CN105117546A - City expressway alignment design optimization method under ice and snow condition - Google Patents

Abstract

The invention provides a city expressway alignment design optimization method under an ice and snow condition. The city expressway alignment design optimization method comprises the following parameter steps: 1) optimizing a maximum slope length parameter under the ice and snow condition; 2) optimizing a maximum gradient parameter under the ice and snow condition; and 3) optimizing a circular curve extremity minimum radius under the ice and snow condition. The city expressway alignment design optimization method has the following advantages that a maximum longitudinal slope, a maximum longitudinal slope length design index value and a suggested reference value of a minimum parking sight distance of the city expressway under the ice and snow condition are put forward, geometrical parameters including the circular curve extremity minimum radius, a highest superelevation rate and the like are standardized, a more detailed geometrical index value reference is provided for the designer of the ice and snow area expressway, and the city expressway alignment design optimization method has an important practical significance for accelerating the safety production and the economic development of northern ice and snow areas.

Description

City expressway Alignment Design optimization method under icy conditions

Technical field

The invention belongs to ice and snow environment Urban Express Roads field, especially relate to city expressway Alignment Design optimization method under a kind of icy conditions.

Background technology

Ice and snow not only makes through street coefficient of road adhesion reduce, cause the decline of automobile dynamic quality, the probability making automobile occur to skid and break away increases, and make the increase of stopping sight distance of vehicle, make vehicle rear-end collision, possibility out of control and dangerous increase, the security of Expressway Traffic in serious threat, greatly weakens the traffic capacity of cold district city expressway, Expressway Traffic safety and operational efficiency is caused to having a strong impact on.Ice and snow is as the key factor having a strong impact on the city expressway traffic capacity, and the domestic research for it in early days but mainly concentrates on the research of snow disaster in pastoral area risk indicator system and Early-warning Model, and research face limitation is larger.

According to the difference of ice and snow to the influence degree of road, ice and snow road can be divided into following three levels: snowy road surface, ice film road surface, slab road surface.Snowy road surface refers to, and there is accumulated snow on road surface; Ice film road surface refers to that road surface is compacted snow face and covers; Slab road surface refers to that road surface is by the ice face of snowmelt formation.In order to reduce the interference that ice and snow road runs Expressway Traffic, can by maximum ramp length, the limit grade under the different icy conditions in adjustment through street, the geometric parameters such as specification MINIMUM CURVE RADIUS and maximum superelevation rate reduce the impact that ice and snow environment brings.

Reasonably determine that above-mentioned parameter is the key that solution ice and snow road affects through street, from current research conditions, still nobody proposes corresponding algorithm and theoretical research for the determination of above parameter, the also not relevant canalized design method in Practical Project.

Summary of the invention

In view of this, the present invention is intended to propose city expressway Alignment Design optimization method under a kind of icy conditions, to provide a set of specification ice and snow area design parameter optimization method of city expressway and building of model.

For achieving the above object, technical scheme of the present invention is achieved in that

City expressway Alignment Design optimization method under a kind of icy conditions, comprises the optimization of following parameter:

1) Optimized model of Maximal slope length parameter under icy conditions:

First, the computing formula of the stopping sight distance L under icy conditions is shown in as follows

In formula: L ₀for reaction distance, t=2.5s (judge time 1.5s, working time 1s); Lz is braking distance; L ₁for safe distance; φ is road friction coefficient, is divided into the friction factor under accumulated snow, snow slab and ice film condition under icy conditions; F is rolling resistance coefficient; I is the road longitudinal grade gradient;

Stopping sight distance under recycling icy conditions and the relation between speed and the gradient carry out Reduction calculation to length of grade limiting parameter, and reduction relation is shown in following formula,

In formula: L _{ice and snow}it is the stopping sight distance under icy conditions; L _normallyit is the stopping sight distance under normal condition; S _{ice and snow}it is the length of grade under icy conditions; S _normallyit is Maximal slope length under normal condition;

Finally try to achieve Maximal slope length limiting parameter S under icy conditions _{ice and snow};

2) Optimized model of ruling grade parameter under icy conditions:

Under ice and snow environment pavement conditions, the computing formula that can obtain dynamic factor maximal value under friction traction condition is as follows,

In formula: for the dynamic factor under friction traction condition; Z is the normal pressure of vehicle to ground; for road friction coefficient; G _afor gross combination weight;

Under ice and snow road condition, the maximum gradeability of vehicle depends primarily on work as the angle of gradient time little, visual then Z=G _drive, G _drivefor driving wheel load; Bogie is about 0.66 ~ 0.76G, and car is about 0.57 ~ 0.65G, for attachment coefficient; Above-mentioned formula (3) can be converted into:

Maximum power factor value when various types of vehicles travels with friction speed V on ice and snow road can be calculated by above formula (4)

Under normal weather, the gradient size that automobile can overcome is i=D _max-f; So vehicle maximum gradeability I model is under icy conditions:

Arrive can be obtained fom the above equation on the different speed of a motor vehicle, different road surface, and the through street maximum longitudinal grade gradient under attachment coefficient condition;

3) circular curve Limit infinitesimal radium under icy conditions:

Automobile circular curve Limit infinitesimal radium formula under horizontal sliding state of limit equilibrium is as follows,

$R_{\min }=\frac{V^2}{127(u_{max}+i_{max})}---\left(12\right)$

In formula: V is the design rate of through street at different levels; μm ax is maximum transversal force coefficient; i _maxfor the maximum superelevation slope of circular curve.

Further, 2) in, according to the performance of the engine of automobile, the quadratic function that dynamic factor D can be converted to speed V is as follows,

Dynamic factor $D=P^{V^2}+QV+W---\left(7\right)$

In formula, P, Q, W are the performance parameter of automobile, are calculated as follows:

$P=-\frac{1}{G}\[\frac{7.036{\mathrm{U\γ}}^3{\mathrm{\η}}_T(M_{max}-M_N)}{r^3{(n_N-n_M)}^2}+\frac{KA}{21.15}\]---\left(8\right)$

$Q=\frac{5.305{\mathrm{U\γ}}^2{\mathrm{\η}}_T{n}_M}{r^{2}G{(n_N-n_M)}^2}(M_{max}-M_N)---\left(9\right)$

$W=\frac{{\mathrm{U\γ\η}}_T}{rG}\[M_{max}-\frac{M_{max}-M_N}{{(n_N-n_M)}^2}{n}_M^2\]---\left(10\right)$

In formula, U is rate of load condensate; Mmax is maximum engine torque; M _nmoment of torsion under peak power; n _mthe rotating speed that peak torque is corresponding; n _nthe rotating speed that-peak power is corresponding; Wherein γ is total gear ratio,

γ＝i ₀·i _k(11)

In formula: i ₀primary actuator deceleration ratio, i _kfor wheel box gear ratio;

The dynamic characteristic parameter D under different gear can be obtained by above-mentioned formula, obtain on the different speed of a motor vehicle, different road surface based on the maximum grade climbing performance model formation (5) of motor vehicle under the icy conditions set up, and the through street maximum longitudinal grade gradient under attachment coefficient condition.

Further, described cornering ratio μm ax can determine a μm ax value by Riding Stability of Automobile, or determines a μm ax value by road-ability, or determines a μm ax value by fuel and tire consumption.

Relative to prior art, the present invention has following advantage:

To the optimizing research of longitudinal gradient length of grade, the every restriction index parameter of the gradient in highway layout under ice and snow weather condition, the suggestion reference value of the maximum longitudinal grade of city expressway under icy conditions, maximum longitudinal grade length of grade design objective value and minimum stopping sight distance is proposed, the geometric parameters such as specification circular curve least limit radius and maximum superelevation rate; For ice and snow area through street deviser provides the value reference of more detailed Geometrical index, the northern ice and snow safety in production of promotion, economic development are of great practical significance.

Accompanying drawing explanation

Form the part of the invention accompanying drawingbe used to provide the further understanding to the invention, the schematic description and description of the invention, for explaining the invention, does not form the improper restriction to the invention.? in accompanying drawing:

fig. 1for the invention embodiment the Yellow River board truck speed-dynamic factor figure;

fig. 2for the invention embodiment santana speed-dynamic factor figure.

Embodiment

It should be noted that, when not conflicting, the embodiment in the present invention and the feature in embodiment can combine mutually.

North most area is because be subject to snowfall, accumulated snow, icing impact winter, and its City road traffic system is greatly affected, and time serious, ice and snow even blocks whole urban transportation, and under compared with normal condition, traffic hazard occurs more frequent; Ice and snow road attachment coefficient reduces, this restrict the transport condition of automobile, thus cause automotive performance to be difficult to give full play to, therefore, be necessary the design objective studying city expressway longitudinal gradient section under icy conditions, and corresponding design objective recommended value is proposed, for the city expressway Alignment Design in many ice and snow area provides reference.This theoretical system can make up the blank that city expressway under icy conditions builds required call parameter field, for the parameter choose in city expressway construction process provides strong support.

Below with reference to the accompanying drawings and describe the present invention in detail in conjunction with the embodiments.

City expressway Alignment Design optimization method under icy conditions, comprises and optimizes following parameter:

Parameter 1) Optimized model of the longest length of grade parameter under icy conditions

Show 6.3.3-2 according to Urban Express Roads code (CJJ129-2009), the maximum longitudinal grade length under the different longitudinal gradient condition in through street is specified by such as following table 1-1:

Table 1-1

This method considers to revise existing specification on the basis of code, therefore reduction is carried out all on this basis.

In prior art, the longest length of grade determination method for parameter has based on service level, velocity contrast and heart rate growth-rate method, said method feasibility is poor, heart rate rate of growth inherently one more difficultly record parameter and under icy conditions, how heart rate becomes also cannot obtain accurate data, in addition, the length of grade that the method for heart rate rate of growth is calculated and normal value difference are very large, cannot improve specification length of grade regulation do one relatively rationally and reliable reference for reality.

Length of grade and stopping sight distance are all the functions of i and V, there is very close contact between the two, and utilizing the stopping sight distance under icy conditions and the relation between speed and the gradient to limit the length of grade of specification sheet based on this point the present invention, to carry out reduction be rational.

In " Urban Express Roads code " CJJ129-2009, in 6.2.7 bar regulation Urban Express Roads, the minimum stopping sight distance of motor vehicle sees the following form 1-2:

Table 1-2

In northern ice and snow area, the reduction of coefficient of road adhesion, the present invention considers the impact of road conditions on stopping sight distance, to providing minimum stopping sight distance computing formula and reference value more in detail accurately.

Stopping sight distance refers to and stop crossed distance completely to automobile from there is danger signal.Only have and just can not crash when the distance of danger signal occurring source distance headstock is greater than stopping sight distance.The computing formula of the stopping sight distance L of the inventive method is shown in following formula:

In formula: L ₀reaction distance, t=2.5s (judge time 1.5s, working time 1s); Lz braking distance; L ₁safe distance, gets 2 meters; φ road friction coefficient, to get under icy conditions friction factor under accumulated snow, snow slab and ice film condition and is respectively φ=0.3,0.2,0.1; F is rolling resistance coefficient, and getting coefficient of rolling resistance under icy conditions is f=0.015; The i=road longitudinal grade gradient.

Can show that the stopping sight distance L under different ice and snow road condition is as shown in table 2 by above formula (1),

Table 2

Because length of grade and stopping sight distance are all the functions about i and v, there is very close contact between the two, utilizing the stopping sight distance under icy conditions and the relation between speed V and gradient i to limit length of grade based on this point the inventive method, to carry out reduction algorithm be rational.

Reduction relation is shown in following formula, the longest length of grade parameter S under can trying to achieve icy conditions _{ice and snow}:

That is:

In formula (2), (3): L _{ice and snow}it is the stopping sight distance under icy conditions; L _normallyit is the stopping sight distance under normal condition; S _{ice and snow}it is the length of grade under icy conditions; S _normallyit is Maximal slope length under normal condition.

Length of grade restriction after the length of grade reduction coefficient that can be drawn by above formula (2) and reduction under different icy conditions is respectively as table 3, table 4:

Table 3-reduction coefficient table

The selection of this method longitudinal gradient gradient i value obtains according to " Urban Express Roads code " CJJ129-2009, and regulatory requirements Maximal slope length is as table 1-1;

Table 4 (regulatory requirements Maximal slope length is multiplied by reduction coefficient, and reduction coefficient calculates according to the reduction coefficient table calculated)

Maximal slope length S in table _{ice and snow}m the computing method of () are that regulatory requirements Maximal slope length is multiplied by reduction coefficient, reduction coefficient calculates according to the reduction coefficient table calculated.As 100km/h, code requirement 700m, tabling look-up 3 obtains reduction coefficient 0.5, and the Maximal slope length after reduction is exactly 350m.

Ice-patch surface friction factor φ is 0.1

Parameter 2) Optimized model of ruling grade parameter under icy conditions

The longitudinal gradient gradient is one of key parameter of profile of road, the rational longitudinal gradient gradient has larger impact to minimizing traffic hazard, the raising traffic capacity, minimizing investment, in longitudinal gradient section, gradient size affects the access of vehicle, according to dynamics of vehicle principle, known vehicle traction is by the restriction of pavement friction condition.Under icy conditions, because coefficient of road adhesion declines, vehicle travels the frictional traction be subject to if vehicle is under travel speed V and car weight G permanence condition, then can obtain the computing formula of dynamic factor maximal value under friction traction condition:

In formula: for the dynamic factor under friction traction condition; Z is the normal pressure of vehicle to ground; for road friction coefficient, get 0.1 or 0.2; G _afor gross combination weight.

T<T _max, then therefore under icy conditions, due to the decline of coefficient of road adhesion, the tractive force of vehicle can not be fully played.So the maximum gradeability of vehicle depends primarily in such cases work as the angle of gradient time little, visual then Z=G _drive, G _drivefor driving wheel load; Bogie is about 0.66 ~ 0.76G, and car is about 0.57 ~ 0.65G. for attachment coefficient.Above-mentioned formula (4) can be converted into:

In formula: R _wfor travelling air resistance, G _afor gross combination weight, R _w=KAV ², K, A are the coefficient calculating air resistance, for road friction coefficient;

Can first numerical value by above formula (5), the traction condition that namely rubs calculate maximum power when various types of vehicles travels with friction speed V on ice and snow road because of under maximum power factor value

The climbing capacity i that automobile itself possesses _maxmore much larger than the Max. slope of plant road run in actual travel, but depend primarily on the maximal friction between ground and wheel in the maximum gradeability of many ice and snow areas automobile.If tractive force is less than or equal to the adhesion between tire and road surface all the time, then can not there is the phenomenon that dallies in doughnut.Ensure automobile normal running and wheel does not dally and non-slip adequate condition is P _t≤ P _attached, namely driving power is less than attachment power.

If automobile up slope travels with at the uniform velocity stable, dv/dt=0, and do not consider height above sea level coefficient, then can determine the gradient size that automobile can overcome under the certain speed of a motor vehicle of different gear.Under normal weather, the gradient size that automobile can overcome is i=D _max-f; During ice and snow road coefficient of rolling resistance f=0.015, the value of slope overcome is i=D _max-f.So vehicle maximum gradeability I model is under icy conditions:

Above-mentioned I model is the maximum gradeability model of vehicle because design ruling grade must be less than maximum gradeability, not so vehicle cannot travel, therefore by this value as the ruling grade value in highway layout.

Simulated example:

According to the vehicle of ice and snow urban expressway traffic composition, determine the key motorcycle type of Longitudinal Slope Design, choose the representative vehicle that Santana 2000GSI is kart, the Yellow River board JN150 type diesel truck (8T) is as the representative vehicle of large car, calculate under different pavement conditions, various vehicle max. climb slope I, the performance parameter of three kinds of representative vehicles sees the following form 5:

Table 5

According to the performance of the engine of automobile, dynamic factor D can be converted to the quadratic function of speed V

Dynamic factor $D=P^{V^2}+QV+W---\left(7\right)$

In formula, P, Q, W are the performance parameter of automobile, are calculated as follows:

$P=-\frac{1}{G}\&lsqb;\frac{7.036{\mathrm{U\&gamma;}}^3{\mathrm{\&eta;}}_T(M_{max}-M_N)}{r^3{(n_N-n_M)}^2}+\frac{KA}{21.15}\&rsqb;---\left(8\right)$

$Q=\frac{5.305{\mathrm{U\&gamma;}}^2{\mathrm{\&eta;}}_T{n}_M}{r^{2}G{(n_N-n_M)}^2}(M_{max}-M_N)---\left(9\right)$

$W=\frac{{\mathrm{U\&gamma;\&eta;}}_T}{rG}\&lsqb;M_{max}-\frac{M_{max}-M_N}{{(n_N-n_M)}^2}{n}_M^2\&rsqb;---\left(10\right)$

In formula, U is rate of load condensate, gets 90% here; Mmax is maximum engine torque; M _nmoment of torsion under peak power; n _mthe rotating speed that peak torque is corresponding; n _nthe rotating speed that-peak power is corresponding; Wherein γ is total gear ratio,

γ＝i ₀·i _k(11)

In formula: i ₀primary actuator deceleration ratio, i _kfor wheel box gear ratio.

The dynamic characteristic parameter D of each vehicle under different gear can be obtained by above-mentioned formula, result of calculation sees the following form 6, table 7,

Table 6: P, Q, W calculated value under board truck (8T) the different gear of the Yellow River

Table 7: P, Q, W calculated value under the different gear of Santana

According to the dynamic factor-rate curve of city expressway typical vehicle composition, as Fig. 1shown in; Motor vehicle speed as Fig. 2shown in;

Two kinds of typical vehicles are obtained on the different speed of a motor vehicle, different road surface based on the maximum grade climbing performance model formation (6) of motor vehicle under the snowfall condition set up, and the through street maximum longitudinal grade gradient under attachment coefficient condition, and the longitudinal gradient ruling grade when attachment coefficient of road is 0.1 (i.e. ice-patch surface) under providing icy conditions is as suggestion reference value, see the following form 8, in table, the maximum longitudinal grade meter gradient calculates according to formula 6, according to example, first calculate dynamic factor D, then calculate gained according to formula 6;

Table 8

Parameter 3) MINIMUM CURVE RADIUS and maximum superelevation rate (e under icy conditions _max) Optimized model of parameter:

Vehicle, when turning, due to the effect of centrifugal force, makes vehicle be subject to the effect of transverse force and cause vehicle transversely slippage unstability, and directly can affect the operational stability of driver under that force.So, need in design to determine circular curve Limit infinitesimal radium, the determination of circular curve Limit infinitesimal radium is will according to the mechanical property of running car and driving trace, set up the speed of a motor vehicle and circular curve radius and and horizontal hypervelocity between common relation, under the prerequisite guaranteeing traffic safety, by horizontal analysis, automobile circular curve least radius formula under horizontal sliding state of limit equilibrium can be obtained as follows:

$R_{\min }=\frac{V^2}{127(u_{max}+i_{max})}---\left(12\right)$

In formula: V is the design rate (km/h) of through street at different levels; μm ax is maximum transversal force coefficient; i _maxfor the maximum superelevation slope of circular curve part.

When given road speed v, least radius Rmin just depends on the maximum transversal force coefficient μ of permission _maxwith maximum superelevation slope i _max.Therefore, determine Rmin value, first should make μ _maxvalue and i _max.

3.1) cornering ratio μ _maxdetermination

Described permission maximum transversal force coefficient μ _maxvalue, to the mechanical stability requirement of driving when not only will consider that automobile travels on bend, also to consider the level of comfort of passenger, and the situation etc. of automobile combustion section and tire wear, μ can be determined from multiple angle _maxvalue.

3.1.1) μ is determined by Riding Stability of Automobile _maxvalue

Experimentally analyze, work as μ _maxduring=0.15-0.16, automobile can be ensured with higher speed safety traffic on dry behaviour with moist road, by μ _maxthe bend of=0.07 design, under quiet condition icy on road, automobile also can safety traffic.

3.1.2) μ is determined by road-ability _maxvalue

Cornering ratio μ _maxvalue is different, and when automobile travels on bend, the sensation of passenger is also different.From the comfortableness of passenger, μ _maxvalue maximumly should be no more than 0.15-0.20 preferably no more than 0.10.

3.1.3) μ is determined by fuel and tire consumption _maxvalue

Technical criterion for highway controls the cornering ratio of highway at different levels, μ _maxwithin=0.15, to ensure that the driving conditions of highway bend worsens not too much.

3.2) maximum superelevation slope i _maxdetermination

When the speed of a motor vehicle is higher in order to the larger superelevation of equilibrium centrifugation power.But the speed of driving vehicle on road is also inconsistent.Particularly on the route of mixed traffic, not only will look after express, also will consider the security of slow train, for slow train, as excessive in superelevation rate, exceed the cornering ratio between tire and road surface, vehicle has the danger that maximum resultant gradient glides along road surface, therefore.Must meet:

e _max≤f _w(13)

In formula: f _wbe the lateral adhesion coefficient on 1 year mesoclimate road surface in severe season, i.e. maximum transversal force coefficient, e _maxrepresent maximum superelevation rate, superelevation rate is the abbreviation of superelevation rate.

Urban Express Roads regulations stipulate, for accumulated snow frost region, the value of maximum superelevation slope must not more than 6%, and the tolerable superelevation rate of the different speed of a motor vehicle is as table 9; Maximum superelevation slope and resultant gradient are as table 10;

Table 9

Table 10:

In " specification of the highway route design " JTGD20-2006 to the regulation of the limit radius value of design circular curve just without frost region, and under icy conditions, the limit value of circular curve radius must be determined according to actual pavement state.The computing formula of Limit infinitesimal radium is (12):

Cold district is by testing much little than muddy road surface state of ice and snow road friction co-efficient value in winter recorded, when the ultimate value that the circular curve radius designed adopts standard to specify, because ice and snow road in winter can not provide enough friction conditions to driving, and road speed and traffic safety is made all to be difficult to be guaranteed.Under icy conditions, the friction factor between truck and road surface is relatively little, in order to fully ensure the safety of through street, the mountain area driving under icy conditions, therefore adopts the friction condition between bogie and ice and snow road to be controling parameters.

Therefore maximum transversal force coefficient f _wdesirable μ _maxthe maximum conditions of=0.084-0.09, namely 0.084, calculate the circular curve Limit infinitesimal radium under icy conditions.Existing employing coefficient of friction resistance f _was the index calculating circular curve least radius.That is:

$R_{\min }=\frac{V^2}{127(i_{max}+f_w)}---\left(14\right)$

According to analysis above, consider under icy conditions, vehicle is also little relative to muddy road surface with the friction factor on road surface, so the maximum transversal force coefficient f used when the through street design of ice and snow area _wget μ _max=0.084, maximum superelevation slope requirement is maximum gets 6%.So, allow the Limit infinitesimal radium value used under icy conditions can being calculated by formula, and value of advising, it is as shown in table 11,

Table 11

The present invention is from the angle of traffic safety, emphasis is to the research of every restriction index parameters such as longitudinal gradient length of grade, the gradient and MINIMUM CURVE RADIUS in northern ice-snow field song design under ice and snow weather condition, the suggestion reference value of the maximum longitudinal grade length of grade of city expressway under icy conditions, maximum longitudinal grade slope design index value and minimum stopping sight distance is proposed, the geometric parameters such as specification MINIMUM CURVE RADIUS and maximum superelevation rate.For northern ice and snow area through street deviser provides the value reference of more detailed Geometrical index, the northern ice and snow safety in production of promotion, economic development are of great practical significance.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.

Claims (3)

1. city expressway Alignment Design optimization method under icy conditions, is characterized in that the optimization comprising following parameter:

1) Optimized model of Maximal slope length parameter under icy conditions:

First, the computing formula of the stopping sight distance L under icy conditions is shown in as follows

In formula: L ₀for reaction distance, t=2.5s (judge time 1.5s, working time 1s); Lz is braking distance; L ₁for safe distance; φ is road friction coefficient, is divided into the friction factor under accumulated snow, snow slab and ice film condition under icy conditions; F is rolling resistance coefficient; I is the road longitudinal grade gradient;

Stopping sight distance under recycling icy conditions and the relation between speed and the gradient carry out Reduction calculation to length of grade limiting parameter, and reduction relation is shown in following formula,

In formula: L _{ice and snow}it is the stopping sight distance under icy conditions; L _normallyit is the stopping sight distance under normal condition; S _{ice and snow}it is the length of grade under icy conditions; S _normallyit is Maximal slope length under normal condition;

Finally try to achieve Maximal slope length limiting parameter S under icy conditions _{ice and snow};

2) Optimized model of ruling grade parameter under icy conditions:

Under ice and snow environment pavement conditions, the computing formula that can obtain dynamic factor maximal value under friction traction condition is as follows,

In formula: for the dynamic factor under friction traction condition; Z is the normal pressure of vehicle to ground; for road friction coefficient; G _afor gross combination weight;

Under ice and snow road condition, the maximum gradeability of vehicle depends primarily on work as the angle of gradient time little, visual then Z=G _drive, G _drivefor driving wheel load; Bogie is about 0.66 ~ 0.76G, and car is about 0.57 ~ 0.65G, for attachment coefficient; Above-mentioned formula (3) can be converted into:

Maximum power factor value when various types of vehicles travels with friction speed V on ice and snow road can be calculated by above formula (4)

Under normal weather, the gradient size that automobile can overcome is i=D _max-f; So vehicle maximum gradeability I model is under icy conditions:

Arrive can be obtained fom the above equation on the different speed of a motor vehicle, different road surface, and the through street maximum longitudinal grade gradient under attachment coefficient condition;

3) circular curve Limit infinitesimal radium under icy conditions:

Automobile circular curve Limit infinitesimal radium formula under horizontal sliding state of limit equilibrium is as follows,

$R_{\min }=\frac{V^2}{127(u_{max}+i_{max})}---\left(12\right)$

In formula: V is the design rate of through street at different levels; μ _maxfor maximum transversal force coefficient; i _maxfor the maximum superelevation slope of circular curve.

2. city expressway Alignment Design optimization method under icy conditions according to claim 1, is characterized in that: 2) in, according to the performance of the engine of automobile, the quadratic function that dynamic factor D can be converted to speed V is as follows,

Dynamic factor $D=P^{V^2}+QV+W---\left(7\right)$

In formula, P, Q, W are the performance parameter of automobile, are calculated as follows:

$P=-\frac{1}{G}\&lsqb;\frac{7.036{\mathrm{U\&gamma;}}^3{\mathrm{\&eta;}}_T(M_{max}-M_N)}{r^3{(n_N-n_M)}^2}+\frac{KA}{21.15}\&rsqb;---\left(8\right)$

$Q=\frac{5.305{\mathrm{U\&gamma;}}^2{\mathrm{\&eta;}}_T{n}_M}{r^{2}G{(n_N-n_M)}^2}(M_{max}-M_N)---\left(9\right)$

$W=\frac{{\mathrm{U\&gamma;\&eta;}}_T}{rG}\&lsqb;M_{max}-\frac{M_{max}-M_N}{{(n_N-n_M)}^2}{n}_M^2\&rsqb;---\left(10\right)$

In formula, U is rate of load condensate; Mmax is maximum engine torque; M _nmoment of torsion under peak power; n _mthe rotating speed that peak torque is corresponding; n _nthe rotating speed that-peak power is corresponding; Wherein γ is total gear ratio,

γ＝i ₀·i _k(11)

In formula: i ₀primary actuator deceleration ratio, i _kfor wheel box gear ratio;

The dynamic characteristic parameter D under different gear can be obtained by above-mentioned formula, obtain on the different speed of a motor vehicle, different road surface based on the maximum grade climbing performance model formation (5) of motor vehicle under the icy conditions set up, and the through street maximum longitudinal grade gradient under attachment coefficient condition.

3. city expressway Alignment Design optimization method under icy conditions according to claim 1, is characterized in that, described cornering ratio μ _maxμ can be determined by Riding Stability of Automobile _maxvalue, or determine μ by road-ability _maxvalue, or determine μ by fuel and tire consumption _maxvalue.