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(11) | EP 0 179 990 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method for variable valve timing in an internal combustion engine |
| (57) A method for variable valve timing in an internal combustion engine where by inclining
the longitudinal axis (10) of a hydraulic valve adjuster (12), the pivot point of
the valve rocker arm (36) changes thereby changing the rocker arm ratio. The hydraulic
valve adjusters (12), under control of an electronic control unit (58), are adjusted
to a predetermined height and by doing so the pivot end of the rocker arm (36) is
changed thereby changing the rocker arm ratio resulting in valve timing change. |
[0001] This invention relates to engine control systems in general and more particularly to electrohydraulic control systems for controlling the timing of the intake and exhaust valves in internal combustion engines.
Background of the Invention
Prior Art
[0002] It has been long recognized by engine builders and more particularly by specialists in high performance engines that control of valve timing will yield desired engine operation results. The ideal timing of intake and exhaust valves at idle conditions, at normal load range conditions and at high performance conditions is very different. Since valves are controlled by cams it is necessary to compromise the timing to suit a particular purpose. In production engines, valve timing is a compromise leaning towards the normal load or speed ranges to the detriment of the idle range and the high performance range. Likewise in high performance engines the timing is adjusted toward the high performance demands of the engine and therefore at the idle and normal load ranges valve timing is not optimal.
[0003] In my earlier patent application entitled "Engine Valve Timing Control System" filed on January 30, 1984, I disclosed an engine valve timing control system using the engine oil supply to operate the hydraulic valve adjusters. By controlling the fluid pressures pulses developed within the oil supply as a result of hydraulic valve adjuster operation, very high pulsed pressures are directed to the various hydraulic valve adjusters to assist in returning or re-extending the hydraulic valve adjusters to their normal position between engine cycles. The system is a microprocessor based control system wherein various engine sensors sense the engine conditions and the microprocessor in response to the sensed engine conditions addresses a memory unit containing a map of engine conditions versus valve opening times. From the memory unit a signal is supplied to a particular timer unit for a given cylinder. The timer, operating in conjunction with a known position of the piston in the cylinder will operate electrohydraulic solenoid valves for directing and maintaining a predetermined amount of oil in an associated hydraulic valve adjuster.
[0004] In that system, the electronic control system controlled the flow of the hydraulic oil supply out of the hydraulic valve adjusters. The camshaft, operating on the rocker arm with the rocker arm pivoting on the valve stem caused the hydraulic valve adjuster to collapse forcing the oil out of the hydraulic valve adjuster until the desired operating time was reached.. At that time, a solenoid controlled valve closed preventing the flow of oil thereby forming a rigid oil link. The camshaft, continuing rotating, shifted the pivot point of the rocker arm from the valve stem to the hydraulic valve adjuster causing the valve to open. In the system of that application, the longitudinal axis of the hydraulic valve adjuster and the longitudinal axis of the valve stem are parallel. In conventional engines, the effects of hydraulic valve adjuster height on the valve motions causes changes in valve height opening.
[0005] In the present system, additional valve timing control is achieved by inclining the longitudinal axis of the hydraulic valve adjuster by a predetermined angle, 0, relative to the axis of the valve stem. In this manner, the pivot point of the rocker arm changes as the hydraulic valve adjuster is collapsed thereby changing the ratio of the arm length from the pivot point to point on the cam applying force to the rocker arm. With this added control, it is possible to increase valve opening height or lift or if valve lift is to be maintained, the amount of hydraulic valve adjuster stroke is adjusted.
Summary of the Invention
[0006] A method for variable valve timing in an internal combustion engine having at least one timing cam controlling a rocker arm for at least one engine valve. The method comprises the steps of determining the rocker arm ratio as a function of the distances between the centerline of the timing cam and the pivot point of the rocker arm and the longitudinal axis of the valve. The next step providing hydraulic valve adjusters for controlling the pivot point of the rocker arms. Then positioning the longitudinal axis of the hydraulic valve adjuster at an angle intersecting the longitudinal axis of the valve. Followed by the step of adjusting the height of the valve adjuster to move the pivot point of the rocker arm along the longitudinal axis of the hydraulic valve adjuster thereby changing the rocker arm ratio and then rotating the timing cam for setting the rocker arm pivot on the hydraulic valve adjuster. Finally opening the valve a predetermined height as a function of the location of the pivot point on the hydraulic valve adjuster.
Brief Description of the Drawings
[0007] These and other advantages will become apparent from the following drawings and detailed description.
FIGURE 1 illustrates the prior art wherein the centerline of the hydraulic valve adjuster is parallel to the centerline of the valve stem.
FIGURE 2 is a graphic representation of the operation of the valve in FIGURE 1.
FIGURE 3 illustrates the angular relationship of the centerline of the hydraulic valve adjuster to the centerline of the valve stem in the preferred embodiment.
FIGURE 4 is a graphic representation of the operation of the valve in FIGURE 3.
FIGURE 5 illustrates another embodiment according to the invention.
Detailed Description
[0008] For a detailed description of the basic engine valve timing control system wherein the collapse of the hydraulic valve adjuster is used to control valve lift by using a portion of the cam ramp to collapse the hydraulic valve adjuster rather than opening the valve, United States Patent Application having Serial No., 575,355 entitled "Engine Valve Timing Control System" filed on January 30, 1984 is expressly incorporated herein by reference. FIGURE 1 herein illustrates the conventional parallel relationship of the centerline 10 or longitudinal axis of the hydraulic valve adjuster 12 to the longitudinal axis 14 of the valve means 16. The valve means 16 has a valve member 18, a valve stem 20, a keeper block 22, and a spring 24 bearing against the keeper block for biasing the valve member 18 closed on a valve seat 26. In that system the height of the valve member 18 opening or lift and the duration of valve opening is inversely proportional to the distance (d) of the hydraulic valve adjuster 12 collapse.
[0009] FIGURE 2 is a graphic representation of the change in valve member 18 opening on the ordinate with degrees of rotation of the camshaft 28 on the abscissa. The first curve 30 illustrates the hydraulic valve adjuster 12 not collapsed (d=0) and is the normal operation. The slope at the beginning and the end of the curve 30 is smooth indicating that the valve means 16 follows the cam profile 32 and the closing of the valve means 16 on the valve seat 26 is during the period of slow travel of the valve means 16. The second curve 34, which is the last curve in the family because d=MAX, the hydraulic valve adjuster 12 is collapsed, shows that the opening of the valve means 16 begins on the rise of the cam 32 and the speed of the valve means 16 is very fast. In a similar manner, the valve means 16 on closing is moving very fast when the valve member 18 seats and will probably rebound generating noise and causing more valve wear than the system of the first curve 30. The portion of all curves below the horizontal line, called "valve seat", are not actual conditions but illustrate the opening and closing of the valve member 18 on the valve seat 26 during the rise and fall, respectively, of the cam 32. The rocker arm 36 ratio is not changed but the valve means 16 lift and duration are variable.
[0010] FIGURE 3 illustrates the improvement to the above system wherein the pivot point of the rocker arm 36 may be constantly variable to achieve desired valve operations at various engine speeds. The longitudinal axis of the hydraulic valve adjuster 10 is in a non-parallel relationship to the longitudinal axis of the valve means 16.
[0011] In the diagram of FIGURE 1, the rocker arm ratio (Rr) is defined as
where:
a = length from the cam centerline to the valve centerline; and
b = length from the cam centerline to the pivot point on the hydraulic valve adjuster.
[0012] In the previous patent application, control of the hydraulic valve adjuster 12 collapse is described in order to vary the time for valve opening. In addition, the length of time the valve means 16 is open and its closing time is a function of the opening time. In that disclosure, valve lift is not controlled but is a function of opening time. The earlier the opening, the higher the valve lift.
[0013] In the diagram of FIGURE 3, the rocker arm 36 ratio is determined as it varies from one extreme when the adjuster is extended:
or
to when the rocker arm adjuster is collapsed
or
where:
be = length from the cam centerline to the pivot point on the hydraulic valve adjuster when the adjuster is fully extended; and
bc = length from the cam centerline to the pivot point in the hydraulic valve adjuster when the adjuster is fully collapsed.
[0015] As previously stated, hydraulic valve adjusters 12 are provided for controlling the pivot point of the rocker arm 36. By positioning the centerline 10 or longitudinal axis of the hydraulic valve adjuster 12 at angle θ intersecting the centerline or longitudinal axis of the valve means 16, "inclination angle", therefore
where
d = the height of the hydraulic adjuster fully extended minus the height of the hydraulic adjuster fully collapsed, "total lifter collapsew.
[0017] Thus, the rocker arm 36 ratio (Rr ) can be varied as a function of:
a = length from the cam centerline to valve stem centerline;
d = total hydraulic valve adjuster collapse
θ = angle between hydraulic valve adjuster centerline and the valve stem centerline; and
be = length from the cam centerline to the pivot point on the hydraulic valve adjuster when the adjuster is fully extended
[0018] By correctly selecting θ, the inclination angle between the centerline 10 of the hydraulic valve adjuster 12 and the valve means 16 centerline 14, the rotation of the cam 32 sets the pivot point and the amount of lift can be selected. If the inclination angle θ in FIGURE 2 is increased, the rocker arm 36 ratio is decreased as the hydraulic valve adjuster 12 collapses and the dimension bc is increased or lengthened, the lift or height of the valve opening decreases. As stated in the previous patent application, as the timing cam 32 rotates, the rocker arm 36 pivot bears against the hydraulic valve adjuster 12 and as long as the control solenoid 40 is open, the fluid flows out of the adjuster 12 and the adjuster collapses until the hydraulic flow path is closed. It is this movement that determines the pivot point.
[0019] In a system where maximum change in valve lift is desired, the reduction in rocker arm 36 ratio gives a greater possible change in valve lift as the total hydraulic valve adjuster 12 collapse goes from d=0 to d=MAX in FIGURE 4. Conversely, in a system where a fixed amount of valve lift change is desirable and the hydraulic valve adjuster 12 collapses from d=0 to d=X in FIGURE 4, the reduction in rocker arm 36 ratio can be used to minimize the amount of hydraulic valve adjuster 36 stroke necessary. Either effect adds significantly to the flexibility of a variable valve timing system.
[0020] By placing the hydraulic valve adjuster 12 at the angle 0 from the valve means 16, two considerations or strategies are available. The first strategy is to have the greatest change in valve means 16 lift from a maximum when the hydraulic valve adjuster is not collapsed, d=0, to the smallest valve means 16 lift when the hydraulic valve adjuster 12 is collapsed, d=MAX. If this strategy is used, the size of the control elements, namely the hydraulic valve adjuster 12 and the control solenoid 40 must be sized to control the hydraulic valve adjuster 12 collapse. Typically, this means that more hydraulic oil is controlled by the control solenoid 40 as it flows from the large hydraulic valve adjuster 12.
[0021] The second strategy is one that the engine builder determines that a fixed change in the valve means 16 opening is desired for two different engine operations. The largest valve lift is typically for high speed or heavy load and the smallest or second valve lift is at idle where the effects of valve timing control will make up for throttle body loses. This example, is illustrated in FIGURE 4 wherein d is either "0" (zero) or "X". Also in this example, the size of hydraulic valve adjuster 12, hence the amount and control of hydraulic oil, is smaller than in the first strategy.
[0022] FIGURE 4 graphically illustrates the effects of variable rocker arm 36 ratios which can and will be achieved by a suitable selection of the angle 0. If the angle -8- equals zero, then the system of the prior identified patent application is applicable, however by having the angle-e-equal a finite number of degrees, the rocker arm 36 ratio is reduced as the hydraulic valve adjuster 12 collapses.
[0023] Another embodiment of variable valve timing system that also effects valve lift is shown in FIGURE 5 where the hydraulic valve adjuster is replaced by a linear solenoid 42 and a lever means 44. One end of the rocker arm 46 bears on the end of the valve stem 20, a portion 48 adapted to follow the timing cam 32, and a pivot portion 50 or lever pivot, which is a moveable pivot is located by another pivoting lever 52. The rocker arm 46 has a designed shape portion 48 to accomplish the amount of valve lift with the time of opening.
[0024] The moveable pivot 50 operates to change the rocker arm 46 ratio and is biased by means such as a spring 54 to return to a home position. The solenoid 42, being a linear solenoid, moves its actuator or plunger 56 a distance proportional to the time electric power is applied to the solenoid. When the electric power is removed, the bias means 54 restores or returns the plunger 56 and therefore the rocker arm 46 to its home position. This system does not require hydraulic fluid but does require large power linear solenoids.
[0025] Electric power is supplied to the linear actuator 42 by means of an electronic control unit 58 which is adapted to generate valve timing signals in response to a plurality of engine operating signals 60. The signals generated for this embodiment are similar to those generated for the embodiment shown in FIGURE 3 in that in each, the timing of the signal is proportional to the desired valve timing.
determining the rocker arm ratio as a function of the distances (b, a) between the centerline of the timing cam (32) and the pivot point of the rocker arm and the longitudinal axis of the valve (16),
providing hydraulic valve adjusters (12) for controlling the pivot point of the rocker arm (36),
positioning the longitudinal axis (10) of the hydraulic valve adjuster (12) at an angle (0) intersecting the longitudinal axis (14) of the valve (16),
adjusting the height of the valve adjuster (12) to move the pivot point of the rocker arm (36) along the longitudinal axis (10) of the hydraulic valve adjuster (12) thereby changing the rocker arm ratio,
rotating the timing cam (32) for setting the rocker arm (36) pivot on the hydraulic valve adjuster (12), and then
opening the valve (16) a predetermined height as a function of the location of the pivot point on the hydraulic valve adjuster (12).
a shaft (28) operatively coupled to the main drive shaft of the engine,
at least one timing cam (32) connected to said shaft (28) and rotatable therewith,
an engine valve means (16) mounted for reciprocal movement in a direction along its longitudinal axis (14) and transverse to said shaft (28) in the engine, said valve means (16) having a valve member (18), a valve stem (20), a keeper block (22) and a spring (24) bearing against the keeper block for biasing said valve member closed on a valve seat (26),
a rocker arm (36) having one end bearing against the valve stem (20), another portion adapted to follow said one timing cam and a pivot end, and
a hydraulic valve adjuster (12) mounted in the engine, the longitudinal axis (10) of said adjuster (12) mounted at an angle (0) intersecting the longitudinal axis (14) of the engine valve means (16), said adjuster having a reciprocal piston means mounted along said axis (10) forming a pivot for said rocker arm (36) so that as the piston reciprocates the pivot point changes changing the distance (b) from the centerline of said timing cam (32) to said pivot point.
a shaft (28) operatively connected to the main drive shaft of the engine,
at least one timing cam (32) connected to said shaft (28) and rotatable therewith,
an engine valve means (16) mounted for reciprocal movement in a direction along its longitudinal axis (20) and transverse to said shaft (28) in the engine, said valve means (16) having a valve member (18), a valve stem (20), a keeper block (22) and a spring (24) bearing against the keeper block (22) for biasing said valve member (18) closed on a valve seat (26),
a rocker arm (46) having one end bearing against said valve stem (20), portion (48) adapted to follow said one timing cam (32) and a pivot portion having a pivot (50),
lever means (52) connected to said pivot (50) adapted to move said pivot along an arcuate path,
an electronic control unit (58) adapted to generate valve timing signals in response to a plurality of engine operating signals (60), and
a linear actuator means (42) attached to said rocker arm (46) and adapted to move said rocker arm in response to said valve timing signals from said electronic control unit (58) to vary the position of said pivot (50) relative to said timing cam (32).