EP4153854B1

EP4153854B1 - Method for generating a command signal of the value of idle speed for a combustion engine, control unit and tractor

Info

Publication number: EP4153854B1
Application number: EP21727228.5A
Authority: EP
Inventors: Massimo Ribaldone; Simone Tremolada; Giorgio GAVINA
Original assignee: Same Deutz Fahr Italia SpA
Current assignee: Same Deutz Fahr Italia SpA
Priority date: 2020-05-19
Filing date: 2021-05-03
Publication date: 2024-05-01
Anticipated expiration: 2041-05-03
Also published as: IT202000011605A1; EP4153854A1; WO2021234485A1

Description

The present invention relates to a method for generating a command signal of the idle speed value for a combustion engine of a tractor. Furthermore, the present invention relates to a control unit for a tractor and a tractor or compact tractor comprising such a control unit.
It is worth noting that the word "tractor" herein means both agricultural tractors and, more in general, large machines, such as earth-moving machines, preferably derived from agricultural tractors or off-highway machines, i.e., in general, specific machines for power operations, e.g., actions directly on the ground, such as tilling, or actions for loading and unloading material. On the other hand, "compact tractor" means the type of vehicle typically of small size, e.g., used in the vineyard sector.
In other words, the context in which the present invention finds specific application is the agricultural and/or off-highway vehicle sector.
In particular, the present invention relates to the engine idle speed management for this type of vehicles.
For many years, there has been a consolidated trend towards reducing the displacement of combustion engines above all due to tractor layout constraints and to regulations linked to the continuous demand for reduced emissions. In this context, the engine displacement must be reduced to maintain the final engine layout and reduce fuel consumption at the same time. As an example, in the prior art, document US2014/083392A1 discloses a method for handling the idle speed value of a vehicle.
By virtue of the availability of increasingly sophisticated injection systems, the same power can be achieved with smaller displacements.
However, even if the same nominal power can be achieved, it is difficult to achieve the same performance at low engine speeds as with the relatively large displacements.
This leads to unpleasant side effects in terms of engine stalling when higher power at low engine speed is required.
For example, it is known that tractors are connected to a series of mechanical and hydraulic users which absorb power when activated. Whenever such users require a high power absorption, the combustion engine runs the risk of stalling because it cannot provide sufficient dynamic to compensate for the higher power demand.
For the aforesaid reasons, the person skilled in the art is inclined to readjust the power required by the users, thus decreasing their performance.
An even more depressing contribution to the above-mentioned problems is the need to ensure ever-lower fuel consumption.
Disadvantageously, moreover, the reduction of engine displacement often results in poorly programmable variations of engine speed and/or sudden acceleration and deceleration, with consequent impairment of vehicle comfort, generally measured and known as Noise Vibration Harshness (NVH).
It is an object of the present invention to overcome the aforesaid drawbacks which are typical of the background art.
In particular, it is an object of the present invention that of avoiding engine stalling due to high power demands, especially at low engine speeds, and at the same time keeping the typical conditions of design and use of the users unchanged as much as possible.
Furthermore, it is an object of the present invention, the possibility of guaranteeing non-stalling of the engine also on existing tractors or established tractor design configurations, i.e., without making substantial modifications of a structural type to the tractor or the users.
The aforementioned purposes are achieved by a method of generating a command signal of the idle speed value for a combustion engine of a tractor, by a control unit for a tractor, and by a tractor or compact tractor according to the appended independent claims. The claims dependent thereon describe variant preferred embodiments.
The features and advantages of the method, the control unit, and the tractor according to the present invention will be apparent from the following description, given by way of non-limiting example, according to the accompanying figures, in which:

figure 1 shows a flow chart of part of the method according to an embodiment of the present invention;
figure 1a shows a flow chart of part of the method according to a variant embodiment of the present invention;
figure 2 shows a chart of the function which binds a first engine idle speed value Eic1 as a function of the cooling fluid temperature signal Tc, according to an embodiment of the method according to the present invention;
figure 3 illustrates a chart of the function which binds a second engine idle speed value Eio1 relative to the transmission fluid temperature signal value To, according to an embodiment of the method according to the present invention;
figure 4 shows a flow chart of part of the method according to an embodiment of the present invention;
figure 4a shows a flow chart of part of the method according to a variant embodiment of the present invention;
figure 5 illustrates a chart of the function which binds a third engine idle speed value EiV1 as a function of the tractor speed signal Vtr, according to an embodiment of the method according to the present invention;
figure 6 illustrates a chart of the function which binds a fourth engine idle speed value Eiθ as a function of the steering wheel angular velocity signal dθ/dt, according to an embodiment of the method according to the present invention;
figure 7 illustrates a chart of the function which binds a fourth engine idle speed value Eiθ relative to the tractor speed signal values Vtr, once a determined steering wheel angular velocity threshold value dθth has been exceeded, according to an embodiment of the method according to the present invention;
figure 8 shows from the top down, a chart as a function of time of the hydraulic distributor activation command DcomON, a chart as a function of time of the hydraulic fluid flow delivery signal Df to the hydraulic distributor, and a chart of the fifth engine idle speed value Eihd as a function of time, according to an embodiment of the present invention;
figure 9 shows a chart of the sixth idle engine speed value Eipto as a function of time, in the case of activation of the power take-off command, according to an embodiment of the present invention;
figure 10 diagrammatically shows a tractor control unit and respective control unit input and output signals, according to an embodiment of the present invention.

The present invention thus relates to a tractor, e.g., such as an agricultural tractor, an earthmoving machine, or an off-highway machine, e.g., for plowing, or material loading-unloading actions. Furthermore, the present invention relates to a compact tractor, typically of more compact size than the tractor.
The tractor or compact tractor according to the present invention (not shown in the accompanying figures) are understood to be equipped with all the mechanical and electrical components typical of the above-mentioned types of tractors, which will therefore not be listed for simplicity and clarity of presentation, but which are understood to be included in the present discussion, since they are known to the person skilled in the art.
Furthermore, a compact tractor or equivalent vehicle will also be equivalently understood when referring to a tractor.
In particular, for the purposes of the present invention, the tractor according to the present invention comprises a transmission fluid temperature sensor suitable for detecting the temperature of the transmission fluid of the tractor transmission group.
Furthermore, the tractor further comprises a cooling fluid temperature sensor adapted to detect the temperature of the cooling fluid of the engine of the tractor.
Additionally, the tractor comprises a tractor speed sensor adapted to detect the linear movement speed of the tractor and a control unit operatively connected to at least the transmission fluid temperature sensor, the cooling fluid temperature sensor, and the tractor speed sensor.
The tractor control unit is also an object of the present invention. Such a control unit comprises:

a first electrical connection suitable for receiving a transmission fluid temperature signal To related to the temperature of the transmission fluid of the transmission group of the tractor;
a second electrical connection suitable for receiving a cooling fluid temperature signal Tc which is related to the temperature of the cooling fluid of the engine of the tractor;
a third electrical connection suitable for receiving a tractor speed signal Vtr on the control unit, related to the linear movement speed of the tractor;
a fourth electrical connection suitable for sending a command signal Ei for the idle speed value for the combustion engine of the tractor.

Furthermore, the control unit comprises a processor operatively connected to aforesaid first, second, third, and fourth electrical connections and appropriate storage means.
In particular, said processor is configured to execute the steps of the method which will be described in the remainder of the present description, in particular at least steps d1) to e) which will be mentioned below or in any case all the steps which will be mentioned below and which are suitable for being executed on the processor.
In the remainder of this discussion, the term "select" will refer to an operation of selecting and storing a value by the processor in a processor volatile memory or storage means, to be successively used to generate an appropriate signal to the engine speed management system.
The present invention thus also relates to a method for generating a command signal Ei for the idle speed value for a combustion engine of a tractor. Such a command signal Ei is thus intended to determine the engine idle speed.
The aforesaid method comprises the steps of:

a) providing the control unit comprising the processor;
b) receiving the transmission fluid temperature signal To which is related to the temperature of the transmission fluid of the transmission group of the tractor, and receiving the cooling fluid temperature signal Tc which is related to the temperature of the cooling fluid of the engine of the tractor;
c) receiving the tractor speed signal Vtr on the control unit.

Figure 2 illustrates an exemplary chart of the function which binds a first engine idle speed value Eic1 relative to the transmission fluid temperature signal value Tc.
Such a method further provides that step d1) is executed on the processor, which firstly provides receiving the cooling fluid temperature signal Tc, and if the cooling fluid temperature signal Tc is lower than a cooling fluid temperature threshold Tcth, a first idle engine speed value Eic1 is selected as a function of the cooling fluid temperature signal Tc.
Figure 3 illustrates an exemplary chart of the function which binds a second engine idle speed value Eio1 relative to the transmission fluid temperature signal values To.
The method further provides that step d2) is executed on the processor, which provides receiving the transmission fluid temperature signal To, and successively if the transmission fluid temperature signal To is lower than a transmission fluid temperature threshold Toth, a second idle engine speed value Eio1 is selected as a function of the transmission fluid temperature signal To.
In particular, figure 5 illustrates an exemplary chart of the function which binds a third engine idle speed value EiV1 relative to the tractor speed signal values Vtr.
Additionally, the method of the present invention provides executing step d3) on the processor, which firstly provides identifying whether the tractor speed signal Vtr is not zero, and, in the affirmative case, selecting a third engine idle speed value EiV1 as a function of the value of the tractor speed signal Vtr.
Once having executed the steps d1, d2 and d3, the method further comprises the step e), which provides calculating the desired idle speed value Eid as a function of the first Eid, the second Eio1, and the third idle speed value EiV1.
It is apparent that both the first engine idle speed value Eic1, the second engine idle speed value Eio1, and the third engine idle speed value EiV1 are all higher than a nominal idle engine speed Ein of the combustion engine. Preferably, such an idle speed nominal value Ein is comprised between 700 and 850 rpm, generally 800. Thus, for example, the first engine idle speed value Eic1, the second engine idle speed value Eio1, the third engine idle speed value EiV1, are each at least equal to 900 or 1000 rpm.
Step f) of the method is executed on the control, unit, which provides generating a command signal Ei for the engine idle speed value as a function of the desired idle speed value Eid calculated on the processor in step e) .
By virtue of the aforesaid steps of the method, the effect of raising the engine idle speed is achieved when a higher power demand of the engine is expected, such as when the cooling fluid or the transmission fluid is still cold (e.g., in the winter) and their increased viscosity, due to temperature, requires higher engine efforts. Similarly, the method allows to raise the engine idle speed in the starting phase, at low tractor forward speeds. This ensures that the engine responds promptly, only when required, and avoids engine stalling. In particular, this occurs in a synergistic and controlled manner depending on a plurality of parameters (cooling fluid temperature, transmission fluid, and tractor speed).
According to the invention, such a desired idle speed value Eid is calculated as the maximum value between the first Eic1, the second Eio1, and the third idle speed value EiV1.
Preferably, the processing of the desired engine idle speed value Eid to obtain a command signal Ei of the engine idle speed value is, for example, an electrical or electro-mechanical or electro-hydraulic conversion or a level conversion, to adapt it to the reception by the engine.
Figure 1 shows a flow chart of an embodiment of the method, comprising the aforesaid steps of d1 and d2. In particular, in this embodiment, first of all, the method comprises checking whether the running engine is still warming up. In particular, if an engine start time (engine ON) greater than a predetermined warm-up time (tWU) has elapsed, the method provides checking whether the cooling fluid temperature signal Tc is lower than the transmission fluid temperature signal To. In other words, in this variant, the method provides that the cooling fluid temperature threshold Tcth is equal to the detected value of the transmission fluid temperature signal To. Thus, if Tc < To, the method provides generating the first idle engine speed value Eic1 as a function of the cooling fluid temperature signal Tc (Eid=f(Tc)). Conversely, if To < Tc, i.e., if the transmission fluid temperature threshold Toth is equal to the detected cooling fluid temperature signal value Tc, the method provides generating the second idle engine speed value Eio1 as a function of the transmission fluid temperature signal To (Eid=f(To)).
According to a variant embodiment of the method, the first engine idle speed value Eic1 is constant for a determined range of cooling fluid temperature values Tc below the cooling fluid temperature threshold Tcth, while it assumes a value proportional to the value of the cooling fluid temperature signal Tc above the cooling fluid temperature threshold Tcth, e.g., shown in figure 2.
Preferably, the second idle engine speed value Eio1 is constant for a determined range of transmission fluid temperature values To below the transmission fluid temperature threshold Toth, while it assumes a value proportional to the value of the transmission fluid temperature signal To above the transmission fluid temperature threshold Toth, e.g., as shown in figure 3.
Preferably, for both the transmission fluid temperature signal To and the cooling fluid temperature signal Tc, above a respective predetermined temperature threshold Tcth2, Toth2, the first Eic1, and the second idle speed value Eio1 are each equal to the nominal engine idle speed Ein.
Figure 4 shows a flow chart of an embodiment of the method, comprising the aforesaid step d3 of the method. In particular, in this embodiment, first of all, the method provides checking within a determined time interval ts (counter < ts) whether the status of the movement command activated by an operator for moving the tractor is in neutral, braked, or detached clutch status for at least a determined percentage threshold higher than 50% (i.e., clutch pedal pressed for a determined percentage threshold), e.g., for at least 90%. If the movement command status is in either neutral, braked, or clutch disengaged condition for at least a specified percentage threshold, the method provides generating the third engine idle speed value EiV1 equal to the nominal idle engine speed value Ein. If, on the other hand, the movement command status is neither neutral, nor braked, nor with the clutch detached for at least a determined percentage threshold, e.g., greater than 90%, the method provides generating the third engine idle speed value EiV1 as a function of the tractor speed signal Vtr.
According to a variant embodiment of the method, the third engine idle speed value EiV1 is constant for a determined range of tractor speed signal values Vtr below the tractor speed threshold Vth, while it assumes a value proportional to the value of the tractor speed signal Vtr above the tractor speed threshold Vth, e.g., shown in figure 5.
Preferably, above a second predetermined tractor speed threshold Vth2, the third idle speed value EiV1 is equal to the nominal idle engine speed Ein.
The checking of the movement command status (neutral, braked, with the clutch disengaged) allows the engine idle speed value to be varied only when necessary, i.e., when the tractor starts moving, while it allows the nominal idle speed to be maintained when the tractor is stationary in neutral or braked.
With reference to figures 6 and 7, an embodiment of the method provides in particular:
c1) receiving or calculating an angular position signal θ of a steering wheel of the tractor and/or an angular velocity signal dθ/dt of a steering wheel of the tractor;
on the processor:
d4) after receiving or calculating the angular velocity signal of the steering wheel dθ/dt, if the angular velocity signal of the steering wheel is higher than a steering wheel angular velocity threshold value dθth, selecting a fourth idle speed value Eiθ as a function of the tractor speed signal Vtr, said fourth idle speed value Eiθ being higher than a nominal idle speed value Ein. In this variant, in step e) of the method, calculating the desired idle speed value Eid is as a function of the first Eid, the second Eio1, the third EiV1, and also the fourth idle speed value Eiθ.
The effect of step d4 of the method is to be able to raise the idle engine speed as a function of the angular velocity of the steering wheel, i.e., how quickly the operator moves the steering wheel. This is useful because the higher the angular velocity of the steering wheel, the greater the demand for fluid flow from the hydraulic steering wheel system on the tractor. Again in this case, a greater hydraulic fluid flow for hydraulic steering requires more dynamic effort from the engine in a short time interval.
Preferably, the angular velocity signal dθ/dt is calculated on the processor by deriving the angular position signal.
According to an embodiment, the tractor further comprises an electronic command which allows to double the displacement of the hydraulic steering system, i.e., allows to double the steering angle, the number of steering wheel turns being the same. This results in a doubling of the hydraulic fluid movement of the steering system. In this variant, the method provides that if the electronic command which allows to double the displacement of the hydraulic steering wheel system is active, the fourth engine idle speed value Eiθ is always constant and higher than the nominal idle engine speed value Ein, regardless of the angular steering wheel speed value dθ/dt.
With reference to figure 8, according to a further embodiment, the method further comprises the steps of:
c2) detecting a command signal for hydraulic distributor activation DcomON, which is related to the activation of a distributor command that is made by an operator of the tractor;
on the processor:
d5) selecting a predetermined fifth idle speed value Eihd, said fifth idle speed value Eihd being higher than a nominal idle speed value Ein. In this variant, in step e), calculating the desired idle speed value Eid is as a function of the first Eid, the second Eio1, the third EiV1, and the fifth idle speed value Eihd.
Preferably, in this variant, after step f), the method provides waiting for a predetermined time interval Δt1 before sending a signal for supplying the flow of hydraulic fluid Df to the hydraulic distributor.
Step d5) of the method and the waiting for a predetermined time Δt1 are particularly effective in the case of activation of tractor hydraulic distributors (users) of the on-off type. In this case, indeed, the effect is obtained of increasing the idle engine speed in a predictive manner, i.e., in advance of the command to activate the hydraulic fluid flow to operate the hydraulic distributor. Again, the effect is to compensate in advance for a request for more power and dynamics to the engine, only at the time of need, avoiding a potential engine stalling.
With reference to figure 9, according to a further embodiment, the method comprises the steps of:
c3) detecting a command signal for power takeoff activation PTOcomm, which is related to the activation of a command for the power takeoff that is made by an operator of the tractor;
on the processor:
d6) after step c3), selecting a sixth idle speed Eipto, said sixth idle speed value Eipto being higher than a nominal idle speed value Ein. In this variant, in step e), calculating the desired idle speed value Eid is as a function of the first Eid, the second Eio1, the third EiV1, and the sixth idle speed value Eipto.
Preferably, in this variant, after step f), the method involves waiting for a third predetermined time interval Δt3 before sending a signal for coupling the clutch of the power takeoff (Clutch_on).
Power take-off preferably means the typical power take-off generally located at the rear of the tractor with a power take-off shaft connected to the drive shaft by an on-off or proportional clutch.
Again in this case, step d6) of the method and the waiting for a third interval of time Δt3 are particularly effective in the case of activation of tractor power takeoffs of the on-off type. In this case, indeed, the effect is to increase the engine idle speed in a predictive manner, i.e., in advance of the clutch activation command for coupling the power takeoff to the drive shaft. Again, the effect is to compensate in advance for a request for more power and dynamics to the engine, only at the time of need, avoiding a potential engine stalling.
According to a further embodiment of the method, it is provided to:
c4) detecting a command signal for compressor activation for a cabin air conditioning system, which signal is related to starting the compressor of the air conditioning system of the cabin of the tractor;
on the processor:
d7) after step c3), selecting a predetermined seventh idle speed value, said seventh idle speed value being higher than a nominal idle speed value Ein. In this variant, in step e), calculating the desired idle speed value Eid is as a function of the first Eic1, the second Eio1, the third EiV1, and the seventh idle speed value.
The effect obtained in this case is a preventive increase in engine speed in a preferably constant manner, in the case of operation of the cabin air conditioning system, in particular the air conditioning compressor.
It is apparent that a preferred variant of the method provides that in step e), calculating the desired idle speed value Eid is dependent on the first Eic1, the second Eio1, the third EiV1, the fourth Eiθ, the fifth Eihd, and the sixth idle speed value Eipto. For example, it is preferably the maximum between the first Eic1, the second Eio1, the third EiV1, the fourth Eiθ, the fifth Eihd, and the sixth idle engine speed value Eipto.
Furthermore, according to a preferred embodiment, the method provides that, in step e), the calculation of the desired engine idle speed value Eid is as a function of the first Eid, the second Eio1, the third EiV1, the fourth Eiθ, the fifth Eihd, and the sixth Eipto and the seventh engine idle speed value. For example, it is preferably the maximum among them.
According to any one of the variants of the method described heretofore or otherwise a preferred variant of the present invention, the method further comprises the step of sending a transmission group command signal St to a tractor electronic transmission group control unit to vary the transmission ratio of the transmission group so that the speed of the tractor is maintained unchanged as a result of the change in engine speed determined by the command signal (Ei) of the engine idle speed value.
Particularly in this variant, the tractor should preferably include a continuously variable transmission (CVT) group. In this manner, the transmission group command signal can operate continuously on the transmission ratio as a function of the command signal (Ei) of the set engine idle speed value. This avoids inadvertent sharp acceleration of the tractor when the clutch is engaged.
An example embodiment of the method according to the embodiment comprising sending the control signal transmission group is shown in figure 1a, as a variant of the method described in figure 1. A further example of the method according to the embodiment comprising sending the control signal transmission group is shown in figure 4a, as a variant of the method in figure 4. In the above variants, after calculating the desired engine idle speed value Eid, or simultaneously or immediately before (or immediately after) sending the command signal Ei of the idle engine speed value, the method comprises generating and sending a transmission unit command signal Str to an electronic control unit of the tractor transmission group, to vary the transmission ratio of the transmission group to maintain the speed of the tractor unchanged following the variation of the desired engine idle speed value Eid, and thus the engine speed determined by the command signal Ei. For example, if the command signal Ei provides an increase in the idle engine speed, the transmission command signal Str will be configured to generate a reduction in the transmission ratio of the tractor transmission. Vice versa, if the command signal Ei provides a decrease in the idle engine speed compared to the current condition, the transmission group command signal Str will be configured to generate an increase in the transmission ratio of the tractor transmission group.
It is understood that, in the present discussion, the words generate or calculate or the like mean the generation or calculation executed on an electronic medium, e.g., by means of an electronic processing unit, such as a processor. For example, such a processor is the processor of the control unit on the tractor.
Furthermore, it is apparent that the tractor electronic control unit preferably either comprises or coincides with the transmission group electronic control unit. If the electronic control unit of the tractor is separate from the electronic control unit of the transmission group, said control units are operationally linked to exchange signals with each other. It is further apparent that the transmission group control unit is operationally connected to the transmission group to determine the variation of the mechanical transmission ratio.
Innovatively, the method of generating a command signal of the idle speed value for a combustion engine of a tractor, the respective control unit, and the tractor comprising such a control unit, a tractor, or a compact tractor allows to achieve the set objectives, i.e., to increase the engine idle speed to prevent it from shutting down and to increase performance, but only in case of actual need to prevent unwanted consumption.
Furthermore, innovatively, the present invention allows to obtain an excellent compromise between minimizing consumption and ensuring performance.
Furthermore, the engine idle speed management obtained by virtue of the method according to the present invention allows to improve the comfort perceived in the passenger compartment by the operator, in terms of NVH.
Advantageously, also when retrofitting (downsizing) engines on existing tractors, the present method allows the same hydraulic actuators and power takeoffs to be used without any technical modifications.
In other words, advantageously, given a global need to reduce emissions and displacements of tractor engines (and thus also engine powers), the method according to the present invention allows to compensate the occasions of request for an increase in performance in a predictive manner, without having to redesign the users, reducing their performances.
Furthermore, advantageously, the method according to the present invention allows to use all the sensors already present as standard on tractors, with no need to modify any electronic control unit or to add particular torque or engine power detection sensors.
Thus, it was advantageously possible to achieve the objects set in a simple, compact, and inexpensive manner both in terms of resources used and final costs.
It is apparent that a person skilled in the art may make changes to the invention described above, all of which are contained within the scope of protection as defined in the following claims to satisfy contingent needs.

Claims

Method for generating a command signal (Ei) for the value of idle speed for a combustion engine of a tractor, said method comprising the steps of:
a) providing a control unit comprising a processor;

b) receiving a transmission fluid temperature signal (To) which is related to the temperature of the transmission fluid of the transmission group of the tractor, and receiving a cooling fluid temperature signal (Tc) which is related to the temperature of the cooling fluid of the engine of the tractor;

c) receiving a tractor speed signal (Vtr) on the control unit, said tractor speed signal (Vtr) relating to the speed of linear movement of the tractor;
on the processor:
d1) after receiving the cooling fluid temperature signal (Tc), if the cooling fluid temperature signal (Tc) is lower than a cooling fluid temperature threshold (Tcth), selecting a first value of idle speed (Eic1) as a function of the cooling fluid temperature signal (Tc), said first value of idle speed (Eic1) being greater than a nominal idle speed value (Ein) of the combustion engine;

d2) after receiving the transmission fluid temperature signal (To), if the transmission fluid temperature signal (To) is less than a transmission fluid temperature threshold (Toth), selecting a second idle speed value (Eio1) as a function of the transmission fluid temperature signal (To), said second idle speed value (Eio1) being greater than the nominal idle speed value (Ein);

d3) if the tractor speed signal (Vtr) is not zero, selecting a third idle speed value (EiV1) as a function of the value of the tractor speed signal (Vtr), said third idle speed value (Eic1) being greater than the nominal idle speed value (Ein) of the combustion engine;

e) calculating the desired idle speed value (Eid) as the maximum value between the first (Eic1), the second (Eio1) and the third idle speed value (EiV1);

on said control unit:

f) generating a command signal (Ei) for the idle speed value for the engine as a function of the desired idle speed value (Eid) calculated on the processor in step e).
Method according to claim 1, further comprising the step of:
c1) receiving or calculating an angular position signal (θ) of a steering wheel of the tractor and/or an angular velocity signal (dθ/dt) of a steering wheel of the tractor; on the processor:
d4) after receiving or calculating the angular velocity signal of the steering wheel (dθ/dt), if the angular velocity signal of the steering wheel is greater than a steering wheel angular velocity threshold value (dθth), selecting a fourth idle speed value (Eiθ) as a function of the tractor speed signal (Vtr), said fourth idle speed value (Eiθ) being greater than a nominal idle speed value (Ein);

wherein, in step e), calculating the desired idle speed value (Eid) is a function of the first, the second, the third and the fourth idle speed value.
Method according to any of the preceding claims, further comprising the step of:
c2) detecting a command signal for hydraulic distributor activation (DcomON), which is related to the activation of a distributor command that is made by an operator of the tractor;

on the processor:
d5) selecting a predetermined fifth idle speed value (Eihd), said fifth idle speed value (Eihd) being greater than a nominal idle speed value (Ein);

and wherein, in step e), calculating the desired idle speed value (Eid) is a function of the first (Eic1), the second (Eiol), the third (EiV1) and the fifth idle speed value (Eihd) .
Method according to claim 3, wherein, after step f), the method involves waiting for a predetermined time interval (Δt1) before sending a signal for supplying the flow of hydraulic fluid (Df) to the hydraulic distributor.
Method according to any of the preceding claims, further comprising the step of:
c3) detecting a command signal for power takeoff activation (PTOcomm), which is related to the activation of a command for the power takeoff that is made by an operator of the tractor;

on the processor:
d6) after step c3), selecting a sixth idle speed (Eipto), said sixth idle speed value (Eipto) being greater than a nominal idle speed value (Ein);

and wherein, in step e), calculating the desired idle speed value (Eid) is a function of the first (Eic1), the second (Eiol), the third (EiV1) and the sixth idle speed value (Eipto) .
Method according to claim 5, wherein, after step f), the method involves waiting for a third predetermined time interval (Δt3) before sending a signal for coupling the clutch of the power takeoff (Clutch_on).
Method according to any of the preceding claims, further comprising the step of:
c4) detecting a command signal for compressor activation for a cabin air conditioning system, which signal is related to starting the compressor of the air conditioning system of the cabin of the tractor;

on the processor:
d7) after step c3), selecting a predetermined seventh idle speed value, said seventh idle speed value being greater than a nominal idle speed value (Ein);

and wherein, in step e), calculating the desired idle speed value (Eid) is a function of the first (Eic1), the second (Eiol), the third (EiV1) and the seventh idle speed value.
Method according to any one of claims 1 to 2, 3, 5 wherein, in step e), calculating the desired idle speed value (Eid) is dependent on the first (Eic1), the second (Eiol), the third (EiV1), the fourth (Eiθ), the fifth (Eihd) and the sixth idle speed value (Eipto).
Method according to any one of the preceding claims, further comprising the step of:
sending a transmission group control signal to an electronic control unit of the transmission group of the tractor, said control signal being configured to vary the transmission ratio of the transmission group so as to keep the speed of the tractor unvaried after the variation in the idle speed for the motor determined by the command signal (Ei) of the idle speed for the engine.
Control unit for a tractor, comprising
- a first electrical connection suitable for receiving a transmission fluid temperature signal (To) which is related to the temperature of the transmission fluid of the transmission group of the tractor;

- a second electrical connection suitable for receiving a cooling fluid temperature signal (Tc) which is related to the temperature of the cooling fluid of the engine of the tractor;

- a third electrical connection suitable for receiving a tractor speed signal (Vtr) on the control unit, said tractor speed signal (Vtr) relating to the speed of linear movement of the tractor;

- a fourth electrical connection suitable for sending a command signal (Ei) for the idle speed value for the engine;

- a processor operatively connected to said first, second, third and fourth electrical connections and to storage means;
said processor being configured to execute the steps from b), c), d1), d2), d3), e) and f) of the method according to claim 1.
Tractor, comprising:
- a transmission fluid temperature sensor suitable for detecting the temperature of the transmission fluid (To) of the transmission group of the tractor;

- a cooling fluid temperature sensor suitable for detecting the temperature of the cooling fluid (Tc) of the engine of the tractor;

- a tractor speed sensor suitable for detecting the speed of linear movement (Vtr) of the tractor;

- a control unit according to claim 10 which is operatively connected to the transmission fluid temperature sensor, the cooling fluid temperature sensor and the tractor speed sensor.
Computer implemented program comprising coding instructions suitable for implementing the steps from b), c), d1), d2), d3), e) and f) of claim 1 when said program is executed on the control unit according to claim 10.