Patent Publication Number: US-11396832-B2

Title: Valve timing adjusting device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation application of International Patent Application No. PCT/JP2019/039872 filed on Oct. 9, 2019, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2018-192791 filed on Oct. 11, 2018. The entire disclosures of all of the above applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a valve timing adjusting device. 
     BACKGROUND ART 
     A valve timing adjusting device has variable valve mechanisms at both of an intake valve and an exhaust valve. There are two types of drive system for the variable valve mechanism: hydraulic type and electric type. 
     SUMMARY 
     A valve timing adjusting device of the present disclosure includes an intake variable valve mechanism and an exhaust variable valve mechanism. The intake variable valve mechanism is configured to vary a valve timing of an intake valve of an internal combustion engine. The exhaust variable valve mechanism is configured to vary a valve timing of an exhaust valve of the internal combustion engine. The exhaust variable valve mechanism includes an exhaust electric driving portion and an exhaust phase shifting portion disposed in a rotation transmission path between a crankshaft of the internal combustion engine and an exhaust camshaft. The exhaust phase shifting portion includes an input shaft connected to the exhaust electric driving portion and is configured to shift a rotation phase of the exhaust camshaft relative to the crankshaft by reducing a speed of a rotation of the input shaft. The input shaft rotates in a rotational direction opposite to a rotational direction of the crankshaft when advancing the rotation phase. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings, 
         FIG. 1  is a schematic view of an internal combustion engine to which a valve timing adjusting device of a first embodiment is applied; 
         FIG. 2  is a schematic cross-sectional view of the valve timing adjusting device taken along a line II-II in  FIG. 1 ; 
         FIG. 3  is a schematic view of a valve timing adjusting device of a second embodiment; 
         FIG. 4  is a schematic view of a valve timing adjusting device of a reference embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     To begin with, examples of relevant techniques will be described. 
     A valve timing adjusting device has variable valve mechanisms at both of an intake valve and an exhaust valve. There are two types of drive system for the variable valve mechanism: hydraulic type and electric type. An electric variable valve mechanism is applied for the exhaust valve. 
     Normally, a default phase of the exhaust variable valve mechanism is the most advanced phase. However, the electric exhaust variable valve mechanism is not biased in an advance angle direction by a force such as a spring force. Thus, when the energization is cut or stopped by a failure and when the variable valve mechanism receives a positive torque, a phase of the variable valve mechanism may be shifted in a retard angle direction. In this case, the valve overlap becomes large and a ratio of fresh air in an intake air becomes low, which leads to insufficient torque and may make an internal combustion unable to start. 
     The present disclosure has been made in view of the above points and it is objective of the present disclosure to provide a valve timing adjusting device that can secure an engine startability. 
     A valve timing adjusting device of the present disclosure includes an intake variable valve mechanism and an exhaust variable valve mechanism. The intake variable valve mechanism is configured to vary a valve timing of an intake valve of an internal combustion engine. The exhaust variable valve mechanism is configured to vary a valve timing of an exhaust valve of the internal combustion engine. The exhaust variable valve mechanism includes an exhaust electric driving portion and an exhaust phase shifting portion disposed in a rotation transmission path between a crankshaft of the internal combustion engine and an exhaust camshaft. The exhaust phase shifting portion includes an input shaft connected to the exhaust electric driving portion and is configured to shift a rotation phase of the exhaust camshaft relative to the crankshaft by reducing a speed of a rotation of the input shaft. The input shaft rotates in a rotational direction opposite to a rotational direction of the crankshaft when advancing the rotation phase. 
     According to this, when the electric driving portion is de-energized or fails, a phase of the exhaust phase shifting portion is automatically shifted to the most advanced angle phase. That is, the phase of the exhaust phase shifting portion is automatically returned to the default phase. This phase shift to the most advanced angle phase and keeping the most advanced angle phase can be achieved without using a phase rock mechanism or a biasing spring. Therefore, it is possible to prevent a decrease in the ratio of fresh air to the intake air due to excessive valve overlap, so that engine startability can be ensured. 
     Hereinafter, multiple embodiments of a valve timing adjusting device will be described with reference to the drawings. In the embodiments, substantially the same components are denoted by the same reference numerals and description thereof is omitted. 
     First Embodiment 
     As shown in  FIGS. 1 and 2 , a valve timing adjusting device of a first embodiment is disposed in a rotation transmission path between a crankshaft  91  of an internal combustion engine  90  and camshafts  92  and  93 . The valve timing adjusting device is configured to adjust valve timings of an intake valve and an exhaust valve (not shown). The valve timing adjusting device  10  includes an intake variable valve mechanism  20  and an exhaust variable valve mechanism  30 . 
     The exhaust variable valve mechanism  30  includes an electric motor  31  and a phase shifting portion  33 . The electric motor  31  is an electric driving portion and configured to output a rotational force from a motor shaft  32  when being energized. 
     The phase shifting portion  33  includes a driving rotating member  34 , an input shaft  35 , a driven rotating member  36 , and a reduction mechanism  37 . The driving rotating member  34  includes a housing  38  and a sprocket  39  disposed outside of the housing  38 . The sprocket  39  is connected to the crankshaft  91  through a chain  94 . The driving rotating member  34  is configured to rotate in conjunction with the crankshaft  91 . 
     The input shaft  35 , the driven rotating member  36 , and the reduction mechanism  37  are disposed in the housing  38 . The input shaft  35  is connected to the motor shaft  32 . The driven rotating member  36  is fastened to the exhaust camshaft  93 . 
     The reduction mechanism  37  is disposed between the housing  38  and the driven rotating member  36  and configured to transmit a rotation between the housing  38  and the driven rotating member  36 . When the internal combustion engine  90  drives and the crankshaft  91  rotates, the rotational force of the crankshaft  91  is transmitted to the driving rotating member  34  through the chain  94 . The rotational force of the driving rotating member  34  is transmitted to the exhaust camshaft  93  through the reduction mechanism  37  and the driven rotating member  36 . Thereby, a cam of the exhaust camshaft  93  selectively opens and closes the exhaust valve. 
     The reduction mechanism  37  is configured to reduce a rotational speed of the input shaft  35  and transmit a rotation of the input shaft  35  to the driven rotating member  36 . When the rotational force of the input shaft  35  rotates the driven rotating member  36  in a reverse direction relative to the driving rotating member  34 , a relative rotation phase of the exhaust camshaft  93  relative to the crankshaft  91  is shifted. Hereinafter, the relative rotation phase of the exhaust camshaft  93  relative to the crankshaft  91  is simply referred to as a rotation phase. The phase shifting portion  33  is configured to shift the rotation phase by reducing a rotational speed of the input shaft  35  and transmit the rotation of the input shaft  35  to the exhaust camshaft  93 . 
     When the driven rotating member  36  relatively rotates in a forward direction (i.e., an engine rotating direction) relative to the driving rotating member  34 , an opening/closing timing of the exhaust valve is advanced. When the driven rotating member  36  relatively rotates in a reverse direction (i.e., a reverse direction to the engine rotating direction) relative to the driving rotating member  34 , the opening/closing timing of the exhaust valve is retarded. A relative rotation range of the driven rotating member  36  is restricted between the most advanced angle position and the most retarded angle position by the reduction mechanism  37 . The most advanced angle phase is defined as a rotation phase corresponding to the most advanced angle position. The most retarded angle phase is defined as a rotation phase corresponding to the most retarded angle position. 
     The intake variable valve mechanism  20  has a similar configuration to that of the exhaust variable valve mechanism  30  except for the following features. That is, the intake variable valve mechanism  20  includes, as components corresponding to a configuration of the intake variable valve mechanism  20 , an electric motor  21 , a motor shaft  22 , a phase shifting portion  23 , a driving rotating member  24 , an input shaft  25 , a driven rotating member  26 , a reduction mechanism  27 , a housing  28 , and a sprocket  29 . 
     As shown in  FIG. 1 , a rotational direction R 1  of the input shaft  35  to advance the rotation phase is a reverse direction to a rotational direction R 3  of the crankshaft  91  (i.e., the engine rotational direction). A rotational direction R 2  of the input shaft  35  to retard the rotation phase is the same as the rotational direction R 3  of the crankshaft  91 . When a reduction ratio of the reduction mechanism  37  is defined as A, A&lt;0. 
     In the first embodiment, the reduction ratio of the intake phase shifting portion  23  and the reduction ratio of the exhaust phase shifting portion  33  have opposite signs. That is, when the reduction ratio of the reduction mechanism  27  is defined as B, A&lt;0 and B&gt;0. 
     In the first embodiment, a product (Tm×|A|) of an average torque Tm of the motor shaft  32  of the electric motor  31  when de-energized and an absolute value of the reduction ratio A of the phase shifting portion  33  is greater than a difference (Tc−Tv) between an average torque Tc of the exhaust camshaft  93  and an average friction torque Tv of the phase shifting portion  33 . That is, (Tm×|A|)&gt;(Tc−Tv). 
     (Advantages) 
     As described above, in the first embodiment, the rotational direction R 1  of the input shaft  35  is opposite to the rotational direction R 3  of the crankshaft  91  when advancing the rotation phase. As a result, when the electric motor  31  is de-energized or fails, the phase of the exhaust phase shifting portion  33  is automatically shifted to the most advanced angle phase. That is, the phase of the phase shifting portion is automatically shifted to the default phase. This phase shift to the most advanced angle phase and keeping the most advanced angle phase can be achieved without using a phase rock mechanism or a biasing spring. Therefore, it is possible to prevent a decrease in the ratio of fresh air to the intake air due to excessive valve overlap, so that engine startability can be ensured. 
     Further, in the first embodiment, the reduction ratio of the intake phase shifting portion  23  and the reduction ratio of the exhaust phase shifting portion  33  have opposite signs. Thus, the default phase of the exhaust phase shifting portion  33  is set to the most advanced angle phase and the default phase of the intake phase shifting portion  23  is set to the most retarded angle phase. 
     Further, in the first embodiment, a product (Tm×|A|) of the average torque Tm and the absolute value |A| of the reduction ratio A is larger than a difference (Tc−Tv) between the average torque Tc and the average friction torque Tv. Therefore, when the energization to the electric motor  31  is cut or the electric motor  31  fails, the phase of the phase shifting portion  33  is surely shifted to the most advanced angle phase by the friction torque of the electric motor  31 . 
     Second Embodiment 
     In a second embodiment, as shown in  FIG. 3 , the electric driving portion of the exhaust variable valve mechanism  40  is configured with an electromagnetic actuator  41  such as an electromagnetic clutch. The reduction mechanism  37  is driven by the electromagnetic actuator  41 . As described above, the electric driving portion may be the electromagnetic actuator  41 . Also in this way, the phase of the exhaust phase shifting portion  33  is automatically shifted to the most advanced angle phase when the energization is cut or stopped by a failure, and similar advantages to those of the first embodiment can be obtained. 
     Other Embodiments 
     In other embodiments, the drive system of the intake variable valve mechanism is not limited to the electric system and may be a hydraulic system or the like. 
     Reference Embodiment 
     In a reference embodiment shown in  FIG. 4 , a phase shifting portion  81  of an intake variable valve mechanism  80  includes a reduction mechanism  82 . A phase shifting portion of an exhaust variable valve mechanism  85  includes a reduction mechanism  87 . The reduction ratio of the intake phase shifting portion  81  and the reduction ratio of the exhaust phase shifting portion  86  have opposite signs and A&gt;0 and B&lt;0. 
     The present disclosure has been described, based on the embodiments. However, the present disclosure is not limited to the embodiments and the structures. The present disclosure also includes various modification examples and modifications within the scope of equivalents. Furthermore, various combination and formation, and other combination and formation including one, more than one or less than one element may be made in the present disclosure.