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EP-4737234-A1 - HYDRAULIC CIRCUIT OF A WORK OR AGRICULTURAL VEHICLE

EP4737234A1EP 4737234 A1EP4737234 A1EP 4737234A1EP-4737234-A1

Abstract

Hydraulic circuit (HC) for an agricultural or work vehicle, wherein the agricultural or work vehicle comprises at least one working part such as an arm, a hydraulic lift, etc., a braking system (BI) comprising service braking means (7) and parking braking means (3, SAHR), and a user interface (14) for receiving a braking request from a user of the vehicle; wherein the hydraulic circuit comprises a variable displacement hydraulic pump (1), operatively connected to a directional valve assembly (4) for supplying said at least one working member, comprising a discharge valve (2) for recirculating hydraulic oil through cooling means, wherein said braking system comprises at least one braking valve (7) for actuating said service brake, operatively connected to said hydraulic pump, said parking braking means are configured to activate in response to said braking request, when a fault in said service braking means (7) is detected, said discharge valve is set so that an opening pressure threshold of the discharge valve is greater than a maximum supply pressure value of said at least one braking valve (7).

Inventors

  • GARRAMONE, Adriano
  • LIBERTI, STEFANO
  • GRAVILI, ANDREA

Assignees

  • CNH Industrial Italia S.p.A.

Dates

Publication Date
20260506
Application Date
20251103

Claims (12)

  1. Hydraulic circuit (HC) for an agricultural or work vehicle, wherein the agricultural or work vehicle comprises - at least one working part such as an arm, a hydraulic lift, etc.. - a braking system (BI) comprising service braking means (7) and parking braking means (3, SAHR), and a user interface (14) to receive a braking request from a user of the vehicle; wherein the hydraulic circuit comprises a variable displacement hydraulic pump (1), operatively connected to + a directional valve assembly (4) for supplying said at least one working member, comprising an exhaust valve (2) for recirculating hydraulic oil through cooling means, + said braking system - comprising at least one braking valve (7) for actuating said service brake, operatively supplied by the hydraulic pump, - wherein said parking braking means are configured to activate in response to said braking request, under failure conditions of said service braking means (7), - wherein said relief valve is set such that an opening pressure threshold is greater than a maximum supply pressure value of said at least one braking valve (7).
  2. Circuit according to claim 1, wherein said at least one braking valve (7) is directly connected to the hydraulic pump.
  3. A circuit according to claim 1 or 2, wherein said user interface (14) of the service brake (7) is a brake pedal having a stroke range, such that the service braking demand depends on the position of said brake pedal within said stroke range.
  4. A circuit according to claim 3, wherein said parking braking means (3, SAHR), comprises friction material adapted to be actuated by a spring and released hydraulically by a proportional valve (3), adapted to modulate the activation of the parking brake release by a hydraulic action in opposition to said effect.
  5. A circuit according to claim 4, wherein said proportional valve (3) is controlled proportionally to said brake pedal position within said stroke range.
  6. Circuit according to any of the preceding claims, comprising an electronic processing unit (CU) operatively connected to at least one first position sensor (11) adapted to detect the current position of the brake pedal (14) for the purpose of calculating the service braking request and consequently controlling said proportional valve (3) of the parking braking means.
  7. A circuit according to any preceding claim, further comprising monitoring means (10) configured to detect said failure in said service braking means (7).
  8. A circuit according to claim 7, wherein said monitoring means (10) comprise a pressure sensor operatively associated with said service braking means.
  9. A circuit according to any preceding claim, wherein said service braking means (7) comprise friction material and a related hydraulic actuator.
  10. An agricultural or work vehicle comprising at least one working member such as an arm, a hydraulic lift, etc. and a hydraulic circuit (HC) for powering - a braking system (BI) of the vehicle, comprising service braking means (7) and parking braking means (3, SAHR), and a user interface (14) for receiving a braking request from a user of the vehicle; wherein the hydraulic circuit comprises a variable displacement hydraulic pump (1), operatively connected to + a directional valve assembly (4) for supplying said at least one working member, comprising an exhaust valve (2) for recirculating hydraulic oil through cooling means, + said braking system - comprising at least one braking valve (7) for actuating said service brake, operatively supplied by the hydraulic pump, - wherein said parking braking means are configured to activate in response to said braking request, under failure conditions of said service braking means (7), - wherein said relief valve is set such that an opening pressure threshold is greater than a maximum supply pressure value of said at least one braking valve (7).
  11. Vehicle according to claim 10, wherein the hydraulic circuit (HC) complies with any one of claims 1 - 9, and wherein the vehicle is equipped with a hydrostatic transmission.
  12. Vehicle according to claim 11, wherein said processing unit (CU) is configured to perform an inching function, performing hydrostatic braking, as a function of said brake pedal position detected by said position sensor (11) according to claim 6.

Description

Field of the invention The present invention relates to the field of braking systems of work or agricultural vehicles, in particular to the field of hydraulic braking systems. State of the art Work or agricultural machines are generally equipped with an internal combustion engine, which drives a variable displacement hydraulic pump in rotation, which powers a hydraulic motor operationally connected to the hydraulic pump defining a so-called hydrostat, in which a hydraulic forward line and a hydraulic return line interconnect the hydraulic pump with the hydraulic motor. The displacement of the hydraulic pump is adjustable and depends on an electrical regulation and on the hydrostatic load perceived by the hydraulic pump itself. The hydraulic pump of the hydrostat contributes to the braking of the vehicle depending on the position of the brake pedal, realizing the so-called "inching" function or hydrostatic braking. The service brake includes mechanical friction elements in mutual contact, which, as known, cause the vehicle to slow down when one is pressed against the other, such as the brake pads against a relating disk. However, the service brake is activated only when the brake pedal is pressed beyond a predetermined position threshold. Starting from the release position of the brake pedal, several consecutive ranges of positions are identified. The first interval is associated with the "brake filling" condition. In these conditions, the hydraulic circuit of the service brake is preloaded, so as to bring the mechanical friction elements into mutual contact, but without the development of any appreciable friction force. The first interval is divided into two sub-intervals. In the first of the two sub-intervals the brake filling function is performed, and at the same time the "inching" procedure is performed, in which the hydraulic pump of the hydrostat is controlled so as to reduce its displacement proportionally to how much the brake pedal is depressed. Machines with two friction brakes, one on the front axle and one on the rear axle, are equipped with two separate brake valves. Each brake valve is powered by a dedicated accumulator, this allows in the event of failure of one of the brake valves, to brake the vehicle through the other brake valve which continues to receive oil from its own hydraulic accumulator. Figure 1 shows a hydraulic circuit HC of an agricultural or work vehicle. It comprises a variable displacement "Loading Pump" 1 and a "closed center" directional valve assembly 4 to power a work tool, such as an articulated arm, a hydraulic lift, etc.. The directional valve assembly 4 is controlled by a processing unit (not shown), configured to receive a control signal from a joystick (not shown) and process the control signal to control the valve assembly consequently. The hydraulic circuit also includes the braking system BC and in particular, a pair of braking valves 7 and 8 powered by two respective accumulators 6 operationally connected to the Loading Pump 1 via a recharging valve 5 which, by means of a hysteresis cycle, recharges the hydraulic accumulators. The braking valves act separately on the front and rear axles of the vehicle, respectively. The shuttle valve 9 is used to retain the oil at both accumulators 6. It is therefore clear that the hydraulic source of the brake valves 7 and 8 are the hydraulic accumulators and only indirectly the charging pump 1, which supplies the directional valve group 4 and the charging valve 5 in parallel. The minimum displacement of the charging pump 1 is greater than zero, in order to circulate oil through the cooling system, via the exhaust valve 2 included in the directional valve group 4. The exhaust valve 2 is operationally connected with at least one radiator, so as to allow the hydraulic oil to cool through the radiator. The position sensor 11 associated with the stroke of the service brake pedal generates a signal that is used by the processing unit to realize the inching function. The pressure sensor 10 located on the hydraulic braking line generates a pressure signal used by the processing unit to perform other vehicle functions, including gear shifting, switching on the brake lights, etc. Valve 3, associated with the SAHR brake (spring applied hydraulic release), is used in ON/OFF mode to control the SAHR parking brake integrated into the front axle. The SAHR brake generally uses the same disc pack as the front axle brake but is activated by a different control parallel to that of the service brake. It is activated in negative ways, that is, when valve 3 is at rest, the value of the hydraulic pressure in the control circuit is approximately zero and a spring activates the SAHR brake, while when valve 3 is energized the pressure in the circuit becomes greater than the force of the spring and the SAHR brake is deactivated. EP3868620B1 of the same applicant, describes a scheme in which, in the event of an emergency, the SAHR parking brake is impl