Abstract:
An improved cylinder head for a railroad track switch operator includes totally self-contained electronics and pneumatics for easy and direct replacement of a cylinder head on a prior art switch operator. The improved cylinder head has enhanced porting to improve air flow and speed of operation, a voltage control module permitting the unit to operate with either 24 volt or 12 volt line power, and recessed portions for covering or enclosing delicate and/or sensitive components for maximized protection in harsh outdoor installations.

Description:
BACKGROUND OF THE INVENTION 
     The present invention pertains to an operator for a railroad track switch and, more particularly, to an improved cylinder head assembly for a pneumatically driven operator. 
     Railroad track switch operators or switch machines of the prior art are powered by a number of different types of actuators. Pneumatic cylinders and hydraulic cylinders are commonly used with the piston rods of such cylinders operatively connected to the switch points to selectively move the points between the two positions. Electric motor and fluid motor-driven actuators are also used. In addition, many switch operators also provide the capability for alternate manual operation. 
     In a railroad yard, a large number of switch points may be used and they are typically connected to a central monitoring and control system for automatic or semi-automatic operation. The operation of multiple switch points also typically includes a common electric power supply for operating valves and a common pressurized fluid supply for pneumatic or hydraulic cylinder operators. Thus, pneumatic switch operators are connected to a common source of compressed air and the operating valves used to control the pneumatic cylinders receive electric power from a common electric power supply line. In the United States, the railroad industry has adopted both 12 volt and 24 volt DC as standard switch operator power supplies. 
     The use of two different operating voltage standards has resulted in difficulties in operator repair and replacement and has also resulted in operational difficulties within a given system. Twelve volt operators may operate adequately over a voltage range between about 9 and 14 volts, whereas 24 volt operators may operate adequately over a range of about 19 volts to 26 volts. However, neither type of operator will operate in the voltage range needed to power the other type of operator and, furthermore, there is a dead band of about 4 to 6 volts between the respective ranges where neither operator will work. In addition, typical line voltage drops in large 24 volt systems often result in voltage variations that adversely affect operation or drop so low as to prevent operation. 
     Prior art pneumatic operators, though made to effect a point switch in about 0.5 second, would benefit from faster operation, particularly where the operator is subject to voltage variations due to line voltage losses and the like. Tracks switch operators of the prior art have also been characteristically difficult to service and repair. Electric power for the operating valve and compressed air to supply the motive force for the cylinder are typically supplied directly to the cylinder head. Removal and replacement of the valve typically requires manual disconnection of a number of electric leads and the removal of mounting bolts for the valve, all in a time consuming and inefficient manner. These maintenance and service problems are compounded when they must be performed in cold or other inclement weather. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an improved cylinder head assembly is provided for a pneumatic railroad track switch operator that addresses and eliminates or substantially improves all of the problems in prior art operators. The typical prior art pneumatic track switch operator includes a solenoid-operated spool valve that directs compressed air from a source to the piston of a double acting pneumatic cylinder. A prior art cylinder head may include a mounting surface for the spool valve and is further provided with internal air flow porting to control the flow of compressed air and exhaust air to and from the cylinder. Such porting typically includes a compressed air inlet port, a first supply passage that directs compressed air to one side of the piston to stroke the piston in a first direction and receives exhaust air from the same side of the piston when the piston is stroked in the opposite direction, a second supply passage that directs compressed air to the other side of the piston to stroke the piston in the opposite direction and receives exhaust air from that other side of the piston when the piston is stroked in the first direction, a first exhaust port that receives air from the first supply passage and a second exhaust port that receives air from the second supply passage. In accordance with the present invention, the improved cylinder head assembly comprises means for interconnecting the first and second exhaust ports to permit the flow of exhaust air from either of said supply ports to pass through both of the exhaust ports; recessed portions in the cylinder head for receiving electric power connections for operating the spool valve; voltage control means for applying 12 volt electric operating power to the spool valve from line voltage in excess of about 14 volts and for passing line voltage between about 14 volts and a minimum operating voltage directly to the spool valve; the voltage control means comprising a control module that is received in one of the recessed portions in the cylinder head; and interface means in another of the recessed portions of the cylinder head that defines the valve mounting surface for receiving the spool valve and provides direct connection to the ports and plug-in electric power connection to the voltage control module. 
     The voltage control module is preferably operative over a voltage range of from about 26 volts to about 9 volts. The module includes means for converting line voltage in the range of about 26 volts to about 14 volts to an operating voltage of about 12 volts. The module also includes means for passing line voltage in the range of about 14 volts to about 9 volts directly to the valve. 
     In the improved cylinder head assembly of the present invention, the interface means includes a first internal passage extending between said recesses and an operating power electrical conductor in the passage connecting the voltage control module and the plug-in connection. The cylinder head also includes a second internal passage and a line voltage power conductor within the second passage providing electric power at line voltage to the control module. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevation view of a prior art pneumatic cylinder for a railroad track switch operator on which is mounted the improved cylinder head assembly of the present invention. 
     FIG. 2 is an enlarged end elevation taken on line  2 — 2  of FIG.  1 . 
     FIG. 3 is a vertical section through the cylinder head and associated valve taken on line  3 — 3  of FIG.  2 . 
     FIG. 4 is a vertical section taken on line  4 — 4  of FIG.  3 . 
     FIG. 5 is a sectional detail taken on line  5 — 5  of FIG.  3 . 
     FIG. 6 is a sectional detail taken on line  6 — 6  of FIG.  3 . 
     FIGS. 7A and 7B are horizontal sectional details taken on line  7 A, 7 B- 7 A, 7 B of FIG. 4 showing the control valve in each of its two operational positions. 
     FIG. 8 is a vertical sectional detail taken on line  8 — 8  of FIG.  4 . 
     FIGS. 9A and 9B are horizontal sectional views through the entire switch operator showing generally schematically the air flow in the operator corresponding to the valve positions of FIGS. 7A and 7B, respectively. 
     FIG. 10 is a vertical sectional detail taken on line  10 — 10  of FIG.  4 . 
     FIG. 11 is a vertical sectional detail taken on line  11 — 11  of FIG.  3 . 
     FIGS. 12A and 12B are end elevation views of the cylinder head and control valve (separated for clarity) showing the interrelationship between the air flow porting and the direction of air flow corresponding to the control valve and cylinder positions of FIGS. 7A,  9 A and  7 B,  9 B, respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows the general arrangement and FIGS. 9A and 9B , somewhat schematically, a track switch operator  10  utilizing a pneumatic cylinder  11  of a prior art construction and an improved cylinder head  12  of the present invention utilizing a commercially available 4-way solenoid pilot operated control valve  13 . The valve  13  may be a 6600 Series valve manufactured by Mac Valves, Inc. of Wixom, Mich. The prior art cylinder  11  includes a cylinder body  14  which defines the internal cylinder wall for a piston  15  and attached piston rod  16 . The cylinder head  12  is attached to the piston end of the cylinder body  14  and the rod  16  extends through the opposite end of the cylinder body where it is supported along a portion of its length by an integral extension sleeve  17 . The sleeve  17  carries conventional seals and provides a grease reservoir for lubrication of the piston rod  16 . The free end of the piston rod is connected to the track switch points in a conventional manner such that reciprocating movement of the piston and attached piston rod will move the switch points from one position to another, all in a manner well known in the art. 
     In FIGS. 1 and 9A, the piston  15  is shown in its fully retracted position within the cylinder body  14 . Compressed air admitted to the piston end of the cylinder (immediately adjacent the cylinder head  12 ) will move the piston to extend the piston rod  16  to the phantom line position of FIG.  1  and the position of FIG.  9 B. Simultaneously, air within the cylinder body  14  on the opposite rod end of the piston will pass into the open end of an exhaust channel  18  from which it passes in a reverse direction axially along the cylinder body  14  and into the cylinder head  12  from which it is exhausted, after passage through related control porting in the valve  13 , as will be described in greater detail below. 
     In a railroad switching yard, operation of each of the many switch points is handled by an operator  10  of this type. A central source of compressed air supplies operating air pressure to each cylinder  11 . Direct current power to operate the control valve  13  is supplied from a common electric power source, typically supplying power at a nominal line voltage of either 12 volts or 24 volts. All of the switches in a rail yard are monitored from a central control tower or station to determine position, and are controlled by generating a signal from the tower to change the switch position as needed. 
     Referring also to FIGS. 2-4 and  6 , compressed air from a common supply line enters the cylinder head  12  via an air inlet port  20  in the bottom face of the cylinder head. It should be noted that normal orientation of a switch operator  10  is horizontal so that the piston rod  16  reciprocates along a horizontal axis. Thus, the position of the air inlet port  20  is typically on the bottom of the operator as it is installed. From the air inlet port  20 , compressed air flows along an air inlet passage  21  that includes an internal leg  22  providing a common supply of compressed air to both sides of the control valve  13  which directs it back through the cylinder head and to one side or the other of the piston  15 , depending upon the position of the valve spool  23 . In FIG. 7B, the valve spool  23  has been shifted to the right to direct incoming compressed air into a first supply passage  24  in the cylinder head  12  (which in industry terminology is commonly referred to as the “reverse supply port”). As is well understood in the operation of double acting cylinders, the first supply passage  24  will receive exhaust air from the cylinder when the cylinder is operated in the opposite direction, as will be discussed. Referring also to FIGS. 9B and 12, the first supply port  24  extends horizontally through the cylinder head  12  between a valve mounting face  25  on the outside of the cylinder head and a cylinder mounting face  26  on the inside of the cylinder head where it has open communication with the head end of the piston  15 . A second supply passage  27  extends through the cylinder head between the valve mounting face  25  and the cylinder mounting face  26  where it opens into communication with the exhaust channel  18 . The second supply passage  27  includes an internal offset leg  28  (FIGS. 4 and 8) to provide air flow to the radial outer edge of the cylinder body  14  in which the exhaust channel  18  is located. With the valve spool  23  in the right hand position of FIG. 7B, flow from the air inlet passage  21  into the second supply passage  27  is blocked. However, in the right hand position of the valve, communication between the second supply passage  27  and an exhaust passage  30  is open as shown in FIG.  12 B. In the right hand position, exhaust flow from passage  27  passes into the control valve chamber and exits into an exhaust inlet  19  in the mounting face  25  of the cylinder head. The exhaust inlet  19  connects directly with exhaust passage  30 . The exhaust passage  30  extends horizontally between opposite sides of the cylinder head and interconnects diametrically opposite exhaust ports  31  through which air is exhausted to atmosphere. In FIG. 12B, arrows  29 C show the direction of flow of the supply of compressed air and arrows  29 E show the direction of exhaust flow. 
     In FIGS. 7A and 12A, the valve spool  23  is shifted to the left hand position whereby flow through the operator  10  is reversed. In this position, compressed air flows to the rod end of the cylinder via the second supply passage  27  while exhaust from the piston end of the cylinder flows out through the first supply passage  24 . The arrows  29 C in FIG. 12A show the direction of compressed air flow and the arrows  29 E show the direction of exhaust air flow. 
     A significant feature of the improved cylinder head  12  of the present invention is the single common air inlet passage  21  which serves to supply compressed air to both the first and second supply passages  24  and  27  (depending on valve position), and the common exhaust passage  30 , which receives exhaust air which permits the flow of exhaust air through both exhaust ports  31 . The combination of these common inlet and exhaust passages increases the volumetric flow through the cylinder in cylinder operation in either direction. The result is increased operating speed in both directions. In particular, the common connection of the exhaust ports  31  eliminates a major exhaust flow restriction. The stroke time of the cylinder may, for example, be reduced by one-third or more from 450 ms to 300 ms. 
     Referring particularly to FIGS. 1-5, the improved cylinder head  12  of the present invention also includes features which substantially enhance assembly and serviceability, increase reliability and durability, and further enhance performance. The cylinder head  12  is preferably made from an iron casting which includes a main body  32  that contains the air flow passages and porting previously described, and a raised semi-circular segment  33  that defines a large internal recess  34  for receipt of a voltage control module  35 . Just below the raised segment  33  there is located the valve mounting face  25  in which is located the air flow porting described above and which is adapted to mate with and provide an interface with a mounting surface  36  on the control valve  13 . Because the valve mounting face  25  is recessed from the outer edge of the raised segment  33 , the flat lower wall  37  of the raised segment provides a protective wall for the control valve  13  when it is mounted to the cylinder head. In the normal horizontal orientation in which the switch operator is mounted, the protective side wall  37  overlies a substantial portion of the valve. This is important because, in the rugged environment in which these switch operators are installed and operate, they are typically stepped on and subjected to other rough treatment. 
     As may be seen in FIGS. 3,  4  and  6 , in the valve mounting face  25  of the cylinder head, there are a pair of recessed bores  39  for plug-in connectors  38 . The connectors  38  are aligned with mating connectors recessed in the mounting surface  36  of the control valve such that, when the control valve is bolted to the valve mounting face  25 , electrical connections are automatically established. Thus, after interposing a suitable gasket  49  between the valve mounting face  25  on the cylinder head and the mounting surface  36  on the valve, complete pneumatic and electrical connections may be established with four mounting bolts  40 . 
     As best shown in FIGS. 3,  4  and  5 , DC operating power at supply line voltage is brought into the recess  34  in the raised segment  33  of the cylinder head through one or both of a pair of line openings  41  on opposite sides of the wall defining the recess  34 . Appropriate connections between the supply line or lines  56  is made first to the voltage control module  30  at the terminals  42  provided thereon. The control module itself includes a circuit board  43  which carries the electrical components on the face opposite the terminals  42 . The circuit components  55  extend into a secondary recess  44  at the bottom of recess  34  formed by the semi-circular raised segment  33 . Electrical leads  57  from the control module circuit board  43  to the control valve  13  extend through an internal passage  45  extending from the secondary recess  44  to the lower ends of the bores  39  containing the plug-in connectors  38 . The control module circuit board  43  rests on a shoulder  46  defined by the transition between the bottom of the recess  34  and secondary recess  44 . The circuit board  43  may be conveniently held in place with a pair of mounting screws  47 . The leads from the plug-in connectors  38  which pass through the internal passage  45  and into the secondary recess  44  are preferably connected to the control module circuit board  43  with removable plugs that are contained in the secondary recess and is easily accessible for connection or disconnection when the control module circuit board is removed from its mounting. The entire recess  34  is conveniently closed by a removable, weather tight cover  48  held in place with a number of machine screws  50 . 
     The function of the voltage control module  35  will now be briefly described. As indicated in the background portion of the specification above, tracks switch operators in the U.S. typically operate with 24 volt DC or 12 volt DC power. This, of course, makes compatibility of an operator designed to run at one voltage difficult or impossible for use in a system operating at the other voltage. Another and possibly more serious problem, however, is that in 24 volt systems, it is not uncommon for the line voltage to drop below the effective operating voltage because of line losses that inevitably occur over a long and extended supply system. Typically, if line voltage drops below about  18 - 19  volts, a 24 volt operator will cease to function. In addition, standard 12 volt systems are typically designed to operate at a maximum voltage of about  13 - 14  volts. Thus, there is a dead band of about 5 volts between the minimum effective operating voltage for a 24 volt system and the maximum operating voltage for a 12 volt system. 
     The solenoid operated control valve  13  operates at a nominal 12 volts DC and the voltage control module  35  permits the control valve to function with incoming line voltages that range from a maximum typically encountered in a 24 volt system (i.e. about 26 volts) to the minimum effective operating voltage for the valve (i.e. about 9 volts). Thus, the circuit board  43  for the voltage control module utilizes conventional solid state components including a voltage regulator  52  that, in one mode of operation, steps down any incoming line voltage above about 14 volts to 12 volts and, in a second mode of operation, permits line voltage from about 14 volts down to the minimum operating voltage for the valve to pass through directly to the valve. Preferably, the voltage control module circuit also includes a diode arrangement that makes the circuit polarity insensitive to protect the circuit from inadvertent application of voltage at the wrong polarity. The circuit is also preferably provided with automatically resettable fuses, thereby precluding the need for manual resetting. 
     The cylinder head  12  is designed for direct retrofit replacement on existing switch machines. The improved cylinder head  12  is attached to the cylinder body with bolted connections  51  that pass through the cylinder head and thread into suitably tapped holes in the cylinder body  14 . As previously indicated, the improved cylinder head of the present invention is adaptable to retrofit applications to either 24 volt or 12 volt switch machines. Assembly, servicing and maintenance of the cylinder head are straightforward and simple. The control valve  13  may be removed for service or replacement with four mounting bolts  40 . The plug-in electrical connectors  38  preclude the need to make manual terminal disconnections. To remove the entire cylinder head  12 , the electric power supply lines  56  are disconnected from the terminals  42  (after removing the access cover  48 ) and the four bolted connections  51  are removed. If necessary, the voltage control module  35  may be removed from the secondary recess  44  by removing two mounting screws  47  and unplugging the connection through the internal passage  45  to the control valve  13 . 
     Additional features which enhance serviceability and operability of the improved cylinder head  12  of the present invention include the use of easily removable threaded plugs  53  for one or the other of the electric supply line openings  41 , and the use of machine screws  50  for the cover  48  that have heads sized to match the terminal nuts  54  on the voltage control module  35 . The latter feature facilitates terminal connection tasks by eliminating the use of another tool. Finally, apart from the entry of the line voltage conductors through the line openings  41  and into the recess  33 , all other electrical conductors and connections are housed within the cylinder head, completely protected and easily connected or disconnected with plug-in connectors.