Hydraulic pressure control method and apparatus for an automatic transmission

Abstract: The automatic transmission includes a friction engaging element A signal pressure generation element (15) generates an output pressure (Po) to be supplied to the friction engaging element, according to an input electrical signal (I). A a main map which specifies a relationship between a signal pressure (P SOL ) for generating an output pressure (Po) corresponding to a required output value (P*) and the electrical signal (I) at this time. The various output pressures (Po) which are actually generated when various electrical signals (I) based upon various signal pressures (P SOL ) are input to the signal pressure generation element (15) are measured in advance. The relationship between these measured values (Po) and the signal pressures (P SOL ) at that time is stored in a control device; the relationship with the signal pressure (P SOL ) corresponding to the required output value (P*) is compensated based upon the relationship between these stored measured values (Po) and signal pressures (P SOL ). When the required output value (P*) is input, the electrical signal (I) is obtained from the main map based upon the compensated value (P SOL *) for signal pressure, and this is input to the signal pressure generation element (15).

Description: The present invention relates to a hydraulic pressure control method and apparatus, for an automatic transmission for a vehicle, in which a signal pressure is produced by an electrical signal, and an output pressure is controlled by this signal pressure. An automatic transmission for a vehicle performs speed changing by selectively engaging a plurality of frictional elements, such as clutches and brakes. If at this time the engagement pressure for a frictional element is not appropriate, there is a possibility that speed change shock may occur or that the speed changing response may be slow. In this connection, it is proposed in Japanese Patent Laying-Open Publication Heisei 8-270777 to perform transition control for the line pressure which engages the frictional elements. A hydraulic pressure control circuit for an automatic transmission produces a signal pressure by driving a solenoid, and controls by this signal pressure an engagement pressure for a frictional element which is an output pressure, or a line pressure which controls engagement of a frictional element, so as to perform speed changing. However, there is the problem that the relationship between the drive electrical signal for the solenoid and the output pressure cannot be accurately determined, due to variation or individual differences in circuit resistance. In order to solve this problem, it has been conceived to store a complete set of data relating to actually measured output pressure for each level of electrical signal within the control device, to derive from this database the value of electrical signal which corresponds to the required value for the output pressure, and to send an electrical signal of this value as a command to the solenoid. In this case, an expanded memory capacity becomes necessary for storing the above database, and the cost is increased. US-A-4 956 776 discloses a hydraulic pressure control method and an automatic transmission in accordance with the preambles of claims 1 and 5 respectively. The present invention provides a hydraulic pressure control method as set forth in claim 1 and an automatic transmission as set forth in claim 5. Brief Description of the Drawings Fig. 1 is a general view of an automatic transmission for a vehicle. Fig. 2 is a system diagram showing hydraulic pressure control apparatus of an automatic transmission to which the hydraulic pressure control method according to the present invention is applied. Fig. 3 is a flow chart showing a procedure which determines a relationship between solenoid pressure and clutch engagement pressure, according to the preferred embodiment of the present invention. Fig. 4 is a set of characteristic graphs used in the process whose flow chart is shown in Fig. 3, of which (a) shows actually measured data values for output pressure, (b) is a main map for a signal pressure, and (c) shows the relationship between signal pressure and output pressure. Description of the Preferred Embodiment Referring to Fig. 1, a control device 10 which functions as hydraulic pressure control apparatus controls a control valve 20, and supplies operating hydraulic fluid at a predetermined pressure level to an automatic transmission which is connected to an engine. Referring to Fig. 2, the control device 10 (which employs a hydraulic pressure control method in accordance with the present invention) comprises a clutch engagement pressure required value calculation section 11, a solenoid pressure calculation section 12, a solenoid drive current calculation section 13, a solenoid drive circuit 14, and a solenoid 15. The clutch engagement pressure required value calculation section 11 inputs various items of information for hydraulic pressure control. Based upon this information, the clutch engagement pressure required value calculation section 11 calculates a required value P* for the clutch engagement pressure as an output pressure which corresponds to the transmission input torque etc. Based upon a relationship (which is derived as will be described in detail hereinafter) between a clutch engagement pressure Po and a solenoid pressure P SOL which serves as a signal pressure, the solenoid pressure calculation section 12 derives a required solenoid pressure value P SOL * which corresponds to the clutch engagement pressure required value P*. The solenoid drive current calculation section 13 derives a required solenoid drive current I* (an electrical signal) from this required solenoid pressure P SOL *, based upon a main map, derived and stored in advance, which specifies the relationship between solenoid drive current I and solenoid pressure P SOL . The clutch engagement pressure required value calculation section 11, the solenoid pressure calculation section 12, and the solenoid drive current calculation section 13 constitute the control device 10, which is fitted as an integral unit to the main body of the automatic transmission. The required solenoid drive current I* is supplied via the solenoid drive circuit 14 to the solenoid 15, which is a signal pressure generation element. This solenoid 15 controls the opening amount of a control valve 20, and thereby produces the required solenoid pressure P SOL * according to the required solenoid drive current I*. Further, the hydraulic pressure control apparatus controls the clutch engagement pressure Po by the required solenoid pressure P SOL * so as to bring it to be equal to the clutch engagement pressure required value P*. The relationship between the clutch engagement pressure Po and the solenoid pressure P SOL in the solenoid pressure calculation section 12 is determined during the manufacture of the hydraulic pressure control apparatus by the flow chart shown in Fig. 3, and is stored within the control device 10. The details of the control by the solenoid pressure calculation section 12 will now be explained with reference to Fig. 3. This control starts upon the completion of preparations for measurement of the clutch engagement pressure Po, and first in steps 21 and 22 the solenoid drive current I is repeatedly output at each solenoid drive current I which is varied solenoid drive current I, and for each current value the clutch engagement pressure Po is actually measured as shown in Fig. 4(a). In step 23 a decision is made as to whether or not this actual measurement has been performed a predetermined number of times n. For example, in the case of the preferred embodiment, n=3. In step 24, the table map for the solenoid which most closely resembles the actually measured data of Fig. 4(a) is selected as the main map. For example, a solenoid table map which embodies a relationship between the solenoid drive current I and the solenoid pressure P SOL like that shown in Fig. 4(b) is selected as the main map. It should be understood that the drive characteristic of the solenoid is measured in advance during manufacture and stored. A relationship like Fig. 4(c) between the solenoid pressure P SOL and the clutch engagement pressure Po is approximately calculated from these actually measured data of Fig. 4(a) and the main map of Fig. 4(b) as a linear function like Po = A x P SOL + B by, for example, the method of least squares. The coefficient A and the constant B in this approximate linear relationship respectively constitute a coefficient for compensation A and an offset B. In step 25, during manufacture of the hydraulic pressure control apparatus, the coefficient for compensation A and the offset B are stored in the control device 10 as a relationship between the clutch engagement pressure Po and the solenoid pressure P SOL for the solenoid pressure calculation section 12. This coefficient for compensation A and this offset B are used during the calculation of the required solenoid pressure P SOL * by the solenoid pressure calculation section 12. In this manner, first, the required solenoid pressure P SOL * which corresponds to the clutch engagement pressure required value P* is derived by the solenoid pressure calculation section 12 using the coefficient for compensation A and the offset B, in other words using the relationship shown in Fig. 4(c) between the clutch engagement pressure Po and the solenoid pressure P SOL . Next, the case will be considered of deriving the required solenoid drive current I* for generating the required solenoid pressure P SOL * by the solenoid drive current calculation section 13, based upon the main map which gives the relationship between the solenoid drive current I and the solenoid pressure PsoL shown in Fig. 4(b). In this case, it is possible accurately to control the output pressure Po to the output pressure required value P*, since the relationship shown in Fig. 4(c) between the clutch engagement pressure Po and the solenoid pressure P SOL compensates for deviation of the relationship between the drive current I for the solenoid 15 and the output pressure Po caused by variation or individual differences in circuit resistance. Moreover, no expanded memory capacity is required, since it is only the relationship between the solenoid pressure P SOL and the clutch engagement pressure Po which is stored in the control device 10, so that it is possible to implement the above-described compensation cheaply with a memory of small capacity. Further, with this embodiment, it becomes possible further to reduce the memory capacity, since the relationship between the solenoid pressure P SOL and the clutch engagement pressure Po is obtained according to the least squares method, and the compensation coefficient A and the compensation offset B between them are stored in the control device 10. Since the control device is fixed to the automatic transmission and they are formed into one unit, it is possible to record the relationship between the signal pressure and the output pressure in the control device in their original state as separate units before mounting the automatic transmission to the vehicle, and thus by the above-described approximate calculation it becomes possible to simplify the automatic transmission yet further.

Claims: A hydraulic pressure control method for an automatic transmission comprising a friction engaging element and a signal pressure generation element (15) which generates a signal pressure (P SOL ) for controlling an output pressure (Po) which is to be supplied to the friction engaging element according to an input electrical signal (I) and a main map which specifies a relationship between a signal pressure (P SOL ) for generating an output pressure (Po) corresponding to a required output value (P*) and the electrical signal (I) at this time, wherein: various output pressures (Po) which are actually generated when various electrical signals (I) based upon various signal pressures (P SOL ) are input to the signal pressure generation element (15) are measured in advance, and the relationship between these measured values (Po) and the signal pressures (P SOL ) at that time is stored in a control device; the relationship with the signal pressure (P SOL ) corresponding to the required output value (P*) is compensated based upon the stored relationship between these measured values (Po) and signal pressures (P SOL ); and when the required output value (P*) is input, the electrical signal (I) is obtained from the said main map based upon the compensated value (P SOL *) for signal pressure, and this is input to the signal pressure generation element (15); characterised in that the compensation of the signal pressure (P SOL ) based upon the required output value (P*) is approximately calculated as a linear function, and the coefficient and the constant of the approximated linear function are stored in the control device. A hydraulic pressure control method claim 1, wherein the signal pressure generation element is a solenoid (15) which regulates a hydraulic pressure of the automatic transmission, and the said output pressure (Po) is an engagement pressure of a frictional element. A hydraulic pressure control method as claimed in claim 1 or 2, wherein a least squares method is used for the said approximate calculation. A hydraulic pressure control method as claimed in any preceding claim, wherein the control device is fitted into the main body of the automatic transmission as an integral unit. An automatic transmission including: a solenoid (15) which generates a signal pressure (P SOL ) for controlling an output pressure (Po) which is to be supplied to a friction engaging element of the automatic transmission, according to an input electrical signal (I); and a control device which controls the electrical signal to the solenoid (15); wherein the control device executes a program in the following manner: it stores a signal pressure (P SOL ) for generating an output pressure (Po) corresponding to a required output value (P*), and a main map which specifies a relationship with the electrical signal (I) at that time; various output pressures (Po) which are actually generated when various electrical signals (I) based upon various signal pressures (P SOL ) are input to the solenoid (15) are measured in advance, and it stores the relationship between these measured values (Po) and the signal pressures (P SOL ) at this time; it compensates the relationship with the signal pressure (P SOL ) corresponding to the required output value (P*) based upon the stored relationship between these measured values (Po) and the signal pressures (P SOL ); and when the required output value (P*) is input, it obtains the electrical signal (I) from the said main map based upon the compensated value (P SOL *) for the signal pressure, and inputs this to the solenoid; characterised in that the compensation of the signal pressure (P SOL ) based upon the required output value (P*) is approximately calculated as a linear function, and the coefficient and the constant of the approximated linear function are stored in the control device.

Inventors: ISHII SHIGERU, SUGIUCHI MASASHI, ISHII, SHIGERU, SUGIUCHI, MASASHI
Applicants: NISSAN MOTOR, NISSAN MOTOR COMPANY, LIMITED
Application year: 2000
Main classification: F16H61
IPC codes: F16H61