WO2008095344A1

WO2008095344A1 - A kind of split-power final reduction gear

Info

Publication number: WO2008095344A1
Application number: PCT/CN2007/000591
Authority: WO
Inventors: Hong Jiang; Xiaochun Wang
Original assignee: Hong Jiang; Xiaochun Wang
Priority date: 2007-01-31
Filing date: 2007-02-17
Publication date: 2008-08-14
Also published as: CN101016932A; CN100462586C

Abstract

This invention relates to a kind of split-power final reduction gear comprises a final driving casing (1), two driving pinions (2) and (4), a pair of split-power cylindrical gears (3) and (5), heavy-duty differential assembly (6) and a driven gear (7). Input power applies to either driving pinion (2) or (4), then half of the input power is shifted to the other driving pinion through split-power cylindrical gears (3) and (5). The driven gear (7) is supported on the differential assembly (6), and same number of teeth are machined in both sides of it. The driven gear engages with both driving pinions, concentrates the power from two transmission branches to itself and in tern transfers the power to differential assembly. With present invention, hub reductors can be eliminated while ground clearance were kept unreduced, thus the cost of driving axles is cut down, fuel consumption and noise are decreased.

Description

A KIND OF SPLIT-POWER FINAL REDUCTION GEAR

FIELD OF THE INVENTION

The present invention relates to a kind of final reduction gear for wheel vehicle driving axles, particularly relates to a kind of split-power final reduction gear.

BACKGROND ART OF THE INVENTION

In order to improve off-road performance and crossing ability, many off-road utility vehicles, off-road trucks and engineering vehicles require larger ground clearance. For many situations, the ground clearance is mainly determined by both driving wheel diameter and the diameter of final reduction gear. In order to meet required output torque, the diameter of the driven gear in a single-reduction axles which is widely used for most common vehicles must be rather large, can hardly meet required ground clearance at the same time. Thus many engineering vehicles have to adopt axles with double-stage reduction involving a stage of hub reductors. The gear ratio in the first reduction of a double-stage reduction axle is greatly decreased, therefore the output torque of the driven gear in this stage is reduced, so the driven gear can be downsized and ground clearance is increased. However, double-stage reducers have problems of higher price, lower efficiency, higher noise and oil temperature in hub reductor when vehicle is driving at a higher speed. Since hub reductors locate within wheel hubs, the heat dissipating condition is not good, higher oil temperature will not only lead to earlier ageing in oil and oil seals, it may also cause to higher tyre pressure, which is possible leading to rupture of tyres and problems in traffic safety. The fuel consumption of vehicles equipped with double reduction axles with hub reductors is obviously higher than those with single reduction axles, therefore double reduction axle is not an ideal layout.

Moreover, for both the most commonly used single and double reduction axles, teeth are only machined in one side of the driven gear. During the engagement with driving gears, the driven gear must carry unbalanced axial thrust along differential axis, will generate a larger deformation under sever-service application, which will influence normal contact between tooth surfaces, limit its load capacity. In order to bear large axial thrust of the driven gear applying on differential case under sever-service application, the driven gears are usually bolted to franges which is usually reinforced with ribs, which will cause churn loss when vehicle drives at a higher speed. In available final reduction gears, the torque from driven gear is transferred to the frange at first, and in turn through the differential case to the cross. Therefore, both frange and differential case will not only bear large-axial thrust, but also large torque, so the case wall must be thick enough to carry the load. In addition to the load, the differential case is generally divided into two pieces from the position of the central plane of the cross so that the cross and planet pinions are possible to be assembled, and a group of bolts must run through the section corresponding to the least wall thickness, the different casing is generally designed rather thick. The arrangement of a differential case with a frange and thicker wall is not favorable to light weight fabrication of final reduction gears, the size and load capacity of differential gears situated within the differential case is limited as well. The axial thrust transferred to the differential casing is finally transferred to the final driving casing through a pair of conical roller bearings. However, conical roller bearings have lower efficiency and higher frictional torque when they work under heavy axial thrust.

SUMMARY OF THE INVENTION

The object of present invention is to provide a kind compact, heavy-duty split-power final reduction gear, being possible to greatly enhance the load capacity of the final reduction gear within limited space, so that hub reductors can be eliminated while the ground clearance and crossing ability are kept unchanged. In this way, the coast of driving axles is possible to be greatly cut down, fuel consumption and noise being reduced.

To realize the object, the technical scheme of present invention is a split-power final reduction gear at least comprising: a final driving casing; a differential assembly, located in the final driving casing; a driven gear, supported on the case of differential assembly; driving gears, held in the final driving casing;

The characteristic is that the driven gear is a combined one, same numbers of teeth are machined in both sides of the driven gear, and two driving pinions with the same numbers of teeth are adopted, each of them engages with the teeth machined in one side of the driven gear corresponding to the pinion, and a pair of cylindrical gears, each of them mounted on the shaft of one driving pinion, engage with each other, composing a pair of split-power gears with a gear ratio of 1 :1. The input power is applied to one of the driving pinions, then one half of the input power is shifted to the other driving pinion through the split-power gear pair, and finally the input power converges to the combined driven gear from its mesh with both driving pinions.

According to present invention, the said differential assembly involves a differential case, a cross held in the differential case, plural pinions supported on the legs of the cross, and a pair of side gears, each one is in mesh with all pinions.

According to present invention, a bore is machined in the center of said driven gear, and the driven gear is supported on the differential case by slide fit. The ends of said cross legs protrude from the bores machined in differential case, keyed to the bore of the driven gear. Four key slots corresponding to the ends of the cross legs are machined in the bore of the driven gear, and the end of each cross leg is machined into a key, fitting with the key slot made in the bore. The torque is directly transferred to the cross through keys and key slots, therefore the differential case does not carry any torque.

According to present invention, the cross is a built-up one, which involves a central square, a piece of long pin and two pieces of short pins. Two crossing bores are machined in the central square, said long pin runs through the central square, both ends of the long pin are machined into keys, fitting with two opposite key slots made into the bore of the driven gear; one end of each short pin is machined into a key, fitting with one of the key slots of the driven gear, while the other end plunges into the bore of central square, stops on the outer circle of the long pin.

According to present invention, all components including the pinions and built-up cross in the differential are possible to be assembled by means of inserting the components one after another, and the differential case can be integrated at the position where the cross is held, need not to be divided into two pieces and held together with bolts as those used in standard differentials. Together with the fact that the differential case in present invention does not carry the output torque, the wall of the differential case can be designed to be rather thin. In this way, for given outer diameter of the differential case, larger differential gears can be assembled into the case, and load capacity of the differential assembly is enhanced.

According to present invention, the driven gear can make some axial float along the axis of differential to ensure the axial thrust of both driving pinions applying to the combined driven gear is just the same in amplitude, so that the transmitted power is equally distributed to both transmission branches .

According to present invention, the split-power cylindrical gears are keyed to or splined to the shafts of driving pinions.

According to present invention, the split-power cylindrical gears are a pair of helical gears, having the same helix angle, being opposite in hand of spiral. Based on the structure of present invention, some obvious effects can be listed as follows: since the teeth on both sides of the combined driven gear are in mesh with driving pinions at the same time, the axial thrusts that the pinions apply to the driven gear will offset with each other, the problem of unbalanced axial thrust in common final reduction gears is avoided, even if under sever-service application, no obvious deformation will appear on the driven gear, and the problems in engagement caused by the deformation of the driven gear are naturally avoided; in addition of the fact that both gear pairs are working together, load capacity of the driven gear is greatly increased, the requirement to output large torque within limited space can be realized. Since the axial thrusts applied to the combined driven gear are balanced with each other, no franges are required to carry axial load, in addition of the fact that the wall of differential casing can be rather thin, the structure can be very compact. For given outer diameter of the differential case, larger differential gears can be assembled in, load capacity of the differential is enhanced, being possible to match the load capacity of split-power final reduction gears. Therefore, within limited space, the output torque of present split-power final reduction gear for driving axles can be increased by several times, thus hub reductors can be eliminated without ground clearance being reduced, the coast of driving axle can be cut down, and fuel consumption of the vehicle is reduced as well.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic section view of the split-power final reduction gears;

FIG. 2 is a schematic view of the connection between the combined driven gear and the cross of the differential and the structure of the built-up cross; FIG 3 is a schematic section view of the combined driven gear; FIG 4 is a schematic planform of FIG 3;

FIG 5 is a schematic view of the structure of the long pin in built-up cross;

FIG 6 is a schematic side view of FIG 5;

FIG 7 is a schematic planform of FIG 5; FIG 8 is a schematic view of the structure of the short pin in built-up cross;

FIG 9 is a schematic side view of FIG 8;

FIG 10 is a schematic planform of FIG 8;

FIG 11 is a schematic section view of the central square;

FIG 12 is a schematic side view of FIG 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As illustrated in figure 1, the split-power final reduction gear according to present invention involves at least a final driving casing 1, a differential assembly 6 located in the final driving casing 1, a driven gear supported on differential assembly 6, and two driving pinions 2 and 4 located in the final driving casing 1 and in individually in mesh with the driven gear 7. In order to describe easily, it is supposed that the final reduction gear is located in a rear driving axle, being observed along the driving direction of the vehicle, the two driving pinions 2 and 4 are individually described as the left driving pinion 2 and right driving pinion 4. As illustrated in figures 1 and 3, same numbers of teeth are machined in both sides of the driven gear 7. The left driving pinion 2 and right driving pinion 4 have the same number of teeth, individually engages with the driven gear 7. The left split-power cylindrical gear 3 is supported on and splined to the gear shaft 21 of the left driving pinion 2, and the right split-power cylindrical gear 5 is supported on and splined to the gear shaft 41 of the right driving pinion 4. The left and right split-power cylindrical gears 3 and 5 engage with each other, the gear ratio between them is 1 :1. Based on the structure mentioned above, the input power can apply to either the left driving pinion 2 or the right driving pinion 4 of the split-power final reduction gear, then the split-power gear pair, composed of cylindrical gears 3 and 5, with a gear ratio of 1 :1, will shift one half of the input power to the other driving pinion, and finally the input power will converge to the driven gear 7 from its engagement with both driving pinions 2 and 4.

Thus, in the working process of present split-power final reduction gear, the driven gear 7 engages with both driving pinions 2 and 4 at the same time, which individually situated on each side of the driven gear, the axial thrusts the driving pinions applying to the driven gear 7 and differential assembly 6 in engagement process will offset with each other, the problem of unbalanced axial thrust in available final reduction gears is avoided; in addition of the fact that both gear pairs are working together, load capacity of the driven gear is greatly increased, the requirement to output large torque within limited space can be realized. Since the axial thrusts applied to the combined driven gear are balanced with each other, no franges are required to carry axial load; in addition of the fact that the wall of differential casing can be rather thin, the structure is very compact. For given outer diameter of the differential case, larger differential gears can be assembled in, and the load capacity of the differential is enhanced, being possible to match the load capacity of split-power final reduction gears. Therefore, within limited space, the output torque of present split-power final reduction gear can be increased by several times, thus hub reductors can be removed without ground clearance being reduced, the coast of driving axle can be cut down, and fuel consumption of the vehicle is reduced as well.

As illustrated in figure 1, the differential assembly 6 involves: differential case 61, end covers 62, the cross 65 which is held in the differential case 61, plural pinion gears 62 supported on the legs of cross 65, and a pair of side gears 64, each of them in mesh with the pinions.

According to present invention, as illustrated in figures 1 and 2, a bore 71 is machined in the center of the driven gear 7, through bore 71 the driven gear 7 is supported on the differential case 61 by slide fit. The ends of said cross legs protrude from the bores machined in differential case 61 and keyed to the bore 71 of the driven gear 7. Thus the torque is directly transferred to the cross through key connection, the differential case does not carry any torque, and the thickness of the wall of the differential case 61 can be further reduced. In this way, for given outer diameter of the differential casing 61, larger differential gears can be assembled into the case, and load capacity of the differential 6 is enhanced.

As illustrated in figure 2, as a specific example, four keys 651 are individually machined in each end of the legs of the cross 65, and corresponding to the keys 651, 4 key slots 72 are machined in the bore 71 of the driven gear 7. Through the engagement of key slots 72 and keys 651, the torque is directly transferred form the driven gear 7 to the cross 65 in the differential assembly 6.

As illustrated in figure 2 and figures 5 to 12, the cross 65 of present invention can be a built-up cross. The built-up cross comprises a central square 66 located within the front ends of 4 pinions 63, a piece of long pin 67 and two pieces of short spins 68. Two crossing bores 661 are machined in the central square 66, said long pin 67 runs through central square, both ends of the long pin are machined into keys 651, fitting with two key slots 72 machined in the bore 71 of the driven gear 7; one end of each short pin 68 is machined into a key 651, fitting with one key slots 72 of the driven gear 7, while the other end plunges into the bore 661 of central square 66, stops on the outer circle of the long pin 67. According to mentioned structure, all components including the pinions 63 and built-up cross 65 in the differential assembly 6 are possible to be assembled by means of inserting the components one after another, and the differential case 61 can be integrated at the position where the cross 65 is held, need not to be divided into two pieces and held together with bolts as those commonly used in standard differentials, thus the wall thickness of the ■ differential case61 can be further reduced. In this way, for given outer diameter of the differential case 61, larger differential gears can be assembled into the case 61, and load capacity of the differential assembly 6 is further enhanced.

According to present invention, as illustrated in figures 1 to 4, the key slots 72 can be made along the axis of the differential assembly in the driven gear 7, and each key slot 72 runs through the bore 71 of the driven gear 7 along the axis of the differential assembly, thus the axial position of the driven gear is not limited by the keys 651 in the ends of the legs of the cross 65, together with the fact that the driven gear 7 is supported on the differential case 61 by slide fit, the axial position of the driven gear 7 is not limited by the differential case 61. Therefore, the axial position of the driven gear 7 is automatically determined in the engagement process with both driving pinions at the same time, being possible to make some axial float along the axis of heavy-duty differential assembly to adjust the distribution of the load in left and right transmission branches, and finally reaches a balance when the load is equally distributed to left and right branches, under this situation the axial thrust of both driving pinions applying to the combined driven gear is just the same, so that the power is guaranteed to be equally distributed to both transmission branches.

According to present invention, as a specific example as illustrated in figure 1 , the said power-split cylindrical gears 3 and 5 are splined to gear shafts 21 and 41 of the driving pinions 2 and 4.

According to present invention, since the driving pinions 2 and 4 have the same number of teeth, the gear pair composed by split-power cylindrical gears 3 and 5 have a gear ratio of 1 :1 (having the same number of teeth), and the number of teeth in both sides of the driven gear is just the same, the transmission ratio in both left and right branches is strictly the same, no kinematical interference will occur.

As a specific example as illustrated in figure 1, the input power applies to the right driving pinion 4, through the power-split gear pair composed by cylindrical gears 5 and 3, one half of the input power is shifted to the left driving pinion 2, and finally converges to the combined driven gear 7. In order that the phase angles between the driving pinions 2 and 4 can meet the phase angles between the grooves machined in both sides of the driven gear 7 to avoid an over large axial float of the driven gear 7, which may influence normal engagement between tooth flanks, some suitable technological process or adjusting mechanism can be adopted to ensure correct phase angles between transmission components. For this preferred embodiment, in order that the phase angles between the left and right driving pinions 2 and 4 can meet the phase angles between the grooves machined in both sides of the driven gear 7, both left and right power-split cylindrical gears are helical gears, having the same helix angle and opposite hand of spiral, and the corresponding technological process is that the end planes of the split-power cylindrical gear 5 are ground in accordance with the measurement in assembling. By means of changing the distribution of grinding allowance between two ends to adjusting the phase angle of the right driving pinion 4 relative to the left driving pinion 2, correct phase angles between transmission components can be guaranteed. Based on the structure of preferred embodiment, a strict matching in phase angles between two transmission branches after power split can be realized, and correct engagement position between two driving pinions and the driven gear is guaranteed.

For present invention, elements such as bearings 11, 12 and 13, bearing caps 14, end caps 15, sand cap 16, oil seal 17 and oil seal housing 18 are also situated in final reduction casing 1, their structure and position are nearly the same of conventional design, are not to be described here. Utilizing the methods presented in present invention that the input power is distributed to two driving pinions 2 and 4, the torque is directly transferred from the driven gear 7 to the cross 65 and small wall thickness is utilized in differential case design, the output torque of the final reduction gear can be increased by several times within limited space, hub reductors can be eliminated without ground clearance being reduced, the coast of driving axle can be cut down, and fuel consumption of the vehicle is reduced as well.

The practical structure and technological process provided in preferred embodiment example is only used to demonstrate the embodiment method and possibility of present invention, not used as a limitation to the invention.

Claims

1. A kind of split-power final reduction gear at least comprising: a final driving casing; a differential assembly, located in the final driving casing; a driven gear, supported on the case of differential assembly; driving gears, located in the final driving casing, in mesh with the driven gear; the characteristic is that the driven gear is a combined one, same number of teeth are machined in both sides of the driven gear, and two driving pinions with the same numbers of teeth are adopted, each of them engages with the teeth machined in one side of the driven gear corresponding to the pinion, and a pair of cylindrical gears, each of them mounted on the shaft of one driving pinion, engage with each other, composing a pair of split-power gears with a gear ratio of 1 : 1 , and the input power applies to one of the driving pinions of said final reduction gear, then one half of the input power is shifted to the other driving pinion through the split-power gear pair, and finally the input power converges to the combined driven gear from its mesh with both driving pinions.

2. The split-power final reduction according to Claim 1, wherein the said differential assembly involves a differential case, a cross held in the differential case, plural pinions supported on the legs of the cross, and a pair of side gears, each one of them in mesh with all pinions.

3. The split-power final reduction according to Claim 2, wherein a bore is machined in the center of said driven gear, the driven gear is supported on the differential case by slide fit between the bore and the differential case, and the ends of said cross legs protrude from the bores machined in differential case, keyed to the bore of the driven gear.

4. The split-power final reduction according to Claim 3, wherein four key slots corresponding to the ends of the cross legs are machined in the bore of the driven gear, and the end of each cross leg is machined into a key, fitting with the key slot made in the bore, thus the torque is directly transferred to the cross through keys and key slots, therefore the differential case does not carry any torque.

5. The split-power final reduction according to Claim 4, wherein the key slots are made along the axis of the differential assembly in the driven gear, and each key slot runs through the bore of the driven gear along the axis of the differential assembly.

6. The split-power final reduction according to Claim 3, wherein the said differential case is integrated at the position where the cross is held.

7. The split-power final reduction according to Claim 2, wherein the said cross is a built-up cross, which comprises a central square, a piece of long pin, and two pieces of short pins, among the components, two crossing bores are machined in the said central square, the said long pin runs through the central square, both ends are keyed to the bore of the driven gear, one end of a short spin is keyed to the bore of the driven gear, while the other end plunges into the bore in the central square, stops at the outer circle of the long pin.

8. The split-power final reduction according to Claim 1, wherein the said split-power cylindrical gears are keyed or splined to the gear shafts of the driving pinions.

9. The split-power final reduction according to Claim 1, wherein the said split-power cylindrical gears are a pair of helical gears, having the same helix angle, and opposite hand of spiral.