EP2628862B1 - Mobile work machine with energy recovery for driving the motor cooling - Google Patents

Description

The invention relates to a mobile machine according to claim 1.

From the publication " Less emissions, less costs. Hydrostatic fan drives from Rexroth "from Bosch Rexroth AG; Order No. RD 98 065; Edition 09/2010 various mobile machines, in particular tractors, combines, excavators and bulldozers are known. These mobile working machines have a number of first hydraulic consumers, in particular a traction drive motor for driving the wheels or the chains and several working drives in the form of cylinders for adjusting, for example, a cantilever arm; a dozer blade or a hoist. A first pump with an adjustable displacement volume delivers hydraulic fluid from a tank to the first consumers. Such a variable displacement pump is particularly energy-saving. The first pump is driven by an internal combustion engine, usually a diesel engine. The internal combustion engine has a liquid cooling system, in which the cooling liquid is passed through a cooler in the form of a finned heat exchanger in order to cool it by releasing heat into the ambient air. The coolant thus cooled is pumped through the internal combustion engine to cool it. The coolant heats up again and then flows back to the radiator.
The ambient air is conveyed through the cooler with the help of a fan wheel so that particularly intensive cooling takes place. The fan wheel is rotated by a hydraulic fan motor. Furthermore, a second pump with an adjustable displacement volume is provided, which can deliver hydraulic fluid from the tank to the fan motor. The second pump is also from the internal combustion engine and usually at the same speed as the first pump. By adjusting the displacement volume of the second pump, the speed of the fan motor can be continuously adjusted so that the coolant is cooled to the optimal temperature.

From the DE 43 42 006 Several different hydraulic drive systems for a vehicle are known. In a hydraulic drive system, two pumps are provided to supply different hydraulic consumers. One of these consumers drives a fan wheel. In another hydraulic drive system, a pressure accumulator is provided.

The DE 10 2011 012 905 A1 discloses a hydraulic fan drive which has a hydraulic pump whose displacement is adjustable, a hydraulic motor for driving a fan wheel and a pressure line. The pressure line is connected to a pressure inlet of the hydraulic motor and to the hydraulic pump. A hydraulic accumulator is connected to the pressure line. The displacement of the hydraulic motor is adjustable. With the hydraulic fan drive, due to the hydraulic accumulator connected to the pressure line, by feeding in pressure medium beyond the amount that is swallowed by the hydraulic motor, energy can be temporarily stored that is used in other operations on the machine, for example when braking or when lowering a load , becomes free. The pressure changes in the pressure line associated with the intermediate storage and the delivery of energy can be compensated for by a change in the absorption volume of the hydraulic motor in such a way that the torque delivered by the hydraulic motor corresponds to the desired fan speed.

The object of the invention is to make the mobile machine more energy-efficient. The operating behavior of the mobile machine should not change in a way that is perceptible to the user. The mobile work machine should also be particularly simple.
According to the independent claim, this object is achieved in that a pressure accumulator is provided for storing hydraulic fluid under pressure, the pressure accumulator being in fluid communication with the first consumers in such a way that hydraulic fluid flowing back from at least one first consumer flows into the pressure accumulator can, but not vice versa, the pressure accumulator being in fluid communication with the second consumer in such a way that hydraulic fluid can flow from the pressure accumulator to the second consumer. Pressure accumulators are known as energy accumulators. According to the invention, the accumulator is loaded with the hydraulic fluid flowing back from the first consumers. However, the first consumers are driven exclusively by the first pump and not by the hydraulic fluid stored in the pressure accumulator that the operating behavior of the mobile work machine that is perceptible to the user does not change. The stored hydraulic fluid is used exclusively to drive the second consumer and therefore to cool the internal combustion engine. If the operating behavior of the engine cooling changes somewhat as a result, this is not perceived by the user.

It should be noted that the hydraulic fluid flowing back from the first consumers typically only flows back with high volume flows for a short time. In contrast, the fan drive requires a low but sustained volume flow. The different time behavior of the volume flows mentioned can be easily adapted to one another by means of the pressure accumulator. It should also be noted that the fan drive has a very low energy recovery potential, so that it is not a disadvantage if the energy recovery is restricted to the first consumers.

Advantageous developments and improvements of the invention are specified in the dependent claims.

The second pump can be set up in such a way that it can also be operated as a motor, wherein it has an adjustable displacement volume, wherein it is in fluid communication with the pressure accumulator in such a way that hydraulic fluid can flow from the tank into the pressure accumulator and vice versa. The hydraulic fluid stored under pressure in the pressure accumulator can thus be used to drive the second pump. Since the first and second pumps and the internal combustion engine are in rotary drive connection with one another, the second pump drives the first pump and relieves the load on the internal combustion engine. In this way, in cases in which more hydraulic fluid is stored in the pressure accumulator than the second consumer, the first consumers can also be driven. It should be noted that this form of energy recovery has only an imperceptible effect on the operating behavior of the mobile machine, especially for the first consumers.

Fig. 1

einen hydraulischen Schaltplan einer erfindungsgemäßen mobilen Arbeitsmaschine.

At least a first consumer can be designed to raise and lower external loads against gravity. Such consumers have a particularly high potential for energy recovery. An example of such a first consumer is the hydraulic motor for driving the winch of a crane. The external load mentioned is the load attached to the crane hook. Another example is the various hydraulic cylinders called on the arm of a bucket excavator. The mentioned external load is the excavator bucket with its contents.
A continuously adjustable return orifice and a return pressure compensator can be connected in the fluid connection between the first consumers and the pressure accumulator, the return pressure compensator being connected to the return orifice so that it can regulate the pressure drop at the return orifice to a predefinable value. The hydraulic fluid flowing back from the first consumers usually has a different pressure than the content of the pressure accumulator, so that a pressure adjustment is necessary. The speed of movement of the consumer should only change depending on the setting of the return orifice, the storage pressure not having any influence on the speed of travel of the consumer. This is exactly what is achieved by the proposed interconnection of the return orifice and the return pressure compensator.
The fluid connection between the first consumers and the pressure accumulator can be connected to the tank such that hydraulic fluid flows from the first consumers into the tank when the pressure in the pressure accumulator is greater than the accumulator-side pressure on the return orifice. If the pressure in the pressure accumulator is too high, the hydraulic fluid flowing back from the first consumers cannot flow into the accumulator. This means that it must flow into the tank at least indirectly. Here it can be considered to let the hydraulic fluid mentioned flow directly into the tank via the second consumer or via the second motor-operated pump. However, it is also possible to drain the hydraulic fluid mentioned directly into the tank. With the second alternative, energy is lost unused, but it is much easier to achieve.
The invention is explained in more detail below with reference to the accompanying drawing. It shows:

Fig. 1

a hydraulic circuit diagram of a mobile machine according to the invention.

Fig. 1 shows a hydraulic circuit diagram of a mobile work machine 10 according to the invention. The mobile work machine 10 comprises an internal combustion engine 40, preferably a diesel engine, which has a first and a second pump 30; 32 drives at the same speed, namely the speed of the crankshaft. The first pump 30 conveys hydraulic fluid from a tank 16 to a plurality of first consumers 11; 13. The individual consumers 11; 13 flowing amount of fluid can be controlled by means of a valve assembly 20. Every first consumer 11; 13, a separate consumer assembly 21, which can be assembled as a whole, is assigned to the valve assembly 20. The valve assembly 20 comprises a pump line 22 which passes through all consumer assemblies 21, the first pump 30 being connected to the pump line 22. Furthermore, the valve assembly 20 comprises a tank line 23 which passes through all consumer assemblies 21, the tank line 23 being connected to the tank 16.

In each consumer module 21, a proportional directional control valve (not shown) is provided, which is thus connected to the pump and tank lines 22; 23 is connected that it is the movement of the associated consumer 11; 13 can control by sending the consumer 11; 13 flowing and consumer 11; 13 throttles back flowing fluid flow by means of continuously adjustable orifices. Each proportional directional control valve is preferably assigned a pressure compensator (not shown) which can regulate the pressure drop at the orifices, preferably at the orifices in the inlet, to a predeterminable value, so that the movement speeds of the first consumers 11; 13 depends solely on the setting of the associated proportional directional control valves, which is set electrically by the control device 17.

Furthermore, the load pressures of all consumers, insofar as they move, are interconnected in the valve assembly 20 such that the highest load pressure is present on the load pressure line 24. The load pressure line 24 is connected to a delivery pressure regulator 31 connected, which adjusts the continuously adjustable displacement volume of the first pump 30 such that the delivery pressure of the first pump 30 is above the maximum load pressure mentioned by a predeterminable pressure difference. A possible valve assembly is for example in the DE 10 2010 009 704 A1 shown in more detail.

The first consumers 11 are connected to the valve assembly 20; 13 connected, namely a hydraulic travel drive motor 11, with which one or more wheels 12 of the mobile work machine 10 are driven, so that it can be moved relative to the ground. Furthermore, a hydraulic cylinder 13 is provided with which an external load 14 can be raised against the direction of gravity 15. When the external load 14 is lowered, hydraulic fluid flows back from the cylinder 13 under pressure. This returning hydraulic fluid is usually throttled by the associated proportional directional control valve and returned to the tank line 23.

In the present invention, this fluid flow is fed to a continuously adjustable return orifice 60, which is connected in series with a return pressure compensator 61. The return orifice 60 is preferably integrated in the associated proportional directional control valve. The valve slide of the return pressure compensator 61 is pressed into an open position by a spring 62. On the spring side, the tank or storage-side pressure is connected to the return orifice 60, the consumer-side pressure being connected to the return orifice 60 on the spring side. The return orifice 60 thus forms a 2-way flow control valve together with the return pressure compensator 61, so that the lowering speed of the first consumer in the form of the cylinder 11 essentially depends only on the setting of the return orifice 60. The total pressure drop at the return orifice 60 and the return pressure compensator 61 corresponds to the pressure difference between the load pressure at the cylinder 11 and the pressure in the pressure accumulator 50. Consequently, the entire orifice load is not throttled by the return orifice 60, but only a part. The energy which corresponds to the remaining pressure is stored in the pressure accumulator 50 in the form of pressurized hydraulic fluid.

In the event that the load pressure mentioned is lower than the pressure in the accumulator 50, a first regeneration valve 63 is provided, which is connected in series to the return pressure balance 61 on the tank or accumulator side, the regeneration valve 63 optionally returning the hydraulic fluid to the accumulator 50 or can lead directly into the tank 16. A regeneration pressure sensor 68 is also provided, which measures a regeneration pressure on the tank or storage side on the return orifice 60. The regeneration pressure sensor 68 and the first regeneration valve 63 are connected to the control device 17, which comprises a programmable digital computer. For the sake of clarity, in Fig. 1 all connecting lines between the control device 17 and the equipment connected to it, namely the sensors 55; 44; 68 and the electrically operated valves 63; 45; 51; 53 and the adjustment mechanism of the second pump 32; not shown. A storage pressure sensor 55, which measures the storage pressure in the pressure accumulator 50, is connected to the control device 17. Depending on the regeneration pressure and the accumulator pressure, the control device 17 adjusts the first regeneration valve 63 such that the hydraulic fluid flowing back flows either directly into the tank 16 via the tank outlet 65 or to the pressure accumulator 50 via the accumulator outlet 64. It is also conceivable that the first regeneration valve 63 is actuated purely hydraulically by means of pressure compensators. This is cheaper but less flexible.

The pressure accumulator 50 is connected to the accumulator outlet 64 of the first regeneration valve 63 via a accumulator valve 51. The storage valve 51 is designed as a leak-free seat valve. In the closed position, the accumulator valve 51 works as a non-return valve, allowing only a fluid flow into the accumulator 50, but not in the opposite direction. In the open position, the storage valve 51 can be flowed through in both directions. The accumulator valve 51 is pressed by a spring into the closed position, in which only the accumulator 50 can be loaded. By electrical control on the part of the control device 17, it can be in the open position are switched in which the pressure accumulator 50 can be both loaded and unloaded.

For the sake of safety, the pressure accumulator is connected to a storage pressure-limiting valve 52 and an emergency drain valve 53, which can discharge the contents of the pressure accumulator 50 into the tank 16. The accumulator pressure limiting valve 52 in the form of a leak-free seat valve limits the accumulator pressure to a predetermined maximum value, so that the pressure accumulator 50 cannot burst. The emergency drain valve 53 is also designed as a seat valve and is pressed into the open position by a spring 54, whereby it can be switched into the closed position by means of electrical control on the part of the control device 17. If the control device 17 fails or is switched off, the otherwise existing electrical control signal is no longer present at the emergency drain valve 53, so that the pressure accumulator 50 empties automatically.

The second consumer in the form of the hydraulic fan drive motor 41 is also connected to the memory output 64 of the first regeneration valve 63. The fan drive motor 41 is preferably designed in the form of an external gear motor and accordingly has a constant displacement volume. The fan drive motor 41 drives a rotatable fan wheel 42, which directs an air flow onto a cooler 43. The cooler 43 is designed in the form of a finned heat exchanger through which a cooling liquid flows, the air flow mentioned being able to cool the cooling liquid. The cooler 43 is provided with a temperature sensor 44 which measures the temperature of the cooled cooling liquid at the outlet of the cooler 43. The cooler is connected to the internal combustion engine 40 via a ring line 46, so that the coolant can be conveyed in the circuit by a coolant pump 47. That is, warm coolant flows from the internal combustion engine 40 to the cooler 43 and is cooled there. The cooled coolant flows from the cooler 43 back to the internal combustion engine 40 and is heated there again. The waste heat of the internal combustion engine 40 is thus released into the ambient air via the cooling liquid.

The pressure side of the second pump 32 is also connected to the storage port 64 of the first regeneration valve. The first pump 32 normally draws hydraulic fluid from the tank 16 and conveys it to the fan drive motor 41 in order to drive it. The first regeneration valve 63 is in a switch position in which the storage connection 64 is blocked. The speed of the fan drive motor 41 can be adjusted by adjusting the displacement volume of the second pump 32. The fan valve 45 is fully open.

If the regeneration pressure sensor 68 indicates a higher pressure than the storage pressure sensor 55, the first regeneration valve 63 is switched by the control device 17 into the left position, so that the first consumers 11; 13 hydraulic fluid flowing back under pressure is loaded into the pressure accumulator 50. If the condition mentioned is no longer present, the first regeneration valve 63 is switched to the right switching positions.

If the accumulator pressure is sufficiently high, the displacement volume of the second pump is set to zero, the accumulator valve 51 being opened. Hydraulic fluid can thus flow from the pressure accumulator 50 to the fan drive motor 41. The speed of the fan drive motor 41 is controlled with the fan valve 45.

If the storage pressure is too high, the displacement volume of the second pump 32 is set so that it works as a motor. As a result, part of the pressure accumulator content flows into the tank 16 via the second pump 32. The drive torque generated in this way relieves the internal combustion engine 40 and thus saves diesel fuel.

If the storage pressure is too low to drive the fan drive motor 41, there are several options. The fan drive motor 41 can be driven by the second pump 32 alone. In addition, the volume flow of the second pump 32 can be so can be set large so that the pressure accumulator 50 is loaded again to the required extent. However, it can also be considered to further discharge the pressure accumulator 50 to the suction side of the second pump 32 with a second regeneration valve. The decision between the options mentioned must be made on the basis of the volume flow that is expected from the first consumers 11; 13 flows back, the best possible use of the mechanical drive energy provided by the internal combustion engine being sought.

Reference list

10th

Mobile work machine

11

Traction drive motor

12th

wheel

13

cylinder

14

external load

15

Direction of gravity

16

tank

17th

Control device

20

Valve assembly

21

Consumer assembly

22

Pump line

23

Tank line

24th

Load pressure line

30th

first pump

31

Discharge pressure regulator

32

second pump

40

Internal combustion engine

41

Fan drive motor

42

Fan wheel

43

cooler

44

Temperature sensor

45

Fan valve

46

Loop

47

Coolant pump

50

Pressure accumulator

51

Accumulator valve

52

Accumulator pressure relief valve

53

Emergency drain valve

54

Spring of the emergency drain valve

55

Accumulator pressure sensor

60

Flashback

61

Return pressure balance

62

Return pressure compensator spring

63

first regeneration valve

64

Memory output

65

Tank outlet

68

Regeneration pressure sensor

Claims (5)

1. Mobile work machine (10) having a plurality of first hydraulic consumers (11; 13) and a second hydraulic consumer (41), the first consumers (11; 13) comprising a traction drive and/or a work drive of the mobile work machine (10), it being possible for a first pump (30) with an adjustable displacement volume to convey hydraulic fluid out of a tank (16) to the first consumers (11; 13), it being possible for a second pump (32) to convey hydraulic fluid out of the tank (16) to the second consumer (41), an internal combustion engine (40) being provided which is in a rotary drive connection with the first and the second pump (30; 32), the second consumer (41) driving a rotatable fan impeller (42) for cooling the internal combustion engine (40), a pressure accumulator (50) being provided for storing pressurized hydraulic fluid, the pressure accumulator (50) being fluidically connected to the first consumers (11; 13) in such a way that hydraulic fluid which flows back from at least one first consumer (13) can flow into the pressure accumulator (50), but not vice versa, with the result that the first consumers (11; 13) are driven exclusively by way of the first pump (30) and not by way of the hydraulic fluid which is stored in the pressure accumulator (50), the pressure accumulator (50) being fluidically connected to the second consumer (41) in such a way that hydraulic fluid can flow from the pressure accumulator (50) to the second consumer (41).
2. Mobile work machine according to Claim 1, characterized in that the second pump (32) is set up in such a way that it can also be operated as a motor, the said second pump (32) having an adjustable displacement volume, the said second pump (32) being fluidically connected to the pressure accumulator (50) in such a way that hydraulic fluid can flow out of the tank (16) into the pressure accumulator (50) and vice versa.
3. Mobile work machine according to either of the preceding claims, characterized in that at least one first consumer (13) is configured to raise and to lower external loads counter to gravity.
4. Mobile work machine according to one of the preceding claims, characterized in that a steplessly adjustable return diaphragm (60) and a return pressure compensator (61) are fluidically connected between the first consumers (11; 13) and the pressure accumulator (50), the return pressure compensator (61) being connected to the return diaphragm (60) in such a way that it can adjust the pressure drop at the return diaphragm (60) to a predefinable value.
5. Mobile work machine according to Claim 4, characterized in that the fluidic connection between the first consumers (11; 13) and the pressure accumulator (50) is connected to the tank in such a way that hydraulic fluid flows from the first consumers (11; 13) into the tank when the pressure in the pressure accumulator (50) is greater than the accumulator-side pressure at the return diaphragm (60).

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