JPH0221530Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a brake device for a vehicle.

Large vehicles such as trucks and tractors have a large dead weight and a large cargo weight when loaded.
Naturally, the brake load when trying to stop and when going downhill is also severe. Therefore, if the service brake is used excessively, there is a risk of burnout or premature wear of the friction shoes and pads. For this reason, auxiliary brake devices that utilize the mechanical characteristics of the engine itself have been proposed for the purpose of supplementing the regular brake. One is the so-called exhaust brake device, which blocks the exhaust passage of the engine and causes the piston to perform exhaust work to produce a braking effect when the vehicle is running under engine braking. The valve, or a third valve provided separately from the normal intake valve and exhaust valve, is opened near the compression top dead center of the piston when the vehicle is running under engine braking, and the compressed air inside the cylinder is pumped out of the cylinder. This is an engine braking device designed to discharge the engine. In the latter brake device, the compressed air discharged not only when using the exhaust valve but also when using the third valve,
The pressurized air is normally discharged into the exhaust pipe via a pressurized air discharge passage that joins the exhaust port in the cylinder head or joins the exhaust manifold downstream of the exhaust port. On the other hand, some of the energy held in the engine exhaust gas is recovered to increase the engine output.
With the main purpose of improving fuel efficiency, turbochargers, which consist of an exhaust gas turbine driven by engine exhaust gas and a compressor driven by the turbine to compress the intake air of the engine, have become widely used. . Furthermore, as a characteristic of vehicle engines, the rotational speed and load change widely during operation, so in order to ensure that the exhaust gas turbine is always operated efficiently according to the amount of exhaust gas discharged from the engine, A system in which a movable nozzle is provided in the exhaust gas introduction passage to the turbine rotor is often adopted. In a turbocharger equipped with this type of exhaust gas turbine with a movable nozzle, by fully closing the movable nozzle, the exhaust passage of the engine can be blocked and the above-mentioned exhaust braking effect can be achieved.

The present invention provides a brake device comprising a vehicle engine having a turbocharger equipped with the above movable nozzle-equipped exhaust gas turbine, and absorbing exhaust work by blocking the movable nozzle when the vehicle runs under engine brake; The present invention also relates to an improvement in a brake device for a vehicle, which includes at least one of the third valve or the exhaust valve that absorbs compression work.

Now, in this type of brake system, when the engine is running under engine braking and the engine speed is high, the number of times the piston is discharged during the exhaust stroke naturally increases, and in addition, the piston is compressed at the top dead center of the compression stroke. If the air is discharged into the exhaust pipe the same number of times, there is a risk that the pressure in the exhaust pipe will rise excessively when the movable nozzle of the exhaust gas turbine is closed to block the exhaust passage. In this case, the pressure difference between the negative pressure inside the cylinder that occurs during the intake stroke of the piston and the high positive pressure inside the exhaust pipe overcomes the valve spring that normally biases the exhaust valve in the closing direction, and the valve drive mechanism There is a possibility that the exhaust valve will open and close on its own regardless of the situation. If the exhaust valve opens and closes by itself, the severe impact when the valve closes will damage the valve seat, causing problems with engine durability, and in extreme cases, the push rod cup and ball may separate. Failure to do so may result in serious malfunction. In order to avoid such problems, for example, a notch is provided in a part of the exhaust brake valve so that the exhaust valve does not open and close automatically even when the engine rotates at high speed, which can occur when the vehicle is running under engine brake. It is necessary to limit its full closure, but
In this case, there is a problem that the exhaust gas is not sufficiently blocked when the engine rotates at low speed, and the exhaust braking effect is reduced.

The present invention has been devised in view of the above, and is a third valve provided separately from the normal intake valve and exhaust valve in one or more cylinders of a vehicle engine, or a third valve provided separately from the normal intake valve and exhaust valve. A brake device that opens near the compression top dead center of the piston to discharge compressed air inside the cylinder to the outside of the cylinder, and a movable nozzle of an exhaust gas turbine with a movable nozzle driven by the exhaust gas of the engine. is equipped with a brake device that closes at least partially to block the engine exhaust passage when the vehicle is running under engine braking, and when the engine speed is low while the vehicle is running under engine braking. The movable nozzle of the exhaust gas turbine is substantially fully closed, and during the engine braking operation, when the engine speed is high, the movable nozzle is opened slightly without being fully closed, and the movable nozzle is opened slightly to inject the air into the exhaust passage. The gist of the present invention is to provide a brake system for a vehicle, characterized in that the pressure is maintained at a pressure below the limit pressure at which the exhaust valve of the engine self-opens and closes.

The embodiments of the present invention will be described in detail with reference to painted drawings. Reference numeral 10 in the figure is a cylinder head of a multi-cylinder diesel engine of a vehicle (not shown), and only one cylinder is shown in the figure for simplicity. 12 is the cylinder block (of course the cylinder liner is included), 14 is the piston, 16
is a connecting rod. An intake port 18 and an exhaust port 20 are provided inside the cylinder head 10, and an intake valve 24 and an exhaust valve 26 are provided between these ports and the cylinder 22. Further, the cylinder head 10 is provided with a third valve 28 for all or some of the cylinders of the engine, and a pressurized air discharge passage 30 opened and closed by the third valve is connected to the exhaust port within the cylinder head 10. 20. Numerals 32, 34, and 36 are valve springs that normally bias the intake valve 24, exhaust valve 26, and third valve 28 in the closing direction. The third valve 28 has a plunger 38 at its top,
The plunger is slidably fitted into the pressure oil cylinder 40. The pressure oil cylinder 40 is connected to the third valve 28
It is connected to an oil pump 44 via a distribution valve 42 that supplies pressure oil to each pressure oil cylinder 40 near the compression top dead center of the cylinder equipped with the cylinder. It is controlled by a first control box 46 which senses the presence of the valve and instructs the distribution valve. A turbocharger 48 includes an exhaust gas turbine 50 driven by engine exhaust gas and a compressor 52 connected to the gas turbine.
The exhaust gas turbine 50 is connected to the exhaust port 20 of each cylinder of the engine via an exhaust pipe 54, while the pressurized air outlet of the compressor 52 is connected to the intake port 18 of the engine via an intake pipe 56. There is. Furthermore, the exhaust gas turbine 50 has a movable nozzle 58 schematically shown in the figure.
The movable nozzle 58 originally operates the exhaust gas turbine 50 according to the operating state of the engine in order to operate the exhaust gas turbine 50 most efficiently, in other words, to more effectively recover the energy held by the engine exhaust gas. is provided and is known per se. 60 is a pneumatic actuator that adjusts the opening degree of the movable nozzle 58; 62 is a control valve that supplies and discharges operating compressed air to and from the actuator 60;
4 is a compressed air tank connected to the control valve 62;
A second control box 66 controls the operation of the control valve 62. The control box 66 detects that the vehicle is in an engine braking state, opens the control valve 62, operates the actuator 60, detects the engine rotation speed at that time, and controls the control valve 62 via the control valve 62. It controls the stroke amount of the actuator 60, that is, the opening degree of the movable nozzle 58.

In the first and second control boxes 46 and 66, one means for detecting that the vehicle is running under engine braking is to use a power source such as an on-board battery, an accelerator switch, a clutch switch, and, if desired, a manual operation. Electrical circuits in which switches are connected in series are known. Also, as a device for detecting engine rotation speed, a device consisting of a radial protrusion fixed to an arbitrary shaft that rotates in conjunction with the crankshaft, such as a camshaft, and an electromagnetic coil arranged opposite to the protrusion is well known. and is widely used in practice.

In the above device, when the vehicle is running under engine braking and the engine speed is low, the control valve 62 is operated in response to a command from the second control box 66 to supply compressed air from the compressed air tank 64. is supplied to the actuator 60 to substantially fully close the movable nozzle 58 of the exhaust gas star pin. Therefore, the exhaust pipe 54 of the engine is sufficiently blocked, the exhaust work of the piston 14 is large, and a sufficient exhaust braking effect is produced. On the other hand, even if the vehicle is running under engine braking, if the engine speed at that time is higher than a predetermined speed, the actuator 60 operates in the same manner according to the command from the second control box 66. Its stroke is limited, and the movable nozzle 58 is held at a partially opened degree, which is slightly more open than fully closed. On the other hand, when the vehicle is running under engine braking regardless of the engine speed, the distribution valve 42 is operated by a command from the first control box 46, and the piston of each cylinder equipped with the third valve 28 is activated. When the compression reaches near the top dead center, pressure oil is supplied from the pump 44 to the pressure oil cylinder 40 and the plunger 38 is pushed down. This overcomes the valve spring 36 and opens the third valve 28, allowing the compressed air in the cylinder 22 to flow into the pressurized air discharge passage 30.
The air is discharged from the exhaust port 20 into the exhaust pipe 54.

Therefore, if the movable nozzle 58 of the exhaust gas turbine 50 is substantially fully closed while the engine is running under engine braking and the engine speed is high, the number of times the piston 14 exhausts gas will naturally increase in proportion to the engine speed. At the same time, the number of times compressed air is discharged from the third valve 28 is naturally large, so the pressure within the exhaust pipe 54 rises rapidly. Therefore, when the engine speed exceeds a certain limit, the opening force of the exhaust valve 26 due to the pressure difference between the negative pressure inside the cylinder 22 generated during the intake stroke and the high positive pressure inside the exhaust pipe 54 is applied to the valve spring 34. Overcoming the valve closing force of The cup and ball of the push rod may even separate, but according to the device of the present invention, when the engine speed is high, the movable nozzle 58 of the exhaust gas turbine does not fully close, but only opens to a certain degree. That is, exhaust valve 2
Since the opening degree is controlled such that the pressure below the limit pressure that causes the self-opening and closing of the exhaust valve 6 is maintained in the exhaust pipe 54, problems caused by the self-opening and closing of the exhaust valve can be reliably prevented. When the engine speed decreases as a result of engine braking and exhaust braking, the actuator 60 further moves to a full stroke via the control valve 62 in response to a command from the second control box 66 that detects this, and the movable nozzle 58 is almost fully closed, and a sufficient exhaust braking effect can be obtained.

Furthermore, according to the device of the present invention, a portion of the compressed air in the exhaust pipe 54 is transferred to the movable nozzle 58 by the partial opening degree of the movable nozzle 58 of the exhaust gas turbine.
The compressor 52 is driven by acting on the rotor of the exhaust gas turbine 50, and the intake pressure supplied into the cylinder 22 via the intake pipe 56 increases. For this reason, the compression work of the piston 14 in the compression stroke increases, which has the advantage of further increasing the engine braking effect.

In the above embodiment, as an auxiliary brake device of the vehicle, when the vehicle is running under engine braking,
Although a device has been described that uses both a device that opens the third valve 28 near the piston compression top dead center to absorb the compression work and a so-called exhaust brake device that closes the movable nozzle of the exhaust gas star pin, the present invention can be applied even when the former is absent. is valid. Furthermore, it is clear that the same effect as described above can be obtained even if the exhaust valve 26 is opened near the top dead center of the compression stroke in place of the third valve 28. Further, in the above embodiment, a pneumatic actuator is illustrated as the actuator 60, but an electric or electro-mechanical actuator, for example,
Of course, a reversible motor and a screw/nut type drive device may be used instead. Furthermore, in the above embodiment, since the engine rotation speed and the pressure in the exhaust pipe 54 are approximately proportional, the engine rotation speed is introduced into the second control box 66 as a control factor, but the pressure in the exhaust pipe 54 is Alternatively, the displacement of the bellows may be directly detected by, for example, a bellows, and the displacement of the bellows may be introduced into the control box 66 as an electrical or mechanical quantity signal. Furthermore, it is clear that the portions of the first and second control boxes 46, 66 that detect the engine braking state of the vehicle can be shared. Note that the driving means for the third valve 28 is not limited to the illustrated structure;
Of course, it is also easily possible to employ cam drive in the same way as the intake and exhaust valves.

As described above, the vehicle braking device according to the present invention includes a third valve provided separately from the normal intake valve and exhaust valve in one or more cylinders of the vehicle engine, or the above-mentioned exhaust valve. A brake device that opens near the compression top dead center of the piston to discharge the compressed air inside the cylinder to the outside of the cylinder when running under engine braking, and an exhaust gas equipped with a movable nozzle that is driven by the exhaust gas of the engine. A brake device equipped with a brake device that closes a movable nozzle of a turbine when the vehicle is running under engine braking to at least partially block the exhaust passage of the engine. When the engine speed is low, the movable nozzle of the exhaust gas turbine is substantially fully closed, and during the engine braking operation, when the engine speed is high, the movable nozzle is not fully closed but slightly opened. It is characterized by a structure in which a pressure below the limit pressure that causes the engine's exhaust valve to self-open and close is maintained in the exhaust passage, and effectively exerts a braking effect when the vehicle is running under engine braking. Furthermore, by controlling the opening degree of the movable nozzle of the exhaust gas turbine according to the engine speed, damage to the engine can be reliably prevented, which is extremely advantageous.

[Brief explanation of the drawing]

The accompanying drawings are schematic layout diagrams showing one embodiment of the present invention. 10... Cylinder head, 38... Plunger, 12... Cylinder block, 40... Pressure oil cylinder, 14... Piston, 42... Pressure oil distribution valve, 24... Intake valve, 46... First control box , 26...exhaust valve, 48...turbocharger, 28...third valve, 54...exhaust pipe, 58
...Movable nozzle, 62...Control valve, 60...Actuator, 66...Second control box.

Claims (1)

[Scope of utility model registration request] A third valve provided separately from the normal intake valve and exhaust valve in one or more cylinders of a vehicle engine, or the above-mentioned exhaust valve, is opened near the compression top dead center of the piston when the vehicle is running under engine braking. A brake device configured to discharge compressed air in a cylinder to the outside of the cylinder, and a movable nozzle of an exhaust gas turbine with a movable nozzle driven by the exhaust gas of the engine are closed when the vehicle runs under engine braking. In a vehicle equipped with a brake device configured to at least partially block the exhaust passage of the engine, when the engine speed is low while the vehicle is running under engine braking, the movable nozzle of the exhaust gas turbine is substantially completely blocked. When the engine speed is high during engine braking, the movable nozzle is not fully closed but slightly opened to create a limit pressure at which the engine exhaust valve self-opens and closes in the exhaust passage. A vehicle brake device characterized in that it is configured to maintain the following pressure.