HYDRAULIC CAM FOLLOWER

Abstract: An hydraulic cam follower for actuating the valves of internal combustion engines and the like comprises a hollow cylindrical body (1) closed at one end and slidably mounted on a sleeve (4) fixed relative to the body (1), a piston (8) slidably mounted within the sleeve (4), the outer end of the piston (8) being in engagement with a push rod (9), a chamber (20) being defined between the inner end of the piston (16) and the closed end of the body (1) and containing hydraulic fluid. Displacement of the body (1) by the cam (2) displaces the hydraulic fluid which moves the piston (8) within the fixed sleeve (4) to give the push rod (9) a longer and quicker stroke than the stroke of the body (1).

Description: "HYDRAULIC CAM FOLLOWER" This invention relates to a hydraulic cam follower for actuating the tappets of internal combustion engines and the like. 5. Cam shafts of engines are usually connected in their operation to the tappets of valves, or directly to the valve stems through means which compensate for wear, temperature and other differences which would increase the amount of slack between the tappet and 10. the cam follower. According to a known method the tappets are operated by direct contact or through a push rod and rocker gear to a cam follower which is guided axially and positioned adjacent a cam so that it moves under 15 the influence of the cam, spring loading being provided to return the cam follower after displacement to ensure that at all times it maintains contact with the cam. Hydraulic cam followers are of two types, each 20. however using a fluid such as oil to take up any slack in the action, the one type being actuated by engine oil and the other being self-contained by having a sealed oil supply which takes up the necessary slack should it occur. 25. The principle of operation is to have between the cam follower member and the push rod or valve stem a member which is kept extended from the cam follower by oil pressure between the cam follower and this member, the arrangement however being such that over a time 30. oil is drawn into the space between the cam follower and the inner end of the _____________ member which operates the tappet to fill this space so that when the cam pushes on the cam follower, because of the presence of oil which is sealed in position the cam follower and tappet member move simultaneously, 5. but during such motion some oil is expressed from the oil reservoir within the cam follower and the loss is replaced when the cam follower is stationary, either from engine oil supply or from a sealed reservoir forming a part of a cam follower assembly. 10. In the devices as used herebefore motion of a cam follower is simply transmitted to the valve which it operates so that the cam follower requires to move a distance such that proper opening and closing of the valve occurs. 15. Because it is necessary to shape a cam to give a relatively gradual lift and return of a cam follower, the action of operating the valve is slowed down because if fast lift cams are used excessive noise and bounce tend to occur. 20. It is an object of the present invention to provide an improved system in which this problem is overcome and this is achieved according to this invention by so arranging the cam follower and the mechanism which transmits the cam follower motion to 25. the valve that the movement is amplified. In other words, the cam follower need only operate part of the distance required to normally move the valve or other mechanism coupled to it the required distance and this is achieved by applying 30. what could be termed as a hydraulic intensifier of movement in the assembly. This is achieved according to this invention by using a hollow cam follower 1 which has one end closed to engage the cam and has its other end open 3 and a sleeve 4 which projects down in the hollow of the cam 5. follower in sealing relationship, this sleeve being fixed in relation to the cam shaft. The sleeve 4 is fixed to a further sleeve 5 which abuts against a member 6 fixed to the engine block. The sleeve 4 can float relying on the spring 10. tension of spring 7 to keep the cam follower body 1 acting between further sleeve 5 and the cam follower 1 on the cam shaft 2 and the further sleeve 5 against the fixed member 6. Projecting down within the sleeve 4 is a piston 8 15. which has its outer end engaged by a push rod 9 through push rod seal 10 or other mechanism to be operated by the cam system, and this piston 8 has an oil supply to it which can be fed through an aperture 11 in the cam follower and on aperture 12 in the 20. sleeve to an aperture 13 which opens to an oil-way 14 extending axially within the piston. The sleeve 4 has its inner end 15 terminating some distance from the closed end of the cam follower 1 so that the spring 7 urges the cam follower 1 down onto the cam 2 at all 25. times. The piston 8 at its inner end 16 is provided with a valve member 17, a spring 18 acting on the valve and piston 8 to force the piston upwardly to eliminate the clearance in the valve train. The piston has the 30. oil-way 14 through it with a non- return valve 19 to allow oil from the oil-way 14 to be fed into the oil reservoir 20 in the cam follower. Because the inner end of the cam follower serves as a reservoir 20 for oil supplied through the oil-way and the non-return valve, any movement of the cam follower in the direction of the fixed sleeve causes 5. displacement of oil from the reservoir and this displaced oil lifts the piston 8 which because it is inside of the hollow sleeve 16 is substantially smaller than the inner diameter of the cam follower which corresponds to the outer diameter of the sleeve 10. and therefore as oil in the oil reservoir is put under pressure by the cam follower being displaced by the cam, the displaced oil moves the piston in the fixed sleeve to give to the tappet or valve stem or the like, a quicker and longer stroke than the stroke of a 15. cam follower. Hence a small movement of the follower gives a quicker and longer stroke of the piston and hence to the valve to very rapidly open the valve. As the spring 7 between the fixed sleeve and the cam follower 1 tends to force the cam follower down 20. into contact with the cam, the cam follower drops as the load of the cam moves away from beneath the cam follower and this allows the piston to be returned by spring pressure or the like from the push rod or the valve stem to again move down to its lower position, 25. this action recurring each time the cam follower is moved outwardly by the cam and returns . The oil reservoir is kept replenished by the oil entering through the oil-way and the one way valve in the piston 19 and therefore should during a pressure Q stroke oil be lost by squeezing between the outer surface of a fixed sleeve and the inner surface of a cam follower or between the inner surface of the fixed sleeve and the outer surface-—— ■— , of the piston, such oil will immediately be replaced from the oil-way when the piston comes to rest so that at all times the amount of oil in the oil reservoir will be such that the correct lift will be given to 5. the push rods or valve stems or the like. It is possible to seal one of the leakage paths with "0" rings or metal piston rings and contain only one controlled leakage path. It will therefore be realised that because it is 10. necessary to lift the cam follower a much shorter distance than the actual movement required of a push rod or valve, the cam can be differently shaped and because of the intensification of the lift, the valve or whatever is actuated by the cam will have a much 15. faster opening and closing, and can therefore have a relatively longer dwell in its fully open position than was possible previously. The loads on the cam required to give relatively high lift to the cam follower are thus reduced. 20. As shown in FIG. 2 the invention is not limited to a purely hydraulic valve, and as shown in FIG. 2 the piston 8 is adapted to contact the end of the cam follower 1. A spring 21 opening between the end of the sleeve 4 and the end of the cam follower 1 25. maintains the cam follower down into contact with the cam load. Oil is fed into the reservoir 20 in a manner similar to FIG. 1 and on the cam forcing the follower upwardly, the oil in the reservoir 20 to be displaced 3Q_ moves the piston upwardly a greater distance and at a greater rate than the movement of the follower 1, in a manner similar to the previous embodiment. In this embodiment some adjustment may be required to adjust the clearance between the cam load and the valve A smoother action may result if the smaller centre piston is held, and the sleeve slotted to allow its upward movement over the rail sleeve. The slots are only at the top and only deep 5. enough to allow for the length of strokes. Oil would still have to be fed up the push rod to feed the tappets but this could be done with a spring loaded sleeve in the lower end of the push rod sitting on the oil hole. 10. By means of the mechanism outlined therefore, it is possible for a relatively short movement of a cam follower to have a greater stroke of the piston, thereby enabling a much better form of cam to be generated which will have a fast lift and return with 15. a relatively longer dwell therebetween should this be desirable and it will be realised also that these advantages are possible by the simple inclusion of a fixed sleeve between the cam follower and the piston which sleeve can conveniently be fitted to a plate 2o. which can extend along the engine above the various cams so that the device can be used as a replacement for the normal type of cam followers in which the cam follower and piston co-operate to give a unit of a specific overall length and in which these move 25. together without the piston having a greater motion than the cam follower. OM

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS: 1. A hydraulic cam follower having a hollow cylindrical body closed at one end to engage a cam and a piston having a portion to engage a push rod, characterised in that said piston is slidably mounted 5. within a cylindrical sleeve within said cylindrical body, said cylindrical sleeve being maintained in fixed relationship with said cam shaft, means for feeding oil to a chamber between said piston and said closed end whereby movement of said body relative to 10. said sleeve causes amplified movement of said piston. 2. A hydraulic cam follower as defined in Claim 1 characterised in that said sleeve is adapted to engage at its outer end a member fixed relative to said cam shaft, said inner end of said sleeve being spaced from 5. said closed end of said cylindrical body. 3. A hydraulic cam follower as defined in Claim 1 or Claim 2 characterised in that said means to feed oil to said chamber comprises a series of radial ports through said casing, sleeve and piston, said piston 5. being hollow and opening at its end adjacent said closed end into said chamber, a one-way valve being positioned in said piston to allow flow of oil into said- chamber, a leakage path being provided for the slow return of said oil. 4. A hydraulic cam follower as defined in Claim 3 characterised in that said piston is maintained spaced from said closed end by a spring, and hydraulic pressure in said chamber whereby said hydraulic cam 5. follower functions as a hydraulic valve lifter, the clearance in said valve train being maintained hydraulically. 5. A hydraulic cam follower as defined in Claim 3 characterised in that said piston contacts the end of said closed cam follower so that the cam follower in its valve closed position acts as a mechanical valve 5. lifter. 6. A hydraulic cam follower substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

Inventors: WRIDE D
Applicants: WRIDE D
Application year: 1980
Main classification: F01L1
IPC codes: F01L1