GB2566088A

GB2566088A - CVT V-belt clamping

Info

Publication number: GB2566088A
Application number: GB1714157.3A
Authority: GB
Inventors: Pattakos Manousos; Pattakos John; Pattakos Efthimios; Pattakos Emmanouel
Original assignee: Individual
Current assignee: Individual
Priority date: 2017-09-04
Filing date: 2017-09-04
Publication date: 2019-03-06
Also published as: GB201714157D0

Abstract

A V-belt CVT drive comprising a driving pulley and a driven pulley connected by a belt, wherein each pulley comprises two conical sections with opposed points which are axially movable with respect to each to each other. The springs which push the driven pulley to clamp the belt are variably or pivotally inclined with respect to the axis of the driven shaft, being inclined farther from the axial direction at a longer transmission ratio than at a shorter transmission ratio. This is in order to prevent over-clamping, and saves energy and material wear. The component of the force exerted by the spring in the axial direction is reduced as the conical sections move farther apart, reducing the clamping force when less clamping force is required. The spring housing may be subject to increasing inertial or centrifugal forces as the speed of the drive increases, and the springs may be provided in cartridges to mitigate the effects of these forces.

Description

CVT V-BELT CLAMPING

BACKGROUND ART

Closest prior art is the US2015/0323065A1 patent application publication titled “CVT V-BELT OVER-CLAMPING”, wherein they are presented some “dynamic” ways for compensating the overclamping that, among others, causes significant power loss at the longer transmission ratios, and fast wear of the V-belt.

V-belt over-clamping compensation systems are also presented in the US4.541.820, EP1099885, US6,243,638 and CN101975269 patent documents.

The V-belt CVT’s (CVT: Continuously Variable Transmission) are widely used in scooters, ATV’s (ATV: All Terrain Vehicle), sleds etc.

While the efficiency (i.e. the ratio of the output power to the input power) of a conventional V-belt CVT peaks, at the shorter transmission ratios and the heavier loads, even above 95%, the efficiency drops well below 85% at the longer transmission ratios (overdrive) and the lighter loads.

The low efficiency of the conventional V-belt CVT at the long transmission ratios comes from its architecture according which: a variator (or governor) at the drive pulley pushes its two halves close to each other, while a spring in the driven pulley is resisting and is trying, through a constant length V-belt, to keep the two halves of the drive pulley away from each other.

Among the objects of the present invention is to reduce the overclamping of the V-belt at the longer transmission ratios by arranging properly one or more springs in the driven pulley. The relative axial motion of the two halves of the driven pulley varies the inclination of the springs and the axial forces they apply.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows the arrangement of a V-belt CVT at a short transmission ratio (the left pulley is the drive pulley)

Fig. 2 shows what Fig. 1 at a long transmission ratio.

Fig. 3 shows the radial and axial forces applied by a compressed spring to its supports.

Fig. 4 shows a spring at two positions, with the support whereon the right end of the spring abuts, immovable.

Fig. 5 shows the “spring caused clamping force” versus the distance between the two halves of the driven pulley.

Fig. 6 shows the driven pulley of a first embodiment of the present invention at a long transmission ratio.

Fig. 7 shows what Fig. 6 with the driven pulley at a short transmission ratio.

Fig. 8 shows what Fig. 6 from a viewpoint on the rotation axis of the pulley.

Fig. 9 shows what Fig. 7 from a viewpoint on the rotation axis of the pulley.

Fig. 10 shows what Fig. 6 from another viewpoint.

Fig. 11 shows what Fig. 7 from another viewpoint.

Fig. 12 shows what Fig. 10 after the removal of the covers of the spring cartridges.

Fig. 13 shows what Fig. 11 after the removal of the covers of the spring cartridges.

Fig. 14 shows exploded the driven pulley shown in Fig.10, without the springs.

Fig. 15 shows exploded the driven pulley shown in Fig. 11, without the springs.

Fig. 16 shows a driven pulley of the prior art, at a long transmission ratio wherein the coil spring is heavily compressed.

Fig. 17 shows the driven pulley of the prior art at a short transmission ratio wherein the coil spring is lightly compressed.

Fig. 18 shows a second embodiment of the present invention wherein the springs of the driven pulley (which is shown at a long transmission ratio) are not coplanar with the rotation axis of the pulley.

Fig. 19 shows what Fig. 18 with the driven pulley at a short transmission ratio.

Fig. 20 shows what Fig. 18 from another viewpoint.

Fig. 21 shows what Fig. 19 from another viewpoint.

Fig. 22 shows what Fig. 18 from a viewpoint on the rotation axis of the pulley.

Fig. 23 shows what Fig. 19 from a viewpoint on the rotation axis of the pulley.

Fig. 24 shows what Fig. 18 with the covers whereon the spheres (where the springs abut) are secured on.

Fig. 25 shows what Fig. 19 with the covers whereon the spheres are secured on.

Fig. 26 shows what Fig. 24 from a different viewpoint.

Fig. 27 shows what Fig. 25 from a different viewpoint.

Fig. 28 shows what Fig. 18 from a different viewpoint and partly exploded.

Fig. 29 shows what Fig. 19 from a different viewpoint and partly exploded.

Fig. 30 shows exploded the driven pulley of the second embodiment.

Fig 31 shows the basic geometry of a spring arrangement and the resulting axial and perpendicular forces.

Fig 32 shows the axial force resulting versus the spring inclination angle, for various lengths of the spring.

BRIEF DESCRIPTION OF THE INVENTION

In Fig. 1 a V-belt CVT is shown at a short transmission ratio (drive shaft: 1, drive pulley: 2, driven shaft: 3, driven pulley: 4, V-belt: 5). The torque M provided by the drive shaft 1 loads the V-belt by a force F=M/R2, wherein R2 is the radius at which the V-belt runs on the drive pulley 2.

In order to avoid “belt slippage” in the drive pulley, a minimum clamping of the V-belt between the two conical halves of the drive pulley 2 is required.

The same for the rear pulley: a minimum clamping is required, otherwise the pulley cannot apply the required force on the V-belt. In Fig. 2 the transmission ratio (defined as the ratio of the angular velocity of the driven pulley 4 to the angular velocity of the drive pulley 2) is long, about double than in Fig. 1.

With the same torque M provided by the drive shaft 1, the substantially bigger radius R2’ the V-belt runs on the drive pulley 2 reduces substantially the force F’ loading the V-belt (F’/F=R2/R2’) and proportionally the required clamping of the belt between the two conical halves of the drive pulley 2, and similarly it reduces proportionally the required clamping of the V-belt between the two conical halves of the driven pulley 4.

Instead, as shown in Figs. 16, 17, the driven pulley spring of a conventional CVT is heavily compressed at the longer transmission ratios (Fig 16).

So, while at the longest transmission ratio (overdrive) the working force F’ along the V-belt is about half than the working force F along the V-belt at the shortest transmission ratio (for the same torque provided on the drive shaft), the clamping of the V-Belt in the driven pulley (and consequently in the drive pulley, too) is substantially more than double than the clamping really necessary. The arrangement of the spring (Figs. 16, 17) is the cause of this problem in the conventional CVT’s: the longer the transmission ratio, the heavier the axial force the driven pulley spring provides, and the higher the clamping of the V-belt. Fig. 5 shows the “spring caused clamping force” versus the distance between the two halves of the driven pulley for a conventional CVT and for a CVT made according the present invention (to be noted: at Omm distance, the two halves are at the closest to each other position, which means the V-belt is running at the maximum diameter in the driven pulley).

In the present invention the arrangement of the springs is such that, while for higher and higher transmission ratios the springs are more and more compressed (providing a stronger and stronger force), the axial forces the springs apply on the two halves of the driven pulley (and the clamping of the V-belt this forces cause) is reduced.

In Fig. 3 the same spring is shown at three different lengths (compressions). In all three cases the horizontal dimension of the spring is the same. As the spring is compressed, the force (FS, FL) it applies along its direction increases: FL>FS (the L stands for longer ratios, the S stands for shorter ratios). Analyzing the total force FL in an axial component force FLA parallel to the rotation axis 3A of the driven shaft 3 (the A in the FLA stands for axial) and in a perpendicular component force FLP on a plane perpendicular to the rotations axis 3A (the P in the FLP stands for perpendicular), and similarly for the FS which is analyzed in an axial component force FSA (parallel to the rotation axis 3A) and in a perpendicular component force FSP (on a plane perpendicular (normal) to the rotation axis 3A), despite the increase of the total force the spring applies at the longer ratios (because it is further compressed), the axial component of the force can reduce substantially at the longer transmission ratios (and proportionally can reduce the clamping of the V-belt), as shown in Fig. 5.

PREFERRED EMBODIMENTS

In a first embodiment, Figs. 6 to 15, instead of the “axial” spring used in the driven pulley of the conventional CVT’s (Figs. 16 and 17), oblique springs are disposed between the parts of the driven pulley.

The approach of the two conical halves of the driven pulley compresses the oblique springs further, it also increases their leaning angle. The result is an about three times weaker clamping on the belt at the longest transmission ratio (or overdrive), without risking belt slippage.

The “cartridge-like” springs prevent the springs from bending (due to extreme centrifugal forces) at the higher revs of the driven pulley.

The torque cam (shown in Figs. 14 and 15) functions as usual. If the driven pulley of a scooter CVT is modified according the present invention, the ramps and the roller weights of the variator have also to be modified to fit with the substantially different clamping of the V-belt along the operating range.

After the modification, the scooter (or vehicle in general) will have better mileage (a part of the fuel previously burnt to provide energy consumed in the CVT as friction, is saved), the scooter will have higher top speed (at the longest transmission ratio the power consumed previously as friction in the CVT, now pushes the scooter forwards), the CVT will run colder and will need less energy for cooling I ventilation, the V-belt will last far longer (because it avoids running under extreme over-clamping).

In the first embodiment the springs are shown arranged “coplanar with the rotation axis of the driven pulley.

But this is not necessary.

In a second embodiment, Figs. 18 to 30, the springs are arranged between two covers, with the one cover secured on the one half of the driven pulley, and with the other cover moving axially together with the moving half of the driven pulley. The springs are arranged obliquely and eccentrically relative to the rotation axis of the driven pulley.

Due to their eccentricity, the springs undergo strong centrifugal forces when the driven pulley runs at high revs (worth to note: in a conventional scooted having an engine running at 10,000rpm maximum, the driven pulley spins at 20,000rpm maximum). The covers provide surfaces receiving the centrifugal forces applied onto the springs, and keeping them in place.

In the specific case (but not obligatory) there are formed in each cover three spherical extensions. Each spring abuts / is supported I is trapped at one side on a spherical extension of the one cover, and at its other side on a spherical extension of the other cover.

The torque cam (shown in Fig 30) remains functional as in the conventional CVT’s.

As the two conical halves of the driven pulley move away from each other (which means: the V-belt is running at smaller diameters on the driven pulley, which means longer transmission ratios), the springs get more and more oblique (more “vertical”) to the rotation axis of the driven pulley. Despite the stronger forces the more compressed springs apply to the covers, the axial force drops and the clamping of the V-belt between the two conical parts of the driven pulley drops.

The previous are explained in the Figs. 3 and 4.

The result is shown in the plot of Fig. 5.

In comparison to a conventional CVT providing the same “spring” caused clamping force (FSA) at the shortest transmission ratio, the springs in the driven pulley of the present invention cause, at the longest transmission ratio, a clamping which is about three times lower than the clamping in the conventional CVT, and this without any risk of belt slippage.

At the intermediate transmission ratios the difference is smaller, but still significant, saving fuel, reducing the wear of the V-belt, reducing the temperature in the CVT casing, improving the performance, etc.

In the Fig 31 it is shown the arrangement of a spring (actually of an axis of a spring) as those used in the preferred embodiments. The relaxed length of the spring (i.e. the length of the spring when it is unloaded) is L, and its projection on a horizontal axis has constant length D due to its arrangement.

The axis of the spring has an inclination f relative to the rotation axis of the driven pulley (the rotation axis of the driven pulley is not shown, but it is parallel to the dashed-dot lines of Fig 31).

The total force provided by the spring is Ft along the spring “axis”, with:

Ft=(L-(D/sin(f)))*k, wherein k is the stiffness of the spring.

The axial component of the Ft is Fa, with:

Fa=(L*cos(f)-(D/tan(f)))*k

In Fig. 32 it is shown the resulting axial force versus the spring inclination angle of the arrangement of Fig 31, for springs having various lengths. For the specific plot (but not obligatory) the stiffness k of each spring is taken reverse proportional to its length, which means constant k*L (to make springs of constant k*L one could use the same wire, the same coil diameter and the same pitch).

Following the curve “L/D=2.5”, one can see that the resulting axial force is zero until f=23.5 degrees (relaxed spring, asin(1/2.5)=23.5 degrees). Then the spring is progressively compressed.

Until f=48 degrees the axial force increases with the compression of the spring (but not linearly).

After the 48 degrees (at which the curve “L/D=2.5” maximizes), while the further increase of the angle f of the spring axis causes the further compression of the spring (because its effective length reduces), the resulting axial force reduces.

From 60 to 90 degrees (at 90 degrees the resulting axial force gets zero) the drop of the axial force varies, more or less, linearly with the angle f.

Designing the driven pulley and its springs so that at the shortest transmission ratio (i.e. completely closed driven pulley and V-belt running at the maximum diameter on the driven pulley) the spring inclination to be f=53 degrees, and at the longest transmission ratio (i.e. completely open driven pulley and V-belt running at the minimum diameter on the driven pulley) the spring inclination to be f=75 degrees, the resulting axial force (and the clamping it causes on the V-belt) reduces progressively and substantially as the transmission ratio increases. The resulting axial force (and the clamping it causes) at the longest transmission ratio is nearly 50% of what it is at the shortest transmission ratio. The 50% reduction of the clamping force at the longest transmission ratio fits well with what the Figs. 1 and 2 show.

The same mechanism can be used in other applications wherein the displacement of a member relative to another member causes the compression of some spring and an axial force resisting to the motion.

The mechanism fits also with bicycles having a V-belt CVT for the transmission from the pedals to the rear wheel (as in the GB 2,526,675 patent, for instance). The reduction of the over-clamping (and of the associated friction loss) is more significant in a bicycle because of the small available power.

The simplicity is among the characteristics of the present invention.

The saving of fuel and of power are also characteristics of the present invention.

The “automatic operation” is also a characteristic of the present invention: after the assembly of the driven pulley, the reduction of the clamping force is realized automatically without external parts or control systems.

Claims

1. A V-belt continuously variable transmission comprising at least: a drive shaft (1);

a drive pulley (2) comprising two conical halves on the drive shaft (1), at least the one conical half of the drive pulley (2) being axially movable with respect to the drive shaft (1);

a driven shaft (3) rotating about a rotation axis (3A);

a driven pulley (4) comprising two conical halves (4A, 4B) on the driven shaft (3), at least the one conical half of the driven pulley (4) being axially movable with respect to the driven shaft (3);

a V-belt (5), the V-belt (5) is engaging the drive and driven pulleys (2, 4) and is transmitting power between the drive and the driven shafts (1,3) at a transmission ratio defined as the ratio of the angular velocity of the driven pulley (4) to the angular velocity of the drive pulley (2), with the transmission ratio varying continuously between a longest transmission ratio and a shortest transmission ratio;

a spring (6) acting by forces on the two conical halves of the driven pulley (4), said forces pushing the two conical halves (4A, 4B) of the driven pulley (4) closer to each other towards a smaller transmission ratio, said forces causing a clamping of the V-belt (5) between the two conical halves of the driven pulley (4), characterized in that while said forces are stronger at a longer transmission ratio than at a shorter transmission ratio, the direction of said forces varies substantially causing a weaker clamping of the V-belt between the two conical halves of the driven pulley (4) at the longer transmission ratio than at the shorter transmission ratio.

2. A V-belt continuously variable transmission according claim 1, wherein:

an inclination angle f between an axis along the spring (6) and an axis parallel to the rotation axis (3A) of the driven shaft (3) being substantially bigger than 45 degrees at the longest transmission ratio.

3. A V-belt continuously variable transmission according claim 1, wherein:

an inclination angle f between an axis along the spring (6) and an axis parallel to the rotation axis (3A) of the driven shaft (3) being substantially bigger than 20 degrees at the shortest transmission ratio.

4. A V-belt continuously variable transmission according claim 1, wherein:

the angle f between an axis along the spring (6) and an axis parallel to the rotation axis (3A) of the driven shaft (3) is varying between no more than 85 degrees and no less than 25 degrees.

5. A V-belt continuously variable transmission according claim 1, wherein:

the angle f between an axis along the spring (6) and an axis parallel to the rotation axis (3A) of the driven shaft (3) is varying between no more than 80 degrees and no less than 30 degrees.

6. A V-belt continuously variable transmission according claim 1, wherein:

for each transmission ratio said forces have a direction at an angle f relative to a direction of the rotation axis (3A) of the driven shaft (3), at longer transmission ratios the angle f is bigger.

7. A V-belt continuously variable transmission according claim 1, wherein:

there is a plurality of springs (6).

8. A V-belt continuously variable transmission according claim 1, wherein:

there is a plurality of springs (6) arranged at a substantial eccentricity from the rotation axis (3A) of the driven shaft (3).

9. A V-belt continuously variable transmission according claim 1, wherein:

at longer transmission ratios an axis of the spring (6) gets more parallel to a plane perpendicular to the rotation axis (3A) of the driven shaft (3).

10. A V-belt continuously variable transmission according claim 1, wherein:

the spring (6) is supported by surfaces formed in the driven pulley and receiving inertia centrifugal forces generated during the rotation of the spring (6).

11. A V-belt continuously variable transmission according claim 1, wherein:

the spring (6) is a cartridge spring, with the casing of the cartridge receiving inertial centrifugal forces of the spring.

12. A V-belt continuously variable transmission according claim 1, wherein:

at the longest transmission ratio said forces having an axial component FLA, parallel to the rotation axis (3A) of the driven pulley (3), and a perpendicular component FLP on a plane normal to the rotation axis (3A), with the perpendicular component FLP being at least two times larger than the axial component FLA.