METHOD FOR AN OPEN-LOOP AND/OR CLOSED-LOOP CONTROL OF A HYDRAULIC SYSTEM OF A MOTOR VEHICLE

Abstract

A method for the control of a hydraulic system of a motor vehicle is provided. A high-pressure branch is fed by a main oil pump which is driven by an internal combustion engine. The high-pressure branch or a low-pressure branch is fed by an additional oil pump depending on a switch position of a switching valve. The additional oil pump is used for feeding the high-pressure branch or the low-pressure branch depending on a total volume flow demand and on the volume flow available from the main oil pump. A nominal rotation speed of an electric motor which drives the additional oil pump is determined based on a volume flow balance, a valve status of the switching valve, a low-pressure pump map or a high-pressure pump map. Depending on the valve status, either the low-pressure pump map or the high-pressure pump map is used to determine the nominal rotation speed.

Claims

1. A method for at least one of an open-loop control and a closed-loop control of a hydraulic system of a motor vehicle, the method comprising: providing a main oil pump driven by an internal combustion engine; providing an additional oil pump driven by an electric motor; providing a high-pressure branch, wherein the high-pressure branch is at least partially fed by the main oil pump; providing a low-pressure branch; feeding one of the high-pressure branch and the low-pressure branch through use of the additional oil pump depending on a switch position of a switching valve, wherein the additional oil pump is used for feeding one of the high-pressure branch and the low-pressure branch depending on a total volume flow demand and a volume flow available from the main oil pump; and determining a nominal rotation speed of the electric motor based on a volume flow balance, a valve status of the switching valve, and one of a low-pressure pump map and a high-pressure pump map, wherein, depending on the valve status of the switching valve, either the low-pressure pump map or the high-pressure pump map is used for determining the nominal rotation speed of the electric motor.

2. The method according to claim 1, which comprises determining a volume flow control deviation based on the nominal rotation speed of the electric motor, an actual rotation speed of the electric motor, the valve status of the switching valve, and one of the low-pressure pump map and the high-pressure pump map, wherein depending on the valve status, either the low-pressure pump map or the high-pressure pump map is used for determining the volume flow control deviation.

3. The method according to claim 2, which comprises determining the volume flow balance based on the volume flow control deviation plus a difference between the total volume flow demand and the volume flow available from the main oil pump.

4. The method according to claim 1, which comprises providing the main oil pump as a fixed displacement pump.

5. The method according to claim 1, which comprises: providing the main oil pump as a variable displacement pump; and calculating an adjustment factor by dividing the total volume flow demand by a maximum possible delivery volume flow of the variable displacement pump, wherein, if the adjustment factor assumes a value of less than one, a variable volume flow is calculated by multiplying the adjustment factor by the maximum possible delivery volume flow of the variable displacement pump, and otherwise the maximum possible delivery volume flow of the variable displacement pump is used as the volume flow available from the variable displacement pump.

6. The method according to claim 1, which comprises feeding the low-pressure branch with the additional oil pump precisely when the total volume flow demand cannot be covered solely by the volume flow available from the main oil pump, but a volume flow demand of the high-pressure branch can be covered by the volume flow available from the main oil pump.

7. The method according to claim 1, which comprises delivering into the high-pressure branch with the additional oil pump when the volume flow available from the main oil pump alone can neither cover the total volume flow demand nor a volume flow demand of the high-pressure branch.

8. The method according to claim 1, which comprises ensuring, through use of a suitable system configuration, a supply to the low-pressure branch through leakage.

9. The method according to claim 1, which comprises supplying, in driving situations in which the internal combustion engine is switched off, at least the high-pressure branch by using the additional oil pump, wherein gears are selected and deselected or preselected depending on a speed of the motor vehicle in order to avoid high rotation speeds of transmission components or a clutch components co-rotating on an output side.

10. A control configuration, comprising: a control unit for at least one of an open-loop control and a closed-loop control of a hydraulic system of a motor vehicle, wherein a main oil pump is driven by an internal combustion engine, wherein an additional oil pump is driven by an electric motor, wherein a high-pressure branch is at least partially fed by the main oil pump, wherein one of the high-pressure branch and a low-pressure branch is fed by the additional oil pump in dependence on a switch position of a switching valve, wherein the additional oil pump is used for feeding one of the high-pressure branch and the low-pressure branch in dependence on a total volume flow demand and a volume flow available from the main oil pump; and said control unit determining a nominal rotation speed of the electric motor based on a volume flow balance, a valve status of the switching valve, and one of a low-pressure pump map and a high-pressure pump map, wherein depending on the valve status of the switching valve, either the low-pressure pump map or the high-pressure pump map is used for determining the nominal rotation speed of the electric motor.

11. A hydraulic system comprising: a main oil pump driven by an internal combustion engine; an additional oil pump; a high-pressure branch configured to be at least partially fed by said main oil pump; a low-pressure branch; a switching valve, one of said high-pressure branch and said low-pressure branch being fed by said additional oil pump in dependence on a switch position of said switching valve, wherein said additional oil pump feeds one of said high-pressure branch and said low-pressure branch in dependence on a total volume flow demand and a volume flow available from said main oil pump; and said additional oil pump being driven by an electric motor, wherein a nominal rotation speed of said electric motor is determined based on a volume flow balance, a valve status of said switching valve, and one of a low-pressure pump map and a high-pressure pump map such that, depending on the valve status of said switching valve, either the low-pressure pump map or the high-pressure pump map is used for determining the nominal rotation speed of said electric motor.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0053] FIG. 1 is a highly diagrammatic depiction of a hydraulic system with a main oil pump and an additional oil pump in accordance with the invention;

[0054] FIG. 2 is a diagrammatic depiction of the control system of the additional oil pump according to the invention;

[0055] FIG. 3 is a diagrammatic depiction of the determination of a nominal rotation speed of the electric motor of the additional oil pump through the use of two pump maps, namely a high-pressure pump map and a low-pressure pump map in accordance with the invention;

[0056] FIG. 4 is a diagrammatic depiction of the determination of a valve status in accordance with the invention;

[0057] FIG. 5 is a diagrammatic depiction of the determination of a volume flow control deviation through the use of the two pump maps in accordance with the invention; and

[0058] FIG. 6 is a diagrammatic depiction of a control system of an optional variable displacement pump according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0059] Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a hydraulic system 1. The hydraulic system 1 has a main oil pump 2. The main oil pump 2 is driven by an internal combustion engine VKM. The hydraulic system 1 furthermore has an additional oil pump 3. The additional oil pump 3 is driven by an electric motor 4. The main oil pump 2 and the additional oil pump 3 deliver transmission oil via a suction filter 5 from a transmission oil sump 6. The main oil pump 2 supplies transmission oil to a mechatronic unit 7. Corresponding actuators 8 or also a clutch 9 are supplied with pressurized oil from the mechatronic unit 7. The clutch 9 is in particular formed as a dual clutch.

[0060] The hydraulic system 1 now has a high-pressure branch 10 and a low-pressure branch 11. The actuators 8 and the clutch 9 are part of the high-pressure branch 10. A cooling system 12, a wheelset lubrication 13 and a return 14 are part of the low-pressure branch 11. The transmission is supplied with cooling oil or lubricating oil via the cooling system 12 or the wheelset lubrication 13, as indicated in FIG. 1 by the two pinions on the left of the illustration.

[0061] The additional oil pump 3 now delivers corresponding oil to the mechatronic unit 7 in parallel to the main oil pump 2. Here, a check valve 15 is provided between the mechatronic unit 7 and the additional oil pump 3. The check valve 15 may be integrated in the mechatronic unit 7 or arranged separately from the mechatronic unit 7, and be connected to the mechatronic unit 7 via a supply line 16.

[0062] Furthermore, preferably a check valve 17 is arranged in the supply line 16 downstream of the main oil pump 2. In one embodiment, the check valve 17 may be integrated in the main oil pump 2. Alternatively, the check valve 17 may be integrated in the mechatronic unit 7 or formed separately from the main oil pump 2 and the mechatronic unit 7, and arranged as depicted in FIG. 1. In the embodiment shown in FIG. 1, the main oil pump 2 is configured as a fixed displacement pump. In an alternative embodiment, the main oil pump 2 may be configured to be adjustable, or be configured as a variable displacement pump.

[0063] A switching valve 18 is now provided downstream of the additional oil pump 3. The one output of the switching valve 18 is functionally actively connected to the check valve 15 and hence to the supply line 16 of the high-pressure branch 10. The other output of the switching valve 18 is connected to the low-pressure branch 11. The switching valve 18 is configured as a slide valve. It is reset via a spring. The switching valve 18 is activated via an electric pre-control valve (not shown) in the mechatronic unit 7. The switching valve 18 is for this connected to the mechatronic unit 7 via a control line 19. The control line 19 is part of the high-pressure branch 10.

[0064] The main oil pump 2 can now be charged by the additional oil pump 3, wherein the mechatronic unit 7 is connected via the return 14 to the intake tract of the main oil pump 2. The return 14 or the corresponding supply line can be switched by means of the mechatronic unit 7. If no pressurized oil and no cooling oil volume flow are required, apart from system leakages, the oil volume flow from the additional oil pump 3 flows via the return 14 into the intake tract of the main oil pump 2. When the intake tract of the main oil pump 2 is filled with oil, no intake difficulties occur.

[0065] The transmission oil flows back accordingly into the transmission oil sump 6 via a further return (not shown).

[0066] The open-loop or closed-loop control of the hydraulic system 1, in particular of the electric motor 4 and switching valve 18, will now be explained below with reference to FIG. 2. The method is implemented in a control unit.

[0067] The input parameters of the method are the actual rotation speed n.sub.EM,Act of the electric motor 4 and the volume flow demands—namely the volume flow demand Q.sub.HD of the consumers of the high-pressure branch 10, and the volume flow demand Q.sub.ND of the consumers of the low-pressure branch 11—and the volume flow Q.sub.VKM available from the main oil pump 2. The various hydraulic regions, namely the high-pressure branch 10 and the low-pressure branch 11, each report a different demand in the form of volume flow demands Q.sub.HD and Q.sub.ND.

[0068] The volume flow demand Q.sub.HD includes the leakage of the high-pressure branch 10, a dynamic reserve for actuating the clutch 9, a dynamic reserve for actuating the gear selector and a dynamic safety reserve, and special states. Special states include for example start-stop driving situations, sailing with the internal combustion engine switched off, and similar. The leakage may be obtained from a map measured on the test bench.

[0069] The volume flow demand Q.sub.ND of the low-pressure branch 11 may include in particular the demand for cooling 12 of the clutch 9, the demand for wheelset lubrication 13 and where applicable a safety offset.

[0070] The volume flow Q.sub.VKM describes the volume flow currently delivered by the main oil pump 2. The volume flow Q.sub.VKM available from the main oil pump 2 may be formed preferably from a temperature T.sub.sump of the transmission oil in the transmission oil sump 6 and from the rotation speed n.sub.VKM of the internal combustion engine VKM by means of a corresponding map.

[0071] Firstly, the open-loop control of the switching valve 18 depending on the volume flow demands Q.sub.HD and Q.sub.ND will be explained:

[0072] In a method step 20, the volume flow demands Q.sub.HD and Q.sub.ND are added to form a total volume flow demand Q.sub.B,Tot. In a method step 21, the total volume flow demand Q.sub.B,Tot is compared with the supply provided by the mechanical pump, namely the volume flow Q.sub.VKM. In the method step 21, the difference between Q.sub.B,Tot and Q.sub.VKM is formed. The result of the method step 21 is the volume flow balance ΔQ.sub.1, This first volume flow balance ΔQ.sub.1 may be positive or negative. The total volume flow demand Q.sub.B,Tot is included positively in the first volume flow balance ΔQ.sub.1. The volume flow Q.sub.VKM available from the main oil pump 2 is included negatively in the first volume flow balance ΔQ.sub.1.

[0073] If the first volume flow balance ΔQ.sub.1 has a value of less than or equal to zero, the supply available from the main oil pump 2 is sufficient. The electric additional oil pump 3 is not switched on. The nominal rotation speed n.sub.EM,Nom (setpoint rotation speed) of the electric motor 4 is set to zero (see FIG. 2).

[0074] If the first volume flow balance ΔQ.sub.1 has a value greater than zero, the total volume flow demand Q.sub.B,Tot cannot be covered solely by the main oil pump 2. In this case, in a further method step 22, a second volume flow balance ΔQ.sub.2 is formed, wherein the volume flow demand Q.sub.HD of the high-pressure branch 10 is compared with the volume flow Q.sub.VKM available from the main oil pump 2. The volume flow demand Q.sub.HD is included positively and the available volume flow Q.sub.VKM negatively in the second volume flow balance ΔQ.sub.2. From this second volume flow balance ΔQ.sub.2, it can be seen whether the supply provided by the main oil pump 2, namely the volume flow Q.sub.VKM available from the main oil pump 2, is sufficient to cover the volume flow demand Q.sub.HD of the high-pressure branch 10.

[0075] Depending on whether the volume flow balance ΔQ.sub.2 is greater than, equal to or less than zero, the valve status HD and ND is set. This method step 23 is depicted in FIG. 4. If the second volume flow balance ΔQ.sub.2 is greater than or equal to zero, the volume flow Q.sub.VKM from the main oil pump 2 is not sufficient to supply the consumers with highest priority with the volume flow demand Q.sub.HD of the high-pressure branch 10. The hydraulic switching valve 18 is opened so that the additional oil pump 3 supplies a volume flow additionally to the high-pressure branch 10. The low-pressure branch 11 is here now no longer directly supplied with a volume flow from the additional oil pump 3. In the case where ΔQ.sub.2 is greater than zero, a corresponding system design with sufficient leakages at the same time ensures the supply of the low-pressure branch 11 with the volume flow demand Q.sub.ND. The valve status HD=1, ND=0 is output.

[0076] The additional oil pump 3 delivers to the high-pressure branch 10 if the volume flow Q.sub.VKM available from the main oil pump 2 alone can no longer cover either the total volume flow demand Q.sub.B,Tot or the volume flow demand Q.sub.HD of the high-pressure branch 10.

[0077] In the case where the second volume flow balance ΔQ.sub.2 is less than zero, the supply from the main oil pump 2, namely the volume flow Q.sub.VKM available from the main oil pump 2, is sufficient to supply the consumers of the high-pressure branch 10 with the corresponding volume flow. The hydraulic switching valve 18 is closed. Thus in a further step, firstly the surplus amount available or the volume flow balance ΔQ.sub.2 is distributed into the low-pressure branch 11. Secondly, the remaining demand is controlled using the additional oil pump 3 in the required range, namely up to the volume flow demand Q.sub.ND or above. The valve status HD=0, ND=1 is output.

[0078] The additional oil pump 3 feeds the low-pressure branch 11 precisely when the total volume flow demand Q.sub.B,Tot cannot be covered solely by the main oil pump 2, but the volume flow demand Q.sub.HD of the high-pressure branch 10 can be covered by the volume flow Q.sub.VKM available from the main oil pump 2.

[0079] The closed-loop control of the additional oil pump 3 will now be discussed with reference to FIGS. 2, 3 and 5.

[0080] In a method step 24, a volume flow control deviation Q.sub.Deviation is now formed from the valve status, the nominal rotation speed n.sub.EM,Nom of the electric motor 4 and an actual rotation speed n.sub.EM,Act of the electric motor 4 (see FIG. 2 and FIG. 4).

[0081] The disadvantages cited initially are now avoided in that the nominal rotation speed n.sub.EM,Nom of the electric motor 4 is determined from the third volume flow balance ΔQ.sub.3, the valve status of the switching valve 18, a low-pressure pump map 26 or a high-pressure pump map 27, wherein depending on the valve status, either the low-pressure pump map 26 or the high-pressure pump map 27 is used to determine the nominal rotation speed n.sub.EM,Nom. The high-pressure pump map 27 is based on measurements and describes as precisely as possible the correlation between the rotation speed of the electric motor n.sub.EM and the volume flow delivered at this speed by the additional oil pump 3 into the high-pressure branch 10. The low-pressure pump map 26 is also based on measurements and describes as precisely as possible the correlation between the rotation speed n.sub.EM of the electric motor 4 and the volume flow delivered at this speed by the additional oil pump 3 into the low-pressure branch 11.

[0082] For this (see FIG. 5), in a method step 25, the difference between the nominal rotation speed n.sub.EM,Nom and the actual rotation speed n.sub.EM,Act is formed. Now using the low-pressure pump map 26 or high-pressure pump map 27, a volume flow control deviation Q.sub.Deviation is determined. The low-pressure pump map 26 is used if the switching valve 18 is closed and the additional oil pump 3 is delivering into the low-pressure branch 11, i.e. valve status HD=0, ND=1. The high-pressure pump map 27 is used if the switching valve 18 is open and the additional oil pump 3 is delivering into the high-pressure circuit 10, i.e. valve status HD=1, ND=0.

[0083] In a method step 28 (see FIG. 2), a third volume flow balance ΔQ.sub.3 is now determined from the first volume flow balance ΔQ.sub.1 and the volume flow control deviation Q.sub.Deviation. This third volume flow balance ΔQ.sub.3 is used in a method step 29 (see FIG. 2 and FIG. 3) to determine the nominal rotation speed n.sub.EM,Nom of the additional oil pump 3 using the low-pressure pump map 26 or high-pressure pump map 27, depending on the valve status. Depending on the valve status, either the low-pressure pump map 26 or the high-pressure pump map 27 is used. The low-pressure pump map 26 is used when the switching valve 18 is closed and the additional oil pump 3 is delivering into the low-pressure branch 11. The high-pressure pump map 27 is used when the switching valve 18 is open and the additional oil pump 3 is delivering into the high-pressure circuit 10.

[0084] The delivery quantity OEM of the additional oil pump 3 also depends on the temperature T.sub.Sump of the oil in the transmission oil sump 6, wherein the correlation between the nominal rotation speed n.sub.EM,Nom and the delivery quantity Q.sub.EM can be described for example by a further map.

[0085] The optional variable displacement pump mechanism will now be discussed below in more detail with reference to FIG. 6. The method takes into account a variable displacement pump mechanism for generating the flow quantity Q.sub.VKM and an adjustment factor f.sub.Adjust. Firstly, the adjustment factor f.sub.Adjust is calculated. This results from dividing the total volume flow demand Q.sub.B,Tot (=Q.sub.HD+Q.sub.ND) by the maximum possible delivery volume flow Q.sub.VKM,100% (n.sub._.sub.VKM) of the variable displacement pump. The maximum possible delivery volume flow Q.sub.VKM,100% (n.sub._.sub.VKM) is dependent on the current rotation speed n.sub.VKM of the internal combustion engine VKM. Only if the adjustment factor f.sub.Adjust has a value of less than one is the variable delivery volume flow Q.sub.VKM,Adjust calculated by multiplying the adjustment factor f.sub.Adjust by the maximum possible delivery volume flow Q.sub.VKM,100% (n.sub._.sub.VKM). The delivery volume flow Q.sub.VKM,Adjust here forms the volume flow Q.sub.VKM available from the main oil pump 2.

[0086] Otherwise, the variable displacement pump is opened to the maximum and can be regarded in the further assessment as a fixed displacement pump. The maximum possible delivery volume flow Q.sub.VKM,100% (n.sub._.sub.VKM) is used as the available volume flow Q.sub.VKM. In addition, the model outputs the adjustment factor f.sub.Adjust. From this, via a separate map of the variable displacement pump, the pump adjustment can be calculated. If the variable displacement pump is adjusted hydraulically, the calculated adjustment requirement is included in the volume flow demand Q.sub.HD as an additional requirement.

LIST OF REFERENCE CHARACTERS

[0087] 1 Hydraulic system [0088] 2 Main oil pump [0089] 3 Additional oil pump [0090] 4 Electric motor [0091] 5 Suction filter [0092] 6 Transmission oil sump [0093] 7 Mechatronic unit [0094] 8 Actuator [0095] 9 Clutch [0096] 10 High-pressure branch [0097] 11 Low-pressure branch [0098] 12 Cooling [0099] 13 Wheelset lubrication [0100] 14 Return [0101] 15 Check valve [0102] 16 Supply line [0103] 17 Check valve [0104] 18 Switching valve [0105] 19 Control line [0106] 20 Method step: addition of Q.sub.HD and Q.sub.ND [0107] 21 Method step: formation of difference between Q.sub.B,Tot and Q.sub.VKM [0108] 22 Method step: formation of difference between Q.sub.HD and Q.sub.VKM [0109] 23 Method step: determination of valve status [0110] 24 Method step: determination of volume flow control deviation Q.sub.Deviation [0111] 25 Method step: formation of difference between N.sub.EM,Nom and n.sub.EM,Act [0112] 26 Low-pressure pump map [0113] 27 High-pressure pump map [0114] 28 Method step: determination of volume flow balance ΔQ.sub.3 [0115] 29 Method step: determination of n.sub.EM,Nom [0116] VKM Internal combustion engine [0117] n.sub.EM,Act Actual rotation speed of electric motor [0118] N.sub.EM,Nom Nominal rotation speed of electric motor [0119] Q.sub.HD Volume flow demand of high-pressure circuit [0120] Q.sub.ND Volume flow demand of low-pressure circuit [0121] Q.sub.VKM Volume flow available from main oil pump [0122] Q.sub.B,Tot Total volume flow demand [0123] ΔQ.sub.1 First volume flow balance [0124] ΔQ.sub.2 Second volume flow balance [0125] ΔQ.sub.3 Third volume flow balance [0126] Q.sub.Deviation Volume flow control deviation [0127] n.sub.VKM Current rotation speed of internal combustion engine [0128] Q.sub.VKM,100% (n.sub._.sub.VKM) Maximum possible delivery volume flow of variable displacement pump [0129] Q.sub.VKM,Adjust Delivery volume flow of variable displacement pump [0130] f.sub.Adjust Adjustment factor