control device for an electrical vacuum pump and method for activating an electrical vacuum pump

Abstract

A control device for an electrical vacuum pump includes: a determination unit designed for the purpose of detecting an operating parameter of the electrical vacuum pump, which is dependent on an operating duration of the electrical vacuum pump, and detecting a controlled variable for the electrical vacuum pump, a switching unit designed for the purpose of activating or deactivating the electrical vacuum pump as a function of a comparison of the controlled variable to at least one setpoint value, and a regulating unit designed for the purpose of changing the at least one setpoint value of the controlled variable as a function of the operating parameter.

Description

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The present invention relates to a control device for an electrical vacuum pump and a method for activating an electrical vacuum pump, in particular in motor vehicles having a brake booster.

2. DESCRIPTION OF THE RELATED ART

Electrical vacuum pumps are used in motor vehicles to generate a partial vacuum in the vacuum chamber of a brake booster. The electrical vacuum pump may be used as the sole vacuum source or in addition to a further vacuum source, for example, an internal combustion engine or a mechanical vacuum pump.

The electrical vacuum pump is conventionally activated using the partial vacuum, which is measured in the vacuum chamber of the brake booster, or the pressure difference in the brake booster as a controlled variable. When the differential pressure falls below a predefined lower threshold value, i.e., when the partial vacuum in the vacuum chamber of the brake booster becomes excessively low, the electrical vacuum pump is activated, to build up a higher differential pressure again. If a predefined upper threshold value is exceeded, i.e., if the partial vacuum in the vacuum chamber of the brake booster has again assumed a dimension sufficient for the proper operation of the brake booster, the electrical vacuum pump is deactivated again.

Electrical vacuum pumps are designed differently with respect to their thermal carrying capacity. During the operation of the electrical vacuum pumps, their operating temperature increases with the running time. If the operating temperature of an electrical vacuum pump exceeds a predetermined critical temperature, thermal overload and therefore defects of the electrical vacuum pump may occur. Therefore, electrical vacuum pumps usually may not be in operation continuously and must adhere to a predetermined ratio of operating time to non-operating time.

U.S. patent application publication US 2006/0158028 A1 describes a method for activating an electrical vacuum pump of a brake booster. To protect the electrical vacuum pump, a minimum velocity of the vehicle is determined, below which activation of the electrical vacuum pump is prevented.

BRIEF SUMMARY OF THE INVENTION

The present invention is based on the idea of designing the activation of an electrical vacuum pump in such a way that the critical temperature of the electrical vacuum pump is reached only seldom or not at all, so that automatic deactivation of the electrical vacuum pump does not occur in critical driving situations. The higher the cumulative operating duration of the electrical vacuum pump in a preceding predetermined time span, the lower is the upper setpoint value of the controlled variable set, to avoid a high load of the electrical vacuum pump in a short period of time. The activation of the electrical vacuum pump therefore is carried out adaptively and may dynamically regulate the temporary cumulative operating duration of the electrical vacuum pump in a noncritical range.

The present invention therefore provides, according to one specific embodiment, a control device for an electrical vacuum pump, having a determination unit, which is designed for the purpose of detecting an operating parameter of the electrical vacuum pump, which is dependent on an operating duration or a temperature of the electrical vacuum pump, and detecting a controlled variable for the electrical vacuum pump, a switching unit, which is designed for the purpose of activating or deactivating the electrical vacuum pump as a function of a comparison of the controlled variable to at least one setpoint value, and a regulating unit, which is designed for the purpose of changing the at least one setpoint value of the controlled variable as a function of the operating parameter.

Furthermore, according to one specific embodiment, the present invention provides a system having an electrical vacuum pump, which is designed for the purpose of generating a partial vacuum for a brake booster in a motor vehicle, and a control device according to the present invention, which is designed for the purpose of activating the electrical vacuum pump.

In addition, according to one specific embodiment, the present invention provides a method for activating an electrical vacuum pump, having the steps of detecting an operating parameter of the electrical vacuum pump, which is dependent on an operating duration or a temperature of the electrical vacuum pump, detecting a controlled variable for the electrical vacuum pump, changing at least one setpoint value of the controlled variable as a function of the operating parameter, comparing the controlled variable to the at least one setpoint value to generate a control signal, and changing the operating state of the electrical vacuum pump as a function of the control signal.

In one advantageous specific embodiment, the control device may include a runtime counter, which is designed for the purpose of ascertaining the operating parameter, which is dependent on the percentage total operating duration of the electrical vacuum pump, and providing the operating parameter to the determination unit. The relative operating duration of the electrical vacuum pump may thus be determined.

The runtime counter may preferably be designed for the purpose of incrementing the operating parameter at uniform time intervals while the switching unit keeps the electrical vacuum pump in the activated state, and decrementing the operating parameter at uniform time intervals while the switching unit keeps the electrical vacuum pump in the deactivated state. The operating duration of the electrical vacuum pump may thus be obtained in a simple way as a cumulative value.

The controlled variable may advantageously be a partial vacuum generated by the electrical vacuum pump, the at least one setpoint value including an upper threshold value, and the switching unit being designed for the purpose of deactivating the electrical vacuum pump if the partial vacuum exceeds the upper threshold value. In this way, a temporary early shutdown of the electrical vacuum pump may occur if an overload of the electrical vacuum pump is imminent. This reduces in particular the probability that the electrical vacuum pump must be automatically deactivated in real driving operation of a motor vehicle.

In one preferred specific embodiment of the method according to the present invention, the at least one setpoint value may be reduced by a predetermined amount if the operating parameter exceeds a parameter threshold value. A simple setpoint value adaptation may thus take place in one or multiple discrete setpoint value steps.

In one alternative specific embodiment, the at least one setpoint value may be continuously lowered with an increase of the operating parameter. A uniform reduction of the deactivation threshold and a finely adjustable threshold value adaptation are thus carried out.

In one advantageous specific embodiment of the method according to the present invention, the detection of the operating parameter may include detecting the operating temperature of the electrical vacuum pump. This has the advantage that a temperature model may be used, which specifies the dependence of the operating temperature of the electrical vacuum pump on the operating duration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of a system having an electrical vacuum pump in a motor vehicle according to one specific embodiment of the present invention.

FIG. 2 shows a schematic view of a method for activating an electrical vacuum pump according to another specific embodiment of the present invention.

FIG. 3 a shows a schematic view of a characteristic curve graph for the activation of an electrical vacuum pump according to another specific embodiment of the present invention.

FIG. 3 b shows a schematic view of a characteristic curve graph for the activation of an electrical vacuum pump according to another specific embodiment of the present invention.

FIG. 4 shows graphs of the time curve of a differential pressure and an operating duration of an electrical vacuum pump during an activation of the electrical vacuum pump according to another specific embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the figures of the drawings, identical and functionally identical elements, features, and components—if not otherwise noted—are each provided with the same reference numerals. It is understood that components and elements in the drawings are not necessarily shown to scale to one another for the sake of clarity and comprehensibility.

FIG. 1 shows a schematic view of a system 10 having an electrical vacuum pump 13 in a motor vehicle. System 10 includes a control device 12, an electrical vacuum pump 13, which is activated by control device 12, a brake booster 14, and optionally a further vacuum source 15. Further vacuum source 15 may be, for example, an internal combustion engine of the motor vehicle or a mechanical vacuum pump. Electrical vacuum pump 13 and optionally further vacuum source 15 are designed for the purpose of generating a partial vacuum in a vacuum chamber of brake booster 14.

Control device 12 and electrical vacuum pump 13 may be included in an overall system unit 11. It may also be possible that control unit 12 is integrated into the electronics of electrical vacuum pump 13. Alternatively, control device 12 may be implemented in an engine control unit or another control unit of a motor vehicle. Control device 12 includes a determination unit 12a, a switching unit 12d, and a regulating unit 12c. Furthermore, control device 12 may include a runtime counter 12b.

Switching unit 12d is designed for the purpose of activating or deactivating electrical vacuum pump 13 as a function of a comparison of a controlled variable to one or multiple setpoint values. For example, switching unit 12d may activate electrical vacuum pump 13 if a partial vacuum or a pressure difference in the vacuum chamber of brake booster 14 sinks below a lower threshold value. In this case, electrical vacuum pump 13 is put into an active operating state to increase the partial vacuum of brake booster 14. When the partial vacuum or the pressure difference generated by electrical vacuum pump 13 is sufficiently large, i.e., when the partial vacuum exceeds an upper threshold value, switching unit 12d may again deactivate electrical vacuum pump 13. The setpoint values may include the lower threshold value and the upper threshold value.

Determination unit 12a is designed for the purpose of detecting the controlled variable of electrical vacuum pump 13, for example, a partial vacuum or a pressure difference in the vacuum chamber of brake booster 14.

Furthermore, determination unit 12a is designed for the purpose of detecting an operating parameter of electrical vacuum pump 13, which is dependent on an operating duration or a temperature of electrical vacuum pump 13. The operating parameter may be a count of runtime counter 12b, for example. The count of runtime counter 12b may be incremented at uniform time intervals for this purpose, while switching unit 12d keeps electrical vacuum pump 13 in the activated state.

Similarly, the count of runtime counter 12b may be decremented at uniform time intervals while switching unit 12d keeps electrical vacuum pump 13 in the deactivated state. In this way, the operating parameter may represent a measure of the cumulative operating duration of electrical vacuum pump 13. In particular, the operating parameter may specify a percentage value, during which electrical vacuum pump 13 was in an active operating state over a predetermined time span in the past. In other words, the operating parameter may provide information about how high the load of electrical vacuum pump 13 is. The higher the operating parameter, the longer the cumulative operating time of electrical vacuum pump 13.

Alternatively, it is also possible that the operating parameter is a value which specifies the operating temperature of electrical vacuum pump 13. For example, the operating parameter may be estimated via a temperature model of electrical vacuum pump 13. In particular in cases in which, for example, after the entire system is activated, runtime counter 12b still has a very low value, but the operating temperature already has a high initial value because of external influences, it may be advantageous to use the operating temperature as the operating parameter instead of the runtime counter content.

Regulating unit 12c is designed for the purpose of changing the setpoint value(s) of the controlled variable as a function of the operating parameter. For example, regulating unit 12c may raise or lower the upper threshold value for the partial vacuum, depending on how high the cumulative operating duration of electrical vacuum pump 13 is presently at the instantaneous point in time. Regulating unit 12c may similarly also raise or lower the lower threshold value for the partial vacuum depending on how high the cumulative operating duration of electrical vacuum pump 13 is presently at the instantaneous point in time.

FIG. 2 shows a schematic view of a method 20 for activating an electrical vacuum pump, in particular electrical vacuum pump 13 in FIG. 1. Method 20 may be carried out, for example, by control device 12 in FIG. 1.

In a first step 21, an operating parameter of the electrical vacuum pump is detected, which is dependent on an operating duration of the electrical vacuum pump, and a controlled variable for the electrical vacuum pump is detected. In a second step 22, at least one setpoint value of the controlled variable is changed as a function of the operating parameter.

In a third step 23, the controlled variable is compared to the at least one setpoint value to generate a control signal. In a fourth step 24, the operating state of the electrical vacuum pump is changed as a function of the control signal.

With reference to FIGS. 3a, 3b, and 4, an exemplary specific embodiment of the method in FIG. 2 is described in greater detail hereafter. In the exemplary specific embodiment, the at least one setpoint value is changed by raising or lowering an upper threshold value pT for the partial vacuum. However, it is understood that a change of the at least one setpoint value may also include raising or lowering a lower threshold value for the partial vacuum.

FIG. 4 shows graphs of the time curve of a differential pressure and an operating duration of an electrical vacuum pump during an activation of the electrical vacuum pump. In first graph 40, the time curve of the partial vacuum generated by electrical vacuum pump 13 or of differential pressure p is shown as the detected controlled variable in brake booster 14. In second graph 41, which represents the same time curve as graph 40 in the abscissa, the activation signal of switching unit 12d for electrical vacuum pump 13 is shown. An activation signal of logical zero keeps electrical vacuum pump 13 in an inactive operating state, i.e., in a deactivated operating state, while an activation signal of logical one keeps electrical vacuum pump 13 in an active operating state, i.e., in an activated operating state. In third graph 42, which represents the same time curve as graph 40 in the abscissa, the time curve of operating parameter x, in particular the count of runtime counter 12b, is shown. The actual value of the operating parameter may be an arbitrarily established numerical value, which is only defined for comparison purposes. In particular, the operating parameter may assume discrete values at incremental intervals, for example, integral or natural numbers. The discrete values are not shown in FIG. 4 for the sake of clarity and comprehensibility.

FIG. 4 shows an exemplary simulation in which electrical vacuum pump 13 is repeatedly activated and deactivated again. At the beginning, electrical vacuum pump 13 is activated by switching unit 12d. Partial vacuum p increases because of the evacuation activity of electrical vacuum pump 13, while electrical vacuum pump 13 is in an active operating state. When partial vacuum p has reached a threshold value pT, switching unit 12d may set the activation signal in graph 41 to logical zero, to deactivate electrical vacuum pump 13. Because of the evacuation activity of electrical vacuum pump 13, which is no longer existent, partial vacuum p no longer increases. For example, partial vacuum p may remain constant at the level of upper threshold value pT. It may also be possible that partial vacuum p decreases again.

While electrical vacuum pump 13 was activated, operating parameter x rose from the (exemplary) value zero to a value greater than zero. For example, operating parameter x may be incremented by a runtime counter at periodic time intervals by a predetermined amount, as long as the activation signal in graph 41 assumes the value of logical one. This may result in an increase of the value of operating parameter x with a constant slope. As soon as switching unit 12d again deactivates electrical vacuum pump 13, the operating parameter may be decremented again by the predetermined amount at the periodic time intervals. This may result in a drop of the value of operating parameter x having a constant gradient. In this way, operating parameter x reflects the cumulative percentage operating duration of electrical vacuum pump 13.

If partial vacuum p—as shown in the simulation in graph 40—falls below a lower threshold value, switching unit 12d may be designed for the purpose of putting electrical vacuum pump 13 back into an active operating state. The value of operating parameter x may be incremented again in this case. The lower threshold value has been shown to be constant over the operating duration of electrical vacuum pump 13 in the present exemplary embodiment. However, it is also possible to design the lower threshold value to be dynamically variable, i.e., to change the lower threshold value as a function of the parameter threshold values explained hereafter.

While electrical vacuum pump 13 is now in an activated state, it may occur that the value of operating parameter x increases above a first parameter threshold value x1, as indicated in graph 42 at point in time t1. Regulating unit 12c may be designed in this case for the purpose of changing, for example, reducing, upper threshold value pT. Regulating unit 12c may resort to a characteristic curve for this purpose, which specifies the relationship between the value of operating parameter x and the change of upper threshold value pT.

Exemplary characteristic curves are shown in the graphs of FIGS. 3a and 3b. In FIG. 3a, characteristic curve 30a is a step function. If the value of operating parameter x is above first parameter threshold value x1, regulating unit 12c is designed for the purpose of adapting upper threshold value pT by change amount Δ=0, i.e., upper threshold value pT remains at the predefined value. However, if the value of operating parameter x is above first parameter threshold value x1, but below a second parameter threshold value x2, regulating unit 12c is designed for the purpose of adapting upper threshold value pT by change amount Δ=Δ1. Finally, if the value of operating parameter x is above second parameter threshold value x2, regulating unit 12c is designed for the purpose of adapting upper threshold value pT by change amount Δ=Δ2.

In the exemplary time curve of FIG. 4, regulating unit 12c may be designed, for example, for the purpose of lowering upper threshold value pT by amount Δ1 from point in time t1. This is indicated in graph 40 by lowered threshold value pT-Δ1. If partial vacuum p increases due to the evacuation activity of electrical vacuum pump 13, switching unit 12d is designed for the purpose from point in time t1 of comparing controlled variable p to the changed upper threshold value, i.e., to the reduced upper threshold value. If partial vacuum p thus reaches upper threshold value pT-Δ1, switching unit 12d is designed for the purpose of again deactivating electrical vacuum pump 13.

After the controlled variable falls below the lower threshold value again, switching unit 12d again activates the electrical vacuum pump. Similarly as explained with reference to point in time t1, operating parameter x increases above second parameter threshold value x2 at point in time t2, so that regulating unit 12c decreases upper threshold value pT-Δ1 again to pT-Δ2.

In this way, a dynamic adaptation of upper threshold value pT to the operating duration of electrical vacuum pump 13 is carried out, so that in the event of higher load of electrical vacuum pump 13, the run times are shortened. Accordingly, regulating unit 12c may raise upper threshold value pT again in the event of a lower load of electrical vacuum pump 13, as shown in FIG. 4 as an example at point in time t4, if operating parameter x sinks below the parameter threshold values.

FIG. 3 b shows an alternative characteristic curve 30b for regulating unit 12c. Characteristic curve 30b is composed of interpolated partial sections between parameter threshold values x3, x4, x5, and x6, so that in the event of a change of operating parameter x, a continuous adaptation of upper threshold value pT results. It is clear that the characteristic curves shown in FIGS. 3a and 3b are only of an exemplary nature, and the number of the parameter threshold values, the gradients of the characteristic curves, and the values of change amounts may assume other arbitrary values.

Corresponding characteristic curves as shown in FIG. 3a or 3b may also be specified for the lower threshold value. The characteristic curves for the lower threshold value may be set equal to the characteristic curves for the upper threshold value, for example.

Claims

1-10. (canceled)

11. A control device for an electrical vacuum pump, comprising: a determination unit configured to (i) detect an operating parameter of the electrical vacuum pump, wherein said operating parameter is dependent on one of an operating duration or a temperature of the electrical vacuum pump, and (ii) detect a controlled variable for the electrical vacuum pump;a switching unit configured to one of activate or deactivate the electrical vacuum pump as a function of a comparison of the controlled variable to at least one setpoint value; anda regulating unit configured to change the at least one setpoint value as a function of the operating parameter.

12. The control device as recited in claim 11, further comprising: a runtime counter configured to (i) ascertain the operating parameter, wherein said operating parameter is dependent on a percentage total operating duration of the electrical vacuum pump, and (ii) provide the operating parameter to the determination unit.

13. The control device as recited in claim 12, wherein the runtime counter is configured to (i) increment the operating parameter at uniform time intervals while the switching unit maintains the electrical vacuum pump in the activated state, and (ii) decrement the operating parameter at uniform time intervals while the switching unit maintains the electrical vacuum pump in the deactivated state.

14. The control device as recited in claim 11, wherein the controlled variable is a partial vacuum generated by the electrical vacuum pump, the at least one setpoint value includes an upper threshold value, and the switching unit is configured to turn off the electrical vacuum pump when the partial vacuum exceeds the upper threshold value.

15. A system, comprising: an electrical vacuum pump configured to generate a partial vacuum for a brake booster in a motor vehicle; anda control device configured to activate the electrical vacuum pump, wherein the control device includes: a determination unit configured to (i) detect an operating parameter of the electrical vacuum pump, wherein said operating parameter is dependent on one of an operating duration or a temperature of the electrical vacuum pump, and (ii) detect a controlled variable for the electrical vacuum pump;a switching unit configured to one of activate or deactivate the electrical vacuum pump as a function of a comparison of the controlled variable to at least one setpoint value; anda regulating unit configured to change the at least one setpoint value as a function of the operating parameter.

16. A method for activating an electrical vacuum pump, comprising: detecting an operating parameter of the electrical vacuum pump, wherein said operating parameter is dependent on one of an operating duration or a temperature of the electrical vacuum pump;detecting a controlled variable for the electrical vacuum pump;changing at least one setpoint value for the controlled variable as a function of the detected operating parameter;comparing the detected controlled variable to the at least one setpoint value to generate a control signal; andchanging the operating state of the electrical vacuum pump as a function of the control signal.

17. The method as recited in claim 16, wherein the at least one setpoint value is reduced by a predetermined amount if the operating parameter exceeds a parameter threshold value.

18. The method as recited in claim 16, wherein the at least one setpoint value is continuously lowered with an increase of the operating parameter.

19. The method as recited in claim 16, wherein the controlled variable is a partial vacuum generated by the electrical vacuum pump, the at least one setpoint value includes an upper threshold value, and the change of the operating state includes a shutdown of the electrical vacuum pump when the partial vacuum exceeds the upper threshold value.

20. The method as recited in claim 17, wherein the operating parameter is an operating temperature of the electrical vacuum pump.