Self-compensating spade assembly

FIELD OF THE INVENTION

The invention relates to spade assemblies suitable for use on artillery such as vehicle-mounted mortars and howitzers.

BACKGROUND OF THE INVENTION

In artillery vehicles such as mortars and howitzers, considerable recoil forces are generated as a fired projectile leaves the weapon mounted on the vehicle. The common approach in dealing with recoil forces is to fit so-called spade assemblies to the vehicle so that it is braced during firing.

The spade assemblies are typically arranged as two arms pivotally mounted to one side of the vehicle and positioned so that they penetrate the soil. This arrangement transfers recoil forces from the weapon to the ground, and discourages the vehicle from moving under the influence of recoil forces.

Many artillery vehicle are often relatively light in weight in relation to the significant recoil forces that can be generated during firing. In many cases, a weapon is mounted on a vehicle chassis or other wheeled structure which is easily displaced by recoil forces. Accordingly, spade assemblies are typically an important component of such vehicles or other wheeled structures.

The use of spade assemblies is associated with various shortcomings. During recoil, the spade assemblies tend to compress the soil on which they act, and the vehicle tends to return to its former position after firing. Accordingly, a gap is formed between the spade assembly and the soil.

Subsequent refiring causes the spade assembly to come into contact with the soil again, after the gap between the spade assemblies and the soil is closed. This can cause considerable stresses in the spade assemblies and in the structure of the vehicle mounting. These stresses can cause significant damage and possible failure if appropriate structural reinforcements are not provided.

Further, free-play between the spades and the soil can reduce the accuracy of firing. When low-fire rate accuracy is required, one approach has been to ure-layn the weapon to compensate for angular shifts of the vehicle after each firing.

It is an object of the invention to address these and other deficiencies associated with existing spade assembly arrangements.

SUMMARY OF THE INVENTION

The invention provides a self-compensating spade assembly suitable for use on a vehicle having a mounted weapon generating a recurring recoil force, the spade assembly including:

an elongate spade arm;

a spade mounting at one end of the spade arm for mounting the spade to the vehicle; and

a ground contacting portion at the other end of the spade arm, the ground contacting portion including a support plate and a spade portion which are mutually positioned so that when the spade assembly is in use, the spade portion penetrates the earth on which the weapon is standing, and the support plate rests against the earth to at least partly transfer recoil forces from the weapon to the earth;

characterised in that the spade arm has a compensating means able to regulate the length of the spade arm to ensure that the ground contacting portion is generally maintained in firm contact with the earth on which the weapon is standing.

Preferably, the compensating means includes a telescopic engagement of two relatively slidable members defining a sealed chamber containing a source of hydraulic or pneumatic pressure which acts to bias the spade assembly in an extended position.

Preferably, the spade assembly can be maintained generally rigid in compression when the weapon is being repeatedly fired. Preferably, this is achieved by the use of an automatic locking arrangement which ensures that, during use, the length of the spade assembly can be increased but not decreased. Preferably, this is achieved by providing a hydraulically actuated system in which the volumes of distinct chambers are adjusted by regulating the flow from one chamber to the other, thus adjusting the relative position of the slidable members.

The invention further includes a vehicle having mounted thereon one or more spades according to the first aspect of the invention.

Preferably, two spade assemblies are used in combination to assist in stabilising a vehicle during recurrent firing. Preferably, the spade assemblies are in use angularly orientated at 40° below horizontal, and mutually positioned so that they define an included angle of 90°. This outwardly defined assists in stabilising the vehicle against recoil forces acting laterally as well as transversely of the weapon.

DESCRIPTION OF DRAWINGS

FIG. 1

is an isometric view of a vehicle fitted with self-compensating spades constructed in accordance with an embodiment of the invention.

FIG. 2

is a plan view of the weapon shown in FIG.

1

.

FIG. 3

is a partial side view of the weapon shown in

FIG. 1

, detailing one of the spade assemblies shown in FIG.

1

.

FIG. 4

is a cross-sectional drawing of one of the spade assemblies shown in FIG.

1

.

FIG. 5

is a side cross-sectional view of a compensating cylinder included as part of the spade assembly shown in

FIGS. 1 and 2

.

FIG. 6

is a schematic hydraulic circuit diagram of a valve mechanism included as part of the spade assembly shown in FIGS.

1

and

2

.

DESCRIPTION OF EMBODIMENT

FIGS. 1 and 2

show compensating spade assemblies

10

pivotally attached at the rear of an artillery vehicle

100

. The vehicle

100

is track-driven, and can have a weapon (not shown in

FIGS. 1 and 2

) mouted on an upper portion of the vehicle

100

.

Stoppers on the vehicle

100

(also not shown in the drawings) determine the angular orientation of the spade assemblies

10

relative to the vehicle

100

, when the spade assemblies

10

are moved into their downwardly extending position prior to use, as indicated in

FIGS. 1 and 2

. When the vehicle

100

is being driven or transported, the two generally identical spade assemblies

10

can be swung into a generally vertical position away from the ground.

FIGS. 3 and 4

show one of the compensating spade assemblies

10

in greater detail. In

FIG. 3

, it is seen that the spade assembly

10

has at one end a spade mounting

12

which, as illustrated more clearly in FIG,

4

, includes a boss portion defining a circular opening

103

and having two side plates

105

as supports. A mounting pin

102

can be placed in the circular opening

103

, to ensure that the spade assembly

10

is pivotally mounted to a mounting member

104

integrally or otherwise joined with the vehicle

100

. This arrangement is shown in FIG.

3

.

FIG. 4

shows a cross-sectional view of the spade assembly

10

. The spade assembly

10

includes a spade mounting

12

, a ground contacting portion

15

, and a spade arm

14

joining the spade mounting

12

and the ground contacting portion

15

. The ground contacting portion

15

has a spade portion

16

and a support plate or float

18

. The ground contacting portion

15

contacts the ground and assists the spade assembly

10

to transfer forces from vehicle

100

to the ground. The spade mounting

12

allows the spade assembly to be mounted with a vehicle

100

. The spade arm

14

can be adjusted in length as later described to provide the compensating action of the spade assembly

10

.

The spade portion

16

and float

18

both have generally flat surfaces. The shape of the spade portion

16

is better shown in FIG.

3

. The spade portion

16

is partially tapered towards its distal end which has two teeth

17

. This tapered and toothed profile is designed to allow the spade portion

16

to embed into the earth with ease initially and readily engage relatively firm earth. The surface of float

18

is generally flat and rectangular in profile. In use, the ground contacting portion

15

of the compensating spade

10

generally operates in the same way as a conventional spade used on artillery vehicles.

The spade assembly

10

includes an outer housing

24

and inner sleeve

22

. The outer housing

24

and inner sleeve

22

are telescopically displaceable so that the length of the arm portion

14

can be adjusted, to provide a compensating action as later discussed. As indicated in

FIG. 3

, the housing

24

and sleeve

22

both have a cross-sectional profile which is generally rectangular.

Within the spade assembly

10

there is a compensating cylinder

26

including a tubular piston

50

and a cylinder housing

60

. The cylinder housing

60

is attached with the outer housing

24

and the tubular piston

50

is attached with the inner sleeve

22

. In this way, the relative longitudinal displacement of the outer housing

24

and the inner sleeve

22

and thus the length of the spade assembly

10

can be regulated in a predetermined manner by the action of the compensating cylinder

26

as later described.

The cylinder housing

60

and tubular piston

50

of the compensating cylinder

26

are sealingly engaged so as to be relatively slidable. The tubular piston

50

extends into the cylinder housing

60

through an opening

52

in an open end of the housing

60

. The cylinder housing

60

and tubular piston

50

define a cylinder chamber

30

filled with pressurised nitrogen gas (N

2

).

The pressurised gas biases the compensating cylinder

26

towards an extended position, that is with the tubular piston

50

and cylinder housing

60

longitudinally displaced from each other so that the length of the spade assembly

10

is maximised. That is, in the absence of external forces, the pressurised gas acts to extend the length of the spade assembly

10

.

The cylinder housing

60

and tubular piston

50

are respectively provided with a housing ring seal

56

and a piston ring seal

54

. These ring seals

54

,

56

divide the annular space between the housing

60

and tubular piston

50

into a first chamber

32

and a second chamber

38

. A longitudinally oriented duct

34

is defined by a projection on part of the external surface of the cylinder housing

60

. The duct

34

is positioned to allow oil to flow between the first chamber

32

and the second chamber

38

, via valve mechanism

40

and aperture

36

.

The action of the compensating cylinder

26

is regulated by a locking action which is automatically activated during repeated firing of the weapon, so that the length of the spade assembly

10

is predisposed to increase rather than decrease. This locking action is achieved using valve mechanism

40

, which provides a hydraulically operated locking arrangement.

The valve mechanism

40

(indicated by the outlined box depicted in FIG.

5

), connects the first chamber

32

with the duct

34

, which is in fluid communication with the second chamber

38

via the aperture

36

. The valve mechanism

40

regulates the flow of oil between these first and second chambers

32

and

38

through duct

34

, and thus governs the relative positions of the cylinder housing

60

and tubular piston

50

. The flow of oil between the two chambers

32

,

38

adjusts the relative volumes of these chambers and accordingly adjusts the length of the spade assembly

10

.

When the oil pressure in the first chamber

32

is higher than the oil pressure in the second chamber

38

, the contacting portion

15

is generally retracted. As oil moves from the first chamber

32

to the second chamber

38

, the volumes of the chambers

32

,

38

adjust to accommodate the transfer of oil, so that as the spade assembly

10

progressively extends, the second chamber

38

reaches its maximal volume while the first chamber

32

reaches its minimal volume.

The transfer of oil between the first and second chambers

32

and

38

, and hence the adjustment in length of the spade assembly, is facilitated by the valve mechanism

40

. The structure of the valve mechanism is shown schematically in FIG.

6

. The valve mechanism

40

communicates with the first chamber

32

through opening

72

. Oil flows from the first chamber

32

through one-way throttle valve

42

to the second chamber

38

through opening

78

, as the compensating tubular piston

50

is progressively extended. Accordingly, the length of the cylinder

26

can be progressively extended, but is not retracted as the oil in the second chamber

38

cannot flow back to the first chamber

32

through the one-way throttle valve

42

. The check valves

46

and

48

server to prevent the oil in chambers

38

and

32

from flowing out to openings

74

and

76

respectively. Any reduction of the amount of oil in the first chamber

38

(that is, leakage back through the one-way throttle valve

42

to the first chamber

32

) is minimal as the recoil forces act only momentarily, for example, for around 100 milliseconds).

The valve mechanism

40

includes pilot-operated check valve

46

which allows oil to flow from the second chamber

38

to flow out through opening

74

so that the compensating cylinder

26

and hence the length of the spade assembly

10

can be retracted after use. This pilot-operated check valve

46

is operated by input oil pressure from the pilot line link to the opening for input opening

76

, when it is required to retract the spade portions

16

at the end of a firing session. The input oil from opening

76

can freely flow through the check valve

48

. This action can be used to retract the cylinder, by allowing oil to flow back into the first chamber

32

through opening

78

. The valve will be closed by the pressure from the pilot line linked from opening

76

to prevent bypass of the input oil through the one-way throttle valve

42

.

The opening

76

in the valve mechanism

40

can be used to input oil externally to the first chamber

32

to retract the tubular piston

50

.

The pressure relief valve

44

discharges oil from the chambers when the oil in the first and second chambers

32

and

38

becomes overly pressurised due to thermal expansion of the oil. As the oil cools, replacement oil can be provided through opening

76

as appropriate.

In this way, the valve mechanism

40

allows relative displacement of the outer housing

24

and inner sleeve

22

so that the distance between the ground contacting portion

15

of the spade assembly

10

and the ground to be adjusted after firing. The compensating action provided by the compensating cylinder

26

allows the float

18

to be generally maintained in firm contact with the earth despite recurring firing of the weapon.

When the weapon is to be used, the vehicle

100

is driven into position, and the spade assemblies

10

pivotally located in their operative position. The vehicle

100

is reversed a small distance so that the spade portions

16

catch against, and are then embedded into the earth due to the motion of the vehicle

100

relative to the ground.

When the weapon is fired, recoil forces act to push the vehicle

100

backwards and downwards. However, the floats

18

and spade portions

16

act against the earth to prevent substantial movement of the vehicle

100

, and the spade portions

16

prevent the spade assemblies

10

from dislodging from the earth. Though the outer housing

24

and inner sleeve

22

can be relatively adjusted, the valve mechanism

40

ensures that the spade assembly

10

is essentially rigid during firing. Of course, a small proportion of the recoil forces will be absorbed by the spade assembly

10

, accompanied by a minimal shortening in the length of the spade assembly

10

.

As some compaction of the soil will inevitably occur after firing, a gap between the float

18

and the earth is typically formed. As this occurs, or very shortly after it occurs, the length of the spade assembly

10

is increased by the compensating action of the outer housing

24

and inner sleeve

22

so that the float

18

is at most if not all times firmly engaged with the earth. Any gap formed between the float

18

and the earth is advantageously compensated so that the weapon is adequately braced before the next firing.

This action allows the vehicle to be maintained in firm contact with the soil to allow for more accurate firing, less stress on the spade assemblies

10

and vehicle chassis. Also, the vehicle

100

is not subject to violent surges in movement due to the recoil forces moving to close gaps formed between the float

18

and the soil.