JPH06116981A - Work machine - Google Patents

Abstract

PURPOSE:To reduce vibrations occurring to the entire body of a work machine, and to improve habitability in an operator's cabin by controlling vibrations of a counterweight. CONSTITUTION:A sealed-up container 41 containing vibration-proof liquid rubber 39 is fixed between the upper and the lower attachment plates 32 and 33 of an attachment part 31 on the revolving frame side. A projecting end of a rod 43 projecting beyond the sealed-up container 41 through vibration-proof rubber 42 is fixed to a mounting part 36 of a counterweight 35 on the upper plate 36A side through a mounting plate 48 or the like. When the counterweight 35 makes relative displacement in the vertical direction against the attachment part 31, a buffer plate 45 in the sealed-up container 41 makes vertical displacememnt, making the liquid 44 in the sealed-up container 41 flow through a restriction passage 51. As damping force is produced at this time, vibration of the counterweight 35 is attenuated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a working machine such as a hydraulic excavator provided with a counterweight, in particular,
The present invention relates to a working machine that reduces vibration of a counterweight with respect to a body frame.

[0002]

2. Description of the Related Art FIGS. 6 to 10 show an example of a hydraulic excavator as a working machine according to the prior art.

In the figure, 1 is an undercarriage, 2 is an upper revolving structure which is rotatably mounted on the lower traveling structure 1 and constitutes a working machine body, and the upper revolving structure 2 is as shown in FIG. In addition, a swing frame 3 as a main body frame having a skeleton structure, an operator's cab 4, a machine room 5, and a counterweight 6 mounted on the swing frame 3 are provided. It is attached to each attachment portion 16. On the front side of the revolving frame 3, a working device 7 is provided on each bracket portion 15 of a main frame 8 which will be described later so as to be able to lift and lower, and the upper revolving structure 2 balances the working device 7 with a counter on the rear side. Weight 6 is used. Further, the counterweight 6 is formed in a hollow structure, and the counterweight 6 is filled with a weight adjusting material (not shown) made of concrete, iron pieces or the like, and its weight is adjusted according to the weight of the working device 7. It is supposed to be done.

As shown in FIG. 7, the revolving frame 3 is provided with a main frame 8 and a plurality of overhanging frames 9, 9, ... Which are fixed to the left and right sides of the main frame 8 and project in the left-right direction. And the left and right side frames 10, which are fixed to the tip ends of the respective overhanging frames 9 and extend in the front-rear direction,
The frame structure is composed of 10 and 10.

The main frame 8 has a plate 11 which constitutes a connecting portion with a turning device (not shown), and a pair of left and right beams 12, which are erected on the plate 11 and extend in the front-rear direction. And a beam plate 13 composed of a plate body provided substantially vertically on the plate 11.
It is formed by joining a long plate-shaped upper flange 14 on top. Then, the main frame 8 is formed by each beam plate 13
The front side is a pair of bracket portions 15, 15, and the working device 7 is pin-connected to each bracket portion 15.

16, 16 are left on the rear side of the main frame 8,
The mounting portion for the counterweight 6 provided separately on the right is shown, and each mounting portion 16 is integrally formed on the rear end side of each beam plate 13 and the upper mounting plate 17 protruding rearwardly.
And a lower mounting plate 18 that is opposed to the mounting plate 17 in the vertical direction and is integrally formed on the rear end side of the plate 11, for example.
And is provided by being joined between the mounting plates 17 and 18, and
It is composed of a plurality of holding cylinders 19 and 19 which are separated from each other later, and bolt holes 17A and 18A are formed in the respective mounting plates 17 and 18 coaxially with the holding cylinder 19 as shown in FIG. The counterweight 6 is placed on each of the mounting portions 16 and is detachably fixed by each bolt member 22 described later.

Reference numerals 20 and 20 denote a pair of mount portions formed in a concave shape on the lower surface side of the counterweight 6 for mounting the counterweight 6 on each mounting portion 16 of the revolving frame 3. As shown in FIG. 8, the reference numeral 20 is made of a steel material and has a substantially U-shaped cross section so that the lower end side is open. The lower end side is surrounded by the lower plate 6A of the counterweight 6.
It is fixed to the above by means such as welding. Further, as shown in FIG. 9, bolt insertion holes 20B, 20B are formed in the upper plate portion 20A of each mount portion 20 so as to be spaced apart from each other in the front-rear direction, and inside the counterweight 6 above the upper plate portion 20A. Positioned, the screw seats 21 and 21 in which screw holes 21A coaxial with the respective bolt insertion holes 20B are formed are fixed by means such as welding. Reference numeral 22 denotes a bolt member for fixing the counterweight 6 to each mounting portion 16 of the revolving frame 3.

In the prior art thus constructed, when the counterweight 6 is mounted on each mounting portion 16 of the swivel frame 3, bolt mounting holes 17A and 18A of each mounting portion 16 are formed as shown in FIGS. The counterweight 6 is placed on each mounting portion 16 using a counterweight attaching / detaching device (not shown) or the like so that the bolt insertion holes 20B of each mounting portion 20 are aligned with each other. Then, from the lower side of each mounting portion 16, each bolt member 22 is inserted into the bolt insertion hole 18A of the mounting plate 18, the holding cylinder 19, the bolt insertion hole 17A of the mounting plate 17, and the bolt insertion hole 20B of the mounting portion 20 with a washer 23.
The counterweight 6 is removably fixed on each mounting portion 16 by inserting the male screw portion 22A of each bolt member 22 into the screw hole 21A of each screw seat 21. .

[0009]

By the way, in the above-mentioned prior art, each mounting portion 16 for the counterweight 6 is integrally formed by projecting rearward to the rear end side of the main frame 8 of the revolving frame 3 to form a counter. Each mounting part 2 of the weight 6
By mounting each bolt member 22 on each screw seat 21 of the counterweight 6 via each mounting portion 16 in a state where 0 is placed on each mounting portion 16, a rear end side of the revolving frame 3 is provided. Since the counterweight 6 is merely attached directly, the following problems occur.

Firstly, when the hydraulic excavator is excavating or running, external impacts and vibrations are easily transmitted directly to the counterweight 6 through the main frame 8 of the revolving frame 3, and the heavy counterweight. When 6 starts to vibrate due to inertial force, this vibration is transmitted to the entire hydraulic excavator through the revolving frame 3, and the vibration of the entire hydraulic excavator is amplified.

Secondly, when the vibration of the entire hydraulic excavator is amplified by the counterweight 6, this vibration is transmitted to the operator's cab 4 via the revolving frame 3, and the operator's cab 4 vibrates greatly to improve steering stability. Impairs habitability. In addition, construction machines such as hydraulic excavators tend to have a higher running speed as a recent tendency. The higher the running speed, the greater the vibration of the counterweight 6 and the worse the comfortability of the cab 4. There's a problem.

Thirdly, when vibration of the entire hydraulic excavator increases during excavation work or traveling of the hydraulic excavator, there is a problem in that work stability and traveling stability of the hydraulic excavator are deteriorated.

Fourthly, the shock and vibration applied to the counterweight 6 act as stress on the mounting plates 17 and 18 of each mounting portion 16, so that the strength of each mounting portion 16 is significantly reduced and the mechanical life is shortened. There is a problem of shortening.

The present invention has been made in view of the above-mentioned problems of the prior art. The present invention can prevent external impacts and vibrations from being directly transmitted to the counterweight, and can prevent the vibrations of the counterweight and the working machine as a whole. The purpose is to provide a working machine that can be reduced at an early stage.

[0015]

In order to solve the above-mentioned problems, the present invention provides a working machine main body having a driver's cab and a machine room mounted on a main body frame consisting of a main frame and left and right side frames. A working device which is located on the front side of the working machine body and is attached to the main frame of the body frame, and in order to balance with the working device, the working machine body has a counter on the rear side of the body frame. In a working machine provided with a weight, a mounting portion for the counterweight is provided on the rear side of the main frame in the main body frame of the working machine body, and a liquid sealed inside is provided between the mounting portion and the counterweight. Is provided with a first vibration damping body for damping vertical vibrations, and a column for supporting the counterweight in the front-rear direction is provided on the rear side of the main body frame of the working machine main body. And set, second buffering the vibration in the longitudinal direction by rubber cushion between the struts and the counterweight
The configuration adopted is characterized by the provision of the vibration damping body.

In this case, the first vibration absorbing body is formed in a cylindrical shape with a bottom, and a sealed container in which a liquid is sealed,
A rod which is provided on one end side of the closed container via a vibration-proof rubber, one end side of which protrudes out of the closed container, and the other end side of which serves as a buffer portion for generating a damping force to the liquid in the closed container. However, it is preferable that the protruding end side of the rod is fixed to the counterweight and the bottom side of the closed container is fixed to the mounting portion of the main frame.

[0017]

With the above structure, when vibrations during running or working are transmitted to the counterweight through the body frame,
The first vibration damping body can buffer the vibration in the vertical direction with the liquid enclosed therein, and the second vibration damping body can buffer the vibration in the front-rear direction by the vibration damping rubber, so that the vibration of the counterweight can be reliably reduced.

In particular, the first vibration damper is configured to generate damping force in the liquid in the closed container at the buffer portion of the rod, so that the counterweight can be reliably damped from vertically vibrating. Vibration of the counterweight can be reduced early by the damping force of the liquid.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those of the prior art shown in FIGS. 6 and 7 described above are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numerals 31 and 31 denote mounting portions for a counter weight 35, which will be described later, which are provided on the rear side of the main frame 8 so as to be spaced apart left and right, and each mounting portion 31 has been described in the prior art. Almost the same as the mounting portions 16, each of which includes an upper mounting plate 32 and a lower mounting plate 33.
Is formed with a substantially U-shaped cutout 32A extending in the longitudinal direction on the mounting plate 32, and the mounting plate 33 is provided with the cutout 32A.
Bolt insertion holes 33A, 33A are formed in front and rear positions at positions vertically opposed to A. Then, in each of the mounting portions 31, a closed container 41 of a liquid anti-vibration rubber 39 described later is inserted into the notch 32A of the mounting plate 32 as shown in FIG. 2, and the bottom portion 41B side of the closed container 41 is on the mounting plate 33. Is fixed by a bolt 50 described later via a bolt insertion hole 33A.

Reference numerals 34 and 34 denote mounting brackets, which are positioned on the rear end side of the revolving frame 3 and are erected upright from the rear end side of each side frame 10, as the base end side of each mounting bracket 34. Is fixed to the upper surface on the rear end side of each side frame 10 by means such as welding, and a through hole 34A is formed on the front end side at a height substantially corresponding to the height of the center of gravity of the counterweight 35. Each mounting bracket 34 supports the counterweight 35 in the front-rear direction via each vibration isolator 52 described later.

Reference numeral 35 denotes a counterweight used in this embodiment. The counterweight 35 has substantially the same structure as the counterweight 6 described in the prior art, and its lower surface plate 3
5A is provided with a pair of mount portions 36 (only one is shown) as shown in FIG.
The upper plate portion 36A is spaced from the left and right by the bolt insertion holes 36.
B and 36B are drilled. Then, screw seats 37, 37 located in the counterweight 35 on the upper side of the upper plate portion 36A and having screw holes 37A coaxial with the respective bolt insertion holes 36B are fixed by means of welding or the like. There is. Further, as shown in FIGS. 4 and 5, each screw seat 38 having a screw hole 38A at a position facing the through hole 34A of each mounting bracket 34 is fixed to the front plate 35B of the counterweight 35 by means such as welding. Has been done.

Reference numeral 39 denotes a liquid vibration isolating rubber as a first vibration damper provided between each mounting portion 31 of the revolving frame 3 and the counterweight 35, and the liquid vibration isolating rubber 39 is as shown in FIG. , A closed container 41 formed in a bottomed tubular shape and integrally provided with a stepped tubular bracket tube 40 on the upper end side
And a rod 43, which is provided in the bracket cylinder 40 of the closed container 41 via a stepped tubular vibration-proof rubber 42 and has an upper end protruding outside the bracket cylinder 40, and a rod 43 integrally formed on the lower end side of the rod 43. A buffer plate 45 provided as a buffer portion for generating a damping force in a liquid 44 such as an oil liquid sealed in the closed container 41, and the buffer plate 45 is a disk having a diameter slightly smaller than the inner diameter of the closed container 41. It is formed into a shape. And
A plug 46 is fitted to the lower end side of the cylindrical portion 41A of the closed container 41, and the plug 46 is filled with the liquid 44 and then the closed container 4 is inserted.
1 is sealed.

A reinforcing plate 47 is fixed to the bottom portion 41B of the closed container 41 by welding or the like, and a screw hole 47A is formed in the central portion of the reinforcing plate 47. On the other hand, rod 4
The mount portion 3 of the counterweight 35 is provided on the protruding end side of
The mounting plate 48 on which 6 is mounted is fixed by means such as welding,
On both the left and right sides of the mounting plate 48, bolt insertion holes 48A, at positions corresponding to the respective bolt insertion holes 36B of the mount portion 36,
48A is drilled. Then, the respective bolt insertion holes 4
8A and 36B have bolts 49,
49, the bolts 49 are inserted into the counterweight 3
By being screwed into each of the screw seats 37 of No. 5, the protruding end side of the rod 43 is fixed to the mount portion 36 of the counterweight 35 via the mounting plate 48.

Here, the liquid anti-vibration rubber 39 is a closed container 41.
The bracket cylinder 40 of the notch 32A of the mounting plate 32
And the bracket tube 40 is inserted into the upper surface of the mounting plate 32.
2 is mounted on the mounting portion 31 of the revolving frame 3 by screwing the bolts 50 onto the reinforcing plate 47 from the lower surface side of the mounting plate 33 with the flange portion 40A mounted thereon. Then, the buffer plate 45 of the liquid anti-vibration rubber 39
Forms a throttle passage 51 for the liquid 44 with the closed container 41, and exerts a squeezing action on the liquid 44 in the closed container 41 when the rod 43 is displaced upward and downward relative to the closed container 41, and attenuates the liquid 44. It is configured to generate force. Further, an annular bulging portion 42A is integrally formed on the upper end side of the anti-vibration rubber 42, and the bulging portion 42A is fixed when the mount portion 36 of the counterweight 35 is fixed on the mounting plate 48 as shown in FIG. The mounting plate 48 is attached to the flange portion 40 of the bracket cylinder 40.
Direct contact with A is prevented.

Next, in FIG. 4, reference numeral 52 denotes a pair of vibration damping members (second vibration damping members) provided between each mounting bracket 34 of the revolving frame 3 and each screw seat 38 of the counterweight 35 ( As shown in FIG. 5, each vibration isolator 52 is a spacer that holds the mounting bracket 34 from the front-rear direction around the through hole 34A of the mounting bracket 34 and extends in the front-rear direction on the inner peripheral side. A pair of anti-vibration rubbers 53, 53, each having an insertion hole 53A, and a front and rear of each anti-vibration rubber 53, and a cylindrical portion on the outer peripheral side serving as a stopper portion 54A, and a bolt insertion hole 54B at the center of the bottom portion. A pair of disc-shaped stoppers 54, 54 each having a groove formed therein, a through hole 34A of the mounting bracket 34, and a spacer insertion hole 53A of each anti-vibration rubber 53. It And a spacer 55 are inserted from the stopper 54 side located on the front side in the spacer 55 in a screw hole 38A tip end side into the threaded seat 38 of the counterweight 35
And a bolt member 56 that is a male screw portion 56A that is fastened via.

Thus, each vibration isolator 52 has a bolt member 56.
By tightly screwing the screw to the screw seat 38, each stopper 5
Each of the anti-vibration rubbers 53 is compressed and deformed between the four anti-vibration rubbers 5
With the initial load applied to the mounting bracket 3, the mounting bracket 34 is sandwiched by the anti-vibration rubbers 53 from the front-rear direction. The anti-vibration body 52 supports the counterweight 35 with respect to the mounting bracket 34 via each antivibration rubber 53, and particularly damps the vibration of the counterweight 35 in the front-rear direction.
Further, gaps S1 and S2 are formed between the mounting bracket 34 and the tip of the stopper portion 54A of each stopper 54,
Amplitude (stroke) of the counterweight 35 in the front-rear direction
Is regulated within the range of these gaps S1 and S2.

The hydraulic excavator according to this embodiment has the above-mentioned structure. Next, the vibration damping action of each liquid vibration isolator 39 and each vibration isolator 52 will be described.

First, impacts and vibrations applied to the hydraulic excavator during excavation work by the working device 7 or traveling of the vehicle by the lower traveling body 1 are caused by the respective liquid-preventing liquids from the respective mounting portions 31 and the respective mounting brackets 34 of the revolving frame 3. It is transmitted to the counterweight 35 through the vibration rubber 39 and each vibration isolator 52,
At this time, the vibration of the counterweight 35 is damped by the liquid antivibration rubber 39 and the antivibration bodies 52.

In this case, when the vertical vibration is transmitted from the respective mounting portions 31 of the swivel frame 3 to the counterweight 35 via the respective liquid vibration isolating rubbers 39, the liquid vibration isolating rubbers 39 are provided.
The rod 43 is relatively displaced in the vertical direction in FIG. 3 with respect to the closed container 41, and the liquid 44 in the closed container 41 is absorbed by the buffer plate 4
5 causes the liquid to flow through the peripheral throttling passage 51 at this time, so that at this time, the liquid 44 in the closed container 41 is given a throttling action to generate a damping force, and the counterweight 35 is raised above the mounting portion 31 of the swivel frame 3. ， Buffering relative displacement below,
It is possible to suppress the vertical vibration of the counterweight 35 to be small. Further, the vibration damping rubber 42 provided on the liquid vibration damping rubber 39 is elastically deformed at this time, so that the displacement of the rod 43 with respect to the closed container 41 is suppressed to a small level, and
The bulging portion 42A on the upper end side prevents the mounting plate 48 on the counterweight 35 side from directly contacting the flange portion 40A of the closed container 41, and can prevent the shock from being transmitted from the mounting portion 31 to the counterweight 35.

On the other hand, when the vibration in the front-rear direction is transmitted from each mounting bracket 34 of the revolving frame 3 to each front plate 35B side of the counterweight 35 through each vibration isolator 52, each vibration isolation rubber 53 of the vibration isolator 52 is moved. It is possible to elastically deform and buffer the vibration at this time, and it is possible to reliably reduce the transmission of shock and vibration in the front-rear direction to the counterweight 35.

Further, due to the vibration of the revolving frame 3 and the inertial force of the counterweight 35, the counterweight 35 is
Even with respect to vertical vibrations generated by the liquid vibration damping rubber 39, damping force can be reliably damped by the vibration damping liquid 39, and the vibrations from the counterweight 35 can be applied to the mounting portions 3 respectively.
1. It is possible to effectively reduce the transmission to the turning frame 3 via the main frame 8. Further, with respect to the longitudinal vibration generated from the counterweight 35, each vibration can be buffered by each vibration isolating rubber 53 of the vibration isolator 52, and the longitudinal vibration of the counterweight 35 can be reduced at an early stage. .

Thus, according to the present embodiment, the counterweight 35 is arranged on each mounting portion 31 of the swivel frame 3 via each liquid antivibration rubber 39, and each mounting bracket 34 of the swivel frame 3 and the counterweight. Since each vibration isolator 52 is arranged between the liquid isolator 35 and the liquid vibration isolator 35, the vibration generated by the inertia of the counterweight 35 and the impact generated during excavation work or traveling of the hydraulic excavator is prevented. The vibrating rubber 39 and the vibration isolator 52 can reliably absorb the vibration, and the vibration of the entire hydraulic excavator can be effectively reduced.

Further, since the vibration of the entire hydraulic excavator can be reduced, the vibration of the operator's cab 4 can be effectively reduced, the habitability can be improved, and the work stability and the running stability can be surely improved. You can Further, it is possible to prevent the vibration from the counterweight 35 from being transmitted to the revolving frame 3 with a large amplitude, so that the mounting plates 32 and 33 of each mounting portion 31 can be prevented.
Since it is possible to prevent a large stress from being applied to the mounting parts 31 and the like, the mechanical strength of each mounting part 31 can be secured, and the life of each mounting part 31 can be effectively extended.

Although the hydraulic excavator has been described as an example of the working machine in the above embodiment, the present invention is not limited to this, and may be used for a working machine having a working device such as a hydraulic crane or an earth auger. .

Further, the counterweight 3 of each vibration isolator 52
Although it is desirable that the mounting position for 5 be equidistant from the center of gravity of the counterweight 35, by adjusting the initial load of each of the antivibration rubbers 53 of the antivibration bodies 52 located on the left and right sides, respectively. You may take measures.

[0037]

As described above in detail, according to the present invention, the body weight of the working machine body is provided with the counter weight mounting portion on the rear side of the main frame, and between the mounting portion and the counter weight. A first vibration damping body that damps vertical vibrations by a liquid sealed inside is provided, and a column for supporting the counterweight in the front-rear direction is provided upright on the rear side of the main body frame of the working machine main body. Since the second vibration absorbing body that absorbs the vibration in the front-rear direction is provided by the vibration isolating rubber between the support column and the counterweight, when the vibration during traveling or working is transmitted to the counterweight through the main body frame, The first vibration damping body buffers the vibration in the vertical direction with the liquid sealed inside, and the second vibration damping body can buffer the vibration in the front-rear direction by the vibration isolating rubber, and the vibration of the counterweight can be reliably reduced. Above, it is possible to effectively reduce the vibration of the entire working machine, comfort of the cab, the working stability and running stability can be greatly improved.

In particular, by constructing the first vibration buffer body so that the damping force is generated in the liquid in the closed container at the buffer portion of the rod, it is possible to reliably dampen the vertical vibration of the counterweight, and the counterweight can be reliably damped. Various effects can be achieved, such as that the vibration of the weight can be reduced at an early stage by the damping force of the liquid.

[Brief description of drawings]

FIG. 1 is a perspective view showing a swing frame of a hydraulic excavator according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view showing an enlarged liquid anti-vibration rubber according to an embodiment.

FIG. 3 is an enlarged cross-sectional view of essential parts showing a state in which the liquid anti-vibration rubber in FIG. 2 is attached to a counterweight.

FIG. 4 is an external view of a main part broken view showing a state in which a counterweight is attached to the rear side of a revolving frame via a vibration isolator.

5 is an enlarged vertical cross-sectional view showing a vibration isolator in FIG.

FIG. 6 is a perspective view showing a conventional hydraulic excavator.

FIG. 7 is an exploded perspective view of a swing frame and a counterweight of the hydraulic excavator.

FIG. 8 is an arrow VIII-VI in FIG. 7 showing the counterweight.
It is a II-direction partial sectional view.

9 is a bottom view of the counterweight shown in FIG.

FIG. 10 is an enlarged cross-sectional view of a main part showing a state in which a counterweight is attached to the rear side of a revolving frame.

[Explanation of symbols]

 2 Upper revolving structure (working machine main body) 3 Revolving frame (main body frame) 4 Driver's cab 5 Machine room 7 Working device 8 Main frame 10 Side frame 31 Mounting portion 34 Mounting bracket (strut) 35 Counterweight 39 Liquid anti-vibration rubber (No. 1) 1 vibration buffer) 41 airtight container 42, 53 vibration-proof rubber 43 rod 44 liquid 45 buffer plate (buffer) 52 vibration-proof body (second vibration buffer) 54 stopper

Claims (2)

[Claims] 1. A work machine main body having a driver's cab and a machine room mounted on a main body frame composed of a main frame and left and right side frames, and a main body of the main body frame located on the front side of the work machine main body. A work machine comprising a work device attached to a frame, and a counter weight provided on the work machine main body at a rear side of the main body frame for balancing with the work device. Is provided with a mounting portion for the counter weight on the rear side of the main frame, and a first vibration damping body is provided between the mounting portion and the counter weight for damping vertical vibrations by a liquid enclosed therein. In addition, a pillar for supporting the counterweight in the front-rear direction is provided upright on the rear side of the main body frame of the working machine body, and a vibration-proof rubber is provided between the pillar and the counterweight. A working machine provided with a second vibration absorbing body for absorbing vibration in the front-back direction. 2. The first vibration damping body is formed in a cylindrical shape having a bottom, a sealed container in which a liquid is sealed, and one end of the sealed container is provided with a vibration proof rubber, A rod protruding from the closed container and the other end serving as a buffer for generating a damping force in the liquid in the closed container, and fixing the protruding end of the rod to the counterweight, The working machine according to claim 1, wherein a bottom side of the closed container is fixed to a mounting portion of the main frame.