Method for determining gear ratio of power steering system as function of vehicle speed and steering wheel angle
Patent Information
- Application Number
- JP2023011731
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-02-07
- Filing Date
- 2023-01-30
- Publication Date
- 2026-01-15
AI Technical Summary
Existing power steering systems, particularly in steer-by-wire systems, suffer from an upper steering wheel angle limit that varies with vehicle speed, leading to impaired driving experiences due to torque steer effects during acceleration and return effects during deceleration, and difficulty in finding the proper counter-handle angle during loss of grip.
A method to determine the gear ratio as a function of vehicle speed and steering wheel angle, ensuring a single upper steering wheel angle corresponds to the upper rack position, using equations to define the gear ratio and incorporating limit variations and grip handle angles to maintain vehicle controllability.
This approach stabilizes the steering wheel angle feel regardless of vehicle speed changes, eliminating torque steer and return effects, and simplifies finding the correct counter-handle angle during oversteer, thereby enhancing driving comfort and safety.
Smart Images
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Abstract
Description
[Technical Field]
[0001] The present invention relates to the field of power steering systems, and more particularly to a method for determining a gear ratio for a power steering system, as well as a vehicle equipped with a power steering system that achieves such a gear ratio. Summary of the Invention [Problem to be solved by the invention]
[0002] The purpose of a vehicle steering system is to allow a driver to control the vehicle trajectory by modifying the azimuth angle of the wheels, also called the yaw angle of the vehicle, with the steering wheel. The azimuth angle of the wheels (hereinafter referred to as the "wheel angle") is particularly related to the angle of the steering wheel (hereinafter referred to as the "steering wheel angle"). The driver changes the steering wheel angle by applying force to the steering wheel.
[0003] Generally, a steering system comprises several elements, including the steering wheel, a rack, and two wheels, each connected to a tie rod. The rack is the component used to operate the wheels. The rack takes on several positions along the casing, hereafter referred to as rack positions. More precisely, the rack is displaced between two stops on the casing, which define a lower limit rack position and an upper limit rack position that allows the wheels to reach a maximum azimuth angle. For example, it is known to specify rack positions by a steering wheel angle value. Generally, a rack position of zero corresponds to a steering wheel angle of zero, which allows the vehicle to follow a straight track. Of course, the invention is not limited to this embodiment, and the rack position of zero may correspond to another steering wheel angle.
[0004] In a mechanical or traditional type electric power steering system, there is a mechanical link between the steering wheel and the rack, typically formed by a steering column, and therefore the ratio between the change in steering angle and the change in rack position (hereinafter referred to as the gear ratio) is typically determined by a mechanical element via the gear ratio of the pinion.
[0005] However, there are mechanical steering systems with variable gear reduction, also known as "active front steering", in which the gear ratio can be adjusted by software.
[0006] In electric power steering systems without a mechanical link, also known as "steer-by-wire," the steering wheel is mechanically decoupled from the rack. In this case, the steering system has a steering unit that is mechanically independent from the rack-and-pinion unit. In other words, forces applied to the steering unit are not mechanically transmitted to the rack unit and vice versa.
[0007] In a "steer-by-wire" steering system, like a mechanical steering system with variable gear reduction, the ratio between change in steering wheel angle and change in rack position is adjusted by software, allowing, for example, the gear ratio to change depending on the rack position and / or vehicle speed.
[0008] Generally, the gear ratio is low at low speeds to facilitate maneuvering the vehicle and high at high speeds to improve vehicle controllability, and therefore the gear ratio is a function of vehicle speed.
[0009] An obvious drawback of this relationship is that it has an upper limit on the steering angle that varies depending on the vehicle speed, as shown in Figure 1. In practice, the steering angle A v is a different rack position X c Therefore, the upper limit of the steering angle A v1sup , A v2sup , Av3sup Fixed upper rack position X for each csup In other words, the driver can turn the steering wheel more or less depending on the speed of the vehicle.
[0010] This leads to an impairment of the driver's driving experience. In fact, the driver feels the torque steer effect of the steering wheel, i.e., an increase in the upper limit of the steering angle, during acceleration, while feeling the torque steer effect, i.e., a decrease in the upper limit of the steering angle, during deceleration. Finally, during the loss of grip in oversteer, it is difficult to find the appropriate counter steering angle. [Means for solving the problem]
[0011] The object of the present invention is to remedy all or part of the aforementioned drawbacks by proposing a method for determining a gear ratio for a power steering system of a vehicle, said power steering system comprising a steering wheel for determining a steering wheel angle and a rack for determining a rack position, said rack position varying between a lower rack position and an upper rack position, said gear ratio defining the ratio between said rack position and said steering wheel angle or between said steering wheel angle and said rack position, said method being characterized in that it comprises a definition step in which said gear ratio is defined as a function of the vehicle speed and the steering wheel angle, such that said upper rack position corresponds to a single upper steering wheel angle.
[0012] The rack position corresponds to an image value of the rack position, which can be measured directly on the rack or obtained by inference or calculation, for example, the image of the rack position can be obtained by the position of an auxiliary motor that corrects the rack position, by a position sensor, by an angle sensor, or by the azimuth angle of the wheel or wheel yaw angle.
[0013] The rack position varies between two stops, one of which represents the upper limit of the rack position. The stops can be physical or virtual. It is generally accepted that a rack position of 0° corresponds to the center of the rack.
[0014] Similarly, the steering wheel angle corresponds to an image value of the steering wheel angle which can be measured directly on the steering wheel or obtained by inference or calculation, for example the steering wheel angle image can be obtained by the position of a motor exerting a torque on the axis of the column supporting the steering wheel, or by an absolute angle sensor positioned on said axis of the column supporting the steering wheel.
[0015] VGR is the gear ratio, A v The steering angle, X c When the rack position is, the gear ratio is calculated by the following formula: [Equation 1] VGR=A v / X c Or, the following formula: [Equation 2] VGR=X c / A v is obtained by
[0016] It is generally accepted that the formula (2) is the reciprocal of the gear ratio. Therefore, in the following explanation, we will consider calculating the gear ratio using the formula (1).
[0017] According to the invention, the gear ratio depends on the vehicle speed, which ensures good maneuverability at low speeds by determining a low gear ratio and good controllability at high speeds with a high gear ratio.
[0018] According to the present invention, the gear ratio also depends on the steering wheel angle. Thus, the gear ratio is adapted as a function of the steering wheel angle so that the upper rack position corresponds to a single upper steering wheel angle. In other words, regardless of the vehicle speed, the steering wheel angle varies over a range whose upper limit is the upper steering wheel angle.
[0019] In this way, when the driver turns the steering wheel to position it according to the upper limit steering angle and the rack at the upper limit rack position, the driver's feeling will not change even if the vehicle speed increases or decreases. In other words, the steering wheel remains positioned at the upper limit steering angle. Therefore, there is no steering torque steer or return effect like in the state of the art. Finally, when there is a loss of grip in oversteer, it is easy to find an appropriate counter steering angle.
[0020] The invention may also have one or more of the following features, considered alone or in combination:
[0021] According to one embodiment, the power steering system is of the "steer-by-wire" type, or mechanical type with variable gear reduction.
[0022] Therefore, it is easy to realize a variable gear ratio.
[0023] According to one embodiment, the upper handle angle is [Equation 3]X csup / 5 and [number 4]X csup Included between .2.
[0024] where X csup is the upper rack position.
[0025] According to one embodiment, the definition step determines, for the vehicle speed considered, a limit variation determination step in which a limit variation of the gear ratio as a function of the steering wheel angle is determined so as to ensure controllability of the vehicle below this limit variation; a grip handle angle determination stage in which a grip handle angle is determined, which corresponds to a handle angle above which the vehicle is no longer controllable; and a characterization step in which the gear ratio is defined such that below the grip handle angle the variation in the gear ratio is equal to or less than the limit variation.
[0026] The definition step comprises, for each vehicle speed value, a step of determining a limit variation, a step of determining a grip handle angle, and a step of characterization.Indeed, the limit variation and the grip handle angle depend inter alia on the vehicle speed.
[0027] The gear ratio limit variation corresponds to the steering coefficient of the gear ratio curve as a function of the steering wheel angle for the vehicle speed considered, i.e. for a given vehicle speed. The limit variation is the threshold above which the gear ratio varies too quickly to ensure controllability of the vehicle at the speed considered. In other words, if the gear ratio varies according to a value smaller than the limit variation, the vehicle can be controlled, whereas if the gear ratio varies according to a value larger than the limit variation, the vehicle is not necessarily controllable, i.e. there is a significant risk of controllability being impaired.
[0028] The grip handle angle is a threshold value that corresponds to the grip limit of the vehicle, in other words, above which the vehicle cannot be controlled at the speed considered.
[0029] The limit variation and the grip handle angle represent two criteria for defining the gear ratio to ensure vehicle controllability. In other words, below the grip handle angle, the gear ratio variation must be equal to or less than the limit variation so that the driver can control the vehicle.
[0030] According to one embodiment, the limit variation is determined when the vehicle is in at least one grip condition that is not favorable for vehicle controllability.
[0031] This allows the vehicle to be controlled whatever the grip conditions are, provided that the gear ratio variation is below the limit variation.
[0032] According to one embodiment, the limit variation is determined as a function of at least one life condition of the vehicle.
[0033] The life conditions of a vehicle correspond to everything that affects the reaction of the vehicle, such as the surface condition of the lane, the surface condition of the wheels, the weight of the vehicle and its distribution within the vehicle.
[0034] The limit variation is therefore adapted to at least one life condition of the vehicle.
[0035] According to one embodiment, the gear ratio is defined in the characterization step such that above a grip handle angle the gear ratio variation is greater than a limit variation.
[0036] If the grip handle angle is exceeded, the vehicle cannot be controlled, so the driver wants to reach the upper limit of the grip handle angle as soon as possible.
[0037] According to one embodiment, the step of determining the limit variation and / or the grip handle angle is carried out by means of a mathematical model or physical tests.
[0038] According to one embodiment, the grip handle angle is determined when the vehicle is in at least one grip condition that is favorable to vehicle controllability.
[0039] According to one embodiment, the grip handle angle is determined as a function of at least one vehicle life condition.
[0040] According to one embodiment, the at least one preferred grip condition is dry ground.
[0041] Dry surface means a surface with a grip coefficient greater than 0.8.
[0042] The present invention also relates to a vehicle equipped with a power steering system that implements a gear ratio determined in accordance with the present invention. [Brief explanation of the drawings]
[0043] The invention will be better understood thanks to the following description of embodiments according to the invention, given as non-limiting examples and illustrated with reference to the accompanying schematic drawings, in which: [Figure 1] FIG. 1 is a diagram of rack position as a function of steering angle by realizing gear ratios according to the state of the art. [Figure 2] FIG. 2 is a diagram of gear ratio as a function of steering wheel angle according to the present invention. [Figure 3] FIG. 3 is a diagram of rack position as a function of steering angle by implementing a gear ratio according to the present invention.
[0044] Only the elements necessary for understanding the invention are shown. To facilitate reading the figures, identical elements have the same reference numbers from one figure to another. DETAILED DESCRIPTION OF THE INVENTION
[0045] A mechanical steering system with variable gear reduction, also known as "active front steering," or an electric power steering system without a mechanical link, known as "steer-by-wire," can be used to adjust the steering angle A v Determine the handle and rack position X c The rack is displaced between two stops on the casing, and the stops have an upper rack position X that allows the wheels to reach their maximum azimuth angle. csup , and the lower rack position. The stops may be real or virtual. In FIG. 3, rack position X c varies in angle from -530° to 530°. However, only the part from 0° to 530° is shown, with 0° being the center of symmetry.
[0046] VGR is the gear ratio, A v The steering angle, X c When the rack position is, the gear ratio VGR is [Equation 5] VGR=A v / X c Formula or [Equation 6] VGR=X c / A v Formula According to rack position X c and steering angle A v Ratio of, or steering angle A v and rack position X c It is defined as the ratio of
[0047] It is generally accepted that the formula (2) is the reciprocal of the gear ratio. Therefore, in the following explanation, we will consider calculating the gear ratio using the formula (1).
[0048] Rack Position X c corresponds to an image value of the rack position, which can be measured directly on the rack or obtained by inference or calculation. For example, the image of the rack position is c can be obtained by the position of the auxiliary motor correcting for azimuth or yaw of the wheel.
[0049] Similarly, steering angle A v corresponds to an image value of the steering wheel angle, which can be measured directly on the steering wheel or obtained by inference or calculation. For example, the steering wheel angle image can be obtained by the position of a motor exerting a torque on the axis of the column supporting the steering wheel, or by an absolute angle sensor positioned on said axis of the column supporting the steering wheel.
[0050] The method according to the invention performs a definition step during which the upper rack position X csup is the single upper limit of the steering angle A vsup The gear ratio VGR corresponds to the vehicle speeds V1, V2, V3 and the steering angle A v It is defined as a function of
[0051] More precisely, the definition step includes a step of determining the limit variation for the vehicle speeds V1, V2, V3 considered, i.e. for a given vehicle speed V1, V2, V3, and a step of determining the grip handle angle A vad_V2 , A vad_V3 and a characterization step.
[0052] In the stage of determining the limit variation, the steering angle A is set to ensure the vehicle controllability below this limit variation. v The limit variation of the gear ratio VGR as a function of the steering wheel angle A is determined for the vehicle speeds V1, V2, and V3 considered, as shown in FIG. v The variation limit corresponds to the steering coefficient of the curve of the gear ratio VGR as a function of V. The variation limit is a threshold value above which the gear ratio varies too quickly to ensure controllability of the vehicle at the considered speeds V1, V2, V3. In other words, if the gear ratio VGR varies by a value smaller than the variation limit, the vehicle can be controlled, whereas if the gear ratio VGR varies by a value larger than the variation limit, the vehicle is not necessarily controllable, i.e., there is a significant risk of controllability being impaired. In one embodiment, the variation limit is determined when the vehicle is in at least one grip condition that is not favorable for vehicle controllability and / or the variation limit is determined according to at least one life condition of the vehicle.
[0053] Grip handle angle A vad_V2 , A vad_V3 During the decision stage, the steering angle A above which the vehicle is no longer controllable is determined. v Grip handle angle A corresponding to vad_V2 , A vad_V3 Grip handle angle A is determined. vad_V2 , A vad_V3 are threshold values corresponding to the grip limit of the vehicle for the vehicle speeds V1, V2, and V3 considered. In other words, the grip handle angle A vad_V2 , A vad_V3 above which the vehicle becomes uncontrollable, i.e. cannot be controlled, at the speeds V1, V2, V3 considered.
[0054] According to one embodiment, the grip handle angle A vad_V2 , A vad_V3 is determined when the vehicle is in at least one grip condition that is favorable for vehicle controllability, for example, the at least one favorable grip condition is dry ground.
[0055] According to one embodiment, the grip handle angle A vad_V2 , A vad_V3 is determined according to at least one life condition of the vehicle.
[0056] The characterization step defines the gear ratio VGR for the vehicle speeds V1, V2, V3 considered. More specifically, the gear ratio VGR is determined by the grip handle angle A vad_V2 , A vad_V3 The limiting fluctuation and grip handle angle A are defined so that the fluctuation of the gear ratio VGR is less than the limiting fluctuation. vad_V2 , A vad_V3 represent the two constraints that define the gear ratio VGR so as to guarantee the controllability of the vehicle. In other words, the grip handle angle A vad_V2 , A vad_V3 Below this, the gear ratio variation must be below a limit variation so that the driver can control the vehicle.
[0057] According to one embodiment, the gear ratio VGR is also proportional to the grip handle angle A vad_V2 , A vad_V3 is defined in the characterization step such that above this the variation in gear ratio VGR is greater than the limit variation.
[0058] According to one embodiment, the limit variation and / or grip handle angle A vad_V2 , A vad_V3 The determination step is carried out by mathematical modelling or physical testing.
[0059] Thus, according to the invention, the gear ratio VGR depends on the vehicle speeds V1, V2, V3, thereby ensuring good maneuverability at low speeds by determining a low gear ratio and good controllability at high speeds by determining a high gear ratio.
[0060] According to the present invention, the gear ratio VGR is v Therefore, the gear ratio VGR depends on the upper rack position X csup is the single upper limit of the steering angle A vsup To correspond to this, the steering angle A v In other words, regardless of the vehicle speeds V1, V2, and V3, the steering angle A v is the upper limit of the steering angle A vsup The range varies over a range up to
[0061] In this way, when the driver turns the steering wheel at the upper limit steering angle A vsup , and upper rack position X csup If the steering wheel is turned so as to be positioned according to the rack, the driver's sensation will not change even if the vehicle speed V1, V2, V3 increases or decreases. In other words, the steering wheel is turned so as to be positioned according to the rack. vsup Therefore, there is no steering torque steer or return effect as in the state of the art. Finally, when there is a loss of grip in oversteer, an appropriate counter steering wheel angle A v is easy to find.
[0062] FIG. 2 shows the steering angle A according to the present embodiment in response to three different vehicle speeds V1, V2, and V3. v FIG. 10 is a graph showing the gear ratio VGR as a function of
[0063] FIG. 3 shows the steering angle A for each of three vehicle speeds V1, V2, and V3. v Rack position X as a function of c This shows:
[0064] For each vehicle speed V1, V2, and V3, the grip handle angle A vad_V2 , Avad_V3 Similarly, we determined the limit variation of the gear ratio VGR. In Figure 2, the grip handle angle at speed V1 is not shown because at speed V1 the vehicle is controllable over the entire range of the handle angle. At speed V2, the grip handle angle A vad_V2 is equal to 45°, and at speed V3, the grip handle angle A vad_V3 is equal to 18°. Note that the grip handle angle A vad_V2 , A vad_V3 Before this, the gear ratio VGR fluctuation is below the limit fluctuation. vad_V2 , A vad_V3 After that, regardless of the fluctuation value of the gear ratio VGR, the upper rack position X csup is the upper limit of the steering angle A vsup The variation of the gear ratio VGR is selected to correspond to:
[0065] Of course, the invention is not limited to the embodiments described and shown in the accompanying drawings: modifications remain possible, particularly in terms of the configuration of the various elements or by substitution of technical equivalents, without departing from the scope of protection of the invention.
Claims
1. 1. A method for determining a gear ratio (VGR) for a vehicle power steering system, comprising: The power steering system ｖ ) and the rack position (X ｃ and a rack for determining the rack position (X ｃ ) is the lower limit rack position and the upper limit rack position (X ｃｓｕｐ ) and the gear ratio (VGR) varies between the rack position (X ｃ ) and the steering wheel angle (A ｖ ) or the steering wheel angle (A ｖ ) and the rack position (X ｃ ) and define the ratio The method is to determine the upper limit rack position (X ｃｓｕｐ ) is the single upper limit handle angle (A ｖｓｕｐ ) so that the gear ratio (VGR) corresponds to the vehicle speed (V1, V2, V3) and the steering angle (A ｖ ) as a function of
2. 10. The method of claim 1, wherein the power steering system is of the "steer-by-wire" type or of the variable gear reduction mechanical type.
3. The upper limit handle angle (A ｖｓｕｐ ) is [Equation 7] X ｃｓｕｐ / 5 and [Number 8] X ｃｓｕｐ . 2 and X ｃｓｕｐ 3. The method of claim 1 or 2, wherein: is the upper rack position.
4. The definition step is performed by: for the vehicle speeds (V1, V2, V3) considered: The steering wheel angle (A ｖ a limit variation determination step in which the limit variation of the gear ratio (VGR) as a function of the gear ratio (VGR) is determined so as to ensure controllability of the vehicle below this limit variation; The steering angle (A ｖ ) corresponding to the grip handle angle (A ｖａｄ＿Ｖ２ , A ｖａｄ＿Ｖ３ ) is determined by the grip handle angle (A ｖａｄ＿Ｖ２ , A ｖａｄ＿Ｖ３ ) decision stage; The grip handle angle (A ｖａｄ＿Ｖ２ , A ｖａｄ＿Ｖ３ 2. The method of claim 1, further comprising a characterization step in which the gear ratio (VGR) is defined such that the gear ratio (VGR) is less than the limit variation and the variation of the gear ratio (VGR) is less than the limit variation.
5. The grip handle angle (A ｖａｄ＿Ｖ２ , A ｖａｄ＿Ｖ３ 5. The method of claim 4, wherein the gear ratio (VGR) is defined in the characterization step such that above VGR, the variation of the gear ratio (VGR) is greater than the limit variation.
6. Limit fluctuation and / or grip handle angle (A ｖａｄ＿Ｖ２ , A ｖａｄ＿Ｖ３ 5. The method of claim 4, wherein the determining step of (a) is performed by mathematical modeling or physical testing.
7. The grip handle angle (A ｖａｄ＿Ｖ２ , A ｖａｄ＿Ｖ３ 5. The method of claim 4, wherein the vehicle speed is determined when the vehicle is in at least one grip condition that is favorable to controllability of the vehicle.
8. 8. The method of claim 7, wherein the at least one favorable grip condition is dry ground.
9. A vehicle equipped with a power steering system that realizes a gear ratio (VGR) determined by the method of claim 1.