Abstract:
A valve actuation system and method for use in an internal combustion engine including at least one combustion cylinder having a piston and an engine valve. The valve actuation system includes a hydraulic pump, a high-pressure reservoir, and an electro-hydraulic valve actuator. The hydraulic pump is configured to produce a hydraulic output based on a valve-piston clearance profile of at least one cylinder of the combustion engine. The high-pressure reservoir is coupled with the hydraulic pump. The electro-hydraulic valve actuator is coupled with the high-pressure reservoir via a first control valve and configured to actuate at least one engine valve of the combustion engine according to an output of the hydraulic pump.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to an electro-hydraulic device for actuating a control element of an internal combustion engine. More particularly, the present invention relates to a system and method for regulating a high-pressure hydraulic supply to electro-hydraulic engine valve actuators. 
   2. Description of the Background Art 
   The internal combustion engine is well known and has garnered much attention since its creation. Because of its ubiquitous use, substantial efforts are constantly made to improve designs for the internal combustion engine and for its control systems. Of the many advancements made, independent valve actuation and electronic fuel injection were conceived to improve performance and efficiency over cam-based engines. 
   With independent valve actuation systems, the engine valves can come in contact with the engine pistons. This valve—piston collision can cause serious engine damage leading to engine failure. Therefore, valve actuation systems are contemplated that prevent such valve-piston collisions from occurring. 
   Piston-valve collision has been of particular concern for electro-hydraulic valve-trains on non-freewheeling engines, such as heavy-duty diesel engines. The current solution for solving this problem relies heavily on feedback control based upon valve lift measurements, which is neither reliable nor cost effective. For example, U.S. Pat. No. 6,092,495 describes a method of controlling electronically controlled valves to prevent interference between the valves and a piston. While the system can prevent piston-valve collision, it is flawed because a failure in the electrical control system could cause severe engine damages. 
   Thus, there is a need for new and improved systems and methods for valve control in a combustion engine that provide reliable piston-valve clearance. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the present invention, a system and method are provided for regulating high-pressure hydraulic supply to an electro-hydraulic valve actuator. The present invention provides reliable piston-valve clearance. 
   Another aspect of the present invention is generally characterized in a valve actuation system for use in an internal combustion engine comprising at least one combustion cylinder having a piston and an engine valve. The valve actuation system includes a hydraulic pump, a high-pressure reservoir, and an electro-hydraulic valve actuator. The hydraulic pump is configured to produce a hydraulic output based on a valve-piston clearance profile of the cylinder of the combustion engine. The high-pressure reservoir is coupled with the hydraulic pump. The electro-hydraulic valve actuator is coupled with the high-pressure reservoir and configured to actuate at least one engine valve of the combustion engine according to an output of the hydraulic pump. 
   The above and other features and advantages of the present invention will be further understood from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings wherein like reference numerals are used throughout the various views to designate like parts. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic diagram showing an embodiment of an electro-hydraulic valve actuation system for a combustion engine according to the present invention. 
       FIG. 2  is a graph of the piston-valve clearance characteristics of a computer simulation of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of an internal combustion engine  100  having an electro-hydraulic valve actuation system according to the present invention is shown in  FIG. 1 . The engine  100  includes at least one piston-driven combustion cylinder (not shown) in communication with at least one engine control valve  106  (e.g., intake or exhaust valve), an electro-hydraulic actuator  102  for opening and closing valve  106 , and a hydraulic pump  104 . The hydraulic pump  104  may be a cam-driven pump and is fluidly connected to the electro-hydraulic valve actuator via a high-pressure reservoir  110 . 
   In the embodiment shown in  FIG. 1 , hydraulic pump  104  includes a plunger  104   b  that is driven by a cam  104   a . The geometry (i.e., shape) of the cam  104   a  can be selected to drive the plunger  104   b  as desired to charge the pressure of the fluid in the high-pressure reservoir  110 . Preferably, the geometry of the cam is selected based on the piston-valve clearance curve for the combustion cylinder, such that when the engine piston is moving close to the valve  106 , the high-pressure begins to drop; that is, the cam  104   a  starts to move away from the plunger  104   b . For example, as shown in  FIG. 1 , cam  104   a  may have concave portions  104   a - 1  and  104   a - 2  corresponding to a crank angle of the engine when the engine piston moves close to the engine valve  106 , thereby allowing plunger  104   b  to move toward cam  104   a  when piston-valve clearance becomes small. 
   Electro-hydraulic actuator  102  includes control valves  102   a  and  102   b , which are preferably electric solenoid valves, check valves  102   c  and  102   f , control chamber  102   d , and a plunger  102   e . Control valves  102   a  and  102   b  can be opened and shut to control the direction of plunger  102   e  to actuate the engine valve  106 , and can be controlled electronically, such as via an electronic control unit (ECU) or processor (not shown). Control valve  102   a  (high-pressure control valve) allows high-pressure hydraulic fluid to travel into the control chamber  102   d , to force the plunger  102   e  to travel away toward valve  106 . Hydraulic fluid may be allowed to return to the high-pressure reservoir  110  via check valve  108  one-way only. Opening control valve  102   b  (low-pressure control valve) allows high-pressure fluid in the control chamber  102   d  to travel to low-pressure, which may be connected to a low-pressure hydraulic fluid supply, such as a regulated low-pressure reservoir (not shown). Check valve  102   f  allows hydraulic fluid to flow back to the control chamber  102   d , should the pressure in control chamber  102   d  decrease below the pressure of the low pressure hydraulic fluid supply. 
   Check valve  102   c  allows fluid to flow from the control chamber  102   d , one-way only, to the high-pressure reservoir  110 , when the pressure in the control chamber  102   d  exceeds the pressure in the high-pressure reservoir  110 . Thus, even when control valve  102   b  is closed, check valve  102   c  creates a feedback loop—as the cam  104   b  moves away from the plunger  104   a , the pressure in the high-pressure reservoir  110  begins to drop below the pressure in the control chamber  102   d , and check valve  102   c  opens. Thus, piston-valve collision can be prevented reliably without reliance on electronic control systems. 
   A hydraulic accumulator  112  is in fluid connection to the high-pressure reservoir  110 . The accumulator  112  is able to store excessive hydraulic fluid when the high-pressure control valve  102   a  is closed and yet plunger  104   a  continues to pump fluid into reservoir  110 . The piston  112   a  of the accumulator tends to respond to low-pressure fluctuation more than high frequency fluctuation. Here, the pressure drop due to the cam  104   a  shape design as the engine piston moves close to the valve  106  is high frequency. Therefore, the accumulator  112  is preferably slow to react to this fluctuation, which allows the pressure to fluctuate to a significant level such that the check valve  102   c  can open. 
   In operation, the cam-driven hydraulic pump  104  supplies high-pressure hydraulic fluid to the electro-hydraulic valve actuator  102 . The cam  104   a  is preferably mechanically linked to the engine crankshaft (not shown) with a 2:1 ratio (i.e., the engine crankshaft rotates two revolutions while the cam  104   a  rotates one revolution). The cam profile is preferably shaped to correspond to the piston-valve clearance profile, so that as the engine piston moves toward the engine valves and the instantaneous piston-valve clearance becomes smaller, the pump plunger  104   b  moves toward the cam  104   a . As the plunger  104   b  moves toward the cam  104   a , the hydraulic pressure in high-pressure reservoir  110  drops. As a result, check valve  102   c  opens and high-pressure hydraulic fluid travels from control chamber  102   d  to reservoir  110 , which allows the engine valve  106  to move away from the engine piston to avoid piston-valve collision even when control valve  102   b  is still closed. Control valves  102   b  is opened to allow hydraulic fluid to return to the low-pressure region. Control valves  102   a  and  102   b  are closed, and as the engine piston moves away from top-dead center position, the hydraulic pressure in the high-pressure reservoir  110  is built back up. Control valve  102   a  is then opened to cycle engine valve  106  for the next combustion event. 
   Referring now to  FIG. 2 , we assume that the low-pressure control valve  102   b  has failed to open before the top dead center to avoid piston-valve collision.  FIG. 2  shows a simulation of valve clearance and valve lift, versus timing of the cylinder. The top graph shows the control signal for the high-pressure control valve  102   a , the middle graph shows the control signal for the low-pressure control valve  102   b , and the bottom graph shows valve lift and clearance (piston-valve clearance profile). The bottom axis of each graph is the crank angle of the engine, which corresponds to the position of the piston. 
   In operation, high-pressure control valve  102   a  is initially closed to allow high-pressure to build up in reservoir  110 . High-pressure control valve  102   a  is opened, which causes plunger  102   e  to actuate valve  106  to open. The initial valve lift is shown as approximately 12 mm and settles quickly at about 10 mm. As the engine piston approaches the valve  106 , the valve  106  begins to close (i.e., valve lift decreases). One can see that the piston-valve clearance becomes small as the piston approaches top-dead-center, but piston-valve collision is avoided even before the low-pressure control valve  102   b  is opened. 
   As a result of the novel mechanical design of the present invention, piston-valve collision can be prevented even if there is a failure in the electronic control system. 
   While the invention has been described in detail above, the invention is not intended to be limited to the specific embodiments as described. It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific embodiments described herein without departing from the inventive concept. 
   It will be appreciated that the present invention can be implemented in a number of types of internal combustion engines. The engine can have any number of cylinders.