A METHOD FOR OPERATING AN ELECTRIC AIR COMPRESSOR ASSEMBLY

Abstract

A method for operating an electric air compressor assembly. The assembly includes an electric motor and a compressor which is mechanically coupled to the electric motor and which is capable of providing compressed air to a tank The method comprises monitoring the temperature of at least one component of the electric air compressor assembly and controlling the motor speed as a function of said temperature running the motor at a first speed S1, which results in the temperature increasing; when the temperature reaches a temperature threshold, which is lower than a maximum admissible temperature, running the motor at a second speed S2>S1 until a predetermined desired pressure in the tank is reached.

Claims

1. A method for operating an electric air compressor assembly, especially in a vehicle, said assembly including an electric motor and a compressor which is mechanically coupled to the electric motor and which is capable of providing compressed air to a tank, the method comprising: monitoring the temperature of at least one component of the electric air compressor assembly and controlling the motor speed as a function of said temperature; running the motor at a first speed S1, which results in the temperature increasing; when the temperature reaches a temperature threshold, which is lower than a maximum admissible temperature, running the motor at a second speed S2>S1 until a predetermined desired pressure in the tank is reached.

2. The method according to claim 1, wherein:
0.5Tmax<T1<0.7Tmax.

3. The method according to claim 1, wherein:
1.1S1<S2<1.3S1.

4. The method according to claim 1, S1 is comprised between 2300 and 2700 rpm, and/or S2 is comprised between 2700 and 3300 rpm.

5. The method according to claim 1, further comprising monitoring the temperature of the electric motor or the temperature of the compressor.

6. The method according to claim 1, wherein the motor is run at the second speed S2 during a period which is comprised between 5 s and 35 s, preferably between 15 s and 25 s.

7. The method according to claim 1, wherein, in case the method is implemented during the inflating phase, the motor is run at the second speed S2 during a period which is comprised between 5 and 20% of the total inflating phase duration, preferably between 7 and 15%.

8. The method according to claim 1, wherein, in case the method is implemented during the cycling phase, said cycling phase including a succession of pressure increasing stages and pressure consumption stages, the motor is run at the second speed S2 during at least one pressure increasing stage, during a period which is comprised between 5 and 20% of the duration of said pressure increasing stage, preferably between 7 and 15%.

9. An arrangement comprising: a tank; an electric air compressor assembly including an electric motor and a compressor which is mechanically coupled to the electric motor and which is capable of providing compressed air to the tank; a temperature sensor for sensing the temperature of at least one component of the electric air compressor assembly; a pressure sensor for sensing the pressure in the tank; a controller capable of controlling the motor speed as a function of said temperature according to the method of claim 1.

10. A vehicle comprising an arrangement according to claim 9, at least one air actuated component such as brakes or auxiliaries, and a pneumatic circuit for carrying air from the tank to the component(s).

11. The vehicle according to claim 10, further comprising a vehicle ECU (electrical control unit), and in that the controller capable of controlling the motor speed as a function of said temperature is said vehicle ECU.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

[0044] In the drawings:

[0045] FIG. 1 is a schematic drawing of a vehicle including an electric air compressor assembly according to an embodiment of the invention;

[0046] FIG. 2 is a graph of temperature versus time in an assembly of the invention and in the prior art;

[0047] FIG. 3 is a graph of pressure versus time in an assembly of the invention;

[0048] FIG. 4 is a graph of pressure versus time in an assembly of the prior art;

[0049] FIG. 5 is a graph of motor speed versus time in an assembly of the invention;

[0050] FIG. 6 is a graph of motor speed versus time in an assembly of the prior art.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

[0051] FIG. 1 schematically shows a vehicle 1 equipped with an electric air compressor assembly 10.

[0052] The vehicle 1 can be a truck, a bus, a construction equipment, etc. It can be a hybrid vehicle or a full electric vehicle. The vehicle 1 comprises a vehicle ECU 2 (electrical control unit) and a vehicle power network 3.

[0053] The electric air compressor assembly 10 includes an electric motor 11 and a compressor 15 which is mechanically coupled to the electric motor 11. The electric motor 11 is part of a motor assembly 12 which further comprises a controller 13 capable of controlling the electric motor 11, and a converter 14.

[0054] A power supply line 5 provides the high or low voltage power required to operate the controller 13 and the converter 14 from the vehicle power network 3.

[0055] A communication line 6, such as a CAN bus, connects the vehicle ECU 2 and the controller 13 to allow communication between these components. Thus, via the communication line 6, the vehicle ECU 2 can control the controller 13 and the electric motor 11, and the controller 13 can send data and/or status information on the electric motor 11 and/or compressor 15 to the vehicle ECU 2. Such data may include the temperature(s) of the motor or compressor, the voltage(s) of the motor or compressor, etc.

[0056] The vehicle 1 further comprises at least one air actuated component 7, such as brakes or auxiliaries, the purpose of the electric air compressor assembly 10 being to provide air to said air actuated component(s) 7. The vehicle 1 is equipped with a pneumatic circuit 8 for carrying said air.

[0057] More precisely, in the pneumatic circuit 8, atmospheric air is sucked; it preferably flows through a filter 9 in which it can be dried and cleaned; air then enters the compressor 15 which provides compressed air to a tank 22 before air is carried towards the air actuated component(s) 7.

[0058] The electric air compressor assembly 10 is part of an arrangement 20 which can further comprise: [0059] the tank 22; [0060] a temperature sensor 21 for sensing the temperature of the electric motor 11 and/or a temperature sensor 25 for sensing the temperature of the compressor 15; [0061] a pressure sensor 23 for sensing the pressure in the tank 22; [0062] the controller 13.

[0063] The invention provides a method for operating the electric air compressor assembly 10. The method aims at providing an appropriate pressure level to the air actuated component(s) 7, while avoiding too high temperatures that would cause unwanted shutdowns or even damages. According to the invention, such an operating method involves a thermal management of the electric air compressor assembly 10 based on the motor speed control.

[0064] The method comprises monitoring the temperature T of at least one component of the electric air compressor assembly 10 and controlling the motor speed S as a function of said temperature T. Said temperature can be the temperature of the electric motor 11, measured by the temperature sensor 21, or the temperature of the compressor 15, measured by the temperature sensor 25.

[0065] The method also comprises: [0066] running the motor 11 at a first speed S1, which results in the temperature T increasing; [0067] when the temperature T reaches a temperature threshold T1, which is lower than a maximum admissible temperature Tmax, running the motor 11 at a second speed S2 higher than S1, until a predetermined desired pressure Pset in the tank 22 is reached.

[0068] In practice, the motor speed S can be controlled by the controller 13 from the vehicle ECU 2, which sends a specific speed request depending on the measured temperature T, and possibly on further parameters such as the pressure P measured by the pressure sensor 23, any failure detection, etc. Alternatively, the temperature sensor 21 or 25 could directly send the sensed information to the vehicle ECU 2; in this embodiment, the vehicle ECU 2 is capable of directly controlling the motor speed S as a function of said temperature T.

[0069] FIG. 2 schematically shows the evolution of temperature T over time t.

[0070] According to the invention, as illustrated by the solid line, the motor 11 is run at speed S1 during a first step, which results in the temperature T increasing, for example substantially linearly, until it reaches the temperature threshold T1. This corresponds to working point A on the graph. S1 can be comprised between 2300 and 2700 rpm, for example around 2500 rpm, while T1 can be comprised between 0.5 Tmax and 0.7 Tmax, for example around 0.6 Tmax.

[0071] From T1, the motor 11 is run at speed S2 which is higher than S1, until the predetermined desired pressure Pset in the tank 22 is reached, which corresponds to working point B on the graph. In an embodiment, S2 is comprised between 1.1 S1 and 1.3 S1. S2 can be comprised between 2700 and 3300 rpm, for example around 3000 rpm. During this subsequent second step, the temperature T increases from T1 to T2, for example substantially linearly. As can be seen in FIG. 2, at point B, i.e. when the predetermined desired pressure Pset has been reached, the temperature T2 is lower than the maximum admissible temperature Tmax which is advantageous, as it provides a safety margin regarding overheating. In practice, T2 can be around 0.9 Tmax.

[0072] FIG. 2 also shows in dotted line the evolution of temperature T over time t according to the prior art, wherein, in the period of time illustrated, the motor speed is kept constant at speed S1, until working point B′ on the graph. As can be seen, this results in temperature T increasing, for example substantially linearly, up to and then above T1. At point B′, the temperature T is higher than the maximum temperature T2 reached thanks to the method of the invention. Moreover, in some operating conditions, the temperature at B′ may be equal to Tmax, which requires the compressor 15 to be stopped, even if the predetermined desired pressure Pset in the tank 22 has not been reached.

[0073] Comparison between the solid line and the dotted line of FIG. 2 shows that the invention makes it possible to reach the predetermined desired pressure Pset faster than in the prior art, while also ensuring the temperature reached is kept lower and, in any event, lower than the maximum admissible temperature Tmax.

[0074] Reference is now made to FIGS. 3 and 4 which show the evolution of pressure P over time t, respectively with the method of the invention and in the prior art, and to FIGS. 5 and 6 which show the evolution of motor speed S over time t, respectively with the method of the invention and in the prior art.

[0075] In the graphs are illustrated both: [0076] an inflating phase IP that is a transition phase in which, from a stopped state of the motor 11, pressure P in the tank 22 is increased from 0 bar to the predetermined desired pressure Pset; [0077] and a cycling phase CP that correspond to a permanent regime once the pressure P in the tank 22 has reached the predetermined desired pressure Pset. The cycling phase CP includes a succession of pressure increasing stages and pressure consumption stages. More specifically, from a pressure equal to Pset, also called Pcut-off, the compressor 15 is stopped and air is consumed, making pressure decrease down to a lower threshold Plt, also called Pcut-in. At this lower threshold Plt, the compressor 15 is started again to make pressure increase up to Pset again, and this cycle repeats.

[0078] Pset and Plt are determined so that, in the range of pressure comprised between Plt and Pset, the pressure level provided to the air actuated component(s) 7 is suitable for a proper operation. For example, Pset can be around 10.5 bar while Plt can be around 9-9.5 bar.

[0079] FIGS. 3 and 5 show an embodiment in which the method of the invention is implemented during the inflating phase IP.

[0080] As can be seen, from 0 bar (i.e. a stopped state of the motor 11), pressure P in the tank 22 is increased during successive steps up to Pset, by the operation of the compressor 15. In this embodiment, the motor speed S is first of all decreased by increments down to S1, which results in the pressure P keeping on increasing, but more and more slowly. Then, from the above mentioned working point A, i.e. when temperature T has reached the temperature threshold T1, the motor speed S is increased to S2 which is higher than the previous value S1 of the motor speed, in the preceding step. This results in an increase of pressure P which is faster than in the preceding step.

[0081] In the exemplary embodiment of FIGS. 3 and 5, the inflating phase IP may comprise the following successive steps: [0082] the motor 11 is run at speed S.sub.0a during Δt.sub.0a. S.sub.0a can be around 3000 rpm; Δt.sub.0a can be in the range of 150-200 s, for example around 175 s; [0083] the motor 11 is run at speed S.sub.0b during Δt.sub.0b. S.sub.0b is lower than S.sub.0a, for example around 2800 rpm; Δt.sub.0a can be lower than Δt.sub.0a, in the range of 80-110 s, for example around 95 s; [0084] the motor 11 is run at speed S1 during Δt1. S1 is lower than S.sub.0b, for example around 2500 rpm; Δt1 can be lower than Δt.sub.0b, in the range of 30-50 s, for example around 35 s; [0085] the motor 11 is run at speed S2 during Δt2. S2 is higher than S1, for example around 3000 rpm. However, S2 is not necessarily equal or close to S.sub.0a. Δt2 can be lower than Δt1, in the range of 20-30 s, for example around 25 s. This step is carried out until the predetermined desired pressure Pset in the tank 22 is reached, which corresponds to working point B.

[0086] The last above mentioned step, between working points A and B, during which the motor is run at speed S2 may be carried out during a period Δt2 which is comprised between 5 and 20% of the total inflating phase duration, preferably between 7 and 15%.

[0087] Pressure at working point A may be comprised between the lower threshold Plt and the predetermined desired pressure Pset.

[0088] The pressure P0 at which the motor speed S changes from S.sub.0a to S.sub.0b may be around 6-7 bar, while the pressure P1 at which the motor speed S changes from S.sub.0b to S1 may be around 8-9 bar.

[0089] The pressures P0, P1, as well as the motor speeds S.sub.0a, S.sub.0b, S1 in the first steps may be parameters defined in order to respect regulation, noise level, etc.

[0090] From working point B, the motor 11 is stopped, and then begins the cycling phase CP, with successive pressure increasing stages and pressure consumption stages. Although the motor speed during the pressure increasing stages is shown in FIG. 5 as being equal to S1, other values are possible.

[0091] FIGS. 4 and 6 are similar to FIGS. 3 and 5, respectively, according to a method of the prior art. The inflating phase IP may comprise the following successive steps from 0 bar: [0092] the motor is run at speed S′.sub.0a, which may be equal to S.sub.0a, until pressure reaches P0.

[0093] This step can last during the same duration Δt.sub.0a as with the invention; [0094] the motor is run at speed S′.sub.0b, which may be equal to S.sub.0b, until pressure reaches P1.

[0095] This step can last during the same duration Δt.sub.0b as with the invention; [0096] and then, the motor is run at speed S1 until the predetermined desired pressure Pset in the tank 22 is reached, which corresponds to working point B′. This step is carried out during Δt′1.

[0097] As can be seen from the comparison between FIGS. 3 and 4, Δt′1 is higher than Δt1+Δt2. (the difference being shown by reference 5). In other words, owing to the specific step between working points A and B, during which the motor is run at a higher speed S2>S1, during a short time, the invention makes it possible to reach the predetermined desired pressure Pset earlier than in the prior art. This is of paramount importance as it results in lower temperatures in the motor 11 and compressor 15, which are critical operational factors.

[0098] In an embodiment, the duration of inflating phase IF may be reduced by 5-10% with the method of the invention as compared with the prior art.

[0099] Owing to the invention, in which a higher motor speed is used for a short time at the end of the inflating phase, and as compared to the prior art method: the predetermined desired pressure Pset is reached earlier, meaning that the inflating phase is shorter; temperature increases faster but to a lower value; compressor is stopped earlier; temperature decreases faster to an acceptable value.

[0100] The above description of an embodiment of the method according to the invention should not be considered as limitative.

[0101] According to a variant, more or less steps (during which the motor 11 is run at a given speed S) may be carried out before the last step during which the motor 11 is run at speed S2.

[0102] Besides, alternatively or in addition, the invention could be implemented during the cycling phase CP. In that case, the motor is run at the second speed S2 during at least one pressure increasing stage, during a period which is comprised between 5 and 20% of the duration of said pressure increasing stage, preferably between 7 and 15%.

[0103] It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims.