The present invention is directed to a motor vehicle vacuum pump, in particular to an electric rotary vane vacuum pump for providing vacuum to a motor vehicle brake booster.

Electric vacuum pumps are driven by an electric motor and are typically used in motor vehicles for providing vacuum to a brake booster of a motor vehicle braking system, in particular for providing vacuum to a vacuum chamber of the brake booster. The electric vacuum pump can be the only vacuum source for the brake booster, or can be used in combination with other vacuum sources as for example an intake system of an internal combustion engine.

The brake booster utilizes the pressure difference between its vacuum chamber pressure and the surrounding atmospheric pressure to enhance a mechanic brake force which is generated by pressing the brake pedal of the motor vehicle and which mechanically actuates the motor vehicle braking system. Providing the brake booster vacuum chamber with an adequate vacuum is therefore crucial to ensure a reliable operation of the brake booster and, as a result, to ensure a reliable and convenient operation of the motor vehicle braking system.

Modern motor vehicle electric vacuum pumps are provided with an electronically commutated electric motor which is free of mechanically abrading brush contacts and which allows an electronical control of its rotational motor speed. This provides a relatively durable and efficient motor vehicle vacuum pump.

Such a motor vehicle vacuum pump is, for example, disclosed in WO 2017/028839 Al. The vacuum pump comprises a pumping unit with a rotatable pump rotor, and an electronically commutated electric motor for driving the pump rotor. The vacuum pump also comprises a pump control unit which provides closed-loop control of a rotational motor speed of the electric motor and therefore ensures a constant rotational motor speed even in case of load and/or supply voltage fluctuations.

Generally, motor vehicle manufacturers specify a set of evacuation-time-dependent target-pressure values which the motor vehicle vacuum pump needs to meet within an evacuation cycle which starts at atmospheric pressure. For safety reasons, the motor vehicle manufacturers particularly demand a relatively high initial evacuation rate to achieve a rapid evacuation of the brake booster vacuum chamber after starting the motor vehicle and thus to ensure a correct function of the motor vehicle brake booster.

The motor vehicle vacuum pump of WO 2017/028839 Al therefore has to be operated at a relatively high rotational motor speed during the entire evacuation cycle to realize the specified high initial evacuation rate. The extensive pump operation at this high rotational motor speed causes a relatively high wear of the vacuum pump and thus a relatively short pump lifetime.

An object of the present invention is therefore to provide a reliable and long-living motor vehicle vacuum pump. This object is achieved with a motor vehicle vacuum pump with the features of claim 1.

The motor vehicle vacuum pump according to the present invention is provided with a pumping unit with a rotatable pump rotor. Preferably, the vacuum pump is a vane pump wherein the pump rotor comprises a rotor body which is eccentrically arranged in a substantially cylindrical pumping chamber and which comprises several radially slidable rotor vanes. During pump operation, the rotor vanes are in touching radial contact with a pumping chamber sidewall and define several rotating pumping-chamber compartments whose volume varies within one pump rotor revolution.

The motor vehicle vacuum pump according to the present invention is also provided with an electronically commutated electric motor for driving the pump rotor. The electronically commutated electric motor allows to electronically control a rotational motor speed of the electric motor. Typically, the electronically commutated electric motor is energized with a pulse-width-modulated drive energy, wherein an effective electrical drive power and thereby the rotational motor speed is controlled by controlling a duty cycle of the pulse width modulation. Typically, the electric motor comprises an electromagnetic motor stator with at least one stator coil, and comprises a permanent-magnetic motor rotor which is co-rotatably connected with the pump rotor. The motor vehicle vacuum pump according to the present invention is also provided with a pump control unit which is configured to control the variable rotational motor speed of the electric motor. Preferably, the pump control unit is configured to provide a closed-loop control of the variable rotational motor speed, i.e. the pump control unit is configured to continuously adapt a motor drive power based on a motor-speed feedback signal to realize a desired set motor speed. According to the present invention, the pump control unit comprises a wear-reduction control module which is configured to actively control the variable rotational motor speed during an evacuation cycle which starts when the electric motor is switched on.

The wear-reduction control module is configured to set the variable rotational motor speed corresponding to a defined starting speed value at the start of each evacuation cycle. The starting speed value is defined relatively high to generate a relatively high initial pumping performance at the beginning of the evacuation cycle. This ensures a relatively high initial evacuation rate as demanded by the motor vehicle manufactures and thus provides a reliable motor vehicle vacuum pump. The starting speed value can be invariant so that the electric motor is always started with the same rotational motor speed, or can be variable and defined depending on a present vacuum chamber difference/negative pressure at the start of the evacuation cycle. The starting speed value is typically defined in the range of 4000 revolutions per minute (RPM) to 5000 RPM. Generally, the specifications of the motor vehicle manufacturers permit significantly lower evacuation rates in the further progress of the evacuation cycle. According to the present invention, the wear-reduction control module is therefore also configured to set the variable rotational motor speed corresponding to at least one wear-reduction speed value within the same evacuation cycle, wherein each wear-reduction speed value is significantly lower than the starting speed value. The at least one wear-reduction speed value is defined in that way that the resulting wear-reduction rotational motor speed is significantly lower than the starting rotational motor speed but is high enough to realize an evacuation rate which is sufficient to meet the motor vehicle manufacturer's specifications. Because the vacuum pump according to the present invention is operated at relatively low wear-reduction rotational motor speeds during most time of the evacuation cycle, the wear of the vacuum pump is significantly reduced compared to a vacuum pump which is continuously operated at the starting motor speed. This provides a reliable and long-living motor vehicle vacuum pump.

In a preferred embodiment of the present invention, the pump control unit is configured to determine at least one evacuation parameter, and wherein the wear-reduction control module is configured to set the variable rotational motor speed based on the at least one evacuation parameter. The evacuation parameter can, for example, be a present evacuation time elapsed since the start of the evacuation cycle, a present difference pressure, a present negative pressure, a present absolute pressure, a present evacuation rate, or any other parameter which indicates a present evacuation status. The wear-reduction control module can be configured to determine a present wear-reduction parameter based on the at least one evacuation parameter and/or can be configured to determine a setting point, i.e. the point at which the variable motor speed is set to the wear-reduction speed value, based on the at least one evacuation parameter. This provides an evacuation-status-dependent control of the variable rotational motor speed and thus an efficient and reliable motor vehicle vacuum pump.

Preferably, an evacuation timer is provided which is configured to count an elapsed evacuation time, wherein one evacuation parameter is defined based on the elapsed evacuation time. The elapsed evacuation time always indicates the time elapsed since the start of the present evacuation cycle, i.e. the elapsed evacuation time is always reset to zero if a new evacuation cycle is started. The evacuation timer allows a time-based control of the variable rotational motor speed and, in particular, a time-based determination of the setting point at which the variable motor speed is set to the wear-reduction speed value. This allows a relatively simple control of the variable rotational motor speed and thus provides a cost-efficient motor vehicle vacuum pump.

In a preferred embodiment of the present invention, a pressure sensor connector is provided which is configured to, typically periodically, receive a pressure parameter provided by a motor vehicle pressure sensor, wherein one evacuation parameter is defined based on the pressure parameter. Preferably, the vacuum pump is provided with a vehicle-data-bus connector which is configured to provide a data communication with other motor vehicle units via a vehicle data bus system, e.g. via a motor vehicle CAN bus system. In this case, the pressure parameter is typically received via the vehicle data bus system meaning that the pressure sensor connector is defined by the vehicle-data-bus connector. Alternatively, the vacuum pump can be provided with a separate pressure sensor connector for providing a direct electrical connection to the motor vehicle pressure sensor. The pressure parameter can be received via an analog pressure signal whose present amplitude and/or frequency indicates the present pressure parameter, or can be received via a digital signal transmitting a digitally encoded pressure parameter. Generally, the pressure parameter can be received via any kind of signal allowing a parameter transmission. Typically, the pressure parameter indicates a present negative pressure or, in other words, a present difference pressure of a vacuum chamber of a motor vehicle brake booster relative to a present atmospheric pressure. In this case, a higher pressure parameter indicates a lower absolute vacuum chamber pressure. However, the pressure parameter can also indicate the absolute vacuum chamber pressure. For simplification, in the following description of the present invention, a higher (positive) pressure parameter always indicates a higher vacuum and thus a lower absolute vacuum chamber pressure, and a lower (positive) pressure parameter always indicates a higher vacuum and thus a lower absolute vacuum chamber pressure. The pressure parameter allows a pressure-based control of the variable rotational motor speed. The pressure parameter in particular allows a pressure-threshold-based setting of the variable rotational motor speed, i.e. the variable rotational motor speed is set corresponding to the wear-reduction speed value if the pressure parameter reaches/exceed a respective pressure threshold value. This allows a relatively simple control of the variable rotational motor speed and thus provides a cost-efficient motor vehicle vacuum pump.

Preferably, a wear-reduction map storage is provided which stores a wear-reduction control map with at least one evacuation-parameter-dependent wear-reduction speed value, and wherein the wear-reduction control module is connected to the wear-reduction map storage and is configured to set the variable motor speed based on the wear-reduction control map. The wear-reduction control map is defined in that way that the set wear-reduction speed values are as low as possible to minimize pump wear but as high as required to meet the specifications of the motor vehicle manufacturer. The wear-reduction control map is typically determined experimentally and is specific to different motor vehicle manufacturer/models. The wear-reduction control map can comprise a continuous sequence of evacuation-parameter-dependent wear-reduction speed values with a constant evacuation-parameter step size. Alternatively, the wear-reduction control map can comprise only the at least one wear-reduction speed value and a respective evacuation-parameter threshold value which defines the respective setting point for the at least one wear-reduction speed value. Preferably, the wear-reduction control map comprises a plurality of different wear-reduction speed values. Typically, the number of different wear-reduction speed values is one lesser than a number of target-pressure values specified by the motor vehicle manufacturer so that the number of different present rotational motor speeds (including the starting motor speed) is equal to the number of target-pressure values. The map-based control of the variable rotational motor speed allows a simple adaption of the motor vehicle vacuum pump for different motor vehicle manufacturer/models by programming a manufacturer/model-specific wear-reduction control map. This provides versatile motor vehicle vacuum pump.

In a preferred embodiment of the present invention, a target-value storage is provided which stores at least one, typically at least three, evacuation-time-dependent target-pressure value(s). The target-value storage in particular stores the at least one target-pressure value and a target-pressure time for each target-pressure value, wherein the target-pressure time indicates the evacuation time at which the respective target-pressure value needs to be reached. The target-value storage preferably comprises all evacuation-time-dependent target-pressure values specified by the motor vehicle manufacturer. The wear-reduction control module is connected to the target-value storage in that way that the wear-reduction control module can access the at least one evacuation-time-dependent target-pressure value. The wear-reduction control module is configured to determine a present wear-reduction speed value based on the at least one evacuation parameter and on the at least one target-pressure value, and to set the variable rotational motor speed corresponding to the present wear-reduction speed value. The wear-reduction control module is in particular configured to continuously compare the present evacuation parameters with the specified target-pressure values and to adapt the present wear-reduction speed value in that way that the target-pressure values are reached with the lowest possible (average) rotational motor speed. This provides a versatile and long-living motor vehicle vacuum pump.

More preferably, the pump control unit is configured to store at least the last two received pressure parameters to allow a determination of a present actual evacuation rate, and the wear-reduction control model is configured to determine the present wear-reduction speed value by comparing the present actual evacuation rate with a present required evacuation rate. The wear-reduction control model is in particular configured to determine the present evacuation rate by evaluating the stored at least last two pressure parameters, and is configured to determine the required evacuation rate by evaluating the present pressure parameter, the present elapsed evacuation time and one evacuation-time-dependent target-pressure value. The present required evacuation rate is in particular determined by comparing the present pressure parameter with the next higher target-pressure value and by comparing the present elapsed evacuation time with the respective target-pressure time. The wear-reduction control model is configured to decrease the present wear-reduction speed value if the present evacuation rate is higher than the required evacuation rate, and to increase the present wear-reduction speed value if the present evacuation rate is lower than the required evacuation rate. The present required evacuation rate and/or the present actual evacuation rate is typically provided with a defined tolerance to avoid a continuously fluctuating rotational motor speed. The wear-reduction control model continuously adapts the variable rotational motor speed in that way that the present actual evacuation rate complies with the evacuation rate which is required to meet the next higher target-pressure value. The target-pressure values are therefore reached with a relatively low average rotational motor speed. This provides a versatile and long-living motor vehicle vacuum pump.

In a preferred embodiment of the present invention, each wear-reduction speed value which is set by the wear-reduction control module is at least 100 RPM, preferably at least 200 RPM, lower than the starting speed value. The wear-reduction speed values therefore generate only relatively low pump wear. This provides a long-living motor vehicle vacuum pump. Two embodiments of the present invention are described with reference to the enclosed drawings, wherein figure 1 shows a schematic illustration of a part of a motor vehicle braking system with a motor vehicle brake booster and with a motor vehicle vacuum pump according to a first embodiment of the present invention, figure 2 shows exemplary progressions of a pressure parameter and of a rotational motor speed of the vacuum pump of figure 1 as a function of an elapsed evacuation time within an evacuation cycle starting at atmospheric pressure, figure 3 shows the vehicle braking system of figure 1 with a motor vehicle vacuum pump according to a second embodiment of the present invention, and figure 4 shows an exemplary illustration of a correlation between present evacuation parameters and a present rotational motor speed of the vacuum pump of figure 3.

Fig. 1 shows a motor vehicle vacuum pump 10 which is used in a motor vehicle braking system 12 for providing a vacuum to a vacuum chamber 14 of a motor vehicle brake booster 16. The motor vehicle braking system 12 also comprises a motor vehicle pressure sensor 18 which is fluidically connected to the vacuum chamber 14 and which is configured to measure a vacuum chamber difference pressure relative to atmospheric pressure. The motor vehicle pressure sensor 18 is furthermore configured to provide a pressure parameter P, which indicates the measured vacuum chamber difference pressure, to a motor vehicle control unit 20. The motor vehicle control unit 20 is connected to a vehicle data bus system 22 which is configured to allow a data communication between connected motor vehicle units.

The motor vehicle vacuum pump 10 comprises a pumping unit 24 with a rotatable pump rotor 26. In the present embodiment, the motor vehicle vacuum pump 10 is a rotary vane pump wherein the pump rotor 26 comprises a plurality of rotor vanes which are configured to be radially slidable and to rotate within a substantially cylindrical pumping chamber. The pumping unit 24 is flu id ica lly connected to the vacuum chamber 14 of the motor vehicle brake booster 16 via a check valve 28. The pumping unit 24 is configured to evacuate the vacuum chamber 14.

The motor vehicle vacuum pump 10 also comprises an electronically commutated electric motor 30 which is configured to drive the pump rotor 26 via a rotor shaft 32 which is co-rotatably connected with the pump rotor 26. The electric motor 30 is configure to be operated with a variable rotational motor speed.

The motor vehicle vacuum pump 10 also comprises a pump control unit 34 which is configured to provide a closed-loop control of the variable rotational motor speed of the electric motor 30. The pump control unit 34 is connected to the vehicle data bus system 22 via a vehicle-data-bus connector 36 which is configured to allow a data communication via the vehicle data bus system 22. In the present embodiment, the pump control unit 34 is configured to periodically read out the pressure parameter P from the motor vehicle control unit 20 via the vehicle data bus system 22. The vehicle-data-bus connector 36 thus defines a pressure sensor connector 38 which is configured to receive the pressure parameter P provided by the motor vehicle pressure sensor 18. In an alternative embodiment, the pump control unit 34 can be directly electrically connected to the motor vehicle pressure sensor 18 via a separate pressure sensor connector 38. The pressure parameter P defines a first evacuation parameter.

According to the present invention, the pump control unit 34 comprises a wear-reduction control module 40 which is configured to actively control the present rotational motor speed MS within an evacuation cycle which starts when the electric motor 30 is switched on.

In the present embodiment, the pump control unit 34 also comprises an evacuation timer 42 which is configured to count an elapsed evacuation time ET which is the time elapsed since the start of the evacuation cycle. The elapsed evacuation time ET defines a second evacuation parameter.

In the present embodiment, the wear-reduction control module 40 comprises a wear-reduction map storage 44 which stores a wear-reduction control map 46 with two evacuation-parameter-dependent wear-reduction speed values WRS1,WRS2. The wear-reduction control map 46 in particular comprises the two wear-reduction speed values WRS1,WRS2 and two respective evacuation-parameter threshold values T1,T2, one for each wear-reduction speed values WRS1,WRS2. In the present embodiment, the evacuation-parameter threshold values T1,T2 are pressure threshold values. Alternatively, the evacuation-parameter threshold values T1,T2 can be evacuation-time threshold values. In the present embodiment, the wear-reduction speed values WRS1,WRS2 both are at least 200 RPM lower than a defined starting speed value STS. In the present embodiment, the starting speed value STS is invariant and is in the range of 4000 RPM to 5000 RPM. The wear-reduction control module 40 is configured to set the present rotational motor speed MS corresponding to the starting speed value STS at the start of each evacuation cycle. The electric motor 30 is therefore started with a relatively high present rotational motor speed MS to generate a relatively high initial evacuation rate.

The wear-reduction control module 40 is also configured to monitor the evacuation parameters, in particular to monitor the pressure parameter P, and to set the present rotational motor speed MS based on the present pressure parameter P and the wear-reduction control map 46. In the present embodiment, the present rotational motor speed MS is set to the first wear-reduction speed value WRS1 if the pressure parameter P reaches the first evacuation-parameter threshold value T1 at an elapsed evacuation time ET1, and is set to the second wear-reduction speed value WRS2 if the pressure parameter P reaches the second evacuation-parameter threshold value T2 at an elapsed evacuation time ET2. The present rotational motor speed MS remains corresponding to the second wear-reduction speed value WRS2 until the end of the evacuation cycle.

Fig. 2 exemplarily shows resulting progressions of the present rotational motor speed MS and of the pressure parameter P as a function of the elapsed evacuation time ET for an evacuation cycle which starts at atmospheric pressure so that the pressure parameter P which indicates the present vacuum chamber difference pressure relative to atmospheric pressure is zero (P=0) at the start of the evacuation cycle. Fig. 2 also shows three evacuation-time-dependent target-pressure values PT1-PT3 specified by the motor vehicle manufacturer. Fig. 3 shows a motor vehicle braking system with an alternative embodiment of the motor vehicle vacuum pump according to the invention. Elements/Features of this motor vehicle braking system which provide the same functionality as the corresponding elements/features of the motor vehicle braking system of figure 1 are provided with the same reference number as in figure 1.

The pump control unit 34' of the motor vehicle vacuum pump 10' of figure 3 comprises a target-value storage 48 which stores the three evacuation-time-dependent target-pressure values PT1-PT3 shown in fig. 2. The target-value storage 48 in particular stores the three target-pressure values PT1-PT3 and three respective target-evacuation-time values ETT1-ETT3.

The pump control unit 34' also comprises an evacuation parameter storage 50. The pump control unit 34' is configured to store at least the last two received pressure parameters Pn,Pn-l with the respective elapsed evacuation time ETn,ETn-l (n: natural number).

The wear reduction control module 40' of the pump control unit 34' is connected to the target-value storage 48 and to the evacuation parameter storage 50 in that way that it can access the target-pressure values PT1-PT3, the stored pressure parameters Pn,Pn-l and the respective elapsed evacuation times ETn,ETn-l.

The wear reduction control module 40' is configured to determine a present wear-reduction speed value WRSn based on the target-pressure values PT1-PT3 and on the stored evacuation parameters, specifically the stored pressure parameters Pn,Pn-l and the respective elapsed evacuation times ETn,ETn-l. The wear reduction control module 40' is furthermore configured to set the present rotational motor speed MS corresponding to the present wear-reduction speed value WRSn.

The wear reduction control module 40' is in particular configured to determine a present actual evacuation rate ERAn by evaluating the pressure difference between the last two received pressure parameters Pn,Pn-l and the time difference between the respective elapsed evacuation times ETn,ETn-l. The wear reduction control module 40' is furthermore configured to determine a present required evacuation rate ERRn by evaluating the pressure difference between the present pressure parameter Pn and the next higher target-pressure value PTn and the time difference between the present elapsed evacuation time ETn and the next higher target-evacuation-time value ETTn. The wear reduction control module 40' is configured to decrease the present wear-reduction speed value WRSn if the present actual evacuation rate ERAn is higher than the present required evacuation rate ERRn, and to increase the present wear-reduction speed value WRSn if the present actual evacuation rate ERAn is lower than the present required evacuation rate ERRn.

The wear reduction control module 40' is therefore configured to continuously adapt the present wear-reduction speed value WRSn and thus the present rotational motor speed MS based on the present evacuation parameters ETh,Rh and the specified target-pressure values PT1-PT3.

The correlation between the present evacuation parameters ETh,Rh and the present rotational motor speed MS is exemplarily illustrated based on the two evacuation parameter pairs (ETn-l|Pn-l),(ETn|Pn) in the two graphs in fig. 4. The slope of the lines in the upper graph indicate the respective present actual evacuation rate ERAn-l,ERAn (solid lines) and the respective present required evacuation rate ERRn-l,ERRn (dashed lines) for the two evacuation parameter pairs (ETn-11 Pn-l),(ETn| Pn).

At the elapsed evacuation time ETn-1, the actual evacuation rate ERAn-1 is higher than the required evacuation rate ERRn-1 so that the rotational motor speed MS is set corresponding to the wear-reduction speed value WRSn-1 which is lower compared the preceding wear-reduction speed value WRSn-2. At the elapsed evacuation time ETn, the actual evacuation rate ERAn is lower than the required evacuation rate ERRn so that the present rotational motor speed MS is set corresponding to the wear-reduction speed value WRSn which is higher compared the preceding wear-reduction speed value WRSn-1.

Reference List

10;10' motor vehicle vacuum pump 12 motor vehicle braking system 14 vacuum chamber 16 motor vehicle brake booster 18 motor vehicle pressure sensor 20 motor vehicle control unit 22 vehicle data bus system 24 pumping unit 26 pump rotor 28 check valve 30 electronically commutated electric motor 32 rotor shaft 34;34' pump control unit 36 vehicle-data-bus connector 38 pressure sensor connector

40;40' wear-reduction control module 42 evacuation timer 44 wear-reduction map storage 46 wear-reduction control map 48 target- value storage 50 evacuation parameter storage elapsed evacuation time

ETT1-ETT3 target-evacuation-time values

MS present rotational motor speed

P pressure parameter

PT1-PT3 target-pressure values ERA actual evacuation rate ERR required evacuation rate T1,T2 evacuation-parameter threshold values

WRS1,WRS2 wear-reduction speed values

WRSn present wear-reduction speed value