Mechanical control of a Toroidal Continuously Variable Transmission (CVT)

FIELD

[0001] The present disclosure generally relates to Toroidal CVTs.

More specifically, the present disclosure is concerned with the mechanical control of the ratio of a toroidal CVT.

BACKGROUND

[0002] CVTs are well known transmission mechanisms that can change trough an infinite number of gear ratios between upper and lower limits. Toroidal CVTs, which are also well known, include a disks and roller arrangement that transmits power between the disks, wherein one disk is the input and the other disk is the output. Such CVT transmissions are generally used when transmission ratios have to be finely adjusted.

[0003] When used in vehicles, the control of such a CVT transmission conventionally requires that a secondary input is made available to the user so as to enable the user to set the transmission ratio according to the user's requirements. This means that the user is presented with a more complex set of driving inputs to manage.

BRIEF DESCRIPTION OF THE DRAWINGS [0004] In the appended drawings: [0005] Figure 1 is a side elevation view of a toroidal CVT provided with mechanical links, the CVT being shown in an underdrive configuration;

[0006] Figure 2 is a top plan view of the CVT of Figure 1 ;

[0007] Figure 3 is a side elevation view of the CVT of Figure 1 shown in an overdrive configuration;

[0008] Figure 4 is a top plan view of the CVT of Figure 3;

[0009] Figure 5 is a side elevation view of the CVT of Figure 1 shown in an overdrive configuration with a non-negligible load applied to the output of the CVT;

[0010] Figure 6 is a top plan view of the CVT of Figure 5; and

[0011] Figure 7 is a schematic view of a drivetrain using a CVT with mechanical links.

DETAILED DESCRIPTION

[0012] An object is generally to provide an improved mechanical control for a toroidal CVT.

[0013] More specifically, in accordance to an illustrative embodiment, there is provided a mechanical control assembly for a toroidal CVT including an input disk and an output disk, both rotatable about a longitudinal axis, rollers connecting the input and output disks. The CVT also includes a control mechanism so configured as to control the angle of the rollers between an overdrive position and an underdrive position, and a rotation blocker selectively preventing rotation of the rollers about the longitudinal axis and a casing. The mechanical control assembly comprising means connecting a user input to the control mechanism so as to selectively move the control mechanism when the user input is actuated, and means connecting the rotation blocker to the casing so as to allow the rotation blocker to pivot when a load applied to the output disk of the CVT increases above a threshold.

[0014] In accordance with another aspect, there is provide a drivetrain including a prime mover having an output, a toroidal CVT having an input connected to the output of the prime mover and an output. The toroidal CVT including an input disk and an output disk, both rotatable about a longitudinal axis of the CVT, rollers connecting the input and output disks, a control mechanism so configured as to control the angle of the rollers between an overdrive position and an underdrive position, a rotation blocker selectively preventing rotation of the rollers about the longitudinal axis and a casing. The CVT also including a mechanical control assembly comprising means connecting a user input to the control mechanism so as to selectively move the control mechanism when the user input is actuated, and means connecting the rotation blocker to the casing so as to allow the rotation blocker to pivot when a load applied to the output disk of the CVT increases above a threshold.

[0015] The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one", but it is also consistent with the meaning of "one or more", "at least one", and "one or more than one". Similarly, the word "another" may mean at least a second or more.

[0016] As used in this specification and claim(s), the words

"comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "include" and "includes") or "containing" (and any form of containing, such as "contain" and "contains"), are inclusive or open-ended and do not exclude additional, unrecited elements or process steps.

[0017] The term "about" is used to indicate that a value includes an inherent variation of error for the device or the method being employed to determine the value.

[0018] It is to be noted that the expression "prime mover" is to be construed herein and in the appended claims as an internal combustion engine a turbine engine, or any other mechanical power production element or assembly.

[0019] It is to be noted that while the expression "Toroidal CVT", standing for Continuously Variable Transmission is used herein to describe the illustrated dual-cavity full toroidal CVT, this expression is to be construed herein and in the appended claims as any type of toroidal CVT such as, for example, half-toroidal CVT and single cavity toroidal CVT.

[0020] It is to be noted that the expression "overdrive" when used herein in the context of a CVT, is to be construed herein and in the appended claims as a condition where the CVT ratio is such that the CVT output speed is higher than the CVT input speed. The CVT ratio (of output speed to input speed) is therefore higher that one to one (1 : 1 ).

[0021] It is to be noted that the expression "underdrive" when used herein in the context of a CVT, is to be construed herein and in the appended claims as a condition where the CVT ratio is such that the CVT output speed is lower than the CVT input speed. The CVT ratio (of output speed to input speed) is therefore lower that one to one (1 : 1 ).

[0022] The expressions "connected" and "coupled" are interchangeable and should be construed herein and in the appended claims broadly so as to include any cooperative or passive association between mechanical parts or components. For example, such parts may be assembled together by direct coupling or connection, or indirectly coupled or connected using further parts. The coupling and connection can also be remote, using for example a magnetic field or else.

[0023] The expression "input", without reference to a specific component such as a shaft, should be construed herein and in the appended claims, as including any movable part of an object, an assembly, a system or a mechanism that is used to receive a mechanical work from same or from another assembly, system or mechanism. Similarly, the expression "output" should be construed as including a similar part that is used to transfer a mechanical work.

[0024] Other objects, advantages and features of the mechanical control of a toroidal CVT will become more apparent upon reading of the following non-restrictive description of illustrative embodiments thereof, given by way of example only with reference to the accompanying drawings.

[0025] The illustrative embodiment of the mechanical control of a

CVT describes a system to mechanically control the ratio of the CVT as a function of the throttle position of the prime mover and of the load applied to the output, for example by the wheels of the vehicle. [0026] Turning now more specifically to Figure 1 of the appended drawings, the toroidal CVT 10 includes two input disks 12 and 14 connected to an input shaft 16, itself directly or indirectly connected to a prime mover (not shown). An output disk 18, positioned between the input disks 12 and 14, is connected therewith via rollers 20. The rollers 20 are so mounted to a spider assembly 21 that their angle may vary under the action of a control mechanism. A pivot action of a control ring 22 is used to change the angle of the rollers 20 with respect to a longitudinal axis of the CVT 10 to thereby change the ratio between the input disks and the output disk. The CVT 10 also includes a so- called rotation blocker 24 that is conventionally used to fixedly connect the spider assembly 21 to a casing (not shown), housing the CVT, so as to prevent rotation of the spider 21 about the longitudinal axis defined by the input shaft 16.

[0027] Generally stated, it is proposed to connect the control ring 22 to a pivot arm of the throttle control of the prime mover (generally referred to herein as the acceleration pedal) via a first tension spring assembly 30 so as to allow the acceleration pedal to selectively move the control ring 22 towards the overdrive position when the acceleration pedal is depressed. A second tension spring assembly 32 is also provided in the opposite direction to act as a return mechanism to return the control ring 22 to an underdrive position when the acceleration pedal is released. The second tension spring assembly connecting the control ring 22 to the casing, not shown but schematically illustrated as 23.

[0028] It is to be noted that the use of a tension spring and/or damper 30 between the pivot arm of the acceleration pedal and the control ring 22 ensures that the change of ratio of the CVT is slower than the increase of rotational speed of the prime mover. This gives to the user a more conventional driving feeling since the rotational speed of the prime mover increases as usual when the pedal is depressed and the ratio of the CVT changes more gradually.

[0029] The rotation blocker 24 conventionally preventing the spider

21 , and thus the rollers 20 from rotating along with the input and output disks is no longer fixedly mounted to the casing 23 but is mounted thereto via a third tension spring assembly 34. The force of the third tension spring assembly 34 is so chosen that when the load applied to the output of the CVT is greater than a predetermined threshold, the force of the tension spring assembly 34 is overcome and the supplemental load placed on the output moves the rotation blocker 24 so that the ratio of the CVT is changed towards the underdrive. This change of CVT ratio increases the torque that may be applied by the output of the CVT.

[0030] In operation, Figures 1 and 2 illustrate the mechanically controlled CVT 10 in a full underdrive position. The tension spring assemblies 30 and 32 are so designed that the full underdrive position (in this case, Win/Wout = 2.45 or 2.45: 1 ) is maintained while the prime mover is under a setpoint speed (for example 1500 rpm). When the prime mover reaches about 1500 rpm, the force from the acceleration pedal trying to move the control ring equals the force of the tension spring assemblies 32. When the speed of the prime mover increases above the 1500 rpm threshold, the control ring 22 begins to move, to thereby decrease the ratio of the CVT towards the full overdrive 0.41 : 1 ratio. Accordingly, the speed of the output of the CVT will increase both since the rotation speed of the prime mover increases and since the ratio of the CVT decreases.

[0031] Figures 3 and 4 illustrate the mechanically controlled CVT 10 in a full overdrive position. The tension spring assemblies 30 and 32 are so designed that the full overdrive position is achieved when the acceleration pedal is fully depressed and has been in that position for a predetermined time. As can be seen from these figures, when the CVT reaches its full overdrive position, the tension spring assembly 32 is fully extended and the control ring 22 has been rotated.

[0032] One skilled in the art will understand that while the two extreme positions have been presented in Figures 1 to 4, a multitude of intermediate positions of the acceleration pedal and thus of the control ring 22 may be achieved.

[0033] When a load applied to the output of the CVT 10 is greater than the threshold determined by the third tension spring assembly 34, the rotation blocker 24 pivots so as to increase the ratio of the CVT towards the underdrive to thereby decrease the rotational speed of the output of the CVT while maintaining the same rotational speed at the prime mover.

[0034] In other words, since the ratio of the CVT is generally determined by the angular difference between the control ring 22 and the rotation blocker 24, the present system proposes to allow this ratio to be modified both by movements of the control ring 22 caused by the movement of the acceleration pedal and by movements of the rotation blocker 24 caused by an increase of the load present on the output of the CVT when it overcomes the force of the third tension spring assembly 34 and therefore increases the ratio (by changing it towards the full underdrive).

[0035] Figures 5 and 6 illustrate the mechanically controlled CVT 10 when such a load has been applied to the output of the CVT. One can see that the rotation blocker 24 has been moved in the direction of arrow 50 and that the tension spring assembly 34 has been elongated. [0036] Finally, Figure 7 illustrates a drivetrain 100 including a prime mover in the form of an Internal Combustion Engine (ICE) 102 having an output connected to the input of the CVT 10. The output of the CVT 10 being connected to a load 104. A user input 106, for example an acceleration pedal, is conventionally connected to the throttle of the ICE 102 and to the control ring of the CVT 10 as discussed hereinabove.

[0037] One skilled in the art will understand that the force of the tension spring assembly 34 is determined according to the supplemental load to be allowed on the output of the CVT before the change of ratio towards the underdrive. It is believed to be within the reach of one skilled in the art to calculate the force of the tension spring assembly 34 according to the system requirements.

[0038] Of course, while tension springs assemblies were described herein as being the static forces of the CVT control, other types of spring assemblies or other mechanical, hydraulic or hybrid systems could be used.

[0039] It is to be noted that while a control ring 22 was described as the control mechanism to move the angle of the rollers 20, other control mechanisms could be used to achieve the same goal.

[0040] One skilled in the art will also understand that while the disks

12 and 14 have been described hereinabove as input disks and disk 18 has been described as an output disk, these functions could be reversed.

[0041] It is also to be noted that while full overdrive and underdrive ratios are mentioned hereinabove, the actual numbers depend on the actual CVT used and do not define a requirement for the above described mechanical control of a CVT.

[0042] It is to be understood that the mechanical control of a toroidal

CVT is not limited in its application to the details of construction and parts illustrated in the accompanying drawings and described hereinabove. The mechanical control of a toroidal CVT is capable of other embodiments and of being practiced in various ways. It is also to be understood that the phraseology or terminology used herein is for the purpose of description and not limitation. Hence, although the mechanical control of a toroidal CVT has been described hereinabove by way of illustrative embodiments thereof, it can be modified, without departing from the spirit, scope and nature thereof.