Internal-combustion engines – Poppet valve operating mechanism – Hydraulic system
Reexamination Certificate
2000-09-15
2002-11-05
Paschall, Mark (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
Hydraulic system
C123S090150, C123S090160, C123S090430, C123S090460, C123S090550
Reexamination Certificate
active
06474277
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the control of engine valves, such as intake and exhaust valves. In particular, the invention relates to methods and apparatus for controlling valve seating velocity.
BACKGROUND OF THE INVENTION
Engine combustion chamber valves, such as intake and exhaust valves, are almost universally of a poppet type. These engine valves are typically spring loaded toward a valve closed position. In many internal combustion engines the engine cylinder intake and exhaust valves may be opened and closed by fixed profile cams in the engine, and more specifically by one or more fixed lobes which may be an integral part of each of the cams. The use of fixed profile cams makes it difficult to adjust the timings and/or amounts of engine valve lift to optimize valve opening times and lift for various engine operating conditions, such as different engine speeds.
A variety of systems exist to regulate the timing of engine valve opening by controlling the hydraulic pressure that acts on a slave piston which actuates the engine valve. These systems include “common rail” systems in which a solenoid control valve opens a path from a source of high pressure fluid to the top of the slave piston at precise times. One such common rail system is described in Cosma et al., U.S. Pat. No. 5,619,964, assigned to the assignee of the present application.
Another method of adjusting valve timing and lift, given a fixed cam profile, has been to incorporate a “lost motion” device in the valve train linkage between the valve and the cam. Lost motion is the term applied to a class of technical solutions for modifying the valve motion proscribed by a cam profile with a variable length mechanical, hydraulic, or other linkage means. In a lost motion system, a cam lobe may provide the “maximum” (longest dwell and greatest lift) motion needed over a full range of engine operating conditions. A variable length system may then be included in the valve train linkage, intermediate of the valve to be opened and the cam providing the maximum motion, to subtract or lose part or all of the motion imparted by the cam to the valve.
This variable length system (or lost motion system) may, when expanded fully, transmit all of the cam motion to the valve, and when contracted fully, transmit none or a minimum amount of the cam motion to the valve. An example of such a system and method is provided in Hu, U.S. Pat. Nos. 5,537,976 and 5,680,841, which are assigned to the same assignee as the present application and which are incorporated herein by reference.
In the lost motion system of U.S. Pat. No. 5,680,841, an engine cam shaft may actuate a master piston which displaces fluid from its hydraulic chamber into a hydraulic chamber of a slave piston. The slave piston in turn acts on the engine valve to open it. The lost motion system may include a solenoid valve and a check valve in communication with the hydraulic circuit including the chambers of the master and slave pistons. The solenoid valve may be maintained in a closed position in order to retain hydraulic fluid in the circuit. As long as the solenoid valve remains closed, the slave piston and the engine valve respond directly to the motion of the master piston, which in turn displaces hydraulic fluid in direct response to the motion of a cam. When the solenoid is opened temporarily, the circuit may partially drain, and part or all of the hydraulic pressure generated by the master piston may be absorbed by the circuit rather than be applied to displace the slave piston.
Another example of an engine valve actuator is disclosed in U.S. Pat. No. 5,186,141, “engine Brake Timing Control Mechanism,” issued to D. Custer on Feb. 16, 1993 (the “'141 patent”), incorporated by reference herein. The actuator disclosed in the '141 patent does not provide for engine valve seating control, although it could benefit from such control.
Engine valves are required to open and close very quickly, therefore the valve spring is typically very stiff. When the valve closes, it may impact the valve seat with such force that it eventually erodes the valve or the valve seat, or even cracks or breaks the valve. In mechanical valve actuation systems that use a valve lifter to follow a cam profile, the cam lobe shape provides built-in valve-closing velocity control. In common rail hydraulically actuated valve assemblies, however, there is no cam to self-dampen the closing velocity of an engine valve. Furthermore, in some lost motion applications the engine valve needs to be closed at an earlier time than that provided by the cam profile. This earlier closing may be carried out by rapidly releasing hydraulic fluid to an accumulator in the lost motion system. In hydraulic lost motion systems, a rapid draining of fluid from the slave piston may allow an engine valve to “free fall” and seat with an unacceptably high velocity. Free fall results when the rate of closing the engine valve is governed by the hydraulic fluid flow to the accumulator instead of by the fixed cam profile. Engine valve seating control may also be required for applications (e.g. centered lift) in which the engine valve seating occurs on a high velocity region of the cam. Electromagnetic valve actuation may also require valve seating control.
As a result of the foregoing there is a need to limit valve seating velocities. The need for limited valve seating velocities conflicts with the need for rapid valve opening rates. Some attempts have been made to solve the problem by providing separate fill and drain ports for slave pistons. U.S. Pat. No. 5,577,468 discloses one system for limiting valve seating velocity. Existing methods for controlling engine valve seating velocity may be costly, inaccurate, and cause excessive valve closing variations. Existing systems also fail to accommodate the need for adjustments due to variations in engine valve lash between cylinders.
Applicants approached the valve seating challenge with the understanding that valve seating velocity should be less than approximately 15 in/sec (0.38 m/sec). Absent steps to control valve seating velocity, the valves could seat at a velocity that is an order of magnitude greater. Applicants also determined that valve seating control preferably should be designed to function when the closing valve gets within 0.5 to 0.75 mm of the valve seat. The combination of valve thermal growth, valve wear, and tolerance stack-up can exceed 0.75 mm, resulting in the complete absence of seating velocity control or in an exceedingly long seating event if measures are not taken to adjust the lash of the valve seating control to account for such variations. It is also assumed that, preferably, valve seating control should not significantly reduce initial engine valve opening rate, and valve seating control should be capable of operating over a wide range of valve closing velocities and oil viscosities.
Valve catch devices used to control valve seating velocity may use hydraulic fluid flow restriction to produce pressure that acts on an area of the slave piston to develop a force to slow the slave piston and reduce seating velocity. The area on which the pressure acts may be very small in such devices which in turn requires that the pressure opposing the valve return spring be high, and the controlling flow rate be low. Low controlling flow rates result in an increased sensitivity to leakage and manufacturing tolerances. In addition, these devices may restrict the hydraulic fluid flow that produces valve opening.
A known valve catch (seating) system developed to provide valve seating control is disclosed in co-pending U.S. patent application Ser. No. 09/383,987, filed Aug. 26, 1999, hereby incorporated by reference and which is shown as system
100
in FIG.
1
. The system
100
includes a slave piston
120
disposed within an actuator housing
110
. The slave piston
120
is slidable within the housing
110
so that it may open an engine valve (not shown) below it. A screw body
130
extends through the top of the housing
110
and abuts
Schwoerer John A.
Vanderpoel Richard
Collier Shannon Scott PLLC
Dahbour Fadi H.
Diesel Engine Retarders, Inc.
Paschall Mark
Yohannan David R.
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