Flow amplifier in hydraulic steering system of a transport vehicle

A flow amplifier in the hydraulic steering system of a transport vehicle comprises a three-position hydraulically operated hydraulic directional control valve having a single sliding spool valve and internal hydraulic pilot lines connected, when in the crossover position, to external portholes made in a sleeve of the three-position hydraulically operated hydraulic directional control valve provided with plungers spring-loaded on their outside end faces. The flow amplifier incorporates also a pair of intensifying chokes, a air of pilot chokes, and a pair of regulating chokes made in the sliding spool valve with a possibility of varying their restriction areas along the direction of travel of the sliding spool valve.

FIELD OF THE INVENTION 
The invention relates generally to transport-vehicle manufacturing 
industry, more specifically, to hydraulic steering systems of wheeled 
vehicles, and has particular reference to flow amplifiers (or 
intensifiers) used in hydraulic steering systems of transport vehicles. 
Flow amplifiers are applied in hydraulic steering systems of heavy-duty 
vehicles in a set with a hydraulically operated steering wheel unit, a 
steering unit of the metering-out type that effects proportioned feed of 
the hydraulic fluid to a consumer, in a given particular case, to a flow 
intensifier, in a direct ratio with the degree of the steering gear shaft 
angular displacement. Such systems make it possible to utilize high power 
capacities of the steering system despite small size and mass 
characteristics of a hydraulically operated steering wheel unit and also 
to provide for a proportional travel of the rod of a hydraulic actuating 
cylinder with respect to the amount of angular displacement of the 
steering gear shaft. 
BACKGROUND OF THE INVENTION 
One prior-art flow amplifier (cf. U.S. Pat. No. 4,356,759, Cl. B62D 5/08, 
1982) is known to comprise a three-position hydraulically operated 
spool-type directional control device and a flow intensification system 
incorporating three variable flow restrictors or chokes. The directional 
control device is in fact a hydraulic directional control valve involving 
two sliding spool valves of which one is a reversing and the other, a 
regulating one. The reversing spool valve is a three-position one and 
effects alteration of the direction of flows in the hydraulic lines of the 
actuating hydraulic cylinder and in the internal hydraulic pilot lines of 
the directional control valve. The regulation spool valve provides for 
precise operation of the flow amplifier. 
Flow intensification is attained due to an outside power source using the 
principle of a throttle or restrictive control, that is, maintaining the 
same differential pressure on both of the flow restrictors, of which the 
one having a smaller restriction area (the pilot restrictor) is supplied 
along the hydraulic pilot lines of the hydraulically operated steering 
wheel, while the other one having a larger restriction area (the 
intensifying restrictor), is supplied from an outside power source. The 
same differential pressure on both of the flow restrictors is maintained 
by changing the restriction area of a third (regulating) flow restrictor 
interposed between the external power source and the intensifying flow 
restrictor. The regulating flow restrictor is essentially a metering or 
throttling land of the regulating spool valve provided in the hydraulic 
pressure line of the outside power source before the inlet of the 
intensifying flow restrictor. Each of the end chambers of the regulating 
spool valve confined within its ends and the sleeve walls, communicates 
with the input of the respective pilot or intensifying flow restrictor. 
Then a total (amplified) flow from the pilot and intensifying restrictors 
is admitted to the reversing spool valve and further on to the actuating 
hydraulic cylinder of the system, whereupon the hydraulic fluid is 
expelled, from the opposite chamber of said cylinder, into the return line 
to be drained back into the tank. 
However, the aforediscussed known flow amplifier suffers from too low 
operating precision on low-rate flows and high power losses on high-rate 
flows, a disadvantage accounted for by the fact that no automatic control 
of the restriction areas of the pilot and intensifying flow restrictors is 
provided in response to a change in the rate (or intensity) of flow; in 
addition, the flow amplifier in question suffers from inadequate operating 
reliability, too high specific metal content, as well as technological and 
constructional complicacy due to the provision of a two-spool valve 
directional control device. 
Known in the present state of the art is also a flow amplifier in the 
hydraulic steering system of a transport vehicle (cf. a prospectus of 
Danfoss Co., Denmark, No. 6/82-02, 1982), featuring the same 
constructional arrangement as described hereinabove, i.e., it comprises a 
three-position hydraulically operated spool-type directional control 
device incorporating two sliding spool valves, a regulating and a valving 
(directional-control), and internal hydraulic pilot lines. The housing of 
the flow amplifier has a number of external portholes adapted for 
communicating the internal hydraulic pilot lines with the hydraulic power 
lines (i.e., pressure, return (exhaust), and cylinder supply lines) of the 
hydraulic steering system, and with its two external hydraulic pilot 
lines. The flow amplification circuit incorporates three variable flow 
restrictors or chokes, viz., a regulating, an intensifying, and a pilot 
one, which are provided in the regulating spool valve of the 
three-position hydraulically operated spool-type directional control 
device with a possibility of varying their restriction areas along the 
direction of the sliding spool valve travel. 
The aforegiven constructional arrangement of the flow amplifier provides 
for an automatic control of the restriction areas in the pilot and 
intensifying flow restrictors in response to a change in the flow 
intensity. This is attained due to the fact that the flow restrictors are 
in fact the throttling lands of the regulating spool valve whose position 
and hence the opening of the pilot and intensifying flow restrictors, 
depends on the intensify of the hydraulic fluid flow. This makes it 
possible to maintain adequate operating precision of the flow amplifier on 
low-intensity flows and to minimize power losses when operating on 
high-intensity flows. However, inherent in the aforediscussed 
constructional arrangement of the flow amplifier are such disadvantages as 
too low operating reliability, high specific metal content, as well as 
technological and constructional complicacy due to the provision of a 
two-spool valve three-position hydraulically operated spool-type 
directional control device. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide higher 
operating-reliability, to reduce specific metal content and to render the 
flow amplifier in the hydraulic steering system of a transport vehicle 
less complicated both technologically and constructionally. 
Said object is accomplished due to the fact that in a flow amplifier of the 
hydraulic steering system of a transport vehicle, comprising a 
three-position hydraulically operated spool-type directional control 
device having internal hydraulic pilot lines, which are connected, when in 
the crossover (neutral) position, to external port-holes made in the 
sleeve of said device to communicate it with external hydraulic pilot 
lines of the steering system, an intensifying choke, a regulating choke, 
and a pilot choke which are provided in the sliding spool valve of said 
three-position hydraulically operated spool-type directional control 
device with a possibility of varying their restriction areas along the 
direction of the sliding spool travel, according to the invention, said 
three-position hydraulically operated spool-type directional control 
device is in fact a three-position hydraulically operated single-spool 
hydraulic directional control valve provided with two plungers 
spring-loaded on their outside end faces, two internal hydraulic pilot 
lines of said plungers, each of said lines communicating with the 
respective external porthole, and additionally provided a pilot choke, an 
intensifying choke and a regulating choke, which are made in the sliding 
spool valve with a possibility of varying their restriction areas along 
the direction of the sliding spool valve travel, each of the plungers 
being axially traversable for its inside end face to interact with the 
respective end face of the sliding spool valve when the three-position 
hydraulically operated single-spool hydraulic directional control valve is 
in the crossover position, while one of the internal hydraulic pilot lines 
is communicable with the input of the intensifying flow restrictor when 
the three-position hydraulically operated single-spool hydraulic 
directional control valve is in the operating position. 
It is expedient that the flow amplifier, according to the invention, be 
provided with four correction or compensation flow restrictors or chokes, 
of which two should be located upstream of the inputs of the pilot chokes, 
and two other, upstream of the inputs of the intensifying chokes. 
In the flow amplifier under consideration, the directional control device 
is in fact a three-position hydraulically operated single-spool hydraulic 
directional control valve provided with three pairs of variable flow 
restrictors or chokes (i.e., pilot, intensifying and regulating chokes, a 
pair of each type), which are capable of varying their restriction areas 
in the direction of the sliding spool valve travel, as well as with two 
plungers which establish two additional control chambers confined between 
said plungers and the valve sleeve. The plungers cause the sliding spool 
valve to travel from the crossover position to the operating position, and 
vice versa, depending on the direction of the hydraulic fluid flow in the 
external hydraulic pilot lines. Once the sliding spool has been shifted to 
the operating position, the plungers assume the position corresponding to 
a complete releasing of the sliding spool valve from their action, while 
one of the sliding spool valve control chambers is disconnected from the 
external hydraulic pilot line and gets connected to the input of the 
intensifying choke. Thus, the sliding spool valve starts performing the 
regulating functions. Inasmuch as the plungers do not affect the 
regulation process under such operating conditions, they can be installed 
in the sleeve with rather great diametral clearances packed with rubber or 
polymer seals, which proves to be a simple procedure both from 
constructional and technological viewpoints since the springs of the 
plungers that actuate the sliding spool valve to return to the crossover 
position, can be accommodated inside the plungers within their linear 
dimensions, thus not increasing the overall dimensions of the proposed 
flow amplifier. On the other hand, dispensing with another sliding spool 
valve in the constructional arrangement of the flow amplifier enables one 
to substantially simplify its construction and production process, 
increase its operating reliability, as well as to reduce its overall 
dimensions and mass as compared with the two-sliding spool valve 
construction of the flow amplifier, with the operating precision and low 
power losses remaining unaffected.

DETAILED DESCRIPTION OF THE INVENTION 
A flow amplifier 1 is installed in a hydraulic steering system, comprising 
a hydraulically operated steering wheel 2 provided with external hydraulic 
pilot lines 3 and 4, a hydraulic pressure line 5 and a hydraulic return 
line 6, as well as an actuating hydraulic cylinder 7 provided with 
hydraulic communicating lines 8 and 9. The pressure line 5, the return 
line 6 and the hydraulic cylinder communicating lines 8 and 9 are in 
effect hydraulic power lines. The flow amplifier 1 comprises a 
three-position hydraulically operated spool-type directional control 
device 11 enclosed in a sleeve 10. The aforesaid device is in fact a 
three-position hydraulically operated single-spool hydraulic directional 
control valve provided with internal hydraulic pilot lines 12, 13 and one 
sliding spool valve 14, as well as with plungers 15 and 16 which are 
loaded with springs 17, 18 on their outside end faces 19, 20. The sliding 
spool valve can assume any of the three positions corresponding to its 
position in the sleeve 10, i.e., crossover (central) position, and two 
operating positions (which are the extreme positions in FIG.1). 
The plungers 15 and 16 define control chambers 25, 26 of the sliding spool 
valve 14, said chambers being confined between inner end faces 21, 22 of 
the plungers 15, 16, the sleeve 10, and end faces 23, 24 of the sliding 
spool valve 14 and being connected to the internal hydraulic pilot lines 
12, 13. Besides, control chambers 27, 28 of the plungers 15, 16 are 
established by outer end faces 19, 20 thereof and by the sleeve 10, said 
control chambers being connected to internal hydraulic pilot lines 29, 30 
of the plungers 15, 16. The flow amplifier 1 incorporates also a pilot 
choke 31, an intensifying choke 32 and a regulating choke 33, as well as 
additionally provided a pilot choke 34, an intensifying choke 35 and a 
regulating choke 36, all of said chokes being made in the body of the 
sliding spool valve 14 as throttling or metering lands (omitted in the 
Drawing). The sleeve 10 has a plurality of external portholes adapted for 
communication with the hydraulic power lines, viz., an external porthole 
37 for connection to the hydraulic pressure line 5, an external porthole 
38 (shown at the bottom of the Drawing) for connection to the hydraulic 
return line 6, and external portholes 39, 40 for connection to the 
hydraulic communicating lines 8, 9. Another two external portholes 41, 42 
are provided in the sleeve 10 to communicate with the external hydraulic 
pilot lines 3, 4 of the steering system. The plungers 15, 16 with their 
inner end faces look towards the end faces 23, 24 of the sliding spool 
valve 14 and are axially traversable for interacting with said end faces 
23, 24. The travel of the plungers 15, 16 towards the end faces 23, 24 of 
the sliding spool valve 14 is limited by stops 43, 44 whose position 
determines the crossover position of the sliding spool valve 14. 
The pilot chokes 31 and 34 are for control of the position assumed by the 
sliding spool valve 14 for the hydraulic fluid to pass from the external 
hydraulic pilot lines 3 and 4 to the actuating hydraulic cylinder 7. The 
intensifying chokes 32, 35 are for flow amplification in ratio with the 
flow passing through the pilot chokes 31, 34 and for the hydraulic fluid 
to pass to the actuating hydraulic cylinder 7. The regulating chokes 33 
and 36 are for establishing the same pressure at the input of the 
intensifying chokes 32, 35 and at the input of the pilot chokes 31, 34 to 
provide linearity of the flow characteristics of the flow amplifier 1. 
With the sliding spool valve 14 in the crossover position, the control 
chambers 25, 26 of the spool valve 14 communicate with the external 
portholes 41, 42 via the internal hydraulic pilot lines 12, 13 of the 
sliding spool valve 14 and internal hydraulic lines 45, 46. The control 
chambers 27, 28 of the plungers 15, 16 communicate with the external 
portholes 41, 42 through the hydraulic lines 29, 30. The pressure line 5, 
the cylinder communicating lines 8, 9 and the return line 6 are blocked by 
the regulating lands of the sliding spool valve 14. 
For the sake of explanation of intercommunications taking place in the 
working position (e.g., the left-hand one), let us transfer the left-hand 
portion "A" of the drawing to its centre along the arrow "i". Thence the 
chambers 27, 25 are connected, as before, to the external porthole 41 
along the internal hydraulic lines 29 and 12, 45 respectively, while the 
chamber 28 is connected to the external porthole 42 through the internal 
hydraulic line 30. In this case the internal hydraulic line 46 is open, 
whereby the control chamber 26 of the sliding spool valve 14 is connected 
only to the input of the intensifying choke 32 through the internal 
hydraulic lines 13, 47. 
Connected to the external porthole 41 is also the input of the pilot choke 
31 whose output is connected to the output of the intensifying choke 32 
and to the external porthole 39. The external porthole 40 is connected to 
the external porthole 38. The hydraulic pressure line 5 is connected to 
the input of the intensifying choke 32 via the external porthole 40, the 
regulating choke 33 and the hydraulic line 47. 
Upon transferring the right-hand portion "B" of the drawing to its centre 
along the arrow "j", in the right-hand working position of the flow 
amplifier, the chambers 28, 26 communicate with the external porthole 42 
through the internal hydraulic lines 30 and 13, 46 respectively, while the 
control chamber 27 of the plunger 15 communicates with the external 
porthole 41 along the internal hydraulic line 29. Since the internal 
hydraulic line 45 is open in this case, the control chamber 25 of the 
sliding spool valve 14 is connected only to the input of the intensifying 
choke 35 through the internal hydraulic lines 12, 30. Connected to the 
external porthole 42 is also the input of the pilot choke 34 whose output 
is connected to the output of the intensifying choke 35 and to the 
external porthole 40. The external porthole 39 is connected to the 
external porthole 38, while the hydraulic pressure line 5 is connected to 
the input of the intensifying choke 35 via the external porthole 40, the 
regulating choke 36 and the hydraulic line 48. 
The flow amplifier 1 is also provided with four correction or compensation 
chokes of which chokes 49 and 50 are installed before the inputs of the 
pilot chokes 31 and 34, respectively, while two other correction chokes 
51, 52 are situated before the input of the intensifying choke 32 on the 
internal hydraulic line 47, and before the input of the intensifying choke 
35 on the internal hydraulic line 48, respectively. 
The plungers 15, 16 are installed in the sleeve 10 with rather great 
diametral clearances, which are packed with seals 53, 54 made of, e.g. 
rubber. 
The flow amplifier 1 in the hydraulic steering system of a transport 
vehicle operates as follows. 
Since when in the initial position all the control chambers 25, 26, 27, 28 
are under the same pressure, the plungers 15, 16 are actuated by their 
respective springs 17, 18 to travel until meeting the respective stops 43, 
44, thus shifting, with their respective inner end faces 21, 22, the 
sliding spool valve to the crossover (central) position, wherein all the 
hydraulic power lines, i.e., the pressure line 5, the return line 6 and 
the hydraulic cylinder communicating lines 8 and 9 are blocked. Once the 
hydraulically operated steering wheel unit has been turned, the hydraulic 
pressure line 5 gets connected, in the hydraulically operated steering 
wheel 2, to one of the external hydraulic lines 3 and 4, depending on the 
direction of turn of the hydraulically operated steering wheel 2, while 
the other of said internal hydraulic lines is connected to the hydraulic 
return line 6. As a result, the pressure balance in the control chambers 
25, 26 of the sliding spool valve 14, as well as that in the control 
chambers 27, 28 of the plungers 15, 16 is disturbed. With the 
hydraulically operated steering wheel 2 turned in a direction 
corresponding to intercommunication of the hydraulic pressure line 5 with 
the hydraulic line 6 and intercommunication of the hydraulic line 4 with 
the hydraulic return line 6, there occurs initial travel of the sliding 
spool valve 14 and the plunger 16 to the right as along the arrow "i" in 
the Drawing, since the control chambers 26 and 28 are connected, through 
the internal hydraulic lines 30, 13 and 46, 4, to the hydraulic return 
line 6, while the control chambers 25 and 27 are under the operating 
pressure admitted to them along the internal hydraulic lines 29, 45 and 3, 
5. In this case the plunger 15 is retained, by the spring 17, in the same 
position as before, since no differential pressure is effective in the 
chambers 25 and 27. With further displacement of the sliding spool valve 
14 along the arrow "i" to its left-hand working position, the internal 
hydraulic line 46 is blocked, and the hydraulic fluid flow passes from the 
hydraulically operated steering wheel 2 along the hydraulic pressure line 
3 to the input of the pilot choke 31 and, on passing there-through, is 
admitted to the hydraulic cylinder communicating line 8 and to the 
actuating hydraulic cylinder 7, whence the hydraulic fluid flows along the 
hydraulic communicating line 9 to the hydraulic return line 6. At the same 
time the main flow of the hydraulic fluid is directed from the source of 
hydraulic fluid (not shown) along the hydraulic pressure line 5 and 
through the regulating choke 33, to the input of the intensifying choke 32 
and, on passing therethrough, is also admitted to the actuating hydraulic 
cylinder 7. Inasmuch as, with the sliding spool valve 14 in the position 
under consideration, the input of the intensifying choke 32 communicates, 
via the hydraulic lines 47 and 13, with the chamber 26 (with the hydraulic 
line 46 open), and the chamber 28 communicates with the hydraulic return 
line, the plunger 16 is urged to travel to the rightmost position. In this 
case, the sliding spool valve 14 remains in the balanced position due to 
the pressure effective in the chamber 25 and corresponding to the inlet 
pressure of the pilot choke 31 (hydraulic lines 12 and 45) and under the 
action of the pressure effective in the chamber 26 and corresponding to 
the inlet pressure of the intensifying choke 32 (hydraulic lines 13 and 
49). Thus, the pressure in the chamber 25 is equal to the sum of the 
externally applied load and of the pressure losses on the pilot choke 31, 
while the pressure in the chamber 26 is also equal to the sum of the 
externally applied load and of the pressure losses on the intensifying 
choke 32. 
Since the pilot choke 31 and the intensifying choke 32 have their outputs 
joined together, so the linearity of the flow characteristics of the flow 
amplifier 1 can be attained by merely maintaining a pressure at the input 
of the pilot choke 32 equal to the inlet pressure of the pilot choke 31. 
In this case, the hydraulic fluid flow admitted to pass to the actuating 
hydraulic cylinder 7 is equal to: 
##EQU1## 
where: Q.sub.1 --summary flow of hydraulic fluid admitted to the actuating 
hydraulic cylinder 7 through both of the chokes 31 and 32; 
Q.sub.2 --flow of hydraulic fluid admitted to the actuating hydraulic 
cylinder 7 through the intensifying choke 32; 
Q.sub.3 --flow of hydraulic fluid admitted to the actuating hydraulic 
cylinder 7 from the hydraulically operated steering wheel 2 through the 
pilot choke 31; 
F--restriction area of the intensifying choke 32; 
f--restriction area of the pilot choke 31; 
k--flow gain of the flow amplifier 1. 
The higher the ratio of F/f the larger the flow gain of the flow amplifier 
1. The pressure balance at the inputs of the chokes 31 and 32 is 
maintained by virtue of an automatic control of the degree of opening of 
the restriction area of the choke 33 and hence of the rate of fluid flow 
passing to the choke 32. As soon as the shaft of the hydraulically 
operated steering wheel 2 starts rotating at a higher speed, the rate of 
fluid flow along the hydraulic pressure line 3 increases and hence rises 
the inlet pressure of the pilot choke 31 and the pressure in the chamber 
25. As a result, the sliding spool valve 14 changes its position, thus 
opening all the three chokes, i.e., the pilot choke 31, the intensifying 
choke 32, and the regulating choke 33 and thereby increasing the rate of 
fluid flow admitted to pass through the regulating choke 33 to the 
intensifying choke 32 and hence increasing the pressure at the input of 
the intensifying choke 32 and in the chamber 26. Since an increase in the 
rate of fluid flow admitted to the actuating hydraulic cylinder 7 is 
followed by an automatic shifting of the sliding spool valve 14 to open 
all the chokes 31, 32, 33 waste of pressure spent for the regulating 
process is but insignificant. 
Upon reversal of the shaft of the hydraulically operated steering wheel 2 
the flow amplifier 1 operates in a similar way as described before, with 
the sole exception that engaged in operation are the other chokes, i.e., 
the intensifying choke 35, the pilot choke 34 and the regulating choke 36. 
With a view to attaining higher precision of its operation the flow 
amplifier 1 incorporates also the correction chokes 49, 50, 51 and 52 
adapted to compensate for unaccounted pressure losses occurring in the 
passageways of the flow amplifier 1. 
The proposed invention makes it possible to considerably simplify the 
construction of the flow amplifier 1 and reduce its specific metal 
content, as well as increase its operating reliability due to the 
provision of the hydraulically operated spool-type directional control 
device 11 as hydraulically operated single-spool hydraulic directional 
control valve provided with the plungers 15, 16, though these plungers do 
not increase the overall dimensions of the hydraulic directional control 
valve. Incorporation of additional chokes into the constructional 
arrangement, of the sliding spool valve 14, i.e., the intensifying choke 
35, the pilot choke 34 and the regulating choke 36 enables the flow 
amplifier to operate in both modes using the same sliding spool valve 14.