JPH054534B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a hydraulic control method for a belt-type continuously variable transmission (hereinafter referred to as "CVT") used as a power transmission device for a vehicle.

[Conventional technology]

CVT has speed increasing ratio e (=output side rotational speed Nout/
It can continuously control the input side rotational speed (Nin) and is used as an excellent power transmission device that improves the fuel consumption efficiency of vehicles. In a belt-type CVT, a belt is placed between a pair of input-side disks with variable effective diameters and between a pair of output-side disks with variable effective diameters, and a hydraulic cylinder is installed on each of the input-side disks and the output-side disks. The hydraulic pressure supplied to this hydraulic cylinder controls the pressing force of the input-side disk and the output-side disk, changing their respective effective diameters, making it possible to perform stepless speed ratio control (Japanese Patent Application Laid-Open No. 56−66553). The control pressure of the hydraulic cylinders on the driven side (usually the output side disk) of the input side disk and the output side disk is line pressure. This line pressure is controlled by an electromagnetic relief valve in relation to the power transmitted by the belt, thereby suppressing drive loss of the oil pump while avoiding belt slippage. However, since the hydraulic cylinder rotates integrally with the disk, centrifugal force acts on the hydraulic medium within the hydraulic cylinder, and this centrifugal force causes the actual oil pressure to be larger than the intended value for control purposes. This increases the pressing force on the disk, deteriorating the transmission efficiency of the CVT and shortening the lifespan of each CVT component. As a conventional countermeasure against this problem, a method is known in which the centrifugal force of the hydraulic medium itself is structurally offset by providing a balance chamber (for example, Japanese Patent Laid-Open No. 58-621491).

[Problem to be solved by the invention]

However, this method has a problem in that it is limited to canceling out approximately 50% of the centrifugal force generated, and it is not possible to make sufficient corrections. In addition, in the above-mentioned Japanese Patent Application Laid-open No. 56-66553, an oil reservoir is provided in the part that physically rotates with the input side (drive side) hydraulic cylinder,
A method has been disclosed in which line pressure (control pressure) is controlled based on the oil pressure value of this oil sump.
As is clear from the fact that this technology focuses on the rotation speed on the input side (drive side), it is an attempt to take into account changes in engine torque with respect to rotation speed, and is not a technology for canceling centrifugal force. Ta. An object of the present invention is to provide a hydraulic control method for a belt-type CVT that is free from practical difficulties and can offset increases in line pressure caused by centrifugal force.

[Means to solve the problem]

The present invention provides a belt-type continuously variable transmission including a pair of input side disks which are arranged oppositely and whose distance changes in relation to the oil pressure of a hydraulic cylinder; a pair of output side disks, the distance between which varies with respect to;
A belt is provided between a pair of input side disks and a pair of output side disks to transmit rotational torque, and the control pressure that controls the belt tension in the hydraulic control device is the power source of either the input side disk or the output side disk. In a method for controlling hydraulic pressure of a belt type continuously variable transmission configured to transmit the control pressure to a hydraulic cylinder on the driven side in a transmission system, detecting the rotational speed of the hydraulic cylinder on the side to which the control pressure is transmitted, By correcting the pressure so as to decrease it substantially in proportion to the square of the detected rotational speed,
The above objectives have been achieved.

[Effect]

According to the present invention, attention is paid to the following fact. That is, the increase ΔPl in the line pressure (control pressure) Pl due to centrifugal force is expressed by the following equation. ΔPl=ρ・ω ² /4・(R2 ² +R1 ² ) ...(1) However, ρ: Density of hydraulic medium ω: Angular velocity of hydraulic cylinder R2: Radius of hydraulic cylinder R1: Radius of boss part of hydraulic cylinder σ , R2, and R1 are constant regardless of the operating state of the engine, and ω ² is the square of the rotational speed Nc of the hydraulic cylinder.
Since it is proportional to Nc ² , ΔPl can be replaced by the following equation. ΔPl=K・Nc ² ...(2) However, K is a constant. Therefore, in the present invention, the rotational speed Nc of the hydraulic cylinder on the side to which the line pressure Pl is transmitted is detected, and the line pressure is corrected to decrease in accordance with the increase in the detected rotational speed Nc. As a result, the increase in line pressure Pl due to centrifugal force and the decrease in line pressure PL due to correction cancel each other out, and the final result in the hydraulic cylinder is line pressure
Since Pl has a value commensurate with the power transmitted by the belt, it is possible to prevent deterioration of CVT transmission efficiency, increase of oil pump drive loss, and shortening of the life of each CVT component. Furthermore, in the present invention, there is no need to add a CVT structure or provide a pitot tube, and the structure is simple because it is only necessary to change, for example, the electric control signal of the electromagnetic relief valve by the amount corresponding to the correction amount. Easy to put into practical use. In addition, in order to cancel centrifugal force almost completely, the above (2)
According to the formula, it is desirable to reduce the line pressure (control pressure) in proportion to the square of the rotational speed Nc, but the present invention does not necessarily require a reduction in exact proportion to the square.

【Example】

Embodiments of the present invention will be described with reference to the drawings. In FIG. 1, the CVT 1 includes a pair of input side disks 2a, 2b and a pair of output side disks 4a, 4.
b, and a belt 6 that is hung between the input side disks 2a, 2b and between the output side disks 4a, 4b. One input side disk 2a
is provided on the input shaft 8 so as to be movable in the axial direction and fixed in the rotational direction, and the other input side disk 2b is fixed on the input shaft 8 in the axial direction and rotational direction. Further, one output side disk 4a is fixed to the output shaft 10 in the axial direction and rotational direction, and the other output side disk 4b is provided on the output shaft 10 so as to be movable in the axial direction but fixed in the rotational direction. It is being The opposing surfaces of the pair of input side disks 2a, 2b and the pair of output side disks 4a, 4b are formed into gentle conical shapes, and the cross section of the belt 6 is formed into an isosceles trapezoid. The belt 6 is attached to the input side disks 2a, 2
As the pressing force of the output side disks 4a and 4b increases and decreases, the engaging radius (effective radius) on the disks 2a, 2b, 4a, 4b changes, and as a result, the speed increasing ratio e of the CVT 1 (=output side disk 4a,
Rotational speed Nout of 4b/input side disks 2a, 2
The rotational speed Nin) of b changes. The input shaft 8 is connected to the crankshaft 14 of the engine 12 via a clutch 16, and the oil pump 18 is connected to the crankshaft 14 of the engine 12.
Pump shaft 20 passing through the hollow space of input shaft 8
It is connected to the crankshaft 14 via. Oil pump 18 supplies oil from oil sump 22 to line pressure oil passage 24 . The electromagnetic relief valve 26 controls the relief amount of oil from the line pressure oil passage 24 to the drain oil passage 28, that is, the return flow rate, thereby controlling the line pressure Pl. The flow rate control valve 30 is connected to an oil passage 32 and a line pressure oil passage 24.
Alternatively, the connection with the drain oil passage 28 is controlled to control the flow rate of oil to the oil passage 32. The hydraulic cylinder of the output side disk 4b is connected to the line pressure oil path 24, and the hydraulic cylinder of the input side disk 2a is connected to the oil path 32. The pressing force of the output side disks 4a, 4b, that is, the line pressure Pl, is maintained at the minimum value necessary to ensure the power transmission of the belt 6, and the pressing force of the input side disks 2a, 2b is
Controls the speed increasing ratio e of CVT1. When increasing the speed increasing ratio e, the flow rate of oil sent from the flow rate control valve 30 to the oil passage 32 is increased and the input side disc 2
The radius of engagement of the belt 6 at points a and 2b is increased. Since the working area of the hydraulic cylinder of the input side disk 2a is larger than the working area of the hydraulic cylinder of the output side disk 4b, even though the oil pressure of the hydraulic cylinder of the input side disk 2a is below the line pressure Pl, the speed increasing ratio e can also be greater than 1. The electronic control unit 34 includes a CPU (central processing unit) 38 connected to each other by a data bus 36;
RAM40, I/F (interface) 42,
It includes an A/D (analog/digital converter) 44 and a D/A (digital/analog converter) 46. The ignition signal of the ignition device 48 is an engine rotation speed signal, and the detection signals of the rotation angle sensors 50 and 52 are
The input side rotation speed signal and the output side rotation speed signal of the CVT 1 are sent to the I/F 42. The throttle sensor 54 detects the throttle opening θ, and its detection signal is sent to the A/D 44. Electromagnetic relief valve 26 and flow control valve 30 receive control signals from D/A 46 via amplifier 56 . To roughly explain the operation of CVT1, the target engine rotation speed Ne' is set as a function of the throttle opening θ, etc., and the target engine rotation speed
Deviation ΔNe of actual engine rotational speed Ne from Ne′
The speed increasing ratio e of the CVT 1 is controlled in relation to. As mentioned above, the output side disks 4a, 4b
The pressing force of the oil pump 18, that is, the line pressure Pl is
In order to control the drive loss, the belt 6 is controlled to the minimum value necessary to ensure power transmission without slipping on the disks 2a, 2b, 4a, 4b.
The line pressure Pl is defined, for example, by the following equation. Pl=C・Te・(Nin+Nout)/Nout...(3) However, C: Constant determined from the structure of CVT1 Te: Engine torque. The solid line in FIG. 2 shows the relationship of equation (3). However, the speed increase ratio e=Nout/Nin. However, the hydraulic cylinder of the output side disk 4b is
Since the output disc 4b rotates integrally with the output disc 4b, a centrifugal force as shown in FIG. 3 is generated in relation to the rotational speed of the output disc 4b. However, the hydraulic pressure conversion values in FIG. 3 are set as R2 = 100 mm, R1 = 0 mm, and ρ = 0.85 g/cm ³ in the above-mentioned equation (1). Therefore, the line pressure Pl in the hydraulic cylinder is the second
As shown by the broken line in the figure, the oil pressure rises above the original control oil pressure. In the present invention, in the hydraulic cylinder, the line pressure Pl is calculated by subtracting the increase in line pressure Pl due to centrifugal force ΔPl in advance.
is generated at the pressure regulating valve 26. As a result, the final oil pressure in the hydraulic cylinder becomes the value shown by the solid line in FIG. It can be prevented. FIG. 4 is a flowchart of a control routine for the electromagnetic relief valve 26. The minimum line pressure g (e,
Te), and calculate the increase in line pressure due to centrifugal force K・Nout ² (however, the rotational speed of the output side disk 4a
A control voltage h(Pl) corresponding to the value Pl obtained by subtracting Nout=rotational speed Nc of the hydraulic cylinder of the output side disk 4b from g(e, Te) is output to the electromagnetic relief valve 26. Therefore, the line pressure Pl generated in the electromagnetic relief valve 26 becomes g(e, Te)-K·Nout ² , and the final oil pressure in the hydraulic cylinder of the output side disc 4b becomes g(e, Te). To explain each step in detail, in step 62, the engine rotation speed Ne (detected from the ignition signal of the ignition device 48), the input side rotation speed Nin, the output side rotation speed
Read Nout and throttle opening θ. In step 64, the speed increasing ratio e=Nout/Nin is calculated. In step 66, the engine torque Te is calculated from the engine rotational speed Ne and the throttle opening θ. step 68
Now, calculate the line pressure Pl using the following formula. Pl=C・Te・(Nin+Nout)/Nout −K・Nout ² =C・Te {(1+e)/e} −k・Nout ² =g(e, Te)−K・Nout ² ……(4) Step At 70, the control pressure Vr of the electromagnetic relief valve 26 is calculated as a function h (Pl) of Pl, and Vr is output.

【Effect of the invention】

As explained above, according to the present invention, it is possible to perform control that accurately takes into account (offsets) the increase in centrifugal oil pressure, and it becomes possible to perform power transmission as intended, thereby preventing a decrease in transmission efficiency. This has the excellent effect of preventing deterioration in the durability of each CVT component.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of the entire electronically controlled engine equipped with CVT, Figure 2 is a diagram showing line pressure according to power transmission, and Figure 3 is a diagram showing line pressure increase due to centrifugal force. , FIG. 4 is a flowchart of the control routine for the electromagnetic relief valve. 1...CVT, 2a, 2b...input side disk,
4a, 4b...output side disk, 6...belt,
18...Oil pump, 34...Electronic control device,
38...CPU, 52...Rotation angle sensor.

Claims (1)

[Claims] 1. A belt-type continuously variable transmission includes a pair of input side disks that are arranged oppositely and whose distance between them changes depending on the oil pressure of a hydraulic cylinder; A belt in a hydraulic control device is provided with a pair of output-side disks whose distance between the two is changed by changing the distance between the two, and a belt that is hung between the pair of input-side disks and the pair of output-side disks and transmits rotational torque. In a hydraulic control method for a belt type continuously variable transmission configured such that a control pressure for controlling tension is transmitted to a hydraulic cylinder of an input side disk or an output side disk which is a driven side in a power transmission system, the control The rotational speed of the hydraulic cylinder on the side to which pressure is transmitted is detected, and the control pressure is
A hydraulic control method for a belt-type continuously variable transmission, characterized in that the hydraulic pressure is corrected so as to be reduced substantially in proportion to the square of the detected rotational speed.