WO2017211808A1

WO2017211808A1 - Continuously variable transmission system

Info

Publication number: WO2017211808A1
Application number: PCT/EP2017/063688
Authority: WO
Inventors: Benoit Emile Joseph Marie LENAERTS
Original assignee: Punch Powertrain N.V.
Priority date: 2016-06-07
Filing date: 2017-06-06
Publication date: 2017-12-14
Also published as: CN210461659U; BE1023743B1

Abstract

Continuously variable transmission system for a vehicle, arranged for being used during sailing. The system includes a variator having at least one friction element arranged for being actuated hydraulically to apply a clamping force onto a torque transmitting member coupled to the at least one friction element. The variator is arranged for, during sailing, refraining from hydraulically actuating the at least one friction element, while still providing a clamping force of the at least one friction element onto the torque transmitting member that is sufficient to prevent slip.

Description

Continuously variable transmission system

FIELD OF THE INVENTION

The invention relates to continuously variable transmission system. More in particular, the invention relates to a continuously variable transmission system optimized for sailing.

BACKGROUND TO THE INVENTION

In automotive "sailing" refers to a particular maneuver wherein a vehicle proceeds at a normal driving speed, such as within the interval between 30 km/h and 120 km/h, the driver is not pushing the accelerator pedal and cruise control is deactivated. If these conditions are met for a certain amount of time and the vehicle is equipped with the proper hardware for turning the engine off and restarting it without the intervention of the driver, a control strategy manages engine stops and keeps the vehicle in sailing mode until the enabling conditions are met for an engine restart.

The main goal of introducing sailing is to have lower fuel consumption.

Although the driver is not pushing the accelerator pedal or cruise control is not regulating the vehicle speed, with the engine on there would be a certain amount of fuel injected into the engine to avoid the engine stall. In a typical driving cycle this amount of fuel can be up to some 8 or 9% of the total.

A continuously variable transmission (CVT) is an automatic transmission allowing change through a continuous range of effective gear ratios. An input from a prime mover to an input shaft can be used to deliver variable output speeds and torques at an output shaft, while the input can be maintained at a constant angular velocity. A CVT can comprise a variator for providing a mechanical power transmission. The variator can comprise two friction elements, wherein a first friction element is connected to a second friction element through a torque transmitting member, such as a (push) belt or a chain. A first conical pulley can be connected to the input shaft. A second conical pulley can be connected to the output shaft. The first pulley can include a fixed and an axially moveable sheave. The second pulley can include a fixed and an axially moveable sheave. A belt, such as a segmented steel V-belt, clamped between the two pairs of conical sheaves of the pulleys may be arranged, wherein the gap between the sheaves and thereby the belt running radius can be adjusted by axial movement of the moveable sheave. The variator can change its gear ratio continuously.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a continuously variable transmission (CVT) that is optimized for sailing.

In a drivetrain for enabling sailing the transmission is requested to promptly open the drivetrain when sailing is enabled and, similarly, promptly being ready to engage the drivetrain once the engine is restarted.

According to a first aspect is provided a continuously variable transmission system. The CVT system is arranged for being used during sailing of a vehicle. The CVT system comprises a variator having at least one friction element arranged for being actuated hydraulically and a torque transmitting member coupled to the at least one friction element. The variator can be arranged for, during sailing, refraining from hydraulically actuating the at least one friction element, while still providing a clamping force of the at least one friction element onto the torque transmitting member that is sufficient to prevent slip. This provides the advantage that during sailing slip of the torque transmitting member relative to the at least one friction element can be avoided. This prevents damage to the torque transmitting member and/or friction element during sailing.

Moreover, refraining from hydraulically actuating the at least one friction element during sailing provides the advantage that more energy is conserved during sailing. If an oil pump would have to be operational during sailing for actuating the at least one friction element for providing the clamping force sufficient to avoid slip, energy would be consumed during sailing by the oil pump.

It will be appreciated that the oil pump can be driven by the engine. Therefore, during sailing when the engine has been stopped the engine cannot drive that oil pump. Hence, refraining from hydraulically actuating the at least one friction element during sailing provides the advantage that no additional oil pump, such as an electric oil pump needs to be provided. Thus, advantageously the CVT system is free from an electric oil pump. Alternatively, the CVT system is arranged for stopping the electric oil pump during sailing.

Optionally, the CVT system is arranged such that during sailing, the amount of oil inside the hydraulic circuit is sufficient to ensure lubrication of the mechanical components of the CVT system.

Optionally the CVT system includes a clutch interposed between the engine and the variator. The CVT system can be arranged to set the clutch to a mode in which the clutch does not transfer torque and preferably does not slip.

Optionally, the variator includes a first friction element coupled to an input shaft of the variator and a second friction element coupled to an output shaft of the variator. The first friction element can be a first conical pulley. The second friction element can be a second conical pulley. The first pulley can include a fixed and an axially moveable sheave. The second pulley can include a fixed and an axially moveable sheave. The torque transmitting member can be a belt such as a pushbelt or chain. The belt, can be a segmented steel V-belt. The belt can be clamped between the two pairs of conical sheaves of the pulleys. A gap between the sheaves and thereby the belt running radius can be adjusted by axial movement of the moveable sheave(s). The variator can change its gear ratio continuously.

Optionally, the variator is arranged for, during sailing, refraining from hydraulically actuating the second friction element, while still providing a clamping force of the second friction element onto the torque transmitting member that is sufficient to prevent slip.

Optionally, the variator is arranged for, during sailing, refraining from hydraulically actuating the first friction element, while still providing a clamping force of the first friction element onto the torque transmitting member that is sufficient to prevent slip.

Optionally, the at least one friction element is biased such that, in the absence of actuation of the at least one friction element, a clamping force of the at least one friction element onto the torque transmitting member is sufficient to prevent slip of the torque transmitting member relative to the friction element. Bias can be provided by a biasing element, such as a spring, e.g. a helical spring.

The biasing element can exert a predetermined force on the at least one friction element so that the at least one friction element can exert the clamping force onto the torque transmitting member that is sufficient to prevent slip of the torque transmitting member relative to the friction element. Alternatively, or additionally, the biasing element can exert a predetermined force on the at least one friction element such that the variator can generate a certain ratio during a sailing maneuver. The predetermined biasing force of the biasing member can be determined taking into account the required clamping force for preventing slip. It is noted that the higher the required clamping force the higher the required biasing force. The higher biasing force can be achieved by a stiffer spring. The

predetermined biasing force of the biasing member can be determined taking into account the geometry of the at least one friction element. For example, when the friction element is a pulley, the bigger the pulley, the higher the required biasing force. The predetermined biasing force of the biasing member can be determined taking into account the geometry and type of belt (e.g. chain, push belt).

Optionally, the CVT system includes a transmission control unit (TCU). The TCU can be arranged for receiving a request to initiate sailing mode of the CVT system. Upon receiving the request to initiate sailing mode, the TCU can suspend hydraulic actuation of the at least one friction member. Upon receiving the request to initiate sailing mode the TCU can bring the clutch into a mode in which the clutch does not transfer torque and preferably does not slip. The TCU may e.g. bring the clutch below the so-called biting point. In an embodiment, the TCU may bring the pressure on clutch plates below 0.3 bar.

The TCU can be arranged to suspend hydraulic actuation of the at least one friction member until the TCU receives a request to end sailing mode and to resume driving mode in which the engine is providing torque. The TCU can be arranged to maintain the clutch in the mode in which the clutch does not transfer torque and preferably does not slip until the TCU receives a request to end sailing mode and to resume driving mode in which the engine is providing torque.

According to a second aspect is provided a continuously variable transmission system for a vehicle. The CVT system is arranged for being used during sailing of a vehicle. The CVT system comprises a variator having at least one friction element arranged for being actuated hydraulically and a torque transmitting member coupled to the at least one friction element. The system is free from an electric oil pump for providing hydraulic pressure for actuating the at least one friction element. Alternatively, the system includes an electric oil pump for providing hydraulic pressure for actuating the at least one friction element and the system is arranged for stopping the electric oil pump during sailing.

According to a third aspect is provided a continuously variable transmission system for a vehicle. The CVT system comprises a variator having at least one friction element arranged for being actuated to apply a clamping force onto a torque transmitting member coupled to the at least one friction element. The at least one friction element is biased such that, in the absence of actuation of the at least one friction element, a clamping force of the at least one friction element onto the torque transmitting member is sufficient to prevent slip of the torque transmitting member relative to the friction element. This provides the advantage that while the at least one friction element is not being actuated, e.g. during sailing, slip of the torque transmitting member relative to the at least one friction element can be avoided. This prevents damage to the torque transmitting member and/or friction element while the at least one friction element is not being actuated, e.g. during sailing. Moreover, refraining from actuating the at least one friction element provides the advantage that energy is conserved.

Optionally, the at least one friction element is arranged for being actuated hydraulically. Then the at least one friction element is biased such that, in the absence of hydraulic actuation of the at least one friction element, a clamping force of the at least one friction element onto the torque transmitting member is sufficient to prevent slip of the torque transmitting member relative to the friction element.

Optionally, the variator includes a first friction element coupled to an input shaft of the variator and a second friction element coupled to an output shaft of the variator. The first friction element can be a first conical pulley. The second friction element can be a second conical pulley. The first pulley can include a fixed and an axially moveable sheave. The second pulley can include a fixed and an axially moveable sheave. The torque transmitting member can be a chain or a belt such as a pushbelt. The belt, can be a segmented steel V-belt. The belt can be clamped between the two pairs of conical sheaves of the pulleys. A gap between the sheaves and thereby the belt running radius can be adjusted by axial movement of the moveable sheave(s). The variator can change its gear ratio continuously. Optionally, the second friction element is biased such that, in the absence of actuation of the second friction element, a clamping force of the second friction element onto the torque transmitting member is sufficient to prevent slip of the torque transmitting member relative to the second friction element.

Optionally, the first friction element is biased such that, in the absence of actuation of the first friction element, a clamping force of the first friction element onto the torque transmitting member is sufficient to prevent slip of the torque transmitting member relative to the first friction element.

Optionally, biasing is provided by a spring, such as a compression spring, pressing the moveable sheave in the direction of the fixed sheave. It is noted that a biasing spring may be used in continuously variable transmission systems arranged for hydraulic actuation of the sheaves, which systems are not suitable for being operated in sailing mode. It is noted that the biasing spring according to the invention provides a higher biasing force so as to prevent slip of the torque transmitting member relative to the friction element when the friction element is not hydraulically actuated. For example, the biasing spring for preventing friction may have a stiffness of at least twice, preferably at least 2.5 times, the stiffness of the biasing spring that is unable to prevent slip.

The invention also relates to a drive train including an engine and a continuously variable transmission as described herein.

The invention also relates to a vehicle including a continuously variable transmission as described herein.

The invention also relates to a method of operating a continuously variable transmission system having a variator with at least one friction element and a torque transmitting member coupled to the at least one friction element. The method includes during driving hydraulically actuating the at least one friction element, so as to provide a clamping force onto the torque transmitting member that is sufficient to transmit torque. The method includes during sailing refraining from hydraulically actuating the at least one friction element, while still providing a clamping force of the at least one friction element onto the torque transmitting member that is sufficient to prevent slip. The method can include initiating sailing mode. Initiating sailing mode includes disengaging the clutch, stopping the engine and stopping hydraulically actuating the at least one friction element. Initiating sailing mode can be controlled by a control unit. The method can include terminating sailing mode. Terminating sailing mode includes resuming

hydraulically actuating the at least one friction element, starting the engine and engaging the clutch. Terminating sailing mode can be controlled by the control unit.

It will be appreciated that any of the aspects, features and options described in view of the CVT system apply equally to the drive train, vehicle and the described methods. It will also be clear that any one or more of the above aspects, features and options can be combined.

BRIEF DESCRIPTION OF THE DRAWING

The invention will further be elucidated on the basis of exemplary embodiments which are represented in a drawing. The exemplary embodiments are given by way of non-limitative illustration. It is noted that the figures are only schematic representations of embodiments of the invention that are given by way of non-limiting example.

In the drawing:

Fig. 1 shows a schematic diagram of an embodiment of a CVT system. DETAILED DESCRIPTION

Fig. 1 is a schematic diagram of an example of a continuously variable transmission, CVT, system 1. The CVT system includes a variator 2 allowing change through a continuous range of effective gear ratios. The variator 2 includes a first friction element 4 coupled to an input shaft 6 of the variator 2 and a second friction element 8 coupled to an output shaft 10 of the variator 2. In Figure 1 the first friction element 4 is a first conical pulley. In Figure 1 the second friction element 8 is a second conical pulley. The first pulley 4 include a fixed sheave 4a and an axially moveable sheave 4b. The second pulley 8 includes a fixed sheave 8a and an axially moveable sheave 8b.

The first friction element 4 is connected to the second friction element 8 through a torque transmitting memberl2. In this example the torque transmitting member 12 is a chain or belt such as a pushbelt. The belt, can e.g. be a segmented steel V-belt. The belt 12 is clamped between the two pairs of conical sheaves 4a, 4b, 8a, 8b of the pulleys 4, 8.

In Figure 1 the second friction element 8, viz. the moveable sheave 8b of the second pulley 8, is biased. Biasing force is provide by a biasing element 14. In this example the biasing element 14 is a compression spring.

In Figure 1 the CVT system 1 includes a clutch 16 for engaging and disengaging an input shaft 18 of the CVT system with the input shaft 6 of the variator 2.

The CVT system 1 can be used as follows. When the CVT system 1 is used in a vehicle, during normal driving conditions the CVT system 1 will transfer torque from an engine presented at the input shaft 18 to the output shaft 10. From the output shaft 10 torque may be transferred to one or more wheels of the vehicle. A gap between the sheaves 4a, 4b, 8a, 8b and thereby the belt 12 running radius can be adjusted by axial movement of the moveable sheave(s) 4b, 8b. The variator 2 can hence change its gear ratio continuously. In order to provide sufficient clamping force between the pulleys 4, 8 and the belt 12 to avoid slipping of the belt relative to the pulleys 4, 8, the moveable sheaves 4b, 8b are clamped against the belt 12. This clamping is effected hydraulically using the hydraulic actuators 4c, 8c. The clamping force is sufficient to prevent slip.

The CVT system 1 can also be used during sailing mode. The main goal of introducing Sailing is to have lower fuel consumption. Although the driver is not pushing the accelerator pedal and cruise control is not regulating the vehicle speed, with engine on there would be a certain amount of fuel injected to avoid the engine stall. In a typical driving cycle this amount of fuel can be up to 8-9% of the total. Therefore, during sailing mode the engine is stopped. Thus, no torque is provided at the input shaft 18. When sailing is started, the CVT system 1 is requested to promptly release the clutch 16. When sailing is stopped, similarly, promptly the clutch 16 needs to be engaged once the engine is restarted.

In this example, the hydraulic actuators 4c, 8c are actuated using pressurized oil. The oil is pressurized using an oil pump (not shown). The oil pump is driven by the engine. Therefore, during sailing mode, when the engine is stopped, there may be insufficient oil pressure to actuate the hydraulic actuators 4c, 8c. Nevertheless, during sailing the output shaft 10 is still connected to the rotating wheels of the vehicle. Therefore, insufficient oil pressure might increase the risk of the belt 12 slipping with respect to the pulleys 4, 8, especially the second pulley 8. This risk is mitigated by the dimensioning of the biasing element 14. The biasing element 14 is such that the biasing force on the second moveable sheave 8b is sufficient for preventing the belt 12 to slip relative to the second pulley 8.

It is noted that a biasing element may be used in continuously variable transmission systems arranged for hydraulic actuation of the sheaves, which systems are not suitable for being operated in sailing mode. It is noted that the biasing spring 14 of Figure 1 provides a higher biasing force so as to prevent slip of the belt 12 relative to the second pulley 8 when the second pulley 8 is not hydraulically actuated. Opting for a stiffer spring 14 at the secondary pulley 8 brings benefits in terms of reliability of the system 1 since it ensures the required clamping force on the belt 12 for any critical scenario, even with low hydraulic pressure. The biasing member 14 according to Figure 1 can also provide that the gear ratio of the variator 2 can be within the desired operating range of 0.443 - 0.7, allowing a smooth restart of the engine as well as a smooth clutch 16 re- engagement. Furthermore, such gear ratio allows the system 1 to work with a low primary speed of the first pulley 4. The low primary speed may minimize the centrifugal forces at the input shaft 6 and, as a consequence, it may help the system 1 having low pressure on clutch 16 plates.

The control algorithm developed for Sailing also ensures a prompt restart of the transmission. The TCU monitors the actions from the driver in order to quickly react to a torque demand; as a consequence of this, the TCU can promptly fill the hydraulic circuit while the engine is restarting and have the drivetrain engaged in a very short time. This can provide the driver with a quick and smooth response of the vehicle.

It is noted that hydraulic pressure during sailing mode could be provided using an oil pump that is not driven by the engine, e.g. an electrically driven oil pump. Nevertheless, use of such oil pump during sailing would increase energy consumption during sailing. Therefore, the CVT system 1 of Figure 1 is free from an electric oil pump. It is noted that even if the CVT system 1 were provided with an electric oil pump, the electric oil pump can be shut down during sailing, since the biasing member 14 effectively prevents slip. The CVT system 1 can further include a transmission control unit, TCU, 20. When performing sailing mode the TCU 20 receives from an Engine Control Unit, ECU, a request of opening the drivetrain as quickly as possible. In this situation the TCU needs to make sure that this maneuver is performed without jeopardizing the transmission itself and its components. The pressure on clutch plates of the clutch 16 is preferably be below the so-called biting point, e.g. around 0.3 bar, in order to avoid torque transfer and any slipping, which could result in a high heat generation and, eventually, consistent clutch wear. The pressure applied on the secondary pulley 8 is preferably high enough to have enough clamping force on the belt 12, which otherwise would eventually slip and, therefore, could be damaged. The amount of oil inside the hydraulic circuit of the CVT system 1 is preferably enough to ensure constant lubrication of the mechanical components and to have a prompt restart once Sailing maneuver is completed.

When the conditions for sailing mode are met, the ECU may transmit a request to initiate sailing mode to a motor management unit, MMU, and to the TCU 20. The TCU 20 in this example is be arranged for receiving the request to initiate sailing mode of the CVT system 1. Upon receiving the request to initiate sailing mode, the TCU 20 brings the clutch 16 below the biting point and suspends hydraulic actuation of the pulleys 4, 8. It is also possible that the TCU 20 allows actuating hydraulic pressure to decrease due to engine shutdown. Then the MMU can stop the engine. The CVT system 1 is now in sailing mode.

When the driver actuates the accelerator or cruise control sailing mode will be terminated. The ECU may transmit a request to end sailing mode to the TCU 20. Upon receiving the request to terminate sailing mode, the TCU 20 again hydraulically actuates the pulleys 4, 8. The MMU restarts the engine and the TCU 20 engages the clutch 16.

Herein, the invention is described with reference to specific examples of embodiments of the invention. It will, however, be evident that various

modifications and changes may be made therein, without departing from the essence of the invention. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, alternative embodiments having combinations of all or some of the features described in these separate embodiments are also envisaged.

For example, the TCU and/or ECU can be embodied as dedicated electronic circuits. The TCU and/or ECU can also, partly, be embodied as software code portions executed on a programmable computer.

However, other modifications, variations, and alternatives are also possible. The specifications, drawings and examples are, accordingly, to be regarded in an illustrative sense rather than in a restrictive sense.

For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words 'a' and 'an' shall not be construed as limited to 'only one', but instead are used to mean 'at least one', and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to an advantage.

Claims

1. Continuously variable transmission system for a vehicle, arranged for being used during sailing, comprising:

a variator having at least one friction element arranged for being actuated hydraulically to apply a clamping force onto a torque transmitting member coupled to the at least one friction element,

wherein the variator is arranged for, during sailing, refraining from hydraulically actuating the at least one friction element, while still providing a clamping force of the at least one friction element onto the torque transmitting member that is sufficient to prevent slip.

2. Continuously variable transmission system according to claim 1, wherein the at least one friction element is biased such that, in the absence of hydraulic actuation of the at least one friction element, the clamping force of the at least one friction element onto the torque transmitting member is sufficient to prevent slip of the torque transmitting member relative to the friction element.

3. Continuously variable transmission system according to claim 1 or 2, wherein the system is free from an electric oil pump, or wherein the system includes an electric oil pump and the system is arranged for stopping the electric oil pump during sailing.

4. Continuously variable transmission system for a vehicle, arranged for being used during sailing, comprising

a variator having at least one friction element arranged for being actuated hydraulically and a torque transmitting member coupled to the at least one friction element,

wherein the system is free from an electric oil pump for providing hydraulic pressure for actuating the at least one friction element, or wherein the system includes an electric oil pump for providing hydraulic pressure for actuating the at least one friction element and the system is arranged for stopping the electric oil pump during sailing.

5. Continuously variable transmission system according to any one of the preceding claims, including a transmission control unit arranged for receiving a request to initiate sailing mode of the CVT system and arranged for upon receiving the request to initiate sailing mode suspending hydraulic actuation of the at least one friction member.

6. Continuously variable transmission system according to claim 5, wherein the transmission control unit is arranged for upon receiving the request to initiate sailing mode the bringing the clutch into a mode in which the clutch does not transfer torque and preferably does not slip.

7. Continuously variable transmission system according to claim 5 or 6, wherein the transmission control unit is arranged for receiving a request to end sailing mode and arranged for upon receiving the request to end sailing mode hydraulically actuate the at least one friction member.

8. Drive train including an engine and a continuously variable transmission according to any one of claims 1-7.

9. Vehicle including a continuously variable transmission according to any one of claims 1-7.

10. Method of operating a continuously variable transmission system having a variator with at least one friction element and a torque transmitting member coupled to the at least one friction element, the method including:

during driving, hydraulically actuating the at least one friction element, so as to provide a clamping force onto the torque transmitting member that is sufficient to transmit torque; and

during sailing, refraining from hydraulically actuating the at least one friction element, while still providing a clamping force of the at least one friction element onto the torque transmitting member that is sufficient to prevent slip.

11. Method according to claim 10, including:

initiating sailing mode, wherein initiating sailing mode includes disengaging the clutch, stopping the engine and stopping hydraulically actuating the at least one friction element.

12. Method according to claim 10 or 11, including:

terminating sailing mode, wherein terminating sailing mode includes resuming hydraulically actuating the at least one friction element, starting the engine and engaging the clutch.