A HYDRAULIC SUSPENSION SYSTEM FOR A VEHICLE

Abstract: In a hydraulic suspension system, a plurality of actuators (1) having working fluid chambers (2) are provided. Each actuator is adapted to increase and decrease vehicle height as the results of the supply and the discharge of working fluid into and from its working fluid chamber, respectively. A plurality of accumulators (132, 134, 136, 138) are connected with the associated working fluid chambers. Working fluid supply passages (18) supply working fluid into the working fluid chambers and working fluid discharge passages (48) discharge working fluid from the working fluid chambers. Pressure control devices (32, 34, 36, 38) are provided in the supply passages and the discharge passages. Each pressure control device means is adapted to control the supply of the working fluid into and the discharge from the associated working fluid chamber to adjust the pressure within the chamber. The suspension system further comprises flow resistance control devices. Each flow resistance control device is adapted to adjust at least one of the first flow resistance (124, 126, 128, 130) between the associated working fluid chamber and the associated accumulator and the second flow resistance of the associated discharge passage in response to the flow rate of the working fluid discharging through the discharge passage so that the higher the discharging flow rate is, the higher the ratio of the second to the first flow resistances may be, not only to reduce the flow rate of the working fluid discharging from the working fluid chamber through the discharge passage but also to increase the flow rate of the working fluid flowing into the accumulator from the working fluid chamber.

Description: Background of the Invention Field of the Invention The present invention relates to a suspension system for a vehicle such as an automobile, and more particularly, to a hydraulic suspension system according to the preamble of claim 1. Description of the Prior art As described, for example, in Japanese Patent Laid-Open Publication No. Showa 63-219408 (1988), a suspension system is well known in the art as a hydraulic suspension system for a vehicle such as an automobile, which comprises actuators provided between a vehicle body and corresponding suspension arms and adapted to increase and decrease vehicle heights as the results of the supply and the discharge of working fluid into and from their working fluid chambers, respectively, accumulators connected with the working fluid chambers by passages having therein flow restrictions, working fluid supply passage means for supplying working fluid into the working fluid chambers, working fluid discharge passage means for discharging working fluid from the working fluid chambers, pressure control means such as pressure control valves which are provided in the working fluid supply passage means and the working fluid discharge passage means and which are adapted to control the supply of the working fluid into and the discharge from the working fluid chambers so as to adjust the pressures within the working fluid chambers to their desired levels. In such a hydraulic suspension system, as the pressure within the working fluid chamber in each actuator repeatedly increases and decreases due to the bounds and rebounds of a vehicle wheel, working fluid is repeatedly supplied into and discharged from the working fluid chamber to compensate for the pressure variation within the chamber, resulting in the increased energy consumption of the working fluid. In view of this, as described, for example, in Japanese Laid-Open Publication No. Showa 62-292517 (1987), a hydraulic suspension system has been known in the art which comprises a first hydraulic system including a pressure control valve and a second hydraulic system including an accumulator and a passage having therein a flow restriction and connecting the accumulator and the working fluid chamber in the associated actuator, wherein the damping force in the first hydraulic system is set to be higher than that in the second hydraulic system when the vibration input into the actuator is higher in frequency than a predeterminate value to thereby limit the response of the pressure control valve to higher frequency vibration inputs so that the energy consumption of the working fluid may be prevented from increasing due to the bounds and rebounds of the vehicle wheel. However, in the hydraulic suspension system described in the above-mentioned Japanese Patent Laid-Open Publication No. Showa 62-292517, since the flow resistance of the first hydraulic system is set so as to meet the above requirement by judiciously setting the inner diameter and the length of the flow line between the pressure control valve and the actuator, the freedom of setting to satisfy the requirement is rather small. That is, if the flow resistance of the first hydraulic system is set so high that the action of the pressure control valve may be effectively limited against higher frequency vibration inputs, it is too high for lower frequency vibration inputs, resulting in the aggravated response in controlling the attitude of a vehicle body. Conversely, if the flow resistance of the first hydraulic system is not set high enough, the energy consumption of the working fluid is not well reduced. In the preamble of claim 1, it is proceeded from a hydraulic suspension system for motor vehicles as is shown in the EP-A-0 249 227. For the absorption of vibrations at a vehicle wheel, this known suspension system provides on the respective wheel suspension a hydraulic cylinder, to the pressure chamber of which a working pressure is adapted to be applied by means of a hydraulic pump. For the control of the working pressure, a control valve is inserted in a pressure line between pump and pressure chamber, said control valve being controlled by a controller in accordance with the vibrations of the vehicle and combining the working cylinder optionally with the hydraulic pump or a tank. Further, an accumulator is provided, which is connectable to the pressure line directly in front of the pressure chamber of the hydraulic cylinder. Control valve and accumulator are respectively allocated to an independent hydraulic system which, depending on the oscillation amplitude of the vehicle, are used for damping the vibration. Thus, this known suspension system substantially corresponds to the prior art already cited above. The subject matter of the invention is based on the object of further developing the hydraulic system according to the preamble of claim 1 to the effect that it is capable of reducing the energy consumption of working fluid without aggravating the response in controlling the attitude of a vehicle body. According to the invention, this problem is solved by the features of the main claim. The consumption is dependent upon the frequency and amplitude of the bounding and rebounding, but in any event it is dependent upon the rate of discharge of the working fluid from the working fluid chambers. This consumption of the working fluid due to the bounding and rebounding of the vehicle wheel occurs on the basis that the pressure control means for controlling the pressure of the working fluid in the working fluid chamber of the actuator operates in such a manner that it supplies or replenishes the working fluid from the working fluid source to the working fluid chamber when the pressure of the working fluid chamber decreases from a certain standard, and discharges the working fluid from the working fluid chamber when the pressure of the working fluid in the working fluid chamber increases from a certain standard. Based upon such a pressure control construction for the working fluid chamber of the actuator and taking into consideration the effect of the accumulator connected to the working fluid chamber of the actuator on the amount of consumption of the working fluid according to the frequency and the amplitude of the bounding and rebounding of the vehicle, i.e. after all the rate of the discharge of the working fluid from the working fluid chamber, the idea of the present invention is to increase the flow resistance of the discharge passage relative to the flow resistance of the passage connecting the accumulator with the working fluid chamber or to decrease the flow resistance of the passage connecting the accumulator with the working fluid chamber relative to the flow resistance of the discharge passage, i.e. to increase the ratio of the flow resistance of the discharge passage to the flow resistance of the passage connecting the accumulator with the working fluid chamber. The formulation of the enclosed claim 1 as well as of dependent claims 2 to 11 has further also served to clarify that the pressure control means including the variable throttle means controls the supply of the working fluid from the working fluid source means to the respective working fluid chambers and the discharge of the working fluid from the respective working fluid chambers through respective discharge passages, so that the working fluid is supplied to the respective working fluid chambers according to a decrease of the pressure of the working fluid in the corresponding working fluid chambers and the working fluid is discharged from the respective working fluid chambers according to an increase of the pressure of the working fluid in the corresponding working fluid chambers. In other words, it has been made clear that the control of the working pressure in the working fluid chamber of the actuator is inevitably bound with a consumption of the pressurized working fluid from the working fluid source means. The accumulator can reduce such a consumption of the working fluid by temporarily sacrificing the firmness of its dumping performance, so that it absorbs the working fluid more readily than normally desirable by the ratio of the flow resistance of the discharge passage to the flow resistance of the passage between the accumulator and the working fluid chamber being temporarily increased. As will be realized, assuming that Q and Q' mean respectively the increasing and decreasing volume change quantities per unit time of the working fluid chamber in each actuator due to the rebound and the bound of the associated vehicle wheel; Q₁ means the flow rate of the working fluid flowing from accumulator into the working fluid chamber; Q₁' means the flow rate of the fluid flowing from the working fluid chamber into the accumulator; Q₂ means the flow rate of the working fluid flowing into the fluid chamber through the supply passage means; and Q₂' means the flow rate of the fluid discharging from the working fluid chamber through the discharge passage means, these variables have the following relationships: Q = Q₁ + Q₂ Q' = Q₁' + Q₂' According to the present invention, the variable throttle means are provided for adjusting at least one of the flow resistances. Each variable throttle means is adapted to respond to the flow rate of the working fluid discharging through the discharge passage means and to adjust at least one of the flow resistances so that the more the discharging flow rate is, the higher the ratio of the second flow resistance to the first flow resistance may be. Accordingly, when vibrations of higher frequency and higher amplitude are input into the actuator in such a case where the vehicle runs on a rough road, the ratio of the flow resistance of the discharge passage means (second flow resistance) to the flow resistance between the working fluid chamber and the accumulator means first flow resistance is increased by the variable throttle means in response to the increase in flow rate of the working fluid discharging through the discharge passage means, to thereby not only reduce the flow rate Q₂' of the working fluid discharging from the working fluid chamber through the discharge passage means but also to increase the flow rate Q₁ of the working fluid flowing into the accumulator means from the working fluid chamber, resulting in the reduced energy consumption of the working fluid. On the other hand, when the volume of the working fluid chamber in each actuator changes in a moderate manner in such a case where the vehicle runs on a good road or the attitude control of the vehicle body is effected, the flow rate of the working fluid discharging through the discharge passage means is so low that the ratio of the second to the first flow resistances is kept low enough to assure the condition where the working fluid can freely discharge from the working fluid chamber through the discharge passage means, which enables the comfortability control and the attitude control to be well effected without a substantial delay in response. The present invention is now described in terms of embodiments with reference to the attached drawings. Brief Description of the Drawings In the accompanying drawings: Fig. 1 is a schematic diagram showing the first preferred embodiment of the hydraulic suspension system of the present invention; Fig. 2 is a schematic partial diagram showing only the area for the rear right vehicle wheel in the second preferred embodiment of the hydraulic suspension system of the present invention; Fig. 3 is a schematic partial diagram similar to Fig. 2 showing the third preferred embodiment of the hydraulic suspension system of the present invention; Fig. 4 is a graph showing a specific characteristic of the variable flow restriction incorporated in the embodiment shown in Fig. 3; Fig. 5 is a schematic partial diagram similar to Fig. 2 showing an embodiment modified from the embodiment shown in Fig. 3; Fig. 6 is a schematic partial diagram similar to Fig. 2 showing the fourth preferred embodiment of the hydraulic suspension system of the present invention; Fig. 7 is a graph showing a specific characteristic of the variable flow restriction incorporated in the embodiment shown in Fig. 6; Fig. 8 is a schematic partial diagram similar to Fig. 2 showing the fifth preferred embodiment of the hydraulic suspension of the present invention; Fig. 9 is a schematic partial diagram showing the area for the rear vehicle wheels in the sixth preferred embodiment of the hydraulic suspension system of the present invention; Fig. 10 is a schematic partial diagram similar to Fig. 2 showing the seventh preferred embodiment of the hydraulic suspension system of the present invention; Fig. 11 is a graph showing the specific characteristic of the variable flow restriction incorporated in the embodiment shown in Fig. 10; Fig. 12 is a schematic partial diagram similar to Fig. 2 showing the eighth preferred embodiment of the hydraulic suspension system of the present invention; Fig. 13 is a graph showing the specific characteristic of the variable flow restriction incorporated in the embodiment shown in Fig. 12; Fig. 14 is a schematic partial diagram similar to Fig. 2 showing the ninth preferred embodiment of hydraulic system of the present invention; and Fig. 15 is a graph showing the specific characteristic of the variable flow restriction incorporated in the embodiment shown in Fig. 14. Corresponding reference numerals indicate corresponding parts throughout the diagrams of the drawings. Description of the Preferred Embodiments Referring to the drawings, Fig. 1 is a schematic diagram showing the first preferred embodiment of the hydraulic suspension system of the present invention. The suspension system shown in the figure includes actuators 1FR, 1FL, 1RR and 1RL provided corresponding to front right, front left, rear right and rear left vehicle wheels, not shown, respectively, and these actuators have therein working fluid chambers 2FR, 2FL, 2RR, and 2RL, respectively. In the figure, 4 designates a reserve tank which contains oil serving as working fluid, and the tank 4 is fluidly connected to the suction side of a pump 6 by a suction flow line 10 having therein a filter 8 for removing any foreign matter from oil. To the pump 6 is connected a drain line 12 which collects the oil leaking within the pump and returns it to the reserve tank 4. The pump 6 is drivingly connected with and rotationally driven by an engine 14, the rotational speed of which is detected by a rotational speed sensor 16. A high pressure flow line 18 is connected with the discharge side of the pump 6. A check valve 20 is incorporated in the high pressure flow line 18, which permits only the flow of oil in the direction from the pump towards the actuators, and between the pump 6 and the check valve 20 is provided an attenuator 22 which serves to absorb or dampen the pressure pulsation of the oil discharged from the pump, thereby reducing the pressure variation. The high pressure flow line 18 is connected with one ends of a high pressure flow line 18F for the front vehicle wheels and a high pressure flow line 18R for the rear vehicle wheels, with which are connected accumulators 24 and 26, respectively. These accumulators contain therein pressurized gas and serve to absorb pressure variation of the oil and to accumulate pressure. A high pressure flow line 18FR for the front right vehicle wheel and a high pressure flow line 18FL for the front left vehicle wheel are connected at their one ends with the high pressure flow line 18F, while a high pressure flow line 18RR for the rear right vehicle wheel and a high pressure flow line 18RL for the rear left vehicle wheel are connected at their one ends with the high pressure flow line 18R. The high pressure flow lines 18FR, 18FL, 18RR and 18RL have therein filters 28FR, 28FL, 28RR and 28RL, respectively, and lines are connected at their other ends with ports P of pilot-operated three-port switching control valves 40, 42, 44 and 46 included in pressure control valves 32, 34, 36 and 38, respectively. The pressure control valve 32 comprises the switching control valve 40, a flow line 50 fluidly communicating the high pressure flow line 18FR and a low pressure flow line 48FR for the front right vehicle wheel with each other, a fixed flow restriction 52 and a variable flow restriction 54 both provided in the flow line 50. The switching control valve 40 has, in addition to the port P, ports R and A which are connected with low pressure flow line 48FR and a connecting flow line 56, respectively. The switching control valve 40 may be a spool type valve adapted to take in as pilot pressures the pressure Pp within the flow line 50 between the flow restrictions 52 and 54 and the pressure Pa within the connecting flow line 56, and to be shifted to a switching position 40a wherein it fluidly communicates the ports P and A with each other when the pressure Pp is substantially higher than the pressure Pa; a switching position 40b wherein it cuts the communication among the all the ports when the pressure Pp and Pa are substantially equal to each other; and a shifting position 40c wherein it fluidly communicates the ports R and A with each other when the pressure Pp is substantially lower than the pressure Pa. The variable flow restriction 54 is adapted to vary its effective flow area by means of the electric current supplied to its solenoid 58 being controlled and to cooperate with the fixed flow restriction 52 to variably control the pilot pressure Pp. Similarly, the pressure control valves 34, 36 and 38 comprise pilot-operated, three-port switching control valves 42, 44 and 46 corresponding to the valve 40, flow lines 60, 62 and 64 corresponding to the flow line 50, fixed flow restrictions 66, 68 and 70 corresponding to the flow restriction 52, and variable flow restriction 72, 74 and 76 corresponding to the flow restriction 54, respectively. The variable flow restrictions 72 - 76 have solenoids 78, 80 and 82, respectively, corresponding to the solenoid 58. The switching control valves 42, 44 and 46 have the same construction as the switching valve 40, and have the ports R connected with one ends of a low pressure flow line 48FL for front left vehicle wheel, a low pressure flow line 48RR for rear right vehicle wheel, and a low pressure flow line 48RL for rear left vehicle wheel, respectively, and the ports A connected with one ends of connecting flow lines 84, 86 and 88, respectively. The switching valves 42, 44 and 46 are spool type valves adapted to take in as pilot pressures the pressures Pp within the associated flow lines 60, 62 and 64 between the associated fixed and the variable flow restrictions and the pressures Pa within the associated flow lines 84, 86 and 88, and to be shifted to switching positions 42a, 44a and 46a, respectively, wherein they fluidly communicate the ports P and A with each other when the pressures Pp are substantially higher than the pressures Pa; shifting positions 42b, 44b and 46b wherein they shut the communications among the all the ports when the pressures Pp and Pa are substantially equal to each other; and shifting positions 42c, 44c and 46c wherein they fluidly communicate the ports R and A with each other when the pressures Pp are substantially lower than the pressures Pa. As is schematically shown in Fig. 1, the actuators 1FR, 1FL, 1RR and 1RL include cylinders 106FR, 106FL, 106RR and 106RL defining the working fluid chambers 2FR, 2FL, 2RR and 2RL and pistons 108FR, 108FL, 108RR and 108RL, respectively, which are reciprocally inserted into the associated cylinders. While in the embodiment shown, the actuators are located between a vehicle body, not shown, and associated suspension arms, also not shown, with each cylinder being coupled to the associated suspension arm and the lower extremity of the rod portion of each piston being coupled to the vehicle body, each cylinder may be coupled to the vehicle body and each piston may be coupled the associated suspension arm. Drain flow lines 110, 112, 114 and 116 are fluidly connected at their one ends with the cylinders 106FR, 106FL, 106RR and 106RL, respectively, of the actuators. The other ends of the drain lines 110, 112, 114 and 116 are connected with a drain flow line 118, which is in turn connected with the reserve tank 4 by way of a filter 120 so that the oil leaking from the working fluid chambers may be returned into the tank. To the working fluid chambers 2FR, 2FL, 2RR and 2RL are connected accumulators 132, 134, 136 and 138, respectively, serving as hydropneumatic springs by way of passages 124, 126, 128 and 130, respectively, having therein flow restrictions. The pistons 108FR, 108FL, 108RR and 108RL have therein flow lines 140FR, 140FL, 140RR and 140RL, respectively. These flow lines fluidly connect the associated flow lines 56, 84, 86 and 88 and the associated working fluid chambers 2FR, 2FL, 2RR and 2RL with each other, and have therein filters 142FR, 142FL, 142RR and 142RL, respectively. At the locations adjacent to the actuators 1FR, 1FL, 1RR and 1RL are installed vehicle height sensors 144FR, 144FL, 144RR and 144RL, respectively, each detecting the distance between the vehicle body and the associated vehicle wheel. The connecting flow lines 56, 84, 86 and 88 have therein pilot-operated cut-off valves 150, 152, 154 and 156, respectively. The flow lines 56, 84, 86 and 88 are connected between the associated pressure control valves and the cut-off valves with the flow line 50, 60, 62 and 64 in the pressure control valves on the downstream side of the associated variable flow restrictions by flow lines 158, 160, 162 and 164, respectively. The flow lines 158, 160, 162 and 164 have therein relief valves 166, 168, 170 and 172, respectively, which are adapted to take in as pilot pressures the pressures within the associated flow lines 158, 160, 162 and 164, respectively, upstream thereof, i.e., on the side of the associated connecting flow lines, and to open when the pilot pressures exceed predeterminate values to thereby conduct some oil within the connecting flow lines to the flow lines 48FR, 48FL, 48RR and 48RL. The cut-off valves 150, 152, 154 and 156 are adapted to retain their closed condition whenever the pressure differences between the pressures within the high pressure flow lines 18FR, 18FL, 18RR and 18RL upstream of the associated pressure control valves 40, 42, 44 and 46, respectively, and the pressures within the flow lines 158, 160, 162 and 164 downstream of the associated relief valves 166, 168, 170 and 172, respectively, i.e., the pressures within the flow lines 48FR, 48FL, 48RR and 48RL respectively are not more than predeterminate values, and to increase their opening degree with the increase in the pressure differences in the range where the differences exceed the predeterminate values. The flow lines 48FR and 48FL are connected at their other ends with one end of a low pressure flow line 48F for the front vehicle wheels, while the flow lines 48RR and 48RL are connected at their other ends with one end of a low pressure flow line 48R for the rear vehicle wheels. The flow lines 48F and 48R are connected at their other ends with one end of a low pressure flow line 48. The flow line 48 has therein an oil cooler 174 and is connected at the other end with the reserve tank 4 by way of a filter 176. The high pressure flow line 18 is fluidly connected at a position between the check valve 20 and the attenuator 22 with the low pressure flow line 48 by a flow line 178. The flow line 178 has therein a relief valve 180 which is adapted to open when its pilot pressure is more than a predeterminate value. In the embodiment shown, the high pressure flow line 18R and the low pressure flow line 48R are connected with each other by a flow line 188 which has therein a filter 182, a flow restriction 184 and a normally open electromagnetic on-off valve 186 including a solenoid 190 for adjusting the valve opening. The on-off valve 186 is adapted to open when its solenoid 190 is energized and to control the flow rate of the oil flowing therethrough when the energizing electric current is adjusted. The high pressure flow line 18R and the low pressure flow line 48R are additionally connected with each other by a flow line 194 which have therein a pilot-operated on-off valve 192. The on-off valve 192 is adapted to take in as pilot pressures the pressures on both sides of the flow restriction 184 and to remain in its closed position 192a when no substantial pressure difference exists between the pressures on both sides of the flow restriction 184 and to be switched over to its open position 192b when the pressure on the side of the high pressure flow line 18R relative to the flow restriction 184 is substantially higher than the pressure on the side of the low pressure flow line. Thus, the flow restriction 184, the electromagnetic on-off valve 186 and the on-off valve 192 cooperate with each other to define a bypass valve 196 which selectively communicates the high pressure flow line 18R and the low pressure flow line 48R with each other, and controls the flow rate of the oil flowing from the high pressure flow line to the low pressure flow line. Further in the embodiment shown, a pressure sensor 198 is provided at the high pressure flow line 18R for detecting the oil pressure within the flow line. Compression coil springs 199FR, 199RL, 199RR and 199RL serving as suspension spring are interposed between upper sheets attached to the rod portions of the pistons incorporated in the actuators and lower sheets secured to the cylinders. According to this embodiment, since the cut-off valves 150, 152, 154 and 156 are adapted to operate based upon the balance between the pressure differences between the oil pressures within the high pressure flow lines 18FR, 18FL, 18RR and 18RL and those within the flow lines 158, 160, 162 and 164 and the reacting forces exerted by the self-contained springs, when the actuators are input with vibrations of higher frequency and higher amplitude in such a case where the vehicle runs on a rough road, and, as a result, the flow rate of the oil flowing through the low pressure flow lines 48FR, 48FL, 48RR and 48RL is increased, the pressures within the flow lines 158, 160 and 162 are increased thereby and the cut-off valves are driven toward their closed positions to partially close themselves. The cut-off valves thus partially closed will produce the same effect as that orifices are formed in the flow lines 56, 84, 86 and 88 between the switching valves 40, 42, 44 and 46 in the pressure control valves 32, 34, 36 and 38 and the working fluid chambers 2FR, 2FL, 2RR and 2RL. That is, the ratios of the flow resistances of the flow lines to the flow resistances of the passages 124, 126, 128 and 130 having the flow restrictions are increased so that it is hard for the oil to flow between the pressure control valves and the working fluid chambers to reduce the flow rate Q2′, resulting in the reduced energy consumption of the working fluid. When the vibrations input to the actuators are of lower frequency and lower amplitude in such a case where the vehicle runs on a good road, the flow rate of the oil flowing through the low pressure flow lines 48FR, 48FL, 48RR and 48RL is not so high that each cut-off valve is retained in its closed position as long as the pressures within the high pressure flow lines 18FR, 18FL, 18RR and 18RL are high enough, ensuring the condition under which the controls on the comfortability and the attitude of the vehicle body can appropriately be performed. According to this embodiment, therefore, in addition to the inherent function where each cut-off valve is maintained in its closed position whenever the pressure difference between the pressures within the associated high pressure and low pressure flow lines is not more than the predeterminate value, to thereby prevent the vehicle height from lowering due to the discharge of the oil out of the working fluid chambers, it can perform the function of the flow resistance control means which, in response to the flow rate of the oil flowing through the associated low pressure flow line, increases the ratios of the flow resistances of the connecting flow lines 56, 84, 86, and 88 to the flow resistances of the passages 124, 126, 128 and 130 as the flow rate increases. According to this embodiment, parts can be reduced in number and the construction of the hydraulic suspension system can be simplified as compared with a system which is provided separately with both inherent cut-off valves and flow resistance control means. Further, in a system having the flow resistance control means in the low pressure flow lines 48FR, 48FL, 48RR and 48RL, since the discharge flow rate Q₂′ may be reduced but the supply flow rate Q₂ can not be reduced, the volume of the oil within the working fluid chambers will tend to increase gradually to enlarge the vehicle height. On the contrary, according to this embodiment, both the supply flow rate Q₂ and the discharge flow rate Q₂′ can be reduced, which eliminates the tendency of the gradual increase in vehicle height. Fig. 2 shows a schematic partial diagram showing only the area for the rear right vehicle wheel in the second preferred embodiment of the hydraulic suspension system of the present invention. It is to be noted that the constructions for the other vehicle wheels are same as that shown in Fig. 2 and are omitted in Fig. 2 for the sake of clarity. The same goes with Figs. 3, 5, 6, 8, 9, 10, 12 and 14 referred to later. In this embodiment, the low pressure flow line 48RR has therein a flow restriction 200 and the flow line 62 is connected with the low pressure flow line 48RR downstream of the flow restriction 200. The cut-off valve 154 is adapted to take in as pilot pressures the oil pressure within the high pressure flow line 18RR and the oil pressure within the low pressure flow line 48RR upstream of the flow restriction 200 and to maintain its closed position whenever the pressure difference between the pilot pressures is not more than the predeterminate value and to increase its valve opening gradually when the pressure difference exceeds the predeterminate value and as the pressure difference increases. According to this embodiment, since the flow of oil is restricted by the flow restriction 200 when it flows through the low pressure flow line 48RR to increase the pressure within the low pressure flow line upstream of the flow restriction, it serves as a flow rate detecting means which senses the flow rate of the oil flowing through the low pressure flow line 48RR. As the cut-off valve 154 is adapted to take in as one of the pilot pressures the oil pressure within the low pressure flow line 48RR upstream of the flow restriction 200, it can respond to the flow rate of the oil flowing through the low pressure flow line more precisely in comparison with the first embodiment shown in Fig. 1. According to this embodiment, therefore, in addition to the same operation and benefits being obtained as in the first embodiment, it can control more positively the flow resistances between the pressure control valves and the actuators. Fig. 3 is a schematic partial diagram view similar to Fig. 2 showing the third preferred embodiment of the hydraulic suspension system of the present invention and Fig. 4 is a graph showing the specific characteristic of a variable flow restriction incorporated in the embodiment shown in Fig. 3. In the third embodiment, as is the case with the second embodiment shown in Fig. 2, a flow restriction serving as a flow rate detecting means is provided in the low pressure flow line 48RR. A variable flow restriction 202 serving as a flow resistance control means is provided in the connecting flow line 86 between the pressure control valve 36 and the cut-off valve 154. The variable flow restriction 202 takes in as pilot pressures the oil pressures upstream and downstream of the flow restriction 200 and, as shown in Fig. 4, is so adapted that the flow area of its internal passage may be maintained at a maximum value A₁ whenever the pressure difference ΔP between the pilot pressures is not more than a first predeterminate value P₁, the flow area may gradually be reduced from the maximum value A₁ to a minimum value A₂ as the pressure difference ΔP increases in the rage between the first predeterminate value P₁ and a second predeterminate value P₂, and the flow area may be maintained at the minimum value A₂ whenever the pressure difference ΔP is not less than the second predeterminate value P₂. Fig. 5 is a schematic partial diagram similar to Fig. 2 showing an embodiment modified from the third embodiment shown in Fig. 3. In this modified embodiment, the connecting flow line 86 has therein a flow restriction 204 between the cut-off valve 154 and the actuator 1RR. A bypass flow line 206 is connected with the connecting flow line 86 on both sides of the flow restriction 204 and has therein the variable flow restriction 202. In the third embodiment shown in Fig. 3 and the modified embodiment shown in Fig. 5, when the oil flowing through the low pressure flow line 48RR increases in flow rate and the pressure difference ΔP between the pilot pressures of the variable flow restriction 202 is not less than the first predeterminate value P₁ and not more than the second predeterminate value P₂, the flow area A of the variable flow restriction 202 provided in the bypass flow line 206 is gradually reduced as the pressure difference increases, which raises the ratio of the flow resistance of the connecting flow line 86 to the flow resistance of the passage 128 with the flow restriction to thereby reduce the flow rate Q₂′ of the oil flowing through the pressure control valve 36 and the low pressure flow line 48 so that the consumption of oil is reduced. According to the third and the modified embodiments, since the variable flow restriction 202 serving as the flow resistance control means and the cut-off valve 154 are provided separately from each other, the systems can perform the control on the ratio of the flow resistance of the connecting flow line 86 to the flow resistance of the passage 128 with the flow restriction and the cutting-off of the communication of the connecting flow line more positively comparing with the system in which, as in the first and the second embodiments shown in Figs. 1 and 2, the cut-off valves serves as flow resistance control means as well. Fig. 6 is a schematic partial diagram similar to Fig. 2 showing the fourth preferred embodiment of the hydraulic suspension system of the present invention and Fig. 7 is a graph showing the specific characteristic of a variable flow restriction incorporated in the embodiment shown in Fig. 6. In this embodiment, the flow restriction 200 is provided in the connecting flow line 86 between the pressure control valve 36 and the cut-off valve 154, and a variable flow restriction 208 is provided in the flow line 86 between the flow restriction 200 and the cut-off valve 154. The variable flow restriction 208 takes in as the pilot pressures the oil pressures on both sides of the flow restriction 200 and is so adapted that, as shown in Fig. 7, the flow area A of the internal passage thereof may be maintained at a maximum value A₁ whenever the absolute value of the pressure difference ΔP between the pilot pressures is not more than a predeterminate value P₁, the flow area A may gradually be reduced from the maximum value A₁ to a minimum value A₂ as the absolute value of the pressure difference ΔP increases in the range where the absolute value is between the first predeterminate value P₁ and a second predeterminate value P₂, and the flow area A may be maintained at the minimum value A₂ whenever the absolute value of the pressure difference is not less than the second predeterminate value P₂. According to this embodiment, since both the flow restriction 200 and the variable flow restriction 208 are provided in the connecting flow line 86, in either case where oil flows in the discharge and the supply directions, the flow area A of the internal passage in the variable flow restriction is gradually reduced as the absolute value of the pressure difference ΔP between the oil pressures on both sides of the flow restriction 200 increases in the range between the first and the second predeterminate values, to thereby reduce both the discharge flow rate Q₂′ and the supply flow rate Q₂ of oil so that the oil consumption is reduced. According to this embodiment, as described above, the supply flow rate of the oil can be reduced as well as the discharge flow rate, the system can eliminate the tendency in which the vehicle height gradually increases due to the bounds and rebounds of the vehicle wheels as in the first to third embodiments. It should be understood that the flow restriction 200 may be provided in the connecting flow line between the cut-off valve 154 and the variable flow restriction 208. Fig. 8 is a schematic partial diagram similar to Fig. 2 showing the fifth preferred embodiment of the hydraulic suspension system of the present invention. In this embodiment, as is the case with the second embodiment shown in Fig. 2, the flow restriction 200 serving as the flow rate detecting means is provided in the low pressure flow line 48RR, and a variable flow restriction 210 is provided in the low pressure flow line 48RR between the flow restriction 200 and the switching valve 44 in the pressure control valve. The variable flow restriction 210 is adapted to take in as the pilot pressures the oil pressures upstream and downstream of the flow restriction 200, has the same construction as the variable flow restriction 202 shown in Fig. 3, and accordingly has the specific characteristic shown in Fig. 4. In this embodiment, as the oil flowing through the low pressure flow line 48RR increases in flow rate and the pressure difference between the oil pressures on both sides of the flow restriction 200 increases accordingly, the flow area of the internal passage in the variable flow restriction 210 is reduced to increase the flow resistance of the low pressure flow line 48RR so that it becomes harder for the oil to flow, and conversely, as the oil flowing through the low pressure flow line 48RR decreases in flow rate and the pressure difference between the oil pressures on both sides of the flow restriction 200, the flow area of the internal passage in the variable flow restriction 210 is increased to reduce the flow resistance of the low pressure flow line so that it becomes easier for the oil to flow. Thus the flow restriction 200 and the variable flow restriction 210 cooperate with each other to define a constant flow valve which limits the flow rate of the discharging oil to a value which is not more than a predeterminate value. In this embodiment, therefore, when the volume of the working fluid chamber 2RR decreases at a rate which is not less than a predeterminate value, the ratio of the flow resistance of the low pressure flow line 48RR to the flow resistance of the passage 128 with the flow restriction is increased so high that only the oil can flow through the low pressure flow line 48RR at a flow rate which is not more than the predeterminate value, resulting in the increased flow rate Q₁′ of the oil flowing into the accumulator 136 and the reduced oil consumption. It should be understood that the flow restriction 200 may be provided upstream of the variable flow restriction 210. Fig. 9 is a schematic partial diagram showing the area for the rear vehicle wheels in the sixth preferred embodiment of the hydraulic suspension system of the present invention. In this embodiment, the flow restriction 200 and the variable flow restriction 212 are provided in the low pressure flow line 48R for the rear vehicle wheels, and specifically the variable flow restriction 212 is positioned downstream of the flow restriction 200. The variable flow restriction 212 is adapted to take in as the pilot pressures the oil pressures upstream and downstream of the flow restriction 200, has the same construction as the variable flow restriction 208 shown in Fig. 6, and accordingly has the specific characteristic shown in Fig. 7. Thus the flow restriction 200 and the variable flow restriction 212 cooperate with each other to define a constant flow valve as in the fifth embodiment shown in Fig. 8. Especially, since the flow restriction 200 and the variable flow restriction 212 are provided in the low pressure flow line 48R for the rear vehicle wheels, the variable flow restriction 212 serving as the flow resistance control means raises the ratio of the flow resistance of the low pressure flow line 48R to the flow resistance of the passages 128 and 130 having therein the flow restrictions as the flow rate of the oil flowing through the low pressure flow line 48R increases, resulting in the reduced oil consumption. According to this embodiment, the flow restriction 200 and the variable flow restriction 212 are not provided in the low pressure flow line for each vehicle wheel but are provided in the low pressure flow lines common to the pairs of right and left vehicle wheels so that the flow restrictions and the variable flow restrictions may be less in number in comparison with the first through the fifth embodiments to simplify the construction of the hydraulic suspension system. It should be understood that the flow restriction 200 may be provided downstream of the variable flow restriction 212 and a pair of the flow restriction 200 and the variable flow restriction may be provided in the single low pressure flow line for all the vehicle wheels such as the flow line 48 shown in Fig. 1. Figs. 10 and 12 are schematic partial diagrams similar to Fig. 2 showing the seventh and eighth preferred embodiments, respectively, of the hydraulic suspension system of the present invention, and the Figs. 11 and 13 are graphs showing specific characteristics of variable flow restrictions incorporated in the embodiments shown in Fig. 10 and 12, respectively. In these embodiments, the accumulator 136 is fluidly connected with the connecting flow line 86 by the passage 128 comprised of a flow restriction 214 and the flow line 216. Specifically in the seventh embodiment shown in Fig. 10, the flow line 216 is connected with the connecting flow line 86 between the accumulator 136 and the flow restriction 214 by a flow line 218 and the latter has therein a variable flow restriction 220. The flow restriction 220 takes in as the pilot pressures the oil pressures upstream and downstream of the flow restriction 200 provided in the low pressure flow line 48RR, and, as shown in Fig. 11, is so adapted that the flow area of its internal passage may be maintained at a minimum value A₁, which could be 0, whenever the pressure difference ΔP between the pilot pressures is not more than a first predeterminate value P₁, the flow area may gradually be increased from the minimum value A₁ to a maximum value A₂ as the pressure difference ΔP increases in the range between the first predeterminate value P₁ and a second predeterminate value P₂, and the flow area may be maintained at the maximum value A₂ whenever the pressure difference ΔP is not less than the second predeterminate value P₂. In this embodiment, as the oil flowing through the low pressure flow line 48RR increases in flow rate and the pressure difference ΔP between the oil pressures on both sides of the flow restriction 200 is increased in the range between the first and the second predeterminate values, the flow area A of the internal passage in the variable flow restriction 220 is gradually increased as the pressure difference increases, resulting in the increased ratio of the flow resistance of the connecting flow line 86 and the low pressure flow line 48RR to the flow resistance between the accumulator 136 and the working fluid chamber 2RR. Therefore, the flow rate Q₁′ of the oil is increased which flows into the accumulator 136, while the flow rate Q₂′ of the oil is decreased which discharges through the low pressure flow line 48RR, so that the oil consumption is reduced. In the eighth embodiment shown in Fig. 12, the flow line 216 is connected with the connecting flow line 86 between the accumulator 136 and the flow restriction 214 by the flow line 218 and the latter has therein a variable flow restriction 222. The flow restriction 222 takes in as the pilot pressures the oil pressures on both sides of the flow restriction 200 provided in the connecting flow line 86 and, as shown in Fig. 13, is so adapted that the flow area A of its internal passage may be maintained at a minimum value A₁, which could be 0, whenever the absolute value of the pressure difference ΔP between the pilot pressures is not more than a first predeterminate value P₁, the flow area A of its internal passage may gradually be increased from the minimum value A₁ to a maximum A₂ as the pressure difference ΔP increases when the absolute value of the pressure difference ΔP is in the range between the first predeterminate value P₁ and the second predeterminate value P₂, and the flow area A of its internal passage may be maintained at the maximum value A₂ whenever the absolute value of the pressure difference is not less than the second predeterminate value P₂. In this embodiment, when the oil increases in flow rate which flows through the connecting flow line 86 and the absolute value of the pressure difference ΔP between the oil pressures on both sides of the flow restriction 200 is increased in the range between the first and the second predeterminate values, the flow area A of the internal passage in the variable flow restriction 222 is gradually enlarged as the pressure difference increases so that the flow resistance between the accumulator 136 and the working fluid chamber 2RR is gradually reduced. According to this embodiment, therefore, as in the fourth embodiment shown in Fig. 6, the system can reduce both the discharge flow rate Q₂′ of the oil discharged through the low pressure flow line 48RR and the supply flow rate Q₂ of the oil supplied through the pressure control valve so that it can reduce not only the oil consumption but also eliminate the tendency in which the vehicle height gradually increases as the vehicle wheels repeatedly bound and rebound. It is to be noted that in the embodiments shown in Figs. 10 and 12, the passage 216 and the flow restriction 214 may be omitted and the accumulator 136 may be connected with the connecting flow line 86 only by the flow line 218 having the variable flow restriction 220 or 222. Fig. 14 is a schematic partial view similar to Fig. 2 showing the ninth preferred embodiment of the hydraulic suspension system of the present invention and Fig. 15 is a graph showing a specific characteristic of a variable flow restriction incorporated in the embodiment shown in Fig. 14. In this embodiment, an auxiliary accumulator 228 is connected with the connecting flow line 86 by a flow line 226 having therein a variable flow restriction 224. The flow restriction 224 is adapted to take in as the pilot pressures the oil pressures on both sides of the flow restriction 200 provided in the connecting flow line 86, has the same construction as the variable flow restriction 222 shown in Fig. 12, and has a specific characteristic shown in Fig. 15. In this embodiment, when the absolute value of the pressure difference between the oil pressures on both sides of the flow restriction 200 is not more than the predeterminate value, the flow area A of the internal passage in the variable flow restriction 224 is kept zero to retain shut the communication between the auxiliary accumulator 228 and the connecting flow line 86; when the absolute value of the pressure difference is in the range between the first and the second predetermined value, the flow area A of the internal passage is gradually increased as the absolute value of the pressure difference increases to fluidly connect the auxiliary accumulator 228 and the connecting flow line 86 with each other and to gradually reduce the flow resistance therebetween. According to this embodiment, therefore, in addition to the energy consumption of the working fluid being reduced by the reduction in the discharge flow rate Q₂′ and the supply flow rate Q₂ of the oil, the auxiliary accumulator 228 can serve as an additional spring in the event where the vehicle wheels rapidly bound and rebound, so that the total spring rate is reduced to enhance the comfortability of the vehicle. It is to be understood that the flow restriction 200 may be provided in the low pressure flow line 48RR. While, as the discharge flow rate of the oil increases, the ratio of the flow resistance of the working fluid discharge passage to the flow resistance between the working fluid chamber and the accumulator is raised by increasing the flow resistance of the connecting flow line 86 or the low pressure flow line 48RR or 48R in the first through sixth embodiments and by reducing the flow resistance between the working fluid chamber and the accumulator in the seventh through ninth embodiments, any of the first through sixth embodiments and any of the seventh through ninth embodiments may be combined with each other in a desired manner to enhance the control on the ratio of the flow resistances. While in the second through ninth embodiments each flow resistance control means is adapted to respond hydraulically to the discharge flow rate detected by the associated flow rate detecting means, a flow rate sensor may be provided for detecting the discharge flow rate and the flow resistance control means may be made to respond to a signal such as an electric signal indicative of the discharge flow rate detected by the associated flow rate detecting means. The means for controlling the pressure within the associated working fluid chamber is not limited to such a pressure control valve as in the embodiments shown, it may be for example a flow control valve which is adapted to control the flow rate of the oil supplied to and discharged from the working fluid chamber in response to the value detected by the associated pressure sensor which detects the oil pressure within the working fluid chamber so as to control the pressure within the working fluid chamber to a desired pressure. In a hydraulic suspension system, a plurality of actuators having working fluid chambers are provided. Each actuator is adapted to increase and decrease vehicle height as the results of the supply and the discharge of working fluid into and from its working fluid chamber, respectively. A plurality of accumulators are connected with the associated working fluid chambers. Working fluid supply passages supply working fluid into the working fluid chambers and working fluid discharge passages discharge working fluid from the working fluid chambers. Pressure control devices are provided in the supply passages and the discharge passages. Each pressure control device means is adapted to control the supply of the working fluid into and the discharge from the associated working fluid chamber to adjust the pressure within the chamber. The suspension system further comprises flow resistance control devices. Each flow resistance control devices is adapted to adjust at least one of the first flow resistance between the associated working fluid chamber and the associated accumulator and the second flow resistance of the associated discharge passage in response to the flow rate of the working fluid discharging through the discharge passage so that the higher the discharging flow rate is, the higher the ratio of the second to the first flow resistances may be, not only to reduce the flow rate of the working fluid discharging from the working fluid chamber through the discharge passage but also to increase the flow rate of the working fluid flowing into the accumulator from the working fluid chamber.

Claims: A hydraulic suspension system for a vehicle comprising: a working fluid source means (4, 6) for supplying a working fluid at an elevated pressure; a plurality of actuators (1FR, 1FL, 1RR, 1RL) having respective working fluid chambers (2FR, 2FL, 2RR, 2RL) and being adapted to increase the vehicle height at corresponding portions of a vehicle body according to the supply of the working fluid from said working fluid source means to the respective working fluid chambers and to decrease the corresponding vehicle body portions according to the discharge of the working fluid from the respective working fluid chambers; a plurality of accumulators (132, 134, 136, 138; 228) connected respectively with corresponding ones of said working fluid chambers by means of corresponding connection passages (124, 126, 128, 130); pressure control means (32, 34, 36, 38) for controlling the supply of the working fluid from said working fluid source means to said respective working fluid chambers and the discharge of the working fluid from the respective working fluid chambers through respective discharge passages (48FR, 48FL, 48RR, 48RL) to thereby adjust the pressures within said working fluid chambers to control the comfortability and/or the attitude of the vehicle body, characterised by variable throttle means (150, 152, 154, 156, 202, 208, 210, 212, 220, 222, 224) for controlling a ratio of a flow resistance in each of said discharge passages (48FR, 48FL, 48RR, 48RL) to a flow resistance in each corresponding one of said connection passages (124, 126, 128, 130) so that the ratio is increased as the rate of discharge of working fluid through said discharge passage from the corresponding working fluid chamber increases. A hydraulic suspension system according to claim 1, wherein said variable throttle means (150, 152, 154, 156, 202, 208, 210, 212) are adapted to variably throttle the respective discharge passages (48FR, 48FL, 48RR, 48RL) with respective flow areas thereof decreasing along with increase of the rate of the discharge of the working fluid from the corresponding working fluid chambers. (Figs. 1, 2, 3, 5, 6, 8, 9) A hydraulic suspension system according to claim 2, wherein the respective flow areas of said variable throttle means are progressively decreased along with progressive increase of the rate of the discharge of the working fluid from the corresponding working fluid chambers. (figs. 4, 7) A hydraulic suspension system according to claim 1, 2 or 3, wherein said variable throttle means (150, 152, 154, 156, 202, 208) also variably throttle the supply of the working fluid from said working fluid source means to the respective working fluid chambers with respective flow areas thereof decreasing along with increase of the rate of the discharge of the working fluid from the corresponding working fluid chambers. (Figs. 1, 2, 3, 5, 6) A hydraulic suspension system according to claim 1, wherein said variable throttle means (220, 222, 224) are adapted to variably throttle the respective connection passages (128, 226) with respective flow areas thereof increasing along with increase of the rate of the discharge of the working fluid from the corresponding working fluid chambers. (Figs. 10, 12, 14) A hydraulic suspension system according to claim 5, wherein the respective flow areas of said variable throttle means are progressively increased along with progressive increase of the rate of the discharge of the working fluid from the corresponding working fluid chambers. (Figs. 11, 13, 15) A hydraulic suspension system according to claim 5, wherein said variable throttle means (222, 224) also variably throttle the respective connection passages (128, 226) with respective flow areas thereof increasing along with increase of the rate of the supply of the working fluid from said working fluid source means to the corresponding working fluid chambers. (Fig. 12, 14) A hydraulic suspension system according to claim 7, wherein the respective flow areas of said variable throttle means are progressively increased along with progressive increase of the rate of the supply of the working fluid from said working fluid source means to the corresponding working fluid chambers. (Figs. 11, 13, 15) A hydraulic suspension according to any one of claims 1-8, wherein said variable throttle means are each a valve (150, 152, 154, 156, 202, 208, 210, 212, 220, 222, 224) adapted to change flow area thereof according to a pilot pressure difference supplied thereto, said pilot pressure difference being obtained across a throttle means (200) provided in a passage (48RR) for discharging the working fluid from a corresponding one of said working fluid chambers alternatively a passage (86) for supplying the working fluid from said working fluid source means to the corresponding working fluid chamber. (Figs. 2, 3, 5, 6, 8, 10, 12, 14) A hydraulic suspension according to claim 1 or 2, wherein said variable throttle means (150, 152, 154, 156) are valves each provided in a common passage (56, 84, 86, 88) for supplying the working fluid from said working fluid source means to each corresponding one of said working fluid chambers and discharging the working fluid from the corresponding working fluid chamber and adapted to shut off said common passage when the pressure of the working fluid of said working fluid source means is lower than a determinate threshold pressure value. (Fig. 1, 2) A hydraulic suspension according to any one of claims 1-10, wherein said pressure control means (32, 34, 36, 38) comprise three position switching valves (40, 42, 44, 46) each adapted to take a first switch position (40a, 42a, 44a, 46a) for supplying the working fluid from said working fluid source means to a corresponding one of said working fluid chambers when the pressure of the working fluid in the corresponding working fluid chamber is lower than the pressure of the working fluid of said working fluid source means, a second switch position (40b, 42b, 44b, 46b) for blocking the corresponding working fluid chamber against both the supply and the discharge of the working fluid thereto and therefrom when the pressure of the working fluid in the corresponding working fluid chamber is the same as the pressure of the working fluid of said working fluid source means, and a third switch position (40c, 42c, 44c, 46c) for discharging the working fluid from the corresponding working fluid chamber when the pressure of the working fluid in the corresponding working fluid chamber is higher than the pressure of the working fluid of said working fluid source means. (Figs. 1, 2, 3, 5, 6, 8, 9, 10, 12, 14)

Inventors: BUMA, SHUUICHI, HATTORI, KATSUHIKO, IKEMOTO, HIROYUKI, ISOGAI, SIGETAKA, KOMAZAWA, OSAMU, ONUMA, TOSHIO, YONEKAWA, TAKASHI
Applicants: AISIN SEIKI KABUSHIKI KAISHA, TOYOTA CENTRAL RESEARCH AND DEVELOPMENT LABORATORIES, INC., TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1989
Main classification: B60G17
IPC codes: B60G17, B60G23