U.S. patent number 3,921,609 [Application Number 05/498,277] was granted by the patent office on 1975-11-25 for variable duration hydraulic valve tappet.
This patent grant is currently assigned to Jack L. Rhoads. Invention is credited to James E. Rhoads.
United States Patent |
3,921,609 |
Rhoads |
November 25, 1975 |
Variable duration hydraulic valve tappet
Abstract
A hydraulic valve lifter for use in high performance engines to
prevent valve overlap at low operating speeds, the lifter having a
restricted oil bleed passageway leading to the pressure chamber to
prevent the lifter from pumping up to a fully solid condition at
low speeds, the passageway being narrow enough to become
substantially inoperative at high speeds to produce effectively
solid lifter action.
Inventors: |
Rhoads; James E. (La Mesa,
CA) |
Assignee: |
Rhoads; Jack L. (Taylor,
AZ)
|
Family
ID: |
23980355 |
Appl.
No.: |
05/498,277 |
Filed: |
August 16, 1974 |
Current U.S.
Class: |
123/90.55;
123/90.57 |
Current CPC
Class: |
F01L
1/245 (20130101) |
Current International
Class: |
F01L
1/20 (20060101); F01L 1/245 (20060101); F01L
001/14 () |
Field of
Search: |
;137/513.3,513.5
;123/90.55,90.16,90.56,90.57,90.58 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myhre; Charles J.
Assistant Examiner: O'Connor; Daniel J.
Attorney, Agent or Firm: Branscomb; Ralph S.
Claims
I claim:
1. In a hydraulic valve lifter having a hollow cylindrical body
with a closed lower end for engagement with a cam; a hollow
cylindrical plunger axially slidable in said body and enclosing a
pressure chamber in the lower end of the body; an external
collecting channel on said body to receive oil from a pressurized
source; a port opening into said body from said channel; a port in
said plunger communicating with said first mentioned port to admit
oil into the plunger; and a one-way valve in said plunger opening
into said pressure chamber:
an improvement comprising:
at least one restricted oil bleed passageway providing, at all
points of operation of the hydraulic valve lifter, continuous
communication between said pressure chamber and said collecting
channel; said oil bleed passageway being substantially
dimensionally independent of temperature induced volumetric changes
in said valve lifter;
the cross sectional area of at least a portion of said bleed
passageway being insufficient to sustain oil bleed beyond a
predetermined flow rate at high engine speed.
2. Structure according to claim 1 wherein said body has an internal
channel communicating with the first mentioned port and said bleed
passageway includes a duct defined by a flat portion on the outer
surface of said plunger extending from said pressure chamber to
said internal channel.
3. Structure according to claim 1 wherein said plunger has an
enternal peripheral channel communicating with said parts and said
bleed passageway includes a duct defined by a flat portion on the
outside of said plunger extending from said pressure chamber to
said peripheral channel.
4. Structure according to claim 1 wherein said valve has a seating
and a wafer sealing element therefrom having a groove traversing at
least a portion of the seating side thereof, whereby the passageway
provided from said pressure chamber to the interior of said chamber
through said groove comprises a portion of said bleed passageway.
Description
BACKGROUND OF THE INVENTION
With conventional types of hydraulic valve lifters, each valve
actuating push rod seats in a plunger axially slidable in a lifter
body, and the lifter body rides on one lobe of the cam. Oil from
the engine lubrication system is introduced under pressure between
the body and plunger and at increased engine speeds the valve
lifter assembly expands axially to tighten the linkage in the valve
actuating train. Many lifters are designed to trap oil in the body
chamber and pump up to an effectively solid condition at relatively
low speed. However, with high performance cams the valves are timed
to have considerable overlap in order to provide for a large flow
through the engine. At low speeds this large overlap is not
necessary and the engine runs inefficiently, resulting in a loss in
low speed horsepower. Basically, increasing the valve lash will
shorten valve open duration and reduce overlap, since more
crankshaft rotation is necessary to overcome the lash in the valve
train. This will result in an improvement in low speed performance.
However, excessive lash causes considerable noise and wear at
idling and low speeds. Decreasing lash, as by tightening or pumping
up the lifters, will lengthen valve duration and improve high speed
performance.
Another hydraulic valve lifter invented by applicant and described
in U.S. Pat. No. 3,304,925, permits oil bleed from the pressure
chamber to occur at a predetermined minimum speed but prevents
bleed at high speeds, causing the desired solid lifter action to
occur. However, it has been found that under certain circumstances
it is not necessary to prevent oil bleed below a minimum speed and
there are reasons for designing the lifter to allow bleeding at low
as well as intermediate speeds.
SUMMARY OF THE INVENTION
The valve lifter described herein is designed to provide favorable
characteristics over the entire speed range. At low and
intermediate speeds a closely controlled oil leak in the pressure
chamber is permitted to prevent pumping up to a fully solid
condition. At high speeds the motion is so rapid that the oil can
no longer escape to any degree through the restricted leak path and
the lifter becomes effectively solid.
This is accomplished by providing a bleed passageway to the
pressure chamber which is continually open at all operating speeds
and may be manifested in several different configurations,
including a flat ground on the side of the plunger and a groove,
port, or other irregularity provided in the check valve or valve
seating at the bottom of the piston to prevent the valve from
completely sealing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view, taken axially along a valve lifter,
showing the mechanism in the valve closed position;
FIG. 2 is a similar sectional view with the mechanism in the valve
open position;
FIG. 3 is a perspective view of the plunger;
FIG. 4 is a sectional view, similar to a portion of FIG. 1, showing
a wafer type check valve;
FIG. 5 is an enlarged perspective view of the wafer check valve
element;
FIG. 6 is a perspective view of an alternative wafer element;
and
FIG. 7 is a perspective view of a further wafer element.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 and 2 show the valve lifter 10 axially slidably mounted in a
bore 12 in a portion of the engine head casting 16. A single valve
is shown, there being one lifter for each valve in the engine, with
each lifter operated by a lobe 18 on a comshaft 20. In the head 16
is an oil gallery 22 with a supply duct 24 leading to bore 12 to
supply oil to the lifter from the pressure side of the engine oil
system.
Valve lifter 10 comprises a cylindrical body 26 having a closed
lower end 28, and axially slidable within the body is a hollow
cylindrical plunger 30. In the upper end of plunger 30 is a cup 32
in which is seated the end of a push rod 34, the push rod being
coupled to a conventional rocker arm and valve, not shown. Plunger
30 is retained by a snap ring 36 in a groove 38 within the upper
end of body 26. Body 26 has an external peripheral collecting
channel 40 which registers with the supply duct 24. A port 42
communicates from channel 40 to the interior of body 26 and plunger
30 has a peripheral channel 44 which registers with port 42 at all
times. From channel 44 a port 46 leads to the interior of plunger
30, so that oil is continuously admitted into the inner chamber 48
of the plunger from the oil gallery regardless of any rotational or
axial displacement experienced by the lifter components.
At the lower end of plunger 30 is a small outlet 50, the lower end
of which is closed by a check valve 52 having a sealing element 53
held in place against the seating 54 by a seating spring 55, the
spring and valve being held in place by a perforated retaining cage
56. The space between plunger 30 and the lower end of body 26
comprises a pressure chamber 58 and in this chamber is a return
spring 60 which biases the plunger upwardly out of the body, until
stopped by the snap ring 36. In normal assembly the plunger 30 is
pressed down against return spring 60 by the push rod 34, which is
loaded by the much stronger valve spring, not shown.
The structure thus far described is conventional and representative
of hydraulic valve lifters, which may vary somewhat in porting and
check valve arrangements. In operation the plunger chamber 48
receives oil under pressure at each upward stroke of the lifter,
the oil being forced down through check valve 52 into pressure
chamber 58. At low pressure the plunger rides low in the body and
is raised by increasing pressure to tighten the valve train. With
no return leakage, or only that which may occur through the normal
sliding clearance of plunger 30 in the body 26, the oil in chamber
58 is pumped up rapidly and the lifter becomes effectively
solid.
The novel action is provided by a bleed passageway providing
continuous communication between the pressure chamber 58 and the
oil collecting channel 40. The valve lifter described in the
previously mentioned U.S. Pat. No. 3,304,925 also provided a bleed
passageway but it was not continuously open, being blocked at low
speeds. The continuously open passageway can be incorporated in
several different ways which would not be possible in the earlier
unit, and one form, in which the passageway includes a bleed duct
62 comprising a flat 64 ground along the outer surface of the
plunger from the bottom to the channel 44, is simply an extension
of the earlier bleed duct and has the advantage of being easier to
mill. Body 26 has an internal return channel 66 extending axially
to port 42, and since the channel 66 is in constant communication
with the channel 44, there is provided at all times a complete
passageway from the pressure chamber 58 to the channel 66 and to
the external collecting channel 40 and thus to the oil gallery
22.
In operation, as the engine speed increases and the oil pressure
rises, the lifter will attempt to pump up. However, since oil can
leak from the pressure chamber through the bleed passageway, the
pumping up will be retarded. As higher engine speeds are achieved,
the resistance of the bleed passageway effectively increases since
it is too narrow to pass oil in quantity at high speeds, resulting
in the gradual pumping up of the lifters with increased engine
speed and effectively solid lifter at high speeds.
It has been found in tests that a flat portion 64 ground off to
provide a bleed duct having a depth on the order of from two to
five thousandths of an inch will provide the required
characteristics in the engine of a passenger automobile. The exact
amount will depend on the normal oil pressure in the engine, the
cam design with regard to valve timing and duration and to the
overall performance range of the engine. In racing engines it would
be possible to enlarge the bleed duct to as much as ten or fifteen
thousandths of an inch. An oil bleed of this magnitude would result
in considerable valve lash and noise at idle speeds, but this can
be tolerated in a racing engine.
The crucial requsite for proper operation of the lifter resides in
the continually open bleed passageway between the pressure chamber
and the collecting channel 40 so the pressure chamber can bleed to
the oil gallery 22. Other groove configurations in the plunger
surface, and even in the internal surface of the cylinder body, are
conceivable which would produce the desired result. In addition,
the check valve 52 could be altered slightly so that it cannot
completely seal, whereby a bleed pathway would be defined through
the valve, plunger chamber 48, and through the ports 42 and 46.
This could be accomplished in numerous ways, such as scoring or
etching the ball 53 if a ball check valve is used, providing a
notch 68 or other irregularity in the valve seating 54 as shown in
FIG. 4.
Three other means of altering the check valve are shown as examples
in FIGS. 5-7, in which a wafer check valve is used rather than a
ball check valve. The wafer sealing element 53' is apertured 70 in
FIG. 5 and provided with radial and diametric grooves of
insufficient size to sustain oil bleed at high engine speed on its
sealing surface at 72 and 74 in FIGS. 6 and 7 respectively, any of
which produce the obvious result of rendering a complete seal of
the check valve impossible and providing a proper bleed passageway
from the pressure chamber 58 to the collecting channel 40.
The various arrangements described herein are adaptable to a
variety of engines and can be incorporated into many existing types
of valve lifter, without requiring any changes in the engines. In
fact existing lifters already in use can be modified in accordance
with this disclosure. It is understood that minor variation from
the form of the invention disclosed herein may be made without
departure from the spirit and scope of the invention, and that the
specification and drawings are to be considered as merely
illustrative rather than limiting.
* * * * *