Parking lock device for automatic transmission

A parking lock device for an automatic transmission includes: a parking gear externally fixed to the output shaft; a parking lock pole displaced between a lock position, where the parking lock pole latches onto the parking gear to disable rotation of the parking gear, and an unlock position, where the parking lock disengages from the parking gear to enable rotation of the parking gear; a parking rod for displacing the parking lock pole toward and away from the parking gear; a drive lever that moves the parking rod; and a booster mechanism interposed between the parking rod and the drive lever that increases the driving force of the drive lever. Thus, the parking lock device makes the driving force applied by the drive lever when unlocking as small as possible and prevents inadvertent unlocking when in a locked state, thereby achieving smooth operation and enhanced reliability.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2007-006099 filed on Jan. 15, 2007 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a parking lock device for an automatic transmission for a vehicle. The parking lock device causes a pawl of a parking lock pole to latch onto a parking gear, which is externally fixed to an output shaft of an automatic transmission, to lock and prevent rotation of the output shaft, and disengages the pawl from the parking gear to unlock and allow rotation of the output shaft.

2. Description of Related Art

In an automatic transmission for a vehicle, generally, a parking range (P), a reverse range (R), a neutral range (N), a drive range (D), and the like are set as the selectable shift ranges.

For instance, such an automatic transmission has a parking lock device for bringing the output shaft of the automatic transmission into a non-rotatable locked state when the parking range P is selected with a shift lever installed near the driver's seat of the vehicle (see, for example, Japanese Patent Application Publication No. 62-218261 (JP-A-62-218261), Japanese Patent Application Publication No. 9-267726 (JP-A-9-267726), and Japanese Patent Application Publication No. 9-240442 (JP-A-9-240442)).

This parking lock device includes a parking gear, a parking rod, a parking lock pole, and a drive lever.

Operation of the parking lock device will be described. First, when the parking rod is pushed to one side in its axial direction to tilt the parking lock pole, and the pawl of this parking lock pole is latched onto the parking gear externally fixed to the output shaft, the output shaft is brought into a non-rotatable locked state.

Further, when the parking rod is pulled to the other side in its axial direction to tilt the parking lock pole in a direction opposite to the above-mentioned direction, and the pawl of the parking lock pole is disengaged from the parking gear, the output shaft is brought into a rotatable unlocked state.

It should be noted that the parking rod is pushed or pulled in the axial direction by the drive lever that is tilted in response to an operation of placing the shift lever into the parking range or an operation of releasing the shift lever from the parking range. This parking rod is directly connected to a predetermined portion of the drive lever.

As the drive lever of this parking lock device, some related art devices use, for example, the manual valve lever of a range selector (see, for example, Japanese Patent Application Publication No. 9-267726 (JP-A-9-267726)).

The range selector is generally configured as follows. That is, when the shift lever installed near the driver's seat of the vehicle is operated by the driver, the manual valve lever is tilted. The state of a manual valve, which is a constituent element of a hydraulic controller for switching shift ranges, is changed in accordance with this tilting movement of the manual valve lever, thereby establishing the shift range selected by the above-mentioned shift change operation.

It should be noted that as the mode of power transmission between the manual valve lever and the shift lever, there is a type in which power is directly transmitted by mechanically coupling and connecting the manual valve lever and the shift lever by using a power transmission member such as a shift rod or shift cable, or the like, and a type in which the shift lever and the manual valve lever are not connected together by the power transmission member but are detached from each other, and when the shift lever is operated by the driver of the vehicle, the position of the selected shift range is detected by a sensor or the like, and the manual valve lever is driven by an actuator such as a motor so as to establish the detected shift range.

The above-mentioned related art still leaves room for improvements in the following respects.

As a general tendency, when a vehicle is stopped on a downhill slope, the same forward rotation torque as that at the time of forward movement is input to the output shaft from the driving wheels, whereas when the vehicle is stopped on an uphill slope, reverse rotation torque is input to the output shaft from the driving wheels.

When, in a state with the parking lock device locked, the above-mentioned forward rotation torque is input to the output shaft, this makes the pawl of the parking lock pole prone to disengage from the parking gear. In this case, the driving force of the manual valve lever (drive lever) required for bringing the parking lock device into an unlocked state can be made relatively small.

On the other hand, when, in a state with the parking lock device locked, the above-mentioned reverse rotation torque is input to the output shaft, the pawl of the parking lock pole bites into the parking gear. In this case, the driving force of the manual valve lever (drive lever) required for bringing the parking lock device into an unlocked state needs to be made relatively large.

However, since this phenomenon is established on the basis of the positional arrangement of the tilting axis of the parking lock pole with respect to the parking gear, if this positional arrangement differs, a phenomenon reverse to that mentioned above is established.

In view of the phenomenon as described above, generally, the engaging force or the like of a latch lever with each position groove of the manual valve lever is adjusted to allow suitable setting of the driving force of the manual valve lever required for achieving the above-mentioned unlocked state.

From the viewpoint of safety, this setting is desired to ensure that unlocking does not easily occur. However, in that case, the driving force to be applied by the drive lever at the time of unlocking needs to be set large, resulting in an increase in the requisite operation force of the shift lever.

In contrast, although it may be possible to use assist means such as a motor for facilitating the unlocking operation, this leads to an increase in equipment cost.

SUMMARY OF THE INVENTION

The present invention provides a parking lock device that locks the output shaft of an automatic transmission in a manner that prevents or allows rotation of the output shaft, as appropriate, and, by means of a simple configuration, minimizes the driving force that is applied by the drive lever when unlocking, and also prevents inadvertent unlocking when the output shaft is locked, thereby achieving smooth operation and enhanced reliability.

According to one aspect of the present invention, there is provided a parking lock device which brings an output shaft of an automatic transmission into a non-rotatable locked state or a rotatable unlocked state as required, the parking lock device includes: a parking gear externally fixed to the output shaft; a parking lock pole displaced between a lock position, where the parking lock pole approaches and latches onto the parking gear to thereby disable rotation of the parking gear, and an unlock position, where the parking lock pole separates and disengages from the parking gear to thereby enable rotation of the parking gear; a parking rod pushed and pulled to displace the parking lock pole toward or away from the parking gear; a drive lever supported in a tiltable manner that pushes or pulls the parking rod in a longitudinal direction of the parking rod; and a booster mechanism interposed between the parking rod and the drive lever, that increases a driving force of the drive lever applied when locking or unlocking the parking lock device and converts the driving force into a pressing force or a pulling force on the parking rod.

According to this configuration, the use of the booster mechanism increases the pressing force or pulling force on the parking rod even when the driving force applied by the drive lever when locking or unlocking the parking lock device is small. Accordingly, the parking lock device can be easily and reliably locked or unlocked with a relatively small force.

Therefore, the driving force of the drive lever required when stopping a vehicle on a uphill slope or a downhill slope to lock or unlock the parking lock device may be minimized.

Furthermore, the overall configuration is simple, which only involves interposing a mechanical booster mechanism between the driver lever and the parking rod. This is advantageous in reducing equipment cost as compared with a case where power assist means such as an expensive motor is equipped as described in the related art.

The booster mechanism may include a link which pivots about a position in the driver lever separated from a tilting axis and on one end of the parking rod. When the drive lever is tilted to a locking side, the link is positioned so that the link is aligned in a straight line with the parking rod and pushes the parking rod in the manner of a strut, and when the drive lever is tilted to an unlocking side, the link is positioned so that the link is inclined at a predetermined angle with respect to the parking rod and pulls the parking rod.

According to this configuration, the link and the drive lever constitute a toggle joint type booster mechanism.

In the booster mechanism as described above, due to the tilting movement of the drive lever, a tangential force (equivalent to a driving force) acts on the joint portion between the drive lever and the link, and the tangential force is increased by the boosting action and converted into a pressing force or pulling force that acts on the parking rod at the joint portion between the link and the parking rod.

This increases the pressure force or pulling force on the parking rod even when the tangential force, that is, the driving force of the drive lever, is small.

The booster mechanism may further include: a fixed link attached at both ends to a tilting axis and a position separated from the tilting axis in the drive lever; a movable link which is pivoted on the position in the driver lever separated from the tilting axis and on one end of the parking rod, and which, when the fixed link is tilted to the locking side integrally with the drive lever, is positioned so that the movable link is aligned in a straight line with the parking rod and pushes the parking rod in the manner of a strut, and when the fixed link is tilted to the unlocking side integrally with the drive lever, is positioned so that the movable link is inclined at a predetermined angle with respect to the parking rod and pulls the parking rod; a connecting bar whose both ends are engaged with elongated guide holes respectively provided in the fixed link and the movable link so as to extend between their both ends; and a stopper that prevents the fixed link and the movable link from bending opposite to an unlocking side in a state when the fixed link, the movable link, and the parking rod are aligned in a straight line.

According to this configuration, the two links constitute the booster mechanism of a toggle joint type. Thus, in the same manner as mentioned above, it is possible to increase the pressure force or pulling force on the parking rod even when the tangential force, that is, the driving force of the drive lever is small.

In addition, the movements of the two links are coordinated with each other by the connecting bar, thereby making the movements of the links smooth. Further, the stopper provides enhanced reliability of operation, such as by preventing the two links arranged in a straight line from bending inadvertently to the side opposite to the unlocking side.

Further, the ends of the elongated guide hole in the fixed link and of the elongated guide hole in the movable link, which are located near each other, may be extended so as to be offset to a side opposite to the unlocking side with respect to a line connecting the tilting axis of the drive lever and a pivot point at which the movable link is pivoted on the one end of the parking rod, in the state when the fixed link, the movable link, and the parking rod are aligned in a straight line.

According to this configuration, if, conversely to the normal operation, an axial load is applied toward the movable link from the parking rod, moments act to move the joint portions of the links to the stopper side.

Due to this operating principle, it is possible to keep the links aligned in a straight line and prevent the links from becoming unlocked as a result of bending.

With the parking lock device according to the present invention, it is possible, by means of a simple configuration, to make the driving force to be applied by the drive lever when shifting to an unlocked state as small as possible and prevent inadvertent unlocking when in a locked state. This makes it possible to achieve smooth operation and enhanced reliability of the parking lock device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described below with reference to the drawings.FIGS. 1 to 15show an embodiment of the present invention.

Before describing a portion to which features of the present invention are applied, an overview of an example of an automatic transmission to which a parking lock device according to the present invention is to be applied will be described with reference toFIGS. 1 and 2.

FIG. 1is a schematic diagram of an automatic transmission to which the present invention is to be applied, andFIG. 2is a perspective view showing a range selector and a parking lock device shown inFIG. 1.

In these figures, reference numeral1denotes an automatic transmission for a front-engine, rear-drive (FR) vehicle.

As shown inFIG. 1, the automatic transmission1mainly includes an input shaft2, a torque converter3, an oil pump4, a transmission mechanism unit5, a hydraulic controller6, an output shaft7, and the like. A transmission controller8controls the gear changes in the automatic transmission1.

The operation of the automatic transmission1can be summed up as follows. When the rotation of a crankshaft (not shown) of the engine1is input to the input shaft2via the torque converter3, the speed of the rotation input to the input shaft2is changed at a suitable gear ratio by the transmission mechanism unit5before being output from the output shaft7.

Although not illustrated in detail, the transmission mechanism unit5is configured by, for example, a plurality of planetary mechanisms. Alternatively, the transmission mechanism unit5can be configured as, for example, a gear mechanism having a plurality of gears, a continuously variable transmission mechanism called CVT, or the like.

The hydraulic controller6controls the gear change operation of the transmission mechanism unit5described above. Although not illustrated in detail, the hydraulic controller6includes at least a plurality of linear solenoid valves for controlling engaging operations of various brakes and clutches used in the transmission mechanism unit5, and a manual valve9for supplying hydraulic fluid to the respective linear solenoid valves as required.

The manual valve9supplies hydraulic fluid to each linear solenoid valve as appropriate from a suitable port in order to establish a neutral range N, a drive range D, or a reverse range R in accordance with an operation of a shift lever10by the driver.

The shift lever10is installed near the driver's seat of a vehicle, and is manually operated and placed into an arbitrary shift range (parking range P, reverse range R, neutral range N, or drive range D).

The manual valve9is configured as a so-called spool valve, and includes a valve body9ahaving various feed ports and exhaust ports (not shown), and a spool9baccommodated in the valve body9aso as to be axially displaceable. The valve body9ais fixed to the case of the automatic transmission1.

The manual valve9displaces the spool9bto one side or the other in the axial direction of the spool9bto position the spool9bat a predetermined position, thereby establishing the parking range P, the reverse range R, the neutral range N, or the drive range D as appropriate.

Further, the above-described automatic transmission1is equipped with a range selector20and a parking lock device30.

The range selector20changes the state of the manual valve9of the above-described hydraulic controller6in order to establish a gear position (such as the parking range P, the reverse range R, the neutral range N, or the drive range D) of the automatic transmission1corresponding to a shift range selected by the shift lever10, for example. As shown inFIGS. 2 and 3, the range selector20mainly includes a manual valve lever21, a shift control shaft22, an actuator23, and a latch lever24.

The manual valve lever21may be titled in, for example, four steps in coordination with shift ranges (the parking range P, the reverse range R, the neutral range N, and the drive range D) selected by the shift lever10. The manual lever21axially displaces the spool9bof the manual valve9in accordance with its tilt position.

Corrugated grooves are provided on one end side21aof the manual valve lever21. The corrugated grooves include the number of grooves (four grooves) corresponding to the four shift positions (the parking range P, the reverse range R, the neutral range N, and the drive range D) of the shift lever10. As shown inFIGS. 3 and 4, for example, marks “P, R, N, D” are written near the four grooves.

The front end of the spool9bof the manual valve9is joined to the other end side21bof the manual valve lever21. The front end of a parking rod33of the parking lock device30abuts against a projection member21c.

When the manual valve lever21is tilted as appropriate, the spool9bis axially displaced to advance and retract, thereby establishing the parking range P, the reverse range R, the neutral range N, or the drive range D.

The manual valve lever21is integrally joined to one end of the shift control shaft22.

The shift control shaft22is rotatably supported on the case or the like of the automatic transmission1, and is rotationally driven in a suitable direction by the actuator23.

Although not illustrated in detail, the actuator23includes, for example, a suitable motor and reduction gear mechanism (warm gear or the like). The transmission controller8controls the operation of the actuator23.

The latch lever24maintains the four tilt positions of the manual valve lever21individually. The latch lever24has, at the other end of its main body made of a leaf spring or the like whose one end is fixed to the case of the automatic transmission1, a pin24athat is engaged with one of the corrugated grooves in a sector arm21aof the manual valve lever21.

The transmission controller8is configured as a commonly known ECU (Electronic Control Unit). For example, the transmission controller8detects the position of the shift lever10by a range position sensor11, and drives the actuator23to control the hydraulic controller6, thereby establishing a suitable gear position, that is, a power transmission path in the transmission mechanism unit5.

The range position sensor11detects the range position, parking range (P), the reverse range (R), the neutral range (N), the drive range (D), and the like in which the shift lever10is placed.

Next, a gear change operation will be briefly described. For example, when the shift lever10is operated by the driver, the selected range is detected by the shift position sensor11, and on the basis of the detected range position, the transmission controller8rotationally drives the actuator23in a suitable direction, thus causing the shift control shaft22and the manual valve lever21integrated with the shift control shaft22to rotate, that is, to tilt by a predetermined angle.

This tilting of the manual valve lever21causes the spool9bof the manual valve9to slide, and the manual valve9of the hydraulic controller6is switched to a range selected from “P”, “R”, “N”, and “D”, so a suitable gear position is established within the transmission mechanism unit5.

The manual valve lever21is set and held in position as the pin24aof the latch lever24engages with an arbitrary groove in its sector arm21a.

Next, the basic configuration of the parking lock device30according to an embodiment of the present invention will be described in detail with reference toFIGS. 3 to 5.

The parking lock device30disables rotation of the output shaft7of the automatic transmission1when the driver selects the parking range P with the shift lever10. The parking lock device30basically includes a parking gear31, a parking lock pole32, and the parking rod33.

The parking gear31is externally fixed to the output shaft7, and the parking lock pole32is arranged near the parking gear31so that the lock pole32is able to tilt on its one end side as an axis. Provided at a halfway position in the longitudinal direction of the parking lock pole32is a pawl32athat is fit into or detached from between teeth of the parking gear31.

The parking rod33may be displaced toward its front end or its rear end substantially in parallel with the output shaft7due to tilting movement of the manual valve lever21that serves as a tilting lever.

The front end of the parking rod33is connected to the manual valve lever21via a booster mechanism40described later. A taper cone34for allowing the parking lock pole32to tilt is provided at the rear end of the parking rod33.

It should be noted that reference numeral35denotes a coil spring for pressing the taper cone34to the parking gear31side, and reference numeral36denotes a snap ring that is latched and fixed onto the parking rod33and receives one end of the coil spring35. Reference numeral37denotes a guide for guiding the axial displacement of the parking rod33.

The basic operation of the parking lock device30will be described.

First, when the manual valve lever21is tilted into a position as shown inFIG. 3, the parking rod33is pushed toward the rear, and the large-diameter-side portion of the taper cone34pushes the parking lock pole32upwards so that its pawl32ais inserted in between the teeth of the parking gear31. As a result, the output shaft7is non-rotatably locked in this state.

On the other hand, when the manual valve lever21is tilted into a position as shown inFIG. 4, the parking rod33and the taper cone34are pulled toward the front, and the force with which the parking lock pole32is pushed up by the taper cone34is released. Accordingly, the parking lock pole32moves downwards, and its pawl32acomes out from between the teeth of the parking gear31. As a result, the output shaft7is unlocked and able to rotate.

Now, the portion to which the features of the present invention is applied to the parking lock device30described above will be described in detail with reference to FIGS.3to15.

First, to unlock the parking lock device30, the manual valve lever21is tilted. In this regard, a contrivance is made to make the requisite driving force at this time as small as possible while preventing inadvertent unlocking when in a locked state.

Specifically, the booster mechanism40is interposed between the front end of the parking rod33and the manual valve lever21.

The booster mechanism40is a toggle joint type booster mechanism, and mainly includes a fixed link41, a movable link42, a connecting bar43, and a stopper44.

The fixed link41and the movable link42are each made of a two-ply strip plate, and are arranged adjacent to each other at a predetermined spacing with respect to the thickness direction. Further, the fixed link41and the movable link42are connected together at pivots45and46with the other end of the fixed link41and one end of the movable link42overlapped with each other. The other end of the fixed link41is thus pivoted on one end of the movable link42.

In the body portions of the links41and42, elongated guide holes41aand42aare respectively provided so as to penetrate the body portions in the thickness direction and extend in the longitudinal direction. The shape of the elongated guide holes41aand42awill be described later in detail.

The connecting bar43has guide pins43aand43bintegrally provided at each end of the connecting bar43of a single stripe, respectively. The guide pins43aand43bof the connecting bar43are respectively inserted in the elongated guide holes41aand42aof the links41and42with some play. The connecting bar43coordinates the movements of the links41and42to each other, thereby making the movements of the links41and42smooth.

The stopper44plays the following role. That is, in a state with the links41and42aligned so as to be continuous in a straight line, that is, when the parking lock device30is brought into a locked state, the stopper44prevents the links41and42from being inadvertently bent to the opposite to the unlocking side under an excessive momentum while keeping the links41and42arranged in a straight line. As such, the stopper44functions as a support plate or the like fixed to the case or the like of the automatic transmission1.

The fixed link41is integrally fixed to the manual valve lever21. Specifically, one end of the fixed link41is attached to the shift control shaft22serving as the tilting axis of the manual valve lever21, and the pivot45on the other end side of the fixed link41, that is, on the side connected to the movable link42, is attached to the projection member21cof the manual valve lever21.

The front end of the parking rod33is attached to the other end of the movable link42via a pivot47. The other end of the movable link42is thus pivoted on the front end of the parking rod.

Prior to assembly, the above-described pivots45,46, and47are each formed as, for example, a pin having a flange provided at one end. After the pin is passed through through-holes of the members to be connected together while leaving a predetermined gap as shown inFIG. 9, the distal end of the pin is caulked to form a flange, thereby preventing detachment. Further, the distal end of the shift control shaft22, and both ends of the guide pins43aand43bof the connecting bar43are also each assembled and caulked to form a flange in the same manner as mentioned above. It should be noted, however, the connecting structures may be fastened using a bolt and nut arrangement.

The position of the booster mechanism40may be changed as shown inFIG. 3, where the fixed link41and the movable link42are aligned in a straight line, or as shown inFIG. 4, where they are bent to form a V-shape, as the fixed link41integrally attached to the manual valve lever21changes its position following the tilting movement of the manual valve lever21.

The shape and placement of the elongated guide holes41aand42aof the links41and42are designed to prevent the links41and42from easily bending in a V-shape when an axial load is input from the parking rod33while the links41and42are aligned in a straight line. These arrangements will be described below with reference toFIG. 7.

First, the elongated guide holes41aand42aof the links41and42extend in a direction orthogonal to the longitudinal direction at the ends positioned close to each other. The elongated guide holes41aand42aare thus formed in a substantially L-shape.

Further, the centerline N of each of the elongated linear portions of the elongated guide holes41aand42ais arranged so as to be offset toward the unlocking side (side opposite to the stopper44) by a predetermined amount a, with respect to each of the centerlines L of the fixed link41and movable link42that extend continuously in a single line in a state with the fixed link41and the movable link42aligned in a straight line with the parking rod33.

Further, the extended ends of the elongated guide holes41aand42aare extended to a position where, when the guide pins43aand43bare arranged at the extended ends, the centers P of the guide pins43aand43bare offset to the side opposite to the unlocking side (stopper44side) with respect to the centerline L.

With the elongated holes41aand42aformed as described above, if, as shown inFIG. 11, an axial load Fa is applied from the parking rod33toward the movable link42, moments M1and M2act on the links41and42, which cause pivoted portions (45and46) of the links41and42to move toward the stopper44, respectively. It should be noted that the axial load Fa is generated as a reaction force from the parking rod33when a ratcheting operation is performed to move the shift lever10from the drive range D into the parking range P, for example.

Due to this operating principle, it is possible to keep the links41and42aligned in a straight line while preventing the links41and42from easily bending to the unlocking side.

Next, the operation of the parking lock device30when the above-described booster mechanism40is provided will be described, with reference toFIGS. 3,4, and10.

First, for example, when the shift lever10is moved from the drive range D to the parking range P, as shown inFIG. 3, the shift control shaft22and the manual valve lever21are tilted in the arrow A1direction (counterclockwise direction) in the drawing by the actuator23as described above. The pin24aof the latch lever24is thus engaged with the parking position groove of the manual valve lever21.

Simultaneously, the fixed link41is tilted in the same direction integrally with the tilting movement of the manual valve lever21, so the pivots45and46that connects the fixed link41with the movable link42are pushed in the arrow B1direction (upwards) in the drawing. This causes the fixed link41and the movable link42to be positioned so that they lie continuous to the parking rod33in a straight line as shown inFIGS. 3 and 10A.

When the fixed link41and the movable link42lie continuous to the parking rod33in a straight line, the distance between the one end of the fixed link41to the other end of the movable link42is at a maximum, which means that the parking rod33is pushed to the maximum in the arrow C1direction (rearwards) in the drawing. The parking lock pole32is thus pushed up by the taper cone34, bringing the parking gear31into a non-rotatable locked state.

On the other hand, when the shift lever10is moved from the parking range P to the reverse range R, as shown inFIG. 4, the shift control shaft22and the manual valve lever21are tilted in the arrow A2direction (clockwise direction) in the drawing by the actuator23. The pin24aof the latch lever24is thus engaged with the reverse position groove of the manual valve lever21.

Simultaneously, the fixed link41is tilted in the same direction together with the tilting movement of the manual valve lever21, so the pivots45and46that connect the fixed link41with the movable link42are pulled in the arrow B2direction (downwards) in the drawing. This causes the fixed link and the movable link42to be positioned so that they are bent in a V-shape as shown inFIGS. 4 and 10B.

In this state, the distance between the one end of the fixed link41to the other end of the movable link42decreases, which means that the parking rod33is pulled by a predetermined distance in the arrow C2direction (forwards) in the drawing. The parking lock pole32is thus lowered by the taper cone34, bringing the parking gear31into a rotatable unlocked state.

In addition, when the shift lever10shifts into the neutral range N and when the shift lever10shifts into the drive range D, as shown inFIGS. 10C and 10D, respectively, the angle formed between the fixed link41and the movable link42, which are bent in a V-shape, progressively decreases, and the stroke that pulls the parking rod33forwards increases.

Next, in connection with the operation of the parking lock device30as described above, the advantage of providing the booster mechanism40will be described with reference toFIGS. 12 and 13.

First, the relationship between the driving force of the manual valve lever21and the pressing force on the parking rod33in the above-described locked state will be described with reference toFIG. 12.

When the manual valve lever21is tilted counterclockwise in the drawing, a tangential force F0(equivalent to a driving force) acts on the pivots45and46that connect the fixed link41with the movable link42. The tangential force F0is increased by the boosting action of the booster mechanism40, thereby generating a pressing force Fpat the pivot47that connects the movable link42to the parking rod33. Here, F1denotes a component force of the tangential force F0.

In this way, when locking the parking lock device30, a very large pressing force F0is obtained with respect to the parking rod33by means of a small tangential force F0, that is, by means of a small driving force of the manual valve lever21.

Further, the relationship between the driving force of the manual valve lever21and the pressing force on the parking rod33in the above-described unlocked state will be described with reference toFIG. 13.

When the manual valve lever21is tilted clockwise in the drawing, a tangential force −F0(equivalent to a driving force) directed opposite to that mentioned above acts on the pivots45and46that connect the fixed link41with the movable link42. The tangential force −F0is increased by the boosting action of the booster mechanism40, which generates a pulling force −Fpat the pivot47that connects the movable link42to the parking rod33. It should be noted that −F1denotes a component force of the tangential force −F0.

In this way, when unlocking the parking lock device30, a very large pulling force −Fpmay be obtained with respect to the parking rod33by means of a small tangential force −F0, that is, by means of a small driving force of the manual valve lever21.

In the boosting mechanism40, when unlocking from a locked state, in which the fixed link41and the movable link42are aligned in a straight line as shown inFIG. 10A, by bending the links41and42in a V-shape as shown inFIGS. 10B to 10D, and when locking from an unlocked state conversely, the displacement ΔX of the pivots45and46and the displacement ΔY of the pivot47can be determined by the following equation.
ΔX=(Y/2)sin θ and ΔY=Y−2×[(Y/2)cos θ]=Y(1−cos θ)

In the above equation, Y is the distance from the center of the shift control shaft22to the center of the pivot47in the booster mechanism40, and θ is the angle formed by the links41and42when bent in a V-shape.

For reference, the relationship between ΔX and ΔY when Y is set as, for example, “10” is indicated by the graph ofFIG. 14. Also, on the basis of the data shown inFIG. 14, the relationship between the angle θ of bend, and the amplification factor of the pressing force or pulling force on the parking rod33is shown in the graph ofFIG. 15.

As is apparent from the graphs ofFIGS. 14 and 15, by using the booster mechanism40described above, the force with which the pivots45and46are pulled in the ΔX direction with the manual valve lever21in order to unlock the parking lock device30is amplified by a factor of several tens to several hundreds as the force pulling the parking rod33in the ΔY direction in early stages.

In addition, for reference, the case where the vehicle is stopped on a slope will be described.

As described above with reference to the related art, as a general tendency, when a vehicle is stopped on a downhill slope, the same forward rotation torque as that at the time of forward movement is input to the output shaft7from the driving wheels, whereas when the vehicle is stopped on an uphill slope, a reverse rotation torque is input to the output shaft7from the driving wheels.

In the parking lock device30illustrated in this embodiment, if, for example, the above-mentioned forward rotation torque is input to the output shaft7while the parking lock device30locked, the pawl32aof the parking lock pole32is prone to disengage from the parking gear31. Accordingly, as shown inFIG. 11, the axial load Fa directed to the unlocking side acts on the parking rod33.

At this time, the moments M1and M2respectively act on the links41and42of the booster mechanism40to move the pivoted portions (45and46) of the links41and42to the stopper44side, thereby keeping the links41and42aligned in a straight line as it is and preventing the links41and42from bending to the unlocking side. The parking lock device30remains locked.

On the other hand, if the above-mentioned reverse rotation torque is input to the output shaft7while the parking lock device30is locked, the pawl32aof the parking lock pole32engages the parking gear31.

Accordingly, a relatively large driving force of the manual valve lever21is required to unlock the parking lock device30. At this time, according to this embodiment, when shifting to an unlocked state, the driving force of the manual valve lever21is increased by the boosting action of the booster mechanism40as appropriate to act as a pulling force on the parking rod33, so that the parking rod33is pulled strongly even when the driving force of the manual valve lever21is small. The pawl32aof the parking lock pole32may be thus disengaged from the parking gear31.

As described above, in the parking lock device30according to the embodiment to which the features of the present invention are applied, the manual valve lever21is connected to the parking rod33via the booster mechanism40. It is thus possible to increase the pressing force or pulling force on the parking rod33even when the driving force applied by the manual valve lever21when shifting to a locked state or unlocked state is small.

Accordingly, the parking lock device30can be easily and reliably locked or unlocked with a relatively small force.

Therefore, the driving force to be applied by the manual valve lever21when locking the parking lock device or unlocking the parking lock device from an unlocked state can be made small.

Furthermore, in this embodiment, the booster mechanism40adopts a relatively simple configuration of a toggle joint type using the plurality of links41and42and the like, which proves advantageous in reducing equipment cost as compared with a case where power assist means such as an expensive motor is equipped as described above with reference to the related art.

It is to be understood that the present invention is not limited to the above-described embodiment, but covers all such modifications and applications as fall within the scope of the claims and their equivalents. Hereinafter, other embodiments of the present invention will be exemplified.

(1) While the above-mentioned embodiment is directed to the parking lock device30equipped in a front-engine, rear-drive (FR) automatic transmission, this can also be a parking lock device equipped in a front-engine, front-drive (FF) automatic transmission.

(2) While in the above-mentioned embodiment the manual valve lever21of the range selector20is used as the drive lever for driving the parking rod33of the parking rod device30, this may be another independent drive lever.

(3) While the above-mentioned embodiment is directed to the case where the manual valve lever21of the range selector20is driven by the manual actuator23, this may be of a type in which, as in the related art, the manual valve lever21and the shift lever10are mechanically connected together by a power transmission member such as a shift rod or a shift cable, and the manual valve lever21is driven by the operating force on the shift lever10applied by the driver.

(4) The booster mechanism40described in the above-mentioned embodiment can also adopt a configuration in which the fixed link41is omitted, and the fixed link41is substituted for by the manual valve lever21itself.

In that case, it is necessary to provide the elongated guide hole41aof the fixed link41in the manual valve lever21.

(5) The booster mechanism40described in the above-mentioned embodiment can also adopt a configuration in which the connecting bar43is omitted.