FREQUENCY DEPENDENT PRESSURE AND/OR FLOW FLUCTUATION MITIGATION IN HYDRAULIC SYSTEMS
Active suspension systems including actuators with combinations of accumulators and flow restrictions, as well as their methods of operation, are described. In some embodiments, methods and constructions for mitigating pump ripple and/or resonances between different hydraulic components are also described.
1 . An actuator comprising:
a housing including a first volume and a second volume;
a piston slidably disposed between the first volume and second volume;
a hydraulic device fluidly coupled to the first volume and the second volume along a first flow path extending between the first volume and the second volume;
an electric motor/generator operatively coupled to the hydraulic device; and
at least one blow-off valve disposed in the piston to provide selective fluid communication between the first volume and the second volume, wherein the at least one blow-off valve opens when a velocity of the hydraulic device exceeds a threshold rotational velocity.
2 . The actuator of claim 1 , further comprising at least one flow restriction disposed along the first flow path extending between the first volume and the second volume through the hydraulic device, wherein the at least one flow restriction is configured to create a pressure differential across the piston to open the at least one blow-off valve when a flow rate through the first flow path exceeds a threshold flow rate.
3 . The actuator of claim 2 , wherein the threshold flow rate is proportional to the threshold rotational velocity of the hydraulic device.
4 . The actuator of claim 1 , further comprising at least one of a first accumulator disposed between the hydraulic device and the first volume and a second accumulator disposed between the hydraulic device and the second volume.
5 . The actuator of claim 4 , wherein the actuator includes both the first accumulator and the second accumulator, and wherein the at least one blow-off valve includes a first blow-off valve that selectively permits flow from the first volume to the second volume and a second blow-off valve that selectively permits flow from the second volume to the first volume.
6 . The actuator of claim 5 , further comprising a first flow restriction disposed between the first accumulator and the first volume and a second flow restriction disposed between the second accumulator and the second volume.
7 . The actuator of claim 6 , wherein the first flow restriction and the second flow restriction are configured to create a pressure differential across the piston to open the first blow-off valve when a flow rate through the first flow path in a first direction exceeds a threshold flow rate, and to open the second blow-off valve when the flow rate through the first flow path in a second direction exceeds the threshold flow rate.
8 . A vehicle comprising:
an active suspension system including one or more actuators, wherein each actuator comprises:
a housing including a first volume and a second volume with a piston slidably disposed between the first volume and second volume;
a hydraulic device fluidly coupled to the first volume and the second volume along a first flow path extending between the first volume in the second volume;
an electric motor/generator operatively coupled to the hydraulic device;
a second flow path extending between the first volume and the second volume that bypasses the hydraulic device; and
a valve that selectively permits flow through the second flow path based at least partly on a comparison of an operating parameter of the vehicle and a predetermined threshold.
9 . The vehicle of claim 8 , wherein the operating parameter is a pressure differential across the piston, and wherein the valve permits flow through the second flow path when the pressure differential is less than a threshold pressure differential and prevents flow through the second flow path when the pressure differential is greater than the threshold pressure differential.
10 . The vehicle of claim 8 , wherein the operating parameter is a vehicle velocity, and wherein the valve permits flow through the second flow path when the vehicle velocity is greater than a threshold velocity and prevents flow through the second flow path when the vehicle velocity is less than the threshold velocity.
11 . The vehicle of claim 10 , wherein the threshold velocity is between or equal to 20 mph and 30 miles per hour.
12 . The vehicle of claim 8 , further comprising at least one flow restriction disposed along the second flow path.
13 . The vehicle of claim 12 , further comprising a first accumulator disposed along the first flow path between the hydraulic device and the first volume and a second accumulator disposed along the first flow path between hydraulic device and the second volume.
14 . The vehicle of claim 13 , wherein the at least one flow restriction is constructed to damp a resonance between the first accumulator and the second accumulator.
15 . A method of operating an actuator of an active suspension system of a vehicle, the method comprising:
flowing fluid between a first volume and a second volume of an actuator through a hydraulic device along a first flow path extending between the first volume and the second volume during a first mode of operation; and
flowing at least a portion of the fluid along a second flow path that bypasses the hydraulic device during a second mode of operation based at least partly on a comparison of an operating parameter of the vehicle and a predetermined threshold.
16 . The method of claim 15 , wherein the predetermined threshold is a pressure differential across a piston of the actuator, and wherein fluid flows along the second flow path during the second mode of operation when the pressure differential is less than a threshold pressure differential.
17 . The method of claim 15 , wherein the predetermined threshold is a vehicle velocity, and wherein fluid flows along the second flow path during the second mode of operation when the vehicle velocity exceeds a threshold velocity.
18 . The method of claim 17 , wherein the threshold velocity is between or equal to 20 mph and 30 miles per hour.
19 . The method of claim 15 , further comprising flowing the portion of the fluid through at least one flow restriction disposed along the second flow path.
20 . The method of claim 15 , wherein a first accumulator is disposed along the first flow path between the hydraulic device and the first volume and a second accumulator is disposed along the first flow path between hydraulic device and the second volume.
21 . The method of claim 20 , further comprising damping a resonance between the first accumulator and the second accumulator with at least one flow restriction.