WO2009106852A1

WO2009106852A1 - A method of controlling vehicle speed change

Info

Publication number: WO2009106852A1
Application number: PCT/GB2009/000566
Authority: WO
Inventors: Peter Miller; Tom Robinson; Andrew Preece
Original assignee: Ricardo Uk Limited
Priority date: 2008-02-29
Filing date: 2009-02-27
Publication date: 2009-09-03
Also published as: GB0803862D0

Abstract

A method of controlling vehicles speed change comprises obtaining information about drive conditions for an impending drive period, processing said information to obtain a speed change profile according to optimisation criteria for said impending period, and controlling vehicle speed change according to said profile.

Description

A method of controlling vehicle speed change

The invention relates to a method of controlling vehicle speed change and a vehicle including a control system for controlling speed change. hi vehicles typically, for changing vehicle speed the brake or accelerator are used as appropriate. In an hybrid vehicle including both an internal combustion engine and an electric motor, energy can be recovered to slow the vehicle down by coupling the vehicle wheels to a generator for the electric motor (called regenerative braking) and the electric motor can be used to provide all or part of the acceleration.

In vehicles including active cruise control systems, where the vehicle's speed is changed automatically rather than by a driver, the rate of acceleration and/or deceleration is normally set relatively fast.

The invention is set out in the claims. By obtaining information about drive conditions for an impending period the vehicle can be accelerated or decelerated in a manner to minimise fuel consumption and/or undesirable emissions such as CO₂. This can be achieved automatically for example by changing the vehicle's speed using an active cruise control system.

Embodiments of the invention will now be described by way of example, with reference to the drawings of which:

Fig 1 shows, in overview, drive conditions for an impending drive period for a vehicle;

Fig 2 is a block diagram showing components of a vehicle including a control system as described herein; Fig 3 shows the steps involved in implementing the method described herein;

Fig. 4 is a graph showing a performance optimisation map for engine speed and torque; and

Fig. 5a, b and c show an example drive profile In overview the approach described herein recognises that by obtaining information about drive conditions for an impending drive period, vehicle speed change can be controlled according to an optimised speed change profile which can be generated based on the driving conditions which will be encountered during that period allowing control of the vehicle speed in such a manner as to optimise fuel consumption and/or minimise emissions.

As can be seen from the schematic diagram shown in Fig 1 illustrating a potential set of drive conditions for an impending period, in an extremely simplified form, a vehicle may detect heavy traffic in the road ahead (region A) followed by a clear space (region B) and then an uphill stretch (region C) all in a constant speed limit area (it will be appreciated, of course, that this information can be obtained and stored in any appropriate form). Armed with this information a processor within a vehicle can process the information to obtain an optimised speed change profile optimising engine efficiency or emissions such as Nox, Hc, Co2 to control the vehicle speed, for example through an automatic cruise control system, according to the profile derived, as discussed in more detail below.

Turning to Fig 2, a system for implementing the method can be further understood. The system includes one or more sensors, receivers or other information gathering devices 200 which obtain information concerning impending drive conditions and feed them to a processor 202. The processor 202 processes the information to obtain an optimised speed change profile for the corresponding impending period and feeds this to an active cruise control system 204. The active cruise control system can be of a known type that automatically varies the vehicle speed as required, and controls the engine or actuators 206 as appropriate to then attain the desired vehicle speed change profile.

Turning to Fig 3, the steps involved can be understood in more detail. At step 300 the system obtains future information, for example impending drive conditions, such that route and road conditions ahead are fully and accurately known. This knowledge can be obtained by using historical data from a navigation system or map which can include historical information on average speeds for time of day or week and so forth or real-time data by a telematic capability. This real-time data may include information on traffic ahead (including accidents, measured average speed), the car ahead (using vehicle to vehicle communication) or the road infrastructure (for example, a traffic light may use a short range communications link to indicate that it is soon to change). Indeed any appropriate information can be obtained including the actual speed limit such as speed set points that are legislatively imposed either temporarily or permanently. Another factor is static virtual speed limits such as alterations to the actual speed limit based on temporary but static local considerations such as sharp bends or inclines - indeed these may change over time; for example wet or icy road conditions may require a lower speed limit. Another factor is dynamic virtual speed limits comprising dynamic triggers for virtual speed limits such as heavy traffic which can be detected in real time or derived from historic congestion information. Of course, any appropriate road conditions can be included such as junctions, slippery or flooded roads and so forth. The information thus obtained is provided to a processor 302 which can process information in any appropriate manner to obtain an optimised speed change profile. For example, according to one approach at 304 dynamic programming is applied according to which a predetermined algorithm is applied to the obtained data to provide the theoretically optimal approach. According to a complementary or alternative approach at step 306 optimal speed changes can be precalculated for various conditions and fixed pre-set rates can be used. For example, a multidimensional look-up table may be provided combining both road conditions, relevant time periods and distances to allow fixed rates of change to be applied. At step 308 the drive profile is fed to the active cruise control system which controls the vehicle engine and other relevant actuators at step 310 to apply the optimised drive profile.

In order to optimise efficiency during speeding up or slowing down, inherent characteristics of the engine or vehicle can be used. For example, with a non-hybrid vehicle the engine's efficiency depends upon the load on it (Fig 4).

As can be seen in the plot of Fig. 4 which shows, on the X axis, engine speed in rpm and on the Y axis torque in Nm, within the confines a limiting torque curve 400 and plotting along lines of constant power for 402, various optimum mappings are available to minimise NOx, 404, hydrocarbons HC, 406, and fuel economy (which above approximately 2000 rpm is limited by the maximum torque 400), 408. From this it will be seen that for, say, a given value of torque there is an optimum engine speed (the relation between the two being determined, for example, by the gear ratio) for each of the different purposes. Looking, for example, at the ideal line for NOx 404, it will be seen that if a torque of 60Nm is required then an engine speed of approximately 2500 rpm is required. It will be noted that a different optimal rpm value is required for ideal HC and thus, according to one approach, the optimum ratio for obtaining the desired rpm can be obtained by weighting the importance of different optimisation values according to some weighting algorithm, deriving the optimal rpm value and corresponding gear ratio from the torque accordingly. Indeed this weighting algorithm may vary depended on the specific environment - for example on open roads fuel efficiency may be the most important factor whilst in urban environments minimised NOx may be the most important. It will further be seen that, given information concerning future road conditions a required torque profile can be developed for the corresponding time period and the required rpm and gear ratio values then extrapolated according to the optimisation algorithm. The engine will also have a fuel cut-off so that it draws no fuel when at "zero load" for example slowing down while still in gear. There is thus an optimum rate of acceleration (where "optimum" is defined as some function of factors including fuel used, CO2 generated, NOx generated, HC generated, time to travel a given distance) and an optimum rate of deceleration (based on making best use of the fuel cut-off). For example, this can involve changing gear as appropriate as well as control of the vehicle's throttle, brake, etc

Hence, because the vehicle has information about impending drive conditions and improving requirements to accelerate or decelerate, the optimal timing, manner or rate of acceleration or deceleration can be determined as appropriate. This can provide an improvement on, for example, known active cruise control systems which will simply accelerate or decelerate relatively quickly when the requirement is identified without consideration of the impact on fuel economy or emission. Instead, recognising the need to change the speed from a first speed to a second speed in view of a future hazard or circumstance, the vehicle could be accelerated at a lower rate over a longer period of time, for example, or decelerated earlier using the engine to slow the vehicle. Alternatively, acceleration or deceleration steps may be shortened or delayed. For example, where the vehicle identifies a need to accelerate but also identifies that it is about to descend a hill, it can rely on natural or inherent acceleration instead of requiring engine actuation.

In a similar manner, a hybrid vehicle can be controlled to optimise efficiency. Indeed, for a hybrid vehicle yet further flexibility is available as an electrical machine is present which can allow regenerative braking and electrical boost. Yet further an ECVT (electronic continuously variable transmission) gearbox again allows further parameters for efficient speed change in the vehicle. Here therefore the optimum rate of braking will normally be when the amount of regeneration power is maximised and with information containing impending driving conditions the timing of this can be varied appropriately. Again acceleration could be controlled in any appropriate manner as indicated above with the extra capability to use either the electric machine and/or the combustion engine to optimise the journey. It will further be seen that the entire route does not need to be known in advance. Indeed, less than 1 mile (1.6km) knowledge of the route ahead gives enough information for almost perfect optimisation control. Even shorter distances are sufficient to provide useful efficiency gains even if not fully optimised.

As a simple example of operation and referring, for example, to the drive profile shown in Figs. 5a to 5c with a plan or bird's eye view (Fig. 5a), a side elevation (Fig. 5b) and as an optimal vehicle speed profile (Fig. 5c), this shows a number of fixed speed limit changes zones A, B, C (70->30->70) and one "virtual" speed limit zone D due to a sharp bend (feature 500 max speed 50). It also shows a hill (feature 502). If we assume a hybrid vehicle with the task of minimising fuel consumption the system may calculate that the optimal approach to this section of road is as shown in the speed profile. The initial slow down could use a combination of the slope of the hill and regenerative braking to slow the vehicle from 70mph to 30mph (feature 504- this would thus use no fuel, and may collect some electrical energy that can then be used later). When the hill descent starts the speed limit is still 30mph so regenerative braking would be used to collect electrical energy (feature 502). After the speed limit changes to 70mph the downward slope will be used for acceleration, boosted as required by electrical energy (that obtained by regenerative braking feature 508). The sharp curve ahead means that the vehicle may not reach 70mph, but if it exceeds 50mph regenerative braking is again used to slow the vehicle down to a safe speed for the curve (feature 510). If the vehicle was a conventional vehicle a similar approach would be used — however regenerative braking is not available but the engine speed can be maintained in these periods so fuel is cut-off to the engine. Of course the optimal speed profile might be somewhat different due to the lack of regenerative braking and electrical boost, but the general shape would still be the same.

In terms of the various components of the system it will be appreciated that the system can be operated in any appropriate kind of vehicle whether hybrid or not and with a gasoline/petrol or diesel engine of any type, and electric motor of any appropriate type where required. Information can be obtained from historical data, from telematic systems, from sensors on the vehicle or from receivers receiving information from data sources or sensors external to the vehicle. The processor and active cruise control system can be separate or integrated and each comprises any appropriate known device such as an engine control unit. The active cruise control system can control any of the normal vehicle engine inputs including fuel, engine timing and gear change. The control algorithms can be implemented in hardware, software or firmware and in any language or other appropriate form.

As a result of the arrangement described one or several parameters eg fuel consumption and vehicle emissions can be optimised. For example, a control scheme can minimise both fuel consumption and NOx at the same time with an appropriate scheme based on known engine efficiency and emission creation information either as the parameters for dynamic programming or as precalculated and stored in a look-up table or other data storage device. As a result, the amount, rate, timing and nature of deceleration or acceleration stimuli can be appropriately determined to enhance operation of the vehicle based on knowledge of an impending period of the drive.

It will be appreciated that the information can be used in any type of drive and for any kind of vehicle and can be optimised to accommodate additional constraints to fuel efficiency/reduced emissions, such as comfort, for example, by slowing down for bends or safety (when range of visibility is reduced, or other hazards are present or potentially present) whilst maintaining fuel/emission efficiency. Hence the approach permits, say, optimising CO2 and safety while not exceeding certain limits set by comfort constraints (eg maximum acceleration/deceleration and yaw rate limits) and completing the journey within a time limit while not exceeding the legal speed limits using dynamic programming. Of course perfect optimisation may not be obtainable but improved fuel efficiency or emission reduction can be considered to be a useful and desirable optimisation.

Claims

CLAIMS:

1. A method of controlling vehicle speed change comprising obtaining information about drive conditions for an impending drive period, processing said information to obtain a speed change profile according to optimisation criteria for said impending period and controlling vehicle speed change according to said profile, in which the speed change comprises at least one of acceleration or deceleration and the speed change profile determines at least one of the rate, manner, timing or duration of vehicle speed change, and in which the speed change profile allows acceleration or deceleration by virtue of at least one of engine gear change, regenerative braking, or boost from an electrical machine.

2. A method as claimed in any preceding claim in which the speed change profile is optimised for at least one of fuel efficiency, emission reduction, driver or passenger safety, or driver or passenger comfort.

3. A method as claimed in any preceding claim in which the impending drive period information comprises at least one of an actual speed limit, a static virtual speed limit or a dynamic virtual speed limit

4. A method as claimed in any preceding claim in which the impending drive period information is obtained using one of stored historical data.

5. A method as claimed in any preceding claim in which the impending drive period is sufficiently long for maximum optimisation of the speed change profile.

6. A method as claimed in any one of claims 1 to 4, in which the impending drive period is of sufficient duration for partial optimisation of the speed change profile.

7. A method as claimed in any preceding claim in which the information is processed according to one of dynamic programming or pre-stored values.

8. A vehicle control system including a component for obtaining information concerning drive conditions for an impending period, a processor for processing said information to obtain a speed change profile according to an optimisation criterion for said impending period and a controller for controlling vehicle speed change according to said profile, in which the speed change comprises at least one of acceleration or deceleration and the speed change profile determines at least one of the rate, manner, timing or duration of vehicle speed change, and in which the speed change profile allows acceleration or deceleration by virtue of at least one of engine gear change, regenerative braking, or boost from an electrical machine.

9. A system as claimed in claim 8, in which the component for obtaining information about drive conditions comprises at least one of a data storage component and a telematics component.

10. A system as claimed in claim 8 or 9, in which the controller comprises an active cruise control system.

11. A vehicle including a vehicle control system as described in any of claims 8 to 10.

12. A vehicle as claimed in claim 11 comprising a hybrid vehicle.

13. A computer program for implementing a method as claimed in any of claims 1 to 7.

14. A computer arranged to operate under instructions of a computer program as claimed in claim 13.

15. A computer as claimed in claim 14 comprising an engine control unit for an active cruise control system.

16. An apparatus or method substantially as described herein.