Abstract:
A parking lock device that is installed in a transmission of a vehicle includes a gear, a lock, a receiver, a cam, and a damper. The lock has a pawl that can be engaged in a tooth space between the teeth of the gear. The lock moves between an engagement position at which the pawl is engaged in the tooth space to lock the gear and a retreat position at which the pawl is not engaged in the tooth space. The receiver is arranged to be fixed to a case of the transmission. The cam moves forward and backward with respect to a gap between the receiver and the lock. The cam holds the lock at the engagement position when having entered the gap. The damper is provided in a vibration transmission path to dampen vibrations transmitted to the case of the transmission.

Description:
INCORPORATION BY REFERENCE 
       [0001]    The disclosure of Japanese Patent Application No. 2013-029238 filed on Feb. 18, 2013 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to a parking lock device that locks a shaft connecting to wheels to prevent a vehicle from moving when the vehicle is parked. 
         [0004]    2. Description of Related Art 
         [0005]    A parking lock device of a vehicle has a gear that is fixed to a shaft connecting to wheels, and a lock that is engaged in a tooth space of the gear to lock the gear. It should be noted herein that the shaft connecting to the wheels means a shaft that rotates while establishing a relationship of being constantly fixed to the wheels. The gear is locked to lock the wheels, thereby preventing the vehicle from moving when the vehicle is parked. 
         [0006]    The parking lock device is provided in a transmission of the vehicle. The transmission is a device that has a function of converting rotational speeds and torques of outputs of prime movers such as an internal combustion engine, an electric motor and the like, which are mounted on the vehicle, and delivering the outputs to the wheels. There is also known a device that is equipped with a differential for permitting a difference in rotational speed between right and left driving wheels as well as a shifting mechanism that carries out speed conversion and torque conversion. Examples of the transmission include, for example, a manual multistage transmission, an automatic multistage transmission, and a continuously variable transmission. Besides, there is also known a transmission for a hybrid vehicle that also incorporates an electric motor for driving the vehicle in addition to a shifting mechanism. 
         [0007]    An example of the configuration of a parking lock device of a vehicle is disclosed in Japanese Patent Application Publication No. 2006-131109 (JP-2006-131109 A). 
       SUMMARY OF THE INVENTION 
       [0008]    There is a backlash between the gear and the lock. If the gear undergoes rotational fluctuation, the gear and the lock move relatively to each other within a range of the backlash and come into contact with each other. An impact caused at the time of the contact is transmitted to a case of the transmission, and radiated to the outside as noise. 
         [0009]    The invention provides a parking lock device that prevents noise from being produced due to a contact between a gear and a lock. 
         [0010]    An aspect of the invention relates to a parking lock device that is installed in a case of a transmission of a vehicle. The parking lock device includes a gear, a lock, a receiver, a cam, and a damper. The gear includes a plurality of teeth arranged in a circumferential direction of the gear. A tooth space is defined between the plurality of teeth. The lock includes a pawl to be engaged in the tooth space. The lock is moveable between an engagement position and a retreat position. In the engagement position, the pawl is engaged in the tooth space to lock the gear. In the retreat position, the pawl is not engaged in the tooth space. The receiver is fixed to the case of the transmission. The cam is moveable into and out of a gap defined between the receiver and the lock. The cam holds the lock in the engagement position when having entered into the gap. The damper dampens vibrations that are generated when the gear and the lock come into contact with each other. The damper is provided on a vibration transmission path that transmits the generated vibrations to the case of the transmission. The vibration transmission path is formed of the lock, the cam, and the receiver. 
         [0011]    The parking lock device according to the invention includes the gear, the lock that can lock the gear, and the cam that controls the movements of the lock. The gear has the plurality of the teeth arranged in the circumferential direction thereof. The lock has the pawl that can be engaged in the tooth space between the teeth of the gear, and can move between the engagement position at which the pawl is engaged in the tooth space and the retreat position at which the pawl is not engaged in the tooth space. The cam controls the movements of the lock, and holds the lock at the engagement position. Specifically, the cam can move forward and backward with respect to the gap between the receiver, which is arranged at a position fixed to the case of the transmission, and the lock. By entering this gap, the cam moves the lock to the engagement position to hold it at this position. When the cam retreats from the gap between the receiver and the lock, the lock is allowed to move to the retreat position. Alternatively, when the cam retreats from the gap between the receiver and the lock, the cam may retreat the lock to the retreat position. Vibrations resulting from a contact between the gear and the lock are transmitted to the case of the transmission via the lock, the cam, and the receiver. The vibrations transmitted to the case are transmitted through the case, and reach, for example, an outer wall that partitions the inside and outside of the transmission from each other, so that noise is radiated therefrom. The damper that damps the vibrations transmitted through this vibration transmission path is provided on this path. 
         [0012]    By providing the damper on the aforementioned vibration transmission path, noise radiated from a surface of the case of the transmission as a result of a contact between the gear and the lock can be abated. 
         [0013]    In the aforementioned parking lock device, the damper may be provided on the receiver. The receiver can be a component separate from the case of the transmission. 
         [0014]    In the aforementioned parking lock device, the damper may be a weight. The weight functions as a mass damper that damps vibrations in a region in which the weight is provided, depending on the mass of the weight. Besides, the weight can be directly provided on a member that constitutes the aforementioned vibration transmission path, or can also be provided via an arm that extends away from the member that constitutes the transmission path. The weight can be provided on the receiver. The weight can also be formed integrally with the receiver, or can also be configured separately from the receiver and then fixed thereto. 
         [0015]    In the aforementioned parking lock device, the damper may be a dynamic damper. The dynamic damper includes a mass, and an elastic that is interposed between the mass and the receiver. The dynamic damper suppresses the transmission of vibrations in the vicinity of a natural frequency that is determined by the mass and the elastic. The dynamic damper can be provided on the receiver. The dynamic damper can also be formed integrally with the receiver, or can also be configured separately from the receiver and then fixed thereto. 
         [0016]    In the aforementioned parking lock device, the receiver may be a component separate from the case of the transmission, and the damper may be an elastic member disposed between the case of the transmission and the receiver. Rubber can be employed as the elastic member. 
         [0017]    In the aforementioned parking lock device, the gear may be provided on a shaft that is constantly connected to an output shaft of an internal combustion engine that is mounted on the vehicle. Noise that is produced when the gear vibrates upon receiving rotational fluctuation of the output shaft of the internal combustion engine can be suppressed. 
         [0018]    Noise that is radiated when a lock and a gear of a parking lock mechanism come into contact with each other can be suppressed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
           [0020]      FIG. 1  is a view showing the overall configuration of a power unit according to the invention; 
           [0021]      FIG. 2  is a perspective view showing the overall configuration of a parking lock device according to an embodiment of the invention; 
           [0022]      FIG. 3  is a lateral sectional view of the parking lock device shown in  FIG. 2 ; 
           [0023]      FIG. 4  is a front view of the parking lock device shown in  FIG. 2 ; 
           [0024]      FIG. 5  is a view showing a transmission path of vibrations generated in the parking lock device; 
           [0025]      FIG. 6  is a perspective view showing an essential part of a parking lock device according to another embodiment of the invention; 
           [0026]      FIG. 7  is a lateral sectional view of the parking lock device shown in  FIG. 6 ; and 
           [0027]      FIG. 8  is a lateral sectional view of still another parking lock device. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0028]    The embodiments of the invention will be described hereinafter with reference to the drawings.  FIG. 1  is a skeleton view showing the overall configuration of a power unit  10  of a vehicle according to the present embodiments of the invention. The power unit  10  has an internal combustion engine  12  and two electric motors  14  and  16  as prime movers that drive the vehicle. The internal combustion engine  12  can be configured as a reciprocating piston engine such as an Otto engine, a diesel engine or the like. The two electric motors will be referred to as the first electric motor  14  and the second electric motor  16 . The two electric motors function as electric generators as well. For example, the first electric motor  14  can generate electricity by being driven by the internal combustion engine  12 . The second electric motor  16  can generate electricity by being driven by the inertia of the vehicle. 
         [0029]    The power unit  10  has a transmission  20  that converts speeds of outputs of the prime movers  12 ,  14  and  16  and delivers the outputs to driving wheels  18 . The transmission  20  includes a differential  22  for permitting a difference in speed between the right and left driving wheels  18 . This transmission  20  is sometimes referred to as a transaxle. Furthermore, the first electric motor  14  and the second electric motor  16  are built in the transmission  20 . The transmission  20  is configured with movable structures such as gears, shafts and the like accommodated in a transmission case  24 . The transmission case  24  includes an outer wall that partitions the inside and outside of the transmission  20  from each other, and a region that supports the respective accommodated movable structures. The outer wall, the region that supports the movable structures, and a region that is fixedly provided thereon will be entirely regarded as the transmission case  24  in the following description. 
         [0030]    The transmission  20  includes a planetary gear mechanism  26 . An output shaft of the first electric motor  14  is connected to a sun gear  28  of the planetary gear mechanism  26 , and an output shaft of the internal combustion engine  12  is connected to a planetary carrier  30  via a torsional damper. A ring gear  34  is provided on an output sleeve  36 . The planetary carrier  30  rotatably supports a planetary pinion  38  that meshes with the sun gear  28  and the ring gear  34 . The sun gear  28 , the planetary carrier  30  and the ring gear  34  as three elements of the planetary gear mechanism  26  are related to one another such that if rotational speeds of any two of the elements are determined, a rotational speed of the other one element is automatically determined. A first output gear  40  is provided on the output sleeve  36 , and the first output gear  40  meshes with a counter driven gear  44  on a countershaft  42 . The counter driven gear  44  in turn meshes with a second output gear  46  that is linked with an output shaft of the second electric motor  16 . A final drive gear  48  is provided on the countershaft  42 , and this final drive gear  48  meshes with a final driven gear  50  that is fixed to a differential case of the differential  22 . A well-known differential can be adopted as the differential  22 , and the description thereof is omitted herein. 
         [0031]    A parking lock device  52  of this transmission  20  is provided on the output sleeve  36  and that region of the transmission case  24  which faces the output sleeve  36 . A parking gear  54  is provided on an outer peripheral face of the output sleeve  36 , and a parking pawl  56  is provided on the transmission case  24  side in such a manner as to mesh with the parking gear  54 . The details of the parking lock device  52  will be described later. 
         [0032]    A power transmission path from the first output gear  40  to the driving wheels  18  is constituted of constantly meshed gear pairs and shafts. As a result, the driving wheels  18  and the first output gear  40  rotate while establishing a certain relationship corresponding to a gear ratio between the gears of the power transmission path. That is, if the first output gear  40  is stopped from rotating, the driving wheels  18  are also stopped from rotating. The parking gear  54  is provided on the output sleeve  36  together with the first output gear  40 . Therefore, the driving wheels  18  can be locked by stopping the parking gear  54  from rotating. 
         [0033]    Besides, the output sleeve  36  is provided with the ring gear  34  as well. The parking gear  54  is constantly connected to the output shaft of the internal combustion engine  12  via the ring gear  34 , the planetary pinion  38 , the planetary carrier  30 , and a torsional damper  32 . Thus, if the output shaft of the internal combustion engine  12  undergoes rotational fluctuation, this rotational fluctuation is transmitted to the parking gear  54 . In particular, in this transmission  20 , since the torsional damper  32  is provided on the output shaft of the internal combustion engine  12 , the amplitude of rotational vibrations of the parking gear  54  may become large in the vicinity of a resonance frequency of a vibration system including this torsional damper  32 . For example, in the case where the internal combustion engine  12  is a reciprocating piston engine, the output shaft of the internal combustion engine  12  undergoes rotational fluctuation due to reciprocating movements of a piston, intermittent combustion and the like. If the frequency of this rotational fluctuation becomes close to the aforementioned resonance frequency, the vibration system resonates. For example, the start of the internal combustion engine  12  may be accompanied by the passage of the resonance frequency of the aforementioned vibration system while the rotational speed of the internal combustion engine  12  rises. At this time, if the parking lock device  52  is locked, the parking gear  54  and the parking pawl  56  that meshes therewith may come into contact with each other to produce noise audible to passengers of the vehicle. The parking lock device  52  of this embodiment of the invention is structured such that no noise is produced when the parking gear  54  rotationally vibrates upon receiving rotational fluctuation of the internal combustion engine  12  or due to other causes. The parking lock device  52  will be described hereinafter. 
         [0034]      FIGS. 2 to 4  are views showing the details of the parking lock device  52 . The parking gear (the gear)  54  is constituted of a plurality of teeth  58  that are arranged on an outer periphery of the output sleeve  36  in a circumferential direction thereof. The parking pawl (a lock)  56  has a pawl  62  that can be engaged in tooth spaces  60  as regions among the teeth  58 , and is turnably supported by a support shaft  64  that is fixed to the transmission case  24 . The parking pawl  56  turns and thus can move between an engagement position at which the pawl  62  is engaged in a certain one of the tooth spaces  60  and a retreat position at which the pawl  62  has exited a certain one of the tooth spaces  60 . Besides, the parking pawl  56  is urged in a direction toward the retreat position by urging means (not shown), for example, a spring. 
         [0035]    A cam receiver (a receiver)  66  is fixed to the transmission case  24 . A cam (a cam)  68  that can move into and out of a gap between this cam receiver  66  and the parking pawl  56  is arranged. A direction in which the cam  68  moves toward the gap between the cam receiver  66  and the parking pawl  56  will be referred to hereinafter as an advance direction, and a direction in which the cam  68  moves away from the gap between the cam receiver  66  and the parking pawl  56  will be referred to hereinafter as a retreat direction. The cam  68  is slidably arranged on a parking rod  70  that penetrates therethrough. The cam  68  assumes a substantially cylindrical shape, and is arranged coaxially with the parking rod  70  that penetrates an inner void of the cylinder. A tapered face is formed on a front face of the cam  68  in the advance direction. Besides, a tapered face or tapered faces are formed on one or both of the cam receiver  66  and the parking pawl  56  in such a manner as to face the tapered face of this cam  68 . The parking rod  70  is provided with urging means for urging the cam  68  in the advance direction. The urging means is, for example, a spring  72 , and is preferably a coiled spring. This spring  72  is located between a spring shoe  74  that is fixedly provided on the parking rod  70  and the cam  68 , and urges the cam  68  in the advance direction. A stopper  75  that determines limit positions of the movements of the cam  68  in the advance direction is provided on the parking rod  70 . In a free state, the cam  68  is moved to such a position as to hit the stopper  75  by the spring  72 . 
         [0036]    A presser plate  76  is fixed to an end face of the transmission case  24 . The presser plate  76  prevents the cam receiver  66  from falling off from the transmission case  24 , and supports the parking pawl  56  from laterally thereof. Due to this lateral support, when the parking pawl  56  receives a force through the advancement of the cam  68 , this force prevents the parking pawl  56  from being greatly displaced. 
         [0037]    It is preferable that the cam receiver  66  be formed of a material with high abrasion resistance such as steel, cast iron or the like, in consideration of abrasion resulting from the advancement and retreat of the cam  68 . In particular, in the case where the transmission case  24  is made of a material that is relatively likely to abrade, such as aluminum alloy or the like, it is preferable that the cam receiver  66  be made of steel or the like as a component separate from the transmission case  24 . In the case where the transmission case  24  is made of a material with excellent abrasion resistance or where abrasion causes no problem, the cam receiver  66  can also be configured as part of the transmission case  24  instead of a component separate from the transmission case  24 . 
         [0038]    Next, the operation of the parking lock device  52  will be described. During lock operation, the parking rod  70  is first moved in the advance direction. Due to this movement, the spring  72  is compressed, and the spring force applied to the cam  68  increases. When the pawl  62  of the parking pawl and a certain one of the tooth spaces  60  of the parking gear are in such a positional relationship as to face each other, the cam  68  urged by the spring  72  presses the parking pawl  56 , and turns this parking pawl  56  toward the parking gear  54 . As a result, the parking pawl  56  moves to the engagement position to mesh with the parking gear  54 , so that the vehicle is locked. On the other hand, in the case where the pawl  62  of the parking pawl is located at such a position as to face a certain one of the teeth  58  of the parking gear, even if the cam  68  is urged by the spring  72 , the parking pawl  56  is prevented from turning. If the vehicle slightly moves etc. from this state and the parking gear  54  rotates so that the pawl  62  of the parking pawl faces a certain one of the tooth spaces  60 , the parking pawl  56  turns by being pressed by the cam  68 . Thus, the parking pawl  56  moves to the engagement position to mesh with the parking gear  54 , so that the vehicle is locked. 
         [0039]    In order to unlock the vehicle, the parking rod  70  is moved in the retreat direction. Due to this movement, the stopper  75  is hooked on the cam  68 , and the cam  68  moves in the retreat direction together with the parking rod  70  and exits from the gap between the parking pawl  56  and the cam receiver  66 . The unsupported parking pawl  56  turns in such a direction as to move away from the parking gear  54  due to an urging force of urging means (not shown), and moves to the retreat position, so that the vehicle is unlocked. 
         [0040]    If the parking gear  54  vibrates in a rotational direction as indicated by an arrow of  FIG. 4  when the parking lock device  52  is locked, the parking gear  54  turns by an amount corresponding to a backlash, and the teeth  58  of the parking gear and the pawl  62  of the parking pawl repeatedly come into contact with each other. An impact of this contact is transmitted to the transmission case  24  via the parking pawl  56 , the cam  68  and the cam receiver  66 , and causes the transmission case  24  to vibrate. 
         [0041]      FIG. 5  is a view showing the outline of a transmission path of vibrations resulting from a contact between the parking gear  54  and the parking pawl  56 . If the parking pawl  56  vibrates as indicated by, for example, arrows of  FIG. 5  due to the contact, these vibrations are transmitted to the transmission case  24  via the cam  68  and the cam receiver  66 . The vibrations are further transmitted through the inside of the transmission case  24 , and cause the outer wall and the like of the transmission case  24  to vibrate. These vibrations are radiated as noise. In order to suppress the transmission of these vibrations, the parking lock device  52  has a mass damper in the vibration transmission path. More specifically, the parking lock device  52  has an arm portion  78  that extends from the cam receiver  66 , and a weight (a damper)  80  that is provided at an end of the arm portion  78 . The arm portion  78  extends parallel to the direction in which the parking rod  70  extends, and the weight  80  is arranged at a tip position of a distal end of the parking rod  70 . The weight  80 , the arm portion  78 , and the cam receiver  66  can be configured as an integral component. Besides, the weight  80  (or the weight  80  and the arm portion  78 ) may be configured as a component separate from the cam receiver  66 , and fixed afterwards. The weight may also be provided in a region other than the cam receiver  66 . Because of the mass of the weight  80 , the vibrations are suppressed and restrained from being transmitted. That is, the weight  80  functions as a mass damper. 
         [0042]    The weight, namely, the mass damper may be provided at any position on the vibration transmission path. However, it is more effective to provide the weight on the cam receiver  66  as an input point of vibrations to the transmission case  24 , or in the vicinity thereof. 
         [0043]      FIGS. 6 and 7  are views showing the overall configuration of a parking lock device  82 . The parking lock device  82  is different from the aforementioned parking lock device  52  in the configuration for suppressing vibrations. While the mass damper is configured to suppress vibrations in the parking lock device  52 , a dynamic damper is configured to suppress vibrations in the parking lock device  82 . The parking lock device  82  is identical in other configurational details to the parking lock device  52 . Components identical to those of the parking lock device  52  are omitted in the drawings or denoted by the same reference symbols respectively, and the description thereof will be skipped. 
         [0044]    The parking lock device  82  has the arm portion  78  that extends from the cam receiver  66 , and a damper receiving portion  84  that is provided at an end of the arm portion  78 . The arm portion  78  extends parallel to the direction in which the parking rod  70  extends, and the damper receiving portion  84  is arranged at the tip of the distal end of the parking rod  70 . The damper receiving portion  84 , the arm portion  78 , and the cam receiver  66  can be configured as an integral component. Besides, the damper receiving portion  84  (or the damper receiving portion  84  and the arm portion  78 ) may be configured as a component separate from the cam receiver  66 , and fixed afterwards. 
         [0045]    A damper portion (a damper)  86  is linked with the damper receiving portion  84 . For example, the damper portion can be linked with the damper receiving portion  84  by securely screwing a bolt passed through a through-hole of the damper portion  86  into a threaded hole provided through the damper receiving portion  84 . The damper portion  86  has a base portion  88  that has a flange provided at one end of a cylinder, and an annular weight portion  90  that surrounds the periphery of a cylindrical region of the base portion  88 . An elastic layer  92  that is constituted by an elastic material such as rubber or the like is provided between the base portion  88  and the weight portion  90 . The elastic layer  92  can be provided on one or both of a cylindrical outer peripheral face of the base portion  88  and a lateral face of the flange portion. The dynamic damper with the elastic layer  92  and the weight portion  90  serving as a spring and a mass respectively is formed. This dynamic damper can suppress the transmission of vibrations in the vicinity of a natural frequency that is determined by a spring constant of the elastic layer  92  and a mass of the weight portion  90 . It is preferable that the natural frequency be adjusted to a frequency with remarkable transmission of vibrations, or to a frequency of noise radiated into a vehicle interior and audible to passengers. Besides, the masses of the damper receiving portion  84  and the damper portion  86  operate as weights. Therefore, a damping effect in a wide range can also be expected instead of an effect as a mass damper, namely, an effect in a limited frequency range. 
         [0046]    The dynamic damper may be provided at any position on the vibration transmission path. However, it is more effective to provide the dynamic damper on the cam receiver  66  as an input point of vibrations to the transmission case  24  or in the vicinity thereof. Besides, the dynamic damper may be directly linked with the cam receiver  66  without providing the arm portion  78  and the damper receiving portion  84 . Specifically, for example, a threaded hole can be provided through the cam receiver  66 , and a bolt passed through a through-hole of the damper portion  86  can be securely screwed thereto. 
         [0047]      FIG. 8  is a view showing the overall configuration of a parking lock device  94 . The parking lock device  94  is different from the aforementioned parking lock devices  52  and  82  in the configuration for suppressing vibrations. While the mass damper or the dynamic damper is configured to suppress vibrations in the aforementioned parking lock devices  52  and  82 , the parking lock device  94  is a vibration isolating layer that is interposed in a vibration transmission path. The parking lock device  94  is identical in other configurational details to the parking lock device  52 . Components identical to those of the parking lock device  52  are omitted in the drawings or denoted by the same reference symbols respectively, and the description thereof will be skipped. 
         [0048]    In the parking lock device  94 , the cam receiver  66  is fixed to the transmission case  24  via a vibration isolating layer (a damper)  96  that is made of an elastic member such as rubber or the like. In the case where the vibration isolating layer  96  is constituted by rubber, the rubber can be linked with the cam receiver  66  and the transmission case  24  through, for example, baking. Besides, the rubber can also be linked with the cam receiver  66  and the transmission case  24  using an adhesive. Even if the cam receiver  66  vibrates, these vibrations are damped by the vibration isolating layer  96  made of the elastic member and then transmitted to the transmission case  24 . It is preferable that the vibration isolating layer  96  be provided in the vicinity of the cam receiver  66  at an input position of vibrations to the transmission case  24 . Besides, the vibration isolating layer  96  can also be used in combination with the aforementioned mass damper or dynamic damper.