Patent Application
20150107556
The present invention relates to a method for control of at least one speed regulator according to the preamble of claim 1 and a system for control of at least one speed regulator according to the preamble of claim 24.
The present invention relates also to a computer programme and a computer programme product which implement the method according to the invention.
In motor vehicles, e.g. cars, trucks and buses, an engine system is usually controlled by means of a regulator, a so-called speed regulator, which may be situated in an engine control unit of the vehicle but may also be situated elsewhere on board. The speed regulator regulates a torque which is demanded from the engine system and which usually varies over time, e.g. when the speed of a vehicle has to be altered or the vehicle comes to an upgrade or a downgrade.
a depicts schematically an example of a heavy vehicle 100, e.g. a truck, bus or the like. The vehicle depicted comprises a forward pair of wheels 111, 112 and a rear pair of tractive wheels 113, 114. It further comprises a power train with an engine system 130 which in a conventional way, via an output shaft 102 from the engine system is connected to a gearbox 103, e.g. via a clutch 106.
An output shaft 107 from the gearbox 103 drives the tractive wheels 113, 114 via a final gear 118, e.g. a conventional differential, and driveshafts 104, 105 which are connected to said final gear. The engine system 130 may be equipped with a turbo unit 131.
Cruise control is now usual in motor vehicles such as cars, trucks and buses. One purpose of cruise control is to achieve a uniform predetermined vehicle speed either by adjusting the engine torque to avoid deceleration or by applying brake action on downhill runs where the vehicle is accelerated by its own weight. A more general purpose of cruise control is to provide the vehicle's driver with easy driving and more comfort.
a and
The set speed vset may therefore be regarded as an input signal to the cruise control, and the reference speed vref as an output signal from the cruise control which is used as a target speed vdes for control of the engine by means of the speed regulator. In other words, the reference speed vref here serves as the set-point value for the vehicle's speed and is herein also referred to as the target speed vdes.
One skilled in the art will appreciate that the cruise control 110 may also be replaced by a command from the driver. Thus the target speed vdes may also be conveyed to the speed regulator 120 as a result of the driver operating the vehicle's controls, e.g. an acceleration control such as an accelerator pedal or the like.
In today's traditional cruise controls (CCs) the reference speed vref is identical with the set speed vset chosen by the user of the system, e.g. a driver of the vehicle. These CCs therefore maintain a constant reference speed vref corresponding to the set speed vset chosen by the driver. The value of the reference speed vref here changes only when adjusted by the user during the journey.
There are today cruise controls known as economical cruise controls, e.g. Ecocruise and the like, which try to estimate current running resistance, also have knowledge about the historical running resistance and allow the reference speed vref to differ from the set speed vset chosen by the driver. A cruise control which allows such difference is herein referred to as a reference-speed-regulating cruise control.
There are various types of regulators. We describe here the function and the algorithm of a PID regulator, but one skilled in the art will appreciate that other types/variants of regulators work in similar ways. The present invention may be implemented for all such other types/variants of regulators.
A PID regulator is a regulator which gives an input signal u(t) to a system, e.g. the engine system 130, on the basis of a difference e(t) between a desired output signal r(t), which in this specification corresponds to the target speed vdes, and an actual output signal y(t) which in this specification corresponds to the actual speed vact. In the case referred to below, e(t)=r(t)−y(t) according to
in which
A PID regulator regulates in three ways, viz. by a proportional amplification (P; Kp), by an integration (I; Ki) and by a derivation (D; Kd).
The constants Kp, Ki and Kd affect the system as follows.
An increased value for the amplification constant Kp leads to the following changes in the PID regulator:
An increased value for the integration constant Ki leads to the following changes in the PID regulator:
An increased value for the derivation constant Kd leads to the following changes in the PID regulator:
The regulating algorithm for a PID regulator is well-known to one skilled in the art, who will also be familiar, as mentioned above, with other types/variants of regulators/regulating algorithms and their similarities to/differences from the PID regulator.
If the speed regulator 120 has for a lengthy period had in its algorithm a relatively large regulating error e, it is, depending on the function of the speed regulator's regulating algorithm, not possible to make the rapid changes in the torque M which are required to be able to follow an optimum curve for the vehicle's actual speed vact and thereby be able to optimise the vehicle's speed profile, with consequent potential for also optimising its fuel consumption.
In other words, an inertia of the torque M is built up over the time which the algorithm in the speed regulator 120 takes to perform its calculations, owing to regulating error e incorporated in the algorithm. There is therefore risk of torque uprampings and downrampings being slow, e.g. at large steps in the set-value vdes. This slowness may cause problems as regards optimum control of speed adjustment and fuel consumption.
The regulating error e in the speed regulator is due to the difference between the speed set-point value, i.e. the target speed vdes, and the current value of the vehicle's speed, i.e. the actual speed vact. Particularly when there are relatively large changes in the vehicle's actual speed vact, e.g. when travelling uphill or downhill, this regulating error e will be relatively large for relatively long periods of time, with consequent build-up of inertia of the torque M.
Reference-speed-regulating cruise controls, e.g. “look-ahead” cruise controls (LACC), use knowledge about road sections ahead to determine the configuration of the reference speed vref. The reference speed vref is therefore here allowed, within a speed range, to differ from the set speed vset chosen by the driver, in order to achieve more economical operation from a fuel perspective. LACCs typically adjust the reference speed vref to achieve a desired profile for the vehicle's actual speed vact over a predetermined distance traveled. As the reference speed vref here serves as the target speed vdes in the regulating algorithm, these adjustments of the reference speed vref often cause the regulating error e in the regulating algorithm, thereby building up the inertia of the torque M.
An object of the present invention is to make rapid changes possible for the torque M.
This object is achieved by the aforesaid method for control of at least one speed regulator, according to the characterising part of claim 1. It is also achieved by the aforesaid system for control of at least one speed regulator, according to the characterising part of claim 23.
The present invention makes rapid changes in the torque M possible by enabling the system to choose whether a previous build-up is to be maintained or not for the torque M. According to the present invention this may be achieved by influencing the inertia which arises from an incremented memory term/memory element of the regulating algorithm.
The memory element of the regulating algorithm is related to the history of the speed regulator, since the memory element typically depends on an integration of the regulating error e in the algorithm. If for example a relatively large regulating error e is integrated upwards, e.g. before a change in the target speed vdes takes place, the vehicle's actual speed vact would in previous known systems react slowly when the change in the target speed vdes takes place. With the present invention, the vehicle's actual speed vact reacts considerably more quickly to the change in the target speed vdes, since the influence of the regulating algorithm upon the engine system is curtailed if the memory term has an undesirable configuration, as it does in one embodiment if its absolute amount decreases after a change, e.g. a step, in the target speed vdes has been identified.
In one embodiment of the present invention, the curtailment of the regulating algorithm's influence takes the form of a temporary departure from regulation based on the algorithm. Here an engine torque demanded may for example be limited at the change in the target speed vdes. After this limitation of torque demanded has initially been utilised after the change in the target speed vdes, the system reverts to regulation based on the algorithm.
In one embodiment of the present invention, the curtailment of the regulating algorithm's influence takes the form of manipulation of the memory term in the algorithm, e.g. by the memory term being set to a suitable value initially at the change in the target speed vdes.
In one embodiment, this suitable value to which the memory term is set is zero (0), corresponding to elimination of the memory term in the regulating algorithm. The algorithm thus no longer remembers what previously happened during the regulation of the engine system, and the engine system's torque inertia has therefore been considerably reduced, which means that a desired speed curve can be followed more exactly, resulting in cruise control and speed regulation which are more efficient from a fuel economy perspective.
The present invention thus results in cruise control which is more fuel-efficient, which a driver will also intuitively regard as positive, since irritating delays in the system are minimised and a more instantaneous speed regulation is achieved.
In one embodiment of the present invention, losses in the power train may also be controlled when a change, e.g. a step, in the target speed vdes has been identified. Here it is for example possible to choose to influence parasitic losses, e.g. in a generator, a cooling fan or an air processing system which consume energy in the power train. A further example of measures to reduce the losses in the power train comprise lowering the exhaust backpressure considerably and/or operating the gearbox in such a way that less energy is consumed by engaging a higher gear or freewheeling. Another aspect is that an increased running resistance will enable the vehicle to reach a lower speed more quickly if this is desirable.
The invention is explained in more detail below with reference to the attached drawings, in which the same reference notations are used for similar items, and
a is a schematic drawing of a vehicle,
b is a schematic diagram of a cruise control, a speed regulator and an engine system,
The method begins with a first step [201] in which a change in the target speed vdes is identified. As a second step [202] of the method, which is performed if a change in the target speed vdes is identified at the first step [201], an absolute amount is determined for a memory term of the regulating algorithm used by the regulating system. This memory term is related to a history of how the speed regulator previously regulated the engine system. If PID regulation is used, the magnitude of the I term ∫0te(τ)dτ d is determined by determining its absolute amount |∫0te(τ)dτ|.
The third step [203] of the invention assesses whether the I term's absolute amount |∫0te(τ)dτ| has a desirable configuration or not. An example of an undesirable configuration is if the absolute amount decreases after the change in the target speed vdes. This may for example happen when an engine torque M demanded of the engine system 130 changes from a substantially maximum engine torque to a drag torque, as illustrated in
In the fourth step [204] of the method, which is performed if at the third step [203] it is determined that the I term's absolute amount |∫0te(τ)dτ| has an undesirable configuration, the present invention results in a curtailment of the regulating algorithm's influence upon the engine system.
According to the present invention, curtailment of the regulating algorithm's influence therefore allows the regulating system to choose whether a previous build-up is to be maintained or not for the torque M, enabling rapid changes in the torque M.
In one embodiment of the present invention, the curtailment of the regulating algorithm's influence takes the form of manipulation of the memory term in the regulating algorithm.
The memory term may here be determined to have any suitable value which enables rapid changes for the torque M. The memory term may here be set to this suitable value initially when the change in the target speed vdes has been detected.
In one embodiment this suitable value is one which causes the memory term in the regulating algorithm to take out, i.e. compensate for, a proportional term and a derivative term in the algorithm. If for example a PID regulating algorithm is used, the I term is therefore given a value such that it initially takes out the P term and the D term.
In one embodiment, this suitable value is zero (0), corresponding to elimination of the memory term in the regulating algorithm for the speed regulator 120. The memory term is related to a history of the speed regulator's regulation of the engine system 130, so the algorithm after the elimination no longer remembers what previously happened during the regulation of the engine system. The torque inertia of the engine system may thus be considerably reduced. As described above, the elimination takes place here if a change in the target speed vdes has been detected and it is determined that the memory term's configuration is undesirable.
In one embodiment the memory term's configuration is undesirable if its absolute amount decreases after a change, e.g. a step, in the target speed vdes has been identified. The memory element of the regulating algorithm depends typically on integration of the regulating error e in the algorithm and therefore on the speed regulator's history. This is exemplified for a PID regulator in
This elimination of the memory term in the regulating algorithm enables a rapid change in the torque M. This rapid change is here possible because the inertia of the torque M built up through the influence of the regulating error e during the algorithm's control of the engine system 130 consequently disappears.
The present invention thus enables quicker upramping or downramping of the torque M, since the speed regulator 120 no longer remembers the regulating error e which previously affected the algorithm.
Curve vact
Curve vact
An absolute value and a configuration for the memory term in the regulating algorithm are determined and assessed. A reference-speed-regulating cruise control for example decides whether to lower the reference speed vdes so that a simulated vehicle speed vsim along curve 301 will not fall below the lowest permissible speed vmin. In this embodiment of the present invention, the memory term in the algorithm has to be eliminated if a change in the target speed vdes takes place which results in an undesirable configuration of the memory term's absolute amount. This makes it easier for the simulated vehicle speed vsim and the actual vehicle speed vact to be followed up. As a non-limitative example it may be mentioned that the regulating error e in the example illustrated in
As the present invention eliminates the memory term in the regulating algorithm, and hence also the inertia in the torque M, the result is a much more flexible actual speed vact
In one embodiment of the present invention, the curtailment of the regulating algorithm's influence takes the form of temporary departure from regulation based on the algorithm.
Here an engine torque demanded may for example be limited at the change in the target speed vdes. After this limitation of engine torque demanded has initially been utilised after the change in the target speed vdes, the system reverts to regulation based on the algorithm. To achieve a smooth transition when the system reverts to regulation according to the regulating system, it is possible in one embodiment of the invention for the memory term in the algorithm to be initiated, i.e. to be given a value, so that it assumes a value which results in a gentle transition to regulation according to the algorithm.
In the example depicted in
In one embodiment of the present invention, the speed regulator according to the invention uses a PID algorithm, i.e. the speed regulator is a PID regulator.
As described above, there is often a regulating error e in the algorithm which is integrated upwards in the PID regulator. This is illustrated schematically in
The P term in the PID algorithm takes the form in this embodiment of the term for proportional amplification, which in previous known solutions, Pact
As may be seen in
The I term in the PID algorithm takes the form in this embodiment of the memory term, which is integrated upwards to a larger and larger value when there is a regulating error e. In previous known solutions, Iact
The elimination of the I term may in practice take place in such a way that the integrating term is set to the value zero, as depicted in
After the elimination, the I term for this embodiment, Iact
The D term in the PID algorithm takes the form in this embodiment of the term for derivation, which in previous known solutions, Dact
The corresponding term for previous known solutions, Dact
In one embodiment of the present invention, not only the speed regulator 120 but also the function of the turbo unit 131 in the engine system 130 is also guided when a change in the target speed vdes has been identified, if the I element's absolute amount has an undesirable configuration. In other words, the turbo function is guided if it is desirable that a simulated vehicle speed vsim in the reference-speed-regulating cruise control should correspond to the actual speed vact.
In one embodiment, the function of the turbo unit 131 is affected by this form of control in that the turbo pressure decreases considerably. Here the turbo pressure is therefore dumped immediately when it is found that there is a change in the target speed vdes, if the I element's absolute amount has an undesirable configuration, resulting in reduced engine friction losses (since the air resistance during the compression decreases with decreasing exhaust backpressure) and in less fuel consumption for the vehicle.
In one embodiment of the present invention, not only the curtailment of the regulating algorithm's influence upon the speed regulation but also at least one power train resistance-changing measure also takes place when it has been found that there is a change in the target speed vdes and the I element's absolute amount has an undesirable configuration.
An example of a power train resistance-reducing measure is a change in the gear ratio of the gearbox 103 in the vehicle 100. The resistance in the power train may be reduced by engaging a neutral gear. The running resistance may also be reduced by engaging a higher gear, i.e. a gear which involves a lower engine speed and hence also less friction in the engine. This results in less running resistance because of the lower engine speed, which means that the vehicle acquires a slower/gentler change in the actual speed vact in response to a change in the target speed vdes.
These reductions in the resistance in the power train reduce the vehicle's total fuel consumption and also the wear on the power train components. In particular, changing up to higher gears results in a lower speed for the engine system 130 and consequently smaller losses in the power train as a whole.
An example of a power train resistance-increasing measure is a change in the gear ratio of the gearbox 103 in the vehicle 100. The resistance in the power train may here be increased by a downward gear change, i.e. by engaging a gear which results in a higher engine speed, increased running resistance and also greater counterforce in engine braking. This makes use of the fact that the friction pertaining to the engine increases with increasing engine speed, i.e. the power train resistance increases with increasing speed of the engine.
It is important here to achieve in the context of a reference-speed-regulating cruise control, e.g. an LACC, a good match between a simulated vehicle speed vsim and an actual vehicle speed vact at a lowering. In one embodiment, the parasitic losses and/or the resistance in the power train components may also be increased in order to achieve quicker speed lowering on heavy vehicles.
In one embodiment of the present invention, the curtailment of the regulating algorithm's influence, i.e. the manipulation or elimination of the memory term in the algorithm, the temporary departure from regulation according to the algorithm, and/or possibly the dumping of the turbo pressure and/or the change in the gear ratio of the gearbox 103, causes a relatively large decrease in the torque M taken out of the engine system 130. The magnitude of this decrease should with advantage be such as to be found comfortable for a driver and/or passengers in the vehicle 100. Good comfort and operating sensation for the vehicle are thus maintained even when a substantial fuel saving is made.
The decrease has in one embodiment to be as great as possible without being found uncomfortable, which mostly depends on the vehicle's train weight, since the train weight reduces the influence of propulsive torque and causes comfortable running.
In one embodiment of the present invention, information about road sections ahead is used to identify whether there is a change in the target speed vdes and whether the I element's absolute amount has an undesirable configuration. Such information about the road section ahead may comprise one or more from among topography, road curvature, traffic situation, roadworks, traffic density and road surface state.
Information from a cruise control and/or a speed regulator may also be used for this identification of a change in the target speed vdes and of an undesirable configuration of the I element's absolute amount, since accelerations and/or decelerations and/or torque requirements may thus be predicted. Driver input may also be used in the identification.
As mentioned above, knowledge of road sections ahead may be used in economical cruise controls, e.g. LACCs. It may for example comprise prevailing topography, road curvature, traffic situation, roadworks, traffic density and road surface state. It may also comprise a speed limit on the road section ahead, and a traffic sign beside the road. One embodiment of the present invention uses at least one of these kinds of knowledge in identifying the change in the target speed vdes and an undesirable configuration of the memory term, and to determine an influence of parasitic losses and resistances in the power train so that a simulated speed vsim and an actual speed vact become as equal to one another as possible. This is highly advantageous and computationally efficient, since these kinds of knowledge are readily available on board the vehicle. They may therefore be used here for various purposes, both for cruise control and to identify the change in the target speed vdes and an undesirable configuration of the memory term. The control of at least the speed regulator 120 and possibly also the turbo unit 131 and/or the gearbox 103 according to the present invention may thus be implemented with very little in terms of extra calculations or complexity.
These kinds of knowledge may for example be obtained by means of location information, e.g. GPS (global positioning system) information, map information and/or topographical map information, weather reports, information communicated between vehicles and information communicated by radio.
For example, information about the topography of road sections ahead may be used to identify upgrades and/or downgrades on which regulating error may occur, e.g. because of dragging of the engine system 130. The change in the target speed vdes and an undesirable configuration of the memory term may thus also be identified.
If a reference-speed-regulating cruise control is used in the vehicle, a change in the actual speed vact may be because the reference speed vref, which then corresponds to the target speed vdes, changes relative to the set speed vset. Regulating error e, due for example to dragging of the engine system 130, may occur in association with such speed changes, so information from the cruise control may be used in identifying the change in the target speed vdes and in identifying an undesirable configuration of the memory term.
In a similar way, information about curvature of road sections ahead may be used to identify coming speed changes and regulating error e, and hence to identify the change in the target speed vdes and to identify an undesirable configuration of the memory term, since the regulating error e arises from the fact that the actual speed vact often drops at bends, particularly at sharp bends, before increasing again after them.
Similarly, information about traffic situations on road sections ahead may be used to identify coming changes in the target speed vdes and to identify undesirable configurations of the memory term. Here knowledge about, for example, a red light ahead may conceivably be used to identify at least one likely change in speed close to the red light, resulting in regulating error e.
Knowledge of roadworks ahead may also be used to identify coming changes in the target speed vdes and to identify undesirable configurations of the memory term, since speed limits and hence regulating error e usually occur close to roadworks.
Information about traffic density on road sections ahead may also be used to identify coming changes in the target speed vdes and to identify undesirable configurations of the memory term, since traffic queues will for example make it necessary to reduce speed, whereupon regulating error e occurs.
Road surface state also affects vehicle speed, since a lower speed needs to be maintained where the surface state is bad, e.g. when there is ice, than where it is good. Information about the surface state of road sections ahead may thus also be used to identify coming changes in the target speed vdes and to identify undesirable configurations of the memory term.
Driver input may also be used to identify coming changes in the target speed vdes and to identify undesirable configurations of the memory term. Here the user interface may for example be equipped with at least one input device which the driver can use. If the driver sees that a change in the target speed vdes and an undesirable configuration of the memory term are likely to occur shortly, he/she may here make some kind of input which the system interprets to the effect that such a situation will arise. As a non-limitative example, the driver may make such an input if he/she sees a stationary queue, an accident or an area of bad surface on the road ahead, or a long downgrade coming. Here such input may be interpreted to the effect that a change in the target speed vdes and an undesirable configuration of the memory term will occur after a first amount of time has elapsed since the input.
As mentioned above, in reference-speed-regulating cruise controls, e.g. LACCs, the reference speed vref is allowed to differ from the set speed vset. In one embodiment of the present invention, a change in the target speed vdes and an undesirable configuration of the memory term are regarded as identified if the magnitude of the reference speed vref changes. This is illustrated schematically in
Here the knowledge that speed changes which follow changes in the reference speed vref are based on the memory term is used, since the regulating error is integrated upwards during the time when the speed change takes place. Immediately then identifying a change in the target speed vdes and an undesirable configuration of the memory term on the basis of this knowledge results in a very quick and effective curtailment of the influence of the regulating algorithm, e.g. elimination of the memory term in the algorithm.
In one embodiment of the invention the elimination takes place each time the magnitude of the reference speed vref changes.
One skilled in the art will appreciate that the method for control of at least one speed regulator according to the present invention may also be implemented in a computer programme which, when executed in a computer, causes the computer to conduct the method. The programme usually takes the form of a computer programme product 503 (depicted in
The control unit 500 is further provided with respective devices 511, 512, 513, 514 for receiving and sending input and output signals. These input and output signals may comprise waveforms, pulses or other attributes which the input signal receiving devices 511, 513 can detect as information and which can be converted to signals which the calculation unit 501 can process. These signals are then conveyed to the calculation unit. The output signal sending devices 512, 514 are arranged to convert signals received from the calculation unit in order, e.g. by modulating them, to create output signals which can be conveyed to other parts of systems on board the vehicle, e.g. to the speed regulator 120, the engine system 130, the turbo unit 131 or the gearbox 103.
Each of the connections to the respective devices for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (controller area network) bus, a MOST (media oriented systems transport) bus or some other bus configuration, or a wireless connection.
One skilled in the art will appreciate that the aforesaid computer may take the form of the calculation unit 501 and that the aforesaid memory may take the form of the memory unit 502.
One aspect of the present invention proposes a system for control of at least the speed regulator and in certain embodiments for control also of a turbo unit 131 and/or a gearbox 103. The system according to the invention comprises an identification unit adapted to identifying a change in the target speed vdes. The system comprises also a determination unit adapted to determining an absolute amount for the memory term in the regulating algorithm. The system comprises also a curtailment unit adapted to curtailing the algorithm's influence upon the engine system if the memory term's absolute amount has an undesirable configuration. In one embodiment of the invention this curtailment may take the form of eliminating the memory term in the algorithm.
One skilled in the art will also appreciate that the above system may be modified according to the various embodiments of the method according to the invention. The invention relates also to a motor vehicle, e.g. a truck or a bus, which is provided with the system for controlling at least the speed regulator according to the invention.
The present invention is not restricted to the invention's embodiments described above but relates to and comprises all embodiments within the protective scope of the attached independent claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1250349-6 | Apr 2012 | SE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/SE2013/050350 | 3/28/2013 | WO | 00 |
