Power transmitting system of a vehicle

Power system including differential-mechanism, clutch-mechanism, power-mechanism and dog-clutch disposed between an input rotary member to receive drive-force from a drive power source and output rotary-member to transmit drive-force to drive-wheels, the differential-mechanism including an input rotary element, output rotary element and reaction rotary element; the clutch-mechanism connecting two rotary elements of the input, output and reaction rotary elements of the differential-mechanism, to each other, the power-mechanism having predetermined gear ratio, and dog-clutch selectively placing a power path between the output rotary element and output rotary-member, in power transmitting state and power cutoff state; transmitting drive-force to drive-wheels while the clutch-mechanisms and dog-clutch are placed in engaged states. The dog-clutch engagement retainer mechanism holds the dog-clutch in engaged state while the power system turns in parking-lock-position inhibiting output rotary-member motion, and switching the dog-clutch from engaged to released when the power system switches to non-parking-lock position permitting the output rotary-member motion.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims the priority from Japanese Patent Application No. 2014-105717 filed on May 21, 2014, the disclosure of which is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a power transmitting system of a vehicle, wherein a differential mechanism, a power transmitting mechanism and a dog clutch are disposed between a drive power source and drive wheels.

2. Description of Related Art

There is well known a power transmitting system of a vehicle, comprising a differential mechanism, a clutch mechanism, a power transmitting mechanism and a dog clutch which are disposed between an input rotary member provided to receive a drive force from a drive power source of the vehicle and an output rotary member provided to transmit the drive force to drive wheels of the vehicle. The differential mechanism includes an input rotary element, an output rotary element and a reaction rotary element, and the clutch mechanism selectively connects two rotary elements of the input, output and reaction rotary elements of the differential mechanism, to each other. The power transmitting mechanism has a predetermined gear ratio, and the dog clutch is configured to selectively place a power transmitting path between the differential mechanism and the output rotary member, in a power transmitting state and a power cutoff state. WO/2013/176208 A discloses an example of such a vehicle power transmitting system, which has a power transmitting path provided with a continuously variable transmission mechanism, and a power transmitting path provided with a gear mechanism. These two power transmitting paths are arranged in parallel with each other between an input shaft and an output shaft of the power transmitting system. In the power transmitting path provided with the gear mechanism, a forward/reverse switching mechanism, a gear train and a dog clutch (claw clutch or positive clutch) are disposed in this order of description between the input and output shafts, in a direction from the input shaft toward the output shaft. The forward/reverse switching mechanism is provided with a planetary gear set, and a forward drive clutch for selectively connecting two rotary elements of the planetary gear set to each other. This vehicle power transmitting system can be configured such that a speed ratio of the power transmitting path provided with the gear mechanism is higher than a highest speed ratio (corresponding to the lowest gear position) of the power transmitting path provided with the continuously variable transmission mechanism. This configuration permits the vehicle to be driven with a large drive force upon starting of the vehicle, for instance, when the forward drive clutch and the dog clutch are both placed in engaged states to select the power transmitting path provided with the gear mechanism.

By the way, it is considered to control the dog clutch such that the dog clutch is held in its released state while an engine is held at rest, in view of a possibility that the vehicle is towed, and is switched to its engaged state when the engine is started. According to this control of the dog clutch, there is a risk of a failure to bring the dog clutch into the engaged state (namely, an “up-lock” of the dog clutch) due to a failure of meshing of spline teeth of the dog clutch (synchro-mesh mechanism) in abutting contact of tooth faces with each other, which may take place upon a so-called “garage shifting” action (from a parking position P to a drive position D, for example) of a shift lever just after the engine is started. This phenomenon results in a failure to speedily start the vehicle. Where the power transmitting path provided with the gear mechanism has a high speed ratio and the dog clutch is controlled to be held in the engaged state while the engine is held at rest, so that the dog clutch is ready for starting the vehicle, on the other hand, a rotary motion the speed of which is raised when the vehicle is towed is input from the output rotary member to the differential mechanism, so that the differential mechanism has a large difference among rotating speeds of its rotary elements, giving rise to a risk of deterioration of durability of the differential mechanism due to excessively high rotating speeds of the rotary elements such as a pinion gear. In this respect, it is noted that the problems described above had not been publicly recognized at the time the present invention was made.

SUMMARY OF THE INVENTION

The present invention was made in view of the background art described above. It is therefore an object of the present invention to provide a power transmitting system of a vehicle, which permits speedy starting of the vehicle after switching of the power transmitting system from its parking lock position to its non-parking-lock position, and which prevents a risk of deterioration of durability of a differential mechanism during towing or traction of the vehicle.

The object indicated above is achieved according to a first aspect of the present invention, which provides a power transmitting system of a vehicle, comprising a differential mechanism, a clutch mechanism, a power transmitting mechanism and a dog clutch which are disposed between an input rotary member provided to receive a drive force from a drive power source of the vehicle and an output rotary member provided to transmit the drive force to drive wheels of the vehicle, the above-described differential mechanism including an input rotary element, an output rotary element and a reaction rotary element, the above-described clutch mechanism selectively connecting two rotary elements of the above-described input, output and reaction rotary elements of the above-described differential mechanism, to each other, the above-described power transmitting mechanism having a predetermined gear ratio, and the above-described dog clutch being configured to selectively place a power transmitting path between the above-described output rotary element and the above-described output rotary member, in a power transmitting state and a power cutoff state, and wherein the above-described drive force is transmitted to the above-described drive wheels while both of the above-described clutch mechanism and the above-described dog clutch are placed in engaged states, the power transmitting system further comprising a dog-clutch engagement retainer mechanism configured to mechanically hold the above-described dog clutch in the engaged state while the power transmitting system is placed in a parking lock position for mechanically inhibiting a rotary motion of the above-described output rotary member, and to switch the above-described dog clutch from the engaged state to a released state when the power transmitting system is switched to a non-parking-lock position for mechanically permitting the rotary motion of the output rotary member.

According to the first aspect of the invention described above, the dog clutch is mechanically held in the engaged state while the power transmitting system is placed in the parking lock position, so that a synchromesh mechanism and a hub sleeve of the dog clutch remain aligned in phase with each other and are ready for the dog clutch to be placed in the engaged state (i.e., remain aligned as the dog clutch is released), even if the dog clutch is once switched to the released state when the vehicle is started after the power transmitting system is switched to the non-parking-lock position, whereby the dog clutch can be subsequently speedily brought into the engaged state, without occurrence of the so-called “up-lock”. Accordingly, the vehicle can be speedily started after the power transmitting system is switched to the non-parking-lock position. In addition, the dog clutch is not mechanically held in the engaged state while the power transmitting system is placed in the non-parking-lock position, so that it is possible to avoid a large difference among rotating speeds of the rotary elements of the differential mechanism in the released state of the dog clutch when the vehicle is towed in the non-parking-lock position (neutral position) of the power transmitting system. It is therefore possible to prevent a risk of deterioration of durability of the differential mechanism during towing of the vehicle.

According to a second aspect of the invention, the power transmitting system according to the first aspect of the invention further comprises: a clutch switching member configured to switch the above-described dog clutch between the engaged state and the released state; and a parking lock switching member configured to switch the power transmitting system between the parking lock position and the non-parking-lock position. The dog-clutch engagement retainer mechanism mechanically holds the above-described dog clutch in the engaged state, by holding the above-described clutch switching member and the above-described parking lock switching member in engagement with each other while the clutch switching member is located at a position for placing the dog clutch in the engaged state and while the parking lock switching member is located at a position for placing the power transmitting system in the parking lock position. According to this second aspect of the invention, the dog-clutch engagement retainer mechanism mechanically holds the dog clutch in the engaged state in an adequate manner, while the power transmitting system is placed in the parking lock position, and switches the dog clutch in an adequate manner from the engaged state to the released state when the power transmitting system is switched to the non-parking-lock position.

The object indicated above is also achieved according to a third aspect of the invention, which provides a power transmitting system of a vehicle, comprising a differential mechanism, a clutch mechanism, a power transmitting mechanism, a dog clutch, a clutch switching member, and a parking lock switching member, which are disposed between an input rotary member provided to receive a drive force from a drive power source of the vehicle and an output rotary member provided to transmit the drive force to drive wheels of the vehicle, the above-described differential mechanism including an input rotary element, an output rotary element and a reaction rotary element, the above-described clutch mechanism selectively connecting two rotary elements of the above-described input, output and reaction rotary elements of the above-described differential mechanism, to each other, the above-described power transmitting mechanism having a predetermined gear ratio, the above-described dog clutch being configured to selectively place a power transmitting path between the above-described output rotary element and the above-described output rotary member, in a power transmitting state and a power cutoff state, the above-described clutch switching member being configured to switch the above-described dog clutch between an engaged state and a released state, and the above-described parking lock switching member being configured to switch the power transmitting system between a parking lock position for mechanically inhibiting a rotary motion of the above-described output rotary member, and a non-parking-lock position for mechanically permitting the rotary motion of the above-described output rotary member, and wherein the above-indicated drive force is transmitted to the above-described drive wheels while the above-described clutch mechanism is placed in an engaged state and while the above-described dog clutch is placed in the engaged state, the power transmitting system being characterized in that: the above-described clutch switching member includes a protrusion; the above-described parking lock switching member includes a hook portion which is held in engagement with the above-described protrusion of the above-described clutch switching member located at a position for placing the above-described dog clutch in the engaged state when the power transmitting system is placed in the parking lock position, and is not held in engagement with the above-described protrusion when the power transmitting system is placed in the non-parking-lock position; and the above-described protrusion prevents a movement of the above-described clutch switching member toward a position for placing the above-described dog clutch in the released state, when the protrusion is held in engagement with the above-described hook portion of the above-described parking lock switching member.

According to the third aspect of the invention, the dog clutch is mechanically held in the engaged state while the power transmitting system is placed in the parking lock position, so that a synchromesh mechanism and a hub sleeve of the dog clutch remain aligned in phase with each other and are ready for the dog clutch to be placed in the engaged state (i.e., remain aligned as the dog clutch is released), even if the dog clutch is once switched to the released state when the vehicle is started after the power transmitting system is switched to the non-parking-lock position, whereby the dog clutch can be subsequently speedily brought into the engaged state, without occurrence of the so-called “up-lock”. Accordingly, the vehicle can be speedily started after the power transmitting system is switched to the non-parking-lock position. In addition, the dog clutch is not mechanically held in the engaged state while the power transmitting system is placed in the non-parking-lock position, so that it is possible to avoid a large difference among rotating speeds of the rotary elements of the differential mechanism in the released state of the dog clutch when the vehicle is towed in the non-parking-lock position (neutral position) of the power transmitting system. It is therefore possible to prevent a risk of deterioration of durability of the differential mechanism during towing of the vehicle.

According to a fourth aspect of the invention, the power transmitting system according to the third aspect of the invention is configured such that the above-described protrusion functions to provide a ratchet device which permits a movement of the above-described clutch switching member relative to the above-described hook portion toward the position for placing the above-described dog clutch in the engaged state, and prevents the movement of the clutch switching member toward the position for placing the dog clutch in the released state. According to this fourth aspect of the invention, the dog clutch is mechanically held in the engaged state in an adequate manner while the power transmitting system is placed in the parking lock position, and the dog clutch is switched in an adequate manner from the engaged state to the released state when the power transmitting system is switched to the non-parking-lock position. In addition, the dog clutch can be switched from the released state to the engaged state even while the parking lock switching member is placed in the position for placing the power transmitting system in the parking lock position, so that the dog clutch can be switched from the released state to the engaged state when the power transmitting system is switched to the parking lock position after the vehicle has been towed.

According to a fifth aspect of the invention, the power transmitting system according to any one of the first through fourth aspect of the invention further comprises a continuously variable transmission disposed in parallel with the above-described power transmitting mechanism, between the above-described input rotary member and the above-described output rotary member, and a first clutch configured to selectively place a first power transmitting path through which the drive force is transmitted from the above-described drive power source to the above-described drive wheels through the above-described continuously variable transmission, in a power transmitting state and in a power cutoff state. The power transmitting system is further configured such that the power transmitting mechanism has at least one gear position, and the above-described differential mechanism is disposed in a second power transmitting path through which the drive force is transmitted from the drive power source to the drive wheels through the above-described power transmitting mechanism, the above-described clutch mechanism selectively places the above-described second power transmitting path in a power transmitting state and in a power cutoff state, and the above-described dog clutch is disposed between the above-described clutch mechanism and the above-described output rotary member, to selectively place the above-described second power transmitting path in the power transmitting and power cutoff states. In the power transmitting system according to this fifth aspect of the invention wherein the continuously variable transmission and the power transmitting mechanism are disposed in parallel with each other between the input and output rotary members, the vehicle can be speedily started after the power transmitting system is switched to the non-parking-lock position, and the deterioration of durability of the differential mechanism during towing of the vehicle can be avoided.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the drawings, a preferred embodiment of the present invention will be described in detail.

Embodiment

FIG. 1is the schematic view showing an arrangement of a vehicle10to which the present invention is applicable. As shown inFIG. 1, the vehicle10is provided with a vehicle drive power source in the form of an engine12, drive wheels14, and a power transmitting system16disposed between the engine12and the drive wheels14. The power transmitting system16includes, within a stationary member in the form of a housing18; a fluid-operated power transmitting device in the form of a known torque converter20connected to the engine12; an input shaft22connected to the torque converter20; a continuously variable transmission mechanism in the form of a known belt-type continuously variable transmission24(hereinafter referred as a continuously variable transmission24) connected to the input shaft22; a forward/reverse switching device26connected to the input shaft22; a power transmitting mechanism in the form of a gear mechanism28connected to the input shaft22through the forward/reverse switching device26and disposed in parallel with the continuously variable transmission24; an output shaft30which is an output rotary member of both of the continuously variable transmission24and the gear mechanism28; a counter shaft32; a speed reducing gear device34consisting of a pair of gears which mesh with each other and which are respectively rotated with the output shaft30and the counter shaft32; a differential gear device38connected to the counter shaft32such that a differential gear36of the differential gear device38is rotated with the counter shaft32; and a pair of axles40connected to the differential gear device38. In the power transmission system16constructed as described above, a drive power, force or torque generated by the engine12is transmitted to the pair of drive wheels14through the torque converter20, the continuously variable transmission24or the forward/reverse switching device26and the gear mechanism28, the speed reducing gear device34, the differential gear device38, and the axles40.

As described above, the power transmitting system16is provided with the continuously variable transmission24and the gear mechanism28, which are disposed in parallel with each other, between the engine12(or the input shaft22which is an input rotary member receiving a drive force of the engine12) and the drive wheels14(or the output shaft30which is an output rotary member from which the drive force of the engine12is transmitted to the drive wheels14). Thus, the power transmitting system16has a first power transmitting path through which the drive force of the engine12is transmitted through the continuously variable transmission24from the input shaft22to the drive wheels14(that is, to the output shaft30), and a second power transmitting path through which the drive force of the engine12is transmitted through the gear mechanism28from the input shaft22to the drive wheels14(that is, to the output shaft30). In the power transmitting system16, one of the first and second power transmitting paths is selectively placed in a power transmitting state depending upon a running state of the vehicle10. The power transmitting system16is provided with clutches for selectively placing the first and second power transmitting paths in the power transmitting state. Namely, the power transmitting system16is provided with a first clutch in the form of a CVT drive clutch C2for placing the first power transmitting path in the power transmitting state or a power cutoff state, and a second clutch in the form of a forward drive clutch C1and a reverse drive brake B1for placing the second power transmitting path in the power transmitting state or a power cutoff state. The CVT drive clutch C2, the forward drive clutch C1and the reverse drive brake B1are power connecting/disconnecting devices, each of which is a known hydraulically operated frictional coupling device (friction clutch) which is placed in an engaged state by a hydraulic actuator. The forward drive clutch C1and the reverse drive brake B1are elements of the forward/reverse switching device26which will be described in detail.

The torque converter20is disposed radially outwardly of, and coaxially with the input shaft22, and is provided with a pump impeller20pconnected to the engine12, and a turbine impeller20tconnected to the input shaft22. A mechanically operated oil pump41is connected to the pump impeller20p, and is operated by a rotary motion of the pump impeller20pdriven by the engine12, to generate a pressurized working oil used to change a speed ratio of the continuously variable transmission24, to give a tension to a transmission belt70of the continuously variable transmission24, to selectively place the above-described clutches C1and C2and brake B1in their engaged and released states, and to lubricate various portions of the power transmitting system16.

The forward/reverse switching device26is disposed in the above-described second power transmitting path, radially outwardly of, and coaxially with the input shaft22, and is constituted principally by a planetary gear set26pof a double-pinion type, the forward drive clutch C1and the reverse drive brake B1. The planetary gear set26pis a differential mechanism including three rotary elements, that is, an input rotary element in the form of a carrier26c, an output rotary element in the form of a sun gear26s, and a reaction rotary element in the form of a ring gear26r. The carrier26cis integrally connected to the input shaft22, and the ring gear26ris selectively fixed to the housing18through the reverse drive brake B1, while the sun gear26sis fixed to a small-diameter gear42which is disposed radially outwardly of, and coaxially of the input shaft22such that the sun gear26sis rotatable relative to the input shaft22. The carrier26cand the sun gear26sare selectively connected to each other through the forward drive clutch C1. Namely, the forward drive clutch C1functions as a clutch mechanism configured to selectively connect two rotary elements of the three rotary elements of the planetary gear set26p, while the reverse drive brake B1functions as a clutch mechanism configured to selectively fix the reaction rotary element of the planetary gear set26pto the housing18.

The gear mechanism28includes the above-indicated small-diameter gear42, and a large-diameter gear46which meshes with the small-diameter gear42and which is disposed radially outwardly of, and coaxially with a gear mechanism counter shaft44such that the large-diameter gear46is rotatable relative to the gear mechanism counter shaft44. Thus, the gear mechanism28functions as a power transmitting mechanism having a predetermined gear ratio (one constant gear ratio or gear stage). An idler gear48is fixedly and coaxially mounted on the gear mechanism counter shaft44such that the idler gear48is rotated with the gear mechanism counter shaft44. Further, a dog clutch (claw clutch or positive clutch) D1is disposed radially outwardly of the gear mechanism counter shaft44, between the large-diameter gear46and the idler gear48, for selectively connecting these large-diameter and idler gears46and48to each other. Accordingly, the dog clutch D1is a dog clutch configured to selectively place a power transmitting path between the sun gear26sand the output shaft30of the power transmitting system16, in a power transmitting state and a power cutoff state, and functions as a third clutch configured to selectively place the above-described second power transmitting path between the forward drive clutch C1and the output shaft30, in the power transmitting state and the power cutoff state. The idler gear48meshes with an output gear56having a larger diameter than the idler gear48. The output gear56is fixedly and coaxially mounted on the output shaft30such that the output gear56is rotated with the output shaft30.

Described more specifically, the dog clutch D1includes a first gear50formed integrally with the gear mechanism counter shaft44, a second gear52formed integrally with the large-diameter gear46, and a hub sleeve54having internal teeth which are engageable with the first and second gears50and52. Further, the dog clutch D1includes a known synchronizing mechanism in the form of a synchro-mesh mechanism S1for synchronizing rotary motions of the first and second gears50and52when these first and second gears50and52are connected to each other. The large-diameter gear46and the gear mechanism counter shaft44are connected to each other when the hub sleeve54is held in engagement with the first and second gears50and52. The dog clutch D1is selectively placed in its engaged and released states, by axial movements of the hub sleeve54by a shift fork62fixed to a fork shaft58and operation of the fork shaft58by an actuator60. The shift fork62functions as a clutch switching member configured to place the dog clutch D1in the engaged and released states. In the power transmitting system16, a forward driving power transmitting path (or a reverse driving power transmitting path) is established in the above-described second power transmitting path, to transmit the drive force of the engine12to the output shaft30through the input shaft22and the gear mechanism28when the forward drive clutch C1(or the reverse drive brake B1) and the dog clutch D1are both placed in the engaged states. In the power transmitting system16, the second power transmitting path is placed in a neutral state (power cutoff state) when at least both of the forward drive clutch C1and the reverse drive brake B1are placed in the released states, or when at least the dog clutch D1is placed in the released state.

The continuously variable transmission24is disposed in a power transmitting path between the input shaft22and the output shaft30. The continuously variable transmission24is provided with a primary pulley64fixedly mounted on the input shaft22, a secondary pulley68fixedly mounted on a rotary shaft66disposed coaxially with the output shaft30, and the above-indicated transmission belt70connecting the primary and secondary pulleys64and68. A drive force is transmitted between the primary and secondary pulleys64and68through forces of friction between the transmission belt70and the pulleys64,68. An effective diameter of each of the pulleys64and68, which is defined by widths of V-grooves of the pulleys64,68for engagement with the transmission belt70, is variable so that a speed ratio (gear ratio) γ of the continuously variable transmission24(=an input shaft speed Ni/an output shaft speed No) is variable. The CVT drive clutch C2is disposed on one of opposite sides of the continuously variable transmission24which is on the side of the drive wheels14, that is, disposed between the secondary pulley68and the output shaft30, to selectively connect and disconnect the secondary pulley68(rotary shaft66) and the output shaft30to and from each other. In the power transmitting system16, a power transmitting path is established in the above-described first power transmitting path, to transmit the drive force of the engine12to the output shaft30through the input shaft22and the continuously variable transmission24when the CVT drive clutch C2is placed in the engaged state. In the power transmitting system16, the first power transmitting path is placed in a neutral state (power cutoff state) when the CVT drive clutch C2is placed in the released state.

Operations of the power transmitting system16will be described by reference toFIG. 2, which is the view for explaining the operations of the power transmitting system16to switch its drive mode.FIG. 2includes tables indicating different combinations of the operating states of the forward drive clutch C1, CVT drive clutch C2, reverse drive brake B1and dog clutch D1, which combinations correspond to respective different drive modes of the power transmitting system16. In the tables, a “o” mark represents the engaged state, while a “x” mark represents the released state.

Initially, a gear drive mode of the power transmitting system16will be described. In the gear drive mode, the drive force of the engine12is transmitted to the output shaft30through the gear mechanism28, that is, through the second power transmitting path. As indicated inFIG. 2, this gear drive mode is established to drive the vehicle10in the forward direction, in the engaged states of the forward drive clutch C1and the dog clutch D1and in the released states of the CVT drive clutch C2and the reverse drive brake B1.

Described more specifically, the rotary elements of the planetary gear set26pof the forward/reverse switching device26are rotated as a unit, in the engaged state of the forward drive clutch C1, so that the small-diameter gear42is rotated with the input shaft22at the same speed, while at the same time the large-diameter gear46meshing with the small-diameter gear42is rotated. In the engaged state of the dog clutch D1, the large-diameter gear46and the gear mechanism counter shaft44are connected to each other, so that the gear mechanism counter shaft44and the idler gear48are rotated. Since the output gear56is held in engagement with the idler gear48, the output shaft30formed integrally with the output gear56is rotated. In the engaged states of the forward drive clutch C1and the dog clutch D1, therefore, the drive force of the engine12is transmitted to the output shaft30through the torque converter20, the forward/reverse switching device26, the gear mechanism28, the idler gear48, etc. In this respect, it is noted that the gear drive mode is established to drive the vehicle10in the reverse direction, in the engaged states of the reverse drive brake B1and the dog clutch D1, and in the released states of the CVT drive clutch C2and the forward drive clutch C1.

Then, a high-speed CVT drive mode and a medium-speed CVT drive mode of the power transmitting system16will be described. In the CVT drive modes, the drive force of the engine12is transmitted to the output shaft30through the continuously variable transmission24, that is, through the first power transmitting path. As indicated inFIG. 2, the high-speed CVT drive mode is established in the engaged state of the CVT drive clutch C2and in the released states of the forward drive clutch C1, the reverse drive brake B1and the dog clutch D1.

Described more specifically, the secondary pulley68and the output shaft30are connected to each other, and are rotated together, in the engaged state of the CVT drive clutch C2. In the engaged state of the CVT drive clutch C2, therefore, the drive force of the engine12is transmitted to the output shaft30through the torque converter20and the continuously variable transmission24. The dog clutch D1is held in the released state in the high-speed CVT drive mode, for the purpose of avoiding dragging of the gear mechanism28, etc. in the high-speed CVT drive mode, and preventing rotary motions of the rotary elements (such as the pinion gear) of the gear mechanism28and the planetary gear set26pat excessively high speeds.

The gear drive mode described above is selected while the vehicle10is held stationary or when the vehicle10is driven at a relatively low running speed. The second power transmitting path has a gear ratio γ1(namely, a gear ratio EL established by the gear mechanism28) which is determined to be higher (i.e. to be lower vehicle running speed) than a maximum gear ratio value γmax of the continuously variable transmission24, which value γmax corresponds to the lowest rotating speed of the secondary pulley. Namely, the vehicle running speed corresponding to the gear ratio γ1is lower than the vehicle running speed corresponding to the maximum gear ratio value γmax of the continuously variable transmission24. For instance, the gear ratio γ1corresponds to a gear ratio of a first-speed gear position of the power transmitting system16, while the maximum gear ratio value γmax of the continuously variable transmission24corresponds to a gear ratio of a second-speed gear position of the power transmitting system16. Accordingly, the gear drive mode and the high-speed CVT drive mode are selected according to shifting lines defined by a shifting map used to shift a known step-variable automatic transmission between its first-speed and second-speed gear positions. Further, in the high-speed CVT drive mode, the gear ratio γ of the continuously variable transmission24is controlled on the basis of a running condition of the vehicle10as represented by an operation amount θacc of an accelerator pedal and a running speed V of the vehicle10, and according to a known CVT shifting method (continuously variable shifting operation). The vehicle drive mode is switched from the gear drive mode to the high-speed CVT drive mode, or from the high-speed CVT drive mode to the gear drive mode, via the medium-speed CVT drive mode also indicated inFIG. 2.

When the vehicle drive mode is switched from the gear drive mode to the high-speed CVT drive mode, for example, the vehicle drive mode is first switched from the gear drive mode to the medium-speed CVT drive mode, that is, the forward drive clutch C1placed in the engaged state to establish the gear drive mode is brought into the released state, and the CVT drive clutch C2placed in the released state to establish the gear drive mode is brought into the engaged state, while the dog clutch D1is kept in the engaged state, so that the medium-speed CVT drive mode is temporarily established by a so-called “clutch-to-clutch (CtoC) shifting operation” in which a releasing action of the forward drive clutch C1and an engaging action of the CVT drive clutch C2are concurrently performed. As a result, the power transmitting system16is switched from the second power transmitting path to the first power transmitting path, so that the power transmitting system16is substantially shifted up. After the second power transmitting path is established (after the vehicle drive mode is once switched to the high-speed CVT drive mode), the vehicle drive mode is then switched from the medium-speed CVT drive mode to the high-speed CVT drive mode, by bringing the dog clutch D1into the released state to avoid an undesired dragging of the gear mechanism28, etc. (to cut off a tractive or towing force input as indicated inFIG. 2), and to prevent the rotary motions of the rotary elements of the planetary gear set26pat excessively high speeds. Thus, the dog clutch D1functions as a tractive force input cutoff clutch for cutting off the tractive force input to the power transmitting system16through the drive wheels14.

When the vehicle drive mode is switched from the high-speed CVT drive mode to the gear drive mode, on the other hand, the vehicle drive mode is first switched from the high-speed CVT drive mode to the medium-speed CVT drive mode, that is, the dog clutch D1placed in the released state to establish the high-speed CVT drive mode is brought into the engaged state, while the CVT drive clutch C2is kept in the engaged state, so that the medium-speed CVT drive mode is temporarily established (for “preparation for a shift-down action” indicated inFIG. 2). In this medium-speed CVT drive mode, a rotary motion is transmitted also to the sun gear26sof the planetary gear set26pthrough the gear mechanism28. Then, the vehicle drive mode is switched from the medium-speed CVT drive mode to the gear drive mode by a clutch-to-clutch (CtoC) shifting operation in which a releasing action of the CVT drive clutch C2and an engaging action of the forward drive clutch C1are concurrently performed. As a result, the power transmitting system16is switched from the first power transmitting path to the second power transmitting path, so that the power transmitting system16is substantially shifted down.

As shown inFIG. 4, the vehicle10is provided with a manually operated member in the form of a shift lever72having a plurality of shift positions Psh, such as a parking position P, a reverse drive position R, a neutral position N and a forward drive position D. An operation of the shift lever72causes a rotary motion of a shaft74(shown inFIGS. 5A and 5B) and a pivotal motion of a detent lever76(shown inFIGS. 5A and 5B) connected to the shaft74, through a linkage mechanism including a link and a cable etc., so that a spool of a manual valve (not shown) connected to the detent lever76is axially moved to control mutual communications of respective oil passages in a hydraulic control unit78of the power transmitting system16depending on the shift position Psh.

When the shift lever72is operated to the parking position P, the power transmitting system16is placed in a parking lock position P (“position” is also referred as “range” in the description of the power transmitting system16) in which each of the first and second power transmitting paths is placed in the power cutoff state, while a rotary motion of a parking gear82(namely, a rotary motion of an output gear83(shown inFIG. 1) formed integrally with the parking gear82) and rotary motions of the drive wheels14are mechanically prevented by a parking lock mechanism80(shown inFIG. 3) provided in the vehicle10. The output gear83is one of a pair of gears of the speed reducing gear device34, which one gear is fixedly mounted on the output shaft30. In the parking lock position P, therefore, a rotary motion of the output shaft30is mechanically prevented. When the shift lever72is operated to the reverse drive position R, the power transmitting system16is placed in a reverse drive position R in which the vehicle10can be driven in the reverse direction. When the shift lever72is operated to the neutral position N, the power transmitting system16is placed in a neutral position N in which each of the first and second power transmitting paths is placed in the power cutoff state. When the shift lever72is operated to the forward drive position D, the power transmitting system16is placed in a forward drive position D in which the vehicle10can be driven in the forward direction. The forward drive position D and the reverse drive position R are vehicle drive positions selected to drive the vehicle10, while the parking lock position P and the neutral position N are non-vehicle-drive positions selected when the vehicle10is not driven. The forward and reverse drive positions D and R, and the neutral position N are non-parking-lock positions for mechanically permitting the rotary motion of the output shaft30.

As shown inFIG. 3, the parking lock mechanism80is provided with the above-described parking gear82, a locking pawl84as locking teeth engageable with the parking gear82to prevent the rotary motion of the output gear83, a locking cam86, and a support pin88. The locking pawl84is pivotable about the support pin88by the locking cam86. The locking cam86is mechanically movable in a direction indicated by an arrow A (indicated inFIG. 3), by the detent lever76(shown inFIGS. 5A and 5B) which is pivoted when the shift lever72is operated. Namely, when the shift lever72is operated to the parking position P, the locking cam86is moved in the direction of the arrow A, so that the locking pawl84is pivoted upwards in a direction indicated by an arrow B, as shown inFIG. 3, for engagement with the parking gear82to mechanically prevent the rotary motions of the drive wheels14connected to the parking gear82, so that the power transmitting system16is placed in the parking lock position P. In the present embodiment, the detent lever76functions as a parking lock switching member provided to switch the power transmitting system16between the parking lock position P and the non-parking-lock positions.

FIG. 4is the functional block diagram showing major portions of a control system provided for controlling the vehicle10, and major portions of the vehicle10to be controlled by the control system. As shown inFIG. 4, the control system includes an electronic control device90which includes a shifting control portion for selectively establishing the different vehicle drive modes of the power transmitting system16described above. The functional block diagram ofFIG. 4shows input and output signals to and from the electronic control device90, and the portions of the vehicle10to which the output signals are applied from the electronic control device90. The electronic control device90includes a so-called microcomputer incorporating a CPU, a RAM, a ROM and an input-output interface. The CPU performs signal processing operations to implement various controls of the vehicle10according to programs stored in the ROM, while utilizing a temporary storage function of the RAM. For example, the electronic control device90implements an output control of the engine12, a shifting control and a belt tension control of the continuously variable transmission24, and a drive mode switching control of the power transmitting system16. The electronic control device90includes independent control units such as an engine control unit for controlling the engine12, and a shifting control unit for controlling the power transmitting system16.

The electronic control device90receives various input signals from various sensors, such as: an output signal of an engine speed sensor92indicative of an operating speed Ne of the engine12; an output signal of an input shaft speed sensor94indicative of an input shaft speed Ni; an output signal of an output shaft speed sensor96indicative of an output shaft speed No corresponding to the vehicle running speed V; an output signal of an accelerator operation amount sensor98indicative of the operation amount θacc of the accelerator pedal; and an output signal of a shift position sensor99indicative of the selected operating position Psh of the shift lever72. The electronic control device90generates various output signals such as: engine output control signals Se for implementing the output control of the engine12; hydraulic control command signals Scvt for hydraulic controls for shifting the continuously variable transmission24; and hydraulic control command signals Sswt for implementing the drive mode switching control of the power transmitting system16, more specifically, for controlling the forward/reverse switching device26, the CVT drive clutch C2, and the dog clutch D1. The hydraulic control command signals Sswt generated by the electronic control device90include command signals to be applied to the hydraulic control unit78for controlling solenoid-operated valves provided to control a hydraulic pressure to be applied to the actuator60for operating the hub sleeve54.

By the way, while the engine12is held at rest before the engine12is started, the oil pump41is also held at rest, so that the dog clutch D1cannot be switched between the engaged and released states, by applying and releasing the hydraulic pressure to and from the actuator60. If the dog clutch D1is placed in the engaged state while the engine12is held at rest, the pinion gear of the planetary gear set26p, for example, is rotated at an excessively high speed with the tractive force input through the drive wheels14when the vehicle10is towed, so that there is a risk of deterioration of durability of the planetary gear set26p. In view of a possibility that the vehicle10is towed, it is desirable to hold the dog clutch D1in the released state while the engine12is held at rest. Since a gear ratio at the lowest gear of the power transmitting system16is equal to the gear ratio EL established by the gear mechanism28, on the other hand, it is desirable to start the vehicle10in the gear drive mode established in the engaged states of both of the forward drive clutch C1and the dog clutch D1. In view of a so-called “garage shifting” action of the power transmitting system16from the parking lock position P to the forward drive position D just after the engine12is started, it is desirable to hold the dog clutch D1in the engaged state while the engine12is held at rest, so that the vehicle10can be speedily started. Thus, whether it is desirable to hold the dog clutch D1in the engaged state or in the released state while the engine12is held at rest depends upon whether the vehicle10is towed while the engine12is held at rest, or whether the garage shifting action of the shift lever72takes place just after the engine12is started. The power transmitting system16according to the present embodiment of the invention is configured to suitably deal with both the towing of the vehicle10and the garage shifting of the shift lever72.

Namely, the power transmitting system16includes a dog-clutch engagement retainer mechanism100(shown inFIGS. 5A, 5B, 6A, and 6B) configured to mechanically hold the dog clutch D1in the engaged state while the power transmitting system16is placed in the parking lock position P, and to switch said dog clutch from the engaged state to the released state when the power transmitting system is switched to any one of the non-parking-lock positions.

FIGS. 5A, 5B, 6A, and 6Bare views illustrating the dog-clutch engagement retainer mechanism100. The dog-clutch engagement retainer mechanism100is placed in an operating state shown inFIGS. 5A and 5B, when the power transmitting system16is placed in the parking lock position P, and in an operating state shown inFIGS. 6A and 6Bwhen the power transmitting system is placed in any one of the non-parking-lock positions.FIGS. 5A and 6Aare plan views of the dog-clutch engagement retainer mechanism100, whileFIGS. 5B and 6Bare side elevational views. InFIGS. 5A, 5B, 6A, and 6Bthe power transmitting system16and the dog-clutch engagement retainer mechanism100are shown partly in cross section, and connections of the system16and the mechanism100with respect to the other members are not shown.

The shift fork62is moved to a position for placing the dog clutch D1in the engaged state when predetermined hydraulic pressure is applied to an oil chamber60aof the actuator60as shown inFIGS. 5A and 5Band is moved to a position for placing the dog clutch D1in the released state, with a biasing force of a spring60bdisposed in the actuator60, when the predetermined hydraulic pressure is released from the oil chamber60a, as shown inFIGS. 6A and 6B.

The shift fork62has a protrusion102. The detent lever76has a hook portion104which is held in engagement with the protrusion102of the shift fork62located at the position for placing the dog clutch D1in the engaged state when the power transmitting system16is placed in the parking lock position P, and is not held in engagement with the protrusion102when the power transmitting system16is placed in the non-parking-lock positions. The dog-clutch engagement retainer mechanism100comprises the protrusion102and the hook portion104. The dog-clutch engagement retainer mechanism100mechanically holds the dog clutch D1in the engaged state, by holding the shift fork62located at the position for placing the dog clutch D1in the engaged state, in engagement with the detent lever76located at an angular position for placing the power transmitting system16in the parking lock position P, as shown inFIGS. 5A and 5B.

The detent lever76has a generally sectoral flat plate which is pivoted about the shaft74. The hook portion104has a projection106formed at an end part of an arc of the detent lever76which is located close to the protrusion102when the detent lever76is located at the angular position for placing the power transmitting system16in the parking lock position P. The projection106extends radially outwardly of the detent lever76and has an end portion which is partially bent toward the protrusion102.

The protrusion102prevents a movement of the shift fork62to a position for placing the dog clutch D1in the released state when the protrusion102is held in engagement with the hook portion104. Described more specifically, the protrusion102and a spring110(described below) functions as a ratchet device which permits a movement of the shift fork62relative to the hook portion104toward the position for placing the dog clutch D1in the engaged state, but inhibits the movement of the shift fork62relative to the hook portion104toward the position for placing the dog clutch D1in the released state. The shift fork62has a hole108formed in a part of a surface opposed to the detent lever76, which part is close to the projection106of the detent lever76located at the angular position for placing the power transmitting system16in the parking lock position P. The hole108is provided to accommodate a part of the protrusion102in the form of a quadrangular prism, and the above-described spring110for biasing the protrusion102toward the projection106prior to the protrusion102, so that the protrusion102partly protrudes out of the hole108toward the projection106. The protrusion102has a slant surface on the side of the fork shaft58(on the side of a movement of the fork shaft58in a direction to bring the dog clutch D1in the engaged state), so that a dimension of the protrusion102in a direction of movement of the shift fork62gradually decreases as the protrusion102protrudes toward the projection106. The protrusion102having the slant surface cooperates with the spring110to constitute the ratchet device with respect to the hook portion104of the detent lever76located at the angular position for placing the power transmitting system16in the parking lock position P.

In the power transmitting system16constructed as described above, the dog-clutch engagement retainer mechanism100holds the dog clutch D1in the engaged state, even when the predetermined hydraulic pressure is not applied to the oil chamber60aof the actuator60, that is, even when the engine12is held at rest, while the power transmitting system16is placed in the parking lock position P, as shown inFIGS. 5A and 5BFurther, the biasing action of the spring60bwith respect to the actuator60holds the dog clutch D1in the released state, when the predetermined hydraulic pressure is not applied to the oil chamber60aof the actuator60, that is, when the engine12is held at rest, while the power transmitting system16is placed in any one of the non-parking-lock positions, as shown inFIGS. 6A and 6B. Accordingly, when the vehicle10is towed in the neutral position N of the power transmitting system16with the engine12held at rest, the dog clutch D1is held in the released state. In addition, the dog clutch D1is switched between the engaged and released states depending upon whether the predetermined hydraulic pressure is applied to or released from the oil chamber60awhile the engine12is in operation in any one of the non-parking-lock positions of the power transmitting system16.

An example of a control operation of the electronic control device90to hold the dog clutch D1in the engaged state will be described. The electronic control device90switches the vehicle drive mode from the high-speed CVT drive mode to the gear drive mode when the electronic control device90has determined a requirement for a shift-down action of the power transmitting system16as a result of reduction of the vehicle running speed V while the accelerator pedal is in a non-operated state during running of the vehicle10in the high-speed CVT drive mode. In this case, the electronic control device90first generates a command signal for operating the hub sleeve54to switch the dog clutch D1from the released state to the engaged state, for switching the power transmitting system16to the medium-speed CVT drive mode. Then, the electronic control device90implements the clutch-to-clutch shift-down action by placing the CVT drive clutch C2in the released state and placing the forward drive clutch C1in the engaged state, as indicated inFIG. 2. When the shift lever72is then operated to the parking position P after the vehicle10is brought to a stop and before the engine12is stopped, the detent lever76is pivoted to the parking lock position P, and the hook portion104is brought into engagement with the projection102. Thus, the dog clutch D1is mechanically held in the engaged state in the parking lock position P of the power transmitting system16, even when the predetermined hydraulic pressure is not applied to the oil chamber60aof the actuator60after the engine12is stopped. Accordingly, the vehicle10can be speedily started by starting the engine12and operating the shift lever72from the parking position P to the forward drive position D, while the power transmitting system16is placed in the parking lock position P.

When the shift lever72is operated to the neutral position N and the vehicle10is towed while the dog clutch D1is held in the engaged state in the parking lock position P of the power transmitting system16, the detent lever76is pivoted to any one of the non-parking lock positions, so that the hook portion104is disengaged from the projection102. As a result, the dog clutch D1is brought into the released state while the predetermined hydraulic pressure is not applied to the oil chamber60aof the actuator60, with the engine12held at rest. Accordingly, during towing or traction of the vehicle10in the neutral position N of the shift lever72, it is possible to avoid the rotary motions of the rotary elements (such as the pinion gear) of the planetary gear set26pat excessively high speeds by the tractive force input through the drive wheels14. In addition, the ratchet device constituted by the protrusion102and the spring110permits the movement of the shift fork62relative to the hook portion104toward the position for placing the dog clutch D1in the engaged state, when the shift lever72is operated from the neutral position N back to the parking position P. Accordingly, the dog clutch D1is brought into the engaged state when the predetermined hydraulic pressure is applied to the oil chamber60aof the actuator60after the engine12is started.

In the power transmitting system16according to the present embodiment of the invention, the dog clutch D1is mechanically held in the engaged state while the power transmitting system16is placed in the parking lock position P, so that the dog clutch D1is kept in the engaged state when the vehicle is started up after releasing the power transmitting system16from the parking lock position P with the predetermined hydraulic pressure applied to the oil chamber60aof the actuator60after the engine12is started in the parking lock position P, or the synchromesh mechanism S1and the hub sleeve54of the dog clutch D1remain aligned in phase with each other and are ready for the dog clutch D1to be placed in the engaged state (i.e., remain aligned as the dog clutch D1is released), even if the dog clutch D1is once switched to the released state when the power transmitting system16is switched to the non-parking-lock position, whereby the dog clutch D1can be subsequently speedily brought into the engaged state, without occurrence of the so-called “up-lock”. Accordingly, the vehicle10can be speedily started after the power transmitting system16is switched to the non-parking-lock position. In addition, the dog clutch D1is not mechanically held in the engaged state while the power transmitting system is placed in the non-parking-lock position, so that it is possible to avoid a large difference among rotating speeds of the rotary elements of the planetary gear set26pin the released state of the dog clutch D1when the vehicle10is towed in the non-parking-lock position (neutral position N) of the power transmitting system16. It is therefore possible to prevent a risk of deterioration of durability of the planetary gear set26pdue to its high speed operation during towing of the vehicle10.

The power transmitting system16according to the present embodiment is further configured such that the dog-clutch engagement retainer mechanism100mechanically holds the dog clutch D1in the engaged state, by holding the shift fork62and the detent lever76in engagement with each other while the shift fork62is located at the position for placing the dog clutch D1in the engaged state and while the detent lever76is located at the position for placing the power transmitting system16in the parking lock position P. Accordingly, the dog-clutch engagement retainer mechanism100mechanically holds the dog clutch D1in the engaged state in an adequate manner, while the power transmitting system16is placed in the parking lock position P, and switches the dog clutch D1in an adequate manner from the engaged state to the released state when the power transmitting system16is switched to the non-parking-lock position.

The power transmitting system16according to the present embodiment is further configured such that the protrusion102cooperates with the spring110to function as the ratchet device which permits the movement of the shift fork62relative to the hook portion104toward the position for placing the dog clutch D1in the engaged state, and prevents the movement of the shift fork62toward the position for placing the dog clutch D1in the released state. Accordingly, the dog clutch D1is mechanically held in the engaged state in an adequate manner while the power transmitting system16is placed in the parking lock position P, and the dog clutch D1is switched in an adequate manner from the engaged state to the released state when the power transmitting system16is switched to the non-parking-lock position. In addition, the dog clutch D1can be switched from the released state to the engaged state even while the detent lever76is placed in the angular position for placing the power transmitting system16in the parking lock position, so that the dog clutch D1can be switched from the released state to the engaged state after the power transmitting system16is switched to the parking lock position P, when the power transmitting system16is switched to the parking lock position after the vehicle10has been towed.

The power transmitting system16according to the present embodiment is further configured such that the continuously variable transmission24and the gear mechanism28are disposed in parallel with each other between the input shaft22and the output shaft30, so that the vehicle10can be speedily started after the power transmitting system16is switched to the non-parking-lock position, and the deterioration of durability of the planetary gear set26pdue to towing of the vehicle10can be avoided.

While the preferred embodiment of the present invention has been described in detail by reference to the drawings, it is to be understood that the invention may be otherwise embodied.

In the illustrated embodiment, the power transmitting system16of the vehicle10is provided with the continuously variable transmission24and the gear mechanism28which are disposed in parallel with each other between the input shaft22and the output shaft30. However, the power transmitting system16may be provided with only one power transmitting path having the gear mechanism28between the input and output shafts22and30. Namely, the principle of the present invention is applicable to a power transmitting system provided with at least: the differential mechanism (such as the planetary gear set26pprovided in the illustrated embodiment) having three rotary elements; the forward drive clutch C1; a power transmitting mechanism (such as the gear mechanism28provided in the illustrated embodiment) having a predetermined gear ratio; and the dog clutch D1. In this sense, the power transmitting mechanism may be any type of transmission device other than the gear mechanism28, for instance, a transmission of a planetary gear type having a plurality of gear positions, and a continuously variable transmission, and the differential mechanism may be a differential gear device having a pinion and a pair of bevel gears meshing with the pinion.

Although the protrusion102provided in the illustrated embodiment takes the form of a quadrangular prism, the protrusion102may take the form of a cylinder or a triangular prism. In this case, the hole108has a cross sectional shape corresponding to the form of the protrusion102. Further, the protrusion102, which cooperates with the spring110to function as a ratchet device in the illustrated embodiment, need not function to provide a ratchet device. For instance, the protrusion102may be replaced by a protrusion which is not biased by the spring110and which does not have a slant surface. However, the protrusion102preferably function to provide a ratchet device that permits the dog clutch D1to be switched from the released state to the engaged state when the power transmitting system16is switched to the parking lock position P after towing or traction of the vehicle10.

Although the gear mechanism28provided in the illustrated embodiment is a power transmitting mechanism having one gear position having a predetermined gear ratio, the gear mechanism28may be replaced by a power transmitting mechanism having a plurality of gear positions having respective different gear ratios γ. That is, the power transmitting mechanism may be a step-variable transmission having two or more gear positions.

Further, the power transmitting system16may be selectively switched to the parking lock position P and the non-parking-lock positions with switching operations of the parking lock mechanism80, in response to an operation of the shift lever72, in a shift-by-wire (SBW) fashion according to electric control signals. The principle of the invention is applicable to this type of control of the power transmitting system16.

In the illustrated embodiment, the gear mechanism28is a power transmitting mechanism having the gear ratio EL higher than the highest gear ratio value γmax (corresponding to the lowest gear) of the continuously variable transmission24. However, the gear mechanism28may be a power transmitting mechanism having a gear ratio EH lower than a lowest gear ratio value γmin (corresponding to the highest gear) of the continuously variable transmission24. The principle of the invention is applicable to this type of power transmitting mechanism. This modification also applies to a power transmitting mechanism having a plurality of gear positions.

In the illustrated embodiment, the belt-type continuously variable transmission24is provided as a continuously variable transmission mechanism, and the CVT drive clutch C2is disposed between the continuously variable transmission24and the drive wheels14(namely, between the secondary pulley68and the output shaft30). However, a troidal type continuously variable transmission may be provided as the continuously variable transmission mechanism. Further, the CVT drive clutch C2may be disposed between the continuously variable transmission24and the engine12(namely, between the primary pulley64and the input shaft22).

In the illustrated embodiment, the vehicle drive mode of the power transmitting system16is switched according to a predetermined shifting map. However, the vehicle drive mode of the power transmitting system16may be switched by calculating a vehicle drive torque required by an operator of the vehicle10, on the basis of the vehicle running speed V and the accelerator pedal operation amount θacc, and determining the gear ratio that satisfies the calculated required vehicle drive torque.

While the hub sleeve54provided in the illustrated embodiment is operated by the hydraulic actuator60, the hub sleeve54may be operated by an electric motor, for example. Further, the dog clutch D1in which the hub sleeve54is kept in engagement with the first gear50in the illustrated embodiment may be a dog clutch in which the hub sleeve54is kept in engagement with the second gear52. Further, the dog clutch D1need not be provided with the synchro-mesh mechanism S1.

In the illustrated embodiment, the engine12provided as the drive power source is a gasoline engine, a diesel engine or any other internal combustion engine. However, the drive power source may be any other type of drive power source such as an electric motor or electric motors, or a combination of an engine and an electric motor or electric motors. Further, each of the forward drive clutch C1, the reverse drive brake B1and the CVT drive clutch C2, which are hydraulically operated frictional coupling devices in the illustrated embodiment, may be an electromagnetic clutch or any other type of frictional clutch.

While the preferred embodiment of the present invention and its modifications have been described for illustrative purpose only, it is to be understood that the invention may be embodied with various other changes and improvements which may occur to those skilled in the art.

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