Vehicle Suspension System with Multiple Modes of Operation

A suspension system including four dampers is disclosed where each damper includes a compression chamber and a rebound chamber. First and second hydraulic circuits interconnect the compression and rebound chambers of the front left and back right dampers, while third and fourth hydraulic circuits interconnect the compression and rebound chambers of the front right and back left dampers. A first bi-directional pump is connected between the first and second hydraulic circuits and a second bi-directional pump is connected between the third and fourth hydraulic circuits. The first and second bi-directional pumps can either pump in the same direction or in opposite directions. The level of pitch and roll stiffness can be adjusted by running the first and second bi-directional pumps to change the pressure in select hydraulic circuits of the system.

FIELD

The present disclosure relates generally to suspension systems for motor vehicles and more particularly to suspension systems that resist pitch and roll movements of a vehicle.

BACKGROUND

Suspension systems improve the ride of a vehicle by absorbing bumps and vibrations that would otherwise unsettle the vehicle body. Suspension systems also improve safety and control by improving contact between the ground and the tires of the vehicle. One drawback of suspension systems is that basic spring/damper arrangements will allow the vehicle to roll/lean right or left during corning (e.g., in turns), pitch forward under deceleration (e.g., under braking), and pitch back under acceleration. The lateral acceleration the vehicle experiences in turns causes a roll moment where the vehicle will lean/squat to the right when turning left and to the left when turning right. The fore and aft acceleration the vehicle experiences under acceleration and braking causes a pitch moment where the vehicle will lean forward loading the front axle during braking and aft, loading the rear axle, under acceleration. These roll and pitch moments decrease grip, cornering performance, and braking performance and can also be uncomfortable to the driver and passengers. Many vehicles are equipped with stabilizer bars/anti-roll bars, which are mechanical systems that help counteract the roll moments experienced during driving. For example, anti-roll bars are typically mechanical linkages that extend laterally across the width of the vehicle between the right and left dampers. When one of the dampers extends, the anti-roll bar applies a force to the opposite damper that counteracts the roll moment of the vehicle and helps to correct the roll angle to provide flatter cornering. However, there are several drawbacks associated with these mechanical systems. First, there are often packaging constraints associated with mechanical systems because a stabilizer bar/anti-roll bar requires a relatively straight, unobstructed path across the vehicle between the dampers. Second, stabilizer bars/anti-roll bars are reactive and work when the suspension starts moving (i.e. leaning). Such mechanical systems cannot be easily switched off or cancelled out when roll stiffness is not needed. Some vehicles do have stabilizer bar/anti-roll bar disconnects that may be manually or electronically actuated, but the complexity and cost associated with these systems make them ill-suited for most vehicle applications.

In an effort to augment or replace traditional mechanical stabilizer bars/anti-roll bars, anti-roll suspension systems are being developed that hydraulically connect two or more dampers in a hydraulic circuit where the extension of one damper produces a pressure change in the other damper(s) in the hydraulic circuit that makes it more difficult to compress the other damper(s) in the hydraulic circuit. This pressure change in the other damper(s) increases the roll stiffness of the suspension system of the vehicle. However, the downside of such systems is that ride comfort is more difficult to achieve because bump forces can be transmitted from one damper to another damper across the hydraulic circuit resulting in unwanted suspension movement. Accordingly, there remains a need for improved vehicle suspension systems that can minimize roll, pitch, and other unwanted suspension movements while maintaining acceptable levels of ride comfort.

SUMMARY

In accordance with one aspect of the subject disclosure, a suspension system is provided that includes four dampers: a front left damper, a front right damper, a back left damper, and a back right damper. The front left damper includes a first compression chamber and a first rebound chamber. The front right damper includes a second compression chamber and a second rebound chamber. The back left damper includes a third compression chamber and a third rebound chamber. The back right damper includes a fourth compression chamber and a fourth rebound chamber.

The suspension system of the present disclosure also includes four hydraulic circuits: a first hydraulic circuit connects the first compression chamber of the front left damper in fluid communication with the fourth rebound chamber of the back right damper, a second hydraulic circuit connects the first rebound chamber of the front left damper in fluid communication with the fourth compression chamber of the back right damper, a third hydraulic circuit connects the second compression chamber of the front right damper in fluid communication with the third rebound chamber of the back left damper, and a fourth hydraulic circuit connects the second rebound chamber of the front right damper in fluid communication with the third compression chamber of the back left damper.

The suspension system of the present disclosure further comprises two bi-directional pumps: a first bi-directional pump that is fluidly connected to and arranged between the first and second hydraulic circuits and a second bi-directional pump that is fluidly connected to and arranged between the third and fourth hydraulic circuits. The first bi-directional pump has a first operating mode for pumping hydraulic fluid in a first direction from the first hydraulic circuit to the second hydraulic circuit and a second operating mode for pumping hydraulic fluid in a second direction from the second hydraulic circuit to the first hydraulic circuit. The second bi-directional pump has a third operating mode for pumping hydraulic fluid in a third direction from the third hydraulic circuit to the fourth hydraulic circuit and a fourth operating mode for pumping hydraulic fluid in a fourth direction from the fourth hydraulic circuit to the third hydraulic circuit.

In accordance with another aspect of the present disclosure, the suspension system further comprises one or more controllers that are electrically connected to the first and second bi-directional pumps. The one or more controllers are programmed to concurrently activate one of the first or second operating modes of the first bi-directional pump and one of the third or fourth operating modes of the second bi-directional pump at the same time. Thus, the first and second bi-directional pumps may pump in the same direction during some operating modes (e.g., pitch control and pressure control operating modes) and in opposite directions during other operating modes (i.e., roll control operating modes).

In accordance with another aspect of the present disclosure, the suspension system further comprises a reservoir. In accordance with this aspect, the first bi-directional pump is connected in fluid communication with the first hydraulic circuit via a first pump line and is connected in fluid communication with the second hydraulic circuit via a second pump line. Similarly, the second bi-directional pump is connected in fluid communication with the third hydraulic circuit via a third pump line and is connected in fluid communication with the fourth hydraulic circuit via a fourth pump line. The reservoir is connected to the first pump line via a first reservoir line and is connected to the second pump line via a second reservoir line.

Again, the first bi-directional pump has a first operating mode for pumping hydraulic fluid in the first direction from the first pump line to the second pump line to decrease fluid pressure in the first hydraulic circuit and a second operating mode for pumping hydraulic fluid in the second direction from the second pump line to the first pump line to increase fluid pressure in the first hydraulic circuit. The second bi-directional pump has a third operating mode for pumping hydraulic fluid in the third direction from the third pump line to the fourth pump line to decrease fluid pressure in the third hydraulic circuit and a fourth operating mode for pumping hydraulic fluid in the fourth direction from the fourth pump line to the third pump line to increase fluid pressure in the third hydraulic circuit.

Advantageously, the suspension system of the present disclosure is able to reduce/eliminate vehicle pitch and roll movements for improved grip, performance, handling, and braking. The reduction of pitch and roll angles improves the comfort, steering feel, agility, and stability of the vehicle. Pitch and roll control is provided by increasing the pitch stiffness or roll stiffness of the suspension system based on the fluid pressure in the system. The level of pitch and roll stiffness can be adjusted by using the bi-directional pumps to change the pressure in select hydraulic circuits of the system. Valves in the hydraulic circuits can also be opened to decouple the dampers in situations where added pitch and/or roll stiffness is not desired or necessary.

DETAILED DESCRIPTION

Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, various comfort valve equipped suspension systems are shown.

In this application, the term “controller(s)” may be replaced with the term “electrical circuit(s).” For example, the term “controller(s)” may refer to, be part of, or include: an Application Specific Integrated Circuit (ASIC); a digital, analog, or mixed analog/digital discrete circuit; a digital, analog, or mixed analog/digital integrated circuit; a combinational logic circuit; a field programmable gate array (FPGA); a processor circuit (shared, dedicated, or group) that executes code; a memory circuit (shared, dedicated, or group) that stores code executed by the processor circuit; other suitable hardware components that provide the described functionality; or a combination of some or all of the above, such as in a system-on-chip.

With reference toFIG.1, a suspension system100for a vehicle is illustrated. The vehicle includes a front left wheel101a, a front right wheel101b, a back left wheel101c, and a back right wheel101d. While it should be appreciated that the vehicle may include a different number of wheels than those shown inFIG.1, in most automotive applications, four wheels are used at each corner of the vehicle body103. As shown inFIG.1, there are four different types of suspension movements that vehicles routinely experience—heave, pitch, roll, and warp. When the suspension system100of the vehicle experiences heave, the vehicle body103either lifts (as illustrated inFIG.1), such as when the vehicle travels over a crest (i.e., hill), or drops, such as when the vehicle travels over a dip (i.e., valley) in the road, which results in either a downward movement (not shown) or upward movement105a-105d(as shown) of all four wheels101a-101dsimultaneously or nearly simultaneously. When the suspension system100of the vehicle experiences pitch, either the front of the vehicle body103lifts and the rear of the vehicle body103drops, such as during hard acceleration, or the front of the vehicle body103drops and the rear of the vehicle body103lifts, such as during hard braking. In the example shown inFIG.1illustrating pitch, the front of the vehicle body103is lifting and the rear of the vehicle body103is dropping (i.e., pitching aft), the front wheels101a,101bexperience upward movement107a,107bwhile the rear wheels101c,101dexperience downward movement107c,107d. The opposite occurs when the front of the vehicle body103is dropping and the rear of the vehicle body103is lifting (i.e., pitching forward). When the suspension system100of the vehicle experiences roll, either the right side of the vehicle body103lifts and the left side of the vehicle body103drops, such as during a hard right turn, or the right side of the vehicle body103drops and the left side of the vehicle body103lifts, such as during a hard left turn. In the example shown inFIG.1illustrating roll, when the right side of the vehicle body103is lifting and the left side of the vehicle body103is dropping (i.e., rolling left), the right wheels101b,101dexperience upward movement109b,109dwhile the left wheels101a,101cexperience downward movement109a,109c. The opposite occurs when the right side of the vehicle body103is dropping and the left side of the vehicle body103is lifting (i.e., rolling right). When the suspension system100of the vehicle experiences warp, either the front right and back left wheels101b,101cexperience lifting (i.e., upward) movement111b,111cwhile the front left and back right wheels101a,101dexperience dropping (i.e., downward) movement111a,111d(as illustrated inFIG.1) or the front right and back left wheels101b,101cdrop while the front left and back right wheels101a,101dlift. As will be explained in greater detail below, the object of the suspension system100described herein is to reduce or eliminate these movements.

With reference toFIG.2, the suspension system100includes a front left damper102a, a front right damper102b, a back left damper102c, and a back right damper102d. While it should be appreciated that the suspension system100described herein may include a different number of dampers than those shown in the drawings, in most automotive applications, four dampers are used at each corner of a vehicle to control vertical movements of the front and rear wheels101a-101dof the vehicle.

Each of the dampers102a,102b,102c,102dof the suspension system100includes a damper housing104a,104b,104c,104d, a piston rod106a,106b,106c,106d, and a piston108a,108b,108c,108dthat is mounted on the piston rod106a,106b,106c,106d. The pistons108a,108b,108c,108dare closed pistons with no fluid flow paths defined within or by the piston structure. The pistons108a,108b,108c,108dare arranged in sliding engagement with and inside the damper housings104a,104b,104c,104dsuch that the pistons108a,108b,108c,108ddivide each damper housing104a,104b,104c,104dinto compression and rebound chambers. As such, the front left damper102aincludes a first compression chamber126aand a first rebound chamber128a, the front right damper102bincludes a second compression chamber126band a second rebound chamber128b, the back left damper102cincludes a third compression chamber126cand a third rebound chamber128c, and the back right damper102dincludes a fourth compression chamber126dand a fourth rebound chamber128d. The rebound chambers128a,128b,128c,128dof the dampers102a,102b,102c,102ddecrease in volume during rebound/extension strokes and increase in volume during compression strokes of the dampers102a,102b,102c,102d. The compression chambers126a,126b,126c,126dof the dampers102a,102b,102c,102ddecrease in volume during compression strokes of the dampers102a,102b,102c,102dand increase in volume during rebound/extension strokes of the dampers102a,102b,102c,102d.

The first compression chamber126aof the front left damper102ais connected in fluid communication with the fourth rebound chamber128dof the back right damper102dvia a first hydraulic circuit120a. The first hydraulic circuit120aincludes a first hydraulic line132athat extends between and fluidly connects the first compression chamber126aof the front left damper102aand the fourth rebound chamber128dof the back right damper102d. The first hydraulic circuit120aalso includes a first pump line134athat extends between and fluidly connects the first hydraulic line132awith a first port116aon a first bi-directional pump110a. The first rebound chamber128aof the front left damper102ais connected in fluid communication with the fourth compression chamber126dof the back right damper102dvia a second hydraulic circuit120b. The second hydraulic circuit120bincludes a second hydraulic line132bthat extends between and fluidly connects the first rebound chamber128aof the front left damper102aand the fourth compression chamber126dof the back right damper102d. The second hydraulic circuit120balso includes a second pump line134bthat extends between and fluidly connects the second hydraulic line132bwith a second port116bon the first bi-directional pump110a.

The second compression chamber126bof the front right damper102bis connected in fluid communication with the third rebound chamber128cof the back left damper102cvia a third hydraulic circuit120c. The third hydraulic circuit120cincludes a third hydraulic line132cthat extends between and fluidly connects the second compression chamber126bof the front right damper102band the third rebound chamber128cof the back left damper102c. The third hydraulic circuit120calso includes a third pump line134cthat extends between and fluidly connects the third hydraulic line132cwith a third port116con a second bi-directional pump110b. The second rebound chamber128bof the front right damper102bis connected in fluid communication with the third compression chamber126cof the back left damper102cvia a fourth hydraulic circuit120d. The fourth hydraulic circuit120dincludes a fourth hydraulic line132dthat extends between and fluidly connects the second rebound chamber128bof the front right damper102band the third compression chamber126cof the back left damper102c. The fourth hydraulic circuit120dalso includes a fourth pump line134dthat extends between and fluidly connects the fourth hydraulic line132dwith a fourth port116don the second bi-directional pump110b.

The suspension system100also includes a front left bridge line140athat extends between and fluidly connects the first hydraulic line132aof the first hydraulic circuit120aand the second hydraulic line132bof the second hydraulic circuit120bat a position located near the front left damper102a, a front right bridge line140bthat extends between and fluidly connects the third hydraulic line132cof the third hydraulic circuit120cand the fourth hydraulic line132dof the fourth hydraulic circuit120dat a position located near the front right damper102b, a back left bridge line140cthat extends between and fluidly connects the third hydraulic line132cof the third hydraulic circuit120cand the fourth hydraulic line132dof the fourth hydraulic circuit120dat a position located near the back left damper102c, and a back right bridge line140dthat extends between and fluidly connects the first hydraulic line132aof the first hydraulic circuit120aand the second hydraulic line132bof the second hydraulic circuit120bat a position located near the back right damper102d. The various hydraulic lines shown in the illustrated example are made of flexible tubing (e.g., hydraulic hoses), but it should be appreciated that other conduit structures and/or fluid passageways can be used.

The first hydraulic circuit120aincludes a first pair of variable flow control valves160,162that are arranged at each end of the first hydraulic line132aand are configured to regulate fluid flow between the first hydraulic circuit120aand the first compression chamber126aof the front left damper102aand between the first hydraulic circuit120aand the fourth rebound chamber128dof the back right damper102d, respectively. Similarly, the second hydraulic circuit120bincludes a second pair of variable flow control valves164,166that are configured to regulate fluid flow between the second hydraulic circuit120band the first rebound chamber128aof the front left damper102aand between the first hydraulic circuit120aand the fourth compression chamber126dof the back right damper102d, respectively. The third hydraulic circuit120cincludes a third pair of variable flow control valves168,170that are arranged at each end of the third hydraulic line132cand are configured to regulate fluid flow between the third hydraulic circuit120cand the second compression chamber126bof the front right damper102band between the third hydraulic circuit120cand the third rebound chamber128cof the back left damper102c, respectively. Finally, the fourth hydraulic circuit120dincludes a fourth pair of variable flow control valves172,174that are configured to regulate fluid flow between the fourth hydraulic circuit120dand the second rebound chamber128bof the front right damper102band between the fourth hydraulic circuit120dand the third compression chamber126cof the back left damper102c, respectively. The variable flow control valves160,162,164,166,168,170,172,174may be passive/spring-biased valves (e.g., spring-disc stacks) or active valves (e.g., electromechanical valves) and operate by controlling fluid flow into and out of the compression chambers126a,126b,126c,126dand rebound chambers128a,128b,128c,128dof the dampers102a,102b,102c,102dto change/adjust the rebound dampening rates and compression dampening rates. By way of example and without limitation, the variable flow control valves160,162,164,166,168,170,172,174may be electromechanical valves with a combination of passive spring-disk elements and a solenoid. The solenoid of the variable flow control valves160,162,164,166,168,170,172,174may be electrically connected to and actuated by one or more controllers180a,180bto change the damping characteristics of the dampers102a,102b,102c,102d(e.g., to soften or firm up the ride).

The first bi-directional pump110aand second bi-directional pump110bare connected to a hydraulic reservoir112(e.g., a tank) by first and second reservoir lines113a,113bthat converge at a common reservoir line114. The first reservoir line113aextends between and fluidly connects the second pump line134band the common reservoir line114, while the second reservoir line113bextends between and fluidly connects the fourth pump line134dand the common reservoir line114. The first bi-directional pump110amay operate (i.e., pump fluid) in two opposing directions115a,115bdepending on the polarity of the electricity that is supplied to the first bi-directional pump110aand the second bi-directional pump110bmay operate (i.e., pump fluid) in two opposing directions115c,115ddepending on the polarity of the electricity that is supplied to the second bi-directional pump110a.

The first port116aof the first bi-directional pump110amay operate as either an inlet port or an outlet port depending on the direction the first bi-directional pump110ais operating in and the same is true for the second port116bof the first bi-directional pump110a. As a result, the first bi-directional pump110acan operate to pump hydraulic fluid from the first hydraulic circuit120aand to the second hydraulic circuit120b, from the second hydraulic circuit120band to the first hydraulic circuit120a, from the first hydraulic circuit120aand to the first reservoir line113a, or from the first reservoir line113aand to the first hydraulic circuit120a. In the example where the first bi-directional pump110ais operating in a first direction115a, the first port116ais operating as an inlet port for the first bi-directional pump110aand the second port116bis operating as an outlet port for the first bi-directional pump110a, the first bi-directional pump110adraws in hydraulic fluid from the first pump line134avia the first port116aand discharges hydraulic fluid into the second pump line134bvia the second port116b. In the example where the first bi-directional pump110ais operating in a second direction115b, the second port116bis operating as an inlet port for the first bi-directional pump110aand the first port116ais operating as an outlet port for the first bi-directional pump110a, the first bi-directional pump110adraws in hydraulic fluid from the second pump line134bvia the second port116band discharges hydraulic fluid into the first pump line134avia the first port116a.

The third port116cof the second bi-directional pump110bmay operate as either an inlet port or an outlet port depending on the direction the second bi-directional pump110bis operating in and the same is true for the fourth port116dof the second bi-directional pump110b. As a result, the second bi-directional pump110bcan operate to pump hydraulic fluid from the third hydraulic circuit120cand to the fourth hydraulic circuit120d, from the fourth hydraulic circuit120dand to the third hydraulic circuit120c, from the third hydraulic circuit120cand to the second reservoir line113b, or from the second reservoir line113band to the third hydraulic circuit120c. In the example where the second bi-directional pump110bis operating in a third direction115c, the third port116cis operating as an inlet port for the second bi-directional pump110band the fourth port116dis operating as an outlet port for the second bi-directional pump110b, the second bi-directional pump110bdraws in hydraulic fluid from the third pump line134cvia the third port116cand discharges hydraulic fluid into the fourth pump line134dvia the fourth port116d. In the example where the second bi-directional pump110bis operating in a fourth direction115d, the fourth port116dis operating as an inlet port for the second bi-directional pump110band the third port116cis operating as an outlet port for the second bi-directional pump110b, the second bi-directional pump110bdraws in hydraulic fluid from the fourth pump line134dvia the fourth port116dand discharges hydraulic fluid into the third pump line134cvia the third port116c.

A front left accumulator142ais arranged in fluid communication with the first hydraulic line132aat the junction where the first hydraulic line132ajoins the front left bridge line140a. As such, the front left accumulator142ais arranged in fluid communication with and regulates fluid pressure within the first hydraulic circuit120a. A front right accumulator142bis arranged in fluid communication with the third hydraulic line132cat the junction between the third hydraulic line132cand the front right bridge line140b. As such, the front right accumulator142bis arranged in fluid communication with and regulates fluid pressure within the third hydraulic circuit120c. A back left accumulator142cis arranged in fluid communication with the fourth hydraulic line132dat the junction between the fourth hydraulic line132dand the back left bridge line140c. As such, the back left accumulator142cis arranged in fluid communication with and regulates fluid pressure within the fourth hydraulic circuit120d. A back right accumulator142dis arranged in fluid communication with the second hydraulic line132bat the junction between the second hydraulic line132band the back right bridge line140d. As such, the back right accumulator142dis arranged in fluid communication with and regulates fluid pressure within the second hydraulic circuit120b. Each of the accumulators142a,142b,142c,142dhave a variable fluid volume that increases and decreases depending on the fluid pressure in the hydraulic circuits120a,120b,120c,120d. It should be appreciated that the accumulators142a,142b,142c,142dmay be constructed in a number of different ways. For example and without limitation, the accumulators142a,142b,142c,142dmay have accumulation chambers and pressurized gas chambers that are separated by floating pistons, flexible membranes, or bellows.

The suspension system100also includes a first pressure sensor124athat is arranged to monitor the pressure in the first hydraulic circuit120a, a second pressure sensor124bthat is arranged to monitor the pressure in the second hydraulic circuit120b, a third pressure sensor124cthat is arranged to monitor the pressure in the third hydraulic circuit120c, and a fourth pressure sensor124dthat is arranged to monitor the pressure in the fourth hydraulic circuit120d. Although other configurations are possible, the first pressure sensor124ais connected to the junction between the first hydraulic line132aand the back right bridge line140dand is therefore arranged to measure fluid pressure in the first hydraulic line132a. The second pressure sensor124bis connected to the junction between the second hydraulic line132band the front left bridge line140aand is therefore arranged to measure fluid pressure in the second hydraulic line132b. The third pressure sensor124cis connected to the junction between the third hydraulic line132cand the back left bridge line140cand is therefore arranged to measure fluid pressure in the third hydraulic line132c. The fourth pressure sensor124dis connected to the junction between the fourth hydraulic line132dand the front right bridge line140band is therefore arranged to measure fluid pressure in the fourth hydraulic line132d.

The suspension system100also includes eight electro-mechanical shut-off (i.e., on/off) valves144a,144b,144c,144d,146a,146b,146c,146d. A front left shut-off valve144ais positioned in the front left bridge line140a, a front right shut-off valve144bis positioned in the front right bridge line140b, a back left shut-off valve144cis positioned in the back left bridge line140c, and a back right shut-off valve144dis positioned in the back right bridge line140d. A first pump shut-off valve146ais positioned in the second pump line134b, a second pump shut-off valve146ais positioned in the fourth pump line134d, a third pump shut-off valve146cis positioned in the first reservoir line113a, and a fourth pump shut-off valve146dis positioned in the second reservoir line113b. In the illustrated example, the shut-off valves144a,144b,144c,144d,146a,146b,146c,146dare semi-active electro-mechanical valves with a combination of passive spring-disk elements and a solenoid that actuates the valve between open and closed positions.

The bi-directional pumps110a,110b, the pressure sensors124a,124b,124c,124d, and shut-off valves144a,144b,144c,144d,146a,146b,146c,146dare electrically connected to controllers180a,180b, which is configured to individually activate (i.e., turn on in forward or reverse) the bi-directional pumps110a,110band individually open and close the shut-off valves144a,144b,144c,144d,146a,146b,146c,146din response to various inputs, including signals from the pressure sensors124a,124b,124c,124d. The anti-pitch and anti-roll capabilities of the suspension system100will be explained in greater detail below; however, fromFIG.2it should be appreciated that fluid pressure in the hydraulic circuits120a,120b,120c,120dcan be adjusted by operation of the bi-directional pumps110a,110bto dynamically adjust the pitch and roll stiffness of the suspension system100, which changes the degree to which the vehicle will lean fore or aft (i.e., pitch) or to one side or the other (i.e., roll). Thus, the suspension system100described herein can either augment or completely replace mechanical stabilizer bars/anti-roll bars. Such mechanical systems require relatively straight, unobstructed runs between each of the front dampers102a,102band each of the back dampers102c,102d. Accordingly, the suspension system100disclosed herein offers packaging benefits because the dampers102a,102b,102c,102donly need to be hydraulically connected to one another and the bi-directional pumps110a,110b.

There are three primary types of suspension movements that the illustrated suspension system100can actively control by changing or adapting the roll and/or pitch stiffness of the vehicle: leaning to one side or the other during cornering (i.e., roll), pitching forward during braking (i.e., brake dive), and pitching aft during acceleration (i.e., rear end squat). Descriptions of how the suspension system100reacts to each of these conditions are provided below.

FIG.3illustrates the suspension system100in a comfort operating mode. When active roll and/or pitch stiffness is not required, the controllers180a,180bmay activate a comfort operating mode by opening the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144d, first pump shut-off valve146a, and second pump shut-off valve146a. Meanwhile, in the comfort operating mode, the third pump shut-off valve146cand fourth pump shut-off valve146dare closed and the first and second bi-directional pumps110a,110bare powered off to maintain substantially equal static pressures within all four hydraulic circuits120a,120b,120c,120d. In the comfort operation mode fluid flow is therefore permitted through valves144a,144b,144c,144d,146a,146bto enhance the ride comfort of the suspension system100and reduce or eliminate unwanted suspension movements resulting from the hydraulic coupling of one damper of the system to another damper of the system (e.g., where the compression of one damper causes movement and/or a dampening change in another damper). For example, when the front left comfort valve144ais open and the front left damper102aundergoes a compression stroke as the front wheel hits a bump, fluid may flow from the first compression chamber126aof the front left damper102a, into the first hydraulic line132a, from the first hydraulic line132ato the second hydraulic line132bby passing through the front left bridge line140aand the front left comfort valve144a, and into the first rebound chamber128aof the front left damper102a. Thus, fluid can travel from the first compression chamber126ato the first rebound chamber128aof the front left damper102awith the only restriction coming from the variable control valves160,164, in any. As such, in the comfort operating mode, the dampers102a,102b,102c,102dare effectively decoupled from one another for improved ride comfort.

FIG.4illustrates the suspension system100in a pitch control operating mode when the vehicle is undergoing acceleration. During acceleration, the momentum of the sprung weight of the vehicle body103tends to make the vehicle body103pitch or squat rearward (i.e., aft), compressing the back left damper102cand the back right damper102d. When this occurs, fluid flows out from the third compression chamber126cof the back left damper102cinto the fourth hydraulic line132dand out from the fourth compression chamber126dof the back right damper102dinto the first hydraulic line132a. As a result of the weight transfer to the back/rear of the vehicle, the front left damper102aand front right damper102bbegin to extend, causing fluid to flow out of the first rebound chamber128aof the front left damper102ainto the second hydraulic line132band out of the second rebound chamber128bof the front right damper102binto the fourth hydraulic line132d. As this occurs, the controllers180a,180bmay activate a pitch control operating mode by closing the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144d, third pump shut-off valve146c, and fourth pump shut-off valve146d, opening the first and second pump shut-off valves146a,146b, and activating the first and second bi-directional pumps110a,110bto pump hydraulic fluid from the first and third hydraulic circuits120a,120cand into the second and fourth hydraulic circuits120b,120d. In this example, the first port116ais operating as an inlet port for the first bi-directional pump110aand the second port116bis operating as an outlet port for the first bi-directional pump110a. Similarly, the third port116cis operating as an inlet port for the second bi-directional pump110band the fourth port116dis operating as an outlet port for the second bi-directional pump110b. Accordingly, the first bi-directional pump110adraws in hydraulic fluid from the first pump line134avia the first port116aand discharges hydraulic fluid into the second pump line134bvia the second port116band the second bi-directional pump110bdraws in hydraulic fluid from the third pump line134cvia the third port116cand discharges hydraulic fluid into the fourth pump line134dvia the fourth port116d. Fluid flow is permitted through the first and second pump shut-off valves146a,146bsuch that the first and second bi-directional pumps110a,110boperate to increase fluid pressure in the second and fourth hydraulic lines132b,132d, which increases the pressure in the third compression chamber126cof the back left damper102cand the fourth compression chamber126dof the back right damper102dmaking the back left damper102cand the back right damper102dmore difficult to compress. This counteracts the momentum of the sprung weight of the vehicle body103as it attempts to pitch or squat rearward (i.e., aft).

FIG.5illustrates the suspension system100in a pitch control operating mode when the vehicle is undergoing deceleration, such as during braking. During braking, the momentum of the sprung weight of the vehicle body103tends to make the vehicle body103pitch or dive forward, compressing the front left damper102aand the front right damper102b. When this occurs, fluid flows out from the first compression chamber126aof the front left damper102ainto the first hydraulic line132aand out from the second compression chamber126bof the front right damper102binto the third hydraulic line132b. As a result of the weight transfer to the front of the vehicle, the back left damper102cand back right damper102dbegin to extend, causing fluid to flow out of the third rebound chamber128cof the back left damper102cinto the third hydraulic line132cand out of the fourth rebound chamber128dof the back right damper102dinto the first hydraulic line132a. As this occurs, the controllers180a,180bmay activate a pitch control operating mode by closing the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144d, third pump shut-off valve146c, and fourth pump shut-off valve146d, opening the first and second pump shut-off valves146a,146b, and activating the first and second bi-directional pumps110a,110bto pump hydraulic fluid from the second and fourth hydraulic circuits120b,120dand into the first and third hydraulic circuits120a,120c. In this example, the first port116ais operating as an outlet port for the first bi-directional pump110aand the second port116bis operating as an inlet port for the first bi-directional pump110a. Similarly, the third port116cis operating as an outlet port for the second bi-directional pump110band the fourth port116dis operating as an inlet port for the second bi-directional pump110b. Accordingly, the first bi-directional pump110adraws in hydraulic fluid from the second pump line134bvia the second port116band discharges hydraulic fluid into from the first pump line134avia the first port116aand the second bi-directional pump110bdraws in hydraulic fluid from the fourth pump line134dvia the fourth port116dand discharges hydraulic fluid into the third pump line134cvia the third port116c. Fluid flow is permitted through the first and second pump shut-off valves146a,146bsuch that the first and second bi-directional pumps110a,110boperate to increase fluid pressure in the first and third hydraulic lines132a,132c, which increases the pressure in the first compression chamber126aof the front left damper102aand the second compression chamber126bof the front right damper102bmaking the front left damper102aand the front right damper102dmore difficult to compress. This counteracts the momentum of the sprung weight of the vehicle body103as it attempts to pitch or dive forward.

FIG.6illustrates the suspension system100in a roll control operating mode when the vehicle is turning left. When the vehicle is placed in a left turn, the momentum of the sprung weight of the vehicle body103tends to make the vehicle lean right towards the outside of the turn, compressing the front right damper102band the back right damper102d. When this occurs, fluid flows out from the second compression chamber126bof the front right damper102band the fourth compression chamber126dof the back right damper102dinto the second and third hydraulic lines132b,132c. As a result of the weight transfer to the right side of the vehicle, the front left damper102aand back left damper102cbegin to extend, causing fluid to flow out of the first rebound chamber128aof the front left damper102aand the third rebound chamber128cof the back left damper102cinto the second and third hydraulic lines132b,132c. As this occurs, the controllers180a,180bmay activate a roll control operating mode by closing the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144d, third pump shut-off valve146c, and fourth pump shut-off valve146d, opening the first and second pump shut-off valves146a,146b, activating the first bi-directional pump110ato pump hydraulic fluid from the first hydraulic circuit120aand into the second hydraulic circuit120b, and activating the second bi-directional pump110bin the opposite direction to pump hydraulic fluid from the fourth hydraulic circuit120dand into the third hydraulic circuit120c. In this example, the first port116ais operating as an inlet port for the first bi-directional pump110aand the second port116bis operating as an outlet port for the first bi-directional pump110a. By contrast, the third port116cis operating as an outlet port for the second bi-directional pump110band the fourth port116dis operating as an inlet port for the second bi-directional pump110b. Accordingly, the first bi-directional pump110adraws in hydraulic fluid from the first pump line134avia the first port116aand discharges hydraulic fluid into the second pump line134bvia the second port116band the second bi-directional pump110bdraws in hydraulic fluid from the fourth pump line134dvia the fourth port116dand discharges hydraulic fluid into the third pump line134cvia the third port116c. Fluid flow is permitted through the first and second pump shut-off valves146a,146bsuch that the first and second bi-directional pumps110a,110boperate to increase fluid pressure in the second and third hydraulic lines132b,132c, which increases the pressure in the second compression chamber126bof the front right damper102band the fourth compression chamber126dof the back right damper102dmaking the front right damper102band the back right damper102dmore difficult to compress. This counteracts the momentum/roll moment of the sprung weight of the vehicle body103as it attempts to roll or lean to the right.

FIG.7illustrates the suspension system100in a roll control operating mode when the vehicle is turning right. When the vehicle is placed in a right turn, the momentum of the sprung weight of the vehicle body103tends to make the vehicle lean left towards the outside of the turn, compressing the front left damper102aand the back left damper102c. When this occurs, fluid flows out from the first compression chamber126aof the front left damper102aand the third compression chamber126cof the back left damper102cinto the first and fourth hydraulic lines132a,132d. As a result of the weight transfer to the left side of the vehicle, the front right damper102band back right damper102dbegin to extend, causing fluid to flow out of the second rebound chamber128bof the front right damper102band the fourth rebound chamber128dof the back right damper102dinto the first and fourth hydraulic lines132a,132d. As this occurs, the controllers180a,180bmay activate a roll control operating mode by closing the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144d, third pump shut-off valve146c, and fourth pump shut-off valve146d, opening the first and second pump shut-off valves146a,146b, activating the first bi-directional pump110ato pump hydraulic fluid from the second hydraulic circuit120band into the first hydraulic circuit120a, and activating the second bi-directional pump110bin the opposite direction to pump hydraulic fluid from the third hydraulic circuit120cand into the fourth hydraulic circuit120d. In this example, the first port116ais operating as an outlet port for the first bi-directional pump110aand the second port116bis operating as an inlet port for the first bi-directional pump110a. By contrast, the third port116cis operating as an inlet port for the second bi-directional pump110band the fourth port116dis operating as an outlet port for the second bi-directional pump110b. Accordingly, the first bi-directional pump110adraws in hydraulic fluid from the second pump line134bvia the second port116band discharges hydraulic fluid into the first pump line134avia the first port116aand the second bi-directional pump110bdraws in hydraulic fluid from the third pump line134cvia the third port116cand discharges hydraulic fluid into the fourth pump line134dvia the fourth port116d. Fluid flow is permitted through the first and second pump shut-off valves146a,146bsuch that the first and second bi-directional pumps110a,110boperate to increase fluid pressure in the first and fourth hydraulic lines132a,132d, which increases the pressure in the first compression chamber126aof the front left damper102aand the third compression chamber126cof the back left damper102cmaking the front left damper102aand the back left damper102cmore difficult to compress. This counteracts the momentum/roll moment of the sprung weight of the vehicle body103as it attempts to roll or lean to the left.

FIG.8illustrates the suspension system100in a combined pitch and roll control operating mode when the vehicle is turning left or right and braking or when the vehicle is turning left or right and accelerating. When the vehicle is placed in a left turn and undergoing deceleration, the momentum of the sprung weight of the vehicle body103tends to make the vehicle lean right towards the outside of the turn and to make the vehicle body103pitch forward, transferring more of the weight of the vehicle body103to the front right wheel101bof the vehicle, compressing the front right damper102band compressing the back right damper102dand the front left damper102ato a lesser degree. When this occurs, fluid flows out from the first compression chamber126aof the front left damper102aand the second compression chamber126bof the front right damper102band the fourth compression chamber126dof the back right damper102dand into the first, second, and third hydraulic lines132a,132b,132c. As a result of the weight transfer to the front right wheel101bof the vehicle, the back left damper102cextends, causing fluid to flow out of the third rebound chamber128cof the back left damper102cand into the third hydraulic line132c. As this occurs, the controllers180a,180bmay activate a combined roll/pitch control operating mode by closing the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144d, third pump shut-off valve146c, and fourth pump shut-off valve146d, opening the first and second pump shut-off valves146a,146b, activating the first bi-directional pump110ato pump hydraulic fluid from the second hydraulic circuit120band into the first hydraulic circuit120a, and activating the second bi-directional pump110bto pump hydraulic fluid from the fourth hydraulic circuit120dand into the third hydraulic circuit120c. This is similar to the pitch control operating mode; however, in the combined roll/pitch control operating mode the second bi-directional pump110bmay be run longer or faster than the first bi-directional pump110aso that the pressure differential between the third and fourth hydraulic circuits120c,120dis greater than the pressure differential between the first and second hydraulic circuits120a,120bto counteract body roll/lean to the right.

When the vehicle is placed in a right turn and undergoing deceleration, the momentum of the sprung weight of the vehicle body103tends to make the vehicle lean left towards the outside of the turn and to make the vehicle body103pitch forward, transferring more of the weight of the vehicle body103to the front left wheel101aof the vehicle, compressing the front left damper102aand compressing the back left damper102cand the front right damper102bto a lesser degree. As this occurs, the controllers180a,180bmay activate the same combined roll/pitch control operating mode described above, but may run the first bi-directional pump110alonger or faster than the second bi-directional pump110bso that the pressure differential between the first and second hydraulic circuits120a,120bis greater than the pressure differential between the third and fourth hydraulic circuits120c,120dto counteract body roll/lean to the left.

When the vehicle is placed in a left turn and undergoing acceleration, the momentum of the sprung weight of the vehicle body103tends to make the vehicle lean right towards the outside of the turn and to make the vehicle body103pitch rearward, transferring more of the weight of the vehicle body103to the back right wheel101dof the vehicle, compressing the back right damper102dand compressing the front right damper102band the back left damper102cto a lesser degree. As this occurs, the controllers180a,180bmay activate a combined roll/pitch control operating mode by closing the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144d, third pump shut-off valve146c, and fourth pump shut-off valve146d, opening the first and second pump shut-off valves146a,146b, activating the first bi-directional pump110ato pump hydraulic fluid from the first hydraulic circuit120aand into the second hydraulic circuit120b, and activating the second bi-directional pump110bto pump hydraulic fluid from the third hydraulic circuit120cand into the fourth hydraulic circuit120d. This is similar to the pitch control operating mode; however, in the combined roll/pitch control operating mode the first bi-directional pump110amay be run longer or faster than the second bi-directional pump110bso that the pressure differential between the first and second hydraulic circuits120a,120bis greater than the pressure differential between the third and fourth hydraulic circuits120c,120dto counteract body roll/lean to the right.

When the vehicle is placed in a right turn and undergoing acceleration, the momentum of the sprung weight of the vehicle body103tends to make the vehicle lean left towards the outside of the turn and to make the vehicle body103pitch rearward, transferring more of the weight of the vehicle body103to the back left wheel101cof the vehicle, compressing the back left damper102cand compressing the back right damper102dand the front left damper102ato a lesser degree. As this occurs, the controllers180a,180bmay activate the same combined roll/pitch control operating mode described above, but may run the second bi-directional pump110blonger or faster than the first bi-directional pump110aso that the pressure differential between the third and fourth hydraulic circuits120c,120dis greater than the pressure differential between the first and second hydraulic circuits120a,120bto counteract body roll/lean to the left.

Thus, the directions115a-115din which the first and second bi-directional pumps110a,110brotate depend on the forces applied to each damper102a-102dof the vehicle, which translate to hydraulic torques placed on the first and second bi-directional pumps110a,110b. A hydraulic torque is the pressure difference between the ports116aand116bof the first bi-directional pump110aand the ports116cand116dof the second bi-directional pump110b, which can be positive or negative. When controller180arequest a positive torque (for example 10 bar) and the pressure differential between ports116aand116bis 7 bar (for example), the first bi-directional pump110aneeds to rotate in the first direction115ato increase the pressure differential from 7 to 10 bar, but if the pressure differential was already higher than 10 bar (for example 13 bar), then the first bi-directional pump110aneeds to run in the opposite direction (i.e., the second direction115b) to reduce the pressure differential to 10 bar, and the controller180awill keep regulating the requested hydraulic torque by rotating the first bi-directional pump110ain both directions115a,115b. Controller180bcontrols the second bi-directional pump110bin a similar fashion.

FIG.9illustrates the suspension system100in a pressure control operating mode. The object of the pressure control operating mode is to increase or decrease the static pressure in all hydraulic circuits120a,120b,120c,120dof the suspension system100by either pumping hydraulic fluid out of the reservoir112and into the hydraulic circuits120a,120b,120c,120d(to increase the static pressure in the suspension system100) or by pumping hydraulic fluid out of the hydraulic circuits120a,120b,120c,120dand into the reservoir112(to decrease the static pressure in the suspension system100). In the pressure control operating mode, the controllers180a,180bopen the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144d, third pump shut-off valve146c, and fourth pump shut-off valve146dand at the same time closes the first pump shut-off valve146aand second pump shut-off valve146a.

To reduce fluid pressure in the hydraulic circuits120a,120b,120c,120dof the suspension system100, the controllers180a,180bactivate the first and second bi-directional pumps110a,110bto pump hydraulic fluid from the first and third hydraulic circuits120a,120cand into the reservoir112via the first and second reservoir lines113a,113b. In this example, the first port116ais operating as an inlet port for the first bi-directional pump110aand the second port116bis operating as an outlet port for the first bi-directional pump110a. Similarly, the third port116cis operating as an inlet port for the second bi-directional pump110band the fourth port116dis operating as an outlet port for the second bi-directional pump110b. Accordingly, the first bi-directional pump110adraws in hydraulic fluid from the first pump line134avia the first port116aand discharges hydraulic fluid into the second pump line134bvia the second port116band the second bi-directional pump110bdraws in hydraulic fluid from the third pump line134cvia the third port116cand discharges hydraulic fluid into the fourth pump line134dvia the fourth port116d. Fluid flow is blocked by the first and second pump shut-off valves146a,146b, which are closed, but the third and fourth pump shut-off valves146c,146dare open, so the hydraulic fluid discharged from the second port116bof the first bi-directional pump110aflows into the first reservoir line113aand the hydraulic fluid discharged from the fourth port116dof the second bi-directional pump110bflows into the second reservoir line113a. Because the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144dare all open, this reduces the static pressure in all of the hydraulic circuits120a,120b,120c,120d.

To raise fluid pressure in the hydraulic circuits120a,120b,120c,120dof the suspension system100, the controllers180a,180bactivate the first and second bi-directional pumps110a,110bto pump hydraulic fluid from the reservoir112and into the first and third hydraulic circuits120a,120c. In this example, the first port116ais operating as an outlet port for the first bi-directional pump110aand the second port116bis operating as an inlet port for the first bi-directional pump110a. Similarly, the third port116cis operating as an outlet port for the second bi-directional pump110band the fourth port116dis operating as an inlet port for the second bi-directional pump110b. Accordingly, the first bi-directional pump110adraws in hydraulic fluid from the second pump line134bvia the second port116band discharges hydraulic fluid into from the first pump line134avia the first port116aand the second bi-directional pump110bdraws in hydraulic fluid from the fourth pump line134dvia the fourth port116dand discharges hydraulic fluid into the third pump line134cvia the third port116c. Fluid flow is blocked by the first and second pump shut-off valves146a,146b, which are closed, but the third and fourth pump shut-off valves146c,146dare open, so the second port116bof the first bi-directional pump110adraws in hydraulic fluid from the first reservoir line113aand the fourth port116dof the second bi-directional pump110bdraws in hydraulic fluid from the second reservoir line113a. Because the front left shut-off valve144a, front right shut-off valve144b, back left shut-off valve144c, back right shut-off valve144dare all open, this increases the static pressure in all of the hydraulic circuits120a,120b,120c,120d.

FIG.10illustrates another suspension system200that shares many of the same components as the suspension system100illustrated inFIGS.2-9, but the first and second bi-directional pumps110a,110bshown inFIGS.2-9have been replaced with first and second dual chamber ball-screw mechanisms252a,252binFIG.10. Rather than repeat the description set forth above, the following paragraphs describe the structure and function of the components inFIG.10that are new and/or different from those shown and described in connection withFIGS.2-9. It should be appreciated that the reference numbers inFIG.10are “200” series numbers (e.g.,200,202a,204a, etc.), but otherwise share the same base reference numbers as the corresponding elements inFIGS.2-9. Thus, the same description for elements100,102a,104aabove applies to elements200,202a,204ainFIG.10and so on and so forth, except as otherwise noted.

As its name implies, the first dual chamber ball-screw mechanism252aincludes a first variable volume chamber254aand a second variable volume chamber254bat opposing ends of a first cylinder housing256a. The first variable volume chamber254ais arranged in fluid communication with the first pump line234aand therefore the first hydraulic circuit220a, while the second variable volume chamber254bis arranged in fluid communication with the second pump line234band therefore the second hydraulic circuit220b. The first and second variable volume chambers254a,254bare separated by a first pair of driven pistons258a,258b, which are connected to a move together in unison with a first threaded rod260a. The first dual chamber ball-screw mechanisms252aalso includes a first motor262athat is arranged in threaded engagement with the first threaded rod260aand is therefore configured to drive the first threaded rod260aand therefore the first pair of driven pistons258a,258bin first and second directions215a,215bwithin the first cylinder housing256a. The first and second directions215a,215bare longitudinally opposed in relation to one another. When the first motor262adrives the first threaded rod260aand thus the first pair of driven pistons258a,258bin the first direction215a, the volume of the first variable volume chamber254aincreases while the volume of the second variable volume chamber254bdecreases. This causes hydraulic fluid in the first pump line234ato flow into the first variable volume chamber254aand hydraulic fluid in the second variable volume chamber254bto flow out into the second pump line234b, which decreases fluid pressure in the first hydraulic circuit220aand increases fluid pressure in the second hydraulic circuit220b. When the first motor262adrives the first threaded rod260aand thus the first pair of driven pistons258a,258bin the second direction215a, the volume of the first variable volume chamber254adecreases while the volume of the second variable volume chamber254bincreases. This causes hydraulic fluid in the first variable volume chamber254ato flow out into the first pump line234aand hydraulic fluid in the second pump line234bto flow into the second variable volume chamber254b, which increases fluid pressure in the first hydraulic circuit220aand decreases fluid pressure in the second hydraulic circuit220b.

The second dual chamber ball-screw mechanism252bincludes a third variable volume chamber254cand a fourth variable volume chamber254dat opposing ends of a second cylinder housing256b. The third variable volume chamber254cis arranged in fluid communication with the third pump line234cand therefore the third hydraulic circuit220c, while the fourth variable volume chamber254dis arranged in fluid communication with the fourth pump line234dand therefore the fourth hydraulic circuit220d. The third and fourth variable volume chambers254c,254dare separated by a second pair of driven pistons258c,258d, which are connected to a move together in unison with a second threaded rod260b. The second dual chamber ball-screw mechanisms252balso includes a second motor262bthat is arranged in threaded engagement with the second threaded rod260band is therefore configured to drive the second threaded rod260band therefore the second pair of driven pistons258c,258din third and fourth directions215c,215dwithin the second cylinder housing256b. The third and fourth directions215c,215dare longitudinally opposed in relation to one another. When the second motor262bdrives the second threaded rod260band thus the second pair of driven pistons258c,258din the third direction215c, the volume of the third variable volume chamber254cincreases while the volume of the fourth variable volume chamber254ddecreases. This causes hydraulic fluid in the third pump line234cto flow into the third variable volume chamber254cand hydraulic fluid in the fourth variable volume chamber254dto flow out into the fourth pump line234d, which decreases fluid pressure in the third hydraulic circuit220cand increases fluid pressure in the fourth hydraulic circuit220d. When the second motor262bdrives the second threaded rod260band thus the second pair of driven pistons258c,258din the fourth direction215d, the volume of the third variable volume chamber254cdecreases while the volume of the fourth variable volume chamber254dincreases. This causes hydraulic fluid in the third variable volume chamber254cto flow out into the third pump line234cand hydraulic fluid in the fourth pump line234dto flow into the fourth variable volume chamber254d, which increases fluid pressure in the third hydraulic circuit220cand decreases pressure fluid in the fourth hydraulic circuit220d.

The first and second motors262a,262bare electrically connected to and controlled by controllers280a,280band rotate in clockwise or counterclockwise directions depending on the polarity of the electric current supplied to the first and second motors262a,262bby the controllers280a,280b. This in turn drives linear/longitudinal movement of the first and second threaded rods260a,260bin opposite directions. The second pump line234band the fourth pump line234dare connected to a hydraulic reservoir212(e.g., a tank) by first and second reservoir lines213a,213bthat converge at a common reservoir line214. A bi-directional pump210is arranged in-line and in fluid communication with the common reservoir line214. The bi-directional pump210may operate (i.e., pump fluid) in two opposing directions215e,215fdepending on the polarity of the electricity that is supplied to the bi-directional pump210by one or more of the controllers280a,280b. Thus, the controllers280a,280bcan implement the same operating modes described above in connection withFIGS.3-9.

A first reservoir shut-off valve246ais positioned in the first reservoir line213aand a second reservoir shut-off valve246bis positioned in the second reservoir line213b, which may be semi-active electro-mechanical valves with a combination of passive spring-disk elements and a solenoid that actuates the valve between open and closed positions. However, it should be appreciated that in the configuration illustrated inFIG.10, the first and second pump shut-off valves146a,146ashown inFIGS.2-9have been eliminated because fluid cannot flow through the first and second dual chamber ball-screw mechanisms252a,252b.

Many other modifications and variations of the present disclosure are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the appended claims.