GB2095357A

GB2095357A - Slack adjusters

Info

Publication number: GB2095357A
Application number: GB8108577A
Authority: GB
Original assignee: Aisin Seiki Co Ltd
Current assignee: Aisin Corp
Priority date: 1981-03-19
Filing date: 1981-03-19
Publication date: 1982-09-29
Also published as: GB2095357B

Abstract

A hydraulic tappet comprises a plunger 13 slidable in a housing 12, and a plunger 16 in the plunger 13. There is a hydraulic reservoir 19 in the plunger 13, and a pressure chamber 21 in the housing 12. A one-way valve 15 allows flow from the reservoir 19 to the pressure chamber 21, and fluid return occurs through a clearance 29 between the housing 12 and the plunger 13, and a passage 30. Springs 22 and 37 respectively bias the first plunger 13 out of and the second plunger 16 into the housing 12. <IMAGE>

Description

SPECIFICATION Slack adjusters The invention relates to hydraulic slack adjusters for valve trains of internal combustion engines in which fluid is sealed in the assembly with no provision for replenishment from an external source.

In the valve trains of internal combustion engines, predetermined valve clearances are generally provided to compensate for thermal expansion of parts.

Slack may be generated in operation, and so hydraulic slack adjusters are used for taking up the clearances and preventing any possible stabilization of the opening and closing of the engine intake or exhaust valves.

The invention provides a slack adjuster comprises ing a housing, a first plunger slidable in the housing, a second plunger slidable in the first plunger, a hydraulic reservoir inside the first plunger, a hydraulic pressure chamber in the housing, a one-way valve allowing flow from the reservoir to the pressure chamber, a return passage allowing flow from the pressure chamber to the reservoir, a first spring biassing the first plunger in a direction out of the housing, and a second spring biassing the second plunger in a direction into the housing.

The second plunger may have an opening therein with an adjustable closure. The return passage preferably comprises a leakage clearance between the housing and the first plunger. Such a slack adjuster can be self-contained, simple in construction, inexpensive to manufacture, and easy to assemble and fill with hydraulic fluid.

Figure lisa longitudinal section through a slack adjuster according to the invention; Figure 2 is a partial section through a modification of the slack adjuster of Figure 1; and Figure 3 is a longitudinal section through a slack adjuster similar to that of Figure 1 but modified for use in an overhead valve internal combustion engine.

Aslack adjuster 10 in Figure 1 comprises a cylindrical housing 12, an upper end of which is open for the reception of a fulcrum member 14. A first plunger 13 is slidably disposed in the cylindrical housing 12, and is provided with an annular seal ring 38 having a K-shaped cross-section in contact with an inner wall of the housing 12. A second plunger 16 made of aluminium is slidable in and divides the interior of the first plunger 13 into a chamber 18 which is open to the atmosphere and a reservoir 19 for hydraulic fluid. There is a pressure chamber 21 between a bottom wall 20 of the first plunger 13 and a bottom wall 11 of the housing 12.

The first plunger 13 is continuously biassed in a direction out of the housing 12, upward as viewed in Figure 1, by a spring 22 between the bottom wall 11 of the housing 12 and a spring retainer 23 secured to the bottom wall 20 of the first plunger 13. Upward movement of plunger 13 is limited by engagement with an annular extension 24 on the fulcrum member 14, and the upward movement of the fulcrum member 14 is restricted by an annular cap 25 secured to the open end of the housing 12. The first plunger 13 is movable downward with the fulcrum member 14. The downward movement of the plunger 13 is limited by an annular shoulder 26 on the inner walk ofthe housing 12.

A fluid passage 28 extends through the bottom wall 20 of the plunger 13 and is controlled by a ball valve 15 normally biassed into engagement with a conical valve seat 20a by a spring 27 between the retainer 23 and the ball valve 15. When the pressure chamber 21 and the reservoir chamber 19 are filled with a working fluid such as siliconeoil, communication between the reservoir 19 and the pressure chamber 21 through the passage 28 is normally interrupted by the ball valve 15. Upon downward movement of the first plunger 13, oil is forced upward through a clearance 29 between the inner wall of the housing 12 and the outer wall of the plunger 13, and passes into the reservoir 19 through passages 30. Upon upward movement of the plunger 13, the fluid within the reservoir chamber 19 passes through the passage 28 into the pressure chamber 21 past the ball valve 15.

The second plunger 16 is sealed in the first plunger 13 by an annular seal ring 31 in an annular groove in the plunger 16. The seal ring 31 has a K-shaped cross-section and is disposed in sliding engagement with an inner wall of the first plunger 13. The second plunger 16 is provided with a stepped bore 32 and a stepped screw35 is threaded into a larger diameter portion thereof. The screw 35 is provided with a bleed passage 34, and has a conical valve portion 33 on an end of a smaller diameter portion which is adapted to engage an annular valve seat 36 formed about the upper end of the smaller diameter portion of the bore 32. When the valve portion 33 of the screw 35 is out of contact with the seat, oil may pass from the reservoir 19 into the atmospheric chamber 18.When valve portion 33 is seated against the annular seat 36, all communication between the reservoir 19 and the atmospheric chamber 18 is interrupted.

During assembly of the slack adjuster, the reservoir 19 and the pressure chamber 21 are filled with oil A up to the upper end of the first plunger 13. The second plunger 16 is then placed on the upper surface of the oil A, and the screw 35 is backed off from the seat 36 to allow communication between the reservoir 19 and the atmospheric chamber 18 through the bore 32 and the passage 34. Then the second plunger 16 is pressed into the first plunger 13 to a predetermined position. Since the volume of the reservoir 19 is decreased by the downward insertion of the second plunger 16, extra oil is forced into the atmospheric chamber 18 through the bore 32 and the passage 34. When the plunger 16 is in the desired position, the valve portion 33 is screwed into contact with the valve seat 36.The spring 37 is located in the atmospheric chamber 18, and the fulcrum 14 is inserted into the housing 12. The annular cap 25 is secured on the end of housing 12 to prevent removal of the fulcrum 14.

In operation, one end of the fulcrum member 14 engages one end of a rocker arm (not shown) and the other end of the rocker arm engages a valve stem (not shown) of an internal combustion engine. The rocker arm is swingable in response to rotation of a cam shaft which is rotated by the crank shaft of the engine. Accordingly, the fulcrum member 14 and the first plunger 13 are reciprocable relative to the hous ing 12 for taking up the slack or operating clearance in the valve train. When the fulcrum 14 and the first plunger 13 are moved downward, the pressure in the pressure chamber 21 increases to assistthe spring 27 in maintaining the valve 15 closed. Pressurized oil in the chamber 21 is therefore forced upward through the clearance 29 between the plunger 13 and the housing 12.The seal ring 38 prcents fluid escape from the housing 12 but allows flow into the reservoir 19 through the passages 30. As a result of the increase of fluid in the reservoir 19, the second plunger 16 is forced upward against the bias of the spring 37.

When the cam shaft is further rotated, the fulcrum member 14 becomes free to move upward, and the spring 22 moves the first plunger 13 and the fulcrum 14 upward. The upward movement of the plunger 13 reduces the pressure in the chamber 21, and allows the ball valve 15 to be moved to the open position.

Fluid in the reservoir 19 returns to the pressure chamber 21 through the passage 28 under the influence of the spring-biased plunger 16. As a result of the reciprocal movement of the plunger 13 relative to the housing 12, the operating clearance in a valve train is kept to zero.

In Figure 2, the construction of the slack adjuster is the same as that shown in Figure 1 with the exception of a second plunger 116. The second plunger 116 differs from the second plunger 16 in Figure 1 in that it does not have a passage between the atmospheric chamber 18 and the reservoir 19. The plunger 116 is slidably disposed within the first plunger 13 and provided with an annular seal 31 as in Figure 1.

During assembly, the first plunger 13 is inserted into the housing until the bottom end of the plunger 13 rests on the shoulder 26 of the housing 12. The pressure chamber 21 and reservoir 19 are then filled with oil while keeping the plunger 13 in contact with the shoulder 26. The second plunger 116 is placed in the first plunger 13 and moved to a predetermined position dictated by the force of the spring 22 as it moves the plunger 13 upward. The volume in the pressure chamber 21 is between the uppermost and lowermost positions of the first plunger 13. The level of oil in the reservoir chamber 19 is related to the volume in the pressure chamber 21.

In Figure 3, a slack adjuster 200 suitable for an overhead valve engine has the bottom 11 of the housing 12 engageable with a cam shaft (not shown) rotated by a crank shaft (not shown). A cup member 201 having air passages 202 is disposed on the upper end of the first plunger 13. The cup member 201 engages the lower end of a pushrod (not shown) which is in contact with a rocker arm (not shown).

When the housing 12 is moved upward in response to the rotation of the cam shaft, the load on the cup member 201 increases and raises the pressure in the pressure chamber 21. Thus, the one-way valve 15 is kept in the closed position, and oil flows from the pressure chamber 21 to the reservoir 19 through the clearance 29 and the passages 30. Accordingly, the first plunger 13 is moved downward relative to the housing 12 by a predetermined distance. When the cam shaft is further rotated, the housing 12 is moved downward to decrease the load on the cup member and the first plunger 13 is moved upward relative to ths housing 12 by the force of the spring 22. The valve 15 is opened and the oil in reservoir 19 flows back into the pressure chamber 21 through the passage 28. The operation of the slack adjuster shown in Figure 3 is essentially the same as that shown in Figure 1.

Claims

1. A slack adjuster comprising a housing, a first plunger slidable in the housing, a second plunger slidable in the first plunger, a hydraulic reservoir inside the first plunger, a hydraulic pressure chamber in the housing, a one-way valve allowing flow from the reservoir to the pressure chamber, a return passage allowing flow from the pressure chamber to the reservoir, a first spring biassing the first plunger in a direction out of the housing, and a second spring biassing the second plunger in a direction into the housing.

2. A slack adjuster according to claim 1 in which the second plunger has an opening therein with an adjustable closure.

3. A slack adjuster according to claim 1 or claim 2 including a stop for limiting movement of the first plunger into the housing.

4. A slack adjuster according to any preceding claim in which the return passage comprises a leakage clearance between the housing and the first plunger.

5. A slack adjuster as herein described with reference to Figure 1, or Figure 1 as modified by Figure 2, or Figure 3 of the drawings.