Patent Publication Number: US-7581462-B2

Title: Transmission

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a mechanical transmission, and more particularly to the construction of a transmission unit of a transmission which includes dual clutches. 
   There are known mechanical automatic transmissions which use no torque converter, as transmissions for vehicles. In these mechanical automatic transmissions, operations (gear selection and shift) in a transmission of a manual transmission and engagement and disengagement of clutches are performed by an actuator, whereby automatic gear changes requiring no torque converters are enabled. The transmission includes a shift shaft which can be moved in a shifting direction and a selecting direction through sliding and rotating, a plurality of shift lugs (shift brackets) which are arranged in the selecting direction, and shift rails (rods) which connect the shift lugs and shift forks, respectively. Furthermore, a shift member (shifter), which is formed into a pawl shape, is provided on the shift shaft in such a manner as to project outwards, and a pair of claw portions is provided on each shift lug in such a manner as to be spaced apart from each other in the shifting direction. In addition, the shift shaft is moved by the actuator in the mechanical automatic transmission, whereby the claw portion of the shift lug is selectively pushed to be moved in the shifting direction by the shift member, so that the shift fork is operated to be moved selectively. 
   Furthermore, in the mechanical automatic transmissions, dual clutch type automatic transmissions having two clutches have been developed. In the dual clutch type automatic transmissions, from a state in which one gear is engaged via one of the clutches, a target gear is engaged via the other clutch, and when the rotational speed of the target gear comes to synchronize with that of the gear engaged via the one clutch, the one clutch is disengaged, whereby no neutral state takes place during the gearchange, and a gearchange is enabled in which there is virtually no interruption of power flow as the gearchange takes places. 
   In this way, in the dual clutch type automatic transmission, since shift operations for the two gears are performed sequentially during the gearchange, the movements of the shift member become complex, and as a result, there is caused a fear that the shifting time becomes long. To cope with this, there has been proposed a mechanical automatic transmission in which a space between a pair of claw portions provided on each shift lug is expanded in the shifting direction, so that a shift member can enter between the pair of claw portions on the shift lug for a target gear which is in a neutral position only by shifting the shift member from between the pair of claw portions of the shift lug which is in a shifted state in the selecting direction, the movements of the shift member being thereby simplified (refer to JP-A-2001-304411). 
   In JP-A-2001-304411, however, in order for the shift member to enter between the pair of claw portions when the shift member is moved to the selecting direction, the pair of claw portions must be disposed in such a manner that the space between the pair of claw portions is expanded relatively wide. Consequently, when a gear is engaged, since a distance over which the shift member is moved from its neutral position to the claw portion for abutment becomes relatively long, there is caused a fear that a quick shift is not attained. 
   In addition, in the event that the pair of claw portions are disposed in such a manner that the space therebetween is expanded relatively wide, force transmitted from the shift member to the claw portion becomes small, and the efficiency is deteriorated. Hereinafter, the reason for the deteriorated efficiency will be described using  FIG. 7 .  FIG. 7  is a schematic diagram showing the construction of a shift mechanism of a shift lug according to the related art (JP-A-2001-304411). 
   As is shown in  FIG. 7 , in the mechanical automatic transmission described in JP-A-2001-304411, a construction is adopted in which a shift member  71  is caused to swing by rotation of a control shaft  70  so as to push a claw portion  73  of a shift lug  72  in a shifting direction. In the construction like this, when a space L 1  between a pair of claw portions  73  is increased, the shift member  71  is caused to push the claw portion  73  while the shift member  71  is tilted largely towards the shifting direction. Assuming that a force exerted on the claw portion  73  by a rotational torque T of the control shaft  70  then is a tangential force F, a distance from a contact point a between the shift member  71  and the claw portion  73  to an axial center C of the control shaft  70  is a distance L 2 , and a tilt angle of a line which connects the contact point a with the axial center C towards the shifting direction is an angle α, a component of the tangential force F in the shifting direction, that is, a component force P 1  which is a force which shifts the shift lug  72  in the shifting direction is obtained by the following equation (1).
 
 P 1= F ×COS α= T ×COS α/ L 2  (1)
 
   In the equation (1), in the event that the distance L 2  is substantially constant irrespective of the angle α, it is found that when the angle α is increased within a range of 0 to 90 degrees, the component force P 1  is decreased. Consequently, in the event that the space L 1  between the pair of claw portions  73  is increased as in JP-A-2001-304411, the force pushing the claw portion  73  towards the shifting direction is decreased, and hence, it becomes difficult to move the shift lug  72  in the shifting direction with good efficiency. 
   SUMMARY 
   It is therefore an object of the invention to provide a transmission which enables quick and efficient gearchanges by simplifying the movements of the shift member without expanding largely the space between the pair of claw portions provided on the shift lug. 
   In order to achieve the object, according to the invention, there is provided a transmission, comprising: 
   a shift member, adapted to be moved in a shifting direction and a selecting direction; 
   a shift lug, having a pair of claw portions spaced apart from each other in the shifting direction; and 
   a shift fork, connected to the shift lug via a shift rail, wherein 
   the shift member is moved by an actuator to push one of the claw portions in the shifting direction to thereby selectively move the shift lug in the shifting direction so as to cause the shift fork to perform a gear shift operation via the shift rail, and 
   the pair of claw portions are disposed so as to be offset from each other in the selecting direction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exemplary diagram of a dual clutch type automatic transmission with six forward gears and one reverse gear to which the invention is applied. 
       FIG. 2  is a perspective view showing the construction of an operating mechanism of shift forks. 
       FIG. 3  is a plan view showing the configuration of a shift lug. 
       FIG. 4  is an explanatory diagram illustrating shifting of control fingers in changing gears according to an embodiment of the invention. 
       FIG. 5  is an explanatory diagram illustrating shifting of control fingers in changing gears according to a related art transmission. 
       FIG. 6  is a schematic diagram showing the construction of a shifting mechanism of the shift lug according to the embodiment. 
       FIG. 7  is a schematic diagram showing the construction of a shifting mechanism of the shift lug according to the related art transmission. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Hereinafter, an embodiment of the invention will be described based on the accompanying drawings. 
     FIG. 1  is an exemplary diagram of a transmission unit  1  of a dual clutch type transmission with six forward gears and one reverse gear to which the invention is applied. 
   As is shown in  FIG. 1 , the transmission unit  1  includes two clutches  2 ,  3 , two main shafts  4 ,  5  which are disposed concentrically and two counter shafts  6 ,  7 . Power is configured to be delivered to the first main shaft  4  from an output shaft  9  of an engine  8  via the first clutch  2 , while the power is configured to be delivered to the second main shaft  5  from the output shaft  9  via the second clutch  3 . 
   The first counter shaft  6  and the second counter shaft  7  are disposed spaced apart in such a manner that their axes become parallel to those of the first main shaft  4  and the second main shaft  5  and are configured to be able to deliver the power to a differential  10  which is disposed at a final stage of the transmission unit  1 . A first speed gear  11 , a second speed gear  12 , a third speed gear  13  and a sixth speed gear  14  are pivotally supported on the first counter shaft  6  in such a manner as to rotate thereon. A fourth speed gear  15 , a fifth speed gear  16  and a reverse gear  17  are pivotally supported on the second counter shaft  7  in such a manner as to rotate thereon, and a parking gear  18  is fixed to the second counter shaft  7 . 
   In addition, four shift forks  20  to  23  are provided in the transmission unit  1 . A first shift fork  20  and a second shift fork  21  are placed in such a manner as to slide to be moved along the axis of the first counter shaft  6 , and a third shift fork  22  and a fourth shift fork  23  are placed in such a manner as to slide to be moved along the axis of the second counter shaft  7 . By sliding to move these shift forks  20  to  23 , the second speed gear  12  and the sixth speed gear  14  are allowed to selectively come in or out of engagement with the first counter shaft  6  (gearchange operations) by the first shift fork  20 , and the first speed gear  11  and the third speed gear  13  are allowed to selectively come in or out of engagement with the first counter shaft  6  (gearchange operations) by the second shift fork  21 . In addition, the fourth speed gear  15  and the reverse gear  17  are allowed to selectively come in or out of engagement with the second counter shaft  7  (gearchange operations) by the third shift fork  22 , and the fifth speed gear  16  and the parking gear  18  are allowed to selectively come in or out of engagement with the second counter shaft  7  (gearchange operations) by the fourth shift fork  23 . The first speed gear  11 , the third speed gear  13  and the fifth speed gear  16  are connected to the first main shaft  4 , while the second speed gear  12 , the fourth speed gear  15 , the sixth speed gear  14  and the reverse gear  17  are connected to the second main shaft  5 . 
   Namely, in the transmission unit  1  of the dual clutch type transmission, gearchanges to/from the first speed gear, the third speed gear and the fifth speed gear can selectively be attained by way of the first clutch  2 , while gearchanges to/from the second speed gear, the fourth speed gear, the sixth speed gear and the reverse gear can selectively be attained by way of the second clutch  3 . 
     FIG. 2  is a perspective view showing the construction of an operating mechanism of the shift forks  20  to  23 . 
   As is shown in  FIG. 2 , the shift forks  20  to  23  are fixed, respectively, to four shift rails  30  which are disposed in such a manner as to move in a back and forth direction (a shifting direction), and furthermore, shift lugs  40  are provided on the shift rails  30 , respectively. The shift lug  40  is a sheet material which is formed into a U-shape to open upwards and is disposed in such a manner that claw portions  41  provided at an upper end portion thereof align in the back and forth direction. The shift lugs  40  are disposed in such a manner that center lines of their openings in the back and forth direction align with one another in such a state that they are disengaged (or in neutral positions). 
   A shift shaft  50  is supported above the shift lugs  40  in such a manner as to extend over the center lines of the openings in the back and forth direction so as to be rotated and moved in an axial direction (a selecting direction). Pawl-like control fingers  51  (shift members) are formed on the shift shaft  50  in such a manner as to project downwards therefrom. Two control fingers  51  are provided in such a manner as to be spaced apart from each other in the axial direction, and the control fingers  51  are disposed in such a way that one control finger  51  is inserted into the openings of the two shift lugs  40 . 
   When the shift shaft  50  is slid in the axial direction so that the control finger  51  is positioned in the opening of the shift lug  40  for a target gear and the shift shaft  50  is then rotated to push the claw portion  41  of the shift lug  40  with the control finger  51 , the shift forks  20  to  23  can be moved in the back and forth direction via the shift rails  30 , so that the gears corresponding to the shift forks  20  to  23  can be engaged or disengaged for gearchange operations. 
   The shift shaft  50  is driven to rotate by a shifting motor  60  and is driven to slide in the axial direction by a selecting motor  61  via a ball screw  63 . The shifting motor  60  and the selecting motor  61  are controlled to be driven by an ECU  62  based on the operation of a gearshift lever, not shown, and the running conditions of the engine  8  and are controlled to be driven in such a manner that gearchanges take place sequentially, for example, when a gearchange to a target gear is implemented. The ECU  62  also controls the operations of the clutches  2 ,  3  when gearchanges take place. Specifically, in changing gears, the ECU  62  controls the other clutch  3  or  2  to be engaged to engage the next gear from a state resulting before a gearchange has taken place in which one of the clutches  2  or  3  is engaged while maintaining the engagement of a gear which is engaged by the one of the clutches  2  or  3 . Then, at a point in time at which the rotational speed of the gear that has just been engaged comes to synchronize with that of the previous gear, the latter gear is disengaged so as to realize a gearchange in which there is virtually no interruption of power flow as the gearchange takes place. 
     FIG. 3  is a plan view showing the configuration of the shift lug  40 . 
   As is shown in  FIG. 3 , the shift lug  40  of this embodiment is formed twisted in such a manner that the pair of confronting claw portions  41  are disposed to be offset from each other in the axial direction. That is, the confronting claw portions  41  are displaced with each other in the axial direction (the selecting direction). 
     FIG. 4  is an explanatory diagram which illustrates shifting of the control fingers  51  when a gearchange takes place. In this figure, as an example, shifting steps of the control fingers  51  are shown from the completion of a gearchange to the fourth speed gear by disengaging the previous or third speed gear to the completion of a gearchange to the fifth speed gear. 
   In the figure, a vertical direction denotes the shifting direction and a horizontal direction denotes the selecting direction. A vertically central position denotes a neutral position. Each pair of claw portions  41  is made to be moved one scale vertically in the figure, and by being moved vertically outwards, a gearchange is made to the gear which corresponds to the claw portion so moved. In addition, the control fingers  51  are made to be moved one scale vertically from the vertical center in the figure when the shift shaft  50  is rotated. 
   (Stand-by state) This stand-by state is a state in which a gearchange to the fourth speed gear has just been completed. In the stand-by state, the right-hand control finger  51   a  has pushed an inner side of the fourth speed gear claw portion  41   f  so as to move it outwards, whereby the fourth speed gear is engaged. In this state, the third speed gear claw portion  41   c  is also moved outwards.
 
(Step 1) The control fingers  51   a ,  51   b  are moved to upper shift positions as viewed in the figure.
 
(Step 2) The control fingers  51   a ,  51   b  are moved leftwards in the figure, so that the left-hand control finger  51   b  is moved to the same horizontal position (the same position in the selecting direction) as the first speed gear claw portion  41   d.  
 
(Step 3) The control fingers  51   a ,  51   b  are moved downwards to the neutral position in the figure, whereby the left-hand control finger  51   b  pushes an inner side of the first speed gear claw portion  41   d  so as to move it downwards. Consequently, the third speed gear claw portion  41   c  is moved to the neutral position, whereby the third speed gear is disengaged (completion of disengagement of the previous).
 
(Step 4) The control fingers  51   a ,  51   b  are moved rightwards in the figure, so that the right-hand control finger  51   a  is brought into abutment with a left side of the reverse claw portion  41   e.  
 
(Step 5) The control fingers  51   a ,  51   b  are moved downwards in the figure, so that the right-hand control finger  51   a  is brought into abutment with an inner side of the fourth speed gear claw portion  41   f.  
 
(Step 6) The control fingers  51   a ,  51   b  are moved rightwards in the figure, so that the right-hand control finger  51   a  is brought into abutment with a left side of the parking gear claw portion  41   h.  
 
(Step 7) The control fingers  51   a ,  51   b  are moved upwards in the figure, so that the right-hand control finger  51   a  pushes an inner side of the fifth speed gear claw portion  41   g  so as to move the fifth speed gear claw portion  41   g  to a shift position, whereby a gearchange to the fifth speed gear is completed.
 
   Thus, in the embodiment, the gearchange from the completion of engagement of the fourth speed gear to the completion of engagement of the fifth speed gear is completed through seven steps. 
   Next, shifting steps of control fingers  51  in a transmission unit according to the related art will be described as a comparison example. 
     FIG. 5  is an explanatory diagram which illustrates shifting of the control fingers  51  when a gearchange takes place, and shifting steps of the control fingers  51  are shown from the completion of a gearchange to the fourth speed gear by disengaging the previous or third speed gear to the completion of a gearchange to the fifth speed gear. 
   In the transmission unit of the related art, a pair of claw portions  41  of each shift lug  40  is not offset in the shifting direction but is disposed in the same position in the shifting direction. 
   (Stand-by state) As with the embodiment of the invention, the right-hand control finger  51   a  has pushed an inner side of the fourth speed gear claw portion  41   f ′ so as to move it outwards, whereby the fourth speed gear is engaged. In this state, the third speed gear claw portion  41   c ′ is also moved outwards.
 
(Step 1) The control fingers  51   a ,  51   b  are moved leftwards in the figure, so that the left-hand control finger  51   b  is brought into abutment with a right side of the first speed gear claw portion  41   d′.  
 
(Step 2) The control fingers  51   a ,  51   b  are moved to upper shift positions in the figure.
 
(Step 3) The control fingers  51   a ,  51   b  are moved leftwards in the figure, so that the left-hand control finger  51   b  is moved to the same horizontal position as the first speed gear claw portion  41   d′.  
 
(Step 4) The control fingers  51   a ,  51   b  are moved downwards to the neutral position in the figure, whereby the left-hand control finger  51   b  pushes an inner side of the first speed gear claw portion  41   d ′ so as to move it downwards. Consequently, the third speed gear claw portion  41   c ′ is moved to the neutral position, whereby the third speed gear is disengaged (completion of disengagement of the previous gear).
 
(Step 5) The control fingers  51   a ,  51   b  are moved rightwards in the figure, so that the right-hand control finger  51   a  is brought into abutment with a left side of the reverse gear claw portion  41   e′.  
 
(Step 6) The control fingers  51   a ,  51   b  are moved downwards in the figure so as to be moved to lower shift positions in the figure.
 
(Step 7) The control fingers  51   a ,  51   b  are moved rightwards in the figure, so that the right-hand control finger  51   a  is brought into abutment with a left side of the parking gear claw portion  41   h′.  
 
(Step 8) The control fingers  51   a ,  51   b  are moved upwards to the neutral position in the figure.
 
(Step 9) The control fingers  51   a ,  51   b  are moved rightwards in the figure, so that the right-hand control finger  51   a  is moved to the same horizontal position as the fifth speed gear claw portion  41   g′.  
 
(Step 10) The control fingers  51   a ,  51   b  are moved upwards in the figure, so that the right-hand control finger  51   a  pushes an inner side of the fifth speed gear claw portion  41   g ′ so as to move the fifth speed gear claw portion  41   g ′ to the shift position, whereby the gearchange to the fifth speed gear is completed.
 
   As has been described heretofore, in the transmission unit of the related art, ten steps are required from the completion of gearchange to the fourth speed gear to the completion of gearchange to the fifth speed gear. 
   In the embodiment of the invention, since the pair of claw portions  41  of each shift lug  40  is formed in such a manner as to be offset in the shifting direction, when shifting the control finger  51  which is positioned between the pair of claw portions  41  of the shift lug  40  towards the neutral position while maintaining the engagement of the gear, two steps (from the stand-by state to step 2) are required, whereas in the embodiment, the shifting is completed in one step (from the stand-by state to step 1). In addition, when shifting the control finger  51  which is in abutment with a side of one of the claw portions  41  of the shift lug  40  which is in the neutral position to the other claw portion  41  so as to push it outwards to thereby shift the shift lug  40 , three steps (from step 7 to step 10) are required in the related art transmission unit, whereas in the embodiment, the shifting is completed in one step (from step 6 to step 7). 
   In this way, in the embodiment, since the number of shifting steps of the control fingers  51  can be reduced largely when a gearchange takes place, a reduction in shift time can be realized. In addition, also in changing gears to the other speed gears, the number of shifting steps of the control fingers  51  can be reduced. 
   In the embodiment, since the necessity is obviated of expanding largely the space between the pair of claw portions of the shift lug  40  relative to the control finger  51  as has taken place in the related art transmission unit, once it is moved, the control finger  51  can be brought into abutment with the claw portion  41  immediately, thereby making it possible to enable a quick gearchange. 
     FIG. 6  is a schematic diagram showing the construction of the shifting mechanism of the shift lug according to the embodiment. 
   In this embodiment, since the space L 3  between the pair of claw portions  41  can be set relatively narrow, the control finger  51  is allowed to push the claw portion  41  while it is tilted little in the shifting direction. Assuming that a force exerted on the claw portion  41  by a rotational torque T of the shift shaft  50  then is a tangential force F, a distance from a contact point a between the control finger  51  and the claw portion  41  to an axial center C of the shift shaft  50  is a distance L 4 , and a tilt angle of a line which connects the contact point a with the axial center C of the shift shaft  50  towards the shifting direction is an angle β, a component of the tangential force F in the shifting direction, that is, a component force P 2  which is a force which shifts the claw portion  41  in the shifting direction is obtained by the following equation (2).
 
 P 2= F ×COS β= T ×COS β/ L 4  (2)
 
   Consequently, in this embodiment, since the space L 3  between the pair of claw portions  41  is relatively narrow and hence the angle β is suppressed to a smaller angle, as is expressed by the equation (2), the component force  2  is reduced largely relative to the tangential force F in no case. In addition, since the distance L 4  remains substantially constant irrespective of the angle β, the rotational torque T of the shift shaft  50  is transmitted with good efficiency as a force which pushes the claw portion  41  in the shifting direction, thereby making it possible to move the shift lug  40  in the shifting direction with good efficiency. 
   In addition, since the control fingers  51  are provided more than one, even in the event that there are many gears to be changed, each control finger  51  is made to operate some of the shift lugs for gearchanges, whereby the shifting distance of each control finger in the shifting direction can be suppressed to a shorter distance. Consequently, the shifting mechanism of the control fingers  51  can be made compact in size with respect to the shifting direction. 
   In addition, the direction in which the claw portions  41  are offset may be set appropriately on each of the shift lugs depending upon the number and arrangement of gears. Additionally, the invention can be applied to a transmission unit with a different number of gears from the embodiment, and the number of control fingers  51  may be set appropriately depending upon the number of gears to be provided. 
   According to an aspect of the invention, by setting appropriately the offset direction of the claw portions in accordance with the arrangement of the shift rail, when the shift member is moved in the sliding direction so as to be brought into abutment with a side of one of the claw portions to change gears, in the event that, following this, the shift member is moved in the shifting direction, the shift member can be brought into abutment with an inner side of the other claw portion. Consequently, since the movements of the shift member in changing gears are simplified without expanding largely the space of the pair of claw portions, a quick and efficient gearchange can be attained. 
   According to an aspect of the invention, the shift member can be moved in the shifting direction and the selecting direction by rotating and shifting the shaft in the selecting direction by the actuator. Consequently, the shifting mechanism for shifting the shift member in the shifting direction and the selecting direction can be realized with the simple configuration. 
   According to an aspect of the invention, since the shift member is provided more than one on the shaft in such a manner as to be spaced apart from each other in the selecting direction, even in the event that there are many gears to be changed and hence so many shift rails are required, each shift member can be set to operate some of the shift rails for gearchanges, whereby the shifting of each shift member in the selecting direction can be reduced. Consequently, the shifting mechanism of the shift members can be made compact in size with respect to the selecting direction.