Steering system for vehicle

Abstract

The purpose of the present invention is to provide steering agility during cornering by applying variable Ackermann geometry to the steering geometry to reduce the Ackermann tendency. The objective of the present invention is achieved by an automobile steering system comprising a rack housing in which a rack bar is movably movable left and right, a tie rod connected to both ends of the rack bar, a knuckle connected to both ends of the tie rod, and a lower arm connected to the knuckle, wherein a variable geometry mechanism for forward and backward movement of the rack housing is installed between a predetermined position of the vehicle body and the rack housing, and thereby the rack housing and the rack bar are moved forward by the driving of the variable geometry mechanism so that the Ackermann tendency can be reduced compared to the original level.

Description

Technology Field

[0001] The present invention relates to a steering system for an automobile, and more specifically, to a steering system for an automobile that can provide steering agility during cornering by applying variable Ackermann geometry to the steering geometry to reduce the Ackermann tendency. Background Technology

[0003] Since the trajectories of the inner wheel and the outer wheel are different when the vehicle is cornering, lateral slippage may occur. To prevent this, most vehicles are equipped with an Ackerman Geometry type steering system in which the steering angles of the inner wheel and the outer wheel are applied differently.

[0004] The above-described Ackermann geometry type steering system refers to a system in which, as shown in FIG. 1, the effective arm length (L1) of the inner ring (100) is applied short and the effective arm length (L2) of the outer ring (200) is applied long, so that when the inner ring (100) and the outer ring (200) rotate at the same center of rotation (C) during cornering, the steering angles of the inner ring (100) and the outer ring (200) are applied differently.

[0005] Referring to the enlarged drawing of Fig. 1, if a difference in steering angle between the inner ring and the outer ring occurs based on the Ackermann geometry, the inner ring slip angle (+) and the outer ring slip angle (-) in the turning direction act in opposite ways.

[0006] Referring to the attached Fig. 2, when a difference in steering angle between the inner and outer wheels occurs based on Ackermann geometry during low-speed turning, a difference occurs between the direction of travel of the vehicle and the direction of travel of the tires, and as a result, an inner wheel slip angle (+) and an outer wheel slip angle (-) acting oppositely are formed. In addition, when a lateral force (F) is applied toward the inside of the vehicle, a kingpin moment (M), which is an anti-restoring moment, is generated by multiplying the lateral force acting on each wheel by the difference in caster trail (distance between the point where the lateral force acts on the kingpin axis) of the inner and outer wheels.

[0007] More specifically, the above kingpin moment (M) is the lateral force (F) acting on the inner ring and the caster trail (C) of the inner ring. i The lateral force (F) acting on the outer ring and the caster trail (C) of the outer ring at the magnitude of the moment (M1) multiplied by ) o The magnitude obtained by subtracting the magnitude of the moment (M2) multiplied by ), i.e., the lateral force directed inward (F) and the difference in caster trail between the inner and outer wheels (C i - C o It has a size multiplied by ).

[0008] Typically, the greater the Ackermann tendency, the smaller the kingpin moment (M), which is the anti-restoring moment; therefore, it is said that the smaller the kingpin moment (M), which is the anti-restoring moment, the greater the Ackermann tendency.

[0009] This Ackermann tendency is closely related to steering return force during low-speed cornering, and accordingly, most vehicles currently on the market are trending toward maximizing the Ackermann tendency to ensure steering return performance during low-speed cornering.

[0010] However, if the above-mentioned Ackermann geometry type steering system is applied with a large Ackermann tendency, two problems arise that degrade handling performance.

[0011] First, setting the Ackermann tendency too high results in a lower dynamic steering gear ratio, which has the problem of reducing steering agility during high-speed cornering.

[0012] Second, as the Ackermann tendency is set higher, the inner wheel slip angle in the turning direction becomes larger than the outer wheel slip angle, leading to the tire friction limit (grip limit) being reached prematurely. This results in an overall increase in understeer tendency and a decrease in limit cornering performance. The problem to be solved

[0014] The present invention has been devised to solve the aforementioned conventional problems, and aims to provide a steering system for an automobile that can improve limit cornering performance and steering agility by configuring the steering geometry as variable Ackermann geometry capable of reducing the Ackermann tendency or returning it to its original level, thereby reducing the Ackermann tendency during high-speed cornering compared to the Ackermann tendency during low-speed or normal driving situations. means of solving the problem

[0016] To achieve the above objective, the present invention provides a steering system for an automobile comprising: a rack housing in which a rack bar is movably movable left and right; a tie rod connected to both ends of the rack bar; a knuckle connected to both ends of the tie rod; and a lower arm connected to the knuckle, wherein a variable geometry mechanism for forward and backward movement of the rack housing is installed between a predetermined position of the vehicle body and the rack housing, so that the rack housing and the rack bar are moved forward by the driving of the variable geometry mechanism, thereby allowing the Ackermann tendency (%) to be reduced compared to the original level.

[0017] In particular, the variable geometry mechanism is characterized by comprising: a mounting plate mounted at a predetermined position on the vehicle body; a motor mounted on one side of the mounting plate; a screw mounted on the other side of the mounting plate so as to be rotatable in place while connected to the output shaft of the motor; and a mounting member having a structure in which the rack housing is mounted on one side and a screw hole into which the screw is inserted is formed on the other side, so as to move back and forth along the screw together with the rack housing when the screw rotates.

[0018] Preferably, both ends of the screw are supported by bearings mounted on a mounting plate.

[0019] Preferably, the output shaft of the screw is equipped with a belt pulley connected by a belt to one end of the screw and the output shaft of the motor.

[0020] Preferably, a guide bar is mounted on the mounting plate at both sides of the screw, and guide holes into which the guide bar is inserted are formed at both ends of the mounting member.

[0021] When the rack housing and rack bar move forward, point T, which is the ball joint point where the rack bar and tie rod are joined, moves forward by the same distance, and at the same time, point H, which is the ball joint point where the tie rod and knuckle are joined, moves inward toward the vehicle.

[0022] Accordingly, the Ackermann tendency is reduced when the ball joint point T, where the rack bar and tie rod are joined, moves forward, and the ball joint point H, where the tie rod and knuckle are joined, moves inward toward the vehicle. At the same time, the actual angle at which the H point on the inner wheel moves in the turning direction centered on the ball joint point B where the knuckle and lower arm meet during turning, and the actual angle at which the H point on the outer wheel moves in the turning direction centered on the B point during turning, are reduced.

[0023] Preferably, depending on the forward movement distance of point T, which is the ball joint point where the rack bar and tie rod are joined, point H, which is the ball joint point where the tie rod and knuckle are joined, moves inward toward the vehicle, and the relative position with point B, which is the ball joint point where the knuckle and lower arm are joined, is varied, thereby determining the reduction size of the Ackermann tendency. Effects of the invention

[0025] Through the above-described means for solving the problem, the present invention provides the following effects.

[0026] By configuring the steering geometry as variable Ackermann geometry that can reduce or restore the Ackermann tendency, the Ackermann tendency during high-speed cornering can be reduced compared to the Ackermann tendency during low-speed or normal driving situations, thereby improving limit cornering performance and steering agility during high-speed cornering. Brief explanation of the drawing

[0028] FIG. 1 is a schematic diagram showing the steering angle and slip angle of the inner and outer rings when an Ackermann geometry type steering system is applied. FIG. 2 is a schematic diagram explaining the principle of generating a kingpin moment when a lateral force is applied to an inner ring and an outer ring having different steering angles and slip angles when an Ackermann geometry type steering system is applied. FIGS. 3 and 4 are configuration diagrams illustrating a rack-type electric steering system. FIG. 5 is a schematic diagram illustrating the state in which the components of a rack-type electric steering system perform steering operations based on Ackermann geometry. FIGS. 6 and 7 are drawings illustrating a variable geometry mechanism for configuring an automobile steering system according to the present invention into variable Ackermann geometry. FIG. 8 is a schematic diagram illustrating that a steering system for an automobile according to the present invention is changed to an arrangement that increases the Ackermann tendency by means of a variable geometry mechanism. FIG. 9 is a schematic diagram illustrating that a steering system for an automobile according to the present invention is changed to an arrangement that reduces the Ackermann tendency by means of a variable geometry mechanism. FIG. 10 is a schematic diagram illustrating the principle in which the Ackermann tendency of an automobile steering system according to the present invention is reduced by a variable geometry mechanism. FIG. 11 is a schematic diagram illustrating that the rack housing, etc. of an automobile steering system according to the present invention is moved forward to reduce the original Ackermann tendency. FIG. 12 is a schematic diagram illustrating a state in which a rack housing, etc. of an automobile steering system according to the present invention is moved to the maximum forward position. FIG. 13 is a graph showing the results of a comparative test of the change in tire slip angle in the original Ackermann tendency and the reduced Ackermann tendency of a steering system for an automobile according to the present invention. Specific details for implementing the invention

[0029] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0030] First, to aid in understanding the present invention, the configuration and operation of a rack-type electric steering system will be explained with reference to the attached FIGS. 3 and 4 as follows.

[0031] Figures 3 and 4 attached illustrate a conventional rack-type electric steering system, where reference numeral 10 indicates a rack housing.

[0032] The above rack housing (10) has a rack bar housed therein that can be moved left and right, and is mounted at a predetermined position on the vehicle body.

[0033] A steering housing (20) is integrally formed on one side of the rack housing (10), and a reduction gear housing (30) is integrally formed on the other side.

[0034] For reference, a pinion-type steering gear that engages with a rack bar in the rack housing (10) is rotatably mounted inside the steering housing (20), and a pinion-type output gear that engages with a rack bar in the rack housing (10) is rotatably mounted inside the reduction gear housing (30).

[0035] At this time, the steering gear mounted in the steering housing (20) is connected via a steering wheel and a steering column, etc., for steering operation by the driver, and the reduction gear housing (30) is equipped with a steering motor (32) for applying rotational power to the output gear.

[0036] Additionally, both ends of the above rack bar are connected to tie rods (40), and both ends of the tie rods (40) are connected to knuckle (50) parts that are connected to a driving wheel via a ball joint (42), etc.

[0037] Therefore, when the driver steers the steering wheel, the steering gear in the steering housing (20) rotates, and at the same time, a steering force is applied to the rack bar in the rack housing (10).

[0038] At the same time, by driving the steering motor (32) in the controller that receives the steering signal, the output gear in the reduction gear housing (30) rotates and transmits the steering force to the rack bar in the rack housing (10).

[0039] For reference, in FIG. 4, point B is the ball joint point where the knuckle (50) and the lower arm (60) meet, and the straight line connecting point B to point C is the kingpin axis, which is the steering rotation axis. Also, point T is the ball joint point where the rack bar and the tie rod (40) meet, serving as a contact point that transmits the force and displacement transmitted from the rack bar to the tie rod, and point H represents the ball joint point where the tie rod (40) and the knuckle (50) meet to transmit the force and displacement transmitted from the tie rod (40) to the knuckle (50).

[0040] Here, the configurations of the above rack-type electric steering system are as follows when steering based on Ackermann geometry.

[0041] Figure 5 attached is a schematic diagram illustrating the state in which the components of a rack-type electric steering system perform steering operations based on Ackermann geometry.

[0042] Referring to FIG. 5, in an Ackermann geometry setting state where point H is located outside of point B and point B is located inside of point H, when a pivoting steering force by the rack bar (12) is applied to the tie rod (40) through point T, steering of the inner ring (100) and the outer ring (200) is achieved around the kingpin axis, which is the steering rotation axis.

[0043] At this time, the greater the steering force transmitted through the tie rod, the shorter the effective arm length (L1) of the inner ring (100) becomes as shown in FIG. 1, and the longer the effective arm length (L2) of the outer ring (200) becomes, and the steering angle of the inner ring (100) becomes larger than the steering angle of the outer ring (200).

[0044] In addition, since the steering angle of the inner ring (100) is greater than the steering angle of the outer ring (200), the angle (δ) at which point H in the inner ring (100) indicated in FIG. 5 moves in the turning direction centered on point B i ) is the angle (δ) at which point H on the outer ring (200) moves in the pivoting direction around point B. o It becomes larger compared to ).

[0045] For reference, the above Ackermann tendency (%) can be expressed by Equation 1 below.

[0046] (Equation 1)

[0047] In Equation 1 above, δ i,ideal represents the ideal maximum angle at which point H in the inner ring (100) moves in a pivoting direction around point B, and δ o,idealrepresents the ideal maximum angle at which point H on the outer ring (200) moves in a pivoting direction around point B, and also δ i,actual represents the actual angle at which point H in the inner ring (100) of the turning direction moves in the turning direction centered on point B, and δ o,actual represents the actual angle at which point H on the outer ring (200) moves in the turning direction around point B.

[0048] As the Ackermann tendency (%) in the aforementioned conventional rack-type electric steering system is set to a large level of about 54%, steering recovery performance can be maximized during low-speed turning.

[0049] In other words, the Ackermann tendency of the rack-type electric power steering system applied to the actual vehicle is set to a level approximately 54% higher, and accordingly, steering recovery performance during low-speed turning is secured.

[0050] However, as the Ackermann tendency (%) for the actual vehicle's steering system is fixed at a large level of about 54%, as described above, it results in the effect of lowering the dynamic steering gear ratio, which causes a problem of reduced steering agility during high-speed cornering. Additionally, the inner wheel slip angle in the turning direction becomes larger than the outer wheel slip angle, causing the tire grip limit to be reached early, and overall, the tendency for understeer increases while simultaneously reducing the limit cornering performance.

[0051] In order to resolve these problems, the present invention focuses on improving limit turning performance and steering agility by configuring the steering geometry applied to a rack-type electric steering system as a variable Ackermann geometry capable of reducing or restoring the Ackermann tendency, thereby reducing the Ackermann tendency during high-speed cornering compared to the Ackermann tendency during low-speed or normal driving situations.

[0052] To this end, the present invention is characterized by configuring the Ackermann geometry of a steering system as a variable Ackermann geometry, comprising a rack housing (10) in which a rack bar (12) is movably movable left and right as shown in FIGS. 8 and 9, a tie rod (40) connected to both ends of the rack bar (12), a knuckle (50) connected to both ends of the tie rod (40), and a lower arm (60) connected to the knuckle (50), by mounting a variable geometry mechanism (300) for forward and backward movement of the rack housing (10) between a predetermined position of the vehicle body and the rack housing (10), so that the rack housing (10) and the rack bar (12) are moved forward by a predetermined distance by the driving of the variable geometry mechanism (300), thereby allowing the Ackermann tendency to be reduced compared to the original level (original specification).

[0053] Figures 6 and 7 attached illustrate a variable geometry mechanism for configuring a steering system for an automobile according to the present invention into variable Ackermann geometry.

[0054] The above variable geometry mechanism (300) comprises a mounting plate (301) mounted at a predetermined position on the vehicle body, a motor (302) mounted on one side of the mounting plate (301), and a screw (303) connected to the output shaft of the motor (302) and mounted on the other side of the mounting plate (301) so as to be rotatable in place.

[0055] In particular, a mounting member (304) that is coupled to the rack housing (10) is connected to the screw (303) so as to be movable back and forth.

[0056] More specifically, the mounting member (304) is in the shape of a rectangular bar, the rack housing (10) is mounted on one side thereof, a screw hole (305) into which a screw (303) is inserted is formed on the other side, and guide holes (306) are formed at both ends to guide stable linear movement of the mounting member (304).

[0057] In addition, bearings (307) are mounted on the mounting plate so that both ends of the screw (303) are rotatably supported.

[0058] In addition, a belt pulley (308) connected by a belt (308) is mounted on one end of the screw (303) and the output shaft of the motor (302), so that the rotational power of the motor (302) can be transmitted to the screw (303) through the belt (308).

[0059] Additionally, a guide bar (309) is mounted on the mounting plate (301) at both sides of the screw (303). This guide bar (309) is inserted into the guide hole (306) of the mounting member (304) and is arranged in a straight line in the front and back directions.

[0060] Accordingly, when the unidirectional rotational power of the motor (302) is transmitted to the screw (303) through the belt (308), the screw (303) rotates in place in one direction, and since the screw (303) is inserted into the screw hole (305) of the mounting member (304), the mounting member (304) can move forward along the screw (303) while receiving linear guidance from the guide bar (309).

[0061] At this time, when the mounting member (304) moves forward along the screw (303) while receiving linear guidance from the guide bar (309), the rack housing (10) and rack bar (12) mounted on the mounting member (304) move forward as shown in FIG. 9, and at the same time, point T, which is the ball joint point where the rack bar (12) and the tie rod (40) are joined, moves forward by the same distance, and point H, which is the ball joint point where the tie rod (40) and the knuckle (50) are joined, moves inward toward the vehicle, thereby reducing the Ackermann tendency (%).

[0062] Conversely, when the rotational power of the motor (302) in the opposite direction is transmitted to the screw (303) through the belt (308), the screw (303) rotates in place in the opposite direction, and since the screw (303) is inserted into the screw hole (305) of the mounting member (304), the mounting member (304) can be moved back to its original rear position along the screw (303) while receiving linear guidance from the guide bar (309).

[0063] At this time, when the mounting member (304) moves back to its original rear position along the screw (303) while receiving linear guidance from the guide bar (309), the rack housing (10) and rack bar (12) mounted on the mounting member (304) move to their original rear positions as shown in FIG. 8, and at the same time, point T, which is the ball joint point where the rack bar (12) and the tie rod (40) are joined, moves backward by the same distance, and point H, which is the ball joint point where the tie rod (40) and the knuckle (50) are joined, moves outward toward the vehicle, thereby increasing the Ackermann tendency (%) to the original setting level (original specification).

[0064] Here, the principle by which the above-mentioned Ackermann tendency is reduced or increased to the original setting level is explained with reference to the attached Fig. 10 as follows.

[0065] Figure 10 attached is a schematic diagram illustrating the principle in which the Ackermann tendency of a steering system for an automobile according to the present invention is reduced by a variable geometry mechanism.

[0066] As described above, the mounting member (304) moves forward along the screw (303) while receiving linear guidance from the guide bar (309), and at the same time, the rack housing (10) and rack bar (12) mounted on the mounting member (304) move forward, and as shown in FIG. 10, the ball joint point T where the rack bar (12) and tie rod (40) are joined moves forward by the same distance (e.g., 25 mm), and at the same time, the ball joint point H where the tie rod (40) and knuckle (50) are joined moves inward toward the vehicle, thereby reducing the Ackermann tendency (%).

[0067] More specifically, when point T, which is the ball joint point where the rack bar (12) and the tie rod (40) are joined, is moved forward by about 25 mm, and point H, which is the ball joint point where the tie rod (40) and the knuckle (50) are joined, is moved inward toward the vehicle, the actual angle at which point H on the inner ring moves in the turning direction around point B and the actual angle at which point H on the outer ring moves in the turning direction around point B are reduced compared to the actual angle at which point H on the inner ring moves in the turning direction around point B and the actual angle at which point H on the outer ring moves in the turning direction around point B when the Ackermann tendency is set to 54%, so that the Ackermann tendency (%) can be reduced as shown in Table 1 below.

[0068]

[0069] For example, as shown in Table 1 above, when point T, which is the ball joint point where the rack bar (12) and tie rod (40) are joined, is in its original position before being moved forward, the Ackermann tendency (%) is 54%, whereas when point T, which is the ball joint point where the rack bar (12) and tie rod (40) are joined, is moved forward by 25mm, the Ackermann tendency (%) can be reduced to 11%.

[0070] In this way, steering recovery performance during low-speed turning can be secured with the above Ackermann tendency (%) set to a large level of 54%, and limit turning performance and steering agility can be improved by reducing the above Ackermann tendency (%) to 11% during high-speed turning.

[0071] Referring to the attached Fig. 12, it was found that the forward movement distance of point T, which is the ball joint point where the rack housing (10) and rack bar (12) and the rack bar (12) and the tie rod (40) are joined, can be moved up to a maximum of 70 mm as a result of analysis testing using a predetermined tool, and accordingly, in order to reduce the Ackermann tendency (%) from 54% to 11%, point T, which is the ball joint point where the rack housing (10) and rack bar (12) and the rack bar (12) and the tie rod (40) are joined, can be easily moved forward by about 25 mm.

[0072] Additionally, depending on the forward movement distance of point T, which is the ball joint point where the rack bar (10) and the tie rod (40) are joined, point H, which is the ball joint point where the tie rod (40) and the knuckle (50) are joined, moves inward toward the vehicle, and the relative position with point B, which is the ball joint point where the knuckle (50) and the lower arm (60) are joined, can be varied, and accordingly, the Ackermann tendency (%) can be varied and determined to a variety of sizes less than 54%.

[0073] In addition, since the amount of forward movement of the rack housing, which is a type of gearbox and is a component of the steering system, is not large at approximately 25mm by the variable geometry mechanism, layout and interference problems with surrounding suspension parts do not occur.

[0074] Figure 13 attached shows the results of a comparative test of the change in tire slip angle in the original Ackermann tendency (54%) and the reduced Ackermann tendency (11%) of the steering system for an automobile according to the present invention.

[0075] As shown in Fig. 13, when the Ackermann tendency (%) is at the original level of 54% before reduction, it can be seen that the slip angle of the inner ring increases rapidly compared to the slip angle of the outer ring, and as a result, the understeer tendency increases and the friction limit of the tire appears sooner.

[0076] On the other hand, when the above Ackermann tendency (%) was reduced from the original level of 54% to 11%, it was found that the increase in the slip angle of the outer ring occurred more rapidly than the increase in the slip angle of the inner ring, and as a result, it was confirmed that a greater lateral force could be generated with less steering than before the reduction of the Ackermann tendency (the original specification) and the friction limit of the tire could be slightly increased. Explanation of the symbols

[0078] 10 : Rack housing 12 : Rack bar 20: Steering housing 30 : Reducer housing 32 : Steering motor 40: Tie rod 42: Ball joint 50 : Knuckle 60 : Lower arm 100 : Inner ring 200 : Outer ring 300: Variable Geometry Mechanism 301 : Mounting plate 302 : Motor 303 : Screw 304 : Mounting member 305 : Screw hole 306 : Guide Hole 307 : Bearing 308: Belt pulley 309 : Guide bar

Claims

Claim 1 A steering system for an automobile comprising a rack housing in which a rack bar is movably movable left and right, a tie rod connected to both ends of the rack bar, a knuckle connected to both ends of the tie rod, and a lower arm connected to the knuckle, wherein a variable geometry mechanism for forward and backward movement of the rack housing is installed between a predetermined position on the vehicle body and the rack housing, so that the rack housing and the rack bar are moved forward by the actuation of the variable geometry mechanism, thereby allowing the Ackermann tendency to be reduced compared to the original level, wherein the variable geometry mechanism comprises: a mounting plate mounted at a predetermined position on the vehicle body; a motor mounted on one side of the mounting plate; and a screw connected to the output shaft of the motor and mounted on the other side of the mounting plate so as to be rotatable in place. A steering system for an automobile, comprising: a mounting member having a structure in which the rack housing is mounted on one side and a screw hole into which a screw is inserted is formed on the other side, and which moves back and forth along the screw together with the rack housing when the screw rotates; wherein when the rack housing and the rack bar move forward, point T, which is a ball joint point where the rack bar and the tie rod are joined, moves forward by the same distance, and at the same time, point H, which is a ball joint point where the tie rod and the knuckle are joined, moves inward toward the vehicle, and depending on the forward movement distance of point T, which is a ball joint point where the rack bar and the tie rod are joined, point H, which is a ball joint point where the tie rod and the knuckle are joined, moves inward toward the vehicle, thereby varying the relative position with point B, which is a ball joint point where the knuckle and the lower arm are joined, and determining the reduction size of the Ackermann tendency. Claim 2 delete Claim 3 A steering system for an automobile according to claim 1, characterized in that both ends of the screw are supported by bearings mounted on a mounting plate. Claim 4 A steering system for an automobile according to claim 1, characterized in that a belt pulley connected by a belt is mounted on one end of the screw and the output shaft of the motor. Claim 5 A steering system for an automobile according to claim 1, characterized in that a guide bar is mounted on a mounting plate at both sides of the screw, and guide holes into which the guide bar is inserted are formed at both ends of the mounting member. Claim 6 delete Claim 7 A steering system for an automobile according to claim 1, characterized in that, while point T, a ball joint point where the rack bar and tie rod are joined, moves forward, point H, a ball joint point where the tie rod and knuckle are joined, moves inward toward the vehicle, the actual angle at which point H on the inner wheel moves in the turning direction around point B, a ball joint point where the knuckle and lower arm meet, and the actual angle at which point H on the outer wheel moves in the turning direction around point B are reduced, thereby reducing the Ackermann tendency. Claim 8 delete

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