Reach truck

Abstract

The invention relates to a reach truck with a lifting mast (3) which is arranged on a vehicle body (1) of the reach truck so as to be displaceable in the longitudinal direction of the vehicle by means of a push cylinder (10) and the lifting mast (3) is provided with a load handling device (4) which can be raised and lowered in the lifting mast (3) by means of a lifting cylinder (11), wherein a lifting control valve (15) with a locking position (15a) and a lifting position (15b) is used to control the lifting cylinder (11) and a push control valve (20) with a retraction position (20a) and an extension position (20b) is used to control the push cylinder (10), wherein the lifting control valve (15) and the push control valve (20) are electrically controlled by an electronic control unit (30) which is connected on the input side to an operating unit (31) that controls the lifting control valve (15) and the push control valve (20).The lifting control valve (15) is designed as a proportional valve that throttles in intermediate positions. The electronic control unit (30) is designed, during the retraction operation of the push cylinder (10) and with additional actuation of the operating unit (31) to control the lifting operation of the load-handling device (4), to actuate the lifting control valve (15), designed as a proportional valve, in the direction of the lifting position (15b) such that the retraction operation of the push cylinder (10) is maintained.

Description

[0001] The invention relates to a reach truck with a lifting mast, wherein the lifting mast is arranged on a vehicle body of the reach truck so as to be displaceable in the longitudinal direction of the vehicle by means of a thrust drive, and the lifting mast is provided with a load-handling device which can be raised and lowered by means of a lifting drive in the lifting mast, wherein the thrust drive has a thrust cylinder and the lifting drive has at least one lifting cylinder, wherein a lifting control valve is provided for controlling the lifting cylinder, which has a locking position and a lifting position for controlling the lifting operation of the load-handling device, wherein in the lifting position a lifting line leading to the lifting cylinder is connected to a delivery line of a hydraulic pump, and wherein a thrust control valve is provided for controlling the thrust cylinder.which has a retraction position for controlling the retraction operation of the thrust cylinder and an extension position for controlling the extension operation of the thrust cylinder, wherein in the retraction position a first pressure medium line connected to a first pressure chamber of the thrust cylinder is connected to the delivery line of the hydraulic pump and a second pressure medium line connected to a second pressure chamber of the thrust cylinder is connected to a reservoir, and wherein in the extension position the first pressure medium line connected to the first pressure chamber of the thrust cylinder is connected to the reservoir and the second pressure medium line connected to the second pressure chamber of the thrust cylinder is connected to the delivery line of the hydraulic pump, wherein the lifting control valve and the thrust control valve are electrically controlled by an electronic control unit which is connected on the input side to an operating unit controlling the lifting control valve and the thrust control valve.

[0002] In reach trucks, a load-handling device is arranged in the mast and can be raised and lowered by means of a lifting drive comprising at least one lifting cylinder. The lifting mast is mounted on a sliding carriage, which is slidably mounted on the truck body of the reach truck by means of a sliding drive comprising one sliding cylinder. A lifting control valve is provided to control the lifting operation of the lifting cylinder; this valve has a locking position and a lifting position. A sliding control valve is provided to control the retraction and extension operation of the sliding cylinder; this valve has a retraction position and an extension position.

[0003] With such reach trucks, during the insertion operation of the push carriage and thus the lifting mast, and additional operation and thus activation of the lifting operation of the load handling device, undesired movement constellations of the push carriage and the load handling device can occur, especially if the lifting operation takes place without a load on the load handling device or with a small load on the load handling device.

[0004] If, while the retraction function of the sliding carriage is active with the thrust control valve in the retraction position and thus the retraction operation of the thrust cylinder is active, the operator simultaneously activates the lifting function by actuating the lifting control valve into the lifting position in order to perform an additional lifting operation of the load-handling device, depending on the hydraulic pressure of the lifting cylinder required for the lifting function at that time (i.e., the time of activation of the lifting operation of the load-handling device) in relation to the hydraulic pressure of the thrust cylinder required for retraction of the sliding carriage, the retraction movement of the sub-carriage may come to an abrupt standstill, while the lifting function and thus the lifting operation of the load-handling device also starts up abruptly at a considerable speed.This results in unintended pushing movements of the lifting mast and / or unintended lifting movements of the load-handling device, which can lead to dangerous operating conditions.

[0005] The present invention is based on the objective of providing a reach truck which is improved with regard to the occurrence of undesired movement constellations in the retraction operation of the lifting mast and additional actuation and thus activation of the lifting operation of the load handling device.

[0006] This problem is solved according to the invention by designing the lifting control valve as a proportional valve that throttles in intermediate positions, wherein the electronic control device is designed to actuate the lifting control valve designed as a proportional valve in the direction of the lifting position during the retraction operation of the push cylinder when the operating unit is additionally actuated to control the lifting operation of the load-handling device, such that the retraction operation of the push cylinder is maintained.

[0007] By designing the lifting control valve as a proportional valve, the electronic control unit enables the lifting control unit, during the retraction phase of the thrust cylinder and when the lifting operation is additionally activated (i.e., simultaneously with the lifting operation), to actuate the lifting control valve, designed as a proportional valve, into a throttling position or intermediate position in the direction of the lifting position. This ensures that the hydraulic oil flow rate delivered by the hydraulic pump is divided between the lifting cylinder and the thrust cylinder, thereby maintaining the retraction phase of the thrust cylinder and preventing the occurrence of undesired movement configurations, particularly in operating conditions where the lifting operation is performed without a load on the load-handling device or with a light load.

[0008] According to an advantageous embodiment of the invention, the electronic control unit is connected to a sensor device that detects the load pressure of the lifting cylinder in the lifting line. The undesired movement configurations of the sliding carriage and the load-handling device described above occur particularly when, during the retraction of the sliding carriage and additional activation of the lifting function of the load-handling device, the hydraulic pressure of the lifting cylinder required for the lifting function (i.e., the load pressure of the lifting cylinder) is lower than the hydraulic pressure of the sliding cylinder required for retraction of the sliding carriage (i.e., the load pressure of the sliding cylinder during retraction). A sensor device, for example a pressure sensor, can be used to easily detect the load pressure of the lifting cylinder in the lifting line for the electronic control unit.

[0009] According to an advantageous embodiment of the invention, the electronic control unit is designed to detect, when only the thrust control valve is actuated to the retracted position, the delivery pressure present in the delivery line of the hydraulic pump and / or the load pressure of the thrust cylinder present in the first pressure chamber of the thrust cylinder. The undesired movement configurations of the thrust carriage and the load-handling device described above occur particularly when, during the retraction operation of the thrust carriage and additional actuation of the lifting operation of the load-handling device, the hydraulic pressure of the lifting cylinder required for the lifting function, i.e., the load pressure of the lifting cylinder, is lower than the hydraulic pressure of the thrust cylinder required for retracting the thrust carriage, i.e., the load pressure of the thrust cylinder during retraction operation.Using a sensor device, such as a pressure sensor, the load pressure of the push cylinder in the first pressure chamber during retraction can be easily detected by the electronic control unit. Alternatively, instead of the load pressure of the push cylinder in the first pressure chamber during retraction, the delivery pressure in the hydraulic pump's delivery line can be detected or calculated when only the push control valve is actuated to the retracted position. This delivery pressure corresponds, with only minor pressure losses, to the load pressure of the push cylinder in the first pressure chamber during retraction.

[0010] The delivery pressure present in the delivery line of the hydraulic pump can be detected by means of a suitable sensor device, for example a pressure sensor.

[0011] According to an advantageous embodiment of the invention, the hydraulic pump is driven by an electric motor, and the electronic control unit is configured to calculate the delivery pressure in the delivery line from the electric motor's electrical control currents. When the electronic control unit is driving the electric motor, the value of the current drive torque of the drive motor, and thus of the hydraulic pump, is readily available in the control unit. This value is calculated, for example, from the current drive currents of the electric motor between an inverter controlling the electric motor and the electric motor itself. From this drive torque, the current pressure at the outlet of the hydraulic pump, and thus the delivery pressure in the hydraulic pump's delivery line, can be easily calculated and thus determined.This makes it possible to do without the sensor device, for example a pressure sensor, which detects the load pressure in the first pressure chamber of the push cylinder.

[0012] According to an advantageous embodiment of the invention, the electronic control unit is configured to determine, in particular to calculate, the delivery pressure in the delivery line when the thrust control valve is actuated solely into the retracted position, and to detect the load pressure of the lifting cylinder in the lifting line when the operating unit is additionally actuated to control the lifting operation of the load-handling device, wherein the electronic control unit is further configured to compare the load pressure of the lifting cylinder with the delivery pressure in the delivery line, and in the event that the load pressure of the lifting cylinder is lower than the delivery pressure, to actuate the proportional valve in the direction of the lifting position in such a way that the delivery pressure in the delivery line is kept constant.The position of the lifting control valve, designed as a proportional valve, can be regulated in such a way that the delivery pressure of the hydraulic pump, which is required for the retraction of the push cylinder, remains constant when the lifting function is engaged. This allows, in a simple manner, during the retraction of the push carriage and additional activation of the lifting operation of the load-handling device, where the load pressure of the lifting cylinder for the lifting function is lower than the hydraulic pressure of the push cylinder required for retraction of the push carriage, the hydraulic oil flow to the lifting drive to be throttled by appropriately controlling the lifting control valve, designed as a proportional valve, in such a way that the retraction movement and thus the retraction operation of the push cylinder is maintained.

[0013] According to an advantageous embodiment of the invention, the electronic control unit for detecting the load pressure of the push cylinder in the first pressure chamber of the push cylinder is connected to a sensor device that detects the pressure in the first pressure medium line. With a sensor device, for example a pressure sensor, the load pressure of the push cylinder in the first pressure chamber of the push cylinder during retraction operation can be easily detected by the electronic control unit.

[0014] According to an advantageous embodiment of the invention, the electronic control unit is configured to detect the load pressure of the thrust cylinder in the first pressure chamber of the thrust cylinder when the thrust control valve is actuated to the retracted position, and to detect the load pressure of the lifting cylinder in the lifting line when the control unit for the lifting operation of the load-handling device is additionally actuated, wherein the electronic control unit is further configured to compare the load pressure of the lifting cylinder with the load pressure of the thrust cylinder, and in the event that the load pressure of the lifting cylinder is lower than the load pressure of the thrust cylinder, to actuate the proportional valve in the direction of the lifting position in such a way that the delivery pressure in the delivery line does not fall below the load pressure of the thrust cylinder.This allows, in a simple manner, during the retraction operation of the sliding carriage and additional activation of the lifting operation of the load-handling device, where the load pressure of the lifting cylinder for the lifting function is lower than the hydraulic load pressure required for retracting the sliding carriage, the hydraulic load pressure in the first pressure chamber of the sliding cylinder can be throttled by appropriately controlling the lifting control valve, designed as a proportional valve, into a throttling position, so that the retraction movement and thus the retraction operation of the sliding cylinder is maintained.

[0015] According to an advantageous embodiment of the invention, the thrust cylinder is designed as a differential cylinder, wherein the first pressure chamber of the thrust cylinder is formed by the piston rod side of the differential cylinder and the second pressure chamber of the thrust cylinder is formed by the piston side of the differential cylinder.

[0016] The invention has a number of advantages.

[0017] The invention makes it possible to control the proportional lift control valve, if necessary, i.e., when the lifting function of the load-handling device is activated while the retraction function of the sliding carriage is activated and the lifting control valve is designed as a proportional valve, and the sensor device that detects the load pressure of the push cylinder during retraction operation, or data in the electronic control unit, for example the control currents of the electric motor, from which the delivery pressure of the hydraulic pump can be determined, by means of the sensor device that detects the load pressure of the lifting cylinder, the lifting control valve designed as a proportional valve, and the lifting control valve designed as a proportional valve, and the lifting control valve designed as a proportional valve, and the lifting control device that detects the load pressure of the push cylinder during retraction operation, or data in the electronic control unit, for example the control currents of the electric motor, from which the delivery pressure of the hydraulic pump can be determined, such that the hydraulic oil flow rate of the hydraulic pump is distributed to both functions and the retraction movement of the sliding carriage is maintained, even if the load pressure of the lifting cylinder is lower than the load pressure of the push cylinder.

[0018] The invention offers a solution that enables simultaneous operation of the insertion function of the sliding carriage and the lifting function of the load-handling device, whereby the load being moved has only a minor, controllable influence on the movement of the load or the load-handling device.

[0019] The invention enables a simple, simultaneous activation of the lifting operation of the load-handling device while the insertion movement of the lifting mast is already activated, without sudden changes in the movement of the load-handling device.

[0020] Compared to a solution where the pressure required to perform the lifting movement is generally increased, for example by a pressure switching valve in the lifting line, the invention uses significantly less energy by throttling in the lifting control valve designed as a proportional valve only when needed, i.e. when the load pressure of the lifting cylinder in lifting operation without load or with a small load is less than the required load pressure of the push cylinder for the insertion movement of the push carriage.

[0021] The invention can be implemented in a simple manner and with low additional costs using the electronic control unit and corresponding sensor devices.

[0022] Further advantages and details of the invention are explained in more detail by way of example using the embodiment shown in the schematic figure.

[0023] The figure shows the hydraulic circuit diagram of a reach truck according to the invention.

[0024] The figure schematically shows a vehicle body 1 of a reach truck, on which a push carriage 2 is arranged to be displaceable in the longitudinal direction of the vehicle.

[0025] A lifting mast 3 is arranged on the push carriage 2, on which a load handling device 4, for example a load fork with two fork tines, is arranged to be raised and lowered.

[0026] The push carriage 2, equipped with the lifting mast 3, can be moved along the vehicle body 1 by means of a push drive 5.

[0027] The load handling device 4 can be raised and lowered in the lifting mast 3 by means of a lifting drive 6.

[0028] The thrust drive 5 has a hydraulic thrust cylinder 10. The lifting drive 6 has a hydraulic lifting cylinder 11 in the illustrated embodiment.

[0029] A lifting control valve 15 is provided for controlling the lifting cylinder 11. This valve has a locking position 15a and a lifting position 15b. The lifting operation of the load-handling device 4 can be controlled by actuating the lifting control valve 15 in the direction of the lifting position 15b.

[0030] The lifting control valve 15 is connected to a delivery line 16 of a hydraulic pump 17 and to a lifting line 18 leading to the lifting cylinder 11. In the lifting position 15b, the lifting line 18 leading to the lifting cylinder 15 is connected to the delivery line 16 of the hydraulic pump 17. In the closed position 15a, the connection between the lifting line 18 leading to the lifting cylinder 15 and the delivery line 16 of the hydraulic pump 17 is closed.

[0031] The lifting control valve 15 is designed as a proportional valve that throttles in intermediate positions.

[0032] A thrust control valve 20 is provided for controlling the thrust cylinder 10. The thrust control valve 20 is connected by means of a branch line 21 to the delivery line 16 of the hydraulic pump 17, to a reservoir line 23 leading to a reservoir 22, to a first pressure medium line 25a connected to a first pressure chamber 10a of the thrust cylinder 10, and to a second pressure medium line 25b connected to a second pressure chamber 10b of the thrust cylinder 10.

[0033] In the illustrated embodiment, the thrust cylinder 10 is designed as a differential cylinder, wherein the first pressure chamber 10a of the thrust cylinder 10 is formed by the piston rod side of the differential cylinder and the second pressure chamber 10b of the thrust cylinder 10 is formed by the piston side of the differential cylinder. The thrust cylinder 10 has a cylinder 10c, which is attached to the thrust carriage 2, and a piston rod assembly 10d, which is longitudinally displaceable within the cylinder 10c and is attached to the vehicle body 1. When the first pressure chamber 10a of the thrust cylinder 10 is pressurized, the thrust carriage 2 with the lifting mast 3 is moved to the left in the figure, and a retraction movement of the thrust carriage 2 with the lifting mast 3 is achieved.When the second pressure chamber 10b of the push cylinder 10 is pressurized, the push carriage 2 with the lifting mast 3 is moved to the right in the figure and an extension movement of the push carriage 2 equipped with the lifting mast 3 is achieved.

[0034] The thrust control valve 20 has a retraction position 20a, which controls the retraction operation of the thrust cylinder 10, and an extension position 20b, which controls the extension operation of the thrust cylinder 10. In the retraction position 20a, the first hydraulic line 25a, connected to the first pressure chamber 10a of the thrust cylinder 10, is connected to the branch line 21 and thus to the delivery line 16 of the hydraulic pump 17, and the second hydraulic line 25b, connected to a second pressure chamber 10b of the thrust cylinder 10, is connected to the reservoir 22. In the extended position 20b, the first pressure medium line 25a connected to the first pressure chamber 10a of the push cylinder 10 is connected to the reservoir 22, and the second pressure medium line 25b connected to the second pressure chamber 10b of the push cylinder 10 is connected to the branch line 21 and thus to the delivery line 16 of the hydraulic pump 17.

[0035] The thrust control valve 20 has a neutral position 20c located between the retracted position 20a and the extended position 20b, in which the branch line 21 is shut off and the two pressure medium lines 25a, 25b to the container 22 are relieved.

[0036] The lifting control valve 15 and the thrust control valve 20 are each electrically actuated and electrically controlled by an electronic control unit 30.

[0037] The control unit 30 is connected on the output side to electrical actuators 35a, 35b, 35c of the lifting control valve 15 and the thrust control valve 20. On the input side, the control unit 30 is connected to an operating unit 31 that controls the lifting control valve 15 and the thrust control valve 20. This operating unit includes one or more joysticks with which an operator can specify and control the lifting operation of the lifting drive 6 as well as the retraction and extension operation of the thrust drive 5.

[0038] In the illustrated embodiment, the hydraulic pump 17 is driven by an electric motor 36, the speed of which can be controlled by the electronic control unit 30.

[0039] The electronic control unit 30 is also connected to a sensor unit 40, for example a pressure sensor, which detects the load pressure of the lifting cylinder 11 in the lifting line 18.

[0040] The electronic control unit 30 is also connected to a sensor unit 41, for example a pressure sensor, which detects the load pressure of the push cylinder 10 in the first pressure medium line 25a and thus in the first pressure chamber 10a of the push cylinder 10.

[0041] The invention works as follows: An operator controls the insertion operation of the sliding carriage 2 and the lifting operation of the load handling device 4 by means of the control unit 31, which may have one or more joysticks, and by means of the electronic control device 30, which is connected to the control unit 31, the electric motor 36, the actuating devices 35a, 35b, 35c of the lifting control valve 15 and the sliding control valve 20 and the sensor devices 40, 41.

[0042] To retract the push carriage 2, the operator activates the control unit 31, which then, via the electronic control unit 30, activates the electric motor 36. This causes the hydraulic pump 17 to pump hydraulic oil from the reservoir 22 into the delivery line 16 and actuates the push control valve 20 in the direction of the retraction position 20a. As a result, hydraulic oil is pumped from the hydraulic pump 17 into the first pressure chamber 10a of the push cylinder 10, and hydraulic oil from the second pressure chamber 10b of the push cylinder 10 can flow back into the reservoir 22. The push carriage 2 is then retracted into the body 1 of the reach truck.The hydraulic load pressure in the first pressure chamber 10a of the thrust cylinder 10, which is necessary for the retraction operation of the thrust cylinder 10 when the thrust control valve 20 is actuated in the retraction position 20a alone, is detected by the sensor device 41 and reported to the electronic control device 30.

[0043] If the operator additionally activates the lifting function of the load-handling device 4 via the control unit 31, the electronic control unit 30 detects the load pressure in the lifting cylinder 11 by means of the sensor device 40 and compares the load pressure of the lifting cylinder 11 with the load pressure of the thrust cylinder 10 detected by the sensor device 41. If the load pressure of the lifting cylinder 11 measured by the sensor device 40 is lower than the load pressure of the thrust cylinder 10, the electronic control unit 30 actuates the lifting control valve 15, designed as a proportional valve, only to such an extent in the direction of the lifting position 15b, i.e., into a throttling intermediate position, that the delivery pressure in the delivery line 16 does not fall below the value required for retracting the thrust cylinder 10, i.e., the load pressure of the thrust cylinder 10.

[0044] This ensures that the insertion movement of the pusher carriage 2 and the lifting movement of the lifting cylinder 11 can be carried out in parallel, without sudden changes in the movement speeds of the pusher cylinder 10 and / or the lifting cylinder 11.

[0045] The invention is not limited to the embodiment shown in the figure.

[0046] Alternatively, the sensor device 41 can be dispensed with and the delivery pressure in the delivery line 16 can be calculated from the electrical control currents of the electric motor 36 by the electronic control device 30 when the thrust control valve 20 is actuated alone into the retracted position 20a.

[0047] If the operator then additionally activates the lifting function of the load-handling device 4 via the control unit 31, the electronic control unit 30 uses the sensor unit 40 to detect the load pressure in the lifting cylinder 11 and compares the load pressure of the lifting cylinder 11 with the calculated delivery pressure in the delivery line 16. If the load pressure of the lifting cylinder 11 measured by the sensor unit 40 is lower than the calculated delivery pressure in the delivery line 16, the electronic control unit 30 actuates the lifting control valve 15, designed as a proportional valve, only to the extent necessary to move it towards the lifting position 15b, i.e., into a throttling intermediate position, so that the delivery pressure in the delivery line 16 is kept constant.

[0048] This also ensures that the insertion movement of the pusher carriage 2 and the lifting movement of the lifting cylinder 11 can be carried out in parallel, without sudden changes in the movement speeds of the pusher cylinder 10 and / or the lifting cylinder 11.

[0049] With the invention, the lifting function at the lifting control valve 15 is only throttled if this is required due to an insufficient load on the load-bearing device 4 during simultaneous retraction operation of the sliding carriage 2.

Claims

1. Reach truck with a lifting mast (3), wherein the lifting mast (3) is arranged on a vehicle body (1) of the reach truck so as to be displaceable in the longitudinal direction of the vehicle by means of a thrust drive (5), and the lifting mast (3) is provided with a load handling device (4) which can be raised and lowered in the lifting mast (3) by means of a lifting drive (6), wherein the thrust drive (5) has a thrust cylinder (10) and the lifting drive (6) has at least one lifting cylinder (11), wherein a lifting control valve (15) is provided for controlling the lifting cylinder (11), which has a locking position (15a) and a lifting position (15b) for controlling the lifting operation of the load handling device (4), wherein in the lifting position (15b) a lifting line (18) leading to the lifting cylinder (11) is connected to a delivery line (16) of a hydraulic pump (17), and wherein for controlling the thrust cylinder (10) a thrust control valve (20) is provided,which has a retraction position (20a) for controlling the retraction operation of the push cylinder (10) and an extension position (20b) for controlling the extension operation of the push cylinder (10), wherein in the retraction position (20a) a first pressure medium line (25a) connected to a first pressure chamber (10a) of the push cylinder (10) is connected to the delivery line (16) of the hydraulic pump (17) and a second pressure medium line (25b) connected to a second pressure chamber (10b) of the push cylinder (11) is connected to a reservoir (22) and wherein in the extension position (20b) the first pressure medium line (25a) connected to the first pressure chamber (10a) of the push cylinder (10) is connected to the reservoir (22) and the second pressure medium line (25b) connected to the second pressure chamber (10b) of the push cylinder (10) is connected to the delivery line (16) of the hydraulic pump (17),wherein the lifting control valve (15) and the thrust control valve (20) are electrically controlled by an electronic control unit (30) which is connected on the input side to an operating unit (31) controlling the lifting control valve (15) and the thrust control valve (20), characterized by the fact that the lifting control valve (15) is designed as a proportional valve that throttles in intermediate positions, wherein the electronic control device (30) is designed to actuate the lifting control valve (15), designed as a proportional valve, in the direction of the lifting position (15b) in the retraction operation of the push cylinder (10) when the control unit (31) is additionally actuated to control the lifting operation of the load-handling device (4), in such a way that the retraction operation of the push cylinder (10) is maintained.

2. Reach truck according to claim 1, characterized by the fact thatthe electronic control unit (30) is connected to a sensor device (40) which detects the load pressure of the lifting cylinder (11) in the lifting line (18).

3. Reach truck according to claim 1 or 2, characterized by the fact that the electronic control device (30) is designed to detect, when the thrust control valve (20) is actuated in the retracted position (20a), the delivery pressure in the delivery line (16) of the hydraulic pump (17) and / or the load pressure of the thrust cylinder (10) in the first pressure chamber (10a) of the thrust cylinder (10).

4. Reach truck according to one of claims 1 to 3, characterized by the fact that the hydraulic pump (17) is driven by an electric motor (36), wherein the electronic control device (30) is designed to calculate the delivery pressure in the delivery line (16) from the electrical control currents of the electric motor (36).

5. Reach truck according to claim 3 or 4, characterized by the fact that the electronic control unit (30) is configured to determine, in particular to calculate, the delivery pressure in the delivery line (16) when the thrust control valve (20) is actuated in the retracted position (20a) alone, and to detect the load pressure of the lifting cylinder (11) in the lifting line (18) when the operating unit (31) is additionally actuated to control the lifting operation of the load-handling device (4), wherein the electronic control unit (30) is further configured to compare the load pressure of the lifting cylinder (11) with the delivery pressure in the delivery line (16), and in the event that the load pressure of the lifting cylinder (11) is lower than the delivery pressure, to actuate the proportional valve in the direction of the lifting position (15b) such that the delivery pressure in the delivery line (16) is kept constant.

6. Reach truck according to one of claims 1 to 3, characterized by the fact thatthe electronic control device (30) for detecting the load pressure of the push cylinder (10) in the first pressure chamber (10a) of the push cylinder (10) is connected to a sensor device (41) that detects the pressure in the first pressure medium line (25a).

7. Reach truck according to claim 6, characterized by the fact thatThe electronic control unit (30) is configured to detect the load pressure of the push cylinder (10) in the first pressure chamber (10a) of the push cylinder (10) when the thrust control valve (20) is actuated in the retracted position (20a) and to detect the load pressure of the lifting cylinder (11) in the lifting line (18) when the operating unit (31) is additionally actuated to control the lifting operation of the load-handling device (4), wherein the electronic control unit (30) is further configured to compare the load pressure of the lifting cylinder (11) with the load pressure of the push cylinder (10) and, in the event that the load pressure of the lifting cylinder (11) is lower than the load pressure of the push cylinder (10), to actuate the proportional valve in the direction of the lifting position (15b) such that the delivery pressure in the delivery line (16) does not fall below the load pressure of the push cylinder (10).

8. Reach truck according to one of claims 1 to 7, characterized by the fact that the thrust cylinder (10) is designed as a differential cylinder, wherein the first pressure chamber (10a) of the thrust cylinder (10) is formed by the piston rod side of the differential cylinder and the second pressure chamber (10b) of the thrust cylinder (10) is formed by the piston side of the differential cylinder.

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