US2704221A

US2704221A - Offset cylinder and piston rod mounting for hydraulic dump bodies

Info

Publication number: US2704221A
Application number: US164761A
Authority: US
Inventors: Jr Joseph M Gwinn
Original assignee: Gar Wood Industries Inc
Current assignee: Gar Wood Industries Inc
Priority date: 1950-05-27
Filing date: 1950-05-27
Publication date: 1955-03-15
Anticipated expiration: 1972-03-15

Description

March 15, 1955 J. M. GwlNN, JR 2,704,221

OFFSET CYLINDER AND PISTON ROD MOUNTING F OR HYDRAULIC DUMP BODIES Filed May 27. 195o 2 sheets-sheet 1 March 15, 1955 J. M. GwlNN, JR 2,704,221

OFFSET CYLINDER AND PIsIoN ROD MOUNTING FOR HYDRAULIC DUMP BODIES Filed May 27, 1950 2 Sheets-Sheet 2 IN V EN TOR.

United States Patent O OFFSET CYLINDER AND PISTON ROD MOUNTING FOR HYDRAULIC DUMP BODIES Joseph M. Gwinn, Jr., Dearborn, Mich., assignor to Gar Wood Industries, Inc., Wayne, Mich., a corporation of Michigan Application May 27, 1950, Serial No. 164,761

7 Claims. (Cl. 298-22) This invention relates to hoists or elevating mechanism of the type that may be employed in dump trucks, and, in particular, refers to hoists that are empowered by pressure lluid such' as oil. One embodiment of the invention is disclosed in a copending application, Serial No. 121,106, filed October 13, 1949, of the present inventor entitled Arm and Tension Link Hoist.

In hoists of the type to which the present invention relates, lifting force is ordinarily furnished by a hydraulic cylinder containing a piston with a rod that passes through a gland to extend outside of the cylinder. The cylinder 1s usually pivoted or otherwise connected to the chassis fr ame or sub-frame and the rod is usually pivoted, either directly or through linkage (such as shown in the aforementioned application), to the body that is to be elevated and lowered, though it is possible to reverse the arrangement. While the present invention is illustrated herein in connection with direct lift hoists wherein the rod is piv oted directly to the bottom of the body and the cylinder to the frame, it can also be used in hoists wherein the rod is connected to the body and the cylinder to the frame through the intermediary of other members.

The invention centers about the locations of the connections between the frame and cylinder and between the rod and body. It resides, principally, in offsetting the axes of these connections, which are usually pivotal, from the axis of the piston rod and the pressure cylinder. The offset or eccentricity is preferably such that the line of force through the rod pivot passes through the axis of the rod at a point of intersection which lies between the piston and the gland when the rod is fully extended.

This construction has several functional advantages of which three will be noted. First, it increases the moment arm of the force applied to the body through the rod. In direct lift hoists, the moment arm is the perpendicular distance from the line through the two pivots to the bodyframe pivot. This distance is increased with the present invention since the offset of the rod-body pivot is upward and the offset of the cylinder frame pivot is downward. The aforementioned copending application shows how the moment arm is increased in arm type hoists. The increase in moment arm enables the use of lower oil pressures or smaller cylinders.

A second advantage lies in the fact that the construction eliminates cocking of the piston and rod axis with respect to the cylinder axis. When the line of force passes through the rod axis at an angle and at a point between the piston and the gland, the side loads on the piston and gland are in the same direction so that the possibility of cooking or binding is eliminated. Thus, the piston rod remains parallel with the axis of the cylinder and good bearing contact is obtained between both the piston and cylinder and the rod and gland to distribute the bearing loads. In conventional constructions, these loads tend to concentrate at the corners of the piston and gland due to the angle assumed by the rod axis relative to the cylinder axis.

A third advantage of the present construction resides in the elimination of piston rod failures due to abnormal conditions and stresses which are difficult to calculate. With ordinary constructions in which the pivot connections of both the cylinder and rod lie on the cylinder and rod axis, or in which only the cylinder base attachment to the frame is offset below the axis, deflections of the assembly due to play or due to elastic deformation or to friction in the pivots increase the bending load on the piston rod and the possible maximum bending stress under 2,704,221 Patented Mar. 15, 1955 conditions of use is almost impossible to estimate. In the construction of the present invention, the load on the rod is oiset or eccentric by design and the maximum bending stress is readily calculated. Play does not increase the bending stress and friction at the rod pivot actually reduces the bending stress due to the oiset load.

It should also be noted that though in most cases the rod will be connected to the body and the cylinder base to the frame, the reverse arrangement, if employed, may also embody the concepts of this invention. ln this case, both the cylinder base connection to the body and the rod connection to the frame will, in accordance with the preferred practice of the invention, be offset and arranged so that the line of force intersects the rod axis between the piston and the gland.

The principles of the invention are more fully described and illustrated in connection with the accompanying drawings, wherein:

Figure l is a side elevation with parts broken away of a dump truck embodying hoist mechanism constructed in accordance with the invention;

Fig. 2 is a plan view, with parts broken away, of the construction shown in Fig. l when the body is elevated so that the pressure cylinder is visible;

Fig. 3 is a vertical axial section through hydraulic elevating mechanism constructed in accordance with the principles of the invention;

Fig. 4 is a vertical axial section through a modified forn of elevating mechanism embodying the invention; an

Fig. 5 is a vertical axial section through conventional hydraulic hoist mechanism and illustrates cocking of the piston and rod in the cylinder and gland.

The dump truck 1 illustrated in Figs. 1 and 2 has a chassis 3 that is supported in a suitable manner upon wheels 5. The body' and its operating mechanism can be mounted directly on the chassis frame, if desired, but in the preferred construction illustrated, the body and its operating mechanism are mounted on an auxiliary subframe 6, and thus form a unit which may be installed on the chassis by bolting the two frames together. The body 7 has longitudinal sills 8 on which are secured downwardly extending legs or brackets 9 adjacent the rear thereof which are journaled by means of pins 11 in suitable bearings 13 in the sub-frame 6. The body 7 is normally supported in a horizontal position, and when dumping is desired. hoist mechanism 15 between the body and the sub-frame 6 is actuated to pivot the body 7 upwardly about the axis of pins 11.

The hoist mechanism 15 that is illustrated in Figs. l to 3 is of the direct actuating type. Thus, it includes a pressure housing or cylinder 17 that is pivoted at its base or forward end 19 to the sub-frame 6. This connection is accomplished through the medium of a pivot plate 21 to which the cylinder 17 is rigidly secured, as best illustrated in Fig. 2. The plate 21 has trunnions 23 that are journaled for pivotal movement on a xed axis in brackets 25 of a suitable type that are rigidly affixed to the inside of the longitudinal side frame members 27 of the subframe 6. The plate 21 may be employed to carry pumps and valves and other hydraulic apparatus generally indicated at 29. The axis of the trunnions 23 is offset below the axis of the cylinder 17 as readily seen in Fig. 1. A piston 31 (Fig. 3) reciprocates within the cylinder 17 as a result of suitable control by apparatus 29 over the oil pressure in the cylinder. The piston 31 has the usual rod 33 connected thereto and extending out the rear end 35 of the cylinder through a suitable gland and bearing device 37. It is understood that the piston and rod may be integral or separate parts joined together, this being immaterial in the practice of the invention.

In accordance with the teachings of this invention, the rod 33 is pivotally connected to the body 7 on a transverse axis which is spaced above the axis of the cylinder and rod. This may be accomplished by means of a fitting 39 that is rigidly secured to the rod end and which has bearing surfaces therein that are adapted to receive a trunnion 41 extending between legs or brackets 43 that are aflixed to the bottom of the body 7. When the body is in lowered position, the piston 31 is adjacent the base 19 of the cylinder 17 as shown in full lines 1n Fig. 3. When rice the body is in elevated position, as the result of the application of oil pressure to the front radial face of the piston 31, the piston 31 will approach the rear end 35 of the cylinder 17 as shown in dotted lines in Fig. 3 (and also in Fig. 4). It will be appreciated that the dotted line positions shown in Fig. 3 is schematic since, in the elevated position, the cylinder and piston and rod unit will be pivoted upwardly from the horizontal position about the fixed trunnion axis 23.

In the direct acting hoist of Figs. l-3, the external forces acting on the cylinder and rod lie along the

straight lines

100 and 102 connecting the centers of front trunnion 23 and rear trunnion 41. Preferably, the eccentricity of the axes of the

trunnions

23 and 41 is such that the line of force intersects the axis of the rod 33 at a point between the piston 31 and the bearing device 37. This relationship preferably exists at all angles of body elevation such as illustrated in Fig. 3 wherein each of the lines of

force

100 and 102, for the mechanism in lowered and elevated positions, respectively, of the body, intersect the axis of the rod 31 at a point between the piston 31 and the gland or bearing device 37.

In the embodiment of Fig. 4, the lines of force do not adhere to the preferred relationship just mentioned, i. e., they do not intersect the rod between the piston 31 and gland device 37 at low angles of body elevation. This is illustrated by the line of force 104 which intersects the rod axis to the rear of the bearing device 37. However, the line of force for the extended rod position at high angles of body elevation (not shown) does pass through the rod axis at a point between the piston 31 and the gland device 37. This relationship of the lines of force to the rod axes is due to the novel mounting of the cvlinder 17 on the frame which is disclosed and claimed in a copending application of the present inventor entitled Floating Cylinder and Link Hoist. Serial No. 252,395, filed October 20, 1951. In this hoist construction, the rear end of the cylinder is pivotally supported at 5 upon the interconnected ends of a forwardly extending link 53 and a rearwardly extending link 55. The rear end of link 55 is pivoted at 57 to a bracket 59 that is fixed on the sub-frame 6 or chassis 3. The forwardlv extending link 53 is pivoted at 60 to a roller or other suitable bearing surface 61 that is provided on the pivot plate 21 at the base of the cvlinder 17. The surface 61 is slidable in a horizontal slot provided bv a bracket 63 afiixed on the sub-frame 6. When the body is fullv elevated. the links 53 and 55 become in substantial rectilinear alignment with each other. lt will thus be recognized that the line of force at the higher angles of elevation approaches the line between the center of pivot 41 and the center of the pivot 60 at the forward end of the link 53, and therefore intersects the rod axis between the piston 31 and the bearing device 37.

It is evident from Fig. l that the unward offset of trunnion 41 from the axis of the rod 33 increases the moment arm of the force applied bv the hvdraulic unit to the body 7. This is the case because the perpendicular distance or moment arm between a line of force passing through the axis of trunnion 41 and the axis of the bodv pivot 11 is greater than the moment arm about the trunnion 11 of a line of force passing through a point on the axis of the rod 33 which corresponds to the axis 41.

Another advantage of the oset or eccentric relationship between bodv and rod pivot 41 is the pre-existing effect that this is known to have on the stress in the rod 33. Maximum bending of the rod occurs at this end as a result of this tvpe of connection. However, in the conventional connection. such as illustrated in Fig. 5 wherein the trunnion 41 lies on the axis of the rod 33, unpredictable manufacturing variations. play between the stationary and moving parts, and friction on the trunnion 41 are likelv to induce eccentricity so that the rod 33 behaves as an unstable column. It is not uncommon for this to result in rod failures due to the fact that the effect of these factors could not be adequately considered in the stress analvsis of the rod. In the present design. this possibility is eliminated by the eccentric construction.

In conventional constructions, it is also common for binding or cocking of the piston and rod. with respect to their respective bearing surfaces in cylinder 17 and bearing and gland device 37. to ocur as indicated in Fig. 5. This causes the axis ofthe rod 33 to assume an angle relative to the axis of the cylinder 17 and concentrates the vertical components of force on the rod on the small areas of contact between the piston and cylinder and the rod and gland device 37. This increases the rate of wear of the unit 15 so that leakage is likely to occur after a relatively short period of usage. In the present preferred construction wherein the line of force intersects the rod axis between the gland 37 and the piston 31, these harmful effects are eliminated. In the regions wherein the line of force has this relationship to the rod axes, its vertical reaction components between the piston 3l and the cylinder 17 and between the rod 33 and the bearing device 37 are both in the same direction. In other words, the transverse force is applied to the rod and piston at a point located between the two points of support rather than outside the two points of support so that the rod and piston are loaded like a simple beam rather than like a cantilever beam. The tendency then is to displace the axis of the rod 33 parallel to the axis of the cylinder. The side reaction loads are therefore distributed over substantially the full possible areas of contact between the piston and the cylinder 17 and the rod and the gland 37. The unit stress is therefore reduced to a minimum as are the friction forces. The magnitude of the side loads on the cylinder and on the gland device 37 is inversely proportional to the distance or overlap between the piston and the rear end 35 of the cylinder. Hence, their harmful effect at low angles of elevation wherein the piston 31 is remote from the end 35 is less than at higher angles of elevation wherein the piston 31 approaches the rear end of the cylinder. Thus, substantial improvement may still be obtained in constructions, such as that of Fig. 4, wherein the desired path of the line of force is not obtained at the lower angles of elevation.

As already indicated, it is preferred that the connections between the cylinder and frame, and between the rod and the body, be both offset on opposite sides of the axis of the unit 15. However, certain benefits of the invention may still be obtained if the base 19 of the cylinder is pivoted to the frame on an axis which lies on its axis as illustrated at 23 in the conventional unit 15' of Fig. 5. It is also evident that the connections between the cylinder and rod and the body and frame could be reversed within the scope of the invention. In this case, the unit 15 of Fig. 3 would be simply rotated 180 degrees about an axis normal to the plan of the drawing so that the base 19 would be pivoted to the body on an axis which is offset upwardly from the axis of the cylinder and the rod 33 pivoted to the sub-frame 6 on an axis which is spaced below the axis of the rod and cylinder.

Other modifications will appear to those in the art, hence, it is not intended to limit the invention to the specific constructions that have been shown herein for the purpose of illustration.

What is claimed is:

l. Hoist apparatus for tilting a body with respect to a frame on which it is mounted, comprising, in combination, a pressure cylinder member having an aperture at one end with a bearing surface in said aperture, a piston in the cylinder, a rod member connected to the piston and extending through the aperture, a movable connection between one of the members and the frame, means for operatively connecting the other member to the body, and an operative connection between the other member and said means, a straight line through said connections intersecting the axis of the members at the higher angles of body elevation at a point between the piston and the bearing surface.

2. Hoist apparatus for tilting a body member with respect to a frame member on which it is mounted, comprising, in combination, a pressure cylinder having au aperture at one end with a bearing surface therein, a piston in the cylinder, a rod connected to the piston and extending through said aperture and supported on said bearing surface, and means whereby said cylinder and rod are operatively connected to different of said memhers on axes that are transverse to the longitudinal axis of the rod and offset from said rod axis on opposite sides thereof in the direction of the respective members to which the cylinder and rod are connected. said means including portions extending from the axes to said cylinder and rod and making fixed angles with respect to the axis of the cylinder and rod, said offset axes being located so that the line of force on the rod intersects the longitudinal rod axis at a point between the bearing surface and the piston whereby the transverse load c omponents on the piston and rod act in the same directlon.

3. Hoist apparatus for tilting a body with respect to a frame on which it is mounted, comprising, in combination, a pressure cylinder pivotally connected to the fram: so as to be located beneath the body, a piston in the cylinder, a rod secured to the piston and extending out of one end of the cylinder, means making a fixed angle with the rod and pivotally connecting the rod to the body, the cylinder and rod pivotal connections being located on opposite sides of the rod axis with the rod pivotal connection spaced between it and the body and located so that the transverse loads on the piston and rod due to the force applied by the rod to the body act in the same direction.

4. A device for separating a pair of relatively movable members comprising a pressure cylinder, a piston in the cylinder, a rod secured to the piston and extending out of one end of the cylinder, said cylinder being pivoted to one member and said rod being pivoted to the other on axes offset on opposite sides of the axis of the rod and spaced fixed distances from said axis, the line of centers of said rod and cylinder pivots intersecting the axis of the cylinder and rod intermediate their ends.

5. Pressure actuated means comprising a hlousing member and a piston and rod member operably disposed within the housing member and extending through one end thereof, means adjacent the other end of housing member for a force transmitting connection, means adjacent the free end of the piston and rod member for a force transmitting connection, said connections beinglaterally offset on opposite sides of the axis of the members and spaced fixed distances from said axis.

6. A pressure actuated body moving device comprising a housing member having a bearing at one end, a piston and rod member operably disposed within the housing and extending through the bearing to the exterior of the housing, connecting means adjacent the end of the housing member opposite the bearing, connecting means adjacent the end of the rod member, both said connecting means extending transversely to their respective members and making xed angles with respect to the axis of the members, said connecting means having a line of centers which intersects the axis of the members at points between the piston and bearing throughout a substantial part of the range of relative movement of the members.

7. Hoist apparatus for tilting a body member with respect to a frame member on which it is mounted comprising, in combination, a pressure cylinder having an aperture at one end, a piston in the cylinder, a rod connected to the piston and extending through said aperture, an arm secured to said rod to extend transversely thereof at a fixed angle, said cylinder being operatively connected to one of the members on a transverse axis spaced transversely from the centerline of the cylinder and rod and on the opposite side of said centerline from said arm, said arm being operatively connected to the other of the members on a transverse axis between the rod axis and the member, said cylinder, piston and rod being located beneath the body member.

References Cited in the file of this patent UNITED STATES PATENTS