EP0185894A1 - Hydraulic system - Google Patents

Abstract

Hydraulic system (1) with a small-capacity oil tank (7), an oil- delivery pump fed from the oil tank (7), oil consuming devices supplied with hydraulic oil by the oil-delivery pump, a return line (2) leading from the oil consuming devices to an oil cooler (5 or 13) connected to the oil tank (7), and also a regulating device which brings the hydraulic oil at the start from low temperatures to optimum operating conditions in as short a time as possible and keeps the operating conditions constant during operation as far as possible within narrow limits, in which the cooling is regulated without moving parts, more specifically by virtue of the fact that the regulating device is designed like a flow-resistance balance, has at least one by-pass line (4 or 9) through which oil flows rectilinearly at least in the working area and with an abruptly constricted cross-section of flow, the length of which is negligible, which by-pass line (4 or 9), bridging the oil cooler (5), is connected indirectly or directly to the return line (2) and the oil tank (7) and whose cross-section of flow, at the constricted point (8), has a flow resistance adapted to the flow resistance of the oil cooler (5), and that the flow resistance of the oil cooler (5) is at least half the flow resistance of the constricted point (8) when the hydraulic oil is in the optimum operating state. <IMAGE>

Description

The invention relates to a hydraulic system with a preferably small-volume oil tank, an oil feed pump fed from the oil tank, oil consumers supplied with pressure oil from the latter, a return line leading from these to an oil cooler connected on the outlet side to the oil tank, and with a control device which deepens the hydraulic oil when starting Bring temperatures to optimal operating conditions for as short a time as possible and keep these optimal operating conditions constant during operation within the narrowest possible limits.

In hydraulic systems, the operating medium "hydraulic oil" has to fulfill several tasks. The primary task is to transport the energy induced by the hydraulic pump in the form of pressure and deliver it to the consumer, where it is converted into mechanical work. The second task is to move the moving parts of the system, i.e. H. to lubricate the sliding surfaces. Another very important task is to absorb the losses that occur in the form of heat each time energy is converted into mechanical work and, in particular, to remove them from the heat-sensitive parts of the system, so that this heat is transferred to the environment, in particular ambient air, at a suitable point can be delivered. Hydraulic oils have a temperature-disproportionate viscosity; at low temperatures the viscosity is very high, at high temperatures it is low and can drop so much that the important lubricating film on cohesive surfaces deepens its cohesion, thereby questioning the lubricating function. At particularly low temperatures, the viscosity can become so high that it causes a very high proportion of the losses in the hydraulic system due to the correspondingly high flow resistance

For this reason, the manufacturers of hydraulic systems try to allow them in such a way that the lowest possible viscosity within a temperature range that is as wide as possible, but which is considerably above the usual ambient air temperatures, at which the mechanical efficiency of the hydraulic system reaches its optimum and at the same time the viscosity is sufficiently high to ensure reliable lubrication. Naturally, this range of optimal operating conditions for the hydraulic oil cannot be expanded at will; rather, it is relatively narrow in practice.

As a result, all hydraulic systems work with reduced poor efficiency until the optimal operating conditions of the hydraulic oil are reached. On the other hand, hydraulic systems are exposed not only to the risk of malfunctions as a result of gas and / or foam formation and to the formation of solid precipitates from the hydraulic oil, but also to the risk of moving parts being destroyed if the range of optimal operating conditions for the hydraulic oil is exceeded in the direction of higher temperatures .

In structurally very simple, primitive hydraulic systems, oil tanks of extremely large capacities are used, so that the heat generated during operation is "buffered" in the large oil volume, e.g. T. can be released into the ambient air through the correspondingly large surfaces of the container. Such systems are simple in construction, but they are expensive to operate. For the reasons already mentioned, hydraulic oil is a very expensive product; filling the container with the required amount causes correspondingly high expenses. As hydraulic oil wears out or wears out, i.e. H. after a certain time, the length of which depends on the frequency and duration of weary operating conditions, becomes inoperative, i.e. must be replaced, the operating expenses are very high because very large quantities of expensive hydraulic oil always have to be bought at certain intervals. Systems of this type also work for a very long time with reduced mechanical efficiency after commissioning; because it takes a long time before the large oil volume reaches the optimal temperature, i.e. H. the optimal operating conditions is warmed. Since the heat transfer from the oil to the tank wall and from the tank wall to the ambient air presents itself as a rather unstable condition, which, among other factors, also depends on the intrinsic temperature of the ambient air, it often happens in systems of this type that the heat buffering capacity of the large one Exhausted oil quantity either due to peak loads in the hydraulic system or due to high ambient air temperatures or due to the simultaneous occurrence of both factors; the system must then be switched off due to the risk of overheating. Such systems are therefore expensive to operate and do not guarantee reliable continuous operation with alternating loads.

To prevent the hydraulic oil from overheating, hydraulic systems have been equipped with oil coolers that cool the oil coming from the return line and return it to the tank. The oil coolers were exposed to a strong flow of cooling air with motor-driven fans or were also cooled with water. This increased the construction effort and the susceptibility to maintenance and malfunction of the hydraulic systems, and the mechanical efficiency was impaired because fan motors consume energy. A shortening of the start-up time, at which the hydraulic oil is too cool to guarantee optimal operating conditions, was not achieved. Rather, the start-up time was extended by the cooling that works immediately when starting

A technical improvement was represented by hydraulic systems in which the temperature-dependent valves, depending on the temperature, either direct the hydraulic oil coming out of the oil return line either bypassing the cooler directly into the tank, in the case of rising temperatures, partly into the tank, partly through the cooler, and at high temperatures exclusively through the Coolers conducted. Since the capacity of the oil tanks of these systems was still very large, this additional construction effort did not lead to a significant reduction in the start-up time

Due to the complicated nesting of oil containers of different volumes, a starting volume was divided from the total oil quantity in other known systems, which achieved a quicker achievement of the optimal operating conditions of the hydraulic oil through a small quantity. However, as soon as the additional quantity of hydraulic oil was included in the operating cycle, there were strong pendulum phenomena, in which the hydraulic oil repeatedly flowed into the oil circuit below the optimal operating conditions and put the cooling out of operation until the newly added part could also have optimal operating conditions. This process was repeated until the entire large volume of oil was warmed up.

However, even this condition did not guarantee a stable mode of operation because the oil coolers ventilated by means of fans must be designed for an air flow rate that corresponds to the maximum heat that can be expected. If such a system operated at partial load, the oil in the cooler was cooled more than necessary, causing new instability. This mode of operation is disadvantageous because hydraulic oil is sensitive to changes in temperature with changes in viscosity. Changes in the viscosity of the hydraulic oil cause changes in the operating behavior of the system's consumers.

The most optimal way of working to date has been achieved with hydraulic systems whose oil tanks have a very small capacity and in which the oil cooler, to which the oil from temperature-dependent valves is supplied as required, works as an air convection cooler.Thanks to the low oil volume, the valve or the temperature-dependent valves work together go through the start-up phase extremely quickly, without the pendulum phenomena that occur with large oil volumes, and there is no instability even after reaching the lifting phase with alternating load, because the air throughput in the oil cooler adjusts itself as an air buoyancy flow without further action by the heat offered by the oil d . that is, with very warm oil, there is a correspondingly strong air flow that dissipates heat; with less warm oil, the air flow is also weaker and less heat is dissipated. In addition to these considerable operational advantages, this system is also characterized by a high degree of efficiency, since no energy is required to drive a fan and the start-up phase, in which the system works with poor efficiency, is extremely short. In addition, there is also the low oil consumption, the lower construction costs because the fan is missing and the higher operational reliability; Advantages that have a very positive effect on the costs of operating a hydraulic system.

All hydraulic systems with controlled cooling work with one or more temperature-dependent valves. Such valves have moving and therefore wear-stressed parts, are expensive to buy, require constant maintenance and care, must be equipped with temperature-sensitive parts, bimetallic or electronic temperature sensors and valve actuators that can be actuated by them, and can, precisely because they are devices with moving parts acts, u. Block by oil deposits, which interferes with the temperature control.

The invention is based on the already described prior art, the task of creating a hydraulic system of the type mentioned, in which the cooling is controlled without moving parts.

To solve this problem, the hydraulic system mentioned at the outset is characterized according to the invention in that the control device is designed in the manner of a flow resistance balance, has a by-pass line which is flowed through in a rectilinear manner at least in the working area and has an abruptly narrowed flow cross-section, the length of which is negligibly small, with the return line and the oil tank, bridging the oil cooler, is directly or indirectly connected and the flow cross-section at the constriction point has a flow resistance adapted to the flow resistance of the oil cooler, and that the flow resistance of the oil cooler is at least half less than the flow resistance of the constriction point is when the hydraulic oil is in optimal operating condition.

The essential difference of the hydraulic system designed according to the invention compared to the described known designs is that although the oil temperature is kept constant by controlled cooling, and in a much better consistency than before, but as a metrological variable no longer, as before, the temperature of the oil , but its bisque is used. Although the viscosity depends on the temperature of the oil and thus a certain temperature range defines optimal operating conditions of the oil, because then the viscosity is also within an optimal range, the detection and technical exploitation of the viscosity of the oil is a much more adapted procedure for the hydraulic system. After all, the way the pressure oil consumers work depends on the viscosity and the quality of the lubricating film is guaranteed by the viscosity of the oil and the efficiency of the system is greatest in an optimal viscosity range.

Known basics from theoretical hydraulics are decisive for the function of the regulation of the hydraulic system designed according to the invention, but have not been used in the sense of the invention so far. Thus, the resistance of a line through which a liquid flows in a straight line with an inconsistent, i.e. H. Sudden, narrowing of the cross-section of small or negligible length of the narrowing is almost independent or constant from the viscosity of the liquid. For the rest, however, the resistance of a line which has a certain cross section and a certain length can be varied depending on the viscosity. The longer the line is, the greater the resistance, and it also increases with the viscosity of the liquid, while decreasing as the viscosity decreases. In the hydraulic system designed according to the invention, two flow resistances are thus connected in parallel between the return line and the oil container, the by-pass line with the constriction representing a constant resistance regardless of the respective viscosity of the hydraulic oil, but the oil cooler forms a resistance, the size of which high viscosity high, low viscosity low.

In practice, the two parallel flow paths, each of which must be able to direct the oil flow from the return line to the oil tank alone, form a "flow resistance balance", which at one end provides the constant flow resistance, which is provided only by the pressure of the liquid and allows liquid quantities depending on the viscosity to flow through behind the constriction or orifice or the pressure difference, while at the other end of this balance the cooler forms a viscosity-dependent flow resistance, by means of which the flow rate increases in a viscosity-dependent manner in the sense of an inclination of the balance when the viscosity decreases, and reduced as the viscosity increases.

If the two resistors are matched to one another in such a way that the flow resistance of the oil cooler is at least half as low as that of the constriction in the by-pass line at the viscosity that the hydraulic oil has at optimal operating conditions, then an automatic function is activated Branch of the oil flows through the cooler and through the by-pass line, which is viscosity-dependent. Since the viscosity is changed by the supply of heat from the hydraulic system, the flow rate through the cooler changes automatically. Since the viscosity changes disproportionately to the temperature, this cooling control also works much more sensitively and sensitively than any temperature-dependent control could; the optimal operating conditions of the oil are therefore kept constant within much narrower limits than with temperature-dependent cooling.

This cooling also starts immediately and continuously as soon as cooling is required. In the case of temperature-dependent valve-controlled cooling, this start of cooling can be done, if at all only approximately with very elaborately designed and expensive valves. As a rule, these valves open disproportionately from the closed position and allow more oil to pass through than would be required during the respective start phase or during the transition to the work phase with cooling, while the increase in oil flow through these valves is disproportionately small if stronger cooling is caused by higher cooling Oil temperatures are required

Another important advantage that the invention offers over temperature-dependent valve-controlled cooling of hydraulic systems is that they start from extremely low temperatures. In such situations, the viscosity of the cold oil is hundreds of times greater than at operating temperature. If, after a certain start time, oil is to flow into the cooler by opening the control valve, the highly viscous oil in it forms a so-called oil plug, which temporarily prevents flow through the cooler. This can lead to disadvantages. According to the invention, however, the cooler is never completely separated from the oil circuit, but takes part in the oil circuit, even if with minimal proportions, so that the extremely cold, highly viscous oil in the cooler is gradually preheated during the general starting phase. Thus, with increasing cooling requirements after the start-up phase, there can also be a smooth transition of the oil flow through the cooler.

The best mode of operation by far is obtained if the hydraulic system designed according to the invention is equipped with an air convection cooler. With air convection cooling, the cooling air flow and thus the heat emission or cooling of the oil in the oil cooler regulates itself depending on the heat supply of the oil. At low ambient temperatures and in the operating state, the oil does not get into the hydraulic user undercooled and never reaches the hydraulic user as undercooled within the underlying cooling capacity. During the operating state, even with strongly changing heat supply / heat accumulation due to different loss in the hydraulic system, with extremely different ambient temperatures, favorable operating conditions of the oil are still achieved after a short start-up time, due to almost fluctuating oil viscosity (which is important for the economic operation of the hydraulic system) and also free of discontinuous, step-like changes. Precisely because the oil viscosity (depending on the oil temperature in the following) is the measured variable for controlling the oil cooling, because in the large working range of hydraulic oils and other oils in hydraulic systems from low to high oil temperatures the viscosity differences to the oil temperature difference steadily decrease from initially disproportionate to underproportional proportions , this ultimately means that larger oil temperature differences at high oil temperatures have smaller viscosity differences. Higher oil temperatures in turn improve the heat transfer to the cooling air. The overall viscosity-dependent control behavior of the device is thus more sensitive and steadier than with temperature-dependent control.

If the invention is used for hydraulic systems with fan cooling or water circulation cooling, it avoids the previously common pendulum phenomena of cooling in these systems, which occurred during the starting phase and under alternating loads. As is known, the amount of the heated oil flowing to the cooler is regulated in each of these systems, but the heat output or the heat withdrawal from the oil is uncontrolled, in contrast to the air convection coolers. H. corresponds to the maximum power for which the cooler is designed. In these systems, oil with a significant low temperature leaves the cooler, which means that the temperature-dependent valves operate with less heating of the oil in the oil consumption and. U. again close the oil flow to the radiator, etc., causing pumping or pendulum signs. However, if control is carried out according to the invention, the result of the supercooling of the oil in the cooler being an increase in viscosity and thus an increase in the flow resistance of the cooler. This changes the distribution ratio of the oil flows through the cooler and the by-pass with its constriction so that the confluence of the two partial flows in the oil tank results in oil with optimal operating conditions.

Of particular advantage is the fact that any temperature-dependent valve-controlled hydraulic system can be converted into a system that is controlled according to the invention according to viscosity. Instead of the valves or the valve, the by-pass line is installed with the appropriate constriction. The size of the constriction can either be determined graphically (with knowledge of the flow resistance of the cooler and its heat emission) or experimentally.

Since the correlations are more difficult than specified in the previous illustration for easier grasping of the inventive concept, the exact theory is also discussed in detail.

In other words, the invention provides, instead of the oil temperature-regulated control valve, which if necessary directs the entire oil flow or partial flow via the oil cooler into the container, an oil viscosity-independent, only oil flow quantity-dependent control aid (from the pressure difference before and after Control aids dependent) to be used, to split the line coming from the hydraulic user into two lines that are capable of absorbing the total oil flow, to lead a line to the oil cooling system in the oil cooler around which the coolant flows, and to lead a line further from the oil cooler to the tank , with the second line leading directly to the tank and providing an orifice or partial orifice as a control aid in this line to regulate the oil flows in the lines to the oil cooling system and directly to the tank via the orifice by structurally influenceable and selectable flow resistances in the oil cooling system and in the orifice .

This aperture can be connected in cooperation with the cooling system of the air-cooled oil convector driven by self-convection.

This diaphragm can also be provided in cooperation with a liquid-cooled oil cooler, the cooling system of which is provided in a container, the container being provided with inflow and outflow for the coolant, or the cooling system being in a free-flowing coolant flow.

The diaphragm is a disk with a sharp-edged central bore or a disk in the form of a circular section or other shaped circular section, the disk being fastened tightly at its edge in the line.

From orifices it is known that the flow rate Q _", apart from the pressure before and after the orifice, is influenced slightly by the density kg / m ³ and not by the viscosity (kinematic viscosity My or cSt (qmm / s) of the oil is influenced by a flow factor alpha that can be structurally influenced, the depends on the cross section of the orifice F _Bi to the cross section of the comprehensive tube F _R For known orifice shapes, alpha can be determined from known diagrams, according to the ratio m = (F _Bi : F _R ) ^2. The flow factor alpha can be ascertained for specially designed orifices. The flow rate Q, through the orifice plate is determined from the known formula Q, = Alpha x F _BI x (2 xgx Δp: γ) ^1/2 ; where Δ p is the differential pressure state before and after the orifice as the flow loss R, in the orifice.

In oil-flow tubes or plates in oil cooling systems of oil coolers and in laminar oil flows (Re 2500), which predominantly prevail in these, the oil flow loss (R,) is known to be linearly dependent on the flow rate (Q,) or the oil flow rate w (qmm / s) and very high Disproportionately dependent on the oil viscosity (via the drag coefficient δ = 64 x Re ^{- 1} , thereby Re = wxdx My ^-1 ; where d = inner tube diameter or hydraulic diameter, My = kinematic viscosity of the oil at the relevant oil temperature (qmm / s) ).

Since the flow loss increases or decreases with turbulent oil flows in plates or tubes, the control effect on the oil is changed somewhat by the relationship for Re _turb = 0.316 x Re ^{0 25} .

, wobei L die Strömungslänge im Rohr oder in der Platte ist.The flow resistance R in the tube or plate system is calculated using the known formula Δ p

, where L is the flow length in the pipe or in the plate.

For the function of the oil cooling device with the corresponding components, it is therefore important that from a cold initial operating state at favorable oil operating temperatures, the amount of heat (J _v ) that results from the transmission losses decreases, approximately the decrease in oil viscosity at the corresponding temperature of the heating oil, that the amount of oil by the cooling system (Q,) of the oil cooler, through which predictable, predominantly viscosity-dependent flow loss characteristics (R,) are determined, and on the other hand, depending on the constructively influenceable, flow-dependent pressure loss characteristics (Q,) of the orifice plate (R,) initially very low, with increasing oil heating then increasing oil share (Q,) is directed to the oil cooling system, near the favorable oil viscosity and therefore oil temperature a no longer increasing oil flow (Q,) is directed to the oil cooling system, so that the initially low oil flow (Q ,) is cooled more than the larger oil flow (Q,) with less Oil viscosity (higher oil temperature), the two oil flows (Q ₁ , Q,) with their different oil temperatures result in or set an oil mixing temperature in the oil tank, the mixing temperature of which is closer to the orifice oil flow (Q ₂ ) in the colder (or cold) operating state, then increasing to Steady state of the device and at maximum ambient temperature the oil temperature in the inlet to the hydraulic oil consumer is close to the outlet temperature of the oil cooling system (Q,) that the resulting total oil flow resistance (Rg _es ) of the device is significantly lower than a flow resistance (R, or R,) with the corresponding total quantities (Qg _es ) in a parallel line alone, the heat transfer from the flowing oil to the cooling medium (heat transfer coefficient K), with the logarithm. Temperature gradients (IgΔ t) between flowing oil and the cooling medium (water or air) that passes by take place in a known, complex, mutually influencing manner, also in connection with the oil heat supply from the oil user to the heat dissipated in the oil cooling system.

The incoming total oil flow (Qg _es ) is divided into the two lines (with Q, to the oil cooling system, with Q, through the orifice to the tank), according to the relevant physical laws, the distribution of the oil flow quantities occurring in parallel lines depending on the flow resistances that occur . The flow losses in the oil cooling system (R,) with the oil quantity Q _1, as well as the flow losses through the orifice R, for the oil quantity Q, can be determined graphically at the corresponding oil temperatures or arithmetically by the known relationship = +, where Rg _is the result Total flow resistance of both parallel lines is. Furthermore, through the relationships R, x Q, = R, x Q ₂ , Q, ⁺ Q, ₌ Qg _es ; where ibei _be R, and R, which are to be considered in the aperture and in the oil cooling system resulting flow resistances in the respective Öttemperaturen and the total quantity Q _ges.

A value R, = (20 - 200) R is required to achieve a favorable regulating behavior of the oil flows, in the cold operating state of the hydraulic system, at the highest oil temperature or in the warm operating state of the oil, the ratio of the flow resistances (R,) of the orifice should be flow loss resistors (R,) of the oil cooling system which 2 to 20-fold value ^{correspond (R,} warm = (2-20 R) warm).

At low ambient temperatures, which are usually also the conditions from the cold start-up state, approx. 80 to 98% of the total oil quantity Qg _es through the panel directly to the oil tank until the corresponding oil heating (corresponding to the design and dimensioning of panel and heating surface). With an operationally favorable oil viscosity range (and thus dependent favorable oil temperature), approx. 5 to 25% of the total oil quantity Qg _es gets directly into the oil tank via the cover (bypassing the oil cooling system).

With the small amount of oil Q initially emanating from the start of commissioning, when the start-up conditions are very cold, due to the oil cooling system, the oil mixing temperature in the oil tank at the outlet to the oil consumer is reduced slightly than the oil temperature of the oil flow Q through the orifice. However, by arresting the orifice to the oil cooling system, it is achieved that from the start of the commissioning of the hydraulic system, a correspondingly small partial oil flow Q, with low flow velocities (with a correspondingly low flow resistance requirement R,) is conveyed through the oil cooling system. This prevents a stagnant "oil plug".

The orifice with the relatively low flow resistance (R,) also acts in the extremely cold state as a safety device against excessive return pressure to the hydraulic user, which could occur as a result of high oil flow resistances in the oil cooling system.

The heating surface formed from the oil-flowing oil cooling system to the surrounding cooling medium is determined for the most unfavorable operating conditions; these are the minimum permissible oil viscosity and at the same time the maximum desired maximum value of the oil temperature and the largest possible ambient temperature of the cooling medium.

The heating surface cannot be changed during operation. The heating surface _size is determined from the relationship F _Hzfl = J xk ^-1 x LgΔ- ¹ , where J is the excess heat quantity to be transferred per unit of time, k the heat transfer coefficient of oil to the surrounding Cooling medium, IgΔt is the logarithmic temperature difference between flowing oil and cooling medium; these values change from the start of operation to the steady state.

This device in the assignment of the oil cooling system, the oil tank, the orifice as control aid and to the user of the useful oil is thus able to quickly bring the oil from an extremely high oil viscosity range to an operationally favorable oil viscosity range. In the event of changes in load, the oil viscosity range is maintained, even at different ambient temperatures of the coolant and in a relatively small viscosity fluctuation range (the operation does not interfere or impair).

Particularly advantageous designs of the screen are characterized in claims 2, 3 and 4.

Exemplary embodiments of the hydraulic system designed according to the invention and overview graphics of the operating parameters are shown in the figures.

• Fig. 1 : eine Schemaansicht einer erfindungsgemäß ausgebildeten Hydraulikanlage mit Luftkonvektionskühfung,
• Fig. 2 : eine der Fig. 1 entsprechende Ansicht einer Hydraulikanlage mit Wasserkühlung,
• Fig. 3 : eine der Fig. 2 entsprechende Ansicht einer Hydraulikanlage mit strömendem Kühlwasser,
• Fig. 4 : eine Ausführungsform des erfindungsgemäß vorgesehenen Regelhilfsorganes in Form einer Blende,
• Fig. 5 : eine Ansicht einer in einer Muffe angeordneten Blende,
• Fig. 6 und 7 : einen Längs- und einen Querschnitt einer weiteren Ausführungsform und Anordnung der Blende,
• Fig. 8 : eine Grafik, die das ermittelte Strömungs-Vertustverhalten der Blende und das des Kühlsystemes bei einer erfindungsgemäß ausgebildeten Hydraulikanlage wiedergibt,
• Fig. 9 : eine weitere Grafik des Betriebsverhaltens der erfindungsgemäß ausgebildeten Hydraulikanlage und
• Fig.10 : eine Grafik, die das Betriebsverhalten der erfindungsgemäß ausgebildeten Hydraulikanlage bei unterschiedlichen Lufttemperaturen und Verwendung eines Luftkonvektionsühlers gemäß Fig. 1 wiedergibt.

It shows

• 1: a schematic view of a hydraulic system designed according to the invention with air convection cooling,
• 2: a view corresponding to FIG. 1 of a hydraulic system with water cooling,
• 3: a view corresponding to FIG. 2 of a hydraulic system with flowing cooling water,
• 4: an embodiment of the auxiliary control element provided according to the invention in the form of an aperture,
• 5: a view of an aperture arranged in a sleeve,
• 6 and 7: a longitudinal and a cross section of a further embodiment and arrangement of the panel,
• 8: a graphic which shows the determined flow-loss behavior of the orifice plate and that of the cooling system in a hydraulic system designed according to the invention,
• 9: a further graphic of the operating behavior of the hydraulic system designed according to the invention and
• FIG. 10: a graphic which shows the operating behavior of the hydraulic system designed according to the invention at different air temperatures and when using an air convection cooler according to FIG. 1.

In Fig. 1, the arrangement of the effective components of the device for needs-based controlled cooling of oils of a hydraulic device is shown schematically, in which the oil cooling system 5 consists of tubes or plates, which is located in a convectionally air-flowed oil cooler 13. The advantage of choosing air as the cooling and heat-dissipating medium is that it can be used at ambient temperatures well below 0 degrees Celsius without further effort. From the hydraulic oil user 1, the oil first reaches the return line 2 and is divided into two lines 3 and ₄ . The line 3 conveys the oil via the air-cooled oil cooling system 5, via the subsequent line section 6 into the oil tank 7, which is advantageously equipped with a small capacity.

The by-pass line 4 conducts the oil via the orifice 8 as a regulating aid with the line 9 connected to it to the oil tank 7. From the oil tank 7, the oil is conveyed to the oil user ₁ via the suction line 10 with the feed pump 11 and the feed line ₁ 2 . The open arrows represent, for example, the ice-sifting air flow as a dissipating cooling medium. When starting up and shortly after starting up the hydraulic system from low ambient temperatures, the oil is drawn off from the oil tank 7 via the suction line 10 and through the feed pump 11 via the oil user 1, Via the return line 2 to the beginning of lines 3 and ₄ promoted by the high flow resistance in the cold start-up state in the oil cooling system 5, which is a multiple of the flow resistance of the orifice 8, the largest part (up to 98%) of the total oil quantity through the Aperture 8 conveyed to the oil container 7. The small amount of residual oil is led through the oil cooling system 5 and the subsequent line section 6 to the oil tank 7. The initially low oil flow through the oil cooling system 5 is correspondingly cooled down. Both oil flows from lines 9 and 6 (or 3 and 4) mix to a mixing temperature , which is initially close to the oil temperature, from the uncooled line 9.

Due to the higher power loss at low oil temperatures, the oil heats up quickly; according to the power loss and the oil quantities to be heated from the oil tank content and the line contents, the heat absorption capacity (storage capacity) of the masses of the entire hydraulic system.

Up to a definable, favorable oil viscosity range (and thus the oil temperature range of an oil type), the oil is conducted in increasing amounts to the oil cooling system 5 of the oil cooler 13.

In the steady state of the hydraulic device, ie when the heat supply in the oil cooling system 5 (from the heat of the hydraulic system) has adjusted to the heat output of the oil in the cooling system 5 (air cooler 13), the oil mixing temperature in the oil container 7 is somewhat lower at a cold ambient temperature and thus the oil viscosity somewhat higher than at high ambient temperatures at which the oil mixing temperature is somewhat higher (and thus the oil viscosity slightly lower), but still in the operating range. For an example, the oil viscosity of 38 cSt results for the frequently used oil HLP ₄ 6 at an ambient air temperature of minus 30 degrees Celsius and an oil mixing temperature of approximately 44 degrees Celsius; at an ambient air temperature of minus 35 degrees Celsius, the oil mixing temperature of approx. 73 degrees Celsius and the associated oil viscosity of 1 ₄ cSt (for example, oil viscosities to the oil temperature 15000 cSt at minus 35 degrees Celsius, 550 cSt at 0 degrees Celsius, 130 cSt at plus 20 degrees Celsius , 70 cSt at plus 30 degrees Celsius oil temperature).

The resulting total pressure loss (R _tot ) from the beginning of the lines 3 and 4 to the outlet of the lines 6 and 9 in the container 7 are in the entire oil temperature application area within the scope of known regulated oil cooling devices or else below, without additional services and expenses; because even known control devices are dependent on viscosity in the loss of flow pressure. In addition, the Flow resistances of the cooling system and control device in known devices add up by connecting the flow resistances in series; decrease according to the present examples with the parallel connection of the flow resistances.

In Fig. 2, the oil cooling system 5, consisting of tubes, is provided in a water-circulating container 18, with cooling water inflow 19 and cooling water outflow 20, shown with the components and the control mode of operation of the oil flows as described in Fig. 1. Appropriate devices must only be provided for heat dissipation with water, but these are also always required for hydraulic devices with liquid-cooled oil coolers.

In Fig. 3, the oil cooling system 5, consisting of tubes or plates, is shown in a flowing liquid stream 14 which is guided by the socket 21, the device operating in the same manner as described above.

4 shows the auxiliary control element, the orifice 8, in an embodiment in which an active part, the orifice body 15, is screwed together as a flat and thin disk with its bore d _Bi between two flanges 16 with the lines 9 and 4 connected to it is. According to the description and the example shown in FIG. 8, the inner diameter d _R and the cross section of the pipes 4 and 9 as another active part directly influence the oil flow and oil resistance behavior, the oil viscosity-related oil flow Q, through the oil cooling system and the oil quantity-related oil flow Q. the container.

5 shows the regulating auxiliary element, the diaphragm 8, in an embodiment in which the diaphragm body 15 is arranged in the sleeve 17 connecting the lines 4 and 9.

In FIG. 6, 7 in longitudinal section in Fig. In cross-section as seen in the pipe longitudinal axis, a visor body shown in the embodiment of a so-called partial screen 15, in which the aperture effect instead of a bore through a portion of the optional height h in the visor body ₁ 5 is done. The pipe cross-section and the free area, due to h in the connection of the flanges, determine the flow factor alpha.

Partial orifices are known to produce steadily increasing or decreasing flow losses even with low oil flow rates. It is advantageous if the partial diaphragm edge is vertical in the horizontal position of lines 4 and 9; this avoids that air or solid excretions can get stuck before or after the diaphragm body 15.

FIG. 8 shows the determined flow loss behavior of the orifice 8 (with R,), almost oil-viscosity and temperature-dependent, with R ₁ , in an exemplary device. On the abscissa are the oil quantity proportions of Q, and Q, of Qg _es (0 - 100% and ₁ 00 - 0%) on the normal scale, on the ordinate the associated flow losses of the oil cooling system (R,) and orifice ( R,) plotted. The points of intersection of the lines at the corresponding oil temperature or oil viscosity on the abscissa give the corresponding proportions of oil Q or Q ₂ that flow to the oil cooling system 5 or through the orifice 8, and on the ordinate the resulting total pressure loss Rges in bar between the line end 2 and the oil tank 7.

It can be seen that by means of structural measures in the orifice 8 or the cooling system 5, the total pressure loss Rg _can be changed or adapted by the individual losses R, and R, and can be adapted to the desired or required oil viscosity behavior and oil cooling behavior of the device. It is therefore sufficient to replace the diaphragm body 15 according to FIGS. 4 to 7 with another diaphragm body 15 in order to correspond to changed oils and operating requirements.

FIG. 9 shows the distribution determined according to FIG. 8, depending on the oil viscosity and temperature, the oil flows through the orifice Q, and through the oil cooling system of the oil cooler 13 (according to FIG. 1) and shows the value of the ratio factor x = Q ,: Q ₂ , which determines the mixing temperature of both oil flows in the oil tank.

• Linienzugbezeichnungen:
  • a) die Ölwärmeabgabe und Wärmeübergabe an das Kühlmedium (Luft) im Ölkühler,
  • b) die Öleintrittstemperatur in das Ölkühlsystem (zugleich Öttemperatur aus dem Hydrauliknutzanwender),
  • c) die Ölaustrittstemperatur aus dem Ölkühlsystem (hier luftgekühft),
  • d) der sich einstellenden Ölmischtemperatur im Ölbehälter.
  • e) der kinematischen Zähigkeit des Öles zum Hydraulikölnutzanwender,
  • f) der Austrittstemperatur des Kühlmediums (hier Luft) aus dem Ölkühlsystem,
  • g) der beispielsweisen Strömungsverluste des Kühlmediums (luft) im Ölkühlsystem (zugleich konvektiver Luftströmungsantrieb),
  • h) der logarithmischen Temperaturdifferenz zwischen ein-und ausströmendem Öl und dem Kühlmedium (Luft),
  • i) der sich einstellende Wärmedurchgangskoeffizient k vom zu kühlenden Öl an das Kühlmedium (hier Luft), der abhängig ist von dem Öldurchfluß durch das Kühlsystem, der Kühlmittelströmungsgeschwindigkeit, der Anordnung der Rohre oder Platten zueinander. Durch die Anordnung der Rohre oder Platten zueinander, deren Größe und Abstände zueinander, läßt sich die Größe k als auch dessen Linienneigung beeinflussen. Jedoch ist damit immer eine Änderung der Kühlmediumströmungsveriuste verbunden;
  • k) Kühlmittelmenge (Luft) durch das Ölkühlsystem.

10 shows, according to the device according to the invention, in an air-cooled and convectively driven oil cooler chosen as an example (according to FIG. 1) in several lines, depending on the ambient air temperature, after reaching the steady state:

• Line names:
  • a) the oil heat emission and heat transfer to the cooling medium (air) in the oil cooler,
  • b) the oil inlet temperature into the oil cooling system (at the same time oil temperature from the hydraulic user),
  • c) the oil outlet temperature from the oil cooling system (here air-cooled),
  • d) the resulting oil mixing temperature in the oil tank.
  • e) the kinematic viscosity of the oil to the hydraulic oil user,
  • f) the outlet temperature of the cooling medium (here air) from the oil cooling system,
  • g) the exemplary flow losses of the cooling medium (air) in the oil cooling system (at the same time convective air flow drive),
  • h) the logarithmic temperature difference between inflowing and outflowing oil and the cooling medium (air),
  • i) the resulting heat transfer coefficient k from the oil to be cooled to the cooling medium (here air), which is dependent on the oil flow through the cooling system, the coolant flow rate, the arrangement of the pipes or plates to one another. The size k and its line inclination can be influenced by the arrangement of the tubes or plates with respect to one another, their size and spacing from one another. However, this always involves a change in the cooling medium flow losses;
  • k) amount of coolant (air) through the oil cooling system.

For the oil coolers 14 and 18 according to FIGS. 2 and 3, there are corresponding conditions and conditions with the orifice 8 in the interaction of the oil cooling system 5 and the oil container 7 with the different cooling media.

Claims (4)

1. Hydraulic system with a preferably small-volume oil tank, an oil feed pump fed from the oil tank, supplied by this with pressure oil Oil consumers, a return line leading from these to an oil cooler connected to the oil tank on the outlet side, and a regulating device which brings the hydraulic oil to optimal operating conditions for as short a time as possible when starting from low temperatures and keeps these optimal operating conditions constant within the narrowest possible limits during operation,
characterized,
that the control device is designed in the manner of a flow resistance balance, has a by-pass line (4, 9) through which there is a straight flow, at least in the working area, with an abruptly narrowed flow cross-section (dBl), the length of which is negligibly small, which with the return line (2) and the oil tank (7), bridging the oil cooler (5), is directly or indirectly connected and its flow cross-section at the constriction point (dBl) has a flow resistance adapted to the flow resistance of the oil cooler (5), and that the flow resistance of the oil cooler (5) is at least half less than the flow resistance of the restriction point when the hydraulic oil is in the optimal operating state. 2. Hydraulic system according to claim 1, characterized in that the constriction (dBl) is designed as an aperture-like body (8) and is installed in a tubular housing (19). 3. Hydraulic system according to claim 1 and / or 2, characterized in that the constriction is designed as a diaphragm-like body (8) and is fixed between two flanges (16) which are arranged on the by-pass line (4, 9) . 4. Hydraulic system according to one or more of claims ₁ to 3, characterized in that in the by-pass line (4, 9) a sleeve (17) is arranged which receives an aperture (8) inside

Images