GB2215413A - Gearbox control unit - Google Patents

Abstract

An hydraulic actuator for a variator-type CVT includes a piston 10 operable by hydraulic pressure in response to an electric input. e.g. from a microprocessor. The pressure on the piston is controlled by a duplex valve 3, 9 such that the pressure on the piston 10 is reduced part way through the stroke. The electric input activates solenoid 1, 2 to apply force to tubular spindle 3 admitting pressure to chamber 6 via inlet 7. Pressure in chamber 6 builds up to balance force of solenoid 2 and is also applied to piston 10 via passage 12. As piston 10 moves against spring 19, pressure will enter chambers via passages 12 and 15. Thus hydraulic fluid acting downwardly on spindle 3 against solenoid 2 acts over a large area (chambers 5 and 6) than initially, resulting in a lower pressure being established in chambers 5, 6. <IMAGE>

Description

GEARBOX CONTROL UNIT This invention relates to an automatic gearbox of the continuously variable transmission (CVT) type, particularly for use in motor cars and commercial vehicles, e.g. those having an internal combustion engine delivering more than about 80 Kw.

CVT has been proposed and been a highly desirable objective of the automotive industry for a number of decades. A belt drive system for CVT has been reported (Van Doorne) but it is believed that there is an undesirably low upper limit on the power that it can transmit. Recently, a heavy duty CVT has been reported (Greenwood, Driveline 84, London, I Mech E, March 1984) wherein a so-called rolling traction drive is used with the variator ratio being determined by the so-called precession angles adopted by the rollers therein.

Control of the aforesaid precession angle tends to be difficult and insensitive and the manufacture of the control unit based thereon often involves a substantial quantity of precision engineering. There is a need to improve the accuracy of the aforesaid control of precession and reduce the cost of manufacture of the unit.

We have now devised a gearbox control system suitable for a CVT, based on a discrete unit. This unit is capable of providing dual force output, particularly by means of a dual pressure device, more particularly from an electro-hydraulic control. The unit overcomes many of the disadvantages associated with known control units for CVT's.

Furthermore, the applicant's gearbox control unit can be disposed within the gearbox housing. Hence the need for dynamic seals is at least reduced or may be eliminated, thereby reducing the hysteresis of the gearbox control unit.

The gearbox control unit according to the present invention allows the combination of an electrically driven duplex valve (described hereinafter) and output hydro-mechanical actuator into a single unit which is often compact. This single unit, e.g. a cartridge, can be mounted onto an internal wall or flange of the gearbox casing. A single unit thereby provides means for the conversion of an electrical input signal into a positioning device with a mechanical output drive. The movement of the piston, which provides the position control with the mechanical output drive, is used to control the precession angle of a CVT, e.g. the CVT described by Greenwood as hereinbefore mentioned.

According to a first aspect of the present invention, there is provided a gearbox control unit comprising; (a) a duplex valve activatable by an electrical actuator; and (b) a piston which incorporates one or more ports adapted and arranged such that the effective ratio as hereinafter defined, can be altered and which is in operational engagement with the duplex valve.

According to a further aspect of the present invention there is provided a gearbox control unit comprising; a gearbox control unit according to the first aspect of the present invention in operative connection with an electrical actuator.

By duplex valve we mean a device which (1) comprises at least a spool and an inner plunger and (2) provides two discrete effective surfaces, each of which can separately be subjected to a varying force from the electrical actuator as hereinafter defined. The inner plunger is moveable within and relative to the spool. Because the areas of the two surfaces differ from each other, each will provide a different hydraulic pressure from the equivalent force from the electrical actuator. In this manner, the ratio between input signal and the hydraulic pressure generated by the duplex valve will change according to the area of the effective surface being used.

An electrical input signal from an appropriate electronic source such as a micro-processor, is used to control an electrical actuator, preferably a proportional solenoid, and this actuator is used to actuate the duplex valve, in particular to drive the moving components thereof, i.e. the spool and inner plunger. The duplex valve is preferably directly activatable by the actuator although we do not exclude the possibility that it may be indirectly activatable.

The duplex valve comprises a spool and an inner plunger, as hereinafter described and illustrated in more detail. A pressure is generated in the duplex valve by the force exerted by the electrical actuator on the moving components of the duplex valve, and this pressure causes movement of the piston. The position of the piston is dictated inter alia by the pressure that has been generated and the reactive force. As the piston moves to a pre-determined position in the stroke thereof, the ratio of the input electrical signal to the output pressure from the duplex valve changes because of the opening of a fluid passage between the two effective surfaces.For the remainder of the stroke of the piston, the force output is reduced because the pressure generated by the duplex valve is lower due to the force exerted by the electrical actuator being effective over a surface of larger surface area.

By larger surface area is preferably the total cross sectional area of the spool. However, we do not exclude the possibility that the larger surface area is generated in such a manner that it is different from the total cross sectional area of the spool.

The gearbox control unit according to the present invention provides a controlled rate of change of fluid flow from the piston chamber in which the piston is disposed to the chamber intermediate the spool and the piston head during the transition from the primary to the secondary pressure range as hereinafter described. This controlled rate of change tends to improve the level of stability of the gearbox control unit through its range of operation; and thereby tends to improve the stability of the gearbox it controls.

By primary pressure range, we mean the output pressure from the duplex valve when the force from the electrical actuator is effective on the area of the end surface of the inner plunger. By secondary pressure range, we mean the output pressure from the duplex valve when the electrical actuator is effective on the larger surface area, preferably of the total cross sectional area of the spool.

The primary pressure is generated where the movement of the inner plunger is constrained by constraining means, e.g. the housing, or a part mounted rigidly thereon, or the restraining action of the piston.

Movement of the piston in one direction is induced by the pressure generated by the duplex valve. The return movement of the piston is induced by suitable means, e.g. a spring mechanism, and/or the force applied to the piston by the mechanism within the gearbox. Such a spring mechanism, where present, may be incorporated in the gearbox control unit or in the mechanism controlling the precession angle of the gearbox, or in both. It will be appreciated that means must be provided to allow the piston to return. For example, this may be via controlled leakage from the chamber intermediate the spool and the piston head as hereinafter described. Alternatively, one or more ports in the piston and associated parts, are adapted and arranged such that fluid can flow from the aforesaid chamber to tank, when the piston is moving from the changeover point towards the start of its stroke. A combination of both controlled leakage and the provision of ports in the piston may be used to control the flow from the aforesaid chamber to tank.

By changeover point we mean the point in the piston's stroke, at which the unit changes from primary to secondary pressure, or vice versa.

By the start of the piston's stroke, we mean the position of the piston prior to receipt of any input signals.

A person skilled in the art, would determine a suitable piston diameter to meet the requirement of the application, but could be from less than 12mm to more than 70mm, but typically would be 25mm.

We do not exclude the possibility that a hollow piston and associated components may be employed. Use of such hollow components often allows a gearbox shaft to run through a certain portion of the gearbox control unit. It will be appreciated that if this layout were to be used, the position of the duplex valve would have to be arranged and adapted such that clearance would be provided for the gearbox shaft.

The hydraulic fluid used in the gearbox control unit of the present invention would be chosen by a person skilled in the art, such that it will be compatible with the particular gearbox.

The invention will be further described by reference to the accompanying drawings, in which: Figure 1 is a graph illustrating typical primary and secondary pressure ranges; Figure 2 illustrates in simple schematic manner, partly in section, a longitudinal view of the gearbox control unit according to the present invention.

Figure 3 is of a detail of the gearbox control unit illustrated in Figure 2 at the actuator end thereof, showing the duplex valve when there is fluid flow connection between the pressure supply and the piston chamber (13) via orifice (14).

Figure 4 is of a detail of the gearbox control unit illustrated in Figure 2 at the actuator end thereof, showing the duplex valve when there is fluid flow connection between the piston chamber (13) via orifice (14) and tank.

Figure 5 is a longitudinal detail, partly in section, of the gearbox control unit illustrated in Figure 2 at the piston end thereof, showing the piston in the primary pressure mode.

Figure 6 is a longitudinal detail, partly in section, of the gearbox control unit illustrated in Figure 2 at the piston end thereof, showing the piston in the secondary pressure mode.

In Figures 3, 4, 5 and 6, parts corresponding to these of Figure 2 are indicated by the same numbering.

Referring firstly to Figure 1 of the drawings, primary and secondary pressures (therein indicated for convenience by the symbols "P" and "S" respectively) are generated according to the input electrical signal, which is usually a variation of current. The output pressures from the duplex valve are often up to about 100 Bar, typically about 12 Bar. The currents are varied, up to approximately 600 milliamps or up to more than 2000 milliamps, typically the variation is from zero or 50 milliamps to about 1000 milliamps. An appropriate range of input signals would be chosen by a person skilled in the art, as is appropriate to a particular gearbox.

In Figure 2, an electrical actuator (1) is attached to an actuator pin (2) which is in driving engagement with spool (3). The spool (3) is disposed in, and moveable within, the bore of a housing (4) which is further formed with a piston chamber (13) of larger bore in which piston (10) is moveable. Within inner chamber (6), defined by the wall and head of the spool, an inner plunger (9), which is moveable within and relative to the length of the spool, is disposed and projects therefrom distant from the actuator pin (2). The aforesaid projecting portion of plunger (9) projects into chamber (5) which is intermediate the spool (3) and the piston head (10). The spool is formed with ports (18) which are engageable with channels (7) and (8) in the housing (4) to allow flow of fluid from the pressure supply and to tank respectively.The housing (4) is further provided with channel (16) to afford fluid flow from chamber (5) to tank.

The spool is provided with ports (11) which are engageable with an orifice (14) and a gallery (12) to afford fluid flow connection between inner chamber (6) and piston chamber (13).

Port (17) in the piston (10) allows fluid flow connection from chamber (5) to tank, as hereinafter described, when the piston is moving from the start of the stroke to the changeover position and vice versa. (This is illustrated in further detail in Figure 5).

In operation, the varying input signal into the electrical actuator (1) provides a varying output force at the actuator pin (2). This pin (2) drives against the spool (3), tending to push the spool along the bore of the housing (4). When chamber (5) is at tank pressure, the force from the electrical actuator is used to generate a pressure in inner chamber (6). By tank pressure, we mean the hydraulic pressure applicable within the gearbox casing. The manner in which the pressure is generated in chamber (6) is for the spool to be moved to uncover the pressure inlet port (7), thereby allowing fluid under pressure into inner chamber (6).

(This is illustrated in further detail in Figure 3). When the pressure in the inner chamber (6) reaches a value where, when acting on the surface area of the inner plunger, it equals the input force, then the spool is in a state of equilibrium and so closes the pressure inlet port (7). Alternatively, where the pressure in inner chamber (6) is higher than that required, then the pressure generated in inner chamber (6) will create a force greater than that exerted by the electrical actuator. This force will cause the spool to move towards the electrical actuator and thereby allow fluid from inner chamber (6) to pass through outlet port (8) to tank. (This is illustrated in further detail in Figure 4). In this mode of operation, the gearbox control unit is said to be working in its primary pressure range.

Fluid under pressure in inner chamber (6) is in fluid flow connection via hole(s) or cross drilling(s) (11) and a gallery (12) with the piston chamber (13). Typically, the flow would be restricted through an orifice (14). The pressure within piston chamber (13) would cause the piston (10) to move against a spring (19) within the gearbox control unit and/or a load (not shown) in the gearbox.

As piston (10) moves through its stroke, hole (15) becomes uncovered, thereby being in fluid flow connection to piston chamber (13). By this means, fluid under pressure passes from piston chamber (13) into intermediate chamber (5). The electric actuator, therefore has to generate pressure in intermediate chamber (5) as well as in the inner chamber (6).

In this manner the gearbox control unit is operating in its secondary pressure range.

It will be appreciated that the gearbox control unit can be used to provide a force reduction as the piston reaches a pre-determined position, which can be a requirement for certain continuously variable transmissions.

Claims (9)

1. A gearbox control unit suitable for a CVT, comprising; (a) a duplex valve as hereinbefore defined activatable by an electrical actuator; and (b) a piston which incorporates one or more ports adapted and arranged such that the effective ratio of the electrical signal to the output pressure from the duplex valve as hereinbefore defined, can be altered and which is in operational engagement with the duplex valve.

2. A gearbox control unit as claimed in claim 1 in operative connection with an electrical actuator.

3. A gearbox control unit as claimed in claims 1 or 2 wherein the duplex valve is directly activatable by the actuator.

4. A gearbox control unit as claimed in claims 1,2 or 3 wherein the electrical actuator is controlled by a micro-processor.

5. A gearbox control unit as claimed in claim 2 wherein the electrical actuator is a proportional solenoid.

6. A gearbox control unit as claimed in any one of claims 1-5 wherein the larger effective surface area of the duplex valve is provided by the total cross-sectional area of the spool.

7. A gearbox control unit as claimed in any one of claims 1-6 wherein the suitable means for inducing return movement of the piston comprises the force applied to the piston by the mechanism within the gearbox.

3. A gearbox control unit as claimed in any one of claims 1-7 wherein the means of allowing the piston to return comprises controlled leakage from the chamber.

9. A gearbox housing containing a gearbox control unit as claimed in any one of claims 1 to 8.