HYDRAULIC OR PNEUMATIC PUMP

Description

[0001] The present invention relates to a pump for a hydraulic or pneumatic cylinder with two pressurizable working chambers, in particular for a steering cylinder.

[0002] With hydraulic steering systems, there is a desire to be able to move the steering manually, especially into the straight-ahead position, even in the event of a defect, for example, a failure of the pressure supply unit or a line break. This can be achieved using a manually operated emergency pump. Such a hand pump usually has a pump chamber and a movable pump element within it, which is controlled via a manual control device, such as a lever. However, a hydraulic steering system must be able to be deflected in two directions. Accordingly, a steering cylinder has two working chambers with associated hydraulic connections for pressure lines. The hand pump must therefore be alternately connected to one of the two working chambers via a changeover valve, depending on the desired steering direction. This makes emergency or manual operation of the steering more complicated and carries the risk of incorrect operation.Particularly in the case of a steering cylinder which must be locked in a safe central position in the event of a fault, it must be ensured that the corresponding valves between the hand pump and steering cylinder as well as the steering cylinder and tank are returned to a safe position at the end of the emergency operation.

[0003] A pump of this type is disclosed in document DE 38 33 484 A1.

[0004] One object of the invention is to provide a pump for actuating a double-acting hydraulic cylinder that enables simple and intuitive operation. Furthermore, a corresponding hydraulic circuit with a double-acting hydraulic cylinder and a pump for deflecting the piston in either stroke direction is to be provided.

[0005] The problem is solved with regard to the pump by the features of claim 1 and with regard to the hydraulic circuit by the features of claim 5. Advantageous embodiments can be found in the dependent claims.

[0006] According to the invention, the pump has two pump chambers, each with a pump element movable in the associated pump chamber, and an actuating element controlling the pump elements, wherein each of the two pump chambers has a pressure connection to be connected to one of the working chambers of the hydraulic cylinder to be actuated, and the actuating element is operatively connected to the two pump elements in such a way that when the actuating element is deflected in a first direction, only a first of the two pump elements is actuated, and when deflected in a second direction, only the second of the pump elements is actuated. The actuating element can preferably be a hand or foot actuating element, but alternatively also be a hydraulically, pneumatically, or electrically driven actuator, or be driven by such an actuator. Of course, the pump can also be provided with more than two pump chambers.For example, the pump can be equipped with double pump cylinders, e.g. two per side or pumping direction.

[0007] By providing a separate pump element for each working chamber, which is controlled by a common actuating element depending on the direction, the deflection direction of the piston is firmly linked to the deflection direction of the actuating element. Additional valves for switching the pumping direction are therefore unnecessary. This enables particularly simple, intuitive and therefore error-free operation of the hand pump. The hydraulic hand pump can be used primarily in hydraulic steering systems when emergency steering functions are required. However, the pump according to the invention can also be used in other systems and applications when a double-acting hydraulic cylinder is to be adjusted via a hand pump. The hand pump is particularly suitable for emergency operation of a double-acting hydraulic cylinder when the actual adjustment device (e.g. the steering) has failed.However, the hand pump according to the invention can also be used in corresponding applications as the sole adjustment device for a double-acting hydraulic cylinder.

[0008] According to the invention, the pump is designed as a piston or plunger pump with two separate pump cylinders and associated pump pistons. This type of pump is particularly robust, compact, and easy to operate. The two pump cylinders each have a side outlet connected to a tank return line in the area of ​​a rear end position of the associated pump piston. This side outlet is released when the pump piston is in its rear end position. When the two pump pistons are retracted, the pressure connections of the pump chambers are relieved via the respective side outlet to the tank. If one pump piston is thus deflected and pressure builds up in one of the working chambers of the hydraulic cylinder, hydraulic fluid from the other working cylinder can flow back to the tank via the other pump chamber. This eliminates the need for an additional discharge valve.A certain amount of idle stroke until the pump piston has passed over the respective side outlet and pressure is built up can be tolerated. This allows the pump to be designed particularly compactly, and the elimination of additional valves for supplying hydraulic fluid from the other working chamber results in a very robust and error-resistant circuit.

[0009] Preferably, the pump pistons can be provided with an integrated check valve or a retractable piston seal. This allows hydraulic fluid located in a dead space between the side outlet and the rear end position of the pump piston to be displaced and / or hydraulic fluid to be retracted upon a return movement of the pump piston. Alternatively, an additional tank relief connection in the rear space of the pump piston would also be conceivable.

[0010] For the direction-dependent coupling of an actuating element to the two pumping elements, any known mechanical coupling devices are conceivable, such as freewheels, locking or pawl arrangements, and the like. In a preferred embodiment, the actuating element can be designed as a lever that can be deflected from a central position into a first and an opposite second direction, thereby controlling either the first or the second pumping element depending on the direction of deflection. The lever can preferably control the pumping elements via an eccentric. This enables a mechanically simple and robust design without additional moving components.

[0011] Another possible use for the pump according to the invention would be the control of a hydraulic motor or other actuators, which is also encompassed within the scope of the present invention. Furthermore, the pump can also be used with the same operating principle in pneumatic circuits to control a double-acting pneumatic cylinder.

[0012] In a hydraulic circuit for a hydraulic steering system, with a steering cylinder comprising a cylinder chamber with a piston sealingly mounted in the cylinder chamber, which divides the cylinder chamber into two working chambers, and at least one piston rod carried by the piston, and with a pump for deflecting the piston in either one or the other stroke direction, the invention provides that the pump has two pump chambers, each with a pump element movable in the associated pump chamber and an actuating element controlling the pump elements, wherein each of the two pump chambers has a pressure connection and the pressure connection of a first of the pump chambers is connected to a first of the working chambers of the steering cylinder and the pressure connection of the second pump chamber is connected to the second working chamber, and the actuating element is operatively connected to the two pump elements in such a way thatWhen the actuating element is deflected in a first direction, only the first of the two pump elements is activated, and when deflected in a second direction, only the second of the pump elements is activated. The pump is used for emergency or manual operation in the event of a failure in a hydraulic primary circuit of the steering system.

[0013] During operation, the steering cylinder is connected to the primary hydraulic circuit of the steering system via appropriate connections. It is important that each of the two pressure lines leading from the pump chambers to the working chambers contains a hydraulically releaseable check valve that opens in the direction of the respective working chamber, with the control connections of the two check valves being cross-connected to the other pressure line. This ensures that the primary hydraulic circuit is decoupled from the hydraulic circuit, i.e. from the hand pump provided for emergency operation. The pump cannot therefore influence the steering cylinder in the idle position, and hydraulic pressure in the primary circuit that deflects the steering cylinder does not affect the pump or the associated hydraulic circuit because the pressure lines leading to the steering cylinder are tightly shut off.

[0014] A pump of the type mentioned above is used, in which the two pump cylinders each have a side outlet connected to a tank return line in the area of ​​a rear end position of the corresponding pump piston. This side outlet is released when the pump piston is in its rear end position. When the two pump pistons are retracted, the pressure connections of the pump chambers are thus relieved via the respective side outlet to the tank. Thus, when one pump piston is deflected to pressurize one of the working chambers of the steering cylinder, hydraulic fluid can flow from the other working chamber back to the tank via the other, non-actuated pump cylinder.

[0015] The two pilot-operated check valves can be integrated, in particular, in the form of a so-called twin pilot-operated check valve, i.e., in the form of opposing check valves with a shared control piston. This can be advantageous because the pressure difference in the pressure lines coming from the pump is then decisive for controlling the opening of one of the check valves. This ensures that only one of the two pilot-operated check valves can be in the unlocked position at any one time.

[0016] Additionally or alternatively, the two hydraulically pilot-operated check valves can be designed as shuttle valves, each with a second pressure connection. For example, a hydraulic steering circuit with a pressure supply unit can be connected to the two second pressure connections of the shuttle valves, via which the working chambers of the steering cylinder can be pressurized with hydraulic pressure in a controlled manner during normal operation. The additional integrated shuttle valve functionality ensures that, in the event of a fault when the hand pump is in operation, the actual steering circuit and its pressure supply unit are shut off from the steering cylinder. In emergency or manual operation, any leakage errors in the actual steering circuit or control circuit of the steering cylinder are thus eliminated, so that emergency operation remains possible even in the event of a hydraulic leak in the steering system.

[0017] To protect the hydraulic circuit from overload or overpressure, the two pressure lines leading from the pump chambers to the working chambers can each be connected to a tank via a pressure relief valve. If, for example, the steering were mechanically blocked, the pressure could be diverted to the tank via the respective pressure relief valve when the hand pump was activated when a critical pressure was reached, preventing a line from bursting or the like.

[0018] Another possible application of the pump according to the invention is, for example, the operation of a truck's cab tilting system. The pump can therefore be used in a hydraulic circuit to control a cab tilting cylinder.

[0019] Further advantages and features can be found in the description of the following embodiments based on the drawings. It shows: Figure 1 shows a hydraulic diagram of a hydraulic circuit not according to the invention with a hand pump, Figure 2 shows an embodiment of a pump piston with a lateral outlet leading to the tank in the area of ​​the end position of the pump piston, and Figure 3 shows a variant with pilot-operated check valves designed as shuttle valves for connecting the steering cylinder to a hydraulic steering circuit.

[0020] The Figure 1The hydraulic circuit shown, not according to the invention, comprises a hand pump 10 designed as a piston pump with two pump cylinders 11a, 11b, each forming a pump chamber in which a pump piston 12a, 12b acting as a pump element is arranged for longitudinal movement. This pump piston is spring-loaded towards its rear end position (rest position) by a return spring 13a, 13b. The hand pump 10 is actuated by an operating lever 14, which is connected to an eccentric 15. The two piston rods 16a, 16b carried by the pump pistons 12a, 12b rest against the eccentric 15, so that by deflecting the eccentric clockwise, the piston rod 16a is pushed in, and by deflecting it counterclockwise from the center position, the opposite piston rod 16b is pushed in. A suction line 17a, 17b opens into the pump cylinder 11a, 11b, which is provided with a suction check valve 18a, 18b and leads to a tank 19.

[0021] The pump 10 is connected to a steering cylinder 30. This has a longitudinally movable, sealed piston 31, which carries a piston rod on each side. The piston 31 divides the interior of the steering cylinder 30 into two working chambers 32a, 32b. Each of these working chambers 32a, 32b is connected to one of the pump cylinders 11a, 11b via a corresponding pressure line 20a, 20b. A hydraulically releasable check valve 21a, 21b is arranged in each of the pressure lines 20a, 20b. The control lines of the two releasable check valves 21a, 21b are connected crosswise to the other pressure line 20b, 20a.

[0022] In front of the two pilot-operated check valves 21a, 21b, a line 22a, 22b branches off from the pressure lines 20a, 20b, leading to a directional control valve 23 serving as a discharge valve. The directional control valve 23 blocks in the Figure 1In the neutral position shown, the directional control valve 23 closes the lines 22a, 22b. In the two other switching positions, the directional control valve 23 connects one of the lines 22a, 22b to a tank return line 24, while the other of the lines 22a, 22b is blocked. The directional control valve 23 is designed as a pre-pressure-controlled slide valve. Its two control ports are connected to the pressure lines 20a, 20b via control lines 27a, 27b. In addition, the directional control valve 23 is spring-loaded toward its center neutral position by return springs 23a, 23b, so that it switches to the blocked center position when depressurized.

[0023] From the two pressure lines 20a, 20b, a line each with a pressure relief valve 24a, 24b acting as an overload valve branches off, each leading to the tank 19. In the event of critical pressure surges in one of the pressure lines 20a, 20b, the corresponding pressure relief valve 24a, 24b opens and allows the excess pressure to escape toward the tank 19.

[0024] Finally, further relief lines 26a, 26b branch off from the pressure lines 20a, 20b, connected to the tank return line, each containing a throttle or relief nozzle 25a, 25b. At the end of an actuation of the hand pump 10, the pressure in the circuit is reduced via these relief lines 26a, 26b, so that the discharge valve 23 moves to the closed central position and the pilot-operated check valves 21a, 21b move to their blocking position.

[0025] The hydraulic circuit functions as follows: If the operating lever 14 of the hand pump 10 is moved from the center position to the left, the piston rod 16a of the pump piston 12a is pushed in via the eccentric 15. Hydraulic fluid in the pump chamber 11a is displaced into the pressure line 20a and, via the relevant control line 27a, initially switches the changeover valve 23 to the right-hand switching position, in which the working chamber 32b of the steering cylinder 30 is connected to the tank return line 24 via the pilot-operated check valve 21b. Further actuation of the hand pump 10 leads to an increase in pressure in the pressure line 20a, so that the pilot-operated check valve 21b now opens. This is achieved by the return spring 23b of the changeover valve 23 being weaker than the closing spring of the check valve 21b. Hydraulic fluid now flows from the pressure line 20a via the check valve 21a into the working chamber 32a of the steering cylinder 30.Hydraulic fluid can be displaced from the working chamber 32b into the tank 19 via the open check valve 21b and the discharge valve 23. Thus, the piston 31 of the steering cylinder 30 moves to the left.

[0026] If the operating lever 14 is returned to the center position, the return spring in the pump chamber 11a moves the pump piston 12a back to its original position. Hydraulic fluid is drawn from the tank into the pump chamber 11a via the intake check valve 18a. The pumping movement with the operating lever 14 from the center position to the left stop and back can be repeated as often as required until the desired steering position of the steering cylinder 30 is reached. As soon as the hand pump 10 remains inactive, any residual pressure in the pressure line 20a can escape via the throttle 25a toward the tank 19, so that the pressure line 20a is again depressurized. The pilot-operated check valve 21b then switches back to the locked state, and the discharge valve 23 returns to its locked center position. The hydraulic circuit therefore no longer influences the subsequent position and deflection of the steering cylinder 30.Rather, it can be operated by the normal steering system connected via lines 33a, 33b.

[0027] When the operating lever 14 is deflected from the center position to the right, the pump piston 12b is actuated in the same way as previously described, and the steering cylinder or its piston 31 is moved to the right via the pressure line 20b. Thus, the deflection of the operating lever 14 is clearly linked to a steering action on the steering cylinder 30, resulting in particularly simple and intuitive operation.

[0028] The function of the switch is primarily used for emergency operation of the hydraulic steering, for example, in the event of a failure of the hydraulic steering system. In particular, a deflected steering cylinder 30 can be returned to its center position via the switch without having to move the vehicle. This is particularly useful for a hydraulic rear-axle steering system, which is locked in the center position in the event of a failure (safe failure state). Thus, even in the event of a loss of hydraulic fluid in the actual hydraulic steering system, the steering can be moved to the straight-ahead position and locked there using the hand pump.

[0029] In Figure 2 an embodiment of a pump cylinder 11b according to the invention is shown, which in the Figure 1The special feature here is that the tank line 17b opens into the pump cylinder 11b via a side branch 110b in the area of ​​an end position of the pump piston 12b. In its Figure 2 In the end position shown, which is completely adjusted to the right, the pump piston 12b releases the side branch 110b and thus the tank return line 17b. In this position of the pump piston 12b, there is a direct connection between the pressure line 20b and the tank line 17b via the interior of the pump cylinder 11b. Thus, a discharge valve 23 as shown in Figure 1 shown, since when the opposite pump piston 12a is actuated, hydraulic fluid can flow back from the second working chamber 32b of the steering cylinder 30 via the interior of the pump cylinder 11b towards the tank 19. A suction check valve 18b as shown in Figure 1shown, can therefore also be omitted. So that the pump piston 12b can reach its end position completely after passing over the side branch 110b, a check valve 120b is integrated into the pump piston 12b, through which hydraulic fluid located in the dead space between the side branch 110b and the end stop can escape. Furthermore, this prevents a vacuum from building up in the left area of ​​the pump cylinder 11b when it springs back, but instead hydraulic oil can immediately flow in from the tank 19. Alternatively, a suction piston seal can be used or a second relief line leading to the tank 19 can be arranged in the area of ​​the end position. In the latter case, a suction valve 18a, 18b can also be provided in order to implement the suction function explained above.

[0030] In the fully retracted end position of the pump pistons 12a, 12b (neutral position), the interior spaces of both pump cylinders 11a, 11b are connected to the common tank 19. If the Figure 1 Thus, in the neutral position of both pump pistons 12a, 12b, the suction check valves 18a, 18b also connect the pressure lines 20a, 20b to the tank 19. When one of the pump pistons 12a, 12b is deflected, a certain idle stroke occurs until the respective pump piston 12a, 12b has moved past the side branch 110a, 110b. From there, the pumping or working stroke of the pump cylinder 12a, 12b begins.

[0031] Thus, no additional valve is required that must be actuated by the operator to enable deflection of the steering cylinder 30 connected to the circuit. The two releasable check valves 21a, 21b securely hold the position of the piston 31 in the steering cylinder 30 in the unactuated state. Furthermore, when the connected steering system is actuated, no hydraulic fluid can be displaced toward the pressure line 20a, 20b or toward the tank 19. Thus, the hydraulic circuit with the pump 10 is largely decoupled from a hydraulic steering system connected to the steering cylinder 30.

[0032] Figure 3 shows a variant of the connection of the hand pump 10 to the hydraulic steering system connected to the steering cylinder 30 via the connections 33a, 33b. The pilot-operated check valves 21a, 21b have an integrated shuttle valve function.

[0033] A shuttle valve is a pneumatic or hydraulic valve with two inputs and one output. The shuttle valve represents the technical implementation of a non-exclusive OR operation in the field of pneumatics and hydraulics. The shuttle valve consists of a housing with two input ports, one output port, and a usually spherical switching element. The shuttle valve therefore has only two defined switching positions. In each of these positions, one input is always blocked by the switching element, preventing hydraulic flow between the inputs.

[0034] If pressure is applied via one of the pressure lines 20a, 20b, the locking element of the respective check valve 21a, 21b is pressed against a second, opposite valve seat 210a, 210b, preventing hydraulic fluid from escaping via the lines 33a, 33b. This ensures that any leaks in the connected hydraulic steering system (cylinder control) are compensated for during manual operation of the pump 10. Thus, the piston 31 of the steering cylinder 30 can be adjusted via the mechanical hand pump 10 even if hydraulic fluid is lost in the hydraulic steering system.

Claims

1. Pump, in particular a hand-operated pump (10) for a hydraulic or pneumatic cylinder (30) with two pressurized working chambers (32a, 32b), in particular a steering cylinder, wherein the pump (10) has two pump chambers (11a, 11b) each with a movable pump element (12a, 12b) in the associated pump chamber and an actuating element (14) controlling the pump elements (12a, 12b), wherein each of the two pump chambers (11a, 11b) has a pressure connection for connection, in each case, to one of the working chambers (32a, 32b), and the actuating element (14) is operatively connected to the two pump elements (12a, 12b) such that on displacement of the actuating element (14) in a first direction only a first of the two pump elements (12a) is controlled and on displacement in a second direction only the second of the pump elements (12b) is controlled, wherein the pump is designed as a piston or plunger pump with two separate pump cylinders (11a, 11b) and the associated pump pistons (12a, 12b), characterized in that the two pump cylinders (11a, 11b) each have a side branch (110b) for connection to a tank return line in the region of a retracted end position of the associated pump piston (12a, 12b), which is released when the pump piston (12a, 12b) is in its retracted end position.

2. Pump according to claim 1, in which the pump pistons (12a, 12b) have an integrated check valve (120b) or a suction piston seal such that hydraulic medium in a dead space between the side branch (110b) and the retracted end position of the pump piston (12a, 12b) can be forced out with a return movement of the pump piston (12a, 12b) and / or hydraulic fluid can be sucked in.

3. Pump according to any one of the preceding claims, in which the actuating element is configured as a manual actuating element (14), in particular as a lever, which can be displaced from a central position into a first and an opposite second direction and thus controls either the first or the second pump element (12a, 12b) depending on the displacement direction.

4. Pump according to claim 3, in which the lever (14) controls the pump elements (12a, 12b) through a cam (15).

5. Hydraulic circuit for a hydraulic steering system, with a steering cylinder (30), which comprises a cylinder chamber, a piston (31) mounted in a sealing manner in the cylinder chamber, which divides the cylinder chamber into two working chambers (32a, 32b), and at least one piston rod supported by the piston (31), and a pump (10) according to any one of claims 2 to 4, for displacing the piston (31) in one or other stroke direction, wherein the pump (10) has two pump chambers (11a, 11b) each with a movable pump element (12a, 12b) in the associated pump chamber (11a, 11b) and an actuating element (14) controlling the pump elements (12a, 12b), wherein each of the two pump chambers (11a, 11b) has a pressure connection, and the pressure connection of a first of the pump chambers (11a) is connected to a first of the working chambers (32a) of the hydraulic cylinder (30) and the pressure connection of the second pump chamber (11b) is connected to the second working chamber (32b), and the actuating element (14) is operatively connected to the two pump elements (12a, 12b) such that on displacement of the actuating element (14) in a first direction only a first of the two pump elements (12a) is controlled and on displacement in a second direction only the second of the pump elements (12b) is controlled and wherein connections (33a, 33b) for connecting the steering cylinder (30) to a hydraulic primary circuit of the steering system are provided and a hydraulically releasable check valve (21a, 21b) decoupling the hydraulic primary circuit from the hydraulic circuit opening in the direction of the respective working chambers (32a, 32b) is arranged in each of the two pressure lines (20a, 20b) leading from the pump chambers (11a, 11b) to the working chambers (32a, 32b), and control connections of the two check valves are connected crosswise to the respective other pressure line (20a, 20b).

6. Hydraulic circuit according to claim 5, in which the two hydraulically releasable check valves (21a, 21b) are configured as change-over valves each with a second pressure connection (210a, 210b), and a hydraulic circuit, in particular a steering circuit, with a pressure supply unit is connected to the two second pressure connections of the change-over valves, through which hydraulic pressure can be applied to the working chambers (32a, 32b) of the steering cylinder (30) in a controlled manner.

7. Hydraulic circuit according to any one of claims 5 or 6, in which the two pressure lines (20a, 20b) leading from the pump chambers (11a, 11b) to the working chambers (32a, 32b) are each connected to a tank (19) through a pressure relief valve (23a, 23b).