US20040079306A1

US20040079306A1 - Variable lift electromechanical valve actuator

Info

Publication number: US20040079306A1
Application number: US10/278,416
Authority: US
Inventors: John Norton; James Alexander; Ha Chung
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2002-10-23
Filing date: 2002-10-23
Publication date: 2004-04-29
Also published as: DE10349379A1; GB0322787D0; JP2004162916A

Abstract

A variable lift electromechanical valve actuator for use with an internal combustion engine. The electromechanical valve includes a first electromagnet, a second electromagnet, and a hydraulic lifting mechanism. The upper electromagnet is fixedly mounted to a housing while the lower electromagnet slides in conjunction with the hydraulic lifting mechanism. Multiple valve lifts are provided for by the movement of the lower electromagnetic electromagnet. Variable valve lift allows for more efficient operation of the engine and reduced power consumption, noise, vibration, and wear concerns.

Description

BACKGROUND OF THE INVENTION

The present invention relates to electromechanical valve actuators and more particularly to variable lift electromechanical valves for internal combustion engines.

Engine valves control the flow in and out of the cylinders in internal combustion engines. Engine valves are typically controlled by camshafts that rotate, at a speed proportional to the crankshaft causing the valves to open and close at specified intervals. An example of a typical valve train includes a rotating camshaft having elliptical lobes which contact tappets or lash compensators on the valve. As the elliptical lobe presses against the tappet, the valve is pushed open at determined intervals, and as the elliptical lobes rotate away from the tappet, the valve is closed by a spring. The opening and closing times of the valves are determined by the geometry of the lobes, and the relative angular position with respect to the crankshaft when the engine is assembled. Manufacturers can adjust this timing by altering the shape, size, and angular location of the elliptical lobes. However, the timing as well as the torque curve is typically fixed at the time the engine is assembled. The amount of valve lift is also determined by the lobes on the camshaft and therefore determined when the engine is assembled. The lack of variable valve timing and variable valve lift reduces engine optimization and therefore may reduce engine efficiency.

Another problem with conventional engines is that they require a throttle body and the associated components. The throttle body restricts air flow into the engine. One problem with using a throttle body is that engine efficiency is reduced due to intake restrictions. When air flows through the throttle body, an air pressure drop occurs across the throttle plate. Therefore, when the intake valve opens under throttled conditions, the piston pulls in air of a lower pressure than the surrounding atmosphere, resulting in engine inefficiencies. Manufacturers have strived to create true throttless engine operation to increase engine efficiency as well as allow for drive-by-wire systems.

To address problems associated with traditional valves activated by camshafts, some manufacturers have attempted to substitute electromechanical valve actuators (also known as electromagnetic valve actuators) in place of camshafts. Generally, these electromechanical actuators include upper and lower electromagnets that are formed from lamination stacks and coiled wire. The electromechanical valve actuators also include an armature located between the electromagnets. The armature generally forms a plane somewhat perpendicular to the valve stem and includes an armature stem, that passes through both the upper and lower electromagnets, in order to open or close a valve.

In operation, the electromagnets are selectively energized, creating a magnetic force to draw the armature to the energized electromagnet. The surface of the electromagnet which the armature contacts may be referred to as a pole face. As the armature moves back and forth in pole face to pole face operation, the valve is opened and closed. Electromechanical valve actuators allow for complete control of the timing of every valve. Electromechanical valve actuators may also open more than one valve at the same time. One problem with electromechanical actuated valves is that as the distance between the armature and the magnetized electromagnet decreases, the magnetic force exponentially increases. The increase in magnetic force causes the armature to increase in velocity as it approaches an energized electromagnet. The armature then impacts the electromagnet, causing noise and vibration. Forceful contact between the armature and electromagnet also may cause excessive wear on the components of the electromechanical valve actuator and other engine components.

Some manufacturers have shaped the power profile supplied to the lamination stack in an effort to soften the impact, but this may increase the time it takes the armature to travel from pole face to pole face. An increase in time to travel from pole face to pole face increases the transition times and may prevent the engine from operating properly because the valve cannot open and close fast enough.

At idle speeds, electromechanical valves may consume a significant portion of power to overcome the springs in the system, and move the armature from the pole face to pole face. Enough power must be applied to the electromagnet to overcome any exhaust pressure in the cylinder during the opening of an exhaust valve, which creates a large draw on the electrical system of the engine at idle speeds. The springs may be sized to accommodate desired valve transition times as well as provide enough force to open against any exhaust pressure. Another problem with electromechanical valves is that they are not capable of operating throttless in all engine conditions. For many electromechanical valves, varying the valve timing still leaves large regions at mid to high flow regimes where they are not able to operate. These voids in operating conditions many times occur in the most desirable operating regions of the engine. Yet another problem is that electromechanical valves are not as efficient as they can be, because the valve lift or how far the valves open can not be changed. Valve lift is generally set by operating conditions that demand maximum flow, which cause inefficient engine operation in low flow conditions.

To solve some of the problems associated with electromechanical valves, a few manufacturers have varied the lift of the valves. Varying the lift of the valves may help increase the efficiency of the engine by allowing the lift of the valve to match the operating conditions. Reduced valve lift at idle conditions also helps to reduce noise, vibration, power consumption, and wear concerns.

A disadvantage some of these systems have is that the valve has only two lift positions, a high and a low position. The inability to adjust the lift throughout the range reduces the optimization of engine operation associated with variable lift and can prevent maximum engine efficiency from being obtained. Another problem with some of these systems is that the spring bias may be offset as the valve lift is changed which may cause the armature plate, when at rest, such as when the valve actuator is unpowered and no magnetic force is applied, to be off center between the lamination stacks. During operation, this bias may cause the armature to be more forcefully attracted to one pole face, causing noise and vibration. This bias may also make it difficult to be attracted to the other electromechanical plate, thereby requiring additional power.

Another system addresses some of these problems by providing a range of variable lifts. The problem with this variable valve lift system is that it is difficult to accurately determine the lift of the valve. The lash in the system may make it even more difficult. Due to the type of and amount of moving parts, the inaccuracy of the system only increases with use. Yet another problem with this system is the increase in moving parts, including the use of an additional motor may decrease the reliability of the system over time.

SUMMARY OF THE INVENTION

The aforementioned problems are overcome in the present invention where an electromechanical valve includes an actuator that adjusts the lower magnet, varying the valve lift, along with the armature spring seat, varying the bias and spring forces, throughout a range of adjustment. More specifically, the present invention includes a variable lift actuator in conjunction with an electromechanical valve, providing variable valve lift while centering the armature in all lift positions between the two electromagnets and reducing the impact forces of the armature against the electromagnets during pole face to pole face operation.

A hydraulic actuator is used to vary the lift of the valve, allowing for maximum engine efficiency by allowing a range of flow depending on the engine requirements, in addition to variable valve timing. The present invention allows true throttless operation through its entire engine speed and load ranges. The valve lift can control the air flow, eliminating the need for a throttle body. Variable valve lift and variable timing allow the engine to provide optimum torque at all rpms, unlike some electromechanical valves, which have gaps in the rpm power band where the engine can not function properly without throttling. Another benefit of the hydraulic actuator providing variable valve lift is that a hydraulic pocket also provides a dampening means, which may reduce impact noise and wear concerns. The present invention also allows complete pole face to pole face movement of the armature no matter what lift is being used. Complete pole face to pole face operation also helps accurately determine the amount of valve lift. Variable valve lift also reduces the spring force thereby reducing noise and wear concerns, as well as reduces the power required to hold the armature against either pole face, especially during engine operation with reduced valve lift. Variable valve lift combined with variable valve timing allows for efficient engine operation and minimal energy consumption.

Further scope of applicability of the present invention will become apparent from the following detailed description, claims, and drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given below, the appended claims, and the accompanying drawings in which: [0014]
FIG. 1 is a sectional view of an engine valve assembly with the valve shown in the fully closed position with reduced lift; [0015]
FIG. 2 is a sectional view similar to FIG. 1 but with the valve shown in its middle position with reduced lift; [0016]
FIG. 3 is a sectional view similar to FIG. 1 but with the valve shown in the open position with reduced lift; [0017]
FIG. 4 is a sectional view similar to FIG. 1 but with the valve being in the closed position with full lift; [0018]
FIG. 5 is a sectional view similar to FIG. 3 showing the valve in a open position set in the mode for full lift; and [0019]
FIG. 6 is a block diagram of the engine valve assembly and control system.[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates an electromechanical [0021] valve actuator assembly 10 which is mounted on an internal combustion engine to open and close the valves (e.g., intake or exhaust valves).
The [0022] electromechanical valve assembly 10 is generally mounted on the cylinder head 12 of the internal combustion engine. While the cylinder head 12 may be formed in a variety of shapes and configurations, it typically includes a port 14, a valve seat 16, and a valve guide 18. The port 14 may be an intake or an exhaust port depending on the function of the valve.
The [0023] valve 20 includes a valve disc or head 22, a tapered portion 24, and a valve stem 26. An upper spring retainer 32 and a lower spring retainer 34 may also be included. The valve 20 and the cylinder head 12 are formed and assembled as generally well known in the art. The valve guide 18 receives the valve stem 26 and aligns the valve 20 as it moves up and down so that a tight seal is formed between the valve seat 16 and the tapered portion 24 surrounding the valve disc 22, when the valve 20 is in its closed position, as may be seen in FIGS. 1 and 4.
The [0024] electromechanical valve actuator 10 generally includes a housing 40 defining a cavity containing electromagnets 52 and 54, an armature stem 60, an armature 70, and a hydraulic lift mechanism 80. The upper and lower electromagnets 52 and 54 move the armature 70 and attached armature stem 60 to drive the engine valve 20 between its open and closed positions.
The [0025] housing 40 may be formed in a variety of sizes and shapes, which may be dictated by space constraints of the internal combustion engine. The housing 40 provides structural rigidity and attaches the electromechanical valve actuator 10 to a cylinder head 12 of an internal combustion engine. Of course, it should be readily apparent to one skilled in the art that a variety of means may be used to provide the structural rigidity or method of attachment.
In the illustrated embodiment, the [0026] upper electromagnet 52 is fixed relative to the housing 40 such as by pins 42 while the lower electromagnet 54 is mounted within the housing 40 so that it is movable relative to the housing 40. Suitable electromagnets are generally well known in the art and can have a variety of shapes that may be formed from the individual plates of magnetically conductive material to form a lamination stack. The electromagnets 52 and 54 may include a coil of wires 53 wound within the lamination stack. The electromagnets 52 and 54 are connected to a source of electrical current (not shown) which can be selectively turned on and off independently by a controller such as an engine management system 100 (FIG. 6). An energized electromagnet 52 or 54 provides magnetic force to attract the armature 70. It should readily be recognized that a separate means may be used in place of the housing 40 to hold the upper electromagnet 52 in place.
The [0027] armature 70 is mounted to move with the armature stem 60 and is located between the upper electromagnet 52 and the lower electromagnet 54. In the illustrated embodiment, the surfaces of the armature 70 facing the electromagnets 52 and 54 are approximately the same size and shape as the surfaces of the electromagnets 52 and 54 facing the armature 70. Of course, it should be readily obvious to one skilled in the art that the sizes and shapes of the armature 70 and of the electromagnets 50 may vary between applications.
An [0028] armature spring 62 and a valve spring 64 operably engage the valve to urge the valve toward its open or closed positions. The armature spring 62 is mounted above the upper electromagnet 52 within the housing 40 to exert a biasing force urging the valve 20 toward its open position. In the illustrated embodiment, the armature spring 62 is a compression spring and is located between the armature spring retainer 32 and the hydraulic lift mechanism 80. The armature spring 62 may be any compression spring known in the art for use with traditional valves or electromechanical valves. The size, shape, and location of the armature spring 62 may vary from application to application. A valve spring 64 is mounted, in the illustrated embodiment, between the cylinder head 12 and the valve spring retainer 34. The valve spring 64 is also a compression spring as shown in the illustrated embodiment. Of course, it should be readily recognized to one skilled in the art that other placements of the springs 62 and 64 are possible and that certain placements may also result in opening and closing of the valves differently than shown in the illustrated embodiment.
The [0029] hydraulic lift mechanism 80 varies the amount of valve lift and, in the illustrated embodiment, includes a hydraulic slide 82 and a hydraulic chamber 84. The hydraulic slide 82 is formed in the illustrated embodiment in the shape of a sleeve having an upper segment 72, a lower segment 74, and a passage 78 to accommodate the upper electromagnet 52 and pins 42. The lower electromagnet 54 is attached to move with the slide 82 by a variety of means such as a compression fit, adhesive, bonding or pins. The hydraulic chamber 84 is defined in the illustrated embodiment at the upper end of the housing 40 by the housing and the hydraulic slide 82. As the pressure in the chamber 84 is varied, the slide 82 moves relative to the housing 40. As the lower electromagnet 54 moves with the slide 82 and the upper electromagnet 52 is fixed to the housing 40, movement of the slide 82 changes the distance between the electromagnets 52 and 54 and the length of the valve stroke.
In the illustrated embodiment, hydraulic fluid in the [0030] hydraulic chamber 84, such as engine oil, is pressurized by the oil pressure of the engine or an auxiliary pump. In some embodiments the hydraulic lift mechanism 80 may include hydraulic lines 86, hydraulic valves 88 and a pump 102. The hydraulic lines 86 provide a fluid connection between the hydraulic chamber 84 and the pump 102. Hydraulic valves 88 may be situated between the hydraulic chamber 84 and the pump 102 to control flow through the hydraulic lines 86. The hydraulic valves 88 control the height of the hydraulic slide 82 in conjunction with the forces from the springs 62 and 64. The hydraulic valve or valves 88 control the fluid pressure in the hydraulic chamber 84. In the illustrated embodiment, the hydraulic valve 88 is a spool valve. A spool valve is used because it uses a series of hydraulic channels to maintain a specified position regardless of the forces acting on the slide 82. The hydraulic valve 88 is controlled by the engine management system 100. The engine management system 100 can easily control valve lift through existing techniques of determining air flow needed to the engine. Of course, the engine management system may be programmed from lab tests or road tests of what valve lifts are needed under specified engine operating conditions to maximize efficiency. In the illustrated embodiment, the pump 102 is the engine oil pump and engine oil is used as the hydraulic fluid. Of course a separate pump as well as separate hydraulic fluid may be used. A separate means for heating the fluid may also be included (not shown).
In operation, the valves are opened and closed as is well known in the art for electromechanical valves. While the system is unpowered, the [0031] armature 70 is in a neutral position, approximately centered between the upper and lower electromagnets 52 and 54 due to the biasing of the springs 62 and 64. Upon start up, either the upper or lower electromagnet 52 or 54 is energized, attracting the armature 70, thereby opening or closing the valve 20. The power is then switched between the electromagnets 52 and 54 causing the armature 70 to travel pole face to pole face, opening and closing the valve 20. As with most electromechanical valves, the timing of the opening and closing may also be varied for more efficient engine operation.
When the [0032] valve 20 is commanded to a full open or full closed position, the armature 70 is attracted to an electromagnet pole face. In order to hold the valve 20 closed enough current must be delivered to the electromagnet pole face to produce a magnetic force larger than the spring force which acts in the opposite direction. The illustrated embodiment has the advantage that during reduced lift operation the hydraulic slide moves resulting in a lower spring force that the electromagnet must overcome. In other words, during low lift operation, the spring force opposing the electromagnet force is reduced. This results in less required electromagnet force and therefore less power consumption by the electromagnet when compared to a stationary full lift actuator.
The amount of valve lift during engine operation may be changed by varying the pressure in the [0033] hydraulic chamber 84 and therefore the position of the slide 82. A low pressure causes the hydraulic slide 82 to be in a reduced lift position, as shown in FIGS. 1-3. Valve spring 64 exerts pressure on the slide 82, causing the slide to move upward during low pressure conditions such as at low rpms. Of course, other means may be used to exert pressure on the hydraulic slide 82 to move the slide 82 to a reduced lift position such as an additional spring or an oil pocket. The reduced valve lift allows for optimized throttless engine operation through all ranges.
As the engine revolutions increase, more flow is needed to and from the cylinders for the engine to operate efficiently and at the desired power levels. Engine oil pressure increases as the revolutions increase and pushes the [0034] hydraulic slide 82 downward to a desired lift, as shown in FIGS. 4 and 5, at the maximum lift. When the hydraulic slide 82 moves downward so does the lower electromagnet 54, causing the armature to travel a greater distance between the upper and lower electromagnets 52 and 54. It should readily be seen that because the hydraulic slide 82 compresses or relaxes spring 62, the armature 70, when at rest, is centered between the upper and lower electromagnets 52 and 54, no matter what lift is being provided.
To provide more precise control over the valve lift, the [0035] hydraulic lifting mechanism 80 may use the hydraulic valves 88 and separate oil pump 102. A separate hydraulic pump 102 also can be helpful to provide full valve lift in any engine operating conditions. For example, a separate pump 102 is useful at low rpms where lots of torque is needed, such as pulling a heavy trailer, to increase valve lift and allow more flow. The hydraulic valves 88 may reduce valve lift at higher rpm conditions where little power is needed from the engine, for example, during operation at constant speeds such as operation of a vehicle on the highway.
In operation, the above electromechanical valve also allows for throttless operation. The variability of the valve lift and timing allows the amount of air entering the cylinder to be controlled without a throttle body or throttle plate. This allows the piston to pull in atmospheric pressurized air, thereby increasing engine efficiency. [0036]
The foregoing discussion discloses and describes an exemplary embodiment of the present invention. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims. [0037]

Claims

What is claimed is:

1. An electromechanical valve comprising:

a first electromagnet;

a second electromagnet spaced from said first electromagnet; and

a hydraulic lifting mechanism coupled to one of said first and second electromagnets to change the spacing between said first electromagnet and said second electromagnet.

2. The electromechanical valve of claim 1 further comprising a housing and wherein said hydraulic lifting mechanism further includes a hydraulic slide moveable relative to said housing, said first electromagnet being fixed to said housing and said second electromagnet being fixed to said hydraulic slid.

3. The electromechanical valve of claim 2 wherein said hydraulic slide and said housing define a pressure chamber, said pressure chamber containing fluid that exerts a pressure on said hydraulic slide, said hydraulic slide being moveable in response to said pressure.

4. The electromechanical valve of claim 2 wherein said first electromagnet is positioned vertically above said second electromagnet.

5. The electromechanical valve of claim 2 further including a pin attaching said first electromagnet to said housing and a passageway defined in said hydraulic slide, said pin passing through said passageway.

6. The electromechanical valve of claim 1 further including a first spring positioned between said first electromagnet and said hydraulic lifting mechanism.

7. The electromechanical valve of claim 1 further comprising a second spring and a cylinder head, said second spring being located between said cylinder head and said lower electromagnet.

8. The electromechanical valve of claim 1 further including an armature having a neutral position, said first spring and said second spring exerting a first pressure and a second pressure on said armature in said neutral position, said first pressure and said second pressure approximately centering said armature between said first electromagnet and said second electromagnet at said neutral position.

9. An electromechanical valve for an internal combustion engine comprising:

an upper electromagnet;

a lower electromagnet spaced from said upper electromagnet,

a hydraulic slide coupled to said lower electromagnet to change the spacing between said lower electromagnet and said upper electromagnet.

10. The electromechanical valve of claim 9 further including an actuator stem, said upper and lower electromagnet surrounding a portion of said actuator stem.

11. The electromechanical valve of claim 10 further including an armature attached to said actuator stem, said armature being located between said upper electromagnet and said lower electromagnet.

12. The electromechanical valve of claim 9 further including a housing defining a defining a fluid chamber containing a fluid that exerts a pressure on said slide, said slide moving relative to said housing in response to said pressure.

13. The electromechanical valve actuator of claim 12 further including a hydraulic pump in fluid communication with said fluid chamber, said hydraulic pump changing a fluid pressure in said fluid chamber.

14. The electromechanical valve actuator of claim 12 further including a cylinder head and valve stem having an open position with a lift relative to said cylinder head, said lift being proportional to said pressure.

15. An internal combustion engine having a variable lift electromechanical valve comprising;

an upper electromagnet;

a lower electromagnet spaced from said upper electromagnet; and

a hydraulic positioning means connected to said lower electromagnet to change the spacing between said upper electromagnet and said lower electromagnet.

16. The internal combustion engine of claim 15 wherein said hydraulic positioning means includes a fluid chamber containing a fluid that exerts a pressure on a hydraulic slide, said hydraulic slide moving said lower electromagnet relative to said upper electromagnet in response to said pressure.

17. The internal combustion engine of claim 17 wherein said fluid exerts a first pressure and a second pressure, said first pressure having a first spacing between said upper electromagnet and said lower electromagnet, said second pressure having a second spacing between said upper electromagnet and said lower electromagnet.

18. The internal combustion engine of claim 17 wherein if said second pressure is greater than said first pressure then said second spacing is greater than said first spacing.

19. The internal combustion engine of claim 17 wherein as said pressure increases said space between said upper electromagnet and said lower electromagnet increases.

20. The internal combustion engine of claim 19 further comprising an upper spring and a lower spring, said upper spring and said lower spring exerting a first spring pressure and a second spring pressure, said first spring pressure and said second spring pressure increasing as said pressure increases.