CN1065960C - Method for automobile air resistance coefficient CD value - Google Patents

Abstract

The present invention relates to a method for testing automobile air resistance coefficient C<D> values. In the method, power values, and rolling resistance values, gradient resistance values and relative air velocity values of both sides of the automobile body when the automobile runs on the road section, and the power values are transmitted when the automobile drives wheels, and corresponds to a plurality of automobile running speed points when the position of each accelerator pedal of the automobile is set; then, the automobile air resistance coefficient C<D> values are calculated, and the calculation formula is disclosed in specification, wherein A is automobile face areas which can be calculated by automobile frontal areas, and can be simplified into A=B*H; B is automobile wheel center distance, and H is the total height of the automobile. The method of the present invention has the advantages of less investment, low cost, convenient test, a little error and good repeatability.

Description

Aerodynamic Drag Coefficient of Automobile C DThe method of testing of value

The present invention is Aerodynamic Drag Coefficient of Automobile C ₀The method of testing of value, the measuring technology of genus automobile parameter.

No matter design a kind of new model or a certain vehicle is reequiped design, save for satisfying the requirement of automobile fuel oil, often the design to car conour has proposed strict requirement, when reducing running car to that part of power that air resistance was consumed.Therefore, all wish to obtain less Aerodynamic Drag Coefficient of Automobile C by exterior design ₀Value.The existing method of testing that is used for Aerodynamic Drag Coefficient of Automobile is the prototype test or the model test of carrying out wind-tunnel.But because of the investment cost that adopts the prototype wind tunnel test is too big, so generally all adopt the car model that dwindles to carry out model wind tunnel test in wind-tunnel, this just must accomplish that geometric similarity is similar to aerodynamics, could obtain test findings comparatively accurately.Yet, though geometric similarity is easier to accomplish that and similar just being difficult to of aerodynamics accomplished.This because aerodynamics similar be meant when model is tested in wind-tunnel with automobile actual travel situation under reynolds number Re should equate, that is: $\mathrm{Re}=\frac{\mathrm{VaLa\&rho;a}}{\mathrm{\&mu;a}}=\frac{\mathrm{VmLm\&rho;m}}{\mathrm{\&mu;m}}---\left(1\right)$

In the formula: La and Lm--are respectively the length of car prortotype and model;

Va and Vm--are respectively the speed of air in automobile driving speed and the wind-tunnel;

ρ a and ρ m--are respectively the density of air in atmosphere and the wind-tunnel;

μ a and μ m--are respectively the coefficient of viscosity of air in atmosphere and the wind-tunnel.

If model is of a size of the 1/n of actual car prortotype size, and the ρ under two kinds of situations is identical with μ, and it is constant to keep the reynolds number Re value, just can only improve the flow velocity of air in the wind-tunnel, makes Vm=nVa, and this is difficult to accomplish; Should also be noted that in wind tunnel test and accomplish the similar of road surface operating mode, automobile is during along road driving, and air is zero (supposing the situation of no natural wind) with respect to the speed on road surface, does not have the boundary layer on the road surface.And in wind tunnel test, it is mobile that air has with respect to the model carrying plane, thereby can form the boundary layer, therefore to C ₀The test of value also can produce error.According to the practice of people's long-term model wind tunnel test, the Aerodynamic Drag Coefficient of Automobile C that model wind tunnel test is measured ₀The error of value is bigger, is generally 10%～20%, and maximum error can reach 40%.Therefore, for the coefficient of air resistance of testing automobile more exactly, must build large tunnel and come the prototype automobile of reality is carried out coefficient of air resistance C ₀The test of value needs very big investment like this, and testing expense is very expensive.

Purpose of the present invention is exactly to have model wind tunnel test testing automobile coefficient of air resistance C now in order to overcome and to solve ₀Test difficulty, the similar requirement of aerodynamics are difficult to accomplish that test result is inaccurate, error is big during value, and with prototype automobile wind tunnel test testing automobile coefficient of air resistance C ₀Value investment again is too big, shortcoming and problems such as expense costliness, and research provides a kind of and had not only saved money but also convenient and swift, and test result Aerodynamic Drag Coefficient of Automobile C more accurately again ₀The method of testing of value.

The inventive method realizes by following method and technology scheme: this method of testing is by measuring in the engine air throttle aperture, be that accelerator pedal of automobile position one a plurality of running car speed of a motor vehicle are regularly put the performance number of corresponding automobile driving car wheel output and the relative air velocity value of resistance to rolling value, grade resistance value and the body of a motor car both sides of automobile on this highway section, carry out Aerodynamic Drag Coefficient of Automobile (C again ₀) calculating of value, its concrete steps are: (1) by several different accelerator pedal of automobile positions, the speed of a motor vehicle (V when measuring automobile the corresponding automobile of each accelerator pedal position at the uniform velocity travelling on the good level road surface _A1, V _A2V _Ai) value, measure the relative air velocity value (V of body of a motor car both sides simultaneously _Aw1, V _Aw2V _Awi); (2) keep the identical technology operating mode of test car, each accelerator pedal position of automobile and corresponding vehicle velocity V when measuring above-mentioned each speed of a motor vehicle with the automobile chassis electric eddy current dynamometer _A1, V _A2V _AiThe time automobile driving car wheel output be used for the automobile air resistance under each corresponding speed of a motor vehicle of balance and the performance number of automobile resistance to rolling; (3) according to the power-balance principle of running car, when automobile at the uniform velocity travels on horizontal good road surface, the running resistance that is subjected to has only resistance to rolling and air resistance, therefore, the output power value of the automobile driving car wheel that records by step (2) can be decomposed into power two parts that power that resistance to rolling consumes and air resistance consume, thereby by air resistance consumed power (P _w) calculating formula, atmidometer coefficient C at last promptly has leisure ₀Value: by $P_W=\frac{C_D{\mathrm{AV}}^3\mathrm{aw}}{76140}----\left(\mathrm{KW}\right)$ : $C_D=\frac{76140P_W}{A{V}^3\mathrm{aw}}----\left(2\right)$

In the formula: A is the front face area of automobile, presses the automobile frontal area and calculates, and can be reduced to A=B.H (m ²)

B-automobile wheel track (m)

H-automobile overall height (m)

The present invention compared with prior art has following advantage and beneficial effect: (road simulation dynamometer of purchasing the electric analogy automobile running resistance only needs 300,000 yuan with interior Renminbi to this method of testing small investment, actual road test only needs several ten thousand yuans with the automobile fifth wheel instrument if need purchase also, in addition all there is this instrument general automobile experiment chamber), test easy (each automobile factory or measuring unit all can find the horizontal good road surface of one section test usefulness in arbitrary area), and with wind tunnel test testing automobile coefficient of air resistance C ₀Value then investment is big, and the whole nation has only the only a few R﹠D institution of the Ministry of Aero-Space Industry just to have the equipment and the condition of wind tunnel test, whenever carries out the coefficient of air resistance C of a vehicle ₀All expense is very big for the mensuration of value, and the cycle is very long.

The inventor once with the inventive method to Aerodynamic Drag Coefficient of Automobile C ₀Value was carried out repeatedly test, be the test case of three different speed of a motor vehicle wherein below: (1) test vehicle and vehicle condition: one of the double-seater light-duty truck CA1020 that China's First Automotive Works is produced, the canvas railway carriage, the canvas top exceeds former pilothouse top 470mm, the wide 1700mm of canvas railway carriage, the railway carriage tail opens wide; (2) automobile has related parameter: total force Ga=17550N during automotive test, automobile overall height H=2.3m, wheelspan B=1.42m, tire pressure P _Before=3.8kg/cm ², P _After=5.8kg/cm ²(3) test segment: Guangdong Fan Yushi city bridge is to ground mass highway section, East Road, Qinghe, Lianhua Shan Mountain port, and this highway section is the straight cement pavements in 6 tracks, and the road surface is almost near level.For eliminating gradient factor, come and go to travel with same highway section and make the max speed value of different solar terms door aperture; (4) certain throttle spacing down (being the gas pedal stationkeeping) travels with the III retaining that to record the maximum stable speed of a motor vehicle be 63.5km/h, and travelling with the IV retaining, to record the maximum stable speed of a motor vehicle be 73.6km/h; Travelling with V retaining, to record the maximum stable speed of a motor vehicle be that (the running section road gradient is zero meter to 74.5km/h, and to establish natural wind be zero, i.e. V _A1=V _Aw1, V _A2=V _Aw2V _Ai=V _Awi); (5) the peak power Pk=(Pw+Pf) that records the automobile driving car wheel output of corresponding operating mode with the DWC-160/150 type automobile chassis electric eddy current dynamometer of South China Science ﹠ Engineering University automobile experiment chamber is respectively 13.3kw, 17.89kw, 18.44kw; (6) the automobile coefficient of rolling resistance of automobile running test highway section operating mode gets 0.02, and promptly resistance to rolling is 0.02Ga=0.02 * 17550N=351N; (7) Aerodynamic Drag Coefficient of Automobile C ₀Being calculated as follows of value: when (a) Va was respectively 63.5km/h, 73.6km/h, 74.5km/h, (Pf=351N * Va) was respectively 6.191kw, 7.176kw, 7.264kw to the power that the automobile resistance to rolling consumes; (b) the air resistance power (Pw=Pk-Pf) that is consumed under the corresponding speed of a motor vehicle operating mode is respectively 7.109kw, 10.714kw, 11.176kw; (c) calculate Aerodynamic Drag Coefficient of Automobile C by Pw ₀Value: by 2. formula $C_D=\frac{76140\mathrm{Pw}}{H.B{.V}^3\mathrm{aw}}$ Calculate, can record C ₀Be respectively 0.6473,0.6265,0.6301, test result such as following table:

(8) as seen, with the coefficient of air resistance C of the inventive method to the measured same automobile of three kinds of different driving cycles from last table ₀Be worth all very approachingly, that the difference maximum is 0.6473-0.6265=0.0208 among the three, and the relative error maximal value is $\mathrm{\&Delta;}=\frac{0.0208}{0.6265}=3.32\%,$ Test result repeatability is described better.

Claims (1)

1, a kind of Aerodynamic Drag Coefficient of Automobile C ₀The method of testing of value, it is characterized in that: by measuring in the engine air throttle aperture, be that accelerator pedal of automobile position one a plurality of running car speed of a motor vehicle are regularly put the performance number and resistance to rolling value, the grade resistance value of automobile on this highway section of the output of corresponding automobile driving car wheel, and the relative air velocity value of body of a motor car both sides, carry out Aerodynamic Drag Coefficient of Automobile (C again ₀) calculating of value, its concrete steps are: (1) by several different accelerator pedal of automobile positions, record the automobile corresponding automobile of each accelerator pedal position speed of a motor vehicle (V during scanning frequency at the uniform velocity on the good level road surface _A1, V _A2V _Ai) value, measure the relative air velocity value (V of body of a motor car both sides simultaneously _Aw1, V _Aw2V _Awi); (2) keep the identical technology operating mode of test car, the automobile driving car wheel when each accelerator pedal position of automobile when measuring above-mentioned each speed of a motor vehicle with the automobile chassis electric eddy current dynamometer and the corresponding speed of a motor vehicle is exported is used for the automobile air resistance under each corresponding speed of a motor vehicle of balance and the performance number of automobile resistance to rolling; (3) according to the power-balance principle of running car, when automobile at the uniform velocity travels on horizontal good road surface, the running resistance that is subjected to has only resistance to rolling and air resistance, therefore, the output power value of the automobile driving car wheel that records by step (2) can be decomposed into power two parts that power that resistance to rolling consumes and air resistance consume, thereby by air resistance consumed power (P _w) calculating formula, atmidometer coefficient C at last promptly has leisure ₀Value: by $\mathrm{Pw}=\frac{C_{0}A{V}_{\mathrm{aw}}^3}{76140}--\left(\mathrm{KW}\right)$ : $C_0=\frac{76140P_w}{A{V}_{\mathrm{aw}}^3}$ In the formula: A is the front face area of automobile, presses the automobile frontal area and calculates, and can be reduced to A=BH (m ²)

B is automobile wheel track (m)

H is automobile overall height (m)