Abstract: An electro-hydraulic control system for a multispeed transmission having a plurality of torque-transmitting mechanisms includes a controller for operably controlling the transmission, a fluid source for supplying hydraulic fluid, and a plurality of torque-transmitting mechanisms being operably selected between an applied and an unapplied state to achieve a plurality of ranges including at least one reverse, a neutral, and a plurality of forward ranges. The system includes a plurality of trim systems having pressure control solenoids and trim valves. The system may also include one or more shift valves disposed in fluid communication with the fluid source and being capable of moving between stroked and de-stroked positions. In any given range, only two of the plurality of torque-transmitting mechanisms may be applied. Moreover, three of the plurality of pressure control solenoids are normally high solenoids, and the remaining solenoids are normally low solenoids.

Abstract: A transmission of a vehicle having a transmission housing which accommodates shifting elements. The transmission has a hydraulic control unit which supplies the shifting elements with hydraulic oil, and which has a valve housing and a duct plate. The valve housing accommodates valves, and the duct plate unit is connected to the transmission housing and contains hydraulic ducts which communicate with hydraulic ducts of the transmission housing, to supply hydraulic oil to the shifting elements. The transmission has a transmission-side power-take-off via which mechanical power can be drawn from the transmission.

Abstract: A dual clutch transmission (500) having a plurality of forward gears and at least one reverse gear (582) where the first gear is operatively engaged by a one-way clutch (594). A pair of actuator control valves (270, 272) is employed to move actuators to engage selective ones of the forward gear sets. A multiplex valve (284) is disposed in fluid communication between the pair of actuator control valves (270, 272) and the actuators associated with the forward gears of the transmission and is adapted to selectively provide fluid communication to the actuators to thereby select the forward gear ratios. A manual valve (185) is operatively connected to the gear shift selector (187) to control the actuator associated with reverse gear (582).

Abstract: A hydraulic control system in a transmission includes a source of pressurized hydraulic fluid and a compensator valve in communication with the source of pressurized hydraulic fluid and a torque transmitting device. The compensator valve is operable to allow communication of the hydraulic fluid from the source of pressurized hydraulic fluid to the torque transmitting device to release the torque transmitting device. A regulation valve is in communication with the source of pressurized hydraulic fluid and the torque transmitting device. The regulation valve is moveable between a first position that prevents the hydraulic fluid from communicating with the torque transmitting device and a second position that allows the hydraulic fluid to communicate with the torque transmitting device to engage the torque transmitting device. An override feature is operable to prevent the compensator valve from communicating the hydraulic fluid to the torque transmitting device when the torque transmitting device is engaged.

Abstract: A transmission system is provided having an input member, an output member, four planetary gear sets, a plurality of coupling members a plurality of torque transmitting devices, a launch clutch, and a hydraulic circuit. Each of the planetary gear sets includes first, second and third members. The torque transmitting devices may include clutches and brakes.

Abstract: A method and system provides a Brake Transmission Shift Interlock Override mode in a vehicle including a shift-by-wire transmission. With power applied and ignition on, a driver will press and hold an override switch for a calibrated time. While the override switch is pressed, the driver presses a non-Park button for another calibrated time. The result will be that the vehicle is placed in the selected range wherein the transmission will not automatically shift to Park upon detecting a triggering event. The driver is able to shift the vehicle from Park, even if an electrical failure prevents the transmission from shifting out of Park. As such the vehicle can be driven until the failure is serviced.

Abstract: An automatic transmission includes: a frictional engagement element arranged to be switched from an engagement state to a disengagement state at a switching from a running range to a neutral range, and including: frictional plates; a first piston arranged to push the frictional plates; a second piston arranged to push the frictional plates; a first hydraulic chamber arranged to receive a hydraulic fluid for pushing the first piston; and a second hydraulic chamber arranged to receive a hydraulic fluid for pushing the second piston; a first discharge speed switching section arranged to switch only a discharge speed of the hydraulic fluid of the first hydraulic chamber; and a control unit configured to increase the discharge speed of the hydraulic fluid of the first hydraulic chamber during a predetermined time period by the first discharge speed switching section at the switching from the running range to the neutral range.

Abstract: A hydraulic control system for a transmission includes a first source of pressurized hydraulic fluid, a second source of pressurized hydraulic fluid, a lubrication subsystem for communicating a pressurized hydraulic fluid through the transmission, and a fluid control device in communication with the first source of pressurized hydraulic fluid. A lubrication regulation valve is in communication with the first and second sources of pressurized hydraulic fluid, the fluid control device, and the lubrication subsystem.

Abstract: The present invention comprehends a plurality of embodiments of a hydraulic control system for various configurations of dual clutch transmissions. The hydraulic control systems all include a regulated source of pressurized hydraulic fluid including an electric pump, a filter and an accumulator, a pair of pressure control valves and a branching hydraulic circuit including pressure or flow control valves, spool or logic valves and two position valves which collectively supply and exhaust hydraulic fluid from a plurality of shift actuators. The actuators are connected to shift rails which include shift forks and are slidable to engage synchronizers and positive clutches associated with the various gear ratios.

Abstract: A method is proposed for blocking inadmissible gearshift processes in a transmission with a plurality of shifting devices which, to carry out a shift process, are moved by actuating devices when a shift command is sent by a control unit (TCU) to the relevant actuating device. The actuating devices are connected for data exchange with one another and with the control unit (TCU) in such manner that the actuating device of the shifting device to be shifted is activated provided that clearance has been given by at least one other actuating device.

Abstract: A hydraulic control system for a automatic transmission includes a plurality of solenoids and valves in fluid communication with a plurality of shift actuators. The shift actuators are operable to actuate a plurality of torque transmitting devices. Selective activation of combinations of the solenoids allows for a pressurized fluid to activate at least one of the shift actuators. The solenoids are configured to provide a forward gear ratio and a reverse gear ratio when the solenoids are deengerized.

Abstract: A hydraulic control apparatus for an automatic transmission, including a sequential shift control means for performing sequential shift control in a case where it is necessary to execute the second shift during execution of the first shift. The sequential shift control includes starting reduction of hydraulic fluid pressure in the third friction element when a parameter that varies in accordance with a degree of progress of the first shift has reached a predetermined value, and performing piston stroke control that includes outputting a high hydraulic pressure command as a hydraulic fluid pressure to the second friction element when the selector valve is switched from the second position to the first position, and subsequent to completion of outputting of the high hydraulic pressure command, outputting a low hydraulic pressure command that is lower than the high hydraulic pressure command.

Abstract: An electro-hydraulic control system is provided for a transmission with a torque-transmitting mechanism that has a dual area piston. When pressurized fluid is provided to a first of the two piston areas, the position of a spring-biased shift valve controls whether pressurized fluid communicates with the second piston area. A solenoid valve in fluid communication with the shift valve is energizable to direct pressurized fluid to the shift valve to urge the shift valve to the unstroked position to which the spring also urges. The shift valve may also be urged by pressurized fluid to the stroked position, but only when the solenoid valve is not energized. The spring maintains the shift valve in the unstroked position when pressurized fluid is directed to the shift valve to act both against and with the spring.

Abstract: A control unit for an electric oil pump of the present invention includes: a one-way valve that permits circulation of operating fluid from the electric oil pump to the friction engagement device and blocks circulation in the opposite direction; an accumulator that is connected to a fluid supply path joining the one-way valve to the friction engagement device and accumulates hydraulic pressure required for operating the friction engagement device; a hydraulic pressure measuring device that measures hydraulic pressure inside the fluid supply path; a vehicle speed measuring device that measures a vehicle speed of the vehicle; and a pressure setting device that sets a first predetermined pressure based on the vehicle speed measured by the vehicle speed measuring device.

Abstract: Eight forward speeds and one reverse speed of an automatic transmission are achieved by: controlling a first clutch by a first pressure control valve controlled a first proportional control solenoid valve and a first pressure switching valve; controlling a second clutch by a second pressure control valve controlled by a second proportional control solenoid valve and a second pressure switching valve; controlling a third clutch by a third pressure control valve controlled by a third proportional control solenoid valve and a third pressure switching valve; controlling a first brake by first and second switching valves and a fourth pressure control valve controlled by a fourth proportional control solenoid valve and a fourth pressure switching valve; and controlling a second brake by a fifth pressure control valve controlled by a fifth proportional control solenoid valve and a fifth pressure switching valve.

Abstract: A flow management valve is operative to enable a multi-range electro-mechanical transmission in first and second ranges. Fluid pressure in a hydraulic circuit is monitored to detect a fault in the flow management valve.

Abstract: An electro-hydraulic control system is provided, preferably for a countershaft transmission, that uses logic valves to multiplex trim systems to more than one torque-transmitting mechanism, thereby minimizing the number of required components. Additionally, the electro-hydraulic control system preferably has more than one failure mode so that the transmission operates at a respective predetermined speed ratio in the event of an interruption in electrical power.

Abstract: A modification to the manual valve of an automatic transmission is provided which improves the shift quality of the automatic transmission when the transmission is shifted from a drive gear to either Park or Neutral. More particularly, the invention provides a control orifice which regulates the release of hydraulic fluid from one or more clutch circuits such that pressure to one or more clutches is gradually released. The gradual release of pressure form the one or more clutches provides an improved shift quality. In alternate embodiments, the present invention provides a further modification to an automatic transmission which allows the control orifice to be circumvented in situations where a rapid swap of pressure from on clutch control solenoid to another is required.

Abstract: A hydraulic control apparatus for an automatic transmission, including a sequential shift control means for performing sequential shift control in a case where it is necessary to execute the second shift during execution of the first shift. The sequential shift control includes starting reduction of hydraulic fluid pressure in the third friction element when a parameter that varies in accordance with a degree of progress of the first shift has reached a predetermined value, and performing piston stroke control that includes outputting a high hydraulic pressure command as a hydraulic fluid pressure to the second friction element when the selector valve is switched from the second position to the first position, and subsequent to completion of outputting of the high hydraulic pressure command, outputting a low hydraulic pressure command that is lower than the high hydraulic pressure command.

Abstract: A hydraulic control system applicable to a power train of a seven-speed automatic transmission for a vehicle having six friction members. Enhanced overall performance is achieved by minimization of shift shock and an enhancement of fuel consumption as a consequence of achieving precise and effective control.

Abstract: There is provided a control system for electro-mechanical transmission that is selectively operative in a plurality of fixed gear modes and continuously variable modes comprising first and second electrical machines and four hydraulically-actuated clutches in fluid communication with a hydraulic circuit comprising first, second and third pressure control devices and first and second flow management valves. The control system is operative to selectively actuate the pressure control devices and the flow management valves based upon a demand for torque, presence of a fault, and temperatures of the electric machines.

Abstract: In a condition of a vehicle which remains stationary or is about to stop and of a forward second speed having a clutch and a brake engaged, an N range is changed from a D range based on a shift lever operation and a forward range pressure is discharged from a manual shift valve. At this time, an orifice and a check ball are used to delay discharge of oil paths which communicate with a linear solenoid valve relative to discharge of an oil path a1 which communicates with a linear solenoid valve. Specifically, release of the brake is delayed relative to release of the clutch, so that a shift by way of a forward first speed through engagement of a one-way clutch can be prevented.

Abstract: A hydraulic control system of an eight-speed automatic transmission for a vehicle. Four clutches and two brakes can by independently controlled by six proportional control solenoid valves by employing pressure control valves and pressure switching valves.

Abstract: In a hydraulic control apparatus for a vehicular automatic transmission, if it is determined that there is a failure that may cause tie-up in an automatic transmission, communication is provided between a first output port and a first drain port in a switching valve. As a result, a hydraulic frictional engagement device, which should be disengaged when there is a failure, is disengaged. Also, a specific shift speed is achieved by controlling the switching valve. Therefore, it is not necessary to select a shift speed that is achieved on the condition that the hydraulic frictional engagement device, which should be disengaged when there is a failure, is engaged. Thus, it is possible to prevent a shift that may impair driveability when there is a failure that may cause tie-up in the automatic transmission.

Abstract: In a driving device that includes a mechanical oil pump operated by power of an engine and a motor oil pump EOP operated by power of a motor, provided in parallel with each other, and check valves on discharge sides of the pumps, and pumps oil from any of the pumps and supplies the oil to a clutch included in a transmission, a through hole 68a for releasing air that communicates with a discharge port 68 is formed in a case 61 of the mechanical oil pump MOP. This allows air trapped in when driving of the mechanical oil pump MOP is started along with a start of the engine to be quickly discharged to quickly increase internal pressure to pressure required for opening the check valve, and thus oil can be supplied to the clutch of the transmission via the check valve to quickly operate the clutch.

Abstract: A control system operable to engage a torque transmitting mechanism, the control system having at least one variable bleed solenoid valve operable to selectively provide pressurized fluid to selectively engage at least one torque transmitting mechanism. An electronic control unit is also provided to provide control to the at least one variable bleed solenoid valve. The electronic control unit commands the variable bleed solenoid valve to provide the pressurized fluid to the at least one torque transmitting mechanism for a first predetermined time and to subsequently substantially disallow the pressurized fluid to the at least one torque transmitting mechanism for a second predetermined time subsequent to the first predetermined time. The electronic control unit subsequently commands an intermediate pressure level to trim the torque transmitting mechanism into engagement. A method for providing engagement to the torque transmitting mechanism is also provided.

Abstract: A first rotary member rotates with a crankshaft and has a first gear. A second rotary member rotates with a camshaft and has a second gear that is axially shifted from the first gear. A planetary rotary member has third and fourth gears, which are eccentrically meshed respectively with the first and second gears to perform a planetary motion. A biasing member is interposed between the planetary rotary member and a planetary carrier, which supports the planetary rotary member. The planetary rotary member is in contact with the biasing member at a contact portion having an axial center. The axial center is located on a radially inner side of a meshed portion between the second and fourth gears, which has a backlash larger than that of a meshed portion between the first and third gears.

Abstract: At the time of a failure in the second group of engagement devices, the manner of input of oil pressures to a fail-safe valve group is changed via a priority degree switching valve on the basis of the state of engagement of engagement devices of the first group in such a manner that the predetermined degrees of priority for the supply of one of oil pressures PC4, PB1 output from linear solenoid valves SL4, SL5 to a corresponding one of a clutch C4 and a brake B1 via the fail-safe valve group are changed so as to avoid an event that the fail-safe gear stage established in order to prevent the occurrence of interlock of the automatic transmission involves a downshift of two or more stages from the speed change stage maintained immediately prior to the occurrence of the failure. Therefore, it is possible to prevent the occurrence of an uncomfortable behavior of the vehicle caused by the shift to the fail-safe gear stage.

Abstract: A hydraulic control system of an automatic transmission that precisely control is operating hydraulic pressure supplied to a frictional element during shifting and can eliminate oil leak under a maximum operating hydraulic pressure. The hydraulic control system controls a hydraulic pressure generated by a hydraulic pump to from an operating hydraulic pressure for a frictional element selectively operating at each shift ratio. A hydraulic line is configured such that the operating hydraulic pressure of the frictional element is controlled by a pressure control valve and a switching valve that are controlled by a solenoid valve. An exhaust hydraulic line of the pressure control valve is connected to an exhaust hydraulic line of the switching valve such that the exhaust hydraulic line of the pressure control valve can be controlled by a switching of the switching valve.

Abstract: A hydraulic linear drive for a hydraulic vehicle transmission actuator has a piston/cylinder unit in which an adjusting piston is arranged so it is longitudinally displaceable in a cylinder housing and subdivides the cylinder space into at least two pressure spaces which can receive hydraulic oil through control lines. The optional pressure action on the two pressure spaces is controllable by a shift valve. A connecting line is provided between the two control lines leading to the pressure spaces and a control valve is provided for optionally releasing or blocking the connecting line to further control the pressure force acting on the piston.

Abstract: A hydraulic control system of a seven-speed automatic transmission that provides enhanced overall performance by achieving precise and effective control by providing a fail-safe function in at least two ways.

Abstract: According to a preferred embodiment of the present invention, a “special neutral” is commanded to initiate the neutral to range shift. The “special neutral” of the present invention is special in that while the transmission output speed remains unconstrained, the transmission input speed is locked at zero. This condition is particularly advantageous because on-coming clutches may be applied without relative motion between the respective clutch plates. Therefore, by initiating the neutral to range shift from the “special neutral” of the present invention, the ratio change may take place irrespective of engine speed, with zero slip loss and more quickly than previously possible.

Abstract: A hydraulic pressure control apparatus for an automatic transmission having plural engaging elements (a first engaging element and a second engaging element) includes plural control valves (a first control valve and a second control valve) controlling each engaging element by supplying controlled hydraulic pressure as output pressure, plural shift valves for switching an oil passage for the line pressure, a fail valve closing an input port and a fail output port thereof while the output pressure is supplied from the second control valve; wherein, once the line pressure is supplied to the control valve through a supply port and a drain port thereof, it outputs the line pressure from as output pressure, and once the line pressure is supplied to the fail valve through the input port and a release port thereof, it outputs the line pressure as output pressure.

Abstract: An automatic transmission control device adjusts a hydraulic pressure of a working fluid to generate pressures applied to a plurality of friction elements of an automatic transmission to control the engagement or disengagement of the friction elements. The control device includes a plurality of electromagnetic valves, a plurality of application pressure control valves, a selector, and a line pressure control valve. The application pressure control valves control pressures applied to the friction elements according to the output pressures of the electromagnetic valves. The selector selects the maximum pressure from the output pressures of the electromagnetic valves. The line pressure control valve controls a line pressure according to the output pressure selected by the selector.

Abstract: An electro-hydraulic control mechanism for use with a multi-speed transmission includes a pair of logic valves, which are manipulated during the ratio interchanges and the ratio establishment by aiding in the distribution of fluid pressure from a plurality of trim valves. The logic valves are retained in specific drive ranges in the event of electrical discontinuance.

Abstract: The present invention is directed to methods and systems for improving the operation of transmissions for automotive vehicles, and in particular the “factory installed” automotive transmissions installed by the original automobile manufacturer. The methods and systems in accordance with the present invention modify both the structural components and the hydraulic circuitry of the original automotive transmissions to enhance the operation of the modified transmissions. The improvements to the operation of the “factory installed” transmissions, and in particular the Allison transmission, include modification of the flow control valve to increase line pressure during lockup; modifications to the rotating clutch module to increase the torque held by the clutch and prevent clutch slippage, and modifications to the trim valves to adjust the pressure applied to the clutches for more efficient operation of the transmission.

Abstract: A control method for an automatic transmission is capable of quickly determining whether gear shifting is permissive. The control method varies the command value input to an engaging-side electromagnetic valve that adjusts a hydraulic pressure applied to a frictional element to be engaged in a target gear in a specific time period, then determines a time variation in another time period of the hydraulic pressure applied to the frictional element that is adjusted by the engaging-side electromagnetic valve according to the input command value and detected by a detecting means. Determination of whether gear shifting is permissive or not on the basis of the time variation is thus determined.

Abstract: A pair of feedback chambers is provided in a supply/discharge switching control valve, and the hydraulic pressure is introduced from a portion on the upstream side of the orifice provided in the communication passage through the second feedback passage, and is introduced from a portion on the downstream side of the orifice provided in the communication passage through the first feedback passage. Therefore, the responsiveness is enhanced, compared with the case where only the first feedback chamber is provided. Also, the overshoot and the undershoot of the fluid pressure, and the pressure fluctuation are effectively suppressed, compared with the case where only the second feedback chamber is provided.

Abstract: Methods and systems for improving the operation of a transmission for an automotive vehicle are provided for modifiying the original hydraulic circuits to increase the capacity or holding ability of the low and reverse clutches when the transmission is shifted into manual low gear to slow down a moving vehicle, to provide a quick and smooth apply of the low and reverse clutches when the driver selects manual low when the vehicle is moving at a relatively high road speed, and to permit the connection of two low hydraulic circuits to feed torque converter and cooler/lubrication circuits by application of relatively low fluid pressure to assure that the necessary pressure required to connect the circuits will be properly applied.

Abstract: A control system and control method for an automotive vehicle having a multiple-ratio automatic transmission having two gearsets arranged in series relationship for delivering vehicle engine power to vehicle traction wheels, each gearset being controlled using friction elements that establish multiple torque flow paths, each gearset being characterized by at least two ratios, which define an overall transmission ratio, synchronous shifting of the gearsets effecting at least one swap-upshift and at least one swap-downshift in the overall transmission ratio, the control system compensating during a swap-shift progression for dynamic interaction between the gearsets.

Abstract: The present invention is directed to methods and systems for improving the operation of transmissions for automotive vehicles, and in particular the “factory installed” automotive transmissions installed by the original automobile manufacturer. The methods and systems in accordance with the present invention modify both the structural components and the hydraulic circuitry of the original automotive transmissions to enhance the operation of the modified transmissions. The improvements to the operation of the “factory installed” transmissions, and in particular the Allison transmission, include modification of the flow control valve to increase line pressure during lockup; modifications to the rotating clutch module to increase the torque held by the clutch and prevent clutch slippage, and modifications to the trim valves to adjust the pressure applied to the clutches for more efficient operation of the transmission.

Abstract: The oil supply device for a change-under-load transmission having a high-pressure circuit and a low-pressure circuit is designed in such a manner that the high-pressure feed line to the consumer devices of the transmission system incorporates an inlet aperture of small size, the low-pressure feed line is connected between the inlet aperture and the consumer device, and the low-pressure feed line can be cut off from the high-pressure feed line by a one-way valve.

Abstract: There is provided a hydraulic control device for an automatic transmission, which is comprised of an engagement state determining section and a protection control section. If the engagement state determining section determines that each clutch, which is supplied with a line pressure via a regulating valve having a spool and has an oil pressure switch disposed in an oil channel, is held in an engaged state when gears are not changed, the protection control section sets a command pressure for the regulating valve to a protective oil pressure lower than the line pressure. This brings the regulating valve into a pressure-regulating state to cause lands of the spool to form apertures that reduce hydraulic vibration applied to the line pressure. This inhibits an oil pressure beyond an acceptable value from being applied to the oil pressure switch, and therefore improves the durability of the oil pressure switch.

Abstract: A hydraulic control system for an automatic transmission includes a 3-4 shift valve that outputs a source pressure through a first path for shift speeds lower than a fourth shift speed established by directly connecting an input shaft with an output shaft of the automatic transmission, i.e., third shift speed. The hydraulic control system further includes a clutch apply control valve that outputs a source pressure through a second path at a shift speed higher than the fourth shift speed, i.e., fifth speed. The 3-4 shift valve and the clutch apply control valve serve to interrupt supply of the source pressure through the first path and the second path, respectively, in the fourth speed or the lock-up stage.

Abstract: A hydraulic control system, in which a powertrain of a 5-speed automatic transmission is controlled using five clutches and three brakes such that fuel consumption is reduced and engine torque is more efficiently utilized. The hydraulic control system includes four pressure control valves, three switching valves, and three fail-safe valves that are controlled by solenoid valves.

Abstract: A hydraulic system for an automatic transmission for a vehicle with an engine having idle-stop control includes a bypass passage which allows communication between a first hydraulic passage downstream of a manual valve and a forward engagement element, a first switching valve arranged on the bypass passage to be switched between a communicating state and a non-communicating state, and a first switching device which switches the first switching valve between the communicating state and the non-communicating state. The first switching device switches the first switching valve to the communicating state when the hydraulic pressure is lower than a predetermined pressure.

Abstract: Apparatus for controlling a vehicle automatic transmission having a hydraulically operated frictional coupling device operable to effect a shifting action of the automatic transmission, a switching valve operable according to a shifting command to effect the shifting action, and a pressure regulating valve operable to control a pressure of a working fluid to be supplied to the frictional coupling device through the switching valve to effect the shifting action, the apparatus including (a) a fluid temperature detector operable to detect a temperature of the working fluid, and (b) a delaying device operable to delay a moment of initiation of an operation of the pressure regulating valve to control the pressure of the working fluid to be supplied to the frictional coupling device for effecting the shifting action, such that the moment of initiation is delayed depending upon the detected working fluid temperature, to reduce a shifting shock of the automatic transmission.

Abstract: An oil pressure control apparatus for an automatic transmission helps ensure sufficient oil pressure to be supplied to a friction engagement element for performing at least either a first shift stage or a reverse shift stage. Further, the oil pressure control apparatus for the automatic transmission effectively performs pressure adjustment of the oil pressure to be supplied to the friction engagement element upon shifting a neutral shift stage to either the first shift stage or the reverse shift stage.

Abstract: When a different speed change request occurs during pre-charging, an indicated pressure is stepwise changed up to a standby pressure for after pre-charge, and a processing in accordance with the different speed change request is commenced with the indicated pressure after the stepwise change, as an initial pressure.

Abstract: An electro-hydraulic control mechanism for use with a multi-speed transmission includes a pair of logic valves, which are manipulated during the ratio interchanges and the ratio establishment by aiding in the distribution of fluid pressure from a plurality of trim valves. The logic valves are retained in specific drive ranges in the event of electrical discontinuance.