WO2003014536A1

WO2003014536A1 - Variable valve timing system for an internal combustion engine

Info

Publication number: WO2003014536A1
Application number: PCT/CA2002/001231
Authority: WO
Inventors: Daniel Guy Pomerleau; Gary Knutson; Dusty Keashly
Original assignee: Absolute Zero Emission Technologies Corp.
Priority date: 2001-08-07
Filing date: 2002-08-07
Publication date: 2003-02-20
Also published as: US20030029402A1

Abstract

The invention describes a rocker arm displacement system for variable valve timing in internal combustion engines. More specifically, the system provides a rocker arm displacement system including a rocker arm having a pivot, a cam-contacting portion and a valve stem contacting portion and a linear displacement system for linear displacement of the cam-contacting portion with respect to a variable profile cam.

Description

VARIABLE VALVE TIMING SYSTEM FOR AN INTERNAL COMBUSTION

ENGINE

RELATED APPLICATIONS This application is related to Canadian Patent Applications 2,257,437 and 2,315,595, and to Applicant's co-pending PCT application to "Improvements in Cam-Contacting Devices" filed August 7, 2001, all of which are incorporated herein by reference.

FIELD OF THE INVENTION The invention describes a rocker arm displacement system for variable valve timing in internal combustion engines. More specifically, the system provides a rocker arm displacement system including a rocker arm having a pivot, a cam-contacting portion and a valve stem contactmg portion and a linear displacement system for linear displacement of the cam-contacting portion with respect to a variable profile cam.

BACKGROUND OF THE INVENTION

The design of an internal combustion engine requires numerous trade-offs between conflicting design or performance parameters particularly with respect to the design of cam profiles and their effect on valve timing. 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 such an engine would be limited by these conflicting parameters leading the designer to compromise with the design to achieve a balance between the parameters. As a result, designers have been forced to focus on a primary performance goal (such as lower emissions) which may be to the detriment of desired engine performance (such as torque or idle stability). These compromises are essentially caused by the lack of the designer's ability to incorporate breathability into the engine-that is, an optimal intake of fuel and air and the exhaust of spent gases after combustion at different operating speeds.

The timing of air intake and exhaust (breathing) is controlled by the shape and phase angle of cams. To optimize breathing, engines require different valve timing at different speeds. When rpm increases, the duration of intake and exhaust stroke decreases with the result that combustion air cannot enter the combustion chamber fast enough and exhaust gases similarly cannot leave the combustion chamber fast enough. The best solution to this problem is to open the inlet valves earlier and close the exhaust valves later. That is, the overlapping between intake period and exhaust period should be increased as rpm increases.

Furthermore, lift and duration of valve opening also affects breathability. At high speed, higher lift quickens air intake and exhaust. However, at lower speed such lift will generate counter effects like deteriorating the fuel and air mixing process resulting in a decrease in output or even misfire. Therefore the lift and duration should also be variable according to engine speed.

With fixed cam engines, a single cam profile is used with the result that engineers choose a single timing sequence (or cam profile) which is usually a compromise based on the desired general characteristics of the vehicle. For example, a van may adopt less overlapping for the benefits of low speed output whereas a racing engine may adopt considerable overlapping for high-speed power. An ordinary sedan may adopt valve timing optimised for mid-range rpm so that both the low speed drivability and high-speed output will not be sacrificed to a significant extent. Similarly, lift and duration is determined for a limited rpm range. In other words, the valve timing is optimized for a limited speed range.

Variable valve timing provides a solution to the above problems by enabling the adjustment of valve timing as rpm changes with the result that power and torque are optimized across a wide rpm band.

Several major manufacturers have designed and implemented various forms of variable valve timing systems. For example, Honda has successfully implemented its VTEC system ( alve Timing Electronic Control) which essentially uses two (or three) different set of cams which are specifically optimized for different rpm ranges and mechanically actuated based on engine speed. The NTEC system does not allow a continuous change of timing but does provide two (or three) distinct phases of performance. The cam-changing system of the NTEC engine is mechanically complex.

Another system is the Toyota NNTL-I which provides both variable cam-phasing and lift and duration. This system does not provide continuous variation of lift and duration but instead utilizes a 2-stage variable lift design.

Other proposed designs include the use of continuously variable cam profiles in which a camshaft having a three-dimensional cam profile is linearly displaced across a cam follower. Such systems allow lift, duration and degreeing to be addressed with a 3 dimensional cam profile. However, such systems have not been successful as a result of the failure of components of cam followers brought on by contact stresses at the cam follower/cam interface. That is, the cam followers of a fixed profile cam minimize the compressive loads of the cam follower on the cam by distributing the compressive load across a wider area. In a continuously variable system, a fine contact point is required in order to optimize the resolution of the cam profile being used. This fine contact point, for a given valve spring pressure, results in higher interface pressures as compared to the standard contacting devices. These higher pressures will cause cam followers, implemented using conventional materials, to fail. Thus, while various variable timing systems have been proposed, there remain several problems with respect to the implementation of the technology to its theoretical potential. That is, the current state-of-the-art as implemented by Honda, Toyota and other major engine manufacturers provides variable valve timing systems which are mechanically complex and which do not provide true continuously variable timing with respect to lift, duration and phasing. Furthermore, variable valve timing systems which propose continuously variable lift and duration have been unsuccessful as a result of cam follower failure.

Accordingly, there has been a need for variable valve timing systems which provide the ability to adjust lift, duration and degreeing with a relatively simple mechanical system which does not require the complex mechanical interplay of many mechanical components. In particular, there has been a need for a system which provides for a fine cam follower/cam interface and which can survive the high compressive loads at this interface. Further still, there has been a need for a variable valve timing system which can be retrofit to existing vehicles by replacing a rocker arm/fixed cam system with a linear displaceable rocker arm/variable profile cam system or factory installed into new engines. Further still, there has been a need for systems which will significantly reduce fuel consumption and emissions particularly during idling without affecting vehicle performance.

In particular, and with reference to applicant's co-pending Canadian application 2,315,595, a solution to cam follower failure is provided in which ceramic materials are used as cam-contacting devices where ceramic materials have been demonstrated to overcome the problems of cam follower failure. More particularly, the use of silicon nitride has been shown to be particularly effective as a material for use as a cam-contacting surface in an internal combustion engine.

SUMMARY OF THE INVENTION

In accordance with one embodiment of the invention, there is provided a rocker arm displacement system for linear displacement of a rocker arm having a cam contacting portion with respect to a rotating, variable-profile cam comprising a linear displacement system operatively connected to a rocker arm. In accordance with another embodiment, there is provided a rocker arm displacement system comprising: a rocker arm having a pivot, a cam contacting portion and a valve stem contacting portion; a linear displacement system for linear displacement of the cam contacting portion with respect to a variable profile cam

In further embodiments, the cam-contacting device has improved thermal dissipation properties including a coefficient of thermal expansion less than 3xl0^"6/degree Celsius.

In other embodiments, the cam contacting system is a ball bearing and a bearing race and support where the coefficient of thermal expansion of the ball bearing is less than the coefficient of thermal expansion of the bearing race and support.

Further still, in preferred embodiments, the cam contacting system is ceramic selected from any one of silicon nitride (including CERALLOY 147-3 IE, 147-3 IN, 147- IE, or 147-1 or equivalents) or silicon carbide.

In other embodiments, it is preferred that the cam contacting devices is selected from

- A - any one of a radiused wheel, a ball bearing, a partial spherical surface or a semi-spherical surface and preferably, the cam contacting surface is selected from any one of CERALLOY 147-3 IE, 147-3 IN, 147-1E, or 147-1 or equivalents. The valve stem contacting portion may also be selected from these materials. In a further still embodiment, the linear displacement system includes a sliding block operatively comiected to a linear displacement cylinder and the sliding block pivotally retains the rocker arm.

It is also preferred that a lash adjustment system is provided within the sliding block, rocker arm or valve stem. In a more specific embodiment , the lash adjustment system is hydraulic and includes a piston within the sliding block for setting the range of motion of the rocker arm within the sliding block.

In a further embodiment, the rocker arm is pivotally connected to the valve stem. In a more specific embodiment, the invention provides a rocker arm displacement system comprising: a rocker arm having a pivot, a cam contacting system and a valve stem contacting system, the cam contacting system a silicon nitride ball bearing rotatably retained within the rocker arm; a silicon nitride valve stem tip for operative engagement with the valve stem contacting system; and a sliding block operatively connected to a linear displacement cylinder for linear displacement of the cam contacting portion with respect to the variable profile cam wherein the sliding block pivotally retains the rocker arm and wherein the sliding block includes a hydraulic lash adjustment system.

In another embodiment, the invention provides a method of retrofitting an internal combustion engine with a rocker arm displacement system as in claim 1, the internal combustion engine having a valve cover, valve stems, a rocker arm assembly and a camshaft comprising the steps of: a) removing the valve cover to expose the valve stems, rocker arm assembly and camshaft; b) removing the camshaft and installing a variable profile camshaft; c) installing a rocker arm displacement system having a rocker arm, a cam contacting portion, a valve stem contacting portion and a linear displacement system. Further still, the invention provides an internal combustion engine characterized by a rocker arm displacement system for linear displacement of a rocker arm with respect to a camshaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described with reference to the following drawings in which:

Figures 1A, IB and 1C are schematic drawings of the geometric design of three embodiments of a rocker arm displacement system showing the relative positions of the valve stem/spring, pivot and cams with respect to a rocker arm;

Figures 2 A and 2B are forward and rear perspective views of a rocker arm displacement system for a variable valve timing system for an overhead cam engine in accordance with one embodiment of the invention;

Figure 2C is a partial cross-sectional view of a rocker arm displacement system for a variable valve timing system for an overhead cam engine in accordance with one embodiment of the invention showing details of a linear displacement cylinder;

Figures 3A and 3B are forward and end. perspective views of a rocker arm displacement system for a variable valve timing system for an overhead cam engine in accordance with another embodiment of the invention;

Figure 3C is a partial cross-sectional view of a rocker arm displacement system for a variable valve timing system for an overhead cam engine in accordance with another embodiment of the invention showing details of a linear displacement cylinder and sliding block; and,

Figure 4 is a schematic diagram of a further embodiment of a rocker arm displacement system for variable valve timing system for an overhead cam engine in accordance with a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION System Overview

With reference to the Figures, a rocker arm displacement system 10 for variable valve timing is described. The system generally includes a rocker arm (R) in operative connection with a valve stem (V)/spring (Vs), a cam contacting device (CCD) contacting a variable profile cam shaft (C) and a linear displacement system (LDS) for linear displacement of the rocker arm with respect to the cam shaft.

Different embodiments of the system are schematically illustrated in Figures 1A, IB and IC wherein options for the geometric layout of the rocker arm (R), camshaft (C), valve stem (V) /spring (Vs, with T showing the direction of spring force) are shown with respect to a rocker arm pivot (P). Figure 1 A shows a rocker arm having a centrally located pivot with both the valve stem/spring and camshaft on the same side of the rocker arm. Figure IB shows a rocker arm with the pivot at one end with a centrally positioned camshaft and with the valve stem/spring on the opposite side and end of the rocker arm. Figure IC shows an embodiment with the pivot at one end with a centrally positioned valve stem spring and with the camshaft on the opposite side and end of the rocker arm.

Figures 2A, 2B and 2C show perspective and cross-sectional views of the embodiment of Figure 1A. The camshaft includes variable profile lobes 20 on a rotating camshaft C. Rocker arms R for each cam are mounted on a rocker shaft 22 at the rocker arm pivot and include cam followers or cam-contacting devices 24 biased against each respective variable profile lobes by valve springs Vs acting on the opposite end of the rocker arm. A linear displacement system (LDS) is operatively connected to the rocker shaft and includes a hydraulic cylinder 26 for linear displacement of the rocker shaft 22 and, hence, linear displacement of the cam followers 24 with respect to the variable profile lobes 20.

As shown in Figure 2A, the cam followers 24 are spherical ball bearings rotatably retained within bearing races within the rocker arm. As described in applicant's co-pending application, Canadian application 2,315,595, the spherical bearing provides a fine contact point with respect to the cam lobe thereby permitting continuous setting of the valve timing between the end limits of the cam 20.

With reference to Figure 2B, the opposite ends of the rocker arms contact the valve stems and include a valve stem contacting device such as valve stem bearing 28 rotatably retained within a tip ball retainer 30 (as shown in Figure 2b). Alternatively, valve stem bearing may be rotatably retained within the rocker arm (not shown). In addition, the rocker arm will preferably include a hydraulic lash adjustment system 32 enabling adjustment of the clearance between the rocker arm and valve stem.

As with the cam follower 24 and camshaft, the valve stem end of the rocker arm is displaced with respect to the valve stem when actuated by the LDS. With reference to Figure 2C, a partial cutaway of the actuation cylinder of the linear displacement system is shown having dual hydraulic oil ports 34. In this embodiment, the actuation cylinder 26 may be positively positioned at a full range of positions across the width of the cam as may be determined by an appropriate control algorithm, such as one where the linear position of the rocker arms is proportional to engine rpm. With reference to Figures 3 A, 3B and 3C, a second embodiment of the system corresponding to that shown schematically in Figure IB is described, hi this embodiment, the pivot is located at one end of the rocker arm with the cam followers located in the middle of the rocker arm and valve stem/spring located at the opposite end.

As shown in Figure 3A, the linear displacement system includes a sliding block 40 which pivotally retains the rocker arm. In this embodiment, the sliding block permits pivotal up and down motion of the rocker arm but prevents side-to-side motion of the rocker arm within the sliding block. As shown, the sliding block is retained within a retaining system 42 allowing linear displacement of the sliding block under the control of the linear displacement cylinder 26. The sliding block may also contain a lash adjustment system 32a permitting adjustment of the clearance between the valve stem and rocker arm. The lash adjustment system may be hydraulically controlled wherein the sliding block includes hydraulic pistons

32b (as shown in cutaway in Figure 3C) for setting the range of motion of the rocker arm.

As in the Figure 2 embodiment, the valve stem includes a valve stem contacting device such as a valve stem bearing 28 rotatably retained within a tip ball retainer 30 (as shown in Figure 3B).

In another embodiment, as shown schematically in Figure 4 (plan view) , the rocker arm is pivoted about a second axis P2 orthogonal to the main pivot axis P of the rocker arm. That is, the rocker arm does not include a tip bearing or roller but rather is pivotally connected to the valve stem and is pivotally connected to the LDS thereby allowing rotational movement of the rocker arm with respect to the valve stem.

Cam Contacting Device The cam-contacting device may be embodied in different forms including a ball bearing, a roller, a tapered wheel and a half sphere as described in applicant's copending applications. The cam-contacting device will preferably provide a fine contact point between the cam-contacting device and cam so as to provide for continuous variability of the cam profile between the different ends of the cam. Furthermore, the cam-contacting device is preferably a ceramic material such as silicon nitride, which provides improved thermal properties between the cam contacting device and the cam to accommodate the high contact stresses.

Valve Stem Contacting System The valve stem contacting system may be embodied in different forms to achieve the result of valve actuation while permitting linear or pivotal movement of the rocker arm with respect to the valve stem. Accordingly, the valve stem contacting system may include a bearing system or other contact system located on either the rocker arm or valve stem or between the rocker arm and valve stem. The bearing system may be a ball bearing or roller bearing. Other contact systems may include flat or curved surfaces engageable with one another and linearly displaceable with respect to one another. The valve stem contacting system preferably utilizes a ceramic material such as silicon nitride, which provides improved thermal properties between the rocker arm and the valve stem to accommodate the high contact stresses. As shown in Figure 4, the rocker arm may also be pivotally connected to the valve stem.

Linear Displacement System The linear displacement system may be actuated by a hydraulic cylinder as described above or other linear motion systems as are known in the art including electro-mechanical systems.

Retrofitability The rocker arm displacement system as described is readily retrofit to existing overhead cam engines. In order to retrofit the system to an existing overhead cam engine, the following general procedure would be followed. Initially, the valve cover would be removed to expose the existing rocker arm and camshaft assembly. The existing fixed profile camshaft would be removed and replaced with a variable profile camshaft. The existing rocker arm assembly would similarly be removed. Any required modification to the valve stem tips would be completed for the particular design of the valve stem contacting system. A new rocker arm displacement assembly would be installed between the camshaft and valve stems, likely requiring the addition of an adaptive plate to permit linear movement of the new rocker arm assembly. Modification to the valve cover will likely be required for the linear displacement system to extend through the valve cover, if required. Alternatively, a specifically designed valve cover assembly may be utilized to accommodate the linear displacement system. The linear displacement system would be connected to an appropriate control system such as an electro-hydraulic, electro-mechanical or electrical system.

It is also envisaged that specific cylinder heads be designed to incorporate a rocker arm displacement system such that retrofitting is not required but rather is factory installed.

Claims

CLAIMS:

1. A rocker arm displacement system for linear displacement of a rocker arm having a cam contacting portion with respect to a rotating, variable-profile cam comprising a linear displacement system operatively connected to a rocker arm.

2. A rocker arm displacement system comprising: a rocker arm having a pivot, a cam contacting portion and a valve stem contacting portion; a linear displacement system for linear displacement of the cam contacting portion with respect to a variable profile cam

3. A rocker arm displacement system as in claim 2 wherein the cam-contacting portion has improved thermal dissipation properties.

4. A rocker arm displacement system as in any one of claims 2 or 3 wherein the cam contacting portion has a coefficient of thermal expansion less than 3xl0^"6/degree Celsius.

5. A rocker ann displacement system as in any of claims 2-4 wherein the cam contacting portion is a ball bearing and a bearing race and support.

6. A rocker arm displacement system as in claim 5 wherein the coefficient of thermal expansion of the ball bearing is less than the coefficient of thermal expansion of the bearing race and support.

7. A rocker arm displacement system as in any one of claims 2-6 wherein the cam contacting portion is ceramic.

8. A rocker arm displacement system as in any one of claims 2-6 wherein the cam contacting portion is any one of silicon nitride or silicon carbide.

9. A rocker arm displacement system as in claim 2 wherein the cam contacting portion is selected from any one of CERALLOY 147-3 IE, 147-3 IN, 147- IE, or 147-1 or equivalents.

10. A rocker arm displacement system as in claim 2 wherein the cam contacting portion is selected from any one of a radiused wheel, a ball bearing, a partially spherical surface or a semi-spherical surface and wherein the cam contacting surface is selected from any one of CERALLOY 147-3 IE, 147-3 IN, 147- IE, or 147-1 or equivalents.

11. A rocker arm displacement system as in any one of claims 2-10 wherein the valve stem contacting portion is silicon nitride.

12. A rocker arm displacement system as in any one of claims 2-11 wherein the linear displacement system includes a sliding block operatively comiected to a linear displacement cylinder and the sliding block pivotally retains the rocker arm.

13. A rocker arm displacement system as in claim 12 wherein the sliding block includes a hydraulic lash adjustment system.

14. A rocker arm displacement system as in claim 13 wherein the hydraulic lash adjustment system includes a piston within the sliding block for setting the range of motion of the rocker arm within the sliding block.

15. A rocker arm displacement system as in any one of claims 2-14 wherein the valve stem includes a tip bearing for engagement with the rocker arm.

16. A rocker arm displacement system as in any one of claims 2-15 wherein the rocker arm has a lash adjustment system adjacent the valve stem end of the rocker arm.

17. A rocker arm displacement system as in any one of claims 2-16 wherein the rocker arm has a tip bearing for engagement with the valve stem.

18. A rocker arm displacement system as in any one of claims 2-17 wherein the cam contacting portion is a ball bearing for engagement with the cam.

19. A rocker arm displacement system as in claim 2 wherein the cam contacting portion is a tapered wheel for engagement with the cam.

20. A rocker arm displacement system as in claim 2 wherein the rocker arm is pivotally connected to the valve stem.

21. A rocker arm displacement system as in claim 2 wherein the rocker arm pivot is located centrally to the valve stem end and cam contacting end of the rocker arm.

22. A rocker arm displacement system as in claim 2 wherein the rocker arm pivot is located at a first end of the rocker arm.

23. A rocker arm displacement system as in claim 5 wherein the cam contacting system is any one of a radiused wheel, a ball hearing, a partial spherical surface or a semi- spherical surface and is a silicon nitride selected from any one of CERALLOY 147- 3 IE, 147-3 IN, 147- IE, or 147-1 or equivalents or a silicon carbide.

24. A rocker arm displacement system as in claim 23 wherein the valve stem contacting portion is silicon nitride.

25. A rocker arm displacement system as in claim 23 wherein the linear displacement system includes a sliding block operatively connected to a linear displacement cylinder and the sliding block pivotally retains the rocker arm.

26. A rocker arm displacement system as in claim 25 wherein the sliding block includes a hydraulic lash adjustment system.

27. A rocker arm displacement system as in claim 26 wherein the hydraulic lash adjustment system includes a piston within the sliding block for setting the range of motion of the rocker arm within the sliding block.

28. A rocker ann displacement system as in claim 27 wherein the valve stem includes a tip bearing for engagement with the rocker arm.

29. A rocker arm displacement system as in claim 28 wherein the rocker arm has a lash adjustment system adjacent the valve stem end of the rocker arm.

30. A rocker arm displacement system as in claim 29 wherein the rocker arm has a tip bearing for engagement with the valve stem.

31. A rocker arm displacement system comprising: a rocker arm having a pivot, a cam contacting system and a valve stem contacting system, the cam contacting system a silicon nitride ball bearing rotatably retained within the rocker arm; a silicon nitride valve stem tip for operative engagement with the valve stem contacting system; and a sliding block operatively comiected to a linear displacement cylinder for linear displacement of the cam contacting portion with respect to the variable profile cam wherein the sliding block pivotally retains the rocker arm and wherein the sliding block includes a hydraulic lash adjustment system.

32. A method of retrofitting an internal combustion engine with a rocker arm displacement system as in claim 1, the internal combustion engine having a valve cover, valve stems, a rocker arm assembly and a camshaft comprising the steps of: a) removing the valve cover to expose the valve stems, rocker arm assembly and camshaft; b) removing the camshaft and installing a variable profile camshaft; c) installing a rocker arm displacement system having a rocker arm, a cam contacting portion, a valve stem contacting portion and a linear displacement system.

33. An internal combustion engine characterized by a rocker arm displacement system for linear displacement of a rocker arm with respect to a camshaft.