Road surface gradient estimation device

Abstract

The invention relates to a road surface gradient estimation device. The road surface gradient estimation apparatus includes: an acquisition unit that acquires each of detection results of an acceleration detection unit that detects acceleration in a front-rear direction of a vehicle and a wheel speed detection unit, and acquires information on power for driving the vehicle; a vehicle includes an acceleration acquisition unit that acquires acceleration and wheel speed of a vehicle, a derivation unit that derives a gradient of a road surface on which the vehicle travels 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 on power for driving the vehicle to derive a second road surface gradient.

Description

Technical Field

[0001] This invention relates to a technique for estimating the slope of the road surface on which a vehicle is traveling. Background Technology

[0002] Japanese Unexamined Patent Application Publication No. 2018-054527 (JP 2018-054527 A) discloses a vehicle control device including a slope estimation unit and a change-limiting unit. The slope estimation unit estimates the slope based on front and rear acceleration sensor values ​​and acceleration obtained from changes in wheel speed. The change-limiting unit limits the change in wheel speed based on the vehicle's acceleration calculated from the torque of the motor. When wheels slip, the change-limiting unit limits the change in wheel speed, and the slope estimation unit estimates the slope based on the change-limiting value. Summary of the Invention

[0003] In the technology disclosed in JP 2018-054527 A, when the detection accuracy of the accelerometer is always reduced prematurely due to offset errors, the estimation accuracy of the slope may be reduced.

[0004] The purpose of this invention is to provide a technique to prevent a decrease in the accuracy of calculating the slope of the road surface on which a vehicle is traveling.

[0005] To address the aforementioned problems, a road slope estimation device according to one embodiment of the present invention comprises: an acquisition unit that acquires each of the detection results of an acceleration detection unit and a wheel speed detection unit that detects acceleration in the longitudinal direction of a vehicle, and acquires information regarding the power used to drive the vehicle; a derivation unit that derives the slope of the road surface on which the vehicle is traveling as a first road slope based on the acquired acceleration and wheel speed; and a correction unit that corrects the derived first road slope based on the information regarding the power used to drive the vehicle to derive a second road slope.

[0006] According to the present invention, a technique can be provided to prevent a decrease in the accuracy of calculating the slope of the road surface on which the vehicle is traveling. Attached Figure Description

[0007] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein like symbols denote like elements, and wherein:

[0008] Figure 1 This is a view illustrating the functional configuration of a road slope estimation system according to an embodiment;

[0009] Figure 2 This is a view used to explain the method used to derive the first road surface slope;

[0010] Figure 3 This is a view used to explain the road surface slope correction process according to the embodiment; and

[0011] Figure 4 This is a view used to explain the correction process for road surface slope based on the variant example. Detailed Implementation

[0012] Figure 1 This is a view illustrating the functional configuration of the road slope estimation system 1 according to an embodiment. The road slope estimation system 1, including a road slope estimation device 10, an acceleration detection unit 12, a wheel speed detection unit 14, a driving state detection unit 16, and a driving assistance device 18, is installed on a vehicle. The road slope estimation device 10 acquires the detection results from the acceleration detection unit 12, the wheel speed detection unit 14, and the driving state detection unit 16, derives the slope of the road surface on which the vehicle is traveling, and outputs the derived road slope to the driving assistance device 18.

[0013] Acceleration detection unit 12 detects the acceleration in the longitudinal direction of the vehicle and sends the detection result to road slope estimation device 10. Wheel speed detection unit 14 detects the wheel speed, which is the rotational speed of the wheel, and sends the detection result to road slope estimation device 10. Wheel speed detection unit 14 can be installed at each wheel and can output the wheel speed of one wheel as the wheel speed, or it can output the average wheel speed of all wheels as the wheel speed.

[0014] The driving status detection unit 16 detects the vehicle's driving status and sends the detection results to the road slope estimation device 10. Information regarding the vehicle's driving status includes the engine's output value (i.e., driving force), the engine's target driving force, the brake's output value (i.e., driving force), the brake's target driving force, vehicle speed, tire friction, and steering angle. The engine's target driving force and the brake's target driving force are command values. The engine's output value, the brake's output value, vehicle speed, and tire friction are information about the power used to drive the vehicle.

[0015] The driver assistance device 18 has the function of assisting the driver while driving, and for example, performs automatic driving control such as cruise control and tracking control. The driver assistance device 18 receives road slope information from the road slope estimation device 10 and issues commands to output power according to the road slope during automatic driving control.

[0016] The road slope estimation device 10 includes an acquisition unit 20, a derivation unit 22, a judgment unit 24, a correction unit 26, an output unit 28, and a storage unit 30. The acquisition unit 20 acquires the detection results of each of the acceleration detection unit and the wheel speed detection unit, which detect acceleration in the vehicle's longitudinal direction, and acquires information about the power used to drive the vehicle. The acquisition unit 20 also acquires driving state information indicating the vehicle's driving state.

[0017] The derivation unit 22 derives the slope of the road surface on which the vehicle is traveling, based on the acceleration and wheel speed in the vehicle's longitudinal direction, as the first road surface slope. Here, refer to... Figure 2 . Figure 2 This is a view used to explain the method used to derive the first road surface slope.

[0018] exist Figure 2 In the diagram, vehicle 32 is traveling on a road surface with a gradient of θ. Vehicle 32 is traveling with a driving force F and receives gradient acceleration (g·sinθ) from the road surface. Vehicle 32 is traveling with an acceleration a calculated from the differential of the wheel speed.

[0019] The acceleration (a + g·sinθ) applied to vehicle 32 is estimated to be equal to the acceleration a′ detected by acceleration detection unit 12. Derivation unit 22 estimates the gradient acceleration (g·sinθ) based on the differential value of wheel speed a, the acceleration a′ in the vehicle's longitudinal direction, and the gravitational acceleration g, using the following equation 1. The road surface gradient θ becomes a negative angle when going downhill and a positive angle when going uphill. Note that although the road surface gradient θ can be set to be a positive angle when going downhill and a negative angle when going uphill, in this case, there is a part with reversed signs in the portion of the road surface gradient θ included in the equation.

[0020] a′–a=g·sinθ…Equation 1

[0021] Here, although the acceleration a′ detected by the acceleration detection unit 12 is used to derive the first road surface slope, the sensor values ​​of the acceleration detection unit 12 may contain offset errors, errors due to temperature, etc. Therefore, the correction unit 26 corrects the derived first road surface slope based on information about the power used to drive the vehicle, in order to derive the second road surface slope. The first road surface slope and the second road surface slope can be either slope acceleration (g·sinθ) or the road surface angle θ.

[0022] Figure 3This is a view used to explain the road slope correction process according to the embodiment. The derivation unit 22 uses Equation 1 to estimate the slope acceleration (g·sinθ) (S10). The derivation unit 22 multiplies the slope acceleration (g·sinθ) by the vehicle weight m (S12) and adds the vehicle driving force f (S14). In S14, as shown in Equation 2 below, the force F to be applied to the entire vehicle is derived.

[0023] -mg · sinθ + f = F … Equation 2

[0024] m is the vehicle weight, which is pre-stored in storage unit 30. The vehicle weight m includes the weight of the occupants. The occupant weight can be a pre-set value. The vehicle driving force f is calculated by adding the output values ​​of the engine, the brakes, the tire friction, and the air resistance. The air resistance is calculated based on the wheel speed. The output values ​​of the engine, the brakes, and the tire friction can be values ​​detected by the driving state detection unit 16, or values ​​calculated by the drive control and braking control system.

[0025] The correction unit 26 performs the correction value derivation process 34, enclosed in dashed lines. The correction unit 26 divides the force F to be applied to the entire vehicle by the vehicle weight m to estimate the driving acceleration a″ (S16). The correction unit 26 derives the difference between the driving acceleration a″ and the acceleration a′ detected by the acceleration detection unit 12 as a temporary correction value (S18). As a result, the error between the estimated value and the actual measured value is derived as a temporary correction value. The correction unit 26 sends the temporary correction value H(s) = 1 as is to the next step in S20.

[0026] The determination unit 24 determines whether the acquired driving state information meets the predetermined stable driving conditions. If the driving state information does not meet the predetermined stable driving conditions, the correction unit 26 discards the temporary correction value and performs latch processing (S22), setting the correction value used as the previous correction value as the current correction value. In the latch processing, when the driving state information meets the predetermined stable driving conditions, the correction unit 26 sets the temporary correction value as the current correction value (S22). When the driving state information does not meet the predetermined stable driving conditions, the correction unit 26 continues to perform correction with the same correction value. The previous correction value refers to the correction value in a cycle, which is the cycle preceding the current calculation cycle.

[0027] When vehicle 32 suddenly stops, turns abruptly, or comes to a complete stop, the predetermined stable driving conditions are not met. This is because when vehicle 32 is not driving stably, the vehicle's driving force f cannot be detected with high precision. For example, the predetermined stable driving conditions are met when the change in the output value of the braking device is equal to or less than a predetermined amount, the change in the steering angle is equal to or less than a predetermined angle, and the wheel speed is equal to or greater than a predetermined speed. Furthermore, the predetermined stable driving conditions include the absence of a malfunction in the acceleration detection unit 12; when a malfunction occurs in the acceleration detection unit 12, the predetermined stable driving conditions are not met.

[0028] The correction unit 26 derives the corrected slope acceleration (S24) by adding the current correction value to the slope acceleration (g·sinθ). The correction unit 26 can output the corrected slope acceleration as the second road surface slope, or it can output the angle θ derived from the corrected slope acceleration as the second road surface slope. The correction unit 26 stores the correction value used in this correction in the storage unit 30. The output unit 28 sends the derived second road surface slope to the driving assistance device 18.

[0029] In this way, the correction unit 26 calculates a correction value based on information related to the power used to drive the vehicle, and uses the correction value to correct the derived first road surface slope in order to derive the second road surface slope. This prevents a decrease in the accuracy of the derived road surface slope even if offset errors occur in the acceleration detection unit 12.

[0030] The correction unit 26 derives correction values ​​based on the estimated slope acceleration (g·sinθ), the detected acceleration a′ in the vehicle's longitudinal direction, the vehicle weight m, and the vehicle driving force f. The correction unit 26 estimates the driving acceleration a″ based on the estimated slope acceleration (g·sinθ) and the vehicle driving force f, and derives the correction values ​​based on the estimated driving acceleration a″ and the acceleration a′ in the vehicle's longitudinal direction (the actual measured value). In this way, the correction values ​​can be derived with high precision using the difference between the estimated driving acceleration a″ and the actual measured acceleration a′.

[0031] When the acquired driving state information does not meet the predetermined stable driving conditions, the correction unit 26 uses the correction value used in the previous correction to correct the first road surface slope, thereby deriving the second road surface slope. The previous correction value is stored in the storage unit 30 in the previous calculation cycle. In this way, correction is performed using the same correction value until the predetermined stable driving conditions are met. As a result of the correction unit 26 performing correction using the previous correction value, correction using unstable correction values ​​can be avoided. When the offset error of the acceleration detection unit 12 is constant, the impact of the offset error can be reduced by the correction unit 26 performing correction using the previous correction value.

[0032] The vehicle weight M is Figure 3 The true value shown in S26 is used for theoretical calculations, but not for actual calculations, because the actual measured value of acceleration is used for actual calculations.

[0033] Figure 4 This is a view used to explain the correction process for the road surface slope according to the variant example. In the variant example, correction unit 26 uses the transmission characteristic G(s) to perform the correction; the transmission characteristic G(s) is information about the power used to drive the vehicle. Storage unit 30 can pre-store the transmission characteristic G(s), and acquisition unit 20 acquires the transmission characteristic G(s) from storage unit 30, etc.

[0034] The transmission characteristic G(s) is a function indicating the relationship between the target driving force of the vehicle and the acceleration in the vehicle's longitudinal direction, where the acceleration in the longitudinal direction is the output of the target driving force. In other words, the transmission characteristic G(s) receives the target driving force inputs from the engine and braking systems and outputs the acceleration in the vehicle's longitudinal direction. The target driving force of the engine and braking systems are command values ​​for the engine and braking systems, and are referred to as the target driving force fr in the vehicle's driving process. The target driving force of the engine and braking systems can be obtained from the driver assistance device 18 that is performing automatic driving control.

[0035] Derivation unit 22 uses Equation 1 to estimate the gradient acceleration (g·sinθ) (S30). Derivation unit 22 derives the gradient force (mg·sinθ) by multiplying the gradient acceleration (g·sinθ) by the vehicle weight m (S32).

[0036] The correction unit 26 performs the correction value derivation process 36, enclosed by a dashed line. The correction unit 26 subtracts the estimated slope force (mg·sinθ) from the target driving force fr in the vehicle's drive to derive the target driving force fr′ with the influence of the road slope added (S34). The correction unit 26 estimates the driving acceleration a″ by inputting the derived target driving force fr′ into the transmission characteristic G(s) (S36).

[0037] The correction unit 26 derives the difference between the acceleration a′ detected by the acceleration detection unit 12 and the driving acceleration a″ (S38). In this way, the error between the actual measured value and the estimated value is derived. Note that the transfer function G′(s), which is the true value indicated in S48, is used for theoretical calculations, not for actual calculations, because the actual measured value of the acceleration is used for actual calculations.

[0038] Correction unit 26 substitutes the difference (a′–a″) derived in S38 into H(s)=G -1(s), to derive the target output value as a temporary correction value (S40).

[0039] The determination unit 24 determines whether the acquired driving status information meets the predetermined stable driving conditions. When the driving status information does not meet the predetermined stable driving conditions, the correction unit 26 discards the temporary correction value and performs a latching process (S42) that sets the correction value used as the previous correction value as the current correction value. In the latching process, when the predetermined stable driving conditions are met, the correction unit 26 sets the temporary correction value as the current correction value (S42). The correction unit 26 stores the current correction value in the storage unit 30.

[0040] The correction unit 26 performs correction by adding the estimated slope force (mg·sinθ) to the current correction value (S44) and further adding the target output value fr (S46), thereby deriving the target output value fr″. The output unit 28 outputs the corrected target output value fr″ to the driving assistance device 18, and the driving assistance device 18 uses the target output value fr″ to control the engine and braking devices.

[0041] The present disclosure has been described above based on embodiments. The present disclosure is not limited to the above embodiments, and various modifications, such as design changes, can be made based on the knowledge of those skilled in the art.

Claims

1. A road slope estimation device, comprising: The acquisition unit acquires each of the detection results from the acceleration detection unit and the wheel speed detection unit that detect acceleration in the longitudinal direction of the vehicle, and acquires information about the power used to drive the vehicle. The derivation unit derives the slope of the road surface on which the vehicle is traveling as a first road surface slope based on the acquired acceleration and wheel speed. as well as A correction unit, based on the information about the power used to drive the vehicle, corrects the derived first road surface slope to derive a second road surface slope.

2. The road slope estimation device according to claim 1, wherein: The acquisition unit acquires driving status information indicating the driving status of the vehicle; The correction unit calculates a correction value based on the information about the power used to drive the vehicle, and uses the correction value to correct the derived first road surface slope in order to derive the second road surface slope. and When the acquired driving status information does not meet the predetermined stable driving conditions, the correction unit uses the correction value used in the previous correction to correct the first road surface slope in order to derive the second road surface slope.

3. The road slope estimation device according to claim 1 or 2, wherein: The acquisition unit acquires the information regarding the power used to drive the vehicle; The derivation unit estimates the gradient acceleration caused by the slope of the road surface in the vehicle based on the acquired acceleration and wheel speed; as well as The correction unit derives the correction value based on the estimated slope acceleration, the detected acceleration in the longitudinal direction of the vehicle, the vehicle weight, and the vehicle driving force.

4. The road slope estimation device according to claim 3, wherein, The correction unit estimates the driving acceleration based on the slope acceleration and the vehicle driving force, and derives the correction value based on the difference between the estimated driving acceleration and the detected value of the acceleration in the forward and backward direction of the vehicle.

5. The road slope estimation device according to claim 1 or 2, wherein: The acquisition unit acquires the target driving force input to the vehicle and indicates the transmission characteristics of 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 to be applied to the vehicle based on the slope of the road surface; as well as The correction unit derives the correction value based on the derived slope acceleration, vehicle weight, the vehicle's target driving force, the transmission characteristics, and the detected acceleration in the vehicle's longitudinal direction.

Images