GB2571139A

GB2571139A - A system and method of assisting a vehicle to travel at a desired speed

Info

Publication number: GB2571139A
Application number: GB1802732.6A
Authority: GB
Inventors: Tachon René
Original assignee: Jaguar Land Rover Ltd
Current assignee: Jaguar Land Rover Ltd
Priority date: 2018-02-20
Filing date: 2018-02-20
Publication date: 2019-08-21
Anticipated expiration: 2038-02-20
Also published as: GB201802732D0; GB2571139B

Abstract

A system for assisting a vehicle (10) to travel at a steady speed, the system comprising: monitoring a signal indicative of a speed of the vehicle (10); monitoring a signal indicative of a state of an actuator (12) that is operable by a driver of the vehicle (10) to control an output of an engine (14) of the vehicle (10); a means to: determine a confidence level that a steady speed of the vehicle (10) is desired based on the signal indicative of a speed of the vehicle (10) and the signal indicative of a state of the actuator (12); interpolate between a normal actuator response map (56) and a modified actuator response map (60) in dependence on the confidence level, and translate the indicated actuator state into an engine output request in dependence on said interpolation, wherein the modified actuator response map (60) is arranged to damp a response of the actuator (12) relative to the normal actuator response map (56); and means for sending the engine output request signal to control an output of the engine (14). A corresponding method is also provided.

Description

The present disclosure relates to a system of assisting a vehicle to travel at a desired speed. Aspects of the invention relate to a system, to a method, to a vehicle, to a computer program product and to a non-transitory computer-readable medium.

BACKGROUND

It is often necessary to hold an automotive vehicle at a steady speed, for example when cruising on a highway or when travelling at a speed corresponding to an applicable speed limit.

Maintaining a steady speed requires a human operator of the vehicle to apply appropriate control to an accelerator pedal to compensate for any changes in vehicle load. The vehicle load may alter in response to a varying road gradient or a change in the road surface condition, for example. Forces such as air resistance and friction that oppose movement of the vehicle also contribute to the vehicle load.

It is noted that the speed of the vehicle is influenced by the vehicle load and so is not directly proportional to the accelerator pedal position. Moreover, the relationship between the pedal position and the vehicle speed is not linear even for a situation where a vehicle travels on a level and consistent surface, since a vehicle engine does not produce a linear power output over its operational range, and friction and air resistance increase non-linearly with vehicle speed. The human operator must take this non-linear response into account when attempting to control the vehicle speed.

A human operator controlling the speed of a vehicle may therefore be considered to correspond broadly to crude compensation control of a non-linear system. Like any controller, the operator is susceptible to instability and over-compensation, which leads to unnecessary actuation of the accelerator pedal and in turn increased energy consumption by the vehicle.

Notwithstanding the fact that a human operator is incapable of providing perfect speed control, to hold the vehicle at the desired speed without any deviation would also require the driver to monitor the vehicle speedometer continuously and react to any disturbances without any break in concentration. This is of course not possible in practice; not least because the operator’s primary focus must be the road ahead.

It is against this background that the present invention has been devised.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a system, a vehicle, a method and a computer program as claimed in the appended claims.

According to an aspect of the invention there is provided a system for assisting a vehicle having an engine to travel at a steady speed, the system comprising: means for receiving: a signal indicative of a speed of travel of the vehicle; and a signal indicative of a state of an actuator that is operable by a driver of the vehicle to control an output of an engine of the vehicle; a means to: determine a confidence level that a steady speed of travel of the vehicle is desired based on the signal indicative of a speed of travel of the vehicle and the signal indicative of a state of an actuator; interpolate between a normal actuator response map and a modified actuator response map in dependence on the determined confidence level; and translate the indicated actuator state into an engine output request in dependence on said interpolation, wherein the modified actuator response map is arranged to damp a response of the actuator relative to the normal actuator response map; and means for sending the engine output request signal to control an output of the engine.

The means for receiving the signal indicative of a speed of travel of the vehicle and the signal indicative of a state of an actuator may comprise one or more electronic processor having an electrical input for receiving said signals. The means for sending the engine output request signal may comprise the one or more electronic processor having an electrical output for sending said signal. The system may have an electronic memory device electronically coupled to the electronic processor and having instructions store thereon; and said means for determining a confidence level, interpolating between a normal actuator response map and a modified actuator response map, and translating the indicated actuator state into an engine output request may comprise the one or more processor being configured to access the memory device and execute the instructions stored therein so that it is operable to determine the confidence level, interpolate between the normal actuator response map and modified actuator response map, and translate the indicated actuator state into an engine output request.

As noted above, a steady vehicle speed may be desired, for example, when cruising on a highway. By detecting such a desire with a certain confidence level through the monitoring of signals and adjusting the engine output request accordingly, assistance can be provided to the driver in a subtle manner that avoids creating an impression of loss of control. In this respect, the interpolation between the normal response map and the modified response map enables dynamic and continuous adjustment of the extent to which assistance is provided in accordance with the confidence level.

The signal indicative of a speed of travel of the vehicle optionally comprises any one or more of: a measurement of vehicle speed produced by a vehicle speed sensor; a measurement obtained from an accelerometer; a measurement obtained from a gyroscope; data that is indicative of a future speed of travel of the vehicle; data output by a navigational system; and data indicative of road conditions ahead of the vehicle. In the latter case, the road conditions may comprise one or more of the following: traffic conditions; junctions; corners; road gradient; velocity profile data; and local speed restrictions.

The system may comprise means for determining a blend ratio that is based on the confidence level, and interpolating between the normal actuator response map and the modified actuator response map in dependence on the blend ratio. The means may comprise the processor carrying out the instructions stored on the memory to determine said blend ratio and interpolate in dependence on said blend ratio.

The system may comprise determining the magnitude of the steady speed of the vehicle which is desired, in which case the confidence level may be adjusted in accordance with the magnitude of the steady speed of the vehicle which is desired.

The modified actuator response map may comprise a lookup table, and or may be generated by the electronic processor warping the normal actuator response map. The modified actuator response map typically comprises a flattened region around a road load point. The road load point is the torque required to match the present vehicle load, i.e. the torque required to overcome external forces on the vehicle to maintain the vehicle at its present speed,

Determining a confidence level that a steady speed of travel of the vehicle is desired may comprise the system comprising means, for example in the form of the one or more electronic processor, to determine a range of deviation over a time period of at least one of: the signal indicative of a speed of travel of the vehicle; and the signal indicative of a state of the actuator. Such embodiments may comprise the one or more electronic processor increasing the confidence level if the deviation remains within threshold limits throughout the time period, and the magnitude of the confidence level may be related to the duration of the time period and/or to the magnitude of the range of deviation.

The signal indicative of a state of the actuator may represent a torque request.

The actuator may comprise an accelerator pedal, in which case the signal indicative of a state of the actuator may be indicative of a position of the accelerator pedal.

The engine output request may comprise a torque demand and/or a power demand, for example.

The system may comprise means, for example in the form of the one or more electronic processor, for setting the confidence level to zero if a deactivation condition is satisfied. Deactivation conditions may include pressing of a brake pedal, or an indication of an approach change in road conditions, for example.

According to another aspect of the present invention there is provided a method of assisting a vehicle to travel at a steady speed. The method comprises monitoring a signal indicative of a speed of travel of the vehicle; monitoring a signal indicative of a state of an actuator that is operable by a driver of the vehicle to control an output of an engine of the vehicle; determining a confidence level that a steady speed of travel of the vehicle is desired based on the signal indicative of a speed of travel of the vehicle and the signal indicative of a state of the actuator; interpolating between a normal actuator response map and a modified actuator response map in accordance with the confidence level that a steady speed is desired, to translate the indicated actuator state into an engine output request, wherein the modified actuator response map is arranged to damp a response of the actuator relative to the normal actuator response map; and issuing the engine output request to control an output of the engine.

Another aspect of the invention provides a vehicle incorporating a control system as described above.

Other aspects of the invention provide a computer program product comprising computer readable code for controlling a computing device to perform the method of the above aspect, and a non-transitory computer readable medium comprising such a computer program product.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which like features are assigned like reference numbers, and in which:

Figure 1 is a schematic representation of a vehicle that is suitable for use with embodiments of the invention;

Figure 2 is a schematic illustration of an accelerator pedal of the vehicle of Figure 1;

Figure 3 is a graph representing the speed of the vehicle of Figure 1 over a time period;

Figure 4 is a block diagram representing a control architecture for the vehicle of Figure 1;

Figure 5 is a block diagram representing a portion of the control architecture of Figure 4; and

Figure 6 is a flow diagram representing a control method according to an embodiment of the invention.

DETAILED DESCRIPTION

Figure 1 shows a vehicle 10 that is suitable for use with embodiments of the invention. It is noted that embodiments of the invention can be applied to vehicles having powertrains comprising petrol or diesel fuelled internal combustion engines, electric powertrains or hybrid powertrains that incorporate both electric propulsion and an internal combustion engine.

The vehicle 10 includes an actuator in the form of an accelerator pedal 12 that is operable by a driver to control the output of an engine 14 of the vehicle 10, and in turn control a speed of the vehicle 10.

Specifically, actuation of the pedal 12 by the driver effects opening or closing of a throttle 16 disposed within an air intake of the engine 14, where opening of the throttle 16 is generally related to the position of the accelerator pedal 12. Such actuation of the pedal 12 by the driver therefore represents a driver torque request or torque demand for a powertrain of the vehicle 10. It is noted that for non-linear actuators such as internal combustion engines the torque delivered for a given pedal position varies with engine speed and other factors.

A position sensor 18 is attached to the accelerator pedal 12 as is conventional. The position sensor 18 is arranged generate a signal indicative of the pedal position, the signal representing any displacement of the pedal 12 from a rest position.

Figure 2 represents the accelerator pedal 12 schematically, and shows that the pedal 12 comprises an elongate lever arm 20 that is supported for rotation about a pivot 22 at one end, and which supports a footpad 24 at its other end. In use, the driver applies pressure to the footpad 24, which causes rotation of the lever arm 20 around the pivot 22.

An indicator arm 26 extends from the pivot 22 almost orthogonally to the lever arm 20, into the position sensor 18. Rotation of the lever arm 20 when the footpad 24 is pressed effects complementary rotation of the indicator arm 26 within the position sensor 18. This enables the position sensor 18 to indicate the position of the pedal 12, for example as an angle of deflection or as a proportion of travel with respect to a maximum range of travel.

Returning to Figure 1, the position sensor 18 is electronically connected to an electronic processor in the form of a speed controller 30. The speed controller 30 is incorporated in a powertrain control module (not shown) in this example, and so signals are transmitted from the position sensor 18 to the speed controller 30 by dedicated wiring 32 using pulse-width modulation. Alternatively, the speed controller could be incorporated in another vehicle control unit, in which case signals may be transmitted from the position sensor 18 by wiring forming part of a conventional vehicle communications bus, including CAN, Flexray or Ethernet. In this way, signals indicative of the pedal position are transmitted from the position sensor 18 to the speed controller 30. In other embodiments, any suitable means for transmitting the signals may be used.

It will be appreciated that although described as a single processor the functions of the speed controller may be distributed across two or more processors in electronic communication with one another. The processor has a memory associated with it that contains instructions that when accessed and executed by the processor cause it to carry out the functions described herein, the memory may also contain one or more look up tables, for example correlating accelerator pedal input to a desired engine power or torque output.

The arrangement shown in Figure 1 implements electronic throttle control, in that there is no direct mechanical link between the accelerator pedal 12 and the throttle 16. Instead, the throttle 16 comprises a valve that can be opened or closed by an electric actuator in response to control signals received from the speed controller 30. In this respect, the speed controller 30 is connected to the throttle 16 through a communications bus 34 to deliver such control signals to the throttle 16.

In the simplest mode of operation, the speed controller 30 operates the throttle 16 to open to an extent that is substantially proportional to the accelerator pedal position as indicated by the position sensor 18. Thus, the speed controller 30 implements a ‘driveby-wire’ approach to controlling the engine throttle 16. There is a relationship between the driver torque request and the extent to which the throttle 16 is opened that is represented by a profile or map, which corresponds to a conventional pedal map that translates a detected pedal position into the driver torque request. The driver torque request in turn is received and modified by the speed controller 30, which then controls the vehicle powertrain through appropriate operation of the throttle 16 according to conventional engine control techniques.

As the skilled person will recognise, the conventional map is not linear as it is tailored to account for any non-linearity in the output of the vehicle engine 14 - in particular with respect to a relationship between torque capability and engine speed - and to provide a particular driver ‘feel’, noting that the driver intuitively expects a linear response from the accelerator pedal 12. For example, the conventional map may be configured to request maximum torque when the accelerator pedal 12 is deflected by only 80% of its range, to make the vehicle 10 seem more powerful and responsive. In off-road or winter driving modes, the sensitivity of the pedal response may be reduced to offer more progressive control.

The conventional map therefore exhibits an initial upward curve for low pedal deflection, a downward gradient at the upper extent of the range of pedal movement, and some minor deviation from a strictly linear profile in between. The conventional map is shown in Figure 5, which will be discussed in more detail later.

In embodiments of the invention, the speed controller 30 does not implement the above simple mode of operation based solely on the conventional map, and instead controls the throttle 16 based on a final torque request that takes other vehicle operating parameters into account alongside the driver torque request indicated by the accelerator pedal position.

In general terms, the speed controller 30 monitors one or more further vehicle parameters to detect an attempt by the driver to hold the vehicle 10 at a steady speed. On detecting such an attempt, the speed controller 30 determines a confidence level that a steady speed is desired, and modifies the nominal relationship between the driver torque request and the accelerator pedal position to damp the response of the accelerator pedal 12 around a road load point. In practice, this entails blending the conventional pedal map with a cruise assist map in accordance with the confidence level to damp the pedal response, as discussed in more detail later in relation to Figure 5.

Briefly, if the confidence level is low the extent to which the conventional map is blended with a cruise assist map is also low, meaning that the vehicle 10 is controlled predominantly based on the conventional map. Conversely, if the confidence level is high, the blending is weighted towards the cruise assist map so that the final torque demand will be based primarily on the cruise assist map.

By damping the response of the accelerator pedal 12, unwanted oscillation of the vehicle speed around the desired value can be reduced, thereby minimising energy consumption during periods of cruising.

The vehicle parameters that are taken into account by the speed controller 30 to detect an attempt to cruise at a constant speed shall now be considered, before moving on to the way in which the pedal response is damped to assist the driver with maintaining a steady speed.

In the arrangement shown in Figure 1, the speed controller 30 receives three further inputs in addition to the signal indicative of the pedal position, namely signals indicative of the vehicle speed, a gradient of the road on which the vehicle 10 is travelling, and vehicle navigational data.

In this respect, the speed controller 30 is electronically connected to at least one road wheel sensor 36 that is associated with a road wheel 38 of the vehicle 10 and is arranged to transmit signals indicative of the vehicle speed, which in this example corresponds to the measured road wheel speed. In this embodiment the speed controller 30 receives signals from the road wheel sensor 36 through the communications bus 34, although other suitable means of communication are possible.

Although only one road wheel 38 and its associated road wheel sensor 36 are shown in Figure 1 for simplicity, it should be appreciated that the speed controller 30 may receive respective signals from several road wheel sensors in practice.

In other arrangements, signals indicative of the vehicle speed could be received from alternative sources, such as a sensor attached to a driveshaft or an engine speed sensor. For example, a speed-over-ground signal derived from data provided by onboard accelerometers, navigational systems and other sources may provide or contribute to the signal indicative of vehicle speed.

The speed controller 30 is also electronically connected to a global positioning system (GPS) unit 40 that transmits navigational data to the speed controller 30. The navigational data may include, for example: a geographical location of the vehicle 10; information regarding road features ahead of the vehicle 10, including corners, junctions and velocity profile data representing historical and current average speed data for vehicles in the present location as indicated by vehicle-to-vehicle data, or infrastructure-to-vehicle data; local speed restrictions; and traffic conditions.

Finally, the speed controller 30 is also connected to a gradient calculation module 42 through the communications bus 34, so that the gradient calculation module 42 can transmit signals indicative of the road gradient to the speed controller 30. The gradient calculation module 42 may be a dedicated component, or may be integrated with another vehicle control unit. The speed controller 30 can use this information together with the indicated vehicle speed to estimate the instantaneous vehicle load with high accuracy, and thereby compensate for the vehicle load in the final torque request on which the control signals that operate the throttle 16 are based. As is conventional, the gradient calculation module 42 typically uses data provided by a combination of onboard accelerometers and gyroscopes to estimate the road gradient using a suitable algorithm.

Accordingly, in this embodiment the speed controller 30 is configured to receive and monitor signals that are indicative of the accelerator pedal position, the vehicle speed, the road gradient and navigational data. In other embodiments, the speed controller 30 may handle further inputs, such as signals indicative of a state of one or more vehicle brakes. It is also possible for the vehicle 10 to make use of vehicle-to-vehicle data, or infrastructure-to-vehicle data, for example to gather information regarding obstacles or other factors ahead of the vehicle 10 that may cause a change in vehicle speed.

The speed controller 30 may be embodied as a dedicated, stand-alone unit. Alternatively, as already noted the speed controller 30 may be integrated within another vehicle controller such as a powertrain control module or an engine control unit, for example.

Figure 3 shows a plot 44 of vehicle speed against time, the plot 44 representing a typical driving cycle in which the vehicle 10 accelerates from rest, at a time designated as ‘t0’, to a nominal speed, at a time designated ‘t1 and then travels at a substantially constant speed over a period ending at a time designated ‘t2’.

Between t1 and t2, the range of deviation of vehicle speed is relatively low, as indicated by a narrow band bordered by upper and lower horizontal dashed lines 46 in Figure 1. This narrow range of vehicle speeds can be used by the speed controller 30 to indicate that the driver is attempting to hold the vehicle 10 at a steady speed, and thereby trigger appropriate blending of a conventional pedal map with a cruise assist map.

This illustrates that, in general terms, the speed controller 30 can monitor the vehicle speed to detect whether the deviation in vehicle speed is within a predetermined threshold over a certain period, and use this low deviation as indicative that the driver is trying to hold the vehicle 10 at a steady speed. The extent and duration of the low deviation may be used to generate a confidence level for the assumed desired speed, which in turn can be used to modify the accelerator pedal response by determining the extent to which the conventional and cruise assist maps are blended. The relationship between the period for which the vehicle speed deviation remains within threshold limits and the confidence level that a steady speed is required can be varied according to the specific requirements of each application.

In a simple implementation, blending may be activated after an initial period of steady vehicle speed of around five seconds, for example. If the vehicle speed deviation then remains within the threshold limits, the confidence level, and in turn the extent of blending, may be increased.

Another means for determining that the driver is attempting to maintain constant speed is to monitor the pedal position, which, like the vehicle speed, may be expected to deviate within a narrow range over a defined period if the driver is trying to hold the vehicle 10 at a certain speed. Thus, determining that the pedal position deviates only within a threshold range over a period of, for example, five seconds, may be used to trigger blending between the conventional map and the cruise assist map.

As an alternative to monitoring vehicle parameters directly in the manner described above, the speed controller 30 may use the navigational data to predict whether the driver will desire a constant speed.

For example, if the navigational data indicates that there are no junctions or corners within a threshold distance, for example 500 metres, this may be used to aid detection of a desire to hold the vehicle 10 at a steady speed. It is noted that the threshold distance may be adjusted according to the instantaneous vehicle speed.

In addition, if a comparison between the navigational data and the instantaneous vehicle speed reveals that the vehicle 10 is travelling close to a relevant speed limit, the speed controller 30 may assume that the driver is attempting to control the vehicle 10 to travel at that limit, and intervene accordingly. Speed restriction information may be obtained from GPS map data or advanced driver assistance systems (ADAS) data, for example.

Another factor that can be considered is traffic data within the navigational data. If the traffic data indicates that the level of traffic surrounding the vehicle 10 is low, so that traffic is free-flowing, this can strengthen an assumption that the driver wishes to hold the vehicle 10 at a continuous speed. Conversely, at higher traffic levels cruising may be considered unlikely.

It should be appreciated that the above factors can be used in any combination to increase a confidence level that the driver desires a constant vehicle speed. For example, if the navigational data indicates that the vehicle 10 is travelling close to the relevant speed limit, the period over which the vehicle speed mustn’t deviate beyond the threshold limits can be reduced. It will be appreciated that there are many further ways that the various indications may be combined to aid detection of a desire for a constant vehicle speed.

Once cruise assistance is triggered, the speed controller 30 continues to blend the conventional map with the cruise assist map until a deactivation condition is met, at which point the confidence level that steady speed is required is reset to zero and control reverts to the conventional map alone. Typically, there may be several possible deactivation conditions, with the fulfilment of any one of them being sufficient to reduce the confidence level to zero.

The deactivation conditions adopted by the speed controller 30 may be similar to those used in a conventional cruise control system, for example, and so might include an indication of tip-in or tip-out of the accelerator pedal 12 or application of a brake pedal.

Additionally, further conditions for deactivation may include: an increase in deviation in the accelerator pedal position; movement of the pedal position away from a position corresponding to the present speed for a predetermined time period after activation of cruise assistance; an indication of an approaching corner or junction; and an indication of an increase in traffic load around the vehicle 10.

Figure 4 shows a possible architecture for the speed controller 30. As shown, the speed controller 30 comprises a blend ratio determination module 50, a pedal maps module 52 and a blending module 54. These modules include processing resources that together define a processing module that is able to determine a confidence level that a steady speed is desired and output an engine output control signal accordingly.

The blend ratio determination module 50 is responsible for determining a confidence level for a desire for constant vehicle speed, and outputting a blend ratio of between 0 and 1 corresponding to that confidence level. The confidence level may be represented as a number between 0 and 1, for example, in which case the blend ratio corresponds directly to the confidence level.

Accordingly, the blend ratio determination module 50 receives inputs relating to relevant vehicle parameters such as those discussed above.

In the example shown in Figure 4, the blend ratio determination module 50 receives six inputs, specifically: a signal indicative of gradient; a signal indicative of driving style; a signal indicative of vehicle speed; a signal indicative of the accelerator pedal position; a signal indicative of a distance to a road junction; and a signal indicative of a local speed limit. It should be appreciated that the inputs shown in Figure 4 are for illustrative purposes only, and the blend ratio determination module 50 may receive any combination of inputs that are relevant to detecting or predicting a desire for a constant vehicle speed.

Based on the received inputs, the blend ratio determination module 50 determines whether the driver appears to be trying to control the vehicle 10 to maintain a constant speed, or whether it is otherwise likely that a constant speed may be desired. If a desire for constant vehicle speed is detected, the blend ratio determination module 50 determines a confidence level associated with the detected desire, and issues a blend ratio to the blending module 54 accordingly.

Although not shown in Figure 4, the blend ratio determination module 50 may also estimate a value for the vehicle speed that the driver seems to be attempting to maintain - or is expected to want to maintain - which is output as a vehicle reference speed. The vehicle reference speed is typically derived based on a filtered value for the vehicle speed, a moving average of the vehicle speed, or a combination of the two.

The pedal maps module 52 includes a readable memory from which it retrieves a conventional pedal map and a cruise assist map, in this example based on three inputs: the vehicle speed, a road load estimate and the accelerator pedal position. The two types of pedal map are represented in Figure 5, which is discussed shortly. Based on the conventional map and the cruise assist map, the pedal maps module 52 derives a driver torque request and a cruise assist torque request respectively, which are forwarded to the blending module 54.

The blending module 54 is responsible for calculating a final torque request by interpolating between the conventional torque request and the cruise assist torque request in accordance with the blend ratio received from the blend ratio determination module 50. The final torque request is then used to determine the control signals that are used to operate the engine throttle 16.

The driver torque request corresponds to the output from the conventional pedal map when the current pedal position is translated into a torque request, as already described. The torque request may optionally be normalised to a torque capability of the vehicle 10, and may take as a frame of reference a vehicle actuator such as the engine 14, or alternatively the road wheel 38. Converting the pedal position into a driver torque request may occur within a pre-processing module (not shown) contained within the speed controller 30, for example.

If the blending module 54 does not receive a blend ratio from the blend ratio determination module 50, the confidence level is assumed to be zero and the final torque request that is output from the blending module 54 is identical to the driver torque request that was received as an input. This situation corresponds to normal driving, in which the engine throttle 16 is controlled entirely based on the conventional pedal map, and so the driver has full control over vehicle acceleration.

However, if the blending module 54 does receive a blend ratio, it interpolates between the driver torque request and the cruise assist torque request and outputs a final torque request accordingly. In this scenario, the final torque request does not match the driver torque request, and so the driver is assisted to some extent by the speed controller 30. This entails damping the driver torque request around a point of road load torque on the pedal map, thus stabilising vehicle speed at the current speed by lessening the effect of small fluctuations in pedal position. The driver retains full control over the vehicle acceleration, but must move the pedal 12 further than if using the conventional pedal map to achieve the same change in engine output.

The process by which the modified torque request is determined is represented in Figure 5, which shows in block diagram form an internal architecture of the pedal maps module 52 in combination with the blending module 54. As shown, in this embodiment the blending module 54 receives two torque requests: the driver torque request T_driver and a cruise assist torque request T_ass.

As has already been described, the driver torque request is generated based on the conventional pedal map 56, which is shown in the upper left corner of Figure 5. The conventional map 56 is plotted as a line representing a function of pedal position, measured as a percentage of the range of travel, against torque. The torque scale starts at an Overrun’ point, which corresponds to a fuel cut condition, for example during engine braking, when no torque is requested, and continues up to a maximum torque that can be generated by the engine 14, Tmax. For a vehicle having a hybrid or electric powertrain, the Overrun’ point would correspond to a condition where the braking torque emulates engine braking in a combustion engine powered vehicle. The conventional map 56 is also calibrated for the indicated road load and vehicle speed that are received by the pedal maps module 52. Alternatively, instead of the twodimensional function shown in Figure 5 the conventional map 56 may be represented by a three-dimensional function having vehicle speed on a third axis.

As Figure 5 shows, the conventional map 56 is generally linear aside from its uppermost and lowermost regions. Therefore, for much of the range of travel of the accelerator pedal 12, any change in pedal position entails a substantially proportional increase or decrease in the resulting driver torque request.

The road load point 58, namely the torque required to match the present vehicle load, i.e. the torque required to overcome external forces on the vehicle to maintain the vehicle at its present speed, is indicated by a circle situated on the function line at a point corresponding to approximately 40% pedal travel, although in practice the road load point can be at any point on the map.

The cruise assist torque request is calculated based on a different pedal map, namely a cruise assist map 60, which is shown in the lower left corner of Figure 5. As can be seen in Figure 5, the cruise assist map 60 has a profile generally corresponding to a cubic function, with the Origin’ of the function being centred on the road load point. Accordingly, the function is flattened so that it is almost horizontal immediately to each side of the road load point. This entails that a small change in pedal position around the road load point will have little effect on the cruise assist torque request.

As already noted, the two torque requests, T_driver and T_ass, are received by the blending module 54, and blended as described above to produce the final torque request, Tfinal. Accordingly, unlike a conventional cruise control system that offers a binary choice between a driver torque request and a cruise torque request, the cruise assist function of this embodiment provides a compromise between the two. The effect of this is to provide damping of the response of the accelerator pedal 12 around the road load point, instead of eliminating the accelerator response entirely as in a conventional cruise control system.

As already noted, the extent to which the pedal map blending module 54 interpolates between the two torque requests is determined according to the blend ratio received from the blend ratio determination module 50, which in turn is determined according to the confidence level that a steady speed is desired.

For example, if the confidence level is high, the interpolation between the torque requests is weighted heavily towards the cruise assist torque request, to maximise damping of the accelerator pedal response and thereby avoid unnecessary actuation. This, in turn, minimises fuel consumption during cruising.

Conversely, if the confidence level is low, for example because the vehicle speed begins to deviate beyond threshold limits, the pedal map blending module 54 will interpolate between the torque requests in a manner that favours the driver torque request, to restore the sensitivity of the accelerator pedal 12 towards normal levels and thus enable the vehicle 10 to change speed and reach the vehicle reference speed more quickly.

In this way, the speed controller 30 offers dynamic damping of the response of the accelerator pedal 12 to help the driver to hold the vehicle 10 at a constant speed in a manner that is imperceptible to them. This avoids the driver sensing interference by the speed controller 30, which could cause them to react inappropriately, for example by releasing the accelerator pedal 12 entirely.

It will be appreciated from the above that the manner in which the pedal map blending module 54 interpolates between the driver torque request and the cruise assist torque request enables a seamless transition between normal operation and cruise assistance as the driver torque request rises or falls with respect to the road load point.

Various techniques may be employed to produce the cruise assist map. For example, a trial and error approach is likely to be effective in generating a map that provides effective assistance for each type of vehicle. Alternatively, the map may be based on computer simulations or mathematical functions.

The cruise assist map will typically be provided in the form of a calibratable lookup table. The flat spot around road load evident in Figure 5 may be less pronounced if the available road load estimators offer low accuracy. This means the affected area around road load can be widened in case the true road load point does not lie in the centre of the modified area.

The cruise assist map including a road load modified area may also be realised by a mathematical modifier that warps an existing pedal map.

The cruise assist map may be specific to the type of vehicle, to account for the varying road dynamics of different models.

However the cruise assist map is produced, it will always retain the characteristic of a flattened region around the road load point so that blending the cruise assist torque request with the driver torque request will result in damping of the accelerator pedal response.

Several variations or enhancements to the techniques outlined above are envisaged to achieve the same effect of assisting a driver with maintaining a steady cruising speed.

For example, as the skilled reader will appreciate, the speed controller 30 could use acceleration requests instead of torque requests, in which case the affected area around road load would be around the zero acceleration point instead of the road load point.

Kalman filtering and other advanced estimation techniques could be used to improve the detections and/or prediction of an attempt to hold the vehicle 10 at a desired speed, to adjust the confidence level accordingly.

It is noted that in embodiments of the invention it is possible to adjust the confidence level dynamically as the vehicle speed varies. For example, if the pedal position gradually changes relative to the position corresponding to an initial detected desired vehicle speed, the blending between the conventional map and the cruise assist map can be adjusted in a complementary manner until the driver naturally returns the accelerator pedal 12 to the road load point.

The cruise assist function may be configured to mitigate the impact on a driver of the effect of rapidly rising road load, for example on encountering a steep incline. In conventional cruise control systems, the increase in engine output to hold the vehicle speed steady against an increasing road load as road gradient increases can give the impression that the vehicle 10 is suddenly accelerating. In embodiments of the invention, blending can be weighted towards the conventional map when the road gradient alters to counteract this problem and therefore maintain the desired subtlety of the cruise assist function. Alternatively, or in addition, the problem may be addressed by reducing the extent to which steep gradients are compensated for in a road load torque calculation.

The function may also be configured to encourage a reduction in vehicle speed on approaching a brow of a hill, to take advantage of gravity in aiding descent of the vehicle 10 and thereby achieve fuel savings.

Also, the confidence level can be adjusted to account for changes in road or traffic conditions indicated by the navigational data, based on a prediction that the driver will react accordingly by controlling the vehicle 10 at a new cruising speed.

The speed controller 30 can also record driver behaviour over time to adapt the manner in which the cruise assist is implemented. For example, a particularly skilled driver may be able to control the vehicle speed to within a narrower range than would usually be expected. The speed controller 30 can monitor such behaviour and modify the thresholds that are applied for determining the confidence level accordingly.

In summary, the use of the cruise assist function as described above has the potential to provide significant reductions in fuel consumption for real-world drive cycles by minimising oscillation of vehicle speed around a desired cruising speed. This benefit can be realised in many types of vehicles, including electric vehicles and hybrid vehicles in addition to the combustion engine powered vehicle 10 referred to above. For example, in an electric vehicle, the speed controller 30 may output a speed target for an electric motor that powers the vehicle, instead of controlling the throttle 16 of an air inlet to a combustion engine.

By way of summary, Figure 6 shows an overview process 60 for providing cruise assist as described above. The process 60 begins with monitoring at step 62 signals that are indicative of the vehicle speed and the position of the accelerator pedal 12. Once sufficient data has been gathered, the confidence level that a steady speed is desired is determined at step 64. The speed controller 30 then interpolates at step 66 between the conventional map 56 and the cruise assist map 60 based on that confidence level, and finally outputs at step 68 the final torque request.

Many modifications may be made to the above examples without departing from the scope of the present invention as defined in the accompanying claims.

For example, although most vehicles use an accelerator pedal as an actuator for enabling the driver to control the vehicle speed, within the scope of the invention it is also possible to use other types of actuator for this purpose. For example, a handoperated lever, button or control pad could be used to generate a driver torque request to control the vehicle speed. For any type of actuator, the driver torque request is derived from a signal indicative of a state of the actuator.

Claims

1. A system for assisting a vehicle having an engine to travel at a steady speed, the system comprising:

means for receiving: a signal indicative of a speed of travel of the vehicle; and a signal indicative of a state of an actuator that is operable by a driver of the vehicle to control an output of an engine of the vehicle;

a means to:

determine a confidence level that a steady speed of travel of the vehicle is desired based on the signal indicative of a speed of travel of the vehicle and the signal indicative of a state of an actuator;

interpolate between a normal actuator response map and a modified actuator response map in dependence on the determined confidence level; and translate the indicated actuator state into an engine output request in dependence on said interpolation, wherein the modified actuator response map is arranged to damp a response of the actuator relative to the normal actuator response map; and means for sending the engine output request signal to control an output of the engine.

2. A system according to claim 1 wherein:

the means for receiving the signal indicative of a speed of travel of the vehicle and the signal indicative of a state of an actuator comprises one or more electronic processor having an electrical input for receiving said signals; and the means for sending the engine output request signal comprises the one or more electronic processor having an electrical output for sending said signal;

the system having an electronic memory device electronically coupled to the electronic processor and having instructions store thereon; wherein said means for determining a confidence level, interpolating between a normal actuator response map and a modified actuator response map, and translating the indicated actuator state into an engine output request comprises the one or more processor being configured to access the memory device and execute the instructions stored therein so that it is operable to determine the confidence level, interpolate between the normal actuator response map and modified actuator response map, and translate the indicated actuator state into an engine output request.

3. The system of claim 1 or claim 2, wherein the signal indicative of a speed of travel of the vehicle comprises one or more of: a measurement of vehicle speed produced by a vehicle speed sensor; a measurement obtained from an accelerometer; or a measurement obtained from a gyroscope.

4. The system of any preceding claim, wherein the signal indicative of a speed of travel of the vehicle comprises data that is indicative of a future speed of travel of the vehicle.

5. The system of claim 4, wherein the signal indicative of a speed of travel of the vehicle comprises data indicative of road conditions ahead of the vehicle, optionally one or more of the following: traffic conditions; junctions; corners; road gradient; velocity profile data; and local speed restrictions.

6. The system of any preceding claim, wherein the signal indicative of a speed of travel of the vehicle comprises data output by a navigational system.

7. The system of any preceding claim, comprising means for determining a blend ratio that is based on the confidence level, and interpolating between the normal actuator response map and the modified actuator response map in dependence on the blend ratio.

8. The system of any preceding claim, comprising means for determining the magnitude of the steady speed of the vehicle which is desired.

9. The system of claim 8, comprising means for adjusting the confidence level in accordance with the magnitude of the steady speed of the vehicle which is desired.

10. The system of any preceding claim, wherein the modified actuator response map comprises a lookup table.

11. The system of any preceding claim, comprising means for generating the modified actuator response map by warping the normal actuator response map.

12. The system of any preceding claim, wherein the modified actuator response map comprises a flattened region around a road load point.

13. The system of any preceding claim, wherein determining a confidence level that a steady speed of travel of the vehicle is desired comprises means for determining a range of deviation of the signal indicative of a speed of travel of the vehicle over a time period.

14. The system of any preceding claim, wherein determining a confidence level that a steady speed of travel of the vehicle is desired comprises determining a range of deviation of the signal indicative of a state of the actuator over a time period.

15. The system of claim 13 or claim 14, comprising means to increase the confidence level if the deviation remains within threshold limits throughout the associated time period.

16. The system of any of claims 13 to 15, wherein the magnitude of the confidence level is dependent upon the duration of the time period.

17. The system of any of claims 13 to 16, wherein the magnitude of the confidence level is dependent upon to the magnitude of the range of deviation.

18. The system of any preceding claim, wherein the signal indicative of a state of the actuator represents a torque request.

19. The system of any preceding claim, wherein the actuator comprises an accelerator pedal, and wherein the signal indicative of a state of the actuator is indicative of a position of the accelerator pedal.

20. The system of any preceding claim, wherein the engine output request comprises one of a torque demand and a power demand.

21. The system of any preceding claim, comprising setting the confidence level to zero if a deactivation condition is satisfied.

22. A method of assisting a vehicle to travel at a steady speed, the method comprising:

monitoring a signal indicative of a speed of travel of the vehicle;

monitoring a signal indicative of a state of an actuator that is operable by a driver of the vehicle to control an output of an engine of the vehicle;

determining a confidence level that a steady speed of travel of the vehicle is desired based on the signal indicative of a speed of travel of the vehicle and the signal indicative of a state of the actuator;

interpolating between a normal actuator response map and a modified actuator response map in accordance with the confidence level that a steady speed is desired, to translate the indicated actuator state into an engine output request, wherein the modified actuator response map is arranged to damp a response of the actuator relative to the normal actuator response map; and issuing the engine output request to control an output of the engine.

23. A vehicle comprising the control system of any one of claim 1 to claim 21.

24. A computer program product comprising computer readable code for controlling a computing device to perform a method of claim 22.

25. A non-transitory computer readable medium comprising the computer program product of claim 24.

Intellectual Property Office