US 3817228 A
A control unit for varying the length of the reciprocatory stroke of a pushrod or other member reciprocated in response to motion of a cam in which a sliding cylinder has a piston slidably mounted therein. The cylinder acts directly on the pushrod and the cam acts on the piston. The outflow of fluid from a space between a closed end of the cylinder and the piston is regulated by a valve so that lifting movement transmitted to the piston from the cam is not wholly transmitted to the cylinder, when the valve is open, because of the outflow, and therefore the lift of the push rod is reduced.
Description (OCR text may contain errors)
United States Patent [191 Bywater June 18, 1974 1 1 CAM MOTION CONTROL UNIT 3,439.661 4/1969 Weiler r. 123/9016  Inventor: John Roger Bywater, 82 Bridge Ln.,
Bramhall, Stockport, England Primary ExaminerManuel A. Antonakas Assistant Examiner-Daniel J. OConnor Attorney, Agent, or Firm-Si1ghr'ue, Rothwell, Mion, Zinn & Macpeak  ABSTRACT A control unit'for varying the length of the reciprocatory stroke of a pushrod or other member reciprocated in response to motion of a cam in which a sliding cylinder has a piston slidably mounted therein. The cylinder acts directly on the pushrod and the cam acts on the piston. The outflow of fluid from a space between a closed end of the cylinder and the piston is regulated by a valve so that lifting movement transmitted to the piston from the cam is not wholly transmitted to the cylinder, when the valve is open, because of the outflow, and therefore the lift of the push rod is reduced.
10 Claims, 3 Drawing Figures CAM MOTION CONTROL UNIT This invention relates to a unit for use in varying the reciprocatory movement of a member which is reciprocated in response to motion of reciprocatory motion producing means.
According to the invention the unit, for interposing between the member to be reciprocated and the reciprocatory motion producing means, comprises a first cylinder, a second cylinder mounted for sliding reciprocation in the first cylinder, and a piston mounted for sliding reciprocation in the first and second cylinders, means through which liquid admitted to a space between the piston and second cylinder can escape therefrom, and means through which liquid admitted to a space between the first and second cylinders can escape therefrom, and said piston being for reciprocation by said reciprocatory motion producing means and said second cylinder being for applying linear motion to the member to be reciprocated.
The invention will now be further described with reference to the accompanying drawings in which:
FIG. 1 is a view partially in section of a unit formed according to the invention together with an hydraulic circuit, a cam, and a valve stem or pushrod to be recip-, rocated via the unit,-
FIG. 2 is a modification of the arrangement in FIG. 1, and
FIG. 3 shows curves demonstrating variation in lift of a valve or pushrod achieved by use of the unit.
In the drawings, like parts are identified by like reference numerals.
Referring to FIG. 1, the unit indicated at 2 is formed with an outer cylinder 4 with an axial bore 6 closed at one end 8 and containing an inner cylinder 10 ina sliding fluid tight fit. Cylinder 10 has an axial bore 12 in which is located in a sliding fluid tight fit an upper end 14 of a plunger or piston 16 also passing in a sliding fluid tight manner through a passage 18 in end 8. Lower end 20 of the piston is in contact with a cam 22 rotatably driven (by means not shown) in the direction of arrow A. Closed upper end 24 of cylinder 10 acts on a member to be reciprocated which in the example shown is a stem 26 of an inlet valve of an internal combustion engine orv a pushrod.
A passage 28 for hydraulic fluid extends through the wall of cylinder 4 into a recess 30 extending around an outer surface of cylinder 10 between the latter and inner surface of the cylinder 4 at a position adjacent to the closed end 24 and extending axially along the cylinder 10. Passages 32 lead from recess 30 into space 8 in an upper part of bore 12 adjacent to closed end 24. Another passage 34 for hydraulic fluid extends through the wall of cylinder 4 into space C in the lower part of bore 6 between the end 8 and lower end 36 of the cylinder 10.
A transverse passage 38 in the piston 16 has a port 40 at each end which are covered by the cylinder 10 when the piston is pushed further thereinto. This passage leads to an axial passage 42 in the piston, which latter passage has a lower opening from which hydraulicfluid can escape.
Hydraulic fluid is supplied to passages 28 and 34 via pipes 44 and 46 respectively and non-return valves 48 and 50 from gallery 52 supplied with fluid from a suitable source, for example, oil pumped from a sump (not shown) of an internal combustion engine. Branched into pipe 44 is another pipe 54 leading to a regulator valve 56 which can be in any position from fully closed to block pipe 54 to fully open. This latter valve may be manually operated or operable by any other desired means. A spring can be suitably located to apply the piston 16 against the cam 22. In the example shown in FIG. 1, this spring is an helical compression spring shown at 58 disposed between the cylinder 4 and the end 20. When valve 56 is fully closed and the space E is filled with liquid, from gallery 52, the lifting of the piston 16 by the movement of cam protruberance 22a causes the cylinder 10 to be lifted by the same amount since the liquid in B is incompressible and cannot escape in the direction of arrowheads D and E and arrow F, nor can it pass through valve 48 which only passes liquid in the direction of arrow G. Therefore, there is no relative movement between piston 16 and cylinder 10, and the valve stem 26 follows the lift of cam 22 exactly. At the same time space C increases in volume filling with liquid flowing through pipe 46 in the direction of arrow H, some of which liquid leaves the space C through passages 40 and 42 in the direction of arrow J As the cam 22 continues to rotate, the usual valve spring (not shown) acts to lower the valve stem 26 which pushes the cylinder 10 down, and also the piston 16 because of the incompressible liquid in space B. Space C decreases in volume and the excess liquid therein leaves through passages 40 and 42 to return to a reservoir, for example, the sump. This lowering also follows the cam exactly so the motion of the stem 26 is as if it were acted on directly by cam 22 and is illustrated by full line curve 60 in FIG. 3 in which the Y axis represents the degree of valve lift and the X axis the angular position of the cam during rotation.
When valve 56 is fully open, the rise and fall of piston 16 pushes liquid out of space B freely and no motion is transmitted to the valve stem 26.
When valve 56 is partially open, liquid leaves space B at a controlled rate which depends on how much valve 56 is open. Therefore, as the piston 16 rises, there is some relative movement between it and the cylinder 10 to reduce the volume of space B. But as the fluid escape rate is less than the rate of rise of the piston the cylinder 10 also rises, but more slowly than when the valve 56 is closed and also does not rise to the same extent as represented by the section between 0 and of the dotted dash curve 62 (FIG. 3). During this rise the space B continues in communication with passage 28 by virtue'of the axial length of the recess 30. Also during this rise, piston 16 moves into cylinder 10 so that porting 40 is blocked as the increasing volume of space C fills up with liquid. As the cam continues to rotate past the 90 position so that protuberance 22a moves from the end 20, the valve stem 26 remains in the lifted position because the incompressible liquid in space C prevents the cylinder 10 descending until the compressed spring 58 moves the piston 16 down relative to cylinder 10 to uncover the ports 40. Thereupon the liquid in space C can escape via passages 40 and 42 and the cylinder 10 and stem 26 descend and eventually follow the final part of curve 62 which now coincides with curve 60.
Thereduction in lift and the dwell at full lift position of the stem 26 can be varied as desired by the degree of opening selected for the valve 56. Also the shape and size of the ports 40 and the passage 38 and the passage 42 can be varied to delay or accelerate the time when the final part of curve 62 coincides with curve 60.
The curve 64 in clashes in FIG. 3 is illustrative of the case when the speed of rotation of cam 22 is increased whenthe valve 56 is fully closed. The point x on the X axis represents the 180 position, so that for curve 64 after 90, the X axis has been stretched. Because of the dash pot effect of the liquid escaping from volume C, the lowering rate of valve stem 26 is relatively slower than the lifting rate, and as shown the curve 64 conforms to the curve 60 up to 90 of cam rotation It should be understood that the terms lifting and lowering are merely used for convenience to identify opening and closing of the valve on stem 26 and the motion of the components in the unit 2 relative to the attitude thereof in FIG. 1. The unit may be in any other attitude desired.
In FIG. 2 the piston 16 is reciprocated by the cam 22 acting on a lever 70 pivotably mounted at 72 on a cylinder head 74. This lever is biased by a compression spring 76 and pivotably mounted at 78 on a linkage 80 pivotably connected at 82 to the end 20 of the piston. The end 24 of the cylinder acts on the stem 26 having a valve head 84 opening and closing a fuel inlet passage 86 to a cylinder 88 of an internal combustion engine. The stem has a collar 90 against which a valve spring 92 is biased.
It will be appreciated that since the profile of the opening and closing curve of the inlet valve 84 is controlled by the valve 56 the latter can be used as a speed regulator in addition to or in place of a conventional throttle in a carburettor.
If desired, springs 58 and 76 may be omitted and the piston 16 moved to uncover ports 40 by virtue of the pressurised fluid supplied to space B acting on the pis- I011.
If desired the valve 56 instead of being a variable orific valve may be a fluid pressure operated valve, for example a spring biased valve, set to open when the fluid pressure in space B and pipe 54 exceeds a predetermined pressure and close when the pressure drops below the predetermined value. In this case the lift curve follows curve (FIG. 3) up to point y and then follows curve 66 to point y at 90 of cam rotation and thereafter is the same as curve 62.
What is claimed is:
l. A unit for use in varying the reciprocatory movement of a member which is reciprocated in response to motion of reciprocatory motion producing means, said unit being for interposing between the member to be reciprocated and the reciprocatory motion producing means and comprising a first cylinder; a second cylinder mounted for sliding reciprocation in the first cylinder, said first and second cylinders defining therebetween a first space having a volume which varies during reciprocation of the second cylinder relative to the first; a piston mounted for sliding reciprocation in the first and second cylinders, the second cylinder and piston defining therebetween a second space having a volume which varies during reciprocation of the piston relative to the second cylinder, a wall of the second cylinder being provided with first passage means through which liquid admitted to the second space can escape therefrom, the piston being formed with second passage means, a side of said piston being formed with port means opening into the second passage means, the port means being covered and uncovered alternately by the second cylinder during said reciprocatory motion of the piston and during the uncovered state, said port means also open into the first space whereby liquid admitted to the first space can leave through the second passage means, and said piston being for reciprocation by said reciprocatory motion producing means and said second cylinder being for applying linear motion to the member to be reciprocated.
2. A unit as claimed in claim 1, comprising the first cylinder formed with a first bore and closed at one end except for a through third passage formed in said one end, the second cylinder being formed with a second bore closed at a first end of said second cylinder extending across the second bore which is open at a second end of the second cylinder adjacent to the one end of the first cylinder, the piston slidably disposed in the second bore and third passage for reciprocation therein and having a first end disposed in said second bore and a second end disposed outside the first cylinder, between an inner surface of the first cylinder and an outer surface of the second cylinder there is defined recess means extending in a direction longitudinally of the cylinders and disposed at a position intermediate the opposite ends of said cylinders, a wall of the first cylinder having fourth passage means formed therethrough and opening at one end into said recess means, the first passage means opening at one end into said recess means and at another end into a space in the second bore at a location intermediate the first end of the piston and the first end of the second cylinder, the wall of the first cylinder having fifth passage means formed therethrough and opening at one end into a space in the first bore at a position adjacent to the said one end of the first cylinder, the port means being at one end of the second passage means which open at the other end externally of the first cylinder, the fourth and fifth passage means being for the flow of liquid therethrough, the piston being also for reciprocation by action of a cam and the first end of the second cylinder being for transmitting linear motion to the member to be reciprocated.
3. A unit as claimed in claim 2, in which spring means is provided to act to urge the piston in a direction outwardly of the cylinders.
4-. A unit as claimed in claim 2, in which the recess means is a recess formed in the second cylinder and extends therearound.
5. A unit as claimed in claim 2, in which the second passage means comprises a plurality of interconnected passage means comprises a plurality of interconnected passages and the port means comprises a plurality of ports.
6. A unit as claimed in claim 2, in which the first passage means comprises a plurality of passages.
7. A unit as claimed in claim 2, in combination with a liquid supply and control system comprising means for supplying liquid to the fourth and fifth passage means to occupy said spaces in the second and first bores respectively, and a valve connected to the fourth passage means to control the escape of liquid from the said space in the second bore.
8. A combination as claimed in claim 7, in which the valve is a variable orifice valve.
9. A combination as claimed in claim 7 in which the valve is operable by fluid pressure.
10. A combination as claimed in claim 7, in which the supply of liquid to the fourth and fifth passages is via non-return valves.