In machine tool and other industrial applications, where positive displacement hydraulic pumps are driven by electric motors, it is common practice to provide an air cooled electric motor in one housing and the hydraulic pump in another housing. Each of these units has its own drive shaft. Normally these shafts are connected by a suitable flexible coupling arrangement and the housings are connected by a mounting adaptor.
In addition, it has been known in the art to provide an integrated electric pump and motor such as shown in U.S. Pat. No. 4,729,717 and co-pending applications Ser. Nos. 07/687,173 filed Apr. 18, 1991 and 07/787,670 filed Nov. 4, 1991.
Among the objectives of this invention are to: 1. provide an integrated electric motor and hydraulic pump wherein the electric motor and the variable displacement hydraulic piston pump are encapsulated in a common housing without drive shafts thus reducing unit size and eliminating parts; wherein the potential for external fluid leakage is reduced by eliminating the need for rotating shaft seals; wherein improved cooling of the electric motor is obtained by using oil cooling thus allowing the use of smaller electric components; wherein noise level of unit is reduced by providing a smaller stiffer structure and reducing the magnitude of the axial hydraulic force that is transmitted to the structure; and wherein fluid pressure pulsations are reduced by increasing the volume of fluid in the discharge port.
In accordance with the invention, the integrated electric motor and hydraulic pump comprises a housing, and an electric motor and a variable displacement piston type hydraulic pump within said housing, the rotor of the electric motor is coaxially mounted on the cylinder block of the hydraulic pump. The stator of the electric motor surrounds the rotor and is mounted in the housing. The housing has an inlet for hydraulic fluid and the fluid flows axially of the pump from one end of the housing over the stator and rotor to the inlet of the hydraulic pump and then outwardly from the outlet of the pump to the actuators or other components of the hydraulic system.