JP4338487B2 - Vehicle steering apparatus having a rack and pinion mechanism - Google Patents

Description

  The present invention relates to a vehicle steering apparatus including a rack and pinion mechanism, and more particularly to a variable gear ratio type steering apparatus in which the gear ratio of the rack and pinion mechanism varies depending on the steering angle.

In a steering system for a vehicle, an appropriate weight and good responsiveness of a steering wheel operation are required in a small steering angle region at high speed traveling, and a lightness of a stationary and a lock-to-lock rotation speed in a large steering angle region at low speed traveling. Reduction is required. In order to satisfy this requirement, for example, Patent Document 1 discloses a variable gear ratio type steering apparatus including a rack and pinion mechanism that changes the amount of translation of the rack relative to the rotation angle of the pinion according to the steering angle. The pinion of this steering device has pinion teeth of different tooth shapes so that the reference pitch circle radius changes with the rotation angle, and in a region where the gear ratio of the rack and pinion mechanism is small, the pinion tooth having the maximum reference pitch circle radius Meshes with the rack teeth. This eliminates the awkward feeling of steering in the small gear ratio region and enables smooth steering.
Japanese Patent Laid-Open No. 55-51665

  In the prior art, since it is necessary to form pinions having pinion teeth of different tooth shapes so that the reference pitch circle radius changes with the rotation angle, the freedom of design of the pinion is limited in order to realize smooth steering. There are difficulties to be done.

  The present invention has been made in view of such circumstances, and the invention according to claims 1 and 2 aims to increase the degree of freedom of design of the pinion in the variable gear ratio type steering device, and to provide a steering feeling. The purpose is to improve the vibration and noise in the rack and pinion mechanism.

According to a first aspect of the present invention, there is provided a vehicle steering apparatus including a rack and pinion mechanism having different gear ratios according to a steering angle, wherein a steering operation is transmitted to the steered wheels via the rack and pinion mechanism. All meshing ratio of the rack and pinion mechanism is always more der is, the tooth root of the tooth thickness is small portions of the rack teeth in the rack of the rack and pinion mechanism, the number of teeth have simultaneous meshing of the rack and pinion mechanism This is a vehicle steering device in which the steering angle range in which is greater than 2 is wider than the steering angle range in which the number of simultaneously meshing teeth is 2 .

According to this, since the total mesh rate is always 2 or more, the rack and pinion mesh smoothly in all regions having a gear ratio different from that region as well as the region where the gear ratio is minimized. As a result, the rack moves smoothly and translates, and the meshing load acting on the rack and pinion is dispersed, reducing the load acting on each rack tooth and each pinion tooth. And since the pinion should just be formed so that the total meshing rate may be 2 or more, it becomes possible to comprise all the pinion teeth with the same tooth profile.
Also, in the rack, in the portion where the tooth thickness at the base of the rack tooth is small, the ratio of the rack tooth and the pinion tooth meshing with a value larger than 2 is increased, so that the load at the time of meshing is distributed to the rack tooth having a larger meshing load. Will be more frequent .

According to a second aspect of the present invention, in the vehicle steering apparatus according to the first aspect, the rack includes a low gear ratio region in which the gear ratio is a low gear ratio, and the gear ratio is greater than the low gear ratio. A high gear ratio region having a high gear ratio is formed, the portion where the tooth thickness of the base of the rack tooth is small is the low gear ratio region, and the meshing point of the rack and pinion mechanism is the low gear ratio region. In the gear ratio region, the position is closer to the tooth tip than the tooth base of the rack tooth .

According to this, in the low gear ratio region where the meshing point is closer to the tooth tip than the tooth base of the rack tooth, the frequency that the number of simultaneously meshing teeth is larger than 2 is increased.

According to invention of Claim 1, the following effect is show | played. That is, not only in the region where the gear ratio is minimum, but also in all regions where the gear ratio is different from this region, the meshing of the rack and pinion proceeds smoothly and the rack smoothly translates. The ring is improved, the generation of vibration and noise is reduced, and the load acting on each rack tooth and each pinion tooth is reduced, so that the durability of the rack and pinion mechanism is improved. In addition, since all pinion teeth can be configured with the same tooth profile, the degree of freedom in designing the pinion increases.
Further, in the rack, in the portion where the tooth thickness at the base of the rack tooth is small, the ratio of the rack tooth and the pinion tooth meshing at a value larger than 2 is increased, so the rack tooth having a larger load at the time of meshing is used. Since the frequency of dispersion is increased and the load acting on each rack tooth to be engaged is reduced, the durability of the rack is improved.

According to the second aspect of the present invention, in the rack and pinion mechanism, in the low gear ratio region, since the load at the time of meshing acts near the tooth tip of the rack tooth, the stress acting on the tooth base of the rack tooth is large. Nevertheless, since the frequency with which the number of simultaneously meshing teeth is larger than 2 is high, it is possible to contribute to the improvement of the durability of the rack.

Hereinafter, embodiments of the present invention will be described with reference to FIGS.
Referring to FIG. 1, a vehicle steering apparatus to which the present invention is applied includes a rack and pinion mechanism G that includes a rack 1 disposed in a gear box and a pinion 2 that meshes with the rack 1. The pinion 2 is formed on a pinion shaft 4 connected to the handle 3 via a connection mechanism including a torsion bar, and the rack 1 is connected to the steered wheels 6 via a steering mechanism including tie rods connected to both ends. The rack shaft 5 is formed. When the handle 3 is operated, the steering force is transmitted to the rack shaft 5 via the coupling mechanism, the pinion shaft 4, the pinion 2 and the rack 1, and the rack shaft 5 which translates in the longitudinal direction A1 and It is transmitted to the steered wheels 6 through the steered mechanism, and the steered wheels 6 are steered. Further, the steering device is provided with a power steering device for applying a steering assist force to the rack shaft 5 based on the steering torque detected by the torsion bar.

  The pinion 2 composed of a helical pinion having a twist angle is a straight line orthogonal to the rotation center line L1 of the rack 1 and the center axis of the rack shaft 5 (or rack 1) parallel to the longitudinal direction A1. It arrange | positions with respect to the rack 1 so that L3 may form the crossing angle (psi). Moreover, the tooth profile of each pinion tooth 2a of the pinion 2 is formed identically. Here, the crossing angle ψ is determined by the mounting layout of the rack and pinion mechanism G on the vehicle body together with the inter-axis distance between the rotation center line L1 of the pinion shaft 4 and the center axis L2 of the rack shaft 5.

The rack 1 is a variable gear ratio type in which the gear ratio R, which is the amount of movement in the longitudinal direction A1 of the rack 1 with respect to the rotational angle θ of the pinion 2, differs in the longitudinal direction A1 according to the rotational angle θ corresponding to the steering angle. It is a rack. The rack 1 has a low gear ratio region E _L , a variable gear ratio region E _V , and a high gear in the longitudinal direction A1 around a neutral position P1 where the pinion 2 meshes when the rotation angle θ is 0. the ratio area E _H is formed. Here, the neutral position P1 of the rack 1 corresponds to the neutral position of the handle 3, that is, the steering angle is zero.

Referring also to FIG. 2, the low gear ratio area E _L is formed in a predetermined range in the longitudinal direction A1 and the neutral position P1, which is also the center point der in the longitudinal direction A1 of rack 1 in the center, the gear The ratio R is the smallest constant low gear ratio _RL . Variable gear ratio region E _V is continuous with the low gear ratio area E _L, are formed on both sides of the predetermined range of the low gear ratio area E _L, than the low gear ratio R _L as the gear ratio R is away from the neutral position P1 also progressively larger variable gear ratio R _V. High gear ratio region E _H is continuous with the variable gear ratio region E _V at a location remote from the neutral position P1 than the low gear ratio area E _L, is formed in a predetermined range on both sides of the low gear ratio area E _L, its gear ratio R is the maximum constant high gear ratio R _H equal magnitude to the maximum gear ratio of the variable gear ratio region E _V.

In relation to the rotation angle θ that is directly proportional to the steering angle, the low gear ratio region E _L is set to a range from the neutral position P1 to the predetermined first rotation angle θ ₁ of the pinion 2, and the high gear ratio region E _H is set to be in a range between the second rotation angle theta ₂ is greater than the first rotation angle theta ₁ to the third rotation angle theta ₃ the handle 3 is locked, the variable gear ratio region E _V is first rotation angle It is set to a range between θ ₁ and the second rotation angle θ _{2. In} the small steering angle region during high speed traveling, the operation of the steering wheel 3 is performed due to the low gear ratio R _L in the low gear ratio region E _L. obtained moderate weight and responsiveness of the good, with a large steering angle region during low-speed running, the high gear ratio R _H in the high gear ratio region E _H, stationary steering reduction in lightness and the lock-to-lock rotational speed of give It is done.

3 and 4, in the low gear ratio region E _L , the meshing pitch circle C of the pinion 2 is set to the minimum meshing pitch circle C ₁ having the smallest radius, and in the high gear ratio region E _H. , meshing pitch circle C, the radius is set to the pitch circle C ₂ have maximum meshing up. Further, the variable gear ratio region E _V, meshing pitch circle C varies between the minimum and maximum meshing pitch circle C ₂ in the longitudinal direction A1.

The meshing pitch circle C is in the range from the rotation angle theta is 0 to the third rotation angle theta _{3 (third} rotation angle theta _{3 (-} [theta] ₃ in the opposite direction corresponds) including.), The minimum in a cross section perpendicular to the shaft meshing pitch circle C ₁ and the maximum meshing pitch circle C ₂ is a cross-section perpendicular to the rotation center line L1, as fall within the scope of the tooth depth h of the rack 1, the pinion teeth 2a and rack teeth Each tooth profile of 1a (see also FIG. 1) is determined. Thus, it decreases the front meshing ratio epsilon ₁ and simultaneously meshing teeth N, and the difficulties such as smooth engagement is difficult is eliminated.

Further, as shown in FIGS. 3 and 4, the tooth thickness 1b and the pitch of the base of the rack tooth 1a in the low gear ratio region E _L are the same as the tooth base of the rack tooth 1a in the high gear ratio region E _H. Each is smaller than the tooth thickness 1c and the pitch.

  Here, since the pinion tooth 2a has a different module, pressure angle, and twist angle on the circles having different radii from the rotation center line L1, the rack tooth 1a, which is a meshing partner, has the module, pressure angle, and twist angle. Are designed to fit each of the pinion teeth 2a.

Specifically, the meshing pitch circle C is obtained as follows. 5, 6, to the rack 1 and pinion 2 engages exactly at the point of engagement, it is necessary to twist angle beta _r of the twist angle and the rack teeth 1a of the pinion teeth 2a are equal . Therefore, first, the helix angle beta _r rack teeth 1a is calculated by Equation (1).

β _r = tan ⁻¹ ((R−L _o · sin ψ) / L _o · cos ψ) (1)
The circle diameter d _r of the meshing pitch circle C is given by equation (2).

d _r = L _o / (π · tan (ψ + β _r )) (2)
here,
L _o : Lead of the pinion 2 R: Gear ratio Further, the meshing point P _m is set so that the meshing of the rack tooth 1a and the pinion tooth 2a proceeds smoothly over the entire operating range of the rack and pinion mechanism G. except when in the end point P _F have starting point P _S and meshing engagement will be described later, a rack and pinion mechanism to keep away from him meshing length t _e1 and unapproachable meshing length t _e2 of G is, any cross section perpendicular to the shaft , The specifications of the rack 1 and the pinion 2 are set so as to be always larger than 0 and so that the total meshing ratio ε obtained by the expression (3) is 2 or more.

ε = ε ₁ + ε ₂ (3)
Here, ε ₁ is the front meshing rate, and ε ₂ is the overlapping meshing rate, which are obtained by Expression (4) and Expression (5), respectively.

_{ε 1 = t e / P b} (4)
ε ₂ = t _eb / P _bt (5)
Here, _{t e} is the total meshing _{length, t eb} overlaps meshing length, the pitch at _{P b} is normal _{pitch, P bt} the longitudinal direction A1 of the rack 1, respectively formula (6) - ( 11).

t _e = t _e1 + t _e2 (6)
t _e1 = (r _a ² −r _g ² ) ^1/2 −r _g · tan α _rs (7)
t _e2 = (r _g / cos α _rs − (H−H _ra )) / sin α _rs (8)
P _b = π · m _rs · cosα _rs (9)
t _eb = b · tan ψ + b · tan β _r (10)
P _bt = π · m _rn / cos β _r (11)
here,
r _g : basic radius of the pinion 2 r _a : tooth tip radius of the pinion 2 α _rs : meshing pressure angle of the rack 1 (cross-section perpendicular to the pinion axis)
H: Distance between axes H _ra : Height of tooth tip of rack 1 (from center axis L2)
m _rs: the axis of the rack 1 perpendicular module m _rn: teeth of the rack 1 perpendicular Module b: rats clauses 1 tooth width Incidentally, in FIG. 5, _{P S} is meshing line _{L m} and the rack 1 of the addendum line La is the intersection of the, and corresponds to the start point of engagement in this specification and claims, P _F is the intersection of the addendum circle of the meshing line L _m and the pinion 2, the specification and the appended This corresponds to the meshing end point in the claims. Further, in FIG. 6, the engagement between the rack 1 and pinion 2 begins from the start point K _1, and ends at end point K _2.

In this way, the entire operation range of the rack and pinion mechanism G corresponding to the entire steering range, that is, the rotation angle θ ranges from 0 to the third rotation angle θ ₃ (the third rotation angle θ ₃ (−θ ₃ on the opposite direction side) In this embodiment, the total meshing ratio ε is set to a value of 2 or more. Therefore, the number N of simultaneous meshing teeth of the rack 1 and the pinion 2 is shown in FIG. As shown in the figure, 2 is the minimum natural number and is a maximum natural number greater than 2, which is 3 or less, and the rack 1 and the pinion 2 are two racks simultaneously according to the change of the rotation angle θ (steering angle). The state in which the teeth 1a and the pinion teeth 2a are engaged and the state in which the teeth are engaged with each other are alternately repeated, and the rack 1 moves in the longitudinal direction A1.

Then, referring to FIG. 8 in which the outline of the meshing surface 10 with the pinion in the rack is shown by shading, when the rotation angle θ is 0, as shown in FIG. 8 (A), the three rack teeth mesh simultaneously. and, in the first rotation angle theta ₁ near, as shown in FIG. 8 (B), it engages two rack teeth 1a are simultaneously in rotation angle theta ₄ near the variable gear ratio region E _V is As shown in FIG. 8C, the two rack teeth are engaged at the same time.

An example of changes in the distant engagement length t _e1 and the close engagement length t _e2 accompanying the rotation of the pinion will be described with reference to FIG. As shown in FIG. 9A, the distant engagement length t _e1 and the close engagement length t _e2 are larger than 0 with respect to the engagement point P _m between the rack teeth 10 and the pinion teeth 21. In the state shown in FIG. 9B in which the pinion 20 is rotated in the rotation direction A2 from the state having, the distant engagement length t _e1 decreases and the close engagement length t _e2 increases. In the state shown in FIG. 9 where the pinion 20 is rotated further (C), meshing point P _m between the rack teeth 11 and the pinion teeth 20 are in the end point P _F meshing, to keep away from him meshing length t _e1 is 0 while becomes, to keep away from him all meshing length t _e which is the sum of the meshing length t _e2 to approach a mesh length t _e1 is equal to the mesh length t _e2 unapproachable. In the state shown in FIG. 9D in which the pinion 2 further rotates, the distant meshing length t _e1 and the close meshing length t _{e2 with} respect to the meshing point P _m between the rack teeth 11 and the pinion teeth 21 Has a value greater than zero.

  In addition, it is preferable from a viewpoint of a precision improvement and a cost reduction to perform the meshing evaluation and intensity | strength evaluation of the rack 1 and the pinion 2 which are obtained in this embodiment using the 3D model of the rack 1 and the pinion 2.

Next, operations and effects of the embodiment configured as described above will be described.
What is the low gear ratio region E _L as well as the low gear ratio region E _{L in} which the gear ratio R is minimized because the total meshing ratio ε of the rack and pinion mechanism G of the vehicle steering device is always 2 or more? In all regions E _V and E _H having different gear ratios R, the meshing of the rack 1 and the pinion 2 proceeds smoothly, and the rack 1 smoothly translates, so that the steering feeling is improved, vibration and Noise generation is reduced. Further, since the loads applied to the rack 1 and the pinion 2 are dispersed and the loads applied to the rack teeth 1a and the pinion teeth 2a are reduced, the durability of the rack and pinion mechanism G is improved. And since the pinion 2 should just be formed so that the total meshing rate may become 2 or more, since it becomes possible to comprise all the pinion teeth 2a by the same tooth profile, the freedom degree of design of the pinion 2 is possible. In addition to increasing, by forming all the pinion teeth 2a in the same tooth profile, the processing becomes easy and the cost of the pinion 2 can be reduced.

In a cross section perpendicular to the shaft of the pinion 2, except when the meshing point P _m is the end point P _F have starting point P _S and meshing engagement, rack and pinion mechanism to keep away from him meshing length t _e1 and unapproachable engagement G Since the long length t _e2 is always larger than 0, the distant meshing length t _e1 and the close meshing length t _e1 are always present, so that the meshing surfaces 10 of the rack teeth 1a and the pinion teeth 2a 10 However, there is no interruption in the direction in which the rotation center line L1 of the pinion 2 extends, and the meshing progresses more smoothly, so that the effects of improving steering feeling and reducing vibration and noise are further enhanced.

The number N of simultaneous meshing teeth of the rack and pinion mechanism G is either 2 or 3 depending on the rotation angle θ, and the tooth thickness of the base of the rack teeth 1a (corresponding to the tooth thickness 1b) is a small portion. In the low gear ratio region E _L , as shown in FIG. 7, the rotation angle θ range in which the simultaneous meshing tooth number N becomes 3 (that is, the steering angle range) is the rotation in which the simultaneous meshing tooth number N becomes 2. by broader than the range of angle theta, the low gear ratio area E _L, since the rack teeth 1a and the pinion teeth 2a at 3 is a value greater than 2 is a number ratio of meshing, more load upon meshing The frequency at which the rack teeth 1a are dispersed is increased and the load acting on the rack teeth 1a meshing with each other is reduced, so that the durability of the rack 1 is improved. In addition, in the low gear ratio region E _L , the mesh point P _m is located closer to the tooth tip than the tooth root of the rack tooth 1a (see FIGS. 3 and 4A), so that the load at the time of meshing is Since the force acting on the tooth tip is increased, the frequency of the simultaneous meshing tooth number N is high even though the stress acting on the tooth root is increased, which can further contribute to the improvement of the durability of the rack 1.

1 is a plan view of a vehicle steering apparatus to which the present invention is applied, centering on a rack and pinion mechanism. 2 is a graph for explaining a relationship between a rotation angle of a pinion and a gear ratio in the rack and pinion mechanism of FIG. 1. In the rack and pinion mechanism of FIG. 1, it is a graph which shows the relationship with the change of the meshing pitch circle with respect to the rotation angle of a pinion, and the tooth height of a rack. In the rack and pinion mechanism of FIG. 1, (A) illustrates the meshing pitch circle in the low gear ratio region, and (B) illustrates the meshing pitch circle in the high gear ratio region. It is a figure for demonstrating the front meshing rate, the distant meshing length, and the near meshing length in the rack and pinion mechanism of FIG. It is a figure for demonstrating the overlap meshing rate in the rack and pinion mechanism of FIG. It is a figure explaining the change of the simultaneous meshing teeth number of the rack and pinion mechanism of FIG. 2A and 2B are perspective views schematically showing a meshing surface of a rack and pinion mechanism in FIG. 1, in which FIG. 1A shows a state where the rotation angle θ is 0, and FIG. 2B shows the vicinity of the first rotation angle θ _1. the state at, (C) shows the state at the rotation angle theta ₄ near the variable gear ratio region E _V, it is a perspective view showing, respectively. It is a figure for demonstrating the change of a distant meshing length and a close meshing length.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Rack, 1a ... Rack tooth, 2 ... Pinion, 2a ... Pinion tooth, 3 ... Handle, 4 ... Pinion shaft, 5 ... Rack shaft, 6 ... Steering wheel, 10 ... Meshing surface,
G: rack and pinion mechanism, A1: longitudinal direction, A2: rotational direction, L1: rotational center line, L2: central axis, L3: straight line, P1: neutral position, R: gear ratio, E _L : low gear ratio region, E V _... variable gear ratio area, E H _... high gear ratio region, C ... meshing pitch circle, h ... tooth height, epsilon ... total meshing rate, P S _... meshing start point, P F _... meshing end point , N: the number of simultaneously meshing teeth.

Claims (2)

In a vehicle steering apparatus that includes a rack and pinion mechanism having different gear ratios according to a steering angle, and an operation of a steering wheel is transmitted to a steered wheel via the rack and pinion mechanism, the entire engagement of the rack and pinion mechanism rate is, Ri always two or more der,
In the rack of the rack and pinion mechanism, the rudder angle range in which the number of simultaneously meshing teeth of the rack and pinion mechanism is greater than 2 at the portion where the tooth thickness at the base of the rack teeth is small is the simultaneous meshing tooth. A steering apparatus for a vehicle characterized by being wider than a steering angle range in which the number is two . The rack is formed with a low gear ratio region where the gear ratio is a low gear ratio and a high gear ratio region where the gear ratio is a higher gear ratio than the low gear ratio,
The portion where the tooth thickness of the base of the rack tooth is small is the low gear ratio region,
2. The vehicle steering apparatus according to claim 1 , wherein an engagement point of the rack and pinion mechanism is located closer to a tooth tip than a tooth root of the rack tooth in the low gear ratio region .

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