WO1992012870A1

WO1992012870A1 - Device for stabilizing the swinging motion of vehicle chassis

Info

Publication number: WO1992012870A1
Application number: PCT/SE1992/000017
Authority: WO
Inventors: Hans Olov Jonsson
Original assignee: Individual
Current assignee: Individual
Priority date: 1991-01-15
Filing date: 1992-01-15
Publication date: 1992-08-06
Anticipated expiration: 1993-07-15
Also published as: SE9100119D0; SE467303B; SE9100119L; AU1176692A

Abstract

The invention relates to an arrangement for dampening, or counteracting, lurching of a vehicle chassis in the event of one of the wheels (3'') of a wheel pair (3) and its axle moves over an irregularity (10) in an otherwise horizontal vehicle supporting surface (11). Each of the wheel axles (3a', 3a'') can by adjusted towards and away from the vehicle chassis (1) in a vertical direction by means of a respective hydraulic piston-cylinder-device (6, 7). The transverse level of the chassis in relation to the horizontal is detected by a level-sensing device (12) which is connected to a hydraulic circuit. In accordance with deviation of the sensing device from a horizontal plane, either one or the other of the piston-cylinder-devices (6 or 7) is placed under pressure so as to urge one wheel (3') and its associated axle (3a'') downwards and therewith raise an adjacent chassis part (1a) towards a horizontal position. In the case of a minor deviation from the horizontal plane (4'), the level-sensing device (12) functions to activate a check valve and therewith open a line (20) which extends between the two piston-cylinder-devices (6, 7), whereupon the higher pressure prevailing in one of the piston-cylinder-devices (7) will pass over to a similarly located space in the other piston-cylinder-device (6).

Description

TITLE OF THE INVENTION :

Device for Stabilizing the Swinging Motion of Vehicle Chassis TECHNICAL FIELD

The present invention relates to an arrangement for damping the lurching or swaying tendencies of a vehicle chassis when one of the vehicle wheels and the axle of a wheel pair passes over a bumpy or irregular surface.

The invention is based on a known arrangement in which each of the wheel axles of a wheel pair is adjustably mounted on a respective hydraulic piston-cylinder-device for vertical movement towards and away from the chassis, and in which sensor means which detect the transverse, horizontal level of the chassis are connected with a hydraulic circuit such as to electrically activate and place under pressure one or the other of the piston- cylinder devices in response to deviations from the horizontal plane, such as to urge a wheel and its axle downwards and therewith urge an adjacent part of the chassis towards a horizontal position.

BACKgPQUNP ART

It will be understood that the hydraulic system may equally as well be a pneumatic system and that the principles on which the invention is based are the same for both systems.

Different embodiments of arrangements of the aforesaid kind are known to the art and the level-sensing device is normally a mercury switch or a mercury rocker arm which will tilt in response to tilting of the vehicle to which it is fitted and make an electric circuit which, when made, activates an electrically actuable valve in a hydraulic circuit, said circuit placing respective piston-cylinder-devices under pressure and causing a wheel and its axle to be pressed downwards and therewith an adjacent part of the chassis towards a horizontal position.

An example of the prior art is found in published speci¬ fication JP-A-59,23714.

It is also known that the mercury rockers used today are liable to produce erroneous impulses in response to engine vibrations, multidirectional impacts and knocks and also in response to the centrifugal force that is generated when the vehicle negotiates curves at high speed. Consequently, it has been necessary to introduce a time delay which makes it necessary for the mer-cury rocker to complete the electric circuit and hold said circuit complete over a predetermined length of time, preferably over a period of one second, before activat¬ ing the piston-cylinder-device.

With regard to the construction of known mercury rock¬ ers, reference is made to US-A-4,099,040.

It is also known that these delay functions are trouble¬ some when the vehicle chassis is subjected to rapid lurching or swaying motion, since the requisite activa¬ tion of the piston-cylinder-device instigated by the control means takes place much too late.

The system also incorporates the drawback that a level sensor of this kind causes hydraulic fluid to be deliv¬ ered to respective piston-cylinder-devices at one and

the same speed, irrespective of whether said piston- cylinder-devices require the supply of oil or not in order to compensate for vehicle lurching, and conse¬ quently it is solely the duration of this activation function that shall be controlled and which determines the volume of hydraulic oil delivered.

A control or regulating arrangement of this kind, par¬ ticularly in the case of terrain vehicles, is often unsatisfactory and does not dampen lurching of the vehicle in the manner desired.

DISCLOSURE OF THE INVENTION

ECHNI AL PROBLEMS

When studying the prior art as described in the afore¬ going, it will be seen that a technical problem is one of realizing the significance of being able to control each of the two piston-cylinder-devices in accordance with the position of the sensor, in several stages or through the intermediary of one or two control or ad¬ juster circuits, a first of the stages being carried out when the deviation from the horizontal plane is small and the second stage being carried out when said devia¬ tion is greater.

Another technical problem is one of realizing that activation of the first stage and the first adjuster circuit will result in a simple adjustment and will solely equalize the occurrence of different hydraulic pressures in the two piston-cylinder-devices.

A qualified insight, and also a technical problem, is one of realizing that when the deviation from the hori¬ zontal plane is small, the aforesaid level-sensing device, or mercury rocker, can be constructed to solely open a check valve in a pipe, or fluid delivery line, between the piston-cylinder-devices, with the aid of an electric circuit, thereby enabling the higher pressure prevailing in one of said piston-cylinder-devices to transfer to the corresponding space in the other piston- cylinder-device, which then raises the adjacent chassis part towards a horizontal position, normally to the same extent as the first piston-cylinder-deviσe lowers an adjacent chassis part towards said horizontal position.

It is also a technical problem to realize those advan¬ tages associated with vibrations which act primarily on the mercury rocker will influence the first stage or the first adjuster circuit, which equalizes solely possible pressure differences between the two piston-cylinder- devices.

It will also be seen that a further technical problem is one of providing a level-sensing device in the form of a mercury rocker so constructed as to enable the device, or rocker, to indicate a small specific deviation and a larger specific deviation, without electrical detection being influenced negatively by engine vibrations, multi¬ directional impacts and knocks, and the occurrence of centrifugal forces when negotiating curves at high speeds.

It will also be seen that a technical problem is one of realizing the importance of mounting in the aforesaid pipe, or line, two electrically actuable, oppositely directed check valves for use at the beginning of a level adjusting process, according to the first adjuster stage, wherein the level-sensing device, or mercury rocker, is arranged to activate one check valve belong¬ ing to the one piston-cylinder-device upon the occur- rence of a predetermined, small deviation, and to acti¬ vate the other check valve belonging to the other piston-cylinder-device when the level deviation is in the opposite direction.

Another technical problem is one of realizing the i por- tance of constructing the level-sensing device so that in the event of given, large deviations from the hori¬ zontal plane, the device will be able to engage the second stage or the second adjuster circuit, through the intermediary of electric circuits, by force-feeding the hydraulic circuit so as to place either one or the other of the piston-cylinder-devices under pressure with the aid of a hydraulic pump.

It will also be seen that a technical problem is one of providing a solution to one or more of the aforesaid technical problems and still provide a level-sensing device in the form of a mercury rocker which will not require the provision of electrical delay circuits and which is able to directly activate electrically the hydraulic circuit of the piston-cylinder-devices, and in which the mercury rocker is so constructed, together with the remainder of the adjuster circuit, that even though engine vibrations, multidirectional impacts and knocks or large centrifugal forces result in non-moti- vated impulses, any such impulse will solely activate a check valve included in the first adjuster circuit or the first stage, this activation of the valve resulting in no level adjustment, or at least solely insignificant adjustment, when the pressures prevailing in the piston- cylinder-devices are mutually equal.

It will also be seen that a further technical problem is one of realizing that the first adjuster circuit shall include a pipe, or fluid delivery line, in which the pressure drop is small with large quantities of oil (large pipe diameter). Another technical problem is one of realizing that the use of two adjuster circuits and one mercury rocker requires the first adjuster circuit to be activated each time the system is engaged and over the period during which the second adjuster circuit is engaged.

In this respect, another technical problem is one of providing two mutually independent and mutually separate adjuster circuits which are able to function commonly with one another via one and the same mercury rocker.

Since an arrangement of the aforedescribed kind requires for its operation a level-sensing device in the form of a mercury rocker, it will be seen that a technical problem is one of realizing the significance of config¬ uring the space in which the mercury collection is enclosed in a particular manner, so that the level- sensing device will have incorporated in its construc¬ tion a safety means necessary for satisfactory control of the piston-cylinder-device.

It will be seen that a further technical problem is one of realizing the significance of configuring the space as a truncated cone, and cilso of realizing the signifi- cance of initially positioning the cone so that its centre line is horizontal, with the electrodes incorpo¬ rated in the space positioned adjacent the smaller circular surface.

It will also be seen that a technical problem is one of realizing the significance of permitting at least two electrodes to be circular and concentrically orientated.

Another technical problem is one of realizing that a mercury rocker of this kind shall have at least three electrodes if it is to be able to control two separate adjuster circuits, and therewith to realize that one electrode shall be formed by the aforesaid space, one electrode shall be formed by a disc in the smaller circular area, and one electrode shall be formed by a ball positioned centrally in said space.

Another technical problem is one of realizing the sig¬ nificance of providing a mercury rocker which when used with terrain vehicles will provide an appropriate delay for activation of at first the first adjuster circuit and then the second adjuster circuit at mutually differ¬ ent inclinations.

It will also be seen that another technical problem is one of realizing that, in this case, the disc shall form an electrode common to both adjuster circuits.

Finally, it will be seen that a qualified technical problem is one of realizing that the conicity of the space constitutes a regulating magnitude which affects the response time and sensitivity of the level-sensing device, such that a small cone angle shall be chosen for a higher degree of responsiveness and a larger cone angle shall be chosen for a lower degree of responsive- ness.

SOLUTION

The present invention relates to a solution of one or more of the aforesaid technical problems with the aid of an arrangement which is able to dampen lateral lurching tendencies of a vehicle chassis when one vehicle wheel pair and its wheel axle passes over an irregularity or bump in the surface on which the vehicle moves, wherein each of the wheel axles can be adjusted towards and away from the chassis in a vertical direction, by a respective hydraulic or pneumatic piston-cylinder- device.

Furthermore, there is used a level sensing device, in the form of a mercury rocker, which functions to detect the level of the chassis transversely and is connected electrically to an hydraulic circuit which, depending on the extent of any deviation of the level sensor from the horizontal plane, places either one or the other of the piston-cylinder-devices of said arrangement under pres¬ sure, such as to press down one wheel and its associated axle and therewith to raise an adjacent chassis part to¬ wards the horizontal.

The present invention is based on the realization that the adjustments made by the piston-cylinder-arrangement can be effected advantageously in two stages with the aid of two position-adjusting circuits, and it is pro¬ posed that in the case of a small deviation from the horizontal plane, the level-sensing device shall func¬ tion to open electrically, through the intermediary of a first adjuster circuit, a check valve incorporated in a pressure equalizing line extending between the piston- cylinder devices of said arrangement, wherein the higher pressure prevailing in one of said piston-cylinder- devices will be transferred at a small pressure drop and in a large flow to a similarly located space in the second piston-cylinder-device of said arrangement, as set forth in the characterizing clause of the following Claim 1.

Other developments which lie within the scope of the invention are set forth in the dependent Claims. Thus, it is proposed that in the case of a specific, small deviation, the aforesaid level-sensing device shall function to activate an electrically-controlled check valve in the first adjuster circuit so as to open the line extending between said similarly located spaces of respective piston-cylinder-devices.

It is also proposed that when the deviation is in one given direction, the level-sensing device shall function to activate a check valve belonging to one of said piston-cylinder-devices, and to activate a check valve belonging to the other of said piston-cylinder-devices when said deviation is in a direction opposite to said given direction.

According to another embodiment, it is proposed that in the event of a given, large deviation from the horizon- tal plane, a second adjuster circuit, known per se, is activated so that the hydraulic circuit will place either one or the other piston-cylinder-device under pressure, by force-feeding.

The invention also relates to a level-sensing device which can be used in an arrangement of the aforesaid kind and in which a mercury body is enclosed in a space or chamber provided with at least three electrodes. It is proposed in accordance with the invention that the aforesaid space has the shape of a truncated cone with the centre line of the cone initially positioned hori¬ zontally and fixed in relation to the vehicle chassis, and with the electrodes positioned adjacent the small circle area.

It is also proposed that at least two electrodes are circular in shape and are concentrically positioned, and that one electrode shall form the actual space or cham¬ ber itself, one electrode shall have the form of a disc in the smaller circular surface, and one electrode shall have the form of a ball positioned centrally in the space. In this regard, it is proposed that the disc forms an electrode which is common to two adjuster circuits.

According to one embodiment of the invention, the coni- city of the truncated conical space is selected so that the level-sensing device will have a responsiveness which is adapted in relation to the application con¬ cerned, and tests carried out in practice have shown that a small cone angle shall be chosen when high re¬ sponsiveness is desired and a large cone angle shall be chosen when a low responsiveness is desired.

ApvANTAgfiS

Those advantages primarily characteristic of the inven¬ tive arrangement reside in the creation of conditions which enable laterally related lurching tendencies of a terrain vehicle to be dampened in several stages, such that when the tendency of the vehicle to lurch is slight, a first adjuster circuit will activate a check valve incorporated in a pressure equalizing line extend¬ ing between the piston-cylinder-devices and to open said line and therewith equalize the pressures, thereby adjusting the vehicle chassis to a horizontal position. When the lurching tendencies of the vehicle are high, a second adjuster circuit is activated so as to forcibly supply the piston-cylinder-devices with working fluid. This ensures smoother passage of the vehicle as it runs over irregularities in the surface on which it moves.

As before mentioned, the invention also relates to a specific level-sensing device which will prevent wrong impulses from being generated as a result of engine vibrations, multidirectional impacts and knocks, or centrifugal forces generated when negotiating curves at high speed. Even though such "wrong" impulses should activate the system?, the stabilizing function of the arrangement will not be influenced negatively.

The primary characteristic features of an arrangement for damping lateral-related lurching tendencies of a vehicle chassis are set forth in the characterizing clause of the following Claim 1, while the characteris- tic features of an inventive level-sensing device are set forth in the characterizing clause of the following Claim 5.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to exemplifying embodiments thereof which are preferred at present and which incorporate features significant of the present invention, and also with reference to the accompanying drawings, in which

Figure 1 illustrates in perspective and highly sche- matically a terrain vehicle having four wheels;

Figure 2 is an end view of a terrain vehicle and shows the wheels of the vehicle resting on an even, horizontal surface;

Figure 3 is an end view which shows tilting of a vehi¬ cle chassis when at least one of the vehicle wheels runs over pronouncedly uneven ground; Figure 4 is an electrical-hydraulic circuit diagram of an adjuster circuit for damping lateral-relat¬ ed lurching tendency of a vehicle chassis according to the invention and capable of operating in two stages via a respective ad¬ juster circuit;

Figure 5 illustrates a first embodiment of a level- sensing device in the form of a mercury rock¬ er; and

Figure 6 illustrates a second embodiment of a level- sensing device.

DESCRIPTION OF EMBODIMENTS AT PRESENT PREFERRED

Figure 1 is a greatly simplified, perspective view of a terrain vehicle 1 having a longitudinal centre axis la, a front wheel pair 2 and a rear wheel pair 3 which are shown resting on a flat horizontal surface 11.

The reference numeral 4 identifies a chassis-related plate which is orientated in a horizontal plane 4' .

The wheels 2'and 2" of the front wheel pair 2 coact mutually via their respective axles 2a' 2a".

The wheels 3' and 3" of the rear wheel pair 3 coact mutually via their respective axles 3a' and 3a".

As will be seen from the end view shown in Figure 2, the rear wheel pair 3 is arranged so that the wheel 3' coacts with the chassis 1 through an axle 3a' while the wheel 3" coacts with the chassis 1 through an axle 3a". A first hydraulic or pneumatic-σylinder-device 6 oper¬ ates between the chassis 1 and the axle 3a', while a second, similar piston-cylinder-device 7 operates be¬ tween the chassis 1 and the axle 3a'.

The invention relates to an arrangement by means of which the tendency of a vehicle chassis 1 (Figure 3) to lurch sideways when one of the wheels 3" and its wheel axle 3a of the wheel pair 3 passes an upwardly project- ing irregularity (bump) 10 in the surface 11 can be dampened or counteracted.

Figure 3 shows the wheel 3" passing over a bump 10 in the horizontal surface 11 at the same time as the wheel 3' passes through a pit or hollow 10' in said surface 11.

The axles 3a', 3a" of respective wheels can be moved towards and away from the chassis in a vertical direc- tion by means of their respective hydraulic piston- cylinder-devices 6, 7 with the aid of a hydraulic cir¬ cuit, and it is known to dampen this vehicle lurching movement by applying a hydraulic pressure to the piston- cylinder-device 6 and therewith raise the right-hand chassis part la with the wheel 3' resting on the surface 11.

The arrangement includes a device 12 which senses, or detects, and monitors the transverse level of the vehi- cle chassis, this device being described below with reference to Figures 5 and 6, said device being connect¬ ed to a hydraulic circuit and to a second adjuster circuit in the manner illustrated in Figure 4 and is operative in causing either one of the piston-cylinder- devices 6, 7 to be placed under pressure when the device 12 detects that the chassis deviates from the horizontal plane, so as to press down one wheel and its associated axle and therewith raise an adjacent chassis part to¬ wards a horizontal position.

As will be seen from Figure 3, when the vehicle 3" is located on the bump 10, the chassis 1 will tilt to the right and the level sensor 12 will indicate tilting of the vehicle chassis.

According to the invention, vehicle tilting is indicated in two stages, by activating a first adjuster circuit and then a second adjuster circuit.

When the vehicle chassis has the position shown in Figure 3, the pressure in the piston-cylinder-device 7 will be higher than the pressure in the piston-cylinder- device 6.

The level-sensing device 12 functions to open a valve incorporated in a pressure equalizing line 20, through the intermediary of a first adjuster circuit, wherein the higher pressure in the piston-cylinder-device 7 will transfer to the piston-cylinder-device 6 and therewith urge the wheel 3' down towards the surface 11 and the chassis edge la will tend to lift at the same time as the chassis edge lb is lowered, therewith dampening the tendency of the vehicle chassis 1 to lurch sideways.

Figure 4 is a schematic illustration of an electric- hydraulic circuit arrangement which includes the two aforementioned adjuster circuits.

The second adjuster circuit is known in principle and includes an oil tank 13, a hydraulic pump 14 and a hydraulic control circuit 15 which can be activated electrically by a mercury rocker 12. Figure 4 is primarily intended to illustrate a state, shown in Figure 3, in which the first adjuster circuit is engaged.

The embodiment illustrated in Figure 4 and activation of the requisite piston-cylinder-devices 6, 7 is such that in the position of the vehicle illustrated in Figure 3, there will be generated in the piston-cylinder-device 7 a higher pressure than in the piston-cylinder-device 6 within the space 7a located around the piston rod 7c within the cylinder 7d.

The cylinder space 6a of the piston-cylinder-device 6 coacts with a pipe 20 belonging to the first adjuster circuit, via an electrically actuable check valve 21, and a line 22 which belongs to the second adjuster circuit and which is connected to the hydraulic circuit 15 by means of a hose fracture valve 23.

Correspondingly, the piston-cylinder-device 7 coacts with an electrically actuable check valve 31 and a line 32, via a hose fracture valve 33.

If it is now assumed that the bump or hillock 10 shown in Figure 3 is of a size such as to cause the level- sensing device 12 to tilt slightly and indicate a minor deviation from the horizontal plane, it is proposed in accordance with the invention that a first adjuster circuit is activated when a mercury body 40 makes an electric circuit (51, 52) and causes current to be delivered on the line 34, so as to open the electric valve 31 and therewith cause the higher pressure pre¬ vailing in the space 7a to pass, in the direction shown by arrow PI, through the line 20 and to the space 6a of the piston-cylinder-deviσe 6, via the check valve 21. It should be mentioned here that the line 20 is dimen¬ sioned for a small pressure drop and a large fluid flow, i.e. has a large diameter, and a pressure sensor 28 is connected for detecting pipe or hose fractures.

When the deviation from the horizontal plane corresponds to a given, greater magnitude, the second adjuster circuit is activated and a signal is sent through an electric line 25 so as to activate, over an electric contact 53, the hydraulic circuit 15 and therewith causing hydraulic pressure to be applied to the piston- cylinder-device 6 through the line 22, as illustrated by the arrow P2.

It is obvious that if the level-sensing device 12 is constructed to activate the check valve 31 belonging to the piεton-cylinder-deviσe 7 in the event of a small deviation in one direction, a deviation in the opposite direction will result in activation of the check valve 21.

Thus, if, in the event of a small deviation, the check valve 31 of the piston-cylinder-device 7 is activated, it will be understood that hydraulic fluid is positively delivered to the other piston-σylinder-device 6 when this deviation increases in the same direction, and vice versa.

Shown in Figures 5 and 6 is a level-sensing device 12 which can be used with an arrangement of the aforedes- cribed kind and which has a mercury collection 40 en¬ closed in a space 41 provided with three electrodes.

The space, or chamber, has the shape of a truncated cone, with the centre axis 42 of the cone oriented horizontally to the chassis in an initial position, and with the electrodes placed adjacent the smaller circular surface 43.

One electrode 51 is formed by the chamber casing, one electrode 52 is formed by a circular plate or disc in the smaller circular surface 43, and a third electrode 53 is formed by a ball 44 located centrally within the chamber 41.

The disc electrode 52 forms a common electrode for both of the two aforesaid adjuster circuits.

The conicity of the casing 51 is selected for a prede¬ termined responsiveness, i.e. a small cone angle is chosen when desiring a high degree of responsiveness, according to Figure 6, while a large cone angle is chosen when desiring a smaller degree of responsiveness to disturbances in the form of vibrations, etc. , accord¬ ing to Figure 5.

In the case of the embodiment shown in Figures 5 and 6, when a predetermined minor deviation occurs, the mercury body 40 will establish electrical contact between the electrodes 51 and 52, so as to activate the first ad- juster circuit and its check valve (21 or 31), and in the event of a predetermined, larger deviation, the mercury collection 40 will establish contact between the electrodes 52 and 54, so as to activate the second adjuster circuit (15, 22 or 32).

In Figure 6, the electrodes are referenced 52', 52' and 53', whereas the mercury collection is referenced 40'.

In the Figure 4 illustration, reference signs within parenthesis have been included when a level sensor 12, according to Figure 5, is adapted to sense or detect tilting of the vehicle chassis to the right (according to Figure 3), and a level-sensing device 12', according to Figure 6, is adapted to detect or sense tilting of the vehicle chassis to the left.

Normally, level-sensing devices 12 of mutually the same construction are used to indicate different angles of vehicle tilting.

It lies within the scope of the invention to connect level-sensing devices in parallel, such as the devices 12, 12', so as to indicate vehicle tilting on one direc¬ tion.

It should be noted that the mercury rockers 12 and 12' can be mounted on a plate which, in turn, is pivotally mounted on a shaft 12" which extends parallel to the vehicle axis la, which means that when the vehicle is driven along a sloping surface, the mercury rockers will be adjusted towards an initially horizontal position.

The system can be replenished and controlled in a known manner, through the intermediary of a control circuit 13a. When the system is replenished with hydraulic oil, the pistons and piston rods 6c, 7c of the piston-cylin¬ der-devices will be raised equally, through the interme¬ diary of the circuit 13a.

It will be understood that the invention is not restric- ted to the aforedescribed and illustrated exemplifying embodiments thereof, and that modifications can be made within the scope of the invention as defined in the following Claims.

Claims

L IMS

1. An arrangement for damping the lurching of a vehicle chassis when one of the wheels (3") of a wheel pair (3) and its associated axle pass over an irregularity (10) in a vehicle supporting surface (11), where each of the wheel axles (3a', 3a") is adjustably mounted for verti¬ cal movement towards and away from the chassis (1) by a respective hydraulic piston-cylinder-device (6, 7), and in which a device (12) which functions to sense or detect the transverse horizontal level of the chassis is connected to a hydraulic circuit (15) which, in response to deviation of the device from the horizontal plane, places under pressure either one or the other of the piston-cylinder-devices (6 or 7), so as to urge a corre¬ sponding wheel (3') and its axle (3a") downwards and therewith raise an adjacent chassis part (la) towards a horizontal position, c h a r a c t e r i z e d in that in the event of a minor deviation from the horizontal plane (4'), the level-sensing device (12) will function to open a line (20), via a check valve (31), between similarly located spaces (6a, 7a) for the piston-cylin¬ der-devices (6, 7), wherein the higher pressure prevail- ing in the one piston-cylinder-device (7) will pass to the other piston-cylinder-device (6) via a non-activated check valve (21).

2. An arrangement according to Claim 1, c h a r a c - t e r i z e d in that in the event of a given minor deviation, the level-sensing device (12) will cause an electrically controlled check valve (31) to open.

3. An arrangement according to Claim 1 or 2, c h a r - a c t e r i z e d in that in the event of a deviation in one direction, the level-sensing device (12) functions to activate a check valve (31) belonging to a first piston-cylinder-device (7), and upon deviation in the opposite direction functions to activate a check valve (21) belonging to the other piston-cylinder-device (6).

4. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that in the event of a given, larger deviation from the horizontal plane, the hydraulic circuit (15) is activated so as to pressurize either the one or the other of the piston-cylinder-devices (6 or 7) via a line (22 or 32).

5. A level-sensing device (12) for use with an arrange- ent according to any one of the preceding Claims, said device comprising a mercury body (40) enclosed in a chamber (41) in which electrodes are fitted, c h a r ¬ a c t e r i z e d in that the chamber (41) has the shape of a truncated cone; in that the centre axis (42) of the cone is initially oriented horizontally; and in that requisite electrodes are positioned adjacent a smaller surface of the cone.

6. A device according to Claim 5, c h a r a c - t e r i z e d in that the electrodes (51, 52) are circular and concentrically positioned.

7. A device according to Claim 5, c h a r a c ¬ t e r i z e d in that one electrode (51) is formed by the casing of the chamber (41), one electrode (52) is formed by a disc in a smaller circular surface, and one electrode (53) is formed by a ball (44) arranged cen¬ trally in the chamber (41).

8. A device according to Claim 5, 6 or 7, c h a r ¬ a c t e r i z e d in that the disc (52) forms an electrode which is common to both adjuster circuits.

9. A device according to any one of Claims 5-8, c h a r a c t e r i z e d in that the conicity of the truncated conical chamber (41) is selected with regard to the responsiveness desired, wherein a small cone angle is chosen when a higher responsiveness is desired.