DE3938539A1 - CONTROL SYSTEM FOR A CONTINUOUSLY ADJUSTABLE CONE DISC BELT GEARBOX - Google Patents

Abstract

A continuously variable transmission includes two conical pulleys (3, 4, 5, 6), one pulley located in the input shaft (1), the other pulley located on the output shaft (2). A drive member (7) in frictional contact with the pulleys (3, 4, 5, 6) transmits torque between them. One conical pulley member (3, 5) is axially fixed and the opposing pulley member (4, 6) is axially movable but non-rotatable on its associated shaft (1, 2). The movable pulley members (4, 6) are actuated by hydraulic servos (A1, A2), loaded by pressure supplied by a pump (8) through a control valve (9) for adjusting and maintaining the transmission ratio. Servos (A1, A2) on the primary shaft (1) and secondary shaft (2) each have an associated torque sensor valve (10, 11) different from that of the other servo. One sensor valve (11) is preceded in a hydraulic control circuit by a minimum pressure valve (12) and followed by the other sensor valve (10).

Description

The invention relates to a control system for a infinitely variable conical pulley belt transmission, the type explained in the preamble of claim 1.

From DE-C2-30 28 490 a control system for a stu continuously variable conical pulley belt transmission, the be in the preamble of claim 1 explained type knows.

In the known conical pulley belt transmission two each arranged on a primary and a secondary shaft Nete conical disk parts provided, which over a between them arranged frictional tension member with each other are connected to transmit torque. One conical disk each part is axially fixed on its corresponding shaft arranged and the respective conical washers part is axially movable, but non-rotatable on its corresponding shaft arranged. The axially movable ke Gel disc parts are connected to cylinder parts, which cooperate with pistons arranged on the shafts and the pressure medium servers which can be acted upon by pressure medium vos form, which one prepared by a pressure medium pump pressure medium via a translation spool is fed accordingly to the setting of Ge to drive translation and maintain the Ensure contact pressure.

The axially fixed conical disk parts are involved a torque sensor in the form of between each other  overlying trough tracks arranged rolling elements together men.

One of the trough lanes is on one with the Pri march and / or the secondary shaft axially firmly connected Ring part formed and the opposite trough path is ax on one of the primary and / or the secondary shaft ial and rotatably arranged ring part formed over a connecting part with an input or output shaft is drivingly connected. This axially movable ring part has an annular piston part which with one in the fixed Conical disk parts trained ring cylinder together acts to form a cylinder / piston arrangement that is in Connection with a pressure medium supply opening in the ent speaking waves and one through the ring piston part controllable pressure medium discharge opening, a torque Form valve-dependent valve arrangement supplying control pressure.

The control system of this known continuously variable Ke gel disc belt transmission consists here in the we substantial from the pressure medium pump, a translation dependent preload valve, the transmission control spool and the torque sensor valve assembly.

From Fig. 2 of the above-mentioned patent is ersicht Lich that the pressure medium flowing through the pressure medium discharge opening is guided via a branch channel into the area between the trough paths of the torque sensor, but this is done only for the purpose of lubrication.

DE-C1-34 03 704 is another control system for a continuously adjustable conical pulley wrap drives the explained in the preamble of claim 1 ten kind known, in which again in the axially fixed cone Partly, a torque sensor valve assembly is provided  which delivers a torque-dependent control pressure, this torque-dependent control pressure over a Basic pressure valve is guided before it is the translation Control valve is fed.

A control system is therefore from the first patent remove at which the torque-dependent control pressure increases next via a ratio-dependent preload valve mo is dulated before it to the translation spool is directed.

From the second-mentioned patent is a control system known, in which a torque-dependent control pressure next to a preset basic pressure valve before it is taken to the translation spool.

The known control systems have the disadvantage that them by the fact that they are the shoot to be broadcast Only consider the moment on one of the two waves infinitely variable over wide operating ranges Conical pulley belt transmission too high contact pressure which lead to the overall efficiency of the transmission by the required pumping power and by the increasing pressure decreasing efficiency of the order Looping transmission undesirably reduce.

The object of the invention is to provide a control system for a infinitely variable conical pulley belt transmission the type explained in the preamble of claim 1 to improve in such a way that by the appropriate consideration adjustment of the torques on both shafts the contact pressure for the frictional tension member can be controlled so precisely that at all times adequate security against a very annoying and damaging slipping the tension member is given, however, that the contact pressure pressure is maintained at the permissible minimum pressure.  

According to the invention, this object is achieved by a Torque sensor valve assembly is modified such that the area between the trough tracks is sealed Cylinder / piston arrangement forms, the effective area of the Effective area of the cylinder / piston arrangement on the movable Ring part ent on the axially fixed conical disk part speaks and this now a torque-dependent dif torque sensor valve arrangement Basic or minimum pressure valve upstream and one ago conventional, a torque-dependent absolute pressure Remote torque sensor valve assembly on the other Shaft is connected downstream, which means the translation tax slide a modified torque-dependent control pressure is supplied, the control of the contact pressure a lower level while maintaining security against slipping.

The invention is based on one in the accompanying drawing Solutions shown embodiment explained in more detail. It shows:

Figure 1 is a schematic representation of a hydraulic circuit diagram according to the prior art.

Fig. 2 is a diagram of the contact pressure over the translation in a hydraulic circuit diagram according to the prior art;

Fig. 3 is a torque sensor valve assembly according to the prior art;

. Figure 4 is a torque sensor valve assembly according to the invention;

Fig. 5 is a schematic representation of a hydraulic circuit diagram according to the invention and

Fig. 6 is a diagram of the contact pressure over the translation in a hydraulic circuit diagram according to the invention.

With continuously adjustable conical pulley belt transmission ben must be ready by the hydraulic pressure medium servos set contact pressure for the tension member according to the occurring torque and the respective gear ratio be managed. Pressures that are too low cause even tuell a slipping of the tension member, which leads to wear or eating and therefore ver must be avoided. The previously known control systems have therefore this contact pressure set so high that this with Security was prevented.

Excessive contact pressures result in an unnecessarily high pump output and a decrease in the efficiency of the Umschlin transmission and thereby lead to an efficiency deterioration of the overall transmission.

If the contact pressure does not exactly correspond to that load-bearing torque controlled, this results in particular in part load areas of a continuously adjustable cone sheave ben belt transmission a rather poor effect degree of the total transmission, which is the reason for that which in itself through the optimal control of the engine speed achievable low fuel consumption of such vehicles not fully with a continuously variable transmission catch is feasible.

In the hydraulic circuit diagram shown schematically in Fig. 1, one starts from the steady state, in the hydraulic pressure fluid servo A 2 on the secondary shaft, a hydrostatic pressure P 2 , by the two elements connected in series, a biasing valve and one Torque sensor type A is determined.

In this case, the pressure of the pressure medium pump is identical to the contact pressure in the hydraulic pressure medium servo A 1 on the primary shaft, and experience has shown that this is approximately 30% higher in order to maintain the selected ratio.

The differential pressure generated by the preload valve is dependent from the current translation and this dependency will technically derived from the fact that a mechanical Transmission member the respective position of the axially ver sliding conical disc parts removed and on the front tension spring of the valve is transmitted. The torque Type A sensor generated pressure is proportional to torque according to the relationship

P = f T,

(P = sensor pressure, f = sensor constant, T = torque).

The level of the contact pressure is therefore an addition of one translation-dependent and a torque-dependent variable.

An example can be seen from the diagram in FIG. 2.

The curve a gives that for the transmission of the maximum torque required pressure curve again. The curve A shows however, the actually set contact pressure.

Due to the different curvature of the two curves results in the intermediate speed range, a clear excess pressure Δ P, which will be seen from Fig. 2, last section in the part represented by the curves c and C, also it is considerably larger.

The curve c gives the half maximum transfer torque necessary contact pressure again during the Curve C shows the actual pressure curve.  

The very large overpressure Δ P cannot significantly ver be reduced, because when curve C is lowered in the area small translations, d. H. near the overdrive, this Curve would run below curve c, resulting in a Would slip through the tension member.

In connection with FIGS. 3 and 4, a known torque sensor valve arrangement in comparison with the torque sensor valve arrangement according to the invention is explained.

Fig. 3 shows the known torque sensor valve assembly, as can be seen from the preamble of claim bil denden mentioned patent.

The known torque sensor valve arrangement is intended here with the designation "Type A" to the difference tion with the torque sensor valve according to the invention order, which is referred to as "Type B" and later explains is tert.

Pressure medium flows in from a pressure medium pump Pressure relief valve and the preload valve to the torque sensor Type A.

The z. B. in the primary shaft 1 with the fixed cone disk part 2 arranged torque sensor type A is formed from an axially movable ring part 3 and an axially fixed ring part 4 with roller bodies 7 arranged between their opposing trough tracks 5 and 6 , the axially movable ring part 3 is connected via a connecting part 8 via a toothing 9 to the drive shaft (not shown). The drive torque introduced leads to an axial movement of the ring part 3 with its piston part 10 in the cylinder 11 on the fixed conical disk part.

The pressure chamber 12 formed between the piston part 10 and the cylinder 11 is supplied with pressure medium in a quantity Q 1 via a supply channel 13 . The piston part 10 interacts with a control edge 14 of a discharge duct 15 , via which pressure medium can flow to an unpressurized area of the transmission with an amount Q 2 reduced only by leakage. Here, a hydrostatic pressure is built up, which is necessary in order to hold the axially displaceable ring part 3 of the torque sensor valve arrangement type A in the position shown in the upper part of FIG. 3. This hydrostatic pressure has to overcome an axial force which results from the torque introduced between the fixed ring part 4 and the movable ring part 3 as a result of the trough tracks 5 and 6 and the rolling elements 7 .

As a result, a torque-dependent control pressure is built up in space 12 .

Fig. 4 shows the torque sensor valve arrangement of type B modified according to the invention, which differs only slightly from the design according to type A and in which reference numerals which correspond in part are thus used. Only modified components are provided with a dash index with reference numerals.

The main difference of the torque sensor type B to the torque sensor type A is that the fixed ring part 4 'in the movable ring part 3 ' is sealed and their pressurized ring surfaces are designed with the same area and that the area between the Muldenbah NEN 5 and 6 via a branch channel 16 with the flowing torque-dependent control pressure from room 12 is struck. The hydrostatic pressure in the discharge duct 15 , which carries the flowing quantity of pressure medium Q 2 , is kept at a certain level via a basic or minimum pressure valve.

The torque sensor valve arrangement type B according to the invention thus does not generate a torque-dependent absolute pressure but a torque-dependent differential pressure between the two pressures in the space 12 and in the discharge duct 15 .

The function of the control system according to the invention is explained in connection with FIGS. 5 and 6.

As can be seen from FIG. 5, the translation-dependent bias valve according to FIG. 1 is replaced by the series connection of a basic or minimum pressure valve and a torque sensor type B.

The basic idea of the new control concept is both on the primary shaft as well as on the secondary shaft Arrange torque sensor, it being immaterial whether a type A torque sensor or a torque sensor according to type B on the primary shaft and on the secondary shaft or but arranged on the secondary shaft and on the primary shaft is, but it is only essential that different Torque sensor valve assemblies on the two shafts be provided.

Apart from the basic or minimum pressure valve, so the contact pressure results

P 2 = f ₁ T ₁ + f ₂ T ₂ ,

(P 2 = contact pressure, f ₁ = sensor constant input shaft, f ₂ = constant sensor output wave, T wave ₁ = torque input, T ₂ = torque output shaft).

The torque on the output shaft is:

T ₂ = i T ₁ ,

(i = translation of the belt transmission).  

From the two previous considerations it follows:

P ₂ = f ₁ T ₁ + if ₂ T ₁ , or
P ₂ = T ₁ (f ₁ + f ₂ i).

This equation means that the contact pressure P _{2 can be represented} as the product of a function that is linearly dependent on the translation i and the torque T. By designing the sensor constants f ₁ and f ₂ , the linear translation function can be given any desired initial value and any required slope.

If you just choose them in the shortest and in the longest translation the actual pressure just that corresponds to the required contact pressure, you get over a pressure curve across the entire translation range has only very low overpressures Δ P and this at each the torque.

Fig. 6 shows the achievable pressure conditions for an inventive control system. Curves a, b, c and d show the required contact pressures for 1-fold, 0.75-fold, 0.5-fold and 0.25-fold maximum torque.

The curves A, B, C and D are the curves of the contact pressure P 2 achievable with the control system according to FIG. 5. The respective excess pressure Δ P is reduced to significantly smaller amounts in comparison to FIG. 2. Since the pressure control according to the equation explained above shows that a contact pressure of P ₂ = 0 would result for a torque T ₁ = 0 (the belt transmission is not loaded), ie the contact pressure would be completely lost and the tension member would begin to slip, In this case, a residual tension or a residual contact pressure which reliably prevents slipping is maintained, for which the basic or minimum pressure valve in the control according to FIG. 5 takes care. It does not drop the contact pressure below a certain given value (e.g. 3 bar).

The control system according to the invention allows a pressure rain contact pressure without significant overpressure ranges, thereby enables the reduction of pumping losses as well an improvement in the efficiency of the Umschlingungsge drive and thereby improves the overall efficiency of the Transmission significantly. The effort required is le only in an additional modified torque sor valve arrangement, but this is eliminated the ratio-dependent preload valve and the one for this required mechanical sensor linkage device compared.

The control system according to the invention is not only on levels loosely adjustable belt transmission of the "Reimers" type but in the same way on the belt transmission "Van Doorne" design applicable, with these the Contact pressure determining secondary valve by a torque ment sensor arrangement and valve arrangement according to the inven is replaced.

Claims (1)

Control system for an infinitely variable conical pulley order loop transmission with two conical pulley parts arranged on a primary and a secondary shaft and a tension member arranged between them in a frictional manner, one conical pulley part being axially fixed and the opposite conical pulley part axially movable but non-rotatably arranged on its respective shaft is and wherein the axially movable conical disk parts are connected to cylinder parts which form pressure medium servos which can be acted upon by pressure medium with the pistons arranged on the shafts and which are supplied by a pressure medium pump with pressure medium via a control slide for adjusting the gear ratio and maintaining the contact pressure, and wherein the axially fixed conical disk parts ( 2 ) interact with a torque sensor (type A) in the form of roller bodies ( 7 ) arranged between one of the opposite trough tracks ( 5 and 6 ), the one Trough path ( 6 ) is formed on an annular part ( 4 ) which is axially fixed to the primary and / or the secondary shaft and the opposite trough path ( 5 ) is formed on an annular part ( 3 ) which is axially and rotatably arranged on the primary and / or the secondary shaft is and this ring part via a connec tion part ( 8 ) with a drive or output shaft trei bend and wherein this axially movable ring part ( 3 ) with a piston part ( 10 ) in a cylinder ( 11 ) in the fixed conical disk part ( 2 ) forms a cylinder / piston arrangement and the cylinder chamber ( 12 ) via a supply channel ( 13 ) is pressurized with pressure medium and pressure medium can flow through a control edge ( 14 ) to a pressure-free guide channel ( 15 ), so that depending a torque-dependent control pressure in the space ( 12 ) forms from the torque, which, in conjunction with a preload valve, maintains the contact pressure for the frictional tension member, and abf leaving pressure medium via a Zweigka channel in the area between the trough tracks is characterized in that

• - On one shaft a torque sensor-Ventilan arrangement (type B) with a in the area between the trough paths ( 5 'and 6 ') a sealed cylinder / piston arrangement of an active surface, which corresponds to the active surface of the opposite side, arranged becomes,
• - This cylinder / piston arrangement via a second channel ( 16 ) of the preset pressure of the basic or minimum pressure of the flowing pressure is supplied by means of the space ( 12 ) to provide a torque-dependent differential pressure and
• - On the other shaft, a torque sensor valve arrangement (type A) is arranged, which provides a torque-dependent absolute pressure and the two torque sensor valve arrangements (type B and type A) are connected in series.