An improved vibration dampening suspension device for the cab of a truck vehicle

Abstract: An improved vibration dampening and shock absorber suspension device for the cab of a truck vehicle is set forth having a base member adapted for mounting to the truck frame and an impact plate adapted for attachment to the truck cab where the impact plate has a lateral dimension which is less than the lateral distance between the side beams of the truck frame. Interposed between the base member and the impact plate is a pair of air springs which are maintained at a constant height by a height control valve. A pair of hydraulic shock absorbers are pivotally connected to both the impact plate and base member where the central axis of the shock absorbers form the opposite sides of a trapezoid.

Description: This invention relates to a suspension device for the cab of a truck vehicle for supporting the cab on the truck chassis to dampen vibration and shock experienced by the truck vehicle thereby enhancing driver comfort and reducing driver fatigue. To provide comfort for truck drivers and reduce driving fatigue experienced by operators of truck vehicles, it is desirable to suspend the operator's cab by utilizing a vibration dampening and shock absorption device intermediate the truck chassis and cab which reduces the shock, vibration and consequent pounding the driver experiences during the operation of the vehicle. Additionally, the continued application of vibration and shock forces to the cab results in structural damage which ultimately results in increased maintenance costs. The load carried by a truck vehicle is supported by the frame which is resiliently carried by suspension springs and supported by the truck wheels. Suspension springs have a high rate of stiffness which makes the ride more jarring on the operator of the vehicle and to dampen the vibration and shock transmitted to the cab, suspension systems have been employed utilizing conventional hydraulic automotive shock absorbers and air springs to dampen jounce and rebound movement of the cab with respect to the truck frame. Typically in the prior art, the air springs and shock absorbers were connected directly to the longitudinal side beam members of the truck frame such that the forces transmitted to the cab were at points remotely located from the cab centre of gravity and consequently resulted in substantial rolling movements and cab sway. The present invention concerns a vibration dampening suspension device for the cab of a truck vehicle of the kind having at least one air spring, a height control valve associated with the or each air spring for maintaining the or each air spring at a pre-selected height, and a pair of hydraulic shock absorbers, each shock absorber having a central axis and a first and second end. Such a vibration dampening suspension device is known from US-A-3944017. More particularly, in the vibration dampening suspension device of the aforesaid US-A-3944017, air springs are used which have a relatively low spring rate to isolate the jounce and vibration of the truck frame from the cab. Shock absorbers are also utilized which contain internal jounce and rebound bumpers that limit the extent of vertical movement of the cab with respect to the truck frame. The air springs are shown to be oppositely mounted immediately above the truck frame and located in direct vertical alignment with the frame. The shock absorbers are also oppositely mounted but with central axis extending in an outward direction from the vertical axis of the frame member where the central axes of the shock absorbers are inclined to the displacement axes of the air springs. Thus, in US-A-3944017, and similarly in the aforesaid art, the forces transmitted to the cab by the air springs and shock absorbers are at a substantial distance from the centre of gravity of the cab thereby causing increased shock, lateral sway and rolling. Consequently, the driver experiences greater discomfort and the cab itself sustains higher force load levels which ultimately results in structural failure. The invention seeks to provide a vibration dampening suspension of the above-mentioned kind which substantially reduces vibration and shock forces experienced by the truck driver. In accordance with the invention as claimed, this object is accomplished in a vibration dampening suspension of the above-mentioned kind by: (a) a base member having a reference axis and adapted for mounting to a frame of the truck vehicle; (b) the shock absorbers being oppositely and laterally spaced from the reference axis, the first end of each shock absorber being pivotally mounted to the base member such that the central axes of the shock absorbers are inclined toward the reference axis so as to form the opposite sides of a trapezoid; (c) an impact plate adapted for attachment to the cab and having a lateral dimension which is less than the lateral distance between side beams of the truck frame, the impact plate being axially spaced from and substantially parallel to the base member for transmitting dampened vibration and shock forces to the cab, the second ends of the shock absorbers being pivotally mounted to the impact plate such that the lateral distance between the second ends is less than the lateral distance between the first ends; and (d) the or each air spring having a displacement axis located intermediate the base member and the impact plate, the or each spring being mounted to the base member and to the impact plate with its displacement axis substantially parallel to the reference axis. A vibration dampening suspension constructed in accordance with the invention has the advantages of being inexpensive to manufacture, reducing the maintenance required on the cab by substantially reducing the shock, vibration and pounding associated with the operation of a truck, and substantially reducing the physical problems associated with the vibration and shock forces a driver ordinarily experiences when operating a truck. The simple construction of the vibration dampening suspension permits adaptation to different types of truck vehicles and cab configurations. In one embodiment of the invention, a pair of air springs, identified by the trade mark "SUPER-CUSHION", Part Number IS5, manufactured by Goodyear Tire and Rubber Company, are located intermediate the base member and impact plate where the air springs have a displacement axis which is substantially parallel to the reference axis of the base plate. A zero delay height control valve is mounted to the base member for maintaining the air springs at a pre-selected height, preferably 6.5 inches. The shock absorbers and air springs are located substantially inboard of the truck frame and are symmetrically disposed about the reference axis of the base member. Although not normally in contact with the impact plate, a pair of rubber snubbers are symmetrically located on the base plate which limit the vertical displacement of the impact plate if failure occurs in the air spring system or during excessive compressive loading. Thus the moments of the shock and vibration forces transmitted through the impact plate about the centre of gravity of the truck cab are substantially reduced which results in greater driver comfort and less structural stress on the cab. In another embodiment of the invention, one air spring is utilized where the displacement axis of the air spring substantially coincides with the reference axis of the base member. In order that the invention may be well understood the aforesaid embodiments thereof, which are given by way of example of the invention, will now be described with reference to the accompanying drawings, in which: Fig. 1 is a side illustration of a truck vehicle and suspended cab embodying a vibration dampening suspension according to the present invention; Fig. 2 is a rear view of the same vibration dampening suspension with the truck chassis shown in cross-section; and Fig. 3 is an expanded side view of the same vibration dampening suspension as depicted in Fig. 1. Referring first to FIG. 1, a truck cab 1 is shown mounted to a truck frame 2. There are numerous methods for mounting the forward portion of a truck cab to the frame. For the purpose of illustrating the present invention, the forward portion of the cab 1 is connected to the frame 2 by interposing between the cab and the frame an elastomeric or rubber donut 3 which serves to dampen the vibration and shock transmitted to the cab. The connection of the forward portion of the truck cab 1 to the truck frame 2 utilizes standard fastening methods which are common in the trucking industry. The rear of cab 1 is suspended from the truck frame 2 by an improved suspension system which is more particularly described in FIG. 2. As shown in FIG. 2, which is a rear view of the assembly of a cab suspension system 10, a base member 11 has a reference axis 12 about which the cab suspension system is symmetrical. The base member 11 is bolted by conventional means to a side beam 4 and a side beam 5 of the truck frame 2. The base member 11 is comprised of a channel beam 13 extending laterally from the reference axis 12 where the ends of the channel beam are rigidly welded to angle brackets 14 and 15 which, in turn, are bolted to rear cab bracket mounts 16 and 17. In this disclosed embodiment of the invention, the rear cab bracket mounts 16 and 17 are bolted to the truck frame. Thus, the base member 11 forms a rigid platform interconnecting the side beam 4 and the side beam 5 of the truck frame 2 such that the shock and vibration forces experienced by the truck frame are transmitted directly to the base member 11. Pivotally mounted to the base member 11 are the first ends of hydraulic shock absorbers 18 and 19 which have, in the preferred embodiment of the invention, respectively, central axis 20 and 21. The shock absorbers are identified by the trademark "Gabriel" and are manufactured by Gabriel Shock, a division of Marymont Corporation, and are of 1 3/16 inch bore for use with cab suspension systems. Hydraulic shock absorbers having bore sizes ranging from 1 inch to 1 1/2 inches may also be utilized in the present invention. Preferably, the shock absorbers 18 and 19 are of the type which dampen sixty percent of the amplitude of vibration when the shock absorber is subject to tensile loading along the central axis and forty percent of amplitude when loaded compressively along the central axis. The second ends of the shock absorbers 18 and 19 are pivotally mounted to a U-shaped channel member 22 which is welded to an impact plate 23. The lateral distance between pivot points 24 and 25 of the second ends of the shock absorbers 18 and 19 is less than the lateral distance between the pivot points 26 and 27 of the first ends of the shock absorbers 18 and 19. Thus, the lateral distances between the pivot points 24 and 25 and the pivot points 26 and 27 form the opposite sides of a trapezoid with the central axes 20 and 21 of the shock absorbers forming the opposite sides of the trapezoid. To accommodate different truck frame configurations, the base member 11 may have a plurality of adjustment apertures. In the present invention, apertures 28 and 29 permit the angle between the reference axis and the central axis of the shock absorbers to be decreased. For example, where the truck frame is made of aluminium and assuming identical forces acting on the truck frame, the amplitude of vibration in the vertical direction may be greater than the amplitude for a truck frame made of steel. To accommodate for these differing frame configurations the base member 11 as shown in FIG. 2 has additional apertures 28 and 29 to permit the first end of the shock absorbers 18 and 19 to be pivotally mounted at these apertures so as to decrease the angle of the central axis of the shock absorbers with the reference axes of the base member thereby permitting the shock absorbers to more efficiently dampen vertical vibration of the truck frame. Additional apertures located on the base member along the arc generated by a radius length equal to the distance between opposing pivot points of the shock absorbers, not shown, may also be used to increase the angle of the central axis of the shock absorbers with the reference axis to more efficiently dampen the lateral or horizonal vibration components. Interposed between the impact plate 23 and the base member 11 are a pair of air springs 30 and 31 which in the preferred embodiment of the invention are manufactured by Goodyear Tire and Rubber Company and identified by the trademark "Super-Cushion", Part Number IS5, air springs. A height control valve 32 is mounted to the base member 11 for maintaining the air springs at a constant height of 6.5 inches regardless of the vertical forces experienced by the suspension system 10. Although not shown, the height control valve incorporates a control rod which is mounted to the impact plate and detects height changes of the air springs. These height changes are relayed to the height control valve 32 which either admits or exhausts air in order to maintain a constant height of 6.5 inches. The air springs used in the present invention may be set to operate between pre-selected heights of 6.2 inches to 7.2 inches. Any standard height control valve having a zero delay may be utilized with the air springs. The height control valve 32 which is preferred in the practice of the present invention is manufactured by Nelson Metal Products Corporation and may be utilized with any type of air spring. US-A-3635460 describes the structure and operation of the height control valve and its disclosures are incorporated herein by reference. In another embodiment of the invention, not shown, a single air spring is utilized where the displacement axis of the air spring substantially coincides with the reference axis 12 of the base member 11. The height control valve in this embodiment also maintains the air spring at a pre-selected height. The vertical displacement of the impact plate 23 is limited by rubber snubbers 33 and 34 which are mounted to snubber towers 35 and 36. The snubbers 33 and 34 are preferably made of rubber, but may be made of other materials provided such materials have elastomeric properties. The snubber towers 35 and 36 are rigid bodies which are fixed to the channel beam 13 of the base member 11. Referring now to FIG. 3, a typical connection of the cab 1 to the impact member 23 is illustrated. As can be seen, a V-shaped channel member 37 supports the base of the truck cab 1 and is bolted to the impact plate 23 through holes 38 and 39 contained in the impact plate. In operation, the passage of truck wheels 6 over a highway will cause the transmission of shock and vibration forces from the truck frame 2 to the base member 11. Located laterally inward from the side beams 4 and 5 of the truck frame are the hydraulic shock absorbers 18 and 19 which have central axes inclined to the reference axis 12 of the base member 11. The ends of the shock absorbers are pivotally mounted to the base member 11 and the impact plate 23. The lateral distance between the pivot points 24 and 25 located on the impact plate is less than the lateral distance between the pivot points 26 and 27 on the base member. Thus, the central axis of the shock absorbers form the opposite sides of a trapezoid with the distance between the pivot points 26 and 27 forming the base of the trapezoid. The resultant of forces transmitted to the truck cab by the shock absorbers is directed inwardly in the direction of the centre of gravity of the cab which minimizes the sway and rolling of the cab. Acting in conjunction with the shock absorbers, a pair of the air springs 30 and 31 also located laterally inward from the side beams of the truck frame dampen the vertical vibration transmitted by the frame to the cab. The forces therefore creating rolling action about the centre of gravity of the cab act through shortened moments arms and therefore the rolling moments are reduced. The suspension system may be modified to accommodate different frame configurations by adjusting the pivot points at the apertures 28 and 29 of the base member 11. The adjustment permits more efficient dampening of the vertical amplitudes of the truck frame vibrations and shock loads. In the embodiment of the invention utilizing one air spring, the displacement axis of the air spring substantially coincides with the reference axis of the base member and the forces transmitted to the cab by the spring act through a limited lateral distance from the centre of gravity of the truck cab. Thus, the sway of the cab is essentially reduced by the forces transmitted through the air spring and the shock absorbers acting through reduced moment arms about the centre of gravity of the cab.

Claims: A vibration dampening suspension device for the cab (1) of a truck vehicle of the kind having at least one air spring (30, 31), a height control valve (32) associated with the or each air spring (30, 31) for maintaining the or each air spring (30, 31) at a pre-selected height, and a pair of hydraulic shock absorbers (18, 19), each shock absorber (18, 19) having a central axis (20, 21) and a first (26, 27) and second (24, 25) end, characterised by: (a) a base member (11) having a reference axis (12) and adapted for mounting to a frame (2) of the truck vehicle; (b) the shock absorbers (18, 10) being oppositely and laterally spaced from the reference axis (12), the first end (26, 27) of each shock absorber (18, 19) being pivotally mounted to the base member (11) such that the central axes (20, 21) of the shock absorbers (18, 19) are inclined toward the reference axis (12) so as to form the opposite sides of a trapezoid; (c) an impact plate (23) adapted for attachment to the cab (1) and having a lateral dimension which is less than the lateral distance between side beams (4, 5) of the truck frame (2), the impact plate (23) being axially spaced from and substantially parallel to the base member (11) for transmitting dampened vibration and shock forces to the cab (1), the second ends (24, 25) of the shock absorbers (18, 19) being pivotally mounted to the impact plate (23) such that the lateral distance between the second ends (24, 25) is less than the lateral distance between the first ends (26, 27); and (d) the or each air spring (30, 31) having a displacement axis located intermediate the base member (11) and the impact plate (23), the or each spring (30, 31) being mounted to the base member (11) and to the impact plate (23) with its displacement axis substantially parallel to the reference axis (12). A suspension device as claimed in claim 1, wherein the base member (11) further comprises adjustment means (28, 29) for selectively changing the angle of inclination of the central axes (20, 21) of the shock absorbers (18, 19) with the reference axis (12). A suspension device as claimed in claim 1 or claim 2, including a pair of snubbers (33, 34) carried by the base member (11) for limiting the vertical displacement of the impact plate (23). A suspension device as claimed in any of claims 1 to 3, wherein there are two said air springs (30, 31) oppositely spaced from the reference axis (12), each air spring (30, 31) having its displacement axis substantially parallel to the reference axis. A suspension device as claimed in any of claims 1 to 3, wherein there is a single said air spring (30; 31) having its displacement axis substantially coinciding with the reference axis (12).

Inventors: CONAWAY RICHARD L, CONAWAY, RICHARD L.
Applicants: APPLIED POWER INC, APPLIED POWER INC.
Application year: 1990
Main classification: B62D33
IPC codes: B62D33