GB2522704A

GB2522704A - Vehicle and method of controlling an electric motor

Info

Publication number: GB2522704A
Application number: GB1401864.2A
Authority: GB
Inventors: Jeremy Greenwood
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2014-02-04
Filing date: 2014-02-04
Publication date: 2015-08-05
Anticipated expiration: 2034-02-04
Also published as: GB2522704B; GB201401864D0

Abstract

A vehicle has an electric motor arranged to provide a driving torque, and a throttle or accelerator which can be set to a throttle angle Î¸ or accelerator position, for example by the driver pressing on a pedal, wherein the electric motor is arranged to vary the driving torque according to the throttle position Î¸, such that at a particular angle or position, Î¸ = Î¸0, the driving torque is set to zero, and wherein the zero torque point Î¸0 varies with the speed of the vehicle. The torque may approach a maximum torque at a maximum throttle position, and may approach a minimum torque, which may be negative, at a minimum throttle position. The system may be used with regenerative braking to provide negative torque, and to imitate in an electric or hybrid vehicle the driving experience of an internal combustion engine vehicle, in that lifting the accelerator pedal causes braking, but starting from rest the accelerator responds instantly.

Description

Vehicle and Method of Controlling an Electric Motor

TECHNICAL FIELD

This invention relates to a vehicle comprising an electric motor and to a method of controlling an electric motor.

BACKGROUND

Vehicles which comprise an electric motor are becoming increasingly common. Some such vehicles comprise only an electric motor, and are typically referred to as Electric Vehicles (EV5), while some comprise an electric motor and some other form of motor. For example, Hybrid Electric Vehicles (HEV5) typically comprise an electric motor and a fuel burning motor such as a petrol motor.

Vehicles which comprise batteries, such as EV5 and HEV5, typically take advantage of regenerative braking. During regenerative braking, the vehicle's wheels are connected to a generator such that the vehicle's momentum drives the generator and in turn charges the battery. This also has the effect of slowing the wheels, hence slowing the vehicle. In EVs and HEVs it is an advantage to provide significant levels of regenerative braking, since this can be used to both charge the batteries and control the vehicle. In particular, tests have shown that regenerative braking can increase the range of off-road vehicles considerably.

Regenerative braking affects the driver's experience of a vehicle's throttle characteristics. By "throttle", of course, is meant the accelerator pedal in normal vehicles, which pedal actuates the motor in an electric vehicle and controls the degree of actuation thereof. Throttle angle is the degree to which the pedal is depressed. Should other than a pedal be employed, then throttle angle means simply the degree of actuation, and can be expressed in percentage terms. Figure 1 shows a graph which illustrates the relationship between throttle angle and electric motor torque in a typical EV. The throttle characteristics in Figure 1 are chosen to mimic the characteristics of a traditional vehicle with an internal combustion engine. Above a certain throttle angle (e.g. 10%), the amount of torque produced by the motor scales linearly with the throttle angle. As such, when the driver increases the throttle angle the torque exerted by the electric motor increases and the vehicle will tend to speed up. Beneath that throttle angle, in region 101 of the graph, the torque is negative.

In region 101 of the graph in Figure 1 the regenerative braking is active, and as such will charge the battery and tend to slow the vehicle down. The amount of regenerative braking varies with the speed of the vehicle, as is indicated by the two lines, one indicating the amount of regenerative braking at 10 miles per hour, and the other indicating the amount of regenerative braking at 5 miles per hour. At 0 miles per hour the regenerative braking falls to zero, meaning that the regenerative brakes do not exert a negative torque on the wheels.

However, braking at 0 miles per hour does help to prevent the vehicle moving.

These characteristics are chosen so that the vehicle imitates the behaviour of a traditional internal combustion engined vehicle where lifting the accelerator pedal causes the engine to become a brake. This can be very useful in HEVs since it provides the driver with a continuity of experience when the vehicle switches between a fuel burning mode and an electric mode.

However, there are disadvantages with this arrangement. For example, when the vehicle is sitting stationary on a driveway, there is a gap between throttle angles of 0 and 10% during which the electric motor does not engage and the vehicle will not move. Thus nothing is happens when the pedal is depressed 10% of its travel. This can be particularly problematic in off-road conditions, in which the vehicle may frequently need to stop and start. Whilst off road, the vehicle may need to overcome heavy resistance when first starting, due to ruts or sharp slopes under the wheels, and the lack of response from the throttle in the lower regions therefore significantly affects the driver's control over the vehicle.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention there is provided a vehicle comprising: an electric motor arranged to provide a driving torque T; and a throttle having a throttle angle B being a degree of actuation by a driver of the vehicle. The electric motor is arranged to vary the driving torque in dependence upon throttle angle, such that at a zero throttle angle B the driving torque is set to zero. The zero throttle angle e0 is arranged to vary with the speed of the vehicle.

In this way the invention provides a vehicle which can respond immediately to changes in throttle angle even at low speed and low throttle angles.

An aspect of the invention provides a method of controlling an electrical motor in a vehicle, the method comprising: providing a throttle and an electric motor, the electric motor arranged to provide a driving torque T; setting the throttle to a throttle angle e; and arranging the electric motor to vary the driving torque with e, such that at a zero throttle angle e0 the driving torque is set to zero. Again, the zero throttle angle is arranged to vary with the speed of the vehicle.

The relationship between eo and speed may be linear, such that for example 80 increases as the speed increases. Alternatively, e and the speed may be related by any desired relationship, the relationship being defined by an equation, a set of equations or by a look-up table. Typically, the motor will be arranged to provide no torque when the throttle is set to a minimum angle 8mjfl and the speed of the vehicle is zero. The motor may then be further arranged to provide a torque T > 0 when 8 > 8min and the speed of the vehicle is zero. As such the vehicle will respond immediately to the driver's wish to move and first actuation of the throttle.

It may be that the vehicle further comprises a brake which is activated when 8 < 80. As such the vehicle may provide the driver with a push-to-go, release-to-stop effect It may be that the brake is or includes a regenerative brake.

Embodiments according to the invention can be arranged so that the torque decreases as the speed of the vehicle increases while the throttle angle is constant. Such embodiments may be advantageous, for example, when driving across a rut. As the vehicle drives into the rut the speed of the vehicle will tend to increase. If the throttle angle is constant, the torque will then decrease, reducing the tendency of the vehicle to lurch forward. As the vehicle reaches the bottom of the rut and begins to climb out of it, the speed of the vehicle will tend to decrease. If the throttle angle is constant, the torque will then increase, helping to propel the vehicle out of the rut. Once clear of the rut, the speed of the vehicle will then tend to increase again. If the throttle angle is constant, the torque will then decrease, again reducing the tendency of the vehicle to lurch forward. As such, the driver is provided with a smoother driving experience without needing to adjust the throttle angle at any stage.

It may be that the zero throttle angle varies with the motor speed of the vehicle. For example the zero throttle angle may vary with the number of revolutions undergone in a second by a component of the vehicle which is driven by the electric motor. Alternatively, it may be that eo varies with the wheel speed of the vehicle.

It may be that T is linearly related to 9 when the speed of the vehicle is constant. It may be that T = a V 9 -b, wherein a and b are constants and V is the speed of the vehicle. It may be that a = 1. It may be that b = 0.

Typically, the throttle can be set to a maximum throttle angle and as e approaches 9max the driving torque approaches a maximum torque Tmax. It may be that the torque exerted by the vehicle at Bmax is fixed, and does not depend upon the speed of the vehicle.

It may be that T = c 9-d, wherein at least one of c and d vary with the speed of the vehicle.

It may be that c is a constant. Alternatively, it may be that d is a constant.

It may be that the throttle can be set to a minimum throttle angle 6mjfl and as U approaches 9min the driving torque approaches a minimum torque Tmin. The minimum torque Tmjn may be less than zero. It may be that the torque exerted by the vehicle at 9min is fixed, and does not depend upon the speed of the vehicle. Typically, 9min is the lowest possible throttle angle.

Typically, is the resting throttle angle, or the angle adopted by the throttle when not acted upon by the driver. In a typical embodiment of the invention, the minimum throttle angle is always less than or equal to the zero throttle angle.

T may become negative as 9 approaches a minimum angle 9mjfl An aspect of the invention provides an apparatus comprising: an electric motor arranged to provide a driving torque T; and a throttle having a throttle angle U being a degree of actuation by an operator of the apparatus. The electric motor is arranged to vary the driving torque in dependence upon the throttle angle, such that at a zero throttle angle e the driving torque is set to zero. The zero throttle angle may be arranged to vary with the speed of the electric motor.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 shows a chart illustrating the relationship between throttle angle and torque in a

prior art vehicle; and

Figures 2, 3, 4, 5 and 6 show charts illustrating the relationship between throttle angle and torque in embodiments according to the invention.

DETAILED DESCRIPTION

Figure 2 shows a graph of the relationship between throttle angle and torque in a vehicle according to the invention. The vehicle is an Electric Vehicle (EV) which comprises an electric motor to drive the wheels. As a result, the relationship between the torque supplied to the wheels by the motor and the angle of the throttle can be configured to any arbitrary relationship. In the embodiment shown in Figure 2, the angle of the throttle 9 and the torque T is defined by the relationship: T =ce-d where c is a positive constant and d changes with the speed of the vehicle V. In this particular embodiment d changes linearly with V such that: d = kV where k is a positive constant. As such: I = c B -kV.

These relationships are illustrated on the graph by three lines which illustrate the relationship between the throttle angle B and the torque I at three different vehicle speeds V, namely zero miles per hour, five miles per and ten miles per hour as labelled on the graph At start up, V = 0 mph, and any increase in throttle angle results in a positive torque, since T = c B. As such, whenever the vehicle is stationary the driver can begin to apply torque to the wheels with only the slightest change in 9, causing the vehicle to respond immediately to the driver's input. In off road conditions this is especially advantageous since if the vehicle is stationary against an obstacle such as a rock or rut in the driving surface, then the driver need only apply slight pressure to begin exerting torque to begin overcoming the obstacle.

This improves the feel of the vehicle for the driver and gives them more precise control over the behaviour of the vehicle.

Once the vehicle is moving, for example at V = 10mph, a positive torque will still be provided to the wheels provided that B > k V I c, as can be derived from the equations above. If B = k Vt c then the torque is zero.

The vehicle whose responses are illustrated in Figure 2 comprises a battery which can be charged with regenerative braking. If B < k V / c then regenerative braking is active and the torque is negative. Hence when the driver releases the throttle sufficiently the regenerative braking will begin to take effect, slowing the vehicle down and charging a battery in the vehicle. Hence the driver is provided with considerable control over the speed of the vehicle, when both speeding up and slowing down, using the throttle alone, just like in a traditional vehicle with an internal combustion engine. However, unlike a traditional vehicle with an internal combustion engine, the responses of vehicles according to the invention can be adjusted to suit the needs of the vehicle and the driver, for example by producing a more pronounced or exaggerated response to the driver's actions. The response may also be less pronounced if this is desired.

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The torque provided by the electric motor is limited by the maximum power of the motor. As the motor speed increases the power consumed to maintain a torque increases. Once the the maximum power is reached, the torque cannot be increased further without first reducing the motor speed. At higher speeds, therefore, the vehicle may not be able to maintain a torque as indicated by Figure 2. In such instances, where the driver has requested a torque which is higher than can be provided by the electric motor, the vehicle provides the maximum available torque.

In alternative embodiments of the invention the relationship between V and d is not linear.

Figure 3 shows a graph of the relationship between throttle angle and torque in a further vehicle according to the invention. Again the vehicle is an Electric Vehicle (EV) which comprises an electric motor to drive the wheels, and again three lines are provided on the graph to illustrate the relationship between torque and throttle at different vehicle speeds. In the embodiment shown in Figure 3, the angle of the throttle 9 and the torque T is again defined by the relationship: T = c e -d.

As can be seen from the graph, this embodiment behaves similarly to the embodiment shown in Figure 2 at low values of e. An immediate torque is applied when 9> 0 and V = 0, while regenerative braking is applied at low values of B where V > 0.

However in this embodiment neither c nor d are constant with respect to V, the speed of the vehicle. Rather, c and d are defined such that at a maximum throttle angle 9ftax, a maximum torque Tmax is applied to the wheels, regardless of V. As such, the driver can exert the maximum torque on the wheels regardless of the speed of the vehicle.

A further embodiment is shown in Figure 4. This embodiment is similar to that shown in Figure 3 except that the relationship between T and B is no longer linear for a given value of V. Figure 5 shows a still further embodiment, similar to that shown in Figure 4, in which the relationship between T and B is also not linear for a given value of V. In the embodiment of Figure 5, the relationship between T and B is arranged such that at a minimum throttle B = 9min, the torque is also set tot a minimum torque T = Tmjn, provided that V>0. At V = 0, the torque T does not drop below zero. This reflects the nature of the regenerative brake, which only acts to slow the vehicle down, and so cannot apply a negative torque when the vehicle is already stationary.

Figure 6 shows a further embodiment, similar to the one shown in Figure 5, in which the curve relating T and 9 at V = 0 is arranged such that T> 0 when 9 > 9min, by introducing a sufficiently steep first section of the curve.

In the examples given above, an EV vehicle is used. However a HEV vehicle, any vehicle comprising an electric motor and any electric motor which is driven by a throttle to provide torque can also be provided with features according to the invention.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps.

Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Aspects and embodiments of the present invention are outlined in the following series of numbered paragraphs: 1. A vehicle comprising: an electric motor, arranged to provide a driving torque T; and a throttle, having a throttle angle 9 being a degree of actuation by a driver of the vehicle, wherein the electric motor is arranged to vary the driving torque in dependence upon the throttle angle, such that at a zero throttle angle Bo the driving torque is set to zero, and wherein the zero throttle angle is arranged to vary with the speed of the vehicle.

2. A vehicle according to numbered paragraph 1, wherein the zero throttle angle varies with the motor speed of the vehicle.

3. A vehicle according to numbered paragraph 1 or numbered paragraph 2, wherein: T=aVB-b wherein a and b are constants and V is the speed of the vehicle.

4. A vehicle according to numbered paragraph 1 or numbered paragraph 2 wherein the throttle can be set to a maximum throttle angle 9, and as B approaches 9max the driving torque approaches a maximum torque Tmax.

5. A vehicle according to numbered paragraph 4, wherein: T =ce-d wherein at least one of c and d vary with the speed of the vehicle.

6. A vehicle according to numbered paragraph 1, numbered paragraph 2 or numbered paragraph 4, wherein the throttle can be set to a minimum throttle angle 9min, and as B approaches the driving torque approaches a minimum torque Tmjn.

7. A vehicle according to any preceding numbered paragraph in which T becomes negative as B approaches a minimum angle B. 8. A method of controlling an electrical motor in a vehicle, the method comprising: providing a throttle and an electric motor, the electric motor arranged to provide a driving torque T; setting the throttle to a throttle angle B; and arranging the electric motor to vary the driving torque with B, such that at 9 = 90 the driving torque is set to zero, wherein B0 varies with the speed of the vehicle.

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9. A method according to numbered paragraph 8, wherein 9 varies with the motor speed of the vehicle.

10. A method according to numbered paragraph 8 or numbered paragraph 9, wherein: T=aVB-b wherein a and b are constants and V is the speed of the vehicle.

11. A method according to numbered paragraph 8 or numbered paragraph 9 wherein the throttle can be set to a maximum throttle angle 9, and as 9 approaches 9max the driving torque approaches a maximum torque Tmax.

12. A method according to numbered paragraph 11, wherein: T =c8-d wherein at least one of c and d vary with the speed of the vehicle.

13. A method according to numbered paragraph 8, numbered paragraph 9 or numbered paragraph 11, wherein the throttle can be set to a minimum throttle angle emin, and as e approaches 9 the driving torque approaches a minimum torque Tmjn.

14. A method according to any of numbered paragraphs 8 to 13 in which T may become negative as 9 approaches a minimum angle 9mn 15. An apparatus comprising: an electric motor arranged to provide a driving torque T; and a throttle having a throttle angle 9 being a degree of actuation by an operator of the apparatus, wherein the electric motor is arranged to vary the driving torque in dependence upon the throttle angle, such that at a zero throttle angle 90 the driving torque is set to zero, and wherein the zero throttle angle is arranged to vary with the speed of the electric motor.

Claims

CLAIMS1. A vehicle comprising: an electric motor, arranged to provide a driving torque T; and a throttle, having a throttle angle B being a degree of actuation by a driver of the vehicle, wherein the electric motor is arranged to vary the driving torque in dependence upon the throttle angle, such that at a zero throftle angle B0 the driving torque is set to zero, and wherein the zero throttle angle is arranged to vary with the speed of the vehicle.
2. A vehicle according to claim 1, wherein the zero throttle angle varies with the motor speed of the vehicle.
3. A vehicle according to claim 1 or claim 2, wherein: T=aVB-b wherein a and b are constants and V is the speed of the vehicle.
4. A vehicle according to claim 1 or claim 2 wherein the throttle can be set to a maximum throttle angle Bmax, and as B approaches Bmax the driving torque approaches a maximum torque Tmax.
5. A vehicle according to claim 4, wherein: T =cB-d wherein at least one of c and d vary with the speed of the vehicle.
6. A vehicle according to claim 1, claim 2 or claim 4, wherein the throttle can be set to a minimum throttle angle Bmin, and as B approaches 9min the driving torque approaches a minimum torque Tmjn.
7. A vehicle according to any preceding claim in which T becomes negative as B approaches a minimum angle 9fljn*
8. A method of controlling an electrical motor in a vehicle, the method comprising: providing a throttle and an electric motor, the electric motor arranged to provide a driving torque T; setting the throttle to a throttle angle B; and arranging the electric motor to vary the driving torque with B, such that at B = B0 the driving torque is set to zero, wherein 90 varies with the speed of the vehicle.
9. A method according to claim 8, wherein e0 varies with the motor speed of the vehicle.
10. A method according to claim 8 or claim 9, wherein: T=aV9-b wherein a and b are constants and V is the speed of the vehicle.
11. A method according to claim 8 or claim 9 wherein the throttle can be set to a maximum throttle angle emax, and as 9 approaches 9max the driving torque approaches a maximum torque Tmax.
12. A method according to claim 11, wherein: T =ce-d wherein at least one of c and d vary with the speed of the vehicle.
13. A method according to claim 8, claim 9 or claim 11, wherein the throttle can be set to a minimum throftle angle 9min, and as 9 approaches 9min the driving torque approaches a minimum torque Tmin.
14. A method according to any of claims 8 to 13 in which I may become negative as 9 approaches a minimum angle 9mjn*
15. An apparatus comprising: an electric motor arranged to provide a driving torque T; and a throttle having a throttle angle e being a degree of actuation by an operator of the apparatus, wherein the electric motor is arranged to vary the driving torque in dependence upon the throttle angle, such that at a zero throttle angle eo the driving torque is set to zero, and wherein the zero throttle angle is arranged to vary with the speed of the electric motor.