WO2012056222A2

WO2012056222A2 - A vehicle

Info

Publication number: WO2012056222A2
Application number: PCT/GB2011/052055
Authority: WO
Inventors: Neil Trueman; Christopher Lewis
Original assignee: Protean Electric Limited
Priority date: 2010-10-26
Filing date: 2011-10-21
Publication date: 2012-05-03
Also published as: GB2484938B; GB201018068D0; GB2484938A; WO2012056222A3

Abstract

A vehicle comprising an engine arranged to apply a torque to a first wheel for moving the vehicle;an electric motor arranged to apply a torque to a second wheel for moving the vehicle; means for determining the torque applied by the engine to the first wheel; and a controller arranged to control the application of torque applied to the second wheel by the electric motor based upon the torque applied by the engine to the first wheel.

Description

A VEHICLE

The present invention relates to a vehicle, in particular a vehicle arranged to have drive provided by both an engine and an electric motor.

With increased interest being placed in environmentally friendly vehicles there has, perhaps unsurprisingly, been a corresponding increase in interest in the use of electric and electric hybrid vehicles. However, due to the large number of existing road vehicles requiring the use of fossil fuels this is likely to slow the rate at which electric vehicles are adopted.

One solution to this problem would be to retrofit existing vehicles, which operate using an internal combustion engine, with an electric motor, where the electric motor is arranged to drive either the same wheels powered by the engine or a number of wheels not coupled to the engine. This would allow the existing fossil fuel refuelling

infrastructure to be used to supplement the electrical charging infrastructure available for electric vehicles. Unfortunately, however, the drive characteristics of an electric motor are typically different to those of an internal combustion engine. Consequently, the retrofitting of an electric motor to a vehicle having an internal combustion engine does not lend itself to allowing the vehicle to have drive provided by both the electric motor and internal combustion engine at the same time.

It is desirable to improve this situation.

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

This provides the advantage of allowing a vehicle having an internal combustion engine to be retrofitted with an electric motor, where the torque applied to the vehicle's wheels from the electric motor is arranged to complement (e.g. match) the torque applied by the internal combustion engine, thereby avoiding vehicle handling characteristics being compromised when the vehicle is being driven by both an electric motor and an internal combustion engine. Similarly, this also allows for a vehicle having an existing internal combustion engine and an electric motor to have improved handling characteristics. This has the additional benefit of improving fuel economy and/or performance.

The preferred embodiment has the additional advantage of allowing the torque characteristics of an electric motor, as applied to a wheel of the vehicle, to complement (e.g. match) the torque applied to a set of wheels from an internal combustion engine using only the vehicle and engine speed information, thereby avoiding the need to make any significant changes to a vehicle when retrofitting an electric motor.

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 speed/torque profile for a vehicle having an internal combustion engine;

Figure 3 illustrates an exploded view of an electric motor as used in an embodiment of the present invention; Figure 4 illustrates an exploded view of the electric motor shown in Figure 3 from an alternative angle;

Figure 5 schematically shows an example for a three phase motor according to an embodiment of the present invention;

Figure 6 illustrates a schematic representation of functions in a control system according to an embodiment of the present invention. Figure 1 illustrates a vehicle 100, for example a car or lorry, having four wheels 101, where two wheels are located in the vehicles forward position in a near side and off side position respectively. Similarly, two additional wheels are located in the vehicles aft position in near side and off side positions respectively, as is typical for a conventional car configuration. However, as would be appreciated by a person skilled in the art, the vehicle may have any number of wheels.

Incorporated within the wheels 101 in the vehicle's aft position are in-wheel electric motors, as described in detail below. Although the current embodiment describes a vehicle having in-wheel electric motors associated with the wheels 101 located in the vehicle's aft position, as would be appreciated by a person skilled in the art the in-wheel electric motors can be located in other wheels. For example, in-wheel electric motors can be located in the front two wheels. Additionally, although the present embodiment describes the use of in-wheel electric motors, other electric motor configurations can be used, for example a centrally mounted electric motor that uses a drive shaft and/or a gearbox to power the respective vehicles wheels. However, for ease of retrofitting the use of in-wheel electric motors is the preferred embodiment.

Coupled to the in-wheel electric motors and to a vehicle communication bus, for example a CAN bus (not shown), is a control unit 102 for controlling the torque generated by the in-wheel electric motor.

Located in the vehicle is an internal combustion engine 103 that is coupled to the two front wheels via a gear box 104, having a plurality of gears, and drive shafts 105. The internal combustion engine 103 is arranged to apply torque to the two front wheels, as is well known to a person skilled in the art. The torque produced by the engine is controlled via a throttle pedal (not shown) situated in the vehicle and operated by a driver of the vehicle. The torque applied by the engine to the wheels is dependent on the engine torque and the selected gear of the gear box, as is well known to a person skilled in the art.

Figure 2 illustrates a typical speed/torque profile applied to wheels of a vehicle by an internal combustion engine for a gear box having 6 gears, where profile 10 illustrates the maximum torque applied in first gear, profile 11 illustrates the maximum torque applied in second gear, profile 12 illustrates the maximum torque applied in third gear, profile 13 illustrates the maximum torque applied in fourth gear, profile 14 illustrates the maximum torque applied in fifth gear, profile 15 illustrates the maximum torque applied in sixth gear. For the purpose of illustration the in-wheel electric motor is of the type having a set of coils being part of the stator for attachment to the vehicle, radially surrounded by a rotor carrying a set of magnets for attachment to a wheel. However, as would be appreciated by a person skilled in the art, the present invention is applicable to other types of electric motors. Typically, upon demand, an in-wheel electric motor will be configured to provide both drive torque and regenerative braking torque.

As illustrated in Figure 3, the in-wheel electric motor 40 includes a stator 252 comprising a rear portion 230 forming a first part of the housing of the assembly, and a heat sink and drive arrangement 231 comprising multiple coils and electronics to drive the coils. The coil drive arrangement 231 is fixed to the rear portion 230 to form the stator 252 which may then be fixed to a vehicle and does not rotate during use. The coils themselves are formed on tooth laminations which together with the drive arrangement 231 and rear portion 230 form the stator 252. A rotor 240 comprises a front portion 220 and a cylindrical portion 221 forming a cover, which substantially surrounds the stator 252. The rotor includes a plurality of magnets 242 arranged around the inside of the cylindrical portion 221. The magnets are thus in close proximity to the coils on the assembly 231 so that magnetic fields generated by the coils in the assembly 231 cooperate with the magnets 242 arranged around the inside of the cylindrical portion 221 of the rotor 240 to cause the rotor 240 to rotate.

The rotor 240 is attached to the stator 252 by a bearing block 223. The bearing block 223 can be a standard bearing block as would be used in a vehicle to which this motor assembly is to be fitted. The bearing block comprises two parts, a first part fixed to the stator and a second part fixed to the rotor. The bearing block is fixed to a central portion 233 of the wall 230 of the stator 252 and also to a central portion 225 of the housing wall 220 of the rotor 240. The rotor 240 is thus rotationally fixed to the vehicle with which it is to be used via the bearing block 223 at the central portion 225 of the rotor 240. This has an advantage in that a wheel rim and tyre can then be fixed to the rotor 240 at the central portion 225 using the normal wheel bolts to fix the wheel rim to the central portion of the rotor and consequently firmly onto the rotatable side of the bearing block 223. The wheel bolts may be fitted through the central portion 225 of the rotor through into the bearing block itself.

Figure 4 shows an exploded view of the same assembly as Figure 3 from the opposite side showing the stator 252 comprising the rear stator wall 230 and coil and electronics assembly 231. The rotor 240 comprises the outer rotor wall 220 and circumferential wall 221 within which magnets 242 are circumferentially arranged. As previously described, the stator 252 is connected to the rotor 240 via the bearing block at the central portions of the rotor and stator walls.

Additionally shown in Figure 3 are circuit boards 80 carrying control electronics, otherwise known as motor drive controllers. Additionally in Figures 2 and 3 a V shaped seal 350 is provided between the circumferential wall 221 of the rotor and the outer edge of the stator housing 230. Further, in Figure 4, a magnetic ring 227 comprising a commutation focusing ring and a plurality of magnets is provided for the purpose of indicating the position of the rotor with respect to the stator to a series of sensors arranged on the motor drive controllers 80 of the stator 252.

The electric motor 40 shown in Figures 3 and 4 is a three phase motor having three coil sets. In this embodiment, each coil set includes eight coil sub-sets. However, as would be appreciated by a person skilled in the art, the electric motor could have any number of coil sets and coil sub-sets. The coil sub-sets of each coil set are labelled 44, 46 and 48, respectively in Figure 5. Accordingly, the electric motor illustrated in Figure 5 has a total of twenty four coil sub-sets (i.e. eight coil sub-sets per coil set).

By way of example, in Figure 5 some of the coil sub-sets are highlighted with a If these coil sub-sets were to be powered down, the motor would still be able to operate, albeit with reduced performance. In this way, the power output of the motor can be adjusted in accordance with the requirements of a given application. In one example, where the motor is used in a vehicle such as a car, powering down of some of the coil sub-sets can be used to adjust the performance of the car. In the example shown in Figure 5, if each of the coil sub-sets indicated with an '*' were powered down the motor would have three coil sets with each coil set having two active coil subsets.

Powering down of one or more of the coil sub-sets has the further benefit that in the event of a failure of one of the coil sub-sets, other coil sub-sets in the motor 40 can be powered down resulting in continued operation of the motor 40 in a manner which retains a balanced magnetic field profile around the periphery of the motor for appropriate multiphase operation. A motor drive controller 80 is arranged to drive a group of three coil subsets. For example, a motor drive controller can be associated with the first three coil subsets 44, 46, 48 located at the top of Figure 5. Another motor drive controller 80 is associated with the next three coil subsets, and so on. Accordingly, the in-wheel electric motor includes eight motor drive controllers 80 arranged to drive the respective coil subsets to form a distributed internal motor architecture that uses multiple motor drive controllers 80 for controlling the torque generated by the in-wheel electric motor.

The distributed motor drive controller configuration, where each motor drive controller 80 drives a group of three coil sub-sets with a three phase voltage, can be regarded as a group of logical sub motors. Each logical sub-motor can be driven independently of the other sub motors within the in-wheel electric motor with each logical sub-motor being driven as a three phase motor.

The motor drive controller 80, which acts as an inverter for the associated logical sub- motor, includes a number of switches which may typically comprise one or more semiconductor devices. The motor drive controller 80 includes a printed circuit board upon which a number of components are mounted. The circuit board includes means for fixing the motor drive controller 80 within the electric motor 40, for example, adjacent to the coil sub-sets that the respective motor drive controller controls. In the illustrated example, these means include apertures through which screws or suchlike can pass. In this example, the printed circuit board is substantially wedge-shaped. This shape allows multiple motor drive controllers 80 to be located adjacent each other within the motor, forming a fan-like arrangement. The motor drive controller 80 switches can include semiconductor devices such as MOSFETs or IGBTs. In the present example, the switches comprise IGBTs. However, any suitable known switching circuit can be employed for controlling the current within the coils of the coil sub-set associated with the motor drive controller 80. One well known example of such a switching circuit is the H-bridge circuit.

Each motor drive controller 80 also includes a processor, where the processor is arranged to operate the switches in accordance with a pulse width modulation scheme for controlling the torque of the respective logical sub motor, as is well known to a person skilled in the art. The processor is arranged to receive a torque demand from the master controller 102 via a CAN interface, however any form of communication link between the master controller 102 and the respective motor drive controller 80 can be used.

In response to control signals from the master controller 102 that are indicative of a required torque, each motor drive controller 80 is arranged to pulse width modulate a signal applied to the semiconductor switches that form a three phase H-bridge circuit to control the voltage applied to the set of three coil subsets for the purposes of generating an electric motor torque, as is well known to a person skilled in the art. The torque request will typically be initiated by a user of the vehicle 100 indicating a desire to increase or decrease the acceleration of the vehicle via the operation of a demand device, for example a throttle pedal.

The vehicle is arranged to operate in three modes of operation.

In a first mode of operation the in-wheel electric motors are switched off and all the propulsion is provided by the internal combustion engine driving the front wheels.

In a second mode of operation the in-wheel electric motors are placed in a regeneration configuration with the internal combustion engine being arranged to drive the front wheels. In this mode of operation the in-wheel electric motors generate charge while the internal combustion engine is driving the vehicle via the front wheels. In a third mode of operation the in-wheel electric motors are arranged to drive the aft position wheels while the internal combustion engine is arranged to drive the front wheels, that is to say the in-wheel electric motors and internal combustion engine operate in a blended mode of operation, where the in-wheel electric motors and the internal combustion engine provide torque to the rear and front wheels respectively.

In this mode of operation the control system is arranged to determine the torque being applied by the internal combustion engine to the front wheels of the vehicle, thereby allowing the torque that is applied to the aft position wheels, via the in-wheel motors, to be applied in a complementary manner. Depending on the drive needs of the vehicle the torque applied to the aft position wheels can be selected to either substantially match the torque applied to the front wheels or some predetermined ratio or based upon a predetermined mapping between engine and motor torque as applied to the wheels of the vehicle. This allows the in-wheel motors to work seamlessly with the internal combustion engine to provide a tuneable power assist function.

For the purposes of the present embodiment only the third mode of operation will be described in detail. Based on the following described embodiment, to allow a torque determination of the torque applied by the internal combustion engine to the front wheels to be made, the control system only requires to be provided with updated engine speed, vehicle speed and throttle angle, thereby minimising the modifications required when retrofitting an electric motor to a vehicle. However, other means for determining the torque applied to the wheels driven by the internal combustion engine can be used, for example if gear information is available it is possible to determine torque based on the selected gear and throttle angle. Alternatively, a torque sensor can be used to determine the torque.

However, as stated above, for the purposes of the present embodiment, to determine the torque at the wheels driven by the internal combustion engine it is only required that the control system be provided, for example via a vehicle's CAN bus, updated engine speed, vehicle speed and throttle angle. Once the control system has made a determination of the torque being applied to the front wheels of the vehicle the control system is arranged to determine a complementary torque to be generated by the rear in-wheel electric motors, wherein the complementary torque can be selected to either substantially match the torque applied to the front wheels of the vehicle or some other predetermined ratio.

The process for determining torque at the wheels driven by the internal combustion engine will now be described.

The control unit 102 is arranged to perform a number of functions. A schematic representation of these functions is illustrated in Figure 6. These functions include a Wheel Rolling Radius Determination function 601 , an Assumed Gear Ratio

Determination function 602, a Confirmed Gear Number function 603, an Accelerator Pedal Torque Limit Map function 604 and a Gear Torque Limit Scalar Maps function 605.

The Wheel Rolling Radius Determination function 601 is arranged to calculate the wheel rolling radius for the wheels being driven by the internal combustion engine. The wheel rolling radius is calculated using the following expression:

Wheel_Rolling_Radius (mm) =

( (Wheel_Diameter + ( 2* Tyre_Width * Tyre_Ratio) ) / 2) - Tyre_Compression_Under_Load

The values for wheel diameter, tyre width, tyre ratio and tyre compression will generally be considered as being constant for a given vehicle. Typically these values will be stored in memory within the control unit 102 and retrieved by the Wheel Rolling Radius Determination function 601 when a torque determination is required. However, any means for providing these values to the control unit 102 may be used.

The wheel rolling radius calculated by the Wheel Rolling Radius Determination function 601 is provided to the Assumed Gear Ratio Determination function 602. Alternatively, a wheel rolling radius value can be pre-calculated away from the vehicle and stored in memory within the control unit 102 for use by the Assumed Gear Ratio Determination function 602.

Using the wheel rolling radius the Assumed Gear Ratio Determination function 602 is arranged to calculate an assumed gear ratio of the gear box, which is being used by the gear box to translate the engine torque to the front wheels of the vehicle. The gear ratio is calculated using the following expression:

Assumed Gear Ratio =

2 *PI*Wheel_Rolling_Radius(m) *Engine_Speed(rpm) /

(Vehicle_Speed(kph)*( 1000/3600) *Final_Drive_Ratio*60 )

As stated above, typically the engine speed and vehicle speed will be provided to the control unit 102 from vehicle sensors located in the vehicle via a vehicle bus, for example a CAN bus. The Final Drive Ratio will typically be stored in memory within the control unit 102, however the Final Drive Ratio can be provided to the control unit 102 by any suitable means.

The calculated assumed gear ratio is then used by the Confirmed Gear Number function 603 to determine the gearbox gear being used. The gearbox gear being used is determined using the following expression, where initially a determination is made as to whether reverse gear or neutral has been selected. If reverse gear or neutral has been selected no torque determination is made: If ( Reverse _Gear_Selected is TRUE )

Confirmed Gear _Number = -1 ( Reverse )

Else

If( Neutral Gear Selected is TRUE OR Clutch Switch Selected is TRUE)

Confirmed Gear _Number = 0 ( Neutral )

Else

If ( Neutral Gear Ratio < Assumed Gear Ratio <

Sixth _Gear_Ratio*Gear_Ratio Scaling _F actor)

Confirmed _G ar Number = 6

Else

If ( Sixth _Gear_Ratio_C*Gear _Ratio _Scaling _F actor _ C < Assumed _Gear_Ratio < Fifth Gear _Ratio*Gear _Ratio _Scaling_Factor)

Confirmed Gear Number = 5

Else If ( Fifth Gear Jiatio * Gear Jiatio Scaling _F actor < Assumed _Gear_Ratio < Fourth_Gear_Ratio*Gear_Ratio_Scaling_Factor)

Confirmed Gear _Number = 4

Else

If ( Fourth Gear _Ratio *Gear_Ratio Scaling _F actor < Assumed _Gear Ratio < Third_Gear_Ratio*Gear_Ratio_Scaling_Factor)

Confirmed Gear_Number = 3

Else

If ( Third Gear Jiatio *Gear Jiatio Scaling J^actor < Assumed _Gear Ratio < Second Gear _Ratio*Gear _Ratio _Scaling_Factor)

Confirmed Gear_Number = 2

Else

Confirmed Gear_Number = I An example of different gear ratios is listed in the below table.

For example, if the Assumed Gear Ratio Determination function 602 calculates an assumed gear ratio of 2.237 this is used by the Confirmed Gear Number function 603 to identify that the gearbox is most likely to be in second gear. To improve accuracy, the Confirmed Gear Number function 603 is arranged to have maximum and minimum gear ratio threshold values associated with each gear, thereby creating a band of gear ratio values associated with each gear. This ensures that minor errors in the determined gear ratio still results in a correct gear being identified.

5

Associated with each gear is a gear torque limit scalar map. The gear torque limit scalar map provides a table of the percentage of maximum torque that each in- wheel electric motor can provide for each gear that the vehicle is being used in at predetermined vehicle speeds. In other words, the gear torque limit scalar map provides a representation of the 0 internal combustion engine speed/torque profiles by mapping the percentage of maximum torque of the in-wheel electric motors corresponding to the torque envelope that the internal combustion can provide to the front wheels of the vehicle for each given gearbox gear. 5 An example of a gear torque limit scalar map is:

Confirmed Gear Map

Gear Number

Reverse_Gear_Scaling_Map (%) 0 70 12 0

For example, when a determination has been made that the vehicle's gearbox is in first gear and the vehicle is travelling at 10 km/h, the maximum torque that the in- wheel electric motors can provide without exceeding the torque applied by the internal combustion engine 103 to the front wheels via the gearbox when in first gear is 70% of the maximum achievable torque that the in- wheel electric motors can provide.

Similarly, when the vehicle's gearbox is in sixth gear and the vehicle is travelling at 78 km/h, the maximum torque that the in- wheel electric motors can provide without exceeding the torque applied by the internal combustion engine 103 to the front wheels via the gearbox when in sixth gear is 32% of the maximum achievable torque that the in- wheel electric motors can provide. For other vehicle speeds, the Gear Torque Limit Scalar Maps function 605 is arranged to interpolate values from the speeds included within the gear torque limit scalar map. Any suitable form of interpolation can be used.

Accordingly, by limiting the in- wheel electric motor torque in this manner this avoids the risk that the in-wheel electric motors will provide more torque to the rear wheels of the vehicle than that provided by the internal combustion engine 103 to the front wheels of the vehicle. Although, as stated above, any predetermined ratio of electric motor torque and internal combustion engine torque can be used. As such, the in-wheel electric motor torque may be selected to be a predetermined amount greater or less than the torque generated by the internal combustion engine. However, for the purposes of the present embodiment, the in-wheel electric motor torque is arranged to substantially match the torque generated at the front wheels from the internal combustion engine 103.

Using the determined gear ratio and vehicle speed, the Gear Torque Limit Scalar Maps function 605 uses the maximum torque envelope to determine the maximum torque that the in-wheel electric motors can develop for a given speed to avoid exceeding the torque being applied by the internal combustion engine to the front wheels of the vehicle.

To match the torque applied to the rear wheels by the in-wheel electric motors the determined maximum torque generated by the Gear Torque Limit Scalar Maps function 605 is scaled according to the throttle demand of the driver of the vehicle. Any suitable scaling function can be used. For example, if a linear scaling function is used, when the throttle pedal has been pressed half way down the determined maximum torque generated by the Gear Torque Limit Scalar Maps function 605 is scaled by half. For example, when the gearbox is in third gear and the vehicle is travelling at 29 km/h the maximum torque value that can be used to avoid exceeding the torque generated at the front wheels of the vehicle by the internal combustion engine is 70%. However, if the throttle pedal has only been pressed half way down this value is further limited by half, namely to 35% of the maximum in-wheel electric motor torque. However, for a non-linear scaling function the torque value will be limited by an appropriate value for the given non- linear relationship.

Claims

1. A vehicle comprising an engine arranged to apply a torque to a first wheel for moving the vehicle; an electric motor arranged to apply a torque to a second wheel for moving the vehicle; means for determining the torque applied by the engine to the first wheel; and a controller arranged to control the application of torque applied to the second wheel by the electric motor based upon the torque applied by the engine to the first wheel.

2. A vehicle according to claim 1 , wherein the controller is arranged to control the application of torque applied to the second wheel by the electric motor so that the torque applied to the second wheel substantially matches the torque applied by the engine to the first wheel.

3. A vehicle according to claim 1 or 2, wherein the engine is arranged to apply torque to the first wheel via a gear box and the means for determining the torque applied by the engine to the first wheel includes means for determining the speed of the vehicle and means for determining a throttle demand for controlling engine torque, wherein the means for determining the torque is arranged to calculate the torque using the determined speed of the vehicle and throttle demand based on a torque profile associated with a gear or gear ratio of the gear box that is being used to drive the first wheel.

4. A vehicle according to claim 3, wherein the gear box includes a plurality of selectable gears or gear ratios and the means for determining torque applied by the engine to the first wheel includes means for determining the selected gear or gear ratio of the gear box.

5. A vehicle according to claim 4, wherein the means for determining the selected gear or gear ratio of the gear box is arranged to determine the selected gear or gear ratio using a rolling radius of the wheel, the engine speed and the vehicle speed.

6. A vehicle according to any one of claims 3 to 5, wherein the means for determining the torque applied by the engine to the first wheel includes a memory for storing a torque profile associated with each gear or gear ratio of the gear box.

7. A vehicle according to claim 1 , wherein the means for determining the torque applied by the engine to the first wheel includes a torque sensor.

8. A vehicle according to any one of the preceding claims, wherein the electric motor is an in-wheel electric motor.

9. A method of applying torque to a wheel of a vehicle, wherein the vehicle includes an engine arranged to apply a torque to a first wheel for moving the vehicle, an electric motor arranged to apply a torque to a second wheel for moving the vehicle, the method comprising controlling the application of torque applied to the second wheel by the electric motor based upon the torque applied by the engine to the first wheel.