FLOW CONTROL

Abstract

The present invention relates to a device for controlling the flow through an oil cooler, comprising at least one oil tank (1) and at least one oil pump (7), a means (12) for determining the oil temperature, a cooling means (4) for cooling the oil, wherein said means (4) can be circumvented via a bypass (9), as well as an engine control unit (13). The device has a means (11), controllable via the engine control unit (13) by which the oil flow can be controlled via the means for cooling (4) and/or via the bypass (9). The device further comprises a means for predictively controlling the oil flow via the cooling means (4) and/or via the bypass (9).

Description

The invention relates to a device for controlling the flow of oil through an oil cooler. In particular the invention relates to such a device for use on vehicles, such as agricultural machines.

Devices for controlling the flow of oil through an oil cooler are known. FIG. 1 by way of example shows a block diagram of working or transmission hydraulics, as are usual in mobile machines. An oil tank 1 holds a volume of oil. An oil-air cooler 4 is arranged in front of this. This cooler 4 has a bypass valve 5 connected in parallel. The actual circuit of the vehicle can vary greatly depending upon the scope of application and is simply represented by symbol 6. An oil pump 7 with constant displacement is used for supplying the circuit 6. Other pumps with constant or variable displacement can also be used in addition to this pump. If only one pump is used, usually this works with constant displacement. In front of the cooler 4 a sensor 8 is provided for determining the dynamic pressure. The bypass valve 5 connected in parallel has a spring tension of 5 bar for example. The parallel connection of the bypass valve 5 ensures that a maximum decrease in pressure of 5 bar can occur over the cooler 4. Consequently the cooler 4 is protected from too high internal pressures, which could exceed the permissible bursting pressure. Thus valve 5 represents a simple and reliable means of protection for the cooler 4.

A disadvantage of this arrangement is that even at low oil temperatures oil always flows through the cooler 4. The constant, actually unwanted, cooling of the oil at low temperatures is a side effect of this arrangement. It stems from the fact that oil warms up relatively slowly. Slow warming of the oil produces losses of efficiency and can also result in malfunction of valves or cavitation in pumps. The disadvantages mentioned occur even if an oil-oil heat exchanger or an oil-water heat exchanger is used instead of the oil-air cooler 4. In an oil-oil heat exchanger, outside air is not used as cooling agent for the cooling medium but a second oil. This oil originates from another oil circuit and, as cooling agent, has a lower temperature than the medium to be cooled.

FIG. 2 shows an alternative embodiment to FIG. 1. In this case the bypass valve 5 has been replaced by a thermostatically-controlled oil temperature regulator OETR 5. The OETR 5 has as many intermediate positions as desired. In position a, the OETR 5 opens a bypass branch 9 to the tank 1 and completely closes the inflow 10 to the cooler 4. This position is assumed at low temperatures. An expanding material element 17 which is provided on one side of the OETR 5 ensures that in the basic setting the OETR 5 assumes a position, wherein the entire oil is directed via the bypass branch 9, is provided on one side of the OETR 5. The expanding material element 17 expands when the oil temperature rises. As a result of the expansion of the expanding material element 17 against a spring 5a the valve moves to operating position b, thus gradually releasing the oil flow to the cooler 4 and gradually closing the flow to the bypass 9 for the cooler 4. In operating position b the oil flows both via the bypass branch 9 and via the cooler inflow 10. With increasing oil temperature the valve moves to operating position c, the oil now flowing completely to the cooler 4 in order to reach a high cooling capacity. The passage to the bypass branch 9 is blocked.

The disadvantage of this circuitry is that the OETR 5 represents a comparatively large and expensive component. The total amount of oil must always flow through the OETR and the oil reacts relatively sluggishly to changes in temperature. Furthermore the switching response cannot be influenced, for example to adapt to different operating conditions. The disadvantages mentioned occur even if an oil-oil heat exchanger or an oil-water heat exchanger is used instead of the oil-air cooler 4.

On this basis it is an object of the present invention to avoid the disadvantages of the aforementioned flow control devices in a simple and economical way. According to one aspect of the invention there is provided a device for controlling the flow through an oil cooler, comprising at least one oil tank, at least one oil pump, an oil temperature measurement means for determining the oil temperature, a cooling means for cooling the oil and an engine control unit wherein said cooling means can be circumvented via a bypass and the device has a flow control means controllable by the engine control unit to control the oil flow through the cooling means and/or via the bypass, characterised in that the device has a predictive means for predictively controlling the oil flow via the cooling means and/or via the bypass.

In this case predictive means the prognostic control of the oil flow. Such control prevents temperature spikes in the oil, which can develop if a circuit reacts too slowly to a rise in temperature. Predictive control for example can be implemented by data determined by a temperature sensor being passed onto an engine control unit and evaluated by this. The oil temperature in this case is used as a control variable of a characteristic diagram. Based on this the engine control unit continually calculates a temperature gradient, that is to say the temperature rise or temperature fall is continually monitored over time. If a high temperature gradient is detected, a higher cooling capacity demand results in order to prevent the permissible limit temperature of the oil from being exceeded. By closing the means for controlling the oil flow, a larger quantity of oil is fed to the cooler and thus the cooling capacity is increased.

According to a further aspect of the invention there is provided a method for controlling the oil temperature in a device, comprising the following steps:

• • Determination of the oil temperature by oil temperature measurement means transmission of the determined values to the engine control unit,
  • computation of the cooling capacity demand,
  • control of the oil flow via the cooling means and/or via the bypass, wherein the control takes place via the flow control means, characterised in that the method is carried out predictively.

The flow control device has a control means controllable via the engine control unit for controlling the oil flow through the cooling means and/or via the bypass.

Thus, a substantial improvement is obtained in relation to the prior art. The cooler is substantially better protected from damage. This is attributed to the fact that in operation the internal pressure is always less than the bursting pressure. Furthermore warming of the oil is substantially accelerated due to the fact that the bypass branch can be kept open for a long time. A further advantage is that the dynamic pressures before the cooler, which are usually known to be high can be avoided. This is important to the extent that the high dynamic pressures can have disadvantageous functional effects on the operation of the hydraulic system.

In a preferred embodiment the flow control means controllable via the engine control unit is a proportional throttle valve and/or an on-off valve and/or a hydraulic check valve.

It has also been proved advantageous to control the engine speed from the engine control unit, since the delivery of the pump is proportional to the engine speed. In the event that the drive speed of the pump falls and the oil temperature rises at the same time this form of control is particularly advantageous. This operational case is to be found quite frequently in working hydraulics since high energy loss and rising oil temperatures occur at average engine speeds. In the case of falling engine speeds and reduced output from the pump, the cooling capacity of the oil cooler reduces, although due to rising oil temperature a higher cooling capacity demand is present. As a result of the preferred embodiment the possibility now exists of closing the means for controlling the oil flow further and of increasing the oil flow to the cooler despite falling engine speed. Thus the reduction in the oil flow through the cooler can be compensated by closing the bypass valve more powerfully and thus achieving a higher cooling capacity. The advantages mentioned occur even if an oil-oil heat exchanger or an oil-water heat exchanger is used in place of the oil-air cooler.

In a further advantageous embodiment of the invention the means for cooling the oil temperature is an oil-air cooler and/or an oil-oil heat exchanger and/or an oil-water heat exchanger.

Additionally it has proved advantageous if the flow control device has a reflux filter. In this case it is of particular advantage if this reflux filter can be freely circumvented via a bypass valve.

It has also proved particularly advantageous if the device, in a preferred embodiment, has two separate circuits for the working and transmission hydraulics.

Of really special preference in this case is a vehicle, in particular a tractor, which comprises a device in accordance with the above description.

The invention will now be described, by way of example only, with reference to the following drawings in which:

FIG. 1 is a flow control device in the prior art;

FIG. 2 is another flow control device in the prior art;

FIG. 3 is a preferred embodiment of the invention;

FIG. 4 is a further preferred embodiment, in which the controllable means is an on-off valve;

FIG. 5 is a further embodiment, in which a hydraulic check valve is used;

FIG. 6 is a further embodiment of the invention, in which the circuits for the working and transmission hydraulics are separate;

FIG. 7 is a further preferred embodiment; and

FIG. 8 is an embodiment, in which the circuit has been simplified.

In the following explanations the reference symbols designate the same or comparable parts.

FIG. 3 shows a preferred embodiment of a flow control device through which oil from an oil tank 1 flows. The device has a flow control means 11, with as many intermediate positions as desired, for controlling the oil flow. A temperature sensor 12, which is present in the system, continuously measures the oil temperature in the inflow 10 of the cooler 4 and transmits this to an engine control unit (ECU) 13. The engine control unit 13 has an output, which can be a pulse-width-modulation (PWM) output which activates an oil flow control means 11. If the oil is cold there is no activation of the oil flow control means; thus the bypass branch 9 is completely open in operating position a. The component cooler 4 comprising the valve and the pipes is designed such that none or only very little oil flows over the cooler 4. When the oil temperature increases the oil flow control means 11 is activated, to operating position b directing a portion of the oil flow, dependent upon the level of increase in the oil temperature, to the cooler inflow 10 and the remaining portion to the bypass branch 9. With higher oil temperatures and demands for higher cooling capacity the oil flow control means 11 is completely closed, to operating position c, and the entire oil flow is directed to the cooler 4. A characteristic diagram which is based on measurements or calculations can be programmed in the engine control unit 13.

Here the following applies:

Q_ges=Q_BP+Q_K

Q_BP=f(I)

Q_ges=f(n)

Q_K=Q_ges−Q_BP

wherein:
Ges=entire,
BP=bypass,
K=cooler,
I=current and
n=engine speed.

From this it can be derived what current (I) is necessary, in order for a given oil temperature and engine speed (n) to direct a certain oil flow to the cooler, so as to obtain a certain cooling capacity. In the event of power failure or cable break the oil flow control means 11 changes to the bypass position a and therefore it is guaranteed that the bypass 9 is opened, and in cold weather starting conditions the cooler 4 suffers no damage. In the event of an error, for example, a cable break or short-circuit in the electrical connection between engine control unit 13 and oil flow control means 11, the operator can close the oil flow control means 11 by switching an emergency manual control d and thus ensure cooling.

FIG. 4 shows a further preferred embodiment of the flow control device. In this embodiment a 2/2 on-off valve is used as oil flow control means 11. Instead of having as many intermediate positions as desired only the two fixed operating positions c and a are provided. The advantages specified in FIG. 3 are also valid for FIG. 4 with the difference that on and off switching of the cooler 4 takes place without intermediate steps.

FIG. 5 shows a further preferred embodiment of the flow control device. This preferred embodiment, as the oil flow control means 11, has an electrically-operated check valve 11. This check valve by way of example has a response pressure of 5 bar. The check valve 11 is opened by an electric current, directing the oil flow to the bypass 9 and ensuring that the cooling capacity is reduced, in order to guarantee fast oil warming. In the event of power failure or a cable break, the check valve 11 changes to the bypass position a and therefore ensures that the bypass 9 is opened and the cooler 4 does not suffer damage in cold weather starting conditions. As an advantage of this embodiment it is mentioned that the fail safe function of the means 11, fulfils both the requirement to limit the cooler internal pressure and providing the cooling capacity, without making additional emergency hand operation necessary.

FIG. 6 shows a preferred embodiment, in which the circuit for the working and transmission hydraulics are separate. An oil pump 7a with constant displacement draws from a tank 1a and feeds the working hydraulics circuit 6a. The working hydraulics circuit 6a can also be supplied by further pumps not illustrated here. In this case only further circuitry of the working hydraulics circuit 6a is fed by the pump 7a. The flow control means 11a which is connected in parallel to a heat exchanger 14 is located in the further circuitry. An oil pump 7b with constant displacement draws from a tank 1b and feeds the hydraulic system 6b. The transmission hydraulic system 6b can also be supplied by further pumps, not illustrated here. Of significance here is that the further circuitry of the transmission hydraulics 6b is only fed by pump 7b. A cooling means 4 which is protected by the parallel-connected means 11c is located in the further circuitry. The second side of the heat exchanger 14 is located in the further circuitry of the cooler 4. The heat exchanger 14 can be of a plate or of a tube bundle construction. The heat exchanger 14 is designed to transfer the heat energy of the oil circuit at the higher temperature to the circuit at the lower temperature. The temperatures of the transmission oil circuit 6b are measured by the temperature sensors 12b and 12c, the temperature of the working hydraulic system 6a being measured by the temperature sensor 12a. The sensors 12a, 12b and 12c are connected to the engine control unit 13, so that the flow control means 11a, 11b and 11c are activated. Thus each of the individual coolers has an element to control the temperature and to control the cooling capacity. The advantages of the cooler control therefore have an effect in each of the individual circuits.

If a vehicle is started in the cold and while standing or during slow journeys delivers high hydraulic power, this can lead to the fact that the oil temperature in the working hydraulic system 6a rises very quickly and the oil temperature in the transmission oil circuit 6b remains low. For certain groups of vehicles such as agricultural tractors this is a typical case of operation. The flow control means 11a in the working hydraulic system would be fully activated and closed, since a high temperature is registered in the working hydraulic system 6a and a high cooling capacity should be obtained. The flow control means 11b and 11c are now not activated and open, since a low temperature is registered in the transmission oil circuit 6b and the oil is directed to the cooling means 4 and to the heat exchanger 14. Since no cooling agent flows through the heat exchanger 14, the oil in the working hydraulic system 6a is not cooled and there is a danger of overheating. This problem is solved by the preferred embodiment in the following way: above a certain temperature difference between temperature sensors 12a and 12b, the flow control means 11b is closed by energisation and the cooling agent is directed to the heat exchanger 14. As a result the temperature in the circuit 6a falls and the temperature in the circuit 6b rises. This heat transfer has the consequence that circuit 6a is protected from overheating and the circuit 6b is warmed up. The heating of the oil in circuit 6b improves the efficiency in circuit 6b. Thus fuel consumption is reduced, whenever the vehicle starts to move after stationary operation. If the temperature at sensor 12c rises above a certain level, it is necessary to dissipate heat energy from the vehicle into the environment. This takes place by energizing the flow control means 11c. By specific activation of the flow control means 11c the cooling capacity of the cooling means can be regulated within certain limits. In the event that the transmission oil becomes hot due to fast road travel, the flow control means 11c and 11b are opened. The oil in circuit 6a remains at a low temperature for a long time if the working hydraulics 6a are not running, as is usual in the case of road travel. This is particularly the case if circuit 6a is equipped with one or more variable pumps (not illustrated). Due to the low-loss standby operation of this type of pump the oil only warms up very slowly. The preferred embodiment solves this problem as follows: above a certain temperature difference between temperature sensors 12b and 12a, the flow control means 11a is activated and closed, and the medium to be warmed up in circuit 6a is directed to the heat exchanger 14. Thus the temperature in the circuit 6a rises and the temperature in the circuit 6b falls. This heat transfer has the consequence that the temperature in the circuit 6b reduces and the oil in circuit 6a warms up. The heating of the oil in circuit 6a reduces the likelihood of cavities forming in the pumps in circuit 6a. Furthermore as a result of the heating of the oil, the switching times of the solenoid valves in circuit 6a are reduced, and their operational reliability improved. By this method of controlled heat transfer the circuit—not illustrated in detail—under certain circumstances may be simplified, while other means for heating the oil can be dispensed with.

FIG. 7 shows a further preferred embodiment of the invention. The flow control means 11c has been replaced by the check valve 16. The check valve 16 takes over the function of protecting the cooler 4 from too high internal pressure and indirectly takes over the flow control and thus the cooling performance.

FIG. 8 shows a further preferred embodiment of the invention. The flow control means 11b and 11c from FIG. 6 or 11b and the check valve 16 from FIG. 7 are replaced by a single control means 11b, in order to reduce the component complexity and the costs. In the circuit according to FIG. 8, heat energy can be transferred in a controlled way from circuit 6a to 6b and from circuit 6b to circuit 6a. The circuit according to FIG. 8 does not offer the possibility of separating the control for the performance of cooler 4 from the control for the performance of heat exchanger 14.

Claims

1-9. (canceled)

10. An oil cooling arrangement comprising:

a first transmission oil cooling circuit including a first oil pump, a first oil tank, a first oil temperature sensing means and an oil cooler;

a second separate oil cooling circuit for hydraulic consumers including a second oil pump, a second oil tank and a second oil temperature sensing means;

the two circuits being thermally interconnected by a heater exchanger through which both circuits flow separately;

by pass means in the first circuit for bypassing flow in the first circuit around the cooler and heat exchanger;

by pass means in the second circuit for bypassing flow in the second circuit around the heat exchanger, and

control means arranged to receive signals from the first and second temperature sensing means and for opening at least one of the bypass means in a predictable manner dependent on the temperature signals received by the control means.

11. An arrangement according to claim 10 in which the cooler and heat exchanger in the first circuit each have their own bypass means which is controlled by the control means and the heat exchanger has its own bypass means in the second circuit also controlled by the control means.

12. An arrangement according to claim 11 in which the bypass means each comprise solenoid operated fluid flow control valves connected in parallel to the cooler and heat exchanger in the first and second circuits.

13. An arrangement according to claim 10 in which the cooler and heat exchanger each have their own by-pass means in the first and second circuits, the bypass means for the heat exchanger in the first and second circuits comprising solenoid operated fluid flow control valves operated by the control means, and the by pass means for the cooler comprises a spring loaded check valve.

14. An arrangement according to claim 10 in which the cooler and heat exchanger have a single by pass means which by passes both the cooler and heat exchanger and which is operated by the control means.

15. An arrangement according to claim 10 in which the single by pass means comprises a single solenoid operated fluid flow control valve controlled by the control means.

16. An arrangement according to claim 14 in which the by pass means for the heat exchanger in the second circuit comprises a solenoid operated fluid flow control valve controlled by the control means.