Actuation method for a hydraulic system with a pump and multiple valves, and hydraulic system

Abstract

A method actuates a hydraulic system for an actuation device of a motor vehicle. The hydraulic system has a pump and multiple valves which are each arranged between a system rail connected to a pump outlet and a hydraulic consumer. The pump is switched between a normal operation and an enhanced operation according to an existing total energy demand of the hydraulic consumers. In normal operation, the pump is driven when the system pressure is below a lower pressure threshold and switched off when the system pressure is above an upper pressure threshold. In the enhanced operation, the pump is permanently driven and each of the valves is operated according to an individual energy demand of the respective hydraulic consumer as soon as the system pressure achieves or exceeds a threshold value.

Claims

1. A method for actuating a hydraulic system for an actuation device of a motor vehicle, wherein the hydraulic system has a pump, multiple valves each arranged between a system rail connected to a pump outlet and at least one hydraulic consumer, wherein the pump is switched between a normal operation and an enhanced operation according to an existing total energy demand of the at least one hydraulic consumer, wherein, in normal operation, an existing system pressure in the system rail is determined at regular time intervals and a target pressure of the system rail is calculated, and an upper pressure threshold and a lower pressure threshold are established on the basis of the target pressure, wherein the pump is driven when the system pressure is below the lower pressure threshold and switched off when the system pressure is above the upper pressure threshold, and wherein, in the enhanced operation, the pump is continuously driven and each of the valves is operated according to an individual energy demand of the respective hydraulic consumer after the system pressure achieves a threshold value, wherein the total power requirement determining a switchover between normal operation and enhanced operation corresponds to a total volume flow requirement of all consumers, wherein the enhanced operation is activated when the total volume flow requirement is above and upper volume flow threshold value, and normal operation is activated when the total volume flow requirement is below a lower volume flow threshold value.

2. The method according to claim 1, wherein, in normal operation, actuation of the valves is decoupled from actuation of the pump.

3. The method according to claim 1, wherein the upper volume flow threshold value and the lower volume flow threshold value are formed by a fixed constant or a temperature-dependent and/or system pressure-dependent variable.

4. The method according to claim 1, wherein the total volume flow requirement is calculated based on the sum of a first partial volume flow requirement determined by a first hydraulic consumer and a second partial volume flow requirement determined by at least one further second hydraulic consumer, wherein the specific partial volume flow requirement is determined based on a pressure-volume function stored in software.

5. The method according to claim 1, wherein a maximum system voltage is applied to an electric motor driving the pump both in normal operation and in enhanced operation.

6. The method according to claim 1, wherein a pressure relief valve is arranged in the system rail.

7. The method according to claim 1, wherein the target pressure is a maximum value from a group of target consumer pressures required by a specific individual consumer.

8. The method according to claim 1, wherein the upper pressure threshold is calculated using a first load factor based on the target pressure and the lower pressure threshold is calculated using a second load factor based on the target pressure, wherein the at least one load factor is a fixed constant or a temperature-dependent and/or system pressure-dependent variable.

9. A method of controlling a hydraulic system, the hydraulic system including an electrically driven pump and a plurality of regulator valves feeding corresponding consumers, the method comprising: in response to a total flow demand rising above an upper flow threshold, operating in an enhanced mode in which the pump is driven with a first current level, and the regulator valves are held steady until a system pressure exceeds a first pressure threshold, after which the regulator valves are operated based on pressure demands of the respective consumers; and in response to the total flow demand falling below a lower threshold, operating in a normal mode in which the regulator valves are operated based on the pressure demands of the respective consumers, the pump is driven with the first current in response to the system pressure falling below a lower pressure threshold, and the pump is turned off in response to the system pressure rising above an upper pressure threshold.

10. The method of claim 9, wherein the lower pressure threshold is calculated by adding a first increment to a maximum of pressure demands of the consumers and the upper pressure threshold is calculated by adding a second increment to the maximum of the pressure demands of the consumers.

11. A method for actuating a hydraulic system for an actuation device of a motor vehicle, wherein the hydraulic system has a pump, multiple valves each arranged between a system rail connected to a pump outlet and at least one hydraulic consumer, wherein the pump is switched between a normal operation and an enhanced operation according to an existing total energy demand of the at least one hydraulic consumer, wherein, in normal operation, an existing system pressure in the system rail is determined at regular time intervals and a target pressure of the system rail is calculated, and an upper pressure threshold and a lower pressure threshold are established on the basis of the target pressure, wherein the pump is driven when the system pressure is below the lower pressure threshold and switched off when the system pressure is above the upper pressure threshold, and wherein, in the enhanced operation, the pump is continuously driven and each of the valves is operated according to an individual energy demand of the respective hydraulic consumer after the system pressure achieves a threshold value, wherein the upper pressure threshold is calculated using a first load factor based on the target pressure and the lower pressure threshold is calculated using a second load factor based on the target pressure, wherein the at least one load factor is a fixed constant or a temperature-dependent and/or system pressure-dependent variable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the control method is now explained in more detail with reference to figures.

(2) In the Figures:

(3) FIG. 1 shows a representation of a state machine to illustrate an actuation strategy of a hydraulic system,

(4) FIG. 2 shows a basic illustration of a hydraulic system according to a first exemplary embodiment, which can be actuated with the actuation strategy according to FIG. 1,

(5) FIG. 3 shows a basic illustration of a hydraulic system according to a second exemplary embodiment, which can also be actuated with the actuation strategy according to FIG. 1 and, compared to the first exemplary embodiment, is equipped with a pressure limiting valve, and

(6) FIG. 4 shows a basic illustration of a hydraulic system with a pressure accumulator designed according to the prior art.

(7) The figures are only schematic in nature.

DETAILED DESCRIPTION

(8) A hydraulic system 1, which is designed to carry out a method, has, according to a first exemplary embodiment, the structure shown in FIG. 2. In contrast to the hydraulic system 1′ of the prior art, the hydraulic system 1 does not comprise a pressure accumulator. Multiple branches 10a, 10b, 10c branch off from the system rail 5, each of which can be connected to a hydraulic consumer 6a, 6b, 6c (K0, K1, K2) with the interposition of a valve 3a, 3b, 3c. The valves 3a to 3c assigned to the individual consumers 6a to 6c are each implemented as pressure regulating valves/pressure reducers. Also in a typical manner, as can be seen in connection with a further hydraulic system 1 according to a second embodiment in FIG. 3, a pressure limiting valve 11, may be incorporated in a system rail 5 connected to an output 4 of a pump 2.

(9) As can also be seen in FIG. 2, the hydraulic system 1 is equipped with a pump 2 driven by an electric motor 7. The pump 2 is thus operated/controlled via the electric motor 7. The pump 2 is connected to a reservoir 9 with its input 8. The output 4 of the pump 2 is connected to the system rail 5. The branches 10a to 10c run from the system rail 5 to the valves 3a to 3c. The specific branch 10a to 10c is coupled to a hydraulic consumer 6a to 6c as a function of the position of the valve 3a to 3c. Accordingly, in this embodiment, a first branch 10a branching off from the system rail 5 can be coupled to a first hydraulic consumer 6a via a first valve 3a. Another, along the system rail 5 offset to the first branch 10a, second branch 10b can be coupled to a second consumer 6b via a second valve 3b. A third branch 10c, which in turn is offset from the two first and second branches 10a and 10b, can be coupled to a third consumer 6c via a third valve 3c. According to further embodiments, however, it is in principle also possible to provide fewer than three consumers 6a, 6b, 6c, such as only two consumers or more than three consumers. The consumers 6a, 6b, 6c are each part of an actuating device of a clutch (K0, K1, K2) of a drive train, for example in the form of a pressure cylinder.

(10) The hydraulic system 1 shown in connection with FIG. 3 according to the second exemplary embodiment differs from the first exemplary embodiment only in the provision of the pressure limiting valve 11, which is connected to the system rail 5. The rest of the structure of the hydraulic system 1 according to FIG. 3 corresponds to the hydraulic system 1 according to FIG. 2.

(11) A method for actuating the hydraulic system 1 is illustrated in connection with FIG. 1. The method can be implemented both with the hydraulic system according to FIG. 2 and with the hydraulic system according to FIG. 3.

(12) The pump 2 can be switched between its normal operation and its enhanced operation as a function of an existing total power requirement (total volume flow requirement Q_req) of the hydraulic consumers 6a, 6b, 6c.

(13) Normal operation is that operation of the pump 2 in which an existing system pressure p_sys is determined/measured in the system rail 5 at regular time intervals and a target pressure p_sys_set of the system rail 5 is calculated. The target pressure p_sys_set is that value which represents the highest pressure value to be set in the system. The target pressure p_sys_set is thus a maximum value from the group of consumer target pressures required at the specific individual consumer 6a, 6b, 6c. An upper pressure threshold p_h and a lower pressure threshold p_l are defined on the basis of the target pressure p_sys_set. The upper pressure threshold p_h and the lower pressure threshold p_l are calculated on the basis of an additional factor that represents a fixed constant or a temperature-dependent variable. The pump 2 is driven when the system pressure p_sys is below the lower pressure threshold p_l and switched off when the system pressure p_sys is above the upper pressure threshold p_h. Thus, in normal operation, a certain pressure level is always kept constant in the system rail 5 (between the lower pressure threshold p_l and the upper pressure threshold p_h). The pump 2 is switched between its switched-off and switched-on state in order to maintain this pressure level.

(14) An additional enhanced operation of the pump 2 is implemented. This enhanced operation is activated when the total power requirement Q_req exceeds a certain power requirement. The total power requirement Q_req of all consumers 6a, 6b, 6c is determined as the total power requirement. The total volume flow requirement Q_req is a sum of partial volume flow requirements (V_1_req, V_2_req, . . . ) of all individual hydraulic consumers 6a, 6b, 6c at the specific point in time. The specific partial volume flow requirement is determined using a pressure-volume function stored in software. Accordingly, enhanced operation is activated/normal operation is deactivated when the total volume flow requirement Q_req is above an upper volume flow threshold value Q_h and normal operation is activated/enhanced operation is deactivated when the total volume flow requirement Q_req is below a lower volume flow threshold value Q_l. The upper volume flow threshold Q_h and the lower volume flow threshold Q_l are each calculated/derived either by a fixed constant or a temperature-dependent and system pressure-dependent variable.

(15) In the enhanced operation, the pump 2 is then permanently driven. As already in the case when the pump 2 is driven in normal operation, the electric motor 7 is permanently driven with a fixed (maximum) voltage value (system voltage) in the enhanced operation. Each of the valves 3a, 3b, 3c designed as pressure relief valves is operated in the enhanced operation at least temporarily depending on an individual power requirement of the specific hydraulic consumer 6a, 6b, 6c as soon as the system pressure p_sys reaches or exceeds a threshold value p limit. In other words, the specific valve 3a, 3b, 3c is used for pressure reduction when the system pressure p_sys in the system rail 5 reaches or exceeds the threshold value p limit.

(16) The valves 3a, 3b, 3c are typically fully decoupled/independent of an actuation of the pump 2/the electric motor 7.

(17) In connection with FIG. 1, a typical calculation and determination of the specific values that implement the switchover are listed. A motor voltage is designated by U motor in this figure. A system voltage is designated with U b. A valve flow which actuates the specific valve 3a, 3b, 3c is designated by I_valve_1 (first valve 3a), I_valve_2 (second valve 3b). Since the specific valve 3a, 3b is implemented as a pressure relief valve, the valve flow I_valve_1, I_valve_2 is controlled by a function according to the corresponding target pressure that is to be implemented at the valve 3a, 3b (f (p_1_set); f (p_2_set)). When the limit pressure value/threshold value p limit is reached, the actuation of the valves 3a, 3b is switched over accordingly in the enhanced operation. This results in the following mathematical relationship:

(18) Since conventional pressure relief valves are used, there is usually a mathematical relationship between the target pressure (p_1_set; p_2_set) according to the valve and the valve flow (I_valve_1; I_valve_2). This means that the pressure after valve 3a, 3b, 3c is controlled by the valve flow, i.e. I_valve=f (p_1_set) or p_1_set=f−1 (I_valve)

(19) In order to use the actuation strategy that is visualized in FIG. 1, the following signal values must be determined for each time step i: 1. For the pressure interfaces, p_h and p_l of the pressure hysteresis-control must be determined mathematically as follows:
p_sys_set=max(p_1_set,p_2_set, . . . )
p_h=p_sys_set±dp_h
p_1=p_sys_set±dp_l

(20) Here, dp_h and dp_l are stored constants or depend on the operating temperature and p_sys_set from a function/characteristic field. The following applies:
dp_h>dp_l>0
and consequently
p_h>p_l>p_sys_set

(21) In order to know whether an event intervention, i.e., the activation of enhanced operation, is necessary, Q_req, Q_h and Q_l are determined mathematically:
Q_req=(V_1_req+V_2_req+. . . )/(ti−ti−1)
with
V_1_req=max[(V_1(p_1_seti)−V_1(p_1_seti−1)),0]
V_2_req=max[(V_2(p_2_seti)−V_2(p_2_seti−1)),0]

(22) In a further preferred embodiment, Q_req is also determined mathematically as follows:
Q_req=(V_1_req+V_2_req+. . . )/(ti−ti−1)
with
V_1_req=max[(V_1(p_1_seti)−V_1(p_1_acti)),0]
V_2_req=max[(V_2(p_2_seti)−V_2(p_2_acti)),0]

(23) The functions V_1 and V_2 are pressure-volume characteristics stored in software. Q_h and Q_1 are constants or depend on the operating temperature and p_sys_set from a function/characteristic field. p_1_seti is a target pressure at the first hydraulic consumer 6a at a point in time i; p_2_seti is a target pressure at the second hydraulic consumer 6b at time i. Accordingly, p_1_seti−1 is a target pressure at the first hydraulic consumer 6a at a time i−1 and p_2_seti−1 is a target pressure at the second hydraulic consumer 6b at the time i−1. p_1_acti is an actually present (actual) pressure at the first hydraulic consumer 6a at time i and p_2_acti0 is an actually present (actual) pressure at the second hydraulic consumer 6b at time i.

(24) The motor voltage U b to be applied is preferably a constant, but in further versions it is also calculated using a function/characteristic field of the operating temperature and p_sys_set. The motor voltage U b to be applied can also result directly from pressure regulation.

(25) In other words, the basic idea is to identify an event with a high power requirement and to react to it in a targeted manner. Based on this idea, there are two modes of operation: Normal operation and event intervention (enhanced operation).

(26) In order to assess whether a change must be made between normal operation and event intervention, the total volume flow requirement of all consumers 6a, 6b, 6c (Q_req) is calculated. If the value is above an upper threshold Q_h, the “event intervention” mode is activated. If the value is below a lower threshold Q_l, the “normal operation” mode is activated.

(27) In order to simplify actuation in normal operation and in enhanced operation, the maximum available voltage is preferably always applied to the pump motor 7 when the pump 2 is to be driven. The system 1 preferably contains a pressure relief valve 11 on the system rail 5, which prevents an excessively high system pressure p_sys during the event intervention.

LIST OF REFERENCE SYMBOLS

(28) 1 Hydraulic system 2 Pump 3a First valve 3b Second valve 3c Third valve 4 Output 5 System rail 6a First consumer 6b Second consumer 6c Third consumer 7 Electric motor 8 Input 9 Reservoir 10a First junction 10b Second junction 10c Third junction 11 Pressure relief valve