Circuit for enabling or disabling hydraulic actuating devices

Abstract

The invention relates to a circuit for enabling or disabling hydraulic actuating devices, in particular for enabling the braking system of a hydraulic propel drive, having a device for checking the pressure level in working lines or control lines of hydraulic circuits, a maximum or minimum pressure level being checked in two or more working lines or control lines. An ‘OR’ logic circuit is provided for checking the pressures. In said ‘OR’ logic circuit, two or more pistons are arranged in series in a common bore. In each case one of the pressures to be checked is introduced into one of the spaces between the pistons and the space between one of the pistons and the base of the bore.

1 . Circuit for enabling or disabling hydraulic actuating devices, in particular for enabling a braking system of a hydraulic propel drive, having a device for checking the pressure level in working lines or control lines of hydraulic circuits, 
 a maximum or minimum pressure level being checked in two or more working lines or control lines,    an ‘OR’ logic circuit ( 1 ) being provided for checking the pressures,    the ‘OR’ logic circuit (I) being formed as a series arrangement of two or more pistons (KI, K 2 , K 3 , K 4 ) in a common bore ( 2 ),    in each case one of the pressures to be checked being introduced into one of the spaces between the pistons (K i, K 2 , K 3 , K 4 ) and the space between one of the pistons (KI) and the base ( 3 ) of the bore.    
   
   
       2 . Circuit according to  claim 1 , a return spring ( 4 ) being provided which pushes the pistons (KI, K 2 , K 3 , K 4 ) into contact with one another in the base ( 3 ) of the bore.  
   
   
       3 . Circuit according to one of  claim 1 , the return spring ( 4 ) being arranged at one side between a piston (K 4 ) and a wall ( 5 ) which terminates the bore.  
   
   
       4 . Circuit according to one of  claim 1 , the space upstream of the outer piston (K 4 ), which is situated at the side remote from the base of the bore, being connected to a lower pressure level than is to be expected in the working lines.  
   
   
       5 . Circuit according to  claim 4 , the lower pressure level being approximately constant.  
   
   
       6 . Circuit according to one of  claim 1 , the pistons (KI, K 2 , K 3 , K 4 ) having annular grooves ( 11 ) at the periphery at each end to ensure a maximum guide length for a minimum piston length, said annular grooves ( 11 ) generating small annular webs ( 12 ) between the piston end sides ( 13 ) and the annular grooves ( 1  in such a way that an unbroken connection between the supply ducts ( 14 ) and the piston end sides ( 13 ) is ensured during the stroke of the piston (KI, K 2 , K 3 , K 4 ), and the pistons (Ki, K 2 , K 3 , K 4 ) are held in the bore ( 2 ) in a floating manner.  
   
   
       7 . Circuit according to one of  claim 1 , piston end sides ( 13 ) of the pistons (KI, K 2 , K 3 , K 4 ) having transverse grooves ( 15 ) for improving pressure distribution over the piston end side.  
   
   
       8 . Circuit according to one of  claim 1 , all the pistons (K 1  K 2 , K 3 , K 4 ) being of identical design and being symmetrical in order to avoid them being incorrectly interchanged.  
   
   
       9 . Circuit according to one of  claim 1  a device for detecting the position of the outer piston (K 4 ) of the ‘OR’ logic circuit ( 1 ) being provided on that waIl ( 5 ) which is situated opposite the base of the bore.  
   
   
       10 . Circuit according to  claim 9 , the device for detecting the position of the outer piston (K 4 ) being a transducer.  
   
   
       11 . Circuit according to  claim 10 , the transducer being a proximity switch.  
   
   
       12 . Circuit according to  claim 10 , the transducer being a displacement transducer.  
   
   
       13 . Circuit according to  claim 10 , the transducer being a load cell for measuring the supporting force of the return spring.  
   
   
       14 . Circuit according to  claim 9 , the device for detecting the position of the outer piston (K 4 ) of the ‘OR’ logic circuit (I) being a control piston ( 8 ) which generates a pressure signal when it is displaced.  
   
   
       15 . Circuit according to  claim 14 , the control piston being formed by the outer piston (K 4 ) which, when displaced, generates the pressure signal.  
   
   
       16 . Circuit according to one of  claim 14 , the position of the outer piston (K 4 ) of the ‘OR’ logic circuit ( 1 ) being detected by means of a pressure sensor.  
   
   
       17 . Circuit according to one of  claim 14 , the control piston ( 8 ) generating a hydraulic signal as a function of the position of the outer piston (K 4 ), said hydraulic signal being supplied to the actuating device in the form of a hydraulic pressure.  
   
   
       18 . Circuit according to one of  claim 14 , the pressure generated by the displacement of the control piston ( 8 ) being used as a brake pressure.  
   
   
       19 . Circuit according to one of  claim 10 , a display device being provided which visually or audibly displays the output signal of the transducer.  
   
   
       20 . Circuit according to one of  claim 9 , the device for detecting the position of the outer piston (K 4 ) of the ‘OR’ logic circuit (I) comprising a load spring ( 9 ) between the outer piston (K 4 ) and a control piston ( 8 ) which is actuated by an electromagnet ( 7 ).  
   
   
       21 . Circuit according to  claim 20 , the spring force of the load spring ( 9 ) being matched to the magnet force characteristic curve such that the electromagnet ( 7 ) can move the control piston ( 8 ) at relatively low spring force values, and is capable of holding the control piston ( 8 ) at relatively high spring force values.  
   
   
       22 . Circuit according to  claim 21 , the load spring ( 9 ) simultaneously forming the return spring ( 4 ).