DE29507623U1 - Hydraulic relief device for attachments - Google Patents

Description

Applicant: Matthias Gießler, D-77933 Lahr

Designation: Hydraulic relief device for attachments

Description

The invention relates to a hydraulic relief device for a hydraulic lifting device of a commercial vehicle for lifting an attachment from a lowered working position into a raised transport position with a hydraulic lifting cylinder that can be pressurized by a hydraulic pump, the hydraulic lifting pressure line of which can be subjected to a residual pressure by the relief device in the working position to reduce the contact force of the attachment on the ground, wherein a pressure accumulator is provided to maintain the residual pressure.

A relief device of the generic type is known (DE-PS 36 28 427), which is intended to reduce the contact force of the scraper bar of a snow plow on a road to be cleared. This reduction in the contact force results in a reduction in the

Wear of the scraper bar is reduced, so that the service life of the scraper bar can be increased.

A relief cylinder or the lifting cylinder of a lifting device for the snow plow is provided as a relief device, via which a relief force directed essentially vertically upwards can be applied to reduce the scraping or contact forces of the plowshare. The pressure acting in the relief cylinder or lifting cylinder to generate the force is regulated by a pressure relief control device, via which the actual pressure value prevailing in the relief cylinder or lifting cylinder can be regulated to the set pressure target value if it deviates from a pressure target value that can be set in the pressure relief control device. The known pressure relief control device reduces the scraping or contact forces of the plowshare on the ground to be cleared and also constantly regulates them back to a desired, adjustable target value of the contact forces during the clearing process. This is an active and dynamic control process that requires complicated electronic control. These controls or regulations have expensive and fault-prone electronic circuits, which are intended to ensure that a preselected target pressure in the lifting cylinder or in the relief cylinder is constantly

to keep constant. Such controls must always be operated in suitable temperature ranges in order to reliably rule out malfunctions. Furthermore, with the known relief device, a constant oil supply from the hydraulic pump is necessary in order to be able to apply the appropriate control pressures to keep the set pressure constant in the lifting cylinder or in the relief cylinder. Excess oil flow, i.e. oil flow not required for the control process, is partially diverted to pressureless circuits via control valves or circuits with flow dividers and fed back into an existing oil reservoir. The constant operation of the hydraulic pump means that an increased constant energy requirement is necessary because the unused, excess oil flow always leads to energy losses, which must be provided by the drive of the hydraulic pump. Furthermore, the constant oil supply from the hydraulic pump leads to undesirable heating of the hydraulic oil.

From DE 33 37 789 A1, a hydraulic suspension arrangement for an agricultural device with a so-called gas-oil collector is known, which is connected to the pressure chamber of at least one hydraulic cylinder. The agricultural attachment is supported by the hydraulic cylinder, i.e. raised and lowered. In the case of agricultural devices,

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in particular the desire that the attachment, which is, for example, in a lowered but still above the ground position due to the corresponding pressure being applied to the hydraulic cylinders, does not touch the ground with its full weight when it accidentally touches the ground, but is relieved accordingly so that it is easier to guide or raise the attachment.

According to this previously published document, a pressure accumulator is provided for this purpose. This pressure accumulator is basically closed under normal operating conditions by interposing a check valve. The check valve only opens when the attachment is placed on the ground, whereby the load-bearing pressure prevailing in the pressure chambers of at least one hydraulic cylinder is relieved to a certain extent. If the pressure in the hydraulic cylinder drops below the pressure prevailing in the pressure accumulator when the attachment is placed on the ground, the check valve opens and the desired relief takes place. This means that an attachment that is constantly resting on the ground, such as a snow plow, cannot be effectively relieved with this relief device, since the relieving effect only occurs when the attachment moves upwards, as only then does the check valve open. Furthermore, it is not possible to

to ensure rapid adjustment of the relief to a specific desired relief pressure.

In another known hydraulic relief device (DE-PS 43 04 133) for a lifting device, a pressure accumulator is provided that can be charged via the hydraulic circuit provided on the motor vehicle side. In relief mode, the pressure accumulator is decoupled from the hydraulic circuit on the motor vehicle side via a corresponding changeover valve and the lifting device is coupled to the pressure accumulator. In this operating state, a changeover arrangement can be automatically switched to a relief position starting from a pressure in the pressure accumulator below a relief pressure setpoint and subsequent increasing pressure when the relief pressure setpoint is reached, so that the pressure accumulator is connected to the pressure chamber of the hydraulic cylinder of the lifting device intended for pressure relief. If the relief pressure actual value rises above the relief pressure setpoint, the changeover valve arrangement can be used to switch to an overload switching position in such a way that the pressure chamber of the hydraulic cylinder or pressure accumulator used for relief is automatically connected to a return line. If the pressure falls below the relief pressure

If the actual value falls below the relief pressure setpoint, the pressurized pressure line of the vehicle-side hydraulic circuit is automatically connected to the pressure accumulator via the changeover valve arrangement to increase the relief pressure. The changeover valve arrangement switches between the relief switching position and the overload switching position or the pressure accumulator filling circuit in the manner of a hysteresis. The switching points are recorded by a pressure sensor arranged in the pressure accumulator or in the pressure chamber of the hydraulic cylinder and passed on to the changeover valve arrangement via appropriate switching electronics, which causes the changeover valve arrangement to switch using appropriate switching signals from the switching electronics. Using another changeover valve arrangement, the hydraulic cylinder is connected to the pressure line of the vehicle hydraulics to raise the attachment and to the pressure-free return line leading to the oil reservoir to lower the attachment.

In this known hydraulic relief device, several directional valves are therefore necessary for switching between the raised state of the attachment, the lowered state of the attachment and the activation of the relief device in order to enable the described functionality. Furthermore, a

A corresponding electronic circuit is indispensable in order to ensure a corresponding reduction in the contact force of the attachment on the ground in certain pressure ranges. This makes the known relief device complicated and expensive in its construction. The relief device is also prone to failure due to the large number of components and the electronic circuit provided, so that it must be constantly maintained. Furthermore, the hydraulic pump must be operated continuously in order to be able to carry out the control processes described.

The invention is based on the object of creating a relief device of the generic type which has a robust, less prone to failure, simple and cost-effective structure. Furthermore, it should be able to be operated with a minimum of energy expenditure.

The object is achieved according to the invention in that a check valve is provided in the lifting pressure line, which opens when the attachment is raised and closes when the attachment is lowered, and that a residual pressure valve is arranged in a shunt line parallel to the check valve, via which the pressure in the lifting cylinder side is

Output line section of the lifting pressure line is reduced until a predetermined residual pressure is reached, and that the pressure accumulator on the lifting cylinder side is hydraulically coupled to the output line section between the check valve or the residual pressure valve and the lifting cylinder.

The design of the relief device according to the invention means that it can be manufactured extremely cost-effectively from just a few components. Furthermore, the pressure accumulator and the residual pressure valve provided, via which the pre-pressure in the pressure accumulator can be preset, ensure an extremely simple and therefore reliable, trouble-free structure. Furthermore, no switching processes for activating or deactivating the relief device are necessary for raising the attachment and for lowering it, so that the relief device according to the invention is extremely immune to faults of any kind.

The embodiments according to claims 2 to 6 provide a relief device which, with a small size and a simple, cost-effective design, can be retrofitted at any time to an existing hydraulic system for lifting attachments.

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The relief valve arranged parallel to the residual pressure valve and the check valve allows the lifting pressure line to be completely relieved of pressure, so that the lifting pressure line can be detached from the hydraulic pump at any time in order to dismantle the lifting device from the commercial vehicle.

The use of two pressure accumulators according to claim 4 and their opposite arrangement on the distributor block enables the valves to be loaded and unloaded evenly, so that they cannot become distorted or jammed. Furthermore, the distributor block achieves an extremely compact design, so that the relief device according to the invention can be easily retrofitted to existing lifting devices. The pressure accumulators can also be arranged coaxially to one another on the distributor block, so that the connecting channel connecting them runs in a straight line in the distributor block and the flow conditions are thus improved, whereby shorter reaction times can be achieved when lifting the attachment due to the lower flow losses.

The relief device according to the invention enables the lifting cylinder or a separate relief cylinder with a

to apply a certain pre-pressure without the hydraulic pump having to be operated. The pre-pressure in the lifting cylinder means that when the relief device is used, for example in conjunction with a lifting device on snow plows, a reduction in the wear on the scraper bar of up to 65% is achieved, while at the same time the fuel consumption of the commercial vehicle can be reduced by up to 20 % . Due to the simple and therefore cost-effective design according to the invention, the investment in such a relief device on a commercial vehicle is amortized after replacing three scraper bars on a snow plow, for example.

Due to the use of simple components, such as the pressure accumulator, the residual pressure valve, the non-return valve or the relief valve as well as a simple display manometer, the relief device according to the invention is extremely robust, and a maximum level of operational safety is achieved due to the absence of sensitive, complicated electronic components and power supplies. Even when retrofitting the relief device according to the invention to an existing lifting device on a commercial vehicle, no cables need to be laid inside the vehicle, since it is only necessary to install the relief device with its distributor housing in the lifting pressure line.

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For this purpose, the distributor housing is provided with corresponding pressure line connections.

Before the relief device is put into operation, the hydropneumatic pressure accumulators must be pressurized with the appropriate pneumatic pre-pressure and the residual pressure valve must be adjusted to the set pre-pressure. Nitrogen, for example, can be used as the pneumatic medium. After these two measures have been carried out, the relief device according to the invention is ready for use. No other settings are necessary to ensure safe operation.

To lift the attachment, the hydraulic pump is first switched on so that pressure is built up in the pressure line section of the lifting pressure line connected to the distributor housing, which is located in front of the residual pressure valve, the check valve and the relief valve. This pressure build-up continues through corresponding connecting channels in the distributor housing in the pressure accumulators until a corresponding system pressure is built up, which is sufficient to lift the attachment. The system pressure is thereby controlled by the check valve that opens when the attachment is lifted or when the pressure is built up by the hydraulic pump and a

corresponding connecting channel of the distributor housing to the output line section of the lifting pressure line, which hydraulically connects the distributor housing to the lifting cylinder. When the attachment is raised, the positive effect is that the attachment does not hang "rigidly" on the supporting frame of the commercial vehicle due to the almost incompressible medium oil, but is cushioned by the pressure accumulator.

When the attachment is lowered, the directional control valve normally used to control the lifting cylinder is, for example, put into the floating position, whereby the lifting pressure line is hydraulically short-circuited with an oil return line of the lifting cylinder, which is always present, and the lifting pressure line is thus relieved of pressure. The attachment sinks to the ground, whereby the system pressure drops until the set pre-pressure is reached and the residual pressure valve closes, so that no more oil can flow out. The outlet line section of the lifting pressure line is therefore not completely relieved, but a desired residual pressure remains in it in order to significantly reduce the contact force of the snow plow with its scraper blades on the ground, for example. In this lowered position, the hydraulic pump is also switched off at the same time, so that it no longer delivers its full oil flow, which results in a

significant energy savings can be achieved. In this operating position, the oil heated up by the pumping action of the hydraulic pump when the snow plow is raised can cool down again, as no more energy is supplied to it by the hydraulic pump, which is now at a standstill.

During travel, a snow plow, for example, changes its position relative to the vehicle due to uneven ground or similar, so that the lifting cylinder or the piston rod of the lifting cylinder is moved back and forth in the vehicle. In a normal snow plow or under normal conditions, the stroke of the piston rod in the lifting cylinder is around 3 to 4 cm. The pressure accumulators are adjusted to this volume change corresponding to this stroke and the associated change in the pre-pressure in such a way that the pre-pressure only fluctuates within a relatively small pressure range. The average pre-pressure in the pressure accumulators and the setting of the residual pressure valve can be adjusted to the lifting cylinder or to the weight of the attachment in such a way that the attachment or the snow plow still safely maintains its grip on the ground despite the relieving pre-pressure.

During operation, no further losses occur except for the leakage oil losses of the lifting cylinder, so that the

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The pre-pressure essentially always fluctuates in the same range when driving over uneven ground. If the pre-pressure drops below a certain minimum value after a long period of operation due to the low leakage oil losses, the pre-pressure can be brought back to the pre-determined pre-pressure set by the residual pressure valve at any time by briefly switching on the hydraulic pump, so that the relief device according to the invention can be handled in the simplest way.

It has also been shown that the pre-pressure fluctuations caused by the small lifting distances of the lifting cylinder caused by the unevenness of the ground have a fluctuation range which is unproblematic for the practical operation of the relief device.

The invention is explained in more detail below with reference to the drawing. It shows:

Fig. 1 is a schematic representation of a lifting device with a hydraulic relief device according to the invention.

The lifting device 1 shown in Fig. 1 consists essentially of a lifting cylinder 2, a hydraulic pump 3, a remotely controlled directional control valve 4, a lifting pressure line 5 and a

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Oil return line 6 and an oil reservoir 7. A relief device 8 is coupled into the lifting pressure line 5, which is made up of two hydropneumatic pressure accumulators 9, 10, a display pressure gauge 11, a check valve 12, a relief valve 13 and a residual pressure valve 14. A distributor housing 26, shown schematically in phantom line, is provided to accommodate the check valve 12, the residual pressure valve 14 and the relief valve 13, whereby an extremely compact design is achieved. The two pressure accumulators 9, 10 and the display pressure gauge 11 are arranged on the outside of the distributor housing 26. The coupled relief device 8 divides the lifting pressure line 5 into a pressure line section 15 and an output line section 16. The pressure line section 15 connects the directional control valve 4 arranged on a commercial vehicle 27 (phantom line) via a quick coupling connection 18 with a corresponding pressure connection P of the relief device 8. The relief device 8 is connected to the lifting cylinder 2 via an output connection A and via the output line section 16. The lifting cylinder 2 is connected to the oil reservoir 7 via the oil return line 6 via a second quick coupling connection 19 and via the directional control valve 4, so that in the relieved state or when lifting an attachment

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Oil from the lifting cylinder 2 flows back into the oil reservoir 7, from where it is sucked in by the hydraulic pump 3 via a corresponding suction line 28.

When lifting, the piston rod 20 moves forward in the direction of arrow 21 so that leakage oil in the front chamber 22 of the lifting cylinder 2 is pressed back into the oil reservoir 7 via the oil return line 6. When unloading or lowering, the piston rod 20 of the lifting cylinder 2 is moved in the direction of arrow 23 by the weight of the attachment so that the attachment is lowered until it touches the ground.

When lifting, as shown in the directional valve position in Fig. 1, the pressure connection P of the relief device 8 is pressurized, which is transferred via the check valve to the pressure accumulators 9 and 10 or to the pressure gauge 11. When a certain filling level or pressure is reached in the pressure accumulators 9, 10, the lifting process begins with the lifting cylinder 2.

When the pressure line section 15 is lowered or depressurized, pressure oil flows through the outlet line section 16 via the residual pressure valve 14 and the pressure line section 15 back into the oil reservoir 7, whereby in this case the directional control valve 4 is switched to its second switching position and the

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Lifting pressure line 5 is short-circuited with the oil return line 6. When a predetermined pre-pressure is reached, which is applied to the pressure accumulators 9, 10 and to which the residual pressure valve 14 is set accordingly, the residual pressure valve 14 closes so that the residual pressure in the output line section 16 as well as in the pressure accumulators 9, 10 and the display pressure gauge 11 is maintained. When lowering or after lowering the attachment, the hydraulic pump 3 is switched off.

Due to slight fluctuations of the attachment due to unevenness of a road surface on which the attachment, for example a snow plow, slides along, the piston rod 20 moves alternately in the direction of the arrows 21, 23, so that small quantities of pressure oil are pressed into the two pressure accumulators 9, 10 via the outlet line section 16 or are pressed back into the lifting cylinder 2 by the pre-pressure when the piston rod 20 moves in the direction of the arrow 21. During this back and forth movement of the piston rod 20, the pre-pressure, which is essentially maintained by the pressure accumulators 9, 10, changes within small limits.

During longer periods of operation, leakage oil enters the front

Chamber 22 of the lifting cylinder 2, so that the pre-pressure drops slightly as the operating time increases. When a predetermined minimum value is reached, which can be read off on the display pressure gauge 11, the hydraulic pump 3 is manually activated so that the pre-pressure in the pressure accumulators 9 can be raised to the predetermined value again via the check valve. The display pressure gauge 11 is provided for checking or setting the pre-pressure, on which the set pre-pressure can be read off.

The relief device 8 according to the invention provides a relief device for lifting devices for lifting attachments on commercial vehicles, which is extremely simple and inexpensive in its construction consisting of a few components. Furthermore, the relief device according to the invention consists of extremely robust individual parts, so that the relief device has a high degree of operational reliability. In addition, no constant energy losses in the form of heat losses are produced, since the hydraulic pump is only switched on when lifting or for short-term pressure regulation of the pre-pressure to reduce the contact force of the attachment on the ground.

Claims (5)

Applicant: Matthias Gießler, D-77933 Lahr Description: Hydraulic relief device for attachments Protection claims 1. Hydraulic relief device for a hydraulic lifting device of a commercial vehicle for lifting an attachment from a lowered working position into a raised transport position with a hydraulic lifting cylinder that can be pressurised by a hydraulic pump, the hydraulic lifting pressure line of which can be pressurised with a residual pressure by the relief device in the working position to reduce the contact force of the attachment on the ground, wherein a pressure accumulator is provided to maintain the residual pressure,
characterized, that a check valve (12) is provided in the lifting pressure line (5), which opens when the attachment is raised and closes when the attachment is lowered and that a residual pressure valve (14) is arranged in a shunt line (25) parallel to the check valve (12), via which the pressure in the lifting cylinder-side output line section (16) of the lifting pressure line (5) is reduced until a predetermined residual pressure is reached during lowering, and that the pressure accumulator (9, 10) on the lifting cylinder side is hydraulically coupled to the output line section (16) between the check valve (12) or the residual pressure valve (14) and the lifting cylinder (2). 2. Relief device according to claim 1, characterized in that the pressure accumulator (9, 10) is formed by a hydropneumatic pressure accumulator (9, - 10). 3. Relief device according to claim 1 or 2, characterized in that a relief valve (13) is provided parallel to the residual pressure valve (14) and the check valve (12), via which the lifting pressure line (5) can be completely relieved. 4. Relief valve according to one of claims 1 to 3, characterized in that two hydropneumatic pressure accumulators (9, 10) are provided, which are arranged opposite one another on a distributor block (26). are arranged, in which the residual pressure valve (14), the check valve (12) and the relief valve (13) are integrated. 5. Relief device according to one of claims 1 to 4, characterized in that a display manometer (11) is provided for setting and monitoring the residual pressure.