WO1986001162A1

WO1986001162A1 - Lever assembly with force modification

Info

Publication number: WO1986001162A1
Application number: PCT/US1984/001703
Authority: WO
Inventors: James G. Starling; Bertwin E. Behrends; Charles E. Holzinger; David S. Ohaver
Original assignee: Caterpillar Tractor Co.
Priority date: 1984-08-13
Filing date: 1984-11-13
Publication date: 1986-02-27
Also published as: FR2568832A1

Abstract

Control valves having a valving element which is movable against an increasing biasing force for controlling fluid flow to and from an actuator are useful in construction vehicles to control a clutch and/or a brake. The increasing biasing force of the springs adds to the operator's fatigue. Some systems use pressure responsive surfaces on the spool to offset the added spring forces but these require a source of pressure that can be varied relative to spool position. The present lever assembly (22) provides an input shaft (78) having a lever (80) secured thereto with a cam surface (84) defined on the lever (80) and a force transmitting mechanism (106) adapted to transmit a variable force to a control spool (44/46) in response to the position of the lever (80). The force transmitting mechanism (106) in combination with a profile (86) on the cam surface (84) effectively reduces the required input force needed to move the spool (44/46) against an increasing biasing force resisting movement of the spool (44/46) thus reducing operator fatigue.

Description

Lever Assembly With Force Modification

Technical Field

This invention relates generally to a lever assembly and more particularly to a lever assembly having a mechanism to effectively change the magnitude of the required force needed by the operator to overcome an increasing biasing force which is resisting lever movement.

Background Art

Lever assemblies are provided on vehicles and other apparatus to control operation of valves, brakes, release mechanisms, etc. These assemblies normally provide a mechanical advantage so that an operator does not have to apply a large amount of force to actuate a valve or. other components. In most situations, the lever or the component being actuated, is moved against an increasing bias of one or more springs. Consequently, the longer the stroke required for the component being actuated, the greater the amount of force needed to overcome the increasing spring force. These added efforts made by the operator over extended periods of time physically fatigues the operator.

Some have used varying pressure levels acting on a differential area to offset the increasing spring force. This requires additional components and pressure responsive surfaces on the valve spool along with a pressure source that either increases or decreases with the valve spool movement. Furthermore, it is impractical to provide an intermediate step or "feel" for the operator to denote a given operational position without adding additional bulky springs.

OMPI _ ^ IPO Λ>j N_ATIO : Spring biased cam arrangements have also been used to detent a spool or lever in various positions but these arrangements require additional elements or springs to hold the valve or lever in the operational condition. Consequently, additional forces are required to move the lever into or out of the detented position.

Lever arrangements having a cam located thereon have been used to allow actuation -of one valve prior to actuation of a second valve. Howeyer, these arrangements use springs that continually add additional resistance as the lever is being moved. Thus, the increasing spring force of each valve becomes additive as both valves are being actuated. The use of springs with a light force and a low spring rate are not practical because the valve needs a sufficient biasing force to maintain it in a neutral position and the operator needs a "bump" or "feel" to indicate that he has completed modulation of the one valve and ready to start modulation of the other valve with further movement of the lever. Consequently, a light rate spring would not provide the noted requirements. Furthermore, the spring must have sufficient force to move the valving element back to a neutral or initial position without concern of the valve element "sticking" .

The present invention is directed to overcoming one or more of the problems as set forth above.

Disclosure of the Invention

In one aspect of the present invention, a lever assembly has an input shaft and a lever secured to the input shaft being adapted to move a valving element against an increasing biasing force in response

OMPI s& IPO Λ> to an input force. A cam surface is formed on the lever and defines a profile having a ramp portion. A means is provided for transmitting a force to the cam surface so that the magnitude of the required input force needed to move the lever against the increasing biasing force is controllably varied in response to the position of the lever.

The present invention provides a cam-lever arrangement having a biasing force subjected to the cam surface so that a resultant force can be passed through the lever depending on lever position to aid the input force. This arrangement further allows a "bump" or a "feel" to be placed anywhere in the total lever travel to indicate to the operator that a certain functional position has been reached. Furthermore, this arrangement reduces the_ amount of input effort needed so that operator fatigue is reduced.

Brief Description of the Drawings ^' . Fig. 1 is a partial schematic and diagrammatic representation of a lever assembly associated with a steering clutch and brake valve and incorporating an embodiment of the present invention;

Fig. 2 is an enlarged .sectional view of the lever assembly shown in Fig. 1;

Fig. 3 is an enlarged sectional view of a portion of the lever assembly shown in Fig. 2; and

Fig. 4 is a graph illustrating the relationship between the pressure levels in a clutch and brake and the linear travel of the valving elements plus the relationship between the input torque and travel of the valving elements. Best Mode for Carrying Out the Invention

Referring now to the drawings, and more particularly to Fig. 1, a clutch and brake valve 10 is shown for use in a control system 12 of a vehicle (not shown) having a pressure-applied, spring-released clutch 14 and a spring-applied, pressure-released brake 16. The control system 12 further includes a pump 18, a reservoir 20 and a lever assembly 22.

^■ The clutch and brake valve 10 includes a housing 2.4 having first and second bores 26,28 defined therein. First, second and third chambers 30,32,34 respectively surrounds the first bore 26 at axially spaced locations. Since the second bore 28 is substantially the same as the first bore 26, prime numbers are used to identify corresponding chambers 30',32',34'. An inlet port 36 is defined in the housing 24 and intersects the first chamber 30,30' of each of the fi-rst and second bores 26,28. A drain port 38 is defined in the housing 24 and intersects the third chamber 34,34' of each of the first and second bores 26,28. A first work port 40 is defined in the housing 24 and intersects the second chamber 32 of the first bore 26. A second work port 42 is defined in the housing 24 and intersects the second chamber 32' of the second bore 28.

First and second valving elements, such as first and second spools 44,46, are respectively slideably disposed in the first and second bores 26,28. The first spool 44 is movable between first, second and third positions while the second spool 46 is movable between first and second positions. First and second springs 48,50 respectively bias the respective first and second spools 44,46 to their first position as shown. As is well known in the art and clearly shown in Fig. 1, each of the spools 44,46 controls the fluid flow to and from the respective clutch 14 and brake 16.

A conduit 52 connects the pump 18 with the inlet port 36 and a conduit 53 connects the drain port 38 with the reservoir 20. A relief valve 54 is connected to the conduit 52 and, as is well known in the art, adapted to control the maximum pressure level of the fluid from the pump 18. The pressure-applied, spring-released clutch

14 includes an actuator 56 having a pressure chamber 58, a spring chamber 60 and a spring 62 located in the spring chamber 60. A conduit 64 connects the pressure chamber 58 with the first work port 40 of the valve 10. The spring-applied, pressure-released brake 16 includes an actuator 66 having a pressure chamber 68, a spring chamber 70 and a spring 72 located in the spring chamber 70. A conduit 74 connects the pressure chamber 68 of the brake actuator 66 with the second work port 42 of the vaive 10. ^* .

The lever assembly 22 includes an input shaft 78 mounted in a housing 79 and having a lever 80 extending therefrom. First and second rollers 81,82 are rotatably secured to the lever 80 and adapted to contact the respective first and second spools 44,46 on the ends opposite the respective first and second springs 48,50. As is more clearly shown in Fig. 2, a cam surface 84 is located on the lever 80. The cam surface defines a profile 86 having a shoulder 88, sequentially followed by a recess 90, a first step portion 92, a first ramp portion 94, a second step portion 96 and a second ramp portion 98.

A means 106 is provided in the lever assembly 22 for transmitting a force to the cam surface 84 so that the magnitude of an input force is controllably varied in response to the position of the lever 80. The force transmitting means 106 includes a spring biasing mechanism 108 secured to the housing 79 and in contact with the cam surface 84. The spring biasing mechanism 108 includes a spring element, such as a leaf spring 110, connected at one end to the housing 79 by any suitable fastening means, such as a bolt 112. As shown in Fig. 3, first and second bearing members 114,116 are -secured at a spaced apart relationship to the other end of the leaf spring 110. A cylindrical member 118 is rotatably disposed in the first and second bearing members 114,116. Snap rings 120 located on each end of the cylindrical member 118 retains the cylindrical member 118 in the bearing members 114,116 in a well known manner.

In the graph, as shown in Fig. 4, a phantom line 126 represents the relationship of the pressure in the clutch 14^' relative to movement of the first spool 44 between its first, second and third positions. A solid line 128 represents the relationship of the pressure in the brake 16 relative to movement of the second spool 46 between its first and second positions. A dashed line 130 represents the relationship of the input torque needed on the input shaft 78 relative to movement of the first and second spools 44,46.

It should be recognized that the lever assembly 22 could be mounted in the housing 24 as opposed to the separate housing 79. Even though the best mode uses a lever 80 that actuates two valve spools 44,46, it is noted that the subject invention is also usable in a system having only one valve spool. Furthermore, the subject lever assembly would be applicable to any lever arrangements that is being moved against an increasing biasing force. Industrial Applicability

During normal operation of a vehicle using pressure-applied, spring-released clutches and spring-applied, pressure-released brakes for control of the vehicle, pressurized fluid from the pump 18 is directed through the clutch and brake valve 10 to the pressure chambers 58,68 of the respective clutch 14 and brake 16. Pressurized fluid in the pressure chamber 58 applies the clutch 14 while pressurized fluid in the pressure chamber 68 releases the brake. To release the clutch, an input force is applied to rotate the input shaft 78. The input force is transferred through the lever 80 to the end of the spool 44 thus moving the spool 44 from the first position, at which the first work port 40 communicates with the inlet port 36 and is blocked from the drain port 38, to the second position, at which the first work port 40 is blocked from the inlet port 36 and open to the drain port 38. Further rotation of the input shaft 78 moves the first spool 44 from the second position to the third position, at which the first work port 40 remains blocked from the inlet port 36 and open to the drain port 38. Between the first and second positions of the first spool 44, the fluid flow to the clutch 14 is variably controlled. By venting the pressurized fluid from the pressure chamber 58 of the clutch 14, the force of the spring 62 releases the clutch 14.

As is more clearly shown in Fig. 1, rotation of the input shaft 78 to move the first spool 44 between its first and second positions has no effect' on the second spool 46 since the second roller 82 does not initially contact the end of the second spool 46. Once the input shaft 78 is rotated far enough to move the first spool 44 to its second position, the roller 82 contacts the end of the second spool 46. Further rotation of the input shaft 78 moves the second spool 46 from its first position, at which the second port 42 communicates with the inlet port 36 and is blocked from the drain port 38, to the second position, at which the work port 42 is blocked from the inlet port 36 and open to the drain port 38.

Initial rotation of the input shaft 78 is resisted only by the first spring 48 as the first spool 44 moves between its first and second positions. Further rotation of the input shaft 78 is resisted by the combined forces of both springs 48,50 as the first spool 44 moves between its second and third positions and the second spool 46 moves between its first and second positions. The profile 86 of the cam surface 84 in conjunction with the force transmitting means 106 provides the operator with a "feel" which indicates the end of a particular mode of operation or the beginning of another mode of operation. More particularly, when the cylindrical member 118 is located in the recess 90, both of the spools 44,46 are in their respective first positions. Consequently, the clutch 14 is engaged and the brake 16 is released. Additional input torque or operator effort is needed to rotate the lever 80 since the cylindrical member 118 must roll up the step portion 92 against the bias of the leaf spring 110. This added effort is an indication to the operator that he is about to initiate clutch disengagement.

As the cylindrical member 118 rolls along the first ramp portion 94, due to rotation of the lever, the increasing resisting force of the spring.48 requires additional effort from the operator. The profile of the first ramp portion 94 has a negative slope which results in a force vector that generates a force on the spool 44 that effectively reduces the

O PI required input force needed to move the spool 44 against the bias of the spring 48. This vector force reduces the effort that the operator has to apply to the input shaft 78. It is recognized that making the ramp portion 94 more negative further reduces the operator's effort. Conversely, by making the ramp portion 94 with a neutral or positive slope, the operator's effort is increased.

Once the cylindrical member 118 contacts the second step portion 96, additional force is needed on the lever 80 to force the cylindrical member 118 up the second step portion 96. This "bump" is an indication to the operator that the first spool 44 is at its second position and the clutch 14 is fully released. Furthermore, it indicates to the operator that with further rotation of the input shaft 78, the brake 16 will be progressively applied.

Upon adding the extra effort to the input shaft 78, the cylindrical member 118 rolls up the second step portion 96. This rotation of the input shaft 78 initiates movement of the second spool 46 from its first position towards its second position to controllably vent fluid from the pressure chamber 68 and apply the brake 16. As the cylindrical member 118 rolls on the negative slope of the second ramp portion 98 due to rotation of the lever 80, a vector force acts in combination with the input force through the lever 80 to move the spools 44,46 against the combined increasing bias of the springs 48,50. This vector force effectively reduces the operator's effort as indicated above with respect to the first ramp portion 94. Furthermore, the slope of this ramp portion 98 may also be varied to either increase or decrease the operator's effort. The brake 16 is fully applied once the spools 44,46 reaches their end of travel. ϋpon release of the input force, the lever 80 is rotated back to the initial position in response to the bias of the springs 48,50 moving the first and second spools 44,46 back to their first positions. The shoulder 88 provides a positive stop so that rotation of the lever 80 is stopped and the cylindrical member 118 stops in the recess 90.

The graph in Fig. 4 illustrates one example of a system using the present invention. In this example, the relief valve 54 is set to control the maximum pressure of the fluid from the pump 18 at 2800 kPa (406 psi). The maximum spool travel is 20 mm (.787 in.) and the input effort to the input shaft 78 is illustrated as input torque on the input shaft 78. The line 126 illustrates the pressure modulation of the pressure in the clutch 14. As shown, once the spool 44 is moved approximately 8 mm, the clutch 14 is fully released. The line 130, which ^• represents the input torque on the input shaft 78, illustrates on the left side the effort needed to cause the cylindrical member 118 to be moved from the recess 90. At approximately 8 mm of spool travel, the line 130 illustrates the effort or "bump" needed to move the cylindrical member 118 relative to the second step portion 96. -The line 128 illustrates the pressure modulation of the pressure in the brake 16. As noted previously, the two slopes in the line 130 can be varied by changing the profile of the respective first and second ramp portions 94,98. The height of the steps in the line 130 can be changed by changing the height of the respective first and second steps 92,94 or by changing the biasing force of the leaf spring 110. The lever assembly as set forth above provides an arrangement that eliminates extra "bump" springs which adds extra cost and requires additional space for

CMPI mounting the extra springs. Operator fatigue is reduced by providing a force which helps the operator's input effort depending on the position of the lever 80 on the input shaft 78.

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.

Claims

1. In a lever assembly (22) having an input shaft (78) and a lever (80) secured to the input shaft (78) adapted to move a valving element (44/46) against an increasing biasing force in response to an input force, the improvement comprising: a cam surface (84) formed on said lever (80), said cam surface (84) defining a profile (86) having a ramp portion (94); and means (106) for transmitting a force to the cam surface (84) so that the magnitude of the required input force needed to move the lever against the increasing biasing force is controllably varied in response to the position of said lever (80).

2. The lever assembly (22), as set forth in claim 1, including a housing (78) and wherein said force transmitting means (106) includes a spring biasing mechanism (1-08) secured to said housing (79) and in contact with said cam surface (84).

3. The lever assembly (22), as set forth in claim 2, wherein said spring biasing mechanism (108) includes a cylindrical member (118) in contact with said cam surface (84).

4. The lever assembly (22), as set forth in claim 3, wherein said spring biasing mechanism (108) includes a spring element (110) connected to said housing (79) and being adapted to apply a force to the cam surface (84) .

OMPI

5. The lever assembly (22), as set forth in claim 4, wherein said spring element (110) is a leaf spring and said cylindrical member (118) is secured to one end of said leaf spring (110) and the other end of the leaf spring (110) is secured to said housing (79).

6. The lever assembly (22), as set forth in claim 5, including bearing members (114,116) secured to the one end ^'of the leaf spring (110) and wherein said cylindrical member (118) is rotatably mounted in said bearing members (114,116).

7. The lever assembly (22), as set forth in claim 1, wherein said profile (86) of the cam surface (84) includes a recess (90) sequentially followed by a step portion (92) and said ramp portion (94).

8. The lever assembly (22), as set forth in claim 7, wherein said profile (86) of the cam surface (84) further includes a second step portion (96) adjacent said ramp portion (94) and a second ramp portion (98) adjacent the second step portion (96).

9. The lever assembly (22), as set forth in claim 8, wherein said first ramp portion (94) defines a negative slope relative to the force transmitting means (106), said negative slope being adapted to generate a force that is additive to said input force to effectively reduce the required input force needed to move the lever against the increasing biasing force in response to the position of the lever (80).

O PI

10. The lever assembly (22), as set forth in claim 9, wherein said second step portion (96) defines a slope adapted to require an increase in said input force to rotate said lever (80) relative to said force transmitting means (106), and said second ramp portion (98) defines a negative slope relative to the force transmitting means (106), said negative slope being adapted to generate a force that is additive to said input force to effectively reduce the required input force needed to move the lever (80) against the increasing biasing force in response to the position of the lever (80) .

11. The lever assembly (22), as set forth in claim 10, including a housing (79) and wherein said force transmitting means (106) includes a spring mechanism (108) secured to the housing (79) and having a cylindrical member (118) rotatably mounted thereon and in contact with said cam surface (84).

12. A lever assembly (22) for a clutch and brake valve (10), comprising: a housing (24) ; first and second valving elements (44,46) slideably disposed in said housing (24); a single input shaft (78) mounted on the housing (24) ; a lever (80) secured to the single input shaft (78) and being adapted to contact each of the valving elements (44,46) and to move the valving elements

(44,46) from a first position towards.a second position against an increasing spring force in response to an input force being applied to the input shaft (78); a cam surface (84) formed on said lever (80), said cam surface (84) defining a profile (86) having a recess (90), a first step portion (92) adjacent the recess (90), a first ramp portion (94) adjacent the step portion (92), a second step portion (96) adjacent the first ramp portion (94), and a second ramp portion (98) adjacent the second step portion (96); and means (106) for transmitting a force to the cam surface (84) so that the magnitude of the required input force needed to move the lever (80) against the increasing biasing force is controllably varied in response to the position of said lever (80).

13. The lever assembly (22), as set forth in claim 12, wherein said force transmitting means (106) includes a spring biaisng mechanism (108) secured to the housing (24) and having a cylindrical member (118) rotatably mounted thereon and in contact with said cam surface (84), said spring biasing mechanism (108) being adapted to apply a force to the cam surface (84).

14. The lever assembly (22), as set forth in claim 13, wherein each of the first and second ramp portions (94,98) define a negative slope relative to the force transmitting means (106), each of said negative slopes being adapted to generate a force that is additive to said input force to effectively reduce the required input force needed to move the lever against the increasing biasing force in response to the position of the lever (80).

O PI

15. The lever assembly (22), as set forth in claim 14, wherein said cylindrical member (118) is located in said recess (90) when said first and second valving elements (44,46) are in the first position and in abutting relationship with said second step portion (96) when the first valving element (44) is at the second position and said second valving element (46) remains in the first position.

16. The lever assembly (22), as set forth in claim 15, wherein movement of the lever (80) relative to the cylindrical member (118) on the second ramp portion (98) of the cam surface (84) moves the second valving element (46) towards the second position while simultaneously moving the first valving element (44) towards a third position.

17. The lever assembly (22), as set forth in claim 16, including a fluid operated clutch (14) selectively controlled by the first valving element (44) and a fluid operated brake (16) selectively controlled by the second valving element (46).

18. The lever assembly (22), as set forth in claim 17, wherein movement of the first valving element

(44) from the first position to the second position releases the fluid operated clutch (14) while movement between the second and third positions maintains the clutch (14) in the released condition.

19. The lever assembly (22), as set forth in claim 18, wherein movement of the second valving element (46) from the first position to the second position progressively applies the fluid operated brake (16).

OMPI < WIPO ^