Patent Application
20060096562
1. Field of the Invention
The invention pertains to the field of valves for a variable cam timing system. More particularly, the invention pertains to a VCT with a reed valve with multiple ports.
2. Description of Related Art
Engine performance of an engine having one or more camshafts can be improved, specifically in terms of idle quality, fuel economy, reduced emissions, or increased torque, by way of a variable cam timing (VCT) system. Variable cam timing refers to controlling/varying the angular relationship or phase between one or more camshafts, which drive the engine's intake and/or exhaust valves, and the crankshaft, which is connected to the pistons. For example, the camshaft can be “retarded” for delayed closing of intake valves at idle for stability purposes and at high engine speed for enhanced output.
Likewise, the camshaft can be “advanced” for premature closing of intake valves during mid-range operation to achieve higher volumetric efficiency with correspondingly higher levels of torque. In a dual-camshaft engine, retarding or advancing the camshaft is accomplished by changing the positional relationship of one of the camshafts, usually the camshaft that operates the intake valves of the engine, relative to the other camshaft and the crankshaft. Accordingly, retarding or advancing the camshaft varies the timing of the engine in terms of the operation of the intake valves relative to the exhaust valves, or in terms of the operation of the valves relative to the position of the crankshaft.
Many VCT systems incorporating hydraulics include an oscillatable rotor secured to a camshaft within an enclosed housing, where a chamber is defined between the rotor and housing. A “phaser” is all of the parts of the engine which allow the camshaft to run independently of the crankshaft. In a vane phaser, the rotor includes vanes mounted outwardly therefrom to divide the chamber into separated first and second fluid chambers. Such a VCT system often includes a fluid supplying configuration to transfer fluid within the housing from one side of a vane to the other, or vice versa, to thereby rotate the vane of the rotor with respect to the housing in one direction or the other. Such rotation is effective to advance or retard the position of the camshaft relative to the crankshaft. These VCT systems may either be “self-powered” having a hydraulic system actuated in response to torque pulses flowing through the camshaft, or may be powered directly from oil pressure from an oil pump. Additionally, mechanical connecting devices are included to lock the rotor and housing in either a fully advanced or fully retarded position relative to one another. Check valves are used to control the oil flow to the fluid chambers in the vanes. Check valves allow oil to flow freely in one direction while preventing the oil from going in the opposite direction.
In a conventional VCT system, prior art reed check valves cover a single port with support only at the edges of the diameter. The single port design creates difficulties because of the physical limits of the material properties for the reed valve. When the check valve is “closed”, the reed valve is sealed across the seat, and prevents backflow (zero backflow). In this position, the backpressure on the reed valve may be high enough to plastically deform and eventually cause the reed valve to fail.
Referring to
To reduce the stress on the valve and eliminate the chance of failure, the seat diameter (hole/port size) may be reduced. But, reducing the seat diameter restricts flow, and negatively affects VCT performance.
Therefore, there is a need in the art for an improved design for a reed valve that can sustain high pressures without restricting flow.
A reed valve seat with multiple ports allows a reed valve to operate under extreme pressures in a variable cam timing system. A check valve includes a valve seat in a variable cam timing phaser with a contact surface and multiple ports for fluid in control passages within the phaser to flow through. A reed creates a seal with the contact surface of the valve seat when the reed contacts the valve seat such that reverse flow of fluid in the variable cam timing phaser is prevented.
The present invention improves a check valve seat design for a reed valve. This reduces stress levels while maintaining or exceeding the flow rates of the single-holed valve seats of the prior art. By changing the seat geometry from a single port to multiple smaller ports, the exposed surface area of each port is reduced. By decreasing the amount of exposed surface area, the stress on the reed is decreased. This decreases the stress on the reed valve. By adding additional ports, the stress on the reed stays at acceptable levels, while the flow rate may be increased. The flow rate depends on the entire area of the ports. Therefore, if the total area of the multiple ports is greater than the single port in the prior art, the flow rate is increased.
Although four ports, all with the same diameter and area, are shown in the Figure, the present invention is not limited to four ports or ports that are all the same size. The number of ports and their desired size is system dependent. It depends on the rate at which the phaser is going to be moved and on the total torsional energy available. Packaging also affects the number of ports used.
For example, since the pressure and energy are known for a given system, the preferred port area is the largest port area that can withstand the pressure in that system. To obtain the same amount of flow in the reed valves of the present invention as with the single holed reed valves of the prior art, one would use a number of ports with an area that would together be equal or greater than the same area of the single port. Alternatively, the ports may have different areas as long as the total area is equal or greater than the area of the single port. If less or greater flow rates are desired than that obtained with a single port, the ports and their areas are adjusted accordingly.
Assume, for example, that a 6 mm diameter single port provides a certain desired flow rate in a particular system. Assume also that a 3 mm port is the largest size port able to withstand the pressure in that system. Flow is controlled by the area available. A 6 mm hole has an area of 28.27 mm2, while a 3 mm hole has an area of 7.07 mm2. 28.27 mm2 divided by 7.07 mm2 equals 4. Thus, four ports, each with a 3 mm diameter, result in the same area as the 6 mm single port of the prior art. A reed valve assembly with four 3 mm ports is able to withstand higher pressures than a single 6 mm port, while maintaining the same area.
Alternatively, multiple ports may have an increased area compared to a single port design. A valve with a 5.5 mm diameter single port provides a certain desired flow rate in a particular system. This single port has an area of 23.75 mm2. A valve with four ports, each having a diameter of 3.5 mm and an area of 9.62 mm , has a total area of 38.48 mm2.
In a cam torque actuated (CTA) phaser, torque reversals in the camshaft caused by the forces of opening and closing the valves move the vane (76). The CTA advance and retard chambers (78), (80) are arranged to resist positive and negative torque pulses in the camshaft and are alternatively pressurized by the cam torque. The control valve, shown as a spool valve (74) in the figures, includes a spool (79) and is received in a sleeve (87) of the rotor. The position of the spool (79) controls the motion (e.g. to move towards the advance position or the retard position) of the phaser. The spool valve (74) in the CTA system allows the rotor in the phaser to move by permitting fluid flow from the advance chamber (78) to the retard chamber (80) or vice versa, depending on the desired direction of movement. Positive cam torsionals are used to retard the phaser and negative cam torsionals are used to advance the phaser.
More specifically, in the null position, as shown in
Makeup oil is supplied to the phaser to make up for leakage and enters line (88) through the check valve (89), and moves into the necessary chamber.
Makeup oil is supplied to the phaser to make up for leakage and enters line (88) through the check valve (89), and moves into the necessary chamber.
In another embodiment, the spool valve (74) may also be externally or internally connected to a stationary rotary actuator. The housing in a rotary actuator does not have an outer circumference for accepting drive force and motion of the housing is restricted as shown by the two-headed arrow (250). The restriction of the housing ranges from not moving the housing at all to the housing having motion restricted to less than 360°. All movement, other than the twisting of the shaft is done by the rotor. The rotor and the vane move or swing through the distance as defined and limited by the housing. All of the cyclic load is on the rotor and the rotor accepts all of the drive force.
In this embodiment, the spool valve (74) may by externally or internally connected to the stationary rotary actuator (200). In the rotary actuator (200), the housing (201) does not have an outer circumference for accepting drive force and motion of the housing is restricted. A stop (202) restricts (250) the movement of the rotary actuator to less than 360°. The rotary actuator includes reed valves (104) and (204) with multiple ports to withstand high pressure.
In another embodiment, shown in
In another embodiment, the CTA system described above is preferably mounted to the side of the engine in a self contained unit. In this embodiment, the CTA system, including the reed check valves (104) and (204) of the present invention, as well as the spool valve, is packaged in the self-contained unit mounted to the side of the engine.
In the cam torque actuated (CTA) phaser shown in
In terms of the spool valve, the force of the actuator and the force of the spring are balanced in the null position and the spool is positioned such that fluid from the supply enters the spool valve (428) and moves through common line (416) and reed check valves (104), (204) to the advance line (408) and the retard line (410) respectively. From the advance line (408) and the retard line (410) fluid enters the advance chamber (402) and the retard chamber (404).
To move towards the retard position, as shown in
Makeup oil is supplied to the phaser to make up for leakage and enters line (418) through the check valve (424), and moves into the necessary chamber.
To move towards the advance position, as shown in
Makeup oil is supplied to the phaser to make up for leakage and enters line (418) through the check valve (424), and moves into the necessary chamber.
As in other embodiments, although check valve (424) is shown as a ball check valve in the figures, the check valve (424) may be a reed check valve (104) of the present invention.
In yet another embodiment, the reed valve (104) of the present invention is used in a torsion assist (TA) VCT system. U.S. Pat. No. 6,883,481, issued Apr. 26, 2005, entitled “Torsional Assisted Multi-Position Cam Indexer Having Controls Located in Rotor” discloses a single check valve TA, and is herein incorporated by reference.
The phaser operating fluid, illustratively in the form of engine lubricating oil, flows into the recesses (302) (labeled “A” for “advance”) and (303) (labeled “R” for “retard”) by way of a common inlet line (313). An inlet reed check valve (104) prevents the hydraulic fluid from backflowing into the engine oil supply. Compared to the check valves (104) and (204) in
Inlet line (313) terminates as it enters the spool valve (320). The spool valve (320) includes a spool (322). The spool (322), which is preferably a vented spool, is slidable back and forth. The spool (322) includes spool lands (319) and (320). The spool lands (319) and (320) are preferably cylindrical lands and the spool preferably has three positions. The null position is shown in
To maintain a phase angle, the spool (322) is positioned at null. The camshaft is maintained in a selected intermediate position relative to the crankshaft of the associated engine, referred to as the “null” position of the spool (322). Make up oil from the supply fills both chambers (302) and (303). When the spool (322) is in the null position, spool lands (319) and (320) block both of the inlet lines (308) and (310).
Advance chamber reed check valve (104) is located in the advance chamber inlet line (308) while retard chamber reed check valve (204) is located in the retard chamber inlet line (310). Having the check valves in the advance and retard chambers instead of having a single check valve in the supply reduces leakage.
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.
