GB2339605A

GB2339605A - A CVT with a hydraulic control system

Info

Publication number: GB2339605A
Application number: GB9808758A
Authority: GB
Inventors: Bernard Crawshaw Leggat
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-04-25
Filing date: 1998-04-25
Publication date: 2000-02-02
Also published as: GB9808758D0

Description

2339605 MPROVEMENTS TO THE HYDRAULIC CONTROL IN CONSTANTLY VARIABLE

TRANSMISSIONS, This invention relates to constantly variable transmissions which are more usually known by and referred to herein as types CVT or CTX.

CTX transmissions operate in a different manner compared to conventional automatics, one aspect of this difference being that relatively high oil pressures (typical range 7 - 30 bar) are required to maintain traction between the steel belt and pulleys, whilst significantly lower pressures (typical range I - 6 bar) are required to operate the drive clutches, these two oil pressures (high & low) are respectively termed secondary pressure and clutch pressure.

It is well known that some CTX transmissions develop a condition whereby forward and reverse clutch engagement from park or neutral is unacceptably harsh, even at engine idle speeds below 800 R.P.M. and in some instances may cause the engine to stall.

Diagnostic pressure tests on vehicles which develop this condition will show that idle speed clutch pressures are substantially in excess of the -6 to I bar requirement for soft engagement.

Procedure to rectify the aforementioned condition would normally involve the fitting of replacement springs to the clutch pressure valve (4) in the valve body (VB) or even a modified version of the valve (4). It is an object of the present proposal to show that clutch pressures in contemporary valve bodys may be adversely influenced by way of relatively high oil pressures passing gallery (A) in the valve body (VB) and into the relatively low pressure gallery (B) via clearances between the secondary valve (3) and valve body (VB).

During operation of the clutches gallerys (B) and (C) Fig: 5 are conduitly connected to the engine pitot tube (E.P) and are all (B) (C) and (E.P) interconnected via the declutching valve (6).

It is proposed herein to provide means by which secondary oil presssure in gallery A (Figs: 1.2.3. & 6.) may be prevented from passing into the engine pitot gallery (B) via the clearances which are formed between the secondary valve (3) and the valve body.

Such means is provided by forrning an oil collecting gallery (G) within the valve body bore (Fig: 1) or alternatively may be formed upon the secondary valve (3) (Fig: 2) an apperture (H) also being provided for the purpose of exhausting oil from the gallery (G) (Figs: I & 2), the oil collecting gallery (G) may be formed within the valve body (V.B.) (Fig: 1) by using a suitably constructed tool with a retractable cutter (Fig: 4). Alternative means to prevent oil transferring from the gallery (A) to the gallery (B) may be provided in the form of a substantial seal (S) (Fig: 3) which may be installed within a groove formed upon the secondary valve.

KEY TO DRAWINGS, FIGO 1. Is a schematic part section of a valve body (VB) and secondary valve (3) wherein is shown a preferred embodiment of the present proposal, having an oil collecting gallery (G) which may be formed in the valve body (VB) by using a retractable cutting tool such as in Fig: 4 the gallery (G) being also provided with an exhaust apperture (H).

FIG:2. Is a schematic section of a valve body (VB) and secondary valve (3) wherein the oil collecting gallery (G) is formed upon the moveable part of the secondary valve (3:)) the gallery (G) also being provided with an exhaust apperture (H).

FIG: 3. Is similar to Fig: 2, but is not provided with an exhaust apperture, and is provided with a substantial seal (S) or 0 ring.

F1GD 4. Is a schematic part view of a cutter body (CB) having a moveable cutter (R) and (L) which may be inserted into the valve body (CB) and rotated to form a gallery (G) (such as in Fig: 1.) the cutter body having a moveable member (RL) upon which pressure may be applied or decreased to respectively raise (R) or lower (L) the cutter.

FIG: 5. Is a schematic view of the relatively low pressure clutch control circuit and wherein oil pressure is shown (arrowed) entering the engine pitot (E.P.) and is directed simultaneously to gallerys (B) & (C) of the secondary valve (31) and the clutch pressure valve (4) respectively. The declutching valve (6) is depicted in the'switched on'position, since during normal operation this valve would only be'switched off when the gear selector is at park or neutral.

FIG: 6. Is a general view on the valve body (VB) and its component parts.

B. C. LEGGAT.

1-6 Position of the valves in the valve body assembly 8 Clutch switching valve I Ratio control damping valve 9 Auxiliary accumulator valve 12 Primary valve 10 Accumulator valve 3 Secondary valve I I Lever 4 Clutch pressure valve 12 Selector shaft Clutch pressure limiting valve 13 Engine braking valve 6 Declutching valve 14 Throttle valve 7 Reverse inhibiting valve 0 The switchim, functions of the automatic Note- Not all (lie passages in the valve C transmission are controlled in the valve body body assembly are continuously assembly. tinder pressure; however, they are allways filled with Automatic Transmission Fluid (ATF).

I

Claims

CLAIMS.

1. An improvement to the hydraulic control system in constantly variable automatic transmissions by the provision of means by which secondary oil pressure in gallery (A) (Figs 1,2,3 & 6) may be prevented from passing into the engine pitot gallery (B) via clearances which are formed between the secondary valve (33) and the valve body (VB).

Such means comprising an oil collecting gallery (G) to which is conduitly connected an apperture (H) for the purpose of exhausting oil ftom the gallery (G).

2. Improvements as claimed in Claim I wherein the oil collecting gallery (G) is formed upon the valve body (VB).

3. Trnprovements as claimed in Claim I or Claim 2 wherein the oil collecting gallery (G) may be formed upon the valve body (VB) (Fig 1) by using a suitably constructed cuttin g tool such as in Fig 4 wherein is shown a cutter body (CB) being provided with a member (RL) which is moveable and constructed in such a manner that pressure may be applied or decreased upon the cutting member (R) to respectively raise (R) or lower (L) the cutting member during operation.

4. Improvements as claimed in Claim 1 wherein the oil collecting gallery may be formed upon the secondary valve (3) (Fig 2).

5. Improvements as claimed in Claim 4 wherein a seal or '0' ning may be installed upon the oil collecting gallery (G) formed upon the secondary valve (3) (Fig2).

6. Improvements to the hydraulic control in constantly variable transmissions substantially as described herein with reference to figures 1-6 of the accompanying drawings.