Hydrostatic drive system

Abstract

Hydrostatic drive system (1) of a mobile work machine, in particular an industrial truck, with a working hydraulic system (4) comprising at least one consumer (25; 26; 27; 28; 29) and / or a hydraulic steering device (5), which can be supplied by a pump (2) designed as a load-sensing pump with an adjustable delivery volume and which is in driving connection with an internal combustion engine (3), and with a hydraulic fan drive (6) for generating a cooling air flow for a heat exchanger device (12), wherein the fan drive (6) is supplied with pressure medium by the load-sensing pump, wherein the fan drive (6) is controlled by means of a directional control valve (WV) designed as a slide valve and a pressure compensator (DW) assigned to the directional control valve (WV), characterized in that the pressure compensator (DW) is arranged upstream of the directional control valve (WV) in a line leading to the directional control valve (WV). Conveyor branch line (35 in Fig.3), wherein the pressure compensator (DW) is acted upon by the load pressure of the fan drive (6) in the direction of a flow position (D) and by the delivery pressure of the pump (2) in the direction of a blocking position (S).

Description

[0001] The invention relates to a hydrostatic drive system of a mobile work machine, in particular an industrial truck, with a working hydraulic system comprising at least one consumer and / or a hydraulic steering device, which can be supplied by a pump designed as a load-sensing pump with an adjustable delivery volume and which is in driving connection with an internal combustion engine, and with a hydraulic fan drive for generating a cooling air flow for a heat exchanger device, wherein the fan drive is supplied with pressure medium by the load-sensing pump, wherein the fan drive is controlled by means of a directional control valve designed as a slide valve and a pressure compensator assigned to the directional control valve.

[0002] In such combustion-engine-powered mobile work machines, a load-sensing pump with adjustable flow rate and thus displacement is generally provided to supply the working hydraulics and hydraulic steering hydraulics. This pump is driven by the combustion engine. To supply the hydraulic fan drive, which generates a cooling air flow for a heat exchanger, for example, an oil cooler for cooling the pressure medium of the hydrostatic drive system, it is already known from DE 10 2008 054 084 A1 to supply the fan drive with pressure medium from the load-sensing pump. In DE 10 2008 054 084 A1, a pressure reducing valve with an electrically adjustable set pressure is provided as the control valve for controlling the fan drive. The set pressure of this pressure reducing valve is reported to the demand flow control device of the load-sensing pump as the load pressure of the fan drive to control the pump's flow rate.To change the set pressure of the pressure reducing valve, DE 10 2008 054 084 A1 provides an electrically controlled pilot valve that generates the set pressure of the pressure reducing valve from the pump's discharge pressure. In DE 10 2008 054 084 A1, the fan drive can only be operated in one direction of rotation. Furthermore, the pressure reducing valve and the pilot valve require additional special valves, which increase the construction effort for controlling the fan drive.

[0003] DE 36 17 262 A1 discloses a generic hydrostatic drive system with the features of the preamble of patent claim 1.

[0004] DE 10 2010 005 319 A1 discloses a hydrostatic fan drive.

[0005] DE 196 46 444 A1 discloses an electro-hydraulic system for mobile work machines.

[0006] The present invention is based on the object of providing a generic drive system in which the fan drive can be controlled in both directions of rotation with little construction effort and which is improved with regard to energy consumption.

[0007] This object is achieved according to the invention in that the pressure compensator is arranged upstream of the directional control valve in a delivery branch line leading to the directional control valve, wherein the pressure compensator is acted upon by the load pressure of the fan drive in the direction of a flow position and by the delivery pressure of the pump in the direction of a blocking position. The use of a directional control valve with an associated pressure compensator enables the fan drive to be controlled with standard components in a load-sensing-controlled drive system, which are also used to control the consumers of the working hydraulics, for example a lifting drive of a load handling device, a tilt drive of a lifting mast and one or more additional consumers, for example a sideshift device or a fork adjustment device, in a work machine designed as an industrial truck.The pressure compensator ensures in a simple way that pressure medium flows to the fan drive at a constant pressure corresponding to the load pressure of the fan drive. Since the load pressure of the fan drive results from the air resistance at a fan impeller of the fan drive and thus the speed of the fan drive is a function of the pressure due to the air resistance at the fan impeller, the speed of the fan drive can be kept constant in a simple way using the pressure compensator. The fan drive can therefore be controlled by the directional control valve and the pressure compensator with standard valves, resulting in low construction costs for the valve device controlling the fan drive. In addition, the fan drive can be easily operated in both directions of rotation using a directional control valve designed as a slide valve. This allows the cooling air flow at the heat exchanger device to be reversed in a simple way and with little construction work.The reversal of the cooling air flow through the inventive use of a directional control valve designed as a slide valve makes it easy to blow dirt out of the heat exchanger, thereby enabling easy cleaning of the heat exchanger device.

[0008] According to the invention, the pressure compensator is arranged upstream of the directional control valve in a delivery branch line leading to the directional control valve, wherein the pressure compensator is acted upon by the load pressure of the fan drive toward a flow position and by the delivery pressure of the pump toward a blocking position. With such a pressure compensator on the inlet side of the directional control valve, the pressure at the fan drive can be easily kept constant in accordance with the load pressure of the fan wheel when a consumer of the working hydraulics and / or the steering device is actuated simultaneously and the consumer or the steering device has a higher load pressure.

[0009] According to a preferred embodiment of the invention, the directional control valve is designed as a directional control valve that throttles in intermediate positions, having a neutral position, in particular an open center position, a first control position for a first direction of rotation of the fan drive, and a second control position for a second direction of rotation of the fan drive. With such a three-position, four-port directional control valve, which is connected to a pump delivery line, a reservoir line, and the two consumer lines of the fan drive, the fan drive can be easily operated in both directions of rotation to reverse the cooling air flow.A directional control valve with an open center position, in which both sides of the fan drive are connected to a reservoir, further simplifies and reduces the construction effort of the valve assembly controlling the fan drive, as no additional valves, such as anti-cavitation valves, are required to protect the non-actuated fan drive against damage. By eliminating such additional valves, which are usually built into the fan drive, the fan drive has a simple design with correspondingly low construction effort.

[0010] The construction effort for controlling the fan drive can be further reduced if, according to an advantageous embodiment of the invention, the directional valve for controlling the fan drive is designed as a valve section of the control valve block comprising the directional valves of the consumers of the working hydraulics. The control valve block comprising the directional valves of the consumers generally has a modular design, since, depending on the design of the work machine, there are no or a different number of additional consumers and thus a different number of directional valves with associated pressure compensators and thus valve sections in the control valve block.By installing a valve section with the directional control valve controlling the fan drive and the associated pressure compensator in the control valve block of the working hydraulics, the valve device for controlling the fan drive can be manufactured in a particularly simple manner using standard components on the control valve block of the working hydraulics.

[0011] A shuttle valve device is expediently provided, which is connected on the inlet side to a load pressure line carrying the load pressure of the fan drive and a load pressure signaling branch line carrying the highest load pressure of the working hydraulics and / or the load pressure of the steering system, and on the outlet side to a load pressure signaling line connected to a demand flow control device of the load-sensing pump. With a shuttle valve device, the load pressure of the fan drive or the highest load pressure of the controlled consumers of the working hydraulics or the load pressure of the steering system can be easily reported via the load pressure signaling line to the demand flow control device of the pump to regulate the flow rate and thus the flow of the load-sensing pump.

[0012] According to a preferred embodiment of the invention, the load-sensing pump is set to a minimum delivery rate when the consumers of the working hydraulics and / or the steering device are not actuated in a standby mode of the drive system, for example when the working machine is stationary, and an unload valve is assigned to the delivery line of the load-sensing pump, which is connected to a container on the output side and is acted upon in the direction of a blocking position by the load pressure present in the load pressure signaling line and by a spring device and in the direction of a flow position by the delivery pressure of the pump.The load-sensing pump of the working hydraulics, for example an axial piston pump with an adjustable swash plate, pivots to a minimum flow rate during standby operation when consumers are not activated and, depending on the drive speed of the combustion engine, delivers a minimum flow rate, which is then diverted to the reservoir at the unload valve. When consumers are not activated, the pump generates a discharge pressure to open the unload valve that corresponds to the force of the spring device on the unload valve. The product of the minimum pump flow rate and the opening pressure of the unload valve represents a power loss that can be used to drive the fan device. This power loss, resulting from the opening pressure of the unload valve and the minimum flow rate of the load-sensing pump, is typically between 1.5 and 3 kW.If the maximum drive power of the fan drive is in the range up to 6 kW, approximately 50% of the drive power of the fan drive can be covered by the power loss of the unload valve. This results in energy savings in the drive system according to the invention, which leads to an increase in the efficiency of the drive system and a reduction in the fuel consumption of the combustion engine driving the load-sensing pump.

[0013] Particular advantages arise when a retarder brake valve device is assigned to the delivery line of the load-sensing pump. During braking of a travel drive of the work machine, the pump's delivery line is connected to the reservoir via the retarder brake valve device that generates brake pressure. Such retarder brake valve devices are used to prevent the combustion engine from revving to impermissibly high speeds during braking of the travel drive, where the travel drive is supported by the combustion engine. By means of the retarder brake valve device, the delivery flow delivered by the load-sensing pump during braking is throttled to a reservoir at the retarder brake valve device, which is set to a brake pressure, and converted into heat.The product of the load-sensing pump's flow rate and the retarder brake valve device's brake pressure thus represents braking power, which is converted into heat at the retarder brake valve device. According to the invention, the braking energy during braking of the drive system of the working machine with the retarder brake valve device active can be used by the consumers of the working hydraulics and thus the fan drive. As a rule, the required braking pressure at the retarder brake valve device exceeds the load pressure of the fan drive. This makes it possible to increase the efficiency of the drive system and reduce the fuel consumption of the combustion engine, since during braking of the drive machine with the retarder brake valve device active, which requires high cooling capacity, the fan drive can be driven without additional energy consumption.

[0014] Preferably, the directional control valve of the fan drive is connected on the input side to the pump delivery line and the unload valve and / or the retarder brake valve device is connected on the input side to a delivery branch line branching off from the delivery line. By branching off the unload valve or the retarder brake valve device from the delivery line of the load-sensing pump and thus the parallel connection of the directional control valve of the fan drive and the unload valve as well as the retarder brake valve device with respect to the pump delivery line, it is easily possible for the pressure supplied by the pump to be applied to the directional control valve of the fan drive in standby mode of the drive system and / or braking mode with the retarder brake valve device active with the corresponding pressure, ieThe opening pressure of the unload valve or the brake pressure of the retarder brake valve device provides a volume flow from which the fan drive can be driven in an energy-efficient manner. Furthermore, the parallel connection of the fan drive to the unload valve and / or the retarder brake valve device makes it easy for the fan drive to be driven by the load-sensing pump when the retarder brake valve device is not activated and outside of standby mode with the unload valve closed, in order to provide the appropriate cooling capacity to the heat exchanger device.

[0015] Particular advantages arise when the directional control valve controlling the fan drive can be controlled by an electronic control device. With an electronic control device, the fan drive can be operated by appropriately actuating the directional control valve depending on the required cooling capacity and / or depending on the operating conditions of the machine. If the heat exchanger device is designed as an oil cooler for cooling the pressure medium of the hydrostatic drive system, the fan drive can be easily controlled depending on the required cooling capacity, for example in conjunction with a temperature sensor that detects the temperature of the pressure medium and is connected to the electronic control device.

[0016] According to an advantageous development of the invention, the fan drive is actuated by actuating the directional control valve into a control position by means of the electronic control device during standby operation and / or braking operation of the working machine. If the electronic control device is operatively connected to the actuators, for example joysticks, the consumers of the working hydraulics and / or an accelerator or brake pedal of the travel drive, the electronic control device can easily detect standby operation and / or braking operation of the working machine in order to drive the fan drive in these operating states by appropriately actuating the directional control valve into a control position using the braking energy at the active retarder brake valve device and / or the power loss at the unload valve with little or no additional energy consumption.

[0017] Particular advantages arise if the electronic control device is connected to a sensor device which detects the load pressure of the working hydraulics and / or the load pressure of the steering device, whereby the electronic control device stops the activation of the directional control valve which controls the fan drive if a limit load pressure of the working hydraulics and / or the steering device is exceeded. If a consumer of the working hydraulics or the steering device and the fan drive are actuated at the same time, this can result in energetically unfavourable operation of the fan drive if the load pressure of the activated consumer of the working hydraulics or the steering device is higher than the load pressure of the fan drive, since the difference between the highest load pressure of the consumer of the working hydraulics or the steering device which controls the pump delivery rate and the highest load pressure of the consumer of the working hydraulics or the steering device which controls the pump delivery rate is used up.of the steering device and the lower load pressure of the fan drive is compensated for at the pressure compensator assigned to the directional control valve of the fan drive. Such energetically unfavorable operation of the fan drive, in which the load pressure of the fan drive is significantly below the load pressure of the simultaneously controlled consumers of the working hydraulics or the steering device, can be easily detected by a sensor device that detects a limit load pressure, since the load pressure of the fan wheel resulting from the air resistance of the fan wheel is usually known or can be estimated, for example 50 bar. By selecting the limit load pressure accordingly, for example in the range of 200-300 bar, energetically unfavorable operation of the fan drive can therefore be easily determined.If the electronic control unit stops activating the directional control valve controlling the fan drive, thus moving the directional control valve to the neutral position to shut down the fan drive, the volume flow to the fan drive is reduced to zero, so that no power loss occurs at the pressure compensator associated with the directional control valve of the fan drive. Energy-inefficient operation of the fan drive can thus be easily compensated for by the electronic control unit.

[0018] Further advantages and details of the invention will be explained in more detail with reference to the embodiment shown in the schematic figures. Fig. 1 a circuit diagram of a hydrostatic drive system according to the invention and Fig. 2 a section of the circuit diagram of the Fig. 1 with the directional control valves of the working hydraulics in an enlarged view, Fig. 3 a directional control valve according to the invention for controlling the fan drive and Fig. 4 a section of the Fig. 1 with a retarder brake valve device and an unload valve in an enlarged view.

[0019] In the Fig. 1 shows a circuit diagram of a hydrostatic drive system 1 of a mobile work machine designed, for example, as an industrial truck, in particular a forklift truck.

[0020] The drive system 1 comprises a pump 2 designed as a load-sensing pump, for example an axial piston machine in swash plate design with an adjustable swash plate, which is in driving connection with an internal combustion engine 3 designed, for example, as a diesel engine and is intended to supply a working hydraulic system 4, a hydraulic steering device 5 and a hydraulic fan drive 6.

[0021] The drive system 1 further comprises a transmission 7 as the travel drive of the work machine. In the illustrated embodiment, the transmission 7 is designed as a hydrostatic transmission comprising a hydrostatic travel pump 8 and at least one hydraulic motor 9a, 9b. The travel pump 8 is also in driving connection with the internal combustion engine 3. The hydrostatic transmission 7 is preferably designed as a closed circuit. In the illustrated embodiment, the travel pump 8 is designed as a pump with an adjustable displacement. The hydraulic motors 9a, 9b can have a constant displacement or—as illustrated in the exemplary embodiment—an adjustable displacement. However, an electric transmission or a mechanical transmission or a hydromechanical converter transmission can alternatively be used as the travel drive 7.

[0022] The fan drive 6 is formed by a hydraulic motor 10 with a constant displacement. The motor 10 drives a fan wheel 11, which generates a cooling air flow for a heat exchanger device 12. In the present embodiment, the heat exchanger device 12 is formed by a liquid cooler for the pressure medium of the drive system 1. The heat exchanger device 12 is arranged in a return line 14 leading to a container 13. In the illustrated embodiment, the return line 14 is connected to an outlet line 15 of the drive system 7 and a return line 16 of an unload valve 17.

[0023] It is also possible to design the heat exchanger device 12 as a cooler package or as a multi-zone cooler in order to additionally form a liquid cooler of the internal combustion engine 3 by means of the heat exchanger device 12.

[0024] The pump 2 for supplying the working hydraulics 4 and / or the steering device 5 is connected on the inlet side to a tank line 20 connected to the tank 13 and delivers into a delivery line 21.

[0025] A priority valve device 22 is arranged in the delivery line 21 of the pump 2, which ensures the preferential supply of the steering device 5 by the pump 2. A delivery branch line 23 for supplying the consumers of the working hydraulics 3 is connected to the outlet of the priority valve device 22.

[0026] When the mobile work machine is configured as a forklift, the working hydraulics 4 comprises several consumers 25-29, for example, a lifting drive 25 for raising and lowering a load-handling device, a tilt drive 26 for tilting a lifting mast, and one or more additional consumers. In the illustrated embodiment, the additional consumer is a sideshifter or fork positioner with two hydraulic cylinders 27. In addition, the illustrated embodiment provides further additional consumers 28, 29, with which attachments, such as a bale or paper clamp, can be operated.

[0027] The working hydraulics 4 comprises a directional control valve designed as a slide valve with a pressure compensator assigned to the corresponding directional control valve to control each consumer. The lifting drive 25 is - as shown in the Fig. 2 is shown in more detail - by means of a directional control valve WV1 with associated pressure compensator DW1. A directional control valve WV2 with associated pressure compensator DW2 is provided to control the tilt drive 26. The two hydraulic cylinders of the additional consumer 27 are controllable by means of directional control valves WV3 and WV4 with corresponding pressure compensators DW3 and DW4. A directional control valve WV5 with associated pressure compensator DW5 is used to actuate the additional consumer 28. Accordingly, a directional control valve WV6 with associated pressure compensator DW6 is provided to actuate the additional consumer 29. The directional control valves WV1 to WV6 are each connected to the delivery branch line 23 and thus the delivery line 21 of the pump 2 with the corresponding pressure compensator DW1-DW5 interposed and are connected to a tank branch line 37 and corresponding consumer lines.The directional control valves WV 1 to WV 6 are arranged in a control valve block 31 of the working hydraulics 4 together with the associated pressure compensators DW1 to DW6 and the priority valve device 22 as well as a pressure relief valve 30 associated with the delivery line 21. The directional control valves WV1-WV6 with the corresponding pressure compensators DW1-DW6 each form a valve section, thus enabling a modular design in which a further variant of the control valve block 31 can be formed with only one directional control valve WV5 or WV6 and corresponding pressure compensator DW5 or DW6 for one of the two additional consumers 28 or 29, or a further variant without the directional control valves WV5 and WV6 and the corresponding pressure compensators DW5 or DW6 for the additional consumers 28, 29.

[0028] For controlling the flow rate of the pump 2 designed as a load-sensing pump, a demand flow control device 35 is provided, which can be controlled by a highest load pressure of the controlled consumers of the working hydraulics 4 and / or the steering device 5, which is present in a load pressure signaling line 36.

[0029] According to the invention, a directional control valve WV designed as a slide valve with an associated pressure compensator DW is provided for controlling the fan drive 6. The directional control valve WV with an associated pressure compensator DW is arranged as an additional valve section in the control valve block 31 of the working hydraulics 4.

[0030] The directional control valve WV controlling the fan drive 6 is - as shown in the Fig. 3 is shown in more detail - as a directional control valve throttling in intermediate positions with a neutral position N, a first control position S1 for a first direction of rotation of the fan drive 6 and a second control position S2 for a second direction of rotation of the fan drive 6.

[0031] The directional control valve WV is connected by a branch line 35 to the delivery branch line 23 of the control valve block 31 and thus to the delivery line of the pump 2. By means of a branch line 36, the directional control valve WV is connected to the reservoir branch line 37 of the control valve block 31, which is connected to a reservoir line 38 leading to the reservoir 13. In addition, the directional control valve WV is connected to a first connecting line 40a, which is connected to a first connection of the motor 10 of the fan device 6, and to a second connecting line 40b, which is connected to a second connection of the motor 10 of the fan device 6.

[0032] The neutral position N of the directional control valve WV is designed as an open center position in which the connecting lines 40a, 40b are connected to the branch line 36 relieved to the reservoir 13. When the directional control valve WV is actuated in the direction of the first control position S1, the connecting line 40b is connected to the branch line 35 and the connecting line 40a is connected to the branch line 36. Accordingly, when the directional control valve WV is actuated in the direction of the second control position S2, the connecting line 40a is connected to the branch line 35 and the connecting line 40b is connected to the branch line 36.

[0033] The pressure compensator DW is arranged upstream of the directional control valve WV in the delivery branch line 35 leading to the directional control valve and has a flow position D and a blocking position S. The pressure compensator DW is subjected to the load pressure of the fan drive 6 and a spring F in the direction of the flow position D and to the delivery pressure of the pump 2 in the direction of the blocking position S. The load pressure of the fan drive 6 is detected in the control positions S1 and S2 of the directional control valve WV, with the load pressure of the fan drive 6 being reported to a load pressure line 41 which is led to a spring side of the pressure compensator DW acting in the direction of the flow position D. The delivery pressure of the pump 2 is applied to the pressure compensator DW in the direction of the blocking position S by means of a control line 42 which is connected to the branch line 35 via the pressure compensator DW.

[0034] To protect and limit the pressure applied to the fan drive 6, secondary safety valves designed as pressure relief valves 43a, 43b are provided, which in the control position S1 or S2 limit the load pressure applied in the load pressure line 41 and thus the delivery pressure applied to the fan drive 6.

[0035] The directional control valve WV of the fan drive 6 is identical to the directional control valves WV1 to WV6 in terms of circuitry and design and differs from the directional control valves WV1 to WV6, which have a closed neutral position, only by the open neutral position N. The pressure compensator DW of the fan drive 6 is identical to the pressure compensators DW2 to DW6 of the double-acting consumers 26-29 in terms of circuitry and design.

[0036] The load pressure line 41, which carries the load pressure of the fan drive 6, is connected via a line 45 to a first inlet of a shuttle valve device 46, to whose second inlet a load pressure signaling branch line 47 is connected, in which the highest load pressure of the consumers 25-29 of the working hydraulics or the load pressure of the steering device 5 is present. The output of the shuttle valve device 46 is connected to the load pressure signaling line 36 leading to the demand flow control device 35.

[0037] The Fig. The unload valve 17, shown in more detail in Figure 4, is connected on the inlet side to a delivery branch line 50 branching off from the delivery line 21 of the pump 2. The unload valve 17 is acted upon by the delivery pressure of the pump 2 in the direction of an open position connecting the delivery branch line 50 with the return line 16 leading to the reservoir. For this purpose, a corresponding control line 51 is provided, which leads from the delivery branch line 50 to a corresponding control surface of the unload valve 17. In the direction of a blocking position, the unload valve is acted upon by the highest load pressure present in the load pressure signal line 36 of the consumers of the working hydraulics 4 or the steering device 5 or the load pressure of the fan drive 6, which also controls the delivery rate of the pump 2 at the demand flow control device 35. In the direction of the blocking position, the unload valve 17 is additionally acted upon by a spring device 52.

[0038] In the Fig.4 also shows a retarder brake valve device 60, with which an additional braking effect can be generated during braking of the travel drive 7 of the work machine. The retarder brake valve device 60 is arranged in a branch line 61 connecting the delivery branch line 50, which branches off from the delivery line 21 of the pump 2, to the reservoir line 38 leading to the reservoir 13. In the present exemplary embodiment, the retarder brake valve device 60 consists of a flow regulator 62 and a pressure regulator 63, wherein the flow regulator 62 controls the volume flow delivered via the branch line 61 from the delivery line 21 of the pump 2 to the reservoir 13 during braking, and the pressure regulator 63 controls the corresponding brake pressure. When the retarder brake valve device 60 is not activated, the flow regulator 62 is in a blocking position that shuts off the branch line 61.When the retarder brake valve device 60 is activated, the flow regulator 62, which throttles in intermediate positions, is actuated toward an open position, so that the pump's delivery flow flows to the pressure regulator 63, which is set to a required brake pressure in order to convert braking energy into heat by throttling the delivered delivery flow to the reservoir. At the flow regulator 62, the brake pressure set at the pressure regulator 63 is reported to the load pressure signaling line 36 when the retarder brake valve device 60 is activated, in order to pivot the pump 2 in the direction of increasing the delivery flow and thus the delivery flow when the retarder brake valve device 60 is activated.

[0039] The directional control valve WV of the fan drive 6 and the directional control valves WV1 to WV6 of the remaining consumers 25-29 of the working hydraulics are electrically controllable. For this purpose, an electronic control device 70 is provided, which is connected on the input side to at least one actuator 71, for example a joystick, for controlling the consumers 25-29 of the working hydraulics 4. Furthermore, the control device 70 is connected to an accelerator or brake pedal 72 controlling the travel drive. During braking, the flow regulator 62 and the pressure regulator 63 of the retarder brake valve device 60 can be controlled by means of the control device 70 via electrically actuated pilot valves 64, 65 to generate an additional braking torque.

[0040] The electronic control device 70 is further connected to a sensor device 75 that detects the temperature of the pressure medium flowing into the heat exchanger device 12. Furthermore, the control device 70 is connected to a sensor device 76 designed as a pressure sensor, which detects the highest load pressure of the consumers 25-29 of the working hydraulics 4 or the load pressure of the steering device 5 present in the load pressure signaling branch line 47.

[0041] If no consumers of the working hydraulics 4 and / or the steering device 5 are actuated in the drive system 1, the drive system 1 is in standby mode, in which the pump 2 is set to a minimum delivery rate. The minimum volume flow delivered by the pump 2 in standby mode is reduced to the reservoir 13 at the unload valve 17, which is opened by the delivery pressure of the pump 2 against the setting of the spring 52. The product of the minimum delivery flow of the pump 2 in standby mode and the opening pressure of the unload valve 17 set on the spring 52 represents a power loss in standby mode.

[0042] During braking operation of the traction drive 7, the retarder brake valve device 60 is activated, causing the pump 2 to pivot to a flow rate set on the controlled flow regulator 62, and the flow rate delivered by the pump to the reservoir is throttled via the brake pressure set on the controlled pressure regulator 63. The product of the flow rate set on the flow regulator 62 and the brake pressure set on the pressure regulator 63 represents the braking energy, which is converted into heat in the active retarder brake valve device 60.

[0043] The control of the fan drive 6 according to the invention by an additional valve section with a directional control valve WV and a pressure compensator DW assigned to the directional control valve WV results in a number of advantages.

[0044] The directional control valve WV with the associated pressure compensator DW is a standard component of the drive system 1, so that the valve device for controlling the load-sensing fan drive 6 requires little additional construction effort. Furthermore, with the directional control valve WV and corresponding control positions S1, S2, the fan drive 6 can be easily operated in both directions of rotation to reverse the cooling air flow.

[0045] A further advantage of the control of the fan drive 6 according to the invention is that the fan drive 6 can be driven by the directional control valve WV integrated in the control valve block 31 of the working hydraulics 4 through the branching connection of the unload valve 17 and the branching connection of the retarder brake valve device 60 to the delivery line 21 of the pump 2 in standby mode and / or in braking mode from the loss line of the unload valve 17 or the braking energy of the retarder brake valve device 60, so that the drive of the fan drive 6 does not require any additional energy. This results in improved efficiency of the drive system with reduced fuel consumption of the internal combustion engine 3. The electronic control device 70 can determine the standby mode based on the signals from the actuator 71 or the braking mode based on the signal from the accelerator or brake pedal 72 and can determine the braking mode in standby mode orin braking operation, the directional control valve WV is actuated accordingly into a control position S1 or S2, so that the fan drive 6 can be driven in an energetically favorable manner from the power loss in stand-by operation and / or the braking energy when the retarder brake valve device 60 is actuated.

[0046] Simultaneous actuation of the fan drive 6 and a consumer 25-29 of the working hydraulics 4 or the steering device 5 can result in energetically unfavorable operation of the fan drive 6. Since the load pressure of the fan drive 6 is generally significantly below the load pressure of a consumer 25-29 of the working hydraulics 4, for example the load pressure when lifting a load on the lifting drive 25, the pressure compensator DW assigned to the actuated directional control valve WV of the fan drive 6 would, by applying pressure in the direction of the blocking position S, regulate the difference between the delivery pressure of the pump 2 determined from the highest load pressure and the load pressure of the fan drive 6 and reduce the delivery pressure of the pump 2 present at the directional control valve WV of the fan drive 6 accordingly.In order to avoid these losses at the pressure compensator DW of the fan drive 6 when another consumer is operated at the same time, the control device uses the pressure sensor 76 to detect the load pressure of the consumer of the working hydraulics 4 or the load pressure of the steering device 5 in the load pressure signaling branch line 47 and actuates the directional control valve WV of the fan drive 6 into the neutral position if the load pressure detected at the pressure sensor 76 exceeds a certain limit load pressure, which can be predefined and / or adjustable. By actuating the directional control valve WV of the fan drive 6 into the neutral position N, the volume flow flowing to the fan drive 6 is reduced to zero, so that no throttling losses occur at the pressure compensator DW and no power loss is generated. In operating states in which the simultaneous operation of the fan drive 6 and another consumer of the working hydraulics 4 orthe steering device 5 of the consumer of the working hydraulics 4 or the steering device 5 has a higher load pressure and a large difference occurs between the higher load pressure of the further consumer of the working hydraulics 4 or the load pressure of the steering device 5 and the lower load pressure of the fan drive 6, an energetically unfavorable operation of the fan drive 6 with high losses at the pressure compensator DW of the fan drive 6 can be effectively avoided by the control device 70 and corresponding control of the directional control valve WV in the neutral position N.

[0047] Overall, a control of the fan drive 6 according to the invention is thus achieved with a low construction effort for the valve device formed from a conventional directional control valve WV with associated pressure compensator DW and an operation of the fan drive 6 with low energy consumption from the power loss at the unload valve 17 in standby mode or the braking energy in braking mode with active retarder brake valve device 60 is made possible.

Claims

[1] Hydrostatic drive system (1) of a mobile work machine, in particular an industrial truck, with a working hydraulic system (4) comprising at least one consumer (25; 26; 27; 28; 29) and / or a hydraulic steering device (5), which can be supplied by a pump (2) designed as a load-sensing pump with an adjustable delivery volume and which is in driving connection with an internal combustion engine (3), and with a hydraulic fan drive (6) for generating a cooling air flow for a heat exchanger device (12), wherein the fan drive (6) is supplied with pressure medium by the load-sensing pump, wherein the fan drive (6) is controlled by means of a directional control valve (WV) designed as a slide valve and a pressure compensator (DW) assigned to the directional control valve (WV), characterized by that the pressure compensator (DW) is located upstream of the directional control valve (WV) in a delivery branch line (35 in Fig.3), wherein the pressure compensator (DW) is acted upon by the load pressure of the fan drive (6) in the direction of a flow position (D) and by the delivery pressure of the pump (2) in the direction of a blocking position (S). [2] Hydrostatic drive system according to claim 1, characterized by that the directional control valve (WV) is designed as a directional control valve (WV) throttling in intermediate positions with a neutral position (N), in particular an open middle position, a first control position (S1) for a first direction of rotation of the fan drive (6) and a second control position (S2) for a second direction of rotation of the fan drive (6). [3] Hydrostatic drive system according to claim 1 or 2, characterized by that the directional control valve (WV) for controlling the fan drive (6) is designed as a valve section of the control valve block (31) comprising the directional control valves (WV1-WV6) of the consumers (25-29) of the working hydraulics (4). [4] Hydrostatic drive system according to one of claims 1 to 3, characterized by that a shuttle valve device (46) is provided, which is connected on the input side to a load pressure line (41, 45) carrying the load pressure of the fan drive (6) and to a load pressure signaling branch line (47) carrying the highest load pressure of the working hydraulics (4) and / or the load pressure of the steering device (5) and on the output side to a demand flow control device (35 in Fig. 1 and Fig. 4) the load pressure signal line (36 in Fig. 1 and Fig. 4) is connected. [5] Hydrostatic drive system according to one of claims 1 to 4, characterized bythat the load-sensing pump (2) is set to a minimum delivery rate when the consumers (25-29) of the working hydraulics (4) and / or the steering device (5) are not actuated in a stand-by mode of the drive system (1), and an unload valve (17) is assigned to the delivery line (21) of the load-sensing pump (2), which is connected on the output side to a container (13) and is guided in the direction of a blocking position by the pressure signaling line (36 in Fig. 1 and Fig. 4) and by a spring device (52) and in the direction of a flow position by the delivery pressure of the pump (2). [6] Hydrostatic drive system according to one of claims 1 to 5, characterized bythat a retarder brake valve device (60) is assigned to the delivery line (21) of the pump (2), wherein in a braking operation of a travel drive (7) of the working machine, the delivery line (21) of the pump (2) is connected to the container (13) via the retarder brake valve device (60) generating a brake pressure. [7] Hydrostatic drive system according to claim 5 or 6, characterized by that the directional control valve (WV) of the fan drive (6) is connected on the inlet side to the delivery line (21) of the pump (2) and the unload valve (17) and / or the retarder brake valve device (60) are connected on the inlet side to a delivery branch line (50) branching off from the delivery line (21). [8] Hydrostatic drive system according to one of claims 1 to 7, characterized by that the directional control valve (WV) can be controlled by means of an electronic control device (70). [9] Hydrostatic drive system according to claim 8, characterized bythat the fan drive (6) is actuated by actuating the directional control valve (WV) into a control position (S1; S2) by means of the electronic control device (70) during standby operation and / or braking operation of the working machine. [10] Hydrostatic drive system according to claim 8 or 9, characterized by that the electronic control device (70) is connected to a sensor device (76) which detects the load pressure of the working hydraulics (4) and / or the load pressure of the steering device (5), wherein the electronic control device (70) stops the actuation of the directional control valve (WV) which controls the fan drive (6) when a limit load pressure of the working hydraulics (4) and / or the steering device (5) is exceeded.

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