Road surface gradient estimation device

Abstract

This technology provides a way to suppress the decrease in accuracy when deriving the gradient of the road surface on which a vehicle is traveling. [Solution] The road surface gradient estimation device 10 includes an acquisition unit 20 that acquires the detection results of an acceleration detection unit 12 and a wheel speed detection unit 14 that detect acceleration in the longitudinal direction of the vehicle, and acquires information regarding the output of the vehicle drive; an extraction unit 22 that derives the gradient of the road surface on which the vehicle is traveling as a first road surface gradient based on the acquired acceleration and wheel speed; and a correction unit 26 that corrects the derived first road surface gradient based on information regarding the output of the vehicle drive to derive a second road surface gradient.

Description

Technical Field

[0001] The present invention relates to a technique for estimating the gradient of the road surface on which a vehicle is traveling.

Background Art

[0002] Patent Document 1 discloses a vehicle control device including a gradient estimation unit that estimates a gradient based on the front and rear acceleration sensor values and the acceleration obtained from the change amount of the wheel speed, and a change amount limiting unit that limits the change amount of the wheel speed based on the calculated acceleration of the vehicle according to the torque of the motor. This change amount limiting unit limits the change amount of the wheel speed when the wheel slips, and the gradient estimation unit estimates the gradient based on the change amount limit value.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique described in Patent Document 1, when the detection accuracy of the acceleration sensor is constantly reduced due to an offset error or the like in advance, the estimation accuracy of the gradient may be reduced.

[0005] An object of the present invention is to provide a technique for suppressing a decrease in the accuracy of deriving the gradient of the road surface on which a vehicle is traveling.

Means for Solving the Problems

[0006] To solve the above problems, a road surface gradient estimation device according to one aspect of the present invention includes: an acquisition unit that acquires the detection results of an acceleration detection unit and a wheel speed detection unit that detect acceleration in the longitudinal direction of the vehicle, respectively, and acquires information regarding the output of the vehicle drive; a derivation unit that derives the gradient of the road surface on which the vehicle is traveling as a first road surface gradient based on the acquired acceleration and wheel speed; and a correction unit that corrects the derived first road surface gradient based on information regarding the output of the vehicle drive to derive a second road surface gradient. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a technology that suppresses the decrease in accuracy in deriving the gradient of the road surface on which a vehicle is traveling. [Brief explanation of the drawing]

[0008] [Figure 1] This figure shows the functional configuration of the road surface gradient estimation system in the embodiment. [Figure 2] This is a diagram illustrating the method for deriving the first road surface gradient. [Figure 3] This is a diagram illustrating the road surface gradient correction process in the embodiment. [Figure 4] This diagram illustrates the correction process for the road surface gradient in the modified example. [Modes for carrying out the invention]

[0009] Figure 1 shows the functional configuration of the road surface gradient estimation system 1 of the embodiment. The road surface gradient estimation system 1 comprises a road surface gradient estimation device 10, an acceleration detection unit 12, a wheel speed detection unit 14, a driving state detection unit 16, and a driving support device 18, and is mounted on a vehicle. The road surface gradient estimation device 10 acquires the detection results of the acceleration detection unit 12, the wheel speed detection unit 14, and the driving state detection unit 16, derives the road surface gradient while the vehicle is driving, and outputs the derived road surface gradient to the driving support device 18.

[0010] The acceleration detection unit 12 detects the acceleration of the vehicle in the longitudinal direction and sends the detection result to the road surface gradient estimation device 10. The wheel speed detection unit 14 detects the wheel speed, which is the rotational speed of the wheels, and sends the detection result to the road surface gradient estimation device 10. The wheel speed detection unit 14 is provided for each wheel and may output the wheel speed of any of the wheels as the wheel speed, or it may output the average value of the wheel speeds of all wheels as the wheel speed.

[0011] The driving state detection unit 16 detects the vehicle's driving state and sends the detection result to the road surface gradient estimation device 10. Information regarding the vehicle's driving state includes the engine output value (i.e., driving force), the engine's target driving force, the brake system output value (i.e., driving force), the brake system's target driving force, vehicle speed, tire friction force, and steering angle. The engine system's target driving force and the brake system's target driving force are command values. The engine system output value, the brake system output value, vehicle speed, and tire friction force are information regarding the output of the vehicle drive.

[0012] The driver assistance device 18 has functions to assist the driver, and for example, it performs automatic driving control such as cruise control control and follow control. The driver assistance device 18 receives road surface gradient information from the road surface gradient estimation device 10 and commands an output corresponding to the road surface gradient during automatic driving control.

[0013] The road surface gradient estimation device 10 comprises an acquisition unit 20, a derivation unit 22, a determination unit 24, a correction unit 26, an output unit 28, and a storage unit 30. The acquisition unit 20 acquires the detection results of an acceleration detection unit and a wheel speed detection unit that detect acceleration in the longitudinal direction of the vehicle, respectively, and acquires information regarding the output of the vehicle drive. The acquisition unit 20 also acquires driving state information that indicates the driving state of the vehicle.

[0014] The derivation unit 22 derives the gradient of the road surface on which the vehicle is traveling as the first road surface gradient, based on the vehicle's longitudinal acceleration and wheel speed. Refer to Figure 2. Figure 2 is a diagram illustrating the method for deriving the first road surface gradient.

[0015] In Figure 2, vehicle 32 is traveling on a road surface with a road surface gradient θ. Vehicle 32 is moving with a vehicle driving force F and is subjected to a gradient acceleration (g·sinθ) from the road surface. Vehicle 32 is traveling with an acceleration a calculated from the derivative of the wheel speed.

[0016] The acceleration (a+g·sinθ) acting on the vehicle 32 is estimated to be equal to the acceleration a' detected by the acceleration detection unit 12. The derivation unit 22 estimates the gradient acceleration (g·sinθ) using the following equation 1 based on the derivative a of the wheel speed, the acceleration a' in the longitudinal direction of the vehicle, and the acceleration g due to gravity. The road surface gradient θ is a negative angle on a downhill slope and a positive angle on an uphill slope. Note that it is also possible to make the downhill slope a positive angle and the uphill slope a negative angle, but in that case, there will be a place in the equation where the sign of positive and negative will be reversed in the road surface gradient θ part. a'-a=g·sinθ ···Equation 1

[0017] Here, when the first road surface gradient is derived, the acceleration a' detected by the acceleration detection unit 12 is used, but there is a possibility that the sensor value of the acceleration detection unit 12 may have offset errors or temperature errors. Therefore, the correction unit 26 corrects the derived first road surface gradient based on information regarding the output of the vehicle drive to derive the second road surface gradient. The first road surface gradient and the second road surface gradient may be the gradient acceleration (g·sinθ) and the road surface angle θ.

[0018] Figure 3 is a diagram illustrating the road surface gradient correction process in the embodiment. The derivation unit 22 estimates the gradient acceleration (g·sinθ) using Equation 1 (S10). The derivation unit 22 multiplies the gradient acceleration (g·sinθ) by the vehicle weight m (S12) and adds the vehicle driving force f (S14). In S14, the force F acting on the entire vehicle is derived as shown in Equation 2 below. -mg·sinθ+f=F ···Equation 2 m is the vehicle weight, which is pre - held in the storage unit 30. The vehicle weight m includes the weight of the passengers. The weight of the passengers may be a preset value. The vehicle driving force f is calculated by adding the output value of the engine device, the output value of the brake device, the frictional force of the tires, and the air resistance respectively. The air resistance is calculated according to the vehicle speed. The output value of the engine device, the output value of the brake device, and the frictional force of the tires may be values detected by the running state detection unit 16, and may receive those calculated by the drive control and brake control systems.

[0019] The correction unit 26 executes the correction value derivation process 34 surrounded by a dashed line. The correction unit 26 divides the force F applied to the entire vehicle by the vehicle weight m to estimate the running acceleration a” (S16). The correction unit 26 derives the difference between the running acceleration a” and the acceleration a’ detected by the acceleration detection unit 12 as a temporary correction value (S18). Thus, the error between the estimated value and the actual measured value is derived as the temporary correction value. In S20, the correction unit 26 sends the temporary correction value as it is to the next step with H(s)=1.

[0020] The determination unit 24 determines whether the acquired running situation information satisfies the predetermined stable running conditions. When the correction unit 26 does not satisfy the predetermined stable running conditions, the correction unit 26 discards the temporary correction value and executes a latch process of using the correction value used in the previous correction value as the current correction value (S22). In the latch process, when the predetermined stable running conditions are satisfied, the correction unit 26 sets the temporary correction value as the current correction value (S22). While the predetermined stable running conditions are not satisfied, the correction unit 26 continues to correct with the same correction value. The previous correction value refers to the correction value one cycle before the current calculation cycle.

[0021] The specified stable driving conditions are not satisfied when the vehicle 32 is suddenly braking, suddenly steering, or stopped. This is because when the vehicle 32 is not driving stably, the vehicle driving force f cannot be accurately detected. For example, the specified stable driving conditions are satisfied when the change amount of the output value of the braking device is less than or equal to a predetermined amount, the change amount of the steering angle is less than or equal to a predetermined angle, and the vehicle speed is greater than or equal to a predetermined speed. Also, the specified stable driving conditions include that the acceleration detection unit 12 is not malfunctioning. If the acceleration detection unit 12 is malfunctioning, the conditions are not satisfied.

[0022] The correction unit 26 adds the gradient acceleration (g·sinθ) and the current correction value to derive a corrected gradient acceleration (S24). The correction unit 26 may output the corrected gradient acceleration as the second road surface gradient, or may output the angle θ derived from the corrected gradient acceleration as the second road surface gradient. The correction unit 26 causes the storage unit 30 to store the correction value used in the current correction. The output unit 28 sends the derived second road surface gradient to the driving support device 18.

[0023] Thus, the correction unit 26 calculates a correction value based on information related to the output of vehicle driving, and corrects the derived first road surface gradient with the correction value to derive a second road surface gradient. Thereby, even if an offset error or the like occurs in the acceleration detection unit 12, it is possible to suppress a decrease in the derivation accuracy of the road surface gradient.

[0024] The correction unit 26 derives a correction value based on the estimated gradient acceleration (g·sinθ), the detected acceleration a' in the vehicle longitudinal direction, the vehicle weight m, and the vehicle driving force f. The correction unit 26 estimates a driving acceleration a'' based on the estimated gradient acceleration (g·sinθ) and the vehicle driving force f, and derives a correction value based on the difference between the estimated driving acceleration a'' and the actual measured acceleration a' in the vehicle longitudinal direction. Thereby, the correction value can be accurately derived based on the difference between the estimated driving acceleration a'' and the actual measured acceleration a'.

[0025] The correction unit 26 derives a second road surface gradient by correcting the first road surface gradient with the correction value used in the previous correction if the acquired driving condition information does not meet predetermined stable driving conditions. The previous correction value is stored in the storage unit 30 during the previous calculation cycle. As a result, the correction is performed with the same correction value until the predetermined stable driving conditions are met. By correcting with the previous correction value, the correction unit 26 can avoid correcting with an unstable correction value. If the offset error of the acceleration detection unit 12 is constant, the correction unit 26 can reduce the effect of the offset error by correcting with the previous correction value.

[0026] The true vehicle weight M shown in S26 in Figure 3 is used in theoretical calculations, but it is not used in actual calculations because the measured value of acceleration is used.

[0027] Figure 4 is a diagram illustrating the road surface gradient correction process in a modified example. The correction unit 26 in the modified example performs the correction using the transmission characteristic G(s), which is information regarding the output of the vehicle drive. The storage unit 30 may store the transmission characteristic G(s) in advance, and the acquisition unit 20 acquires the transmission characteristic G(s) from the storage unit 30 or the like.

[0028] The transmission characteristic G(s) is a function that shows the relationship between the target driving force of the vehicle and the resulting acceleration in the longitudinal direction of the vehicle. In other words, the transmission characteristic G(s) receives the target driving force of the engine unit and the target driving force of the brake unit as inputs and outputs the acceleration in the longitudinal direction of the vehicle. The target driving force of the engine unit and the target driving force of the brake unit are command values ​​to the engine unit and brake unit, and are called the target driving force fr of the vehicle drive. The target driving force of the engine unit and the target driving force of the brake unit may be obtained from the driver assistance device 18 during automatic driving control.

[0029] The derivation unit 22 estimates the gradient acceleration (g·sinθ) using Equation 1 (S30). The derivation unit 22 multiplies the gradient acceleration (g·sinθ) by the vehicle weight m to derive the gradient force (mg·sinθ) (S32).

[0030] The correction unit 26 executes the correction value derivation process 36 enclosed by the dashed line. The correction unit 26 subtracts the estimated gradient force (mg·sinθ) from the target driving force fr of the vehicle drive and derives the target driving force fr' with the effect of the road surface gradient added (S34). The correction unit 26 puts the derived target driving force fr' into the transmission characteristic G(s) and estimates the driving acceleration a'' (S36).

[0031] The correction unit 26 derives the difference between the acceleration a' detected by the acceleration detection unit 12 and the running acceleration a'' (S38). This derives the error between the actual measured value and the estimated value. Note that the transfer function G'(s), which is the true value shown in S48, is used in theoretical calculations and is not used in actual calculations because the actual measured value of acceleration is used.

[0032] The correction unit 26 calculates H(s) = G -1 Substitute the difference (a'-a) derived in S38 into (s) and derive the target output value as a provisional correction value (S40).

[0033] The determination unit 24 determines whether the acquired driving condition information satisfies predetermined stable driving conditions, and the correction unit 26, if the predetermined stable driving conditions are not met, discards the provisional correction value and performs a latch process to set the correction value used in the previous correction value as the current correction value (S42). In the latch process, if the predetermined stable driving conditions are met, the correction unit 26 sets the provisional correction value as the current correction value (S42). The correction unit 26 stores the current correction value in the storage unit 30.

[0034] The correction unit 26 adds the estimated gradient force (mg·sinθ) and the current correction value (S44), and then adds the target output value fr to derive the corrected target output value fr'' (S46). The output unit 28 outputs the corrected target output value fr'' to the driving support device 18, and the driving support device 18 controls the engine and brake systems with the target output value fr''.

[0035] The present disclosure has been explained above based on the examples described. The present disclosure is not limited to the examples described above, and various modifications such as design changes can be made based on the knowledge of those skilled in the art. [Explanation of symbols]

[0036] 1 Road surface gradient estimation system, 10 Road surface gradient estimation device, 12 Acceleration detection unit, 14 Wheel speed detection unit, 16 Driving state detection unit, 18 Driving support device, 20 Acquisition unit, 22 Derivation unit, 24 Judgment unit, 26 Correction unit, 28 Output unit, 30 Memory unit, 32 Vehicle.

Claims

1. An acquisition unit acquires the detection results from an acceleration detection unit and a wheel speed detection unit that detect the acceleration in the longitudinal direction of the vehicle, respectively, and acquires information regarding the output of the vehicle drive, A derivation unit that derives the gradient of the road surface on which the vehicle is traveling as a first road surface gradient based on the acquired acceleration and wheel speed, A road surface gradient estimation device characterized by comprising: a correction unit that corrects the derived first road surface gradient based on information regarding the output of the vehicle drive to derive a second road surface gradient.

2. The acquisition unit acquires driving status information indicating the driving status of the vehicle, The correction unit calculates a correction value based on information regarding the output of the vehicle drive, corrects the derived first road surface gradient with the correction value, and derives a second road surface gradient. The road surface gradient estimation device according to claim 1, characterized in that the correction unit derives a second road surface gradient by correcting the first road surface gradient with the correction value used in the previous correction when the acquired driving state information does not satisfy predetermined stable driving conditions.

3. The acquisition unit acquires information regarding the output of the vehicle drive, The derivation unit estimates the gradient acceleration generated in the vehicle due to the road surface gradient based on the acquired acceleration and wheel speed. The road surface gradient estimation device according to claim 1 or 2, characterized in that the correction unit derives a correction value based on the estimated gradient acceleration, the detected acceleration in the longitudinal direction of the vehicle, the vehicle weight, and the vehicle driving force.

4. The road surface gradient estimation device according to claim 3, characterized in that the correction unit estimates the driving acceleration based on the gradient acceleration and the vehicle driving force, and derives a correction value based on the difference between the estimated driving acceleration and the detected value of the acceleration in the longitudinal direction of the vehicle.

5. The acquisition unit acquires the target driving force input to the vehicle and the transmission characteristics showing the relationship between the target driving force and the detected acceleration in the longitudinal direction of the vehicle. The derivation unit derives the gradient acceleration acting on the vehicle based on the road surface gradient, The road surface gradient estimation device according to claim 1 or 2, characterized in that the correction unit derives a correction value based on the derived gradient acceleration, the vehicle weight, the target driving force of the vehicle, the transmission characteristics, and the detected acceleration in the longitudinal direction of the vehicle.

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