WO1998006964A1

WO1998006964A1 - Method for controlling pressure in a vari-speed transmission

Info

Publication number: WO1998006964A1
Application number: PCT/EP1997/004323
Authority: WO
Inventors: Ralf Vorndran; Hubert KÖNIG; Herbert Mozer
Original assignee: Zf Friedrichshafen Ag
Priority date: 1996-08-14
Filing date: 1997-08-08
Publication date: 1998-02-19
Also published as: DE19632747A1; EP0918963A1

Abstract

The invention pertains to a method for controlling pressure in a vari-speed transmission, based on a system with cone pulleys and belts, wherein a pressure calculation is made during partial braking. The reversal of the direction of rotation that occurs at the variable speed gear (4) upon partial braking is taken into account.

Description

Method for pressure control of a CVT

The invention relates to a method for pressure control of a CVT in overrun mode.

Continuously variable automatic transmissions, hereinafter referred to as CVT, usually consist of the following modules: starting unit, forward / reverse driving unit, variator, intermediate shaft and differential. The variator in turn consists of a pair of primary conical disks, a looping element and a pair of secondary conical disks. Each pair of conical disks consists of a conical disk that is fixed in the axial direction and a conical disk that can be moved in the axial direction. The torque transmission capacity and the ratio of the CVT are determined via the axial position of the conical pulleys. Such a structure is known from ATZ Automobiltechnische Zeitschrift 96 (1994), No. 6, page 380. A general method for pressure calculation for a CVT is known from drive technology 26 (1987), No. 8, page 45. EP-PS 0 451 887 discloses the use of such a method in connection with two electronic transmission control units.

In the prior art described above, no distinction is made between pulling and pushing operations. However, since the torque transmission direction on the variator is inverted in overrun mode, the prior art has the disadvantage of an incorrect pressure calculation.

The invention therefore has the task of ensuring an error-free pressure calculation for the overrun operation. The object is achieved according to the invention by determining the pressure level in the adjustment space of the pair of secondary disks according to the formula with the detection of overrun operation:

p_SEK = (kP / kS) • cos α ^• M_t • SF / (• 2μ ■ R • A_SEK)

here mean:

cos α: cosine of the cone pulley angle M_t: turbine torque μ: coefficient of friction of the cone pulley / belt element

R: Radius of the loop on the primary pulley A_SEK: effective adjustment surface of the secondary pulley kP / kS: force ratio of primary / secondary pulley SF: safety factor

The solution according to the invention has the advantage that the contact pressure calculation also takes into account the fact that the primary disk becomes a torque-determining part of the variator in overrun mode.

In one embodiment, it is proposed that the turbine torque be calculated according to the following relationship in overrun mode:

M t = MM + MP + M Seh + M Vb + [J Ges - (dω / dt)] here mean:

M M: torque delivered by the drive unit

M_P: Torque of the pump according to the contact pressure requirement M_Sch: Drag torque of the drive unit

M_Vb: torque loss of the additional consumers

J_Ges- (dω / dt): Sum of the dynamic moments of all consumers that load the variator in overrun

This embodiment offers the advantage that the calculation of the turbine torque includes the dynamic moment for the mass acceleration of all additional consumers and a quasi-static part. The quasi-static part is made up of the following parts: current torque output by the drive unit in overrun mode, absorption torque of the pump, drag torque of the drive unit as a function of temperature and speed, and loss torque of the additional consumers, such as. B. steering aid, generator or air conditioning.

An exemplary embodiment is shown in the figures.

Show it:

1A shows a program flow chart;

1B is a pull / shear characteristic and

Fig. 2 is a system diagram. 1A shows a program flow chart for the pressure calculation. The program begins with the SI query as to whether the vehicle is in overrun mode. The decision is made on the basis of a pull / push characteristic. This is shown in Fig. IB. If it is determined in the SI query that the vehicle is in the train area, the pressure calculation for the variator takes place in step S3 in accordance with the train calculation. If it is determined in the SI query that the vehicle is in the pushing area, the pressure calculation is carried out in accordance with the pushing function in step S2. In step S4, the pressure value thus calculated for the variator is output in current values.

IB shows a pull / shear characteristic. Speed values of the drive unit, here motor speed n_Mot, are shown on the abscissa. Values of an accelerator pedal position or throttle valve information are shown on the ordinate. The actual pull / shear characteristic curve is shown with reference symbol A, values above the characteristic curve A representing the pull range and values below the characteristic curve the shear range.

2 shows a highly schematic system diagram of a CVT. An internal combustion engine is shown with reference number 1, consisting of the two blocks 5 for the

Mass moment of inertia, 6 for the torque given by the internal combustion engine in overrun mode and 7 for the absorption torque of the pump. Reference number 2 denotes a hydrodynamic converter with its moment of inertia 8. Reference number 3 shows a forward drive clutch. Reference number 4 shows the variator, consisting of the primary conical pulley pair 11, the secondary conical pulley pair 12 and the looping element 13. The adjustment of the primary conical pulley benpaares happens via the force of the hydraulic medium on the area AI. The secondary conical pulley pair is also adjusted via the force of the hydraulic medium on surface A2. As further blocks arranged in the drive train, reference numeral 9 shows the moment of inertia of the drive and reference numeral 10 the moment of inertia of the primary pulley set. The speed of the primary shaft 14 is measured via a speed sensor 16. The speed of the secondary shaft 15 is measured via a speed sensor 17. Reference numeral 18 shows a current / pressure converter which converts current values into a pressure value for the forward driving clutch 3. Reference numeral 19 shows a pressure measuring device for the pressure level of the pair of secondary conical disks. Reference numeral 20 denotes an electronic transmission control unit which determines the required pressure level from the input variables described above and additionally from the train / push 21 driving state detection. For the overrun mode, the pressure level in the adjustment space of the secondary disc pair 12 is calculated according to the following formula:

p SEK = (kP / kS) • cos α • M t • SF / (• 2μ • R • A SEK)

here mean:

cos α: cosine of the cone pulley angle

M_t: turbine torque μμ :: coefficient of friction of the conical pulley / belt element

R: Radius of the loop on the primary pulley A_SEK: effective adjusting surface secondary disc kP / kS: force ratio primary / secondary disc SF: safety factor

Under cone pulley angle is to be understood the angle of the cone pulley flank with respect to the horizontal, z. B. 11 degrees. The force ratio kP / kS is usually determined using a corresponding diagram. The safety factor is determined from tests.

The turbine torque in turn is calculated according to the following relationship:

M_t = M_M + M_P + M_Sch + M_Vb + [J_Ges • (dω / dt)]

here mean:

M_ _M: torque output by the drive unit

M_ P: Torque of the pump according to the contact pressure requirement

M_ Seh: Drag torque of the drive unit

M Vb: torque loss of the additional consumers

J Ges- (dω / dt) Sum of the dynamic moments of all consumers that load the variator in overrun

The turbine torque calculated in this way contains a dynamic factor J_GeS '(dω / dt) and a quasi-static factor, which is composed of the following variables: current torque M_M emitted by the drive unit, absorption torque of the pump M_P, drag torque of the drive unit in Dependence of the temperature M_Sch and the speed and torque loss of additional consumer M_Vb, such as steering aid, generator or air conditioning. The size towing M_Sch of the drive unit is usually determined using a characteristic map, so that M_Sch = f (Teta, n_Mot) applies. Teta means the coolant temperature and n_Mot the speed of the drive unit. The characteristic diagram is designed in such a way that the influence on the quantity M_Sch approaches zero when the operating temperature of the drive unit is reached. The size M_Vb can be from a map or a digital, so z. B. Air conditioning "on" or "off", information can be obtained from consumers.

reference numeral

1 internal combustion engine 2 hydrodynamic converter

3 Forward drive clutch

4 variator

5 Mass moment of inertia of the internal combustion engine

6 Thrust torque of the internal combustion engine. 7 Torque of the pump

8 Mass moment of inertia of hydrodynamic converter

9 Mass moment of inertia drive

10 Mass moment of inertia Pπmar set

11 pair of primary cone pulleys 12 pair of secondary cone pulleys

13 Umschlmgungsorgan

14 Pπmarwelle

15 secondary wave

16 Pπmarwelle speed sensor 17 Secondary shaft speed sensor

18 Forward drive clutch pressure control

19 Pressure measuring device pair of secondary conical pulleys

20 electronic ticket control

21 entrance-sized train / push

Claims

P a t e n t a n s r u c h e

1. Method for pressure control of an electro-hydraulically controlled CVT of the conical pulley type, in which the torque transmission is determined via the pressure level in the adjustment space of the secondary pulley pair and a translation is determined via the pressure level in the adjustment space of the primary pulley pair, characterized in that the detection of overrun operation means that Pressure level in the adjustment space of the secondary disc pair is determined according to the formula:

p SEK = (kP / kS) • cos • M_t • SF / (• 2μ • R • A_SEK)

here mean:

cos α cosine of the cone pulley angle

M_t: turbine torque μ = coefficient of friction of the conical pulley / belt element

R: Radius of the loop on the primary pulley

A_SEK effective adjustment surface secondary disc kP / kS force ratio primary / secondary disc

SF: safety factor

2. The method according to claim 1, characterized in that the thrust torque (M_t) is calculated according to the following relationship in overrun mode:

M_t = M_M + M_P + M_Sch + M_Vb + [J_Ges ^■ (dω / dt)] here mean:

M_ _M: torque output by the drive unit

M_ _P: Torque of the pump according to the contact pressure requirement

M_ _Sch; Drag torque of the drive unit

M_ _Vb: torque loss of the additional consumers

J Ges (dω / dt Sum of the dynamic moments of all consumers that load the variator in overrun

3. The method according to claim 2, characterized in that the pump torque (M_P) is determined via a characteristic map, input variables of the characteristic map being the speed of the drive unit (n_Mot) and the setpoint value of the contact pressure (p_ASW), so that: M_P = f ( n_Mot, p_ASW).

. Method according to Claim 2, characterized in that the drag torque of the drive unit (M_Sch) is determined using a characteristic map, so that:

M_Sch = f (Teta, n_Mot), the input variable Teta corresponding to the coolant temperature of the drive unit and n_Mot to the speed of the drive unit.

5. The method according to claim 4, characterized in that when the operating temperature of the drive unit is reached, the influence of the sum (M_Sch) from the characteristic diagram goes to zero.