Road gradient estimation device

Abstract

A control device 50 as a road gradient estimation device estimates the road gradient of a road on which a vehicle 10 is traveling on the basis of an inertial acceleration derived on the basis of an inertial force in a traveling direction of the vehicle 10 and an actual acceleration derived on the basis of the amount of change in the vehicle speed of the vehicle 10. The control device 50 includes a forward / backward movement determination unit M11 for modifying a forward / backward movement determination indicating whether the vehicle 10 is moving backward. The control device 50 includes an acceleration correction unit M12 that acquires the inertial acceleration as a first acceleration and the actual acceleration as a second acceleration, and, when the forward / backward movement determination is modified, performs correction to invert the sign of the first acceleration or the second acceleration. The control device 50 includes a gradient estimation unit for estimating the road gradient on the basis of the difference between the first acceleration and the second acceleration.

Description

Road gradient estimation device

[0001] The present invention relates to a road gradient estimation device.

[0002] As described in Patent Document 1, a method for estimating road gradient is known in which the road gradient is estimated by calculating a gravitational acceleration component based on the longitudinal component acting on the vehicle and the actual acceleration component of the vehicle acquired by a wheel speed sensor.

[0003] Furthermore, Patent Document 1 states that it is unclear whether the vehicle is moving forward or backward from the actual acceleration component of the vehicle acquired by the wheel speed sensor. Therefore, for example, when the vehicle is moving backward, the estimated road gradient may deviate from the actual road gradient.

[0004] Therefore, Patent Document 1 discloses a road gradient estimation device that prohibits estimation of the road gradient except when power is being output to move the vehicle forward, and sets the estimated value of the road gradient to a predetermined set value.

[0005] Japanese Patent Application Laid-Open No. 2016-190602

[0006] In the road gradient estimation device disclosed in Patent Document 1, the predetermined setting value does not reflect the road gradient on which the vehicle is actually traveling, and therefore the road gradient cannot be estimated when the vehicle is traveling backward.

[0007] A road gradient estimation device for solving the above problem is a road gradient estimation device that estimates the road gradient of a road on which a vehicle is traveling based on an inertial acceleration derived based on an inertial force in the vehicle's direction of travel and an actual acceleration derived based on an amount of change in the vehicle speed, and includes: a forward / backward travel determination unit that changes a forward / backward travel determination indicating whether the vehicle is traveling in reverse depending on whether the vehicle is traveling in reverse; an acceleration correction unit that acquires one of the inertial acceleration and the actual acceleration as a first acceleration and the other as a second acceleration, and that performs a correction to invert the sign of the first acceleration or the second acceleration when the forward / backward travel determination by the forward / backward travel determination unit is changed; and a gradient estimation unit that estimates the road gradient based on the difference between the first acceleration and the second acceleration.

[0008] The road gradient can be estimated whether the vehicle is moving forward or backward.

[0009] Fig. 1 is a configuration diagram showing an embodiment of a road gradient estimation device and an outline of a vehicle equipped with the road gradient estimation device. Fig. 2 is a schematic diagram showing a state in which a braking force is applied to a vehicle moving forward so as to climb a slope, thereby stopping the vehicle. Fig. 3 is a flowchart showing the flow of processing executed by the road gradient estimation device of Fig. 1 when estimating a road gradient. Fig. 4 is a flowchart showing the flow of processing executed by the road gradient estimation device of Fig. 1. Fig. 5 is a flowchart showing the flow of processing executed by the road gradient estimation device of Fig. 1.

[0010] An embodiment of a road gradient estimation device will be described below with reference to FIGS. 1 to 5. The expression "at least one" used in this specification means "one or more" of the desired options. More specifically, the expression "at least one" used in this specification means "only one option" or "both of the two options" if the number of options is two. When the number of options is two, "at least one" can also be expressed as "at least one." As another example, the expression "at least one" used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

[0011] 1 shows a control device 50 as a road gradient estimation device and a vehicle 10 equipped with the control device 50. An example of the vehicle 10 will be described. For example, the vehicle 10 is equipped with a brake operating member 11, a plurality of wheels, a plurality of friction brakes 20, and a brake actuator 30. The brake operating member 11 is a member that is operated by the driver when applying a braking force to the vehicle 10. An example of the brake operating member 11 is a brake pedal. The plurality of wheels include two front wheels 12 and two rear wheels 13.

[0012] In this embodiment, a state in which the front wheels in the traveling direction of the vehicle 10 are the front wheels 12 is referred to as moving forward. On the other hand, a state in which the front wheels in the traveling direction of the vehicle 10 are the rear wheels 13 is referred to as moving backward.

[0013] <Friction Brake> The multiple friction brakes 20 each apply a braking force to a corresponding wheel. The friction brake 20 has a wheel cylinder 21, a rotating body 22, and a friction portion 23. The rotating body 22 rotates integrally with the wheel. Therefore, braking force is applied to the wheel by pressing the friction portion 23 against the rotating body 22. The force pressing the friction portion 23 against the rotating body 22 increases as the wheel hydraulic pressure, which is the hydraulic pressure in the wheel cylinder 21, increases. Therefore, the friction brake 20 can apply a greater braking force to the wheel as the wheel hydraulic pressure increases.

[0014] <Brake Actuator> The brake actuator 30 controls the wheel hydraulic pressure in the plurality of wheel cylinders 21 to control the braking force applied to the wheels 12, 13. For example, the brake actuator 30 has a pressure source that supplies brake fluid to the plurality of wheel cylinders 21. The pressure source is, for example, an electric pump and an electric cylinder. The brake actuator 30 can individually adjust the wheel hydraulic pressure in the wheel cylinder 21 for the front wheels 12 and the wheel hydraulic pressure in the wheel cylinder 21 for the rear wheels 13.

[0015] 1, the detection system of the vehicle 10 includes a plurality of sensors that output detection signals to the control device 50. The plurality of sensors includes, for example, a plurality of wheel speed sensors 102 and a longitudinal acceleration sensor 103. The plurality of sensors may include a brake sensor 101. If the vehicle 10 is an autonomous vehicle, the plurality of sensors may not include the brake sensor 101.

[0016] The brake sensor 101 detects information related to the driver's operation of the brake operating member 11. An example of the brake sensor 101 is a stroke sensor that detects the amount of operation of the brake operating member 11 by the driver.

[0017] A wheel speed sensor 102 is provided for each of the plurality of wheels. Each of the plurality of wheel speed sensors 102 detects the rotational speed of the corresponding wheel. The rotational speed of the wheel based on the detection signal of the wheel speed sensor 102 is referred to as the "wheel speed VW." The traveling speed of the vehicle 10 calculated based on the wheel speeds VW of the plurality of wheels 12, 13 is referred to as the "vehicle speed VS."

[0018] The longitudinal acceleration sensor 103 detects the acceleration in the longitudinal direction of the vehicle 10 out of the accelerations acting on the vehicle 10. The detection system employs a sensor as the longitudinal acceleration sensor 103 that detects the inertial force acting on the vehicle 10 in the longitudinal direction of the vehicle 10. The longitudinal acceleration of the vehicle 10 derived based on the detection signal of the longitudinal acceleration sensor 103 is referred to as "inertial acceleration Gxg."

[0019] [Inertial Acceleration] The inertial acceleration Gxg corresponds to the inertial acceleration derived based on the inertial force in the traveling direction of the vehicle 10. In the following description, the inertial acceleration Gxg is assumed to be a positive value when the vehicle 10 traveling forward on a horizontal road is accelerating. In this case, the inertial acceleration Gxg takes, for example, the following values: The inertial acceleration Gxg is a negative value when the vehicle 10 traveling forward on a horizontal road is decelerating. The inertial acceleration Gxg is a negative value when the vehicle 10 traveling backward on a horizontal road is accelerating. The inertial acceleration Gxg is a positive value when the vehicle 10 traveling backward on a horizontal road is decelerating.

[0020] [Actual Acceleration] By differentiating the vehicle speed VS with respect to time, the actual acceleration Gxw can be calculated based on the amount of change in the vehicle speed VS per unit time. In the following description, the actual acceleration Gxw is assumed to be a positive value when the vehicle 10 is accelerating. In this case, the actual acceleration Gxw is assumed to be a negative value when the vehicle 10 is decelerating.

[0021] Such actual acceleration Gxw does not include a factor indicating whether the vehicle 10 is moving forward or backward. To explain this using a specific example, when the vehicle 10 is moving forward on a horizontal road, the positive and negative signs of the inertial acceleration Gxg and the actual acceleration Gxw are the same. In contrast, when the vehicle 10 is moving backward on a horizontal road, the positive and negative signs of the inertial acceleration Gxg and the actual acceleration Gxw are different. This is because the actual acceleration Gxw is calculated as the amount of change in the vehicle speed VS. Therefore, when the vehicle speed VS is the same when the vehicle 10 is moving forward and when it is moving backward, the same value is calculated as the actual acceleration Gxw whether the vehicle 10 is moving forward or backward.

[0022] 1, the vehicle 10 is provided with a front / rear determination means 60. As will be described in detail later, by using the front / rear determination means 60, it is possible to obtain information for detecting whether the vehicle 10 is moving backward. The front / rear determination means 60 can output the obtained information to the control device 50.

[0023] An example of the forward / rearward determination means 60 is a shift device. The shift device is an operating member that the driver operates to select the drive state of the drive system equipped in the vehicle 10. By operating the shift device, one range can be selected from multiple ranges. The multiple ranges include, for example, D range, R range, N range, and P range. The D range is the range for forward driving. The R range is the range for reverse driving. The N range is the neutral range. The P range is the parking range. The shift device outputs a shift signal to the control device 50 relating to the range selected by the driver's operation. Based on this shift signal, it can be detected whether the vehicle 10 is moving forward or backward.

[0024] Other examples of the front / rear determination means 60 include a camera, a radar, a motor angular velocity sensor, etc. The vehicle 10 may be equipped with only one of the devices exemplified as the front / rear determination means 60, or may be equipped with a plurality of such devices.

[0025] The camera is a device that monitors the surroundings of the vehicle 10. The front / rear determination means 60 preferably includes at least one of a camera that monitors the front of the vehicle 10 and a camera that monitors the rear of the vehicle 10, among the cameras that monitor the surroundings of the vehicle 10.

[0026] It is possible to detect whether the vehicle 10 is moving forward or backward based on the image captured by the camera while the vehicle 10 is traveling. In addition to the image, it is also possible to detect whether the vehicle 10 is moving forward or backward by capturing a plurality of still images arranged in chronological order.

[0027] The camera may output information obtained by processing the captured video, images, etc. to the control device 50. For example, the camera may output the relative position of the vehicle 10 with respect to a specific object observable from the video to the control device. Based on the transition of the relative position, it can be detected whether the vehicle 10 is moving forward or backward.

[0028] The radar can detect the relative position of the vehicle 10 with respect to objects around the vehicle 10. Based on the transition of the relative position, it can be detected whether the vehicle 10 is moving forward or backward.

[0029] The motor angular velocity sensor is a sensor that detects the angular velocity of a traction motor in a vehicle 10 that is equipped with a traction motor as a drive device. The motor angular velocity sensor can detect the rotation direction of the traction motor. The rotation direction of the traction motor is opposite when the vehicle 10 is moving forward and when it is moving backward. Based on the rotation direction of the traction motor, it can be detected whether the vehicle 10 is moving forward or backward.

[0030] <Relationship Between Acceleration and Road Gradient> The relationship between the acceleration of the vehicle 10 and the road gradient will be described with reference to Figure 2. Figure 2 illustrates a state in which the vehicle 10, traveling forward so as to climb a slope, is decelerated by the application of a braking force. In Figure 2, the forward direction Z1 indicating the traveling direction of the vehicle 10, i.e., the direction in which the vehicle 10 moves forward, is shown as a solid arrow. In addition, the reverse direction Z2 indicating the direction opposite to the forward direction Z1 is shown as a dashed arrow.

[0031] 2 in the direction opposite to the forward direction Z1, include a gravitational acceleration component Gg and a braking force. The braking force is equal to an inertial acceleration Gxg derived based on the inertial force of the vehicle 10. An actual acceleration Gxw derived based on the amount of change in the vehicle speed of the vehicle 10 is equal to the sum of the gravitational acceleration component Gg and the inertial acceleration Gxg. In other words, the gravitational acceleration component Gg is equal to the difference between the inertial acceleration Gxg and the actual acceleration Gxw.

[0032] Here, the gravitational acceleration component Gg is a component of gravitational acceleration corresponding to the road gradient. Therefore, the road gradient can be estimated based on the difference between the inertial acceleration Gxg and the actual acceleration Gxw. The gravitational acceleration component Gg is also called the road gradient component. The smaller the road gradient, the smaller the difference between the inertial acceleration Gxg and the actual acceleration Gxw, i.e., the road gradient component.

[0033] 2, the arrow indicating the gravitational acceleration component Gg is a schematic representation of the direction of the gravitational acceleration component, but does not represent the magnitude of the gravitational acceleration component. Similarly, the arrow indicating the inertial acceleration Gxg and the arrow indicating the actual acceleration Gxw are a schematic representation of the direction of the acceleration, but do not represent the magnitude of the acceleration.

[0034] <Control Device> As shown in FIG. 1 , the control device 50 includes a processing circuit 51. An example of the processing circuit 51 is an electronic control device. In this case, the processing circuit 51 includes, for example, a CPU 52, a first memory 53, and a second memory 54. The first memory 53 stores a control program executed by the CPU 52. The second memory 54 stores calculation results of the CPU 52, etc. The CPU 52 executes the control program stored in the first memory 53 to realize various functions. For example, the control device 50 functions as a road gradient estimation device that estimates the road gradient of the road on which the vehicle 10 is traveling based on an inertial acceleration derived based on the inertial force in the traveling direction of the vehicle 10 and an actual acceleration derived based on a change in the vehicle speed of the vehicle 10.

[0035] <Functional Configuration of Processing Circuit> The functional configuration of the processing circuit 51 will be described with reference to Fig. 1. The CPU 52 executes the control program in the first memory 53, causing the processing circuit 51 to function as multiple functional units. Examples of the functional units include a forward / reverse determination unit M11, an acceleration correction unit M12, a gradient estimation unit M13, a determination storage unit M14, and an estimated value storage unit M15. The functional units may include a braking control unit M21.

[0036] [Braking Control Unit M21] The braking control unit M21 can control the braking actuator 30 to activate the plurality of friction brakes 20. By activating the plurality of friction brakes 20, the braking control unit M21 can adjust the sum of the braking forces applied to the wheels of the vehicle 10.

[0037] [Forward / reverse determination unit M11] The forward / reverse determination unit M11 changes the forward / reverse determination indicating whether the vehicle 10 is moving backward or not, depending on whether the vehicle 10 is moving backward or not.

[0038] The forward / reverse determination unit M11 can change the forward / reverse determination based on information input from the front / rear determination means 60. For example, the forward / reverse determination unit M11 can change the forward / reverse determination based on information input from at least one of the front / rear determination means 60. Note that when the vehicle 10 is stopped, the forward / reverse determination unit M11 changes the forward / reverse determination to a determination that the vehicle 10 is not moving in reverse.

[0039] Hereinafter, examples of determinations [A1] to [A5] will be specifically described as examples of how the forward / reverse determination unit M11 changes the forward / reverse determination. [A1] The forward / reverse determination unit M11 can change the forward / reverse determination based on the shift signal.

[0040] [A2] The forward / backward movement determination unit M11 can change the forward / backward movement determination based on an image captured by a camera. It can also change the forward / backward movement determination based on a plurality of still images arranged in chronological order.

[0041] [A3] The forward / backward determination unit M11 can change the forward / backward determination based on a signal output by the radar. [A4] The forward / backward determination unit M11 can change the forward / backward determination based on a signal output by the motor angular velocity sensor.

[0042] [A5] The forward / reverse determination unit M11 can change the forward / reverse determination based on the amount of change per unit time in the inertial acceleration and the amount of change per unit time in the actual acceleration. Specifically, the forward / reverse determination is changed as follows. If the absolute value of the difference between the amount of change per unit time in the inertial acceleration and the amount of change per unit time in the actual acceleration is equal to or greater than a specified determination value ΔJth for a specified time Tth, the forward / reverse determination unit M11 changes the forward / reverse determination to a determination that the vehicle 10 is not moving backward. On the other hand, if the absolute value of the difference is smaller than the determination value ΔJth, or if the state in which the absolute value of the difference is equal to or greater than the determination value ΔJth has not continued for the specified time Tth, the forward / reverse determination is changed to a determination that the vehicle 10 is not moving backward.

[0043] The amount of change in acceleration per unit time, i.e., jerk, can be obtained by differentiating acceleration with respect to time. The amount of change in inertial acceleration per unit time, i.e., the value obtained by differentiating inertial acceleration Gxg with respect to time, is defined as the first jerk Jg. The amount of change in actual acceleration per unit time, i.e., the value obtained by differentiating actual acceleration Gxw with respect to time, is defined as the second jerk Jw.

[0044] The absolute value of the difference is the jerk difference |ΔJ|. The jerk difference |ΔJ| represents the absolute value of the value obtained by subtracting the value of the second jerk Jw from the value of the first jerk Jg. The judgment value ΔJth is a value calculated in advance by experiment or the like in order to determine that the deviation between the first jerk Jg and the second jerk Jw is large when the jerk difference |ΔJ| is equal to or greater than the judgment value ΔJth.

[0045] The above-mentioned specified time Tth is a value calculated in advance through experiments, etc., in order to determine that the inertial acceleration Gxg and the actual acceleration Gxw are changing so as to diverge when the state in which the jerk difference |ΔJ| is equal to or greater than the judgment value ΔJth continues for the specified time Tth or more.

[0046] The jerk difference |ΔJ| being equal to or greater than the determination value ΔJth means that the deviation between the first jerk Jg and the second jerk Jw is large. In this case, the inertial acceleration Gxg and the actual acceleration Gxw are changing so as to deviate from each other. If this change continues for a specified time period Tth or longer, it can be determined that the vehicle 10 is moving backward.

[0047] As described above, the first jerk Jg and the second jerk Jw can be calculated as the time differential of the inertial acceleration Gxg and the time differential of the actual acceleration Gxw, respectively. In this case, it can be said that both the longitudinal acceleration sensor 103 for detecting the inertial acceleration Gxg and the wheel speed sensor 102 for detecting the actual acceleration Gxw correspond to the longitudinal determination means 60.

[0048] [Acceleration Correction Unit M12] The acceleration correction unit M12 obtains one of the inertial acceleration Gxg and the actual acceleration Gxw as the first acceleration G1, and the other as the second acceleration G2.

[0049] When the forward / reverse determination by the forward / reverse determination unit M11 is changed, the acceleration correction unit M12 corrects the first acceleration G1 or the second acceleration G2 by inverting the sign of the acceleration G1 or the second acceleration G2. The configuration for inverting the sign of the acceleration G1 or the second acceleration G2 will be described in detail later.

[0050] The acceleration correction unit M12 may execute a correction process to correct at least one of the first acceleration G1 and the second acceleration G2 so that the difference between the first acceleration G1 and the second acceleration G2 becomes smaller as the pitch angle of the vehicle 10 becomes larger. Generally, there is a correlation between the magnitude of the deceleration of the vehicle 10 during braking and the magnitude of the pitch angle of the vehicle 10. Therefore, the correction process can be performed so that the difference between the first acceleration G1 and the second acceleration G2 becomes smaller as the deceleration of the vehicle 10 becomes larger in the direction that decelerates the vehicle 10.

[0051] The deceleration indicates the rate of change of the speed of the vehicle 10. In this embodiment, the deceleration takes a positive value when the vehicle 10 is decelerating, regardless of whether the vehicle 10 is moving forward or backward. The greater the change in the speed of the vehicle 10 in the deceleration direction, the greater the deceleration value. The deceleration can be calculated based on, for example, the inertial acceleration Gxg, the actual acceleration Gxw, etc.

[0052] [Gradient Estimation Unit M13] The gradient estimation unit M13 executes a gradient estimation process. The gradient estimation process is a process for estimating a road gradient based on the difference between the first acceleration G1 and the second acceleration G2. For example, the gradient estimation unit M13 can calculate an estimated gradient value θ as a value estimating the road gradient based on a road gradient component obtained by subtracting the value of the second acceleration G2 from the first acceleration G1.

[0053] [Decision Holding Unit M14] When detecting a change in whether the vehicle 10 is moving in reverse or not, if the probability of the change is low, the judgment holding unit M14 can cause the forward / reverse determination unit M11 to maintain the forward / reverse determination without changing it. On the other hand, when detecting a change in whether the vehicle 10 is moving in reverse or not, if the probability of the change is high, the judgment holding unit M14 causes the forward / reverse determination unit M11 to change the forward / reverse determination.

[0054] An example of determining whether the probability of a transition between reverse and reverse is low when a transition between reverse and forward is detected will be described. Consider a case in which the traveling vehicle 10 transitions from forward to reverse. Before the forward vehicle 10 begins to reverse, the vehicle 10 passes through a stopped state, even if only for a short time. In other words, if the vehicle speed VS is temporarily not detected as zero, even if a transition between forward and reverse is detected, the transition may not actually have occurred. Therefore, if the vehicle speed VS is smaller than a specified vehicle speed determination value VSth1 during a specified period P1 including the time when the transition is detected, it can be determined that the probability of the transition is high. On the other hand, if the vehicle speed VS is equal to or greater than the vehicle speed determination value VSth1 throughout the specified period P1 including the time when the transition is detected, it can be determined that the probability of the transition is low. The vehicle speed determination value VSth1 can be set, for example, to a value corresponding to the vehicle speed VS immediately before the vehicle 10 stops. The specified period P1 can be set to a value calculated in advance through experiments, for example.

[0055] [Estimated Value Holding Unit M15] The estimated value holding unit M15 can hold the gradient estimated value θ when an estimated value holding condition is met.

[0056] The estimated value holding unit M15 determines that the estimated value holding condition is met, for example, while at least one of the absolute value of the rate of change per unit time of the inertial acceleration Gxg and the absolute value of the rate of change per unit time of the actual acceleration Gxw is equal to or greater than a specified threshold value Jth. In this case, while the estimated value holding condition is met, the estimated value holding unit M15 holds the estimated value of the road gradient before the absolute value became equal to or greater than the threshold value Jth.

[0057] In the above, the absolute value of the change in the inertial acceleration Gxg per unit time corresponds to the absolute value of the first jerk Jg, and the absolute value of the change in the actual acceleration Gxw per unit time corresponds to the absolute value of the second jerk Jw.

[0058] The threshold value Jth is a value calculated in advance through experiments, etc., in order to determine that the vehicle 10 is performing sudden braking, sudden acceleration, sharp turning, etc. when at least one of the absolute value of the first jerk Jg and the absolute value of the second jerk Jw is greater than or equal to the threshold value Jth.

[0059] The estimated value holding unit M15 may determine that the estimated value holding condition is satisfied while the vehicle speed VS is equal to or less than the specified low speed determination value VSth2. In this case, while the estimated value holding condition is satisfied, the estimated value holding unit M15 holds the estimated value of the road gradient before the vehicle speed VS became equal to or less than the low speed determination value VSth2.

[0060] <Gradient Estimation Process> The flow of the gradient estimation process performed by the processing circuitry 51 will be described with reference to Fig. 3. The processing circuitry 51 repeatedly executes a series of processes shown in Fig. 3.

[0061] In step S101, the processing circuit 51 determines whether the vehicle 10 is moving backward based on the forward / reverse determination. If the forward / reverse determination indicates that the vehicle is moving backward, the processing circuit 51 determines that the vehicle is moving backward. If the forward / reverse determination does not indicate that the vehicle is moving backward, the processing circuit 51 determines that the vehicle is not moving backward.

[0062] If the processing circuit 51 determines that the vehicle 10 is moving backward (S101: YES), the processing proceeds to step S103. On the other hand, if the processing circuit 51 determines that the vehicle 10 is not moving backward (S101: NO), the processing proceeds to step S102.

[0063] In step S102, the processing circuit 51 acquires the raw value of the inertial acceleration Gxg as the first acceleration G1. Further, the processing circuit 51 acquires the raw value of the actual acceleration Gxw as the second acceleration G2. After that, the processing circuit 51 proceeds to step S104.

[0064] In step S103, the processing circuit 51 acquires the raw value of the inertial acceleration Gxg as the first acceleration G1. Furthermore, the processing circuit 51 acquires a value obtained by inverting the sign of the actual acceleration Gxw as the second acceleration G2. At this time, the processing circuit 51 may invert the sign of the actual acceleration Gxw by multiplying the second acceleration G2 by "-1" after acquiring the actual acceleration Gxw, or may invert the sign of the actual acceleration Gxw by acquiring the value obtained by multiplying the actual acceleration Gxw by "-1" as the second acceleration G2. After that, the processing circuit 51 proceeds to step S104.

[0065] In step S104, the processing circuit 51 executes a correction process based on the deceleration of the vehicle 10. For example, the first acceleration G1 is corrected so that the difference between the first acceleration G1 and the second acceleration G2 becomes smaller as the deceleration of the vehicle 10 increases in the direction of deceleration of the vehicle 10. The object to be corrected in the correction process may be at least one of the first acceleration G1 and the second acceleration G2. The object to be corrected in the correction process is not limited to the first acceleration G1, but may also be the second acceleration G2, or both the first acceleration G1 and the second acceleration G2.

[0066] In the next step S105, the processing circuit 51 executes a gradient estimation process. Specifically, the processing circuit 51 calculates a road gradient component based on the difference between the first acceleration G1 and the second acceleration G2. The processing circuit 51 can update the gradient estimate value θ based on the road gradient component. Thereafter, the processing circuit 51 ends the series of processes shown in FIG. 3.

[0067] <Processing for Holding Estimated Value> A processing flow when the gradient estimated value θ is held by the processing circuit 51 will be described with reference to Fig. 4. The processing circuit 51 repeatedly executes a series of processes shown in Fig. 4.

[0068] In step S201, the processing circuit 51 determines whether the estimated value holding condition is satisfied. If the estimated value holding condition is satisfied (S201: YES), the processing circuit 51 proceeds to step S203. On the other hand, if the estimated value holding condition is not satisfied (S201: NO), the processing circuit 51 proceeds to step S202.

[0069] In step S203, the processing circuitry 51 prohibits updating of the gradient estimate value θ. Thereafter, the processing circuitry 51 ends the series of processes shown in Fig. 4. In step S202, the processing circuitry 51 permits updating of the gradient estimate value θ. Thereafter, the processing circuitry 51 ends the series of processes shown in Fig. 4.

[0070] For example, while updating of the gradient estimate θ is prohibited, the calculation result of the gradient estimation process is discarded. As a result, while the estimate value holding condition is satisfied, the gradient estimate θ immediately before the estimate value holding condition is satisfied is held.

[0071] Alternatively, the gradient estimation process may be configured not to be executed while updating of the gradient estimate θ is prohibited. Even with this configuration, the gradient estimate θ immediately before the estimate hold condition is satisfied is held while the estimate hold condition is satisfied.

[0072] <Processing for Holding Determination> A processing flow when the forward / reverse determination is held by the processing circuit 51 will be described with reference to Fig. 5. The processing circuit 51 repeatedly executes the series of processes shown in Fig. 5.

[0073] In step S301, if the processing circuit 51 detects a change between whether the vehicle 10 is moving forward or backward (S301: YES), the processing proceeds to step S302. On the other hand, if the processing circuit 51 has not detected a change between whether the vehicle 10 is moving forward or backward (S301: NO), the processing circuit 51 ends the series of processes shown in Fig. 5. For example, if the forward / reverse determination unit M11 detects information that changes the forward / reverse determination, the processing circuit 51 can determine that a change between whether the vehicle 10 is moving forward or backward has been detected.

[0074] In step S302, the processing circuit 51 determines whether the probability of the switch detected in step S301 is low. If the probability is low (S302: YES), the processing circuit 51 proceeds to step S304. On the other hand, if the probability is high (S302: NO), the processing circuit 51 proceeds to step S303.

[0075] In step S303, the processing circuit 51 changes the forward / reverse determination. Thereafter, the processing circuit 51 ends the series of processes shown in Fig. 5. In step S304, the processing circuit 51 holds the previous forward / reverse determination. Thereafter, the processing circuit 51 ends the series of processes shown in Fig. 5.

[0076] <Functions and Effects> The functions and effects of this embodiment will be described. When the forward / reverse determination is changed by the processing of steps S101 to S103 shown in FIG. 3, the sign of the second acceleration G2 is reversed. For example, when switching from forward to reverse, a value obtained by reversing the sign of the actual acceleration Gxw is acquired as the second acceleration G2. The value of the inertial acceleration Gxg is acquired as the first acceleration G1. Subsequently, when switching from reverse to forward again, the value of the actual acceleration Gxw is acquired as the second acceleration G2. The value of the inertial acceleration Gxg is acquired as the first acceleration G1.

[0077] In this way, in this embodiment, when the vehicle 10 is moving backward, the actual acceleration Gxw, which does not include an element indicating whether the vehicle 10 is moving forward or backward, is inverted in positive and negative to add an element depending on whether the vehicle 10 is moving backward or not.

[0078] Therefore, even when the vehicle 10 is moving backward, the gravitational acceleration component Gg, i.e., the road gradient component, can be calculated with high accuracy. This makes it possible to estimate the road gradient regardless of whether the vehicle 10 is moving forward or backward. Furthermore, it is possible to estimate the road gradient even when the vehicle 10 turns or brakes while moving forward or backward. As a specific example, it is possible to estimate the road gradient even when the vehicle 10 brakes while moving backward to climb a slope. Furthermore, it is possible to estimate the road gradient even when the vehicle 10 brakes while moving backward to descend a slope.

[0079] If the forward / reverse determination is changed erroneously, the accuracy of the gradient estimate θ will decrease. For example, if the shift signal is unintentionally switched while the vehicle is traveling due to an incorrect operation or abnormality of the shift device, the forward / reverse determination may be changed erroneously. Furthermore, if the vehicle is equipped with a mechanism configured to connect and disconnect the transmission of power between the output shaft and the wheels, and the mechanism temporarily disconnects the transmission of power while the vehicle is traveling forward, the rotation speeds on both sides of the mechanism may differ. If the rotation speed on the drive unit side and the rotation speed on the wheel side do not match in this way, information may be detected as if the vehicle is traveling in reverse. If the forward / reverse determination is changed based on such detection, the forward / reverse determination may indicate that the vehicle is traveling in reverse, even though the vehicle is traveling forward. In other words, the forward / reverse determination may be changed erroneously.

[0080] In this regard, the control device 50 can change the forward / reverse determination based on information input from at least one of the front / rear determination means 60. For example, the control device 50 can be configured to change the forward / reverse determination when information input from two of the front / rear determination means 60 both indicates reverse while the vehicle is moving forward. This configuration that changes the determination based on a match between multiple pieces of information can improve the accuracy of determining whether the vehicle 10 is moving backward, compared to a configuration that changes the forward / reverse determination based on information input from one of the front / rear determination means 60.

[0081] Furthermore, according to the control device 50, when a change in whether the vehicle 10 is moving in reverse is detected, if the probability of the change is low, the forward / reverse determination is not changed in response to the detected change, and the forward / reverse determination is maintained. For example, if the vehicle speed VS is equal to or greater than the vehicle speed determination value VSth1 over a specified period P1 that includes the time when the change in whether the vehicle 10 is moving in reverse is detected, the forward / reverse determination is maintained. This improves the accuracy of changing the forward / reverse determination. This prevents a decrease in the accuracy of the gradient estimate value θ.

[0082] In a situation where the vehicle body is subject to pitching motion, the inertial force that generates the pitching motion is reflected in the inertial acceleration Gxg. Therefore, when pitching motion occurs, the accuracy of the gradient estimate θ may decrease. In this regard, the control device 50 can correct at least one of the first acceleration G1 and the second acceleration G2 so that the difference between the first acceleration G1 and the second acceleration G2 decreases as the pitch angle of the vehicle 10 increases. This makes it possible to prevent the accuracy of the gradient estimate θ from decreasing when pitching motion occurs.

[0083] According to the control device 50, when the jerk difference |ΔJ|, which is the absolute value of the difference between the first jerk Jg and the second jerk Jw, remains equal to or greater than the determination value ΔJth for a specified time, the forward / reverse determination can be changed to a determination that the vehicle 10 is moving backward. With this configuration, it is possible to determine whether the vehicle 10 is moving backward even when an abnormality occurs such as a loss of information from the forward / reverse determination means 60 other than the longitudinal acceleration sensor 103 and the wheel speed sensor 102. This makes it possible to estimate the road gradient even when the abnormality occurs.

[0084] When the vehicle 10 is braking suddenly, starting suddenly, turning suddenly, or the like, the inertial acceleration Gxg and the actual acceleration Gxw change abruptly, which may reduce the accuracy of the gradient estimate θ calculated based on the inertial acceleration Gxg and the actual acceleration Gxw. In this regard, the control device 50 does not update the gradient estimate θ while at least one of the absolute value of the first jerk Jg, which is the time derivative of the inertial acceleration Gxg, and the absolute value of the second jerk Jw, which is the time derivative of the actual acceleration Gxw, is equal to or greater than a specified threshold value Jth. While at least one of the absolute value of the first jerk Jg and the absolute value of the second jerk Jw is equal to or greater than the specified threshold value Jth, the gradient estimate θ before the absolute value became equal to or greater than the threshold value Jth is maintained. This allows the most recent gradient estimate θ to be maintained when the vehicle 10 is braking suddenly, starting suddenly, turning suddenly, or the like. This prevents the accuracy of the gradient estimate θ from being reduced.

[0085] When the vehicle speed VS of the vehicle 10 is low, the accuracy of the actual acceleration Gxw calculated based on the vehicle speed VS may decrease. This may result in a decrease in the accuracy of the calculated gradient estimate θ. In this regard, the control device 50 maintains the gradient estimate θ that was obtained before the vehicle speed VS became equal to or less than the low-speed determination value VSth2 while the vehicle speed VS is equal to or less than the specified low-speed determination value VSth2. This prevents the accuracy of the gradient estimate θ from decreasing.

[0086] The gradient estimated value θ calculated by the road gradient estimation device of this embodiment can be referenced when controlling a vehicle equipped with the road gradient estimation device. For example, the gradient estimated value θ can be used when performing control such as adjusting the braking force to suppress vehicle body roll when the vehicle 10 stops. As a specific example, even when braking is performed while the vehicle 10 is reversing up a slope, control can be performed using the highly accurate gradient estimated value θ. Furthermore, even when braking is performed while the vehicle 10 is reversing down a slope, control can be performed using the highly accurate gradient estimated value θ.

[0087] The use of the estimated gradient value θ calculated by the road gradient estimation device is not limited to controlling the vehicle equipped with the road gradient estimation device. As an example, the estimated gradient value θ may be collected by a processing circuit external to the vehicle. An example of an external processing circuit is a data center. For example, map information including road gradient information can be created by collecting the estimated gradient value θ along with vehicle position information at the time the estimated gradient value θ was estimated.

[0088] (Modifications) This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0089] In the above embodiment, the configuration in which the process of retaining the estimated value shown in Fig. 4 is performed is exemplified. However, this process is not essential. The gradient estimated value θ may be permitted to be updated regardless of whether the estimated value retention condition is met.

[0090] In the above embodiment, the configuration in which the process for maintaining the forward / reverse determination shown in Fig. 5 is performed is exemplified. However, this process is not essential. The forward / reverse determination may be changed when a change in the vehicle 10 between forward and reverse is detected, regardless of whether the probability is low or not.

[0091] In the above embodiment, when a change in whether the vehicle 10 is moving backward is detected, the determination as to whether the probability of the change is low is made based on the vehicle speed VS. The determination as to whether the probability is low can also be made as follows. For example, the determination holding unit M14 determines that the probability is low when all of the determination examples made by the forward / reverse determination unit M11 do not match. On the other hand, the determination holding unit M14 determines that the probability is high when all of the determination examples made by the forward / reverse determination unit M11 match. For example, when a forward / reverse determination determines that the vehicle is moving forward, if reverse is detected in one of the above modes [A1] to [A5] and forward is detected in the remaining four modes, the determination as to the probability is low.

[0092] In the above embodiment, the correction process is performed as step S104 in the process flow shown in FIG. 3 . However, the correction process may be omitted. That is, it is not essential to correct at least one of the first acceleration G1 and the second acceleration G2 so that the difference between the first acceleration G1 and the second acceleration G2 decreases as the pitch angle increases. In this case, the processing circuit 51 proceeds to step S105 after step S102 or S103.

[0093] In the above embodiment, the process in step S102 in the process flow shown in Fig. 3 uses the value obtained by inverting the sign of the actual acceleration Gxw as the second acceleration G2. The value to be inverted is not limited to the second acceleration G2, and may be the first acceleration G1. For example, in step S102, the process may be configured to obtain the value obtained by inverting the sign of the inertial acceleration Gxg as the first acceleration G1, and obtain the value of the actual acceleration Gxw as the second acceleration G2.

[0094] Alternatively, it is not necessary to specify the target whose sign is to be inverted. When the determination of whether the vehicle 10 is moving backward is changed, the sign of the first acceleration G1 or the second acceleration G2 may be inverted. For example, when the vehicle 10 switches from forward to reverse, the second acceleration G2 is obtained by inverting the sign of the actual acceleration Gxw. The first acceleration G1 is obtained by the inertial acceleration Gxg. Subsequently, when the vehicle 10 switches from reverse to forward again, the second acceleration G2 is obtained by inverting the sign of the actual acceleration Gxw, and the first acceleration G1 is obtained by inverting the sign of the inertial acceleration Gxg.

[0095] Even with the above modification, the positive and negative signs of the first acceleration G1 and the second acceleration G2 can be aligned, so that, as with the above embodiment, the road gradient can be estimated regardless of whether the vehicle 10 is reversing or not.

[0096] In the above embodiment, a configuration is described in which it is determined whether the vehicle 10 is moving in reverse based on a shift signal output by a shift device. If the vehicle 10 is equipped with a driving assistance device, the processing circuit 51 can also determine whether the vehicle 10 is moving in reverse as follows. The driving assistance device can automatically change the range without the driver's operation. The processing circuit 51 may determine whether the vehicle 10 is moving in reverse based on a shift signal output by the driving assistance device.

[0097] In the above embodiment, the actual acceleration Gxw is calculated based on the detection signal of the wheel speed sensor 102. Alternatively, the actual acceleration Gxw may be calculated as follows.

[0098] As an example, the vehicle 10 is equipped with a GNSS receiver. The GNSS receiver can acquire position information by receiving signals from positioning satellites. When the vehicle 10 is equipped with a GNSS receiver, the processing circuit 51 may calculate the actual acceleration Gxw based on changes in the position information of the vehicle 10 that can be acquired by the GNSS receiver.

[0099] As another example, the vehicle 10 is equipped with a rotation angle sensor that detects the rotation speed of an output shaft that transmits the driving force of the drive unit. The output shaft is, for example, a crankshaft, a rotating shaft of a travel motor, etc. When the vehicle 10 is equipped with a rotation angle sensor that detects the rotation speed of the output shaft, the processing circuit 51 may calculate the actual acceleration Gxw based on the rotation speed of the output shaft.

[0100] In the above embodiment, the inertial acceleration Gxg is calculated based on the detection signal of the longitudinal acceleration sensor 103. Alternatively, the inertial acceleration Gxg may be calculated as the inertial force generated in the vehicle during braking. For example, the inertial acceleration Gxg may be calculated based on the braking request and the driving force of the vehicle.

[0101] The processing circuitry 51 may be configured as a circuit including one or more processors operating according to a computer program, one or more dedicated hardware circuits such as dedicated hardware for performing at least some of the various processes, or a combination thereof. Dedicated hardware may include, for example, an application-specific integrated circuit (ASIC). The processor includes a CPU and memory such as RAM and ROM, which stores program code or instructions configured to cause the CPU to perform processes. The memory, i.e., storage medium, includes any available medium accessible by a general-purpose or dedicated computer.

[0102] In the above embodiment, the processing circuit 51 includes the braking control unit M21. However, the processing circuit 51 does not have to include the braking control unit M21. For example, the vehicle may include another processing circuit that realizes a function equivalent to the braking control unit M21. In this way, some of the functions realized by the processing circuit 51 may be realized by another processing circuit included in the vehicle. The processing circuits included in the vehicle can communicate with each other via an in-vehicle network, for example.

Claims

1. A road gradient estimation device that estimates the road gradient of a road on which a vehicle is traveling based on inertial acceleration derived based on the inertial force in the vehicle's direction of travel and actual acceleration derived based on changes in the vehicle's speed, comprising: a forward / backward travel determination unit that changes a forward / backward travel determination indicating whether the vehicle is traveling in reverse depending on whether the vehicle is traveling in reverse; an acceleration correction unit that acquires one of the inertial acceleration and the actual acceleration as a first acceleration and the other as a second acceleration, and that corrects the first acceleration or the second acceleration by reversing its sign when the forward / backward travel determination by the forward / backward travel determination unit is changed; and a gradient estimation unit that estimates the road gradient based on the difference between the first acceleration and the second acceleration.

2. The road gradient estimation device according to claim 1, further comprising a judgment holding unit that, when detecting a change in whether the vehicle is moving in reverse or not, causes the forward / reverse judgment unit to change the forward / reverse judgment if the probability of the change is high, and causes the forward / reverse judgment unit to hold the forward / reverse judgment without changing it if the probability of the change is low.

3. The road gradient estimation device according to claim 1 or 2, wherein the acceleration correction unit corrects at least one of the first acceleration and the second acceleration so that the difference between the first acceleration and the second acceleration becomes smaller as the pitch angle of the vehicle increases.

4. A road gradient estimation device according to claim 1 or 2, wherein the forward / backward determination unit changes the forward / backward determination to a determination that the vehicle is moving backward when a state in which the absolute value of the difference between the amount of change per unit time of the inertial acceleration and the amount of change per unit time of the actual acceleration is equal to or greater than a specified determination value continues for a specified time, while changing the forward / backward determination to a determination that the vehicle is not moving backward when the absolute value of the difference is smaller than the determination value or when the state in which the absolute value of the difference is equal to or greater than the determination value does not continue for the specified time.

5. A road gradient estimation device according to claim 1 or 2, further comprising an estimated value holding unit that holds the estimated value of the road gradient before the absolute value of the change in the inertial acceleration per unit time and the absolute value of the change in the actual acceleration per unit time remains equal to or greater than a specified threshold value, while the absolute value of the change in the inertial acceleration per unit time and the absolute value of the change in the actual acceleration per unit time remain equal to or greater than a specified threshold value.

6. A road gradient estimation device according to claim 1 or 2, further comprising an estimated value holding unit that holds the estimated value of the road gradient before the vehicle speed becomes equal to or less than a specified low speed judgment value while the vehicle speed is equal to or less than the specified low speed judgment value.

7. The road gradient estimation device according to claim 2, wherein the judgment holding unit, when detecting a change in whether the vehicle is reversing or not, determines that the probability of the change is high if the vehicle speed becomes lower than a specified vehicle speed judgment value during a specified period including the time when the change is detected, and, when detecting a change in whether the vehicle is reversing or not, determines that the probability of the change is low if the vehicle speed is equal to or higher than the vehicle speed judgment value during the specified period including the time when the change is detected.

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