WO2009048787A1

WO2009048787A1 - Dual clutch split path power shift transmission

Info

Publication number: WO2009048787A1
Application number: PCT/US2008/078586
Authority: WO
Inventors: Richard Mizon
Original assignee: Magna Powertrain Usa, Inc.
Priority date: 2007-10-09
Filing date: 2008-10-02
Publication date: 2009-04-16

Abstract

A transmission includes an input shaft, an output shaft and a reduction unit operable to provide first and second drive ratios. The reduction unit is driven by the input shaft. A differential is simultaneously driven by the input shaft and an output shaft from the reduction unit. The output shaft of the transmission is driven by the differential.

Description

DUAL CLUTCH SPLIT PATH POWER SHIFT TRANSMISSION

FIELD

[0001] The present disclosure relates to an automatic transmission for a motor vehicle. More particularly, a dual clutch, split path, power shift transmission is discussed.

BACKGROUND [0002] A variety of automatic transmissions have been designed to transfer power from an engine to a vehicle drive line in an attempt to operate a vehicle's engine within a desired operating speed while propelling the vehicle through a relatively wide range of ground speeds. Some of the known automatic transmissions may be characterized as power shift transmissions where the flow of power from the engine to the drive line is not interrupted during automatic transmission shifting between various gear ratios.

[0003] At least one of the power shift transmissions includes a dual clutch coupled to an output shaft of the engine. A first input shaft is driven by a first clutch of the dual clutch, while a second input shaft is driven by a second clutch of the dual clutch. Based on the arrangement of input shafts, speed gears and clutch components, odd numbered speed gears such as first, third and fifth gears are connected to the first input shaft while the second input shaft is connected to the even numbered speed gears. Power travels from the engine through one of the clutches of the dual clutch, one of the first and second input shafts and through the appropriate speed gears to an output shaft of the transmission. Shifting between even and odd numbered gear ratios occurs by concurrently activating one clutch and deactivating the other clutch of the dual clutch. While this arrangement has functioned in the past, the number of gear ratios and the spacing therebetween may be limited by the speed gear arrangement previously described. SUMMARY

[0004] A transmission includes an input shaft, an output shaft and a reduction unit operable to provide first and second drive ratios. The reduction unit is driven by the input shaft. A differential is simultaneously driven by the input shaft and an output shaft from the reduction unit. The output shaft of the transmission is driven by the differential.

[0005] Furthermore, a transmission includes an input shaft, an output shaft and a dual clutch driven by the input shaft. The dual clutch has a first clutch concentrically positioned in relation to a second clutch. The first clutch is operable to couple the input shaft to a first parallel shaft. The second clutch is operable to couple the input shaft to a second parallel shaft. First, third and fifth speed gear sets are selectively driven by the first parallel shaft. Second, fourth and sixth speed gear sets are selectively driven by the second parallel shaft. A differential gear set is driven by the input shaft and one of the speed gear sets.

The differential gear set drives the output shaft of the transmission.

[0006] Furthermore, a transmission includes an input shaft, an output shaft and a reduction unit operable to provide first and second drive ratios. A differential is driven by the input shaft and simultaneously drives the reduction unit and the transmission output shaft.

[0007] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DRAWINGS

[0008] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

[0009] Figure 1 is a schematic depicting an input controlled variable ratio transmission;

[0010] Figure 2 is a schematic depicting an output controlled variable ratio transmission;

[0011] Figure 3 is a schematic depicting an input controlled dual clutch single planetary power shift transmission; [0012] Figure 4 is a schematic depicting a power flow for a first drive ratio of the transmission depicted in Figure 3; [0013] Figure 5 is a schematic depicting a power flow for a second drive ratio of the transmission depicted in Figure 3;

[0014] Figure 6 is a schematic depicting an output controlled dual clutch single planetary power shift transmission; [0015] Figure 7 is a schematic depicting a power flow during operation in a first drive ratio of the transmission depicted in Figure 6; and

[0016] Figure 8 is a schematic depicting a power flow during operation in a first drive ratio of the transmission depicted in Figure 6.

DETAILED DESCRIPTION

[0017] The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. [0018] Figure 1 is a schematic representing an input controlled variable ratio transmission 10 having a summing differential 12 driven by two different inputs. A thru-shaft 14 provides a first input. A variable ratio reduction unit 16 is driven by a parallel shaft 18. Both thru-shaft 14 and parallel shaft 18 are simultaneously driven by an input shaft 20. The output of reduction unit 16 provides the second input to summing differential 12. Summing differential 12 is driven by thru-shaft 14 and a reduction unit output shaft 22. Summing differential 12 combines the power flows from reduction unit output shaft 22 and thru-shaft 14 to provide power to an output shaft 24.

[0019] Summing differential 12 maybe constructed using bevel gears, simple planetary gear sets or compound planetary gear sets. The output characteristics of transmission 10 may be calculated to determine gear ratios useful for vehicle power transfer.

Ratio Calculation [0020] The general speed equation for summing differential 12 is: ω, -R,,.ω, +(R, -l).ω, = 0 1.1 where ω₀ is the angular velocity of output shaft 24; ω, is the angular velocity of input shaft 20; ω_ris the angular velocity of reduction unit output shaft 22; and

R_d is the gear ratio summing of differential 12:

Where R_t =—^L- with the reaction member held stationary. C0_o The general speed equation for variable ratio reduction unit 16 is:

Cb₁ = /?, .ω, 1.2 where R_v is the gear ratio of reduction unit 16.

Let an overall ratio R =— therefore ω_o

R =_^ 1.3

^'' (R_j +R_j -I) or

R J*--™- 1.4

Torque Calculation

[0021] Torque is transferred by thru-shaft 14 and reduction unit output shaft 22 as inputs to summing differential 12. The torque transferred by the various transmission elements may be calculated by noting that to obtain equilibrium of summing differential 12, the sum of the element torques must equal zero.

T₁ +T₁ +T,=0 1.5 where T_x is the torque transferred by thru-shaft 14; T_r represents the torque transferred by reduction unit output shaft 22; and

T₀ is the torque transferred by output shaft 24.

[0022] Furthermore, if frictional losses are neglected, the work into the summing differential 12 equals the work out.

T xo +T₁Xo₁ +T_nxo_n =0 1.6 In the case where T_r.ω_r= 0 and using the equation 1.1 yields:

T^-R₁₁J_x 1.7

From equation 1.5

and

_{T =} W ⁺«< -™* _{T ! 9}

R₁ -K where T₁ is the torque transferred by input shaft 20. [0023] The percentage of power transferred through the reduction unit may also be calculated. Power Split Calculation

[0024] Power through reduction unit 16 and reduction unit output shaft 22 equals ω_r. T_r. Total power out from transmission 10 equals ω₀. T₀. A percentage of power being transferred through reduction unit output shaft 22 maybe calculated as:

*P, - '*^• - '> 1.10

(R₁ + R₁₁ - 1)

[0025] Figure 2 depicts an output controlled variable ratio transmission

40. Transmission 40 is similar to transmission 10 in that power is transmitted through two paths. Furthermore, each transmission 10, 40 includes summing differential 12 and reduction unit 16. Other elements may be substantially similar and will retain their previously introduced referenced numerals.

[0026] Input shaft 20 provides power to summing differential 12. A first differential output shaft 42 provides input power to reduction unit 16. A reduction unit output shaft 44 is drivingly coupled to a transmission output shaft 46. It should be appreciated that the torque provided to transmission output shaft 46 includes not only torque provided by reduction unit output shaft 44 but also torque provided by a second differential output shaft 48.

[0027] When analyzing transmission 40, ratio, torque and power split calculations may be made similar to those described in relation to input controlled variable ratio transmission 10. Ratio Calculation

[0028] For example, the general speed equation for reduction unit 16 of transmission 40 is:

Cu₁ = R, .ω, 2.1 Combining this equation with equation 1 .1 yields:

R_y = -(R_/ - I)₁R₁ + R ₁ 2.2 or

^ = <*' - *' > 2.3

⁽fl,, - D

Torque Calculation [0029] As previously discussed, if frictional losses are neglected, work into the summing differential 12 equals the work out.

T M₁ + T₁ .ω, + T₁.ω, = 0 2.4

In the case where T_r.ω_r = 0 in view of equation 1 .1 yields

T = -/?,, J, 2.5 From equation 1 .5

T₁ = (R, - DT₁ 2.6

Power Split Calculation

[0030] Power through reduction unit 16 and reduction unit output shaft 44 equals ω_r. T_r. Total power into transmission 40 equals ω,. T,. A percentage of power through geared reduction output shaft 44 is

₌ <«, - ".*, _{2 7}

R

[0031] The basic concepts previously described relating to the input controlled variable ratio transmission 10 and output controlled variable ratio transmission 40 may be applied to transmissions having a relatively large number of forward and reverse gear ratios making the transmissions suitable for application in a wide range of vehicular configurations including passenger cars, on highway tractors, off highway vehicles and construction equipment. An advantage of implementing the split path power transmission includes providing great flexibility in the choice of final drive ratios available during transmission use. For example, it is contemplated that a seven speed transmission suitable for application to a light truck would provide the following gear ratios:

Gear Ratio 5.63 pnd

Gear Ratio 3.68

3^rd Gear Ratio 2.41

₄,h Gear Ratio 1 .65

5^th Gear Ratio 1 .23

6^th Gear Ratio 0.98

7^th Gear Ratio 0.73

Reverse Ratio -5.63

Table 1

[0032] Figure 3 depicts a first transmission 100 providing seven forward speed gears and one reverse speed gear arranged as an input controlled dual clutch single planetary power shift transmission. Transmission 100 includes a twin clutch module 102, a headset module 104, a speed gear module 106 and a summing module 108. Transmission 100 includes an input shaft 1 10 supplying power to twin clutch module 102 as well as a thru-shaft 1 12. Input shaft 1 10 and thru-shaft 1 12 rotate at the same speed and may be integrally formed with one another. Thru-shaft 1 12 provides torque to summing module 108. Summing module 108 provides power to output shaft 1 14.

[0033] Twin clutch module 102 includes an outer clutch 1 16 and an inner clutch 1 18. Outer clutch 1 16 includes a drum 120 fixed for rotation with input shaft 1 10 and a hub 122 driving a first headset 124 of headset module 104. A plurality of outer clutch plates 126 are in splined engagement with drum 120. A plurality of inner clutch plates 128 are in splined engagement with hub 122. Outer plates 126 are interleaved with and driven into engagement with inner clutch plates 128 when outer clutch 1 16 is placed in an engaged mode to transfer torque from input shaft 1 10 to first headset 124.

[0034] Inner clutch 1 18 includes a drum 130 fixed for rotation with input shaft 1 10 and a hub 132 in driving engagement with a second headset 134 of headset module 104. A plurality of outer clutch plates 136 are in splined engagement with drum 130. A plurality of inner clutch plates 138 are positioned in splined engagement with hub 132. Outer clutch plates 136 are interleaved with inner clutch plates 138 such that when a compressive force is supplied to the clutch plates, inner clutch 1 18 may be placed in an engaged mode to transfer torque from input shaft 1 10 to second headset 134.

[0035] First headset 124 includes a drive gear 140 fixed for rotation with hub 122. Drive gear 140 is in meshed engagement with a driven gear 142 fixed for rotation with a first parallel shaft 144. Second headset 134 includes a drive gear 146 in meshed engagement with a driven gear 147. Driven gear 147 is fixed for rotation with a second parallel shaft 148.

[0036] As most clearly depicted in Figure 3, first parallel shaft 144 is associated with a first speed gear set 150, a third speed gear set 152, a fifth speed gear set 154 and a seventh speed gear set 156. First speed gear set 150 includes a first drive gear 158 rotatably supported on first parallel shaft 144 in meshed engagement with a common first and reverse driven gear 160. Common first and reverse driven gear 160 is fixed for rotation with a concentric shaft 162 co-axially aligned with and rotatably supported on thru-shaft 1 12.

[0037] Third speed gear set 152 includes a third drive gear 164 supported for rotation on first parallel shaft 144. A common second and third driven gear 166 is in meshed engagement with third drive gear 164 as well as fixed for rotation with concentric shaft 162. Fifth speed gear set 154 includes a fifth drive gear 168 rotatably supported on first parallel shaft 144. A common fourth and fifth driven gear 170 is in meshed engagement with fifth drive gear 168. Common fourth and fifth driven gear 170 is fixed for rotation with concentric shaft 162. Seventh speed gear set 156 includes a seventh drive gear 172 in meshed engagement with a common sixth and seventh driven gear 174. Common sixth and seventh driven gear 174 is fixed for rotation with concentric shaft 162.

[0038] In similar fashion, second parallel shaft 148 is selectively drivingly associated with a reverse speed gear set 180, a second speed gear set 182, a fourth speed gear set 184 and a sixth speed gear set 186. [0039] Reverse speed gear set 180 includes a reverse gear 188 rotatably supported on second parallel shaft 148. Reverse gear 188 is in meshed engagement with common first and reverse driven gear 160. Second speed gear set 182 includes a second drive gear 190 rotatably supported on second parallel shaft 148 and in meshed engagement with common second and third driven gear 166. Fourth speed gear set 184 includes a fourth drive gear 192 supported for rotation on second parallel shaft 148 and drivingly engaged with common fourth and fifth driven gear 170. Sixth speed gear set 186 includes a sixth drive gear 194 in meshed engagement with common sixth and seventh driven gear 174.

[0040] A first dog clutch 200 is selectively operable to drivingly interconnect first parallel shaft 144 with first speed gear set 150 or third speed gear set 152. First dog clutch 200 includes a hub 202 fixed for rotation with first parallel shaft 144 and an axially movable sleeve 204 in splined engagement with hub 202. Sleeve 204 may selectively drivingly engage a first set of teeth 206 formed on first drive gear 158 or a third set of teeth 208 formed on third drive gear 164. A second dog clutch 210 is operable to selectively drivingly interconnect second parallel shaft 148 with reverse gear set 180 or second speed gear set 182. In particular, second dog clutch 210 includes a hub 212 fixed for rotation with second parallel shaft 148 and a sleeve 214 splined for axial movement relative to hub 212. Sleeve 214 is selectively engageable with a reverse set of teeth 216 formed on reverse gear 188 or a second set of teeth 218 formed on second drive gear 190.

[0041] A third dog clutch 220 is operable to selectively drivingly interconnect second parallel shaft 148 with fourth speed gear set 184 or sixth speed gear set 186. Third dog clutch 220 includes a hub 222 fixed rotation with second parallel shaft 148 and a sleeve 224 drivingly engaged with hub 222. Sleeve 224 is selectively axially movable to engage a fourth set of teeth 226 formed on fourth drive gear 192 or a sixth set of teeth 228 formed on sixth drive gear 194.

[0042] A fourth dog clutch 230 is operable to selectively drivingly interconnect first parallel shaft 144 with fifth speed gear set 154 or seventh speed gear set 156. Fourth dog clutch 230 includes a hub 232 fixed for rotation with first parallel shaft 144. An axially movable sleeve 234 is in splined engagement with hub 232. Sleeve 234 may be selectively moved to drivingly engage a fifth set of teeth 236 formed on fifth drive gear 168 or a seventh set of teeth 238 formed on seventh drive gear 172.

[0043] Summing module 108 is depicted as a simple planetary gear set having a sun gear 250 fixed for rotation with concentric shaft 162. A ring gear 252 is fixed for rotation with output shaft 1 14. A plurality of planet gears 254 are supported for rotation on a carrier 256. Each of planet gears 254 are meshingly engaged with sun gear 250 and ring gear 252. Carrier 256 is fixed for rotation with thru-shaft 1 12. Table 2 and Table 3 contain potential ratio information that would provide the desired overall gear ratios previously presented.

Differential Ratio Rd = 0 85

Planetary Ratio Rp = 5. 67

Headset 1 Ratio RM = 1 .7

Headset 2 Ratio Rh2 = 1 .3

Table 2

Table 3

[0044] Figure 4 depicts a power flow through transmission 100 to provide the first forward gear ratio. Prior to providing torque in the first forward gear ratio, first dog clutch 200 may be actuated to pre-select first gear by axially translating sleeve 204 to engage first teeth 206 on first drive gear 1 58. At this time, first parallel shaft 144 is drivingly coupled to first speed gear set 150. Once the first speed gear has been pre-selected, outer clutch 1 16 is engaged to transfer torque from input shaft 1 10 to first headset 124 and launch the vehicle from rest. First headset 124 transfers torque to first parallel shaft 144 and first speed gear set 150 as previously described. Concentric shaft 162 is driven by first speed gear set 1 50 and provides drive torque to sun gear 250 of summing module 108. Concurrently, input shaft 1 10 provides drive torque to thru-shaft 1 12 to drive carrier 256 of summing module 108. The dual path input to summing module 108 causes ring gear 252 to rotate and drive output shaft 1 14. The first power path transferring torque from input shaft 1 10 to summing module 108 is depicted as a first line type. The second power path to summing module 108 is shown in another line type while the output from summing module 108 is identified with a third line type.

[0045] To shift from first gear to second gear, second dog clutch 210 is activated to pre-select second gear. More specifically, sleeve 214 is axially translated to engage second teeth 218 of second drive gear 190. At this time, second parallel shaft 148 is drivingly coupled to second speed gear set 182. The first gear to second gear shaft may be accomplished as a power shift without interrupting torque transfer from input shaft 1 10 to output shaft 1 14.

[0046] To accomplish the power shift, inner clutch 1 18 is engaged while outer clutch 1 16 is disengaged. Once the clutch-to-clutch shift has been completed, power is transferred as depicted in Figure 5 where input shaft 1 10 transfers power to inner clutch 1 18 and second headset 134. Second headset 134 transfers torque to second parallel shaft 148. Power continues to be transferred to second speed gear set 182 to drive concentric shaft 162. Concentric shaft 162 is fixed for rotation with sun gear 250 of summing module 108. During second gear, the parallel power input through the second path including thru-shaft 1 12 and carrier 256 continues to be provided. Based on the new relative rotational speeds of sun gear 250 and carrier 256, ring gear 252 rotates at a different rotational speed than when in first gear. Accordingly, output shaft 1 14 rotates at the new rotational speed.

[0047] Similar shifts may be accomplished between the gears associated with first parallel shaft 144 and the gears associated with second parallel shaft 148 throughout transmission usage. The first power path, the second power path and the output power path are once again indicated with different line types in Figure 5. It should be noted that the inner clutch 1 18 is used for launching the vehicle from rest in a reverse direction. [0048] Figure 6 depicts another transmission 300 providing seven forward speed gears and one reverse speed gear. The transmission 300 is arranged as an output controlled dual clutch single planetary power shift transmission. Transmission 300 is substantially similar to transmission 100. Accordingly, like elements will retain their previously introduced reference numerals. In particular, the arrangement of components of transmission 300 is substantially the same as the arrangement of components found in transmission 100. However, the direction of power flow has been reversed.

[0049] As such, summing module 108 is driven by an input shaft 302 while an output shaft 304 is driven by twin clutch module 102 and an output from summing module 108. The remaining components and the interconnections between the components are substantially similar if not identical to those previously described in relation to transmission 100 other than the relative positioning of individual speed gear sets in relation to summing module 108 and twin clutch module 102. As such, a repetitious description of each of these components will be avoided.

[0050] To provide a first gear forward drive ratio, first dog clutch 200 is translated to drivingly engage sleeve 204 with teeth 206 formed on first drive gear 158. To launch a vehicle equipped with transmission 300 from a resting conditioning, outer clutch 1 16 is engaged while inner clutch 1 18 remains disengaged. Figure 7 depicts the flow of power through transmission 300 operating in the first forward gear ratio. Input torque is provided to input shaft 302 from a source of power of the vehicle. Power is transferred to ring gear 252 of summing module 108. Power is transferred through the planetary gear set to carrier 256. Carrier 256 drives thru-shaft 1 12 which in turn is fixed for rotation with output shaft 304. The second power path providing an input to summing module 108 includes torque being transferred from thru-shaft 1 12 through outer clutch 1 16 to first headset 124. First headset 124 drives first parallel shaft 144 and first speed gear set 150. First speed gear set 150 drives concentric shaft 162 such that power is supplied to sun gear 250. Accordingly, power is input to summing module 108 via ring gear 252 along a first power path and via sun gear 250 along a second power path. Output provided by carrier 256 is determined based on the two inputs previously described.

[0051] Figure 8 depicts the power flow through transmission 300 when operating in the second forward gear ratio. To shift from first gear to second gear, second dog clutch 210 is operated to drivingly interconnect second parallel shaft 148 and second speed gear set 182. This is accomplished by axially translating sleeve 214 to engage teeth 218 of second drive gear 190. Next, outer clutch 1 16 is disengaged while inner clutch 1 18 is engaged. At this time, torque is transferred from input shaft 302 through summing module 108 and output by carrier 256 to thru-shaft 1 12. Torque is transferred through inner clutch 1 18 to drive second headset 134 which in turn drives second parallel shaft 148. As mentioned, second parallel shaft 148 is drivingly coupled to second speed gear set 182 thereby driving concentric shaft 162 and sun gear 250. Tables 4 and 5 contain potential ratios that may provide the desired overall gear ratios.

Table 4

Table 5

[0052] While elements 200, 210, 220, and 230 were previously described as the dog clutches, it should be appreciated that each of these elements may be replaced by a synchronizer if desired. Furthermore, the particular transmissions 100 and 300 described include a series of fixed ratio devices acting as the gear reduction unit previously described at reference numeral 16. However, it should be appreciated that a variable ratio device may be utilized without departing from the scope of the disclosure. Furthermore, while transmissions operable to provide seven forward gears and one reverse gear ratio were described, it should be appreciated that any number of forward and reverse gear ratios are contemplated as being within the scope of the present disclosure. Furthermore, while the outer clutch of twin clutch module 102 has been described as being operable to launch the vehicle from rest in the forward direction and for shifting, the inner and outer clutches may be reversed. It should also be appreciated that the clutches may be formed as wet or dry, single or multi-plate, cone, magnetic particle or virtually any type of clutch operable to transfer torque between two rotating members.

Claims

CLAIMSWhat is claimed is:

1 . A transmission comprising: an input shaft; an output shaft; a reduction unit operable to provide first and second drive ratios and being driven by said input shaft; and a differential being simultaneously driven by said input shaft and an output from said reduction unit, said output shaft being driven by said differential.

2. The transmission of claim 1 further including a dual clutch assembly driven by said input shaft and having a first clutch operable to drive said reduction unit at said first ratio and a second clutch operable to drive said reduction unit at said second drive ratio.

3. The transmission of claim 2 wherein said first clutch is operable to drivingly couple said input shaft and a first parallel shaft supporting a first drive gear providing said first drive ratio.

4. The transmission of claim 3 wherein said second clutch is operable to drivingly couple said input shaft and a second parallel shaft supporting a second drive gear providing said second drive ratio.

5. The transmission of claim 4 further including a first headset driven by said first clutch and driving said first parallel shaft.

6. The transmission of claim 5 further including a second headset driven by said second clutch and driving said second parallel shaft.

7. A transmission comprising: an input shaft; an output shaft; a dual clutch driven by said input shaft and having a first clutch concentrically positioned in relation to a second clutch; said first clutch operable to couple said input shaft to a first parallel shaft, said second clutch operable to couple said input shaft to a second parallel shaft; first, third and fifth speed gear sets selectively driven by said first parallel shaft; second, fourth and sixth speed gear sets selectively driven by said second parallel shaft, and a differential gear set driven by said input shaft and one of said speed gear sets, wherein said differential gear set drives said output shaft.

8. The transmission of claim 7 wherein said differential gear set is a planetary gear set having a carrier driven by said input shaft, a sun gear driven by one of said speed gear sets and a ring gear driving said output shaft.

9. The transmission of claim 8 further including speed gear clutches to selectively drivingly interconnect said speed gear sets to one of said first and second parallel shafts.

10. The transmission of claim 9 further including a concentric shaft interconnecting said speed gear sets to said planetary gear set and rotating about a common axis with said input shaft.

1 1 . The transmission of claim 10 further including a first headset positioned in series between said first clutch and said first parallel shaft.

12. The transmission of claim 1 1 further including a second headset positioned in series between said second clutch and said second parallel shaft.

13. A transmission comprising: an input shaft; an output shaft; a reduction unit operable to provide first and second drive ratios; and a differential being driven by said input shaft and simultaneously driving said reduction unit and said output shaft.

14. The transmission of claim 13 further including a dual clutch assembly drivingly interconnecting said input shaft and said reduction unit.

15. The transmission of claim 14 wherein said dual clutch assembly includes a first clutch operable to drivingly couple said input shaft and a first parallel shaft supporting a first drive gear providing said first drive ratio.

16. The transmission of claim 15 wherein said dual clutch assembly includes a second clutch operable to drivingly couple said input shaft and a second parallel shaft supporting a second drive gear providing said second drive ratio.

17. The transmission of claim 16 further including a first headset in series between said first clutch and said first parallel shaft.

18. The transmission of claim 17 further including a second headset in series between said second clutch and said second parallel shaft.

19. The transmission of claim 18 further including third and fifth drive gears selectively driven by said first parallel shaft to provide third and fifth gear ratios.