Method for fine-tuning a variable gear steering column and vehicle equipped with a variable gear power steering system

Abstract

To provide a method for fine-adjusting a variable gear steering column according to a speed V of a vehicle.SOLUTION: A method of the present invention includes the steps of: characterizing a desired handling of a vehicle for a speed V1 and characterizing a desired stability for a speed V2; determining a gear ratio value G1 that enables the desired handling to be obtained at the speed V1 and a gear ratio value G2 that enables the desired stability to be obtained at the speed V2; and calculating a parameter p2 based on the speed V1, the speed V2, the value G1, and the value G2 such that the relationship between the gear ratio G and the speed V of the vehicle can be defined by the formula G=p2+p1 / V in a case where the speed V is configured between a first threshold and a second threshold.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to the field of power steering systems, and more particularly to power steering systems including variable gear steering columns and methods for fine tuning variable gear steering columns. [Background technology]

[0002] It is known to use a variable gear steering column to dynamically adjust the relationship between the steering wheel angular position and the rack position, which determines the yaw direction of the steering wheels, depending on the state of the system (angle position, ...) and the state of the vehicle (vehicle speed, ...), and conventionally this adjustment leads to defining a variable gear ratio, for example in the form of the ratio between rack position (mm) and steering wheel angle (turns), or the ratio between steering wheel angle and wheel angle, so that at low vehicle speeds, in a first case, a high speed and in a second case, a low speed, in the first case, an acceleration and in the second case, a deceleration, etc. This adjustment leads to defining a variable gear ratio, so that for example one can have a vehicle that is more agile / passive at low vehicle speeds and more stable at high vehicle speeds. Summary of the Invention [Problem to be solved by the invention]

[0003] The drawback of existing adjustment methods is that the variation in gear ratio is not perceived as "natural" by the driver and can cause discomfort to the driver compared to a fixed gear ratio, which requires time for the driver to adapt, and can lead to safety issues if the variation is too noticeable.

[0004] The present invention therefore aims to provide a solution to all or some of these problems. [Means for solving the problem]

[0005] To this end, the invention relates to a method for fine-tuning a relationship defining a gear ratio G of a steering column of a power steering system of a vehicle according to a speed V of the vehicle, said gear ratio G defining the ratio between the rack position of the power steering system and the angular position of the steering wheel of the power steering system, or between the angular position of the steering wheel of the power steering system and the rack position of the power steering system, or between the angular position of the steering wheel of the power steering system and the angular position of the steering wheel yaw of the power steering system, respectively; characterizing a desired handling of the vehicle for a first speed of the vehicle and characterizing a desired stability of the vehicle for a second speed of the vehicle; determining a first value of the gear ratio that enables desired handling at a first speed of the vehicle and a second value of the gear ratio that enables desired stability at a second speed of the vehicle; When the speed V is between the first threshold and the second threshold, the relationship between the gear ratio G of the vehicle and the speed V is G=(p2+p1 / V) n and calculating a first parameter p1 and a second parameter p2 according to the first velocity, the second velocity, the first value, and the second value, as defined by:

[0006] According to these configurations, the change in gear ratio according to the inverse of the speed does not cause any particular discomfort compared to a non-variable gear, and is natural for the driver, who does not need time to adapt to the variable gear.

[0007] These configurations allow for a short period of time to fine-tune the relationship that defines the gear ratio as a function of speed, since the number of parameters to be specified is limited.

[0008] According to one embodiment, the invention comprises one or more of the following features, taken alone or in any technically feasible combination:

[0009] According to another embodiment, the gear ratio is equal to the maximum value when the vehicle speed is below a first threshold.

[0010] According to one embodiment, the second parameter p2 is equal to the second value G2.

[0011] With these configurations, the number of parameters to be identified is further limited.

[0012] The present invention also relates to a power steering system of a vehicle, wherein the power steering system has a gear ratio that defines a ratio between a rack position of the power steering system and a steering wheel angle position of the power steering system, or a ratio between the steering wheel angle position of the power steering system and a rack position of the power steering system, or a ratio between the steering wheel angle position of the power steering system and a steering wheel yaw angle position of the power steering system, when a speed V is included between a first threshold value and a second threshold value, p1 and p2 are a first parameter and a second parameter, respectively, when n=1 or n=-1. G=(p2+p1 / V) n The steering column is configured to be dependent on the speed of the vehicle according to

[0013] According to one embodiment, the invention comprises one or more of the following features, taken alone or in any technically feasible combination:

[0014] According to one embodiment, a first value of gear ratio G1 allows for obtaining a desired handling of the vehicle for a first speed V1 of the vehicle, a second value of gear ratio G2 allows for obtaining a desired stability of the vehicle for a second speed V2 of the vehicle, and the first parameter p1 and the second parameter p2 are solutions of the following equation:

[0015]

number

[0016] According to one embodiment, the second parameter is equal to the second value.

[0017] The present invention also relates to a vehicle equipped with a power steering system according to any of the aforementioned embodiments.

[0018] For a better understanding, embodiments and / or examples of the invention will now be described with reference to the accompanying drawings, which represent, by way of non-limiting examples, respective embodiments or examples of devices and / or methods according to the invention, in which the same reference numbers refer to similar elements or elements whose functionality is similar. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is a schematic perspective view of a power steering system with a variable gear steering column; [Figure 2] 1 is a schematic diagram of a power steering system with a variable gear steering column. [Figure 3a] FIG. 1 is a schematic diagram of a variable gear function of a steering column of a power steering system, according to one embodiment. [Figure 3b] 1 is a schematic diagram of a variable gear function of a steering column of a power steering system according to an equivalent embodiment. [Figure 4] 1 is a graph showing the relationship between the gear ratio, represented on the vertical axis in mm / turns, of the steering column of a power steering system of a vehicle, and the speed V, represented on the horizontal axis in km / h, of said vehicle, according to the present invention. [Figure 5] 5 is a graph showing the relationship between another gear ratio, which is the reciprocal of the gear ratio shown in FIG. 4, represented on the vertical axis in turns / mm (or turns / yaw angle) of the steering column of a power steering system of a vehicle according to the present invention, and the speed V of said vehicle, represented on the horizontal axis in km / h. [Figure 6] 3 is a flowchart illustrating method steps according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] In a known manner, in a power steering system 10, the mechanical link between the steering wheel 21 and the steering rack 11 is eliminated. The power steering system 10 comprises two subsystems, as shown in Figures 1 and 2: a steering subsystem 1 (also called a low-level system) which is made up of an actuator that displaces the rack 11 and is connected to the steering wheels 12, 13, and a force feedback subsystem 2 (also called a high-level system) which is made up of an actuator that is connected to the steering wheel 21 and which causes the driver to feel a resistance force. Conventionally, this resistance force is calculated from information in the steering subsystem 1 in order to reproduce the same sensation that would be encountered in a conventional steering system.

[0021] The linkage structure makes it possible to couple the steering subsystem 1 with the haptic feedback subsystem 2. Conventionally, the steering subsystem 1 is controlled in position using a controller 22 arranged to receive a position setpoint calculated from a position measured at the level of the haptic feedback subsystem 2 and from a look-up table or mapping making it possible to manage the kinematic relationship between the steering wheel angular position Pv and the steering angles of the road wheels 12, 13.

[0022] The variable gear steering column comprises an actuator 3 configured to modify the steering angle of the wheels in response to the driver's actions on the steering wheel 21 according to vehicle data (vehicle speed, stability control, ...). Thus, the power steering system 10 with variable gear steering column is able to adjust the relationship between the position Pv of the steering wheel 21 and the position Pc of the rack 11. In particular, this relationship can be dynamically adjusted depending on the state Es of the steering subsystem 1, e.g. angular position, and e.g. vehicle speed.

[0023] Typically the variable gear ratio G of the actuator 3 is predefined so that it is high at low speeds and decreases as speed increases, this allows for having a vehicle that is more convenient / responsive at low speeds and more stable at high speeds.

[0024] FIG. 3 is a schematic diagram of the variable gear function of a steering column of a power steering system according to the embodiment shown in FIG. 3a or according to an equivalent embodiment shown in FIG. 3b.

[0025] FIG. 3a shows an example in which the considered gear ratio is defined as the ratio between the rack position Pc of the power steering system 10 and the steering wheel angular position Pv of the power steering system 10. Alternatively, FIG. 3b shows an embodiment in which another gear ratio G' is considered, which is the reciprocal of the above-mentioned gear ratio between the angular position Pv (e.g., rotation) of the steering wheel 21 of the steering system 10 and the position Pc (e.g., mm) of the rack 11, or between the angular position Pv (e.g., rotation) of the steering wheel 21 and the angular position (yaw angle) of the steering wheel. According to this alternative embodiment, the other variable gear ratio G' is predefined so that the reciprocal of the gear ratio G of the actuator 3 is low at low speeds and increases as the speed increases. Those skilled in the art will understand that the alternatives shown in FIGS. 3a and 3b, respectively, are equivalent.

[0026] The method according to the invention makes it possible to fine-tune the relationship defining the gear ratio G of the steering column of the power steering system 10 of the vehicle as a function of the speed V of the vehicle, The variation of the gear ratio G is perceived as natural by the driver, and this natural aspect is reflected by the fact that the driver does not need time to adapt to this variable gear and this variation does not cause any particular discomfort compared to a non-variable gear ratio; The fine tuning of the relationship defining the gear ratio G as a function of the vehicle speed V is simple, i.e. based on a limited number of parameters.

[0027] Referring to FIG. 6, the method according to the present invention includes the following steps.

[0028] a step 101 of characterising a desired handling of the vehicle for a first speed V1 of the vehicle, for example 30 km / h for a city car, 100 km / h for a sports car or 130 km / h for a road car; characterizing a desired stability of the vehicle for a second velocity V2 of the vehicle, e.g., a maximum velocity of the vehicle, or any other critical velocity with respect to yaw response of the vehicle; determining 102 a first value of gear ratio G1 so as to obtain a desired handling at a first speed V1 of the vehicle and a second value of gear ratio G2 so as to obtain a desired stability at a second speed V2 of the vehicle by adapting said gain G to obtain an appropriate gain at the two previously defined speeds V1 and V2; When the relationship between the gear ratio G and the speed V of the vehicle is such that the speed V is between the first threshold value and the second threshold value, G=p2+p1 / V and calculating 103 a first parameter p1 and a second parameter p2 according to the first velocity V1, the second velocity V2, the first value G1 and the second value G2, as defined by:

[0029] According to an alternative shown in FIG. 3b, when the other variable gear ratio G' is taken into account, the reciprocal of the gear ratio G of the actuator 3 is given by: G'=1 / (p2+p1 / V)=V / (p2×V+p1) is defined by

[0030] Therefore, through the selection of parameters p1 and p2, the operator can completely parameterize the function. The change due to vehicle speed is taken into account by the inverse function (1 / V).

[0031] The parameters p1 and p2 are calculated by considering two feature points. The first point is the low speed V1 with gear ratio G=G1 to obtain the desired handling, The second point is a high speed V2 when the gear ratio G=G2 to ensure vehicle stability.

[0032] p1 and p2 can be found by solving the following equations using a known method.

[0033]

number

[0034] As an alternative to Figure 4, Figure 5 graphically represents the relationship between another gear ratio G', the reciprocal of that represented in Figure 4, of the steering column of a vehicle's power steering system, represented on the vertical axis in turns / mm (or turns / yaw angle), and the speed V of said vehicle, represented on the horizontal axis in km / h.

[0035] According to one embodiment, the function 1 / V, which tends to infinity when the speed V is zero, is limited to a maximum value at low speeds, as represented in Figure 4. Here, there is a variation of the gear ratio G, expressed in mm / rev on the vertical axis, as a function of the vehicle speed V, expressed in km / h on the horizontal axis.

[0036] In one embodiment, the gear ratio G can be expressed as a gain relative to a reference gear. For example, the reference gear may be 50 mm / revolution. In this example, point V1 is equal to 25 km / h where a gear ratio of 1.9 is selected. Point V2 is equal to V at 250 km / h where a gain of 1 is selected. max Others are obtained by applying the above method.

[0037] In one embodiment, p1 / V is a very slow speed and one can choose p2=G2, and only p1 still needs to be determined to fully parameterize the relationship that defines the gear ratio G as a function of speed V.

[0038] According to one aspect, the present invention also relates to a power steering system for a vehicle, said power steering system being adapted such that a gear ratio G between an angular position Pv of said steering wheel 21 and a position Pc of said rack 11 is set according to a speed V of said vehicle. G=p2+p1 / V a variable gear steering column configured as defined by If the velocity V is between the first and second thresholds, p1 and p2 are the first and second parameters, respectively, of the solution of the following equation:

[0039]

number

[0040] According to one aspect, the present invention relates to a vehicle equipped with a power steering system 10 according to the above-described embodiment.

Claims

1. A relationship defining the gear ratio (G) of a variable gear steering column of a vehicle power steering system (10) according to the speed (V) of the vehicle is: a ratio of a rack position (Pc) of the power steering system (10) to a steering wheel angular position (Pv) of the power steering system (10); or the ratio of the steering wheel angular position (Pv) of the power steering system (10) to the rack position (Pc) of the power steering system (10); Or the ratio between the steering wheel angle position (Pv) of the power steering system (10) and the steering wheel yaw angle position of the power steering system (10). according to a gear ratio (G) that defines each of the The method (100) a first low speed V of the vehicle １ and increasing the responsiveness of the vehicle to a high second speed V ２ a step (101) of increasing the stability of the vehicle against a first velocity V of the vehicle １ The first value G of the gear ratio (G) is set to be high responsiveness. １ and a second speed V of the vehicle. ２ The second value G of the gear ratio (G) is set to 0.05 so that stability can be increased. ２ and (102) determining, respectively, The relationship between the gear ratio (G) and the speed (V) of the vehicle is configured such that the speed (V) of the vehicle is between a first threshold value and a second threshold value, and when n=1 or n=−1, G=(p ２ +p １ / V) ｎ The first velocity V is defined by １ , second velocity V ２ , the first value G １ and a second value G ２ The first parameter p １ and a second parameter p ２ a step (103) of calculating A method (100) comprising:

2. the gear ratio (G) is equal to a maximum value when the vehicle speed (V) is less than the first threshold; The method of claim 1.

3. The second parameter p ２ is the second value G ２ is equal to 3. The method according to claim 1 or 2.

4. the ratio of the rack position (Pc) of the vehicle's power steering system (10) to the steering wheel angular position (Pv) of said power steering system (10); or the ratio of the steering wheel angular position (Pv) of the power steering system (10) to the rack position (Pc) of the power steering system (10); Or the ratio between the steering wheel angle position (Pv) of the power steering system (10) and the steering wheel yaw angle position of the power steering system (10). When n=1 or n=−1, the gear ratio (G) that defines each of these three values ​​depends on the speed (V) of the vehicle, and when the speed (V) is between a first threshold value and a second threshold value, p １ and p ２ are the first and second parameters, respectively, and are expressed by the following formula: G=(p ２ +p １ / V) ｎ a variable gear steering column configured according to A power steering system (10) for a vehicle according to any one of claims 1 to 3.

5. A first value of the gear ratio G １ is the first low speed velocity V of the vehicle. １ This allows the vehicle to be more responsive to The second value of the gear ratio G ２ is the second high-speed velocity V ２ This allows the vehicle to be more stable against The first parameter p1 and the second parameter p2 are solutions of the following equation: [Equation 4] A power steering system (10) for a vehicle according to any one of claims 1 to 4.

6. the gear ratio G is equal to its maximum value when the speed V is lower than the first threshold value; A power steering system (10) according to claim 4 or 5.

7. The second parameter p ２ is the second value G ２ is equal to A power steering system (10) according to claim 5 or 6.

8. A vehicle comprising a power steering system (10) according to any one of claims 4 to 7.

Images