Patent Publication Number: US-2019194004-A1

Title: Locking system for a working machine

Description:
FIELD OF THE INVENTION 
     The present invention relates to a locking system for securing an attachment to a working arm of a working machine, to a working machine comprising a locking system, and to a method of disengaging a latch member of a locking system. 
     BACKGROUND OF THE INVENTION 
     A range of interchangeable attachments are commonly provided for use with a working machine, allowing such a machine to be used for a number of different functions. Such attachments have a standard connection arrangement that allows them to be fitted to a common mounting on a working arm of the working machine. For example, attachments such as forks, buckets or sweepers can be interchanged on a working machine. 
     Such attachments are usually secured in place at the free end of the working arm by a pair of pins that extend to engage apertures on the attachment under the control of a hydraulic ram. When the attachment is to be detached from the working arm, the ram retracts and the pins disengage the apertures. The attachment can then be removed from the working arm. 
     Inadvertent detachment of the attachment presents a safety risk. In order to avoid inadvertent detachment of the attachment, the pins should be locked in the extended, engaged position. It is known to lock the pins in the engaged position by means of a manually-operated lock, such as a manually operated tap on the hydraulic line, at the end of the working arm. However, operation of such a lock is time consuming, as the operator of the working machine must leave the cab of the working machine in order to actuate the lock. 
     It is also known to provide a remotely-operated lock for the pins, in the form of an electronic locking system. This allows the operator to release the pins from the engaged position from the cab. However, such a system requires a relatively delicate electronic harness connection at the free end of the working arm, which is difficult and expensive to install and can easily become damaged, sometimes without the knowledge of the operator. It is also difficult to replicate this system across a whole range of working machines, due to the technical challenges of installing the electronic harness connection at the free end of the working arm. 
     The present invention seeks to overcome or at least mitigate one or more of the problems associated with the prior art. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention provides a locking system for securing an attachment to a working arm of a working machine. The locking system comprises a latch member movable between an engaged position, where the attachment is secured to said working arm, and a disengaged position, where the attachment can be removed from said working arm; and a hydraulic circuit configured to lock the latch member in the engaged position. The hydraulic circuit comprises a lock configured to open when the circuit reaches a predetermined pressure such that the latch member is released from the engaged position; a relief valve configured to activate below the predetermined pressure, such that the lock remains closed in normal operation; and an isolation arrangement configured to selectively isolate the relief valve from the circuit upon an operator input, to enable the circuit to reach the predetermined pressure such that the latch member is released. 
     Providing a relief valve that can be isolated from the remainder of the circuit provides a simple and effective means of releasing the latch member, in an arrangement that can advantageously be retro-fitted to an existing working machine, or incorporated into the hydraulic system of a new machine at low cost. 
     The lock may comprise a mechanical valve. The lock comprising a mechanical valve avoids the need for an electronic harness connection at the location of the attachment, where damage is more likely to take place. In addition, there is no requirement for a complicated and expensive installation at the free end of the working arm. 
     The lock may comprise a check valve. A check valve is a simple, effective and reliable form of mechanical valve that can be easily configured to open when the circuit reaches a predetermined pressure. 
     The hydraulic circuit may comprise a pilot line configured to operate the lock. The pilot line aids control of opening and closing the lock. 
     The isolation arrangement for the relief valve may be configured for remote operation. Remote operation of the isolation arrangement allows the latch member to be released without the operator leaving the cab. 
     The isolation arrangement may comprise an electromechanical valve. The electromechanical valve may be a solenoid valve. A solenoid valve provides a reliable switching means for isolating the relief valve from the remainder of the circuit. 
     The pressure differential between the predetermined pressure and the activation pressure of the relief valve may be more than 1,000,000 Pa (10 bar). 
     The pressure differential between the activation pressure of the main relief valve and the predetermined pressure at which the lock will open may be more than 1,000,000 Pa (10 bar). 
     The predetermined pressure may be between 23000000 Pa (230 bar) and 24000000 Pa (240 bar). 
     The relief valve activation pressure may be between 21500000 Pa (215 bar) and 22500000 Pa (225 bar). 
     The system may further comprise a latch member actuator configured to move the latch member between the engaged and disengaged positions. 
     The system may further comprise a first user input for operating the isolation arrangement, and a second user input for operating the latch member actuator, where the first and second user inputs are spaced such that they cannot be operated by a single hand. 
     The first user input may be at least  200 mm from the second user input. 
     Advantageously, two actions must be taken to disengage the latch member, i.e. releasing the latch member using the isolation arrangement, and operating the latch member actuator. An operator must use both hands to operate the first and second user inputs for these actions, reducing the likelihood of inadvertent disengagement of the latch member. 
     The hydraulic locking circuit may form part of an auxiliary circuit configured to selectively supply hydraulic fluid to an attachment to provide a function of the attachment. 
     The locking circuit forming part of an existing circuit reduces complexity, saving cost and space. 
     There is also provided a working machine comprising a working arm for mounting attachments thereto; and a locking system as described above. 
     The isolation arrangement may be located on a valve block located on a main body of the working machine. 
     The relief valve may be located on a valve block located on a main body of the working machine. The lock may be located proximal the free end of the working arm. 
     The locking system may comprise a latch member actuator configured to move the latch member between the engaged and disengaged positions; a first user input for operating the isolation arrangement; and a second user input for operating the latch member actuator. The first and second user inputs may be operable by an operator seated in an operator seat of the working machine without leaving the operator seat. 
     The first and second user inputs may be spaced such that they cannot be operated by a single hand. 
     There is further provided a method of disengaging a latch member of a locking system as described above, the method comprising the steps of:
     a) isolating the relief valve from the circuit; and   b) moving the latch member to a disengaged position.   

     Another aspect of the invention provides a hydraulic circuit configured to operate a function of a working machine. The hydraulic circuit comprises a control valve configured to open when the circuit reaches a predetermined pressure such that the function is operated; a relief valve configured to activate below the predetermined pressure, such that the valve remains closed in normal operation; and an isolation arrangement configured to selectively isolate the relief valve from the circuit upon an operator input, to enable the circuit to reach the predetermined pressure such that the function is operated. 
     Providing a relief valve that can be isolated from the remainder of the circuit provides a simple and effective means of operating a function of a working machine, in an arrangement that can advantageously be retro-fitted to an existing working machine, or incorporated into the hydraulic system of a new machine at low cost. 
     The control valve may comprise a mechanical valve. The control valve comprising a mechanical valve avoids the need for an electronic harness connection at the location of the function. In addition, there is no requirement for a complicated and expensive installation at the location of the function. 
     The control valve may comprise a check valve. A check valve is a simple, effective and reliable form of mechanical valve that can be easily configured to open when the circuit reaches a predetermined pressure. 
     The hydraulic circuit may comprise a pilot line configured to operate the control valve. The pilot line aids control of opening and closing the valve. 
     The isolation arrangement for the relief valve may be configured for remote operation. Remote operation of the isolation arrangement allows operation of the function without the operator leaving the cab. 
     The isolation arrangement may comprise an electromechanical valve. The electromechanical valve may be a solenoid valve. A solenoid valve provides a reliable switching means for isolating the relief valve from the remainder of the circuit. 
     The predetermined pressure may be between 23000000 Pa (230 bar) and 24000000 Pa (240 bar). 
     The relief valve activation pressure may be between 21500000 Pa (215 bar) and 22500000 Pa (225 bar). 
     The predetermined pressure may be between 23000000 Pa (230 bar) and 24000000 Pa (240 bar). 
     The relief valve activation pressure may be between 21500000 Pa (215 bar) and 22500000 Pa (225 bar). 
     The system may further comprise a first user input for operating the isolation arrangement, and a second user input for operating the function, where the first and second user inputs are spaced such that they cannot be operated by a single hand. 
     The first user input may be at least  200 mm from the second user input. 
     Advantageously, two actions must be taken to operate the function. An operator must use both hands to operate the first and second user inputs for these actions, reducing the likelihood of inadvertent operation of the function. 
     The hydraulic locking circuit may form part of an auxiliary circuit configured to selectively supply hydraulic fluid to an auxiliary attachment to provide a function of the attachment. 
     The locking circuit forming part of an existing circuit reduces complexity, saving cost and space. 
     There is also provided a working machine comprising a function; and a hydraulic circuit as described above. 
     The isolation arrangement may be located on a valve block located on a main body of the working machine. 
     The relief valve may be located on a valve block located on a main body of the working machine. The control valve may be located proximal the free end of the working arm. 
     The hydraulic circuit may comprise a first user input for operating the isolation arrangement; and a second user input for operating the function. The first and second user inputs may be operable by an operator seated in an operator seat of the working machine without leaving the operator seat. 
     The first and second user inputs may be spaced such that they cannot be operated by a single hand. 
     There is further provided a method of operating a function of a working machine as described above, the method comprising the steps of:
     a) isolating the relief valve from the circuit; and   b) operating the function.   

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described with reference to the accompanying drawings, in which: 
         FIG. 1  is a side view of a working machine with a locking system according to an embodiment of the invention; 
         FIG. 2  is a perspective view of an attachment for a working machine with part of the locking system of the embodiment of  FIG. 1 ; 
         FIG. 3  is a perspective view of a carriage for an attachment for a working machine with the locking system of the embodiment of  FIGS. 1 and 2 , with an alternative ram arrangement; 
         FIG. 4  is a schematic view of the locking system of the embodiment of  FIGS. 1 to 3 ; and 
         FIG. 5  is a schematic view of a locking system according to a further embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) 
       FIG. 1  shows a working machine generally indicated at  10 . The working machine  10  shown in  FIG. 1  is of the type known as a telehandler or telescopic handler, with an interchangeable attachment  12  mounted to a free end  14   a  of a working arm in the form of a telescopic boom  14 . However, the invention is applicable to other types of working machine where interchangeable attachments are used, such as wheel loaders, excavators and the like. 
     Different types of attachment  12  can be mounted to the working machine  10 , depending on the required function.  FIG. 1  shows an attachment in the form of a fork  12 . However, other types of attachment such as a bucket or a sweeper, or some other suitable attachment, can be mounted to the working machine in place of the fork  12  shown. 
     The attachment  12  is mounted to the free end  14   a  of the working arm  14  and secured by a locking system  16 , as shown in more detail in  FIGS. 2, 3 and 4 . The locking system  16  is configured to interact with a connection arrangement  18  on the attachment  12 . Such a locking system  16  can be provided on the range of working machines described above for use with the range of attachments described, so allowing different attachments to be secured to different working machines. 
     The locking system  16  has a pair of latch members or pins  20  that are mounted to the working arm  14  (other components of the working arm are not shown in  FIG. 2 , to improve clarity). The pins  20  are movable between an engaged position, as shown in  FIGS. 2 and 3 , where the attachment is secured to the working arm  14 , and a disengaged position, where the attachment  12  can be removed from the working arm  14 . In the engaged position, the pins  20  are extended to engage a corresponding engagement feature of the attachment connection arrangement  18 . 
     In this embodiment, the connection arrangement  18  has a pair of hooks  22  and a pair of apertures  24 . The hooks  22  are configured to support the attachment  12  on a carriage  13  on the free end  14   a  of the working arm  14 . The apertures  24  provide the engagement feature of this embodiment, and are configured for engagement by the pins  20 . To reach the disengaged position, the pins  20  are retracted from the apertures  24 , and the attachment  12  can be removed from the working arm  14 . 
     In this embodiment, the pins  20  and the apertures  24  are substantially circular in cross-section. In alternative embodiments, the pins  20  and the apertures  24  are of some other suitable complementary shape. In alternative embodiments, some other type of feature is provided for engagement by the pins  20 , such as a fitting. 
     The pins  20  are operated by a latch member actuator or ram  21  controlled by an auxiliary hydraulic circuit  26 , as shown in  FIG. 4 . The circuit  26  is supplied with hydraulic fluid under pressure by a hydraulic pump  27 , and has a fluid reservoir  29 . The circuit  26  has a first path  26   a , on a first side of the ram  21 , and a second path  26   b , on a second side of the ram  21 . 
     The hydraulic circuit  26  includes a lock  28  that locks the ram  21  so that the pins  20  are in the engaged position. That is, the lock  28  blocks hydraulic fluid flow to prevent the pins  20  being moved from the engaged position. The lock  28  is configured to open when the circuit  26  reaches a predetermined pressure. When the lock  28  opens, the ram  21  is released, and the pins  20  can be moved to the disengaged position so that the attachment  12  can be removed. 
     In this embodiment, the lock  28  is on the second path  26   b  of the circuit  26 . Opening of the lock  28  allows hydraulic fluid to operate the ram  21 , so that the pins  20  are moved towards the disengaged position. 
     The lock of this embodiment is a mechanical valve  28 . In this embodiment, the lock is a spring-loaded check valve  28 . The check valve  28  provides a simple and effective lock that will open only when the circuit reaches the predetermined pressure. The check valve  28  is inherently safe, as the spring resiliently biases a ball into a seat. The check valve  28  has no external moving parts, so is protected from damage. The check valve  28  is adjustable. Springs of different resilience can be used to set the locking system  16  to operate at a range of pressures, depending on the architecture and normal pressure of a particular working machine. 
     The check valve  28  of this embodiment is set to open when the circuit reaches a pressure of 23,500,000 Pa (235 bar), as described above. That is, the cracking pressure of the check valve  28  is 23,500,000 Pa (235 bar). In alternative embodiments other suitable types of check valve, or other suitable mechanical valves, are used. 
     The lock  28  is in this embodiment located at the free end  14   a  of the working arm  14 . Being a mechanical valve, the lock is less likely to be damaged at this location than a more delicate electromechanical valve. 
     The lock  28  remains closed by default due to a relief valve  30  arranged to prevent the second path  26   b  reaching the predetermined pressure. To achieve this, the relief valve  30  is configured to activate at a pressure below the predetermined pressure of the lock  28 . The relief valve  30  will therefore activate and relieve the second path  26   b  pressure before the second path  26   b  pressure is high enough to activate the lock  28 . 
     For example, in this embodiment, the predetermined pressure at which the lock  28  activates is 23,500,000 Pa (235 bar). The relief valve  30  is set to activate at a pressure of 22,000,000 Pa (220 bar). The lock  28  will not therefore activate whilst the relief valve  30  is part of the circuit  26 . 
     The circuit  26  has a free flow return valve  50  in parallel with the check valve  28 , allowing fluid to flow around the check valve  28  in the return direction when the check valve  28  is closed. 
     The circuit  26  has a restrictor  52  adjacent the check valve  28 . The restrictor  52  slows the speed of movement of the ram  21 , by restricting the amount of fluid that reaches the ram  21 . 
     In order to open the lock  28  to release the ram  21 , the relief valve  30  is isolated from the circuit  26 . An isolation arrangement  32  is provided as part of the circuit  26 . The isolation arrangement  32  is located on a main valve block  35  of the working machine  10 . When activated by the operator of the working machine  10 , the isolation arrangement  32  removes the relief valve  30  from the circuit  26 . The pressure at the second path  26   b  can then be increased to the lock  28  activation pressure, so that the lock  28  is opened. The ram  21  is then released. That is, the ram  21  is no longer locked with the pins  20  in the engaged position, allowing the operator to operate the ram  21  so as to move the pins  20  to the disengaged position. The attachment  12  can then be removed. 
     In this embodiment, the auxiliary hydraulic circuit  26  is connected to a main hydraulic circuit  33  of the working machine  10 , which is used to operate the telescopic boom  14  or some other part of the working machine  10 . The main hydraulic circuit has a main relief valve  34 , located on the main valve block  35 . The main relief valve  34  protects the circuit from excess pressure. The lock  28  activates at a pressure below the activation pressure of the main relief valve  34 , so that the lock  28  will open before the main relief valve  34  is activated. In this embodiment, the main relief valve  34  activates at 24,000,000 Pa (240 bar), or in some embodiment, 26,000,000 Pa (260 bar). 
     Advantageously, the circuit  26  of this embodiment makes use of the pressure differential between the relief valve  30  and the main relief valve  34  to control locking of the ram  21 . This use of existing circuits and valve arrangements is time and space efficient, and allows simple and inexpensive retrofitting of the locking system to existing working machines. The relief valve  30  and the isolation arrangement  32  can be independently plumbed between the main valve block  35  and the remainder of the locking system  16 . The relief valve  30  and the isolation arrangement  32  can be fitted to a mechanical valve block with no existing electromechanical valves. The locking system can also be built into new working machines as part of the main valve block. 
     The isolation arrangement  32  of this embodiment is operated remotely, so that the operator does not need to leave the cab  36  of the working machine  10  to release the ram  21 . The isolation arrangement of this embodiment is an electromechanical valve  32 , arranged in series with the relief valve  30 , which in this embodiment is pilot-operated. The electromechanical valve  32  is used to shut off flow to the relief valve  30  and so remove the relief valve  30  from the circuit  26 . In this embodiment, the electromechanical valve is a normally open solenoid valve  32 . In alternative embodiments, some other suitable type of electromechanical valve is used. 
     In an alternative embodiment the isolation arrangement is some other type of remotely operated valve, such as a pilot pressure operated valve, or a mechanically operated valve. In an alternative embodiment, the isolation arrangement is not operated remotely, e.g. it is operated manually. For example, a lever or tap could be used. 
     A first user input  38  located in the cab  36  is used to control the solenoid valve  32 . When the solenoid valve  32  is to be closed, i.e. when the relief valve  30  is to be isolated from the circuit  26 , the user input  38  is activated and an electric current is supplied to the solenoid valve  32 , so that the solenoid valve  32  is closed. In this embodiment, the user input  38  must be continuously operated (e.g. depressed) in order for the solenoid valve  32  to be closed. That is, the operator must keep one hand on the user input  38  in order to release the ram  21 . This safety feature helps to prevent inadvertent release of the pins  20 . 
     The operator uses a second user input  40  to control movement of the ram  21  in order to move the pins  20  between the engaged and disengaged positions. Although shown as levers  38 ,  40  in  FIG. 1 , the first and second user inputs  38 ,  40  are in alternative embodiments in some other suitable form, such as a roller, or a spring-loaded rocker switch. 
     The first and second user inputs  38 ,  40  are separated from one another in the operator&#39;s cab  36 , so that the operator must use two hands to disengage the pins  20  and detach the attachment  12 —a first hand to operate the first user input  38 , and a second hand to operate the second user input  40 . The locking system  16  thus meets the safety requirement of standards BS EN 1459 and EN 1459 and equivalent standards to prevent unintentional lateral displacement and detachment of the attachment. In this embodiment, the first and second user inputs  38 ,  40  are spaced at least 200 mm from one another, so that they cannot be operated by a single hand. In alternative embodiments, the first and second user inputs  38 ,  40  are spaced at least 300 mm from one another. 
     In this embodiment the circuit  26  includes first and second auxiliary couplings  42 ,  44 , one on each of the first and second paths  26   a ,  26   b , for connection to the attachment  12  in order to provide hydraulic control of the attachment  12 . The circuit  26  has a direction control valve  46  on the main valve block  35 , for reversing the direction of flow around the circuit  26  to control movement of the attachment  12 . 
     The circuit  26  has an auxiliary relief valve  48  on the main valve block  35 . In this embodiment, the auxiliary relief valve  48  is set to activate at the same pressure as the relief valve  30 , i.e. 22,000,000 Pa (220 bar). The auxiliary relief valve  48  is located on the first path  26   a  of the circuit  26 . As the check valve  28  is located on the second path  26   b  of the circuit  26 , the auxiliary relief valve  48  does not affect the pressure at the check valve  28 . 
     The isolation arrangement  32  and the relief valve  30  are connected across the auxiliary couplings  42 ,  44 , i.e. across the first  26   a  and second  26   b  paths of the circuit  26 . The relief valve  30  thus acts across the first and second paths  26   a ,  26   b  of the circuit  26 , when the isolation arrangement  32  is open. 
     The configuration of the circuit  26  is such that movement of the pins  20  to the engaged position will occur by default whenever hydraulic fluid is supplied to the attachment via the first path  26   a.    
     The valve pressures described in relation to this embodiment are given as examples only. In alternative embodiments, the predetermined pressure at which the lock will open is set in the range of 23,000,000 Pa (230 bar) to 24,000,000 Pa (240 bar), and the relief valve actuation pressure is in the range of 21,500,000 Pa (215 bar) and 22,500,000 Pa (225 bar). Whatever the pressure range, the pressure at which the lock will open is higher than the relief valve  30  activation pressure, and is lower than the activation pressure of the main relief valve  34 . 
     In this embodiment, the pressure differential between the predetermined pressure at which the lock will open and the activation pressure of the relief valve is 1,500,000 Pa (15 bar). The pressure differential between the activation pressure of the main relief valve and the predetermined pressure at which the lock will open is also 1,500,000 Pa (15 bar). 
     In an alternative embodiment, the pressure differential between the predetermined pressure at which the lock will open and the activation pressure of the relief valve is more than 1,500,000 Pa (15 bar). In an alternative embodiment, the pressure differential between the activation pressure of the main relief valve and the predetermined pressure at which the lock will open is more than 1,500,000 Pa (15 bar). In an alternative embodiment, the pressure differential between the predetermined pressure at which the lock will open and the activation pressure of the relief valve is more than 1,000,000 Pa (10 bar). In an alternative embodiment, the pressure differential between the activation pressure of the main relief valve and the predetermined pressure at which the lock will open is more than 1,000,000 Pa (10 bar). 
     Such a pressure differential provides adequate protection from pressure spikes (e.g. as could be caused by the attachment meeting resistance during operation) that could otherwise cause the valves to malfunction. For example, with a pressure differential that is too small, the relief valves may not open quickly enough to avoid damage should a pressure spike occur. 
       FIG. 5  shows a further embodiment of the invention, with an alternative lock  128 . Features corresponding to those of the previous embodiment are given corresponding reference numbers, with an additional preceding “1”. Only features that differ from those of the first embodiment are discussed in more depth. 
     The lock of this embodiment is, as in the first embodiment, a spring-loaded check valve  128  that will open only when the circuit reaches the predetermined pressure. The relief valve  130  is arranged to prevent the lock  128  opening below the predetermined pressure, as described in relation to the first embodiment. 
     In this embodiment, the check valve  128  is located on the first path  126   a . The check valve  128  is shown in  FIG. 5  in the closed position, with a spring  154  resiliently biasing the check valve  128  to this closed position. In the closed position, an internal check valve  128   a  allows flow towards the ram  121 , but prevents flow away from the ram  121  along the first path  126   a , so that the ram  121  is locked with the pins in the engaged position. 
     An external pilot line  158  connected to the second path  126   b  acts against the spring  154  to open the check valve  128  when the predetermined pressure is reached. In this embodiment, the check valve  128  is set to open when the circuit  126  reaches a pressure of 23,500,000 Pa (235 bar). In this embodiment, that is, the check valve  128  will open when the pressure in the second path  126   b  and the pilot line  158  reaches 23,500,000 Pa (235 bar). The check valve  128  is then moved to an open position, where a free flow return  156  allows fluid to flow away from the ram  121 , so that the ram  121  is no longer locked with the pins in the engaged position. 
     In alternative embodiments, some other suitable pressure is required to overcome the resilient bias of the spring. 
     In order for the second path  126   b  pressure, and thus the external pilot line  158  pressure, to increase over 22,000,000 Pa (220 bar), the relief valve  130  is isolated from the circuit  126  as described in the first embodiment. 
     Using the external pilot line  158  to operate the check valve  128  provides effective control over the check valve  128 . The external pilot line  158  is also effective in locking the ram  121 . In order to lock the ram  121 , the relief valve  130  is returned to the circuit  126 . As a result, the pressure in the external pilot line  158  drops to or below 22,000,000 Pa (220 bar), and the spring  154  can then act to close the check valve  128 . The ram  121  can be moved so that the pins are in the engaged position, and the ram  121  is locked in place by fluid flowing through the internal check valve  128   a  towards the ram  121 . 
     The check valve  128  of this embodiment has internal pilot lines  160 ,  162  which further aid control of the check valve  128 . The first internal pilot line  160  acts to bias the check valve  128  towards the closed position, aiding control of the circuit when the ram  121  is to be locked in place. The second internal pilot line  162  acts to bias the check valve  128  towards the open position, aiding control of the circuit when the ram  121  is to be released. 
     Advantageously, with the arrangement of this embodiment, the full pressure of the circuit can be used to operate the ram  121 , rather than merely the remainder of the pressure that is not expended in activating the check valve. 
     In alternative embodiments, the locking system has a single latching member, or three or more latching members. Multiple latching members are controlled by the same hydraulic circuit, or are controlled by individual hydraulic circuits. 
     Advantageously, the locking system can be retrofitted to a range of working machines, including those with multi-stage booms and single-stage booms, and those with manual hydraulics or servo hydraulics. 
     In alternative embodiments, the system described above is used to operate other functions of a working machine. The system is in alternative embodiments used to lock/unlock a ram used for some function other than securing an attachment to a working arm, such as a hydraulic pickup hitch at the rear of a working machine, where a ram could be used to lower the hitch. In further alternative embodiments, the system is used to operate some function other than a ram. For example, the pressure differential between the lock/control valve, the relief valve, and the main relief valve, is used to control some other function of a working machine, such as a cooling fan that starts working at a pressure of e.g. 10,000,000 Pa (100 bar). Such a system is advantageously deployed in any part of a working machine where the use of electronics is difficult and/or expensive. 
     Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.