Rolling stock accelerator
United States Patent [1 1 Murato et al.  
 1 ROLLING STOCK ACCELERATOR [22] Filed: Apr. 15, 1974 [21] Appl. No.: 461,137  
 [30] Foreign Application Priority Data Apr. 17, 1973 Japan 48-42727 [52] US. Cl. 104/167; 104/162; 104/166 [51] Int. Cl B6lb 13/00 [58] Field of Search 104/147 R, 162, 165, 167, 104/166 [56] References Cited UNITED STATES PATENTS 1,298,285 3/1919 Bogaty 104/167 X 2,624,440 l/l953 Hornberger 104/162 UX 51 Apr. 15, 1975 Primary Examiner-Robert S. Ward, Jr. Attorney, Agent, or FirmSaul .lecies [57] ABSTRACT A rolling stock accelerator is disclosed which will start a railway car or similar vehicle moving from a standing start, and/or accelerate an already moving car at low speed. A number of screw drums having helical fins mounted thereon are disposed axially in parallel with the rails of the track, with a mechanism for controlling their operation, all mounted upon a base. In response to an external signal, each of the screw drums is rotated axially, causing the helical fins to engage the flanges of the car wheels, thereby moving the car forwad or accelerating it by means of the rising surface of the rotating fin impelling the wheel forward.  
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 ROLLING STOCK ACCELERATOR BACKGROUND OF THE INVENTION The present invention relates to an hydraulic rolling stock accelerator for starting and/or accelerating railway rolling stock or similar vehicles at low speeds. (Although there are many types of rolling stock. the word car is used herein to represent any and all such types.)  
  In the prior art of rolling stock accelerators. the plunger of an hydraulic cylinder disposed adjacent to a rail of a railway track is so arranged as to engage a wheel of a car approaching the accelerator. Therefore. a chamber defined by the cylinder and the plunger. which is caused to stroke by the wheel. changes its volume. This chamber is further divided by a sliding valve disposed within the cylinder into an upper and lower chamber. The sliding valve is adapted to be shifted at the ends of the extension and retraction strokes of the plunger in such a way that the upper chamber. that is the chamber below the plunger. may be connected with a low or high pressure hydraulic source through the lower chamber. Therefore. in the retraction or compression stroke in which the plunger in engagement with the wheel is retracted into the cylinder. the upper chamber is connected with the low pressure hydraulic source so that the plunger may be retracted without resistance during almost all of the retraction or compres sion stroke. Thus the plunger may be retracted without decelerating force being applied to the wheel. When the plunger reaches the end of the compression stroke. the sliding valve is mechanically shifted to that the upper chamber is connected with the high pressure hydraulic source so that when the wheel passes over the vertical passing through the pivot of the hydraulic cylinder. the plunger is caused to be extended under the force of the working fluid under high pressure supplied from the high pressure source. thereby accelerating the wheel. At the end of the extension stroke of the plunger. the sliding valve is shifted so that the upper chamber may be connected again with the low pressure hydraulic source in preparation for the next acceleration.  
  However. the conventional rolling stock accelerator of the type described has many defects. First. the accelerating force obtained by each hydraulic cylinder is not sufficient by itself. so that a large number of hydraulic cylinders are required to accelerate a car to the desired speed. Therefore. the initial cost is very expenseive. and a large installation space is required. Second. even though the conventional rolling stock accelerator may accelerate a car. it cannot start a car from a stationary position and then accelerate it. Third. it cannot push a car along an upgraded track.  
 SUMMARY OF THE INVENTION The primary object of the present invention is therefore to provide a novel rolling stock accelerator capable of exerting stronger starting and accelerating forces to such railway cars and similar vehicles.  
  Briefly stated. in the present invention. a number of screw drums having helical fins mounted on their outer surfaces are disposed axially in parallel along the rails of the railway track or the like and are driven by hydraulic motors which in turn are controlled by command units. The helical fins of the screw drums are made to rotate axially and are thereby placed in driving contact with the flanges of the car wheels so that force may be transmitted to the wheels. Thus the car may be accelerated. or started even when it is stationary. Furthermore. the angle of rotation of the screw drum in each acceleration step is automatically controlled so that continuous accelerating may be effected. Moreoever. the screw drums may be selectively shifted between their operative and inoperative positions. so that when they are inoperative. a car may freely pass over the accelerator.  
  The above and other objects. features. and advantages of the present invention will become more apparent from the following description of one preferred embodiment thereof taken in conjunction with the accompany diagrams.  
 BRIEF DESCRIPTION OF THE DRAWING:  
  FIG. I is the plan ofa rolling stock accelerator in accordance with the present invention.  
  FIG. 2 is the side elevation of an hydraulic starteraccelerator unit thereof.  
 FIG. 3 is the plan of FIG. 2.  
 FIG. 4 is the end elevation of FIG. 2.  
  FIG. 5 is the longitudinal vertical cross-section of the control valve assembly incorporated in the hydraulic unit shown in FIG. 2.  
 FIG. 6 is the longitudinal plan cross-section thereof.  
  FIG. 7 is a corss-sectional view taken along the line 7 -7 of FIG. 5.  
  FIG. 8 is a cross-sectional view taken along the line 8-8 of FIG. 5.  
  FIG. 9 is a cross-sectional view taken along the line 9-9 of FIG. 5.  
  FIG. 10 is a longitudinal cross section of a pulse generating valve.  
  FIG. 11 is an hydraulic circuit diagram of the described rolling stock accelerator to explain the mode of operation thereof.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT:  
  The rolling stock accelerator generally indicated by FIG. 1 comprises a number of hydraulic units 22 disposed axially along a pair of rails 21; an hydraulic pressure source 23 for supplying the working fluid to the hydraulic units 22; an hydraulic unit control unit 24. and a number of command units 25 for giving the operational commands to the corresponding hydraulic units 22.  
  Referring to FIGS. 2, 3, and 4. hydraulic-unit 22 includes a drive assembly 26. a control valve assembly 27. and a support assembly 28 which supports the driving and control valve assemblies 26 and 27 in parallel with rail 21 laid over foundation members 30, through a support 29 shown in FIG. 4.  
  The drive 26 generally comprises a screw drum 33 with a pair of helical fins 34 and an hydraulic motor 35. One end of the shaft of screw drum 33 is rotatably supported by arm 31 and the other end by a gear box 32 coupled to hydraulic motor 35. The pair of helical fins 34 mounted upon the screw drum 33 are angularly spaced apart from each other by 180 degrees and have a half-pitch. The rotation of hydraulic motor 35 is transmitted through gear box 32 to screw drum 33 so that the rotating. rising edges of helical fins 34 are placed in driving contact with flanges 36 of the car wheels on rail 21 so as to start or accelerate the car as will be described in greater detail below.  
  The control valve assembly 27 is interposed between arm 31 and gear box 32 in parallel with driving assembly 26. As shown in FIGS. and 6. control valve assembly 27 includes an initial operation valve 37 adapted to give the start signal to hydraulic motor 35. and a rotary valve 38 coupled to screw drum 33 so as to interrupt the flow of the working fluid to hydraulic motor 35. thereby controlling the angle of rotation of screw drum 33.  
  ln the initial operation of valve 37. a spool 40 is normally held in the position shown in FIGS. 5 and 6 under the force of a spring 39 to interrupt the flow of the working fluid supplied through an intake port 41 and a passage 42. But spool 40 is caused to be stroked to the left-hand direction against the spring 39 only when the pilot fluid flows into a pilot chamber 45 from a pilot port 43 through a passage 44. As a result. the working fluid is supplied to hydraulic motor 35 from support port 41, passage 42. an annular grove 46, another annular groove 47, a passage 48 and a motor port 49. The working fluid is returned from hydraulic motor 35 to a return line through another motor port 50. a passage 51. annular grooves 52 and 53, a passage 54 and a discharge port 55. Thus hydraulic motor 35 is rotated in a clockwise direction.  
  The rotary valve 38 comprises a stationary sleeve 56 and a sliding rotor 57 fitted into sleeve 56 and coupled through a rotary member 58 and gear box 32 to screw drum 33 and hydraulic motor 35. In the present case. the gear ratio of the gear box 32 is so selected that the rotor 57 in rotary valve 38 may be rotated at a speed one-half the rotary speed of hydraulic motor 35. For the sake of simplicity. rotor 57 of rotary valve 38 is shown as being rotated through 45 degrees in FIGS. 5 and 6, but when hydraulic motor 35 is deenergized. ports 59 and 60 of rotor 57 are disconnected from ports 61 and 62 of sleeve 56 as shown in FIGS. 7. 8. and 9. The ports 59 and 60 of the rotor 57 are connected with motor ports 49 and 50. respectively. through lateral ports 63 and 64. chambers 65 and 66, ports 67 and 68, annular grooves 69 and 70, ports 71 and 72 of the sleeve 56. annular chambers 73 and 74, and passages 48 and 51. respectively. Ports 61 and 62 of sleeve 56 are connected with passages 75 and 76, respectively.  
  When the working fluid flows into passage 75 while passage 76 is connected with the return line. the working fluid is stopped at port 61 of sleeve 56 so that hydraulic motor 35 is not driven. But when spool 40 of initial operation valve 37 is shifted in response to the flow of the pilot fluid in the manner described above so that hydraulic motor 35 is rotated in a clockwise direction. rotor 57 of rotary valve 38 is rotated to connect its ports 59 and 60 with ports 61 and 62 of sleeve 56. As a result. even after the flow of the pilot fluid is interrupted. the working fluid flows from passage 75 into hydraulic motor 35 through motor port 49 while the working fluid is returned from hydraulic motor 35 to the return line through motor port 50 and port 76. Thus the rotation of hydraulic motor 35 in a clockwise direction may be continued. More particularly, rotation is continued until rotor 57 in rotary valve 38 is rotated in the direction indicated by the arrow through 90 so that communication between ports 59 and 60 on the one hand. and ports 61 and 62 of sleeve 56 on the other hand. is interrupted. Thus screw drum 33 is rotated through 180 degrees in a clockwise direction. Hydraulic motor 35 is caused to rotate in a clockwise direction until rotor 57 rotates through 90. but when it rotates in excess of 90. ports 59 and 62 are connected and ports 60 and 61 are connected so that the flow of working fluid in hydraulic motor 35 is reversed. As a result. hydraulic motor 35 is reversed and reverses rotor 57. In other words. when ports 59 and 60 of rotor 57 are closed by sleeve 56. rotary valve 38 reaches the stable or dead point.  
  However. when rotor 57 is further rotated in a clockwise direction under these conditions. the flow of working fluid in hydraulic motor 35 is reversed so that hydraulic motor 35 is also reversed in direction. As a result. rotor 57 is forced to return its stable point. To overcome this problem. passages 75 and 76 are alternately connected with the pressure and return lines in response to the signal of a detector which is set to detect the timing when the pilot fluid flows into pilot port 43. Therefore. whenever hydraulic motor 35 is rotated in a clockwise direction. as spool 40 in initial control valve 37 is shifted by the pilot fluid flow. the working fluid under pressure is always forced to flow through rotary valve 38 from motor port 49 to hydraulic motor 35. As a result. rotary valve 37 is caused to rotate through 90 in each step by hydraulic motor 35 so that the screw drum 33 is caused to rotate intermittently through 180 in each step in a clockwise direction.  
  In the present case, in order to alternately connect passages 75 and 76 with the pressure and return lines each time when the pilot fluid flows into pilot port 43. a selection valve 77 and a directional control valve 78 are used as shown in FIGS. 5 and 6. A spool 79 in selection valve 77 is normally pressed against a cam 81 formed at the end surface of rotor 57 of rotary valve 38 under the force of a spring 80, in such a way that spool 79 may be shifted as rotor 57 rotates through 90. As a result. the pilot fluid flowing from pilot port 43 into passage 44 is alternately forced to flow from an annular groove 82 through an annular groove 83 and a passage 85 into a left pilot chamber 87 in directional control valve 78 and through an annular groove 84 and a passage 86 into a right pilot chamber 88 of directional control valve 78. At the same time, pilot chambers 87 and 88 of directional control valve 78 are alternately connected to discharge port 55 through passages 85 and 86 and annular grooves 83 and 84, respectively. the annular groove 89. and the passages 90 and 76. respectively. As a result, spool 91 in directional control valve 78 is shifted each time when rotor 57 in rotary valve 38 is rotated through 90 degrees so that passage 75 is connected with supply port 41 through annular grooves 92 and 94, and passage 42, while passage 76 is connected with discharge port 55 through annular grooves 93 and 95. and passage 76 or vice versa. Thus passages 75 and 76 are alternately connected with the pressure and reutrn lines.  
  Referring back to FIGS. 2, 3, and 4, support assembly 28 comprises two pairs of rocking arms 97 to connect arm 31 and gear box 32 to brackets 96. respectively. which in turn are attached to foundation members 30, and two hydraulic cylinders 98 interposed between foundation members 30 and arm 31 and gear box 32. respectively. When the hydraulic cylinders 98 are extended. the edges of the helical fins 34 mounted upon screw drum 33 of driving assembly 26 are moved to the operative position to engage flange 36 of the car wheel.  
 which are slidably fitted into sleeve 101. and an operating arm 107 hinged respectively by pins 105 and 106 to the leading ends of operating rod 103 and an arm 104 extending from valve casing 100.  
  Sleeve 101 defines a cylinder chamber 108 between sleeve 101 and valve casing 100 at one end thereof. A coiled spring 111 is loaded between valve casing 100 and a spring seat 110 mounted on an extension rod 109 extending outwardly from the end of the valve casing so that pulse-generating valve 99 may normally be in the retracted position shown in FIG. under the force of coiled spring 111. In the retracted position. a roller 112 attached to the leading end of operating arm 107 is retracted from the upper surface level of rail 21. But when the working fluid under pressure is forced into cylinder 108 through a port 113 and a passage 114 formed through valve casing 100. spool 102 and hence operating rod 103 are pushed outwardly so that roller 112 at the upper end of operating arm 107 is extended above the surface of rail 21.  
 . Spool 102 is normally held in the position shown in FIG. vl0 under the force of a coiled spring 115 loaded between sleeve 101 and the extension rod 109 so that a delivery port 116 communicates through. as follows: a passage 117; an annular groove 118; a chamber 119; an annular groove 120 of spool 102; a chamber 121: an annular groove 112&#39;. and a passage 123. to a discharge port 124. But when roller 112 at the end of operating arm 107 is pushed down by the wheel. operating arm 107 pushes operating rod 103 and spool 102 inward so that delivery port 116 is connected as follows: through passage 117; annular groove 118; chamber 119; annular groove 125 of spool 102;-chamber 126; annular groove 127; and a passage 128. to a supply port 129. When the working fluid under pressure is forced into pilot chamber 130. between one end of spool 102 and sleeve 101. from pilot port 131 through a passage 132 and an annular groove 133. spool 102 is forced inward regardless of the position of operating arm 107 so that delivery port 116 is connected with supply port 129.  
  Next. referring to FIG. 11., an hydraulic pressure source generally indicated by 23 comprises, as follows:  
 a high pressure pump 134; a low pressure pump 135;  
 relief valves 136 and 137 for controlling the maximum discharge pressures of high and low pressure pumps 134 and 135, respectively; an accumulator 138 with a pilot check valve 139 for storing the working fluid under pressure supplied from high pressure pump 134: the first, second and third sequence valves I40. 141 and 142 inserted in the line connected to low pressure pump 135; accumulators 143, 144, 145. and 146; check valves 147,- 148, 149, 150. 151 and 152. and a pressure pilot valve 153.  
  The control unit generally indicated by 24 comprises solenoid-controlled valves 154 and 155 for shifting hydraulic units 22 between their operative and inoperative positions.  
  Hydraulic units 22, hydraulic pressures source 23. control unit 24 and command unit 25 are hydraulically interconnected as shown in FIG. 11.  
  Next. the mode of operation of the rolling stock accelerator in accordance with the present invention will be described in detail below.  
 I. Shifting of Hydraulic Units to Operative Positions from Inoperative Positions In order to shift hydraulic unit 22 from the inoperative position to the operative position. the solenoidcontrolled valve 154 is energized in response to a signal applied from the exterior so that it is shifted from the left position (FIG. .11 to the right position. As a result. the working fluid under pressure supplied from low pressure pump flows into supply ports 41 and 129 of hydraulic unit 22 and commandunit 25. respectively. When rotor 57 in rotary valve 38 is moved out of the stable point under the above condition. the working fluid under pressure flows from supply port 41 into either of the ports of hydraulic motor 35 depending upon the position of directional control valve 78 and theangular position of rotor 57 away from its stable point. As a result. hydraulic motor 35 is rotated in either clockwise or counter-clockwise direction. Screw drum 33 and rotor 57 in the rotary valve are also rotated until ports 59 and 60 of rotor 57 are closed by sleeve 56, and then stopped.  
  When hydraulic motor 35 is stopped. the discharge pressure of low pressure pump 135 rises so that the first sequence valve is opened. Then the working fluid under pressure flows into hydraulic cylinders 98 in the support assembly of hydraulic unit 22 and into cylinder 108 in the pulse-generating valve 99 through its port 113. Hydraulic cylinders 98 are extended so that screw drum 33 of hydraulic unit 22 is raised to its operative position where the helical fins 34 may engage flange 36 (FIG. 4). Pulse generating valve 99 is so actuated that roller 112 of operating arm 107 is raised above the surface of the rail 21 for engagement with the wheel in the manner described above.  
  Thereafter. the discharge pressure of low pressure pump I35 rises again so that the second sequence valve 141 is opened. As a result. the working fluid under pressure flows from pilot port 131 of pulse-generating valve 99 into the pilot chamber 130 (FIG. 10) so that spool 102 is shifted. Therefore. the working fluid under pressure is forced to flow from supply port 129 through delivery port 116 to pilot port 43 of control valve assembly 27 (FIG. 2) in hydraulic unit 22 so that the initial operation valve 37 (FIG. 6) is shifted. At the same time. selection valve 77 is actuated by cam 81 at one end of rotor 57 in rotary valve 38 so that the working field under pressure is forced into either pilot chamber 87 or 88 (FIG. 5). Thus the angular position of rotor 57 is corrected so that it may rotate in the desired direction. The working fluid under pressure flows from supply port 41 of control valve assembly 27 (FIG. 3) through initial control valve 37 (FIG. 6) into hydraulic motor 35 (FIG. 3) so that the hydraulic motor is rotated in a clockwise direction. Rotor 57 in rotary valve 38 is also rotated in a clockwisedirection so that the working fluid under pressure flows through directional control valve 78 and rotary valve 38 into hydraulic motor 35 (FIG. 3). Hydraulic motor 35 is rotated in a clockwise direction so that rotary valve 38 makes one idle rotation to the next stable point. As a result. selection valve 77 is shifted by cam 81.  
  Thereafter, the discharge pressure of low pressure pump 135 rises again so that pressure pilot valve 153 is shifted to the upper position. As a result. pilot chamber 130 in pulse-generating valve 99 (FIG. 10) is connected through pilot port 131 and pressure pilot valve 153 to the return line so that spool 102 in pulsegenerating valve 99 is pushed outward under the force of coiled spring 115 until it engages with the operating rod 103. in response to the increase in discharge pressure of low pressure pump 135. the third sequence valve 142 is also opened so that pilot check valve 139 is opened. As a result. the liquid under high pressure discharged from high pressure pump 134 flows into supply port 41 of control valve assembly 27 in hydraulic unit 22 and into supply port 129 of pulsegenerating valve 99. Thus the shift of hydraulic unit 22 from its inoperative position to its operative position -s accomplished.  
 ll. Continuous Acceleration Operation When hydraulic unit 22 is shifted to its operative position in the manner described above. the car wheel riding on rail 21 pushes down roller 112 of pulsegenerating valve 99 so that the pulse-like pilot pressure signal is transmitted to initial operation valve 37 and directional control valve 78 in control valve assembly 27 of hydraulic unit 22. The initial operation valve 37 is so actuated as to temporarily connect hydraulic motor with the pressure and return lines so that this motor may rotate in a clockwise direction. Directional control valve 78 is so actuated that the connection of rotary valve 38 with the pressure and return lines is reversed. Therefore. rotary valve 38 is opened by rotation of hydraulic motor 35, caused by the shift of initial operation valve 37. so that the pressure and reutrn lines are connected with hydraulic motor 35 through direcv tional control valve 78 and rotary valve 38. Thus hydraulic motor 35 continues to rotate in a clockwise direction so that screw drum 33 is also caused to rotate in a clockwise direction. The helical fins 34 on screw drum 33 are thus pressed against wheel flange 36 so that an accelerating force is transmitted to the wheel and car. Rotation of hydraulic motor 35 continues until rotor 57 in rotary valve 38 turns through degrees. that is. until screw drum 33 through 180 degrees. When rotor 57 is turned through 90 degrees. its cam 81 causes selection valve 77 to be shifted. Thus screw drum 33 is stopped after it rotates through a predetermined angle. Therefore. the wheel is accelerated by screw dru&#39;m 33 from the time it reaches hydraulic unit 22 until it leaves. thus accelerating the car. As soon as the wheel has left unit 22. rotation of screw drum 33 is interrupted. This process is repeated in like manner for succeeding wheels.  
 lll. Star-ting and Acceleration it is assumed that a car is stationary above hydraulic unit 22. in this case. in response to an external signal. the solenoid-controlled valve 154 (FIG. 11) is shifted to its right position so thatthe working fluid under pressure is supplied from low pressure pump to hydraulic cylinders 98 of support assembly 28 of hydraulic unit 22. and to cylinder 108 of pulse-generating valve 99. As a result, hydraulicunit 22 is shifted to its opera-.  
 tive position in the manner described above. However. there are cases when the hydraulic units cannot be shifted to their operating position because the helical tins of their screw drums are engaged with the car wheel flanges. But when sequence valve 141 is opened in the next step so that pulse-generating valve 99 is opened. hydraulic motor 35 are rotated in a clockwise direction to turn their corresponding drums 33 so that the drums may be shifted gradually to their operating position. However. it should be noted that rotary valves 38 of the hydraulic units. which have not yet been shifted to their operating position. are out of the stable point. Therefore. when sequence valve 142 is opened to open pilot check valve 139. the working fluid under high pressure discharged from high pressure pump 134 is forced through directional control valve 78 and rotary valve 38 into hydraulic motor 35. As a result. hydraulic motor 35 is rotated in a clockwise direction under the force of the working fluid under higher pressure so that the tins of the screw drum are forced against the wheel flange and cause the wheel to turn. Thus the car may be started from a stationary position.  
  When the car wheels that are started in the manner described above push down rollers 112 of pulsegenerating valves 99, the car is gradually accelerated in the manner described in (11) above.  
 IV. Shift to Hydraulic Unit to inoperative Position inders 98 of hydraulic unit 22 forces the cylinders to bev retracted as the extension chambers of hydraulic jacks 98 and cylinder 108 of pulse-generating valve 99 are connected through solenoid-controlled valve 154 and check valve to the return line. Thus both hydraulic units 22 and the pulse-generating valves 99 are returned to the initial or inoperative position so that the car may freely pass over the rolling stock accelerator.  
 V. Speed Control Operation Suitable means for detecting car speed such as a tachometer (not shown) is mounted on screw drum 33, hydraulic motor 35, or rotor 57 of rotary valve 38 in such a way that when the speed of the started and/or accelerated car reaches a predetermined velocity. the solenoid-controlled valves 154 and 155 are actuated in response to a signal from the tachometer so as to return hydraulic units 22 and pulse-generating valves 99 to their inoperative positions. Thus car speed may be controlled in a very simple manner by this present invention.  
  As described above. in this invention. stronger accelerating forces may be applied to rolling stock as com pared with the prior art of telescopic-type rolling stock accelerators. Therefore. the present invention may be used not only for starting and accelerating rolling stock but also for pushing cars along up-graded tracks. Furthermore. when the rolling stock accelerator is retracted to its inoperative position, rolling stock may freely pass over it. Thus the rolling stock accelerator in this present invention may find a wide variety of applications.  
 What is claimed is:  
  l. A Rolling Stock Accelerator comprising the following:  
 A. A number of hydraulic units disposed along the rails of a railway track or the like. B. An hydraulic pressure source for supplying working fluid under pressure to these hydraulic units. C. A command unit for controlling the operation of a number of hydraulic units. each of which includes the following:  
 a. A drive assembly comprising an hydraulic motor and a screw drum having helical fins mounted thereon to make driving contact with the flange of a car wheel. said screw drum being driven by the hydraulic motor.  
 b. A control valve assembly including an initial operation valve adapted to give the start signal to the hydraulic motor in response to a command signal from the command unit. and a rotary drum coupled to the screw drum so as to interrupt the flow of working fluid under pressure to the hydraulic motor. thereby controlling the angle of rotation of said screw drum.  
 . A support assembly including a number of hydraulic cylinders interposed between the base and the drive assembly and command unit so as to selectively shift them from their inoperative positions to their operative positions or vice versa. 2. A Rolling Stock Accelerator comprising the following:  
 A. A number of hydraulic units disposed along the rails ot a railway track or the like. B. An hydraulic pressure source for supplying working fluid under pressure to these hydraulic units. C. A pulse-generating valve adapted to detect a car entering the rolling stock accelerator so as to give a pulse signal. and a number of hydraulic units each of which includes the following:  
 a. A drive assembly comprising an hydraulic motor and as screw drum having helical fins mounted thereon to make driving contact with the flange of a car wheel. said screw drum being driven by the hydraulic motor.  
 h. A control valve assembly including an initial operation valve adapted to give the start signal to the hydraulic motor in response to the pulse signal derived from the pulse-generating valve: a rotary valve coupled to the screw drum in such a way that the flow of working fluid under pressure to the hydraulic motor may be interrupted at angularly symmetrical dead points; a selection valve adapted to be shifted synchronously with the actuation or shift of the rotary valve. and a directional control valve coupled to the selection valve so as to control the direction of the working fluid under pressure flowing to the rotary valve.  
 c. A support assembly comprising a number of hydraulic cylinders interposed between the base and the drive assembly and the pulse-generating valve so as to selectively shift them from their inoperative positions to their operative positions or vice versa.  
  3. A Rolling Stock Accelerator comprising the following:  
 A. A number of hydraulic units disposed along the rails of a railway track or the like.  
 B. An hydraulic pressure source for supplying working fluid under pressure to these hydraulic units.  
 C. A pulse-generating valve adapted to detect a car entering the rolling stock accelerator so as to give a pulse signal. and a number of hydraulic units each of which includes the following:  
 a. A drive assembly comprising an hydraulic motor and a screw drum having helical fins mounted thereon to make driving contact with the flange of a car wheel. said screw drum being driven by the hydraulic motor.  
 b. A control valve assembly including an initial operation valve adapted to give the start signal to the hydraulic motor in response to the pulse signal derived from the pulse-generating valve: a rotary valve coupled to the screw drum in such a way that the flow of working fluid under pressure to the hydraulic motor may be interrupted at angularly symmetrical dead points, thereby controlling the angle of rotation of said screw drum; a selection valve adapted to be shifted synchronously with the actuation or shift of the rotary valve. and a directional control valve coupled to the selection valve so as to control the direction of the working fluid under pressure flowing into the rotary valve.  
 c. A support assembly comprising a number of hydraulic cylinders interposed between the base and the drive assembly and the pulse-generating valve so as to selectively shift them from their inoperative positions to their operative positions or vice versa.  
 D. The said hydraulic pressure source comprising:  
 a. High and low pressure hydraulic sources for supplying working fluid under pressure to accelerate a car.  
 b. A control valve for directing working fluid under pressure supplied from the low pressure hydraulic pressure source to the rotary valves in the control valve assemblies of the hydraulic units. thereby resetting the rotary valves to a dead point.  
 c. A first-sequence valve adapted to be opened after the rotary valves have been reset so as to cause working fluid under pressure supplied from the low pressure source to flow into the hydraulic cylinders in the support assemblies ofthe hydraulic units. thereby shifting the drive assemblies of the hydraulic units and pulse-generating valves to their operative positions.  
 d. A second-sequence valve adapted to be opened after the drive assemblies and the pulsegenerating valves have been shifted to their operative positions so as to direct working fluid under pressure supplied from the low pressure source to the pulse-generating valves. thereby shifting the same so as to cause each of the hydraulic units to idle once.  
 e. A third-sequence valve adapted to be opened after each of the hydraulic units has made one idle operations so as to direct working fluid under pressure supplied from said low pressure source to a pilot check valve and to connect the rotary valves of the control valve assemblies of the hydraulic units with the high-pressure hydraulic source.