GB1565482A

GB1565482A - Devices for eliminating slack

Info

Publication number: GB1565482A
Application number: GB8006/78A
Authority: GB
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 1978-03-01
Filing date: 1978-03-01
Publication date: 1980-04-23

Description

(54) DEVICES FOR ELIMINATING SLACK (71) We, AISIN SEIKI KABUSHIKI KAISHA, of 1, Asahi-Machi, 2-chome, Kariya city, Aichi pref., Japan, a company organised and existing under the laws of Japan, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement: - The invention relates to devices for eliminating slack between mutually movable members, and is particularly but not exclusively concerned with the valve trains of internal combustion engines.

A device according to the invention comprises a cylinder closed at a lower end for contacting one such member, a plunger slidable in the cylinder, a reservoir for hydraulic fluid inside the plunger, a pressure chamber inside the cylinder, means for allowing a relatively slow flow of hydraulic fluid from the pressure chamber to the reservoir, a check valve for allowing a relatively rapid flow of hydraulic fluid from the reservoir to the pressure chamber, and an elastic bag for extending into and sealing the hydraulic fluid in the reservoir and having an inside exposed to atmospheric pressure, and the plunger contacting the other mutually movable member.

Such a device can be self-contained with hydraulic fluid sealed inside and no provision for its replenishment from an external source during operation.

The invention is illustrated by way of example in the drawings wherein: Figure 1 is section through a portion of an internal combustion engine having a valve operating train incorporating a device in accordance with the invention; Figure 2 is a section through the device of Figure 1, showing its internal parts in detail; Figure 3 is a cross section through the device on the line III-III of Figure 2; Figure 4 is a section of an elastic bag member of Figure 2; and Figure 5 is similar to Figure 4 but shows a modified bag.

Referring now in detail to Figure 1, an engine cylinder block 10 comprises a working cylinder 11 having a piston 12 slidable therein. Secured to the top of the cylinder block 10 and forming a combustion chamber 13 above the piston 12 is a cylinder head 14 having a cylinder head port 15 whose communication with combustion chamber 13 is controlled by a poppet valve 16 cooperating with a seat 17 in the closed position. The valve 16 has a stem 18 slidably mounted for reciprocation in a guide 19 in the cylinder head 14. Reciprocal movement of the valve 16 is effected by rotation of a cam 20 driven by the engine in timed relation with the movement of the piston 12. A device 21 for eliminating slack according to the invention is in eternal abutment on the cam 20 and is slidably supported for reciprocation in a bore 22 in the cylinder block 10.

Upward movement of the device 21 is transmitted by a push rod 23 to a rocker arm 24 to actuate the valve 16. The rocker arm 24 is mounted on the cylinder head 14 by a post 25 and nut 26, one end is in contact with the valve stem 18 and the other with the push rod 23. The rocker arm 24 is spherically depressed at the bottom to form a bearing surface 27 which slidably embraces the stud 25 and rocks on a bearing member 28 beneath the nut 26. The bearing surface 27 is provided with an aperture 27a through which the post 25 passes to permit the rocking movement to the rocker arm 24. A valve return spring 29 is positioned between a spring retainer 30 fixed on the valve stem 18 and the cylinder head 14, and serves to maintain the valve 16 normally in the closed position as illustrated.

As shown in Figure 2, the device 21 comprises a cylinder 31 and a plunger 32 slidable therein. Between the closed lower end of the cylinder 31 and the bottom of the plunger 32 is a fluid pressure chamber 33 filled with hydraulic fluid. The plunger 32 is hollow, forming a reservoir 34 which is connected with the pressure chamber 33 through a passage 35 on the bottom of the plunger 32. A ball check valve 36 is retained in the pressure chamber 33 by a spring 37 within a cup-shaped cage 38 to close the passage 35 so that, when released, fluid flows relatively rapidly into the pressure chamber 33 from the reservoir 34, but not in the reverse direction. The end of the cage 38 is provided with apertures 38a which establish communication between the interior and the exterior of the cage 38.A plunger return spring 39 biases the plunger 32 up the cylinder 31 and maintains the cage 38 seated against the bottom of the plunger 32. The spring 39 is stronger than the spring 37.

The sides of the plunger 32 are provided with two apertures 40 in communication with an annular groove 41. A clearance C provides for sliding between the outside of the plunger 32 and the inside of the cylinder 31. Through the clearance C leakage of hydraulic fluid from the pressure chamber 33 takes place at a relatively slow rate during each lift stroke of the cam 20 while the check valve 36 is closed against flow through the passage 35. This leakage fluid is collected in the groove 41 and enters the reservoir 34 through the apertures 40.

The plunger 32 is provided with an outer peripheral groove 42 above the groove 41 in which an adjuster seal in the form of a synthetic rubber O-ring 43 is disposed for liquid-tight sealing engagement with the inside of the cylinder 31. Closing the open upper end of the plunger 32 is a push rod seat 44 which receives a convex lower end 45 of the push rod 23. The thrust of the plunger 32 is transmitted to the push rod 23 through the push rod seat 44. An upper limit stop, in the form of a split snap ring 46 engaging an internal groove 47 in the cylinder 31 above the push rod seat 44, is provided for limiting the upward movement of the plunger 32 and for retaining the device 21 in assembly. A lower limit stop, in the form of a cup 48 fixed to the lower side of the cylinder 31, is provided for limiting the downward movement of the plunger 32 and for mounting the plunger return spring 39.

Within the upper portion of the reservoir 34 is mounted an elastic synthetic rubber bag 48 which has a thick sealing flange 50 providing sealing engagement with the inside of the plunger 32. Above the open upper end of the bag 49 is the push rod seat 44. This has a central hole 51 which is in communication with slots 52 in the push rod seat 44 for connection to atmospheric pressure. The inside 53 of the bag 49 or inner surface 54 thereof is normally in communication with atmospheric pressure through the- central hole 51 and the slots 52. An outer surface 55 of the bag 49 is normally in contact with the fluid in the reservoir 34. Since the bag 49 is elastic, the volume of its interior varies in response to variation in the volume of fluid in the reservoir 34. In Figure 5, a modified bag 56 has a flange 57 in which a metal ring 58 is securely fitted to ensure sealing.

In the operation, each lifting movement of the cylinder 31 in response to rotation of the cam 20 is transmitted to the plunger 32 through the hydraulic fluid in the pressure chamber 33. The upward movement of the plunger 32 is transmitted to the push rod 23 through the push rod seat 44.

As a result, the rocker arm 24 rocks on the bearing member 28 and opens the valve 16 against the valve return spring 29. The spring 29 serves both to maintain the valve 16 normally in the closed position and to return the device 21 to its initial position after each lift stroke of the cam 20. As the load on the valve return spring 29 increases, the fluid pressure in the chamber 33 increases, and the check valve 36 is kept in its seated position at the lower end of the passage 35. Any slight leakage of fluid from the pressure chamber 33 enters the reservoir 34 through the clearance C, the annular groove 41 and the apertures 40. The plunger 32 is lowered in the cylinder 31 and thereby shortens the length L between the push rod seat 44 and the lower surface of the cylinder 31.

When the cam 20 is lowered after completion of each lift stroke, the cylinder 31 moves downwards. As a result, the valve return spring 29 pressure on the push rod seat 44 decreases, and the valve 16 closes.

Since the volume of the pressure chamber 33 is increased by the action of the plunger return spring 39, the fluid pressure in the pressure chamber 33 decreases. This decrease releases the check valve 36 from its seat. Sufficient fluid flows to the pressure chamber 33 through the passage 35 to compensate for the leakage through the clearance C to return the length L to its initial value. At the start of the subsequent lift stroke, the fluid pressure in the chamber 33 again increases, causing the check valve 36 to be again seated, and the operating cycle to be repeated.

The length L of the device 21 may be varied also in response to changes in viscosity of the hydraulic fluid which depend upon temperature.

When a clearance develops anywhere in the valve train between the upper end of the valve stem 18 and the cam 20 due to wear or thermal contraction, the plunger return spring 39 compensates by urging the plunger 32 out of the cylinder 31 and so increasing length L of the device.

On the other hand, thermal expansion in the valve train, for instance due to heating of the engine, allows a certain amount of fluid leakage from the pressure chamber 33 into the reservoir 34 through the clearance C, and thereby shortens the length L.

Filling of the device 31 with fluid is accomplished by first assembling the parts which are to be submerged in the fluid so as to prevent the air from entering the cylinder 31. After assembly, no further addition of fluid is required during the life of the device 21. Thus a self-contained device is obtained, which does not depend upon any external source of fluid in operation. The bag 49 is mounted in the upper portion of the reservoir 34, the inside 53 or the inner surface 54 of which is normally in communication with atmospheric pressure, and the outer surface 55 of which is normally in contact with the fluid in the reservoir 34. As a result, changes in the volume of fluid in the reservoir 34 in operation are compensated for by the elasticity of the bag 49.If the leakage of fluid past the seal ring 43 should occur, the bag 49 will compensate due to its elasticity, so that the pressure acting on the seal ring 43 is lowered, thereby reducing the thrust resistance of the plunger 32. Similarly, changes in the volume of the fluid in the device 21 in response to temperature changes are compensated for by the elasticity of bag 49.

WHAT WE CLAIM IS: - 1. A device for eliminating slack between mutually movable members comprising a cylinder closed at a lower end for contacting one such member, a plunger slidable in the cylinder, a reservoir for hydraulic fluid inside the plunger, a pressure chamber inside the cylinder, means for allowing a relatively slow flow of hydraulic fluid from the pressure chamber to the reservoir, a check valve for allowing a relatively rapid flow of hydraulic fluid from the reservoir to the pressure chamber, and an elastic bag for extending into and sealing the hydraulic fluid in the reservoir and having an inside exposed to atmospheric pressure, and the plunger contacting the other mutually movable member.

2. A device according to claim 1 including a push-rod seat in contact with the plunger and the bag, the seat being provided with a hole to expose the inside of the bag to atmospheric pressure.

3. A device according to claim 2 in which the seat is provided with slots to expose the inside of the bag to atmospheric pressure.

4. A device according to any preceding claim in which the bag is provided with a metal ring in a flange for sealing with the inside of the reservoir.

5. A device according to any preceding claim in which the check valve comprises a ball and a spring biassing the ball.

6. A device according to claim 5 including a cage supporting the spring biassing the ball, and a further spring biassing the cage towards the plunger.

7. A device according to claim 5 or claim 6 including a cup in the bottom of the cylinder on which the spring or springs bear.

8. A device according to any preceding claim in which the means for allowing a slow flow of hydraulic fluid comprises a leakage path, an annular groove in the outside circumference of the plunger and an aperture leading to the inside of the plunger.

9. A device for eliminating slack as herein described with reference to Figures 2, 3 and 4 of the drawings.

10. A device for eliminating slack as herein described with reference to Figures 2, 3 and 5 of the drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. upon temperature. When a clearance develops anywhere in the valve train between the upper end of the valve stem 18 and the cam 20 due to wear or thermal contraction, the plunger return spring 39 compensates by urging the plunger 32 out of the cylinder 31 and so increasing length L of the device. On the other hand, thermal expansion in the valve train, for instance due to heating of the engine, allows a certain amount of fluid leakage from the pressure chamber 33 into the reservoir 34 through the clearance C, and thereby shortens the length L. Filling of the device 31 with fluid is accomplished by first assembling the parts which are to be submerged in the fluid so as to prevent the air from entering the cylinder 31. After assembly, no further addition of fluid is required during the life of the device 21. Thus a self-contained device is obtained, which does not depend upon any external source of fluid in operation. The bag 49 is mounted in the upper portion of the reservoir 34, the inside 53 or the inner surface 54 of which is normally in communication with atmospheric pressure, and the outer surface 55 of which is normally in contact with the fluid in the reservoir 34. As a result, changes in the volume of fluid in the reservoir 34 in operation are compensated for by the elasticity of the bag 49.If the leakage of fluid past the seal ring 43 should occur, the bag 49 will compensate due to its elasticity, so that the pressure acting on the seal ring 43 is lowered, thereby reducing the thrust resistance of the plunger 32. Similarly, changes in the volume of the fluid in the device 21 in response to temperature changes are compensated for by the elasticity of bag 49. WHAT WE CLAIM IS: -

1. A device for eliminating slack between mutually movable members comprising a cylinder closed at a lower end for contacting one such member, a plunger slidable in the cylinder, a reservoir for hydraulic fluid inside the plunger, a pressure chamber inside the cylinder, means for allowing a relatively slow flow of hydraulic fluid from the pressure chamber to the reservoir, a check valve for allowing a relatively rapid flow of hydraulic fluid from the reservoir to the pressure chamber, and an elastic bag for extending into and sealing the hydraulic fluid in the reservoir and having an inside exposed to atmospheric pressure, and the plunger contacting the other mutually movable member.