Hydraulic drive system

A hydraulic drive system consists of a first partial system I and a second partial system II. Each partial system has a pump regulated by the stream required (1,9) and a hydraulic energy consumer connected to its output line (2,10). Load pressure lines (7,13) that sense the maximum load pressure are also provided in each partial system I and II; they are connected with the required flow regulators (8,14) of the pumps (1,9). A coupling device III is provided for connecting the feed lines (2,10) and the load pressure lines (7,13) of the two partial systems I and II. The coupling device III can be switched as a function of a consumer designed for driving and is connected with a circuit logic IV that supervises the driving of this consumer. The circuit logic consists of a NAND (not-and-) element (19) and an UND (and-) element (22).

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention concerns a hydraulic drive system with an initial partial 
system and a second partial system, where the partial system encompass a 
pump regulated by the stream required and hydraulic energy consumers 
connected to its output line, as well as a load pressure line carrying the 
maximum load pressure, and where a coupling device is provided for 
connecting the output line and the load pressure line of the first partial 
system with the output line and the load pressure line of the second 
partial system. 
2. Description of the Art 
Such a drive system is described in the DE-OS 31 46 508. The two partial 
systems are automatically coupled to a single-circuit system as soon as 
the useful stream of pressure medium in the one partial system is greater 
than the maximum useful stream available of the pump of this partial 
system. The coupling and separation occur exclusively as a function of the 
pressure gradient at the multiway valve assigned to the consumer actuated 
and controlling its direction and speed of movement. It makes no 
difference here which consumer is actuated. This can, however, be 
disadvantageous in some cases, e.g. if in the hydraulic drive system of an 
excavator the first partial system that handles the consumer required for 
raising and lowering the excavator column and the second partial system is 
provided for the filling and emptying movement of the excavator shovel. 
When the column is raised and shovel is emptied, the consumer assigned to 
the shovel will have only a slight load pressure, but a high rate of 
movement. On the other hand, the load pressure of the consumer assigned to 
the column is considerably higher and the rate of movement is considerably 
less. Thus, a specific consumer driven by the first partial system may 
have operating requirements which are different than the operating 
requirements of a consumer driven by the second partial system. If both 
partial systems are coupled, a high pressure level will prevail in the 
feed lines as a whole and correspondingly the total feed quantity 
determined by this high pressure level will be less at a constant 
hydraulic power output than when the pumps are operated individually. The 
proportion of transition power to the hydraulic power output, i.e., of the 
proportion of power manifested as fluid volume stream, is thus smaller 
after coupling; on the other hand, the power proportion that is manifested 
as pressure is greater. However, the oil leakage and pressure losses are 
thus also higher. 
The present invention proposes to offer a hydraulic drive system of the 
above type, with which a higher transition or turnover power is 
attainable. 
SUMMARY OF THE INVENTION 
This problem is solved according to the invention in that the coupling 
device is in working connection with a a control means including circuit 
logic that supervises the drive of the consumer. The essential concept of 
the invention accordingly consists in the use of a control means for 
limiting the coupling of the two partial systems into a single-circuit 
system to cases in which this is meaningful, namely to cases in which a 
high total feed stream is required, which depends on the type and 
operating requirements of the consumer to be actuated Thus, the travel 
drive of a hydraulically driven excavator usually has a high feed stream 
requirement. Expediently, the two partial systems will be coupled in 
driving the consumers pertaining to the travel drive. 
To determine which consumers are driven, it is proposed according to an 
advantageous further refinement of the invention for the coupling device 
to be in working connection with a circuit logic supervising the drive of 
the consumers. 
It is also favorable if the partial systems are mutually connected through 
the coupling device when the consumers are not actuated and the circuit 
logic has a not-and-element, whose first input is connected with a signal 
transmitter of at least one consumer whose power supply is provided by the 
coupled partial systems, whose second input is connected with the output 
of an and-element, to the inputs of which signal transmitters of the 
consumers of both partial systems are connected and whose hydraulic power 
supply, with simultaneous actuation, is provided through the proper 
partial system, in which case a signal transmitter of at least one 
consumer of the first partial system is connected to the one input of the 
and-element and a signal transmitter of at least one consumer of the 
second partial system is connected to the other input. 
A circuit logic constructed in this manner requires few individual 
components. The signal transmitters act on the and-element and the 
not-and-element of the circuit logic only when the consumers are driven. 
In the outflow position, i.e., when the consumers are not driven, thus if 
a signal from a signal transmitter is not present at either the 
and-element or not-and-element, there is no signal at the output of the 
circuit logic and the partial systems are then coupled to a single-circuit 
system. Of course, the circuit logic can also be realized with the 
opposite signs, such that the signals are present at the components of the 
circuit logic when the consumers are not driven and there is also a signal 
at the output of the circuit logic and the partial systems are coupled. 
To hold down the switching costs for the separation and coupling of the 
partial systems, according to an expedient refinement of the coupling 
unit, the latter consists of a multiway valve installed between the feed 
lines and the load pressure lines of the partial systems and has an open 
and a closed position, and which is spring-loaded in the opening direction 
and can be acted upon by an output signal of the circuit logic carried in 
a signal line in the closing position. 
The output signal advantageously consists of a hydraulic pressure signal 
and the circuit logic is then formed of hydraulic valves, a first multiway 
valve of which is connected to the signal line and spring-loaded in the 
outflow state it connects the signal line with the output of a second 
multiway valve installed in front of it and in the actuated state it 
connects the signal line to a drain line, in which case the second 
multiway valve, spring-loaded in the outflow state, connects the signal 
line to a drain line and in the actuated state it connects the signal line 
with a line in which a pressure is present as a function of the driving of 
at least one of the consumers pertaining to one of the partial systems. 
Because in many cases the multiway valves installed in front of the 
consumers are driven by means of a control pressure that is produced by a 
consumer actuation element, it proved advantageous to manipulate the 
valves of the circuit logic hydraulically also. In this manner, the 
consumer actuation element constitutes a signal transmitter for driving 
the circuit logic. 
According to another embodiment of the invention that achieves additional 
advantages, it is proposed that the coupling unit consist of a first 
multiway valve located between the feed lines of the partial systems and a 
second multiway valve located between the load pressure lines of the 
partial systems, where the multiway valves that have an open and a closed 
position and throttling in the intermediate positions can be acted on in 
the closing direction by a hydraulic pressure signal in parallel and where 
the working range of the second multiway valve is above the working range 
of the first multiway valve. A signal size-dependent coupling and 
separation of the two partial systems is achieved by the multiway valves 
throttling in intermediate positions; they can be controlled by the 
attendant by manipulating the consumer actuation elements. Speed changes 
in the consumers actuated can be managed in this manner with the sudden 
transition from a single-circuit to the two-circuit system and vice versa. 
Additional advantages and details of the invention are described in greater 
detail with reference to the implementation example shown schematically in 
the following figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A hydraulic drive system, which is provided in this example for a hydraulic 
excavator, consists of two partial systems I and II. The first partial 
system I has an adjusting pump 1 regulated by the stream required, to the 
feed line 2 of which several multiway valves 3, 4, 5 and 6 throttling in 
intermediate positions are connected, with the aid of which various 
hydraulic power consumers (not shown) can be actuated. The multiway valves 
3, 4, 5 and 6 are controlled hydraulically by suitable signal transmitters 
(connections x and y). The highest load pressure of all consumers of the 
first partial system I is communicated through a common load-sensing line 
7 to a required-stream regulator 8 of the adjusting pump 1 and its feed 
volumes are set according to the specifications arbitrarily established at 
the multiway valves for the rates of movement of the consumers. 
The second partial system II also has a required stream-regulated adjusting 
pump 9, to the feed line 10 of which several multiway valves 11 and 12 
throttling in intermediate positions are connected and with the aid of 
which additional hydraulic power consumers (not shown) can be actuated. 
The multiway valves 11 and 12 are controlled hydraulically by signal 
transmitters (connections x and y). The highest load pressure of the two 
consumers of partial system II is communicated through a common 
load-sensing line 13 to a required stream-regulator 14 of the adjusting 
pump 9 and the feed volumes of which are set according to the 
specifications arbitrarily established at the multiway valves 11 and 12 
for the rates of movement of the consumers. 
A coupling device III designed as a multiway valve 15 is provided for 
connecting the two partial systems I and II; it is switched into a line 16 
connecting the two feed lines 2 and 10 and, in parallel with this, into a 
line connecting the two load-sensing lines 7 and 13. The multiway valve 15 
is spring-loaded in the opening direction, in which the feed lines 2 and 
10 and the load-sensing lines 7 and 13 are connected to each other, so 
that the two partial systems I and II are mutually connected in the 
outflow state. In the closure direction, the multiway valve 15 can be 
acted upon by an output signal of a circuit logic IV carried in a signal 
line 18. 
The circuit logic IV consists of a not-and-element 19, whose output is 
connected to the signal line 18. A first input 20 of the not-and-element 
19 is connected in a manner not shown in the Figure with the signal 
transmitters of consumers, whose power supply is to take place through the 
mutually connected partial systems I and II. A second input 21 is 
connected to the output of an and-element 22, which has two inputs 23 and 
24. A signal transmitter of a consumer of the partial system I is 
connected to the input 23 (the signal transmitters of several consumers of 
the partial system I can also be connected) and a signal transmitter of a 
consumer of the partial system II is connected to the input 24 (several 
signal transmitters of several consumers of partial system II can also be 
connected here). The consumers whose signal transmitters are connected to 
the inputs of the and-element 22 are to be supplied from their own partial 
system. 
The circuit logic functions as follows: The partial systems I and II are in 
the outflow position, i.e., coupled in the case of unactuated consumers, 
where the two adjusting pumps 1 and 9 put out the smallest possible feed 
volumes. If a consumer of the partial system I, e.g., the consumer 
provided for turning the upper carriage of the excavator, is driven 
through a signal transmitter whose signal is present at the input 23 of 
the and-element 22, the supplying of the consumer driven is taken over by 
both partial systems I and II, while there is no signal at either the 
second input 24 of the and-element or at the first input 20 of the 
not-and-element 19 and thus there is no signal at the output of the 
and-element 22 (or at the second input 21 of the not-and-element 19) nor 
at the output of the not-and-element 19. 
Now if a consumer of the partial system II is switched on, e.g., a consumer 
for raising and lowering the excavator column, there is a signal at the 
second input 24 of the and-element. Because signals are thus present at 
both inputs, at the output a signal is sent to the second input 21 of the 
not-and-element 19. An output signal is thus also passed on by the 
not-and-element 19, while no signal is present at the first input 20. The 
signal thus present in the signal line 18 effects a switching of the 
multiway valve 15 in the closing direction and thus a separation of the 
two partial systems I and II. The feed streams of the adjusting pumps 1 
and 9 are thus set individually, each according to the highest load 
pressure that is present in the load-sensing lines 7 and 13. 
Now if a signal is also present at the second input 20 of the 
not-and-element 19, because a consumer of the partial system I is driven, 
e.g., the travel drive, to the supplying of which the partial system II is 
also to contribute, no signal will any longer be emitted at the output of 
the not-and-element 19. The multiway valve 15 thus again switches into the 
opening direction and connects the feed lines 2 and 10 and the 
load-sensing lines 7 and 13. 
The actualization of the circuit logic IV by means of hydraulic components 
is shown in FIG. 2. The not-and-element 19 is formed by a spring-loaded 
multiway valve 19a, which is switched into the signal line 18. The 
multiway valve 19a can be acted upon against the spring force by a 
pressure carried in a line 20a, which can be obtained, e.g., from the 
control pressure lines x and y of one of the consumers whose supplying is 
to take place through both partial systems I and II. 
When the multiway valve 19a is acted upon fully, it connects the signal 
line 18 with a drain line 25. In this position, the multiway valve 15, 
which forms the coupling unit, is thus relieved and connects the two 
partial systems I and II. 
The and-element 22 consists of a spring-loaded multiway valve 22a, which in 
the starting position connects the signal line 18 via a line 21a with a 
drain line 26. The multiway valve 22a can be acted upon by the pressure in 
a line 24a against the spring force and then connects the line 21a and the 
signal line 18 with a line 23a. So long as a pressure is present in this 
line 23a and the multiway valve 19a is not acted upon, a pressure signal 
is present in the signal line 18, which effects a separation of the two 
partial systems I and II. 
A coupling device III is shown in FIG. 3; it permits a 
signal-size-dependent coupling of the two partial systems I and II. The 
coupling device III consists of two multiway valves 15a and 15b that 
throttle in intermediate positions. The multiway valve 15a spring-loaded 
in the opening direction is switched into the line 16, which connects the 
feed lines 2 an 10 of the partial systems I and II and can be acted upon 
in the closing direction hydraulically by a pressure carried in the signal 
line 18. 
The multiway valve 15b is switched into the line 17 connecting the 
load-sensing lines 7 and 13 and can be acted upon hydraulically in the 
closing position by a pressure in the signal line 18, which is passed on 
via a branch line 18a to the multiway valve 15b. 
Two control surfaces 27 and 28 acting in the closing direction are provided 
at the multiway valve 15 b, and a control surface 29 acting in the opening 
direction. The control surface 27 is connected to the load-sensing line 7 
of partial system I with the line 17. The control surface 28 is connected 
to the load-sensing line 13 of partial system II with the line 17. The 
control surface 29, which is as large as the control surfaces 27 and 28 
together, is connected to both partial systems via intermediate switching 
of a changeover valve 30 with the line 17 and is thus acted upon with the 
highest of the load pressures of partial system I or partial system II. An 
additional spring, acting in the opening direction, handles a definite 
switching position when the drive system is placed in operation. 
The structure of the circuit logic IV is slightly modified in comparison 
with the construction in FIG. 2. The pressure in the signal line 18 is 
returned via a line 18b to the multiway valve 19b, which carries the 
not-and-element. The and-element consists of two multiway valves 22b and 
22c and a changeover valve 22d, which are switched so that the lower one 
of the pressures present at the inputs 23b and 24b is passed on to the 
line 21a (provided pressure is present at both inputs). The input 
pressures are advantageously taken from the signal transmitters producing 
the control pressure. There are thus variable input pressures so that the 
output pressure signal of the circuit logic is also variable and thus can 
be influenced with the control levers of the consumer actuation elements. 
The working ranges of the two multiway valves 15a and 15b, i.e., the ranges 
in which a switching is effected through a pressure signal in the signal 
line 18 or 18a, are designed so that the working range of the multiway 
valve 15b is above the working range of the multiway valve 15a. For 
example, the multiway valve 15a operates in the control pressure range of 
6-8 bar, i.e., the multiway valve 15a is fully open at 6 bar of control 
and is fully closed at 8 bar of control pressure. 
On the other hand, the multiway valve 15b operates in the control pressure 
range of 8-10 bar. The control pressure carried in the signal line 18 or 
18a is analogous to the lowest control pressure serving as the pressure 
medium source, which is present at the input 23b or 24b. 
The mode of operation of the coupling device is as follows: In the output 
position, the multiway valves 15a and 15b are fully open and thus the 
partial systems I and II are coupled to a single-circuit system. Now if 
there is a variable pressure signal at the input 23b, the valve 22b is 
switched to passage, but because the valve 22c is not controlled, there is 
no control pressure in the line 21a, i.e., at the input of the 
not-and-element. Now if a consumer of the partial system II is controlled, 
there is also a pressure at the input 24b. The two valves thus pass the 
lowest of these pressures on to the multiway valve 19b, which serves as 
the not-and-element and thus to the multiway valves 15a and 15b of the 
coupling unit III. In the control pressure range of 6-8 bar, the valve 15a 
is continuously switched to "separation" against the force of the spring 
as a function of the control pressure. The load-sensing lines 7 and 13 are 
first still connected to each other. The pumps thus still deliver with the 
same pressure. At the multiway valve 15b, the highest load-sensing 
pressure acts in the closing direction on the control surface 29, which is 
as large as the control surfaces 27 and 28 put together. In the opening 
direction, the load-sensing pressure of partial system I acts on the 
control surface 27 and the load-sensing pressure of partial system II on 
the control surface 28. Because the load-sensing pressures in both partial 
systems are still identical, an equilibrium prevails at the multiway valve 
15b, which thus remains open. 
If the input pressure that is passed on to the not-and-element increases 
further, i.e., above 8 bar, the equilibrium at the multiway valve 15b is 
changed and it is continuously shifted in the closing direction, by which 
the load-sensing lines 7 and 13 are separated from each other. Each 
adjusting or variable displacement pump 1 and 9 can now deliver with its 
own pressure level and its own delivery stream, depending on the load 
conditions. Different load-sensing pressures and different delivery 
streams thus set in the two separated partial systems I and II; this does 
not occur suddenly, but is controlled by influencing the control 
pressure-producing consumer actuation elements (which are usually designed 
as hand lever control devices). 
The controlled separation of the two partial systems also functions in the 
reverse direction, i.e., during coupling to a single-circuit system. If 
the excavator is to be operated parallel to the actuation of consumers 
that effect a separation of the two partial systems and a variable signal 
is thus present at the input 20b of the multiway valve 19b acting as a 
not-and-element, the latter is continuously shifted into a position as a 
function of the signal intensity in which the control pressure in the 
signal line 18 and the line 18a is reduced. Due to the fact that the 
highest load-sensing pressure of the two partial systems I and II is 
present at the multiway valve 15b acting in the opening direction, the 
latter is first shifted in the opening direction and thus the load-sensing 
lines 7 and 13 of the partial systems are connected with each other, in 
which case the load-sensing pressure of the partial system with the lower 
load is modified in a control pressure-dependent manner and a 
synchronization of the pump pressures thus occurs. The delivery amounts 
and thus the movement speeds thus do not change in a jerky manner. With a 
further dropping control pressure, the coupling of the two partial systems 
finally takes place. 
While certain presently preferred embodiments of the present invention have 
been described and illustrated, it is to be distinctly understood that the 
invention is not limited thereto but may be otherwise embodied and 
practiced within the scope of the following claims.