CN103998821B - Worm gear mechanism - Google Patents

Abstract

The worm gear mechanism (44) worm gear (80) by worm screw (70) with this worm engaging is constituted.The tooth of the hob (90) that the tooth machining of this worm gear is used, at least face (91c) of tooth top be formed as arc-shaped.The center (93) of the radius of the circular arc in the face of this tooth top is positioned at the position by the centrage (WL') of this hob of the nodel line (94) than this hob.This worm gear carries out tooth machining by this hob.This worm screw is formed as the shape identical with this hob.The gradually remote length of action (L) of this worm gear mechanism is set to bigger than the gradually remote length of action (Llim) of existing worm gear mechanism.

Description

Worm gear mechanism

Technical field

The present invention relates to the improvement technology of a kind of worm gear mechanism.

Background technology

Such as, the power steering gear at vehicle is equipped with worm gear mechanism (for example, referring to patent documentation 1 (figure 14)。)。

The drive mechanism that worm gear mechanism as shown in patent documentation 1 is discussed further below: possess via worm shaft And the worm screw being connected with electro-motor and the worm gear with this worm engaging, by the assist torque of electro-motor generation from worm screw to snail Wheel reinforcement transmission.

In general, by making worm screw rotate and applying power, at the contact point of worm and wheel to the direction of pressing worm gear Place, worm screw accepts the counteracting force from worm gear.If the intensity of worm gear mechanism can be improved, then it is capable of worm gear snail The long lifetime of bar vice mechanism, is therefore desired.

Citation

Patent documentation

Patent documentation 1: Japanese Unexamined Patent Publication 2010-270908 publication

Summary of the invention

The problem that invention is to be solved

The problem of the present invention is to provide the technology of a kind of intensity that can improve worm gear mechanism.

Solution

According to the present invention, in the worm gear mechanism that the worm gear by worm screw with this worm engaging is constituted, worm screw The face of at least tooth top of tooth is formed as arc-shaped, and the radius of the circular arc in the face of this tooth top is centrally located at and leans on snail than the nodel line of worm screw The position of the centrage of bar, in the hob that the tooth machining of this worm gear is used, at least tooth top of the tooth of this hob Face be formed as arc-shaped, the radius of the circular arc in the face of this tooth top is centrally located at the nodel line than hob by the center of hob The position of line, worm gear carries out tooth machining by hob, makes the most remote of the worm gear mechanism that worm and wheel engages Length of action is set to than the worm gear mechanism being made up of the worm screw of involute profile and the worm gear of involute profile gradually Remote length of action is big.

Preferably, at least tooth of worm gear is made up of the formed products of resin.

Invention effect

In the present invention, it is possible to reduce the face pressure of the vicinity of basic circle.It addition, the tooth leaning on tooth bottom side than basic circle can be eliminated The root of shape is cut, therefore, it is possible to be set to and the face engaged by tooth bottom side than basic circle.Thus, even if not increasing the straight of the tooth top of worm gear Footpath, it is also possible to improve contact-ratio, therefore, it is possible to improve the intensity of worm gear mechanism.

Additionally, in the present invention, owing to the coefficient of elasticity of resinous worm gear is little, therefore tooth easily bends.At multiple teeth In the case of engaging with the tooth of worm screw, engagement height is the lowest simultaneously, the load sharing of the tooth of engagement becomes the biggest.But, due to The contact area of the relatively low part of engagement height can be increased, therefore, it is possible to reduce face pressure.

Accompanying drawing explanation

Fig. 1 is the schematic diagram of the electric power-assisted steering apparatus being equipped with worm gear mechanism based on the present invention.

Fig. 2 is the overall structure figure of the electric power-assisted steering apparatus shown in Fig. 1.

Fig. 3 is the 3-3 line sectional view of Fig. 2.

Fig. 4 is the 4-4 line sectional view of Fig. 2.

Fig. 5 is the figure comparing the worm gear shown in Fig. 4 and existing worm gear.

Fig. 6 is the figure that the improving countermeasure to the existing worm gear shown in Fig. 5 illustrates.

Fig. 7 is for the figure by the tooth root shape canalization of the existing worm gear shown in Fig. 5.

Fig. 8 is by the modeled figure of the canalization of the tooth root shape of the existing worm gear shown in Fig. 5.

Fig. 9 be to make the hob shown in Fig. 6 tooth top circular arc central point conjugate after in the case of trochoid curves enter The figure (Shifted Trochoid) of row explanation.

Figure 10 is the figure illustrating envelope based on the negative addendum modification trochoid shown in Fig. 9 (a) and position thereof.

Figure 11 is the figure illustrating envelope based on zero displacement trochoid shown in Fig. 9 (b) and position thereof.

Figure 12 is the figure illustrating envelope based on the normal shift trochoid shown in Fig. 9 (c) and position thereof.

Figure 13 is the figure that the reason to the problem points that the existing worm gear shown in Fig. 5 has illustrates.

Figure 14 is the major part of the worm gear of the profile of tooth being formed with tooth root by the normal shift trochoid shown in Fig. 9 (c) Enlarged drawing.

Figure 15 is the figure illustrated worm screw relative to the engagement of the worm gear employing the profile of tooth shown in Figure 14.

Figure 16 is to revised worm screw and the worm gear employing the profile of tooth shown in Figure 14 based on the worm screw shown in Figure 15 The figure that the state of engagement illustrates.

Figure 17 be to the worm gear shown in Figure 14 engagement with existing worm gear engage the figure compared.

Figure 18 is the figure compared the engagement shown in Figure 17 in detail.

Figure 19 is the figure of experiment illustrating to carry out for the relevant performance verification of engagement to the worm gear shown in Figure 14.

Figure 20 is the figure that the result to the experiment being illustrated in Figure 19 illustrates.

Figure 21 is the figure that the problem that the profile of tooth to the existing worm gear shown in Fig. 5 (a) has illustrates.

Figure 22 is the figure that the action of hob during the cutting of the tooth to the worm gear shown in Figure 21 illustrates.

Figure 23 is the figure that the action of the tooth top to the hob shown in Figure 22 illustrates.

Figure 24 is to illustrate to not produce the figure that the countermeasure attenuated in the middle of produced by the worm gear shown in Figure 21 illustrates.

The figure that the worm gear that Figure 25 is the worm gear shown in Figure 21 to be cut with the non-root shown in Fig. 4 compares.

Figure 26 is the figure that the shape to the tooth root formed by the normal shift trochoid shown in Figure 25 (b) illustrates.

Figure 27 is the figure supplementing the trochoid curves illustrated in fig. 26.

Figure 28 is the figure supplemented the trochoid curves illustrated in fig. 26 further.

Figure 29 is that the worm gear shown in Figure 25 and worm screw are engaged the figure illustrated.

Figure 30 is to for forming the figure that the tooth cutting element (hob) of the worm gear shown in Figure 25 illustrates.

Figure 31 is the figure that the profile of tooth to the worm gear formed by the hob shown in Figure 30 illustrates.

Figure 32 is the figure that the engagement to the existing worm gear (involute profile) shown in Fig. 5 (a) illustrates.

Figure 33 is the figure that the engagement of the worm gear to the present invention shown in Fig. 5 (b) illustrates.

Figure 34 is 34 enlarged drawings of Figure 32.

Figure 35 is 35 enlarged drawings of Figure 33.

Figure 36 is the figure that the correction of the profile of tooth to the worm gear shown in Figure 35 illustrates.

Figure 37 is the figure that the modification to the worm gear shown in Figure 36 illustrates.

Figure 38 is the figure that the correction to the hob required for forming the worm gear shown in Figure 35 illustrates.

Detailed description of the invention

Hereinafter, based on accompanying drawing, the mode being used for implementing the present invention is illustrated.

Embodiment

With reference to the accompanying drawings, worm gear mechanism based on embodiment is equipped on electric power-assisted steering apparatus and in vehicle The example using this electric power-assisted steering apparatus illustrates.

As it is shown in figure 1, electric power-assisted steering apparatus 10 by from the handling maneuver wheel 29 of steering wheel 21 to the vehicle of vehicle, The steering 20 of 29 (such as front-wheels) and apply the assist torque mechanism 40 of assist torque to this steering 20 and constitute.

In steering 20, it is linked with pinion shaft 24 at steering wheel 21 via steering spindle 22 and universal joint 23,23, It is linked with rack shaft 26 at pinion shaft 24 via pinion and rack 25, draws via the horizontal of left and right at the two ends of rack shaft 26 Bar 27,27 and knuckle 28,28 and be linked with the handling maneuver wheel 29,29 of left and right.

Pinion and rack 25 is formed from the little gear 31 of pinion shaft 24 and is formed at tooth bar 32 structure of rack shaft 26 Become.

According to steering 20, driver carries out handling maneuver to steering wheel 21, it is possible to utilize handling maneuver torque And via the drag link 27,27 of pinion and rack 25 and left and right, the handling maneuver wheel 29,29 of left and right is turned to behaviour Vertical.

Assist torque mechanism 40 is following mechanism: is detected by handling maneuver torque sensor 41 and puts on steering wheel 21 The handling maneuver torque of steering 20, Torque test signal based on this handling maneuver torque sensor 41 and by control portion 42 produce control signals, are produced corresponding with handling maneuver torque auxiliary by electro-motor (motor) 43 based on this control signal Help torque, this assist torque is transferred to pinion shaft 24 via worm gear mechanism 44, additionally, by assist torque from little Gear shaft 24 is transferred to the pinion and rack 25 of steering 20.

Handling maneuver torque sensor 41 detection puts on the torque of pinion shaft 24, and is output as Torque test signal, Such as it is made up of magnetic biasing formula torque sensor, torsion bar type torque sensor.

According to electric power-assisted steering apparatus 10, utilize the auxiliary applying electro-motor 43 to the handling maneuver torque of driver The compound torque of torque, it is possible to handling maneuver wheel 29,29 is carried out handling maneuver by rack shaft 26.

As in figure 2 it is shown, housing 51 extends along overall width direction (accompanying drawing left and right directions), rack shaft 26 is housed into can edge And slide axially.It is linked with horizontal drawing via spheric connection 52,52 at the long side direction two ends prominent from housing 51 of rack shaft 26 Bar 27,27.

As it is shown on figure 3, electric power-assisted steering apparatus 10 is by pinion shaft 24, pinion and rack 25, handling maneuver torque Sensor 41 and worm gear mechanism 44 are accommodated in housing 51, are blocked by upper lid portion 53 by the upper opening of housing 51.Turn It is installed on upper lid portion 53 to handling torque sensor 41.

Top 24u, long limit central part 24m and bottom 24d along the pinion shaft 24 extended up and down is borrowed by housing 51 Three bearings (being followed successively by clutch shaft bearing the 55, second bearing 56, the 3rd bearing 57 from the top down) are helped to support as rotating, this Outward, electro-motor 43 is installed, and possesses rack guide 60.Three bearings 55～57 all use rolling bearing.

Rack guide 60 be by be connected to from the side contrary with tooth bar 32 rack shaft 26 guide portion 61 and via Compression spring 62 and press this guide portion 61 adjust bolt 63 constitute tooth bar pressing mechanism.

As shown in Figure 4, electro-motor 43 is installed on the side of housing 51, and possesses horizontal motor drive shaft (output shaft) 43a. This motor drive shaft 43a extends in housing 51, links with worm shaft 46 by shaft coupling 45.Housing 51 is by bearing 47,48 Support both ends 46a, 46b along horizontal-extending worm shaft 46 so that worm shaft 46 can rotate and be limited along axle To movement.Two bearings 47,48 are all made up of rolling bearing.

Worm gear mechanism 44 is that the auxiliary that the assist torque that electro-motor 43 produces is transferred to pinion shaft 24 turns Square transmission mechanism, i.e. force-increasing mechanism.If detailed description, worm gear mechanism 44 by worm screw 70 and engages with this worm screw 70 Worm gear 80 is constituted.Below by worm gear 80 referred to as " wheel 80 ".The centrage CL of wheel 80 is configured to big with the centrage WL of worm screw 70 Cause at right angles.This centrage CL taking turns 80 is also the centrage CL of pinion shaft 24.

Worm screw 70 is integrally formed the metal product in worm shaft 46, such as mechanical realization carbon steel steel (JIS-G- 4051) the ferrum product made from steel such as.The entirety of wheel 80 or the part of at least tooth 81 are the naval stores such as nylon resin.Owing to making naval stores Wheel 80 engage with the worm screw 70 of metal product, therefore, it is possible to be more successfully engaged, and can reduce further and make an uproar Sound.

The ridge 71 (that is tooth 71) of worm screw 70 is set as one.Outer peripheral face shape in the range of complete cycle at wheel 80 Become to have multiple teeth 81 of equal pitch.This is taken turns 80 and is installed to be and is limited relative shifting axially relative to pinion shaft 24 Dynamic, and rotated against by restriction.Such as, wheel 80 links with pinion shaft 24 by sawtooth, spline in a rotational direction, and Pinion shaft 24 it is installed in the axial direction by back-up ring.The worm screw 70 of wheel 80 with driving side by making load side engages, energy Enough torque is transferred to load from worm screw 70 via wheel 80.

Above-mentioned worm gear mechanism 44 seeks various performance.Such as, one of them raising enumerating contact-ratio and height Intensity.Details are described referring to the drawings.

First, the existing worm gear mechanism 200 shown in Figure 21 is illustrated.This worm gear mechanism 200 The profile of tooth of worm gear 220 be tooth top be at the bottom of 221a, tooth be 221c, basic circle be 301, pitch circle (operating pitch circle) be the involute of 302 Profile of tooth.In the position than basic circle 301 outer circumferential side side, the thickness of the tooth that the thickness of tooth 221 becomes maximum position is W2.Long Since Jiu, in order to improve the contact-ratio of worm gear mechanism 200 and realize high intensity, it is known to improve involute profile The method of tooth depth HT of wheel 220.

But, when worm gear 220 by hob by tooth machining time, tooth root 221b is cut-off and produces root and cuts.? The ratio position of the central side of basic circle 301 roller 220, the thickness of the tooth that the thickness of tooth 221 becomes minimum position is W1.As This, owing to tooth root 221b is that centre attenuates, therefore the thickness W1 of tooth is less than W2.As a result of which it is, the bending strength of tooth 221 reduces. It addition, the profile of tooth of wheel 220 becomes the convex form that the radius of curvature at position near basic circle 301 is little.Owing to being that radius of curvature is little Convex, the contact area therefore contacted with worm screw reduces.As a result of which it is, engagement contact surface pressure increases.That is, when increasing involute teeth During tooth depth HT of the wheel 220 of shape, there is the tendency of the reduction causing the reduction of bending strength and face Compressive Strength.

As shown in figure 22, wheel 220 shapes profile of tooth by hob (hobber) 230.The tooth 231 of hob 230 Pitch center 231Ce is positioned at the position (pitch height 312) of line 312.The track of pitch center 231Ce is represented by line 311.Such as this As shown in track 311, the tooth 231 of hob 230 is to move in the way of the rolling of the pitch circle 302 of wheel 220, thus creates and (become Shape) take turns 220 profile of tooth.Now, ratio basic circle 301 portion on the lower during the tooth top 231a of hob 230 digs up the flank of tooth of wheel 220 (is leaned on Nearly one side at the bottom of tooth) part.

As shown in figure 23, the corner of the tooth top 231a of the tooth 231 of hob 230 is formed as the circle of the little radius of curvature specified Arcuation.The track of the corner of tooth top 231a, circular arc center 231b is represented by line 313.Inventor herein obtains and passes through The center 231b making circular arc carries out describing to move as ring and makes the face of tooth root 221 be configured to concave shape (centre attenuate shape) Such opinion.That is, the track 313 of center 231b of the corner of tooth top 231a, circular arc than basic circle 301 by the position of central side Put place and describe ring, as a result of which it is, be considered as the key factor producing incision phenomenon (root is cut).From line 312 to curved shape A length of h till the 231b of center.This length h is referred to as brachium.

In order to prevent the generation of above-mentioned incision phenomenon (root is cut), as shown in figure 24, it is considered to lower the tooth depth of hob 230 HTh.By lowering tooth depth HTh, in the position of the central side than basic circle 301 roller 220, the corner of tooth top 231a, circular arc The track 313 (ring that the center 231b of circular arc is described) of center 231b diminish.Therefore, become to be not likely to produce incision phenomenon (root is cut).But, when lowering tooth depth HTh of hob 230, although become to be not likely to produce incision phenomenon, but take turns the tooth depth of 220 HT step-down.

Return Figure 23, again consider corner, the circular arc center 231b's of the tooth top 231a of the tooth 231 of hob 230 Track 313.Track 313 describes " negative addendum modification trochoid curves ".Track 313 describes reason for this is that of negative addendum modification trochoid curves, Inventor herein thinks that the center 231b of circular arc in corner is present in than pitch height 312 by tooth top 231a side.That is, pass through Making track 313 describe negative addendum modification trochoid curves, the corner of the tooth top 231a of hob 230 is to lean on central side than basic circle 301 Position describe ring mode carry out tooth shear action.The face of tooth root 221b is by under the corner of the tooth top 231a of hob 230 Cut.Cut as a result of which it is, produce root in the face of tooth root 221b.

It follows that contrast shown in Figure 22 based on Figure 25 (a) and Figure 25 (b) existing takes turns the enforcement shown in 220 and Fig. 4 The wheel 80 of example.

What Figure 25 (a) schematically showed shown in Figure 22 existing take turns the pitch circle 302 of 220 and carries out for this is taken turns 220 The profile of tooth of the tooth 231 of the hob 230 of tooth machining.The tooth 231 of hob 230 is represented as bigger than wheel 220.Existing rolling The profile of tooth of the tooth 231 of milling cutter 230 is involute profile, and the corner of tooth top 231a is formed as arc-shaped.The center of circular arc 231b is positioned at tooth top 231a side (the tooth root side of the tooth of wheel 220) relative to the nodel line 312 of hob 230.In this case, in The track 313 of heart 231b describes negative addendum modification trochoid curves.

Figure 25 (b) schematically shows the pitch circle 112 of the wheel 80 of the embodiment shown in Fig. 4 and carries out tooth for this is taken turns 80 The profile of tooth of the tooth 91 of the hob 90 of machining.The tooth 91 of this hob 90 is represented as bigger than wheel 80.The hobbing of embodiment The profile of tooth of the tooth 91 of cutter 90 is involute profile.Wherein, the face 91c of the tooth top of tooth 91 is corrected for the circular arc that radius of curvature is big Shape.This be face 91c in order to not make this tooth top circular arc center 93 (following, be denoted as " center 93 in the face of tooth top ".) rail Mark 313 becomes negative addendum modification trochoid.Specifically, the center 93 of the face 91c of tooth top is positioned against hob relative to nodel line 94 The position of centrage (axis) WL ' of 230.Thus, the track 313 at the center 93 in the face of tooth top describes normal shift trochoid.That is, By being set to normal shift trochoid, it is possible to suppress track as existing description ring.

If summing up above explanation, as described below.In the tooth 91 of the hob 90 of embodiment, at least face 91c shape of tooth top Become arc-shaped.The center 93 of the radius of the circular arc of the face 91c of this tooth top is positioned at leans on hob 90 than the nodel line 94 of hob 90 The position of centrage (axis) WL '.

The worm screw 70 engaged with wheel 80 also preferably forms as the shape identical with hob 90.That is, the tooth 71 of worm screw 70 At least face 71c of tooth top is formed as arc-shaped.The center 73 of the radius of the circular arc of the face 71c of this tooth top is positioned at the joint than worm screw 70 Line 74 is by centrage (axis) WL of worm screw 70 " position.

As shown in figure 26, the track at the center 93 in the face of the tooth top of the wheel 80 of embodiment, as represented by line 313, is described Normal shift trochoid curves.The tooth 81 of the wheel 80 formed by the hob 90 along line 313 (track 313) movement is at tooth root The shape of non-incision is formed as at 81c.Reference 81a is the tooth top of the tooth 81 of wheel 80.Reference 81b is the tooth of tooth 81 The end.

Here, trochoid curves based on Figure 27 and Figure 28 principle to becoming the present invention is supplemented.First, with reference to figure 27, about the dynamic round 402a rolled on fixing circle 401, obtain in the following manner be positioned at dynamic circle 402a point (coordinate X, Y) track, i.e. trochoid curves.It should be noted that this fixing circle 401 has assumed that the circle of the pitch circle of wheel 80.Reference 402a represents the dynamic circle rolled on fixing circle 401.Reference 402b represents distance that distance 402a specifies, at fixing circle The dynamic circle rolled on 401.Line 403 represents the track of the point (X, Y) being positioned at dynamic circle 402.That is, line 403 is trochoid curves. P1 is the point on the line 403 in circle 402a, referred to as arm front end.H is from P1 length (brachium) to fixing circle 401.

With reference to Figure 27, about the dynamic circle 402 rolled on fixing circle 401, obtain in the following manner and be positioned at dynamic circle 402b In the track of point (X, Y), i.e. trochoid curves.

Several 1

X'=(r+r_p)sinθ

Y'=(r+r_p)cosθ

$X-X^{\′}=-(r-h)\sin \left(\frac{{r+r}_p}{r}\mathrm{\θ}\right)$

$Y-Y^{\′}=-(r-h)\cos \left(\frac{{r+r}_p}{r}\mathrm{\θ}\right)$

Thus

$\begin{array}{c}X=\left({r+r}_p\right)\sin \mathrm{\θ}-(r-h)\sin \left\{(1+\frac{r_p}{r})\mathrm{\θ}\right\}\\ Y=\left({r+r}_p\right)\cos \mathrm{\θ}-(r-h)\cos \left\{(1+\frac{r_p}{r})\mathrm{\θ}\right\}\end{array}...\left(11\right)$

With reference to Figure 28, it is considered to the radius of the dynamic circle (with reference to Figure 27, reference 402) describing trochoid curves 403 is ∞ Situation.

Several 2

X'=r_psinθ

Y'=r_pcosθ

X "-X'=-r_pθcosθ

Y "-Y'=-r_pθsinθ

X-X "=-hsin θ

Y-Y "=hcos θ

Thus

$\begin{array}{c}X=(r_p+h)\sin \mathrm{\θ}-r_p\mathrm{\θ}\cos \mathrm{\θ}\\ Y=(r_p+h)\cos \mathrm{\θ}+r_p\mathrm{\θ}\sin \mathrm{\θ}\end{array}...\left(12\right)$

Here, when considering further that (11) formula

Similarly understand

Y=(r_p+h)cosθ+r_pθsinθ

In hob cut flexible utilization this formula consistent with (2) formula

Here, the worm gear mechanism 44 of existing worm gear mechanism 200 with embodiment is contrasted and says Bright.Figure 29 illustrates the engagement of existing worm gear mechanism 200.This worm gear mechanism 200 is by worm screw 210 and snail Wheel 220 composition.Worm screw 210 and wheel 220, the profile of tooth of each tooth be involute profile.The tooth top of the tooth of worm screw 210 and wheel 220 Intersection point between basic circle 301 is set to the first intersection point P11.Intersection point between nodel line 332 and the pitch circle 302 of wheel 220 of worm screw 210 sets It is the second intersection point P12.It is referred to as path of contact 321 by the straight line of the first intersection point P11 and the second intersection point P12.Path of contact 321 and wheel Intersection point between the outside circle 305 of 220 is set to the 3rd intersection point P13.By the length from the first intersection point P11 to the 3rd intersection point P13 Degree is referred to as " length of action ".

Worm screw 210 can engage in the range of the length of action in path of contact 321 with wheel 220.The basic circle 301 of wheel 220 Involute profile is uniquely determined with the number of teeth, torsion angle by coefficient.Therefore, the position of the 3rd intersection point P13 the most uniquely determines. In order to increase length of action, need to increase the external diameter of wheel 220.Accordingly, there exist cannot make worm gear mechanism 200 miniaturization this The problem of sample.

It addition, in the case of using existing worm gear mechanism 200 in Vehicular electric servo steering device, wheel The tooth 221 of 220 is used mostly resin material.In the wheel 220 using resin material, owing to the coefficient of elasticity of material is little, therefore Tooth 221 easily bends.In the case of multiple teeth 221 are simultaneously engaged, engagement height is the lowest, the load sharing of the tooth 221 of engagement Become the biggest.That is, the load putting on each tooth 221 becomes big.

Additionally, in involute profile, be more proximate to basic circle 301, radius of curvature diminishes.Nibbling near basic circle 301 Conjunction face pressure is much larger than the field of conjugate action pressure near pitch circle 302.Accordingly, there exist and be difficult to extend to than basic circle 301 roller path of contact 321 Such problem till the position of central side.

The profile of tooth of the tooth 231 of the existing hob represented by imaginary line in fig. 30 be mesh tooth face be gradually opening of straight line Wire shaped.On the other hand, the profile of tooth of the tooth 91 of the hob 90 of the embodiment represented by solid line in Figure 30 makes crest top land 91c's A part is thinner than involute shape.Specifically, a part of the crest top land 91c of the tooth 91 of the hob 90 of embodiment is set to The substantially arc-shaped connected with involute curve, thus thinning transverse tooth thickness.

Figure 31 is taken turns the tooth 221 of 220 by existing shown in imaginary line by existing hob 230 (with reference to Figure 30) Cut by tooth.Existing tooth 221 produces incision phenomenon (root is cut) in the face of tooth root.As a result of which it is, the flank of tooth of tooth 221 is at basic circle 301 vicinity become significant convex form.

On the other hand, in Figure 31 by the tooth 81 of the wheel 80 of the embodiment shown in solid line by the hob 90 of embodiment Cut by tooth.The transverse tooth thickness of the tooth 91 of this hob 90 is relatively thin.The tooth 81 of wheel 80 will not produce incision phenomenon (root on the face of tooth root Cut).As a result of which it is, the flank of tooth of tooth 81 will not become convex form near basic circle 111.The flank of tooth acting on tooth 81 can be reduced Face is pressed.

Figure 32 illustrates the engagement of existing worm gear mechanism 200, and corresponding with above-mentioned Figure 29 represents.Worm screw 210 with wheel 220 as Figure 34 is represented by hollow arrow, engagement (in path of contact 321) near basic circle 301.

Figure 33 illustrates the engagement of the worm gear mechanism 44 of embodiment, and corresponding with above-mentioned Figure 29 represents.Worm screw 70 with wheel 80 as Figure 35 is represented by hollow arrow, engaging by the position at the bottom of tooth than basic circle 111.Reference 121 is Wheel 80 and the path of contact of worm screw 70.

Figure 36 is illustrated based on the change of the profile of tooth of tooth 81 that change the correction of the transverse tooth thickness of the tooth of hob, wheel 80.Figure The face depression of the tooth root of the existing tooth 221 taking turns 220 represented by imaginary line in 36.In other words, the face at tooth root has Root is cut.This is because, revise the tooth of the tooth 231 of hob 230 (with reference to Figure 23) the most completely.

On the other hand, in an embodiment, as shown in Figure 25 (b), have modified the tooth 91 of hob 90.The correction of this tooth 91 Measure less in the case of the profile of tooth of tooth 81 of wheel 80 represented by fine line in Figure 36.The transverse tooth thickness of the tooth root of tooth 81 is than ever Greatly.The profile of tooth of the tooth 81 of the wheel 80 in the case of the correction of this tooth 91 is relatively big is represented by heavy line in Figure 36.The tooth of tooth 81 The transverse tooth thickness of root becomes much larger.

So, along with the correction quantitative change of the tooth 91 of this hob 90 is big, the depression in the face of the tooth root of the tooth 81 of wheel 80 eliminates, The transverse tooth thickness of tooth root also becomes larger.Further, near basic circle 111, the radius of curvature of the flank of tooth of tooth 81 becomes larger.In other words Saying, the flank of tooth of tooth 81 will not become bigger convex form as in the past in basic circle 111 vicinity.

The tooth 81 of the wheel 80 of above-described embodiment can be set to the tooth 81X of the wheel 80X of the modification shown in Figure 37.This modification The tooth 81X of wheel 80X at least one of transverse tooth thickness of tooth root is set to the transverse tooth thickness of the tooth root than the existing tooth 221 taking turns 220 Greatly.Therefore, the tooth 81X of variation is obtained in that the effect that the tooth 81 with embodiment is equal.If detailed description, existing take turns The profile of tooth of the tooth 221 of 220 is represented by imaginary line in Figure 37.The profile of tooth of the tooth 81 of the wheel 80 of embodiment in Figure 37 by fine line Represent.The profile of tooth of the tooth 81X of the wheel 80X of modification is represented by heavy line in Figure 37.

The profile of tooth of the tooth 81X of this variation is for example formed as the profile of tooth of the tooth 81 of profile of tooth and the embodiment of existing tooth 221 Intermediate shape.Illustrating, the height of the tooth root of the tooth 81 of embodiment is identical with the height of the tooth root of existing tooth 221.So And, the height of the tooth root of the tooth 81 of the aspect ratio embodiment of the tooth root of the tooth 81X of variation is little.Additionally, the tooth 81X of variation The transverse tooth thickness of tooth root is bigger than the transverse tooth thickness of the tooth root of existing tooth 221 and less than the transverse tooth thickness of the tooth root of the tooth 81 of embodiment.Wherein, exist There is not depression in the face of the tooth root of the tooth 81X of variation.

The tooth 81X of variation is special profile of tooth, thus while the machinery of the establishment involute profile of gear-hobbing machine etc. cannot Make the profile of tooth of this variation, but can by employing the injection molded of mould, milling cutter processing directly creates.That is, in reality Execute in example, according to the such round-about way of tooth 81 being created wheel 80 by the revised hob of transverse tooth thickness, it is possible to increase should The face Compressive Strength of tooth 81, bending strength.On the other hand, in variation, in order to improve the face Compressive Strength of tooth 81X, bending by force Spend and can directly create this tooth 81X.Therefore, it is possible to the profile of tooth of the tooth 81X directly and the most meticulously designed.Thus, energy Enough teeth 81 improving embodiment further.For instance, it is possible to change the radius of curvature at the bottom of the tooth depth of gear, tooth, tooth the most meticulously Thick.

When creating tooth 81 shown in above-mentioned Figure 26, embodiment wheel 80, not incision tooth root 221b (does not produce root to cut) Correction δ (with reference to Figure 38) of the tooth 91 of required MIN hob 90, minimum correction δ are with following side Formula is obtained.That is, when illustrating with reference to Figure 38, minimum correction δ of the tooth 91 of hob 90 is asked by following (8) formula Go out.Wherein, this takes turns the profile of tooth of 80 is basic with involute profile Tim.This takes turns 80 to direction Rr in rotary moving (accompanying drawing side clockwise To Rr) rotate.The tooth 91 of hob 90 moves in parallel (moving direction Ds) relative to nodel line Lhp.The tooth 91 of this hob 90 Profile of tooth represented by line Hc.Intersection point between involute position Lia and involute profile Tim of this tooth 81 of the tooth 81 of wheel 80 For cutting point Ps.Starting to take turns the point of the incision of the tooth 81 of 80, in other words incision inferius by this hob 90 is Pr.

Intersection point between the nodel line Lhp of the involute position Lia of the tooth 81 of wheel 80 and the tooth 91 of hob 90 is Px.From Straight line the center CL to intersection point Px of wheel 80 is set to datum line Lp.Have modified the tooth of the hob 90 after minimum correction δ Intersection point between the basic circle 111 of the flank of tooth Th1 of 91 and the tooth 81 of wheel 80 is Py.Straight line by the center CL and intersection point Py of wheel 80 It is set to revise datum line Lt.Revising the datum line Lt inclination angle (correction angle) relative to datum line Lp is θ.This correction angle θ will be big In the pressure angle α of tooth 81 (tooth 91 of hob 90) of wheel 80 as condition (θ ＞ α).

m；The modulus of wheel 80

Z；The number of teeth of wheel 80

Rb；The radius of the basic circle 111 of wheel 80

Rp；The radius of the pitch circle 112 of wheel 80

Rp-Rb·cosθ；Height (wherein, θ ＞ α) from the nodel line Lhp to intersection point Py of the tooth 91 of hob 90.

Several 3

$\mathrm{\δ}=R_b\{(\sin \mathrm{\α}-\sin \mathrm{\θ})-\tan \mathrm{\α}(\cos \mathrm{\α}-\cos \mathrm{\θ})\}+\mathrm{\πm}\frac{(\mathrm{\θ}-\mathrm{\α})Z}{2\mathrm{\π}}...\left(8\right)$

So, in an embodiment, in the hob 90 cutting involute profile, the region of modified tooth profile is, From the nodel line Lhp of hob 90 to the height in tooth top direction, i.e. from the nodel line Lhp to intersection point Py of the tooth 91 of hob 90 The flank of tooth of height scope more than " Rp-Rb cos θ ".And, the height at distance nodel line Lhp is " Rp-Rb cos θ " In intersection point Py, tooth 91 is revised more than minimum correction δ by the direction that transverse tooth thickness is thinning.

The flank of tooth that only have modified the tooth 91 after minimum correction δ is represented by curve Th1.In this case, the tooth 81 of wheel 80 Involute position Lia extend to the position L1 on basic circle 111.It addition, the correction of tooth 91 is more than minimum correction δ In the case of the flank of tooth represented by curve Th2.In this case, the involute position Lia of the tooth 81 of wheel 80 extends to compare basic circle 111 position L2 in the inner part.Thus, it is possible to improve the bending strength of the tooth 81 of wheel 80.

Following discloses become the theory on the basis of the present invention.It should be noted that to general with above-mentioned the present embodiment The reference that element mark is general, and the description thereof will be omitted.

The major subjects of existing research is to make the grinding of profile of tooth of optimal worm screw that worm gear occurs elastic deformation energetically Study carefully.Therefore, the profile of tooth of worm gear there is also room for improvement.

In existing method for designing, in order to make worm gear high intensity, increasing modulus, torsion angle and in terms of geometric Improve contact-ratio.In the methods described above, it is necessary to unconditionally make worm gear footpath maximize.

Inventor herein, in order to break above-mentioned outmoded conventions, is devoted to the high intensity of small-sized worm gear.The present invention challenges Worm gear miniaturization is made to be conceived to the tooth root shape of new worm gear further.As a result of which it is, following design can be reached: pass through Worm screw is made effectively to be engaged to the basic circle (Base-circle) of worm gear below such that it is able to improve contact-ratio.In order to by its entity Change, first, investigate the geometric shape below by the actual basic circle being processed to form.Based on this investigation, will effectively nibble The theory being bonded to below basic circle is referred to as MUB (Meshing Under Base-circle) theory.This MUB is proposed theoretical.

The profile of tooth of the tooth 221 of worm gear 220 shown in Fig. 5 (a), existing is involute profile (Involute Profile).The flank of tooth at this tooth 221 produces by the undercut portion U (Undercut) of existing hob 230 incision.

The profile of tooth of the tooth 81 of worm gear 80 shown in Fig. 5 (b), embodiment is the new shape (New theoretical based on MUB Profile Formed by MUB Theory) profile of tooth.Theoretical based on this MUB, actually make worm gear 80 and (hereinafter referred to as take turns 80), measure length of action and demonstrate the theoretical effect of MUB.The opinion obtained during this research is reported.

Propose to make worm engaging theoretical to the MUB below the basic circle of wheel 80

Fig. 6 illustrates worm gear mechanism (the Contact Line of Worm making existing worm screw engage with wheel Tooth Tip Corner Radius, Contact Line of Involute Worm Wheel).In the past, make wheel 220 large-scale Change, and extend path of contact 321 along tooth top 221a direction to improve contact-ratio.In the present invention, according to conceiving in contrast to this, As long as thinking and can extending path of contact 321 along tooth root 221b direction, then will not maximize and improve contact-ratio.On realizing State target, even if being devoted in basic circle less than 301, the research that also is able to the novel tooth form engaged well.

The tooth 221 utilizing involute profile is engaged to basic circle less than 301, needs by hob (Fig. 5, reference 230) Incision also processes wheel 220, and make elimination gear tip clearance away from worm screw (with reference to Figure 16) engagement.But, when only with above-mentioned side During method engagement, the tooth top 211a of worm screw 210 only contacts with wheel 220, and cannot obtain effective engagement.

Analyze the existing tooth root shape that cannot engage below basic circle

Fig. 7 illustrates the track (Locus of Hob Cutter) of hob.As it is shown in fig. 7, will be by existing involute It is also resolved by tooth root shape canalization that hob 230 is formed.By resolving, even if seeking at basic circle 301 Below, the preferable profile of tooth that also can effectively engage.When the tooth 221 taking turns 220 is fixed on absolute coordinate system and is cut by tooth, hobbing The datum line 312 (Datum Line) of cutter 230 does not slides on the tooth cutting pitch circle of wheel 220 but rolls.The tooth of hob 230 The center 231Ce of (sword) 231 describes the outer trochoid curves 311 of circle.Hob 230 moves along the outer trochoid curves 311 of this circle Time the envelope that formed form the profile of tooth of tooth 221 of wheel 220.Especially the shape of the tooth root 221b of basic circle less than 301 is by rolling The tooth top 231a of milling cutter 230 is formed.

In accompanying drawing, WP represents the application point (Hob Cutter Working Point) of hob 230.Reference 307 Represent the involute shape portion (Involute Profile) of wheel 220.Reference 308 represents the root portion of wheel 220 (Dedendum Formed by Corner Radius)。

Fig. 8 illustrates the envelope (Envelope of Hob Tooth Tip) of the tooth of hob.As shown in Figure 8, tooth is carried out The modelling of the canalization of root shape.First, obtain the line 313 that the tooth top center of arc T of hob 230 describes, it follows that Obtain the envelope 314 when the circle of radius rh moves on this line 313.

When the datum line 312 of hob 230 connects with the phase point B1 of the θ on the pitch circle 302 of wheel 220, line segment A1B1 The line segment being repeatedly wound into for circular arc A0B1, owing to both length is equal, the therefore tooth top center of arc T of hob 230 Coordinate (X, Y) represents as (1) formula, (2) formula with θ as variable.

Several 4

X=(R_p+h)sinθ-R_pθcosθ…(1)

Y=(R_p+h)cosθ+R_pθsinθ…(2)

It follows that obtain the envelope 314 of tooth top center of arc.Point E on envelope 314 is positioned at the line 313 by a T On the normal 315 of (trochoid curves).Owing to being the point that distance TE is consistent with hob tooth top radius rh, therefore such as (3) formula～ (5) formula represents like that.

Several 5

$\frac{\mathrm{dY}}{\mathrm{d\θ}}=h\cos \mathrm{\θ}+R_p\mathrm{\θ}\sin \mathrm{\θ}...\left(3\right)$

$\frac{\mathrm{dY}}{\mathrm{d\θ}}=-h\sin \mathrm{\θ}+R_p\mathrm{\θ}\cos \mathrm{\θ}...\left(4\right)$

$\sqrt{{\left(\frac{\mathrm{dX}}{\mathrm{d\θ}}\right)}^2+{\left(\frac{\mathrm{dY}}{\mathrm{d\θ}}\right)}^2}=\sqrt{h^2+R_p^2{\mathrm{\θ}}^2}...\left(5\right)$

Thus, and some E on envelope (X ', Y ') represent as (6) formula, (7) formula.

Several 6

$\begin{array}{c}{X}^{\′}=X+\frac{r_h}{\sqrt{h^2+R_p^2{\mathrm{\θ}}^2}}\left(\frac{\mathrm{dY}}{\mathrm{d\θ}}\right)\\ =(R_p+h)\sin \mathrm{\θ}-R_p\mathrm{\θ}\cos \mathrm{\θ}-\frac{r_h}{\sqrt{h^2+R_p^2{\mathrm{\θ}}^2}}(h\sin \mathrm{\θ}-R_p\mathrm{\θ}\cos \mathrm{\θ})\end{array}...\left(6\right)$

$\begin{array}{c}{Y}^{\′}=Y+\frac{r_h}{\sqrt{h^2+R_p^2{\mathrm{\θ}}^2}}(-\frac{\mathrm{dX}}{\mathrm{d\θ}})\\ =(R_p+h)\cos \mathrm{\θ}+R_p\mathrm{\θ}\sin \mathrm{\θ}-\frac{r_h}{\sqrt{h^2+R_p^2{\mathrm{\θ}}^2}}(h\cos \mathrm{\θ}+R_p\mathrm{\θ}\sin \mathrm{\θ})\end{array}...\left(7\right)$

Using above-mentioned (6) formula, (7) formula, Fig. 9 (a)～Fig. 9 (c) illustrates that the tooth top circular arc central point making hob 230 conjugates In the case of trochoid curves.According to the displacement direction on the basis of the datum line of hob 230, trochoid curves becomes Change.The negative addendum modification trochoid of Fig. 9 (a) is the curve describing ring.The zero displacement trochoid of Fig. 9 (b) is the friendship between pitch circle 302 Point is with the substantially V word curve in corner.The normal shift trochoid of Fig. 9 (c) is in the lump with concave shape and low curvature convex form Substantially V word curve.

It follows that the envelope formed by each line 313 is investigated.Figure 10 is illustrated based on the bag of negative addendum modification trochoid Winding thread and this envelope is used as position (the Meshing of Gears Formed by Negative of gear of profile of tooth Shifted Trochoid).In Fig. 10, transverse axis is corresponding with the thickness direction of tooth (Tooth Thickness Direction), The longitudinal axis is corresponding with tooth top direction (Tooth Tip Direction).

Till position 316 (Line of Action) can being extended to than position by central side of basic circle 301.So And, the pressure angle (Pressure Angle) of contact point P5 (Contact Point) becomes 75deg (with reference to P6), and becomes the most extremely Till near 90deg.Therefore, worm screw self-locking and becoming can not rotate (with reference to SL).On the other hand, send out in order to avoid above-mentioned situation Raw, when worm screw arrange gear tip clearance away from time, will not come in contact geometrically.In accompanying drawing, PP represents node (Pitch Point).Node refers to the point that the normal of the flank of tooth in the engagement contact point of gear passes through all the time.Line 317 is worm tooth shape (Worm Profile)。

Figure 11 is illustrated based on envelope and position (the Meshing of Gears Formed by thereof of zero displacement trochoid Zero Shifted Trochoid).In fig. 11, transverse axis is corresponding with the thickness direction of tooth, and the longitudinal axis is corresponding with tooth top direction.

The Sergey Novikov that the envelope 314 of basic circle less than 301 becomes circular shape is arc toothed.Therefore, front contact-ratio Become less than 1, it is impossible to meet the condition in the theory of mechanisms of gear, i.e. constant speed.In order to transmit constant speed rotation, need by a plurality of Worm screw comes overlapping and contact-ratio is set to more than 1, therefore makes wheel maximize.In accompanying drawing, MS is for being simultaneously engaged (Meshing Simultaneously) region.

Figure 12 is illustrated based on envelope and position (the Meshing of Gears Formed by thereof of normal shift trochoid Positive Shifted Trochoid).In fig. 12, transverse axis is corresponding with the thickness direction of tooth, the longitudinal axis and tooth top direction pair Should.

Position 316 can extend to lean on than basic circle 301 position of central side.The method of the envelope 314 in contact point Line 315 by node PP, therefore meets the condition in the theory of mechanisms of gear such that it is able to effectively engage all the time.

Figure 13 illustrates the shape (Profile of Dedendum) of tooth root.As shown in FIG. 12 and 13, examine according to above Examine, know and cannot be engaged to basic circle less than 301 with existing involute profile, this is because the shape of tooth root is by negative addendum modification time pendulum Line is formed.

MUB is proposed theoretical

According to above-mentioned research, as long as the tooth root profile of tooth of wheel can be formed by normal shift trochoid, then it is assumed that obtain i.e. Just below basic circle, it also is able to the profile of tooth that effectively engages.In order to realize normal shift trochoid, amplify the tooth top (tooth of hob Top) arc radius, make the central point of circular arc lean on the position of positive direction to conjugate to than the datum line of hob.

Figure 14 illustrates the wheel (MUB Profile of Worm Wheel) being formed tooth root profile of tooth by normal shift trochoid.Figure The engagement of 15 worm screws being shown with this profile of tooth.The tooth top 81a of wheel wears the path of contact of the most such involute and (please exists Accompanying drawing adds reference.), root face can be engaged to basic circle less than 111 along the position of normal shift trochoid.These are two years old Root position (please adds reference at accompanying drawing.) be successfully connected, in all of contact area, meet the theory of mechanisms of gear Condition, therefore, it is possible to confirm to utilize the profile of tooth that this is new can obtain effective engagement.

As shown in figure 15, gradually remote length of action can be extended to LOAmod from the LOA of the existing limit by novel tooth form, and gradually opens Line profile of tooth is compared and can be improved contact-ratio.Here, gradually remote length of action (length of recess path) refer to from node to Length of action till near the tooth top of worm screw.

Even if by above-mentioned basic circle less than 111, also be able to the mesh theory named MUB (Meshing that effectively engages Under Base-circle) theoretical.

Consider the engagement of the elastic deformation of wheel

So far, wheel is studied as rigid body.According to research up to now, if in view of the elastic deformation of wheel, Then can predict and can extend length of action further, therefore to investigate this effect and studied.

When in view of the elastic deformation taken turns, as shown in Figure 15, load sharing concentrates on the A tooth 81A that engagement height is low, because of This revises the transverse tooth thickness of worm tooth end face the most in a negative direction, and lumped load is scattered in other engaging tooths 81B, 81C.

When applying tooth 81, it is possible to pitch circle 112 direction of actual engagement alignment wheel when torque being applied is moved. When making correction worm screw engage with the wheel 80 theoretical based on MUB, as shown in Figure 16, owing to engagement line 121 can be reduced Tilt, therefore compared with result of study hereto, it is possible to extend length of action (with reference to L) further.Wheel can not made big On the premise of type, the contact-ratio being in the past 2.2 is designed as more than 3.0.

It follows that tooth contact zone is investigated.

Figure 17 illustrates the comparison of existing involute profile and the profile of tooth theoretical based on MUB.Transverse axis illustrates that the contact of wheel is high Degree (Contact Height of Worm Wheel).The longitudinal axis illustrates the contact height (Contact on the basis of nodel line Height Above Pitch Line).It is tooth top (addendum) direction on the upside of accompanying drawing, is tooth root on the downside of accompanying drawing (dedendum) direction.The line 341 that the point marked by the square of black connects to is represented existing result.By by white zero The line 342 that the point marked connects to represents the result theoretical based on MUB.Line 343 is the line of the engagement height representing basic circle (Base Line).It is conventional by the region shown in the oblique line of bottom right and MUB both contact area (Contact theoretical Area).It is only contact area theoretical for MUB by the region shown in the oblique line of lower-left.By using the wheel theoretical based on MUB, energy Enough acquisition contact areas in wider array of region.

As shown in Figure 18 (a), the wheel of involute profile 220 be difficult to because of incision to be amplified to mesh regional basic circle 301 with Under.

Wheel 80 as shown in Figure 18 (b), based on MUB theory does not produce incision, therefore, it is possible to mesh regional is good Be amplified to basic circle less than 111.

Engagement test checking theoretical for MUB

In order to verify the meshing performance of the worm screw designed based on the MUB theory proposed, calculating and worm screw phase After the corresponding engagement change of position, actual fabrication worm screw 70 tooth contact when verifying engagement.

As shown in figure 19, verification method is, the flank of tooth worm screw 70 applies blue paste BP, makes worm screw 70 engage with wheel 80, to Worm screw 70 applies torque, and measures the shape in the region that blue paste BP peels off.

Figure 19 (a) illustrates the worm screw 70 being coated with blue paste BP.In accompanying drawing, S is the point contacting beginning between wheel 80 (Start Point of Mesh).E is the point (End Point of Mesh) contacting end between wheel 80.CAa is blue Stick with paste the position that BP peels off, the position (Contact Area of Worm) i.e. contacted with wheel 80.

Figure 19 (b) illustrates the wheel 80 engaged with worm screw 70.In accompanying drawing, Cab be unattached blue paste BP position, i.e. with worm screw The position (Contact Area of Worm Wheel) of 70 contacts.Know worm screw 70 contact and lean on central side to than basic circle 111 Till position.

Figure 20 illustrates these the results.Figure 20 illustrates the contact range (Contact Area of Worm) of worm screw.Horizontal Axle represents the anglec of rotation (Rotation Angle of Worm) of worm screw.The longitudinal axis represents contact height (Contact Height).The measurement result employed in the case of wheel based on involute profile it is illustrated that by the labelling of diamond shape (Actual Measurement of Involute Gear).It is illustrated that by the labelling of triangle and employs based on enforcement Value of calculation (Calculated Point) in the case of the wheel of example.It is illustrated that by the labelling of toroidal and employs based on enforcement Measurement result (Actual Measurement) in the case of the wheel of example.The outside of the point marked by diamond shape and by The region of the inner side of the point that toroidal marks, the region i.e. represented by oblique line are equivalent to utilize wheel based on embodiment to make to nibble Close the amount of area extension.

By on the basis of engaging the phase place of worm screw of beginning geometrically, gradually will enter to tooth top direction from the tooth root of worm screw The direction of rotation of the worm screw in the case of row engagement is set to positive direction.It should be noted that the angular velocity of rotation of wheel is 1.0rps, The input torque of worm screw is 3.2Nm, verifies with this.

The mesh regional of worm tooth-surface is equivalent to the about 1080deg of worm screw rotatable phase, it is therefore evident that contact-ratio is 3.0.With contact-ratio be 2.2 existing profile of tooth compared with, it is possible to by contact-ratio improve 36%.It addition, be able to confirm that the region of engagement of wheel Territory can be amplified to below basic circle well.

These are unanimous on the whole with theoretical study results, therefore, it is possible to the effect that checking MUB is theoretical.Thereby, it is possible to prediction base The engagement of the worm gear mechanism designed in MUB theory.Thus, this MUB theory is small-sized high-strength as requiring to carry The method for designing of the electric power-assisted steering apparatus (EPS) of degree worm gear mechanism is effective.

In order to make wheel miniaturization, proposition is effectively engaged to below basic circle and improves the MUB theory of contact-ratio, by experiment Demonstrate the effect of this theory.As a result of which it is, following description becomes clear and definite.

The known tooth root shape taken turns can be divided into 3 kinds according to the displacement direction of the tooth top circular arc central point of hob Class.Due to the profile of tooth generation self-locking formed by negative addendum modification trochoid, therefore know it and cannot effectively be engaged to below basic circle.By Below the basic circle of profile of tooth formed by zero displacement trochoid, become arc toothed, therefore to meet the constant speed of gear and need Want a plurality of worm screw, know and make wheel maximize.Theoretical according to the MUB that tooth root profile of tooth is formed by normal shift trochoid, do not make wheel On the premise of maximization, in involute profile, even if below the basic circle that cannot engage, also being able to effectively engage.When answering During by MUB theory, in general, in the worm screw that contact-ratio is low, it is also possible to realize 3.0 such high contact-ratios, this point It is confirmed by engagement test.

Although it should be noted that carrying out based on the example that worm gear mechanism is equipped on electric power-assisted steering apparatus Explanation, but worm gear mechanism can also be equipped on other devices, it is not limited to electric power-assisted steering apparatus.

Industrial applicibility

The worm gear mechanism of the present invention is suitable in the electric power-assisted steering apparatus of vehicle using.

Description of reference numerals:

44 ... worm gear mechanism, 70 ... worm screw, 71 ... the tooth of worm screw, 71c ... the face of the tooth top of worm screw, 74 ... worm screw Nodel line, 80 ... worm gear, 90 ... hob, 91 ... the tooth of hob, 91c ... the face of the tooth top of hob, 93 ... hob The center in the face of tooth top, 94 ... the nodel line of hob, WL ... the centrage of worm screw, 210 ... the worm screw of involute profile, 220 ... The worm gear of involute profile, 200 ... existing worm gear mechanism, WL ' ... the centrage of hob, L ... the farthest engage length Degree, Llim ... existing gradually remote length of action.

Claims (4)

1. a worm gear mechanism, the worm gear by worm screw with this worm engaging is constituted, it is characterised in that

The face of at least tooth top of the tooth of described worm screw is formed as arc-shaped, and the radius of the circular arc in the face of this tooth top is centrally located at ratio The nodel line of described worm screw leans on the position of the centrage of described worm screw,

In the hob that the tooth machining of described worm gear is used, the face of at least tooth top of the tooth of this hob be formed as with The arc-shaped that the shape in the face of the tooth top of the tooth of described worm screw is corresponding, the radius of the circular arc in the face of the tooth top of the tooth of described hob It is centrally located at the position of the centrage leaning on described hob than the nodel line of described hob, the tooth top of the tooth of described hob The track at the center in face describes normal shift trochoid, and this worm gear carries out tooth machining by described hob,

The gradually remote length of action making the described worm gear mechanism that described worm screw engages with described worm gear is set to ratio by gradually opening The gradually remote length of action of the worm gear mechanism that the worm screw of line profile of tooth and the worm gear of involute profile are constituted is big,

Described length of action till gradually remote length of action refers near the tooth top from node to worm screw.

Worm gear mechanism the most according to claim 1, it is characterised in that

At least tooth of described worm gear is made up of the formed products of resin.

Worm gear mechanism the most according to claim 1, it is characterised in that

Tooth root at described worm gear does not produce incision.

Worm gear mechanism the most according to claim 3, it is characterised in that

Described worm gear is leaning on the position of tooth bottom side and described worm engaging than the basic circle of described worm gear.