Motor vehicle vacuum pump

Abstract

The invention relates to a motor vehicle vacuum pump (10) comprising a pumping unit (24) with a rotatable pump rotor (26), an electronically commutated electric motor (30) for driving the pump rotor (26), a pressure sensor connector (38) for periodically receiving a pressure parameter (P) provided by a motor vehicle pressure sensor (18), and a pump control unit (34) for controlling a variable motor speed (MS) of the electric motor (30), the pump control unit (34) comprising - a standard operation control module (40) arranged for controlling the variable motor speed (MS) within a standard operation speed range (SSR), - a boost drive control module (42) arranged for overriding the standard operation control module (40) when triggered and setting the variable motor speed (MS) corresponding to boost speed values (BS1, BS2, BSn) higher than the standard operation speed range (SSR), - a safety control module (44) arranged for monitoring the pressure parameter (P) and triggering the boost drive control module (42) based on the pressure parameter (P). The pump control unit (34) according to the invention allows designing a motor vehicle vacuum pump (10) generally for a relatively low standard operation speed range (SSR), but also allows temporarily providing a boosted pump performance in critical situations. This provides a reliable and cost-effective motor vehicle vacuum pump (10).

Description

[0001] This invention relates to a vehicle vacuum pump, and more particularly to an electric rotary vane vacuum pump for providing vacuum to a vehicle brake booster.

[0002] Electric vacuum pumps are driven by electric motors and are commonly used in motor vehicles to provide a vacuum to the brake booster of the vehicle's braking system, particularly to the vacuum chamber of the brake booster. An electric vacuum pump can be the sole vacuum source for the brake booster, or it can be used in conjunction with other vacuum sources, such as the intake system of an internal combustion engine.

[0003] Brake boosters utilize the pressure difference between their vacuum chamber pressure and the surrounding atmospheric pressure to enhance mechanical braking force. This mechanical braking force is generated by pressing the brake pedal of a motor vehicle and mechanically operates (or actuates) the vehicle's braking system. Therefore, providing sufficient vacuum to the brake booster's vacuum chamber is crucial for ensuring the reliable operation of the brake booster and, consequently, for ensuring the reliable and convenient operation of the vehicle's braking system.

[0004] Modern automotive electric vacuum pumps are equipped with electronically commutated motors that do not have mechanically worn brush contacts and allow for electronic control of the motor's speed. This provides a relatively durable and efficient automotive vacuum pump.

[0005] For example, such a vehicle vacuum pump is disclosed in patent document WO 2017 / 028839 A1. The vacuum pump includes a pumping unit with a rotatable pump rotor and an electronically commutated motor for driving the pump rotor. The vacuum pump also includes a pump control unit that provides closed-loop control of the motor speed, and thus ensures a constant motor speed even under load and / or power supply voltage fluctuations.

[0006] For safety reasons, automotive vacuum pumps must be designed to maintain sufficient vacuum in the brake booster's vacuum chamber even during critical driving situations involving repeated brake pedal operations and thus high vacuum requirements. Therefore, the automotive vacuum pump described in patent document WO 2017 / 028839 A1 must be designed to consistently provide relatively high pump performance. This typically requires relatively expensive pump components / materials, resulting in a high price for automotive vacuum pumps.

[0007] Therefore, the technical problem to be solved by the present invention is to provide a reliable and cost-effective vehicle vacuum pump.

[0008] The technical problem is solved by a motor vehicle vacuum pump having the features of claim 1.

[0009] The vehicle vacuum pump according to the invention is equipped with a pumping unit having a rotatable pump rotor. The vacuum pump is preferably a vane pump, wherein the pump rotor includes a rotor body eccentrically arranged in a substantially cylindrical pumping chamber and includes a plurality of radially sliding rotor blades. During pump operation, the rotor blades radially contact the sidewalls of the pumping chamber and define a plurality of rotating pumping chamber compartments, the volume of which varies within one rotation of the pump rotor (or one revolution of the pump rotor).

[0010] The vehicle vacuum pump according to the invention is also equipped with an electronically commutated motor for driving the pump rotor. The electronically commutated motor allows electronic control of the motor speed. Typically, the electronically commutated motor is powered by pulse-width modulated drive energy, wherein the effective electric drive power is controlled by controlling the duty cycle of the pulse-width modulation, thereby controlling the motor speed. The motor typically includes an electromagnetic motor stator having at least one stator coil, and a permanent magnet motor rotor rotatably connected to the pump rotor.

[0011] The vehicle vacuum pump according to the invention is further equipped with a pressure sensor connector for periodically receiving pressure parameters provided by a vehicle pressure sensor. The vacuum pump is preferably equipped with a vehicle data bus connector configured to provide data communication with other vehicle units via a vehicle data bus system, such as the vehicle's CAN bus system. In this case, the pressure parameters are typically received via the vehicle data bus system, meaning the pressure sensor connector is defined by the vehicle data bus connector. Alternatively, the vacuum pump may be equipped with a separate pressure sensor connector for providing a direct electrical connection to the vehicle pressure sensor. The pressure parameters can be received periodically via an analog pressure signal, the current amplitude and / or frequency of which indicates the current pressure parameters, or via a digital signal that periodically transmits digitally encoded pressure parameters. The pressure parameters can generally be received using any type of signal that allows for periodic parameter transmission.

[0012] Pressure parameters typically indicate the current negative pressure, or in other words, the current pressure difference (or differential pressure) between the vacuum chamber of a vehicle's brake booster and the current atmospheric pressure. In this case, a higher pressure parameter indicates a lower absolute vacuum chamber pressure. However, pressure parameters can also indicate absolute vacuum chamber pressure. For the purposes of this invention, a higher (positive) pressure parameter always indicates a higher vacuum level and therefore a lower absolute vacuum chamber pressure, while a lower (positive) pressure parameter always indicates a higher vacuum level and therefore a lower absolute vacuum chamber pressure.

[0013] The vehicle vacuum pump according to the invention is further equipped with a pump control unit configured to control the variable motor speed of the electric motor. Preferably, the pump control unit is configured to provide closed-loop control of the variable motor speed, i.e., the pump control unit is configured to continuously adjust the motor drive power based on the motor speed feedback signal to achieve a desired set motor speed.

[0014] According to the present invention, the pump control unit includes a standard operation control module configured to control a variable rotary electric motor during normal pump operation, i.e., under normal, non-critical vehicle driving conditions. The standard operation control module is configured to control the variable electric motor speed within a standard operating speed range. This standard operating speed range typically includes electric motor speed values ​​ranging from 3000 revolutions per minute (RPM) to 4000 RPM. The standard operation control module is particularly configured to determine the current electric motor speed value within the standard operating speed range and to set the variable electric motor speed accordingly. Preferably, the standard operation control module is configured to determine a current electric motor speed value optimized for wear and / or efficiency. This provides the vehicle vacuum pump with reliable, efficient, and low-wear operation under normal, non-critical conditions and therefore for most of the pump's lifespan.

[0015] According to the invention, the pump control unit further includes a boost drive control module (or enhanced drive control module) for temporarily providing boosted pump performance in abnormal, potentially critical situations. The boost drive control module is positioned superior to the standard operating control module, meaning it is configured to overrule the standard operating control module when triggered. The boost drive control module is configured to temporarily set a variable motor speed corresponding to a boost speed value exceeding the standard operating speed range. This allows for the temporary provision of boosted pump performance when needed, such as in critical motor vehicle driving situations where excessive vacuum demand is caused by repeated brake pedal operation. According to the invention, boost speed values ​​significantly exceeding the standard operating speed range and resulting in excessive motor speeds are, in principle, "harmful" to the vacuum pump; therefore, if the vacuum pump is consistently operated at such excessive boost motor speeds, it may be damaged. The boost speed value is typically at least 10% higher than the maximum standard operating speed value within the standard operating speed range, and preferably equal to or higher than 4500 RPM.

[0016] According to the invention, the pump control unit further includes a safety control module configured to monitor pressure parameters and trigger a boost drive control module based on these pressure parameters. Specifically, the safety control module is configured to detect / anticipate excessive vacuum demand based on the pressure parameters. The safety control module may be configured to evaluate only the current pressure parameters, or it may be configured to evaluate the pressure parameters in a (time) sequence, such as determining the rate of pressure change. The safety control module is configured to trigger the boost drive control module in the event of excessive vacuum demand, thereby causing the vacuum pump to temporarily provide boosted pump performance to handle the excessive vacuum demand. Therefore, the safety control module is configured to trigger the boost drive control module (only) in abnormal, potentially critical situations and especially not during normal pump operation.

[0017] The lift drive control module according to the invention allows the motor to be driven at excessively high, and in principle harmful, lift motor speeds for relatively short, harmless durations. This allows for the temporary provision of lift pump performance in relatively rare cases of excessive vacuum demand, particularly in critical vehicle driving situations. Therefore, the vehicle vacuum pump according to the invention need not be designed to always provide lift pump performance, but can generally be designed for relatively low motor speeds within the standard operating speed range. This provides a reliable and cost-effective vehicle vacuum pump.

[0018] If the vacuum chamber negative pressure / pressure difference of the brake booster drops below the minimum operating pressure threshold, the brake booster can no longer adequately increase braking force. This results in an "unsmooth" and difficult-to-operate brake pedal, reducing driver comfort and potentially leading to insufficient braking force in critical vehicle driving situations. Therefore, in a preferred embodiment of the invention, the safety control module is configured to trigger the boost drive control module when the pressure parameter falls below a defined (or prescribed) minimum operating pressure threshold to provide boosted pump efficiency in this situation. This ensures that the vacuum chamber is quickly and adequately supplied with vacuum chamber negative pressure / pressure difference again. This ensures reliable operation of the vehicle brake booster and thus provides a reliable vehicle vacuum pump. The minimum operating pressure threshold is typically determined experimentally and is specific to different vehicle braking systems. The minimum operating pressure threshold is generally defined in the range of 250 mbar to 350 mbar (negative pressure).

[0019] Automotive vacuum pumps are typically not designed for continuous operation (pumping), but rather for temporary, on-demand operation. Therefore, the pump control unit is preferably configured to shut off the motor when the pressure parameter is equal to or higher than a deactivation (or shutdown) pressure threshold, and to activate the motor when the pressure parameter is lower than a start-up (or activation) pressure threshold. The deactivation pressure threshold is typically defined such that when the vacuum pump is shut off, the vacuum chamber negative pressure / pressure difference is sufficient for multiple brake booster operations. The start-up pressure threshold is typically defined such that, at least under normal conditions, the vacuum pump is activated before the vacuum chamber negative pressure / pressure difference reaches an insufficient pressure level. Therefore, the minimum operating pressure threshold is preferably defined as being lower than the start-up pressure threshold, such that the pressure parameter does not drop below the minimum operating pressure threshold under normal conditions, but only in abnormal, potentially critical situations with excessive vacuum demands. This ensures that the automotive vacuum pump operates only under abnormal conditions and therefore relatively less frequently at, in principle, "harmfully" increased motor speeds. This provides a reliable and durable automotive vacuum pump. The shutdown pressure threshold is typically in the range of 700 mbar to 800 mbar, while the startup pressure threshold is in the range of 450 mbar to 550 mbar (negative pressure). The boost drive control module is typically configured to drive the motor at boost motor speed until the pressure parameters reach / exceed the shutdown pressure threshold, i.e., until the motor is shut off by the pump control unit.

[0020] During normal operation, the maximum standard operating motor speed is typically only 80% of the maximum achievable motor speed of the vehicle vacuum pump. This allows for the provision of different lift motor speed levels. Therefore, in a preferred embodiment of the invention, a safety control module is configured to define lift speed values ​​based on pressure parameters. The safety control module is preferably equipped with a lift speed graph having at least two pressure-related lift speed values. For example, the safety control module can be configured to define a moderate lift speed value when the pressure parameter is between a minimum operating pressure threshold and a maximum lift pressure threshold, and to define a maximum lift speed value when the pressure parameter is below the maximum lift pressure threshold. This provides tiered, demand-based control of the lift motor speed, thereby minimizing pump wear caused by excessively high lift motor speeds. All lift speed values ​​are typically at least 10% higher than the maximum standard operating speed value within the standard operating speed range and preferably equal to or higher than 4500 RPM.

[0021] The vehicle vacuum pump is preferably equipped with a vehicle data bus connector for receiving at least one vehicle parameter via the vehicle data bus system. A safety control module is configured to trigger a lift drive control module based on at least one vehicle parameter and / or define a lift speed value based on at least one vehicle parameter. The at least one vehicle parameter can be read from a vehicle unit / system connected to the vehicle data bus system via the pump control unit, or alternatively, can be written to the vehicle parameter memory of the control unit via a vehicle unit / system connected to the vehicle data bus system. The at least one vehicle parameter may indicate, for example, the current vehicle speed, current vehicle acceleration, current vehicle tilt, or the status of the vehicle's emergency braking system. Typically, the vehicle parameter can be any parameter provided by the vehicle control unit, vehicle sensor system, or any other vehicle unit / system (directly or indirectly) connected to the vehicle data bus system. The vehicle parameter enables the detection / anticipation of situations with high vacuum requirements, such as high-speed driving increasing the risk of relatively long braking processes, or uphill / downhill driving potentially leading to repeated brake pedal operations. This allows the lift drive function to be accurately and predictably adapted to different vehicle conditions, thus providing a reliable, efficient, and durable vehicle vacuum pump. The at least one vehicle parameter can also directly indicate an external lift-drive request. In this case, the safety control module is configured to always (regardless of pressure) trigger the lift-drive control module upon receiving an external lift-drive request. This allows the lift-drive control module to be triggered externally, for example, via the vehicle control unit through the vehicle data bus, and thus provides a universal vehicle vacuum pump.

[0022] In a preferred embodiment of the invention, a vehicle parameter indicates the vehicle speed. The safety control module can, for example, be configured to define a trigger pressure threshold based on the vehicle speed. Since driving noise is relatively low during low-speed driving, the safety control module can be configured, in particular, to define a relatively low trigger pressure threshold when the vehicle speed is relatively low, so as to minimize interfering noise caused by the speed of the boost motor in this situation. The safety control module can also be configured to define a relatively low boost speed value when the vehicle speed is relatively low, so as to minimize the noise generated by the vacuum pump when operating at boost motor speed. This provides a reliable and relatively low-noise vehicle vacuum pump. The safety control module can also be configured to trigger boost drive control independently of pressure when a relatively high vehicle speed is detected, to ensure that the defined target pressure is achieved in the vacuum chamber. This ensures proper operation of the brake booster during high-speed driving and thus provides a vehicle vacuum pump that improves vehicle driving safety.

[0023] A vehicle parameter preferably indicates the emergency braking system status, wherein the safety control module is configured to always and immediately trigger the lift drive control module in the event of emergency braking. This provides maximum pump performance during emergency braking and thus ensures the proper functioning of the vehicle's brake booster, and consequently, the proper functioning of the vehicle's braking system in this situation. This provides a vehicle vacuum pump that improves vehicle driving safety.

[0024] Embodiments of the present invention are described with reference to the accompanying drawings, wherein,

[0025] Figure 1 A schematic diagram of a portion of a motor vehicle braking system having a motor vehicle brake booster and a motor vehicle vacuum pump according to the invention is shown.

[0026] Figure 2 It shows Figure 1 A schematic diagram showing the relationship between the current pressure parameters of the vehicle vacuum pump and the current motor speed.

[0027] Figure 1 A vehicle vacuum pump 10 is shown used in a vehicle braking system 12 to provide a vacuum to the vacuum chamber 14 of a vehicle brake booster 16.

[0028] The vehicle braking system 12 also includes a vehicle pressure sensor 18, which is fluidly connected to the vacuum chamber 14 and configured to measure the pressure difference between the vacuum chamber and atmospheric pressure. The vehicle pressure sensor 18 is also configured to provide a pressure parameter P to the vehicle control unit 20, which indicates the measured vacuum chamber pressure difference. The vehicle control unit 20 is connected to a vehicle data bus system 22, which is configured to enable data communication between the connected vehicle units.

[0029] The vehicle vacuum pump 10 includes a pumping unit 24 having a rotatable pump rotor 26. In this embodiment, the vehicle vacuum pump 10 is a rotary vane pump, wherein the pump rotor 26 includes a plurality of rotor blades configured to slide radially and rotate within a substantially cylindrical pump chamber. The pumping unit 24 is fluidly connected to the vacuum chamber 14 of the vehicle brake booster 16 via a check valve 28. The pumping unit 24 is configured to evacuate the vacuum chamber 14.

[0030] The vehicle vacuum pump 10 also includes an electronically commutated motor 30, which is configured to drive the pump rotor 26 via a rotor shaft 32 rotatably connected to the pump rotor 26. The motor 30 is configured to operate at a variable motor speed.

[0031] The vehicle vacuum pump 10 also includes a pump control unit 34, which is configured to provide closed-loop control of the variable motor speed of the electric motor 30. The pump control unit 34 is connected to a vehicle data bus system 22 via a vehicle data bus connector 36, which is configured to enable data communication via the vehicle data bus system 22.

[0032] In the described embodiment, the pump control unit 34 is configured to periodically read the pressure parameter P from the vehicle control unit 20 via the vehicle data bus system 22. The vehicle data bus connector 36 therefore defines a pressure sensor connector 38, which is configured to receive the pressure parameter P provided by the vehicle pressure sensor 18. In an alternative embodiment, the pump control unit 34 may be directly electrically connected to the vehicle pressure sensor 18 via a separate pressure sensor connector.

[0033] The pump control unit 34 is configured to control the current motor speed MS of the motor 30 based on the pressure parameter P. Specifically, the pump control unit 34 is configured to turn on the motor 30 when the pressure parameter P is below the start-up pressure threshold PA (MS>0), and to turn off the motor 30 when the pressure parameter P is equal to or higher than the deactivation pressure threshold PD (MS=0). In this embodiment, the start-up pressure threshold PA is 500 mbar, and the deactivation pressure threshold PD is 750 mbar.

[0034] According to the present invention, the pump control unit 34 includes a standard operation control module 40, which is configured to actively control the variable motor speed MS during normal pump operation; that is, the standard operation control module 40 is always active if the motor 30 is turned on. The standard operation control module 40 is configured to determine a current standard operating speed value SS optimized in terms of efficiency and wear from a standard operating speed range SSR. In this embodiment, the standard operating speed range includes speed values ​​in the range of 3000 RPM to 4000 RPM.

[0035] According to the present invention, the pump control unit 34 further includes a lift drive control module 42, which is configured to reject the standard operation control module 40 when triggered, and to temporarily set the current motor speed MS corresponding to the current lift speed value BSn that triggers the lift drive control module 42. In this embodiment, the lift drive control module is configured to maintain the current motor speed MS corresponding to the current lift speed value BSn until the pump control unit 34 shuts off the motor 30 when the pressure parameter P reaches / exceeds the shutdown pressure threshold PD.

[0036] According to the present invention, the pump control unit 34 further includes a safety control module 44, which is configured to trigger the lift drive control module 42. In this embodiment, the safety control module 44 includes a lift speed map memory 46, which stores a lift speed control map 48 having two lift speed values ​​BS1 and BS2 and corresponding lift pressure thresholds BP1 and BP2. In this embodiment, the first lift speed value BS1 is 4500 RPM, and the corresponding first lift pressure threshold BP1 is 300 mbar. The second lift speed value BS2 is 5000 RPM, and the corresponding second lift pressure threshold BP2 is 200 mbar. Therefore, the two lift speed values ​​BS1 and BS2 are significantly higher than the standard operating speed range SSR, and the two lift pressure thresholds BP1 and BP2 are lower than the starting pressure threshold PA.

[0037] The safety control module 44 is configured to monitor the pressure parameter P and trigger the lifting drive control module 42 based on the pressure parameter P. Specifically, the safety control module 44 is configured to trigger the lifting drive control module 42 with a first lifting speed value BS1 when the pressure parameter P is between a first lifting pressure threshold BP1 and a second lifting pressure threshold BP2. Furthermore, the safety control module 44 is configured to trigger the lifting drive control module 42 with a second lifting speed value BS2 when the pressure parameter P is below the second lifting pressure threshold BP2.

[0038] Figure 2 The diagram schematically illustrates the corresponding current motor speed MS set by the pump control unit 34 according to the invention based on the pressure parameter P.

[0039] If the pressure parameter P is lower than the second lifting pressure threshold BP2, the current motor speed MS is set corresponding to the second lifting speed value BS2. If the pressure parameter P is between the two lifting pressure thresholds BP1 and BP2, the current motor speed MS is set corresponding to the first lifting speed value BS1. If the pressure parameter P is between the first lifting pressure threshold BP1 and the shutdown pressure threshold PD, the current motor speed MS is set from the standard operating speed range SSR corresponding to the current standard operating speed value SS. If the pressure parameter P is equal to or higher than the shutdown pressure threshold PD, the motor 30 is turned off (MS = 0).

[0040] In this embodiment, the safety control module 44 is further configured to periodically read a first vehicle parameter VP1 from the vehicle control unit 20 via the vehicle data bus system 22, wherein the first vehicle parameter VP1 indicates the current vehicle speed. The safety control module 44 is configured to monitor the first vehicle parameter VP1 and adapt (or adjust) the aforementioned purely pressure-based triggering procedure based on the first vehicle parameter VP1.

[0041] The safety control module 44 is specifically configured to trigger the lift drive control module 42 with a second lift speed value BS2 when the pressure parameter is lower than the first lift pressure threshold BP1, provided that the first vehicle parameter VP1 indicates a vehicle speed higher than a relatively high braking critical speed threshold. The safety control module 44 is further configured to trigger the lift drive control module 42 only when the pressure parameter P is lower than the second lift pressure threshold BP1, provided that the first vehicle parameter VP1 indicates a vehicle speed lower than a relatively low noise critical speed threshold (and the lift drive control module 42 is not triggered if the pressure parameter P is between the two lift pressure thresholds BP1 and BP2).

[0042] In this embodiment, the safety control module 44 is further configured to periodically read a second vehicle parameter VP2 from the emergency braking system control unit 50 via the vehicle data bus system 22, wherein the second vehicle parameter VP2 indicates the current emergency braking system status. The safety control module 44 is configured to monitor the second vehicle parameter VP2, and, when the second vehicle parameter VP2 indicates emergency braking, always and immediately (independent of the pressure parameter P) trigger the lift drive control module 42 with a second lift speed value BS2.

[0043] List of reference numerals

[0044] 10. Motor vehicle vacuum pump

[0045] 12 Motor vehicle braking system

[0046] 14 Vacuum Chamber

[0047] 16 Motor vehicle brake booster

[0048] 18. Motor vehicle pressure sensor

[0049] 20. Motor vehicle control unit

[0050] 22 Vehicle Data Bus System

[0051] 24 Pumping Units

[0052] 26 Pump Rotor

[0053] 28 Check valve

[0054] 30 Electronically commutated motor

[0055] 32 Rotor shaft

[0056] 34 Pump Control Unit

[0057] 36 Vehicle Data Bus Connector

[0058] 38 Pressure sensor connector

[0059] 40 Standard Operation Control Module

[0060] 42. Enhance the drive control module

[0061] 44 Safety Control Module

[0062] 46. ​​Speed ​​Graph Memory

[0063] 48. Speed ​​Control Chart

[0064] 50 Emergency Braking System Control Unit

[0065] BP1 and BP2 increase pressure threshold

[0066] BS1 and BS2 increase speed value

[0067] BSn Current speed increase value

[0068] MS Current motor speed

[0069] P pressure parameter

[0070] PA start-up pressure threshold

[0071] PD deactivation pressure threshold

[0072] SS current standard operating speed value

[0073] SSR standard operating speed range

[0074] VP1 and VP2 vehicle parameters

Claims

1. Motor vehicle vacuum pump (10), comprising - a pumping unit (24) with a rotatable pump rotor (26), - an electronically commutated motor (30) for driving the pump rotor (26), - a pressure sensor connector (38) for periodically receiving a pressure parameter (P) provided by a motor vehicle pressure sensor (18), and - a pump control unit (34) for controlling a variable motor speed (MS) of the motor (30), the pump control unit (34) comprising - a standard operation control module (40) arranged for controlling the variable motor speed (MS) within a standard speed range (SSR), - a boost drive control module (42) arranged for overriding the standard operation control module (40) when triggered and setting the variable motor speed (MS) corresponding to boost speed values (BS1, BS2, BSn) higher than the standard speed range (SSR), - a safety control module (44) arranged for monitoring the pressure parameter (P) and triggering the boost drive control module (42) based on the pressure parameter (P).

2. Motor vehicle vacuum pump (10) according to claim 1, wherein the safety control module (44) being arranged for triggering the boost drive control module (42) when the pressure parameter (P) is below a defined minimum working pressure threshold (BP1, BP2).

3. Motor vehicle vacuum pump (10) according to claim 2, wherein the pump control unit (34) being arranged for switching off the motor (30) when the pressure parameter (P) is equal to or above a deactivation pressure threshold (PD) and switching on the motor (30) when the pressure parameter (P) is below an activation pressure threshold (PA), and wherein the minimum working pressure threshold (BP1, BP2) is below the activation pressure threshold (PA).

4. Motor vehicle vacuum pump (10) according to one of the preceding claims, wherein the safety control module (44) being arranged for defining the boost speed values (BS1, BS2, BSn) based on the pressure parameter (P).

5. The motor vehicle vacuum pump (10) of claim 1, wherein, a vehicle data bus connector (36) is provided for receiving at least one vehicle parameter (VP1, VP2) via a vehicle data bus system (22), and wherein the safety control module (44) is arranged for triggering the boost drive control module (42) based on the at least one vehicle parameter (VP1, VP2) and / or defining the boost speed values (BS1, BS2, BSn) based on the at least one vehicle parameter (VP1, VP2).

6. Motor vehicle vacuum pump (10) according to claim 5, wherein a first vehicle parameter (VP1) is indicative of a motor vehicle speed.

7. Motor vehicle vacuum pump (10) according to claim 5 or 6, wherein a second vehicle parameter (VP2) is indicative of an emergency braking system status, and wherein the safety control module (44) is arranged for always triggering the boost drive control module (42) in case of emergency braking.

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