SE541864C2

SE541864C2 - System for an electrical drive comprising a hydraulic auxiliary brake system

Info

Publication number: SE541864C2
Application number: SE1750259A
Authority: SE
Inventors: Kent Häll; Sven Bjørkgård
Original assignee: Ka Group Ag
Priority date: 2017-03-08
Filing date: 2017-03-08
Publication date: 2020-01-02
Also published as: DE102018103592A1; SE1750259A1

Abstract

A system (1, 1') for an electrical drive comprising an electric motor (4) which comprises a stator and a rotor, the rotor being arranged for rotation about a central longitudinal axis (12) and being rotatable relative the stator, the rotor having a first (20) and second (30) axial end. The system (1, 1') further comprising an auxiliary brake system comprising a hydraulic retardation arrangement (5, 5') which is arranged for mechanical connection with the first or second axial end of the rotor through a mechanical connection arrangement (70) and being arranged to, when activated, apply a braking force via the mechanical connection arrangement (70) to the axial end (20, 30) of the rotor to which it is mechanically connected.

Description

SYSTEM FOR AN ELECTRICAL DRIVE COMPRISING A HYDRAULIC AUXILIARY BRAKE SYSTEM Technical Field The present disclosure relates to a system for an electrical drive, the system comprising an electric motor and an auxiliary brake system. The present disclosure is also related to a vehicle comprising an auxiliary brake system, and to a method for braking an electric motor.

Background When braking a heavy vehicle such as a truck, a low gear and engine brake may be used. Auxiliary brake systems may be used to augment or replace some of the functions of the primary friction-based braking systems. Such auxiliary brake systems may e.g. be compression brakes, hydraulic retarders or electromagnetic retarders.

The development of electric vehicles and electric trucks is currently receiving much interest. Daimler Trucks has for example presented a fully electric heavy truck. In this electric heavy truck the conventional drive train has been replaced by an electrically driven rear axle with electric motors directly adjacent to the wheel hubs. During retardation of an electric heavy vehicle, the electric motor would apart from braking the vehicle also be used as a generator producing electricity. When the battery is fully charged, a problem arises that the vehicle will lose the engine brake function, and the wheel brakes would have to be used, which brakes rapidly will get too warm and thereby brake efficiency will be lost. Daimler Trucks uses an electric resistance device as an auxiliary brake system when the electric motor cannot feed the battery. This electric resistance device is immersed in water. During use the electric resistance device due to its internal resistance will heat up and thereby heat up the water, which is cooled down in a separate radiator on the truck.

Summary An object of the present disclosure is to provide a system for an electrical drive, where the system comprises an electric motor and an auxiliary brake system enabling braking of the electric motor when the battery is fully charged.

Other objects are to provide a vehicle comprising such a system and to provide a method for braking an electric motor.

The invention is defined by the appended independent claims.

Embodiments are set forth in the appended dependent claims and in the figures.

According to a first aspect, there is provided a system for an electrical drive, the system comprising an electric motor which comprises a stator and a rotor, the rotor being arranged for rotation about a central longitudinal axis and being rotatable relative the stator, the rotor having a first and second axial end. The system described further comprising a fluid arrangement for cooling of the stator/rotor. The system further comprising an auxiliary brake system, wherein the auxiliary brake system comprises a hydraulic retardation arrangement being arranged for mechanical connection with the first or second axial end of the rotor through a mechanical connection arrangement, and being arranged to, when activated, apply a braking force via the mechanical connection arrangement to the axial end of the rotor to which it is mechanically connected. The fluid arrangement for cooling of the stator/rotor and the hydraulic retardation arrangement are fluidly interconnected.

With an electrical drive is her meant a system which uses one or more electric motors and/or hybrid motors, a hybrid motor comprising an electric motor and e.g. a diesel motor or a fuel cell arranged in series or in parallel, as its prime source of energy. The prime source of energy transfers kinetic energy to the electrical drive for motion control, which may be used for controlling motion of electrical machines, e.g. electrical trucks, hybrid trucks, pumps etc.

The present system is suitable to be used by an electrical drive and the electric motor of the present system may be mechanically connected to an electrical drive.

The rotor may be arranged within the stator with an air gap between the two components. The stator and rotor may be arranged coaxially with the central longitudinal axis.

The stator and rotor may be arranged in a common motor housing, which may be a closed or open housing.

The first or second axial end of the rotor may be arranged to transfer kinetic energy from the electric motor.

The electric motor is not limited to any specific type of electric motor, but may be any suitable electric motor which converts electrical energy into mechanical energy. The electric motor may be a motor which can operate in both motoring and generating or braking modes to also produce electrical energy from mechanical energy. The electric motor may be a magnetic motor, wherein through interaction between the electric motor's magnetic field and winding currents a force is generated within the motor.

Fluid arrangements are known in the art and may comprise (a) fluid channel(s) arranged for cooling fluid to pass through on the stator and rotor of the electric motor. The fluid may e.g. be water or oil.

The fluid arrangement for cooling of the stator/rotor and the hydraulic retardation arrangement are fluidly interconnected, hence the same kind of fluid should be used in both the fluid arrangement and the hydraulic retardation arrangement.

The hydraulic retardation arrangement may comprise a fluid such as e.g. oil or water.

The hydraulic retardation arrangement may be any suitable retardation arrangement. Some examples of suitable hydraulic retardation arrangements are shown in EP0287099 A2 and WO2015126312 A1.

The hydraulic retardation arrangement is arranged for mechanical connection with the first or second axial end of the rotor through the mechanical connection arrangement, and is arranged to apply a braking force to the axial end of the rotor to which it is mechanically connected and thereby applying a braking force to the motor.

The mechanical connection between the hydraulic retardation arrangement and the rotor may be a constant mechanical connection.

Alternatively, the mechanical connection may be a disconnectable mechanical connection. The disconnectable mechanical connection between the hydraulic retardation arrangement and the rotor may be disconnected (inactivated) when no braking of the rotor is needed and connected (activated) when braking of the motor is needed.

Even if the hydraulic retardation arrangement is in constant mechanical connection with the rotor, this does not necessarily mean that a braking force of any larger influence is applied to the rotor if not the hydraulic retardation arrangement is activated.

If the system is arranged in e.g. an electric or hybrid truck activation of the hydraulic retardation arrangement may be initiated e.g. through pressing of the brake pedal or be actuated by a lever in the cabin.

With this system a braking force is applied on the first or second axial end of the rotor of the motor by means of the (separate) activated hydraulic retardation arrangement, which arrangement is directly mechanically connectable to the first or second axial end of the rotor of the motor, i.e. there is no intermediate system or device, braking the rotation of the rotor and braking the motor.

The present system is possible to make quite compact. The electric motor and the auxiliary brake system, the hydraulic retardation arrangement could be arranged in a common housing. The braking force applied on the first or second axial end of the rotor may be dimensioned such that the system may be used in vehicles. The hydraulic retardation arrangement, when activated, enables braking of the electric motor when the battery is fully charged.

The hydraulic retardation arrangement may comprise a fluid chamber, and an impeller arranged in the fluid chamber, the impeller being arranged to be rotatably driven by the rotor via the mechanical connection arrangement. The hydraulic retardation arrangement may be arranged to, when activated, transmit a viscous drag imposed on a rotating impeller by fluid in the fluid chamber as a braking force via the mechanical connection arrangement to the axial end of the rotor to which the impeller is mechanically connected.

With this system the first or second axial end of the rotor is mechanically connected with the impeller, and may be connected to a central axis of rotation of the impeller.

A fluid level in the fluid chamber may be static and at a level at or close to a maximum fluid level. Alternatively, the fluid level in the fluid chamber is variable e.g. through a valve system. The fluid chamber may be provided with at least one fluid inlet and at least one fluid outlet.

There may be a small clearance between the chamber inner wall and the rotating impeller. The fluid chamber may be vaned.

Upon activation of the hydraulic retardation arrangement, the fluid level in the fluid chamber may be increased by allowing fluid into the chamber through a fluid inlet, thereby increasing the viscous drag on a rotating impeller and slowing down the rotating impeller, and thereby an increased braking force may be transmitted to the rotor.

The degree of retardation may be varied by adjusting the level of fluid in the chamber. A higher fluid level resulting in a larger drag and braking force than a lower fluid level in the fluid chamber.

When not activated the fluid chamber may be empty of fluid.

Alternatively, the fluid chamber may always comprise, activated or nonactivated, some fluid.

If the rotor and the hydraulic retardation arrangement are in constant mechanical connection the impeller rotates with a rotating rotor even if no braking is needed. If the fluid chamber contains some fluid there would be some viscous drag on a rotating impeller, which would be transferred as a braking force on the first or second axial end of the rotor.

The rotor and the hydraulic retardation arrangement may be mechanically disconnectable. Activation of the hydraulic retardation arrangement may then comprise mechanically connecting the rotor and the impeller. After connection the fluid level in the fluid chamber may be increased/decreased, thereby increasing/decreasing the braking force on the rotor.

In case the fluid level in the fluid chamber is static (and close to or at a maximum fluid level) the mechanical connection between the hydraulic retardation arrangement and the rotor should be connectable/disconnectable. Upon connection, a constant and high retardation force is applied on the rotor due to the maximum or close to maximum fluid level in the fluid chamber. When disconnected, the fluid level of the fluid chamber is preferably kept constant at the maximum or close to maximum level.

The hydraulic retardation arrangement may comprise more than one impeller arranged in the fluid chamber, such as 2-4 separate impellers. The impeller may comprise at least one paddle, shovel, blade or vane. The impeller may be provided with e.g. 1-8, 1-4, or 1-2 blades.

The system may further comprise a clutch device arranged for mechanically connecting/disconnecting the hydraulic retardation arrangement to/from the first or second axial end of the rotor.

This means that the mechanical connection arrangement is uninterrupted when the clutch device connects the retardation arrangement to the first or second axial end of the rotor. The mechanical connection arrangement is interrupted when the clutch device disconnects the retardation arrangement from the first or second axial end of the rotor.

The hydraulic retardation arrangement may be activated when the retardation arrangement by means of the clutch device is connected to the first or second axial end of the rotor and a braking force may be applied to the motor. The retardation arrangement may be inactivated when the retardation arrangement by means of the clutch device is disconnected from the first or second axial end of the rotor.

If the fluid level of the fluid chamber is static and at or close to a maximum level a maximum braking force is applied whenever the retardation arrangement is connected to the rotor by means of the clutch device. This means there is an on/off retardation function, which is suitable to be used as a back-up retardation system in e.g. an electrical truck when the battery is fully charged. There is in this case no fine tuning of the braking force from the retardation arrangement as is possible when the fluid level of the fluid chamber of the retardation arrangement is adjustable.

Suitable clutch devices are per se known and could be a lamella coupling.

The fluid level in the fluid chamber may be static and at a maximum or close to a maximum fluid level.

Hence, the braking force which may be applied on the rotor is constant. Close to a maximum fluid level may here be a fluid level deviating from the maximum fluid level with 0-10%.

The system may comprise a valve arrangement arranged for adjustment of a fluid level in the fluid chamber.

Hence, the braking force may be varied by adjusting the fluid level in the fluid chamber.

The mechanical connection arrangement may have a first connecting end for mechanical connection to the hydraulic retardation arrangement and a second connecting end for mechanical connection to the first or second axial end of the rotor, and wherein the mechanical connection arrangement may comprise 1-10 mechanically interconnected connection members.

The mechanical connection arrangement may comprise 1, 1-4, 2-10, 2-8 or 4-6 mechanically interconnected connection members.

The first or second axial end of the rotor may be mechanically connected with the hydraulic retardation arrangement through e.g. a link of mechanically interconnected connection members.

The mechanical connection arrangement may comprise a protruding rotor shaft of the rotor, i.e. a shaft protruding at the first or second axial end of the rotor, the rotor shaft coinciding with the central longitudinal axis around which the rotor rotates and which shaft rotates with the rotor.

The mechanical connection arrangement may consist of the protruding rotor shaft, i.e. the protruding rotor shaft is the mechanical connection arrangement.

The mechanical connection arrangement may comprise a gear assembly.

The gear assembly may comprise one or more of a gear wheel, gear rack, drive belt and gear chain. Step-up gearing may be used to obtain high retarding forces even at low rotational speeds of the impeller.

The gear assembly may comprise or be mechanically connected to the protruding rotor shaft.

The second end of the mechanical connection arrangement and the first or second axial end of the rotor may be arranged for mechanical connection through a splined coupling, a bayonet coupling, a flanged coupling, a screw connection or a key-way connection.

There may be a male/female coupling arrangement mechanically connecting the rotor with the mechanical connection arrangement.

The male coupling portion at the first or second axial end of the rotor may constitute a protruding end of the rotor shaft of the rotor.

The system may further comprise a cooling unit for cooling of fluid for the fluid arrangement.

The fluid in the fluid arrangement will heat up by the rotor/stator and may be cooled by circulating through a cooling unit, e.g. a heat exchanger or radiator.

The system may further comprise a cooling unit for cooling of fluid for the fluid chamber of the hydraulic retardation arrangement.

The fluid in the hydraulic retardation arrangement will heat up by the rotating impeller and may be cooled by circulating through a cooling unit, e.g. a heat exchanger or radiator. The cooling unit may be connected between an inlet and outlet of the fluid chamber for cooling of fluid before entering the fluid chamber through a fluid inlet.

The cooling unit for cooling of fluid for the fluid arrangement and the cooling unit for cooling of fluid for the fluid chamber of the hydraulic retardation arrangement may be the same cooling unit.

Hence, the fluid arrangement for cooling of the stator/rotor and the hydraulic retardation arrangement may be fluidly interconnected at least through the common cooling unit.

Hence, space may be saved in e.g. an electrical truck in which the system may be installed as only one common cooling unit is needed for the fluid arrangement and the hydraulic retardation arrangement.

According to a second aspect there is provided a vehicle comprising any of the systems described above.

According to a third aspect there is provided a vehicle comprising a wheel, a gear connected to the wheel, and an electric motor comprising a stator and a rotor, the rotor being arranged for rotation about a central longitudinal axis and being rotatable relative the stator, the rotor having a first and second axial end, wherein the electric motor is connected to the gear. The vehicle further comprises a fluid arrangement for cooling of the stator/rotor. The vehicle further comprises an auxiliary brake system connected to the electric motor, which auxiliary brake system when activated applies a braking force to the motor. The auxiliary brake system comprises a hydraulic retardation arrangement being arranged for mechanical connection with the first or second axial end of the rotor through a mechanical connection arrangement, and being arranged to, when activated, apply a braking force via the mechanical connection arrangement to the axial end of the rotor to which it is mechanically connected. The fluid arrangement for cooling of the stator/rotor and the hydraulic retardation arrangement are fluidly interconnected.

The vehicle may be a heavy duty vehicle of class 7 (gross vehicle weight rating ranging from 26001 to 33000 lb (11 794 to 14969 kg)) and class 8 (gross vehicle weight rating exceeding 33 000 lb (14969 kg)).

The auxiliary brake system may be directly mechanically connected to the electric motor. Alternatively, the auxiliary brake system may be connected to the electric motor via a continuous variable transmission (CVT). The electric motor may be arranged connected between the gear and the auxiliary brake system. Alternatively, the auxiliary brake system may be arranged connected between the gear and the electric motor.

The braking force may be transferred as a braking force to the rotor of the electric motor directly or by means of the CVT.

According to a fourth aspect there is provided a method for braking an electric motor, wherein the electric motor comprises a stator and a rotor, the rotor being arranged for rotation about a central longitudinal axis and being rotatable relative the stator, the rotor having a first and second axial end, and a hydraulic retardation arrangement being arranged for mechanical connection with the first or second axial end of the rotor. The method comprising activating the hydraulic retardation arrangement such that a braking force is applied to the axial end of the rotor to which the hydraulic retardation arrangement is mechanically connected. The method further comprises cooling of the stator/rotor and the hydraulic retardation arrangement by means of a fluid arrangement for cooling of the stator/rotor fluidly interconnected with the hydraulic retardation arrangement.

The hydraulic retardation arrangement may comprise a fluid chamber and an impeller arranged in the fluid chamber, the impeller being arranged to be rotatably driven by the rotor via the mechanical connection arrangement, wherein activating the hydraulic retardation arrangement may comprise transmitting a viscous drag imposed on a rotating impeller by fluid in the fluid chamber as a braking force via the mechanical connection arrangement to the axial end of the rotor to which the impeller is mechanically connected.

Activating the hydraulic retardation arrangement may comprise mechanically connecting the hydraulic retardation arrangement to the first or second axial end of the rotor.

The method may further comprise a step of deactivating the hydraulic retardation arrangement by mechanically disconnecting the hydraulic retardation arrangement from the first or second axial end of the rotor.

Activating the hydraulic retardation arrangement may as an alternative or in combination with mechanical connection comprise adjustment of a fluid level in the fluid chamber.

An increased fluid level in the fluid chamber results in a higher braking force while a lower fluid level results in a lower braking force.

The method may further comprise a step of deactivating the hydraulic retardation arrangement by decreasing a fluid level in the fluid chamber.

Brief Description of the Drawings Fig. 1 schematically illustrates a system for an electrical drive with a hydraulic retardation arrangement comprising a fluid chamber with a variable fluid level. Fig. 2 shows the same system as in Fig. 1 but a higher fluid level in the fluid chamber is shown.

Fig. 3 schematically illustrates a system for an electrical drive with a hydraulic retardation arrangement comprising a fluid chamber with a static fluid level.

Fig. 4 schematically illustrates a vehicle comprising any of the systems of Figs 1-2 or Fig. 3.

Fig. 5 illustrates the system of Figs 1-2 or Fig. 3 arranged in line with the wheel axis of a vehicle.

Fig. 6 illustrates the system of Figs 1-2 or Fig. 3 arranged offset from the wheel axis of a vehicle.

Fig. 7 an exemplifying functional diagram of the system of any of Figs. 1-2 or Fig. 3 arranged in a vehicle.

Detailed Description In Figs 1-2 and Fig. 3 systems 1, 1' for an electrical drive are shown. The system 1, 1' is here being connected to a gear 3 and wheel 2 for rotation of the wheel 2 of for example an electric truck.

The system 1, 1' comprises an electric motor 4 comprising a stator and a rotor, the rotor being arranged for rotation about a central longitudinal axis 12, a rotor shaft, and being rotatable relative the stator. The rotor has a first axial end 20 and a second axial end 30. Flere it is the first axial end 20 of the rotor which is arranged to transfer kinetic energy from the electric motor 4 via the gear 3 to the wheel 2. The rotor is in the figures illustrated with a rotor shaft 12 protruding outside the rotor in both axial directions.

In Figs 1-3, the motor 4 is arranged in a motor housing 8.

The motor 4 may instead of being an electric motor 4 be a series or parallel hybrid motor comprising an electric motor and e.g. a diesel motor or a fuel cell. If the motor is a series hybrid motor, the electrical drive is arranged for mechanical connection to the electric motor.

To the second axial end 30 of the rotor is an auxiliary break system, a hydraulic retardation arrangement 5, 5' mechanically connected through a mechanical connection arrangement 70. In another embodiment of the system 1, 1', which is not shown in Figs 1-3, the hydraulic retardation arrangement 5, 5' may instead be mechanically connected to the first axial end 20 of the rotor of the motor 4.

The hydraulic retardation arrangement 5, 5' is arranged to, when activated, apply a braking force via the mechanical connection arrangement 70 to the axial end 30 of the rotor to which it is connected, thereby braking the motor.

If the system 1, 1' is arranged in e.g. an electric or hybrid truck activation of the hydraulic retardation arrangement when braking is needed when the battery is fully charged may be initiated e.g. through pressing of the brake pedal or be actuated by a lever in the cabin.

The hydraulic retardation arrangement 5, 5' may comprise a static fluid chamber 60 provided with at least one fluid inlet 40a, 40b, 40c and at least one fluid outlet 50a, 50b, 50c, such that fluid may be fed into/removed from the fluid chamber 60. In Figs 1 -3 several inlets/outlets are illustrated. The fluid may be e.g. water or oil.

In the system shown in Figs 1 and 2, the fluid level in the fluid chamber 60 may be adjusted through e.g. the use of a compensator 9 and a valve 15 (and may comprise also other valve arrangements not shown).

In the system shown in Fig. 3 the fluid level in the fluid chamber is static and at a maximum or close to a maximum fluid level.

In the fluid chamber 60 is arranged an impeller 11 (rotor). The impeller 11 is arranged to be rotatably driven by the rotor via the mechanical connection arrangement 70 mechanically connecting the rotor with the impeller 11. There may be a small clearance between the inner chamber wall of the fluid chamber 60 and the rotating impeller 11. The fluid chamber 60 may be vaned 10 (there is a stator) as in Figs 1-3. Alternatively, the inner wall of the fluid chamber 60 is even.

The hydraulic retardation arrangement 5, 5' may comprise one impeller 11. It is possible that more than one impeller 11 may be arranged in the fluid chamber 60, such as 2-4 separate impellers. The impeller 11 may comprise 1-8 blades, vanes or shovels.

The mechanical connection arrangement 70 has a first connecting end for mechanical connection to the impeller 11 and a second connecting end for mechanical connection to the second axial end 30 (or the first axial end 20) of the rotor. The first connecting end of the mechanical connection arrangement 70 is here connected to a central axis of rotation of the impeller 11. Such connections are known in the art.

The mechanical connection arrangement 70 connecting the hydraulic retardation arrangement 5, 5' and the rotor may be a constant mechanical connection as shown in Figs 1 and 2. Alternatively, the mechanical connection arrangement 70 may be a disconnectable mechanical connection, which may be disconnected by means of e.g. a clutch device 80 as illustrated in Fig. 3. When no braking of the rotor is needed the hydraulic retardation arrangement 5, 5' may be disconnected by means of the clutch device 80 and connected when braking is needed. It is to be understood that also the system of Figs 1 and 2 could be provided with a similar clutch device for connecting/disconnecting the hydraulic retardation arrangement from the first or second end of the rotor.

A fluid level in the fluid chamber 60 of the system shown in Figs 1 -2 may be changed by means of the compensator 9 and valve 15 and fluid may be pumped into/from the fluid chamber 60. If the fluid level is increased in the fluid chamber 60 a rotating impeller 11 will be slowed down as a viscous drag on the rotating impeller 11 is increased. The viscous drag is transmitted via the mechanical connection arrangement 70 to the second axial end 30 of the rotor as a braking force (or to the first axial end 20 in a non-shown embodiment) braking the motor 4. Activation of the hydraulic retardation arrangement 5 may take place by increasing the level of fluid in the fluid chamber 60. The fluid level in the fluid chamber 60 may be increased by allowing fluid into the chamber through the fluid inlet 40b.

When not activated the fluid chamber 60 may be empty of fluid.

Alternatively, there is always fluid to a certain level in the fluid chamber 60.

Activation of the hydraulic retardation arrangement 5' of Fig. 3, in which arrangement 5' the fluid chamber 60 has a static fluid level at a maximum or close to a maximum level, may take place by mechanically connecting the rotor and the hydraulic retardation arrangement via the clutch device 80. The fluid level in the fluid chamber 60 is constant or close to constant when connected to the rotor. The fluid level may be remained constant also when disconnected. Thereby there is a fast maximum braking of the motor as soon as the hydraulic retardation arrangement has been mechanically connected to the rotor by mans of the clutch device 80 as the fluid chamber does not have to be filled first.

The mechanical connection arrangement 70 may comprise one or several interconnected connection members for mechanical connection. The mechanical connection arrangement may constitute a protruding end of the rotor shaft 12 of the rotor.

The mechanical connection arrangement 70 may in other embodiments (not shown) comprise a gear assembly. The gear assembly may comprise one or more of a gear wheel, gear rack, drive belt and gear chain. The gear assembly may also comprise a protruding rotor shaft. Stepup gearing may be used to obtain high retarding forces even at low rotational speeds of the impeller 11.

The second end of the mechanical connection arrangement 70 and the second axial end 30 (or the first axial end 20) of the rotor may be connected through e.g. a splined coupling, a bayonet coupling, a flanged coupling, a screw connection or a key-way connection (not illustrated). The second end of the mechanical connection arrangement 70 may be provided with a projecting portion or a female portion and the first or second axial end of the rotor may have a complementary female portion or projecting portion, i.e. there is a male/female coupling arrangement mechanically connecting an axial end of the rotor with the second end of the mechanical connection arrangement 70.

As shown in Figs 1-3 there is a fluid arrangement 7 for cooling of the electric motor 4 and the stator/rotor therein. Such fluid arrangements 7 are per se known and may comprise (a) fluid channel/channels 7 arranged for cooling fluid to pass through on the stator and rotor of the electric motor 4. The fluid in the fluid arrangement 7 will heat up during cooling of the rotor/stator in the motor 4 and it may be cooled by circulating through a cooling unit 6, e.g. a heat exchanger or radiator.

To secure steady state fluid flow in the fluid arrangement 7 for cooling of the motor 4 while at the same time varying the fluid level in the fluid chamber 60 of the hydraulic retardation arrangement 5 of Figs 1-2 requires a valve arrangement (shown as valve 15 in the figures) for proper adjustment of fluid levels. There may also be a sensor arrangement (not shown) measuring parameters such as temperatures, flow rate, fluid levels, speed of the vehicle etc., which parameters may be used by a control system to optimize fluid levels in the hydraulic retardation system 5 and in the cooling system 7.

With the hydraulic retardation arrangement 5' shown in Fig. 3 the use of a fluid chamber 60 having a static fluid level at a maximum or close to a maximum level requires less peripheral systems (sensors, valves) and is, hence, a less complex system 1' than the system 1 of Figs 1-2. The fluid level of the fluid chamber 60 is at the maximum level when connected to the rotor. It may also be kept at the maximum level when disconnected from the rotor. When mechanically reconnected to the rotor there is an instant maximum braking force applied on the rotor as the fluid level is at its maximum level from the beginning. Securing a steady state fluid flow in the fluid arrangement 7 may, hence, be easier with the system 1' shown in Fig. 3 than with the system 1 shown in Figs 1-2.

A cooling unit 6 may be used for cooling of fluid for the fluid chamber 60 of the hydraulic retardation arrangement 5, 5'. The cooling unit 6 is here fluidly connected between a fluid inlet 40c and fluid outlet 50c of the fluid chamber 60 of the hydraulic retardation arrangement 5, 5' for cooling of fluid before entering the fluid chamber through the fluid inlet 40C. The fluid in the hydraulic retardation arrangement 5, 5' will heat up due to the rotation of the impeller 11 and may be cooled by circulating through the cooling unit 6, e.g. a heat exchanger or radiator.

As shown in Figs 1-3 the fluid arrangement 7 for cooling of the stator/rotor and the hydraulic retardation arrangement 5, 5' may be fluidly interconnected.

The fluid may be water or oil and is the same kind of fluid in both the fluid arrangement 7 and the hydraulic retardation arrangement 5, 5' when these are fluidly interconnected.

As shown in Figs 1-3 the cooling unit 6 for cooling of fluid for the fluid arrangement 7 and the cooling unit 6 for cooling of fluid for the fluid chamber 50 of the hydraulic retardation arrangement 5, 5' may be the same cooling unit 6. Flence, the fluid arrangement 7 for cooling of the stator/rotor and the hydraulic retardation arrangement 5 may be fluidly interconnected at least through the common cooling unit 6.

A system in which the cooling unit 6 may be shared between the hydraulic retardation arrangement 5, 5' and fluid arrangement 7 requires less space in e.g. an electric truck than a system (not shown) in which there are two separate cooling units, one for the hydraulic retardation arrangement 5, 5' and one for the fluid arrangement 7.

As seen in Figs 1-3 the fluid arrangement 7 of the electric motor 4 and the fluid chamber 60 of the hydraulic retardation arrangement 5, 5' may be arranged in such a way that cooled fluid from the cooling unit 6 may be transferred from the cooling unit 6 via the fluid chamber 60 of the hydraulic retardation arrangement 5, 5' to the fluid arrangement 7 of the motor 4.

Heated fluid from the fluid arrangement 7 may be transferred via the fluid chamber 60 of the hydraulic retardation arrangement 5, 5' to the cooling unit 6. In other embodiments, there could be a direct transfer of cooled fluid from the cooling unit 6 to the fluid arrangement 7 and direct transfer of heated fluid from the fluid arrangement 7 to the cooling unit 6 without passing through the fluid chamber 60 of the hydraulic retardation arrangement 5, 5'.

The motor 4 and hydraulic retardation arrangement 5, 5' may be arranged in a common housing (not shown). The fluid arrangement 7 for cooling of the stator/rotor may be arranged in this housing. Alternatively, also the cooling unit(s) is/are located in the housing or may be arranged outside the housing. Hence, it is possible to make the system 1, 1' quite compact.

In connection with the cooling unit 6 there may also be provided a cooling fan as shown in Figs 1-3 for cooling of the cooling unit 6.

In Fig. 4 is a vehicle, truck, 100 illustrated comprising six gears/wheels, wherein each gear/wheel is arranged with one of the systems 1, 1' described above, each comprising an electric motor 4 and a hydraulic retardation arrangement 5, 5'. Alternatively, one or more gears/wheels may share one system 1, 1', or components of a system 1, 1' (not shown).

Fig. 5 illustrates the system of Figs 1-2 or Fig. 3 arranged in line with the wheel axis of a vehicle. In this simplified illustration the suspension arrangement has not been taken into consideration as there are multiple design choices for the system/electrical drive interface.

Fig. 6 illustrates the system of Figs 1-2 or Fig. 3 arranged offset from the wheel axis of a vehicle. This illustration shows one example of a suspension arrangement. Flere, the location of the system does not compete for space with the suspension arrangement. Thereby e.g. more room for electric storage capacity may be created compared to the embodiment shown in Fig. 5.

In Fig. 7 is shown an exemplifying functional diagram of a system described above arranged in a (heavy) vehicle. Starting at the retarder, i.e. hydraulic retardation arrangement, this may be directly interfaced on the electric motor, arranged opposite the interface of a gear. Alternatively, the retarder may interface a continuous variable transmission (CVT), which is arranged at the interface of the electric motor opposite the interface of the gear. The gear may be connected directly to the wheel or connected thereto through a suspension/arm.

During use the electric motor produces heat. The electric motor may be cooled down by cooling liquid. Liquid may also be used in the retarder to create a resistance in the retarder, which may be transferred as a braking force to the electric motor directly or by means of the CVT. Liquid in the retarder may be heated when the retarder is activated/in use. The liquid may be cooled down in a radiator, which in turn may be cooled down by air, e.g. by use of a fan. The liquid coolant for cooling the electric motor and the liquid for the retarder may be the same liquid.

The volume of the liquid in the retarder may be varied by means of a valve arrangement connected to a compensator with liquid, thereby the volume of the liquid in the retarder may be varied and the volume for cooling the electric motor may be controlled. Sensor(s) may be used for measuring the temperature (heat) of the liquid and by means of an algorithm control the valve arrangement to vary the fluid level.

Claims

1. A system (1, 1') for an electrical drive, the system comprising: an electric motor (4) comprising: - a stator; a rotor, the rotor being arranged for rotation about a central longitudinal axis (12) and being rotatable relative the stator, the rotor having a first (20) and second (30) axial end, a fluid arrangement (7) for cooling of the stator/rotor, and - an auxiliary brake system (5, 5'), characterzed in that the auxiliary brake system (5, 5') comprises a hydraulic retardation arrangement (5, 5') being arranged for mechanical connection with the first (20) or second (30) axial end of the rotor through a mechanical connection arrangement (70), and being arranged to, when activated, apply a braking force via the mechanical connection arrangement (70) to the axial end (20, 30) of the rotor to which it is mechanically connected, and wherein the fluid arrangement (7) for cooling of the stator/rotor and the hydraulic retardation arrangement (5, 5') are fluidly interconnected.

2. The system (1, 1') of claim 1, wherein the hydraulic retardation arrangement (5, 5') comprises: - a fluid chamber (60); - an impeller (11) arranged in the fluid chamber (60), the impeller being arranged to be rotatably driven by the rotor via the mechanical connection arrangement (70), - wherein, the hydraulic retardation arrangement (5, 5') is arranged to, when activated, transmit a viscous drag imposed on a rotating impeller (11) by fluid in the fluid chamber (60) as a braking force via the mechanical connection arrangement (70) to the axial end (20, 30) of the rotor to which the impeller (11) is mechanically connected.

3. The system (1,1') of claim 1 or 2, further comprising a clutch device (80) arranged for mechanically connecting/disconnecting the hydraulic retardation arrangement (5, 5') to/from the first (20) or second (30) axial end of the rotor.

4. The system (1') of claim 2 or 3, wherein a fluid level in the fluid chamber (60) is static and at a maximum or close to maximum fluid level.

5. The system (1) of claim 2 or 3, wherein the system further comprises a valve arrangement arranged for adjustment of a fluid level in the fluid chamber (60).

6. The system (1, 1') of any one of claims 1 to 5, wherein the mechanical connection arrangement (70) has a first connecting end for mechanical connection to the hydraulic retardation arrangement (5, 5') and a second connecting end for mechanical connection to the first (20) or second (30) axial end of the rotor, and wherein the mechanical connection arrangement (70) comprises from one to ten mechanically interconnectable connection members.

7. The system (1, 1') of any one of claims 1 to 6, wherein the mechanical connection arrangement (70) comprises a protruding rotor shaft (12) of the rotor, i.e. a shaft protruding at the first or second axial end of the rotor, the rotor shaft coinciding with the central longitudinal axis (12) around which the rotor rotates and which shaft rotates with the rotor.

8. The system (1, 1') of any one of claims 1 to 7, wherein the mechanical connection arrangement (70) comprises a gear assembly.

9. The system (1, 1') of any one of claims 6 to 8, wherein the second connecting end of the mechanical connection arrangement (70) and the first (20) or second (30) axial end of the rotor are arranged for mechanical connection through a splined coupling, a bayonet coupling, a flanged coupling, a screw connection or a key-way connection.

10. The system (1, 1') of claim 1, further comprising a cooling unit (6) for cooling of fluid for the fluid arrangement (7).

11. The system (1, 1') of any one of claims 2 to 10, further comprising a cooling unit (6) for cooling of fluid for the fluid chamber (60) of the hydraulic retardation arrangement (5, 5').

12. The system (1, 1') of claims 10 and 11, wherein the cooling unit (6) for cooling of fluid for the fluid arrangement (7) and the cooling unit (6) for cooling of fluid for the fluid chamber (60) of the hydraulic retardation arrangement (5, 5') is the same cooling unit.

13. A vehicle (100) comprising the system (1, 1') of any one of claims 1 to 12.

14. A vehicle (100) comprising: - a wheel (2); a gear (3) connected to the wheel (2); an electric motor (4) comprising a stator and a rotor, the rotor being arranged for rotation about a central longitudinal axis (12) and being rotatable relative the stator, the rotor having a first (20) and second (30) axial end, wherein the electric motor (4) is connected to the gear. a fluid arrangement (7) for cooling of the stator/rotor; and an auxiliary brake system connected to the electric motor, which auxiliary brake system when activated applies a braking force to the motor, characterzed in that the auxiliary brake system comprises a hydraulic retardation arrangement (5, 5') being arranged for mechanical connection with the first (20) or second (30) axial end of the rotor through a mechanical connection arrangement (70), and being arranged to, when activated, apply a braking force via the mechanical connection arrangement (70) to the axial end (20, 30) of the rotor to which it is mechanically connected, and wherein the fluid arrangement (7) for cooling of the stator/rotor and the hydraulic retardation arrangement (5, 5') are fluidly interconnected.

15. A method for braking an electric motor (4), wherein the electric motor comprises a stator and a rotor, the rotor being arranged for rotation about a central longitudinal axis (12) and being rotatable relative the stator, the rotor having a first (20) and second (30) axial end, and a hydraulic retardation arrangement (5, 5') being arranged for mechanical connection with the first or second axial end of the rotor, the method comprising activating the hydraulic retardation arrangement (5, 5') such that a braking force is applied to the axial end of the rotor to which the hydraulic retardation arrangement (5, 5') is mechanically connected, and cooling the stator/rotor and the hydraulic retardation arrangement by means of a fluid arrangement (7) for cooling of the stator/rotor fluidly interconnected with the hydraulic retardation arrangement (5, 5').

16. The method of claim 15, wherein the hydraulic retardation arrangement comprises a fluid chamber (60) and an impeller (11) arranged in the fluid chamber (60), the impeller being arranged to be rotatably driven by the rotor via the mechanical connection arrangement (70), wherein activating the hydraulic retardation arrangement (5, 5') comprises transmitting a viscous drag imposed on a rotating impeller (11) by fluid in the fluid chamber (60) as a braking force via the mechanical connection arrangement (70) to the axial end (20, 30) of the rotor to which the impeller (11) is mechanically connected.

17. The method of claim 15 or 16, wherein activating the hydraulic retardation arrangement (5, 5') comprises mechanically connecting the hydraulic retardation arrangement (5, 5') to the first (20) or second (30) axial end of the rotor.

18. The method of any one of claims 15 to 17, further comprising a step of deactivating the hydraulic retardation arrangement (5, 5') by mechanically disconnecting the hydraulic retardation arrangement (5, 5') from the first (20) or second (30) axial end of the rotor.

19. The method of claim 16 or 17, wherein activating the hydraulic retardation arrangement (5, 5') comprises adjustment of a fluid level in the fluid chamber (60).

20. The method of any one of claims 16 to 18, further comprising a step of deactivating the hydraulic retardation arrangement (5, 5') by decreasing a fluid level in the fluid chamber (60).