Steering gear

Abstract

It correctly determines straight-line driving even when the vehicle height changes. [Solution] The steering device 100 includes a vehicle information acquisition unit 131 that acquires vehicle information, which is information about the vehicle, including the relative steering angle of the steering member 241 with respect to a predetermined steering angle reference; a midpoint estimation unit 132 that estimates the midpoint of the steering angle based on the relative steering angle and other vehicle information; and a straight-line determination unit 133 that determines whether the vehicle is in a straight-line driving state based on the estimated steering angle, which is the difference between the relative steering angle and the midpoint of the steering angle.

Description

[[Technical Field]]

[0001] The present invention relates to a steering apparatus that steers a vehicle by turning steered wheels provided in the vehicle. [[Background Art]]

[0002] Patent Document 1 discloses a midpoint learning function that updates a steering angle midpoint when a vehicle straight traveling condition for determining that the vehicle is traveling straight and a non-steering condition for determining that a steering wheel is not steered are satisfied.

[0003] Further, Patent Document 2 discloses a cant compensation control technique for compensating for the drift of a vehicle body due to cant in the midpoint learning function. [[Prior Art Documents]] [[Patent Documents]]

[0004] [[Patent Document 1]] Japanese Unexamined Patent Application Publication No. 2017-105277 [[Patent Document 2]] Japanese Unexamined Patent Application Publication No. 2010-95180 [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0005] However, when the vehicle height of the vehicle fluctuates due to loading / unloading of cargo or getting on / off of passengers, the predetermined steering angle reference may deviate from the actual midpoint of the steering angle. Particularly in large vehicles, the actual midpoint of the steering angle fluctuates greatly due to the fluctuation of the vehicle height. If the actual midpoint of the steering angle fluctuates greatly, in the conventional technology, a deviation occurs between the turning angle of the steered wheels and the steering angle which is information for turning the steered wheels, and there is a risk that straight traveling determination, which is determination on whether the vehicle is traveling in a straight traveling state, cannot be performed accurately.

[0006] The present invention has been made in view of the above problem, and provides a steering apparatus that can appropriately perform straight traveling determination even when the vehicle height of the vehicle fluctuates. [Means for solving the problem]

[0007] One steering device according to the present invention includes: a vehicle information acquisition unit that acquires vehicle information, which is information about the vehicle including the relative steering angle of a steering member with respect to a predetermined steering angle reference; a midpoint estimation unit that estimates the midpoint of the steering angle based on the relative steering angle and other vehicle information; and a straight-line determination unit that determines whether or not the vehicle is in a straight-line driving state based on the estimated steering angle, which is the difference between the relative steering angle and the midpoint of the steering angle. [Effects of the Invention]

[0008] According to the present invention, even in vehicles where the steering angle midpoint changes due to fluctuations in vehicle height, it is possible to accurately determine whether the vehicle is going straight. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a simplified diagram showing a vehicle equipped with a steering system. [Figure 2] Figure 2 is a block diagram showing the functional configuration of the computing device included in the steering system. [Modes for carrying out the invention]

[0010] The following describes embodiments of the steering device according to the present invention with reference to the drawings. Note that the following embodiments are examples provided to illustrate the present invention and are not intended to limit it. For example, the shapes, structures, materials, components, relative positional relationships, connection states, numerical values, formulas, the content of each step in the method, and the order of each step shown in the following embodiments are examples and may include content not described below. Furthermore, geometric expressions such as parallel and orthogonal may be used, but these expressions do not indicate mathematical rigor and include substantially acceptable errors and deviations. Similarly, expressions such as simultaneous and identical also include substantially acceptable ranges.

[0011] Furthermore, the drawings are schematic diagrams that have been appropriately emphasized, omitted, or had their proportions adjusted to illustrate the present invention, and therefore differ from the actual shapes, positional relationships, and proportions. Also, the X, Y, and Z axes shown in the drawings represent orthogonal coordinates arbitrarily set for the purpose of explaining the drawings. In other words, the Z axis is not necessarily an axis along the vertical direction, and the X and Y axes are not necessarily located in the horizontal plane.

[0012] Furthermore, in the following, multiple inventions may be described comprehensively as a single embodiment. Also, some of the content described below is described as an optional component relating to the present invention.

[0013] Figure 1 is a simplified diagram showing a vehicle 200 equipped with a steering device 100. The vehicle 200 is a mobile body that travels on the road surface 301 using an engine, electric motor, etc. Specifically, examples of the vehicle 200 include trucks, buses, agricultural machinery, and construction machinery, whose vehicle weight changes greatly depending on the amount of cargo they carry. In this embodiment, the vehicle 200 is equipped with a suspension 220, steering wheels 230, and a steering device 100.

[0014] The suspension 220 is a suspension system that absorbs vibrations and shocks generated in the steering wheels 230, stabilizes the posture of the vehicle body 210, and improves driving performance. For example, the suspension 220 is composed of parts such as coil springs, dampers, arms, stabilizer bars, and bushings. When the vehicle 200 hits uneven surfaces or obstacles on the road surface 301 while in motion, the suspension 220 absorbs the force generated in the steering wheels 230, suppressing the swaying of the vehicle body 210. In addition, the suspension 220 deforms according to the weight of the vehicle and functions in a deformed state. In other words, the height of the vehicle body 210 relative to the road surface 301 decreases as the vehicle weight increases and increases as the vehicle weight decreases.

[0015] The steering device 100 is a device that changes the direction of travel of the vehicle 200 by steering the steering wheels 230. In manual driving, the steering device 100 allows the driver to operate a steering member 241 such as a steering wheel to turn the steering wheels 230 in any direction. In addition, auxiliary torque may be input to the shaft 243 from the electric actuator 242 in conjunction with the operation of the steering member 241. Furthermore, a relatively strong auxiliary torque may be input to the shaft 243 from the hydraulic mechanism 244 in accordance with the operation of the electric actuator 242. In automatic driving, the steering device 100 drives at least one of the electric actuator 242 and the hydraulic mechanism 244 to rotate the shaft 243 based on steering information transmitted from a higher-level ECU (Electronic Control Unit), and steers the steering wheels 230 according to the steering information. The steering device 100 includes a linkage mechanism 110 and a calculation unit 130.

[0016] The linkage mechanism 110 is a mechanism that combines multiple mechanical elements for steering the steering wheel 230. The type of linkage mechanism 110 is not limited, but in this embodiment, the linkage mechanism 110 includes a pitman arm 111 and a drag link 112.

[0017] The pitman arm 111 is attached to the output shaft of the steering box 245 (gearbox), which transmits the rotation of the shaft 243, and receives the rotation output by the steering box 245. The pitman arm 111 rotates and oscillates in conjunction with the rotation of the shaft 243, causing the drag link 112 to reciprocate in the extending direction. The drag link 112 is attached to one end of a tie rod (not shown) which is attached to the wheel of the steering wheel 230, and the steering wheel 230 is rotated via the tie rod. The link mechanism 110, consisting of the pitman arm 111 and the drag link 112, can transmit strong torque and is often used in large vehicles such as buses and trucks.

[0018] FIG. 2 is a block diagram showing the functional configuration of an arithmetic unit 130 included in a steering apparatus. As the arithmetic unit 130, an example of an apparatus having a function of determining that a vehicle 200 is traveling straight and outputting cant compensation torque in accordance with steering torque when straight steering is determined can be given. The arithmetic unit 130 includes a processor, and includes, as processing units implemented by causing the processor to process a straight travel determination program, a vehicle information acquisition unit 131, a midpoint estimation unit 132, and a straight travel determination unit 133. In the case of the present embodiment, the arithmetic unit 130 further includes an accuracy detection unit 134 and a cant compensation torque calculation unit 135.

[0019] The vehicle information acquisition unit 131 acquires vehicle information, which is information related to the vehicle, from various sensors mounted on the vehicle and the like. The vehicle information includes a plurality of types of information. The vehicle information includes at least a relative steering angle. The relative steering angle is the rotation angle of the steering member 241 with respect to a predetermined steering angle reference such as a midpoint set when the vehicle 200 is manufactured, for example. The acquisition source of the relative steering angle is not limited, but in the case of the present embodiment, the relative steering angle is acquired from the steering angle detector 120. The steering angle detector 120 is a sensor that detects the rotation angle of a shaft 243 connected to the link mechanism 110 via a steering box 245. The type of the steering angle detector 120 is not particularly limited, and examples thereof include a resolver and a rotary encoder.

[0020] For example, the steering angle reference at which the vehicle 200 is considered to travel straight is set to 0°, the rotation angle is acquired with a positive value when the steering member 241 is rotated clockwise (rightward rotation) as viewed from the driver and a negative value when rotated counterclockwise (leftward rotation), and information including the absolute rotation angle and the steering direction is used as the relative steering angle. Note that the sign of the rotation angle acquired by the vehicle information acquisition unit 131 may be reversed. In the case of automatic driving, the rotation angle is acquired based on a signal from the steering angle detector 120 that has read the rotation angle of the shaft 243 rotated by the electric actuator 242. Even in the case of automatic driving, the relative steering angle including the same steering direction as in manual driving is acquired.

[0021] The vehicle information may include, in addition to the relative steering angle, at least one of vehicle speed, lateral acceleration, yaw rate, steering angular velocity, wheel speed which is the rotational speed of each wheel, road cant angle, straight traveling information, steering state information, and steering torque, for example.

[0022] The midpoint estimating unit 132 estimates a steering angle midpoint based on the relative steering angle acquired by the vehicle information acquiring unit 131 and other vehicle information. The method for estimating the steering angle midpoint is not limited. In the present embodiment, the midpoint estimating unit 132 estimates the steering angle midpoint based on the relative steering angle, the road cant angle, straight traveling information indicating whether the vehicle is traveling straight, and steering state information indicating whether a steering member 241 is being steered. When the steering member 241 is in a non-steered state where no steering is performed, the midpoint estimating unit 132 estimates the steering angle midpoint at predetermined time intervals, and updates the previously estimated steering angle midpoint with the newly estimated steering angle midpoint. For example, the midpoint estimating unit 132 determines the straight traveling state of the vehicle from the yaw rate, lateral acceleration, wheel speed, etc., and estimates the steering state from the steering assist torque, steering torque, etc. The midpoint estimating unit 132 may estimate, as the steering angle midpoint, a steering angle obtained when a state where the vehicle 200 travels straight and no steering is performed continues for a predetermined period of time.

[0023] An accuracy detecting unit 134 detects estimation accuracy that is the accuracy of the steering angle midpoint estimated by the midpoint estimating unit 132. Although the method for detecting the accuracy is not limited, in the present embodiment, the accuracy detecting unit 134 counts, after a reset, the number of times the midpoint estimating unit 132 has estimated the steering angle midpoint, and detects the counting result as the estimation accuracy. The reset is performed, for example, when the vehicle is brought into an operable state and power is supplied to the arithmetic device 130 after the vehicle has been in an inoperable state and power supply to the arithmetic device 130 has been cut off.

[0024] The straight-line determination unit 133 determines whether the vehicle is traveling in a straight line based on the relative steering angle acquired by the vehicle information acquisition unit 131 and the estimated steering angle, which is the difference between the steering angle midpoint estimated by the midpoint estimation unit 132. For example, the straight-line determination unit 133 may determine that the vehicle is traveling in a straight line if the estimated steering angle is less than the steering angle threshold. In this embodiment, if the estimated accuracy detected by the accuracy detection unit 134 is less than or equal to the accuracy threshold, the straight-line determination unit 133 determines that the vehicle is not traveling in a straight line even if the estimated steering angle is less than the steering angle threshold.

[0025] The straight-line determination unit 133 may also determine whether the vehicle 200 is in a straight-line state by including vehicle information acquired by the vehicle information acquisition unit 131 in addition to the estimated steering angle. The determination method of the straight-line determination unit 133 is not limited. For example, it may include at least one of the following: the wheel speeds of the left and right steering wheels 230 and the left and right driven wheels, the yaw rate of the vehicle 200, and the roll rate of the vehicle 200. The straight-line determination unit 133 may also determine the straight-line state by including steering angular velocity, steering torque, etc.

[0026] The cant compensation torque calculation unit 135 derives a compensation torque corresponding to the steering torque while driving straight on a canted road, based on information obtained from the straight-driving determination unit 133 indicating that the vehicle 200 is in a straight-driving state, and the steering torque obtained from the vehicle information acquisition unit 131. The compensation torque is derived by calculations using maps or functions. The derived compensation torque makes it possible for the driver to reduce the steering torque required while driving straight on a canted road. If the vehicle 200 is not in a straight-driving state, the cant compensation torque calculation unit 135 derives the compensation torque by calculations using maps or functions so that it decreases toward 0.

[0027] It should be noted that the present invention is not limited to the embodiments described above. For example, other embodiments of the present invention may be realized by arbitrarily combining the components described herein, or by excluding some of the components. Furthermore, modifications obtained by applying various modifications to the above embodiments that a person skilled in the art could conceive of without departing from the spirit of the present invention, that is, the meaning indicated by the wording in the claims, are also included in the present invention.

[0028] For example, the straight-ahead determination unit 133 may acquire the pitch angle and roll angle of the vehicle 200 as vehicle information, and determine that the vehicle is not in a straight-ahead state when the variation of at least one of the pitch angle and roll angle exceeds a threshold.

[0029] Furthermore, although the accuracy detection unit 134 was described as detecting the estimation accuracy based on the number of times the midpoint estimation unit 132 estimated the midpoint of the rudder angle, the accuracy detection unit 134 may also detect the estimation accuracy based on the elapsed time since power was supplied to the calculation device 130.

[0030] (summary) The steering device 100 of the first embodiment includes a vehicle information acquisition unit 131 that acquires vehicle information, which is information about the vehicle, including the relative steering angle of the steering member 241 with respect to a predetermined steering angle reference; a midpoint estimation unit 132 that estimates the midpoint of the steering angle based on the relative steering angle and other vehicle information; and a straight-line determination unit 133 that determines whether the vehicle is in a straight-line driving state based on the estimated steering angle, which is the difference between the relative steering angle and the midpoint of the steering angle.

[0031] Conventionally, the straight-line driving state is determined using the relative steering angle based on a midpoint set during manufacturing. However, due to fluctuations in vehicle height, the set midpoint and the actual midpoint may diverge, potentially leading to inaccurate determination of the straight-line driving state. In contrast, according to the first embodiment, the straight-line driving state is determined using the estimated steering angle midpoint, thus correcting the shortcomings in straight-line driving state determination caused by fluctuations in vehicle height. Furthermore, because the straight-line driving state can be correctly determined, the cant compensation torque can be appropriately derived, enabling proper assistance of the driver's steering force when driving straight on a canted road.

[0032] The steering device 100 of the second embodiment includes the first embodiment and comprises an accuracy detection unit 134 that detects the estimation accuracy of the midpoint of the steering angle in the midpoint estimation unit 132, and the straight-line determination unit 133 determines that the vehicle is not in a straight-line driving state if the estimation accuracy is below an accuracy threshold.

[0033] According to the second embodiment, when the estimation accuracy is low, the determination of whether the vehicle is in a straight-ahead state is stopped, preventing the straight-ahead determination unit 133 from outputting an incorrect straight-ahead determination. Consequently, the cant compensation torque calculation unit 135 does not output an incorrect cant compensation torque, and the driver can steer without any discomfort even on a canted road. [Industrial applicability]

[0034] This invention can be used in vehicles equipped with steering, agricultural machinery, construction machinery, automated guided vehicles, and the like. [Explanation of Symbols]

[0035] 100...Steering mechanism, 110...Link mechanism, 111...Pitman arm, 112...Drag link, 120...Steering angle detector, 130...Calculation unit, 131...Vehicle information acquisition unit, 132...Midpoint estimation unit, 133...Straight-line determination unit, 134...Accuracy detection unit, 135...Cant compensation torque calculation unit, 200...Vehicle, 210...Vehicle body, 220...Suspension, 230...Steering wheel, 241...Steering member, 242...Electric actuator, 243...Shaft, 244...Hydraulic mechanism, 245...Steering box, 301...Road surface

Claims

1. A vehicle information acquisition unit acquires vehicle information, which is information about the vehicle including the relative steering angle of the steering member with respect to a predetermined steering angle reference. A midpoint estimation unit estimates the midpoint of the steering angle based on the aforementioned relative steering angle and other vehicle information, A straight-line determination unit determines whether the vehicle is in a straight-line driving state based on the estimated steering angle, which is the difference between the relative steering angle and the midpoint of the steering angle. A steering system equipped with a steering mechanism.

2. The midpoint estimation unit includes an accuracy detection unit for detecting the estimation accuracy of the midpoint of the rudder angle, The straight-line determination unit determines that the vehicle is not traveling in a straight line if the estimation accuracy is below the accuracy threshold. The steering device according to claim 1.

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