What Is the Angular Gyrus?

The roundabout is an arc that changes the radius of the road route from infinity to a certain design value. The spiral curve is generally a roundabout. The spiral curve is used because the car's driving trajectory is very similar to the roundabout. It can also be used as one of the linear elements. At the same time, there are corresponding measuring and setting meters, which meet the conditions of use.

0 Roundabout 0 Introduction

Among the countries that have published road design policies in English, except for North American countries, most countries have stipulated that when the curvature difference between adjacent line elements exceeds a certain amount, a convolute line must be inserted, such as between straight lines and circular curves and A convoluted line must be inserted between two adjacent circular curves, as is the case in China. It can be seen that the original intention of using the convoluted line is to continuously change the plane curvature of the line shape, so that the geometric properties of the line shape are more in line with the driving characteristics of the vehicle because the vehicle trajectory is continuous in curvature. However, in many cases, the roundabout also assumes the function of providing development and change intervals for ultra-high rates, and for small radius curves that need to be widened, the widening value also transitions within the range of the roundabout.

Although the roundabout plays a role in alleviating the abrupt changes in the design values of various linear shapes, there has been a lot of controversy over the impact of the roundabout on road safety for years, even rising to the point of whether the roundabout should be used as a planar linear element. The party supporting the use of the convolute line in the argument is Zegeer and Harw ood. Their investigation results are that the convolute line reduces the accident rate of the flat curve by 2% to 9%. Therefore, it is believed that this line element should be used as much as possible in the linear design; At the same time, Stew art and G regory believe that the roundabout will cause the driver to overestimate the radius of the curve, which may select an excessively high passing speed, and then induce a road accident. As empirical evidence, Stew art changed the three high-incidence curves in Aberdeenshire, Scotland, from "convolute-circular-convolute" (slow-circle-slow) to single curves, and the accident rate decreased after improvement. 80%, so he strongly recommends that the "dangerous line elements" such as roundabouts not be used at all in road design. Perco turned the focus of the debate from whether to use a convoluted line to how long a convoluted line should be.Observations show that too long a convoluted line will increase the difficulty of controlling the direction of the vehicle, because it is difficult for the driver to adapt to excessively long changes. Curvature recognition task. However, Hasan et al. Found in an experiment on the factors that affect the curvature of the plane, that only when the vertical curve is convex, the convoluted line will affect the tester's perception of the plane's curvature. At the same time, no matter which type of vertical curve is, the length of the convoluted line does not become a factor that affects the curvature of the curve. This shows that the reason why the vehicle speed on the "slow-circle-slow" curve is higher than a single curve of the same radius is only in a few cases (the case of a convex vertical curve) due to the driver's illusion caused by the roundabout. In the case of concave vertical curves, straight slopes or flat slopes, there must be other reasons. Therefore, the real influencing factors and how these factors influence the curve driving speed through the roundabout are exactly the issues studied in this article.

To this end, the "road-driver-vehicle-environment" simulation (RDV ES) system is used to simulate and reproduce the vehicle's driving process on single curve and "slow-circle-slow" curve. In the test, following the real-world highway driving conditions, two directions of control modes are set: follow-the-curve (following curve alignment) and tangent-curve (inner-line) control. At the same time, the driving speed is adjusted according to the linear change, that is, variable-speed driving. The entry point of the study is to first obtain the influence of the curve and its parameters on the vehicle trajectory characteristics, and then analyze the impact on the driving speed based on this, because under the condition of constant lateral tolerance acceleration value, the change of the trajectory radius will inevitably cause the desired speed The change. Because the trajectory of the vehicle is very close to the plane of the highway when following the road, the trajectory that affects the trajectory is cut-and-curve driving. In this article, the author analyzes whether the roundabout and its length can help reduce the trajectory curvature when the curve is cut. It means that the vehicle will reach a higher speed on a curve with a roundabout, that is, the roundabout will induce a speed increase. This will provide a new interpretation at the level of vehicle kinematics and driving behavior for the turning curve causing excessive curve speed.

1 Roundabout 1 driving test design

1.1 Test methods

In this paper, the RDVES system is used as the vehicle driving test method. The structure and function of the simulation system are described below. Enter the horizontal, vertical, and horizontal design elements of the test road or the coordinates of the pavement sampling points. The road module of the system can generate a three-dimensional pavement model in space. The vehicle model created with ADAM S software is composed of subsystem models such as suspension, steering, braking, transmission, tires, etc., and has a structure basically the same as that of real vehicles.There are 3 types of models including passenger cars, trucks, and vans. Select as needed. The direction control module provides two control modes: follow-and-turn and cut-and-turn; at the same time, the speed control module provides two options of maintaining constant speed and free shifting. After pairing, it can get 4 combinations of driving modes. By assigning the adhesion coefficient between the road surface units, it is possible to simulate the stagnant water or icing on the local road surface; by applying a lateral force on the vehicle body, it is also possible to simulate the driving process in a crosswind environment. After obtaining the three-dimensional road model, import the appropriate vehicle model, select the required driving mode and set the parameters, and then set the environmental impact parameters to achieve the automatic driving of the vehicle model in different driving modes on the space pavement model. You can directly observe the vehicle's motion status screen, and you can also call up the relevant driving response and driving manipulation curve for analysis.

1.2 Geometric parameters of the test curve

In order to clarify the curve parameter combination, the curve can affect the trajectory characteristics and then change the curve passing speed. In this paper, the author conducts a large-scale variable parameter driving test, curve radius, declination, and curve Both length and pavement width will be used as test variables, and the curve radius is the main variable that plays a controlling role.

The parameter range of the test curve is shown in Tables 1 and 2. Where R is the radius of the curve; A is the plane deflection angle of the curve; WS is the lateral safety distance, that is, the distance between the vehicle body and the curb line; WS (WR) is the lateral safety distance when the road width is WR; Ls is The length of the convoluted line, L sj (A) is the j-th test value of the length of the convoluted line when the deflection angle of the curve is A. In addition, for each set of tests (in the same set of tests, the radius of each curve is equal, the deflection angle and the length of the turning line are variables), a driving test without a turning line is performed, and Lsj = 0 at this time.

1.3 Vehicle direction control and parameter setting

In order to obtain the influence of the curve setting on the vehicle trajectory and speed characteristics, in this paper, two kinds of directional control methods are used: heeling and cutting. The following results are used as the basis for calculation. The following curve driving mode is most common for cautious drivers, and the desired trajectory at this time is the lane centerline. Because the driver's judgment of the center position of the lane is bound to have errors, the lateral position allowable deviation dlat is defined for this purpose, and dlat = 0.4 m on one side. In the simulation, the direction intervention is performed only when the lateral deviation of the trajectory exceeds dlat.

Turn-cut refers to the cornering way of the vehicle close to the inside of the curve, which is often seen on roads with less traffic-when observing or anticipating no oncoming vehicles, the driver will have the opportunity to pass through the entire passage Select the desired trajectory within range. In the RDVES system, cut and bend are simulated by setting constraints when planning the desired trajectory. The desired trajectory that meets these two conditions must be close to the inside of the curve.

Constraint 1: When a straight line enters a curve and then enters a straight line, the curvature of the trajectory gradually increases along the route and then decreases monotonically, reaching the peak curvature at the midpoint of the curve (in the middle of the curve).

Constraint 2: If the corresponding expected trajectory radius in the curve is called the feature radius, then the maximum feature radius is optimal. In order to limit the lateral range of the desired trajectory, the width WC of the driving channel needs to be set in advance when cutting and bending. Since the expected trajectory in the system is defined as the movement trajectory of the geometric center point of the vehicle, and the vehicle has a certain width, in order to ensure that the contour of the vehicle does not exceed the edge of the road surface, the effective body width WV must be deducted from the road surface width when calculating WC And lateral safety distance WS

1.4 Vehicle speed control and parameter setting

The RDVES system implements the automatic driving of the vehicle by following the desired speed, so the expected speed curve along the route must be calculated before the simulation. A large number of measured running speeds indicate that, for a given road, there is an environmental speed. When the curve speed is lower than the environmental speed, the vehicle decelerates into a curve and then accelerates out of the curve; while when the curve speed is higher than the environmental speed, Drive through the curve at ambient speed. The speed of the curve is determined by the allowable lateral acceleration of the driver when driving through the curve.Here it is expressed by aytol, that is, the purpose of the driver to adjust the speed of the curve is to control the lateral acceleration experienced by the vehicle body (or itself) near the aytol. It is also necessary to determine the braking deceleration ab, the longitudinal acceleration ax, and the ambient speed Vmax, which are used to describe the speed change of the vehicle on the curve, the curve, and the curve. It should be noted that aytol, ab, and ax all change with the mileage of the route. The influencing factors include the radius of the curve and the width of the road. Although Vmax is a fixed value for a given road, the geometric parameters of the entire road section are still required. determine.

1.5 Simulation vehicle model

Because the conclusion that the turning line increases the speed of the curve is for small passenger cars (small passenger cars can reach higher speeds on the highway), the small passenger cars are selected as the simulation models in this paper. The vehicle model was created in the ADAM S / Car environment.The structure is a rack-and-pinion steering mechanism, a split drive axle and a swing axle, a double wishbone front and rear suspension, a lateral stabilizer bar, and a disc-clamp hydraulic. The brake, load-bearing body, and tire dynamics model uses the magic formula version proposed by Pacejka in 1997, namely Pacejka97. The main dimensions of the vehicle model are: wheelbase of 2 560 mm, front wheelbase of 1 520 mm, rear wheelbase of 1 594 mm, unloaded vehicle mass of 1 050 kg, unloaded center of gravity height of 520 mm, body length of 4 806 mm , Width 1 800 mm.

2 Influence of Convolution Line 2 on the Trajectory and Velocity Characteristics

First, follow-up and cut tests on a single curve (a curve formed by a single circular curve) are performed to determine whether compared with following driving, cut-and-curve driving will bring utility to the driver and how much effect it can bring. Then carry out the shear-bend test of the "slow-circle-slow" curve under different usage ratios of roundabouts, and then compare with the results of the cut-and-bend test when there are no roundabouts to obtain the use of the roundabouts and their lengths to the trajectory curvature and the curve speed band Coming influence.

The peak of each curve corresponds to the trajectory curvature at the midpoint of the curve. For the same curve (the top two curves are for the same no-turn curve), the cut curve can significantly reduce the trajectory curvature when driving on the curve. More importantly, the turning curve can indeed further reduce the trajectory curvature when driving on a curve, and the longer the turning curve is, the more significant this effect becomes. This finding means that the driver can reach higher speeds on the curve with a roundabout without reducing the lateral allowable acceleration, because the roundabout increases the radius of the trajectory at the center of the curve (in fact, the entire curve The trajectory radius will increase). According to formula (1), the curve speed will increase accordingly.

It can be seen that: the appearance of the turning line increases the speed at the midpoint of the curve (the lowest point of the curve), that is, the turning line does have an impact on the speed; the speed in the entire curve range has been increased, including the control when entering the curve The initial moving speed is due to the decrease of the deceleration demand after the speed of the midpoint of the curve is increased, and the driver can take the deceleration later; The longer the turning line, the greater the speed increase value. Of course, these findings are for the curve of R = 160 m and A = 20 °. More general conclusions will be drawn from the analysis of all the test results below. According to the above analysis, the essence of the effect of the turning line on the speed is whether the use of the turning line slows down the trajectory radius change of the vehicle, so the change of the trajectory radius when the length of the turning line is changed should be obtained.

3 The influence of the convolution line 3 on the trajectory radius

Careful observation, especially in the second set of curves with a 50 ° declination angle, can be found that when the turning line becomes longer, the intersection point of the vehicle trajectory and the road centerline will be advanced when entering the curve; accordingly, the intersection point of the two will be delayed when the curve is exiting As a result, the area enclosed by the trajectory of the vehicle and the center line of the road increases (the "angle" cut off increases). This shows that the convolute line helps the driver to start the cutting and bending behavior early and prolong the cutting and bending process, and also obtains a greater cutting and bending effect. Therefore, it can be considered that the tortuous line changes the topological relationship between the curve and the vehicle trajectory, making it more conducive for the driver to cut and bend. That is, Rcms0. For comparison purposes, the test results in various modes of A and WC without the convolute line in the heel curve mode are also given, namely, Rcms0, f. What combination of curve design parameters (radius, declination, and road width) can be obtained, and setting or lengthening the turning curve can significantly increase the radius of the trajectory on the curve, and in which combination, the turning line pair increases the trajectory Radius no longer works. You can also calculate the curve speed increase and the highest speed that can be achieved when aytol takes any value. This is of great interest to road designers who want to understand the process of the vehicle as much as possible, and then improve the quality of the route design. The conclusions that can be drawn in Figure 6 are:

(1) The turning curve can indeed change the trajectory characteristics on the curve, which is manifested in that the trajectory radius of the midpoint of the curve increases with the length of the turning curve. This confirms that there are indeed factors other than driver's vision that lead to higher speeds with roundabout curves.

(2) For a sharp turn with a radius of 30 m, no matter which combination of parameters (radius, declination, and road width), the turning line can always increase the radius of the track on the curve. When the radius exceeds 65 m, the trajectory radius is very sensitive to the length of the cycloid under certain parameter combinations, while in other combinations, the cycloid can only cause a slight increase in the radius of the trajectory, or even do not work. This shows that not all curves will increase the radius of the trajectory due to the convoluted line.

(3) By comparing Rcms0 and Rcms0, f, it can be concluded that the smaller the deflection angle, the wider the driving aisle, and the greater the effect of cutting and bending on the curve (the larger R cms0). The deflection angle is the decisive factor. When the deflection angle exceeds a certain value, R cms0 is 0. At this time, no matter how wide the channel is, it has no effect. It can also be found in Figure 6 that the high speeds on those small deflection angles of 5 ° to 10 ° are mainly caused by the driver's cutting and bending behavior, and the role of the clothoid is very limited.

(4) When the deflection angle of the curve is in the range of 10 ° ~ 35 °, the longer the turning line is, the larger the radius of the curve of the curve is. In other words, the trajectory can be pulled straighter, which will induce the driver to choose a higher cornering speed. Therefore, it can be considered that within this range of deflection angles, the convoluted line has a significant effect on the trajectory characteristics, at least when the driving lane is 3 to 7 m wide (road width is 5 to 10 m). In fact, 10 ° 35 ° is also the most commonly used deflection angle range for planar linear design.

(5) After the deflection angle of the curve reaches 35 °, the influence of the curve on the trajectory decreases with the increase of the deflection angle. For curves with declination exceeding 70 °, you want to straighten the trajectory by cutting and bending, and you want to further slow down the trajectory radius by the roundabout.It is only feasible when R <65 m. When R 65 m, set or Extending the roundabout can no longer improve the cutting and bending effect of large deflection corners.

(6) For a curve with a deflection angle of 20 ° to 35 °, when Ps increases from 67% to 100%, the increase in the radius of the trajectory caused by the convolute line is significantly greater than the increase when Ps increases from 0 to 67%. This shows that when the curve line transitions from the "slow-circle-slow" combination of 1: 1 to the convex line, the trajectory radius is very sensitive to the use ratio of the convolute line, and it also shows that the vehicle can be on the convex line with the same radius Achieve higher speed. According to the above analysis, the driver's cutting and bending behavior will change the trajectory characteristics in the curve range, and the appearance of the convolute line will further amplify this effect, causing the actual trajectory radius to deviate significantly from the design radius. The basic principle of route design is that the plane alignment and the trajectory are consistent. From this perspective, when the deflection angle of the curve is 10 ° ~ 35 °, the length of the turning line should be as low as possible to reduce the speed of the curve; In addition, the use of a small deflection curve of 5 ° to 10 ° should be minimized, because the trajectory after cutting and bending is already close to a straight line.

4 The effect of the roundabout 4 on the speed of the curve

The trajectory radius of a vehicle on a loud curve, especially for those corners with a small deflection angle, the trajectory radius increases significantly with the increase of the use ratio of the curve. Because the driver adjusts the speed of the vehicle on the curve through his own driving experience, including lateral comfort, lateral safety (body tilt) and direction controllability, etc., these feelings can be directly or indirectly used by lateral acceleration ay to measure. For each driver, there is an allowable value aytol. When driving on a curve, the driver will subconsciously maintain ay near ay tol by selecting the speed. Therefore, under the condition that aytol remains unchanged, when the radius of the curve trajectory increases, the curve speed will inevitably increase accordingly. In fact, for a given curve, the driver chooses to cut corners just to increase the cornering speed, so it is impossible to reduce the lateral acceleration tolerance level in this case.

Of course, for strong aggressive or aggressive drivers, aytol can take a larger value; if it is a simulated track, aytol can get larger.

(1) When R = 30 and 65 m, no law can be found between Sp s, A and WC, which indicates that there is no correlation between the three. When R 90 m, the effect of A on S ps begins to appear. The corresponding curve deflection angle when the speed increase is most sensitive to Ps is 20 °, then 35 °, and the declination angle when it is the least sensitive is 70 °. , 90 °, and 5 °.

(2) If only the speed increase above 2 kmh-1 is considered (the driver may not be able to detect the speed change below 2kmh-1), then the roundabout can only drive the driver when A 50 ° The driver's cornering speed selection behavior has an impact. In a total of 21 tests with V> cms2 km · h-1, there were 13 20 ° curves, accounting for 31.9%, 6 35 ° curves, accounting for 28.6%, and 50 ° curves. There are two, accounting for 9.5%, and the 50 ° curves are all wide road curves (WC = 7 m).

(3) In most cases, for a curve with a deflection angle of 20 °, which is more sensitive to the length of the turning line, it can be found that in the case of a narrow road (WC = 3 m, WR = 5 m), the turning is used. Lines can achieve greater curve speed increases than wide pavement conditions.

(4) Most Vcms curves experience vertices at Ps = 40%, Ps = 50%, and Ps = 67%, and the slope of the curve after the vertice is greater than the slope before the vertice. This shows that in the case where a continuous Vcms-P s curve can be obtained, the curve should be concave. Therefore, it can be considered that the influence of the curve on the curve speed is very limited when the use ratio of the clothoid is low. Only after the length of the convoluted line reaches a certain length ratio, the length can be increased to reflect its effect on the speed characteristics.

For most curves, the turning line that appears between a straight line and a circular curve can always increase the speed of the curve, and the speed increase increases with the length of the turning line. This shows that the high speed of the roundabout curve is indeed a cause of "route-vehicle" kinematics. However, it can also be seen that this speed increase is also affected by other curve design parameters, such as declination, radius, and road width.

Increasing the speed of the curve will make it difficult to control the direction, and it will also increase the severity of off-road accidents and collision accidents, and the designer does not want the curve speed to deviate too far from the designed speed, so it is necessary Control it. From this perspective, designers need to pay special attention to the cooperation with other design elements when arranging the convolute lines. In those declination ranges where the speed increase is more sensitive to the length of the convolute lines, such as 10 ° to 35 °, short convolutions should be used as much as possible. Line or omit it. At the same time, for narrow roads (generally low-grade roads in mountainous areas), try not to use roundabouts to reduce off-road accidents caused by high-speed traffic.

5 Convolution 5

(1) In this paper, a large number of curve driving tests are used to obtain the mechanism of the influence of the turning curve on the vehicle trajectory and speed, thereby explaining the problem of higher speed of the curve when there is a turning curve, that is, the turning curve changes the cutting and bending driving. The topological relationship between the trajectory and the curve line shape increases the trajectory radius within the curve range, which has the effect of "straightening" the curve. Therefore, the driver can choose a higher speed, that is, the roundabout will cause a speed increase. the amount. However, the magnitude of the speed increment also depends on the other three curve line parameters such as deflection angle, road width, and radius. This discovery will help road design and researchers to better understand the law of the effect of the roundabout on vehicle kinematic behavior, provide a basis for the reasonable setting of the roundabout, and finally make the design control concept of the route truly realized.

(2) The analysis in this article is a single curve, but there are a large number of continuous curves in the highway in Zhongshan District. When the straight line between bends is short or no straight line between bends, the cutting and bending effect of the current curve is likely to be affected by adjacent curves, and it will be enlarged or weakened. Therefore, the next step is to study the influence of the inverse curve (including S-curve) and the oval curve on the vehicle trajectory and speed. For the same-direction curve, the length of the middle straight line required by the Chinese design code is much longer than the length of the middle straight line of the reverse curve. Due to the long distance, the influence of adjacent curves can be ignored. From this perspective, the same-direction curve can be regarded as 2 single The combination of curves is applicable to the conclusions of this study. ^[1]