CA1254061A - Differentials - Google Patents
DifferentialsInfo
- Publication number
- CA1254061A CA1254061A CA000486747A CA486747A CA1254061A CA 1254061 A CA1254061 A CA 1254061A CA 000486747 A CA000486747 A CA 000486747A CA 486747 A CA486747 A CA 486747A CA 1254061 A CA1254061 A CA 1254061A
- Authority
- CA
- Canada
- Prior art keywords
- worm
- carrier
- limited slip
- slip differential
- members
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Abstract
ABSTRACT
DIFFERENTIALS
A limited slip differential for driving two coaxial shafts (2,4) comprises a driving gear carrier (6) in which first and second worm members (10C) and (10A) are rotatably mounted on pins (11) parallel to the shafts (2) and (4). The worms (10A and 10C) are extended to form respective helical pinions (24C) and (24A) meshing respectively with helical sun gears (18) and (20) on the shafts (2) and (4). The worms (10A) and (10C) both mesh with a worm wheel (12) (mounted on a transverse pin (14) in the carrier (6) ) on opposite sides thereof and form a reversible worm drive therewith.
DIFFERENTIALS
A limited slip differential for driving two coaxial shafts (2,4) comprises a driving gear carrier (6) in which first and second worm members (10C) and (10A) are rotatably mounted on pins (11) parallel to the shafts (2) and (4). The worms (10A and 10C) are extended to form respective helical pinions (24C) and (24A) meshing respectively with helical sun gears (18) and (20) on the shafts (2) and (4). The worms (10A) and (10C) both mesh with a worm wheel (12) (mounted on a transverse pin (14) in the carrier (6) ) on opposite sides thereof and form a reversible worm drive therewith.
Description
1 27~91-1 This inve.ntion relates to llmited slip differentials for motor vehicles or use in a driving axle or between two driving axles.
Limited slip differentials incorporating reversible worm wheel drives are known, as described in United States Patent Specifications ~los. 2,559,gl6; 2,631,475; 2,859,641 and 4,191,071.
Such differentials are of ~he 'icross-axis planetaryl' type having co-a~ial output shafts each carrying a sun gear in the form of a worm wheel meshing with an associated worm or set of worms. The axis of each worm is thus transverse to and displaced radially from the axis of the sun g~ears. These differentials have spur pinions which increase the radial bulk of the differential and also the correct positioning of the kransverse worm assemblies presents manufacturing difficulties.
In GB-A-124 563 there is disclosed a differential gear assembly which does not specify worms and worm wheels and in which a double pair of differential gear wheels for meshing with a set o~ locking gears so as to form a continuous chain of gears around the driving axle. The double pair of dif~erential gear wheels secure a balanced thrus~ on themselves and balance the radial thrust loads on the entire mechanisms.
However, in the present invention each oi a first pair of diametrically opposed pinions is individually coupled to a single one of a second and similar pair of diametrically opposed pinions by means of an idler worm wheel so that two distinct parallel gear trains are formed between output sun gears. Thus, part of the torque difference between two output gears is provided hy the thrust loads present in the assembly which therefore are lE~ " ,~,,t .; ~
la 27891-1 thus used to induce a part of the locking ac~ion of ~he differen~ial.
GB-A-512 770 discloses a differential gear mechanism which does not have a con~inuous helical formation for both the pinion portion and the worm portion of a worm member as in the differential gear mechanism of the present invention. Indeed the equivalent geariny part of the mechanism shown and described in GB-A-512 770 provides separate helical gears of op~osite hand which interconnect the output shaft and sun gears and moresver ~he helix angle of the worm and wheel gears do not permit the worm and wheel action to be reverslble as in the present invention.
Accordlng to the invention, there is provided a limited slip differential for a vehicle comprising: a year carrier mountable for rotation about an axis of the carrier; a pair of dlametrically opposed first worm members mounted for rotatlon relative to the carrier with their axes parallel to the carrier axis and a similar pair of diametrically opposed second worm members mounted ~or rotation relative to the carrier with their axes parallel to the carrier axis; a first sun gear wheel coaxial with the carrier axis and meshing with the first worm members, a second sun gear wheel coaxial with the carrier and meshing with the second worm members, each worm member comprising a worm portion having a helical thread which meshes with an idler worm wheel and having a continuous tooth form extension forming a helical pinion portion meshing with a respective one of the first and second sun gear wheels, wherein the helix angle of the worm portions of each worm member and the worm wheels is such that the worm drive is reversible and wherein each of the first worm lb 27891-1 members is individually coupled tv a single one o the second worm members by a respective one of the idler wor~ wheels.
Aeeording to a feature of the invention, the idler worm wheels may be rota$ably mounted on a common transverse pin with a spacer bloek therebetween.
'~B
Limited slip differentials incorporating reversible worm wheel drives are known, as described in United States Patent Specifications ~los. 2,559,gl6; 2,631,475; 2,859,641 and 4,191,071.
Such differentials are of ~he 'icross-axis planetaryl' type having co-a~ial output shafts each carrying a sun gear in the form of a worm wheel meshing with an associated worm or set of worms. The axis of each worm is thus transverse to and displaced radially from the axis of the sun g~ears. These differentials have spur pinions which increase the radial bulk of the differential and also the correct positioning of the kransverse worm assemblies presents manufacturing difficulties.
In GB-A-124 563 there is disclosed a differential gear assembly which does not specify worms and worm wheels and in which a double pair of differential gear wheels for meshing with a set o~ locking gears so as to form a continuous chain of gears around the driving axle. The double pair of dif~erential gear wheels secure a balanced thrus~ on themselves and balance the radial thrust loads on the entire mechanisms.
However, in the present invention each oi a first pair of diametrically opposed pinions is individually coupled to a single one of a second and similar pair of diametrically opposed pinions by means of an idler worm wheel so that two distinct parallel gear trains are formed between output sun gears. Thus, part of the torque difference between two output gears is provided hy the thrust loads present in the assembly which therefore are lE~ " ,~,,t .; ~
la 27891-1 thus used to induce a part of the locking ac~ion of ~he differen~ial.
GB-A-512 770 discloses a differential gear mechanism which does not have a con~inuous helical formation for both the pinion portion and the worm portion of a worm member as in the differential gear mechanism of the present invention. Indeed the equivalent geariny part of the mechanism shown and described in GB-A-512 770 provides separate helical gears of op~osite hand which interconnect the output shaft and sun gears and moresver ~he helix angle of the worm and wheel gears do not permit the worm and wheel action to be reverslble as in the present invention.
Accordlng to the invention, there is provided a limited slip differential for a vehicle comprising: a year carrier mountable for rotation about an axis of the carrier; a pair of dlametrically opposed first worm members mounted for rotatlon relative to the carrier with their axes parallel to the carrier axis and a similar pair of diametrically opposed second worm members mounted ~or rotation relative to the carrier with their axes parallel to the carrier axis; a first sun gear wheel coaxial with the carrier axis and meshing with the first worm members, a second sun gear wheel coaxial with the carrier and meshing with the second worm members, each worm member comprising a worm portion having a helical thread which meshes with an idler worm wheel and having a continuous tooth form extension forming a helical pinion portion meshing with a respective one of the first and second sun gear wheels, wherein the helix angle of the worm portions of each worm member and the worm wheels is such that the worm drive is reversible and wherein each of the first worm lb 27891-1 members is individually coupled tv a single one o the second worm members by a respective one of the idler wor~ wheels.
Aeeording to a feature of the invention, the idler worm wheels may be rota$ably mounted on a common transverse pin with a spacer bloek therebetween.
'~B
- 2 - 27891-1 -An embodlment of the invention will now be de6cribed, by way of example, with reference to the accompanylng drawlngs, ln which:
Flgure 1 16 8 chordal 6ectlonal view of a dlfferential accordlng to the invention on ~he line I-I of Figure 2;
Figure 2 16 a cross 6ectional view along the line~ II of F~gure
Flgure 1 16 8 chordal 6ectlonal view of a dlfferential accordlng to the invention on ~he line I-I of Figure 2;
Figure 2 16 a cross 6ectional view along the line~ II of F~gure
3; and Flgure 3 i5 a a~ial ~ectlonal view along the line III-III of Flgure 2.
The differential shown in ~he drawings transmits drlve fro~
transfer gearlng (not shown) to half-6hafts 2 and h of a driven axle, for example of a motor car.
The dlfferential has a gear carrier 6 formed by a bell-6haped hou6ing 7 and a cover member 8 having a flange 8A and a hub portion 9 snugly engaged in the mouth of the housing 7. The flange6 8A may be formed with a rlng of gear teeth or, as ~hown here, wlth a ring of holcs 8B for bolts securing a bevel crown wheel or a transfer gear (not shown). The houslng 7 and cover Member 8 are gecured together by suitable bolts or screw6 (not shown) to form the gear carrier 6.
Four worm members 10~-lOD are rotatably mounted on hollow pin6 11 6upported in the gear carrier 6 at each of their ends. The worm members 10 and their plns 11 are parallel and equally spaced from the axis of the shafts ~ and 4. Each pin 11 is formed with a 6eating llA for a grub screw llB. Two of the worm members, lOA and loc, mesh with a worm wheel 12 at diametrlcally oppo6ed po61tion6.
The wor~ wheel 12 is located between the worm members lOA and lOC
and is rotatably fiupported on a hollow support pin 14 mounted ln the housing 7. The other two worm members, loB and lOD, mesh with a further worm wheel 16 located between them, and also mounted on the 6upport pin 14 but spaced alon~ the support pln 14 by means of a spacer block 17. The pin 14 has a seating 14A for a securlng grub screw lS ln the spacer block 17.
The worm wheels 12 and 16, the spacer block 17 and the ~upport pln 14 are aligned on an axis YY whlch intersects the axls XX at right angles.
Half-shaft sun-gear6 18 and 20 are re6pectlvely 6plined to (or formed lntegrally with) the inner ends of the hal~-shafts 2 and 4 and are aligned on the axis XX. Each half-shaft sun gear is within the gear carrier 6 and meshes wlth an extension one of the worm members of each pair of worm members meshing with a respective worm whe~l. Thus, the half-shaft sun gear 18 meshes with worm members lOB and lOC which mesh respectlvely with worm wheels 16 and 12. The half-shaft sun gear 20 meshes with worm members lOA and lQD which mesh respectively with worm wheels 12 and 16.
Each worm member thus has a worm portion 22, having a h~lical thread and meshing with a worm wheel, and an extension forming a pinion portion 24 meshing with a half-shaft sun gear. The heli~
angle of the worm portions 22 and worm wheels 12 and 16 is such that the worm drive is reversible tin this case 43.1 to the axisJ for the worms) i.e~ operates bi-directionally. In this embodiment the half-shaft sun gears 18 and 20 and the pinion portions 24 of the worm members are helical, the pinion portion 24 being formed by continuations of the worm formation of the worm portions 22.
Each worm member also has a reduced-diameter untoothed portion 25 ad~oining the worm portion to avoid engagement with the other half-shaft sun gear.
In operation, when the vehicle is travelling straight ahead with the road wheels turning at the same speed the gear carrier 6 is rotated about the axis XX. The rotary motion is transmitted to the half-shafts 2 and 4. The half-shafts, the gear carrier 6 and the gearing within the gear carrier rotate as a unit. There is no movement of the worms 10 or worm wheels 12, 16 about their axes.
When the vehicle corners, one half-shaft must rotate faster than the gear carrier 6 and the other half-shaft slower than the gear carrlerO If the half-shaft 2 rotates faster than the gear carrier 6 it, through the half-shaft sun gear 18, causes the worms lOB and loc to rotate about their axes in the gear carrier 6. The worms lOB and lOC in turn cause the worm wheels 16 and 12 to turn zbout the support pin 14. Because the worm drive ls reversible, the worm wheels 16 and 12 cause the worms lOB and lOA to rotate in the opposite sense to worms lOB and lOC. Although the worm drive is reversible, drive ls not transmitted with 100% efficiency from the worm wheels to the worm members. In this embodiment the efficiency
The differential shown in ~he drawings transmits drlve fro~
transfer gearlng (not shown) to half-6hafts 2 and h of a driven axle, for example of a motor car.
The dlfferential has a gear carrier 6 formed by a bell-6haped hou6ing 7 and a cover member 8 having a flange 8A and a hub portion 9 snugly engaged in the mouth of the housing 7. The flange6 8A may be formed with a rlng of gear teeth or, as ~hown here, wlth a ring of holcs 8B for bolts securing a bevel crown wheel or a transfer gear (not shown). The houslng 7 and cover Member 8 are gecured together by suitable bolts or screw6 (not shown) to form the gear carrier 6.
Four worm members 10~-lOD are rotatably mounted on hollow pin6 11 6upported in the gear carrier 6 at each of their ends. The worm members 10 and their plns 11 are parallel and equally spaced from the axis of the shafts ~ and 4. Each pin 11 is formed with a 6eating llA for a grub screw llB. Two of the worm members, lOA and loc, mesh with a worm wheel 12 at diametrlcally oppo6ed po61tion6.
The wor~ wheel 12 is located between the worm members lOA and lOC
and is rotatably fiupported on a hollow support pin 14 mounted ln the housing 7. The other two worm members, loB and lOD, mesh with a further worm wheel 16 located between them, and also mounted on the 6upport pin 14 but spaced alon~ the support pln 14 by means of a spacer block 17. The pin 14 has a seating 14A for a securlng grub screw lS ln the spacer block 17.
The worm wheels 12 and 16, the spacer block 17 and the ~upport pln 14 are aligned on an axis YY whlch intersects the axls XX at right angles.
Half-shaft sun-gear6 18 and 20 are re6pectlvely 6plined to (or formed lntegrally with) the inner ends of the hal~-shafts 2 and 4 and are aligned on the axis XX. Each half-shaft sun gear is within the gear carrier 6 and meshes wlth an extension one of the worm members of each pair of worm members meshing with a respective worm whe~l. Thus, the half-shaft sun gear 18 meshes with worm members lOB and lOC which mesh respectlvely with worm wheels 16 and 12. The half-shaft sun gear 20 meshes with worm members lOA and lQD which mesh respectively with worm wheels 12 and 16.
Each worm member thus has a worm portion 22, having a h~lical thread and meshing with a worm wheel, and an extension forming a pinion portion 24 meshing with a half-shaft sun gear. The heli~
angle of the worm portions 22 and worm wheels 12 and 16 is such that the worm drive is reversible tin this case 43.1 to the axisJ for the worms) i.e~ operates bi-directionally. In this embodiment the half-shaft sun gears 18 and 20 and the pinion portions 24 of the worm members are helical, the pinion portion 24 being formed by continuations of the worm formation of the worm portions 22.
Each worm member also has a reduced-diameter untoothed portion 25 ad~oining the worm portion to avoid engagement with the other half-shaft sun gear.
In operation, when the vehicle is travelling straight ahead with the road wheels turning at the same speed the gear carrier 6 is rotated about the axis XX. The rotary motion is transmitted to the half-shafts 2 and 4. The half-shafts, the gear carrier 6 and the gearing within the gear carrier rotate as a unit. There is no movement of the worms 10 or worm wheels 12, 16 about their axes.
When the vehicle corners, one half-shaft must rotate faster than the gear carrier 6 and the other half-shaft slower than the gear carrlerO If the half-shaft 2 rotates faster than the gear carrier 6 it, through the half-shaft sun gear 18, causes the worms lOB and loc to rotate about their axes in the gear carrier 6. The worms lOB and lOC in turn cause the worm wheels 16 and 12 to turn zbout the support pin 14. Because the worm drive ls reversible, the worm wheels 16 and 12 cause the worms lOB and lOA to rotate in the opposite sense to worms lOB and lOC. Although the worm drive is reversible, drive ls not transmitted with 100% efficiency from the worm wheels to the worm members. In this embodiment the efficiency
4 27891-1 is about 70%. As a result, there is frictional resistance to operation of the device and it functions as a limiked slip differential. The rotation of the worm members lODZ and lOA
causes the sun gear 20 and -~he half-shaft 4 turn backwards relative to the carrier 6.
The steel worm members, worm wheels and spacer block must be robust and wear resistant and in this embodiment the worm wheels (and advantageously the worms and the spacer block especially where engine oil is the only available lubricant) can be case hardened and then receive anti-scuffing treatment such as 'No Scuff' available from British i!eat Treatments Limited of Lowestoft.
The housing 7 is formed wlth large openings 26 both to reduce mass and to assist the circulation of lubricating oil.
Preferably, the lubricating oil ~s hypoid gear oil. Lubrication is ensured by oil passages L drilled in the various components.
The limited slip differential descri~ed above may be used ~o transmit drive to two fur~her 6uch differentials in the two driving axl.es (e.g~ front and rear) of a four-wheel drive vehicle.
In a modification (not shown in the drawings), the grub screws llB and seatings llA are omitted and the untoothed portions 25 of the worms are replaced by flanges of corresponding diameter and axial length on the pins to provide axial location of the latter while allowing them to rotate.
causes the sun gear 20 and -~he half-shaft 4 turn backwards relative to the carrier 6.
The steel worm members, worm wheels and spacer block must be robust and wear resistant and in this embodiment the worm wheels (and advantageously the worms and the spacer block especially where engine oil is the only available lubricant) can be case hardened and then receive anti-scuffing treatment such as 'No Scuff' available from British i!eat Treatments Limited of Lowestoft.
The housing 7 is formed wlth large openings 26 both to reduce mass and to assist the circulation of lubricating oil.
Preferably, the lubricating oil ~s hypoid gear oil. Lubrication is ensured by oil passages L drilled in the various components.
The limited slip differential descri~ed above may be used ~o transmit drive to two fur~her 6uch differentials in the two driving axl.es (e.g~ front and rear) of a four-wheel drive vehicle.
In a modification (not shown in the drawings), the grub screws llB and seatings llA are omitted and the untoothed portions 25 of the worms are replaced by flanges of corresponding diameter and axial length on the pins to provide axial location of the latter while allowing them to rotate.
5 . 2789~-1 If desired, further friction in the differential can be generated by axially biassing the worm members, for example by means of Belleville washers located on the pins between the worms and either the casiny or the pin flanges (if used).
B
B
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A limited slip differential for a vehicle comprising: a gear carrier mountable for rotation about an axis of the carrier;
a pair of diametrically opposed first worm members mounted for rotation relative to the carrier with their axes parallel to the carrier axis and a similar pair of diametrically opposed second worm members mounted for rotation relative to the carrier with their axes parallel to the carrier axis;
a first sun gear wheel coaxial with the carrier axis and meshing with said first worm members, a second sun gear wheel coaxial with the carrier and meshing with said second worm members, each worm member comprising a worm portion having a helical thread which meshes with an idler worm wheel and having a continuous tooth form extension forming a helical pinion portion meshing with a respective one of said first and second sun gear wheels, wherein the helix angle of the worm portions of each worm member and said worm wheels is such that the worm drive is reversible and wherein each of said first worm members is individually coupled to a single one of said second worm members by a respective one of said idler worm wheels.
a pair of diametrically opposed first worm members mounted for rotation relative to the carrier with their axes parallel to the carrier axis and a similar pair of diametrically opposed second worm members mounted for rotation relative to the carrier with their axes parallel to the carrier axis;
a first sun gear wheel coaxial with the carrier axis and meshing with said first worm members, a second sun gear wheel coaxial with the carrier and meshing with said second worm members, each worm member comprising a worm portion having a helical thread which meshes with an idler worm wheel and having a continuous tooth form extension forming a helical pinion portion meshing with a respective one of said first and second sun gear wheels, wherein the helix angle of the worm portions of each worm member and said worm wheels is such that the worm drive is reversible and wherein each of said first worm members is individually coupled to a single one of said second worm members by a respective one of said idler worm wheels.
2. A limited slip differential according to claim 1, further characterised in that said idler worm wheels are rotatably mounted on a common transverse pin with a spacer block therebetween.
3. A limited slip differential according to claim 1 or 2 characterised in that the helix angle of the helical formations of the worms is substantially 43.10.
4. A limited slip differential according to claim 1 characterised in that there are two idler worm wheels, said worm wheels being mounted for rotation in said casing about a common transverse axis.
5. A limited slip differential according to claim 4 characterised in that said idler worm wheels are rotatably mounted on a common transverse pin with a spacer block therebetween.
6. A limited slip differential according to claim 1 further including means for generating additional friction in the differential.
7. A limited slip differential according to claim 6 comprising means for axially biassing the worm members.
8. A limited slip differential according to claim 6 comprising means for axially biassing at least one of the sun gears and/or the worm wheels.
9. A limited slip differential according to claims 7 or 8 wherein the axial biassing means comprises Belleville washers.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000486747A CA1254061A (en) | 1985-07-12 | 1985-07-12 | Differentials |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000486747A CA1254061A (en) | 1985-07-12 | 1985-07-12 | Differentials |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1254061A true CA1254061A (en) | 1989-05-16 |
Family
ID=4130975
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000486747A Expired CA1254061A (en) | 1985-07-12 | 1985-07-12 | Differentials |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1254061A (en) |
-
1985
- 1985-07-12 CA CA000486747A patent/CA1254061A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |