Abstract:
A method for operating a power transmission to produce gear ratio changes includes driveably connecting the transmission input and output in the off-going gear through a friction clutch and primary power path, establishing a potential drive connection between the input and output through a secondary power path, releasing the friction clutch, driveably connecting the input and output through the secondary power path, establishing a potential drive connection between the input and output through the primary power path in the oncoming gear, reapplying the friction clutch, driveably disconnecting the input and output through the secondary power path, and driveably connecting the input and output in the oncoming gear ratio through the friction clutch and primary power path.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the field of transmissions having a layshaft kinematic arrangement, particularly to such transmissions in which gear ratio changes occur without interrupting power flow. 
     2. Description of the Prior Art 
     Automatic transmissions for motor vehicle generally employ multiple planetary gearsets whose components are continuously engaged. The gearset components are alternately held and released against rotation by brakes, and are connected and disconnected to components of other gearsets by clutches so that gear ratio changes occur without affecting the continuous gear engagements and without interrupting the flow of power among the gearset components. 
     Typically manual transmissions have a kinematic arrangement in which a countershaft or layshaft and an output shaft each rotatably support a gear or pinion of a pinion-gear pair associated with a particular gear ratio. Although the gear and pinion are continuously engaged, either the pinion or gear is journalled on its shaft. The journalled component is driveably secured to the shaft by a coupler or synchronizer, which mechanically completes the connection usually after coordinating the speed of the shaft and the speed of the associated gear or pinion. This operation requires use of a friction clutch located in the drive path between the engine output and transmission input. The clutch disengages to interrupt power flow to the transmission before beginning a gear ratio change, and re-engages after completing the gear ratio change to restore power flow to the transmission and drive wheels. 
     Manual transmissions of this type are characterized by a distinctive, perceptible power flow interruption and the potential for harsh speed ratio changes unless the operator employs care and skill while manually operating a clutch pedal and gear selector in coordination with the engine, driven wheels and driving conditions. 
     Automatic transmissions for transmitting power between an input and output, either over a continuously variable range of speed ratios or in discrete step changes among speed ratios, have associated with them several sources of parasitic losses, which adversely affect fuel economy. These losses are associated with a torque converter, open clutches and brakes, hydraulic pump, and gear meshes. 
     In order to avoid these parasitic losses and to improve vehicle fuel economy, an automated shift manual (ASM) transmission has been developed that eliminates many of the low operating efficiency components of an automatic transmission, yet it requires no more driver attention or skill to produce smooth gear ratio changes than does an conventional automatic transmission. 
     An ASM transmission can eliminate or substantially reduce all of the parasitic losses of an automatic transmission except gear mesh losses. An ASM transmission having a layshaft gear arrangement performs gear ratio changes by first interrupting power or torque transmitted from the engine to the transmission, preparing the transmission components associated with the next speed ratio, and then restoring torque. The need in a conventional ASM transmission to interrupt power transmitted from the engine to the transmission input shaft before each gear ratio change can affect the level of harshness, vibration and noise perceptible to a vehicle occupant. 
     SUMMARY OF THE INVENTION 
     An ASM transmission operating in accordance with the present invention avoids entirely any interruption of power during gear ratio changes and avoids the inherent shift control difficulties of ASMs. This invention, however, also reduces the magnitude of parasitic losses to the much lower magnitude associated with a conventional ASM. 
     A transmission for use with the method of this invention includes only one friction clutch for releasably connecting a source of power, such as an engine or motor, and a transmission input. Gear ratio changes are accomplished with the use of couplers, such as synchronizers or dog clutches, which mutually driveably connect components that participate in each speed ratio, produce very little drag loss when engaged, and do not require continuous supply of power to stay engaged. 
     Power interruption during shifting is avoided by providing alternate torque or power paths, which transmit power between a transmission input and the output during a gear ratio change. A secondary power path bypasses the friction clutch, but contains a one-way clutch. Before starting an upshift from a current or off-going speed ratio to the next or oncoming speed ratio gear, the secondary power path is set for a slightly lower speed ratio than the current gear by engaging synchronizers or dog clutches, thereby causing the one-way clutch to overrun. In order to transfer power to the secondary power path, the friction clutch is released and the secondary power path carries torque through the one-way clutch. Transfer of torque to the secondary power path is essentially a downshift to a speed ratio that is slightly lower than the off-going speed ratio. 
     While the secondary power path carries torque, the main or primary power path is set similarly for the destination gear of the gearshift by engaging synchronizers or dog clutches. When the friction clutch is reengaged, torque is transferred back to the primary power path causing the one-way clutch to overrun again. Downshifts are accomplished by reversing this sequence of steps. 
     All the gear ratio changes including the acceleration of the vehicle from a stop or idle condition, usually referred to as launch, use the same friction clutch. The only additional hardware required is a one-way clutch, the gearing, and a coupler on a second layshaft associated with the secondary torque path. 
     The method of the present invention can be applied to all of the up-shifts of a particular transmission or any number of the up-shifts depending upon the number of secondary torque paths that are provided. 
     In realizing these advantages, a method for producing a speed ratio change from an off-going speed ratio to an oncoming speed ratio in a transmission includes the steps of establishing a potential drive connection between an input and output through a secondary power path, disengaging a clutch, driveably connecting the input and output through the secondary power path at a speed ratio that is equal to or less than the speed ratio produced by the off-going speed ratio through the primary power path, establishing a potential drive connection between the input and output through the primary power path in the oncoming speed ratio, and re-engaging the clutch. 
     Upon later disestablishing the potential drive connection between the input and output through the secondary power path, the speed ratio change is completed. The method is applicable both when the oncoming speed ratio is greater than the off-going speed ratio, and when the oncoming speed ratio is less than the off-going speed ratio. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram showing the gear arrangement of the transmission according to the present invention. 
         FIG. 2  is a chart containing an example of the number of teeth for each of the gears and pinions shown in FIG.  1 . 
         FIG. 3  is a chart that indicates the state of engagement of a friction clutch and the couplers corresponding to the steps for producing gear ratio changes in a transmission according to the present invention. 
         FIG. 4  is a chart that shows an example of the resulting speed ratios for various paths and components, a torque ratio and the gear ratio steps corresponding to various operating steps of the chart of FIG.  3 . 
         FIG. 5  is a schematic diagram showing another arrangement of the power path in which the input clutch is located on the first layshaft. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1  a transmission according to the present invention includes an input  10  adapted to driveably connect a power source, such as an internal combustion engine or electric motor, and an output  12  for driving a load, such as the driven wheels of a motor vehicle connected through a powertrain that may include a drive shaft, differential mechanism, and axle shafts. 
     A primary layshaft  14  and secondary layshaft  16 , arranged substantially parallel to the output  12 , each support pinions that are in continually meshing engagement with gears supported rotatably on the output  12 . 
     A clutched input  18 , preferably substantially aligned with output  12 , is releasably connected to input  10  through a friction clutch  22 , whose output element  20  frictionally engages the clutch&#39;s input element  24 , which is drivably connected to input  10 . 
     A pinion  26 , journalled on member  24  and connected to input  10 , is engaged with a gear  28 , which is journalled on secondary layshaft  16 . A one-way clutch  30 , also supported rotatably on layshaft  16 , has an inner race  32  fixed to layshaft  16  and an outer race  34  drivably connected to gear  28 . 
     Clutched input  18  supports a pinion  36 , which is in continual meshing engagement with gear  38 , supported rotatably on primary layshaft  14 . 
     In this way, a primary power path, having a speed ratio that is approximately 0.711 when pinion  36  and gear  38  have the number of teeth specified in  FIG. 2 , is established between input  10  and layshaft  14 . When clutch  22  is engaged, the primary power path causes the speed of layshaft  14  to be approximately 0.711 times the speed of input  10 . A secondary power path, having a speed ratio of approximately 0.703 when pinion  26  and gear  28  have the number of teeth specified in  FIG. 2 , is established between layshaft  16  and input  10 . Clutch  30  drivably connects gear  28  and layshaft  16  when input  10  drives layshaft  16 , and clutch  30  overruns when the speed of layshaft  16  exceeds the speed of gear  28 . When clutch  30  is driving, the secondary power path causes the speed of layshaft  16  to be approximately 0.703 times the speed of input  10 . 
     Spaced axially along output  12  are gear elements of pinion-gear pairs, each member of a pair in continuous meshing engagement with the other member of the pair, and each pair being associated with a particular speed ratio. For example, pinion  40 , which is journalled on layshaft  14 , is in continuous meshing engagement with gear  42 , which is rotatably supported on output  12 . Pinion  40  and gear  42  are associated with the third forward speed ratio. Pinion  44 , journalled on layshaft  14 , is in continuous meshing engagement with gear  46 , rotatably supported on output  12 . Pinion  44  and gear  46  are associated with the fourth forward speed ratio. Pinion  48 , journalled on layshaft  14 , is in continuous meshing engagement with gear  50 , rotatably supported on output  12 . Pinion  48  and gear  50  are associated with the fifth forward gear ratio. 
     Reverse pinion  52 , journalled on layshaft  14 , is in continuous meshing engagement with reverse idler  54 , supported rotatably on an idler shaft  55 . Reverse output gear  56 , which is rotatably supported on output  12 , is in continuous meshing engagement with reverse idler  54 . Pinion  52 , idler  54  and gear  56  are associated with the reverse gear ratio. 
     Also spaced along the axis of output  12  are triplets comprising two pinions, one of each pinion being supported on layshaft  14  and the other on layshaft  16 , and a gear supported on and fixed to output  12 . For example, pinion  58 , which is journalled on layshaft  14 , is in continuous meshing engagement with gear  60 , supported on output  12 . Pinion  62 , which is journalled on layshaft  16 , is also in continuous meshing engagement with gear  60 . Pinion  58 , gear  60  and pinion  62  form a triplet that is associated with the first forward gear ratio. 
     Pinion  64 , journalled on layshaft  14 , is in continuous meshing engagement with gear  66 , supported on output  12 . Pinion  68 , which is journalled on layshaft  16 , is in continuous meshing engagement with output gear  66 . Pinion  64 , gear  66  and pinion  68  form a triplet that is associated with the second forward gear ratio. 
     Couplers  70 ,  82 ,  84  and  86 , are preferably synchronizers of the type used in manual automotive transmissions to connect releasably a gear or pinion to a shaft after first synchronizing the speed of the shaft and that of the pinion or gear. A coupler may also be disengaged from any pinion or gear. An example of such a synchronizer is disclosed in U.S. Pat. No. 4,222,281. Alternatively the couplers may be a toothed clutch having dogteeth that are engaged with clutch teeth on a gear or pinion. This invention may use couplers in any combination of synchronizers and dog clutches. 
     Each coupler, for example coupler  70 , is fixed by a hub  72  on a layshaft  14  for rotation at the speed of that layshaft. In the case where a coupler is a synchronizer, it will be provided with a conical surface  74 ,  76 , which engages mutually with a corresponding conical surface  78 ,  80 , respectively, on the pinions located adjacent the synchronizer. When these conical surfaces are forced together into frictional contact, that engagement synchronizes the speed of layshaft  14  to that of the pinion being engaged and drivably connected through the synchronizer to layshaft  14 . Generally the synchronizer is equipped with a sleeve  81  supported on the hub  72  for sliding movement leftward and rightward into engagement with dogteeth carried on the pinion. When the dogteeth of the sleeve engage those of the pinion, the pinion is connected to the layshaft. 
     The hubs of couplers  82 ,  84  are rotatably secured to shaft  14 ; the hub  88  of coupler  86  is rotatably secured to layshaft  16 . 
     In the case where the coupler  70  is a clutch, movement of the sleeve  81  causes mutual engagement of dog teeth formed on the sleeve and dog teeth carried on the pinions so that a drive connection is made between the pinion and the layshaft, but without first synchronizing the speed of the layshaft and the pinion. 
     A coupler  82 , located between pinions  40  and  44 , releasably connects alternately those pinions and layshaft  14 , and coupler  82  may be disengaged from both pinions. Coupler  84 , located between pinions  48  and  52 , selectively, alternately produces a drive connection between layshaft  14  and the selected pinion, and coupler  84  may be disengaged from both pinions. Another coupler  86  includes a hub  88  driveably connected and supported for rotation on the secondary layshaft  16 . Coupler  86  is located between pinions  62  and  68  in order to selectively produce a drive connection between layshaft  16  and those pinions. 
     In  FIG. 1  the couplers  70 ,  82 ,  84 ,  86  are shown in a neutral position, between the left-hand and right-hand extremities of travel of the connecting element or sleeve, whose engagement with the dog teeth carried on the pinions completes the drive connection of the pinion and associated layshaft. 
     Referring now to  FIG. 3 , operation of the transmission will be discussed with reference to the positional states of the couplers and the applied or released condition of clutch  22 . The transmission is prepared for forward acceleration of the vehicle from rest in the first gear ratio when the engagement sleeve  81  of coupler  70  is moved leftward, the other couplers  82 ,  84  and  86  are in the neutral position, and clutch  22  is disengaged. The power source continually drives input  10  and pinion  26  at the speed of the power source; gear  28  is driven by pinion  26  at the speed ratio of the secondary power path, i.e., 0.703 times the speed of input  10 , provided the gears and pinions have the sizes of the example of FIG.  2 . However, since coupler  86  is in the neutral position, no power is transferred to output  12 , and the speed of output  12  is zero. Next, clutch  22  is applied, either manually by the vehicle operator&#39;s manipulation of a clutch pedal, lever or button, or automatically in response to a signal produced by a transmission electronic control system. When clutch  22  is engaged, primary layshaft  14  is driven through clutch  22 , input  18 , pinion  36 , and gear  38  at the speed ratio of the primary power path, i.e., 0.711 times the speed of input  10 . Output  12  is driven from layshaft  14  through coupler  70 , pinion  58  and gear  60 , which is drivably fixed to output  12 . These actions complete the engagement of the first forward speed ratio, whereby the output  12  is driven at a speed ratio of 0.314. 
     An upshift from the first to the second speed ratio is accomplished in a series of steps that begins by moving the engagement element or sleeve of coupler  86  leftward to drivably connect pinion  62  and the secondary layshaft  16 . This action causes one-way clutch  30  to overrun or permits it to continue to overrun. Then clutch  22  is released, thereby causing one-way clutch  30  to driveably connect layshaft  16  and gear  28 , which drives output  12  through gear  60  at a speed ratio of 0.310, a slight downshift from the first gear ratio, 0.314. Next, the engagement element or sleeve of coupler  70  is moved from the left-hand to the right-hand position, thereby drivably connecting pinion  64  and layshaft  14 . Output  12  remains driven through the secondary power path at a speed ratio of 0.310. Clutch  22  is then applied, causing one-way clutch  30  to overrun, and driving output  12  through the primary power path: pinion  36 , gear  38  and layshaft  14 , which drives second speed pinion  64  and second speed gear  66 . Moving the sleeve of coupler  86  to the neutral position, i.e., out of engagement with pinion  62  completes the upshift to the second speed ratio from the first speed ratio. Output  12  is driven at a speed ratio of 0.548. 
     The torque delivery path in the second forward speed ratio includes input  10 , clutch  22 , input  18 , gear  36 , pinion  38 , layshaft  14 , coupler  70 , pinion  64 , gear  66 , and output  12 . 
     An upshift from a second speed ratio to the third speed ratio is similarly accomplished in a series of steps that begins by moving the selection sleeve of coupler  86  to the right-hand position from the neutral position, thereby driveably connecting pinion  68 , gear  66 , and output  12  through coupler  86 , and layshaft  16 . With the transmission components so disposed, one-way clutch  30  overruns, and the output remains driven through the primary power path at the 0.548 speed ratio. Then clutch  22  is released, which causes clutch  30  to produce a drive connection between layshaft  16  and gear  28 . The output  12  is driven through the secondary power path, pinion  68  and gear  66  at a slightly reduced speed ratio of 0.542. Next, the selector sleeve of coupler  70  is moved to the neutral position and the selector sleeve of coupler  82  is moved to the left-hand position, thereby drivably connecting layshaft  14  and pinion  40 . The output remains driven through the secondary power path at the 0.542 speed ratio. Then clutch  22  is reapplied, which action causes one-way clutch  30  to overrun and output  12  to be driven again through the primary power path, pinion  40  and gear  42  at the third forward speed ratio, 0.809. Finally the upshift to the third speed ratio is completed by disengaging the secondary torque delivery path upon moving the selector element  88  of coupler  86  to the neutral position. 
     In the speed ratio changes described, only speed ratio changes to the second and third forward speed ratios involve transmitting power through the secondary power path, i.e., without interrupting power flow between the engine and the transmission. However, any number of the gear ratio changes could employ the secondary torque delivery path to avoid power interruption, provided a pinion corresponding to each of such speed ratios is supported on layshaft  16  and meshes with the output gear of the corresponding gear ratio. Speed ratio changes to the fourth and fifth speeds involve interrupting power flow from the engine to the transmission by disengaging clutch  22 . 
     An upshift from the third to the fourth forward speed ratio begins with the step of disengaging clutch  22 . Clutch  30  is inoperative during engagement of the third and fourth forward gears and reverse gear. Next, the selection element or sleeve of coupler  82  is moved to the right-hand position, thereby driveably connecting layshaft  14  and pinion  44 . Finally re-engaging clutch  22  complete the fourth forward speed ratio. The torque delivery path for the fourth speed ratio includes input  10 , clutch  22 , input  18 , pinion  36 , gear  38 , layshaft  14 , coupler  82 , pinion  44 , gear  46 , and output  12 . The fourth speed ratio is 1.052. Similarly an upshift from the fourth to the fifth forward speed ratio begins by disengaging clutch  22 . Next, the selector element of coupler  82  is moved from the right-hand position to the neutral position, and the selector element of coupler  84  is moved from the neutral position to the left-hand position, thereby driveably connecting layshaft  14  and pinion  48 . Re-engaging clutch  22  complete the upshift to the fifth forward speed ratio. The torque delivery path for the fifth forward speed ratio includes input  10 , clutch  22 , input  18 , pinion  36 , gear  38 , layshaft  14 , coupler  84 , pinion  48 , gear  50 , and output  12 . The fifth speed ratio is 1.267. 
     Reverse drive is produced when the selector elements of couplers  70 ,  82 , and  86  are in the neutral position and the selector element of coupler  84  is moved to the right-hand position, thereby driveably connecting pinion  52  and layshaft  14 . Reverse idler  54 , which is rotatably supported on idler shaft  55 , reverses the direction of rotation so that gear  56  and the output  12  turn in the opposite direction of rotation from the direction the forward drive gear ratios. Reapplying clutch  22  completes the reverse drive torque delivery path. The torque delivery path for reverse drive includes input  10 , clutch  22  shaft  18 , pinion  36 , gear  38 , layshaft  14 , coupler  84 , pinion  52 , reverse idler  54 , gear  56 , and output  12 . The reverse drive speed ratio is −0.314. 
     The example set out in  FIG. 4  was selected to produce the gear ratios that would result from the transmission embodiment of FIG.  1  and using the gear and pinion sizes of FIG.  2 . 
     The one-way clutch  30  represents a one-way drive connection through which the input is connected to the second layshaft, and may be any of the following: a one-way clutch, a sprag-type one-way clutch, a roller-type one-way clutch, a mechanical diode of the type described in U.S. Pat. Nos. 5,070,978; 5,597,057 and 6,065,576; or a hydraulically actuated friction clutch having an engaged state wherein the second layshaft and input are driveably connected and a disengaged state wherein the second layshaft and input are driveably disconnected. 
     Referring now to the alternate embodiment of  FIG. 5 , an input  10 ′ supports and is driveably connected to both a pinion  26 ′ of the second power path, and a pinion  36  of the first power path. Pinion  26 ′ is engaged with gear  28 , which is supported on the second layshaft; pinion  36  is engaged with gear  38 ′, which is journalled on the first layshaft  14 ′ and is driveably connected to a clutch  22 ′. Gear  28  is connected through a one-way drive connection  30 , to second layshaft  16 . 
     Preferably clutch  22 ′ is a multiple plate friction clutch, and may have a housing  24 ′ connected to gear  38 ′, and a disc  20 ′ carried on layshaft  14 ′. The disc moves alternately into frictional engagement with housing  241  to connect gear  38 ′ and layshaft  14 ′ when the clutch is applied, and out of engagement with the housing to disconnect gear  38 ′ and layshaft  14 ′ when the clutch is released. 
     An ASM transmission operating in accordance with the present invention avoids entirely any interruption of power during gear ratio changes and avoids the inherent shift control difficulties of ASMs. This invention, however, also reduces the magnitude of parasitic losses inherent in the operation of an automatic transmission to a much lower magnitude than the losses associated with a conventional ASM transmission. 
     Although the form of the invention shown and described here constitutes the preferred embodiment of the invention, it is not intended to illustrate all possible forms of the invention. Words used here are words of description rather than of limitation. Various changes in the form of the invention may be made without departing from the spirit and scope of the invention as disclosed.