Abstract:
The invention relates to an apparatus for an internal combustion engine which for each cylinder with associated piston has at least one inlet valve and at least one exhaust valve for controlling the connection between the combustion chamber in the cylinder and an intake system and an exhaust system respectively. A rotatable camshaft with a cam lobe is designed to interact with a main rocker arm and a secondary rocker arm, the two rocker arms serving to transmit the movement of the cam lobe to the inlet/exhaust valve. The cam lobe is arranged to act on both of the rocker arms during each revolution of the camshaft. The secondary rocker arm interacts with a hydraulic piston, which is displaceable in a hydraulic cylinder and which forms part of a hydraulic circuit having a hydraulic fluid source, and which permits switching between at least two different working positions.

Description:
[0001]     The present application is a continuation of PCT/SE2004/001223, filed Aug. 23, 2004, which claimed priority of SE 0302289-4, filed Aug. 25, 2003, both of which are incorporated by reference. 
     
    
       [0002]     The present invention relates to an apparatus for an internal combustion engine which for each cylinder with associated piston has at least one inlet valve and at least one exhaust valve for controlling the connection between the combustion chamber in the cylinder and an intake system and an exhaust system respectively, a rotatable camshaft with a cam curve having at least one cam lobe being designed to interact with a main rocker arm and a secondary rocker arm, the two rocker arms serving to transmit the movement of the cam lobe to the inlet/exhaust valve.  
         [0003]     There are numerous examples of the need to be able to adjust the valve lift in inlet or exhaust valves of an internal combustion engine. Such examples include the activation/deactivation of a compressed-air brake on an internal combustion engine for heavy road vehicles (additional valve movement only operative in engine braking); the generation of valve lift curves of differing width of the Miller-cycle type, for example, for use at different operating points in the engine working range; complete deactivation of the valve movement when isolating certain cylinders at partial load etc., and the institution of internal exhaust gas recirculation via the exhaust valve or via the inlet valve.  
         [0004]     When the facility is required for fixing a rocker arm part in relation to another part, for example, an actuator is required that can overcome the forces occurring between the various parts without any impact occurring when movement of the rocker arm parts relative to one another approaches the limit positions. The movement of the rocker arm is controlled by a cam curve having one or more lobes which define what movements and accelerations the constituent parts must perform in order to achieve the required lifting movements, and this gives rise to forces and torsion in the mechanism.  
         [0005]     It is desirable that apparatuses for producing additional openings of valves should not extend significantly in a longitudinal direction in the space available for the engine valve mechanism. For example, the high compression ratios that occur in modern diesel engines mean that the valve mechanism must be designed for very high contact-pressures. Furthermore, engines of this type may be fitted with some form of compressed-air brake, which requires space for actuating members. Consequently no apparatuses for switching between two valve operating modes should encroach on the existing compressed-air brake system. It is also desirable to be able to perform this switch from one mode to another in a simple way.  
         [0006]     It is furthermore desirable to be able to continuously vary a Miller cycle independently of the crank angle, for variable closure of the inlet valves, for example. Being able to alter the lift curve of the inlet valves during operation may be advantageous at certain operating points in order to achieve lower overall exhaust emission and fuel consumption levels over a running cycle. In order that an engine with a Miller function in the valve lift curve might not exhibit very inferior starting or poor instantaneous response at low speeds, when turbo-charging affords little power, a valve lift profile with normal angle range is required, whilst the Miller cycle can be activated when turbo-charging at high power in order to reduce the compression temperature, thereby achieving a lower nitrogen oxide emission level, for example.  
         [0007]     It is desirable to provide an apparatus which permits switching from one valve operating mode to another in an internal combustion engine, within the functional constraints described above.  
         [0008]     According to an aspect of the present invention, an apparatus is provided for an internal combustion engine, the engine having at least one cylinder and associated piston, each cylinder and associated piston having at least one inlet valve and at least one exhaust valve, the apparatus being adapted to control a connection between a combustion chamber in the cylinder and an intake system and an exhaust system respectively. The apparatus comprises a rotatable camshaft with a cam curve having at least one cam lobe, a main rocker arm and a secondary rocker arm, the cam curve of the rotatable camshaft having at least one cam lobe, the at least one cam lobe being designed to interact with the main rocker arm and the secondary rocker arm, the two rocker arms serving to transmit movement of the cam lobe to a valve. The cam lobe is arranged to act on both of the rocker arms during each revolution of the camshaft, and the secondary rocker arm interacts with a hydraulic piston which is displaceable in a hydraulic cylinder and which forms part of a hydraulic circuit having a hydraulic fluid source, and which permits switching between at least two different working positions. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The invention will be described in more detail below, with reference to examples of embodiment shown in the drawings attached, in which  
         [0010]      FIG. 1  is a curve diagram with various cam lift curves, which can be produced with a valve system according to the present invention,  
         [0011]      FIGS. 2-6  show schematic representations of a valve mechanism in various operating positions with the facility for switching between two operating modes according to the invention,  
         [0012]      FIG. 7  likewise shows one operating position for a second example of embodiment of the invention, and  
         [0013]      FIGS. 8-11  likewise show various operating positions of a valve mechanism according to a third example of embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0014]     In the curve diagram shown in  FIG. 1  the X-axis gives the cam degrees and the Y-axis the lift height. The curve diagram includes a basic curve  10  drawn with a solid line, which at point  11  can be widened along the curve section  12  drawn with a dashed line, in order to produce a delayed closure of inlet valves, so-called delayed Miller cycle, for example. Depending on the geometry between rocker arms, cam lobe and rocker arm rollers, which affects the valve movement, the inlet valves are thereby kept open approximately 20 degrees longer than the valve opening afforded by the basic curve  10 , that is to say the inlet valves are kept open during a certain first part of the engine compression stroke. This gives a lower temperature in the ensuing combustion/expansion and hence a reduced nitrogen oxide content in the exhaust gases. The Miller cycle is described, for example, in U.S. Pat. No. 2,670,595.  
         [0015]     Valve closure according to the curve section  12  can be achieved with all the examples of embodiment of the invention described below. With the example of embodiment of the invention shown in  FIGS. 8-11  it is also possible to achieve continuously variable valve closure within the area between the basic curve  10  and the curve section  12 . This is illustrated in  FIG. 1  by the curve section  13  drawn with a dash-dot line which proceeds from point  14  on the curve section  12 . Curve  13   a  relates to an example of the conditions in which activation of a Miller cycle occurs during actual valve closure, according to examples of embodiment shown in FIGS.  2  to  7 .  
         [0016]     The valve mechanism shown in schematic form in  FIGS. 2-12  is located on a cylinder head and comprises double-seat valves  15  with valve springs  16  and a common yoke  17 .  
         [0017]     The yoke is actuated by a main rocker arm  18 , which is pivotally supported on a rocker arm shaft  19 . On one side of the shaft  19  the main rocker arm  18  has a valve depressor  20 , which interacts with the yoke  17 , and on the other side a rocker arm roller  21 , which interacts with a rotatable camshaft  22  having a cam lobe  22   a . The main rocker arm  18  is furthermore provided with a secondary rocker arm  23 , which is pivotally supported at the outer end of the arm and has a second rocker arm roller  24 . The cam lobe  22   a  has a lift curve which means that the second rocker arm roller  24  comes into contact with the cam lobe, once the first roller  21  has reached its maximum lift and is in descending motion, with low relative speed at point  11 , see  FIG. 1 . That is to say the cam lobe  22   a  comes into contact with point  11  and the rocker arm roller  21  at the same time that a corresponding point IIa resumes cam lobe contact with the rocker arm roller  24 . These two points give virtually the same rocker arm lift and rocker arm speed so that the rolling contact between cam lobe and roller  24  will be resumed without impact.  
         [0018]     The secondary rocker arm  23  is coupled by way of an angled section  23   a  to a hydraulic piston  26 , which is arranged in a hydraulic cylinder  25  in the main rocker arm and which is acted upon by a helical coil spring  27 .  
         [0019]     The hydraulic piston  26  is a part of a hydraulic circuit  28 , arranged in the main rocker arm and supplied with hydraulic fluid via a feed duct  29 , which is connected to the pressure side of the engine lubricating system. The hydraulic circuit also comprises a control valve  30 .  
         [0020]     In the examples of embodiments of the invention shown in  FIGS. 2-7  the control valve  30  takes the form of a pressure-controlled non-return valve, which is controlled via the feed duct  29  that supplies an adjustable pilot pressure (1-4 bar). The spring  31  presses a ball  32  against a seat  33 . A second spring  34  presses on an operating piston  35  and the spring force in the second spring  34  is stronger than in the spring  31  this means that at a low hydraulic pressure the spring  34  and the operating piston  35  with its peaked end section  36  press the ball  32  away from the seat  33 , as can be seen from  FIG. 2 , and the hydraulic fluid can flow in both directions in the feed duct  29 . In this working position the hydraulic piston  26  connected to the secondary rocker arm  23  can move freely in the hydraulic cylinder  25 , which means that the movement of the main rocker arm is generated solely by the contact of the rocker arm roller  21  with the camshaft  22 .  
         [0021]     At a hydraulic pressure exceeding a certain specific value, this pressure acting on the operating piston  35  overcomes the force of the spring  34  and the operating piston  35  is pressed away from the ball  32 , which thereby closes against the seat  33  (see  FIG. 3 ). The hydraulic fluid present between the hydraulic cylinder  25  and the non-return valve is now confined and the secondary rocker arm  23  is activated. When the inlet valves  15  have been fully opened and the cam lobe  22   a  comes into contact with the secondary rocker arm  23  (see  FIGS. 4 and 5 ), the movement of this rocker arm  23  with the hydraulic piston  26  away from the adjustable stop screw  37  will mean that the hydraulic fluid causes the valve depressor  20  to move in a cylindrical bore  38  in the main rocker arm  21 . As a result, the valve opening movement departs from the basic curve  10  (see  FIG. 1 ) and follows the curve section  12 .  
         [0022]     The secondary rocker arm therefore performs the same movement in both of the working positions described above, but in the latter position the movement is hydraulic transmitted to the valve depressor  20 . In order to damp the closing movement at the transition from active to inactive working position (curve section  13  or  13   a  in  FIG. 1 ), when the valves  15  are on the point of closing, the bore  38  is provided with an elastic and/or viscous damping element  39 . A helical coil spring  40 , which ensures that the rocker arm  18  always has contact with the camshaft  22 , is furthermore provided.  
         [0023]     In the event of a further increase in hydraulic pressure, the operating piston  35  moves to expose a passage  41 , which connects the hydraulic cylinder  25  to the feed duct  29  (see  FIG. 6 ). In this working position the valve lift resumes the lifting motion according to curve  10  in  FIG. 1 . The lubricating oil pressure increased to the third pressure level may be used to activate some other function, such as an engine brake device, without the delayed Miller lift curve here described being activated.  
         [0024]      FIG. 7  shows a variant of the example of an embodiment of the invention described above, in which the valve depressor  20  is immovably/adjustably fitted to the main rocker arm  18  by means of a screw thread and a nut  42 .  
         [0025]     In functional terms this does not make any significant difference. However, the damping element  39  needs to be moved so that it acts between the main rocker arm  18  and a fixed point  43  in the engine.  
         [0026]     FIGS.  8  to  11  show a further example of an embodiment of the invention in which the pressure-controlled valve  30  is replaced by a mechanically adjustable hydraulic valve  44 . As in the examples of embodiment described above, this valve  44  comprises a non-return valve having a spring  31 , which presses a ball  32  against a seat  33 .  
         [0027]     The feed duct  29 , however, connects directly to the seat  33  of the non-return valve. A dumping duct  45  is arranged in the main rocker arm  18 , so that it connects a point downstream of the non-return valve to a port in the wall of the hydraulic cylinder  25 . The dumping duct  45  can be opened and closed by means of a rotary valve  46 , which is connected via a linkage  47  to an adjusting device (not shown) on the cylinder head  48 . When the main rocker arm moves about the shaft  19  the dumping duct  45  is automatically opened and closed. The linkage  47  between the main rocker arm  18  and the cylinder head  48  is used in order to transmit the desired proportion of the valve lift range and to define, in terms of the crank angle, the point at which closure of the extended valve lift is to commence. The hydraulic piston  26  also functions as a valve for the hydraulic fluid that is to be drained out of the hydraulic circuit in that the piston, in its outermost position, when the secondary rocker arm  23  is on the base circle, covers the dumping duct  45  in series with the rotary valve  46 . This is in order to reduce the consumption of oil, which would otherwise flow out freely when both roller followers are on the base circle of the cam, see  FIG. 8 .  
         [0028]      FIGS. 8 and 9  show the hydraulic valve  44  set for basic function, that is to say for following the basic curve  10  with rotary valve  46  open.  
         [0029]      FIGS. 10 and 11  show the hydraulic valve  44  set for the Miller function, that is to say for following the curve  12  with rotary valve  46  closed, for example.  
         [0030]     In the example of embodiment described above the linkage  47  between cylinder head and rotary valve is designed with levers and push rod. Alternatively, a rack and pinion mechanism might be used. A further variant could comprise a control rod along the length of the engine which is provided with a wedge-shaped body directly opposite each inlet rocker arm. If this control rod is made to reciprocate in the longitudinal direction of the engine, the wedge-shaped bodies can actuate a hydraulic valve in the main rocker arm  18  at various angular positions of the main rocker arm, thereby starting to dump oil at various crank angles and providing a continuously variable closure of the inlet valve.  
         [0031]     The invention must not be regarded as being limited to the examples of embodiment described above, a number of further variants and modifications being feasible without departing from the scope of the following claims.