GB2509308A

GB2509308A - Heat transfer arrangement for heating battery

Info

Publication number: GB2509308A
Application number: GB1222844.1A
Authority: GB
Inventors: Patrick Robert Marius Brooking
Original assignee: Protean Electric Ltd
Current assignee: Protean Electric Ltd
Priority date: 2012-12-18
Filing date: 2012-12-18
Publication date: 2014-07-02
Anticipated expiration: 2032-12-18
Also published as: GB2509308B; GB201222844D0

Abstract

A heat transfer system 200 for a vehicle having a battery 104 and an electric motor 101 is arranged so that heat generated by operation of the electric motor is transferred to the battery. This arrangement enables a wheeled vehicle comprising the heat transfer system to operate more efficiently by heating the battery, and hence increasing the available energy that can be discharged from the battery, particularly in cold weather. Preferably, the heat transfer system 200 includes a motor heat transfer arrangement 201 and a battery heat transfer arrangement 202, with heat being transferred therebetween. Fluid heated by the electric motor 101 may be transferred from the motor heat transfer arrangement 201 into the battery heat transfer arrangement 202. In alternative embodiments, the heat may be transferred from the electric motor 101 to the battery 104 by other methods, e.g. using heat exchangers (figures 3-5). The heat from the electric motor 101 may be derived from the motor itself and/or from a control device for controlling operation of the electric motor.

Description

A HEATING SYSTEM FOR A VEHICLE

The present invention relates to a vehicle and in particular a vehicle having a heating system for an electric motor traction battery.

With increased interest being placed in environmentally friendly vehicles there has been a corresponding increase in interest in the use of electric vehicles, and consequently the development of electric motor systems for providing drive torque for electric vehicles.

Electric motor systems typically include an electric motor and a control unit arranged to control the torque/speed of the electric motor. Examples of known types of electric motor include the induction motor, synchronous brushless permanent magnet moror, switched reluctance motor and linear motor.

However, as is well known to a person skilled in the art, for a drive torque no be generated by an electric motor it is necessary for the electric motor to be provided with electric current.

Although hybrid vehicles may use a combination of an internal combustion engine and battery for providing charge to an electric motor, for an electric vehicle the power source most commonly used by an electric motor is a battery.

The type of batteries used within electric vehicles include lead acid, nickel metal hydride, lithium based, or any type of battery that operates across the ambient temperature range associated wiTh the relevant electric vehicle.

The battery configuration may include the use of a single battery block, or a battery system that is distributed over the vehicle.

Battery systems disrributed over the vehicle can have the advantage of distributing the battery weight more evenly with the additional benefit of optimizing the use of available spaces wirhin the vehicle.

However, due to the electrochemical operation of a battery becoming less efficient at lower temperatures, battery systems typically impose environmental operating restrictions on electrio vehicles resulting from cold weather. These restriotions manifest themselves in terms of reduced range of an electric vehicle, and a battery accepting less charge when being charged.

Solutions that have been proposed for improving low temperature battery performance for electric vehicles include the use of electrical heaters to pre-heat the battery while the vehicle is parked. The power required to operate the heaters is typically obtained from a static power supply, for example a mains voltage supply.

This solution, however, cannot be used once the vehicle is moving, or if the vehicle is parked in a place where mains voltage is unavailable.

Another proposed solution includes charging the battery with a battery charger, with battery heat being produced as a result of a power loss across the battery's internal resistance.

This solution, however, can only be used on a battery that is able to accept charge. Additionally, the battery must have sufficiently high internal resistance, or the charging current must be sufficiently high, to heat the battery.

A further proposed solution uses energy stored in the battery itself to heat the battery, with electrical resistance heaters chat are activated using a switch, or a transistorized chopper' circuit, or a DC to DC converter. L0

This solution, however, reguires the use of energy within the battery, which will have the effect of reducing the range of the electric vehicle.

Tt is desirable to improve this situation.

In accordance with an aspect of the present invention there is provided a heat transfer system and a vehicle according to the accompanying claims.

The invention as claimed provides the advantage of allowing heat generated by an electric motor, or a control device arranged to control the operation of the electric motor, to raise the temperature of a battery, and hence increase the available energy that can be discharged from the battery.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates a vehicle according to an embodiment of the present invention; Figure 2 illustrates a heat transfer system according to a first embodiment of the present invention; Figure 3 illustrates a heat transfer system according to a second embodiment of the present invention; Figure 4 illustrates an electric vehicle according to a third embodiment of the present invention; Figure 5 illustrates an electric vehicle according to a fourth embodiment of the present invention.

In the following preferred embodiment, a heating system is described in which liquid coolant used to cool an electric motor or motors and/or power electronic systems, within an electric vehicle, is used to heat the vehicle's traction battery. In this way, heat generated by an electric motor is used to raise the temperature of a battery, and hence increase the available energy that can be discharged from it for use by the elecoric motor.

For the purposes of the present embodiment, reference to electric motor is also intended to include reference to an electrical machine That is able to operate in both a motoring mode and generating mode.

Figure 1 illustrates an electric vehicle 100 having a plurality of in-wheel electric motors 101, and an energy storage device 104 such as a battery.

The in-wheel electric motors 101 are arranged to provide torque for driving The vehicle 100, as is well known to a person skilled in the art. Typically an in-wheel electric motor 101 will be incorporated within at least two wheels (not shown) of the vehicle 100, where each in-wheel electric motor 101 is arranged to provide a drive torque to the respective wheel for moving the vehicle. For example, in a car having four wheels, in-wheel electric motors may be incorporated within all four of the wheels or within two of the wheels that are preferably located on the same axis.

For the purposes of the present embodiment the eleotric traction motor or motors is of the type of a DC motor, or an induction motor, or a permanent magnet motor, or a switched reluctance motor, or a hybrid combination of these.

Typically the DC Inonor is controlled using a control device such as a power electronic system known as a voltage chopping circuit, or electronic variable freguency inverter that uses pulse width modulation (PWM) to vary the speed and torque of the motor. Although the control device, which is arranged to control current flow in the electric motor, may be located anywhere within the vehicle, for the purposes of the present embodiment the control device is mounted on the elecoric motor, where heat generated by the control device may be used to heat the battery.

An example of an in-wheel electric motor is described in patent application GB 2 440 251.

During operation of the electric motors 101, the electric motors experience losses that consist primarily of eddy current losses in electric motor laminations and resistive losses in any current conduction paths. All of these, being thermal losses, result in heating of the electric motor. In order to reduce the dimensions of the electric motor while increase its power density, the motor is often liguid cooled using a mixture of water and glycol, or similar fluid. This removes the thermal losses more efficiently than air cooling due to the higher thermal conductivity of the cooling fluid, and permits a smaller size of electrical machine to produce the same torgue and power compared to a fan cooled machine.

The control device for the electric motor 101 also incurs thermal losses resulting from voltage drops and switching losses in the power semiconductor devices contained therein.

Similarly, the advantages of liquid coding of the control device is a reduced footprint and size, which enables, for a given power density, it to occupy less space in an electric vehicle than if it were air cooled.

As stated above, and described in detail below, the thermal energy produced by rhe operation of the traction motor or motors and oontrol devioe is used to heat the electric vehicle battery 104. This permits more effective electrochemical operation of the battery 104 at low ambient temperature.

Although the presenc embodiment describes an electric vehicle 100 having in-wheel electric motors 101, as would be appreciated by a person skilled in the art, an electric vehicle according to an embodiment of the present invention may use any form of electric motor arranged to generate drive torque, for example a single electric motor connected to a drive system that is arranged to transfer the drive torque generated by the electric motor to two or more of the wheels of the vehicle.

The in-wheel electric motors 101 use energy stored in the battery 104 to generate a current flow within the electric motor, which in turn is used to generate the drive torque.

Figure 2 illustrates a heat transfer system 200 for use in the eleotrio vehiole 100 described above.

The heat transfer system 200 includes a motor heat transfer arrangement 201 and a battery heat transfer arrangement 202.

The motor heat transfer arrangement 201 inoludes a motor radiator 210, a first pump 203 and a first valve 204, where coolant is arranged to flow around the motor heat transfer arrangement 201 for providing oooling to the in-wheel eleotric motors 101, as is well known to a person skilled in the art. Typically The ooolant will be a liguid, for example a water/ethylene glycol mixture or similar mixture that has a freezing point well below zero degrees Celsius. However, other fluids could be used. Alternatively, cooling can be provided using non-fluid materials, where cooling can be provided, for example, by conduction. However, for the purposes of the present embodiment, the term heat transfer fluid will be used cc refer to the coolant.

The in-wheel electric motors 101 have conduits within the electric motors to allow heat transfer fluid to flow through the electric motors 101 to aid the removal of heat generated within the electric motors 101, for example within the electric motor coils, as is well known to a person skilled in the art.

The electric motor conduit outlets are coupled to the motor radiator inlet via The first valve 204, where the first valve 204 is arranged upon predetermined criteria, as described in detail below, to decouple the electric motor conduit outlets from the motor radiator inlet and couple the motor heat transfer arrangement 201 to the battery heat transfer arrangemenc 202 to allow heat transfer fluid to flow from the motor heat transfer arrangement 201 to the battery heat transfer arrangement 202.

The motor radiator outlet is coupled to the electric motor cooling conduit inlets via the first pump 2C3, where the first pump 203 is arranged to pump heat transfer fluid around the motor heat transfer arrangement 201, thereby allowing heat transfer fluid to flow through the eleotrio motors 101 to cool The electric motors 101. The motor radiator 210 is used to cool the heat transfer fluid, where the radiator transfers exoess heat energy to the air, with a fan (not shown) typically being used to blow air through the radiator 210 to increase cooling of the heat transfer fluid.

The battery heat transfer arrangement 202 inoludes conduits for allowing heat transfer fluid to flow through and/or around the battery 104 to aid the transfer of heat generated within the motor 101 to the battery 104, as described below.

Additionally, the battery heat transfer arrangement 202 includes a second valve 208 that is operated in conjunction with the first valve 204 to couple the motor heat transfer arrangement 201 to uhe battery heat transfer arrangement 202 to allow heat transfer fluid to flow from the motor heat transfer arrangemeno 201 to the battery heat transfer arrangement 202 upon the 000urrenoe of the predetermined criteria, as described below.

The battery 104 is designed to inolude a conduit (not shown) that is coupled to The battery heat transfer arrangement 202 for allowing the bautery heat transfer arrangement heat transfer fluid to flow through the battery 104 to allow the kinetic heat energy of the heat transfer fluid to be oonduoted via the battery conduit into the battery's eleotroohemical cells, thereby allowing the heat of the battery 104 to be increased, as described below.

The heat conduction may occur either directly through the cell casing or through a heat conductor, Although the presenu embodiment describes the use of conduits for allowing heat transfer fluid, which has been heated up by an electric motor 101, to flow through the battery 104, heat generated by an electric motor may be directed to a battery 104 via other means. For example, blowing air through the battery 104, where the air has been heated up by an electric motor 101. This embodiment is illustrated in Figure 3, where a fan 300 is used to blow air through a liquid/air heat exchanger 301, which is coupled to the motor heat transfer arrangement 201. The air blown through the liquid/air heat exchanger 301 is heated by the liquid/air heat exchanger 301 and blown on to the battery 104.

However, with regard to the embodiment illustrated in Figure 2, where the motor heat transfer arrangement 201 is capable of being coupled to the battery heat transfer arrangement 202, typically the same heat transfer fluid will be used in the battery heat transfer arrangement 202 as for the motor heat transfer arrangement 201. As such, normally the heat transfer fluid will be a liquid. However, other fluids can be used. Alternatively, heat transfer may be provided using non-fluid materials, where heat transfer can be provided, for example, by conduction.

Preferably, the batnery heat transfer arrangement 202 includes a second pump 206, where the second pump 206 is arranged to pump heat transfer fluid around the battery heat transfer arrangemenn 202.

In a preferred embodiment, the predetermined criteria for operating the first valve 204 and the second valve 208 to allow the heat transfer fluid to flow between the motor heat transfer arrangemenu 201 and the battery heat transfer arrangement 202 is The temperature of a component associated with the battery heat transfer arrangement 202 or motor heat transfer arrangemenu 201. In particular, the first valve 204 and the second valve 208 are arranged to allow heat transfer fluid to flow between the motor heat transfer arrangement 201 and the battery heat transfer arrangement 202 upon the temperature of the component being below a predetermined temperature. For example, the predetermined criteria may be the temperature of The battery heat transfer arrangement heat transfer fluid being below a predetermined temperature.

The predetermined temperature will typically be dependent upon the type of bactery and be less than the optimum operating temperature of the battery.

Accordingly, upon the occurrence of the predetermined criteria the first valve 204 is arranged to couple the motor heat transfer arrangement 201 to the battery heat transfer arrangement 202 to allow the heat transfer fluid of the motor heat transfer arrangement 201 to flow into the battery heat transfer arrangement 202. Additionally, the second valve 208 is arranged to couple the battery heat transfer arrangement 202 to The motor heat transfer arrangement 201 to allow the heat transfer fluid of the battery heat transfer arrangemenu 202 to flow into the motor heat transfer arrangemenr 201.

Alternatively, the predetermined criteria may be based on the other criteria, for example the temperature of other components suoh as The battery 104 and/or the temperature of the heat transfer fluid at the second value 208, and/or the -10 -ambient air temperarure, and/or the state of charge of the battery. The temperature of the battery 104 may be determined, for example, by measuring the temperature of components within the battery 104. Additionally, the predetermined criteria may also be based upon the temperature of the motor 101 being at a predetermined temperature or the motor 101 being a predetermined temperature delta above the temperature of the battery 104.

When the first valve 204 and second valve 208 are configured to couple the motor heat transfer arrangement 201 and the battery heat transfer arrangement 202, the heat transfer fluid is arranged to flow through the electric motor 101 and battery 104 while bypassing the motor radiator 210, thereby allowing heat generated by the electric motor 101 to be directed to the batcery 104 to allow the battery temperature to increase.

Once the temperature of the battery heat transfer arrangement heat transfer fluid has risen above the predetermined temperature the first valve 204 and second valve 208 are configured to decouple the motor heat transfer arrangement and batcery heat transfer arrangement, thereby preventing the flow of heat transfer fluid between the motor heat transfer arrangement and the battery heat transfer arrangement while directing the motor heat transfer arrangement heat transfer fluid to the motor radiator 210 for additional oooling of the eleotrio motor heat transfer fluid.

Aocordingly, the first valve 204 and second valve 208 are configured to either isolate the flow of heat transfer fluid between the motor heat transfer arrangement 201 and the battery heat transfer arrangement 202 or couple the motor -11 -heat transfer arrangement 201 and the battery heat transfer arrangement 202 to allow heat transfer fluid to flow between the motor heat transfer arrangement 201 and the battery heat transfer arrangemenc 202 dependent upon whether the predetermined criteria has been established.

The operation of the first valve 204 and second valve 208 will typically be controlled by a central controller (not shown) . However, as would be appreciated by a person skilled in the art, the operation of the valves 204, 208 can be operated by any means.

If the first valve 204 and the second valve 208 are thermostatic valves, that is to say the first valve 204 and second valve 208 are arranged to open and shut based upon the temperature of The fluid at the first valve 204 and second valve 208, the controller can be arranged to override the thermal settings of the valves 204, 208. Alternatively.

if the first value 204 and second valve 208 are not thermostatic valves the operation of the valves will typically be controlled solely by the controller.

Although the presenc embodiment allows heat transfer to occur between the motor heat transfer arrangement 201 and battery heat transfer arrangement 202 by allowing heat transfer fluid to flow between the motor heat transfer arrangement 201 and the battery heat transfer arrangement 202, other forms of heat transfer can be used. For example, heat transfer can be achieved using a heat exchanger coupled between the motor heat transfer arrangement 201 and the battery heat transfer arrangement 202. In this configuration the heat exchanger is used to thermally couple the motor heat transfer arrangement 201 and the battery heat transfer arrangement 202. For example, Figure 4 illustrates a vehicle -12 -having a single traction motor 101 with a motor heat transfer arrangemenn 201 thermally coupled to a battery heat transfer arrangemeno 202 via a heat exchanger 400. Figure 5 illustrates a vehicle 100 having four in-wheel electric motors 101, with a motor heat transfer arrangement 201 thermally coupled to a battery heat transfer arrangement 202 via a heat exchanger 500.

The features in Figures 4 and 5 that correspond to the features in Figure 2 have been given the same reference numerals as those given in Figure 2.

With respect to the embodiment illustrated in Figure 4, a control device 401 for the electric motor 101 is located separately to the electric motor 101 and forms a separate motor heat transfer arrangement item. The motor heat transfer arrangemeno 201 includes a third valve 402 that operates as a bypass valve for bypassing the heat exchanger 400 when the third valve 402 is open. Accordingly, the third valve 402 is arranged to close when the predetermined criteria has been established, as described above, thereby allowing heat transfer fluid within the motor heat transfer arrangement 201 to be directed to the heat exchanger 400 for heating the heat transfer fluid in the battery heat transfer arrangement 202 and oonseguently heat the battery 104.

With respect to the embodiment illustrated in Figure 5, a control device for each in-wheel electric motor 101 is located with the assooiated electric motor 101 and as suoh each electric motor 101 and associated control device forms a single item in the motor heat transfer arrangement 201. As with the embodiment illustrated in Figure 4, the motor heat transfer arrangemeno 201 includes a third valve 402 that is arranged to close when the predetermined criteria, as -13 -described above, has been established, thereby allowing heat transfer fluid within the motor heat transfer arrangement 201 to be directed cc a heat exchanger 500 for heating the heat transfer fluid in the battery heat transfer arrangement 202 and consequently heat the battery 104.

If an increased heacing effect of the battery 104 is reguired, for example in extreme cold weather, the electric motor 101 or motors and/or the associated control device may be operated in an inefficient/reduced efficiency mode to increase heat generation by the electric motor 101, thereby creating additional waste heat that can be used to increase the heating of heat transfer fluid within the motor heat transfer arrangemenc 201 and the battery heat transfer arrangement 202. An example of the electric motor operating in an inefficient mode includes putting the coil current in the d-axis (i.e. orchogonal to the back emf). By placing the current in the d-axis this generates heat within the motor without generating corgue. An example cf the control device operating in an inefficient mode includes performing switching of the inverter switches at a higher PWM frequency or by altering the on times of semiconductors to increase conduction losses.

Although both the traction motor 101 and the battery 104 may be cold when the vehicle is started up, as the vehicle motor 101 will heat up quickly, heat generated by the electric motor 101 wiii be available for heating the battery 104 shortly after startup. This can increase the amount of energy that can be extracted from the battery 104 and correspondingly increase the range of the electric vehicle compared to one with an unheated battery.

-14 -It will be apparent to those skilled in the art that the disclosed subject matter may be mcdified in numerous ways and may assume embodiments other than the preferred forms specifically set ouc as described above, for example the heat transfer system can be utilised in any form of vehicle having an electric motor for generating torque for driving the vehicle. The mocor heat transfer arrangement 201 and battery heat transfer arrangement 202 may be permanently coupled without the need for valves to couple and decouple the motor heat transfer arrangement 201 and battery heat transfer arrangement 202. If valves are used to couple and decouple the motor heat transfer arrangement 201 and battery heat transfer arrangement 202 any number of values may be used.

-15 -

Claims

CLAIMS1. A heat transfer system for a vehicle having a battery and electric motor, wherein the electric motor is arranged to generate a motor torgue for driving the vehicle using energy from the batrery, the cooling system comprising heat transfer means arranged to transfer heat generated by the electric motor to the battery and/or arranged to transfer heat generated by a control device for controlling the operation of the electric motor to the battery.
2. A heat transfer system according to claim 1, wherein the heat transfer means is arranged to transfer heat generated by the electric motor and/or the control device to the battery upon the occurrence of a predetermined criteria.
3. A heat transfer system according to claim 2, wherein the predetermined criteria upon which the transfer means is arranged to transfer heat generated by the electric motor and/or the control device to the battery is if the temperature of the battery is below a predetermined first temperature
4. A heat transfer system according to claim 1, wherein the predetermined criteria upon which the transfer means is arranged to transfer heat generated by the electric motor to the battery is if the temperature of the battery is below a predetermined first temperature and the temperature of the electric motor is greater than the temperature of the battery by a predetermined second temperature.
5. A heat transfer system according to any one of claims 2 to 4, wherein the electric motor and/or the control device arranged to control the operation of the electric motor is -16 -arranged upon a predetermined oriteria to operate at a reduced level cf efficiency.
6. A heat transfer system according to claim 5, wherein the reduced level of efficiency includes generating current in coil windings of the electric motor without any torque being generated by The electric motor
7. A heat transfer system according to any one of the preceding claims, wherein the heat transfer means includes a liguid medium for transferring heat frcm the electric motor and/or a control device to the battery
8. A heat transfer system according to any one of the preceding claims, wherein the heat transfer means includes a motor heat transfer arrangement for transferring heat away from the motor and a battery heat transfer arrangement for transferring heat from the motor heat transfer arrangement to the battery.
9. A heat transfer system according to claim 8, wherein the motor heat transfer arrangement includes a liguid medium for transferring heat from the electric motor.
10. A heat transfer system according to claims 8 or 9, wherein the battery heat transfer arrangement includes a liguid medium for transferring heat to the battery.
11. A heat transfer system according to claims 8 or 9, wherein the engine heat transfer arrangement includes a heat exchanger and the battery heat transfer arrangement includes a fan for blowing air over the heat exchanger and onto the battery.-17 -
12. A heat transfer system according to claim 10 when dependent upon claim 8 and any one of claims 2 to 5, wherein the motor heat transfer arrangement and the battery heat transfer arrangement are coupled to allow the liquid medium tc flow between the mctcr heat transfer arrangement and the battery heat transfer arrangement upon the occurrence of the predetermined criteria via the operaticn of at least one valve -
13. A heat transfer system according to any one of claims 8 to 10, wherein the heat transfer means include a heat exchanger for allowing heat to be transferred between the motor heat transfer arrangement and the battery heat transfer arrangemenu.
14. A heat transfer system according to any one of the preceding claims, wherein the electric motor includes a control device for controlling the flow of charge in the electric motor
15. A heat transfer system according to any one of the preceding claims, wherein the electric motor is an in-wheel electric motor
16. A vehicle comprising a wheel, a battery, an electric motor arranged to generate a torque using charge from the battery, wherein the generated torque is applied to the wheel for moving the vehicle, and heat transfer means according to any one of the preceding claims.-18 -