Method for estimating the road surface on which tracked vehicles travel

Abstract

The method for estimating the road surface on which a tracked vehicle is traveling belongs to the technical field of the technical field of the method for calculating the scene of a tracked vehicle, and solves the technical problem that the existing method has low accuracy in measuring the current scene of the road surface. It includes establishing a mathematical model of the track on multiple different scene roads, and determining the theoretical traction value of the vehicle track under the ground force, and determining the relationship between the maximum shear stress and the cohesion and the internal shear strength angle; determining the expression of the shear stress of the left and right tracks under different road surfaces; obtaining the torque data of the friction between the vehicle track and the ground and the set of track traction observation values ​​within a preset time period; and determining the current scene road surface of the track based on the theoretical traction value, traction value and traction observation value set. The actual track cohesion and internal shear strength angle are calculated through mechanical characteristics to realize the identification of various complex off-road road surfaces and avoid the influence of noise in the image method on the measurement accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of tracked vehicle scene calculation methods, and in particular, relates to a method for estimating a road surface on which a tracked vehicle is traveling. Background Art

[0002] Modern cars usually travel on well-paved roads. A series of dynamics-based road adhesion coefficient observation methods have been developed under standard roads to provide better control basis for the dynamic control of cars. However, in reality, there are still many fields such as agriculture, military, exploration, etc. that still need to be carried out on unrepaired roads. Tracked vehicles have a wide range of applications in the above fields due to their better passability than wheeled vehicles. For skid-steering tracked vehicles, if the current road conditions can be accurately estimated, their control performance can be greatly improved.

[0003] However, for various outdoor road conditions, such as deserts, snowfields, swamps, etc., the ground mechanical properties are more complex than those of standard roads, and the mechanical properties under different road conditions are quite different. Traditional road image recognition methods are difficult to accurately identify all possible road surfaces under different driving conditions, and the observation accuracy will also be affected by the strong nonlinearity of the track and the noise of the sensor.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a method for estimating the road surface on which a tracked vehicle is traveling, so as to solve the technical problem that the existing method has low accuracy in measuring the current scene of the road surface. The technical solution of this case has many technical benefits, as described below:

[0006] A method for estimating a road surface on which a tracked vehicle is traveling is provided, the method comprising:

[0007] Establishing mathematical models of the crawler on a plurality of different road surfaces based on CAM software, and determining theoretical parameter values ​​of each of the different road surfaces;

[0008] Determining the maximum shear stress of the crawler on multiple road surfaces according to the multiple mathematical models, and determining the relationship between the maximum shear stress and the cohesion and the internal shear strength angle;

[0009] Determine the shear stress expression at each point of the left and right tracks;

[0010] Obtaining the torque data of the vehicle's traction wheel or road wheel, and performing calculus processing on the expression to determine the traction force value of the left and right tracks at the current time point, and the observed value of the track driving force within a preset time period;

[0011] Determining actual parameter values ​​of the road surface according to the observed values ​​of the traction force value and the driving force;

[0012] The current scene road surface of the crawler is determined according to the actual parameter value and the theoretical parameter value of the road surface.

[0013] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects:

[0014] The method provided in this case is an off-road road surface identification method based on a mixed Gaussian model. Through the mechanical properties of the vehicle, such as the torque of the towing wheel and / or the road wheel, the actual track cohesion and internal shear strength angle are calculated to achieve identification of various complex off-road road surfaces, avoiding the influence of noise in the image method on the measurement accuracy, and avoiding inaccurate road scene distinction. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A schematic diagram of the inventive method. DETAILED DESCRIPTION

[0017] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work belong to the scope of protection of the present invention.

[0018] It should be noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be embodied in a wide variety of forms, and any specific structure and / or function described herein is merely illustrative. Based on the present invention, it should be understood by those skilled in the art that an aspect described herein can be implemented independently of any other aspect, and two or more of these aspects can be combined in various ways. For example, any number of aspects described herein can be used to implement the device and / or practice the method. In addition, other structures and / or functionalities other than one or more of the aspects described herein can be used to implement this device and / or practice this method.

[0019] like Figure 1 The method for estimating a road surface on which a tracked vehicle is traveling comprises:

[0020] S101: Based on CAM software, a mathematical model of the track on multiple different road surfaces is established, and the theoretical parameter value of each road surface in different scenarios is determined. The theoretical parameter value includes the theoretical traction value of the vehicle track under the ground force, and the theoretical traction value includes the theoretical soil parameter cohesion and the tangent value of the internal shear strength angle of the road surface in different scenarios. Specifically:

[0021] For example, given three different scenario pavements, such as loose sand or saturated clay, swamp, and dense sand, the shear stress and shear displacement of each scenario satisfy:

[0022]

[0023]

[0024] in:

[0025] is the maximum shear stress of the road surface, The shear displacement required to reach the maximum shear stress; is the ratio of the residual shear stress to the maximum shear stress under the ground. and It is the displacement caused by the friction between the track and the road surface;

[0026] S102: Determine the maximum shear stress of the crawler on multiple road surfaces according to multiple mathematical models, and determine the relationship between the maximum shear stress and the cohesion and the internal shear strength angle, specifically:

[0027] The relationship between the maximum shear stress, cohesion and internal shear strength angle is obtained through conversion by Coulomb force formula, and it satisfies:

[0028]

[0029]

[0030] in:

[0031] c (i) is the cohesion under different road conditions, Δ is the normal stress on the contact surface between the track and the ground, φ (i) Internal shear strength angle φ (i) , and These are all known theoretical parameters, and the normal stress Δ at the contact surface between the track and the ground is a known quantity.

[0032] S103: Determine the shear stress expression of each point on the left and right tracks. Generally, a vehicle includes left and right tracks. Therefore, the slip rate of the left and right tracks is s. L and R ,satisfy:

[0033] and in:

[0034] v x is the longitudinal velocity of the vehicle's center of mass; v L is the longitudinal speed of the left track center; v R is the longitudinal speed of the center of the left track, and x represents the longitudinal position of the track, which lays the foundation for the calculation of the traction value.

[0035] S104: Obtain the torque data of the friction between the vehicle track and the ground, such as the torque data of the vehicle's traction wheel or road wheel or other torque data that can reflect the friction between the track and the ground. The torque of the vehicle's traction wheel or road wheel is an actual value. Generally, the actual value can be measured using a torque sensor. The core of the method in this case uses this value to replace the image measurement method and calculate the current road scene through its own accurate torque data. Perform calculus processing on the expression to determine the traction value of the left and right tracks at the current time point, and the observed value of the track driving force within a preset time period;

[0036] The slip ratio of the left and right tracks is converted to s j x, shear stress τ at each point of the track (i) Transformed into 3 (three different scene road) about s j and x, and satisfy:

[0037]

[0038] Integrate the track contact area, and the traction value of the left and right tracks at the current time point for:

[0039]

[0040] The driving force observation value of the preset time period before the current time point is obtained. The actual observation value of the track driving force within the preset time period is determined according to the torque data of the vehicle traction wheel or the road wheel obtained, and meets the following conditions:

[0041] Λ j (s j )={Λ j (s j ,t-N+1),L,Λ j (s j ,t-1),Λ j (s j ,t)};

[0042] S105: Determine the current scene road surface of the crawler according to the above theoretical traction value, traction value and traction observation value set, specifically:

[0043] The Gaussian formula is used to determine the relationship between the observed values ​​of the traction force and the driving force. The theoretical value of the current traction force can be determined through the observed value. Therefore, it satisfies:

[0044] Observed value of driving force Λ j (s j ,t)About The conditional probability of conforming to the Gaussian distribution is:

[0045]

[0046] The Gaussian distribution of the observed values ​​of the inner track driving force within the preset time period satisfies:

[0047]

[0048] The set of observed values ​​of traction for unknown road surfaces The conditional probability of uses the weighted superposition of these three Gaussian distributions to satisfy:

[0049]

[0050] In the formula, weight π={π (1) ,π (2) ,π (3)}satisfy:

[0051] The observed value of the driving force of the current road surface is transformed into a log-likelihood function using the weight law of the mixed Gaussian distribution to determine the actual parameter value. Specifically:

[0052] Observed value of driving force The log-likelihood function satisfies:

[0053]

[0054] use Constraints are imposed, and the log-likelihood function is transformed using the Lagrange multiplier method to determine the likelihood function that satisfies the constraints and satisfies:

[0055]

[0056] By taking the derivative of the likelihood function that satisfies the constraints and setting it equal to 0, we can determine:

[0057]

[0058]

[0059] Multiply each by the corresponding weight force π (1) , π (2) and π (3) And summing, we get:

[0060] λ=-N, and then bring it back into the formula after the likelihood function that satisfies the constraints is derived, and we get:

[0061] Where N (i) Definition:

[0062]

[0063]

[0064] in:

[0065] The membership degree of the nth data point to the i-th Gaussian distribution within the preset time period, N (i) is the membership of all N data points to the i-th Gaussian;

[0066] The likelihood function obtained by using the Lagrange multiplier method to transform the log-likelihood function is transformed (σ (i) ) 2 Take the derivative and make it equal to 0 to obtain the formula for the variance of each Gaussian distribution:

[0067]

[0068] The maximum number of iterations is preset. When the variance of each Gaussian distribution (σ (i) ) 2 When it is less than the preset allowable value, the iteration stops and the last weight π is output. (i), it should be noted that the last weight π (i) It is obtained by using the mixed Gaussian distribution formula based on the actual torque of the traction wheel and the road wheel measured by the time torque sensor;

[0069] According to the last output weight π (i) and the maximum shear stress After transformation, the actual parameter value can be obtained:

[0070] Soil parameters Cohesion

[0071] Tangent of the internal shear strength angle

[0072] S106: Determine the current scene road surface of the crawler according to the actual parameter value and the theoretical parameter value of the road surface, specifically:

[0073] According to the comparison between the tangent value of the actual soil parameter cohesion and the internal shear strength angle and the tangent value of the theoretical soil parameter cohesion and the internal shear strength angle, the scene to which the vehicle belongs is determined, specifically:

[0074] Obtain the theoretical soil parameter cohesion and the tangent value of the internal shear strength angle of the pavement in different scenarios, which can be found through the design specifications of the scenario theoretical traction, that is,

[0075] According to the last output weight π (i) The determined actual soil parameters cohesion and the tangent value of the internal shear strength angle are compared with the theoretical values ​​to determine which pavement scenario it belongs to.

[0076] The significance of the invention in this case is first to avoid the situation where the traditional image measurement method reduces the measurement accuracy due to the presence of noise;

[0077] Secondly, the real-time torque of the actual traction wheel or road wheel is used to calculate different road scenarios, providing the driver with reliable measurement data to facilitate the output control of the operation, such as the amount of throttle;

[0078] Finally, scenes change back and forth in reality. For example, in the green belts that appear in the desert area, the scene road information switches back and forth. It should be emphasized that during night driving, changing weather conditions will affect image acquisition, and the measurement accuracy will be greatly reduced. There will be inconsistencies between the real scene and the scene analyzed by the image, which will mislead the operator. The scene road information calculated by track dynamics is more accurate and is calculated based on the current measured track and ground force conditions.

[0079] The above is a detailed introduction to the product provided by the present invention. Specific examples are used in this article to illustrate the principle and implementation method of the present invention. The description of the above embodiments is only used to help understand the core idea of ​​the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of invention, several improvements and modifications can be made to the invention, and these improvements and modifications also fall within the scope of protection of the invention claims.

Claims

1. A method for estimating a road surface on which a tracked vehicle is traveling, characterized in that: The method comprises: Establishing mathematical models of tracks on multiple different road surfaces based on CAM software, and determining theoretical parameter values ​​of each of the different road surfaces, wherein the theoretical parameter values ​​include theoretical traction values ​​of the vehicle tracks under the force of the ground; Determining the maximum shear stress of the crawler on multiple road surfaces according to the multiple mathematical models, and determining the relationship between the maximum shear stress and the cohesion and the internal shear strength angle; Determine the expression of shear stress of left and right tracks under different road conditions; Obtaining torque data of friction between the vehicle track and the ground, and performing calculus processing on the expression to determine the traction value of the left and right tracks at the current time point, and determining a set of track traction observation values ​​within a preset time period before the current time point; Determining the current scene road surface of the crawler according to the theoretical traction value, the traction value and the traction observation value set includes: Based on the mixed Gaussian model, the relationship between the traction force value and the observed value is determined to obtain the cohesion and internal shear strength angle of the soil; According to the cohesion and internal shear strength angle of the soil, the current scenario road surface of the track is determined.

2. The method according to claim 1, characterized in that Mathematical models for at least three different road surfaces, including at least loose sand or saturated clay, swamp and dense sand, and the shear stress and shear displacement of each of them satisfy: ； ； ,in: is the maximum shear stress of the road surface, The shear displacement required to reach the maximum shear stress; is the ratio of the residual shear stress to the maximum shear stress under the ground, and d is the displacement caused by the friction between the track and the road surface; The relationship between the maximum shear stress, cohesion and internal shear strength angle is obtained by conversion through the Coulomb force formula, and satisfies: ,in: For the cohesion in different road scenarios, Normal stress at the contact surface between the track and the ground, Internal shear strength angle .

3. The method according to claim 2, characterized in that The torque data of the friction between the vehicle track and the ground is obtained by real-time measurement of the torque data of the vehicle's traction wheel or road wheel. The method of performing calculus processing on the expression to determine the traction force value of the left and right tracks at the current time point includes: The left and right track slip ratios are set to and , and satisfy: and ,in: is the longitudinal velocity of the vehicle’s center of mass; is the longitudinal speed of the left track center; is the longitudinal speed of the right track center, Indicates the longitudinal position of the track; The slip ratio of the left and right tracks is converted to , the shear stress at each point of the track Determined as three and The expression satisfies: Integrate the track contact area, and the traction value of the left and right tracks at the current time point for: 。 4. The method according to claim 3, characterized in that: The method for observing the track driving force within the preset time period includes: The actual observed value set of the track driving force within the preset time period is determined based on the torque data of the vehicle traction wheel or the road wheel, and satisfies .

5. The method according to claim 4, characterized in that The method for determining the actual parameter value of the road surface according to the observed values ​​of the current traction force value and the driving force comprises: The conditional probability relationship between the current observed values ​​of the traction force value and the driving force is determined using a mixed Gaussian distribution, and satisfies: ， The Gaussian distribution of the observed values ​​of the inner track driving force within the preset time period satisfies: ， Observed value of traction on unknown road surface The conditional probability of is the weighted superposition of three Gaussian distributions, satisfying: In the formula, the weight satisfy: , The weight law of mixed Gaussian distribution is used to transform the observed set value of the current road driving force into a log-likelihood function to calculate the actual parameter value.

6. The method according to claim 5, characterized in that The method of transforming the log-likelihood function to determine the actual parameter value includes: The set of observed values ​​of the driving force The log-likelihood function satisfies: ; use The constraints are imposed, and the log-likelihood function is transformed using the Lagrange multiplier method to determine the likelihood function that satisfies the constraints: ； By taking the derivative of the likelihood function that satisfies the constraints and setting it equal to 0, we can determine: ， ， , multiplied by the corresponding weight force , and And summing, we get: , and then bring it back into the formula after the likelihood function that satisfies the constraints is derived, and we get: , where Definition: ,in: Within the preset time period Data points for The membership degree of a Gaussian distribution is For all The data points are overall The membership of a Gaussian; The likelihood function obtained by converting the log-likelihood function using the Lagrange multiplier method is Take the derivative and make it equal to 0 to obtain the formula for the variance of each Gaussian distribution: ； The maximum number of iterations is preset, and when the variance of each Gaussian distribution is When it is less than the preset allowable value, the iteration stops and the last weight is output. ; According to the output of the last weight and the maximum shear stress By transformation, we can get: Soil parameters Cohesion , Tangent of the internal shear strength angle .

7. The method according to claim 6, characterized in that: Obtaining the theoretical traction force values ​​of road surfaces in different scenarios, wherein the theoretical traction force values ​​include the tangent value of theoretical soil parameters cohesion and internal shear strength angle; According to the output of the last weight The actual soil parameters determined are cohesion and the tangent of the internal shear strength angle; The scene to which the vehicle belongs is determined by comparing the tangent values ​​of the actual soil parameters cohesion and internal shear strength angle with the tangent values ​​of the theoretical soil parameters cohesion and internal shear strength angle.

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