US 3929206 A
An improved servo hydraulic transducer and method of operating is disclosed. The transducer includes a vibrator and hydraulic lifts connected to an improved hydraulic system. The hydraulic system includes a pump pumping hydraulic fluid at a rate between the maximum average and minimum average from a source thereof into a manifold and high pressure system for a frequency sweep of the vibrator. The high pressure system supplies the hydraulic fluid required by the vibrator in addition to that supplied by the pump during the low frequencies of the sweep, and stores under pressure hydraulic fluid excessive to the vibrator requirements during the high frequencies of the sweep and slack time between sweeps. The hydraulic lifts include a chain and sprocket arrangement for each lift interconnected by a synchronization shaft. An unequal force on one of the hydraulic lifts produces through its chain and sprocket arrangement a moment on the synchronization shaft which is transferred through the chain and sprocket arrangement of the other lift to equalize the bearing force between the hydraulic lifts.
Description (OCR text may contain errors)
United States Patent [191 Bedenbender et al.
1 1 Dec. 30, 1975 [S4] SERVO HYDRAULIC TRANSDUCER AND METHOD OF OPERATION  Inventors: John W. Bedenbender, Plano,
Gilbert ll. Kelly, Irving, both of Text.
 Assignee: Texas Instruments, Corp., Dallas,
22 Filed: Apr. 30, 1973  Appl. No.: 355,838
Primary ExaminerMaynard R. Wilbur Assistant Examiner-T. M. Blum  ABSTRACT An improved servo hydraulic transducer and method of operating is disclosed. The transducer includes a vibrator and hydraulic lifts connected to an improved hydraulic system. The hydraulic system includes a pump pumping hydraulic fluid at a rate between the maximum average and minimum average from a source thereof into a manifold and high pressure system for a frequency sweep of the vibrator. The high pressure system supplies the hydraulic fluid required by the vibrator in addition to that supplied by the pump during the low frequencies of the sweep, and stores under pressure hydraulic fluid excessive to the vibrator requirements during the high frequencies of the sweep and slack time between sweeps. The hydraulic lifts include a chain and sprocket arrangement for each lift interconnected by a synchronization shaft.
An unequal force on one of the hydraulic lifts produces through its chain and sprocket arrangement a moment on the synchronization shaft which-is transferred through the chain and sprocket arrangement of the other lift to equalize the bearing force between the hydraulic lifts.
11 Claims, 19 Drawing Figures U.S. Patent Dec. 30, 1975 Sheet 1 0f13 3,929,206
w NE vv\ w m2 2: $3 m2 U.S. Patent Dec. 30, 1975 Sheet2of 13 3,929,206
US. Patent Dec.30, 1975 Sheet3of13 3,929,206
U.S. Patent Dec.30, 1975 Sheet4of13 3,929,206
MA k Jfli US. Patent Dec. 30, 1975 Sheet6of 13 3,929,206
U.S. Patent Dec.30, 1975 Sheet 10 0f13 3,929,206
R t REACTION MASS M B Fig X F cos (Z 'ft) i PAD I SOIL IMPEDANCE Z r U m 2 m I Hg /2 E e db/OCTAVE w o J I l l 1 IDG FREQUENCY, Hz
2 VOLUME FROM 3 ACCUMULATOR m QMAX m M QA VG T T TIME-b 1 US. Patent Dec. 30, 1975 Sheet110f13 3,929,206
Fig. /4/] FREQUENCY H l hl T +T TIME (t), SEC
UPSWEEPS 4 FREQUENCY Fig.
| a T T T TIME (1;), SEC
DOWNSWEEPS U.S. Patent Dec. 30, 1975 FLOW (Q) avg Sheet 12 of 13 3,929,206
Fig /5 VOLUME FROM ACCUMULATOR, V
T T+T TIME (t). SEC
PUMP VOLUME AVAILABLE TO CHARGE AccUMULAToR, v
PA 1-QP I PUMP l VOLUME TIME US. Patent Dec. 30, 1975 Sheet 13 0f13 3,929,206
REQUIRED VOLUME FROM ACCUMULATOR, V GAL.
UQS/ZH L/( 1 aLvu dEIH/SAS Fig.
SERVO HYDRAULIC TRANSDUCER AND METHOD OF OPERATION This invention relates generally to improvements in the art of seismographic surveying of the type utilizing a mechanical vibrating energy source or transducer,
and more particularly to an improved hydraulically driven system for generating continuous seismic signals having swept frequencies.
In the past, many seismic surveying systems have used a continuous wave seismic signal generated in the earth by a vibrator or seismic transducer. These vibrator assemblies generally have been comprised of a base plate or pad retractably mounted upon a truck type vehicle for transport to a desired field location. Upon arrival at a selected source location, the pad was lowered by a hydraulic lift mechanism into contact with the earths surface and then the truck lifted on the pad by the hydraulic lift mechanism to provide a hold down force upon the pad. Prior lift systems have utilized a pair of load bearing columns, a pair of hydraulic lift cylinders and a synchronizing system to insure coordinated movement of the columns. Where the lift cylinders have extended above the vibrator, they have been mechanically interconnected by a rigid stress member; otherwise a hydraulic interconnection system has been used for synchronization. The pad was vibrated by a double rod-end-piston extending upwardly and downwardly in a mass type cylinder. The mass of the cylinder varied from several hundred to several thousand pounds. An actuator, usually hydraulic, was used to reciprocate the cylinder mass or reaction mass relative to the base plate through a short stroke at predetermined frequencies. The equal and opposite force of reaction reciprocated the base plate through a short vertical stroke at corresponding frequencies, thereby moving the surface of the earth and inducing the desired seismic signal in the earth.
The hydraulic actuator consisted of a pump pumping oil under high pressure from a reservoir through a manifold into a high pressure accumulator and through a servovalve for selectively introducing oil into the cylinder. Oil from the high pressure system was alternately introduced by the servovalve into the cylinder above and below the piston to vibrate the weight bearing cylinder. The oil was returned through the servovalve alternately from below and above the piston into a low pressure accumulator used for dampening oil surges prior to forcing the oil into an oil cooling system for cooling the oil before it was returned to the high pressure system by the pump. The high pressure accumulator in prior system has been a relatively small volume accumulator and used only to smooth out the peaks of the sinusoidal supply required by the vibrator. The pump capacity (0,) was fixed at approximately the average flow (Q required for the lowest desired operating frequency (f,) using the following formula:
where p hydraulic pressure, psi A hydraulic piston area, in f the operating frequency, Hz M, reaction mass, (lb sec)/in 2 The high pressure accumulator size was determined at the lowest operating frequency. The accumulator had to supply a volume equal to the difference between the instantaneous peak flow (O and the average flow (0 required by the vibrator during the period (T,) of the lowest operating frequency. This volume is represented by the following formula:
V: 0.59 T, On, in."
A problem with the prior art is the large size of the hydraulic system required for a mechanical vibrator to produce desired seismic vibrations. A further problem lies with the lift system which is prone to seizure when the mechanical vibrator pad is positioned on uneven earth surfaces.
Thus it is an object of the present invention to pro vide an improved transportable seismic transducer assembly.
Another object of the invention is to provide a seismic transucer assembly with an improved mechanical synchronizing system for insuring coordinated movement of the lift columns with the hydraulic lift system.
Still another object of the invention is to provide an improved hydraulic system for a seismic transducer in which high pressure accumulators are used to supply a major part of the high hydraulic flow for the low frequency portion of the sweep to approximately double the effective power output of the transducer.
Briefly stated the transportable seismic transducer constituting the subject matter of the present invention comprises a vehicle such as, for example, a truck, tractor or tractor drawn trailer supporting a retractable novel transducer or vibrator system. The rectractable transducer is suspended by a pair of hydraulic lifts having a novel mechanical synchronizing system to insure coordinated movement of columns of the hydraulic lifts.
In accordance with a more specific aspect of the present invention, the transducer of the portable transducer has a base plate or pad which is lowered into contact with the earth by means of the hydraulic lifts mounted upon the transporting vehicle. After bringing the pad into contact with the earth, the hydraulic lifts raise the vehicle on the pad to provide a hold down force for maintaining the pad in contact with the earth during vibration of the transducer. The novel mechanical synchronization system for the hydraulic lifts includes a chain and sprocket arrangement for each hydraulic lift. The chain from one hydraulic lift runs over a sprocket at one end of a synchronization shaft, and the chain from the other hydraulic lift runs over a sprocket at the opposite end of this shaft. An unequal force on one of the hydraulic lifts produces through its chain and sprocket arrangement a moment on the synchronization shaft which is transferred through the chain and sprocket arrangement of the other lift to the other lift to equalize the bearing force between the hydraulic lifts.
With the base plate or pad anchored to the ground the vibrator is vibrated to send out into the earth through the pad a series of vibratory sweeps". These sweeps are ordinarily a linear change of frequency with time. Each sweep may be from a low (about 5H2) to a high (about Hz) frequency upsweep or a high to low frequency down sweep. The vibrator includes a weighted cylinder, often referred to as the reaction mass, reciprocately mounted on a double rod-end-piston having the ends thereof connected to the base plate. The cylinder or reaction mass is reciprocately actuated by pressurized hydraulic fluid introduced alternately in the cylinder above the below the piston. The novel hydraulic system comprises a pump capable of pumping a prescribed amount of the total hydraulic fluid required for each sweep and a high pressure aceu mulator system having sufficient capacity and pressure force to provide the remainder of the total fluid required for each sweep.
It has been found that with the practice of the present invention the hydraulic pump and engine used to drive the vibrator of the prior art device can be reduced more than one-half in capacity and produce the same results as the prior art devices, or for the same hydraulic pump and engine the displacement amplitude of the reaction mass can be approximately doubled to increase the amplitude of the seismic signal. Further objects and features of this invention will become obvious from the following description when taken in conjunction with the drawings in which:
FIG. 1 is a side view of a buggy mounted transducer constituting an embodiment of the present invention;
FIG. 2 is a top view of the buggy mounted transducer shown in FIG. 1;
FIG. 3 is an end view of a transducer constituting an embodiment of the present invention;
FIG. 4 is a partial cross-sectional view of the transducer taken along lines 44 of FIG. 2;
FIG. 5 is a partial elevational view with portions broken away to show details of one of the hydraulic lifts;
FIG. 6 is a cross-sectional view of the hydraulic lift of FIG. 5 taken along line 6-6 of FIG. 5;
FIG. 7 is a partial view of the hydraulic lift synchronization and lift control system;
FIGS. 8A and B are schematic diagrams of a hydraulic system for the vibrator or transducer assembly constituting an embodiment of the present invention;
FIG. 9 is a cross-sectional view of the high pressure accumulator utilized in the hydraulic system shown schematically in FIG. 8;
FIG. 10 is a schematic drawing of the electronic controller for the transducer;
FIG. I] is a schematic model of the vibrator transducer;
FIG. 12 is a plot of required hydraulic flow versus transducer operating frequency;
FIG. 13 is a plot of flow versus time for a fixed frequency;
FIGS. 14A and B are representations of frequency sweeps versus time;
FIG. 15 is a plot of hydraulic flow versus time for an upsweep;
FIG. 16 is a plot showing the hydraulic flow pattern plotted against time;
FIG. 17 is a plot showing the required volume from the high pressure accumulator plotted versus sweep rate.
Referring now to the drawings for a detailed description of the improved portable seismic transducer assembly in which there is shown (FIG. 1) a vehicle 10 having front and rear wheels 12 and I4, respectively, which support a chassis comprised generally of frame channels 16, a cab 18, and a conventional engine 20. The engine 20 is connected to drive the rear wheels 14 by a conventional drive train including a drive shaft 22.
The seismic transducer or vibrator assembly 24 (FIGS. 1 and 3) is disposed between the front and rear wheels and connected to the frame members I6 of the truck by a lift system 26 hereinafter described. A prime moveror engine 28, main hydraulic pump 30, high pressure accumulator system 32, low pressure accumulator system 34 (FIG. 2), hydraulic fluid tank 36, hydraulic fluid cooler 38 and associated hydraulic plumbing may be located on the frame members I6 as shown in FIGS. 1 and 2.
The transducer or vibrator assembly 24 (FIG. 3) includes a base plate or pad 40 which may be fabricated in any suitable manner to provide a flat lower base plate surface for engaging the surface of the ground. A transducer frame 42 comprising four vertically disposed frame members 44 extends upwardly from the base plate 40 to a point well above the drive shaft 22 of vehicle 10 (FIG. I). The lower halves of the four frame members 44 (FIG. 3) are reinforced by gusset plates 46. Bottom foot plates 48 are connected to the four vertical members of the frame 42 and the frame is bolted or otherwise attached to the base plate member 40. Top plates 50 are connected to the tops of the frame members 44 and are braced by gusset plates 52.
An upper cross-member 54 is formed by intersecting channels 56. The outer ends of the channels 56 are bolted to their respective top plates 50 by bolts 58. A lower cross-member 60 is constructed similarly to the upper cross-member 54 in that it comprises intersecting channel members 62 having their outer ends welded to points intermediate the four transducer frame forming vertical members 44. The intersections of the upper and lower cross-members 54 and 60 are adapted to receive the ends of a double rod-end piston member 64. The upper and lower ends of the rods of the piston member 64 are securely connected to the intersections of the cross-members 54 and 60, respectively, by a plurality of bolts or screws 66.
The piston member 64 has a piston (FIG. 4)'
within a cylinder 72 formed within a reaction mass 74. Piston 70 is provided with conventional piston rings 76 for insuring a sliding, fluid-tight seal with the interior of the cylinder 72. Hydraulic fluid is introduced into the cylinder 72 alternately on opposite sides of the piston 70 from a manifold control means such as, for example, a standard four port servo control valve 78 directing high pressure oil alternately through upper and lower hydraulic ports 80 and 82. High pressure oil is supplied to the servovalve through a high pressure passage 71 and low pressure oil flows from the servovalve through passage 73. Passages 71 and 73 are connected by hoses to a manifold 232 (FIG. 1) external to reaction mass 74 (FIG. 4). Thus, it will be evident that as hydraulic fluid is introduced through the lower port 82 into the cylinder 72 (FIG. 4) below the piston 70 the reaction mass 74 is driven downwardly relative to the piston member 70, and therefore relative to the pad 40 (FIG. 3). Conversely, when hydraulic fluid is introduced through the upper port 80 (FIG. 4) into the cylinder above the piston 70 the reaction mass 74 will be driven upwardly. As the reaction mass 74 is driven downwardly, an upwardly directed reaction force is applied to the pad 40 (FIG. 3) and when the reaction mass is driven upwardly, a downwardly directed reaction force will be applied to the pad 40. The amount of hydraulic fluid introduced into the cylinder 72 (FIG. 4) is controlled to vibrate the reaction mass 74 to produce varying frequencies of a given frequency range of a sweep.
In normal operation, the reciprocation of the reaction mass 74, (FIGS. 3 and 4) is maintained centered between the upper and lower cross-members 54 and 60 by means of a linear variable-differential transducer (LVDT) 84 (FIG. 2) having its electrical coils (not shown) mounted in a well provided therefor in the reaction mass 74 (FIG. 3). These coils surround a core member (not shown) which is attached to the lower cross-membcr 60. The electrical output of the LVDT 84 is coupled to an electronics controller hereinafter described (FIG. Additional reaction mass support is provided by a pair of strut type arrangements 90 (FIG. 4) mounted in the reaction mass 74. Each strut arrangement (FIG. 4) includes a cylinder 92 having its upper end connected to a hydro-pneumatic accumulator 94 such as, for example, Greer Hydraulics Inc., Model No. AIO8-200. The accumulator is pressurized with a suitable gas such as nitrogen to a pressure of 1,500 psi. A rod type piston 96 having a bearing end 98 in engagement with a stop plate 100 (FIG. 3) attached to the lower cross-member 60 is mounted in the cylinder 92 (FIG. 4). The volume of the cylinder 92 above the rod type piston 96 and the oil volume of the accumulator is filled with oil and connected by a passage (not shown) to a high pressure passage 71. A substantially constant force occurs to aid in centering the reaction mass about the vibrator piston 70 (FIG. 4). Nevertheless, to guard against the eventuality that the reaction mass member 74 may become uncentered and strike either of the upper or lower cross-members, bumper studs 102 (FIG. 4) of a pair of shock absorbers 104 extend outwardly from each of the upper and lower faces of the reaction mass 74 to engage the upper and lower cross-members 54 and 60 (FIG. 3) to cushion and dissipate any striking force of the reaction mass 74.
To prevent the reaction mass 74 from rotating around the piston member 70, two anti-rotation plates 105 are attached to two of the transducer frame members 44 which upon rotation of the reaction mass 74 engage the edges of the reaction mass 74. The transducer frame members 44 and anti-rotation plates 105 thus act as rotation stop members for the reaction mass 74.
A novel synchronized hydraulic lift system 26 (FIGS. 1, 2 and 5) interconnects the transducer to the vehicle frame members 16. This system is comprised of two identical lift units 107 and 109 (FIG. 2) disposed on opposite sides of the transducer; each lift unit is mounted in a bushing box assembly 110 (FIG. 5) attached to frame members 16. As the lift units and attachment journals are similar only one of each need be described. The bushing box 110 (FIGS. 5 and 6) comprises a first pair of oppositely disposed plates 112 which are parallel to the frame members 16 and a second pair of oppositely disposed plates 114 which are normal to the frame members 16. Plates 114 extend beyond plates 112 to form ear portions 114a and 1l4b. Ears 114a are bolted to angle irons 116 which are rigidly secured by bolts or welds to one of the vehicle frame members 16. Bars 11411 and angle irons 118 attached to plate 120 support gussets 121 extending upwardly of the casing 150 (FIG. 5) in support thereof. Angle irons 116 have a channel bar 119 (FIG. 6) attached between them to support a pair of idler sprockets 122 and 124 (FIG. 5) in a vertically spaced and aligned relation one to the other for a lift synchronization chain and sprocket arrangement hereinafter described. Portions of the channel 119 and angle irons 116 are cut away to provide openings therein for feed- 6 ing a chain (FIG. 7) to the idler sprockets 122 and 124 (FIG. 5).
The hydraulic lift unit includes a hydraulic lift cylin der 126 slidably mounted within a bushing 106 which is a part of bushing box 110. The lift cylinder 126 has its lower end connected adjacent a side of pad 40 by a vibration isolation means 128 (FIGS. 1 and 3). The vibration isolation means permit a static hold down load to be applied to the base plate 40 while permitting free vertical reciprocation of the base plate relative to the truck to isolate the truck from the vibrating structure and also for transmitting a tension force from the vertical lift columns 126 to the base plate 40 so that the transducer or vibrator assembly 24 can be lifted for transport. Each isolation means 128 (FIG. 1) comprises two lower mounts 132 for supporting a pair of air springs 136 and an upper shoe 140. The upper shoe 140 has its lower face engaging the upper ends of the air springs 136 and its upper surface connected to the hydraulic lift cylinder 126. To prevent lateral displace ment of the hydraulic lift cylinder 126 relative to the base plate 40 through lateral movement of the air springs 136, three tie rods 142, 144 and 145 (FIGS. 1 and 3) are positioned at ends of the vibrator isolation means 128. Each tie rod 142, 144 and 145 has one end pivotally connected to the base plate 40 and its other end pivotally connected to the upper shoe 140 adjacent its outer edge. To relieve stress on the air springs during lift of the vibrator pad 40, a pair of chains 146 are attached at each air spring to the sides of the upper shoe 140 and to the base plate 40.
The lift cylinder 126 (FIG. 5) is mounted in an outer casing 150 which terminates at the bushing box 110 and is fastened with the bushing box 110 to the vehicle frame member 16. The upper end of the casing 150 is closed by a flanged annular cap 154 in which is mounted the rod 156 of lift cylinder 126. The rod 156 is retained in position by a pivot shaft 160 passing through the lift unit casing 150 and cap 154 and retained therein by retaining rings 162. A piston (not shown) is attached to rod 156 in the cylinder 164 of the lift cylinder 126. Hydraulic fluid is introduced into the lift column cylinder above and below the piston to force the lift cylinder 126 selectively either downwardly to lower the pad 40, to raise the truck from the ground, or upwardly to raise the pad.
The novel lift system described above thus uses a lift cylinder which is also the load bearing column. In prior art lift systems a hydraulic lift cylinder separate from and eccentric to the lift column is used. A prior art lift system is shown in US. Pat. No. 3,306,391 issued 28 Feb. I967. The novel lift synchronizing means de scribed hereinafter may be used either with a prior art lift cylinder and column arrangement or with the novel lift cylinder arrangement described herein.
The novel mechanical synchronizing system (FIGS. 1 and 7) is for synchronizing the operation of the hydraulic lift units and therefore the raising and lowering of the opposite ends of the pad 40. It will be appreciated that if the vibrator pad 40 comes to rest upon uneven ground or if a portion of it comes to rest upon a protruding rock or log, or uneven distribution of the lowering force and hold down force on the hydraulic lifts will result. If this unequal force is not equalized, one hydraulic lift will assume a greater share of the work required to lift the truck assembly; such unequal stress could result in a seizing of the lift columns. A function of the mechanical synchronizing system is to equalize the operating forces on the hydraulic lift units.
The novel mechanical synchronizing system comprises a sprocket and chain arrangement for each lift coupled to a synchronizing shaft 166 (FIG. 7) mounted in the vehicle frame members 16. Each sprocket and chain arrangement is identical, thus only one is described. The sprocket and chain arrangement comprises: the idler sprockets 122 and 124, which as previously mentioned are mounted in the lift column assembly chassis attachment box means 110 (FIG. a sprocket 168 (FIG. 7) mounted on an end of the synchronizing shaft 166; a first adjustable chain support clamp 170 (FIG. 5) rigidly secured to the lift cylinder 126 adjacent its upper end and in line with the idler sprockets 122 and 124; a second adjustable chain support clamp 172 (FIG. 7) attached to the upper shoe 140 at the lower end of the lift cylinder; and a chain 174. The synchronizing shaft 166, being journaled in the frame members 16 behind the lift mechanism and on the centerline between the idler sprockets 122 and 124, the sprocket 168 is positioned rearwardly of the idler sprockets and intermediately to them. Chain 174 has one end attached to the first or upper chain support clamp 170 (FIG. 5) and runs along the lift column casing 150, around idler sprocket 122 (FIG. 7), along the vehicle frame member 16, around sprocket 168 back along the vehicle frame member 16, around idler sprocket 124 and along the lift column to the lower chain support clamp 172.
It will be appreciated that, with each hydraulic lift equipped with the above described chain and sprocket arrangement, the lift carrying weight in excess of the weight carried by the other lift will transfer through sprocket 168 an equalization force or moment to the synchronization shaft 166 and through the chain and sprocket of the other lift to the other lift column to synchronize lift column movement and to equalize the loads between the lifts.
The mechanical synchronizing system includes a novel lift control mechanism on one side of the vehicle only which includes one or more cams adapted to coact with one or more switches to control the operation of the hydraulic lifts. The control mechanism as shown (FIG. 7) includes three cams 176, 178, and 180 and three limit switches 182, 184 and 186. The cams 176-180 are positioned on that portion of chain 174 extending between sprocket 168 and sprockets 122 and 124 and have arms extending outwardly away from the chain in a spaced relation one to another to engage the three limit switches 182-186. The switches are mounted in a vertical line upon a channel 188 attached to one of frame members 16 adjacent the side of sprocket 168 nearest to idler sprockets 122 and 124. Each switch 182-186 includes a rocker arm outwardly spaced one to another to align rollers mounted on the ends of the arms with corresponding cams 176-180 for engagement selectively with the cams. The cams 176-180 are positioned typically on the chain 174 as follows: with the lift assembly in the full up position cam 176 is positioned adjacent sprocket 122, cam 178 is positioned adjacent sprocket 168 and cam 180 is positioned immediately before cam 178. Cam 176 and switch 182 are referred to as a pad half lift cam and switch. Cam 176 is so positioned with respect to switch 182 that movement of the cam 176 with a prescribed amount of lift travel (about inches) from the full up position will trip switch 182 to lift the pad 40 a desired distance off the ground. With cam 176 in this position,
minimum pad lift is obtained; to increase pad ground clearance the cam 176 is moved toward the sprocket 168. The cam 178 and switch 184 are referred to as a sweep interlock cam and switch. Additional lift travel (about 5 inches) from the full up position brings cam 178 in contact with switch 184 to activate the switch and enable an electronic controller for the transducer after the pad hits the ground and the truck is partially lifted (about 2 inches). This switch alleviates the possihility of activating the vibrator while the pad is in the air. By moving cam 178 toward sprocket 168, the interlock switch will be tripped later, that is, at a lower pad position; by moving the cam 178 away from sprocket 168 the interlock switch will be tripped earlier, that is, at a higher pad position. Cam 180 and switch 186 are referred to as a truck half lift cam and switch. Farther lift travel (about 2 inches) will cause cam 180 to trip switch 186 and stop the truck a farther distance (about 4 inches) off the ground. For more truck lift, cam 180 is moved away from sprocket 168 and conversely, for less truck lift cam 180 is moved toward the sprocket 168. The chain and sprocket arrangement can be constructed so that for a chain pitch of one inch, the movement of cam 180 one chain link on the chain will result in a 1 inch change in pad lift. For adjustments of less than one inch, all three cams may be moved by adjusting the adjustable chain clamps 170 and 172 on the top of the lift column and on the foot piece.
For transporting the seismic transducer without assistance of the hydraulic lift system, a pair of support frames 190 and 192 (FIGS. 1 and 2) are provided to support the transducer 24 in the raised position. The support frames 190 and 192 are similar in construction and comprise tubular members welded into a trapezoidally or square shaped frame of which one side 194 forms a tubular axis member which is pivotally connected to the vehicle frame 16 by a pair ofjournals 196 and 198. Dogs 200 are attached to the transducer frame 42 so as to engage the upper member of frame 190 and support the transducer assembly 24 at the proper height. The journals 196 and 198 are positioned on the frame of the truck so that the pivotal support frame may be retracted from the transducer and remain back against the lift column assembly so as not to impair operation of the vibrator.
The hydraulic lifts and transducer cylinder 72 (FIG. 4) are provided hydraulic fluid by a hydraulic system shown schematically in FIGS. 8A and B. The operation of the hydraulic system will first be described. Then the basis for and operation of the novel part of the hydraulic system which is one object of this invention will be described.
The hydraulic system (FIGS. 8A and B) comprises a hydraulic fluid container 36, hereinafter referred to as tank 36, equipped with a fillerbreather 201, a tank drain 202, and a suction filter 204. An oil line 206 couples the tank through a tank shut off valve 208 to a prime pump 210. The prime pump 210 may be an electrical pump operated from the battery of the vehicle. The prime pump 210 pumps oil into a low pressure With the pressure in the low pressure line at 150 psi, the main pump driver or engine 28 (FIG. I) is started and the prime pump 210 (FIG. 8A) is shut off automatically by a prime pump shut off pressure switch 216. The engine 28 drives charge pump 218 to maintain the pressure in the low pressure system at about I50 psi. Charge pump 218 is provided with a relief valve 220 which is set at approximately I80 psi as an additional protection means. The oil pumped by charge pump 218 makes up any internal leakage in the system and the remainder is dumped by relief valve 214 through the case of pump 30 back to tank 36 thus affording cooling for pump 30. The speed of engine 28 is then increased and the pump displacement control 222 of the main pump 30 is moved to the open position thereby permitting the main pump 30 to pump oil from the low pressure system into a high pressure system. The pump displacement control 222 is provided with a pressure override control which is set for 3,000 psi pump pressure to maintain pressure within the high pressure system at 3,000 psi. If the pressure within the low pressure system ever falls below I psi, a pressure switch 224 which is set at I00 psi is activated to shut down the main pump engine 28. The pressure of the high pressure system is measured at the main pump output by gage 226 (FIG. 88) mounted in the panel of vehicle cab 18.
The low pressure side of the main pump 30 (FIG. 8A) is coupled to the outlet of the low pressure system. The low pressure system has as its inlet the low pressure port of the servovalve 78 (FIG. 8B). The servovalve 78 is attached to the vibrator cylinder 72. The low pressure port of servo valve 78 is coupled through a vibrator cylinder shut off valve 228 to the low pressure side 230 of manifold 232. The low pressure side of the manifold 232 has a prime pump check valve 234 coupled to prime pump 210, to allow prime pump 210 (FIG. 8A) to charge the low pressure system but to keep low pressure system oil from feeding back to charge pump 210 when it is shut off. The low pressure outlet of manifold 232 (FIG. 8B) is coupled to two low pressure accumulators 236 and 238 (FIG. 8A) adjacent to the manifold for removing surges in fluid flow out of the manifold and to a third surge preventing accumulator 240 located adjacent to the oil cooler 38 for removing any reverse fluid flow surges in the low pressure system resulting from the introduction of the fluid into the oil cooler 38. The accumulator 240 is coupled to the junction of an oil cooler inlet 24] and a cooler bypass valve 242. An oil cooler outlet 244 is coupled to the junction of the cooler bypass valve 242 and to another surge preventing accumulator 246 to further dampen any surges occurring in the low pressure system. The accumulators 236, 238, 240 and 246 may be, for example, Greer Hydraulic Inc. Hydro-Pneumatic Accumulator, Model No. 30A5TB, charged to a gas pressure of 90 psi when system has zero pressure. The outlet of the accumulator 246 is coupled to a filter 248 to remove any contaminate particles larger than 3 microns in size. The outlet of the low pressure filter 248 is coupled to the low pressure side of the main pump 30. The low pressure side of the main pump 30 is connected to an oil temperature gauge 250 (FIG. 88) located on the panel of the vehicle cab 18. The oil cooler 38 (FIG. 8A) is provided with an air bleed pipe 252 which is coupled to the tank 36 (FIG. 88) to aid in removing air from the hydraulic system. The oil cooler 38 (FIG. SA) has a second outlet 254 coupled also to the relief valve 214.
10 The relief valve 214 being set at psi opens at that pressure to permit oil to flow from cooler outlet 254 through the case of main pump 30 into the tank 36.
The high pressure side of main pump 30 is coupled to the input of the high pressure system. The high pressure system comprises the main pump outlet which is coupled to a filter 256 to remove any particles of approximately 3 microns or above in size. The filter output is coupled to a high pressure check valve 258 (FIG. 8B) located at the high pressure side 260 of manifold 232. The high pressure check valve is to remove any surges in the high pressure system for reflecting back to the pump. The high pressure side 260 of manifold 232 is coupled to a high pressure accumulator system 262 (FIG. 8A) and to the high pressure port of servo valve 78 (FIG. 8B) which controls injection of the high pressure fluid into the vibrator cylinder 72 of transducer 24 (FIG. 3). The piston in the vibrator cylinder 72 divides the high pressure system from the low pressure system at one end of the hydraulic system and the main pump 30 (FIG. 8A) acts to divide the high pressure and low pressure systems at the other end of the hydraulic system. The high pressure accumulator system 262 comprises a pair of accumulators 264 and 266. The high pressure accumulators 264 and 266 may be Greer Hydraulics Inc. Hydro-Pneumatic Accumulators, Model No. 3OA-5TB. These hydro-pneumatic accumulators have a nominal fluid volume 265 of 5 gallons and a gas volume 263 of 1,095 cubic inches and are constructed as shown in FIG. 9. The hydro-pneumatic accumulators are modified to increase their volume of gas by connecting their gas bladder ports to a plurality of gas bottles 268 (FIG. 8A). Each gas bottle has a volume of approximately 1,800 cubic inches. The gas volume of gas bottles 268 and the gas bladders of the high pressure accumulators 262 and 264 are filled with a suitable gas such as, for example, nitrogen at a pressure of 2,800 psi prior to actuation of the high pressure pump. With the pump producing a pressure above that of the accumulators, e.g., 3,000 psi, the pump forces oil into the oil chambers of the accumulators 264 and 266 to compress the nitrogen in the bladders and bottles to an equalizing pressure of 3,000 psi. The novel usage of the high pressure accumulators and nitrogen supply, to be described in more detail hereinafter, is one way in which the improved transducer of this invention is distinguished from prior art transducers. The oil pressure in the high pressure side 260 of the manifold 232 is measured by a high pressure accumulator oil pressure gauge 270 (FIG. 88) mounted in the panel of vehicle cab 18. A bypass valve 272 is coupled to the high pressure side 260 of manifold 232 to allow bypassing oil from high pressure to low pressure systems with out passing through vibrator cylinder 72. Bypass valve 272 is closed when the vibrator is in operation. To protect the high pressure system against damaging high pressure, a relief valve 273 is set at 3,600 psi. The outlet of relief valve 273 is coupled to the low pressure side of manifold 232. To protect the low pressure system from damaging pressure a relief valve 274 is coupled to the low pressure side of manifold 232. The relief valve is set to open at 240 psi and the outlet of the valve is connected to the tank 36 so that oil escaping through the relief valve is collected in the tank.
The hydraulic system for the hydraulic lifts of the transducer comprises a lift valve 276 coupled to a high pressure port of the manifold 232 and to an adjustable pressure reducing valve 278. The pressure reducing valve 278 may be adjusted to introduce oil under pressure to the lower portion of the lift cylinders to provide a desired truck lift pressure to the lift units 107 and 109 (FIG. 2). Oil from the lift units 107 and 109 is returned through the lift valve 276 (FIG. 88) to a low pressure port of manifold 232. Oil under high pressure is also coupled from the lift valve 276 through line 280 to the upper or pad lift side of the lift cylinders of lift units 107 and 109 (FIG. 2).
The operation of the transducer assembly is controlled by an electronics controller 282 (FIG. having its output coupled to a torque motor 284 of servo valve 78. Because of the high flow rate involved in the system of FIG. 8, the servo valve 78 is a three stage valve. The first stage 286 which might be a flapper valve stage is coupled to the torque motor 284 and to the second stage 288; the second stage is coupled to the third stage 290, and the third stage output is controlled by a slidable spool member for selectively introducing oil into the vibrator cylinder 72. The slidable spool member reciprocates to alternately open and close the high pressure channel leading to the upper and lower portions of the vibrator cylinder 72 while closing and opening alternately the upper and lower portions of the vibrator cylinder 72 to the low pressure return channel of the servo valve. The spool of the third stage 290 is coupled to a linear variable-differential transducer 292 whose output is fed back to the electronic controller 282. The electronic controller combines the information from the LVDT 84 mounted in the vibrator cylinder 72 and with information from an accelerometer (not shown) attached to the transducer frame 42 and produces an adjusted sweep signal for proper control of the torque motor 284. The electronic controller 282 may be, for example, a T1 controller available under Part No. 139,066-2 which includes a function generator for generating sweep signals within the transducer assembly 10, or it may be an Electro-Technical Laboratorys Model No. SHV200 Controller. The Electro- Technical Laboratorys Model No. SHV200 includes a receiver for receiving sweep signals generated remotely to the transducer assembly 10.
In operation the transducer truck 10 is moved to a marked source location in an area of seismic operation and the hydraulic system is activated as follows. The electric prime pump 2l0 is activated to pressurize the low pressure side of the hydraulic system to about 150 psi. At this point the main pump engine 28 is started and the prime pump shut off. The main pump 30 pumps oil from the low pressure side into the high pressure side to pressurize the high pressure side to about 3,000 psi pressure. When the high pressure has reached 3,000 psi, oil has been stored on the oil side of the accumulators 264 and 266 until the pressure on the gas side is raised from its inactive pressure (2,800 psi) to its force equalizing pressure of about 3,000 psi; at this point the pressure in the manifold will also be 3,000 psi.
The hydraulic system having been brought up to pressure is ready to operate the transducer assembly. The hydraulic lift units 107 and 109 are activated by opening the lift valve to permit oil to flow from the high pressure side of manifold 232 through line 280 into the hydraulic lift units 107 and 109 to raise the transducer assembly 24 off the frame support 190. The frame support I90 is then pivoted away from the transducer assembly 24 to clear it for operation. The lift valve 276 is then reversed to permit oil to flow from the high pressure side of manifold 232 through reducing valve 278 to lift units 107 and 109 to lower the base plate from its raised position into contact with the ground and to raise the truck off the ground until the truck half lift cam trips the truck half lift switch 186 to stop the hydraulic lift system. When the lift synchronizing chain 174 has reached this position, the sweep interlock cam 178 has tripped the sweep interlock switch 184 to enable the vibrator controller to operate.
With the pad 40 firmly held down by the truck, the electronic controller 282 feeds sweep information to the servo valve torque motor to manipulate the servo valve to selectively introduce oil into the cylinder 72. The control electronics 282 utilizes the three feedback loops of sensors 292, 84 and 293 (FIG. 10) to cause the transducer to operate in accordance with the desired sweep signal.
Having described the operation of the hydraulic system in general it is appropriate to further describe the novel high pressure accumulator system and distinguish it from prior art.
FIG. 11 shows a much simplified model of the vibeator transducer. F cos (2 1r ft) is the alternating force imposed by the hydraulic cylinder between the reaction mass M and the ground pad; f is frequency, Hz, and t is the time/sec. The soil impedance Z, is a complex function of earth properties and frequency; however, it is usually assumed for design purposes that the soil impedance plus the mass of the ground pad is large and thus that the ground pad has no displacement (X, 0). This is not strictly true, of course, but it has been found that the zero pad displacement model is adequate for specifying hydraulic system parameters.
From FlG. H with X, 0 it is seen that the displacement and velocity of M are, respectively F cos (21rft) The force amplitude exerted by the hydraulic piston is F pA when p hydraulic pressure, psi, and A hydraulic piston area, in. The flow supplied to the hydraulic piston must be o pA' sin (21ft) Q AX. Zn/Ml in sec.
The peak flow is pacity.