Patent Application
20060161330
The present application is claiming priority of Italian Patent Application No. B02005A 000025, filed on Jan. 19, 2005 the content of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a cruise management method and device for a road vehicle.
2. Description of Related Art
The accelerator is conventionally directly mechanically connected to the carburettor or the injection control system by a cable; in this case, the driver has full control over the drive torque generated by the engine and therefore over the speed of the vehicle.
The system known as “drive by wire” has recently been proposed, in which the accelerator is connected to a position sensor which reads the position of the accelerator pedal and transmits it to a control unit which manages the drive torque generated by the engine and therefore the speed of the vehicle both as a function of the wishes that the driver expresses by acting on the accelerator pedal, and as a function of parameters depending essentially on the safety of the vehicle (for instance anti-skid and stability control). In other words, when the “drive by wire” system is used, the driver no longer has full control over the drive torque generated by the engine and therefore over the vehicle speed, but the wishes that the driver expresses by acting on the accelerator pedal are always filtered by a control unit as a function of the safety of the vehicle.
Following the introduction of “drive by wire” systems, various control methods have been proposed with a view to optimising the management of the drive torque generated by the engine and therefore of the vehicle speed; moreover, when there is an automatic gear change or a servo-assisted gear change, these control methods have to integrate the management of the drive torque generated by the engine with the choice of the optimum transmission ratio.
An example is disclosed in U.S. Pat. No. 6,819,996 B2 which discloses a control method for a road vehicle, in which the best combination of the speed of rotation of the engine and the transmission ratio of the gear change is calculated as a function of the current speed of the vehicle in order to minimise fuel consumption. A further example is disclosed in German Patent Application DE 1 025 1653 A which discloses a control method for a road vehicle in which the speed of the vehicle is reduced by shifting down the gears rather than by actuating the brakes.
However, the control methods currently available have some drawbacks as the wishes that the driver expresses by acting on the accelerator pedal are not always interpreted correctly; moreover, adequate account is not always taken of the dynamic effect due to the road load (due, for instance, to the positive or negative gradient of the road or the presence of wind) with the result that an inappropriate transmission ratio may be selected.
DE4425957A1 discloses a motor vehicle cruise control device, in which data is fed to the input side of an artificial neuronal network contained in a speed-regulator covering the momentary discrepancy between the desired and actual speeds, and also on the travel state.
DE4301292A1 disclose a fully hand-operated automatic car, in which the operation of the automatic car uses an EM actuator for the throttle valve of the engine; a microprocessor stores a speed set point for comparison with actual speed and a three-digit display shows the speed. A sensor measures the actual speed. And pressure pads in the steering wheel increment the set point, the new value also being shown on the display.
DE10157255A1 discloses a method for improved interaction between driver demand, cruise control system and traction control system in an internal combustion vehicle; the desired engine output torque is adjusted based on the above inputs and vehicle operating conditions.
EP0983894A1 discloses a vehicle speed control system activated so as to control the vehicle speed in a modified way in response to the driver's inputs. When activated, the accelerator position defines a target speed so as to control the vehicle speed to the target speed.
U.S. Pat. No. 6,104,976A1 discloses a vehicle speed control system comprising a section for calculating a command driving force-required to make a sensed vehicle speed equal to a preset command vehicle speed, a section for calculating a command engine output in accordance with the command driving force and the command vehicle speed, a section for calculating a command engine speed corresponding to the command engine output from a predetermined engine torque-versus-speed characteristic relationship in an engine constraint state of minimum throttle setting and fuel cutoff inhibition when the command driving force is negative, and a section for calculating a command transmission ratio in accordance with the command engine speed.
U.S. Pat. No. 6,178,371A1 discloses a speed control method for vehicles having an internal combustion engine and which smoothly controls engine torque to control vehicle speed.
US2003176256A1 discloses a power output apparatus and movable body with power output apparatus mounted thereon; the technique of the invention sets a relationship between the throttle opening (corresponding to the accelerator opening), the vehicle speed, and the target torque of a drive shaft, so as to enable a greater braking torque to be output in a working status of a cruise control system than a braking torque, which is output to the drive shaft in a full closed position of the accelerator opening in a non-working status of the cruise control system.
The object of the present invention is to provide a cruise management method and device for a road vehicle which are free from the drawbacks described above and which are also easy and economic to implement.
The present invention relates to a cruise management method and device for a road vehicle as recited in the attached claims.
The present invention will now be described with reference to the accompanying drawings, which show a non-limiting embodiment thereof, and in which:
In
The automobile vehicle 1 further comprises a passenger space 9 provided with a front seat for the driver and a steering wheel 10, an accelerator control 11 (in particular an accelerator pedal 11), a brake control 12 (in particular a brake pedal 12) and a dashboard 13 comprising a plurality of instruments and push button/switch controls (not shown in detail).
According to a preferred embodiment, the servo-assisted gear change 8 may operate either in a fully automatic way, in which the gears are automatically selected with no intervention by the driver, except for selection of the reverse gear, or in a manual way in which the driver requests a gear change by means of a pair of levers (not shown in detail) disposed at the location of the steering wheel 10.
The accelerator pedal 11 is provided with a position sensor (not shown) which is adapted to calculate, in real time, the position of the accelerator pedal 11 and to translate this position into an electric signal of analogue or digital type. The brake pedal 12 is also provided with a position sensor (not shown) which is adapted to calculate, in real time, the position of the brake pedal 12 and to translate this position into an electrical signal of analogue or digital type.
A control unit 14 is installed on board the automobile vehicle 1 and is adapted to receive as input the electrical signals indicating the position of the accelerator pedal 11 and the brake pedal 12 in order to manage both the internal combustion engine 3 and the servo-assisted clutch 7 and gear change 8. As a function of the position of the accelerator pedal 11 and the brake pedal 12, the control unit 14 in particular tries to interpret the speed wishes of the driver, i.e. it tries to interpret what speed of forward movement of the automobile vehicle 1 the driver is trying to achieve or desired speed DS, and then tries to apply this desired speed, i.e. it tries to manage the internal combustion engine 3 and the servo-assisted gear change 8 to bring the automobile vehicle 1 to the desired speed DS in the smallest possible time compatible with safety requirements, comfort and energy saving.
According to a preferred embodiment, the dashboard 13 is also provided with a cruise control device 15 which may be used by the driver as an alternative to the accelerator pedal 11 and enables the driver to input a desired speed DS which is maintained without any action on the accelerator pedal 11.
The dashboard 13 further comprises a screen 16 which is piloted by the control unit 14 in order to display, in real time, the desired speed DS interpreted by the control unit 14. In other words, as a function of the position of the accelerator pedal 11 and the brake pedal 12, the control unit 14 tries to interpret the speed desired by the driver by calculating a desired speed DS which is used to control the drive torque generated by the internal combustion engine 3; this desired speed DS is also displayed on the screen 16 so that the driver is aware of the final effect of the commands that he has imparted to the accelerator pedal 11 and the brake pedal 12.
According to a further embodiment (not shown), the control unit 14 merely interprets the speed desired by the driver by calculating the desired speed DS and displays this desired speed DS on the screen 16; however, this desired speed DS is not used in any way by the control unit 14 to manage the internal combustion engine 3 and the servo-assisted gear change 8 and is merely a forecast of the final effect of the commands imparted by the driver.
As shown in
According to a preferred embodiment, the desired speed DS is calculated by algebraically combining (in particular adding) the current speed CS with a correction factor determined as a function of the position of the accelerator pedal 11, the position of the brake pedal 12, and the current transmission ratio.
According to an embodiment, the position of the brake pedal 12 is expressed solely by a Boolean signal which assumes only a first value corresponding to a brake pedal 12 which is not depressed and a second value corresponding to a brake pedal 12 which is depressed.
The desired speed DS calculated by the interpretation block 17 is supplied to a coordinator 18 together with a speed signal generated by the cruise control device 15. The speed signal generated by the cruise control device 15 is always zero unless the driver has expressly actuated the cruise control device 15. The coordinator 18 decides whether to use the desired speed DS calculated by the interpretation block 17 or whether to use the speed signal generated by the cruise control device 15. In a preferred embodiment, the coordinator 18 applies only a maximum function and supplies as output the highest value among the desired speed DS calculated by the interpretation block 17 and the speed signal generated by the cruise control device 15.
The coordinator 18 supplies the desired speed value DS both to the screen 16 which merely displays the value of the desired speed DS and to a simulation block 19 which calculates a time evolution of an objective speed OS in order to being the current speed CS into line with the desired speed DS.
According to a preferred embodiment, the screen 16 is provided with a filter of low-pass type in order to subject the desired speed DS to filtering of the low-pass type before the display in order to avoid an overly rapid variation of what is displayed.
The time evolution of the objective speed OS is calculated by using a dynamic model of the vehicle 1 which represents only the longitudinal movement of the vehicle 1 and receives as input the desired speed DS, the current speed CS of the vehicle 1, the current transmission ratio, an estimate of the resistant load at the wheels, the minimum torque that can be actuated at the drive wheels 5 and the maximum torque that can be actuated at the drive wheels 5. The maximum and minimum torques that can be actuated at the drive wheels 5 are calculated as a function of the current transmission ratio, as a function of the maximum and minimum torque values that can be supplied by the internal combustion engine 3 and as a function of an estimate of the torque losses brought about by the transmission 6.
It will be appreciated that the objective speed OS always varies coherently with the variation of the desired speed DS so that when the desired speed DS is increasing, the objective speed OS is also increasing and when the desired speed DS is decreasing, the objective speed OS is also decreasing. It will also be appreciated that the objective speed OS always varies more slowly than the desired speed DS. Following any variation in the transmission ratio, the value of the current speed CS of the vehicle 1 is always assigned to the objective speed OS.
The estimate of the resistant load at the wheels is carried out by an estimation block 20 which initially calculates the speed of the variation of the resistant load at the wheels by means of an asymptotic estimate based on a state observer as a function of the drive torque currently supplied by the engine 3, the speed of rotation of an input shaft of the gear change 8, the current speed CS of the vehicle 1 and the current transmission ratio; the estimate of the resistant load at the wheels is calculated as an integration over time of the speed of variation over time of the estimate of the resistant load at the wheels. It is important to note that the main non-linearities of the elastic characteristic of the transmission are included in a model used in the synthesis of the observer.
The time evolution of the objective speed OS is transmitted from the simulation block 19 to a control block 21 which calculates a time evolution of an objective torque OT at the wheels in order to match the time evolution of the objective speed OS; the objective torque OT at the wheels is then used to control the internal combustion engine 3.
The time evolution of the objective torque OT at the wheels is calculated as a function of the time evolution of the objective speed OS, the current speed CS of the vehicle 1, the current transmission ratio, the estimate of the resistant load at the wheels, the minimum torque that can be actuated at the drive wheels 5 and the maximum torque that can be actuated at the drive wheels 5.
The time evolution of the objective torque OT at the wheels is transmitted from the control block 21 to a coordinator 22 of the torque requests at the wheels, which generates a required torque value RT at the wheels which is used directly to control the internal combustion engine 3. It is preferable for the required torque value RT at the wheels always to be limited to a range between the minimum and maximum torque that can be actuated at the drive wheels 5.
The coordinator 22 of the torque requests at the wheels receives as input the time evolution of the objective torque OT at the wheels from the control block 21, a time evolution of a stabilising torque ST from a traction and stability control system 23 and a time evolution of a damping torque DT from a damping system 24.
The stabilising torque ST is accompanied by a datum indicating the operation to increase or decrease the drive torque; if a decrease is requested, the minimum value between the objective torque OT at the wheels and the stabilising torque ST is taken into account, while if an increase is requested, the maximum value between the objective torque OT at the wheels and the stabilising torque ST is taken into account.
The damping torque DT is added algebraically to the objective torque OT at the wheels if the traction and stability control is not active, i.e. if the stabilising torque ST does not assume significant values; both the damping torque DT and the objective torque OT at the wheels may be positive or negative. The objective torque OT at the wheels in particular assumes negative values when a deceleration of the vehicle 1 is requested, for instance because the current speed CS is greater than the objective speed OS; in this case, the negative value of the objective torque OT at the wheels is translated into an engine brake action and, if necessary, into a shift down from the gear engaged in the gear change 8.
The traction and stability control system 23 calculates the stabilising torque ST needed to ensure the safety of the vehicle 1 in critical conditions and in particular when the drive wheels lose adherence and when the stability of the vehicle 1 is precarious (for instance when it is at risk of swinging round). The purpose of the stabilising torque ST is to cancel out or limit the skidding of the front drive wheels 5 and/or to reset the stability of the vehicle 1; in order to ensure that the action of the traction and stability control system 23 is as efficient as possible, the stabilising torque ST always takes priority over the damping torque DT and the objective torque OT. In particular, if the stabilising torque ST assumes significant values, the coordinator 22 then disregards the damping torque DT.
In order to reduce production costs and obtain adequate mechanical strength, the transmission 6 is not normally subject to much damping; the function of the damping torque DT is to impose a controlled damping on the transmission 6 which is much greater than the natural damping of the transmission 6 itself. In this way, the degree of comfort perceived by the driver of the vehicle 1 is substantially increased as the longitudinal acceleration of the vehicle 1 is damped, i.e. it is free or almost free from oscillation phenomena, both when the transmission ratio is fixed and during the steps of transmission ratio change and starting.
The time evolution of the damping torque DT is calculated by the damping system 24 so as to minimise oscillation phenomena in the transmission 6 of the vehicle 1. In particular, the damping system 24 calculates the time evolution of the damping torque 24 by multiplying a speed of variation over time of a torsion angle of the transmission 6 by a negative coefficient depending on the value of this torsion angle.
The value of the torsion angle of the transmission 6 and the value of the speed of variation over time of this torsion angle are estimated by the estimation block 20. The speed of variation over time of the torsion angle of the transmission 6 is calculated by means of an asymptotic estimate base on an state observer as a function of the drive torque currently supplied by the engine 3, the speed of rotation of an input shaft of the gear change 8, the current speed CS of the vehicle 1, and the current transmission ratio; the torsion angle of the transmission 6 is calculated as an integration over time of the speed of variation over time of this torsion angle. The main non-linearities of the elastic characteristic of the transmission 6 are included in a model used in the synthesis of the observer.
The required torque value RT at the wheels is supplied by the coordinator 22 of the torque requests at the wheels and a coordinator 25 of the engine 3/transmission 6 unit which calculates an objective transmission ratio and thus a required torque value TT at the input of the gear change 8. In particular, the coordinator 25 of the engine 3/transmission 6 unit initially calculates the transmission ratio to be applied, so that the torque at the drive wheels 5 can be achieved with as much precision as possible; subsequently, as the objective transmission ratio is known, the coordinator 25 of the engine 3/transmission 6 unit calculates the required torque value TT at the input of the gear change 8.
A constraint that is imposed on the calculation of the transmission ratio is that of continuation for a minimum time so as to avoid any undesired changes of ratio or changes of ratio that are too close together. In other words, the coordinator 25 of the engine 3/transmission 6 ratio acts in such a way as to maintain the gear currently engaged for a time not lower than a predetermined minimum value (which may be varied as a function of driving style).
The required torque value TT at the input of the gear change 8 is supplied by the coordinator 25 of the engine 3/transmission 6 unit to a coordinator 26 of the drive torque requests which generates as output a control signal for the control of the actuators which regulate the generation of the drive torque of the internal combustion engine 3. The control signal generated by the coordinator 26 of the drive torque requests is formed by a first value which indicates the control value of the instantaneous torque and is used to control the actuators which have a fast effect on the drive torque generation, and a second value which indicates the control value of the predicted torque and is used to control the actuators which have a slow effect on the drive torque generation.
The objective transmission ratio is supplied to a controller 27 of the gear change 8 which uses this signal to calculate the actual transmission ratio. According to the embodiment shown in
According to different embodiment (not shown), the internal combustion engine 3 is replaced by an equivalent reversible electric motor.
According to a further embodiment, the vehicle 1 is also provided with at least one reversible electric motor 28 which may operate in combination with or as an alternative to the internal combustion engine 3. The shaft of the electric motor 28 may be mechanically connected to the gear change 8 either directly or via its own clutch, or the shaft of the electric motor 28 may be directly mechanically connected to the front drive wheels 5. In this case, the coordinator 25 of the engine 3/transmission 6 unit distributes the required torque value RT at the input of the gear change 8 between the internal combustion engine 3 and the electric motor 28. The following data are taken into account for the purposes of this distribution:
the current speed of rotation of the internal combustion engine 3;
the state of combustion of the internal combustion engine 3 (i.e. whether combustion is or is not active),
the load measurement of the internal combustion engine 3 (for instance the pressure or intake flow),
the speed of rotation of the electric motor 28,
the state of actuation of the electric motor 28 (i.e. whether the power actuation of the electric motor 28 is on or off),
a load measurement of the electric motor 28 (for instance the current absorbed by the power actuation of the electric motor 28),
the torque currently supplied by the internal combustion engine 3,
the minimum torque that can be supplied by the internal combustion engine 3,
the maximum torque that can be supplied by the internal combustion engine 3,
the torque currently supplied by the electric motor 28,
the minimum torque that can be supplied by the electric motor 28,
the maximum torque that can be supplied by the electric motor 28.
The distribution logic of the required torque value RT at the input of the gear change 8 may have the purpose of causing each engine to work in the dynamic conditions that are best suited to the type of engine in order to optimise efficiency and thus minimise consumption. Typically, the internal combustion engine 3 is piloted with a torque objective with varies with a relatively limited gradient, while the electric motor 28 is piloted with a torque objective which varies rapidly. In other words, the coordinator 25 of the engine 3/transmission 6 unit separates the dynamics of the internal combustion engine 3 from the dynamics of the electric motor 28. In this way, each engine may always pursue its own objective in the best possible way in relation to its own dynamic capacities.
As an alternative, the distribution logic of the required torque value RT at the input of the gear change 8 may give priority to the use of the electric motor 28 and limit the use of the internal combustion engine 3 only to cases of absolute necessity in order to minimise the pollutant emissions generated by the vehicle 1 (typically during travel in urban areas with limited traffic).
As shown in dashed lines in
The cruise management method and device described above have a number of advantages, as they make it possible correctly to interpret, in every situation, the wishes in terms of the speed of the vehicle 1 that the driver expresses by acting on the accelerator pedal 11 and on the brake pedal 12. Moreover, the driver is adequately assisted and informed through the display both of the real speed via the tachymeter 32 and of the desired speed DS via the screen 16. It is important to note that as a result of the display of the desired speed DS, driving of the vehicle 1 is simpler and more pleasant. Moreover, the possibility of inadvertently exceeding statutory speed limits is substantially reduced.
The cruise management method and device described above make it possible to optimise the choice of transmission ratio in automatic operation of the gear change 8 in any situation and in particular whatever the extent of the vehicle load due to the road gradient, wind or variations of the vehicle mass (generated, for instance, by different numbers of passengers, or changes of the load housed in the boot or the load disposed on the roof).
| Number | Date | Country | Kind |
|---|---|---|---|
| BO2005A 000025 | Jan 2005 | IT | national |
