Shift control system for a working vehicle having a propelling stepless transmission

Information

  • Patent Grant
  • 6347560
  • Patent Number
    6,347,560
  • Date Filed
    Wednesday, March 1, 2000
    24 years ago
  • Date Issued
    Tuesday, February 19, 2002
    22 years ago
Abstract
A shift control system includes a shift pedal (13), a first linkage mechanism (16, 18, 19, 20) for transmitting a downward displacement of the shift pedal to the stepless transmission to change a shift position of the stepless transmission, a retaining mechanism (30, 40, 41, 42) for producing a retaining position corresponding to the shift position to retain the shift position of the stepless transmission, and a shift lever (26) for setting the retaining position retained by the retaining mechanism. A second linkage mechanism (34, 35, 36) is provided for transmitting of an operating displacement of the shift lever to the shift pedal to displace the shift pedal to a depressed position corresponding to the retaining position set by the shift lever and retained by the retaining mechanism. The shift lever, retaining mechanism and second linkage mechanism are attachable and detachable independently of the first linkage mechanism.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




This invention relates to a shift control system for a working vehicle having a propelling stepless transmission. More particularly, the invention relates to a shift control system having a shift pedal, a first linkage mechanism for transmitting a downward displacement of the shift pedal to the stepless transmission to change a shift position of the stepless transmission, a retaining mechanism for producing a retaining position corresponding to the shift position to retain the shift position of the stepless transmission, and a shift lever for setting the retaining position to be retained by the retaining mechanism.




2. Description of the Related Art




An agricultural tractor which is one example of working vehicles may include a hydrostatic stepless transmission for propelling the tractor. A shift pedal and the stepless transmission are interlocked through a linkage mechanism (e.g. a mechanical linkage mechanism with a linkage rod and the like for interlocking the shift pedal and stepless transmission, or an electric or hydraulic linkage mechanism for shifting the stepless transmission with an electric motor or hydraulic actuator in response to a control position of the shift pedal). The stepless transmission is shifted through the linkage mechanism in response to a depression of the shift pedal.




When the agricultural tractor engages in a grass cutting operation with a mower unit attached thereto, the grass cutting operation is carried out in many cases while running at a fixed speed. Thus, the agricultural tractor may include a retaining mechanism for retaining the stepless transmission in a desired shift position, and a shift lever for operating the retaining mechanism. The tractor can run at a fixed speed by operating the retaining mechanism with the shift lever to retain the stepless transmission in the desired shift position, without depressing the shift pedal. This is usually called a cruising function.




Two types of models may be manufactured as working vehicles such as agricultural tractors having a propelling stepless transmission, one with the above retaining mechanism and the other without it. The type with the retaining mechanism must have a construction for mechanically interlocking the retaining mechanism and stepless transmission so that the retaining mechanism is operable to retain the stepless transmission in a desired shift position.




Consequently, when manufacturing the type with the retaining mechanism, the construction of the type without the retaining mechanism (e.g. the linkage mechanism interlocking the shift pedal and stepless transmission) may be altered to mechanically interlock the retaining mechanism and stepless transmission) Then, productivity may be lowered in manufacturing the type with the retaining mechanism and the type without it.




SUMMARY OF THE INVENTION




An object of this invention is to provide a shift control system for a working vehicle having a propelling stepless transmission, which improves productivity in manufacturing the type of vehicle with a retaining mechanism for retaining the stepless transmission in a desired shift position, and the type having no such retaining mechanism.




To fulfilled the above object, this invention proposes a shift control system as set forth at the outset hereof, wherein a second linkage mechanism is provided for transmitting of an operating displacement of the shift lever to the shift pedal to displace the shift pedal to a depressed position corresponding to the retaining position set by the shift lever and retained by the retaining mechanism.




In a working vehicle having a propelling stepless transmission, for example, the shift pedal and stepless transmission may be interlocked through a first linkage mechanism. The stepless transmission is shiftable by a depression of the shift pedal through the first linkage mechanism. When adding a cruising function to such a working vehicle with a retaining mechanism provided for retaining in a desired shift position, and a shift provided for operating the retaining mechanism, the retaining mechanism and shift lever are mounted on a vehicle body, and the retaining mechanism and the shift pedal are interlocked through the second linkage mechanism. With this construction, by operating the shift lever, the shift pedal may be operated to and retained in a desired shift position through the retaining mechanism and second linkage mechanism. Through the shift pedal and first linkage mechanism, the stepless transmission may be retained in a desired shift position.




That is, when providing the retaining mechanism and shift lever for the vehicle body of the type of vehicle not having the retaining mechanism, it is necessary only to interlock the retaining mechanism and shift pedal through the second linkage mechanism. The type of vehicle having the retaining mechanism (i.e. the cruising function) may be obtained with little or no modification made to the first linkage mechanism interlocking the shift pedal and stepless transmission.




When manufacturing the type of vehicle with the retaining mechanism and the type of vehicle without it, the latter may be manufactured without modification, whereas the type with the retaining mechanism may be obtained by adding the retaining mechanism and shift lever to the vehicle body of the type not having the retaining mechanism, and interlocking the retaining mechanism and shift pedal through the second linkage mechanism.




In a preferred embodiment of this invention, the shift lever, retaining mechanism and second linkage mechanism are attachable and detachable independently of the first linkage mechanism. This construction realizes, in a simple way, the cruising type by incorporating the retaining mechanism as an option, and the non-cruising type by removing the retaining mechanism, which may be done at any time as desired.




In a preferred embodiment of this invention, the second linkage mechanism includes a play-accommodating mechanism for permitting a depression of the shift pedal to a higher speed position than the retaining position retained by the retaining mechanism, the play-accommodating mechanism permitting the shift pedal to be depressed the retaining position retained by the retaining mechanism to the higher speed position. With this construction, when the driver desires to temporarily accelerate the type of vehicle having the retaining mechanism and running with the shift pedal, and thus the stepless transmission, retained in a selected shift position by the retaining mechanism, the driver may cause the vehicle to run temporarily at high speed by depressing the shift pedal from the selected shift position to a higher speed position.




In another preferred embodiment of this invention, the retaining mechanism, shift lever and second linkage mechanism are mounted on a support member. The retaining mechanism, shift lever and second linkage mechanism by means of the support member constitute a single unit. To obtain the type of vehicle with the retaining mechanism, the support member may be attached to the vehicle body to incorporate the retaining mechanism, shift lever and second linkage mechanism into the vehicle body. There is no need to attach the retaining mechanism shift lever and second linkage mechanism individually to the vehicle body.




In a working vehicle having the stepless transmission is disposed between right and left body frames, and the shift pedal disposed laterally outwardly of the right body frame, and the first linkage mechanism extending through the right body frame for interlocking the shift pedal and stepless transmission, this invention proposes to interlock the retaining mechanism and shift pedal through the second linkage mechanism laterally outwardly of the right body frame. With this construction, when the retaining mechanism and shift lever are added to a vehicle body of the type having no retaining mechanism, the retaining mechanism and shift pedal may be interlocked easily through the second linkage mechanism laterally outwardly of the right body frame. The type of vehicle having the retaining mechanism may be obtained with little or no modification made to the first linkage mechanism interlocking the shift pedal and stepless transmission.




In a working vehicle such as an agricultural tractor, the stepless transmission is steplessly shiftable forward and backward, and the shift pedal may include a forward pedal portion extending forward, and a rearward pedal portion extending rearward, the forward pedal portion being depressible to shift the stepless transmission for high forward speed, the rearward pedal portion being depressible to shift the stepless transmission for high backward speed. For such a working vehicle, this invention proposes to dispose the retaining mechanism rearwardly of the shift pedal, and to interlock the retaining mechanism and the rearward pedal portion through the second linkage mechanism. Since the retaining mechanism is disposed close to the shift pedal according to this construction, the retaining mechanism and shift pedal may be interlocked easily through the second linkage mechanism. The second linkage mechanism may be reduced in length.




Other features and advantages of this invention will be apparent from the following description of the embodiments to be taken with reference to the drawings.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a side elevation of an agricultural tractor;





FIG. 2

is a side view of a shift pedal and adjacent components;





FIG. 3

is a side view of a trunnion and adjacent components of a stepless transmission;





FIG. 4

is a front view in vertical section of the trunnion and adjacent components of the stepless transmission;





FIG. 5

is a side view in vertical section of a boss of a linkage rod interlocking the stepless transmission (trunnion) and the shift pedal;





FIG. 6

is a side view in vertical section of a shift lever for retaining the shift pedal (stepless transmission) in a desired shift position;





FIG. 7

is a rear view in vertical section of the shift lever for retaining the shift pedal (stepless transmission) in a desired shift position;





FIG. 8

is a perspective view of a cam plate for retaining the shift lever;





FIG. 9

is a plan view of a lever guide of the shift lever;





FIGS. 10A and 10B

are side views of right and left side brake pedals both in a depressed state;





FIGS. 11A and 11B

are side views of the right and left side brake pedals, showing a state where only the right side brake pedal is depressed and a state where only the left side brake pedal is depressed;





FIG. 12

is a side view in vertical section of a retaining mechanism in a different embodiment;





FIG. 13

is a rear view in vertical section of the retaining mechanism in the different embodiment; and





FIG. 14

is a perspective view of a cam mechanism for releasing the retaining mechanism in response to an operation of a side brake pedal.











DESCRIPTION OF THE PREFERRED EMBODIMENTS





FIG. 1

shows an agricultural tractor which is one example of working vehicles. This tractor includes a pair of right and left front wheels


1


, an engine


4


and a clutch


6


arranged on a forward portion of a vehicle body, and a pair of right and left rear wheels


2


and a transmission case


9


arranged on a rearward portion of the vehicle body. The clutch


6


and transmission case


9


are interconnected through a pair of right and left body frames


3


consisting of vertical plates. The right and left body frames


3


are in the form of a tube having a square section with a top plate (not shown) and a bottom plate (not shown) connected thereto. A driving platform


5


is formed on the body frames


3


.




As shown in

FIGS. 1 and 2

, a hydrostatic stepless transmission


7


shiftable forward F and backward R is disposed between the right and left body frames


3


and connected to the front of transmission case


9


. A transmission shaft


8


also disposed between the right and left body frames


3


transmits power from the clutch


6


to the stepless transmission


7


.




A shift pedal


13


for shifting the stepless transmission


7


forward F and backward R will be described next.




As shown in

FIGS. 1 and 2

, the shift pedal


13


is pivotable about a support shaft


11


fixed to an outer side wall of the right body frames


3


. The shift pedal


13


includes a boss


13




a


rotatably mounted on the support shaft


11


, a forward pedal portion


13




f


fixed to the boss


13




a


and extending forward of the vehicle body, and a rearward pedal portion


13




r


fixed to the boss


13




a


and extending rearwardly of the vehicle body.




As shown in

FIGS. 2

,


3


and


4


, a control arm


19


is fixed to a trunnion


12


of stepless transmission


7


between the right and left body frames


3


. The control arm


19


has a control shaft


22


projecting laterally outwardly from the right body frame


3


through a bore


3




a


formed therein. As shown in

FIGS. 2

,


3


and


4


, a control arm


14


is fixed to the boss


13




a


, and a linkage rod


16


is connected to the control arm


14


. Rubber cushions


15


as shown in

FIG. 5

are mounted on an end portion of linkage rod


16


. A boss member


18


fitted on the rubber cushions


15


has a coupling


18




a


connected to the control shaft


22


.




As shown in

FIGS. 2 and 3

, an arm


21


is supported to be pivotable about a transverse axis P


1


of stepless transmission


7


between the right and left body frames


3


. The arm


21


has a roller


21




a


. The arm


21


is biased counterclockwise in

FIG. 3

by a spring


20


to press the roller


21




a


against a V-shaped cam


19




a


formed on the control arm


19


. As shown in

FIG. 2

, a bracket


17


is supported to be pivotable about a transverse axis P


2


on the outer side wall of the right body frame


3


, and a damper


23


is connected between the bracket


17


and control arm


14


. Further, the right body frame


3


supports, fixed to the outer side wall thereof, a stopper


24


for setting a limit to depression of the forward pedal portion


13




f


, and a stopper


25


for setting a limit to depression of the rearward pedal portion


13




r.






With the above construction, when the forward pedal portion


13




f


is depressed, an operating force is transmitted through the linkage rod


16


to shift the stepless transmission


7


(trunnion


12


) forward F to a high speed position. When the rearward pedal portion


13




r


is depressed, an operating force is transmitted through the linkage rod


16


to shift the stepless transmission


7


(trunnion


12


) backward R to a high speed position. A rapid depression of forward or rearward pedal portion


13




f


or


13




r


is eased by the damper


23


. The arm


21


constantly biases the stepless transmission


7


(trunnion


12


) and shift pedal


13


to neutral position N. The rubber cushions


15


prevent vibration of stepless transmission


7


(trunnion


12


) from being transmitted to the shift pedal


13


. Thus, in this embodiment, the linkage rod


16


, boss member


18


, control arm


19


and control shaft


22


constitute a first linkage mechanism for transmitting a downward displacement of the shift pedal


13


to the stepless transmission


7


(trunnion


12


) to change a shift position of stepless transmission


7


(a turning angle of trunnion


12


).




A structure for retaining the shift pedal


13


and stepless transmission


7


in a desired shift position forward F set by a shift lever


26


, i.e. a retaining mechanism, will be described next.




As shown in

FIGS. 6 and 7

, a planar support member


27


shaped rectangular in side view is provided, and a support plate


28


is fixed to support rods


27




a


fixed to the support member


27


. A cam boss member


29


is supported by a boss


27




b


of support member


27


to be rotatable within a predetermined angular range as described later. An end of a control shaft


30


is rotatably supported by a boss


28




a


of support plate


28


. The other end of control shaft


30


is rotatably supported by the cam boss member


29


.




A linkage arm


34


is supported to be pivotable about a transverse axis P


4


of a support arm


27




c


fixed to the support member


27


. A bracket


44


with a slot


44




a


is fixed to a distal end of linkage arm


34


. A control arm


35


is relatively rotatably mounted on the control shaft


30


. A linkage rod


36


is connected between the control arm


35


and linkage arm


34


. As described later, a pin


13




c


of a bracket


13




b


fixed to the rearward pedal unit


13




r


is inserted into the slot


44




a


of bracket


44


to interlock the linkage arm


34


and rearward pedal unit


13




r.






A support member


31


L-shaped in front view is fixed by a spring pin


32


mounted on the control shaft


30


. A control arm


33


U-shaped in side view is supported to be pivotable about a fore and aft axis P


3


at an upper end of support member


31


. The shift lever


26


is fixed to the support member


31


. A ring


37


with a pin


37




a


is slidably mounted on the control shaft


30


. The control arm


33


has a pin


33




a


thereof engaged with the ring


37


. A spring


39


biases the shift lever


26


and control arm


33


counterclockwise in

FIG. 7

(in a direction to move the pin


37




a


away from the control arm


35


). A spring


43


is connected between the support plate and control arm


33


to bias the shift lever


26


to a neutral position N in a lever guide


38


(FIG.


9


).




In the state shown in

FIGS. 6

,


7


and


9


, the shift lever


26


is operated to neutral position N of lever guide


38


. The pin


37




a


is moved rightward

FIG. 7

away from the control arm


35


. When, in this state, the shift lever


26


is operated from the neutral position N to a forward shifting path


38




a


along the lever guide


38


, the control arm


33


slides the ring


37


and pin


37




a


leftward in FIG.


7


. Then the pin


37




a


contacts the control arm


35


from below. When, in this state, the shift lever


26


is operated along the forward shifting path


38




a


, the shift lever


26


rotates the control shaft


30


and pin


37




a


together. The pin


37




a


rotates the control arm


35


with the control shaft


30


.




As shown in

FIG. 7

, the control shaft


30


has splines formed on a leftward portion in

FIG. 7. A

plurality of first friction plates


41


are mounted on the splines of control shaft


30


to be rotatable with the control shaft


30


. A plurality of second friction plates


42


are arranged between the first friction plates


41


to be rotatable relative to the control shaft


30


. One end of each second friction plate


42


is engaged with a pin


29




b


of a cam plate


29




a


fixed to the cam boss member


29


, whereby the second friction plates


42


are fixed to the cam plate


29




a


. A spring


40


is provided for pressing the cam plate


29




a.






As shown in

FIGS. 6

,


7


and


8


, a boss member


45


is supported to be rotatable about a transverse axis P


5


of support member


27


. The boss member


45


has a first arm


45




a


engaged with the cam plate


29




a


. The support member


27


has a stopper


46


for stopping rotation of the cam plate


29




a


counterclockwise from the position shown in FIG.


8


. The cam plate


29




a


is fixed to the position shown in

FIGS. 6 and 7

, by interlocking between a second arm


45




b


of boss member


45


and side brake pedals


10


as described later, and by the stopper


46


.




As shown in

FIGS. 2 and 10A

, a support shaft


47


is fixed to the outer wall of the right body frame


3


, and a pair of bosses


48


are rotatably arranged on the support shaft


47


. Right and left side brake pedals


10


are fixed to the right and left bosses


48


. Right and left side brakes (not shown) are provided for braking the right and left rear wheels


2


independently of each other. The right side brake pedal


10


is mechanically interlocked to the right side brake. The left side brake pedal


10


is mechanically interlocked to the left side brake. A spring


54


is provided for biasing and returning the right and left side brake pedals


10


.




As shown in

FIG. 10A

, a control arm


49


is supported to be pivotable about a transverse axis P


6


on the right body frame


3


. As shown in

FIGS. 6 and 7

, a linkage rod


50


is connected between the second arm


45




b


of boss member


45


and the control arm


49


. As shown in

FIG. 10A

, the right and left bosses


48


have arms


48




a


of different lengths. A link


51


connected to the control arm


49


is connected through a pair of links


52


and a pin


53


to the arms


48




a


of right and left bosses


48


.




In this embodiment, as will be appreciated from the above description, the control shaft


30


, spring


40


and first and second friction plates


41


and


42


constitute a retaining mechanism for producing a retaining position corresponding to a shift position (a rotating angle of trunnion


12


) in which the stepless transmission


7


is to be retained. In this embodiment, the linkage arm


34


, control arm


35


and linkage rod


36


constitute a second linkage mechanism for transmitting a displacement of the shift lever


26


to the shift pedal


13


in order to displace the shift pedal


13


to a depressed position corresponding to the retaining position set by the shift lever


26


and retained by the retaining mechanism.




As seen

FIGS. 1

,


6


and


7


, the shift lever


26


, retaining mechanism and second linkage mechanism, i.e. the shift lever


26


, control shaft


30


, cam plate


29




a


, spring


40


, first and second friction plates


41


and


42


, linkage arm


34


, control arm


35


and linkage rod


36


constitute a single unit independent of the first linkage mechanism and supported by the support member


27


.




Thus, when manufacturing the type of vehicle with no mechanism for retaining the shift pedal


13


and stepless transmission


7


in a desired shift position forward F set by the shift lever


26


, the above unit is not provided for the vehicle body, and the lever guide


38


is omitted also. The control arm


49


, linkage rod


50


, link


51


or


52


or pin


53


shown in

FIG. 10A

is not provided either. (The bosses


48


shown in

FIG. 19A

may be replaced with bosses


48


not having arms


48




a


.)




Next, when manufacturing the type of vehicle with the mechanism for retaining the shift pedal


13


and stepless transmission


7


in a desired shift position forward F set by the shift lever


26


, i.e. the cruising mechanism, as shown in

FIG. 1

,


6


and


7


, the unit is disposed rearwardly of the shift pedal


13


, the support member


27


is fixed to the vehicle body with bolts


55


, the lever guide


38


placed in position, and the pin


13




c


of bracket


13




b


of rearward pedal portion


13




r


is inserted through the slot


44




a


of bracket


44


to interlock the linkage arm


34


and rearward pedal portion


13




r.






As shown in

FIG. 10A

, the control arm


49


, linkage rod


50


, links


51


and


52


and pin


53


are attached. As shown in

FIGS. 6 and 7

, the linkage rod


50


is connected to the second arm


45




b


of boss member


45


.




In the state shown in

FIGS. 6

,


7


and


9


, the shift lever


26


is operated to the neutral position N of lever guide


38


. The first and second friction plates


41


and


42


are pressed by the biasing force of spring


40


to retain the shift lever


26


in the neutral position N with the frictional force. The ring


37


and pin


37




a


are slid by the control arm


33


rightward in

FIG. 7

, with the pin


37




a


lying away from the control arm


35


.




When, in this state, the forward pedal portion


13




f


is depressed, the stepless transmission


7


(trunnion


12


) is shifted forward F to a high speed position. The rearward pedal portion


13




r


causes the linkage arm


34


to pivot upward about the transverse axis P


4


. The linkage rod


36


causes the control arm


35


to pivot clockwise of

FIG. 6

about the control shaft


30


. When the rearward pedal portion


13




r


is depressed, the stepless transmission


7


(trunnion


12


) is shifted backward R to a high speed position. The rearward pedal portion


13




r


causes the linkage arm


34


to pivot downward about the transverse axis P


4


. The linkage rod


36


causes the control arm


35


to pivot counterclockwise of

FIG. 6

about the control shaft


30


.




Next, when the shift lever


26


is operated from the neutral position N to a high speed position along the forward shifting path


38




a


, the control arm


33


slides the ring


37


and pin


37




a


leftward in FIG.


7


. Then the pin


37




a


contacts the control arm


35


from below. In this state, the first and second friction plates


41


and


42


remain pressed by the biasing force of spring


40


to apply the frictional force to the shift lever


26


. As the shift lever


26


is operated along the forward shifting path


38




a


to the high speed position against the frictional force, the shift lever


26


rotates the control shaft


30


and pin


37




a


together clockwise in FIG.


6


. The pin


37




a


rotates the control arm


35


with the control shaft


30


clockwise in FIG.


6


. As a result, the linkage rod


36


causes the linkage arm


34


to pivot upward about the transverse axis P


4


to swing the rearward pedal portion


13




r


upward. The shift pedal


13


and stepless transmission


7


(trunnion


12


) are operated to the high speed position forward F as when the forward pedal portion


13




f


is depressed.




Conversely, when the shift lever


26


is operated toward a low speed position (toward the neutral position N) along the forward shifting path


38




a


against the frictional force, the pin


37




a


is swung counterclockwise in

FIG. 6

to move away from the control arm


35


. The stepless transmission


7


(trunnion


12


) and shift pedal


13


are biased to the neutral position N by the arm


21


shown in FIG.


3


. Therefore, when the shift lever


26


is operated toward the low speed position (toward the neutral position N) along the forward shifting path


38




a


against the frictional force, the shift pedal


13


and stepless transmission


7


(trunnion


12


) is shifted to a low speed position forward F, following the rotation of pin


37




a.






Even when the operator releases the shift lever


26


in a desired shift position after shifting the shift pedal


13


and stepless transmission


7


(trunnion


12


) to a high speed position or low speed position forward F with the shift lever


26


, the shift lever


26


is retained to the desired shift position by a frictional force produced by the spring


40


and first and the second friction plates


41


and


42


. Consequently, the shift pedal


13


and stepless transmission


7


(trunnion


12


) are retained in a desired shift position forward F by the action of arm


21


shown in

FIG. 3

to bias the stepless transmission


7


(trunnion


12


) and shift pedal


13


to the neutral position N and by the pin


37




a


. The lever guide


38


has no backward shifting path, and the shift pedal


13


and stepless transmission


7


(trunnion


12


) cannot be shifted backward R with the shift lever


26


.




When, in this state, the tractor runs temporarily at high speed, the forward pedal portion


13




f


may be depressed. When the forward pedal portion


13




f


is depressed, the control arm


35


pivots clockwise in

FIG. 6

away from the pin


37




a


. Thus the forward pedal portion


13




f


may be depressed with no problem. When the operator removes the foot from the forward pedal portion


13




f


, the control arm


35


is returned into contact with the pin


37




a


by the action of arm


21


shown in

FIG. 3

which biases the stepless transmission


7


(trunnion


12


) and shift pedal


13


to the neutral position N. The shift pedal


13


and stepless transmission


7


(trunnion


12


) return to the state retained in the desired shift position forward F.




As shown in

FIGS. 6

, and


8


, the first arm


45




a


of boss member


45


is engaged with the cam plate


29




a


. The second arm


45




b


of boss member


45


is interlocked to the side brake pedals


10


through the linkage rod


50


as shown in FIG.


10


A. The stopper


46


acts on the cam plate


29




a


. All these features prevent rotation of the cam plate


29




a


when the shift lever


26


is operated against the frictional force. The frictional force is thus steadily applied to the shift lever


26


.




Assume that the right and left side brake pedals


10


are both depressed in the state noted above where the shift pedal


13


and stepless transmission


7


(trunnion


12


) are retained in a desired shift position forward F.




When the right and left side brake pedals


10


are both depressed, as shown in

FIGS. 10A and 10B

, the pair of links


52


and pin


53


move rightward in the drawings, and the link


51


swings the control arm


49


to pull the linkage rod


50


toward the control arm


49


. Then, the boss member


45


and first arm


45




a


are rotated counterclockwise in

FIG. 6

, to rotate the cam plate


29




a


a predetermined angle clockwise in FIG.


6


.




As shown in

FIGS. 7 and 8

, the cam boss member


29


defines a slot


29




c


extending obliquely, and the boss


27




b


has a pin


56


inserted through the slot


29




c


of cam boss member


29


. When the cam plate


29




a


is rotated a predetermined angle clockwise in

FIG. 6

as noted above, the camming action of the pin


56


of boss


27




b


and the slot


29




c


of cam boss member


29


moves cam plate


29




a


, against the force of spring


40


, leftward in

FIG. 7

away from the first and second friction plates


41


and


42


. This eliminates the frictional force for retaining the shift lever


26


in the desired shift position. As a result, the shift lever


26


is returned to the neutral position N of lever guide


38


by the biasing force of spring


43


shown in FIG.


6


. The shift pedal


13


and stepless transmission


7


(trunnion


12


) are returned to the neutral position N by the action of arm


21


shown in

FIG. 3

which biases the stepless transmission


7


(trunnion


12


) and shift pedal


13


to the neutral position N.




Assume that one of the right and left side brake pedals


10


is depressed in the state where the shift pedal


13


and stepless transmission


7


(trunnion


12


) are retained in a desired shift position forward F.




When the right side brake pedal


10


is depressed, as shown

FIGS. 10A

to


10


B, only the right boss


48


and arm


48




a


are rotated clockwise, and the link


51


and the pair of links


52


are only bent upward about the pin


53


. The control arm


49


is not swung at all. When the left side brake pedal


10


is depressed, as shown

FIGS. 10A

to


11


B, only the left boss


48


and arm


48




a


are rotated clockwise, and the link


51


and the pair of links


52


are only bent downward about the pin


53


. The control arm


49


is not swung at all. Thus, when one of the right and left side brake pedals


10


is depressed, the frictional force for retaining the shift lever


26


in the desired shift position is never eliminated, and the shift lever


26


remains in the desired shift position.




Modifications of the Above Embodiment




In the construction shown in

FIGS. 2 and 4

, the bore


3




a


formed in the right vehicle body frame


3


may be eliminated, and the linkage rod


16


, damper


23


and control arm


14


may be arranged between the right and left body frames


3


. The shift pedal


13


disposed laterally outwardly of the right body frame


3


and the control arm


14


disposed between the right and left body frames


3


may be connected to each other by an interlocking shaft (not shown) rotatably extending through the right body frame


3


.




In the construction shown in

FIGS. 1 and 2

, the right and left body frames


3


formed of vertical plates may be replaced with right and left body frames


3


formed of a plurality of square pipe frames arranged at the right side with a predetermined vertical spacing therebetween, and a plurality of square pipe frames arranged at the left side with the predetermined vertical spacing therebetween. With this construction, the linkage rod


16


and the like are disposed to extend through the spacing between the upper and lower frame of the right body frame


3


.




The hydrostatic stepless transmission


7


may be replaced with a belt type stepless transmission (not shown). The hydrostatic stepless transmission


7


or belt type stepless transmission may be disposed in a forward region the vehicle body.




Different Embodiment




A different structure of the retaining mechanism for retaining the shift pedal


13


and stepless transmission


7


in a desired shift position forward F set by the shift lever


26


will be described next with reference to

FIGS. 12

,


13


and


14


. Parts identical to those of the foregoing embodiment are shown with the same reference numerals, and are not particularly described again.




In this embodiment, the spring for pressing the first and second friction plates


41


and


42


is changed from the compression spring


40


to a tension spring


140


. Specifically, a pivotable plate


100


having a pivot pin


110


is provided to be pivotable about a downwardly opening U-shaped cutout formed in a bracket


127




d


attached to the support member


27


. The pivotable plate


100


has a connecting pin


111


disposed at a small distance from the pivot pin


110


, and a connecting bore


112


disposed at a large distance from the pivot pin


110


. The connecting pin


111


is engaged with an upwardly opening U-shaped cutout defined adjacent a free end of a cam boss member


129


. The connecting bore


112


has, attached thereto, one end of the tension spring


140


extending parallel to the axis of cam boss member


129


. The other end of tension spring


140


is attached to a bore of a spring mounting member


140




a


bolted to the support plate


28


. Thus, the first and second friction plates


41


and


42


are constantly pressed by the tension spring


140


through a cam plate


129




a


of cam boss member


129


.




The pivotable plate


100


has, fixed to a free end thereof, an extension rod


101


extending parallel to the axis of cam boss member


129


. The forward end of extension rod


101


defines a right-angled bent portion. When the control arm


33


pivots slightly about the axis P


3


clockwise in

FIG. 12

, the bent portion contacts a push arm


133




a


extending downward from the lower end of control arm


33


, to push the


133




a


leftward in

FIG. 12

against the biasing force of tension spring


140


. When the shift lever


26


is moved along the forward shifting path


38




a


of lever guide


38


, the frictional retaining force of the first and second friction plates


41


and


42


is reduced only by slightly rocking the shift lever


26


about the axis P


3


. This lightens the shifting operation.




The following construction is provided for releasing the above retaining mechanism in response to an operation of the side brake pedals


10


. The boss member


45


supported to be rotatable about a transverse axis P


5


of support member


27


has a cam rod


145




a


attached the an outer peripheral surface thereof and extending obliquely to the transverse axis P


5


. A cam follower rod


102


extends downward from the extension rod


101


for contacting the peripheral surface of cam rod


145


. The cam rod


145




a


is inclined relative to the transverse axis P


5


by such a degree that the cam rod


145




a


displaces the cam follower rod


102


leftward in

FIG. 12

in response to a pivotal movement of boss member


45


caused by the operation of side brake pedals


10


. Consequently, when the side brake pedals


10


are operated, the pivot plate


100


swings clockwise in

FIG. 12

, thereby moving the cam boss member


129


leftward to release the first and second friction plates


41


and


42


.



Claims
  • 1. A shift control system for a working vehicle having a propelling stepless transmission, comprising:a shift pedal; a first linkage mechanism for transmitting a downward displacement of said shift pedal to said stepless transmission to change a shift position of said stepless transmission; a retaining mechanism for producing a retaining position corresponding to said shift position to retain said shift position of said stepless transmission; a shift lever for setting said retaining position retained by said retaining mechanism; and a second linkage mechanism for transmitting of an operating displacement of said shift lever to said shift pedal to displace said shift pedal to a depressed position corresponding to said retaining position set by said shift lever and retained by said retaining mechanism; wherein said shift lever, said retaining mechanism and said second linkage mechanism are attachable and detachable independently of said first linkage mechanism, such that said first linkage mechanism acts independently of said retaining mechanism and said second linkage mechanism.
  • 2. A shift control system as defined in claim 1, wherein said second linkage mechanism includes a play-accommodating mechanism for permitting a depression of said shift pedal to a higher speed position than the retaining position retained by said retaining mechanism, said play-accommodating mechanism permitting said shift pedal to be depressed to said higher speed position, said retaining position retained by said retaining mechanism.
  • 3. A shift control system as defined in claim 1, wherein said retaining mechanism, said shift lever and said second linkage mechanism are mounted on a support member attachable to and detachable from a body of said working vehicle, said the second linkage mechanism being connectable to said shift pedal.
  • 4. A shift control system as defined in claim 1, wherein said stepless transmission is disposed between right and left body frames, said shift pedal being disposed laterally outwardly of said right body frame, said first linkage mechanism extending through said right body frame, said retaining mechanism and said shift pedal being interlocked through said second linkage mechanism laterally outwardly of said right body frame.
  • 5. A shift control system as defined in claim 1, wherein:said stepless transmission is steplessly shiftable forward and backward; said shift pedal includes a forward pedal portion extending forward, and a rearward pedal portion extending rearward, said forward pedal portion being depressible to shift said stepless transmission for high forward speed, said rearward pedal portion being depressible to shift said stepless transmission for high backward speed; and said retaining mechanism is disposed rearwardly of said shift pedal, said second linkage mechanism interlocking said retaining mechanism and said rearward pedal portion.
  • 6. A shift control system for a working vehicle having a propelling stepless transmission, comprising:a shift pedal; a first linkage mechanism for transmitting a downward displacement of said shift pedal to said stepless transmission to change a shift position of said stepless transmission; a retaining mechanism for producing a retaining position corresponding to said shift position to retain said shift position of said stepless transmission; a shift lever for setting said retaining position retained by said retaining mechanism; and a second linkage mechanism for transmitting of an operating displacement of said shift lever to said shift pedal to displace said shift pedal to a depressed position corresponding to said retaining position set by said shift lever and retained by said retaining mechanism; wherein said retaining mechanism, said shift lever and said second linkage mechanism are mounted on a support member attachable to and detachable from a body of said working vehicle, said second linkage mechanism being connectable to said shift pedal.
  • 7. A shift control system as defined in claim 6, wherein said shift lever, said retaining mechanism and said second linkage mechanism are attachable and detachable independently of said first linkage mechanism.
  • 8. A shift control system as defined in claim 6, wherein said second linkage mechanism includes a play-accommodating mechanism for permitting a depression of said shift pedal to a higher seed position than the retaining position retained by said retaining mechanism, said play-accommodating mechanism permitting said shift pedal to be depressed to said higher speed position, said retaining position retained by said retaining mechanism.
  • 9. A shift control system as defined in claim 6, wherein said stepless transmission is disposed between right and left body frames, said shift pedal being disposed laterally outwardly of said right body frame, said first linkage mechanism extending through said right body frame, said retaining mechanism and said shift pedal being interlocked through said second linkage mechanism laterally outwardly of said right body frame.
  • 10. A shift control system as defined in claim 6, wherein:said stepless transmission is steplessly shiftable forward and backward; said shift pedal includes a forward pedal portion extending forward, and a rearward pedal portion extending rearward, said forward pedal portion being depressible to shift said stepless transmission for high forward speed, said rearward pedal portion being depressible to shift said stepless transmission for high backward speed; and said retaining mechanism is disposed rearwardly of said shift pedal, said second linkage mechanism interlocking said retaining mechanism and said rearward pedal portion.
Priority Claims (1)
Number Date Country Kind
11-262042 Sep 1999 JP
US Referenced Citations (5)
Number Name Date Kind
4059025 Waack et al. Nov 1977 A
4341129 Bando Jul 1982 A
4608879 Ishida et al. Sep 1986 A
4620575 Cuba et al. Nov 1986 A
5263385 Hirata et al. Nov 1993 A