Ua4a1a2a3a46.622919.7287414.2917720.994611.138410.870500.596870.365947.9474911.6744817.1501225.193531.296760.996310.687600.424579.2720713.6202320.0084829.392461.429921.101740.762740.4710710.5966515.5659822.8668333.591381.539951.188430.823520.5063211.9212317.5117225.7251937.790301.628861.257990.871120.5311513.2458119.4574728.5835441.989221.698621.312000.906730.5464014.5703921.4032231.4418946.188141.751181.352030.931490.5529015.8949723.3489634.3002550.387071.788451.379600.946540.5514517.2195525.2947137.1586054.585991.812311.396230.953010.5428418.5441427.2404640.0169658.784911.824611.403400.952000.5278619.8687229.1862142.8753162.983831.827161.402550.944570.5072721.1933031.1319545.7336767.182751.821761.395120.931790.4818322.5178833.0777048.5920271.381681.810141.382520.914700.4522723.8424635.0234551.4503775.580601.794021.366120.894330.4193225.1670436.9691954.3087379.779521.775101.347260.871660.3836926.4916238.9149457.1670883.978441.755031.327280.847700.3460727.8162040.8606960.0254488.177371.735421.307470.823390.3071629.1407842.8064462.8837992.376291.717861.289110.799690.2676230.4653744.7521865.7421496.575211.703911.273450.777520.2281231.7899546.6979368.60050100.77411.695091.261690.757770.1892833.1145348.6436871.45885104.97301.692901.255050.741350.15174图6-2汽车各档加速度曲线2〕加速时间由运动学知道加速时间(s)(6-9)式中t——加速时间〔s〕；A——曲线〔1/a-Ua〕下两个速度区间的面积。加速时间t可以图解积分法求的。其具体方法为：将曲线〔a-Ua〕转化为曲线〔1/a-Ua〕，然后即可得某速度区间的加速时间t，且有t=A。加速度的倒数(1/a〕的计算结果见表6-6。表6-6汽车各档的加速度倒数(1/a)1(1/a)2(1/a)3(1/a)40.878421.148761.675412.732680.771161.003701.454342.355330.699340.907661.311062.122810.649370.841451.214301.975050.613930.794921.147951.882720.588710.762201.102871.830160.571040.739631.073551.808650.559140.724851.056471.813410.551780.716211.049301.842150.548060.712561.050421.894430.547300.712991.058691.971320.548920.716781.073202.075420.552440.723321.093252.211070.557410.732001.118162.384820.563350.742251.147232.606290.569790.753421.179662.889550.576230.764831.214493.255600.582120.775731.250483.736580.586890.785271.286154.383750.589940.792591.319655.283220.590700.796781.348886.59009绘制加速度倒数曲线，见图6-3。图6-3汽车各档加速度倒数曲线由图解法可知本车0-60km/h换挡加速时间为44s。易知GD6350的加速性能欠佳。6.1.6汽车的最大爬坡度计算汽车的最大爬坡度计算公式：(6-10)式中——坡度角〔°〕。〔6-11〕式中——汽车的最大爬坡度。根据汽车的“驱动力-行驶阻力平衡图”〔即图6-1〕易知，在最低档时汽车获得最大爬坡度〔角〕。此时：=15.2°所得值根本符合16.7°的设计要求。所以，=tan15.2°=27.2%。6.2汽车经济性指标计算6.2.1汽车百公里油耗曲线及经济车速确实定发动机燃油消耗率拟合公式：〔6-12〕式中个参数参见表6-7。表6-7nB0B1B2B3B412001210.8-410.4670.379-5.06270.1076816081158.7-303.9836.657-2.05530.04307221171035.4-189.7514.524-0.511840.00681642615950.9-121.597.0035-0.185170.001855531031011-98.8934.4763-0.0910770.000689063857930.2-69.7142.9593-0.041380.0003503243531223.9-84.4782.9788-0.0374490.000282348551209.7-45.2910.81113-0.00075215-0.0