WO2020237455A1

WO2020237455A1 - Pneumatic control valve and air-liquid pressure conversion control device

Info

Publication number: WO2020237455A1
Application number: PCT/CN2019/088518
Authority: WO
Inventors: 陈海楼; 成才飞
Original assignee: 南京蒙福液压机械有限公司
Priority date: 2019-05-24
Filing date: 2019-05-27
Publication date: 2020-12-03
Also published as: CN110285109B; CN110285109A

Abstract

An air-liquid pressure conversion control device. The device uses a combination of a large-diameter air cylinder and a small-diameter hydraulic cylinder, and drives a piston of the hydraulic cylinder to reciprocate by utilizing the push-pull reciprocating movement of the air cylinder, so as to complete oil suction and oil output functions of the device. A pneumatic control valve (10) is further disclosed. Air intake is controlled by the pneumatic control valve and then a piston rod (8) is pushed to move, oil cylinders are controlled to output oil alternately to provide pressure, and the oil output pressure of a hydraulic system composed of the oil cylinders is controlled by regulating an air intake pressure by the pneumatic control valve. A hydraulic energy accumulator buffers pressure pulsation, caused by discontinuous oil supply occurring at the reversing moment of the air cylinder, of the air-liquid pressure conversion control device. Moving components such as the piston of the device are made of aluminum alloy materials. The weight of reciprocating movement components is reduced as much as possible while the strength is ensured, the reversing sensitivity is improved, and the pressure pulsation is also reduced while the energy consumption of reversing is reduced.

Description

Pneumatic control valve and gas-liquid pressure conversion control device

Technical field

The invention belongs to gas-liquid conversion equipment, and particularly relates to a pneumatic control valve and a gas-liquid pressure conversion control device.

Background technique

At present, the hydraulic systems of CNC machine tools basically use electric motors to drive hydraulic pumps to provide the high-pressure oil required for the operation of the chuck, tailstock and tool post to drive them. The advantages of this fuel supply method are stable fuel supply pressure, low fuel supply pulsation, and low noise, but the disadvantages of this fuel supply method are also obvious, mainly in the following aspects: First, the oil pump motor unit occupies the upper cover of the fuel tank Larger space; second, the weight of the oil pump motor unit is larger; third, the energy consumption of the oil pump motor unit is larger, especially when the hydraulic system needs to maintain pressure, the oil pump needs to continuously provide high pressure oil to the chuck To maintain the clamping of the chuck, the motor must always run at full speed. This part of the energy is wasted, although most hydraulic stations are now.

Choosing the automatic variable pump reduces the energy consumption of the system to a certain extent, but the hydraulic system always needs to consume a lot of power when running under high pressure, and the motor runs inefficiently under light load. Larger energy consumption also causes the oil temperature of the hydraulic system to rise easily. As a result, the hydraulic system has to take auxiliary measures to increase the oil tank volume and increase the air cooler or water cooler to help the hydraulic system dissipate heat, which makes the hydraulic system larger and occupying There is a lot of space in the inner board of the machine tool, and the heat dissipation design of the hydraulic system needs to be considered for the machine tool, which increases the design workload of the machine tool. At present, the gas-liquid pressurization device can solve the energy consumption problem of the hydraulic system. The gas-liquid pressurization device is driven by the reciprocating action of the cylinder to provide the high-pressure oil required for the operation of the machine tool. It only needs compressed air to blow when the hydraulic system of the machine tool maintains pressure. Keep a certain pressure in the cylinder, and the cylinder does not move. At this time, the energy consumption of the hydraulic system is extremely small, the system does not generate heat, and no heat dissipation device is required. Therefore, the hydraulic system can be greatly reduced in size, but the current gas-liquid pressurization Because the cylinder reciprocates to suck and discharge oil, the device has the disadvantages of unstable oil supply pressure and large oil supply pulsation.

Summary of the invention

Objective of the invention: In view of the above-mentioned shortcomings of the prior art, the first objective of the present invention is to provide a pneumatic control valve, and the second objective is to provide a pneumatic control valve based on the pneumatic control valve to provide a gas-hydraulic pressure conversion control device to increase the pressure of machine tools and hydraulic equipment Stability of output and efficient control.

A pneumatic control valve, including the front side cover of the air valve, the air valve housing, the air valve cylinder liner, the air valve core, the rear side cover of the air valve, the cylinder rear cavity, the cylinder exhaust port, the cylinder front cavity, the air valve and the air valve In the rear chamber, when the high pressure gas enters the air inlet of the pneumatic control valve, the air valve core is pushed back to the rear limit. The air inlet is connected with the cylinder back cavity, the cylinder front cavity is connected with the cylinder exhaust port, and the high pressure gas enters the cylinder. After the cavity, the piston rod of the cylinder is pushed forward, and the piston rod of the cylinder is driven; the piston of the hydraulic cylinder pushes forward, the cylinder pushes the internal hydraulic oil out of the cylinder into the hydraulic valve group of the machine tool, and drives the machine tool cylinder to run. The pneumatic control valve is also included in the cylinder There is a front thimble at the front limit position. When the cylinder piston contacts the firing pin, the high-pressure gas control air flow communicated with the intake port is connected to the rear cavity of the air valve. The high-pressure gas enters the rear cavity of the air valve to push the air valve core forward to the front limit. At this time, high-pressure gas communicates with the front chamber of the cylinder, and the rear chamber of the cylinder communicates with the exhaust port of the cylinder. The high-pressure gas enters the front chamber of the cylinder to push the cylinder piston back. The cylinder piston is pushed by the high pressure gas to return to the cylinder to limit the position at this time. Drive the pistons of the two oil cylinders to pull back. When the pistons of the cylinders retreat to the rear limit, the pistons hit the rear thimble, the high-pressure gas in the back cavity of the air valve is discharged, the air valve core retreats, and the cylinder pistons repeatedly advance forward, forming a repeated action.

Further, the pneumatic control valve includes a connection channel between the cylinder sleeve and the cylinder at the cylinder connection on both sides of the cylinder piston rod, and the connection channel is located on both sides of the air valve core and the upper and lower sides of the cylinder piston rod. Between the contact wall with the cylinder.

Further, the connecting passage of the cylinder connects the front chamber of the cylinder and the cylinder exhaust port when the valve core is in the rear limit position, and connects the rear chamber of the cylinder and the cylinder exhaust port when the valve core is in the front limit position.

A gas-liquid pressure conversion control device. The device is composed of an oil cylinder and an air cylinder. The device is composed of an oil cylinder and an air cylinder. The oil cylinder includes an oil cylinder back cover, a front cylinder barrel, a front piston, an oil cylinder sealing ring, The cylinder body, the cylinder sealing ring, the rear cylinder tube, the piston rod and the cylinder front cover; the cylinder includes the pneumatic reversing valve, the cylinder front cover, the cylinder cylinder tube, the cylinder piston, the striker and the cylinder back cover, and the piston in the cylinder body The piston rod is connected with the cylinder piston in the cylinder. The push-pull reciprocating motion of the cylinder piston drives the front piston of the oil cylinder to reciprocate to complete the oil suction and oil discharge actions of the device. The cylinder piston moves from the front limit of the cylinder to the rear limit of the cylinder. During the process, the cylinder passage and the cylinder rear chamber passage provided on both sides of the piston rod and the cylinder piston correspond to the cylinder rear chamber, cylinder exhaust port, and cylinder front chamber provided on the upper and lower sides of the pneumatic control valve, including the opening and closing state of the control valve.

Further, a cylinder middle body is provided at the junction of the front cylinder tube and the rear cylinder tube of the cylinder part, and two adjacent cylinder tubes and oil passages are tightly connected by a cylinder sealing ring. The cylinder middle body is also provided with an oil suction Check valve and oil outlet check valve, correspondingly connect the oil outlet and suction port;

The front cover of the oil cylinder and the rear cover of the oil cylinder are provided with vent holes to communicate with the atmosphere, and the pistons and the front and rear covers of the cylinder and the oil cylinder are equipped with sealing rings and guide bands to separate each cavity.

The cylinder and the oil cylinder are sealed and fixed by welding or bolts, and the joint is provided with a sealing ring; the device is also provided with a gas-liquid pressurizing device, and the gas-liquid pressurizing device includes a pneumatic pressure regulating valve and a hydraulic accumulator. The pneumatic pressure regulating valve is located at the air inlet of the gas-liquid supercharging device and is connected with the air inlet of the cylinder to adjust the air inlet pressure of the cylinder. The hydraulic accumulator is located at the oil outlet of the device, and the buffer device The pressure pulsation caused by the intermittent oil supply at the moment of cylinder reversal.

Beneficial effects: Compared with the prior art, the pneumatic control valve provided by the present invention can effectively control the stability of pressure output, and has a simple structure, which is suitable for gas-liquid control conversion on a variety of different equipment; in addition, the device provided by the present invention is large The energy consumption is greatly reduced, the hydraulic system is simplified, the energy consumption and heat generation of the hydraulic system are reduced, the heat dissipation device can be omitted, and the volume of the fuel tank can be greatly reduced, and only the fuel consumption of the cylinder can be supplied; Second, the front and rear chambers of the cylinder are fully utilized, and the work efficiency is doubled. The staggered suction and discharge of the front and rear cylinders can also avoid a series of problems caused by the interruption of fuel supply. In addition, the buffer function of the accumulator and the gas-liquid pressurization control device The pressure pulsation is close to that of the oil pump motor unit; third, the utility model does not need to provide three-phase power to the hydraulic system, which simplifies the application circuit of the machine tool and improves the safety of the hydraulic system of the machine tool.

Description of the drawings

Figure 1 is a schematic diagram of the structure of the gas-liquid pressure conversion control device of the present invention;

Figure 2 is a schematic structural diagram of the pneumatic control valve of the present invention when it is in the front limit position;

Figure 3 is a schematic structural diagram of the pneumatic control valve of the present invention when it is in the rear limit;

Detailed ways

In order to describe the technical solution disclosed in the present invention in detail, the following further elaboration is made in conjunction with specific embodiments and drawings.

Aiming at the shortcomings of traditional gas-liquid control devices or gas-liquid pressurization devices, the present invention provides a gas-liquid pressure conversion control device, which uses a combination of a large-diameter cylinder and a small-diameter hydraulic cylinder, and is driven by the push-pull reciprocating motion of the cylinder The piston of the hydraulic cylinder reciprocates to complete the oil suction and oil discharge functions of the gas-liquid booster device. The gas-liquid conversion control device uses a double-acting cylinder to drive two hydraulic cylinders connected in series through a piston rod. The cylinder and the piston of the hydraulic cylinder are rigidly connected, and the oil suction and oil output of the two hydraulic cylinders are staggered with each other. The two actions of oil suction and oil discharge are completed at the same time when moving forward or backward, and the working efficiency of the hydraulic system is doubled.

Specifically, as shown in FIG. 1, a gas-liquid conversion control device is composed of a cylinder and a cylinder. The cylinder includes a cylinder back cover 1, a front cylinder barrel 2, a front piston 3, and a cylinder seal ring. 4. The cylinder body 5, the cylinder sealing ring 6, the rear cylinder tube 7, the piston rod 8, and the cylinder front cover 9; the cylinder includes a cloth moth and more than one combination thereof, and the cylinder includes a pneumatic reversing valve 10 and a cylinder front cover 11 , The cylinder cylinder 12, the cylinder piston 13, the striker 14 and the cylinder rear cover 15. The piston in the cylinder barrel of the device is connected to the cylinder piston 13 in the cylinder through the piston rod 8. The push and pull reciprocating motion of the cylinder piston 13 drives the cylinder The front piston 3 reciprocates to complete the oil suction and oil discharge actions of the device.

The pneumatic control valve 10 includes the air valve front side cover 16, the air valve housing 17, the air valve cylinder liner 18, the air valve core 19, and the air valve rear cover 20. See Figures 2 and 3, and Figure 2 shows the pneumatic control valve. The air valve core 19 is in the front limit position, and the air valve core 19 in FIG. 3 is in the rear limit position.

For pneumatic control valves, when high pressure gas enters the valve intake port, the valve core 19 is pushed back to the rear limit position, the intake port is connected to the cylinder rear chamber 21, and the cylinder front chamber 23 communicates with the cylinder exhaust port 22. Air enters the cylinder back chamber 21, pushing the cylinder piston rod forward. The cylinder piston rod drives the front and rear pistons of the two hydraulic cylinders to push forward. The rear hydraulic cylinder pushes the internal hydraulic oil out of the cylinder at a certain pressure and enters the hydraulic valve group of the machine tool to drive the machine tool cylinder. While running, the front hydraulic cylinder sucks in hydraulic oil at the same time. When the piston of the cylinder advances to the front limit of the cylinder, the piston hits the front thimble. At this time, the high-pressure air control airflow communicating with the intake port is connected to the back chamber 25 of the air valve. The high-pressure gas enters the back chamber 25 of the valve to push the valve core 19 forward to the front limit of the valve. At this time, the high-pressure gas communicates with the front chamber 23 of the cylinder, the back chamber 21 communicates with the exhaust port, and the high-pressure gas enters the front chamber 23 of the cylinder to push The piston of the cylinder moves back, and the piston of the cylinder returns to the rear limit of the cylinder under the push of high-pressure gas. At this time, the piston rod of the cylinder drives the pistons of the two cylinders to pull back. The front hydraulic cylinder pushes the internal hydraulic oil out of the cylinder at a certain pressure and enters the hydraulic pressure of the machine tool. While the valve group drives the machine tool cylinder to run, the next hydraulic cylinder sucks in hydraulic oil at the same time. When the cylinder piston retreats to the rear limit of the cylinder, the piston hits the ejector pin, the high pressure air in the back cavity of the valve is discharged, the valve core retreats, and the cylinder piston repeats Moving forward, such a recurring action is formed. A control airflow port 26 is provided at the cylinder piston rod of the air valve intake port through the connection gap with the cylinder. The cylinder keeps repeating forward and backward movements, pushing the cylinder piston to continuously output pressure oil. In this device, one cylinder drives two cylinders to move in a staggered manner. The oil suction and oil discharge are carried out at the same time, which improves efficiency and avoids the defect of interruption of oil supply of traditional supercharging devices.

Based on the above-mentioned pneumatic control valve, a gas-liquid conversion control device provided by the present invention is composed of an oil cylinder and an air cylinder, and the number can be adjusted according to actual needs. The cylinder piston 13 moves from the front limit of the cylinder to the back limit of the cylinder. During the process, the cylinder passage and the cylinder back chamber passage provided on both sides of the piston rod 8 and the cylinder piston 13 correspond to the cylinder back chamber 17, the cylinder exhaust port 22, and the cylinder front chamber 23 provided on the upper and lower sides of the pneumatic control valve 10, including the control gas The open and closed state of the valve 24.

The connection of the front cylinder tube 2 and the rear cylinder tube 7 of the cylinder part is provided with a cylinder middle body 5, which is closely connected to two adjacent cylinder tubes and oil passages through a cylinder sealing ring 6. The cylinder body 5 is also provided with an oil suction unidirectional The valve and the oil outlet check valve are correspondingly connected to the oil outlet and the oil inlet. The cylinder front cover 1 and the cylinder rear cover 9 are provided with vent holes to communicate with the atmosphere, and the pistons and front and rear covers of the cylinder and the cylinder are equipped with sealing rings and guide bands to separate each cavity.

The energy-saving gas-liquid conversion control device of the present invention uses a large-diameter cylinder combined with a front and rear two-stage small-diameter hydraulic cylinder, which are fixed with long bolts, and a cylinder body with oil distribution function is arranged in the middle of the front and rear two-stage hydraulic cylinders. , There are 2 oil suction check valves and oil discharge check valves in the middle body 5 of the oil cylinder, which separate the oil suction and oil output of the front and rear two-stage hydraulic cylinders without interference with each other. The cylinder and the oil cylinder are integrated with the piston rod 8 , The piston of the second-stage oil cylinder is integrated on the piston rod. The front piston 3 and the cylinder piston 13 of the first-stage oil cylinder are fixed on the piston rod 8 with nuts. In order to prevent the gas holding phenomenon during the operation of the oil cylinder, the front cover 9 and The cylinder back cover 1 is drilled with a vent hole to communicate with the atmosphere. The cylinder and cylinder piston and its front and rear covers are equipped with sealing rings and guide belts to separate the various chambers to achieve the effect of non-interference. The use of large-diameter cylinders The push-pull reciprocating motion drives the reciprocating motion of the piston of the oil cylinder to complete the oil suction and oil discharge functions of the gas-liquid increasing device. When the piston rod advances, the volume of the hydraulic cylinder at the back shrinks, and the hydraulic oil inside is compressed through the oil outlet check valve and pushed out of the cylinder into the hydraulic valve block of the machine tool. At this time, under the action of high pressure oil, the oil suction check valve of the rear cylinder Close to prevent high pressure oil from leaking back to the tank. The volume of the front cylinder increases and a vacuum occurs. At this time, the suction check valve of the front volume opens, and the hydraulic oil in the tank is sucked into the cylinder through the suction check valve. Under the action of high pressure oil, the front cylinder discharges oil. The one-way valve is closed to prevent the high pressure oil from the rear cylinder from running into the front cylinder. When the piston rod retracts, the volume of the front hydraulic cylinder shrinks, and the hydraulic oil inside is compressed through the oil outlet check valve and pushed out of the cylinder into the hydraulic valve block of the machine tool. At this time, under the action of high pressure oil, the suction check valve of the front cylinder Close to prevent high pressure oil from leaking back to the tank. The volume of the rear cylinder increases and a vacuum occurs. At this time, the suction check valve in the back volume opens, and the hydraulic oil in the tank is sucked into the cylinder through the suction check valve. Under the action of high pressure oil, the rear cylinder discharges oil. The one-way valve is closed to prevent high-pressure oil from the front cylinder from running into the front cylinder. The oil suction check valve and oil discharge check valve of the front and rear oil cylinders are integrated in the middle body of the oil cylinder, and output through a main circuit, reducing piping.

The actual operating state of the present invention is as follows:

When high-pressure gas is blown into the rear cavity of the cylinder barrel 12 to push the cylinder piston 13 and the cylinder piston 13 pushes the piston rod 8 forward, the piston rod 8 of the cylinder part drives the two cylinder pistons forward and backward, and the piston rod 8 of the rear cylinder part (Built-in piston) The hydraulic oil inside the rear cylinder tube 7 is pushed out of the cylinder at a certain pressure through the oil outlet check valve and enters the hydraulic valve group of the machine tool to drive the machine tool cylinder. At the same time, the front piston 3 passes the front cylinder tube 2 through the suction sheet. The hydraulic oil is sucked into the valve at the same time. When the cylinder piston is pushed to the end, the piston hits the striker 14 on the cylinder head, the pneumatic reversing valve 10 acts, and the high pressure air is blown into the front cavity of the cylinder barrel 12, and the rear cavity of the cylinder is connected and released. The air hole, the cylinder piston 13 is pushed back to the cylinder by the high pressure gas to limit the position. At this time, the cylinder piston rod drives the two cylinder pistons to pull back, and the front cylinder 2 passes the internal hydraulic oil through the oil outlet check valve at a certain pressure When the cylinder is pushed into the hydraulic valve group of the machine tool to drive the cylinder of the machine tool to run, the rear cylinder tube 7 simultaneously sucks in hydraulic oil. When the cylinder reaches the rear limit, the cylinder piston hits the striker 14 of the cylinder rear cover, and the pneumatic control valve 10 realizes the direction change. The cylinder repeats its forward movement again, and so on.

In the gas-liquid conversion control device, one cylinder drives the two cylinders to move in a staggered manner, and the oil suction and the oil discharge are performed at the same time, which improves efficiency and avoids the defect of interruption of oil supply of the traditional supercharging device. On the other hand, it greatly reduces the energy consumption and heat generation of the device.

Claims

A pneumatic control valve, which is characterized in that it comprises a front side cover (16) of a gas valve, a gas valve housing (17), a gas valve cylinder liner (18), a gas valve core (19), and a rear side cover (20) of the gas valve. ), cylinder rear chamber (21), cylinder exhaust port (22), cylinder front chamber (23), valve (24) and valve rear chamber (25), when high pressure gas enters the air inlet of the pneumatic control valve, it is pushed The valve core (19) is retracted to the rear limit position, the intake port is connected with the cylinder rear chamber (21), the cylinder front chamber (23) is communicated with the cylinder exhaust port (22), and high-pressure gas enters the cylinder rear chamber (21) Then the piston rod of the cylinder is pushed forward, and the piston rod of the cylinder is driven; the piston of the hydraulic cylinder pushes forward, and the cylinder pushes the internal hydraulic oil out of the cylinder into the hydraulic valve group of the machine tool to drive the machine tool cylinder to run. The pneumatic control valve is also included in front of the cylinder There is a front thimble at the limit position. When the cylinder piston contacts the firing pin, the high-pressure gas control air flow communicated with the intake port is connected to the rear chamber (25) of the valve, and the high-pressure gas enters the rear chamber (25) of the valve to push the valve core ( 19) Advance to the front limit position. At this time, the high-pressure gas communicates with the front chamber (23) of the cylinder, the rear chamber (21) of the cylinder communicates with the cylinder exhaust port (22), and the high-pressure gas enters the front chamber (23) to push the cylinder piston back. , The cylinder piston is pushed back by the high pressure gas to return to the cylinder back to the limit. At this time, the cylinder piston rod drives the two cylinder pistons to pull back. When the cylinder piston retracts to the back limit, the piston hits the rear thimble and the air valve back cavity (25 ) The high-pressure gas is discharged, and the gas valve core (19) moves backward.
The pneumatic control valve according to claim 1, characterized in that: the pneumatic control valve comprises a connection passage between the cylinder sleeve (18) and the cylinder at the cylinder connection on both sides of the cylinder piston rod, so The connecting passage is located between the two sides of the air valve core (19) and the upper and lower parts of the cylinder piston rod and the contact wall of the cylinder body.
The pneumatic control valve according to claim 2, characterized in that: the connecting passage of the cylinder connects the front chamber (23) of the cylinder and the exhaust port (22) of the cylinder when the valve core (19) is in the rear limit position. When in the front limit, connect the cylinder rear chamber (21) and the cylinder exhaust port (22).
A gas-liquid pressure conversion control device, the device is composed of an oil cylinder and an air cylinder, and is characterized in that: the device is composed of an oil cylinder and an air cylinder, and the oil cylinder includes an oil cylinder rear cover (1), a front cylinder tube ( 2) Front piston (3), cylinder sealing ring (4), cylinder middle body (5), cylinder sealing ring (6), rear cylinder tube (7), piston rod (8) and cylinder front cover (9); The cylinder includes a pneumatic reversing valve (10), a cylinder front cover (11), a cylinder cylinder (12), a cylinder piston (13), a striker (14) and a cylinder rear cover (15). The piston in the cylinder barrel passes The piston rod (8) is connected with the cylinder piston (13) in the cylinder. The push-pull reciprocating motion of the cylinder piston (13) drives the front piston (3) of the oil cylinder to reciprocate to complete the oil suction and oil discharge actions of the device. The cylinder piston ( 13) During the movement from the front limit of the cylinder to the rear limit of the cylinder, the cylinder passages and the cylinder back chamber passages provided on both sides of the piston rod (8) and the cylinder piston (13) correspond to the upper and lower sides of the pneumatic control valve (10). The cylinder rear chamber (17), the cylinder exhaust port (22), and the cylinder front chamber (23) include the opening and closing states of the control valve (24).
A gas-hydraulic pressure conversion control device according to claim 4, characterized in that: the connection of the front cylinder (2) and the rear cylinder (7) of the cylinder part is provided with a cylinder middle body (5), The two adjacent cylinder barrels and the oil circuit are tightly connected by the oil cylinder sealing ring (6), and the oil cylinder middle body (5) is also provided with an oil suction check valve and an oil discharge check valve, which are correspondingly connected to the oil outlet and the oil suction port .
A gas-liquid pressure conversion control device according to claim 4, characterized in that: the cylinder front cover (1) and the cylinder rear cover (9) are provided with vent holes to communicate with the atmosphere, and the pistons of the cylinder and the cylinder are The front and rear covers are equipped with sealing rings and guide belts to separate each cavity.
The gas-liquid pressure conversion control device according to claim 4, wherein the cylinder and the oil cylinder are sealed and fixed by welding or bolts, and a sealing ring is provided at the joint.
A gas-liquid pressure conversion control device according to claim 4, characterized in that: the device is further provided with a gas-liquid pressurizing device, and the gas-liquid pressurizing device includes a pneumatic pressure regulating valve and a hydraulic accumulator .
A gas-liquid pressure conversion control device according to claim 4, wherein the pneumatic pressure regulating valve is located at the air inlet of the gas-liquid supercharging device and is connected to the air inlet of the cylinder to adjust the air inlet of the cylinder. The pressure, the hydraulic accumulator is located at the oil outlet of the device, and the buffer device is the pressure pulsation caused by the intermittent oil supply at the moment when the cylinder changes.