Patent GB-1462290-A (GB)
Title: Hydraulic control system of an automatic power transmission
IPC: F16H59/20
Filed: 1974-08-30
Abstract: 1462290 Change speed control NISSAN MOTOR CO Ltd 30 Aug 1974 [18 Oct 1973] 37999/74 Heading F2D The invention is based on what is shown in prior Specifications 1,444,641 and 1,462,289, and the description differs from that of those Specifications only by the inclusion of a more detailed explanation, with equations, of the features claimed in this Specification, to which features the present abridgment is exclusively directed. The change speed gear and its hydraulic control circuit are the same as those in the earlier Specifications, the drawings being identical, and as regards Specification 1,462,289 using the same reference numerals. For details of the gear and control circuit as a whole, reference should be made to the abridgment of Specification 1,444,641, which, however, uses different reference numerals for the same items, but which numerals are included here, where appropriate, in brackets after the present numerals. The invention claimed here, and also described in both the earlier Specifications, is directed to obtaining a lower hysteresis (upshift-downshift speed difference) during kickdown operation than during normal, i.e. non- kickdown operation, as illustrated in Fig. 4 (not included in either earlier Specification), in which lines a1, b1 represent, as an example, the up-down 2-3, 3-2 shift pattern for a normal automatic shift, whilst a2, b2 represent the same for automatic shift during kickdown operation, for an existing transmission in which the kickdown hysteresis H2 is of the same order as that H1 for normal shift. Thus if, whilst travelling at the point p in third ratio, the driver performs a kickdown, the point p will be moved to Q, which, being within the hysteresis zone H2 will not produce kickdown until vehicle speed has dropped to b2. In this invention shift valve modifications, described below, reduce the kickdown hysteresis to h and, since the point Q is outside this zone, downshift would occur immediately on kickdown. This is achieved as follows, taking the 2-3 shift valve 110 as example. The 2-3 shift valve 110 has two separate differentially landed spools 548, 550, which remain together in contact for all except forced manual shift (see below) and, when in their lowermost, downshifted position shown, are loaded downwards by a spring 572 with force F1; by line pressure Pl, supplied to a first port 534 from the 1-2 shift valve 108 when upshifted, to act on a differential area A2-A3; by throttle pressure Pt supplied to a topmost second port 546, to act on an area A5; and by hysteresis pressure 320, which is a constant pressure Ph, higher than governor pressure, produced by a spring-loaded hysteresis valve (92 (128)), supplied to a fourth port 542 to act on a differential area A4-A5. The spools are loaded upwards for upshift by governor pressure Pg, supplied to a third, lowermost, port 528 and acting on an area A1. In addition to these four ports the shift valve 110 has a fifth port 544, which receives hysteresis pressure 320 from the kickdown valve (98 (124)), only when that valve is opened at kickdown, thus port 544 being blanked in the downshifted position shown. In the upshifted upper position of the two spools 548, 550, line pressure at the first port 534 passes to the upshift servo line 574 between lands of equal area A2 and hence its downward load on the spools is cancelled, the second port 546 still receives throttle pressure Pt; the fourth port 542 is blanked; whilst the fifth port 544 is without pressure for a normal shift but, during kickdown, receives through the kickdown valve (98 (124)) hysteresis pressure Ph to act on the differential area A4-A5. In both cases governor pressure Pg acts upwards on the same area A1. Hysteresis is the difference between the sums of the downshift forces in the respective downshifted and upshifted positions, which, for a normal (i.e. non kickdown) shift is as follows: For kickdown conditions hysteresis is as follows: Therefore normal shift hysteresis # 1  exceeds kickdown shift hysteresis # 1 <SP>1</SP> by # 1  - # 1 <SP>1</SP> = Ph(A4 - A5). This hysteresis difference can be controlled by varying the hysteresis pressure Ph, by changing the loading spring of the hysteresis valve (92 (128)). In addition, on kickdown, governor pressure Pg is reduced from a boosted value to a basic value on kickdown, to reduce downshift speeds, and at engine idle is substituted by line pressure to upshift all the shift valves to avoid creep. For a forced manual downshift the valve spools 548, 550 are forced apart by line pressure supplied to a port 540 from the manual selector valve 82 (102) in manual 2 and 3 settings, all as described in the abridgment of Specification 1,444,641.