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Title:
HYDRAULIC-CONTROLLED DIFFERENTIAL
Document Type and Number:
WIPO Patent Application WO/1988/004743
Kind Code:
A1
Abstract:
A hydraulic-controlled differential (10) includes a case (12) defining a central chamber with intermeshed control gears (52-58) different ones of which are drivingly-connected via shaft and gear arragements (60-66, 88, 90, 94, 98 and 102) through side chambers to opposite output shafts (86). The central and opposite side chambers of said case (12) are interconnected for fluid communication via control valves (113) for controlling flow of hydraulic fluid between the chambers to effect hydraulic modulation during differential drive for more controllability. A second embodiment (150) for lighter-duty applications incorporates two control gears (152, 154).

Inventors:
WILLIAMSON ARCHIE O (US)
Application Number:
PCT/US1986/002772
Publication Date:
June 30, 1988
Filing Date:
December 19, 1986
Export Citation:
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Assignee:
WILLIAMSON PATENT HOLDING (US)
International Classes:
F16H48/26; (IPC1-7): F16H1/455
Foreign References:
US3251244A1966-05-17
US4272993A1981-06-16
US2532757A1950-12-05
US2655055A1953-10-13
US3040600A1962-06-26
US0831461A1906-09-18
US3232139A1966-02-01
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Claims:
Claims
1. WHAT IS CLAIMED IS: A hydrauliccontrolled differential, which com¬ prises: a case supported for rotation about a transverse axis, said case defining a central chamber and two opposite side chambers; means for effecting rotation of said case; a rotatable output shaft extending outwardly from each side chamber of said case along the transverse axis; at least two control gears supported for rotation in the central chamber of said case, said control gears and the central chamber of said case defining a gear pump with adjacent gears being intermeshed for rotation in opposite directions; means extending between the central chamber and the side chambers of said case for drivingly connecting said control gears with the respective output shaft; the side chambers in said case being fluidly con¬ nected for fluid level and pressure equalization between the side chambers; and control valve means connected between each side chamber and the central chamber of said case adjacent inter mesh of said control gears for limiting maximum fluid flow rate between the chambers to effect hydraulic modulation during differential drive of said output shafts.
2. The differential of Claim 1, wherein said means fo effecting rotation of said case comprises: a longitudinal input shaft; a drive pinion secured to said input shaft fo rotation therewith; and a crown gear secured about said case in engagemen with said drive pinion.
3. The differential of Claim 1, wherein said means drivingly interconnecting said control gears and said output shafts comprises: at least two rotatable shafts, said control gears being individually secured to said shafts for rotation there¬ with; the control shaft supporting one control gear extending in sealed engagement into one of the side chambers and the other control shaft supporting the other control gear extending in sealed engagement into the other side chamber of said case; two internal gears, one positioned in each side chamber of said case and secured to the respective output shaft for rotation therewith; and at least two drive gears, one secured to the re¬ spective control shaft and engaged with the respective inter¬ nal gear in each side chamber of said case.
4. The differential of Claim 1, wherein said control valve means comprises: a slideable valve member positioned in a bore ex¬ tending between each side chamber of said case and the cen¬ tral chamber at the outside points of intermeshing engagement of each adjacent pair of control gears; said valve member being movable between minimum open and maximum open positions; and means for normally biasing each valve member toward the minimum open position.
5. The differential according to Claim 4, wherein said valve member includes an internal bore defining a predeter¬ mined flow rate in the minimum open position, and external grooves defining with the internal bore a predetermined rela¬ tively higher predetermined flow rate in the maximum open position.
6. The differential according to Claim 4, wherein said biasing means comprises a compression spring.
7. A hydraulicmodulated differential, which com prises: a case supported for rotation about a transvers axis, said case defining a central chamber and two opposit side chambers; means for effecting rotation of said case; a rotatable output shaft extending outwardly fro each side chamber of said case along the transverse axis; two pairs of control gears supported for rotation in the central chamber of said case, said control gears and the central chamber defining a gear pump with adjacent gears being intermeshed so that diagonallyopposite gears rotate in the same direction; means extending between the central chamber and each side chamber of said case for drivingly connecting one diagonal pair of control gears with the respective output shaft; the side chambers in said case being fluidly con¬ nected with a portion of the central chamber between said control gears for fluid level and pressure equalization be¬ tween the side chambers; and control valve means connected between each side chamber and the central chamber of said case adjacent inter mesh of said control gears for limiting maximum fluid flow rate between the chambers to effect hydraulic modulation during differential drive of said output shafts.
8. The differential of Claim 7, wherein said means drivingly interconnecting said control gears and said output shafts comprises: two pairs of rotatable shafts, said control gears being individually secured to said shafts for rotation there¬ with; the control shafts supporting one diagonally oppo¬ site pair of control gears extending in sealed engagement into one of the side chambers and the other control shaft supporting the other diagonally opposite pair of control gears extending in sealed engagement into the other side chamber of said case; two internal gears, one positioned in each side chamber of said case and secured to the respective output shaft for rotation therewith; and two pairs of drive gears, one pair secured to the respective control shafts and engaged with the respective internal gear in each side chamber of said case.
9. The differential of Claim 7, wherein said control valve means comprises: a slideable valve member positioned in a bore ex¬ tending between each side chamber of said case and the cen¬ tral chamber at the outside points of intermeshing engagement of each adjacent pair of control gears; said valve member being movable between minimum open and maximum open positions; and means for normally biasing each valve member toward the minimum open position; each valve member being internally and externally configured to permit a predetermined fluid flow rate in the minimum open position and a predetermined larger fluid flow rate in the maximum open position.
10. A hydraulicmodulated differential, which com¬ prises: a case supported for rotation about a transverse axis, said case defining a central chamber and two opposite side chambers; means for effecting rotation of said case; a rotatable output shaft extending outwardly from each side chamber of said case along the transverse axis; two control gears supported for rotation in the central chamber of said case, said control gears and the cen¬ tral chamber defining a gear pump with adjacent gears being intermeshed for rotation in opposite directions; means extending between the central chamber and side chambers of said case for drivingly connecting each con¬ trol gear with the respective output shaft; the side chambers in said case being fluidly con¬ nected for fluid level and pressure equalization between the side chambers; and control valve means connected between each side chamber and the central chamber of said case adjacent the points of intermeshing engagement of said control gears for limiting maximum fluid flow rate between the chambers to effect hydraulic modulation during differential drive of said output shafts.
11. The differential of Claim 10, wherein said means drivingly interconnecting said control gears and said output shafts comprises: two rotatable shafts, said control gears being in¬ dividually secured to said shafts for rotation therewith; the control shafts supporting one control gear extending in sealed engagement into one of the side chambers and the other control shaft supporting the other control gear extending in sealed engagement into the other side chamber of said case; two internal gears, one positioned in each side chamber of said case and secured to the respective output shaft for rotation therewith; and two drive gears, one secured to the respective con¬ trol shaft and engaged with the respective internal gear in each side chamber of said case.
12. The differential of Claim 10, wherein said control valve means comprises: a slideable valve member positioned in a bore ex¬ tending between each side chamber of said case and the cen¬ tral chamber at the outside points of i termeshing engagement of each adjacent pair of control gears; said valve member being movable between minimum open and maximum open positions; and means for normally biasing each valve member toward the minimum open position; each valve member being internally and externally configured to permit a predetermined fluid flow rate in the minimum open position and a predetermined larger fluid flow rate in the maximum open position.
Description:
HYDRAULIC-CONTROLLED DIFFERENTIAL

Technical Field The present invention relates generally to drive trains. More particularly, this invention concerns an im¬ proved hydraulic-controlled differential for positively applying power from a drive shaft to a pair of driven shafts while limiting maximum differentiation between the driven shafts for better safety and control.

Background Art

During maneuvering, it may be necessary for the wheels on opposite sides of a vehicle to rotate at different rates or even in opposite directions. For example, as a four-wheel vehicle rounds a curve, the outer wheels travel a greater distance and therefore must turn faster than the inner wheels. Maneuvering in tight quarters can cause oppos¬ ing wheels to turn in opposite directions. This presents no difficulties if the wheels are either driven independently or mounted on a dead axle for independent rotation, however, with a live axle some compensation is necessary to permit the wheels to turn at different speeds.

Differentials or differential gearing have long been utilized for distributing power between the wheels while permitting one wheel to turn faster than the other, as needed on curves. The differentials of the prior art typically in¬ clude a ring gear driven by a pinion gear mounted on the drive shaft. The ring gear is secured to a differential case or housing for rotation therewith. Each axle includes a co¬ axial bevel gear which meshes at right angles with pinions mounted on spindles within the differential case. hen trav-

eling straight ahead, the differential case is simply driven by the ring gear, and there is no relative motion between the pinion and bevel gears therein. When rounding a curve, how¬ ever, one wheel must travel relatively faster, and the dif¬ ferential rotation of the axles is compensated for by the pinion gears which permit opposite relative rotation of the bevel gears as the pinion gears are being driven by the dif¬ ferential case, such that faster rotation of one axle and wheel is offset by proportionately slower rotation of the other axle and corresponding wheel.

One of the main disadvantages of conventional dif¬ ferentials has been that all power can be applied to one wheel to the exclusion of the other. That is, if one wheel slips on ice or mud while the other wheel is resting on dry pavement, the differential case and pinion gears therein simply turn around the stationary bevel gear of the axle of the wheel with traction on dry pavement, while the bevel gear for the axle of the wheel without traction simply turns with the pinion gears inside the rotating case about the bevel gear for the other axle.

Another disadvantage of the prior differentials has been that there is no provision for controlling the maximum amount of differentiation between opposite axles. This is usually unnecessary when the vehicle is under control and is being operated within design conditions, however, it can be a significant consideration if the vehicle should spin. In a spin, like those experienced when a driver loses control of his vehicle, such as during auto racing, the wheels on oppo¬ site sides of the vehicle tend to rotate in opposite direc¬ tions, which further contributes to the lack of controllabil¬ ity of the vehicle. It would be far preferable to be able to

limit the maximum amount of differentiation between the axle so that, in the event of a spin, the differential would drag causing the vehicle to slide in a more predictable, control lable and safe manner.

Various positive or so-called non-slip differen tials have been available heretofore, however, the prior dif ferentials have been unnecessarily complex and expensive One of the most popular non-slip differentials of the prio art operates only in forward gear but not in reverse. More over, the prior non-slip differentials only limit slip be tween the drive shaft and the axles, but not between th axles.

A need has thus arisen for an improved positiv differential which effects differentiation between a driv shaft and two driven axles so that neither axle can be drive to the exclusion of the other, but which also limits th maximum amount of dif erentiation between the axles so tha they will not turn uncontrollably in opposite direction should the vehicle spin.

Summary of Invention The present invention comprises an improved differ¬ ential which overcomes the foregoing and other difficulties associated with the prior art. In accordance with the inven¬ tion, there is provided a hydraulic-controlled differential including a case defining three chambers: a central chamber and two side chambers, one side chamber for each of the two driven axles. At least one pair of control gears, which are in meshed engagement for rotation in opposite directions, are provided in the central chamber. The control gears and adja¬ cent walls of the central chamber define a gear pump. One of the control gears is connected to a drive gear in one side chamber, while the other control gear is connected to another drive gear in the other side chamber. The drive gears are respectively engaged with internal driven gears secured to the opposite axles. Hydraulic fluid is provided in the cham¬ bers, which are connected in fluid communication by spring- biased control valves. Differential drive of the axles is accomplished primarily by the control gears, drive gears, and driven gears. However, the control gears also function to positively displace hydraulic fluid between the chambers in response to differential drive. The control valves effect hydraulic modulation to limit the maximum rate of fluid transfer so that uncontrolled differentiation cannot occur. Two embodiments are disclosed herein.

Brief Description of Drawings

A better understanding of the invention can be ha by reference to the following Detailed Description in con junction with the accompanying Drawings, wherein:

FIGURE 1 is a sectional view of the differentia incorporating a first embodiment of the invention;

FIGURE 2 is an enlarged sectional view taken alon lines 2-2 of FIGURE 1 in the direction of the arrows;

FIGURES 3 and 4 are enlarged sectional views taken along lines 3-3 and 4-4, respectively, of FIGURE 1 in the direction of the arrows;

FIGURES 5a, 5b and 5c are enlarged illustrations of the control valve;

FIGURE 6 is a sectional view of the differential incorporating a second embodiment of the invention;

FIGURE 7 is an enlarged sectional view taken along lines 7-7 of FIGURE 6 in the direction of the arrows;

FIGURES 8 and 9 are enlarged sectional views taken along lines 8-8 and 9-9, respectively, of FIGURE 7 in the direction of the arrows; and

FIGURE 10 is an enlarged illustration of the control valve.

Detailed Description

Referring now to the Drawings wherein like refer¬ ence numerals designate like or corresponding elements throughout the views, and particularly referring to FIGURE 1, there is shown a hydraulic-controlled differential 10 incor¬ porating a first embodiment of the invention. As will be explained more fully hereinafter, the differential 10 uti¬ lizes a gear arrangement for dividing power between the axles and compensating for differential rotation therebetween, together with a hydraulic flow control arrangement to control the maximum differentiation between the axles and thus improve controllability and safety.

The differential 10 includes a case 12 which is of split, symmetrical construction interconnected by a surround¬ ing circle of transversely extending bolts 14. The case 12 is supported for rotation about a generally transverse axis 16 between a pair of bearings 18 which in turn are mounted in a pair of corresponding arms 20 of a bearing carrier (not shown) . Retaining rings 22 secure bearings 18 and the dif¬ ferential case 12 in place between the bearing carrier arms 20. The bearing carrier and case 12 are enclosed by a hous¬ ing 26 which has been shown schematically for purposes of clarity.

Means are provided for driving the differential case 12. As illustrated, a circular crown or ring gear 32 surrounds case 12 and is secured thereto for rotation by means of suitable fasteners, such as bolts 34, only one of which is shown. A pinion gear 36, which is secured to the end of an input shaft 38, such as by means of a key and keyway as shown, is meshed with the ring gear 32 for driving the case 12 about axis 16. The input shaft 38 in turn is

driven by an engine or motor via a transmission (not shown) Case 12 can also be driven by other means, such as by chain-and-sprocket arrangement, belt-and-pulley arrangement spur gears, or the like. The particular manner in which cas 12 is driven is not critical to practice of the invention.

The case 12 includes a pair of side sections 42 an a pair of end sections 44. An intermediate section 46 i provided between the side sections 42. Bolts 14, which ar preferably located at even circumferentially spaced-apar intervals, interconnect the sections 42, 44 and 46 of th case 12 as shown.

The side sections 42 and the intermediate sectio 46 of case 12 define a central chamber. A pair of bushin plates 48 and seals 50 are provided between the intermediat section 46 and side sections 42 for purposes of furthe defining a fluid-tight central chamber therebetween.

Referring to FIGURES 1 and 2, the central chambe of case 12 includes four control gears 52, 54, 56 and 5 arranged in generally rectangular relationship. Each contro gear is in direct meshed engagement with the adjacent tw gears so that each diagonal pair of gears rotates in the sam direction but opposite to that of the other diagonal pair o gears. The gears 52, 54, 56 and 58 are secured to shafts 60 62, 64 and 66, respectively. Each of the shafts 60, 62, 6 and 66 is in turn rotatably supported between the side sec tions 42 of case 12. For example, bushings 68 and 70 an seals 72, 74, 76 and 78 are provided between the side member 42 and shaft 60. Similar arrangements of bushings and seal are provided between the side member 42 and each of the othe shafts 62, 64 and 66. It will thus be appreciated that th control gears 52, 54, 56 and 58 are individually secured t

shafts 60, 62, 64 and 66, which are supported for rotation between the side members 42 of case 12, which is rotatable between the carrier arms 20.

The control gears 52, 54, 56 and 58, together with the adjacent walls of the central chamber of case 12, func¬ tion as a gear pump.

Referring to FIGURE 1 in conjunction with FIGURES 3 and 4, the side sections 42 and end sections 44 define a pair of side chambers located at opposite ends of the case 12. A rotatable cup-like member 80 extends into each side chamber. Each member 80 includes an inside end within the side chamber and an outside end extending out from that chamber. In par¬ ticular, each member 80 includes a reduced outside end which is journalled for rotation within the associated end section 44 of the case 12. A bushing 82 and seal 84 are provided between the reduced end of each member 80 and the associated end section 44, which is connected to an output shaft 86. As illustrated, the output shafts 86 and members 80 are secured together by splines, however, any suitable type of intercon¬ nection can be utilized. The ends of members 80, which would typically be formed by machining, are closed by plugs 87, welded or otherwise suitably secured in place to prevent oil leakage.

The inside ends of members 80 are drivingly con¬ nected to the control gears 52, 54, 56 and 58 by a shaft and gear drive arrangement. In particular, the inside end of each member 80 defines an internal gear 88. Shafts 60 and 62 extend into the right side chamber shown in FIGURE 1. A gear 90 is secured to the outer end of shaft 60 by means of splines and a retaining ring 92. Similarly, a gear 94 is secured to the outer end of shaft 62 by means of a spline

connection and a retaining ring 96. The drive gears 92 an 94 are not engaged directly with each other, but are bot meshed with the internal gear 88 of the associated member 8 for rotation in the same direction. In similar fashion, th outer ends of the other diagonal pair of shafts 64 and 6 extend into the opposite side chamber. Gear 98 is secure for rotation on the end of shaft 64 by means of splines and retaining ring 100. Gear 102 is secured for rotation on th end of shaft 66 by means of splines and another retainin ring 104. Gears 98 and 102 are not engaged directly wit each other, but are both meshed with the internal gear 88 o the member 80 in the left side chamber of case 12.

Openings 105 are preferably provided in members 8 to facilitate fluid flow within the side chambers.

It will thus be appreciated that the output shaft 86 are positively interconnected with the input shaft 38 by gear arrangement that effects equal or differential drive i the same direction. Normally, when the vehicle is travelin straight ahead, case 12 rotates carrying control gears 52 54, 56 and 58 and drive gears 90, 94, 98 and 102 therei without relative rotation between the gears. The advantage of the invention are particularly evident during differentia drive.

The central and side chambers within case 12 are interconnected for fluid communication at controlled rates of fluid flow which limit the amount of differentiation betwee output shafts 86 so that uncontrolled differentiation cannot occur. Each side section 42 and plate 48 includes a central bore defining a passageway 106 extending between the corre¬ sponding side chamber and a portion of the central chamber inside control gears 52, 54, 56 and 58 as is best seen in

FIGURES 1 and 2. Passageways 106 primarily serve to provide for hydraulic fluid level and pressure equalization between the chambers when there is no differentiation between output shafts 86, but also serve as either supply or return lines between the side chambers and the central chamber during differentiation.

If desired, diagonal holes off passageway 106 can be provided as shown for lubrication of shafts 60, 62, 64 and 66.

In addition to central passageway 106, offset bores 108 are also provided between the central and side chambers. Each corresponding pair of offset bores 108 in sections 42 and bushing plates 48 are joined to a radial cross bore 110 in section 46 that opens onto the central chamber at the out¬ side points of gear intermesh as is best shown in FIGURE 2. Four offset bores 108 are thus provided in each side section 42, and four corresponding radial cross bores 110 are pro¬ vided in the intermediate section 46 of case 12. Closure plugs 112, which are preferably magnetic to pick up any loose metal particles in the hydraulic fluid within case 12, are located in the outside ends of cross bores 110.

Each offset bore 108 includes a control valve 113 comprising a slideable valve member 114 which is normally biased by a compression spring 116 to a closed or "minimum open" position against flow out of the respective side cham¬ ber, as shown in FIGURE 1. The valve members 114, however, include a central bypass hole 118, as is best seen in FIGURE 5, which is sized and dimensioned to permit a predetermined minimum flow rate from the central chamber to the side cham¬ bers when the associated pair of control gears rotate in a direction to discharge fluid and thus increase pressure in

- li¬

the corresponding cross bore 110. Since each cross bore 11 is fluidly connected to two control valves 113, and sinc adjacent control gears rotate in opposite directions, it wil be appreciated that two of the cross bores are under pressur while the other two are under suction during differentiation A bushing 120 and seal 122 are provided between each contro valve 113 and the associated side section 42 and bushin plate 48. The exterior of each valve member 114 is prefer ably fluted as is best seen in FIGURE 5, to provide increase flow area when the valve moves to the open or "maximum open position against spring 116 in response to suction in th associated cross bore 110.

Upon differentiation, it will thus be apparent tha hydraulic fluid is supplied and returned via cross bores 11 between the central chamber and the side chambers at differ ent flow rates controlled by valves 113 to provide modulatio so that uncontrolled differentiation cannot occur. A rela tively larger cross-sectional flow area for suction is desir able to assure that control gears 52, 54, 56 and 58 have a adequate supply of fluid in the central chamber. The rati between the cross section flow areas of valve 113 in th minimum and maximum open positions can be about 1:5 o higher, perhaps up to 1:10, depending upon how quickly lock up is desired.

The hydraulic differential 10 functions in an ad vantageous manner when the vehicle is rounding a curve, applying differential drive to the output shafts 86 in a hy draulically controlled and modulated manner as necessary. However, the advantages of the invention are particularl evident when one of the output shafts is experiencing little or no traction, such as under slippery conditions or when the

vehicle starts to spin out of control. Free full intake of oil but controlled discharge from the central chamber causes the momemtum lock-up of the control gears. Lock-up only releases when pump action stops. Non-slip or limited non- slip differentials have been available heretofore, however, the differential 10 herein also limits differentiation be¬ tween axles by controlling the flow rate between the central and side chambers within case 12. The control gears 52, 54, 56 and 58 within the central chamber operate in effect like a gear pump whose rate of displacement is limited by control valves 113 so as to limit the maximum amount of possible dif¬ ferentiation between the output shafts 86.

A fill opening 124, surrounding cover 126, and removable plug 128 are also provided on case 12 to facilitate filling with hydraulic fluid.

FIGURES 6-10 illustrate a hydraulic-controlled dif¬ ferential 150 incorporating a second embodiment of the inven¬ tion. The differential 150 incorporates numerous component parts which are substantially identical in construction to corresponding components of the differential 10. Such parts have been identified with the same reference numerals as those utilized in conjunction with the differential 10, but have been differentiated therefrom by means of prime ( ' ) notations.

The differential 150 is primarily adapted for lighter-duty applications than the differential 10. In con¬ trast to differential 10, which incorporates four control gears in the central chamber with two drive gears in each side chamber, the differential 150 utilizes two control gears 152 and 154. The intermediate case section 46* is shaped accordingly to define a gear pump with two control gears 152

and 154. The control gear 152 is secured to a shaft 15 extending into one side chamber. A drive gear 158 is secure to the end of shaft 156 in meshed engagement with the inter nal gear 88' in the corresponding side chamber. Similarly the control gear 154 is mounted on a shaft 160 which extend into the opposite side chamber. Another drive gear 162 i secured to the end of shaft 160 in meshed engagement with th other internal gear 88* in the other corresponding side cham ber. As is best seen in FIGURE 7, two control valves 113 ar provided for communicating the side chamber and the centra chamber at opposite points of intermesh between control gear 152 and 154. The shafts 156 and 160 are bored to provid passageways 166 and 168 for pressure equalization between th side chambers. Other than these differences, the differen tial 150 is substantially similar in construction and func tion to the differential 10 described hereinbefore.

From the foregoing, it will thus be apparent tha the present invention comprises an improved differentia having numerous advantages over the prior art. The presen invention enables controlled application of power from the input shaft to the output shafts while controlling the rela¬ tive amount of differentiation between the output shafts to provide greater control and safety. Other advantages will be evident to those skilled in the art.

Although particular embodiments of the invention have been illustrated in the accompanying Drawings and de¬ scribed in the foregoing Detailed Description, it will be understood that the invention is not limited only to the embodiments disclosed, but is intended to embrace any alter¬ natives, equivalents, modifications and/or rearrangements of elements falling within the scope of the invention as defined by the following Claims.