Apparatus for blocking and for adjusting a pressure

An apparatus (10) blocks and adjusts a pressure for a hydraulically controllable actuator (12), particularly a lifting unit (16) of a machine (18). The apparatus (10) allows a working chamber (20, 22) to be selectively connected to a pressure supply unit (94) having a storage device (34) or to a discharge end (66), in particular a reservoir end, by a valve unit (38). In a controlling position of the valve unit (38), when the storage pressure in the storage device (34) is greater than the working pressure in the working chamber (20) of the actuator (12), the storage pressure is relieved in the direction of the discharge end (66) until the working pressure has been reached.

FIELD OF THE INVENTION

The invention relates to an apparatus for locking and adjustment of pressure for a hydraulically controllable actuator, in particular in the form of a lifting mechanism of a working device. At least one working chamber of the actuator can be selectively connected to a pressure supply device, comprising an accumulator device, or to a discharge side, in particular a tank side, by a valve device.

BACKGROUND OF THE INVENTION

Such devices are used in construction equipment, in particular for wheel loaders. These working devices comprise, amongst other things, an actuator for a lifting mechanism having at least one piston cylinder unit for raising and lowering a loading bucket of this lifting mechanism. During operation of the working device, this loading bucket is exposed to various static and dynamic loads that must be controlled by the actuator device. For instance, to receive a payload, the piston cylinder unit, which is then acting as a lifting cylinder, is usually locked to use the full force of the working device for receiving the payload. While driving with a raised load, however, the actuator is to perform the function of a spring-damper unit to prevent the suspended payload, which preferably is to be held in a constant position, from inadvertently swinging upwards. In addition, provisions are to be taken for the event that overloading of the lifting mechanism occurs during operation.

SUMMARY OF THE INVENTION

An object of the invention is to provide an improved device for locking and adjustment of pressure for a hydraulically controllable actuator device that is safely lockable in a control position for receiving the payload and that, in this position or another control position, provides effective spring-damper characteristics.

This object is basically achieved by an apparatus for locking and adjustment of pressure having, in a control position of a valve device at higher accumulator pressure in the accumulator device than the working pressure in one working chamber of the actuator device, this accumulator pressure relieved to the discharge side until the working pressure is reached.

This device has the advantage that, when switching the device from its locking position to a spring-damper mode, the accumulator pressure is first reduced to the pressure level of the working chamber that is to be connected to the accumulator device and that, upon reaching this pressure level, the fluid communication is established between the working chamber and the accumulator device. In this manner, the pressure level in the accumulator device can be advantageously selected to be substantially higher in the lock mode and can be used exclusively for hydraulic locking of the actuator device.

Preferably, respectively subsequent in time to this operation, the working chamber of the actuator device in this control position is fluidly connected with the accumulator device at a working pressure higher than the accumulator pressure.

According to an advantageous embodiment, the valve device comprises a first logic element that compares the working pressure with the accumulator pressure to drive a control line of a second logic element of the valve device, which second logic element controls a possible fluid communication between the one working chamber and the accumulator device. In this manner, the respective higher pressure of work pressure and accumulator pressure is present at the second logic element in the locking direction. The second logic element thus closes particularly reliably and will be kept closed even under particularly high loads of the actuator device, for example, when driving the bucket of the lifting mechanism into a payload to be received with a wheel loader of the working device.

Advantageously, a first control valve of the valve device is connected in the control line that, in a first control position, in the spring-damper mode, establishes a fluid connection to the discharge side and, in a second control position, the lock mode, connects the control line to the operating pressure of the one working chamber of the actuator device. Consequently, the control line is depressurized in the spring-damper mode so that the second logic element is opened after the pressure is relieved and the one working chamber is connected with the accumulator device. In the lock position, in the closing direction of the second logic element, at a minimum the working pressure is present, which, in conjunction with an energy accumulator, ensures a secure closure of the fluid connection via the second logic element.

Preferably, the actuator device is formed from at least one hydraulic working cylinder, the piston side of which partially delimits the one working chamber and the rod side of which partially delimits another working chamber. Alternative concepts at least partly employ hydraulic motors instead of hydraulic working cylinders.

A third logic element of the valve device may be present for controlling the rod side of the working cylinder. The third logic element is connected to the control line and controlling fluid communication between the rod side and the discharge side. By the third logic element, the rod side is also secured against fluid flowing out in the lock mode of the device. In the spring-damper mode, the third logic element can be used to add fluid from the other working chamber and also to replenish fluid into it, given a corresponding formation of the discharge side.

Particularly preferably, a diaphragm or a flow control valve is connected in the control line between the second logic element and the control valve. The diaphragm or flow control valve causes the fluid pressure upstream of the diaphragm or the flow control valve to be kept at a high level until the accumulator device has emptied enough so that the accumulator pressure has dropped to the level of the working pressure. In this manner, the second logic element—and, if applicable, also the third logic element—is kept locked for a longer time.

Advantageously, the accumulator device can be connected with the pressure supply device for pressure supply of the accumulator device by a second control valve of the valve device, which second control valve is controllable by the pressure in the control line. This switching allows for charging of the accumulator device in the lock mode, and thus, a significant increase of the accumulator pressure. The accumulator pressure can then be very advantageously used for locking the second logic element and, if applicable, also the third logic element. This arrangement allows for locking of the actuator device even under maximum load.

Preferably, an additional supply device is provided for additional supply of the actuator device and other components of a working hydraulic system, in particular for controlling the lifting mechanism of the working device. These supply devices may, in particular, have directional valves to purposefully feed working fluid into one of the working chambers of the actuator device or discharge working fluid therefrom. The additional supply device permits the control of the actuator device or any additional components of the working hydraulic system.

Preferably, the logic elements are formed by 2/2-way valves. The logic elements are distinguished by the fact that the fluid pressures present at the fluid connections act in the opening direction of the valve. On the opposing control side, the fluid pressure from the control line acts in the closing direction, possibly enforced by an accumulator.

The first control valve can be an electrically controllable 3/2-way valve. The second control valve can be a 2/2-way valve of a different type than those of the logic elements. The 3/2-way valve allows the control line to be connected in a simple manner with the one working chamber of the actuator device or the discharge side at full opening cross-section. The 3/2-way valve is designed such that it can withstand any occurring operating pressure of the actuator device. Advantageously, the 2/2-way valve can be used to resupply the accumulator device with fluid of determinable pressure via a hydraulic pump (fixed or variable capacity pump) of the pressure supply device.

Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the drawings, discloses a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows an apparatus10according to an exemplary embodiment the invention for locking and adjustment of pressure for a hydraulically controllable actuator device or actuator12in the form of a working cylinder14or generally a piston cylinder unit of a lifting mechanism16of a working device18in the form of a bucket wheel loader. In principle, the actuator device could also be formed as a hydraulic motor (not shown).

The piston cylinder unit14comprises a first working chamber20on a piston side19and a second working chamber22on a rod side21. To move the piston rod unit of the cylinder14and the loading bucket26attached thereto as part of the lifting mechanism16of the wheel loader18, a supply device28of an additional working hydraulic system30, not explained in detail, is provided. The working hydraulic system30, controlled by an operator, can be used to independently supply hydraulic fluid alternately to one of the working chambers20,22and to release it therefrom to purposefully move the components of the wheel loader18during operation, for example, for raising the loading bucket26or for dumping a payload32from the loading bucket26.

Overlayed on this working hydraulic system30, the apparatus10for locking and adjustment of pressure is connected to the actuator device12. This apparatus10establishes fluid communication from the first working chamber20to an accumulator device34in a spring-damper mode, as required, or interrupts the communication in lock mode. Likewise, the second working chamber22of the actuator device12can be connected to the discharge side66, in particular to a tank side, in the spring-damper mode or this fluid communication can be closed in a lock mode.

The apparatus10includes a valve device38, shown in an enlarged view inFIG. 2, with connections40,46for the working chambers20and22, respectively. In the present embodiment, the first working chamber20of the actuator device12is connected to a first fluid connection40of the valve device38. The respective fluid pressure present at the first fluid connection40is referred to as the working pressure. Via a second logic element42in the form of a 2/2-way valve, the first fluid connection40can be further connected with an accumulator connection44, to which the accumulator device34is connected. The respective fluid pressure present at the accumulator connection44is referred to as the accumulator pressure. In the present embodiment, the accumulator device34comprises three hydraulic accumulators of conventional design, such as piston accumulators.

Extending parallel to the first fluid connection40, the second working chamber22of the actuator device12is connected to a second fluid connection46of the valve device38. Via a third logic element48in the form of a 2/2-way valve, this second fluid connection46can be connected with a discharge connection50, leading to the discharge side (tank)66.

In addition to the second logic element42, a first control valve52is connected to the first fluid connection40. In addition, a first check valve56, preferably spring-loaded, which opens toward the first control valve52, and a diaphragm58or throttle downstream from this first check valve56are present in the connecting line54leading from the first fluid connection40to the first control valve52. The first control valve52is preferably constructed as a 3/2-way switching valve. In the illustrated, currentless first control position of the first control valve52, a control line60is connected to the first fluid connection40. By an electrical actuator device (solenoid)62, the first control valve52can be switched against the action of a return spring63into a second control position in which the control line60is connected to a further discharge connection64, to which in turn the tank or discharge side66is connected.

Via the control line60, the control sides68,70of the second logic element42and the third logic element48, respectively, are permanently connected to the first control valve52in its switching position shown in the figures. Accordingly, in lock mode, these control sides68,70can be pressurized with the fluid pressure at the first fluid connection40. Since this fluid pressure is present at the second logic element42in both the opening direction and in the lock direction, and since a valve piston72of the second logic element42is also pressurized in closing direction by an energy accumulator (compression spring)74, the second logic element42is securely closed in its lock position. Likewise, the third logic element48can be pressurized in the closing direction by the fluid pressure at the first fluid connection40in the lock direction and by a much lower fluid pressure at the second fluid connection46in the opening direction. Therefore, the third logic element48is also securely closed in lock mode. In spring-damper mode, however, the fluid can flow from the control line60to the discharge side66and to the tank via the then triggered valve52(left switch representation) and the discharge connection64. In this manner, the corresponding control sides68,70of the second logic element42and the third logic element48are relieved so that these logic elements42,48can switch into the open position (not shown).

To always ensure the locking of the second logic element42and the third logic element48even at a higher load, the control sides68,70of these logic elements42,48are pressurized with the respective higher pressure of the pressures at the first fluid connection40and the accumulator connection44. For this purpose, in addition to the first check valve56, a first logic element76is provided in parallel in the connection line54from the first fluid connection40and the first control valve52. The first logic element76includes a fluid inlet78connected to the accumulator connection44. A fluid outlet80of the first logic element76is connected to the control line60. The fluid pressures at the fluid inlet78and the fluid outlet80of the first logic element76pressurize a valve piston82of this valve in the opening direction. On the opposite control side84, the fluid pressure at the first fluid connection40and an energy accumulator (pressure spring)86act on the valve piston82of the first logic element76in the lock direction.

Furthermore, a diaphragm88or a flow control valve (not shown) is connected in the control line60between the logic elements42,48,76and the first control valve52. At the first logic element76, the pressure at the first fluid connection40, i.e., the working pressure in the working chamber20of the actuator device12, is continuously being compared with the pressure prevailing at the accumulator connection44, i.e., the accumulator pressure. If the accumulator pressure is higher than the working pressure, the first logic element76opens and fluid from the accumulator device34flows into the control line60. In locked mode, wherein the first control valve52is kept deenergized in the switching position shown, thus connecting the control line60with the first fluid connection40, the first check valve56prevents fluid from flowing on this path from the accumulator device34to the first fluid connection40and further into the actuator device12. In the lock direction of the second logic element42and the third logic element48, higher accumulator pressure is now present instead of the lower working pressure. The second logic element42and the third logic element48are therefore closed tightly and remain in the closed position shown even at higher loads and possible pressure shocks originating from the actuator device12.

In spring-damper mode, in which the first control valve52relieves the control line60in the direction of the discharge side66, the diaphragm88or the flow control valve in the control line60prevents the built up pressure from dropping on the control side68,70of the second logic element42and the third logic element48as long as fluid at higher pressure keeps flowing from the accumulator device34via the first logic element76. Hence, in spring-damper mode, the fluid communications are kept closed by the second logic element42and the third logic element48until the accumulator device34has emptied enough for the accumulator pressure to approach the working pressure in the working chamber20. Upon reaching this pressure, the first logic element76is then closed by its energy accumulator86. This action in turn causes the fluid pressure in the entire control line60to drop to the pressure at the discharge side66(tank pressure) and the second logic element42and the third logic element48switch into the open position. In this manner, the piston-side first working chamber20is fluidly connected with the accumulator device34and the desired spring-damper effect of the lifting mechanism16is achieved. The second working chamber22(rod side) can then be resupplied with fluid if needed via the supply device28of the working hydraulic system30.

Hence, in a control position of the valve device38, which position corresponds to the spring-damper mode, if the accumulator pressure of the accumulator device34is higher than the working pressure in the one working chamber20of the actuator device12, the accumulator pressure is relieved into the discharge side66until this working pressure is reached. In this control position, if the working pressure in the one working chamber20is higher than the accumulator pressure, the working chamber20is fluidly connected with the accumulator device34.

To resupply the accumulator device34, the accumulator device34is connected to a hydraulic pump92of another pressure supply device94, which is part of the previously presented working hydraulic system30, via a pressure supply connection90. In the connecting line96coming from the pressure supply connection90and leading in the direction of the accumulator connection44, a pressure regulator or relief valve98as a pressure closing valve, a second control valve100, and a second, preferably spring-loaded, check valve102are provided. The valve98ensures that the accumulator device34can be resupplied only up to a predeterminable maximum accumulator pressure. The second control valve100is, as shown, constructed as a 2/2-way valve of a design different from the logic valves and is also triggered by the control line60. Once the control line60is relieved of pressure in the spring-damper mode, the second control valve100is closed, as shown, due to the action of a return spring and the connection line96between the pressure supply connection90, and accumulator connection44is interrupted so that in this mode no resupply of the accumulator device34takes place. In lock mode, at least the working pressure is present at the control line60, which may be higher than the accumulator pressure so that the second control valve100opens the connection line96in this mode and permits resupplying the accumulator device34to a higher pressure level. The second check valve102opens in the direction of the accumulator connection34, preventing any possible, undesired backflow of hydraulic fluid in the direction of the pressure supply connection90.

This arrangement results in the following sequence in the operation of the apparatus. Via the second logic element42, the piston side in the form of the first working chamber20of the lifting or working cylinder14can be connected to the individual hydraulic accumulators of the accumulator device34. Via the third logic element48, the rod side in the form of the second working chamber22of the working cylinder14can be connected to the tank and the discharge side66, respectively. The individual logic elements are controlled via the triggered 3/2-way valve52. If the 3/2-way valve or 3/2-way switching valve is in its non-energized basic position, shown in the figures, the pressure in the first working chamber20is fluidly connected with the control surfaces68and70of the two logic elements42and48, respectively, via the check valve56and in turn via the 3/2-way valve52. The logic elements42and48then close the connections to accumulators of the accumulator device34and the discharge side66, respectively, free from oil leakage. At the same time, this control pressure in the control line60also switches the 2/2-way valve to the open position (not shown). The accumulators of the accumulator device34are then resupplied from the working hydraulic system (pressure supply device94) via said 2/2-way valve100and the second check valve102until the system pressure is reached or, when using a normally open pressure valve of the type of a pressure regulating or pressure relief valve98, until a maximum manifold pressure is reached depending on the setting on the valve98.

The first logic element76compares the accumulator pressure of the accumulator device34with the cylinder or working pressure, as is present in the first working chamber20of the working cylinder14. If the accumulator pressure is higher than the cylinder or working pressure, the first logic element76goes into an open position and transfers the accumulator pressure to the control surfaces68and70of the second logic element42or third logic element48, respectively. The control surfaces68,70are always connected to the respective highest pressure of the first working chamber20or the accumulator device34. The first check valve56prevents a connection between the accumulator device34and the first working chamber20via the control line60. The second and third logic elements42and48are thus securely closed (lock mode).

To add the individual accumulators of the accumulator device34(spring-damper mode), the 3/2-way valve is then electrically triggered via the actuating device62with the result that the control line60is relieved to tank or drain side66. Due to the relief of the control line60and also as a result of the action of the return spring103, the 2/2-way valve100is then brought into its closed or locking position, shown in the figures, thereby closing the accumulator supply of the accumulator device34from the working hydraulic system30with the pressure supply device94.

If the accumulator pressure is now higher than the working or cylinder pressure in the working chamber20, the first logic element76is in the open position. The pressure of the accumulator device34is then relieved in a controlled manner via the diaphragm88. The dynamic pressure upstream of the diaphragm88continues to keep the second and third logic elements42and48in the closed position during the relieving of the accumulator. Once the accumulator pressure has been lowered to the working or cylinder pressure, the first logic element76then closes and the control surfaces68,70of the two logic elements42and48, respectively, are relieved to discharge side66down to the tank pressure, and the connection of the lifting or working cylinder14opens to the accumulators of the accumulator device34and to the tank or the discharge side66. The lifting or working cylinder14with its working chamber20is then connected with the accumulators of the accumulator device34and the other working chamber22is connected to the tank via the discharge connection50.

The device10according to the invention for locking and adjustment of pressure has the advantage that, when switching the device10to a spring-damper mode, the accumulator pressure is first reduced to the pressure level of the first working chamber20that is to be connected to the accumulator device34and that, only when this pressure level is reached, is the fluid communication established between the working chamber20and the accumulator device34. In this manner, the pressure level in the accumulator device34can advantageously be substantially higher in the lock mode and can be used for hydraulic locking of the actuator device12. To enhance the locking effect, the accumulator pressure in the accumulator device34can be increased further by resupplying to a predeterminable maximum accumulator pressure. This operation results in a smooth and unrestrained operation with the device.

Overall in this manner, a device10is proposed that, in lock mode, can withstand higher loads on the part of the actuator device12and the loading bucket26, placing loads on it. Under utilization of the same accumulator device34at the same, but also at a substantially lower pressure level, provides suspension and damping of the lifting mechanism16with the loading shovel26being in a spring-damper mode for safe operation of the working machine.