Method and system for generating compressed air of at least one vehicle, particularly at least one railway vehicle

Technical field

The present invention generally relates to the field of braking systems, in particular railway braking systems. In particular, the invention relates to a method for generating compressed air of at least one vehicle or a convoy and to a system for generating compressed air of at least one vehicle or a convoy.

Prior art

The prior art will be described below with particular reference to the field of railway vehi cles. Nevertheless, that which is described in the following may also apply, where possible, to vehicles in other fields.

Braking systems and suspension systems for railway vehicles for passenger transport are powered by compressed air.

A system for generating compressed air according to the prior art is illustrated in Figure 1.

Such system for generating compressed air 100 comprises a motor 101 whose motor shaft 102 supplies a driving torque to a motor shaft 103 of a compressor 104 through an elastic coupling 105.

Through an inlet 106, the compressor 104 draws air at atmospheric pressure, compresses it and, through a pneumatic connection 107 and a non-return valve 108, supplies a dryer unit 109. The dryer unit 109 has the purpose of removing the liquid component and the vapor of the water derived from the compression of humid air and supplying dried air to a main res ervoir 110 through a second duct 111 and a second non-return valve 112.

A control unit 113 receives an electrical power supply 115 and measures a pressure in the main reservoir 110 by means of a pressure transducer 114.

When the pressure in the main reservoir 110 assumes a value less than or equal to a minimum value Pmin, the control unit 113 supplies electrical power to the electric motor 101.

When the pressure in the main reservoir 110 assumes a value equal to or greater than a max imum value Pmax, the control unit 113 cuts off the electrical supply to the electric motor 101.

In the railway sector, the minimum value Pmin generally assumes values of between 6bar and 7 bar, and the maximum value Pmax generally assumes values of between 9bar and lObar.

It is prior art that the system for generating compressed air 100 is integrated inside an acous tically insulated metal structure provided with damping connections to the railway vehicle in order to reduce the noise emitted and the vibrations transmitted to a body of the railway vehicle, respectively.

Through a distribution duct 116, the compressed air stored in the main reservoir 110 is sup plied to at least one user system 117, 118, such as, for example, the braking system, the suspension system, the toilets, the pantographs, the doors.

Figure 2 illustrates a typical railway convoy 200 for carrying passengers.

Two compressed air generation systems 201 and 202, corresponding to the compressed air generation system 100 of Figure 1, supply compressed air to a main duct 202, which in turn supplies a main reservoir 204 through a non-return valve 215.

From the main reservoir 204 various systems 205, 206, 207, such as for example the braking system, suspensions, toilets, draw compressed air for their operation.

Two compressed air generation systems 201, 202 are considered necessary for redundancy reasons, i.e. to guarantee a permanent supply of compressed air even in the event of failure of one of the two compressed air generation systems 201, 202 during operational daily ser vice.

A control system 208 alternatively enables the two compressed air generation systems 201, 202 by means of the supply signals 209, 210, this disadvantageously meaning that one of the two compressed air generation systems 201, 202 is on average unused throughout service.

The weight of each compressed air generation system 201, 202 often exceeds 500kg, disad vantageously requiring an unnecessary expenditure of energy to accelerate the mass thereof. This energy is then definitively lost during braking due to poor efficiency of the regenerative braking system or intrinsically dissipative mechanical friction braking.

In general, a single compressed air generation system may supply compressed air at full capacity at the total cost of two systems.

Summary of the invention

An object of the present invention is to provide a method and a system for generating com pressed air of at least one vehicle, in particular at least one railway vehicle, which reduces the weight and the cost compared to compressed air generation systems according to the prior art, while respecting the redundancy requirement.

The aforesaid and other objects and advantages are achieved, according to an aspect of the invention, by a method for generating compressed air of at least one vehicle having the fea tures defined in claim 1 and by a compressed air generation system of at least one vehicle having the features defined in claim 6. Preferred embodiments of the invention are defined in the dependent claims, the content of which is to be understood as an integral part of the present description.

Brief description of the drawings The functional and structural features of some preferred embodiments of a system for gen erating compressed air of at least one vehicle according to the invention will now be de scribed. Reference is made to the accompanying drawings, in which:

- Figure 1 illustrates an exemplary system for generating compressed air of at least one vehicle, particularly at least one railway vehicle, according to the prior art;

- Figure 2 illustrates an exemplary railway convoy for the transport of passengers;

- Figure 3 illustrates a first embodiment of a compressed air generation system of at least one vehicle;

- Figure 4 illustrates a further embodiment of a compressed air generation system of at least one vehicle;

- Figure 5 illustrates a still further embodiment of a compressed air generation system of at least one vehicle;

- Figure 6 illustrates a graph of an exemplary operating cycle of a compressed air generation system of at least one vehicle.

Detailed description

Before describing in detail a plurality of embodiments of the invention, it should be clarified that the invention is not limited in its application to the design details and configuration of the components presented in the following description or illustrated in the drawings. The invention is able to assume other embodiments and to be implemented or constructed in practice in different ways. It should also be understood that the phraseology and terminology have a descriptive purpose and should not be construed as limiting. The use of “include” and “comprise” and their variations is to be understood as encompassing the elements set out below and their equivalents, as well as additional elements and the equivalents thereof.

In a first embodiment, a method for generating compressed air of at least one vehicle, in particular a railway vehicle, comprises the step of: a) selectively connecting, or disconnecting, a first compressor 303, or a second com pressor 307, or simultaneously said first compressor 303 and said second compressor 307, to an electric motor 301 arranged to generate a driving torque. Preferably, the method further comprises the step of measuring a pressure value indicative of the internal pressure of a main reservoir 311 arranged to accumulate compressed air gen erated by said first compressor 303 and said second compressor 307.

The pressure value inside said main reservoir 311 may assume over time a value included in a range of pressures. Such range of pressures includes a null value, a first predetermined pressure value Pmin (greater than said null value) and a second predetermined pressure value Pmax, greater than said first predetermined pressure value Pmin.

Preferably, when the pressure value in said main reservoir 311 is lower than the first prede termined pressure value Pmin, step a) may comprise:

- connecting said first compressor 303 to said electric motor 301;

- connecting said second compressor 307 to said electric motor 301;

- keeping said first compressor 303 and said second compressor 307 connected to said electric motor 301, until the pressure value in said main reservoir 311 reaches or exceeds said first predetermined pressure value Pmin (i.e. until the pressure value in said main res ervoir 311 is equal to the first predetermined pressure value Pmin or higher than the first predetermined pressure value Pmin).

Preferably, in addition or alternatively to what has been said for the condition in which said pressure value is lower than the first predetermined pressure value Pmin, when the pressure value in said main reservoir 311 is equal to or greater than the second predetermined value pressure Pmax, step a) may comprise:

- disconnecting, or keeping disconnected, said first compressor 303 from said electric motor 301;

- disconnecting, or keeping disconnected, said second compressor 307 from said elec tric motor 301;

- keeping said first compressor 303 and said second compressor 307 disconnected from said electric motor 301, until the pressure value in said main reservoir 311 is equal to or less than said first predetermined pressure value Pmin.

Preferably, in addition or alternatively to what has been said for the condition in which said pressure value is lower than the first predetermined pressure value Pmin and for the condi tion in which said pressure value is equal to or greater than the second predetermined value of pressure Pmax, when the pressure value in said main reservoir 311 is equal to the first predetermined pressure value Pmin or comprised between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax, step a) may selectively com prise:

- connecting, or keeping connected, said second compressor 307 to said electric mo tor 301;

- disconnecting, or keeping disconnected, said first compressor 303 from said electric motor 301;

- keeping said second compressor 307 connected to said electric motor 301, and keep ing said first compressor 303 disconnected from said electric motor 301, until the pressure value in said main reservoir 311 is equal to or greater than the second predetermined pressure value Pmax; or,

- disconnecting, or keeping disconnected, said second compressor 307 from said electric motor 301;

- connecting, or keeping connected, said first compressor 303 to said electric motor

301;

- keeping said second compressor 307 disconnected from said electric motor 301, and keeping said first compressor 303 connected to said electric motor 301, until the pressure value in said main reservoir 311 is equal to or greater than the second predetermined pressure value Pmax.

In another aspect of the invention, with reference to Figure 3, a first embodiment of a system for generating compressed air of at least one vehicle, particularly at least one railway vehicle, is illustrated.

Such system for generating compressed air of at least one vehicle comprises an electric mo tor 301 arranged to generate a driving torque.

The system for generating compressed air of at least one vehicle further comprises a first coupling means 304, arranged to selectively assume a first state in which it connects said electric motor 301 to said first compressor 303 or a second state in which it disconnects said motor electric motor 301 from said first compressor 303, and a second coupling means 308, arranged to selectively assume a first state in which it connects said electric motor 301 to said second compressor 307 or a second state in which it disconnects said electric motor 301 from said second compressor 307.

The compressed air generation system of at least one vehicle further comprises a control means 320 arranged to control the transition between the first state and the second state, and vice versa, of said first coupling means 304 and the transition between the first state and the second state, and vice versa, of said second coupling means 308, so that said driving torque generated by said electric motor 301 is selectively supplied to the first compressor 303 or to the second compressor 307 or simultaneously to said first compressor 303 and to said second compressor 307.

For example, the control means may be or comprise at least one of a control unit, a processor, a microprocessor, a controller, a microcontroller, an FPGA, a PLC, or the like.

Preferably, the compressed air generation system of at least one vehicle may comprise a main reservoir 311 arranged to store compressed air generated by said first compressor 303 and said second compressor 307, and a pressure sensor means arranged to measure a pressure value inside said main reservoir 311.

The pressure value inside said main reservoir 311 may assume a pressure value included in a range of pressures. Such range of pressures includes a null value, a first predetermined pressure value Pmin (greater than said null value) and a second predetermined pressure value Pmax, greater than said first predetermined pressure value Pmin.

The pressure sensor means may be or comprise, for example, a pressure sensor or a pressure measuring device, or the like.

Preferably, when the pressure value measured by said pressure sensor means is lower than the first predetermined pressure value Pmin, the control means 320 may be arranged to:

- control said first coupling means 304 so that it is in its first state in which it connects said electric motor 301 to said first compressor 303;

- control said second coupling means 308 so that it is in its first state in which it connects said electric motor 301 to said second compressor 307;

- keep said first coupling means 304 in the first state and said second coupling means 308 in the first state, until the pressure value measured by said pressure sensor means reaches or exceeds said first predetermined pressure value Pmin (i.e. until the pressure value in said main reservoir 311 is equal to the first predetermined pressure value Pmin or higher than the first predetermined pressure value Pmin).

By higher than said first predetermined pressure value Pmin, for example, it may be understood a value equal to the second predetermined pressure value Pmax higher than said first predeter mined pressure value Pmin, or a value between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax.

For example, the control means 320 may:

- cause said first coupling means 304 to assume the first state in which it connects said electric motor 301 to said first compressor 303, so that the driving torque generated by the electric motor 301 is transmitted to said first compressor 303;

- cause said second coupling means 308 to assume the first state in which it connects said electric motor 301 to said second compressor 307, so that the driving torque generated by the electric motor 301 is transmitted to said second compressor 307.

Preferably, when the pressure value measured by the pressure sensor means is lower than the first predetermined pressure value Pmin, said control means 320 may be arranged to:

- drive the electric motor 301, so as to generate a driving torque having a first torque value.

In other words, with reference to the exemplary operating cycle of Figure 6, in an instant TO of ignition of the vehicle or convoy, for example railway vehicle or railway convoy, the control means 320 (e.g. a control unit) may control the first coupling means 304 (e.g. a first electromechanical clutch) and the second coupling means 308 (e.g. a second electromechan ical clutch 308) in their first state in which they transmit the driving torque of the electric motor 301 to the first compressor 303 and to the second compressor 307, and may control the electric motor 301 to rotate at a first speed VI, so as to generate a driving torque having a first torque value, suitable for bringing the pressure in the main reservoir 311 to the first predetermined pressure value Pmin as fast as possible.

In addition or as an alternative to what has been said for the condition in which said pressure value is lower than the first predetermined pressure value Pmin, preferably, when the pres sure value measured by said pressure sensor means is equal to the first predetermined pres sure value Pmin or comprised between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax, the control means 320 may be selectively ar ranged to:

- control said second coupling means 308 so that it is in its first state in which it connects said electric motor 301 to said second compressor 307, and control said first cou pling means 304 so that it is in its second state in which it disconnects said electric motor 301 from said first compressor 303;

- keep said second coupling means 308 in its first state and said first coupling means 304 in its second state, until the pressure value measured by said pressure sensor means is equal to, or greater than, the second predetermined pressure value Pmax, greater than said first predetermined pressure value Pmin; or,

- control said first coupling means 304 so that it is in its first state in which it connects said electric motor 301 to said first compressor 303, and control said second coupling means 308 so that it is in its second state in which it disconnects said electric motor 301 from said second compressor 307;

- keep said first coupling means 304 in its first state, and said second coupling means 308 in its second state, until the pressure value measured by said pressure sensor means is equal to, or greater than, a second predetermined pressure value Pmax, which is greater than said first predetermined pressure value Pmin.

For example, the control means 320 may be arranged to selectively: - if said second coupling means 308 is already in its first state, keep said second coupling means 308 in its first state, and cause said first coupling means 304 to assume or keep the second state in which it disconnects said electric motor 301 from said first com pressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303;

- if said second coupling means 308 is not already in its first state, make said second coupling means 308 assume the first state in which it connects said electric motor 301 to said second compressor 307, so that the driving torque generated by the electric motor 301 is transmitted to said second compressor 307, and cause said first coupling means 304 to assume or keep the second state in which it disconnects said electric motor 301 from said first compressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303; or,

- if said first coupling means 304 is already in its first state, keep said first coupling means 304 in its first state, and cause said second coupling means 308 to assume or keep the second state in which it disconnects said electric motor 301 from said second compressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307;

- if said first coupling means 304 is not already in its first state, make said first cou pling means 304 assume the first state in which it connects said electric motor 301 to said first compressor 303, so that the driving torque generated by the electric motor 301 is trans mitted to said first compressor 303, and cause said second coupling means 308 to assume or keep the second state in which it disconnects said electric motor 301 from said second com pressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307.

For example, referring to the exemplary operating cycle of Figure 6, following the instant T2 in which the second predetermined pressure value Pmax is reached, the pressure in the main reservoir 311 may begin to drop towards the first predetermined pressure value Pmin due to a request for compressed air by one or more users 205, 206, 207. When at instant T3 the pressure in the main reservoir 311 has reached first predetermined pressure value Pmin (i.e. when it is necessary to bring the pressure in the main reservoir from the first predetermined pressure value Pmin to the second predetermined pressure value Pmax), the control unit 320 may choose which of the first compressor 303 and the second compressor 307 is to be coupled to the electric motor 301, and may couple the selected compressor to the electric motor 301 by controlling the coupling means (e.g. the electromechanical clutch) associated with the selected compressor, in its first state in which it transmits driving torque from the electric motor 301 to the selected compressor, and may for example control the electric motor 301 to rotate at a second speed V2, less than or equal to said first speed VI, i.e. V2<V1. The other unselected compressor is not coupled to the electric motor 301 by controlling the coupling means (e.g. the electromechanical clutch) associated with the unse lected compressor, in its second state in which it does not transmit driving torque from the electric motor 301 to the unselected compressor. In the embodiment described above, the preselected compressor may be any one between the first compressor 303 and the second compressor 307.

Preferably, according to a first criterion, the control means 320 may be arranged to measure a first overall activation time of said first compressor 303 and to measure a second overall activation time of said second compressor 307.

When the pressure value measured by said pressure sensor means is equal to the first prede termined pressure value Pmin or comprised between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax, and the first overall activation time of said first compressor 303 is greater than said second overall activation time of said second compressor 307, said control means 320 may be arranged to:

- control said second coupling means 308 so that it is in its first state in which it connects said electric motor 301 to said second compressor 307, and control said first cou pling means 304 so that it is in its second state in which it disconnects said electric motor 301 from said first compressor 303;

- keep said second coupling means 308 in its first state and said first coupling means 304 in its second state, until the pressure value measured by said pressure sensor means is equal to, or greater than, the second predetermined pressure value Pmax, greater than said first predetermined pressure value Pmin. For example, the control means 320 may be arranged to:

- if said second coupling means 308 is already in its first state, keep said second coupling means 308 in its first state, and cause said first coupling means 304 to assume or keep the second state in which it disconnects said electric motor 301 from said first com pressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303;

- if said second coupling means 308 is not already in its first state, make said second coupling means 308 assume the first state in which it connects said electric motor 301 to said second compressor 307, so that the driving torque generated by the electric motor 301 is transmitted to said second compressor 307, and cause said first coupling means 304 to assume or keep the second state in which it disconnects said electric motor 301 from said first compressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303.

When, instead, the pressure value measured by said pressure sensor means is equal to the first predetermined pressure value Pmin or comprised between the first predetermined pres sure value Pmin and the second predetermined pressure value Pmax, and the first overall activation time of said first compressor 303 is shorter than said second overall activation time of said second compressor 307, said control means 320 may be arranged to:

- control said first coupling means 304 so that it is in its first state in which it connects said electric motor 301 to said first compressor 303, and control said second coupling means 308 so that it is in its second state in which it disconnects said electric motor 301 from said second compressor 307;

- keep said first coupling means 304 in its first state, and said second coupling means 308 in its second state, until the pressure value measured by said pressure sensor means is equal to, or greater than, a second predetermined pressure value Pmax, which is greater than said first predetermined pressure value Pmin.

For example, the control means 320 may be arranged to:

- if said first coupling means 304 is already in its first state, keep said first coupling means 304 in its first state, and cause said second coupling means 308 to assume or keep the second state in which it disconnects said electric motor 301 from said second compressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307;

- if said first coupling means 304 is not already in its first state, make said first cou pling means 304 assume the first state in which it connects said electric motor 301 to said first compressor 303, so that the driving torque generated by the electric motor 301 is trans mitted to said first compressor 303, and cause said second coupling means 308 to assume or keep the second state in which it disconnects said electric motor 301 from said second com pressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307.

In other words, in the first criterion just described, when it is necessary to bring the pressure in the main reservoir from the first predetermined pressure value Pmin to the second prede termined pressure value Pmax, the control means 320 (e.g. the control unit) may count the cumulative usage time of the first compressor and the second compressor and choose to connect the compressor with the shortest usage time to the electric motor, in order to better equalize the consumption of the components of the first compressor and the second com pressor, so as to reach the deadline of the maintenance cycle at the same time.

Preferably, according to a second criterion, the control means 320 may be arranged to meas ure a first overall activation time of said first compressor 303 and to measure a second overall activation time of said second compressor 307. The control means 320 may be arranged to:

- - if the first overall activation time of said first compressor 303 is greater than said second overall activation time of said second compressor 307, prevent acti vation of the first compressor 303 for a first inhibition time period;

- - if the first overall activation time of said first compressor 303 is shorter than said second overall activation time of said second compressor 307, prevent acti vation of the second compressor 307 for a second inhibition time period.

In this case, in said first inhibition time period, when the pressure value measured by said pressure sensor means is equal to the first predetermined pressure value Pmin or comprised between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax, said control means 320 may be arranged to: - control said second coupling means 308 so that it is in its first state in which it connects said electric motor 301 to said second compressor 307, and control said first cou pling means 304 so that it is in its second state in which it disconnects said electric motor 301 from said first compressor 303;

- keep said second coupling means 308 in its first state and said first coupling means 304 in its second state, until the pressure value measured by said pressure sensor means is equal to, or greater than, the second predetermined pressure value Pmax, greater than said first predetermined pressure value Pmin.

For example, the control means 320 may be arranged to:

- if said second coupling means 308 is already in its first state, keep said second coupling means 308 in its first state, and cause said first coupling means 304 to assume or keep the second state in which it disconnects said electric motor 301 from said first com pressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303;

- if said second coupling means 308 is not already in its first state, make said second coupling means 308 assume the first state in which it connects said electric motor 301 to said second compressor 307, so that the driving torque generated by the electric motor 301 is transmitted to said second compressor 307, and cause said first coupling means 304 to assume or keep the second state in which it disconnects said electric motor 301 from said first compressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303.

In said second inhibition time period, when the pressure value measured by said pressure sensor means is equal to the first predetermined pressure value Pmin or comprised between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax, said control means 320 may be arranged to:

- control said first coupling means 304 so that it is in its first state in which it connects said electric motor 301 to said first compressor 303, and control said second coupling means 308 so that it is in its second state in which it disconnects said electric motor 301 from said second compressor 307;

- keep said first coupling means 304 in its first state, and said second coupling means 308 in its second state, until the pressure value measured by said pressure sensor means is equal to, or greater than, a second predetermined pressure value Pmax, which is greater than said first predetermined pressure value Pmin.

For example, the control means 320 may be arranged to:

- if said first coupling means 304 is already in its first state, keep said first coupling means 304 in its first state, and cause said second coupling means 308 to assume or keep the second state in which it disconnects said electric motor 301 from said second compressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307;

- if said first coupling means 304 is not already in its first state, make said first cou pling means 304 assume the first state in which it connects said electric motor 301 to said first compressor 303, so that the driving torque generated by the electric motor 301 is trans mitted to said first compressor 303, and cause said second coupling means 308 to assume or keep the second state in which it disconnects said electric motor 301 from said second com pressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307.

In other words, in the second criterion just described, the control unit 320 may re-count the cumulative usage time of the first compressor and second compressor and, for example at the start of the operating day, the control unit 320 may choose the compressor that has the shortest cumulative usage time and, when it is necessary to bring the pressure in the main reservoir from the first predetermined pressure value Pmin to the second predetermined pres sure value Pmax, it may use it for a predetermined period, inhibiting the other compressor in such predetermined period (e.g. all day).

Preferably, according to a third criterion, said control unit may be arranged to define first time-intervals in which activation of the first compressor 303 is prevented and second time- intervals in which activation of second compressor 307 is prevented. Said first time-intervals and said second time-intervals may be alternated to each other over time. When in one of said first time-intervals, the pressure value measured by said pressure sensor means is equal to the first predetermined pressure value Pmin or comprised between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax, said control means 320 may be arranged to:

- control said second coupling means 308 so that it is in its first state in which it connects said electric motor 301 to said second compressor 307, and control said first cou pling means 304 so that it is in its second state in which it disconnects said electric motor 301 from said first compressor 303;

- keep said second coupling means 308 in its first state and said first coupling means 304 in its second state, until the pressure value measured by said pressure sensor means is equal to, or greater than, the second predetermined pressure value Pmax, greater than said first predetermined pressure value Pmin.

For example, the control means 320 may be arranged to:

- if said second coupling means 308 is already in its first state, keep said second coupling means 308 in its first state, and cause said first coupling means 304 to assume or keep the second state in which it disconnects said electric motor 301 from said first com pressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303;

- if said second coupling means 308 is not already in its first state, make said second coupling means 308 assume the first state in which it connects said electric motor 301 to said second compressor 307, so that the driving torque generated by the electric motor 301 is transmitted to said second compressor 307, and cause said first coupling means 304 to assume or keep the second state in which it disconnects said electric motor 301 from said first compressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303.

Moreover, when in one of said second time-intervals, the pressure value measured by said pressure sensor means is equal to the first predetermined pressure value Pmin or comprised between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax, said control means 320 may be arranged to:

- control said first coupling means 304 so that it is in its first state in which it connects said electric motor 301 to said first compressor 303, and control said second coupling means 308 so that it is in its second state in which it disconnects said electric motor 301 from said second compressor 307;

- keep said first coupling means 304 in its first state, and said second coupling means 308 in its second state, until the pressure value measured by said pressure sensor means is equal to, or greater than, a second predetermined pressure value Pmax, which is greater than said first predetermined pressure value Pmin.

For example, the control means 320 may be arranged to:

- if said first coupling means 304 is already in its first state, keep said first coupling means 304 in its first state, and cause said second coupling means 308 to assume or keep the second state in which it disconnects said electric motor 301 from said second compressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307;

- if said first coupling means 304 is not already in its first state, make said first cou pling means 304 assume the first state in which it connects said electric motor 301 to said first compressor 303, so that the driving torque generated by the electric motor 301 is trans mitted to said first compressor 303, and cause said second coupling means 308 to assume or keep the second state in which it disconnects said electric motor 301 from said second com pressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307.

In other words, in the third criterion just described, when it is necessary to bring the pressure in the main reservoir from the first predetermined pressure value Pmin to the second pre determined pressure value Pmax, the control unit 320 may alternatively use the two com pressors at alternate regular periods, for example non-exclusive on alternate days. In this way, the selected compressor may be kept for a period, always at temperature to limit the formation of condensation inside the compressor due to excessive cooling and the wear of the first compressor and the second compressor is balanced.

Preferably, it may apply to all the embodiments described above that when the pressure value measured by said pressure sensor means is between the first predetermined pressure value Pmin and the second predetermined pressure value Pmax, which is greater than the first predetermined pressure value Pmin, the control means 320 may be arranged to: - drive the electric motor 301, so as to generate a driving torque having a second torque value, less than said first torque value.

Preferably, in addition or alternatively to what has been said for the condition in which said pressure value is lower than the first predetermined pressure value Pmin and for the condi tion in which said pressure value is equal to the first predetermined pressure value Pmin or comprised between the first predetermined pressure value Pmin and the second predeter mined pressure value Pmax, when the pressure value measured by said pressure sensor means is equal to or greater than the second predetermined pressure value Pmax, greater than said first predetermined value of pressure Pmin, said control means 320 may be arranged to:

- control said first coupling means 304 so that it is in its second state in which it discon nects said electric motor 301 from said first compressor 303;

- control said second coupling means 308 so that it is in its second state in which it disconnects said electric motor 301 from said second compressor 307;

- keep said first coupling means 304 in its second state, and said second coupling means 308 in its second state, until the pressure value measured by said pressure sensor means is equal to, or lower than, said first predetermined pressure value Pmin.

For example, the control means 320 may be arranged to:

- if said first coupling means 304 is not already in its second state, cause said first cou pling means 304 to assume the second state in which it disconnects said electric motor 301 from said first compressor 303, so that the driving torque generated by the electric motor 301 is not transmitted to said first compressor 303;

- if said second coupling means 308 is not already in its second state, cause said second coupling means 308 to assume the second state in which it disconnects said electric motor 301 from said second compressor 307, so that the driving torque generated by the electric motor 301 is not transmitted to said second compressor 307.

In other words, with reference to the exemplary operating cycle of Figure 6, when at an instant T2 the pressure value Pmax is reached, the control means 320 may turn off the electric motor 301 and control the first coupling means 304 (e.g. the first electromechanical clutch) and the second coupling means 308 (e.g. the second electromechanical clutch 308) in their second state in which they do not transmit driving torque from the electric motor 301 to the first compressor 303 and the second compressor 307, respectively.

Preferably, when the pressure value measured by said pressure sensor means is equal to or higher than the second predetermined pressure value Pmax, the control means 320 may be arranged to:

- drive the electric motor 301, so as to generate a driving torque of zero value.

Preferably, the compressed air generation system of at least one vehicle may comprise a first air dryer means 310 and a second air dryer means 313. The first air dryer means 310 may be arranged to receive the compressed air generated by the first compressor 303 and generate first dried compressed air to be supplied to said main reservoir 311. The second air dryer means 313 may be arranged to receive the compressed air generated by the second compres sor 307 and generate second dried compressed air to be supplied to said main reservoir 311.

For example, the first compressor 303 may feed a first dryer 310, which in turn may feed the main reservoir 311 through a non-return valve 312. The second compressor 307 may feed a second dryer 313, which in turn feeds the main reservoir 311 through a non-return valve 314.

Or, the compressed air generation system of at least one vehicle may comprise only one air dryer means. In this case, the air dryer means may be arranged to receive compressed air generated by the first compressor 303, receive compressed air generated by the second com pressor 307 and generate dried compressed air to be supplied to said main reservoir 311.

For example, referring to Figure 4, the first compressor 303 and the second compressor 307 may supply compressed air to a single dryer 310, for example through two non-return valves 312, 314, respectively.

Preferably, the electric motor 301 may comprise a first drive shaft 302 arranged to transmit driving torque to a first compressor 303 through the first coupling means 304 and a first mechanical coupling 305, and a second drive shaft 306, arranged to be integral with the said first drive shaft 302 and to transmit the driving torque to the second compressor 307 through the second coupling means 308 and a second mechanical coupling 309.

Preferably, in a further embodiment, the electric motor 301 may comprise a drive shaft 501 on which the first coupling means 304 and the second coupling means 308 are arranged to be bound. In this case, the compressed air generation system of at least one vehicle may comprise a first pulley 505 and a second pulley 507. The first pulley 505 may be arranged to be mechanically bound to a shaft 504 of the first compressor 303, and the second pulley 507 may be arranged to be mechanically bound to a shaft 506 of a second compressor 307. The first coupling means 502, 304 may be arranged to transmit driving torque to the first pulley 505 by at least one drive belt 508, and the second coupling means 503, 308 may be arranged to transmit driving torque to the second pulley 507 by at least one drive belt 509.

Preferably, the first coupling means 304 may be an electromechanical clutch.

Preferably, the second coupling means 308 may also be an electromechanical clutch.

For example, the first predetermined pressure value Pmin may generally assume values of between 6bar and 7 bar, and the second predetermined pressure value Pmax may generally assume values of between 9bar and lObar.

In a first implementation example, a compressed air generation system 300 may comprise an electric motor 301 having a first drive shaft 302 for transmitting driving torque to a first compressor 303 through a first coupling means 304, such as for example a first electrome chanical clutch, and a first mechanical coupling 305.

Furthermore, the electric motor 301 may be provided with a second drive shaft 306, integral with the first drive shaft 302, for transmitting driving torque to a second compressor 307 through a second coupling means 308, such as for example a second electromechanical clutch, and a second mechanical coupling 309.

The first compressor 303 may feed a first dryer means 310, for example a first dryer, which in turn may feed the main reservoir 311 through a non-return valve 312. The second compressor 307 may feed a second dryer means 313, for example a second dryer, which in turn may feed the main reservoir 311 through a non-return valve 314.

The control means 320, for example a control unit, may be arranged to:

- receive a power supply 321;

- control, through a power signal 323, the first coupling means 304 in a first state in which the first coupling means 304 transmits driving torque from the electric motor 301 to the first compressor 303 and in a second state in which the first coupling means 304 does not transmit torque from the electric motor 301 to the first compressor 303; and

- drive the second coupling means 308 through a power signal 324 in a first state in which the second coupling means 308 transmits driving torque from the elec tric motor 301 to the second compressor 307 and in a second state in which the second coupling means 308 does not transmits driving torque from the electric motor 301 to the second compressor 307;

- Drive the electric motor 301 at variable speed by means of a group of power signals 325.

The pressure sensor means 321, for example a pressure transducer 321, may measure the pressure inside the main reservoir 311 and send its value 322 to the control unit 320.

In a second implementation example, with reference to Figure 5, the electric motor 301 may have a drive shaft 501 on which the first coupling means 502, for example a first electrome chanical clutch, and a second coupling means, for example a second electromechanical clutch 503, are mechanically bound. Both coupling means 502, 503 may have the peripheral shape of a pulley for driving at least one drive belt. A first pulley 505 may be mechanically bound to a shaft 504 of the first compressor 303, and a second pulley 507 may be mechani cally bound to a shaft 506 of a second compressor 307.

The first coupling means 502 may transmit driving torque to the first pulley 505 by means of at least one drive belt 508. The second coupling means 503 may transmit driving torque to the second pulley 507 by means of at least one drive belt 509.

The control means 320, for example a control unit 320, may be arranged to:

- receive a power supply 321;

- control, through a power signal 323, the first coupling means 503 in a first state in which the first coupling means 503 transmits driving torque from the electric motor 301 to the first compressor 303 and in a second state in which the first coupling means 503 does not transmit torque from the electric motor 301 to the first compressor 303;

- drive the second coupling means 503 through a power signal 324 in a first state in which the second coupling means 503 transmits driving torque from the elec tric motor 301 to the second compressor 307 and in a second state in which the second coupling means 308 does not transmits driving torque from the electric motor 301 to the second compressor 307.

- Drive the electric motor 301 at variable speed by means of a group of power signals 325.

What has been described above for at least one vehicle, for example railway vehicle, may be applied similarly for a plurality of railway vehicles connected to each other to form a convoy, for example a railway convoy.

As described above, the present invention is particularly applicable to the field of railway vehicles/convoys that travel on railway tracks. For example, a vehicle referred to herein may be a locomotive or a wagon, and a route/section may include rails on which the wheels of the locomotive roll. The embodiments described herein are not intended to be limited to vehicles on tracks. For example, the vehicle may be a car, a truck (for example a highway semi-trailer truck, a mining truck, a truck for transporting timber or the like) or the like, and the route may be a road or a trail. For example, a convoy may comprise a plurality of such vehicles connected or associated with each other.

Various aspects and embodiments of a method for generating compressed air of at least one railway vehicle and of a system for generating compressed air of at least one railway vehicle according to the invention have been described. It is understood that each embodiment may be combined with any other embodiment. Moreover, the invention is not limited to the em bodiments described, but may be varied within the scope defined by the appended claims.