Patent Application
20120083985
The present invention relates to a method and a module for regulating a vehicle's speed according to the introduction to the independent claims.
Many vehicles today are equipped with a cruise control to make it easier for the driver to drive the vehicle. The desired speed can then be set by the driver, e.g. via a control device in the steering wheel console, and a cruise control system in the vehicle acts thereafter upon a control system so that it accelerates and brakes the vehicle in order to maintain a desired speed. If the vehicle is equipped with an automatic gearchange system, the vehicle's gears are changed so that the vehicle can maintain the desired speed.
When a cruise control is used in hilly terrain, the cruise control system will try to maintain a set speed on upgrades. This results inter alia in the vehicle accelerating over the crest of a hill and possibly into a subsequent downgrade, making it necessary to brake to avoid exceeding the set speed, which is a fuel-expensive way of running the vehicle.
By varying the vehicle's speed in hilly terrain it is possible to save fuel as compared with a conventional cruise control. This may be done in various ways, e.g. by calculations of the vehicle's current state (as with Scania Ecocruise®). If an upgrade is calculated, the system then accelerates the vehicle uphill. Towards the end of the climb, the system is programmed to avoid acceleration until the gradient has levelled out at the top, provided that the vehicle's speed does not drop below a certain level. Lowering the speed at the end of an upgrade makes it possible to regain speed on a subsequent downgrade without using the engine to accelerate. When the vehicle approaches the bottom of a dip, the system endeavours to use kinetic energy to embark on the next upgrade at a higher speed than an ordinary cruise control. The system will easily provide acceleration at the end of the downgrade in order to maintain the vehicle's momentum. In undulating terrain, this means that the vehicle starts the next climb at a higher speed than normal. Avoiding unnecessary acceleration and using the vehicle's kinetic energy makes it possible to save fuel.
If the topology ahead is made known by the vehicle having map data and GPS, such a system can be made more robust and can also change the vehicle's speed in anticipation.
Published patent application WO 2006/107267 A1 describes a method and a system for controlling the operation of a vehicle with an anticipatory cruise control function. Before the vehicle sets off, steep rises and falls along the itinerary are identified by points. The locations of the points are calculated on the basis of a number of parameters and are stored together with the itinerary before the vehicle sets off.
The object of the present invention is to control the vehicle's speed in a fuel economising way in hilly terrain.
The object described above is achieved according to a first aspect by a method for regulating a vehicle's speed which comprises the steps of:
The invention comprises also according to a second aspect a module for regulating a vehicle's speed, which module comprises:
The method described above achieves a robust and computationally effective algorithm which quickly and reliably generates speed set-point values by which the control system can control the vehicle.
When there is within the horizon an imminent steep upgrade, how much speed the vehicle is expected to lose during the climb is therefore calculated. If the result is below a minimum speed vmin predefined by, for example, the driver or the module, the speed set-point values vref are corrected upwards before the upgrade, but at most up to vmax. Raising the speed before the climb results in a time saving in that the speed will not decrease as much as when using a traditional cruise control which only sets the vehicle's speed according to a reference speed vset. Raising the vehicle's speed before the upgrade therefore only takes place when it is calculated that the vehicle's speed will drop to below a preset minimum speed vmin.
When there is within the horizon an imminent steep downgrade, the system calculates the speed to which the vehicle's speed is expected to increase during the downhill run. If the result exceeds a maximum speed vmax predefined by, for example, the driver or the system, the speed set-point values vref are corrected downwards before the downgrade, but at most down to vmin. Utilising the potential energy on the downhill run by maintaining the raised speed results in a time saving as compared with a traditional cruise control which is not allowed to vary from its reference value vset. Adjustment of the predicted speed during the downhill run therefore only takes place when the vehicle is expected to reach a speed which exceeds a maximum speed vmax.
As the vehicle's speed according to the method is allowed by the module to decrease to vmin on an upgrade, with consequent expectation of accelerating to regain lost speed until after the crest of the hill, i.e. on level road, the result is a time saving as compared with the vehicle having to maintain the reference speed vset during the climb, since it takes more fuel to maintain speed uphill than to regain speed after the climb. If the upgrade is followed by a downgrade, the speed can be kept at a lower level uphill to avoid braking on the downhill run because of the vehicle's speed becoming too high, and the vehicle uses instead the potential energy due to its own weight downhill. If the predicted speed downhill is greater than the reference speed vset adopted by the driver, the predicted speed can be maintained, enabling the vehicle to “swing” into an imminent upgrade.
Preferred embodiments are described in the dependent claims and the detailed description.
The invention is described below with reference to the attached drawings, in which:
Information about a vehicle's itinerary can be used to regulate its speed in anticipation in order to save fuel, increase safety and enhance comfort. Topography greatly affects the control of, in particular, the driveline of heavy vehicles, since much more torque is required uphill than downhill and to make it possible to climb some hills without changing gear.
The vehicle is provided with a positioning system and map information, and position data from the positioning system and topology data from the map information are used to construct a horizon which illustrates the nature of the itinerary. In the description of the present invention, GPS (Global Positioning System) is indicated for determining position data for the vehicle, but it should be appreciated that other kinds of global or regional positioning systems are also conceivable to provide the vehicle with position data, e.g. systems which use a radio receiver to determine the vehicle's position. The vehicle may also use sensors to scan the surroundings and thereby determine its position.
CAN (Controller Area Network) is a serial bus system specially developed for use in vehicles. The CAN databus makes digital data exchange possible between sensors, regulating components, actuators, control devices, etc. and ensures that two or more control devices can have access to the signals from a given sensor in order to use them to control components connected to them.
The horizon is made up of route segments which have characteristics in the form of their length and gradient associated with them. The horizon is here exemplified in matrix form in which each column contains a characteristic for a segment. A matrix covering 80 m forwards of an itinerary may take the following form:
where the first column is the length of each segment in metres (dx) and the second column the gradient in % of each segment. The matrix is to be taken to mean that for 20 metres forwards from the vehicle's current position the gradient is 0.2%, followed by 20 metres with a gradient of 0.1%, and so on. The values for segments and gradients need not be expressed in relative values but may instead be expressed in absolute values. The matrix is with advantage vector-formed but may instead be of pointer structure, in the form of data packages or the like. There are also various other conceivable characteristics for segments, e.g. radius of curvature, traffic signs, various hindrances etc.
Thereafter, the segments within the horizon are placed in various categories in a step B) in which threshold values are calculated for the gradient of segments according to one or more vehicle-specific values, which threshold values serve as boundaries for assigning segments to different categories. The threshold values for the gradient are calculated, according to an embodiment of the invention, by one or more vehicle-specific values, e.g. current transmission ratio, current vehicle weight, the engine's maximum torque curve, mechanical friction and/or the vehicle's running resistance at current speed. A vehicle model internal to the control system is used to estimate running resistance at current speed. Transmission ratio and maximum torque are known magnitudes in the vehicle's control system, and vehicle weight is estimated on-line.
The following are examples of five different categories in which segments may be placed:
To place segments in the categories described above, threshold values are therefore calculated in the form of two gradient threshold values lmin and lmax, where lmin is the minimum gradient for the vehicle to be accelerated by the gradient downhill, and lmax is the maximum gradient at which the vehicle can maintain speed without changing gear uphill. Thus the vehicle's speed can be regulated according to the gradient and length of the road ahead so that the vehicle can be driven in a fuel economising way by means of cruise control in undulating terrain. For example, the tolerance for the “level road” category is preferably between 0.05% and −0.05% when the vehicle travels at 80 km/h. On the basis of the same speed (80 km/h), lmin is usually calculated to be of the order of −2 to −7%, and lmax usually 1 to 6%. However, these values depend greatly on current transmission ratio (gear+fixed rear axle ratio), engine performance and total weight.
In a next step C) the method compares the gradient of each segment with the threshold values, and each segment within the horizon is placed in a category according to the results of the comparisons.
After each segment within the horizon has been placed in a category, an internal horizon for the control system can be constructed on the basis of the classification of segments and the horizon. The internal horizon comprises entry speeds vi to each segment, which are speeds which the control system has to abide by. Each segment also has a final speed vend which is equal to the entry speed vi to the next segment.
For each segment within the horizon which is in a category indicating a steep upgrade or a steep downgrade, the method comprises a step D) for calculating the vehicle's final speed vend after the end of the segment, based inter alia on the entry speed vi to that segment; and if the calculated final speed Vend is outside the range for the vehicle's current reference speed vset which is defined by vmax and vmin, the method performs a step E) to correct the entry speed vi for that segment on the basis of the calculated final speed vend for the segment, which correction is defined by rules for said segment's category so that vmin≦Vend≦vmax, on the supposition that vi is corrected within the same range. vend is therefore corrected to be within the range for vset. If the calculated final speed vend is within the range for vset, the method goes on to the next segment within the horizon instead of correcting the entry speed vi and the final speed vend according to step E). vset is the reference speed set by the driver and desired to be kept by the vehicle's control systems within a range when the vehicle is in motion.
The range is bounded by two speeds vmin and vmax which may be set manually by the driver or be set automatically by calculations of a suitable range is preferably calculated in the regulating module. The vehicle's speed is thereafter regulated in a step F) according to speed set-point values vref based on the entry speeds vi to each segment. Set-point values vref for the control system in the vehicle may therefore be allowed to vary between the two abovementioned speeds vmin and vmax, and when the method predicts an internal horizon for the vehicle's speed, the vehicle's speed may then vary within this range.
According to an embodiment, a speed change requested is ramped between two entry speeds vi to provide the control system with set-point values vref which bring about a gradual increase or decrease in the vehicle's speed. Ramping a speed change results in calculation of gradual speed changes which need to be made to achieve the speed change.
In other words, a linear speed increase is achieved by ramping. All the segments within the horizon are stepped through continuously, and as new segments are added to the horizon the entry speeds vi are adjusted as necessary in segments, within the range of the vehicle's reference speed vset.
The various rules for the segment categories therefore regulate how the entry speed vi for each segment is to be adjusted. If a segment is placed in the “level road” category, no change will take place in the entry speed vi to the segment. Driving the vehicle such that comfort requirements are met involves using Torricelli's equation as below to calculate the constant acceleration or retardation which needs to be applied to the vehicle:
v
end
2
=v
i
2+2·a·s (1)
where vi is the entry speed to the segment, vend the vehicle's speed at the end of the segment, a the constant acceleration/retardation and s the length of the segment.
If a segment is in the “steep upgrade” or “steep downgrade” category, the final speed vend for the segment is predicted by solving equation (2) below:
end
2=(a·vi2+b)·(e(2·a·s/M)−b)/a (2)
where
a=−C
d
·ρ·A/2 (3)
b=F
track
−F
roll
−F
a (4)
F
track=(Teng·ifinal·igear·μgear)/rwheel (5)
F
roll=flatCorr·M·g/1000·(CrrisoF+Cb·(vi−viso)+CaF·(vi2−viso2)) (6)
F
α
=M·g·sin (arctan(α)) (7)
flatCorr=1/√{square root over ((1+rwheel/2.70))} (8)
The vehicle's final speed vend after the end of the segment is thus calculated according to this embodiment on the basis of the entry speed vi to the segment, the force Ftrack acting from the engine torque in the vehicle's direction of movement, the force Froll from the rolling resistance acting upon the vehicle's wheels, and the force Fα acting upon the vehicle because of the gradient α of the segment. In addition, Cd is the air resistance coefficient, ρ the density of the air, A the largest cross-sectional area of the vehicle, Teng the engine torque, ifinal the vehicle's final gear, igear the current transmission ratio in the gearbox, μgear the efficiency of the gear system, rwheel the vehicle's wheel radius, M the vehicle's weight, CaF and Cb speed-dependent coefficients related to the rolling resistance of the wheels, CrrisoF a constant term related to the rolling resistance of the wheels and viso an ISO speed, e.g. 80 km/h.
On segments in the “steep upgrade” category, the final speed vend is thereafter compared with vmin, and if vend<vmin, then vi has to be increased so that
v
i=min(vmax,vi+(vmin−vslut) (9)
otherwise no change in vi takes place, since vend meets the requirement of being within the range for the reference speed.
On segments in the “steep downgrade” category, the final speed vend is compared with vmax, and if vend>vmax, then vi has to be decreased so that
v
i=max(vmin,vi−(vslut−vmax)) (10)
otherwise no change in v1 takes place, since vend meets the requirement of being within the range for the reference speed.
According to an embodiment of the invention, step E) also comprises determining the entry speed vi to the segment according to the length of the segment, and the maximum correction of the entry speed vi is determined by a calculated maximum acceleration or retardation according to rules for the segment categories. Torricelli's equation (1) is preferably used to calculate whether it is possible to achieve vend with the entry speed vi with comfort requirement, i.e. with a maximum constant acceleration/retardation. If this is not possible because of the length of the segment, vi is decreased or increased so that the comfort requirement, i.e. not too much acceleration/retardation, can be maintained. The result is assurance that the vehicle will travel comfortably as regards acceleration and retardation.
On segments in the “gentle upgrade” category, the set-point value vref is allowed to vary between vmin and vset when a new segment is incorporated, i.e. vmin≦vref≦vset. If vref≧vmin, no acceleration of the vehicle is effected. If however vref<vmin, then vref is applied to vmin during the segment, or if vref>vset, then vref is ramped towards vset by means of equation (1). On segments in the “gentle downgrade” category, vref is allowed to vary between vset and vmax when a new segment is incorporated, i.e. vset≦vref≦vmax, and if vref≦vmax no retardation of the vehicle is effected. If however vref>vmax, then vref is applied to vmax during the segment, or if vref<vset, then vref is ramped towards vset by means of equation (1). The five segment categories above may be simplified to three by deleting “gentle upgrade” and “gentle downgrade”. The “level road” category will then cover a larger range bounded by the calculated threshold values lmin and lmax, so the gradient on the segment has to be smaller than imin if the gradient is negative or greater than lmax if the gradient is positive.
When a segment which comes after a segment within the horizon which is in the “gentle upgrade” or “gentle downgrade” category causes a change in the entry speeds to segments in those categories, it may mean that entry speeds and hence the set-point speeds for the control system are corrected and become higher or lower than as indicated by the above rules for the “gentle upgrade or “gentle downgrade” categories. This therefore applies when the entry speeds to segments are corrected according to subsequent segments.
All speed changes requested are therefore preferably ramped by means of Torricelli's equation (1) so that they take place with comfort requirement. Thus it is a general rule not to raise the set-point speed vref on an upgrade, since any possible speed increase of vref has to take place before the climb begins if the vehicle is to be driven in a cost-effective way. For the same reason, the set-point speed vref should not be lowered on a downgrade, since any possible speed decrease of vref has to take place before the downhill run.
Continuous stepping through all the segments within the horizon makes it possible to determine an internal horizon which presents predicted entry speed values vi to each segment. The horizon is preferably updated piecemeal in order to have a constant length, and the internal horizon is updated continually as new segments are added to the horizon, e.g. two to three times per second. According to an embodiment of the invention, determining an entry speed vi involves entry speeds which occur in previous segments being determined by the rules for the segment categories so that said entry speed vi can be fulfilled. Continuous stepping through segments within the horizon involves continuously calculating the entry values vi to each segment, so calculating an entry value vi may entail having to change entry values both forwards and backwards in the internal horizon. Where for example a predicted speed in a segment is outside a set range, it is desirable to correct the speed in preceding segments.
This makes it possible to achieve a desired speed within the speed range and at the same time to drive in a fuel economising way.
In
Segment “A” in
Segment “B” in
below 75 km/h, v3 has to be adjusted upwards by v3−vmin, but at most by vmax−v2, see formula (9).
To exemplify this, three different calculated final speeds v3 are given for the vehicle after segment “B”:
The speed increase to v2 depends also on the length of segment “A”. By using a calculated acceleration or retardation which results in comfort acceptance, i.e. acceleration or retardation which is not uncomfortable for the driver, and by calculating on this supposition the highest entry speed v2 which is possible, e.g. by using Torricelli's equation (1), we can also correct v2 so that the comfort requirement can be maintained during segment “A”.
After an upgrade, the vehicle may be at a lower speed than the reference speed vset adopted by the driver. This deficit may for example be made up by the system on an imminent downgrade (after segment “C” in
Segment “D” in
Segment “E” in
To exemplify this, three different calculated final speeds v7 are given for the vehicle after segment “E”:
The speed increase to v6 depends also on the length of segment “D”, see
After a downgrade, the vehicle may be at a higher speed than the reference speed vset adopted by the driver. This surplus may for example be utilised by the vehicle on an imminent upgrade (after segment F in
The variable set-point speed vref therefore depends on whether the vehicle is heading for a substantial:
The fact that the method identifies the next segment category (“steep upgrade”, “gentle upgrade”, “level road”, “gentle downgrade”or “steep downgrade”) will therefore affect the way method varies the set-point speed.
To avoid consuming unnecessarily large amounts of fuel when a first steep upgrade or a first steep downgrade is followed by a steep upgrade or a steep downgrade within a certain distance L, an embodiment does not allow both acceleration and retardation of the vehicle within the section L. Only acceleration or retardation to a desired speed vref is effected before the next hill. This embodiment is illustrated in
The present invention relates also to a module for regulating a vehicle's speed, as depicted in
The module further comprises a processor unit adapted to performing steps B) to E) as described above. A control system in the vehicle is further adapted to regulating the vehicle's speed according to speed set-point values vref based on the entry speeds vi to each segment. The result is a module which can be used in a vehicle to determine the set-point speed for a control system when there are steep upgrades and downgrades on the itinerary. The module may be part of a control system for which it is intended to determine set-point values or it may be a freestanding module separate from the control system.
The vehicle-specific values of current transmission ratio, current vehicle weight, engine maximum torque, mechanical friction and/the vehicle's running resistance at current speed are preferably determined in the processor unit. The threshold values can therefore be determined on the basis of the vehicle's state at the time. Signals needed for determining these values may be taken from CAN or be detected by suitable sensors.
According to an embodiment, the processor unit is also adapted to calculating the vehicle's final speed vend after the end of the segment on the basis of the force Ftrack acting from the engine torque in the vehicle's direction of movement, the force Froll which is the rolling resistance acting upon the vehicle's wheels, the force Fα acting upon the vehicle because of the gradient α of the segment, and the running resistance. Formula (2) as above is preferably used and it is then possible to predict the final speed vend, thereby providing a reference for being able to change the entry speed vi to the segment. Thus the vehicle's speed can be regulated according to the undulation of the itinerary, in order to drive in a fuel economising way.
According to another embodiment, the processor unit is adapted to determining the entry speed vi to the segment according to the length of the segment, whereby the maximum correction of the entry speed vi is determined by a calculated maximum acceleration or retardation according to rules for the segment categories. Torricelli's equation (1) is preferably used to calculate whether it is possible to achieve vend with the entry speed vi with comfort requirement, and if this is not possible because of the length of the segment, vi is decreased or increased to maintain the comfort requirement, i.e. maintaining not too much acceleration/retardation. Assurance is thus afforded that the vehicle will be driven in a comfortable way as regards acceleration and retardation.
The processor unit is preferably adapted to ramping a requested speed change between two consecutive entry speeds vi in order to provide the control system with gradually increasing or decreasing speed set-point values vref. The result is a gradual increase in speed so that the vehicle is driven without too much acceleration or retardation.
The horizon unit is preferably adapted to determining the horizon continuously so long as the horizon does not exceed a planned itinerary for the vehicle, and the processor unit is preferably adapted to continuously performing the steps for calculating and updating the set-point values for the control system for the whole length of the internal horizon. In an embodiment, the horizon is therefore constructed piecemeal as the vehicle travels along the itinerary. The set-point values vref are calculated and updated continuously irrespective of whether new segments are added or not, since the set-point values to be calculated depend also on how the vehicle-specific values of the vehicle change along the itinerary. According to an embodiment, the processor unit is adapted, when determining an entry speed to determining also entry speeds which occur in earlier segments within the rules for their categories, so that said entry speed vi can be fulfilled. A calculation of an entry value vi may also entail changes to entry values both forwards and backwards in the internal horizon. It is thus possible to achieve desired speeds within the speed range and at the same time drive in a fuel economising way.
According to an embodiment illustrated in
The present invention comprises also a computer programme product comprising computer programme instructions for enabling a computer system in a vehicle to perform the steps according to the method when the computer programme instructions are run on said computer system. The computer programme instructions are preferably stored on a medium which is readable by a computer system, e.g. a CD ROM, USB memory, or they may be transmitted wirelessly or by line to the computer system.
The present invention is not limited to the embodiments described above. Various alternatives, modifications and equivalents may be used. The aforesaid embodiments therefore do not limit the scope of the invention which is defined by the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0950442-4 | Jun 2009 | SE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/SE2010/050591 | 5/31/2010 | WO | 00 | 12/9/2011 |
