汽车理论习题答案

1.3、1）绘制汽车驱动力与行驶阻力平衡图。

2）求汽车的最高车速、最大爬坡度及克服该坡度时相应的附着率。

3）绘制汽车行驶加速倒数曲线，用图解积分法求汽车有Ⅱ档起步加速行驶至70km/h的车速－时间曲线，或者用计算机求汽车用Ⅱ档起步加速至70km/h的加速时间。

n_min=600;

n_max=4000;

m1=2000;

m2=1800;

mz=3880;

g=9.81;

r=0.367;

CdA=2.77;

f=0.013;

nT=0.85;

ig=[5.562.7691.6441.00];

i0=5.83;

If=0.218;

Iw1=1.798;

Iw2=3.598;

Iw=2*Iw1+4*Iw2;

L=3.2;

a=1.947;

b=L-a;

hg=0.9;

g=9.8;

1）绘制汽车驱动力与行驶阻力平衡图：

for i=1:3401

n(i)=599+i;

Ttq(i)=-19.313+295.27*(n(i)/1000)-165.44*(n(i)/1000)^2+40.874*(n(i)/1000)^3-3.8445*(n(i)/1000)^4;

end

for j=1:4

for i=1:3401

Ft(i,j)=Ttq(i)*ig(j)*i0*nT/r;

ua(i,j)=0.377*r*n(i)/(ig(j)*i0);

Fz(i,j)=CdA*ua(i,j)^2/21.15+mz*g*f;

end

end

plot(ua,Ft,ua,Fz),grid

title('汽车驱动力与行驶阻力平衡图');

xxxxxx('ua(km/h)');

yyyyyy('Ft(N)');

2）①汽车的最高车速：

②最大爬坡度：

for k=1:1000

n1(k)=1800+k*0.5;

Ttq(k)=-19.313+295.27*(n1(k)/1000)-165.44*(n1(k)/1000)^2+40.874*(n1(k)/1000)^3-3.8445*(n1(k)/1000)^4; Ft(k)=Ttq(k)*ig(1)*i0*nT/r;

ua(k)=0.377*r*n1(k)/(ig(1)*i0);

Fz(k)=CdA*ua(k)^2/21.15+mz*g*f;

af(k)=asin((Ft(k)-Fz(k))/(mz*g));

end

for k=1:1000

if(af(k)==max(af))

i=tan(af(k));

disp('汽车最大爬坡度=');

disp(i);

end

end

汽车最大爬坡度=0.3522

③相应的附着率：

3）①绘制汽车行驶加速倒数曲线:

n=(n_min:1:n_max);

N=n./1000;

Tq=-19.313+295.27*N-165.44*N.^2+40.874*N.^3-3.8445*N.^4;

Ft1=Tq*ig(1)*i0*nT/r;

Ft2=Tq*ig(2)*i0*nT/r;

Ft3=Tq*ig(3)*i0*nT/r;

Ft4=Tq*ig(4)*i0*nT/r;

ua1=0.377*n*r/ig(1)/i0;

ua2=0.377*n*r/ig(2)/i0;

ua3=0.377*n*r/ig(3)/i0;

ua4=0.377*n*r/ig(4)/i0;

Fw1=CdA*ua1.^2/21.15;

Fw2=CdA*ua2.^2/21.15;

Fw3=CdA*ua3.^2/21.15;

Fw4=CdA*ua4.^2/21.15;

Ff=mz*g*f;

deta1=1+Iw/(mz*r^2)+If*ig(1)^2*i0^2*nT/(mz*r^2); deta2=1+Iw/(mz*r^2)+If*ig(2)^2*i0^2*nT/(mz*r^2); deta3=1+Iw/(mz*r^2)+If*ig(3)^2*i0^2*nT/(mz*r^2); deta4=1+Iw/(mz*r^2)+If*ig(4)^2*i0^2*nT/(mz*r^2); a1=(Ft1- Fw1- Ff)/(deta1*mz);

a2=(Ft2- Fw2- Ff)/(deta2*mz);

a3=(Ft3- Fw3- Ff)/(deta3*mz);

a4=(Ft4- Fw4- Ff)/(deta4*mz);

x1=1./a1;

x2=1./a2;

x3=1./a3;

x4=1./a4;

plot(ua1,x1,'k', ua2,x2, 'b',ua3,x3,'r',ua4,x4,'y'),grid title('加速度倒数曲线');

xxxxxx('ua(km/h)');

yyyyyy('1/a');

②汽车用Ⅱ档起步加速至70km/h的加速时间

2.7、计算与绘制题1中货车的1）汽车功率平衡图；

2）最高档与次高档的等速百公里油耗曲线。

m1=2000;

m2=1800;

mz=3880;

g=9.81;

r=0.367;

CdA=2.77;

f=0.013;

nT=0.85;

ig=[5.562.7691.6441.00];

i0=5.83; If=0.218;

Iw1=1.798;

Iw2=3.598;

n1=[815120716142012 2603300634033804];

Iw=2*Iw1+4*Iw2;

Qid=0.299;

L=3.2;

a=1.947;

b=L-a;

hg=0.9;

g=9.8;

1）汽车功率平衡图：

for j=1:4

for i=1:3401

n(i)=599+i;

Ttq(i)=-19.313+295.27*(n(i)/1000)-165.44*(n(i)/1000)^2+40.874*(n(i)/1000)^3-3.8445*(n(i)/1000)^4;

Pe(i)=n(i)*Ttq(i)/9549;

ua(i,j)=0.377*r*n(i)/(ig(j)*i0);

Pz(i,j)=(mz*g*f*ua(i,j)/3600.+CdA*ua(i,j)^3/76140.)/nT;

end

end

plot(ua,Pe,ua,Pz),grid;

title('功率平衡图');

xxxxxx('ua(km/h)');

yyyyyy('Pe,Pz(kw)');