METHOD FOR CONTROLLING A CONTINUOUSLY VARIABLE TRANSMISSION AND CONTINUOUSLY VARIABLE TRANSMISSION

Abstract

METHOD FOR CONTROLLING A CONTINUOUSLY VARIABLE TRANSMISSION AND CONTINUOUSLY VARIABLE TRANSMISSION. The method of the invention is a method for controlling a slip-free CVT curve comprising a ring wheel (1), a set of planetary wheels (3) and a sun wheel (2), wherein the ring wheel and the sun wheel are fastened together. As in the CVT curves of the prior art, the perpendicular forces (NR, NZ) between the ring wheel and the sun wheel, on the one hand, and the planetary wheels, on the other hand, are well defined when the transmission ratio is constant, i.e., when the rotation angle (8) of the planetary wheels is constant. The perpendicular forces for a constant ratio are called the static values ​​of the perpendicular forces.The method is configured so that during a continuous increase or decrease in the transmission ratio, any force component added to the static values ​​of the first and / or second perpendicular force is either zero or less than a predefined force component that is necessary to maintain a micro-slip condition of the rolling contacts between the planetary gears (3) and the ring and sun gears (1, 2). This force control is applied independently of the speed of the ratio change. A transmission according to the invention is equipped with a control system suitable for implementing the method.

Description

1 / 22 “METHOD FOR CONTROLLING A CONTINUOUSLY VARIABLE TRANSMISSION AND CONTINUOUSLY VARIABLE TRANSMISSION” Field of invention

[0001] The present invention relates to variable transmissions for driving road vehicles, off-road vehicles, agricultural machinery, or for driving auxiliaries in vehicles, as well as industrial components such as generators and compressors in stationary or mobile equipment. The invention relates, in particular, to a control method for a continuously variable transmission (CVT), which utilizes the drill-free rolling of a set of planetary gears on the surfaces of a ring wheel and a sun wheel, whose rolling surfaces are designed according to a specific curve that allows for drill-free rolling. In the present description, the term 'CVT-curve' will be applied to this specific type of transmission. Drill-free rolling means that there is only a small micro-slippage in the torque-transmitting rolling contacts of the drive wheels.Documents WO2009 / 146748A1 and WO2017 / 174106 show examples of this type of transmission. Prior Art.

[0002] The CVT-curve is a type of continuously variable transmission that includes one or more variators as shown in Figure 1 and Figure 2, comprising a ring wheel 1, one or more planetary wheels 3 and a sun wheel 2. The planetary wheels 3 are mounted so as to be freely articulated around their respective joints 5 with respect to a common support ring (not shown) which in the embodiment shown is connected to a housing of Petition 870220089642, dated 09 / 30 / 2022, page 8 / 39 2 / 22 transmission (not shown). The ring wheel 1 and the sun wheel rotate around a common central geometric axis 4.

[0003] The ring, sun and planetary wheels are called drive wheels and are configured to transmit rotation from an input shaft (not shown) connected to ring wheel 1, to the rotation of an output shaft (not shown) connected to sun wheel 2.

[0004] To transmit torque by traction between ring wheel 1 and planetary wheels 3 and between planetary wheels 3 and sun wheel 2, a minimum clamping force NR and NZ is required respectively. These forces are acting perpendicularly in the tangent plane at the contact point 6 between ring wheel 1 and planetary wheel 3 and in the tangent plane at the contact point 7 between planetary wheel 3 and sun wheel 2 respectively. When applying a drive torque to ring wheel 1, sun wheel 2 will be driven with a certain ratio depending on the angle of inclination 8 between the geometric axis of rotation of the planetary wheel and the perpendicular in the common geometric axis of rotation 4 of ring wheel 1 and sun wheel 2. The torques on ring wheel 1 and sun wheel 2 induce traction forces at points 6 and 7 respectively. These traction forces are oriented perpendicularly in the plane of the figure.

[0005] This type of CVT-curve is traditionally controlled by a control system that ensures the maintenance of micro-slip under any steady-state operating condition of the transmission in terms of input shaft speed, transmitted torque, and transmission ratio. In other words, the control system applies values Petition 870220089642, dated 09 / 30 / 2022, page 9 / 39 3 / 22 predefined forces NR and NZ as a function of the working conditions above: when the transmission operates at a given input speed and torque and at a given constant ratio, the predefined forces NR and NZ are applied which ensure that rolling within the micro-slip occurs. As these forces are defined when the ratio is constant, they are henceforth referred to as static clamping forces.

[0006] With reference to Figure 2, when the transmission is transmitting power and its ratio is increasing or decreasing, the tilt angle 8 is varying which also induces transverse forces TR and TZ acting perpendicularly on the traction forces and clamping forces at the contact points 6 and 7. When the transmission ratio is changing, the drive wheels are forced to roll over a variable rolling diameter, inducing transverse slippage at the rolling contacts.Due to this transverse slippage, the rolling drive wheels slide perpendicularly in the rolling direction. The transverse slippage is parallel to the TR and TZ forces shown in Figure 2, while the longitudinal slippage is oriented perpendicular to the plane of the cross-section.

[0007] To maintain micro-slippage conditions during gear ratio changes, currently known control systems augment the static clamping forces NR and NZ with a dynamic force component during the gear ratio change. This is illustrated in Figure 2, which shows the effect of a rapid gear ratio change on the forces. It is observed that the perpendicular forces NR and NZ are greater than the static values. The dynamic force component depends on the speed of the gear ratio change. In other words, during. Petition 870220089642, dated 09 / 30 / 2022, page 10 / 39 4 / 22 When changing the gear ratio, greater clamping forces are applied compared to the static clamping forces applicable for a constant ratio. The dynamic clamping force is only a small percentage of the static clamping force for low and medium gear change speeds, but the dynamic clamping force becomes significant for faster gear changes. Although such very rapid changes occur rarely, the mechanical design and controls must be designed for them anyway, as a very rapid gear change may also be demanded at the maximum torque capacity of the transmission.

[0008] The most common control systems applied to control a CVT-curve use hydraulic power. In the embodiment shown in Figure 1, a stationary cylinder 12 with a hydraulic piston 10 inside it is pushing a thrust bearing (not shown) against the ring wheel 1 and, similarly, another piston 11 in a stationary cylinder 13 is pushing against the sun wheel 2 so that both pistons push the drive wheels together under the influence of hydraulic pressures p1 and p2. The pistons are axially movable under the influence of a hydraulic fluid flowing through the feed lines 14 and 15. By means of these 2 pistons the transmission can be fully controlled, the clamping forces and the tilt angle can be controlled independently. The connection of the input and output shafts to, respectively, the ring wheel and the sun wheel is not shown in detail in the drawings.This connection can, for example, be made by a sliding grooved connection, known as such in the state of the art. Petition 870220089642, dated 09 / 30 / 2022, page 11 / 39 5 / 22 and therefore not described here in detail.

[0009] A gear ratio change is achieved by axially displacing the pistons, which is done by actuating a controlled flow in one cylinder and simultaneously out of the other cylinder, while continuously controlling the pressures p1 and p2 throughout the gear ratio change. The control can be achieved through one or more control circuits, involving pressure sensors and / or displacement sensors, so that the contact forces NR and NZ are controlled at multiple instants throughout the gear ratio change, according to predefined target values. The contact forces NR and NZ are controlled based on an algorithm implemented in the control system and known as such, which takes into account the transmitted torque, the shaft speeds, and the gear ratio change rate.

[00010] The more torque is transmitted, the greater the pressure on hydraulic pistons 10 and 11. The construction of the transmission parts and hydraulic components must be strong enough to withstand these pressures. An increase in pressure due to dynamic clamping forces is therefore a disadvantage, especially during rapid gear changes.

[00011] Pressure control is generally achieved by a pump driven directly by the vehicle's engine or by an electric motor. The pump pressure is regulated to a fixed or variable pressure, so that the pressure is at least as high as the maximum of all hydraulic actuation requirements. The pressure for each actuating piston is regulated by a proportional pressure reducing valve, controlled by an electric solenoid. When the volume in a Petition 870220089642, dated 09 / 30 / 2022, page 12 / 39 6 / 22 actuating cylinder 12 or 13 increases, the solenoid feeds the flow into this cylinder, consuming hydraulic energy from the pump. When the oil volume in an actuating cylinder decreases, the solenoid drains the oil to the transmission sump, dissipating energy. However, solenoid-operated valves cause a significant pressure drop when feeding or draining a high flow, which needs to be compensated for by ensuring a higher pump pressure. This pressure drop makes solenoid-operated control systems particularly inefficient in providing the dynamic clamping forces required by the control method described above, especially in the case of rapid gear changes. Solenoids are also vulnerable to dirt in the hydraulic oil. Small particles of dirt can cause a solenoid to seize, so that the actual pressure does not match the requested pressure.Furthermore, the solenoids are mounted in a hydraulic block, which requires precise and expensive machining. Summary of the invention

[00012] The invention aims to control a slip-free CVT curve without requiring excessive pressure increases during rapid ratio changes. This objective is achieved by the method for controlling a CVT curve according to the appended claims, and by a CVT curve including a control system according to the invention. The method of the invention is a method for controlling a slip-free CVT curve comprising a ring wheel, a set of planetary wheels and a sun wheel, wherein the ring wheel, planetary wheel and sun wheel are fastened together. The perpendicular forces for constant ratio are called Petition 870220089642, dated 09 / 30 / 2022, page 13 / 39 7 / 22 Static values ​​of perpendicular forces. As in the CVTscurve of the prior art, the static values ​​of the perpendicular forces between the ring wheel and the sun wheel, on the one hand, and the planetary wheels, on the other hand, are well defined when the transmission ratio is constant, i.e., when the angle of rotation of the planetary wheels is constant. The method is configured so that during a continuous increase or decrease in the transmission ratio, any force component added to the static values ​​of the first and / or second perpendicular force is either zero or less than a predefined force component that is necessary to maintain a micro-slip condition of the rolling contacts between the planetary wheels and the ring and sun wheels. This force control is applied independently of the rate of change of the ratio.

[00013] The invention relates, in particular, to a method for controlling a continuously variable transmission comprising an input shaft and an output shaft being rotatably arranged around a common central geometric axis of rotation, a ring wheel and a sun wheel being coaxially arranged with respect to the central geometric axis, and at least one set of rotatable planetary wheels, the angle of rotation of the planetary wheels determining the transmission ratio of the transmission, wherein: The transmission works through the free-slip rolling of the planetary wheels on the surfaces of the ring wheel and sun wheel, regardless of the angle of rotation of the planetary wheels. The ring wheel, the planetary wheels, and the sun wheel are fastened together so that the ring wheel exerts a primary influence. Petition 870220089642, dated 09 / 30 / 2022, page 14 / 39 8 / 22 perpendicular force (NR) on any given planetary wheel, and the sun wheel exerts a second perpendicular force (NZ) on said planetary wheel, The method is configured to control the aforementioned first and second perpendicular forces NR, NZ, so that when the transmission operates at a given input speed, a given transmitted torque, and a given constant transmission ratio, a predefined static value of the first and second perpendicular forces are applied, and a micro-slip condition is applied to the rolling contacts between the planetary gears and the ring gear and sun wheel, characterized by: - During a continuous increase or decrease in the angle of rotation and therefore in the transmission ratio, any force component added to the static values ​​of the first and / or second perpendicular force is either zero or less than a predefined force component that is required to maintain the micro-slip condition.

[00014] According to one embodiment, during the increase or decrease of the transmission ratio, one of the perpendicular forces is maintained at the static value while the other is controlled to overcome the tangential reaction forces generated by the change in the angle of rotation.

[00015] According to one embodiment, the ring wheel and the sun wheel are fixed together under the direct or indirect influence of a first and second hydraulic pressure.

[00016] The aforementioned hydraulic pressures can act directly on the respective hydraulic pistons, configured to move axially in the direction of the central geometric axis, and the ring wheel and sun wheel are fixed Petition 870220089642, dated 09 / 30 / 2022, page 15 / 39 9 / 22 to the respective pistons.

[00017] The invention is also related to a continuously variable transmission comprising an input shaft and an output shaft being rotatably arranged around a common central geometric axis of rotation, one or more sets of a ring wheel, a sun wheel being arranged coaxially with respect to the central geometric axis and a set of rotatable planetary wheels, the angle of rotation of the planetary wheels determining the transmission ratio of the transmission, wherein the transmission operates by means of the free-slip rolling of the planetary wheels on the surfaces of the ring wheel and the sun wheel, independently of the angle of rotation of the planetary wheels, wherein the ring wheel and the sun wheel are fastened together so that the ring wheel exerts a first perpendicular force (NR) on any planetary wheel and the sun wheel exerts a second perpendicular force (NZ) on said planetary wheel,characterized in that the transmission comprises a control system configured to control the transmission according to the method of the invention.

[00018] According to one embodiment, the said control system is a hydraulic control system. In the latter case, the transmission can be regulated by a first and a second hydraulic pressure exerted on a first and second hydraulic cylinder by a hydraulic fluid, said pressures acting to lock the ring wheel and the sun wheel together.

[00019] According to one embodiment, the first and second pressures act directly on the respective first and second pistons which are movable within the said first Petition 870220089642, dated 09 / 30 / 2022, page 16 / 39 10 / 22 and second cylinders.

[00020] The aforementioned control system may comprise a first and second motor-pump set, each set comprising a hydraulic pump coupled to an electric motor, said sets being configured to control said first and second pressures in the respective cylinders.

[00021] According to one embodiment, the pump outlet port of one motor-pump assembly is connected to the pump inlet port of the other motor-pump assembly.

[00022] According to one embodiment, the pumps in the motor-pump sets can act as hydraulic motors, and the electric motors in the motor-pump sets can act as generators. Brief description of the figures.

[00023] Figure 1 illustrates the perpendicular forces acting on the drive wheels of a slip-free CVT-curve when the transmission is operating at a constant gear ratio.

[00024] Figure 2 illustrates the forces applied by the control systems of the prior art when the transmission ratio changes at a given rate of change.

[00025] Figure 3 gives an example of the forces applied according to the method of the invention when the transmission ratio changes at a comparable speed as in the case of Figure 2.

[00026] Figure 4 shows a hydraulic control system for controlling a slip-free CVT-curve according to a preferred embodiment of the invention. Petition 870220089642, dated 09 / 30 / 2022, page 17 / 39 11 / 22

[00027] Figure 5 shows a hydraulic control system for controlling a slip-free CVT curve according to an alternative embodiment of the invention. Detailed description of the invention.

[00028] Figure 1 illustrates the basic components described above of a slip-free CVT-curve as known from document WO2017 / 174106 and controlled by hydraulic pressures p1 and p2 acting by means of a piston and a thrust bearing, respectively, on the ring wheel 1 and the sun wheel 2. Other alternatives are possible, in which the ring wheel 1, or the sun wheel 2, is stationary, and the structure to which the joints 5 are coupled is either a central geometric axis or a circumferential ring, being axially movable. The invention is also applicable to these embodiments. However, the invention will be explained based on the embodiment shown in Figure 1, in which the ring wheel 1 and the sun wheel 2 are rotatable and axially movable, and the joints 5 are stationary.

[00029] As indicated in the introduction, Figure 1 shows the perpendicular forces NR and NZ when the transmission is operating at a constant gear ratio. These clamping forces NR and NZ are 'perpendicular' forces in the sense that they are acting perpendicularly in the tangent plane at the contact point 6 between ring wheel 1 and planet wheel 3 and in the tangent plane at the contact point 7 between planet wheel 3 and sun wheel 2. When a drive torque is applied to ring wheel 1, sun wheel 2 is driven with a certain ratio depending on the tilt angle 8 of the planet wheels 3. The torques on ring wheel 1 and sun wheel 2 induce pull forces at the contact points 6 and Petition 870220089642, dated 09 / 30 / 2022, page 18 / 39 12 / 22 7. These traction forces are oriented perpendicularly in the plane of the design. Since the transmission operates without slippage, there is only a small micro-slip in the torque transmission rolling contacts of the drive wheels. Typically, such micro-slip is between 0.1 and 0.3%. Due to the traction forces, this micro-slip is tangential slippage, therefore, the slippage occurs parallel to the rolling direction.

[00030] In the scientific literature on contact mechanics of rolling bodies, microslip is described as follows: 2 three-dimensional bodies roll against each other and are loaded by a perpendicular force at their point of contact, so that the bodies are elastically deformed and a contact area is created. When tension is exerted between the 2 bodies, the slippage between the bodies is called microslip, provided that the contact area comprises a zone where the material points of the 2 bodies adhere to each other. In the remainder of the contact area, the surfaces slide against each other due to the elastic deformation of the bodies. When the adhesion zone disappears (due to high tension or low perpendicular force), the slippage is no longer microslip, but becomes macroslip. In the present description, the scientific meaning described above of 'microslip' and 'macroslip' is applicable.Sometimes, the same terminology is applied to continuously variable belt-driven transmissions (CVTs) where there are no rolling contacts. Any documentation on CVTs that refers to micro-slip and / or macro-slip is therefore not relevant here. Petition 870220089642, dated 09 / 30 / 2022, page 19 / 39 13 / 22 patent application.

[00031] As stated in the introduction and illustrated in Figure 2, the current control strategy for slip-free curve CVTs is to keep the roll always within micro-slip throughout the gear change, applying a dynamic force component that is dependent on the speed of the gear change, and which can become very high in rapid gear changes, leading to high pressure increases in cylinders 12 and 13. This can lead to reduced efficiency, especially when the control system is equipped with solenoid-operated control valves.

[00032] The inventors discovered from theoretical and practical research that dynamic force during ratio changes is not necessary to ensure optimal operation of the slip-free CVT curve. The invention method is based on this counterintuitive discovery. According to the invention method, no micro-slip maintenance dynamic force component is added to the static values ​​of NR and NZ during a continuous increase or decrease in ratio. By 'micro-slip maintenance dynamic force component' is meant a force component that depends on the speed of the ratio change and that is configured to maintain the micro-slip condition during the ratio change.According to a preferred embodiment, the static clamping force for one of the perpendicular forces NR or NZ (which depends on the direction in which the ratio is changing) is applied along the ratio change, regardless of the speed of the change. This is illustrated in Figure 3. Petition 870220089642, dated 09 / 30 / 2022, page 20 / 39 Figure 14 / 22 shows an example of the forces applied in reaction to the same (rapid) change in ratio illustrated in Figure 2. While in the control method of the previous technique, NR and NZ increased considerably, NZ remains the same in Figure 3, while NR only slightly increases in order to overcome the reaction forces TR and TZ generated when rotating around the joint.

[00033] Thus, both NR and NZ continue to be controlled at their static values ​​during the change of ratio, with only a small correction in one of the two to overcome the reaction forces TR and TZ, and thus keep the instantaneous moment around joint 5 equal to zero during the change of ratio. The static value itself may change during the change of ratio. However, what is important is that, according to the preferred embodiment, no dynamic component configured to maintain the micro-slip condition is added to NR or NZ.

[00034] In the case of the transmission disclosed in WO2009 / 146748A1, the geometric axis of articulation intersects with the geometric axis of central rotation, which means that the reaction forces TR and TZ pass through the geometric axis of articulation, not generating a moment around this geometric axis, so that these reaction forces do not need to be compensated. Therefore, in this case, the perpendicular forces NR and NZ can be maintained at their static values ​​throughout the change in ratio, i.e., the component of the added force is zero on both sides.

[00035] Whereas in prior art systems, a rapid change in the ratio generates a significant increase in forces compared to static force values ​​due to the always necessary positive dynamic force component. Petition 870220089642, dated 09 / 30 / 2022, page 21 / 39 15 / 22 to maintain micro-slip, the preferred embodiment of the invention does not add this specific dynamic component to the static values ​​(forces smaller than this specific component can be added, see below). When the ratio change is slow, this dynamic component is not significant, and the forces applied by the embodiments of the invention's method are not very different from the prior art method. However, when the ratio changes rapidly, the forces applied by the invention's method can be considerably smaller than in the prior art method. This means that when the ratio changes very rapidly, it is not necessary to apply high pressures to cylinders 12 and 13 and to the feed lines 14 and 15 towards these cylinders.

[00036] According to some embodiments, a force component smaller than the 'component configured to maintain the micro-slip condition' can be added to the NR and NZ forces during the ratio change, while preferably the force balance on the joint is maintained during the change, i.e., the instantaneous moment around the joint is maintained at zero. The dynamic force components required to maintain micro-slip are well known from the prior art methods described above, so the invention is clearly defined in that when any force component is added to the static values ​​of NR and / or NZ during a ratio change, this force component must be zero or less than the forces required to maintain micro-slip. The invention can also be explained in a purely mathematical manner. According to the prior art, the minimum required values Petition 870220089642, dated 09 / 30 / 2022, page 22 / 39 16 / 22 during a gear change, the clamping forces NR and NZ are a function of the input speed, input torque, transmission ratio, and rate of change of the gear ratio. According to the present invention, the minimum values ​​for the NR and NZ forces are a function of the input speed, input torque (or equivalently, output speed and output torque), and transmission ratio for zero gear change speed. Therefore, for each non-zero gear change speed, the minimum value for NR and NZ in the present invention is always smaller than in the prior art, under equal conditions of input speed, input torque, and transmission ratio, since the dynamic forces applied in the prior art methods are always positive.

[00037] The invention also relates to a CVT-curve equipped with a control system capable of implementing the method of the invention. This can be any suitable control system capable of controlling the NR and NZ forces according to the method, i.e., applying the static forces during any change of ratio, regardless of its speed. A preferred embodiment of a hydraulic control system suitable for carrying out the above method is illustrated in Figure 4. The pressures p1 and p2 are provided by two motor-pump sets 20 and 21, each set comprising a hydraulic pump 20a / 21a which can also act as a hydraulic motor and, rotatably coupled, an electric motor 20b / 21b which can also act as a generator. The electric motors 20b / 21b of the motor-pump sets are powered by a suitable power source, which can be a battery. Petition 870220089642, dated 09 / 30 / 2022, page 23 / 39 17 / 22 a vehicle in which the transmission is installed. Pumps 20a and 21a are connected in such a way that pump 21a, which supplies p2, is coupled between a hydraulic fluid reservoir 30 and the inlet port of pump 20a, which supplies p1. In other words, there is a connection 31 between the outlet port of pump 21a and the inlet port of pump 20a.

[00038] The system is operated through a control algorithm that controls the forces according to the method of the invention. From the design and dimensions of the transmission, the static forces NR, TR, NZ, TZ are defined for each combination of torque, speed, and constant ratio. Through the vector sum of NR and TR, the required pressure on piston 10 is calculated. Similarly, the pressure on piston 11 is calculated from the forces NZ and TZ. When the characteristics of the motor-pump assembly are known, the required electric current for the electric motors of the motor-pump assemblies is defined. During the ratio change, the algorithm does not add a dynamic force component to these static values, which is configured to maintain the micro-slip condition.According to the preferred embodiment, one of the NR and NZ forces is maintained at the static value, while the other is controlled to overcome the TR and TZ reaction forces generated by the joint around the joint when the relationship is changing.

[00039] Closed-loop control during gear changes can be achieved by a pressure sensor in the cylinder on the sun wheel side or on the ring wheel side, possibly in combination with a position sensor in the piston on the ring wheel side, on the sun wheel side or Petition 870220089642, dated 09 / 30 / 2022, page 24 / 39 18 / 22 measuring the output and input speeds of the shaft. Any closed-loop control in terms of sensors and controllers known in the art to regulate a change in ratio while maintaining microslip can also be used in a system according to the invention. The difference lies in the forces, such that while both NR and NZ increase by a dynamic component when microslip needs to be maintained, this increase in both forces is not necessary according to the method of the invention, at least not as a function of the speed of the change in ratio.

[00040] The control described above using pumps completely eliminates solenoids so that all pressure drops and robustness problems of solenoids are overcome, regardless of the rate of change of the ratio. In addition, the control system shown in Figure 4, using motor-pump sets 20 and 21 coupled in the manner described above by connection 31, saves a great deal of hydraulic energy.

[00041] When the gear ratio is changing, one cylinder is being filled while the other is being drained. Both flows are not equal due to the special geometry of the rolling surfaces of the ring wheel and sun wheel, but the flow difference between the filling flow and the draining flow is only a small fraction of each of these flows. In practice, this differential flow is only about 10 to 25% of the flow for one of the cylinders.

[00042] The motor-pump assembly 21 must supply pressure p2 to the corresponding cylinder 13, but it must only supply the small differential flow. Therefore, it must be Petition 870220089642, dated 09 / 30 / 2022, page 25 / 39 19 / 22 is sized only for the correspondingly lower power, instead of the total hydraulic power for this cylinder alone.

[00043] Pressures p1 and p2 are regulated according to the required forces NR, TR, NZ, and TZ. Generally, pressures p1 and p2 are not equal, and their ratio depends on the transmission ratio and other parameters. However, the difference between the two pressures is only a small fraction of the pressure itself. Pump 20a must supply the full flow to cylinder 12, but only above the pressure difference between the two cylinders. Similarly, the motor-pump assembly 20 can be sized for a fraction of the power, about 10% to 25%, that would be required to power cylinder 12 alone.

[00044] In the assembly shown in Figure 4, both motor-pump sets 20 and 21 thus have to supply only about 10% to 25% of the power that would be required if both cylinders were fed individually. Furthermore, changing the transmission ratio in one direction can consume energy, while changing the ratio in the other direction will recover energy, as the pumps can act as hydraulic motors and the electric motors can act as generators. Considering the efficiencies of the pumps, the motors, and the friction of the piston seals, the net energy consumption is only about 40% - 60% of the energy supplied without energy recovery.

[00045] By combining lower energy requirements with energy recovery, the control system shown in Figure 4 consumes only about 5% to 15% of the energy compared to a system optimized with solenoids. Furthermore, the control system in Figure 4 eliminates Petition 870220089642, dated 09 / 30 / 2022, page 26 / 39 20 / 22 completely a hydraulic block.

[00046] The control system shown in Figure 4 therefore constitutes a preferred embodiment of a control system suitable for implementing the method of the invention.

[00047] However, the method according to the invention can also be implemented by other hydraulic control systems. The system in Figure 5, for example, again comprises two motor-pump sets 20 and 21, but now there is no direct connection between the two. This means that both motor-pump sets 20 and 21 need to be able to supply the required full flow and pressure in both cylinders. This configuration is therefore less efficient in terms of energy consumption of the motor-pump sets. Other hydraulic control configurations can be imagined by the person skilled in the art, which are slightly different from the systems in Figures 4 and 5, but which are suitable for implementing the method of the invention. All such variants fall within the scope of the present invention.

[00048] In the motor-pump sets shown in figures 3 and 4, it is not essential that pumps 20a / 21a can act as a hydraulic motor and that electric motors 20b / 21b can act as a generator. If these capabilities are not present, energy recovery is not possible, but the system is still suitable for implementing the method of the invention.

[00049] The method of the invention can also be implemented by a hydraulic control system as currently known in the art, using solenoids, possibly combined with a flow amplifier, otherwise the pressure drop caused by the solenoids makes Petition 870220089642, dated 09 / 30 / 2022, page 27 / 39 21 / 22 It is unlikely that the flow will change rapidly enough towards the cylinders. Even when using flow amplifiers, very rapid ratio changes generate pressure drops. However, using control systems that utilize motor-pump sets, as in the embodiments shown in Figures 4 and 5, this pressure loss problem does not occur, which is why these systems are particularly suitable for implementing the method of the invention. These systems are capable of implementing any ratio change rate that can occur practically without pressure drops.

[00050] Finally, control systems that do not use hydraulic power may also be suitable for implementing the method of the invention, such as control systems using mechanical springs, pneumatic pistons or electromechanical actuators to achieve the necessary clamping forces.

[00051] As stated previously, the invention is not limited to a CVT-curve where the ring wheel and sun wheel are axially movable and directly driven, as by pressures p1 and p2 in the embodiments shown in the drawings. In a transmission where, for example, the ring wheel is stationary and the planetary wheels and sun wheel are driven directly by external forces, the forces NR, TR and NZ, TZ are a known function of these external forces and can be implemented as such in the control algorithm, and can thus also be controlled according to the method of the invention.

[00052] The invention is also applicable to a Reversible Variable Transmission (RVT) as described in Petition 870220089642, dated 09 / 30 / 2022, pp. 28 / 39 22 / 22 PCT / EP2008 / 057009, comprising 2 sets of planetary wheels mounted between a primary ring wheel and a secondary sun wheel, with an intermediate wheel between the two sets. This transmission can also be controlled by two pressures acting on the primary ring wheel and the secondary sun wheel, as in the embodiments described above. The control method according to the invention can be applied as such to this transmission. The control systems shown in Figures 4 and 5 can also be applied as such to an RVT, wherein the motor-pump assembly 20 is connected to the primary ring wheel and the motor-pump assembly 21 is connected to the secondary sun wheel, or vice versa.

[00053] Although the invention has been illustrated and described in detail in the drawings and the preceding description, such illustration and description should be considered illustrative or exemplary and not restrictive. Other variations of the disclosed embodiments may be understood and carried out by those skilled in the art in the practice of the claimed invention, from a study of the drawings, the disclosure and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are stated in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be interpreted as limiting the scope. Petition 870220089642, dated 09 / 30 / 2022, pp. 29 / 39

Claims

1 / 4 CLAIMS 1. Method for controlling a continuously variable transmission, comprising an input shaft and an output shaft being rotatably arranged around a common central geometric axis of rotation (4), a ring wheel (1) and a sun wheel (2) being coaxially arranged with respect to the central geometric axis (4) and at least one set of rotatable planetary wheels (3), the angle of rotation (8) of the planetary wheels determining the transmission ratio, wherein: - the transmission operates through the free-slip rolling of the planetary wheels (3) on the surfaces of the ring wheel (1) and the sun wheel (2), independently of the angle of rotation of the planetary wheels, - the ring wheel (1),The planetary wheels (3) and the sun wheel (2) are clamped together so that the ring wheel (1) exerts a first perpendicular force (NR) on any planetary wheel (3) and the sun wheel (2) exerts a second perpendicular force (NZ) on said planetary wheel (3), - the method is configured to control said first and second perpendicular forces (NR, NZ), so that, when the transmission operates at a given input speed, a given transmitted torque, and a given constant transmission ratio, a predefined static value of the first and second perpendicular force is applied, and a micro-slip condition is applicable to the rolling contacts between the planetary wheels (3) and the ring wheel and sun wheel (1, 2), characterized by the fact that: - during a continuous increase or decrease of the angle of rotation (8) and therefore of the transmission ratio,Any force component added to the static values ​​of the first and / or second perpendicular force must be either zero or less than a predefined force component that is necessary to maintain the micro-slip condition.

2. A method according to claim 1, characterized in that during the increase or decrease of the transmission ratio, one of the perpendicular forces is maintained at its static value while the other is controlled to overcome the tangential reaction forces generated by the change in the angle of rotation.

3. Method, according to any one of claims 1 or 2, characterized in that the ring wheel (1) and the sun wheel (2) are tightened together under the direct or indirect influence of a first and second hydraulic pressure (p1, p2).

4. Method according to claim 3, characterized in that said hydraulic pressures (p1, p2) act directly on the respective hydraulic pistons (10, 11), configured to move axially in the direction of the central geometric axis (4), and wherein the ring wheel (1) and the sun wheel (2) are fixed to the respective pistons (10, 11).

5. Continuously variable transmission, comprising an input shaft and an output shaft being rotatably arranged around a common central geometric axis of rotation (4), one—or more—sets—of a ring wheel (1), a sun wheel (2) being coaxially arranged with respect to the central geometric axis (4) and at least one set of rotatable planetary wheels (3), the angle of rotation (8) of the wheels Petition 870240055880, dated 02 / 07 / 2024, page.13 / 24 3 / 4 planetary gears determining the transmission ratio of the transmission, wherein the transmission operates through free-slip rolling of the planetary gears (3) on the surfaces of the ring gear (1) and the sun gear (2), independently of the angle of rotation of the planetary gears, wherein the ring gear (1) and the sun gear (2) are fixed together so that the ring gear (1) exerts a first perpendicular force (NR) on any planetary gear (3) and the sun gear (2) exerts a second perpendicular force (NZ) on said planetary gear, characterized in that the transmission comprises a control system configured to control the transmission according to the method for controlling a continuously variable transmission, as defined in any one of claims 1 to 4.

6. Transmission, according to claim 5, characterized in that said control system is a hydraulic control system.

7. Transmission, according to claim 6, characterized in that the transmission is regulated by a first and a second hydraulic pressure (p1, p2) exerted on a first and a second hydraulic cylinder (12, 13) by a hydraulic fluid, said pressures acting to clamp the ring wheel (1) and the sun wheel (2) together.

8. Transmission, according to claim 7, characterized in that the first and second pressures (p1, p2) act directly on the respective first and second pistons (10, 11) which are movable within the respective first and second cylinders (12, 13).

9. Transmission, according to claim 7 or 8, characterized in that said control system Petition 870240055880, dated 02 / 07 / 2024, page 14 / 24 4 / 4 comprises a first and second motor-pump assemblies (20, 21), each assembly comprising a hydraulic pump (20a, 21a) coupled to an electric motor (20b, 21b), said assemblies being configured to control said first and second pressures in the respective cylinders (12, 13).

10. Transmission, according to claim 9, characterized in that the pump outlet port of one motor-pump assembly is connected to the pump inlet port of another motor-pump assembly.

11. Transmission, according to claim 9 or 10, characterized in that the pumps (20a, 21a) of the motor-pump sets can act as hydraulic motors, and the electric motors (20b, 21b) of the motor-pump sets can act as generators. Petition 870240055880, dated 02 / 07 / 2024, page 15 / 24

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