Patent Description:
The invention can be applied in heavy-duty vehicles, such as trucks, buses and construction equipment, as well as lighter vehicles such as passenger cars. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as passenger cars.

In vehicles such as in heavy-duty vehicles there is a general need for braking involving dissipation of energy for example to complement friction braking in braking situations requiring prolonged and/or heavy braking.

In electrical vehicles such as vehicles comprising one or more electrical motors e.g. using batteries and/or fuel cell systems for propulsion, it is known to use different types of retarders or resistors for dissipating energy while braking and/or to use any batteries for storing such energy.

However, in braking situations when a relatively high brake power is required for substantial periods of time, it may be that the battery's limits for storing energy is reached before the end of the braking situation. Accordingly, the braking capacity using the battery for energy storage is limited.

As such, there is a need to provide alternative or complementary solutions for dissipating energy during braking of a vehicle, so as to replace and/or complement the storing of braking energy in the battery of an electric vehicle.

Known devices for dissipating braking energy are various types of retarders and/or resistors, which may be arranged for example to retard the drive shaft of a vehicle.

According to its abstract, <CIT> relates to a hybrid electric vehicle including a combustion engine, electric machine, turbocharger, and turbo lag reduction assembly that includes an auxiliary compressor and pressure tank, which are coupled to a clutch driven by a driveshaft powered by vehicle wheel rotation. A controller engages the clutch in response to a braking signal, until the auxiliary compressor recharges the pressure tank. The controller also disengages the clutch in response to one of termination of the braking signal and the pressure tank being recharged with compressed air. Additionally, the controller responds to an engine torque demand signal and discharges compressed air from the pressure tank to an intake manifold of the engine. Further, the controller may discharge a volume of compressed air from the pressure tank to the intake manifold of the engine, until a turbo charge limit signal is received that indicates the turbocharger reached an operating speed.

According to its abstract, <CIT> relates to an engine comprising an compressor, and combustor, and an expander. The compressor compresses the ambient air. The combustor burns the compressed air, and produces exhaust gas. The expander receives the exhaust gases from the compressor, and expands the exhaust gases. The compressor may be a gerotor compressor or a piston compressor having variable-dead-volume control. The expander may be a gerotor expander or a piston expander having variable-dead-volume control. In another embodiment, an engine comprises a piston compressor, a combustor, a piston expander, and a pressure tank. The piston compressor compresses ambient air. The combustor burns the compressed air, and produces exhaust gases. The piston expander receives the exhaust gases from the combustor, and expands the exhaust gases. The pressure tank receives and stores the compressed air from the compressor. In another embodiment, a gerotor compressor or a gerotor expander comprises an inner gerotor, and an outer gerotor. The inner gerotor and the outer gerotor are driven so that they do not touch. The gerotors may be cantilevered or non-cantilevered.

Retarders and resistors often utilise the cooling fluid of a cooling system of the vehicle for dissipating the braking energy. As such, the use of retarders and/or resistors for dissipating braking energy may imply that the cooling system of the vehicle needs to be dimensioned to take care of this energy, resulting in relatively large demands e.g. for radiator area and fan performance in a cooling system.

As such, there is a need to provide alternative or complementary solutions for dissipating braking energy which does not necessarily utilise the cooling system for dissipating braking energy.

Further, there is a requirement for heavy vehicles that the braking system to provide the braking shall be engaged for use already before reaching a braking situation, such as before the vehicle reaches a downhill slope.

As such, there is a need to provide alternative or complementary solutions for dissipating braking energy during braking which enables engagement of the braking system before reaching a braking situation.

Further, there is a general requirement to provide smooth and secure braking, and to limit wear or risk of breakage of the components involved.

As such, there is a need to provide alternative or complementary solutions for dissipating energy during braking which are advantageous in view of wear, risk of breakage of components, and/or in view of providing smooth and secure braking.

The object of the invention is to provide an alternative or an improvement in view of one or more of the above-mentioned needs.

According to a first aspect of the invention, at least one of the objects is achieved by a method according to claim <NUM>.

Thus, there is provided a vehicle arrangement for braking comprising at least a first electric motor comprising a first shaft being arranged to be mechanically connected to a drive shaft of the vehicle via a gear box, and a braking compressor comprising a compressor shaft being arranged to be mechanically connected to the first shaft of the first electric motor via a compressor clutch, such that the first shaft drives the compressor shaft.

The first shaft is connected to the gearbox via a first motor clutch and a first gearbox shaft. The vehicle arrangement further comprises mass flow rate controlling means arranged for controlling the air mass flow rate through the braking compressor.

As such, there is provided an arrangement in which the two clutches, i.e. the first motor clutch and the compressor clutch, allows for selectable engagement or disengagement of the first shaft to the first gearbox shaft, and of the braking compressor to the first shaft. As such, during braking of the vehicle, the first motor clutch and the compressor clutch may both be engaged, such that energy may be transmitted from the drive shaft via the gearbox to the first gearbox shaft, via the first motor clutch to the first shaft. From the first shaft, energy may be transmitted via the compressor clutch to the compressor shaft so as to drive the braking compressor. The braking compressor utilises the energy to compress air.

When the compressor clutch is engaged, the braking compressor will rotate with a compressor speed determined by the speed of the first shaft and any gearing provided between the first shaft and the compressor. As such, the compressor shaft may be subject to substantial torque. Furthermore, to enable mechanical engagement from the drive shaft via the gearbox and the first gearbox shaft, to the first shaft and further to the braking compressor, the torques involved in each mechanical connection need to be controlled.

The provision of the first motor clutch and the compressor clutch provides for a first range of measures for handling the torques, by selectively engaging and disengaging the clutches.

Further, as mentioned in the above, the arrangement comprises mass flow rate controlling means arranged for controlling the air mass flow rate through the braking compressor. By controlling the mass flow rate through the braking compressor, the compressor power and hence the torque on the compressor shaft may be controlled for a specific compressor speed. This control provides for a second range of measures for handling the torques.

Thus, the provision of the first motor clutch, and the compressor clutch in combination with the mass flow rate controlling means provides for a vehicle arrangement which may be controlled for providing braking as will be further described in the below.

Optionally, the compressor shaft is arranged to be mechanically connected to the first shaft via one or more gears providing a gear ratio between the first shaft and the compressor shaft.

The provision of one or more gears means that the speed of the compressor shaft may be considerably increased as compared to the speed of the first shaft. A higher speed of the compressor shaft implies higher torque from the braking compressor. As will be further described in the below, the mass flow rate controlling means arranged for controlling the air mass flow rate through the braking compressor may be used so as to control also these relatively high torques.

For example, the gear ratio may be at least <NUM>, such as at be least <NUM>, such as at least <NUM>. For example, the gear ratio may be between <NUM> to <NUM>, such as between <NUM> to <NUM>.

For example, the gear ratio may be a fixed gear ratio. In other words, the gear ratio is not adjustable.

The mass flow rate controlling means may provide for control of the mass flow rate to at least a plurality of selectable mass flow rates in a range between a minimum mass flow rate and a maximum mass flow rate.

The mass flow rate controlling means may provide for continuous control of the mass flow rate between a minimum mass flow rate and a maximum mass flow rate.

Optionally, the mass flow rate controlling means comprises a means for controlling the air inflow into the braking compressor. By controlling the air inflow it is possible to adapt the air flow rate so as to achieve the desired control of the compressor torque.

Optionally, the mass flow rate controlling means comprises a throttle valve arranged to control the air inflow to the compressor.

The throttle valve may enable continuous control of the air inflow between a fully closed and a fully open position of the throttle valve.

Optionally, the vehicle arrangement may further comprise a braking resistor. Such a braking resistor may be arranged in addition to the braking compressor so as to dissipate further braking energy from the drive shaft in a braking situation.

For example, the vehicle arrangement may comprise a braking resistor dissipating electric energy from the retarding electrical motors.

Optionally, the braking resistor may be arranged to be cooled by an exhaust from the braking compressor. As such, the braking energy used by the braking compressor to compress air may be used to further promote efficient dissipation of energy in a braking situation, by the compressed air from the exhaust of the compressor being used for cooling a braking resistor.

Optionally, the arrangement may comprise a second electric motor comprising a second shaft, being arranged to be mechanically connected to a drive shaft of the vehicle via a gear box. When the arrangement comprises a second electric motor, this second electric motor may be used for propelling or braking the vehicle by the second shaft being connected to the gear box while the first shaft is disengaged from the gear box by the first motor clutch being disengaged.

Further, the arrangement may comprise additional electric motors, for example the vehicle arrangement may comprise three or four electric motors.

Optionally, the first electric motor is connected to a battery. Optionally, when the vehicle arrangement comprises a plurality of electric motors, such as two, three or four electric motors, all of the two, three or four electric motors may be connected to a battery.

In a second aspect of the invention, there is provided a method according to claim <NUM>. As such there is provided a method for braking a motor shaft of an electric motor arranged to be operatively mechanically connected to a drive shaft in a vehicle arrangement of a vehicle, the vehicle arrangement comprising a compressor comprising a compressor shaft being mechanically connected to the motor shaft, the method comprising:.

As such, the method according to the second aspect of the invention may be used for limiting the compressor torque and thus the braking power received from the compressor during braking. For example, if a gear change takes place during braking, this means that the motor shaft speed and hence the compressor torque may increase or decrease swiftly. In accordance with the method according to the third aspect, the mass flow rate of the compressor is controlled so as to maintain the compressor torque on the compressor shaft below a predetermined maximum torque limit, such that the compressor and/or gearing do not risk excessive wear and/or breakage e.g. at a gear shift.

As such, the method may be used for controlling the compressor torque of a braking compressor and comprise:.

Optionally, the compressor torque request may be derived from a braking torque request or a braking power request required for the braking of a vehicle.

Thus, when the brake torque request implies a compressor torque request which is higher than the predetermined maximum torque limit, other braking means of the vehicle may be applied to achieve sufficient braking.

Optionally, the compressor torque request may be derived from an exhaust temperature request to provide a desired temperature of the exhaust air from the compressor.

The method of the third aspect of the invention is not limited for use with the second aspect or the first aspect of the invention. However, the features and advantages of the third aspect are, as will be understood by the following description, advantageously applicable to the second and/or first aspect of the invention.

Optionally, controlling the mass flow rate comprises controlling the mass flow rate to one out of at least a plurality of selectable mass flow rates in a range between a minimum mass flow rate and a maximum mass flow rate.

Optionally, controlling the mass flow rate comprises continuously controlling the mass flow rate between a minimum mass flow rate and a maximum mass flow rate.

Optionally, the method further comprises controlling the mass flow rate by controlling the air intake to the compressor. By controlling the air intake, i.e. the inflow of air, it is possible to adapt the mass flow rate so as to achieve the desired control of the compressor torque.

Optionally, the method comprises controlling the air intake to the compressor by controlling a throttle valve arranged upstream the compressor.

As such, a throttle valve may enable continuous control of the air intake between a fully closed and a fully open position of the throttle valve.

Optionally, the information indicative of the compressor torque comprises information indicative of the compressor power as a function of the compressor speed and the mass flow rate through the compressor. As such, e.g. a mapping of compressor power as a function of compressor speed and mass flow rate through the compressor may be used to provide the information indicative of the compressor torque. For example, such a mapping may be a mapping of compressor power as a function of compressor speed and air intake to the compressor, such as compressor power as a function of compressor speed and diameter of an air intake orifice to the compressor.

Optionally, the information indicative of the compressor speed comprises information of the rotating speed of the motor shaft.

The compressor may optionally be mechanically connected to the shaft via a gear arrangement providing gear ratio between the shaft and the compressor. For example, the gear ratio may be at least <NUM>, such as at least <NUM>, such as at least <NUM>. For example, the gear ratio may be from <NUM> to <NUM>, such as from <NUM> to <NUM>.

As such, optionally the information indicative of the compressor speed comprises information of the gear ratio arrangement.

In a third aspect of the invention, there is provided a vehicle according to claim <NUM>. As such, there is provided a vehicle comprising the vehicle arrangement according the first aspect of the invention.

In a fourth aspect of the invention there is provided a computer program according to claim <NUM>. As such, there is provided a computer program comprising program code means for performing the method of the invention, when the program is run on the control unit of the fourth aspect.

In a fifth aspect of the invention there is provided a computer readable medium according to claim <NUM>.

As such, there is provided a computer readable medium carrying a computer program comprising program code means for performing the method of the second and/or third aspect of the invention, when the program product is run on a control unit.

Advantages and effects of the third, fourth and fifth aspects of the invention are largely analogous to the advantages and effects of the first, second aspects of the invention.

<FIG> depicts a side view of a vehicle <NUM> according to an example embodiment of the invention. The vehicle <NUM> is here a truck, more specifically a heavy-duty truck for towing one or more trailers (not shown). Even though a heavy-duty truck <NUM> is shown it shall be noted that the invention is not limited to this type of vehicle but may be used for any other type of vehicle, such as a bus, construction equipment, e.g. a wheel loader and an excavator, and a passenger car. The invention is also applicable for other applications not relating to vehicles as long as one electric motor or a plurality of electric motors is utilized.

The vehicle <NUM> comprises a vehicle arrangement <NUM>. The vehicle arrangement <NUM> comprises one or more electric motors (not shown in <FIG>) which are used for creating a propulsion force to the vehicle <NUM>.

The vehicle <NUM> further comprises a control unit <NUM> according to an example embodiment of the invention. The control unit <NUM> is thus used for operating the vehicle arrangement <NUM>. Even though an on-board control unit <NUM> is shown, it shall be understood that the control unit <NUM> could also be a remote-control unit <NUM>, i.e., an off-board control unit, or a combination of an on-board and off-board control unit. The control unit <NUM> may be configured to control the vehicle arrangement <NUM> by issuing control signals and by receiving status information relating to the vehicle arrangement <NUM>.

The control unit <NUM> is an electronic control unit and may comprise processing circuitry which is adapted to run a computer program as disclosed herein. The control unit <NUM> may comprise hardware and/or software for performing the method according to the invention. In an embodiment the control unit <NUM> may be denoted a computer. The control unit <NUM> may be constituted by one or more separate sub-control units. In addition, the control unit <NUM> may communicate by use of wired and/or wireless communication means.

<FIG> depicts a schematic illustration of a vehicle arrangement <NUM> according to an example embodiment of the invention, wherein the vehicle arrangement <NUM> is arranged for propulsion of a vehicle, such as the vehicle <NUM> as shown in <FIG>.

The vehicle arrangement <NUM> comprises at least one electric motor, optionally a plurality of electric motors. For example, and as illustrated in <FIG>, the vehicle arrangement <NUM> may comprise a first electric motor <NUM> and a second electric motor <NUM>. However, it is envisaged that three, four our more electric motors may be comprised in the vehicle arrangement <NUM>.

The one or more electric motors <NUM>, <NUM> may for example be connected to an electrical storage system, such as a system comprising one or more batteries and/or to a fuel cell system.

Each electric motor <NUM>, <NUM> comprises a shaft <NUM>, <NUM> being mechanically connected to a gear box <NUM>, which is in turn connected to the driving shaft <NUM> of the vehicle <NUM> for transmitting power from one or more of the electric motors <NUM>, <NUM> to a traction system of the vehicle <NUM>, for example to the traction wheels of the vehicle <NUM>.

Thus, the vehicle arrangement <NUM> may, as in <FIG>, comprise a first electric motor <NUM> having a first shaft <NUM>, and a second electric motor <NUM> having a second shaft <NUM>. The first shaft <NUM> is connected to the gearbox <NUM> via a first motor clutch <NUM> and a first gearbox shaft <NUM>. Further, a braking compressor <NUM> is arranged to be mechanically connected to the first shaft <NUM> via a compressor clutch <NUM>, such that when the compressor clutch <NUM> is engaged, the first shaft <NUM> drives the compressor shaft <NUM>. As such, when the first motor clutch <NUM> and the compressor clutch <NUM> are both engaged, the braking compressor <NUM> may be used in a braking situation of the vehicle <NUM> for dissipating energy transmitted from the drive shaft <NUM> via the gearbox <NUM>, the first gearbox shaft <NUM>, and the first shaft <NUM> to the braking compressor <NUM>. The braking compressor <NUM> will utilise the energy to compress air, which compressed air may be used for various purposes in the vehicle <NUM> such as e.g. cooling.

The compressor shaft <NUM> may, as illustrated in <FIG>, be arranged to be mechanically connected to the first shaft <NUM> via one or more gears <NUM> providing a gear ratio between the first shaft <NUM> and the compressor shaft <NUM>.

Generally, such a gear ratio may be a fixed gear ratio. For example, the gear ratio may be in the range from <NUM> to <NUM>, such as <NUM>. Accordingly, by the gear ratio, a rotation speed of the first shaft <NUM> may result in a higher rotation speed of the compressor shaft.

In a vehicle arrangement comprising a braking compressor <NUM> being mechanically connected to the gearbox <NUM>, such as in the example arrangement <NUM> of <FIG>, the braking compressor <NUM> will experience high compressor speeds (i.e. rotation speed of the compressor) and may also be subject to abrupt changes in compressor speed.

The motor shaft speed (i.e. rotation speed of the shaft) will vary as a function of the vehicle speed and the gearing applied in the gear box. As such, the speed of the first shaft <NUM> and the second shaft <NUM> of the first and second electric motors <NUM>, <NUM>, will vary at different vehicle speeds and at different gearing in the gear box <NUM>.

<FIG> is an example diagram for illustrating the speed of the compressor shaft <NUM> of the braking compressor <NUM> when the compressor clutch <NUM> is engaged to the first shaft <NUM> with a gearing <NUM> providing a gear ratio. It will be understood, that due to the gear ratio of the gearing <NUM> between the first shaft <NUM> and the compressor shaft <NUM>, the speed of the compressor shaft <NUM> may be considerably higher than the speed of the first shaft <NUM>. For example, compressor speeds may be in the range of <NUM><NUM> to <NUM><NUM> rpm. The diagram illustrates schematically the speed of the compressor shaft <NUM> at different vehicle speeds and at different gearing (G1, G2, G3) in the gearbox <NUM>.

Increasing speeds of the compressor shaft <NUM> implies increased power developed by the braking compressor <NUM>, and also an increased torque provided via the shaft and to the one or more gears <NUM>.

In prior art arrangements, there is accordingly a risk that the high torque implies that the mechanical components involved in the connection between the first gearbox shaft <NUM>, the first shaft <NUM> and the compressor shaft <NUM>, such as the one or more gears <NUM>, are overloaded resulting in swift wear or in breakage of the mechanical components.

As will be further described in the below, the presently proposed vehicle arrangement <NUM> and methods utilise control of the first motor clutch <NUM> and the compressor clutch <NUM> to partly alleviate this problem.

In addition, the vehicle arrangement <NUM> comprises a mass flow rate controlling means <NUM> arranged for controlling the air mass flow rate through the braking compressor <NUM>. By provision of the mass flow rate controlling means <NUM>, it is possible to control the power of the braking compressor <NUM>, and thus the torque developed by the compressor <NUM>, at different speeds of the compressor shaft <NUM>. Thus, the mass flow rate controlling means <NUM> enables maintaining the compressor torque, ie. the torque on the compressor shaft <NUM> below a predetermined maximum torque limit.

The mass flow rate controlling means <NUM> may, as illustrated in <FIG>, be a means for controlling the air inflow into the braking compressor <NUM>. Control of the air inflow enables accurate control.

For example, the mass flow rate controlling means <NUM> may be a throttle valve <NUM> arranged to control the air inflow to the braking compressor <NUM>. A throttle valve <NUM> is an example of a valve which may enable continuous control of the air intake and thus the mass flow rate between a minimum mass flow rate and a maximum mass flow rate.

<FIG> illustrates an example of compressor power (which is proportional to the torque) developed by an example compressor at four different compressor speeds, and as a function of the orifice diameter of a throttle intake valve to the compressor. As seen in <FIG>, by diminishing the orifice diameter of the throttle intake valve, i.e. diminishing the mass flow rate of the compressor, the power and thus the torque may be reduced. As such, to maintain the compressor torque below a predetermined torque limit when the compressor speed is increased as a result of an increase in the speed of the first shaft, the orifice diameter of the throttle intake valve may be reduced.

<FIG> illustrates an example of a mapping of corrected mass flow rate versus pressure ratio of a compressor. In this example, the mass flow rate has been varied by controlling the air intake to the compressor using a throttle valve with controllable orifice diameter, at different compressor speeds. <FIG> illustrates how compressor operating points moves in the map when the throttling is applied. As seen, the operating points imply that the compressor pumping limit may be avoided.

By controlling the compressor torque to remain under a predetermined maximum torque value, the power developed by the braking compressor <NUM> and thus the amount of braking energy from the drive shaft <NUM> used by the braking compressor will also be limited. It is envisaged that the vehicle arrangement <NUM> described herein may comprise one or more additional braking elements for dissipating braking energy, which braking elements may compensate for the limitation in the braking provided by the compressor.

For example, the vehicle arrangement <NUM> may comprise one or more sensors to sense the air pressure in the air intake to the compressor <NUM> downstream the mass flow control means <NUM>. As such, information from the sensor may be used to derive the compressor torque. The mass flow control means <NUM> may be adjusted so as to obtain a desired compressor torque by controlling the control means <NUM> towards a desired air pressure signal from the one or more sensors.

The vehicle arrangement <NUM> may, as illustrated in <FIG>, further comprise a flow restrictor <NUM> arranged downstream the braking compressor <NUM>. The flow restrictor <NUM> may be controllable as already known in the art. As such, the flow restrictor <NUM> may have an impact on the mass flow rate through the compressor <NUM>. However, it is believed that the primary regulation of the mass flow rate may advantageously be made by controlling the air intake to the compressor <NUM>.

<FIG> illustrates a second example of a braking arrangement <NUM>. The braking arrangement <NUM> comprises all of the features of the braking arrangement <NUM> as illustrated in <FIG>, to which additional elements are added as examples.

For example, and as in the example arrangement illustrated in <FIG>, the vehicle arrangement <NUM> may further comprise a braking resistor <NUM>. Such a braking resistor <NUM> may be arranged in addition to the braking compressor <NUM> so as to dissipate further braking energy from the drive shaft <NUM> in a braking situation.

Optionally, such additional braking elements, for example a braking resistor <NUM> may be arranged to be cooled by an exhaust from the braking compressor <NUM>. As such, the braking energy used by the braking compressor to compress air may be used to further promote efficient dissipation of energy in a braking situation, by the compressed air from the exhaust of the compressor being used for cooling a braking resistor.

The braking arrangement <NUM> may further, as illustrated in <FIG> comprise one or more batteries <NUM>.

As mentioned in the above, the one or more electric motors may be driven by any arrangement for providing electrical energy, such as one or more batteries and/or fuel cell systems. Also a vehicle not using batteries to provide the propulsion of the vehicle, may comprise one or more batteries to store energy useful for other purposes.

In a braking situation, a battery <NUM> may be used to store energy from the drive shaft <NUM>, using e.g. resistors and/or retarders arranged for this purpose.

The braking arrangement <NUM> may further comprise a first traction inverter <NUM> for the first electric motor <NUM>, and a second traction inverter <NUM> for the second electric motor <NUM>. The braking arrangement may further comprise a junction box <NUM> in communication with the first and second traction inverters <NUM>, <NUM>. The junction box <NUM> is in this example further in communication with a battery <NUM>.

The braking resistor <NUM> may be air cooled via an air cooled resistor element arranged downstream the braking compressor <NUM>, such as downstream the flow restrictor <NUM>. Further, the vehicle arrangement <NUM> may comprise a muffler <NUM>, for example as illustrated in <FIG>, arranged downstream the braking resistor <NUM> comprising the air cooled resistor element. The braking resistor <NUM> may be electrically connected to any electric system in the vehicle, such as to suitable components of the braking arrangement <NUM>.

<FIG> is a flowchart illustrating a method for controlling a vehicle arrangement <NUM> for, such as the vehicle arrangement <NUM> described in relation to <FIG> or <FIG>.

As such, the detecting of an upcoming braking situation may be made based on one or more of the following inputs: present or predicted geographical data, such as GPS (Global Positioning System) data, present or predicted topographical data, present or predicted environmental conditions, e.g. weather conditions, such as ambient temperature and/or wind conditions, gross weight of the vehicle, route of the vehicle, the set or predicted speed of the vehicle, present or predicted traffic conditions.

The method comprises the step of, when the compressor clutch <NUM> is engaged: synchronizing the speed of the first shaft <NUM> of the first electric motor <NUM> with a speed of the first gearbox shaft <NUM> while controlling a mass flow rate of the compressor <NUM> so as to maintain a compressor torque on the compressor shaft below a predetermined maximum torque limit; S40. Thus, the method allows for the first shaft <NUM> to obtain a speed being synchronised with the speed of the first gearbox shaft <NUM>, with the braking compressor <NUM> in mechanical engagement with the first shaft <NUM>. Thus, the method allows for the braking compressor <NUM> to be in an applied state when the first motor clutch <NUM> is engaged, and the first shaft <NUM> having a speed synchronised with the first gearbox shaft <NUM>, is connected to the first gearbox shaft <NUM>. Thus, the braking compressor <NUM> may be applied in mechanical connection with the drive shaft <NUM> in a manner which enables engagement without sudden jerks or excessive torques applied to the mechanical connection.

Also, the synchronisation enables use of relatively simple clutch devices to form the first motor clutch <NUM>, such as a claw clutch.

Further, the method allows for the braking compressor to be applied in mechanical connection with the drive shaft <NUM> already before an upcoming braking situation, as is required by certain safety regulations.

As such, when the method comprises detecting an upcoming braking situation, the step of engaging the first motor clutch <NUM> may be made prior to arriving at the upcoming braking situation.

When the vehicle arrangement <NUM> further comprises a second electric motor <NUM> comprising a second shaft <NUM>, the method steps as described in the above may be performed with the second shaft <NUM> being engaged to the gearbox <NUM>. As such, the vehicle may be propelled using the second electric motor <NUM>, while the method as described in the above is performed.

The method may comprise the step of, before engaging the first motor clutch <NUM>, controlling a mass flow rate of the braking compressor so as to maintain a compressor torque on the compressor shaft <NUM> below a predetermined engagement torque limit when engaging the first motor clutch <NUM>. Such a predetermined engagement torque limit may for example be a minimum torque as available using the mass flow control means at the relevant compressor speed. Thus, at engagement of the first motor clutch <NUM>, the braking compressor <NUM> may provide a minimum torque, i.e. a minimum power. From this state, once the braking situation is present, the mass flow may for example be continuously increased so as to increase braking power in view of the demands of the current braking situation.

The mass flow rate may be controlled so as to always maintain a compressor torque on the compressor shaft <NUM> below a predetermined maximum torque limit when the compressor clutch <NUM> is engaged. As such, it may be ensured that the mechanical connections between the compressor <NUM> and the first shaft <NUM> are not overloaded. As mentioned in the above, the predetermined maximum torque limit may be set in view of the requirements of the components of the mechanical connections of the vehicle arrangement, so as to spare the mechanical connections from excessive wear or from the risk of breaking. Such mechanical connectors may be e.g. the compressor clutch <NUM> and/or the one or more gears <NUM> between the compressor <NUM> and the first shaft <NUM>.

Thus, the method may for example involve the step of controlling a mass flow rate of the compressor so as to maintain a compressor torque on the compressor shaft <NUM> below a predetermined maximum torque limit during the entire duration of the braking situation.

The step of controlling the mass flow rate of the compressor may be performed by a method comprising the steps of.

As such, this method may be used for braking a motor shaft of an electric motor arranged to be operatively mechanically connected to a drive shaft <NUM> in any vehicle arrangement <NUM> of a vehicle <NUM>, wherein the vehicle arrangement <NUM> comprises a braking compressor <NUM> comprising a compressor shaft <NUM> being mechanically connected to the motor shaft <NUM>.

<FIG> is a flow chart illustrating an embodiment of such a method for braking a motor shaft.

When used in combination with the arrangements or methods as described in <FIG>, this implies that the motor shaft is the first shaft <NUM>.

The method for braking a motor shaft may thus be used with the features as described in the above. For example, the method may comprise controlling the mass flow rate to one out of at least a plurality of selectable mass flow rates in a range between a minimum mass flow rate and a maximum mass flow rate. For example, the method comprises controlling the mass flow rate comprises continuously controlling the mass flow rate between a minimum mass flow rate and a maximum mass flow rate.

Optionally, the method further comprises controlling the mass flow rate by controlling the air intake to the compressor. By controlling the air inflow it is possible to adapt the mass flow rate so as to achieve the desired control of the compressor torque. The method may hence comprise controlling the air intake to the compressor by controlling a throttle valve arranged upstream the compressor <NUM>.

Optionally, the information indicative of the compressor torque comprises information indicative of the compressor power as a function of the compressor speed and the mass flow rate through the compressor. As such, e.g. a mapping of compressor power as a function of compressor speed and mass flow rate through the compressor may be used to provide the information indicative of the compressor torque.

The compressor may optionally be mechanically connected to the shaft <NUM> via a gear arrangement <NUM> providing gear ratio between the shaft <NUM> and the compressor <NUM>. For example, the gear ratio may be at least <NUM>, such as at least <NUM>, such as at least <NUM>. For example, the gear ratio may be <NUM> to <NUM>, such as <NUM> to <NUM>.

Claim 1:
A vehicle arrangement for braking comprising
at least a first electric motor (<NUM>) comprising a first shaft (<NUM>) being arranged to be mechanically connected to a drive shaft (<NUM>) of said vehicle (<NUM>) via a gear box (<NUM>), and
a braking compressor (<NUM>) comprising a compressor shaft (<NUM>) being arranged to be mechanically connected to said first shaft (<NUM>) of said first electric motor (<NUM>) via a compressor clutch (<NUM>), such that said first shaft (<NUM>) drives said compressor shaft (<NUM>),
characterized in that said first shaft (<NUM>) is connected to said gearbox (<NUM>) via a first motor clutch (<NUM>) and a first gearbox shaft (<NUM>), said arrangement further comprising
a mass flow rate controlling means (<NUM>) arranged for controlling the air mass flow rate through said compressor (<NUM>).