JPH07242113A - Suspension device - Google Patents

Abstract

PURPOSE:To reduce the power consumption of a hydraulic system, in a suspension device for performing attitude control by supplying/discharging oil to/from a hydraulic cylinder interposed between a car body and each wheel. CONSTITUTION:A high pressure of oil generated in a hydraulic system 22 is accumulated in an accumulator 21, to perform attitude control of a car body by supplying/discharging the oil to/from hydraulic cylinders 18a, 18b, 18c, 18d and gas springs 19a, 19b, 19c, 19d by a supply/discharge device 20. When an accumulating pressure of the accumulator 21 leads to a relief pressure to open an electromagnetic pressure control valve 44, one pilot pressure of a flow control valve 43 is decreased, and a delivery pressure acts in a control piston 46 to reduce a delivery capacity of a variable displacement pump 42. The pressure control valve 44 is controlled in accordance with an operating condition by a controller 23, and in the case of small flow consumption of pressure oil in the supply/discharge device 20, by decreasing the preset relief pressure to reduce the delivery capacity of the variable displacement pump 42, the power consumption of the hydraulic system 22 is reduced to decrease a load of an engine 41.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suspension device for adjusting a vehicle height and controlling a posture of a vehicle such as an automobile.

[0002]

2. Description of the Related Art A hydraulic cylinder for adjusting the vehicle height by supplying and discharging a pressure fluid (oil liquid) is interposed between a vehicle body and each wheel, and a pressure accumulator and a pressure accumulator for accumulating high-pressure oil generated by a hydraulic device. Suspension designed to control the attitude of the vehicle body by controlling the exhaust device (supply / exhaust control valve) to supply and discharge the hydraulic fluid to the hydraulic cylinders of the wheels and the gas springs communicating with the hydraulic cylinders according to the operating conditions. The device is known.

An example of a hydraulic device of this type of suspension device mounted on an automobile will be described with reference to FIG. As shown in FIG. 5, the hydraulic device 1 includes a variable displacement pump 3 directly driven by the engine 2 and a flow rate control valve 4 for adjusting the discharge capacity (the amount discharged per rotation) of the variable displacement pump 3. And a pressure control valve 5.

Variable Displacement Pump The pump 3 is, for example, an axial piston type hydraulic pump, which displaces the control piston 7 in the cylinder 6 and changes the tilt angle of the swash plate to change the piston stroke to change the discharge capacity. It can be controlled. The discharge port of the variable displacement pump 3 is connected to a supply / discharge device (not shown) via an orifice 8 and a check valve 9.

The flow control valve 4 is a 3-port 2-position pilot switching valve. The pump port P ₁ is connected to the discharge side of the variable displacement pump 3, the tank port T ₁ is connected to the drain tank 10, and the cylinder port S is connected. ₁ is connected to the cylinder 6 of the variable displacement pump 3 via the tank port T ₂ of the pressure control valve 5 and the cylinder port S ₂ . Further, the pressures on the upstream side and the downstream side of the orifice 8 are introduced by the pilot conduits 11 and 12, and switching is performed by the pressure difference between these. Then, usually, as shown in FIG, and passed through cylinder port S ₁ and the tank port T ₁ are communicated, the pressure difference between the upstream side and the downstream side by the pressure loss of the orifice 8 is increased as the cylinder port S ₁ It is designed to communicate with the pump port P ₁ .

The pressure control valve 5 is a 3-port 2-position pilot switching valve, the pump port P ₂ is connected to the discharge side of the variable displacement pump 3, and the tank port T ₂ is connected to the cylinder port S ₁ of the flow control valve 4. It is connected to the drain tank 10 via the tank port T ₁ , and the cylinder port S ₂ is connected to the cylinder 6 of the variable displacement pump 3. In addition, the pilot lines 13 and 14 connect the upstream side of the orifice 8 and the check valve 9 to each other.
The pressure of the downstream side, that is, the pressure of the pressure accumulator (accumulator 15) is introduced, and switching is performed by the pressure difference between these. Then, as shown in the figure, the cylinder port S ₂ and the tank port T ₂ are normally communicated with each other, and when the pressure on the supply / discharge device side reaches a predetermined pressure, the cylinder port S ₂
And the pump port P ₂ are communicated with each other. In FIG. 5, 16 is a relief valve for preventing the pressure of the pressure accumulator from rising excessively.

Next, the operation of the hydraulic device configured as described above will be described. The engine 2 speed increases,
When the discharge flow rate of the variable displacement pump 3 (the amount discharged per time) increases, the differential pressure between the upstream side and the downstream side of the orifice 8 increases, and the flow control valve 4 causes the cylinder port S ₁
And the pump port S ₁ communicate with each other. As a result, the discharge pressure of the variable displacement pump 3 is introduced into the cylinder 6, the control piston 7 moves forward, the tilt angle of the swash plate becomes small, and the discharge capacity becomes small. Therefore, the discharge flow rate of the variable displacement pump 3 does not increase more than necessary. Conversely, when the engine speed decreases and the discharge flow rate of the variable displacement pump 3 decreases, the differential pressure between the upstream side and the downstream side of the orifice 8 decreases, and the flow control valve 4 causes the cylinder port S ₁ and the tank port. Switch to a position that allows communication with T ₁ . As a result, the pressure oil in the cylinder 6 is drained from the drain tank 10
And the control piston 7 retracts, the tilt angle of the swash plate increases, and the discharge capacity increases. In this way, the tilt angle of the swash plate is adjusted according to the discharge flow rate and the discharge capacity is adjusted, so that the discharge flow rate is controlled to be substantially constant regardless of the engine speed.

On the other hand, when the accumulated pressure of the accumulator 15 reaches a predetermined pressure, the pressure causes the pressure control valve 5 to switch to a position for connecting the cylinder port S ₂ and the pump port P ₂ . As a result, the discharge pressure is introduced into the cylinder 6, the control piston 7 moves forward, the tilt angle of the swash plate of the variable displacement pump 3 decreases, the discharge capacity decreases, and the discharge flow rate decreases. When the accumulated pressure exceeds the relief pressure, the relief valve 16 relieves the pressure oil to the drain tank. Further, when the pressure of the accumulator 15 decreases due to the oil supply to the hydraulic cylinder and the gas spring, etc., the pressure control valve 5 switches to the position where the cylinder port S ₂ and the tank port T ₂ communicate with each other. As a result, the pressure oil in the cylinder 6 is discharged to the drain tank 10, the control piston 7 retracts, and the tilt angle of the swash plate of the variable displacement pump 3 increases and the discharge capacity increases. In this way, the discharge capacity of the variable displacement pump 3 is reduced to maintain the power consumption by keeping the pressure accumulator at a constant pressure and after reaching the predetermined pressure.

[0009]

However, the suspension device using the conventional hydraulic device described above has the following problems. That is, in the conventional example, the pressure control valve 5
Is switched depending on the relationship between the pressure difference on the pressure accumulator side introduced by the pilot line 14 and the pressure on the discharge side of the variable displacement pump 3 introduced by the pilot line 13 and the set load of the spring, The accumulated pressure is maintained at one predetermined pressure. For this reason,
When the pressure becomes equal to or lower than the predetermined pressure, the displacement of the variable displacement pump 3 is increased, and the engine is always burdened.

Therefore, I do not want to burden the engine,
Even when the engine is started or accelerated, if the accumulated pressure of the pressure accumulator is equal to or lower than a predetermined pressure, the engine is always burdened.

Further, when the pressure oil is not frequently supplied to the hydraulic cylinders and the consumption amount of the pressure oil is small (for example, when the vehicle travels constantly on a highway), the discharge capacity increases and decreases frequently before and after a predetermined pressure. Repeatedly, the flow rate of the oil liquid changes frequently, and the sound and vibration generated thereby tend to give an uncomfortable feeling to the driver who is running quietly due to constant running or the like.

The present invention has been made in view of the above points, and an object of the present invention is to provide a suspension device capable of adjusting the supply pressure of a hydraulic device in accordance with the amount of pressure oil consumed.

[0013]

In order to solve the above-mentioned problems, a first aspect of the present invention relates to a hydraulic cylinder interposed between a vehicle body and each wheel, and a pressure accumulator for supplying pressure oil to the hydraulic cylinder. A device, a hydraulic device connected to the pressure accumulator via a check valve, for supplying pressure oil to the pressure accumulator, and provided between the hydraulic cylinder and the pressure accumulator, the pressure oil being supplied to the hydraulic cylinder. In a suspension device including a supply / discharge control valve for controlling supply / discharge and a controller for controlling the hydraulic device and the supply / discharge control valve to control the vehicle height or the attitude of the vehicle body, the hydraulic device is configured to operate by an engine. A variable displacement pump that is driven and has a discharge capacity adjusting mechanism that adjusts so as to reduce the discharge capacity by the supply of pressure oil, and a main pipeline that supplies the oil liquid discharged from the variable capacity pump to the pressure accumulator side, The A first orifice provided in the pipeline, a pilot control valve for supplying and discharging pressure oil to the displacement control mechanism of the variable displacement pump, and the main pipe for urging the pilot control valve toward the supply position. First of the road
Pilot pipe for guiding pressure oil upstream of the first orifice and a second pilot connected to the downstream side of the first orifice of the main pipe so as to urge the pilot control valve to the discharge position side. A pipe line, a second orifice provided in the second pilot pipe line and having a larger flow resistance than the first orifice, and an electromagnetic pressure control valve for controlling the pressure on the downstream side of the second orifice. It is characterized by having and.

According to a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, a traveling state detecting means for detecting a traveling state and pressure oil for the hydraulic cylinder based on the detection result of the traveling state detecting means. And a set pressure reducing means for reducing the set pressure of the electromagnetic pressure control valve when it is determined that the supply is not frequently performed.

A third aspect of the invention is characterized in that, in addition to the configuration of the first aspect of the invention, an engine starting set pressure reducing means for reducing the set pressure of the electromagnetic pressure control valve when the engine is started is provided. To do.

According to a fourth aspect of the present invention, in addition to the structure of the first aspect of the invention, an acceleration set pressure reducing means for reducing the set pressure of the electromagnetic pressure control valve when the vehicle is in an accelerated state is provided. Is characterized by.

[0017]

With this structure, in the first aspect of the present invention, when the engine speed increases and the discharge flow rate of the variable displacement pump increases, a differential pressure is generated before and after the first orifice. Since the pressure in the first pilot line becomes higher than the pressure in the second pilot line, the pilot control valve moves to the supply position and the pressure oil is supplied to the discharge capacity adjusting mechanism. The discharge capacity decreases and the discharge flow rate does not increase any more. Therefore,
It is possible to prevent the discharge flow rate from increasing too much even if the engine speed increases. Further, when the pressure of the pressure accumulator increases and the pressures of the main pipeline and the second pilot pipeline increase to reach the set pressure of the electromagnetic pressure control valve, the electromagnetic pressure control valve opens and the second pressure control valve opens. The pilot line will not exceed the set pressure. If pressure oil is further discharged from the variable displacement pump in this state, a differential pressure is generated between the upstream side and the downstream side of the second orifice,
As a result, the pressure in the first pilot line is higher than the pressure in the second pilot line. As a result, the pilot control valve moves to the supply position and pressure oil is supplied to the discharge capacity adjustment mechanism, so the discharge capacity of the variable capacity pump decreases,
The pressure of the hydraulic device (the pressure on the upstream side of the check valve provided between the hydraulic device and the pressure accumulator) becomes substantially constant at the set pressure. The set pressure can be adjusted by changing the current supplied to the electromagnetic pressure control valve.

According to the second aspect of the invention, based on the detection result of the traveling state detecting means, when it is determined that the pressure oil is not frequently supplied to the hydraulic cylinder, the electromagnetic pressure control valve By reducing the set pressure, the discharge capacity of the variable displacement pump can be kept small while the accumulated pressure of the accumulator decreases to a predetermined pressure.

Further, according to the third aspect of the invention, since the set pressure of the electromagnetic pressure control valve is lowered at the time of starting the engine, the displacement of the variable displacement pump is reduced at the time of starting the engine, so that the load on the engine starting motor is reduced. The startability of the engine is improved.

Further, according to the fourth aspect of the invention, since the set pressure of the electromagnetic pressure control valve is lowered when the vehicle is accelerated, the discharge capacity of the variable displacement pump is reduced during acceleration, so the load on the engine is reduced and the acceleration performance is improved. Is improved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. In this embodiment, a suspension device for a four-wheeled vehicle will be described as an example.

As shown in FIG. 2, the suspension device 17 of the present invention includes hydraulic cylinders 18a, 18b, 18c, which are interposed between the vehicle body and each wheel and which adjust the vehicle height by supplying and discharging an oil liquid.
18d and gas springs 19a, 19b, 19c and 19d which respectively communicate with these hydraulic cylinders, a supply / discharge device 20 for supplying / discharging pressure oil to / from the hydraulic cylinders and the gas springs, and pressure oil supplied to the supply / discharge device 20. Accumulator 21 for accumulating pressure, and accumulator
A hydraulic device 22 for supplying pressurized oil to 21 and a controller 23 for controlling the supply / discharge device 20, the pressure accumulating device 21, and the hydraulic device 22 according to the operating condition are roughly configured. In the figure, 24
Is a tank and 25 is an oil cooler.

The supply / discharge device 20 includes hydraulic cylinders 18a, 18b.
, 18c, 18d and gas springs 19a, 19b, 19c, 19d
Flow control valves 26a, 26b, 26c, and 26d are provided as supply and discharge control valves for supplying and discharging pressure oil, respectively. The flow rate control valves 26a, 26b, 26c, 26d are 3-port 3-position throttle switching valves, which receive signals from the controller 23 and are solenoid valves.
In accordance with the pilot pressure generated by 27a, 27b, 27c, and 27d, the oil supply position at which the pressure oil from the pressure accumulator 21 is supplied to the hydraulic cylinder side at a predetermined flow rate, and the pressure oil on the hydraulic cylinder side at a predetermined flow rate on the tank 24 side The discharge position for discharging to and the neutral position for stopping the oil supply and discharge can be selectively switched. Further, pressure sensors 28a, 28b, 28c, 28d for detecting pressures on the hydraulic cylinders 18a, 18b, 18c, 18d side are provided.

The pressure accumulator 21 includes an accumulator 29, check valves 30 and 31, a relief valve 32, and a fail-safe valve.
33 and a pilot check valve 34 are provided. Then, the high pressure oil generated in the hydraulic device 22 is transferred to the accumulator 29.
When the accumulated pressure exceeds the relief pressure, the relief valve
The pressure oil is relieved to the tank 24 by 32. Also, during normal operation of the suspension device 17,
Fail safe valve 33 in response to signal from controller 23
Is closed, which causes the pilot check valve 34 to open due to the pressure on the accumulator 29 side, and
It is possible to drain oil to 24, and if an error occurs, the controller
When the signal from 23 stops, the fail-safe valve 33 opens to relieve the pressure oil on the accumulator 29 side to the tank 24, and this closes the pilot check valve 34 to discharge the oil from the supply / discharge device 20 to the tank 24. It is supposed to stop. An accumulator 35 is provided between the pressure accumulator 21 and the hydraulic device 22 to prevent pulsation due to a change in the supply amount of pressure oil of the hydraulic device 22.

The controller 23 is a vehicle including pressure sensors 28a, 28b, 28c, 28d, vertical acceleration sensors 36, vehicle height sensors 37, vehicle speed sensors 38, throttle position sensors 39, lateral acceleration sensors 40, etc. Actuating the solenoid valves 27a, 27b, 27c, 27d of the feeding / discharging device 20 based on signals from various sensors (running state detection means) for detecting the running state of the vehicle and commands for manual switching (not shown) Hydraulic cylinders 18a, 18b, 18c, 18d
And gas springs 19a, 19b, 19c, and 19d to supply and drain oil, and to roll, dive, squat,
Attitude control is performed for pitching and bouncing, and the vehicle height is adjusted according to changes in the load. In addition, the pressure control valve 44 of the hydraulic system 22
An unillustrated control circuit (described later) for controlling (described later) is provided.

Next, the hydraulic device 22 which is the main part of the present invention will be described with reference to FIG. Note that FIG. 1 corresponds to FIG.
It shows the same device as the hydraulic device 22 of
Regarding, the accumulator 29, the check valve 30, and the relief valve 32 are only shown.

As shown in FIG. 1, the hydraulic device 22 is driven by an engine 41 and has a variable displacement pump 42 having a discharge capacity adjusting mechanism composed of a cylinder 45 and a control piston 46, which will be described later, and an oil to be sent to the cylinder 45 of the pump. A pilot control valve 43 for adjusting the discharge amount of the variable displacement pump 42 by adjusting the amount, and an adjusting means for decreasing the discharge displacement of the variable displacement pump 42 when the pressure of the pressure accumulator 21 reaches an adjustable set pressure. And an electromagnetic pressure control valve 44 as

The variable displacement pump 42 is an axial piston type hydraulic pump, and the displacement can be controlled by displacing the control piston 46 in the cylinder 45 and changing the tilt angle of the swash plate to change the piston stroke. It is like this. The discharge port of the variable displacement pump 42 is connected to the accumulator 29 of the pressure accumulator 21 by a main pipe line 47, and the main pipe line 47 is provided with a first orifice 48.

The pilot control valve 43 is a 3-port 2-position pilot switching valve, and the pump port P ₃ is connected to the discharge side of the variable displacement pump 42 by a conduit 49, and the tank port
T ₃ is connected to the drain side tank 24 by a pipe line 50, and the cylinder port S ₃ is connected to a cylinder 45 of the variable displacement pump 42 by a pipe line 51. In addition, a first pilot conduit 52 for introducing a hydraulic pressure upstream of the first orifice 48 of the main conduit 47 and a second pilot conduit 53 for introducing a pressure downstream of the first orifice 48 are provided. It is connected. The second pilot conduit 53 is provided with a second orifice 54. Normally, the spring 55 is located at a position where the cylinder port S ₃ and the tank port T ₃ communicate with each other by the spring 55, and the pressure loss of the first orifice 48 causes a large differential pressure between the upstream side and the downstream side. Cylinder port S ₃
And the pump port P ₃ are communicated with each other.

The electromagnetic pressure control valve 44 is an electromagnetic proportional pressure relief valve in which the relief pressure P _S can be arbitrarily set in accordance with the energizing current, and the line 56 allows the second pilot line 53 to be connected to the second pilot line 53. It is connected to the downstream side of the orifice 54. Then, based on the signal from the controller 23, the relief pressure P _S
(Set pressure) is set, and when the pressure in the second pilot line 53 reaches the set relief pressure, the valve is opened to relieve the pressure oil in the second pilot line 53 to the tank 24. ing.

Next, the control of the relief pressure P _S of the electromagnetic pressure control valve 44 by the controller 23 will be described. In the controller 23, the relief pressure P _S is set to 0 when the engine is started, and the relief pressure P _{S is set} to a relatively low pressure P _L in a state where supply and discharge of oil to the hydraulic cylinder is almost unnecessary, such as during constant traveling on a flat road. , during traveling of the bumpy road, during turning, acceleration or braking, etc., in a state where the supply and discharge oil is frequently performed to the hydraulic cylinder to a relatively high pressure P _H.

The above control flow will be described more specifically with reference to FIG. Vertical acceleration sensor 36 in steps,
Signals from various sensors such as a vehicle height sensor 37, a vehicle speed sensor 38, a throttle position sensor 39, and a lateral acceleration sensor 40 are read. In step, it is determined whether the engine is being started based on the signal read in step. At this time, for example, it can be determined by turning on / off the starter motor switch. Then, if the engine is being started, the procedure proceeds to step and the relief pressure P _S of the electromagnetic pressure control valve 44 is
= 0. If the engine is not being started, proceed to step. In the step, it is determined whether or not the pressure oil is not frequently supplied to the hydraulic cylinder based on the signal read in the step. The situation where the pressure oil is not frequently supplied to the hydraulic cylinder means that the vehicle is traveling on a flat road (good road) for a certain period of time, or the detected value of the vertical acceleration sensor 36 is less than or equal to a predetermined value. This is the case when the detected value of 40 is less than or equal to a predetermined value, the vehicle speed is 0, and the like. Then, the method of determining whether or not constant traveling on a flat road, for example, using the vehicle height sensor 37 and the vehicle speed sensor 38 as the traveling state detection means, the amplitude of the vehicle height sensor 37 is below a predetermined value and the vehicle speed sensor 38 is almost When it is a constant value (the rate of change is small), it is determined to be constant traveling on a flat road (a traveling state on a highway). Alternatively, the operating condition of the flow control valve 26 may be directly detected to determine whether or not the pressure oil is not frequently supplied to the hydraulic cylinder. Then, if the pressure oil is not frequently supplied such as constant traveling on a flat road, the process proceeds to step and the relief pressure P _S = P _L of the electromagnetic pressure control valve 44 is set. On the other hand, if not so, the process proceeds to step and the relief pressure P _S = P _H (> P _L ) of the electromagnetic pressure control valve 44 is set.

The operation of this embodiment having the above-mentioned structure will be described below.

The high pressure oil generated by the hydraulic device 22 is accumulated in the pressure accumulating device 21, and the controller 23 operates the supply / discharge device 20 based on the output signals of various sensors to cause the hydraulic cylinders 18a, 18b, 18c, 18d of the respective wheels. And gas springs 19a, 19b
Attitude control of the vehicle body according to the driving situation is performed by supplying / discharging pressure oil to, 19c, 19d.

In the hydraulic system 22, the electromagnetic pressure control valve 44 is closed when the accumulated pressure of the pressure accumulator 21 (pressure of the accumulator 29) does not reach the set relief pressure P _S of the electromagnetic pressure control valve 44. At this time, the pilot control valve 43 operates by the pressure difference between the upstream side and the downstream side of the first orifice 48, so that the rotation speed of the engine 41 increases and the variable displacement pump.
When the discharge flow rate of 42 increases, the differential pressure between the upstream side and the downstream side of the first orifice 48 increases, and the flow rate control valve 44 switches to a position that allows the cylinder port S ₃ and the pump port P ₃ to communicate with each other. As a result, the discharge pressure is introduced into the cylinder 45 via the conduits 49 and 51, the control piston 46 moves forward, and the tilt angle of the swash plate of the variable displacement pump 42 decreases, so that the discharge capacity decreases. On the contrary, when the engine speed decreases and the discharge flow rate of the variable displacement pump 42 decreases, the differential pressure between the upstream side and the downstream side of the first orifice 48 decreases and the pilot control valve 43 causes the cylinder port S ₃ and the tank. Switch to a position that allows communication with port T ₃ . This allows the cylinder 46
The oil liquid inside is discharged to the drain tank 24 through the pipe lines 51 and 50, and the control piston 46 moves backward to move the variable displacement pump.
The tilt angle of the swash plate 42 increases, and the discharge capacity increases.
In this way, the tilt angle of the swash plate is adjusted according to the discharge flow rate, and the discharge flow rate is controlled to be constant regardless of the engine speed.

When the accumulator 21 is pressurized by the pressure oil discharged from the variable displacement pump 42 and the accumulated pressure reaches the set relief pressure P _S (set pressure) of the electromagnetic pressure control valve 44, the electromagnetic pressure control valve 44 is opened and the pressure oil in the second pilot line 53 is relieved to the tank 24, and the pressure in the second pilot line 53 becomes constant at P _S. When pressure oil is further discharged from the variable displacement pump 42 in this state, the pressure in the first pilot conduit 52 rises, the pilot control valve 43 switches to the low displacement position, and the swash plate of the variable displacement pump 42 tilts. The roll angle becomes small and the discharge capacity becomes small.

When the pressure oil accumulated in the pressure accumulator 21 is supplied to the hydraulic cylinder and the gas spring by the supply / discharge device 20 and is reduced in pressure to a pressure lower than the relief pressure set by the electromagnetic pressure control valve 44, the electromagnetic pressure is reduced. The control valve 44 is closed and the hydraulic pressure in the second pilot line 53 rises to increase the pilot control valve 43.
By moving the control piston 46 backward, the displacement of the variable displacement pump 42 increases.

In this way, the variable displacement pump 42 discharges the same amount of pressure oil as the flow rate consumed by the supply / discharge device 20, so that the accumulated pressure of the pressure accumulator 21 becomes equal to the set relief pressure P of the electromagnetic pressure control valve 44. Maintained at _S. Therefore, the variable displacement pump 42 discharges the oil liquid at the flow rate required by the supply / discharge device 20, and the power consumption can be reduced. FIG. 4 shows the relationship between the engine speed and the displacement when the displacement of the swash plate of the variable displacement pump 42 is controlled to adjust the displacement in three stages.

The set relief pressure P _S of the electromagnetic pressure control valve 44 is controlled by the controller 23 in accordance with the operating condition, and when the engine is started, the set relief pressure P _S is set.
Since = 0, when the variable displacement pump 42 starts to discharge due to the rotation of the starter motor, the electromagnetic pressure control valve 44 opens and the discharge capacity decreases, so the load is reduced and the startability of the engine 41 is improved. Further, in a state where supply and discharge of oil to the hydraulic cylinder is almost unnecessary, such as during constant traveling on a flat road, since the flow rate of pressure oil consumed by the supply and discharge device 20 is small, the set relief pressure P _S is set to a relatively low pressure. By setting P _L , the discharge capacity of the variable displacement pump 42 is maintained for a relatively long time (pressure of the pressure accumulator is
It can be decreased until it falls to P _L or until the set pressure of the pressure accumulator is set to P _H ), which is not constant running on a flat road, etc., and power consumption is reduced to reduce engine 41 The burden is reduced. When traveling on uneven roads,
When the hydraulic cylinder is frequently fed and drained, such as when turning, accelerating, or braking, setting the relief pressure P _S of the electromagnetic pressure control valve 44 to a relatively high pressure P _H A sufficient amount of pressure oil can be accumulated in the pressure accumulator 21 with respect to an increase in the flow rate of pressure oil consumed by the discharge device 20.

As described above, the discharge capacity of the variable displacement pump 42 can be controlled by adjusting the set relief pressure P _S of the electromagnetic pressure control valve 44 by the controller 23, so that the engine can be operated according to operating conditions. The burden can be reduced, and driving performance and fuel efficiency can be improved.

In the above embodiment, it is determined in the step of FIG. 3 whether "the engine is being started?", And in the step, "whether the pressure oil is frequently supplied and discharged?" Although the set relief pressure Ps of the control valve 44 is low, in addition to this, the throttle position sensor
Read 39 signals, and between steps,
A step is provided as means for reducing the set pressure during acceleration that determines whether the throttle is opened below a predetermined value from the signal from the throttle position sensor 39. When the value is above the predetermined value, it is determined that the vehicle is accelerating. Then, the set relief pressure Ps of the pressure control valve 44 may be set to PL and lowered in step. This makes it possible to reduce the discharge capacity of the variable displacement pump during acceleration, reduce the load on the engine during acceleration, and improve the acceleration performance.

[0042]

As described in detail above, the suspension device according to the first aspect of the present invention prevents the discharge flow rate from increasing too much even when the engine speed increases, and at the same time, suppresses the supply pressure of the hydraulic device (hydraulic device). The pressure on the upstream side of the check valve provided between the pressure accumulator and the pressure accumulator can be made substantially constant at the set pressure. Furthermore, the supply pressure of the hydraulic device can be made variable by adjusting the current supplied to the electromagnetic proportional control valve and setting it appropriately, which reduces the load on the engine by setting the supply pressure low, It is possible to arbitrarily increase the accumulated pressure of the pressure accumulator by setting the supply pressure high.

In the second aspect of the invention, the set pressure of the electromagnetic pressure control valve is lowered when it is judged that the pressure oil is not frequently supplied to the hydraulic cylinder, so that the load on the engine is reduced. In addition, it is possible to reduce the generation of noise and vibration due to the change of the flow rate.

Further, according to the third aspect of the invention, since the set pressure of the electromagnetic pressure control valve is lowered at the time of starting the engine, the discharge capacity of the variable displacement pump is lowered at the time of starting the engine, so that the load on the engine starting motor is reduced, The startability of is improved.

Further, according to the fourth aspect of the invention, since the set pressure of the electromagnetic pressure control valve is lowered when the vehicle is accelerated, the discharge capacity of the variable displacement pump is reduced during acceleration, so the load on the engine is reduced and the acceleration performance is improved. Is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a hydraulic device of a suspension device according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a suspension device according to an embodiment of the present invention.

FIG. 3 is a flowchart showing control of set relief pressure of a pressure control valve of the apparatus of FIG.

FIG. 4 is a diagram showing characteristics of a variable displacement pump of the apparatus of FIG.

FIG. 5 is a circuit diagram of a hydraulic device of a conventional suspension device.

[Explanation of symbols]

 17 Suspension device 18a, 18b, 18c, 18d Hydraulic cylinder 19a, 19b, 19c, 19d Gas spring 20 Supply / discharge device 21 Accumulator device 22 Hydraulic device 23 Controller 26a, 26b, 26c, 26d Flow control valve (supply / discharge control valve) 30 Check valve 41 Engine 42 Variable displacement pump 43 Pilot control valve 44 Electromagnetic pressure control valve 47 Main line 48 First orifice 52 First pilot line 53 Second pilot line 54 Second orifice

Claims (4)

[Claims] 1. A hydraulic cylinder interposed between a vehicle body and each wheel, a pressure accumulator for supplying pressure oil to the hydraulic cylinder, and a pressure accumulator connected to the accumulator via a check valve. A hydraulic device that supplies pressure oil, a supply / discharge control valve that is provided between the hydraulic cylinder and the pressure accumulator, and controls supply and discharge of the pressure oil to and from the hydraulic cylinder, and the hydraulic device and the supply / discharge control valve. And a controller for controlling the vehicle height or the attitude of the vehicle body, wherein the hydraulic device is driven by an engine, and the discharge capacity is adjusted so as to reduce the discharge capacity by supplying pressure oil. A variable displacement pump having an adjusting mechanism, a main pipe for supplying oil liquid discharged from the variable displacement pump to the pressure accumulator side, and a first orifice provided in the main pipe.
A pilot control valve for supplying and discharging pressure oil to and from the discharge capacity adjusting mechanism of the variable displacement pump, and pressure oil upstream of the first orifice of the main pipeline so as to urge the pilot control valve to the supply position side. A first pilot line leading the
A second pilot conduit connected to the downstream side of the first orifice of the main conduit so as to urge the pilot control valve to the discharge position side; and the first pilot conduit provided in the second pilot conduit. The second suspension has a second orifice having a larger flow resistance than the second orifice and an electromagnetic pressure control valve for controlling the pressure on the downstream side of the second orifice. 2. A running state detecting means for detecting a running state, and based on a detection result of the running state detecting means, it is determined that pressure oil is not frequently supplied to the hydraulic cylinder. The suspension device according to claim 1, further comprising set pressure reducing means for reducing a set pressure of the electromagnetic pressure control valve. 3. The suspension device according to claim 1, further comprising engine starting set pressure lowering means for lowering the set pressure of the electromagnetic pressure control valve when the engine is started. 4. The suspension device according to claim 1, further comprising acceleration-time set pressure reducing means for reducing the set pressure of the electromagnetic pressure control valve when the vehicle is in an accelerating state.