WO2000042300A1

WO2000042300A1 - Improvements in a variable valve timing system for an internal combustion engine

Info

Publication number: WO2000042300A1
Application number: PCT/CA2000/000033
Authority: WO
Inventors: Daniel G. Pomerleau; Mark Voghell
Original assignee: Aztec Inc.
Priority date: 1999-01-12
Filing date: 2000-01-12
Publication date: 2000-07-20
Also published as: AU3028400A; CA2257437A1

Abstract

The invention relates to improvements in variable valve timing for an internal combustion engine. Specifically, the end design of a valve lifter or valve stem that provides a fine contact point with a variable profile cam that can enable its movement across the cam in order to provide a greater range of valve timing. In addition, the system provides a camshaft and camshaft journal system which allows for axial movement of a cam shaft on the basis of engine rpm and which allows for advancing or retarding a camshaft system on the basis of engine rpm.

Description

Improvements in a Variable Valve Timing System for an Internal Combustion Engine

Field of the Invention

The invention relates to improvements in variable valve timing for an internal combustion engine. Specifically, the invention provides a valve lifter or valve stem that provides a fine contact point with a variable profile cam that can enable its movement across the cam in order to provide a greater range of valve timing. In addition, the system provides a camshaft and camshaft journal system which allows for axial movement of a cam shaft on the basis of engine rpm and which allows for advancing or retarding a camshaft system on the basis of engine rpm.

Background of the Invention

The design of an internal combustion engine requires numerous trade-offs between conflicting performance parameters. For example, in the design of an engine, a designer may wish to minimize exhaust emissions and provide increased fuel economy without compromising satisfactory engine performance. In the past, the design of an such an engine would be limited by such conflicting pararmeters leading the designer to compromise between the parameters. As such, designers will often focus on a primary performance goal which may be to the detriment of desired engine performance (for example, torque or idle stability). Such compromises are often caused by the lack of the designers ability to incorporate breathability into the engine, that is an optimal intake of fuel and air and exhaust of spent gases after combustion.

The breathability of an engine is primarily determined by the physical structure of the cam shaft, cam lobes, valve lifters (and the associated push-rods, rocker arms, if applicable). In particular, the physical shapes of the cams and their relative orientation with respect to one another determine the timing of the intake and exhaust valve opening, the duration of opening, and the timing of valve closure which along with the orientation of respective intake and exhaust valves about the camshaft determine the power map of the cylinder. As a result of the working environment and the physical complexity of these components, adjustment during operation of the engine is difficult and accordingly, most engines utilize a fixed cam timing system wherein the relative timing between valve opening and closure does not vary with engine speed. Accordingly, fixed cam timing engines require trade-offs between the performance parameters of the engine. More specifically, the camshaft function is to open and close valves at the proper time, to fill the cylinders before combustion and to empty them after combustion. The cams are mounted on the camshaft and have a profile which determines the timing of valve opening, the duration of opening and the timing of valve closing. The lifters are in intimate contact with the cam surface and ride the cam surface in order to impart opening/closing forces to the valves. The opening and closing of valves is thereby timed to the rotation of the camshaft which in turn is controlled by the crankshaft.

Accordingly, the physical dimensions or shapes of the cams, lifters and the orientation of the cams with respect to one another are parameters which can be varied in order to obtain desired engine performance.

With respect to the physical dimensions or design of a cam, the following terms are generally used to describe the cam. For example, the base circle of the cam defines the period that the valve is closed, the clearance ramp defines the time of transition between closure and measurable valve lifting, the flank or ramp provides the time for and characteristics of valve opening, the nose defines the time of full valve opening and maximum opening displacement and the duration defines the time that the valve is off its seat.

Each of these parameters of a cam cannot be independently controlled and therefore require compromises between what the physical dimensions of a cam will allow in relation to the other parameters. For example, duration is a compromise between opening the valves long enough to fill and evacuate the cylinders to the loss of dynamic compression by opening the valves too long and increasing lift increases power but is limited by lifter diameter.

With respect to the design of lifters (or tappets), the technology of lifters is variable between engines. Generally, the primary goals of the design of a lifter is to maintain contact between the lifter surface and cam surface while minimizing noise during operation. There are two classes of lifters, solid and hydraulic with each class providing variable contact ends including flat, mushrooms and rollers. The use of hydraulic lifters generally reduces valve lash and noise. A flat tappet-cam normally has a slight taper across its surface whereas the corresponding tappet end surface is normally marginally convex in order to compensate for mis-aligned lifter bores. Roller lifters allow for highly aggressive ramp profiles and, as a result, require high valve spring tensions to keep the roller in contact with the cam. Roller lifters also reduce frictional losses between the lifter and cam and thereby will increase the overall power or efficiency of the engine.

Mushroom lifters have a bulge at the end and are used to provide more lift per duration.

The relative orientation of the intake and exhaust cams with respect to one another contributes to defining the power map of the engine. Specifically, the lobe separation angle or overlap determines the time during which the intake and exhaust valves are opened simultaneously, wherein a wider lobe separation angle generally improves idle quality, idle vacuum and top-end power whereas a narrower lobe separation angle decreases idle quality but provides better mid-range torque.

Degreeing a cam is also a parameter which can be used to affect engine performance and refers to altering the point where the cam activates the valves in relation to the crankshaft. Specifically, retarding the cam shaft, that is, opening a valve later relative to the crankshaft moves the power up the rpm band and can increase horsepower while decreasing lower end torque. In contrast, advancing the cam shaft (opening the valves earlier) has the opposite effect.

In order to address some of the problems associated with fixed cam timing, variable cam timing systems have been designed. Generally, such systems provide a cam lobe having a three- dimensional surface and a lifter camshaft which is allowed to move axially over the three- dimensional cam surface. Accordingly, the axial position of the camshaft will determine the specific cam profile which controls valve timing. Variable valve timing thereby permits the alteration of valve timing during the operation of the engine allowing engine performance to be modified to match operating conditions. Variations in a variable cam system can enable any one of independently phasing the intake cams, independently phasing the exhaust cams, phasing the intake and exhaust equally or phasing the exhaust and intake cams independently of one another.

For example, by diluting the in-cy Under mixture by reducing fuel intake characteristics by providing shorter intake times increases fuel economy but decreases the torque response of the engine. In contrast, by enriching the in-cylinder mixture by increasing fuel intake times by providing more lift and duration leads to an increase in horsepower. A variable valve timing system can accommodate such conflicting objectives by providing different timing profiles depending on the rpm of the engine thereby contributing to improving the breathability of the engine and increasing the manifold pressure.

In high performance applications, the current state-of-the-art recognizes the single axis roller or wheel based lifter as the optimal performance enhancing device for valve train operation. However, as the desire for higher engine rpm has grown, it has been found that wheel based lifters will fail under the higher tension springs utilized in the higher rpm engines. Typically, failure occurs in two ways; roller bearing failure in the wheel itself and/or the catastrophic failure of the lifter, both a result of wheel "flat spotting" which produce valve lifter and valve train vibration.

Furthermore, existing wheel-based lifter designs do not provide direct delivery of lubrication to the roller bearing but rather occurs in an indirect way which decreases the ability to dissipate heat from the bearing surfaces. Accordingly, bearing life may be reduced as the wheel may be in direct contact with the bearing race with minimal oil film between the two surfaces.

To achieve maximum bearing life in a single axle based system, the designer must balance three parameters given that the wheel diameter is maximized within the confines of the lifter body. These three factors are roller bearing diameter, axle diameter and wheel thickness. Each of these parameters must be varied to minimize the compressive and contact stresses on the bearing surfaces, minimize the stresses in the axle and minimize the deflection of the axle which directly affects the contact stresses within the roller bearings.

Summary of the Invention

In accordance with the invention, a variable valve timing system for an internal combustion engine is provided wherein the cams on a camshaft are provided with a variable profile and the camshaft can move axially with respect to the lifters or valves stems contacting the cams. The end design of the valve lifter or valve stem provides a fine contact point such that a continuously variable timing profile can be realized. In addition, the invention provides a camshaft and camshaft journal system which allows for axial movement of the camshaft and/or advancing or retarding a camshaft which is proportional to engine rpm. As well a mechanical fuel injection system is provided.

In a first embodiment, there is provided a system for providing variable cam timing in an internal combustion engine comprising: a camshaft having at least one variable profile cam and means for axial displacement of the at least one variable profile cam with respect to a corresponding cam contacting device, wherein each cam contacting device is adapted to reduce the contact area between the cam contacting device and the variable profile cam.

In further embodiments, the cam contacting device has a semi-spherical end having a radius generally corresponding to the cross-sectional radius of the cam-contacting device, a ball bearing end or a caster end with specific oil/delivery systems.

In a more specific embodiment, the camshaft is supported within camshaft journals adapted to allow simultaneous rotary and axial motion of the camshaft journal and camshaft, for example, wherein the camshaft includes first and second camshaft ends having multiple flat surfaces adapted for mating and sliding engagement with and against corresponding multiple flat surfaces within corresponding first and second camshaft journals. In a further embodiment, the first camshaft end and first camshaft journal includes biasing means for biasing the camshaft from the first camshaft journal and the second camshaft end and second camshaft journal include means for axial displacement of the camshaft against the biasing means and wherein the first camshaft end includes means for adjusting the biasing means.

In another embodiment, the means for axial displacement of the camshaft against the biasing means is a hydraulic pump acting against the second end of the camshaft and the hydraulic pump has an output proportional to the camshaft rotation speed and the axial displacement of the camshaft is proportional to the camshaft rotation speed.

In a further embodiment, the first camshaft end and first journal include high pitch threads for advancing or retarding the camshaft.

In still further embodiments, the system includes a mechanical fuel injection system operatively connected to the camshaft, the mechanical fuel injection system including a needle and needle valve fuel delivery system operatively connected to respective intake valves of the internal combustion engine or a fuel delivery system integral with individual intake valve seats of the internal combustion engine. Brief Description of the Drawings

These and other features of the invention will be more apparent from the following description in which reference is made to the appended drawings wherein:

FIGURE 1 is a cross-sectional view of a lifter or valve stem having a spherical end in accordance with a first embodiment of the invention;

FIGURE 1 ' is a cross-sectional view of a hydraulic lifter having a spherical end and oil delivery port in accordance with a first embodiment of the invention;

FIGURE 1A is a cross-sectional of the end of a lifter or valve stem having a ball bearing in accordance with another embodiment of the invention;

FIGURE IB is a cross sectional view of the end of a lifter or valve stem with a caster in accordance with another embodiment of the invention;

FIGURE IBa is a longitudinal cross-sectional view of the end of a lifter or valve stem with a caster along the lines IBa- IBa from FIGURE IB;

FIGURE lBb is a cross-sectional view of the end of a lifter or valve stem with a caster along the lines lBb-IBb from FIGURE IBa;

FIGURE 1C is a schematic cross sectional view of a valve stem with spherical end or ball bearing in an overhead camshaft engine;

FIGURE 2 is a schematic cross sectional view of a camshaft and journal system adapted for axial movement of a rotating camshaft;

FIGURE 2A is a schematic cross sectional view of a camshaft end adapted for axial movement within a journal along lines 2A-2A from FIGURE 2;

FIGURE 2B is a schematic cross sectional view of a journal adapted to enable axial movement of a camshaft along lines 2B-2B from Figure 2; FIGURE 3 is a schematic end view of a camshaft adapted for axial movement and for advancing or retarding a rotating camshaft;

FIGURE 3A is a schematic cross sectional view of a journal enabling axial movement of a camshaft and for advancing or retarding a rotating camshaft;

FIGURE 4 is a schematic diagram of two embodiments of a mechanically operated fuel injection system;

FIGURE 4A is a schematic plan view of a valve seat incorporating fuel nozzles; and,

FIGURE 4B is a schematic side view of a valve seat incorporating fuel nozzles.

Detailed Description of the Invention

In accordance with the invention and with reference to the Figures, a fuel and air management system for an internal combustion engine is described. More specifically, an improved system for variable cam timing is provided with improved lifters as well as an improved camshaft which allows axial movement of the camshaft.

With reference to Figures 1, 1', 1A, IB and 1C, various designs for the ends 12 of a valve lifter or valve 10 are shown which minimize the contact area between the end 12 and a cam lobe having a varying profile along its axially length and which minimize the stresses on the lifter during axial movement of a cam shaft over the cam lobe. Essentially, the finer the contact point between the lifter or valve stem and the variable profile cam, the greater the range of valve timing points between two absolute grind end points.

In particular, the above designs either eliminate the need for an axle or, alternatively, reduce the stresses on the axle by provided an additional degree of freedom for rotation. In comparison, a lifter body with a barrel radii of 11mm typically contains a roller of radius 7.5mm and has a height or thickness of 10mm yielding a surface area of approximately 471 sq. mm.. In comparison, a rotating sphere design allows for a radius of 10mm yielding a surface area of approximately 1250 sq. mm. Accordingly, for a given lifter body a rotating sphere provides an approximate 2.5 increase in surface area. With reference to Figures 1 and 1 ' , a valve lifter or valve 10 having a rigid semi-spherical end 12 is shown with the radius of the semi-spherical end corresponding to the radius of the valve lifter or stem. The semi-spherical end 12 is preferably cast and hardened or machined and hardened to provide a hard-wearing surface. The semi-spherical end 12 contacts the cam lobe at different positions depending on the axial position of the camshaft and, accordingly, wear is distributed about the spherical end.

Figure 1A shows an end 12 having a ball bearing 14 and race 16. The end 12 of the valve lifter or valve 10 is formed to receive both the ball bearing 14 and the race 16. The race is a screw ring or is friction fit to the end 12 by thermal constriction, pinning or bonding or a suitable combination thereof as would be understood by those skilled in the art. In other embodiments, an oil supply bore 18, 37 is provided through the valve lifter 10 to provide lubrication to the ball bearing 14 from within the structure. Oil supply to the oil supply bore 18, 37 may be provided by an appropriate oil source as shown in the Figures for providing direct and continuous lubrication of the ball bearing for improved heat dissipation.

Figures IB, IBa and lBb show a caster design for the end 12 where a contact roller 20 with contact bearing race 22 and spindle 24 is contained in swivel race 26 secured to the valve lifter or valve 10. The swivel race is adapted to allow the rotation of the spindle 24 with respect to the axis of the valve lifter or valve 10. Accordingly, the surface of the contact roller 20 can rotate in two dimensions when in contact with the surface of a cam. An oil supply bore 18 may also be provided as described above.

One of the key advantages of the rotating sphere lifter over a conventional flat lifter is the ability to increase the cam lobe ramp angle thus allowing for the cam to open and close the valve more quickly from an increased cam lobe/sphere angle and the resultant option for increasing cam lobe ramp angle.

Figure 1C shows an embodiment for an overhead cam engine wherein the end 12 of a valve stem 30 has been adapted as described for Figure 1A above to include a ball bearing 32 and ball bearing race and guide 34 which allow axial movement of the cam over the end 12 of the valve stem 30.

With reference to Figures 2, 2A and 2B, a camshaft system 50 adapted for both rotary and axial movement with respect to lifters or valves is shown. The camshaft 52 includes circular journals 54 for supporting the camshaft 52 and cams 56 having a three-dimensional surface (not shown). A lifter or valve stem 58 adapted for movement over a three-dimensional cam surface as described above is in contact with the cams 56. At a first end 60 of the camshaft 52, rotational force is transmitted to the camshaft 52 through a drive journal 64 in sliding engagement with the end of the camshaft 52 and connected to the crankshaft of the engine via a timing belt (not shown). The end of the camshaft 52 is provided with a plurality of flat drive surfaces 66 (shown in cross section in Figure 2A) which engage within drive journal 64 so as to enable transmission of rotary motion from the drive journal 64 to the cam shaft 52. While a system of eight flat surfaces is shown in Figure 2A, other systems as may be understood by those skilled in the art may also be implemented. The drive journal 64 is also provided with a spring 66 for biasing the camshaft 52 away from the interior of the journal 64, the purpose of which will be described in greater detail below. The tension on spring 66 may be adjusted through tensioning screw 68 on journal 64.

At the second end 62 of the camshaft 52, a similar journal system is provided for supporting the second end of camshaft 52 and for imparting an axial force along the camshaft 52. In this regard, a supporting journal 70 is provided for mating and sliding engagement with the second end of the camshaft 52 having multiple surfaces as described previously for the first end. In one embodiment, the second end of the camshaft 52 acts as a piston 72 within the supporting journal 70 whereby axial displacement of the camshaft 52 is provided by oil pressure acting on the outside surface 74 of the piston 72 from an appropriate pressurized oil source 75.

In operation, an increase in oil pressure against the piston 72will cause axial displacement of the camshaft 52 thereby depressing spring 66 within drive journal 64. Similarly, a drop in oil pressure will enable the release of the compressive force of spring 66 enabling axial movement of the camshaft in the opposite direction.

In one embodiment for the control of the axial displacement of the camshaft, the axial displacement of the camshaft is determined on the basis of engine rpm, that is, the higher the engine rpm, the greater the axial displacement of the camshaft and vice versa. Specifically, in this embodiment, the outer surface of supporting journal 52 is provided with a drive gear which may be used to operate an oil pump (not shown) whose output oil pressure is directly proportional to its rotation speed. Thus, as engine rpm increases the rotational speed of the crankshaft, the rotational speed of the camshaft and oil pump will correspondingly increase leading to a higher oil pressure output which will cause an axial displacement of the camshaft exposing lifters 58 to a different cam profile optimized for engine rpm.

In a further embodiment, the oil pressure acting on piston 72 may be computer controlled.

In a still further embodiment, the piston 72 may be moved using a computer controlled mechanical device enabling axial movement of the camshaft 52 including but not limited to an electronically controlled solenoid.

With reference to Figures 3 and 3A, a mechanical system for axial movement of a camshaft is shown utilizing the increasing centrifugal force of a rotating camshaft to initiate axial movement. In this embodiment, the end of the camshaft may be provided with a high pitch thread 80 which engages within a corresponding high pitch thread 82 within a journal 84 having a biasing spring 86. As rotation speed increases, the increasing centrifugal force of the rotating camshaft will cause an axial movement of the camshaft against spring 86 along threads 80, 82. Similarly, a decreasing rpm will reduce the centrifugal force wherein the compressive force of the spring 86 will cause an opposite axial movement of the camshaft.

This embodiment can allow independent intake and exhaust camshafts to be advanced or retarded with respect to one another by independent control of the axial position of the intake camshaft with respect to the exhaust camshaft.

A further embodiment of the system is shown in Figure 4 wherein two embodiments of a system incoφorating a mechanical fuel injection system is provided. In a first embodiment, the valve seat 6 of the air intake system includes a plurality of fuel nozzles 1 around the valve seat 6 as shown in Figure 4A. With the valve open, fuel under pressure is pumped into the cylinder as the valve 7 is opened. Closure of the valve 7 will cut-off fuel supply. Under normal operation, the delivery of fuel to the cylinder is determined on the basis of engine rpm and may typically involve fuel delivery rates of 4-50 pounds of fuel per hour. Accordingly, a variable fuel pressure regulator controlled on the basis of engine φm may be implemented to control the amount of fuel entering the cylinder. An alternate embodiment of a fuel delivery system incoφorates a needle 2a integral with the valve stem 5 and a needle valve 2 integral with the air intake system. In this embodiment, as the valve opens, the needle 2a opens the needle valve 2 to allow fuel to enter the air intake system and cylinder.

By injecting fuel into the cylinder from the intake valve seat, fuel can be introduced into the cylinder under air pressure which enables the fuel to mixed with air as in enters the cylinder, thereby enhancing ignition efficiency by promoting atomization and/or vaporization of the fuel. Furthermore, a mechanical fuel injection system eliminates the need for magnetically actuated fuel injectors. Still further, by circulating fuel through the valve seat, the fuel is pre-heated which thereby has the effect of cooling the valve seat which will improve valve life.

In an alternate embodiment, a fuel pump may be operated by a plunger-based system operating off a rotating cam shaft. Accordingly, the invention also contemplates providing a three-dimensional cam for matching fuel pump operation to the variable valve timing.

In summary, the systems described above provide a means for primarily mechanically controlling the axial position of a camshaft to provide variable cam timing and/or advancing or retarding an intake or exhaust system which may be readily retrofit to existing engines.

The terms and expressions which have been employed m this specification are used as terms of description and not of limitations, and there is no intention m the use of such terms and expressions to exclude any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claims.

Claims

Claims:

1. A cam contacting device for contacting a variable profile cam comprising a cam contacting end adapted to reduce the contact area between the cam contacting device and the variable profile cam.

2. A cam contacting device as in claim 1 wherein the cam contacting end is a semi-spherical end, the semi-spherical end having a radius generally corresponding to the cross-sectional radius of the cam-contacting device.

3. A cam contacting device as in claim 1 wherein the cam contacting end includes has a ball bearing seated within and retained against the cam contacting end.

4. A cam contacting device as in claim 1 wherein the cam contacting end includes a wheel pivotal about two orthogonal axes.

5. A cam contacting device as in claim 1 wherein the cam-contacting device further comprises an oil delivery port within the cam-contacting device for providing direct lubrication to the contact area between the contact area between the cam contacting device and the variable profile cam.

6. A cam contacting device as in claim 1 wherein the cam-contacting device further comprises an oil delivery port within the cam-contacting device for providing direct lubrication to semi-spherical end.

7. A cam contacting device as in claim 1 wherein the cam-contacting device further comprises an oil delivery port within the cam-contacting device for providing direct lubrication to the ball bearing.

8. A cam contacting device as in claim 1 wherein the cam-contacting device further comprises an oil delivery port within the cam-contacting device for providing direct lubrication to the caster.

9. A system for proving variable cam timing in an internal combustion engine comprising a cam contacting device as in any one of claims 1-8 and a camshaft having at least one variable profile cam and means for axial displacement of the at least one variable profile cam with respect to a corresponding cam contacting device.

10. A system as in claim 9 wherein the camshaft is supported within camshaft journals adapted to allow simultaneous rotary and axial motion of the camshaft journal and camshaft.

11. A system as in any one of claims 9-10 wherein the camshaft includes first and second camshaft ends having multiple flat surfaces adapted for mating and sliding engagement with and against corresponding multiple flat surfaces within corresponding first and second camshaft journals.

12. A system as in claim 11 wherein the first camshaft end and first camshaft journal includes biasing means for biasing the camshaft from the first camshaft journal and the second camshaft end and second camshaft journal include means for axial displacement of the camshaft against the biasing means.

13. A system as in claim 12 wherein the first camshaft end includes means for adjusting the biasing means.

14. A system as in claim 12 wherein the means for axial displacement of the camshaft against the biasing means is a hydraulic pump acting against the second end of the camshaft

15. A system as in claim 14 wherein the hydraulic pump has an output proportional to the camshaft rotation speed and the axial displacement of the camshaft is proportional to the camshaft rotation speed.

16. A system as in any one of claims 11-13 wherein the first camshaft end and first journal include high pitch threads for advancing or retarding the camshaft.

17. A system as in any one of claims 9-16 further comprising a mechanical fuel injection system operatively connected to the camshaft, the mechanical fuel injection system including a needle and needle valve fuel delivery system operatively connected to respective intake valves of the internal combustion engine.

18. A system as in any one of claims 9-16 further comprising a mechanical fuel injection system operatively connected to the camshaft, the mechanical fuel injection system including a fuel delivery system integral with individual intake valve seats of the internal combustion engine.