Patent Publication Number: US-6220289-B1

Title: Hydraulic valve arrangement with locking and floating function

Description:
The invention concerns a hydraulic valve arrangement with locking and floating function, with a control valve, which, for two operating positions connects one motor connection with a pump connection and a second motor connection with a tank connection and vice versa, in a floating position connects both motor connections with the tank connection and in a locking position separates both motor connections from the pump and tank connections, and with two closing valves, each being connected between the control valve and a motor connection and each having a piston loaded by a spring and limiting a spring chamber, the spring chambers being pressure releasable. 
     Known hydraulic valve arrangements of this kind are mainly, but not exclusively, used in tractors, which can be provided with attachment tools, for example snow clearance or street cleaning vehicles. The pressure release of the spring chambers, which is required to keep the closing valves open in the operation positions and in the floating position of the control valve, occurs in that release channels open into the bore of the control valve and the opening is oversteered by its slide. However, sometimes it has turned out that errors occur in the function, particularly in the locking function. 
     The invention is based on the task of providing a hydraulic valve arrangement of the kind mentioned in the introduction, which has a better operating behaviour. 
     According to the invention, this task is solved in that lifting valves are provided for the pressure release, which valves are operated by a control pressure depending on the position of the control valve. 
     This design is based on the assumption that leakages are responsible for the failures, which leakages can never be completely avoided in slide controls. For high requirements, the invention provides the use of lifting valves for pressure release, which can without problems be dimensioned so that they are completely tight in closed position. The dependence of the valve operation of the position of the control valve is effected in that the lifting valves are operated by a position dependent control pressure. Both lifting valves are open in the floating position and closed in the locking position, whereas in the operating position one lifting valve or the other is open optionally. Therefore, corresponding control pressure levels can be provided, to which the lifting valves can be connected in dependence of the position of the control slide. An additional advantage is that leakage losses in connection with the pressure release are avoided. 
     In this connection, it has turned out to be advantageous that the lifting valves open at high control pressure and close at low control pressure. This gives a high certainty that the release process runs properly. 
     Expediently, pressures, which are available in the control valve anyway, are used as control pressure. Thus, the control pressure in the operating positions can be the load pressure. In the locking position the control pressure can be the tank pressure. And in the floating position the control pressure can be a floating signal pressure or the pump pressure. 
     With regard to design it is recommended that the lifting valves have a closure piece which is pressed against its valve seat by means of a spring, and a piston acting upon the closure piece in the opening direction, which piston is loaded by the control pressure in the opening direction and by the tank pressure and a spring in the closing direction. Such a valve is normally closed and opens when a sufficiently high control pressure appears. 
     In a further embodiment of the invention it is provided that the pistons of each pair are arranged in series two and two, and in the operating position the control pressure is led to a control pressure chamber between the pistons, in the floating position commonly to control pressure chambers at the ends of both pairs. In the operating position, therefore, one of the two pistons facing the closure piece is operated, in the floating position, however, both pistons of each pair are displaced. 
     In this connection it is recommended that the control pressure line leading to the control pressure chambers at the ends of both pairs be connected via a throttle with a low-pressure line carrying low pressure. The pressure building up in the piston operating chambers in the locking position can therefore be dissipated via the line carrying low pressure (or tank pressure). 
     A preferred alternative provides that in each case one piston with a control pressure chamber is available, to which, in the operating position, the control pressure is led separately, in the floating position via a closing valve, from a common control pressure line. For each lifting valve one piston will be sufficient, which saves costs. 
     Besides, it is expedient that the control pressure line carrying load pressure in the operating position is con nected to a low pressure in the locking position. One and the same control pressure line can here be used for two operating positions. A normal control valve can be used. Further, automatic pressure dissipation occurs, when the control pressure line is connected with the low pressure. 
    
    
     In the following the invention is described in detail on the basis of two embodiments shown in the drawings, showing: 
     FIG. 1 a diagram of a first embodiment of the valve arrangement according to the invention 
     FIG. 2 details of the valve arrangement in FIG. 1 
     FIG. 3 a diagram according to FIG. 1 of a modified embodiment 
    
    
     FIG. 1 shows a module  1 , which serves the operation of a motor  2 . Its dimensions and embodiment are substantially equal to usual designs. The module  1  has a connection carrying pump pressure P and being connected with a pump line  3 , a connection carrying tank pressure T and being connected with a tank line  4 , a connection carrying load pressure LS and being connected with a load pressure system  5 , a connection carrying floating signal pressure V and being connected with a signal line  6 , a connection carrying low pressure To and being connected with a low pressure line  7 , as well as two motor connections A and B serving as connections for the motor  2 . 
     The pump line  3  leads via a load pressure steered compensating valve  8  to a control valve  9 , which is made as a slide valve and can assume a locking position  10 , two operating positions  11  and  12  as well as a floating position  13 . The control valve  9  operates two motor lines  14  and  15 , which lead to the motor connection A or B, respectively, via a closing valve  16  or  17 , respectively. For pressure release, each closing valve has a lifting valve  18  or  19 , respectively, which will be described in detail in connection with FIG.  2 . 
     Each closing valve  16  or  17 , respectively, has a piston  21 , guided in a housing bore  20 , the front side of said piston cooperating with a valve seat  22 , being loaded by a closing spring  23  and limiting a spring chamber  24 . The spring chamber  24  is connected via a throttle  25  with the second part of the motor line  14  leading to the motor connection A and via a release line  26  and the lifting valve  19  with a line  27  leading to the tank line  4 . The diameter of the valve seat  22  is so much smaller than the outer diameter of the piston  21  that, in case of pressure substantially inside the seat the closing valve can open the spring chamber  24  without pressure release, in case of pressure substantially outside the seat the closing valve can only open the spring chamber  24  with pressure release. The closing valve  17  has the same design; therefore the same reference signs, although with the addition “a”, are used. Here, the release of the spring chamber  24   a  occurs via the release line  26   a  and the lifting valve  18  to the line  27  carrying tank pressure. 
     With the lifting valve  18 , its closure piece  28  is pressed into a tight closing position by means of a spring  29 . For the opening of the lifting valve, two pistons  30  and  31  are provided, which limit a first control pressure chamber  32  between them and at the end have a second control pressure chamber  33 . In the opening direction, the pistons are loaded by a return spring  34  and the tank pressure T. The lifting valve  19  has the same design, therefore also here the same reference signs with the addition “a” are used. 
     The control pressure chamber  32  is connected with a first control pressure line  35  and the control pressure chamber  32   a  with a second control pressure line  35   a . The two control pressure chambers  33  and  33   a  are both connected to a control pressure line  36 . In the locking position  10  the control pressure lines  35  and  35   a  are connected with the tank line  4  and in the operating positions  11  and  12  they carry the correspondingly effective load pressure, LSa or LSb, respectively. In the floating position  13 , the control pressure line  36  is loaded by the floating signal pressure V, which can be equal to an otherwise available pilot pressure or the pump pressure, which is entered via the signal line  6 . 
     As the control pressure lines  35  and  35   a  carrying the load pressure in the operating positions are connected with the tank in the neutral position, an automatic release of the control pressure chambers  32  and  32   a  occurs. These connections require no particular efforts, as they are already available for other reasons. Thus, a pressure build-up in the lifting valves  18  and  19  is out of the question. Accordingly, the two closing valves  16  and  17  cannot open unwantedly. 
     Between the control pressure line  26  and the low-pressure line  7  a throttle  37  is provided, which serves the pressure build-up in the control pressure chambers  33  and  33   a . The low pressure To can be equal to the tank pressure T or a low pressure having a preferably constant level and being independent of the tank pressure. 
     This gives the following modes of operation: 
     1. Locking Function 
     The control valve  9  assumes the position  10  shown, which corresponds to the neutral position. Both control pressure lines  35  and  35   a  are connected with the tank line  4 . The control pressure chambers  32  and  32   a  are under tank pressure T, and due to the pressure dissipation at the throttle  37 , the control pressure line  36  also carries no pressure. Both lifting valves  18  and  19  are therefore closed. Also the motor lines  14  and  15  are separated from the pump line  3 . The motor  2  has a fixed position. As the lifting valves  18  and  19  are closing tightly, there is also no risk that a change of the pressure conditions, such as a negative load at the motor  2 , will cause a closing valve to open. 
     2. Operating Function 
     This corresponds to the position  11  or  12  of the control valve  9 . In the operating position  11 , the supplied pressure fluid presses the closing valve  17  open. At the same time, the lifting valve  19  is opened, as load pressure is supplied via the control pressure line  35   a . Accordingly, the spring chamber  24  of the closing valve  16  is pressure released. Thus, the closing valve  16  can also open under the influence of the returning pressure fluid. Similar conditions apply for the operating position  12 . 
     3. Floating Function 
     In the floating position  13 , the control pressure line  36  is provided with the floating signal pressure V, which is supplied via the signal line  6 . This opens both lifting valves  18  and  19 . Both spring chambers  24  and  24   a  are released. Small pressure increases on one of the motor connections A or B are sufficient to open the closing valves  16 ,  17 . Thus the motor can adjust freely in dependence of its outer loads. The springs  29 ,  29   a  and  34 ,  34   a  can be dimensioned with such a preload that at the end of a floating function the closure pieces return safely into their closing position. 
     The alternative according to FIG. 3 substantially corresponds to FIG.  1 . For changed parts, reference numbers increased by  100  are used. Substantially, merely the two lifting valves  118  and  119  and the corresponding control pressure supply are different. The two lifting valves  118  and  119  merely have one piston with a pressure chamber  132  or  132   a , respectively, which are supplied by the control pressure line  135  or  135   a , respectively. The common control pressure line  136  is connected with the control pressure chambers  132  or  132   a , respectively, via two closing valves  138 ,  138   a . Thus, the floating signal pressure is supplied to both control pressure chambers at the same time. Special measures for the pressure dissipation are not required, as it takes place automatically via the control pressure lines  135 ,  135   a , when the neutral position of the control valve is passed. 
     The lifting valves  18  and  19  need no fixed allocation to the control valve  9  and to the closing valves  16  and  17 . They can therefore be arranged in the valve housing where this is favourable for space reasons or because of the short connecting channels. Therefore, the lifting valves can also be separated from each other and be arranged in another level than the closing valves. 
     Several deviations from the embodiments shown are possible, without leaving the basic idea of the invention. Thus, for example, the release of the control pressure lines  35 ,  35   a ,  135  and  135   a  in the locking position  10  take place to the constant low pressure to in stead of the tank pressure t, so that a pressure increase in the tank has no influence on the lifting valve control.