The present invention relates to a system for levelling a surface and to level detectors primarily, but not exclusively, for use with such a system. The present invention was developed originally for use with caravans and the like and will be described accordingly. However, other uses can be foreseen and the invention is not limited to its use with caravans or similar trailer vehicles. As examples, cranes and fire engines often need to be maintained level, and the present invention may be applied thereto.

When caravans, whether having a single axle or pair of axles, are detached from the motor car which has towed them, they are maintained level by means of a system of corner steadies, in generally a screw-jack at each corner of the caravan. These are lowered to a greater or lesser degree by means of a manually operated windlass. It is often the case that the site chosen for a caravan is not level. In fact, the more picturesque the spot and therefore the more desirable, the less likely it is to be level. In order to judge whether or not the caravan is level, the windlass operator generally receives instructions from a colleague inside the caravan who may judge the degree of levelness by such means as a spirit level or even a marble on the floor. Clearly, this procedure requires a great deal of adjustment to obtain

levelness. This requires time, patience and a certain amount of manual dexterity and strength. It is certainly not possible to be carried out by many of those who are disabled and for whom caravaning is a particularly advantageous way to see the countryside. For those who are fit enough to carry through the procedure, it is not a desirable practice, particularly if one has driven the towing vehicle for many hours.

Efforts have been made to overcome this problem. One version has employed hydraulic corner steadies with a central, (manually operable) pumping station for the hydraulic fluid which can be directed sequentially to any selected one of the steadies. This system still suffers from the disadvantage that an operator's skill is required to decide when the caravan is level and does still require a certain amount of manual dexterity.

Devices used to test the degree of levelness have, in the past, included rolling balls or plumb lines. These suffer from the disadvantage that vibration may make them tremble and thus mis-read or they may take a certain amount of time to settle in the equilibrium position, by which time the operator has gone beyond the stage of levelness. It is an object of the present invention to provide an automatic system for levelling caravans and the like other vehicles.

According to a first aspect of the present invention there is provided a levelling system for a surface comprising a plurality, preferably four, of motor operated means to lift the surface disposed remote from one another at or adjacent edge zones of the surface, a level detector mounted on or parallel to the surface and adapted to give an electrical signal for operation of the one or more lifting means. _

Preferably each lifting means is a screw-jack powered by an electric motor, advantageously of the type used to drive windscreen wipers, or other reversible motors. Each electric motor may be connected to the respective screw jack by a flexible drive shaft, which may be adapted to be disconnectible.

The operating signal may switch a respective relay to pass electric current to the motor. The current to the motor may be switched off when a predetermined current flows, indicative that the screw-jack is in contact with the ground.

The level detector is preferably of the type described with reference to the second or third aspect of the invention. It may have a switch means corres- ponding to each lifting means and oriented towards the respective lifting means, the signal from each switch means actuating the corresponding lifting means.

Where the surface to be levelled is generally rectangular, for example a caravan floor, it is preferred to locate a lifting means at or near each corner and to mount the level detector with a switch means directed towards each corner, the switches being disposed symetrically in a cross formation.

According to a second aspect of the present invention there is provided a level detector comprising a pendulum mounted for pivoting movement in any direction and having a metallic portion at or near its lower end, a plurality, preferably four, of switches actuatable by proximity of said metallic portion and disposed at such spaced locations around said pendulum that they are not actuated when the pendulum is in a central position.

Preferably the switches are reed switches and the metallic portion is magnetic.

Advantageously the pendulum is at least partially immersed in a liquid, for example oil, to damp its movement.

According to a third aspect of the present invention there is provided a level detector comprising a plurality, four in the preferred embodiment, of chambers in fluid flow communication, each chamber having a float and electrical switch means acted on by the float when the level of fluid in the chamber changes, fluid being provided in an amount such that the electrical switch means do not produce an operating signal when the chambers are level. Preferably the electric switch means comprises a pivotable arm and the float contacts the underside to engage it with a fixed contact when the level in the chamber increases.

The float may be restrained substantially from movement in a direction other than vertical by baffle means closing one end of the chamber.

The float preferably acts on the pivotable arm at a point close to. the pivot , whereby small movements of the float are magnified in the region adjacent the fixed contact.

Baffle means of different aperture areas may be provided for the chamber associated with one end of the surface than for the chambers opposite thereto.

Embodiments of the present invention will now £> ^e more particularly described by way of example and with reference to the accompanying drawings, in which:

FIGURE 1 is a plan view of a level detector embodying one aspect of the present invention;

FIGURE 2 is an end elevation, partially cut- away, of the level detector;

FIGURE 3 is a cross-section of one chamber of the level detector;

FIGURE 4 is a cross-sectional view of a level detector embodying another aspect of the present invention; and

FIGURE 5 is a circuit diagram of a control system for levelling a surface.

Referring now to Figure 4 of the drawings there is shown a container 10, the left hand side (as seen in Figure 4) of which houses the control mechanism which will be described in more detail below. The right hand side houses a pendulum 11 suspended by means of an universal joint 12. The lower end of the pendulum 11 is movable within a bath of oil 13 and is formed as a large mass 14 provided with a magnetic zone 15 around its periphery. Disposed outside the bath of oil 13 are reed switches 16 (two are shown, but there are four, each adapted to be located facing a respective corner of the caravan or surface to be levelled). Each switch lό is sensitive to signal when the magnet 15 approaches the switch from its median position. At any one time either one or two switches may be actuated.

The container 10 is affixed to the floor of the caravan, for example, by spring biased adjusting screws so that the pendulum is exactly vertical when the caravan is level. Thus, if any one corner of the caravan is down with respect to the other, the pendulum will move towards that corner and thus actuate the switch lό located in the direction of that corner. The levelling mechanism for that corner will be actuated on the signal of the switch. As the pendulum 11 moves on lifting one corner, other switches may be actuated and the caravan will eventually be level.

Other types of switch may be used, ^' such as Hall effect sensors, other proximity switches, and even contact switches (providing the degree of contact required to trip the switch is only light).

In the second embodiment of level detector, four chambers 1, each substantially identical, are arranged in cruciform pattern and are interconnected for

fluid flow between them. In use, the chambers each are directed towards a respective corner of the caravan. The four chambers are formed, e.g. by vacuum moulding or injection moulding of plastics material, into a sealable square box. The spaces 2 remaining within the box around the cruciform level detector may be used to accommodate relays for controlling the power supplied to the corner steadies.

Each chamber is provided with a pivot arm 3 which passes through the wall of the chamber in a sealed manner and, at its end outside the chamber, is provided with an attachment point 4 for an electric wire. Attached to the pivot arm 3 s a contact arm 5 with, at its end remote from the pivot arm, a pivotable contact 6. This is adapted to contact a fixed contact 7 which may be common for all four chambers.

Within each chamber is a float 8 which bears on the lower surface of the contact arm 5« The float is located quite close to the pivot arm 3 whereby small vertical movements of the float are magnified at the pivotable contact 6. A baffle 9 closes the chamber, which baffle is apertured to allow fluid flow therethrough. The purpose is twofold. Firstly it contains the float so that it always acts on a predetermined point of contact arm 5- Secondly, it prevents fluid surges which would otherwise hinder operation. It has been found advantageous for the baffles of the two chambers facing, in use, rearwardly of the caravan to have larger apertures than the baffles of the two chambers facing forwardly. The purpose of this difference will be explained in more detail below.

The float is a sphere of diameter l-§ inches (38.1 mm) and the chamber, including the baffle, is so dimensioned as to leave a gap of l/lό inch (1.6 mm) around the edges of the float. The device is filled with a predetermined

quantity of fluid so that, when level, the floats are in such a position that a gap of l/lO inch (2.5 mm) exists between contacts 6 and 7 . The preferred fluid is anti¬ freeze which may or may not be diluted with water. Although caravans are used mainly during the summer months it is by no means impossible that the owner will wish to re-site his caravan during weather which would freeze ordinary water. The device can then be sealed, with the electrical connections to the exterior. It is then affixed in position, preferably under the floor of the caravan in a central location. Due to the manner of use, the orientation of location is important. Each chamber should face towards a corner where is located a corner steady and the chambers with small apertured baffles should face towards the front.

At or near each corner of the caravan is located a corner steady and to these are operatively affixed electric motors, for example those used for driving car windscreen wipers. Such motors are reversible and have sufficient torque to drive the corner steadies. Means may be provided to override manually the electrical operation of the corner steadies so that, for example in the event of a flat battery, it is not impossible to level the caravan. One method is to connect each electric motor to its respective corner steady by a flexible drive shaft, which can be disconnected if it is so desired. The steady can then be operated by hand.

In one embodiment each motor has leading thereto three wires. These are a' return wire, a wire for powering the motor to move the corner steady downwardly (and hence the caravan floor upwardly) and one to cause retraction of the corner steady. This latter connection passes through a limit switch to cut-off power to the motor as soon as the steady is in fully retracted position. The feed for

downward movement is connected to one of the four relays in the central box. Within the box, each connection is connected to a respective relay to operate the corner steady motor towards which the chamber is directed. The common feed to fixed contact 7 ideally passes close to the door of the caravan where a switch may be located. Generally there is a cupboard at or near such a location and the switch can be arranged discretely. The switch has three positions: off; level; and retract. As stated above, each corner steady will retract until its motor is stopped by a limit switch marking the full retraction.

Another embodiment requires only two wires to each motor, the reversing being effected by contacts in the door switch reversing the current flow.

If the caravan is perfectly level, none of the switches lό or- contacts 6 will be actuated and thus nothing will happen. In order to operate the level system, the caravan must first be deliberately unlevelled. It is normal to do this by unhitching the caravan and allowing it to stand on its small jockeywheel at the front so that it is in a nose down attitude. The switch is then turned.

With the second level detector embodiment, when the caravan is in a nose down attitude, the fluid will be in the two forward facing chambers and thus these two contacts will be made and the front corner steadies actuated. These will extend until the front of the caravan is level. The back steadies will not be lowered until the fluid reaches the rear facing chambers and it is for this purpose that the baffles have differently sized apertures. Those for the front facing chambers being small, fluid flow from those chambers will be hindered and thus there will be, in effect, a slight delay. This will cause the front of the caravan to rise slightly

above level, thus ensuring that the fluid flows into the rear facing chambers. The rear corner steadies will then be actuated until the caravan floor is level. The larger apertures in the rear facing baffles ensure that there is not a delay introduced and thus the caravan does not go over-level.

Instead of having baffles with different sized apertures, it may alternatively be possible to produce the necessary delay by electrical means. The fluid may be any flowable liquid. Anti¬ freeze liquid is preferred since it is easily obtainable but other liquids may be used, especially alcohol- containing liquids with low freezing points.

Similarly, in the first embodiment of level detector, when the caravan is in its nose down attitude, one or both of the forward facing switches lό will be actuated. The procedure which follows is best described with reference to Figure 5 _. which is an electrical circuit diagram of the control circuit presently preferred, although other circuits could be used which would acheive a similar result.

Normal power circuits in a caravan or vehicle operate at I2v and are supplied by a battery. The voltage supplied to the switches lό is reduced by means of circuit 20 to 5v. Each switch is thus adapted to give a signal via 21 to an EPROM 22 at an input (5 to 8) thereof. In turn the EPROM 22 signals at a respective output (9 to 13) and enables a respective transistor (TR1 to TR4) which thereby causes operation of a respective relay (RLl to RL4) Current may then flow (at I2v) to a respective motor and a corner of the caravan is lifted.

As the pendulum moves, various motors may be operated until the caravan is level. At this point, there will certainly be one corner steady, possibly two or even three corner steadies, in contact with the ground. The

control circuit now switches to a second phase of its operation. The switchover is controlled by the EPROM when it has received no signals from the switches over a predetermined time. In other words, the pendulum is and will remain in its central vertical position. During this first phase, any motor may be operated once or • more times if it should prove necessary.

The second phase involves all four transistors TR1 to TR4 being enabled and thus all four motors being operated. Any corner steady not in contact with the ground will now be lowered so that all four steadies will be in contact with the ground and the caravan will be held level. During this second phase, the pendulum switches are dis¬ abled, so that no further levelling can occur. The current to each motor passes through a respective relay (acting as a current limiter switch) RL5 to RL8. Once a steady contacts the ground, the current requirement of the motor increases. Once the current to a particular motor reaches a predetermined value, for example 2 _ to 3 Amps, the respective relay closes a relay switch fed at 5v from circuit 20. A signal is thereby given to a respective one of four latching circuits 23 which instruct the EPROM to cause that motor to be switched off. This switching out is irreversible during the procedure.

When all four motors have been switched off, the system goes to its third phase when the pendulum switches and the control circuit are disabled. All four of the corner steadies are now in position and the caravan will remain level.

When it is desired to move the caravan or lift the steadies in preparation for relevelling, the initiating door switch is turned. Within the switch are a number of contacts which: reverse the polarity of the drive current to the motors; enable the control circuit, and retain

the pendulum switches disabled.

Since no signals from the switches 16 can be received, the control circuit proceeds directly into phase two. All four motors are energised but with reverse polarity. The corner steadies rise until they reach the point of maximum upward travel when the current increases, thus operating the respective current limiter relay, and stopping the motor.

When all four motors have stopped the system again goes to its third phase and effectively switches itself off.

The system has been described with reference to four pendulum switches and four motors. More or less can be provided if it should prove necessary or desirable. Similarly, the _, system has been described with each switch directed to a corner of the caravan. It need not be. Instead, the four switches may be aligned with the major axes of the caravan (i.e. switches facing front, back, left and right). The EPROM would then be programmed with a different logic, for example to operate both front motors when only the forward facing switch was actuated or to operate only the front left motor when both forward and left facing switches were actuated. The current limiter relays described above obviate the need for limit switches on the corner steadies as described with reference to the other embodiment. It would be possible to utilize the above described control circuit with either the pendulum switch type level detector or the floating ball type or, for that matter, any other type of automatic level detector.

Clearly, if the caravan has one side higher than the other, the corner steadies on the uphill side will stop before those on the downhill side.

Use of the system enables a caravan to be made level and secured level within a matter of minutes

(approximately two minutes) with no effort by the user other than turning a key in an initiating door switch. The system can be operated by a single person and even by those who are disabled.

As stated above, the device has been described with particular reference to caravans, although it may be used in many similar applications.