ITRM20090334A1 - METHOD FOR THE CONTROL OF THE ADVANCEMENT SPEED IN SCOOTER WITH ELECTRIC PROPULSION - Google Patents

Description

DESCRIPTION of the industrial invention entitled:

"Method for controlling the forward speed in electric-powered scooters"

The present invention relates to a method for controlling the forward speed in electric propulsion scooters.

As a result of the ever increasing attention to environmental problems related to the use of vehicles with fossil fuel engines and the ever increasing management costs that these require, the use of electric propulsion vehicles is becoming more and more widespread. A solution of great interest for metropolitan areas is represented by electric scooters, particularly suitable for transport services, for example of the postal type, or for home deliveries.

Numerous administrations have therefore begun to replace motor vehicles with internal combustion engines with electric-powered scooters, obtaining an undeniable advantage in terms of pollution and economic savings. However, the characteristics and behavior of the latter vehicles is in many respects different from traditional means of transport and these differences can create difficulties in driving the vehicle or, in any case, create a certain hindrance.

However, these difficulties can be dangerous and annoying when the scooters are intended for transport services, during which heavy weights must be transported and the vehicle is subject to continuous stops and starts.

It is in fact easy to understand how the two types of engines used, having very different behaviors, respond differently to the accelerator command, providing very different sensations while driving.

More precisely, a combustion engine offers progressive behavior, with a gradual increase in torque, in accordance with the characteristic curve of such engine types. Therefore, to have a smooth start or acceleration, in scooters with internal combustion engines, it will be sufficient to gradually act on the throttle grip which directly adjusts the fuel supply to the engine. On the contrary, in electric scooters, in which a rotating knob is still used to control the accelerator, the behavior of the electric motor is established based on the type of control used.

In other words, following the rotation of the knob, a command signal will be sent which, through an appropriate implementation of a control, will command the electric motor.

Depending on the control modes used, the behavior of the motor will be different.

A first possibility therefore consists in implementing a torque control, in a conceptually similar way to what happens in a scooter with a combustion engine.

Acting on the accelerator will vary the torque delivered by the engine and, consequently, also the speed of the vehicle.

However, this type of control has a disadvantage linked to the fact that when the vehicle proceeds downhill, not acting on the accelerator, the engine does not produce any torque, while, on the contrary, it would be necessary for the engine to automatically produce a braking torque, so such as to slow down the vehicle, similarly to the engine brake in internal combustion engines.

To overcome this drawback, for example, it was decided to allow the accelerator to rotate in two directions of rotation, in the first case by imposing positive torque, in the second case negative torque, thus making the electric motor work as a generator. Such a solution is described in the international patent application n. WO 2003078199.

Even in this case, however, the use of acceleration in these ways is impractical and, above all, scarcely intuitive for a driver accustomed to using traditional motor vehicles. Furthermore, this solution does not make it possible to make the most of regenerative braking, that is, the use of the engine as a generator for recharging the batteries with consequent braking action, as the simple release of the accelerator simply sets zero torque. On the contrary, it may be desirable to have a recovery action even when the scooter is downhill or slows down by proceeding on a flat stretch, for example approaching an intersection. In the system described in the aforementioned patent, this action is delegated to the negative rotation of the acceleration, therefore, an unintuitive and spontaneous movement on the part of the driver.

As an alternative, therefore, a speed control system has been developed that imposes a certain speed on the engine based on the angle of rotation of the throttle grip.

This solution solves the problems related to downhill progress and the lack of intuitiveness of the control, but has the disadvantage of producing accelerations, in particular from standstill and at low speeds, which are excessively abrupt. This behavior can in fact be dangerous when the electric vehicle is used for transport and, consequently, heavy. Furthermore, in general, it does not provide good sensations to the driver who basically has the impression of having poor control of the vehicle.

Therefore, the technical problem underlying the present invention is that of providing a method of controlling the forward speed in electric scooters which allows to obviate the disadvantages mentioned above with reference to the known art.

This problem is solved by the method according to claim 1 and by the scooter according to claim 10.

The present invention has some relevant advantages. The main advantage consists in the fact that the method according to the present invention allows to control an electric scooter in an intuitive, practical way and without creating any difficult situation for the driver. In addition, the method according to the present invention is particularly suitable for integrating with a regenerative braking function, without the need to act on specific commands.

Other advantages, characteristics and methods of use of the present invention will become evident from the following detailed description of some embodiments, presented for illustrative and non-limiting purposes. Reference will be made to the figures of the attached drawings, in which:

Figure 1 is a block diagram of the method for controlling the forward speed in electrically propelled scooters according to the present invention; and Figures 2A and 2B are two graphs which illustrate examples of the function of the variation respectively of the proportional gain and of the integral gain of a PID controller applied in the method according to the present invention.

Incidentally, the term scooter will mean that a category of motor vehicles, with the characteristic conformation of the body, called "step-through", that is, it can be crossed in the lowered section between the seat and the front shield. These vehicles are normally two-wheeled but, in some cases, three-wheeled and the same inventive concepts that will be illustrated below can also be applied to the latter type of vehicles.

With reference therefore to Figure 1, a block diagram is illustrated which summarizes the operation of the speed control method according to the present invention. In general, an electric scooter comprises an electric motor M, an engine control unit CU, in particular comprising the power stage and connected to the accelerator control A and, obviously, to the engine itself, and a battery group BP for the power supply of the scooter.

While driving the scooter, the driver acts on the accelerator control A in order to regulate the forward speed of the vehicle, similar to traditional motor vehicles.

In particular, to act on acceleration A, the driver performs a rotation α of the grip of the same, a rotation that will have a certain amplitude with respect to an initial rest position of the accelerator.

Then, according to methods that will be described in greater detail below, the amplitude of the rotation angle α will be transmitted to the control unit CU, which will associate this angle α with a predetermined target speed vt. In other words, the driver, by turning the throttle grip, selects a speed at which he wishes to proceed, indicated as the target speed.

This operation can be simply carried out through the use of a potentiometer connected to the throttle grip, in order to provide a variable signal according to the angle α.

Inside the control unit CU, the target speed vt is compared with a real speed vr which corresponds to the real forward speed of the scooter, detected, for example, by means of a speed sensor Sv, associated with the engine M. This comparison operation allows to obtain a speed error εv, obtained from the difference between target speed v and real speed vr.

As shown in Figure 1, the CU control unit also includes a CPID PID controller of the speed loop that provides a control signal to the power stage and, consequently, controls the motor.

As known, the PID controller performs a proportional, integral and derivative type adjustment action, which is adjusted on the basis of the respective proportional gains Kp, integral K and derivative Kd.

The response of the motor is therefore strongly influenced by the values of these gains, in particular, a more or less rapid response can be defined on the basis of the set regulation.

In the control method according to the present invention, the PID controller uses gain values, in particular of Kie Kp, which are variable as a function of the speed error εv.

The method according to the present invention foresees in particular the variation of the values of the gains Kie Kp of the speed control loop in such a way as to obtain a very rapid response of the system in case the speed error εv is high, and instead gradually and automatically becomes softer as the error εv decreases.

More precisely, to high values of Kp correspond faster responses and therefore more abrupt behaviors while, and for low values of the gain, the system has a first type and slower response dynamics.

Therefore, to obtain a softer response it is preferable to decrease the proportional gain Kpal and decrease the error εv.

Furthermore, it was experimentally observed that, to obtain a more correct response, it is preferable to increase the integral gain Kial to decrease the error εv.

The method of controlling the speed of advancement according to the present invention is therefore based on a first step of setting the target speed vt, acting on the accelerator control and, in particular, depending on the angle α.

At the same time, the real speed vrdello scooter is detected by means of a special sensor Sv, which is compared with the target speed vt.

The values of the proportional gain Kped integral Kidel PID controller will therefore be variable as a function of the speed error εv, obtained by comparing the real speed vre and the target speed vt.

Then, the electric motor M of the scooter is activated, on the basis of the values of the proportional gain Kped integral Ki, in such a way that the vehicle tends to move to the target speed vt set by the driver.

Thanks to this control methodology, the scooter will decrease its acceleration when it is close to the target speed, thus providing a more intuitive and easier to control behavior for the driver.

For example, if the scooter is stationary and the driver wants to adjust the power obtained to reach a certain speed, he can accelerate a lot to get a quick response. In fact, in this motion the system will use high values of the proportional gain Kpin as the error εv will be large.

If, on the other hand, the driver wants to have a progressive behavior of the vehicle, he will gradually accelerate in such a way as to select small values of Kppiù and therefore obtain a softer response.

With reference to the graphs of figures 2A and 2B, which illustrate a possible example of variation respectively of the proportional gain Kp and the integral gain Kial varying the speed error ε, the method of variation of the gains of the PID controller can be modified according to the speed error determined.

More precisely, as can be seen from the graphs, the trends of the proportional gain Kp and the integral gain Kis are such that they remain constant for speed errors lower than a minimum speed error εvmine higher than a maximum speed error εvmax, while they vary according to as previously described between these values. In this way, possible system instabilities are avoided, which could occur due to excessively low or high values of Kpe Ki gains.

In addition, the variation method can be further modified for speeds close to the maximum speed. In particular, in fact, in this situation, there would be, as the maximum speed approaches, an increasingly smaller speed error, therefore with increasingly slower system responses. Therefore, theoretically, the scooter would never reach its maximum speed. To overcome this problem, it is possible to envisage a different strategy for varying the gains, in particular at high speeds. For example, it will be possible to predict a multiplicative coefficient as a function of the real speed of the scooter or, in general, it will be possible to use mathematical functions, which differ from the trend illustrated in figures 2A and 2B, which take into account the problems that occur at speed. close to the maximum.

In other words, therefore, the proportional gain Kp and the integral gain K may vary as a function of the speed error ε based on predetermined mathematical functions that take into account other parameters relating to the motion of the scooter.

Finally, note that the method according to the present invention provides for the use of a torque controller that transmits a signal to the power stage on the basis of a torque error similarly to what is described for the speed loop.

In this case, the target torque Tt will be set on the basis of a signal provided by the PID controller, as a function of the speed error and therefore of the gains Kp, Ki, Kd of the same.

By means of a special torque sensor ST, a real torque value Tr of the scooter engine is detected, which is compared with the target torque Ttsud said, providing a torque error εT.

The electric motor M of the scooter will then be controlled through the power stage so as to provide the target torque T required.

Therefore, note that, when the driver releases the accelerator, a zero target speed will be set, with a negative speed error, and the target torque that will be set will be negative, thus making the engine work correctly as a brake. This aspect is then particularly advantageous if a regenerative braking system is used, in which the batteries can be recharged when negative torque is required and the engine, to generate the braking effect, works as a generator.

The present invention has been described up to now with reference to preferred embodiments. It is to be understood that there may be other embodiments that refer to the same inventive core, all falling within the scope of the claims set out below.

Claims (10)

CLAIMS 1. Method for controlling the ground speed in electric powered scooters, comprising the steps of: to. set a target speed (vt); b. detect a real speed (vr) of the electric motor (M) of the scooter; c. compare the real speed (vr) with the target speed (vt); d. control the electric motor (M) of the scooter in such a way that it tends to reach said target speed (vt), characterized by the fact that said step of controlling the electric motor takes place through a PID controller (CPID), in which the value of the proportional gain (Kp) of the PID controller (CPID) is variable as a function of a speed error (εv ) obtained from said comparison step between the real speed (vr) and the target speed (vt). 2. Method according to claim 1, in which the value of the proportional gain (Kp) is increased as said speed error (εv) increases. Method according to claim 1 or 2, wherein the value of the <proportional gain (Kp) is such that:> • it remains constant for speed errors lower than a minimum speed error (εvmin) and higher than a maximum speed error <(εvmax);> • varies for speed errors between said minimum speed error (εvmin) and said maximum speed error (εvmax). Method according to one of the preceding claims, wherein the value of the integral gain (Ki) of the PID control (CPID) is variable as a function of said speed error (εv). 5. Method according to claim 4, in which the value of the integral gain (Ki) is decreased as the said speed error (εv) increases. Method according to claim 4 or 5, wherein the value of the integral gain <(Ki) is such that:> • it remains constant for speed errors lower than a minimum speed error (εvmin) and higher than a maximum speed error (εvmax); • varies for speed errors between said minimum speed error (εvmin) and said maximum speed error (εvmax). 7. Method according to one of the preceding claims, in which said step of setting a target speed (Vt) is carried out by acting on the accelerator (A) of the scooter. 8. Method according to claim 5, wherein said target speed (Vt) is associated with the amplitude of the angle of rotation (α) of a throttle control knob (A) of the scooter with respect to an initial rest position. Method according to one of the preceding claims, wherein said step of controlling the electric motor (M) in such a way that the vehicle tends to reach said target speed (vt) comprises further steps of: • set a target torque (Tt); • detect a real torque (Tr) of the electric motor (M) of the scooter; • compare the real torque (Tr) with the target torque (Tt); • command the electric motor (M) so as to provide said target torque (Tt), said target torque (vt) being determined on the basis of a signal provided by said PID controller (CPID), as a function of the speed error (εv) and consequently determined gains (Kp, Ki). 10. Electric propulsion scooter comprising an electric motor (M), a control unit (CU) of said motor (M), associated with an accelerator control (A) and a battery group (BP), said control unit comprising a PID type controller (CPID) of the speed control loop, characterized in that the gains (Kp, Ki) of said PID controller (CPID) are regulated by a method according to one of the preceding claims.