WO1989008785A1

WO1989008785A1 - Control means for hoisting devices

Info

Publication number: WO1989008785A1
Application number: PCT/SE1989/000133
Authority: WO
Inventors: Stig Stenlund; Jan Baecklund
Original assignee: Parator Ab
Priority date: 1988-03-15
Filing date: 1989-03-15
Publication date: 1989-09-21
Also published as: FI92243B; FI904551A0; FI92243C; SE461419B; AU3293489A; SE8800925L; SE8800925D0; EP0424389A1

Abstract

A means at a first piston (1) with two active surfaces (1a, 1b) included in a bogie hoist or similar for movement by means of a pressurized driving medium (10) in two mutually opposite directions. The one active surface (1a) of the first piston (1) is elaborated larger than the other active surface (1b) of the first piston (1). A valve (4) is connected directly between the two active surfaces (1a, 1b) of the first piston (1). The said valve (4) in relation to a given differential pressure is arranged to open and close a channel (3) directly between the said active piston surfaces (1a, 1b). A shut-off valve (5) is also included, which in association with the one turning position of the movement of the first piston (1) is arranged to close the said channel (3).

Description

CONTROL MEANS FOR HOISTING DEVICES

The present invention relates to a control means which is included in hoisting devices, for example in vehicles, where simultaneously aspired to low weight and low cost for the device as well as such fast hoists as can be permitted by the installed hoisting power. The means consists of a duoble-acting cylinder with two differently sized piston surfaces and a valve which controls supplied medium to and from the cylinder so that the piston rod of the cylinder can be controlled or steered in two directions. The use of the device is limited to such hoisting devices with which large hoisting power is required only in one power direction and where the power in the other power direction largely amounts to what is required to overcome for instance inherent weight and friction. Among the lifting devices in which this invention can be incorporated mention may be made of, for example, bogie hoists and so-called load-lifters on trucks.

Through for example the Swedish patent No. 7413748-0 a control device for steering of one or a plurality of cylinders in a bogie hoist is prior art knowledge. The said patent indicates a means for a bogie hoist for, for example, a truck which can be driven faster than with prior art technique.

There is, however, a need for example on trucks to further expedite the cylinder movements of the control means and at the same time to reduce the weight and cost thereof. This is the primary object of the present invention. An essential prerequisite for low weight and low cost of the control means is that the dimensions of both cylinder and valve and of their interlinking guidance components can be kept small. This can seemingly be incompatible with the requirement for increased speed in that increased speed normally involves an increased volumetric flow and thus increased dimensions to counteract an increase in the pressure drop in valves and lines. In many lifting devices for example of type bogie hoist and load-lifter the lifting means and its cylinder perform relatively long movements without large lifting power. The power supplied to the pump of the lifting device is then low or very low in relation to the maximum available power. The time consumed for this long but not

" power-demanding movement often comprises if it is performed with the same speed as at maximum force a dominating share of the total time for the movement.

In, for example, a bogie hoist the lifting arm performs a very long movement before it reaches the bogie axle and can start to lift this.

Since this long movement is necessary in order to permit the resilient movement of the bogie axle without it reaching the lifting arm a shorter time for the movement cannot be attained by the length of the movement decreasing but only by the speed of the movement increasing. In a bogie hoist the bogie is raised when the vehicle gets stuck in order thereby to increase the force on the driving axle. For the roadablϊlity of, for example, a- truck it is of great importance that the bogie can rapidly be lifted and getting stuck avoided. For considerations of cost and weight an increased supplied volumetric flow cannot be accepted and instead this is adapted in the first instance to be able with acceptable speed to cope with the movement requiring the maximum power. In, for example, a load-lifter a loading or an unloading operation is often carried out between ground level and platform level. The load platform thus often goes empty during the lifting movement which then in view of the available lifting power with contemporary technique is performed unnecessarily slowly since the volumetric flow and the speed are adapted to the highest permissible load and the highest available power. A faster lifting movement when the load is low is therefore desirable.

In the aforesaid Swedish patent a technique is shown whereby the volumetric flow at low load can be significantly increased. There are also other methods of increasing the volumetric flow to and from the cylinder. Common to all these solutions is that the volumetric flow increases in the lines between cylinder and valve as well as often inside the valve. In a bogie hoist it is desirable to inrease the idling speed so that this is at least five times as high as under load. The pressure drop in the line is then ordinarily more than twentyfive times higher when idling than when under load. One is therefore obliged to increase the dimensions of lines and usually also of the valve over and above what is justified by only driving with a heavy load. The present invention indicates a solution to this problem whic permits the lines between cylinder and valve as well as the valve itself in view of the lifting movement to only need to be dimensioned in view of the volumetric flow supplied from the pump to the valve and . not for the higher volumetric flow that the speed of the cylinder during idling it itself requires. Both the lines between cylinder and valve and the valve itself can thus be given the smallest possible dimensions and thus weight and cost.

The present invention is based on the provision in the piston between the piston surface which has a piston rod and the piston surface which lacks a piston rod of a built-in valve. This valve can only permit a volumetric flow in one direction going from the piston side with a piston rod towards the side without a piston rod and then only on condition that the pressure on the piston side with a piston rod exceeds the pressure on the piston side without a piston rod by a certain minimum value. If the outer valve starts to steer the volumetric flow towards the piston side without a piston rod and if the outer valve simultaneously closes and prevents the volumetric flow from passing from the cylinder side where the piston rod is situated a pressure differential will occur across the piston and a certain minimum value determined by the inner valve in the piston a volumetric flow will commence to pass through the valve in the piston from the piston side with a piston rod to the piston side without a piston rod. Concurrently with this, the piston rod starts to move out of the cylinder at a speed which is dependent only on the volumetric flow supplied from the outer valve and the cross- sectional area of the piston rod. The diameter of the piston thus does not affect the speed of the piston rod. The volumetric flow supplied is normally the same as that supplied to the outer valve from the pump. For reasons of cost and weight the pump is usually single and provided with a fixed displacement which means that the volumetric flow in the main can only be varied by varation of the pump speed. The speed increase attained when the piston rod moves out of the cylinder will be dependent on the ratio between the area of the piston and the area of the piston rod. If the diameter of the piston rod is 50% respectively 40% of the piston diameter the speed increase upon the movement of the piston rod out of the cylinder will be 4 respectively 6.25 times, in, for example, a bogie hoist a speed increase of 6.25 times is suitable and possiible during the time the lifting arm is performing its long and light-going movement. At the same time as the speed increases and the volumetric flow passes through the valv inside the piston the possible force of the cylinder is limited. In order to build up the minimum pressure differential across the pisto a relatively high pressure is required on the piston side without a piston rod. With a piston rod diameter that is 50% respectively 40% of the piston diameters the pressure on the piston side without a piston rod will be 3 respectively 5.25 times as high as the pressure differential at which the valve inside the piston opens. How high this pressure differential needs to be is decided by the power requiremen when the piston rod is steered into the cylinder. In, for example, a bogie hoist where the lifting arm during the idling movement only needs to overcome an inherent weight and friction this pressure differential can be chosen low, or about 10-20 bar. The pressure on the piston side without a piston rod at which the cylinder can commence supplying power can as above with a piston rod diameter 40% of the piston diameter amount to 52.5-105 bar. With the invention and thanks to the valve placed in the piston of the cylinder a very high piston rod speed can be attained when the need of power is low. The high speed can, with the invention, be attained at the same time as the outer valve and the line to the cylinder are flowed through by at most the volumetric flow of the pump, i.e. at most by the volumetric flow which goes in the outer valve and line to the cylinder during power-demanding lifts. The out valve and lines can thus be dimensioned as small as possible, whereupon the lowest weight and cost can be combined with high speed at low power requirements. The outer valve in this invention closes when the piston rod moves out of the cylinder flow passage from the cylinder side where the piston rod goes as long as the fast non-power-demanding movement continues. When the piston rod of the cylinder encounters an increasing external force which opposes the movement of the piston rod out of the cylinder the pressure increases on both sides o the piston with a pressure differential between them which is virtually constant. At a certain pressure that is lower than the highest pressure the outer valve opens so that the volumetric flow can pass from the side of the cylinder where the piston rod goes via a valve to a tank. In that the pressure differential across the valve then changes direction and also magnitude the flow across the valve built into the piston ceases. The force which can be transmitted via the piston rod can now increase since high prssure can now only act on the piston side which lacks a piston rod and the piston side with a piston rod is only exposed to the low pressure that will be a consequence of the flow from the piston-rod side of the cylinder out through the cylinder through the line through valve and thence to the tank. The cylinder is now able to generate maximum power during the movement of the piston rod out of the cylinder.

The outer valve in the present invention can be elaborated in several different ways. In vehicles the pump is usually provided with fixed displacement. The volumetric flow is proportional to the speed.

Often the pump is driven by an electric motor the speed of which is influenced by the pressure. It is very common, for example in the case of a bogie hoist, for the start of the pump to be co-ordinated with an electrically controlled directional valve which is included as a subcomponent in the valve. It is also common for the pump to be stopped by pressure switches that trip when the cylinder and the lifting device have reached limit positions. Since lifting devices on vehicles are to stand still during a very large share of a journey the capability of retaining the cylinder in position is very important and leads to a requirement for high tightness in the valve of the cylinder. The functionally and economically viable and suitable valve elaboration is to supplement an electrically or by some other means controlled directional valve of slide type which has inadequate tightness with a load-holding presteered valve of so-called seat type which gives the wanted tightness. This type of valve which is essentially presteered by the directional valve cannot open flow paths from the cylinder via pressure only inside the cylinder or in the lines between cylinder and outer valve. In such a load-holding valve each line to the cylinder has its own valve cone with seat seal. The valves are elaborated as check valves for which reason flow to the cylinder is possible if the valve cone is supplied with a volumetric flow from the directional valve between the cone and the pump. In

SUBSTITUTE f 6 order to permit a volumetric flow to pass from the cylinder via the cone to the directional valve and thereafter to the tank it is require that the valve cone be lifted from its seat to an open position with force exerted on the cone. This opening is accomplished by allowing the pressure from the volumetric flow to the other side of the cylinder to act on the piston surface to a so-called pilot cone which in its turn, exerts pressure on and opens the seat valve cone. No volumetric flow from the one side of the cylinder can thus pass to a tank via the outer valve without pressure and volumetric flow being supplied to the other side by the directional valve.

In the present invention the cylinder shall be supplied upon a piston-rod movement out of the cylinder and when the power requirement is low with a volumetric flow on the side of the cylind without a piston rod at the same time as the load-holding cross- steered valve of the outer valve shall be closed. In order for this to function the pressure from the supplied volumetric flow must be prevented from opening the seat valve on the piston-rod side of the cylinder until the pressure on both sides of the piston has reached a relatively high pressure. Upon start of the movement no pressure is exerted on the piston-rod side of the cylinder and consequently the pressure on the side of the cylinder without a piston rod endeavours to open the seat valve on the piston-rod side of the cylinder. There are several possible elaborations of the load-holding valve in order prevent this. The best and simplest is to allow the pilot cone which endeavours to open the seat-valve cone on the piston-rod side of th cylinder to act against a spring which can also be pretensioned to reduce the necessary impact path. The valve cone on the piston-rod side of the cylinder cannot now open until either pressure acting on quick starting only on the side of the cylinder without a piston rod has attained a certain value or the pressures on both sides of the cylinder piston have attained a relatively high pressure. The lower level for pressure only on the side of the cylinder without a piston rod decided by the spring force should be chosen in view of how rapidly the directional valve of the outer valve switches to full volumetric flow and in view of, for example, how much the piston r must move out of the cylinder before the pressure on the piston-ro side is developed. Here the choice will be dependent upon, for example, the resilience of the hose, if there is a risk of air in the medium, etc. A practical spring force in, for example, a bogie hoist gives an opening at approx. 50-60 bar. A suitable level thus lies in the vicinity of the pressure at which the piston rod starts to be able to provide power when moving out of the cylinder and when volumetric flow starts to go via the valve in the piston of the cylinder.

In the present invention the outer valve switches down the piston-rod speed upon movement out of the cylinder from high speed and low force to low speed at a certain piston-rod force which gives a pressure on the side of the cylinder without a piston rod which lies at a relatively large distance above the pressure at which the cylinder starts generating power and at such a distance from the maximum permissible pressure or the pressure affected by the power switch that this does not risk being attained in any situation liable to occur in view of the operation of the lifting device. It is appropriate to go high in pressure which can safely be carried through and thereby to prolong the rapid movement as long as this can take place. The switching point of the presteered valve when the valve cone on the side of the cylinder without a piston rod starts to open is attained when the force on the pilot cone against the side of the cylinder without a piston rod balances out the force on the spring at the opening position plus the force on the valve cone on the piston-rod side of the cylinder. The opening pressure at the switching point can therefore be determined by adapting the diameters of the pilot cone and of the seat of the valve cone to the spring which brakes the pilot piston and the pressure drop prevailing across the valve built into the cylinder. The diameter of the pilot cone must be larger than the diameter of the valve cone. If the difference is small the pressure at the switching point will be high and if the difference is large the pressure at the switching point will be low. After switching, the pressure will be very low in the piston-rod side of the cylinder and the speed will also be low whereupon the pressure on the side of the cylinder without a piston rod also falls. The external force, however, is usually relatively unchanged if the switching takes place rapidly. The pressure that is exerted on the side of the cylinder without a piston rod after the switching shall, at the same external force as priort to the switching, be sufficiently high to overcome via the area of the pilot cone the braking force on the pilot cone from the spring in the position where the valve disc on the piston-rod side of the cylinder is opened and then also be able to overcome the differential pressure acting across the valve cone and endeavouring to close it. The valve in the present invention must thus, for smooth and distinct function, be adapted to the power requirement of the cylinder upon rapid movement, the pressure drop across the valve built into the piston of the cylinder upon opening and flowing therethrough and to the propagation of pressure on both sides of the cylinder upon rapid starting of the fast movement as well as to both slow and rapid increase of the external force upon movement of the piston rod out of the cylinder. The dimensioning and adaptation of the outer valve as well as the choice of ratio between cylinder diameter and piston-rod diameter and of the opening and flow pressures of the valve built into the piston of the cylinder must thus be adapted to the peculiar nature of the lifting device. An arrangement according to the present invention is then dimensioned differently for, say, a bogie hoist than for, say, a load-lifter. The primary feature distinguishing the two lifting arrangements is the ratio between the power requirement for the heaviest load and when idling. A bogie hoist will, with its unusually low power requirement during the idling movement, be able to be given a faster idling movement than what is possible and also from other viewpoints suitable in the case of a load-lifter.

When a steering arrangement according to the invention is steered in the opposite direction to the lifting movement, in other words when the piston rod moves into the cylinder, the movement is driven by the outer load as long as this exists and is able to overcom the friction and pressure drop from the flow in the lines and valve of the cylinder. The movement is subsequently driven by a pressure drop across the piston of the cylinder generated by the pump. Obviously a pressure drop across the piston of the cylinder can then not exist which is higher than the differential pressure of the valve built into the piston of the cylinder upon opening. or throughflow. The possible pressure drop across the piston of the cylinder without the valve in the piston of the cylinder opening must therefore be sufficiently high to permit the piston rod to be driven to the wanted position inside th cylinder. The present invention is therefore limited to use in arrangements with on the whole only large forces in one direction an with relatively small power requirements in the other direction and with relatively small power requirements in the other direction as the case generally is in lifting devices of various kinds and then also others than those encountered on vehicles. Among typical stationary lifting devices which can benefit by a steering arrangement accordin to the invention mention may be made of, for example, lifting tables.

In a control means or steering arrangement according to the present invention the piston rod is steered inside the cylinder until the piston bottoms or comes to lie relatively close to the inner postion. When the piston movement is unable, owing to an external stop or to bottoming of the piston, to .travel any further, the pressur on the piston-rod side rises. Since the valve, which is built into the piston of the cylinder, normally can open at a certain pressure drop across the piston of the cylinder throughout the entire range of trav of the cylinder beyond the limited range of travel which lies at the stop position which is indicated by an external stop or by an internal stop in that the piston of the cylinder bottoms in the limit position o the cylinder the valve built into the piston of the cylinder must have the characteristic that the flow path from the piston-rod side of the cylinder to the side of the cylinder without a piston rod is blocked or flow can only take place at such a high pressure drop that for exampl a pressure switch gives a signal whereupon the directional valve in the outer valve closes and the volumetric flow to the cylinder ceases The valve built into the piston of the cylinder according to the present invention can be elaborated in a large number of different ways. A common and appropriate embodiment which is reliable and economical is that the valve in the first instance consists of a spring-loaded check valve of seat type. The choice of spring force then gives the opening pressure at the same time as the seat valve gives a reliable and good tightness. Within the range at the bottom position where the flow path between the piston-rod side of the cylinder and its side without a piston rod must be closed or heavily throttled flow can be prevented in a numbers of ways that differ in principle, among which mention may be made of: A first valve which permits flow in one direction with a lowest pressure drop accomplished for example with the above- described spring-loaded check valve, is supplemented with a second valve connected in series with the first valve and which is open throughout the entire range of travel of the cylinder except within the range of travel where the valve is to be closed and where it is the position of the piston of and the supplementary valve connected in series that in the vicinity of the bottom position of the piston closes the flow path. In a preferred embodiment such a supplementary second valve connected in series will be described.

A single valve which permits flow in one direction with a lowest pressure drop accomplished for example with the above- described spring-loaded check valve within the major share of the flow range, supplemented with an action which causes that opening of the valve within the range of travel at the bottom position of the cylinder at which flow may not take place from the piston-rod side of the cylinder to the side of the cylinder without a piston rod cannot take place or can only take place at a very high pressure drop. This embodiment can be realized for example in the preferred embodiment with a spring-loaded check valve in that the valve within the range of travel at the inner limit position of the piston is prevented from opening by a raised spring force either by the force in the first spring at the inner limit position being further tensioned and being permitted to act against the check-valve cone so that its opening and throughflow pressure is drastically increased or by the check- valve cone being elaborated so that it, if it opens, has such flow paths through or around the cone that these can be blocked by elements which, in the limit positions of the cylinder and by th position of the piston, are displaced to a position which closes or severely throttle the flow paths and which gives a very high pressure even at a negligible througflow.

The invention will now be described in greater detail and with reference to the accompanying drawings, wherein Fig. 1 shows idle running of a hydraulically or pneumatically driven first piston in the forward direction, Fig. 2 shows the approximate position at which th first piston and then more specifically its piston rod is loaded, Fig. 3 shows the position in which the first piston completes its return movement, Fig. 4 shows an example of the type of bogie hoist for vehicles, to which the invention can be applied, Fig. 5 shows the firs piston with its piston rod and associated parts in greater detail and Fig. 5 a-j illustrate certain variants thereof.

The bogie hoist in Fig. 4 comprises lifting members 14, 15 wit for example, rollers, which are arranged to be moved towards two arms (not shown), in one ends of which an axle of a pair of bogie wheels is rotatably secured and in the other ends, of which a spring assembly of a second pair of wheels is secured. The lifting members 14, 15, which _. obviously can have different embodiments than those shown here, are manoeuvred by means of a crankshaft 16 which, in turn, is manoeuvred by means of a crankshaft 16 which, in turn, is manoeuvred by the piston rod 2 of a first, appropriately hydraulically driven piston 1.

Connected to the bogie hoist is a manoeuvring device 17 which incorporates a device (not shown) which includes for example a drive motor, pump, pressure tank, oil filter, air filter, etc., and steering members for steering of the raising and lowering movements of the bogie hoist.

The manoeuvring device 17, as previously mentioned, incorporates a not-shown pressure source 10 or a pump as well as a similarly not-shown tank 9, in addition to the first hydraulic piston 1 , the piston rod 2 of which for example can manoeuvre the aforesaid crankshaft 16 in a bogie hoist. The manoeuvring device 17 includes a fourth, pretensioned check valve 6 in the supply line from the pressure source 10, a 4-way directional valve 7 which for example can be electrically actuated and which steers a pressure medium from the pressure source 10 to either side partly of a second hydraulic piston 11 , partly to either active side of the surface 1 a or 1 b respectively of the first piston 1. The second piston 11 is provided partly with a piston rod 12 which with its one end is arranged to influence a first check valve 18, pretensioned for example by means of a spring and with its other end a second check valve 19, pretensioned for example by means of a spring, partly with a spring 8.

The first piston 1 with associated piston rod 2 is shown more closely in Fig. 5. The first piston 1 has two active sides or surfaces 1a and 1b, against which the driving pressure of the drive medium from the pressure source 10 can exercise its effect during different parts of the movement of the first piston 1 in reciprocating directions. It should be noted that the one active surface 1a, to the left in Fig. 5, is chosen not unessentially larger than the second active surface 1b.

It is evident from Fig. 5 that the piston rod 2 running through the first piston 1 or alternatively the first piston 1 is provided with a channel 3 which can connect the two sides of the first piston 1 directly with each other under certain conditions. The said channel 3 is arranged closed by a cone 4 which interacts with a seat 3a located in the channel 3. The cone 4 is held against the seat 3a by means of one end of a suitably chosen tensioned spring 4a, the other end of which presses a shut-off valve 5 against a seat 3b to protrude a shor distance beyond - to the left in Fig. 5 - the limiting surface 1a of the first piston 1. Upon movement of the shut-off valve 5 - to the right i Fig. 5 - the shut-off valve is pressed so far that against the seat 3b it obstructs its associated throughfiow holes and compresses the spring 4a, whereby the cone 4 is forced against the seat 3a and reliably shuts off the channel 3. The manoeuvring device works in the following way during idling. The directional valve 7 is activated, for example by a closing of an electric circuit, and has assumed the position shown in Fig. 1. Pressure medium from the pressure source 10 is fed to the^" fourth, spring-tensioned check valve 6, which is lifted by the medium, and this is transported on via the first, spring-tensioned check valve 18 to side 1a - seen in Fig. 1 - of the first piston 1 and drives the first piston 1 towards the right in Fig. 1. The return flow from the right- hand side of the first piston 1 - seen in Fig. 1 - builds up - on accoun of a second check valve 19 being closed - a counterpressure which almost immediately becomes greater than the driving pressure on account of the differing surfaces 1b and 1a of the first piston 1. Hereby a differential pressure develops across the valve 4, which 1 3 under the influence of the adapted springs 4a opens the channel 3, through which medium from the piston-rod side 1 b of the first pist 1 flows directly over to the drive side of the first piston 1 via hole behind the seat 4 - viewed in the flow direction through the channel - via the spring 4a and via holes before the shut-off valve 5, viewe in the flow direction through the channel 3. This overflowing of medium continues until the piston rod 2 of the first piston 1 encounters a powerful resistance, this position being illustrated in Fig. 2. This rapid and direct overflowing of return medium reduces t duration of the idling periods by more than 50% in comparison with prior art technique, i.e. the duration of the idling periods will be approximately 2-3 seconds instead of 7-10 seconds. Since the idlin period comprises an essential part of the entire movement the results will be a significant increase in the speed of the first pisto 1 during its movement until the piston rod 2 is loaded, i.e. to the point at which the lifting members 14, 15 make contact with the levers in order to lift the pair of bogie wheels.

When such contact takes place a pressure increase occurs in t system, the said pressure increase resulting in a rise in the pressur on the left-hand side 1a of the first piston 1 and a lowering of the pressure on the piston-rod side 1 b of the first piston 1 , whereby th cone 4 again seals against the seat 3a and the flow condition illustrated in Fig. 2 results, namely that an increased pressure from the pressure medium acts on the left-hand side of the second piston 11. The spring 8, which works between the left-hand side of the second piston 11 and an impact surface, is so adapted that it resist the pressure which is generated during idle-running of the first piston 1 but gives way for the higher pressure during running in the loaded condition. The second piston 11 and consequently the right- hand end of the piston rod 12 rigidly connected thereto influences an lifts the second, spring-tensioned check valve 19, whereby the retur flow from the rigt-hand side of the first piston 1 passes via the second check valve 19 to the tank 9.

When the first piston 1 is to perform a return movement, i.e. when the pair of bogie wheels is to be lowered again, the directional valve 7 is activated to its right-hand position according to Fig. 3. Hereby the pressure medium from the pressure source 10 is conduct via the fourth check valve partly to the right-hand side of the second piston 11 , causing the second piston 11 to move towards the left according to Fig. 3 and to open the first check valve 18, and partly towards the right-hand side of the first piston 1 , whereby the return flow from the left-hand side of the first piston 1 passes via the first check valve 18 to the tank 9, and when the first piston 1 reaches its left-hand turning position - seen in Fig. 3 - the shut-off valve 5 makes contact with the cylinder bottom of the piston 1 , whereby the shut-off valve 5 is moved as above and prevents the cone 4 from moving from the seat 3a. In other words, in this position the channel 3 is definitely blocked irrespective of any pressure difference. By this means it is possible - if so desired - to shut off the driving pressure in a not-shown manner with the aid of, for example, pressure switches. When the directional valve 7 is moved to the neutral position the first piston 1 is locked in its chosen position partly by the first check valve 18 and partly by the fourth check valve 6.

The invention is intended in the first instance for bogie hoists but is also usable in other contexts in which it is desired to speed up one running period in relation to another running period with a different load.

SUBSTITUTE SHEET

Claims

WHAT WE CLAIM AND DESIRE TO SECURE BY LETTERS PATENT IS:

1 . A means for controlling of the movements of a lifting device by means of a cylinder with two differently sized pressure surfaces and in which the piston has in any case on at least one of the sides of the piston an outer valve and between these and the two pressure surfaces of the cylinder two lines through which the cylinder can be supplied with medium under pressure so that movement can take place in two opposing directions, c h a r a c t e r i z e d in that the cylinder can move with a relatively high speed of movement at low external force and with such a direction of movement that the piston rod which is sited in the side of the piston with the smaller pressure surface moves out of the cylinder whereupon the outer valve only supplies the cylinder side with the larger surface with medium at the same time as the other cylinder side with the smaller pressure surface has its flow path through the outer valve closed, whereupon medium at a certain predetermined differential pressure across the piston of the cylinder and throughout the entire stroke of the cylinder apart from and in the immediate vicinity of the inner position for the piston rod with the larger cross-sectional area sitting in the piston side with the smaller pressure surface, can flow through an inner valve in or at the piston of the cylinder in one single direction of flow from the piston side with the smaller pressure surface to the piston side with the large pressure surface, whereupon the outer valve, upon increase of the outer force and thus also of the pressure on the larger pressure surface opens a flow path from the cylinder side with the smaller pressure surface through the valve to a tank at a certain predetermined pressure below the maximum pressure of the medium which is supplied to the outer valve, whereupon at the same time the speed of movement of the cylinder decreases when the flow through the inner valve ceases and the external force can be maintained through essentially only a high but reduced pressure acting on the larger pressure surface.

2. A means as claimed in Claim 1 , c h a r a c t e r i z e d in that the valve provided in or at the piston in the cylinder has one single valve opening and one single sealing place whose possible throughflow area is closed or drastically reduced or whose differential pressure upon throughflow is drastically increased at or in the vicinity of the inner position for the piston rod with the larger cross-sectional area.

3. A means as claimed in Claim 2, c h a racte ri z ed in that the valve consists of a spring-loaded check valve which at the inner position for the piston rod with the larger cross-sectional area has its throughflow area closed or drastically reduced or its closing force through further spring loading drastically increased.

4. A means as claimed in Claim 1, cha racte rized in that the inner valve provided in or at the- piston in the cylinder at least at or in the vicinity of the inner position for the piston rod with the larger cross-sectional area has two or more valve openings connected in series and sealing places when a first valve opening and a single sealing place always throughout the entire stroke can open for flow in one single direction at a certain predetermined differential pressure across the piston of the cylinder and other valve openings and sealing places at or in the vicinity of the inner position for the piston rod with the larger cross sectional area closing or drastically reducing the possible throughflow area or whose differential pressure upon throughflow drastically increases.

5. A means as claimed in Claim 1, c h a ract e ri z ed in that the first valve opening and the first sealing place consists of a spring-loaded check valve.

6. A means as claimed in Claim 4, characterized in that one or more valve openings and one or more sealing places after the first valve opening and the first sealin place is/are closed or drastically reduce(s) its/their possible througflow area or drastically increase(s) its/their differential pressure upon throughflow or in the vicinity of the inner position for the piston rod with the larger cross-sectional area.

7. A means as claimed in any one of Claims 4, 5 and 6, c h aracte r i z e d in that the throughflow area and throughflow holes of a second valve cone are covered over and sealed by the force movement of the valve cone at and in the vicinity of the inner position for the piston rod with the larger cross-sectional area, whereupon the flow path between the two sides of the piston is closed or drastically reduces its throughflow area.

8. A means as claimed in Claim 1 , c h a r a c t e r i z e d in that the outer valve consists of a directional valve and a presteered valve connected in series therewith consisting of a pilot-controlled valve cone with seat seal for each side of the cylinder and a pilot cone located between them which can open the flow passage out from a cylinder side with the aid of pressure acting on the pilot cone from the other cylinder side.

9. A means as claimed in Claim 8, c h a r a c t e r i z e d in that the pressure from the cylinder side with the larger pressure surface of the piston acts on one side surface of the pilot cone upon opening of the opposite valve cone and flows out from the cylinder side with the smaller pressure surface, whereupon the force on the pilot cone is balanced by the force from a spring which opposes opening of the valve cone and from the forces which endeavour to close the valve cone essentially coming from pressure acting on the cone, the spring force being so adapted that opening of the valve cone cannot take place during the time pressure is being built up on the smaller pressure surface of the cylinder, and in that the spring force and the diameter of the pilot cone and the sealing diameter of the valve cone are so adapted that the valve cone is opened at a predetermined pressure lower than the maximum pressure of the medium which is supplied to the outer valve and with adapation to the differential pressure prevailing across the piston of the cylinder before the opening and which is determined by the throughflow pressure of the inner valve.

10. A means at a first piston (1) with two active surfaces (1 a, 1b) included in a bogie hoist or similar for movement by means of a pressurized driving medium (10) in two mutually opposite directions, c h a r a c t e r i z e d in that the one active surface (1 a) of the first piston (1) is elaborated larger than the other active surface (1 b) of the first piston (1), that a valve (4) is connected directly between the two active surfaces (1a, 1b) of the first piston (1), that the said valve (4) in relation to a given differential pressure is arranged to open and close a channel (3) directly between the said active piston

SUBSTITUTE S surfaces (1a, 1b) and by a shut-off valve (5), which in association with the one turning position of the movement of the first piston (1) is arranged to close the said channel (3).

11. A means as claimed in Claim 10, with a piston rod (2) running out from the second active surface (1b) of the piston (1), c h a racte ri z e d in that the other active surface (1b) of the piston (1) is smaller than the one active surface (1a) of the piston (1) so that a driving pressure generated by the driving medium (10) exerted on the one, larger active surface (1a) of the piston (1) creates on the other, smaller active surface (1b) of the piston (1) such a differential pressure which is chosen to be able to manoeuvre the said valve (4) to open the said channel (3) running directly from the piston-rod side (1b) of the piston (1) to the one, active larger surface (1a) of the piston (1).

12. A means as claimed in Claim 11, with the piston rod (2) running through the first piston (1), c h a racte ri ze d in that the piston rod (2) is elaborated with the said channel (3) in which the said valve (4) and the said shut-off valve (5) are located.

13. A means as claimed in any of the preceding Claims, c h aracte rized in that the said valve (4) consists of a cone (4) tensioned by a spring (4a) against a seat (3a) in the piston rod (2), th characteristic of the spring (4a) being so chosen that the cone (4) opens at the said given differential pressure and closes if the differential pressure is lower than the said differential pressure.

14. A means as claimed in any one of the preceding Claims, c h a racte ri z ed in that the said shut-off valve (5) is so located that it is manoeuvred by a casing surrounding the first piston (1).